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  • On virus growth and form
    Phys. Rep. (IF 28.295) Pub Date : 2020-01-15
    Roya Zandi; Bogdan Dragnea; Alex Travesset; Rudolf Podgornik

    We review approaches aimed at deciphering the physical mechanisms responsible for viral structure and assembly. We discuss the basic principles of condensed matter physics, macroscopic electrostatics and elastomechanics as they apply to nanosized two-dimensional biomolecular shells with spherical topology and icosahedral symmetry, as well as their proper extension to nonspherical structures pertinent to retroviruses. We examine the relation between the virus structure, the physical interactions that are driving their (self)assembly and the thermodynamics of transition from an isotropic protein solution to the assembled shell state, and discuss the driving forces for large-scale structural reorganizations characterizing maturation processes in the already assembled nano-shells. We furthermore review physical models corresponding to the condensed states of confined genome-carrying biopolymers in viral nano-shells during virus self-assembly and host-cell infection processes, and show how the combination of discrete and continuum coarse grained mechanics, commonly used in the fundamental physical description of viruses, together with the pertinent description of generic long-range electrostatic and specific short-range interactions give insight into the details of structural order and mechanical properties of viruses and elucidates their role in nano-container and nano-machine functions.

    更新日期:2020-01-15
  • Variable-range hopping charge transport in organic thin-film transistors
    Phys. Rep. (IF 28.295) Pub Date : 2020-01-10
    O. Marinov; M.J. Deen; J.A. Jiménez-Tejada; C.H. Chen

    The charge transport in organic thin-film transistors (OTFTs) is assessed in terms of variable range hopping (VRH), by numerical simulations, analytical analyses and comparisons to published experimental results. A numerical simulator, built on the fundamental relations for VRH, provides a simple key dependence that the sum of hopping energy and energy bending under bias is equal to the hopping energy in the bulk material, the latter a bias-independent function of the absolute temperature. This relation binds electrostatics and VRH in OTFTs, at various assumptions for density of states (exponential, double-exponential and normal distributions). It generates and confirms many analytical expressions accumulated over the years for mobility, conductance, potential profiles in the depth of the organic semiconducting film and their relation to bias, film-thickness, also explaining the performance of OTFTs at elevated temperatures. The relations between charges, mobility and bias in OTFTs adhere from the above key dependence. We provide a method to obtain the distribution of the hopping time, which establishes explanations to non-stationary effects in OTFTs, such as dispersive transport, non-reciprocal transitions between on and off-states of the OTFT (usually attributed to gate bias stress and charge build-up), and low-frequency noise in the OTFT channel current.

    更新日期:2020-01-11
  • Computational network biology: Data, model, and applications
    Phys. Rep. (IF 28.295) Pub Date : 2019-12-30
    Chuang Liu; Yifang Ma; Jing Zhao; Ruth Nussinov; Yi-Cheng Zhang; Feixiong Cheng; Zi-Ke Zhang

    Biological entities are involved in intricate and complex interactions, in which uncovering the biological information from the network concepts are of great significance. Benefiting from the advances of network science and high-throughput biomedical technologies, studying the biological systems from network biology has attracted much attention in recent years, and networks have long been central to our understanding of biological systems, in the form of linkage maps among genotypes, phenotypes, and the corresponding environmental factors. In this review, we summarize the recent developments of computational network biology, first introducing various types of biological networks and network structural properties. We then review the network-based approaches, ranging from some network metrics to the complicated machine-learning methods, and emphasize how to use these algorithms to gain new biological insights. Furthermore, we highlight the application in neuroscience, human disease, and drug developments from the perspectives of network science, and we discuss some major challenges and future directions. We hope that this review will draw increasing interdisciplinary attention from physicists, computer scientists, and biologists.

    更新日期:2019-12-30
  • Incomplete fusion reactions using strongly and weakly bound projectiles
    Phys. Rep. (IF 28.295) Pub Date : 2019-12-27
    V. Jha; V.V. Parkar; S. Kailas

    The phenomenon of incomplete fusion (ICF) using both the strongly and weakly bound projectiles below an incident energy of ≈ 10 MeV per nucleon is reviewed. Various reaction mechanisms responsible for ICF, such as projectile breakup followed by fusion, massive transfer or transfer of nucleon(s) to higher energy states of target leading to formation of a composite system have been described. Several theoretical models developed for the description of ICF and its contribution to non-elastic breakup modes or stripping of nucleon(s) from projectile have been summarized. The experimental techniques employed for the measurements of observables characterizing the ICF process and its distinct features have been described. Current interests in the studies of ICF with both strongly and weakly bound projectiles, e.g., the effect of projectile and target structure on ICF, its contribution to the reaction cross sections and competition with the complete fusion (CF) process have been discussed. Systematic studies of ICF, TF, α-particle production and reaction cross sections based on available data and its dependence on reaction parameters have been presented. The applications of ICF process in the population of high angular momentum states in nuclei and its utility in extracting nuclear data that are relevant for nuclear technology applications and nuclear astrophysics, especially using surrogate reaction method have been described. Perspectives of future studies with the weakly bound nuclei, especially the ICF studies in reactions using unstable radioactive ion beams have been provided.

    更新日期:2019-12-27
  • A review of recent advances in thermophysical properties at the nanoscale: From solid state to colloids
    Phys. Rep. (IF 28.295) Pub Date : 2019-12-12
    Lin Qiu; Ning Zhu; Yanhui Feng; Efstathios E. Michaelides; Gaweł Żyła; Dengwei Jing; Xinxin Zhang; Pamela M. Norris; Christos N. Markides; Omid Mahian

    Nanomaterials possess superior optical, electrical, magnetic, mechanical, and thermal properties, which have made them suitable for a multitude of applications. The present review paper deals with recent advances in the measurement and modeling of thermophysical properties at the nanoscale (from the solid state to colloids). For this purpose, first, various techniques for the measurement of the solid state properties, including thermal conductivity, thermal diffusivity, and specific heat capacity, are introduced. The main factors that affect the solid state properties are grain size, grain boundaries, surface interactions, doping, and temperature, which are discussed in detail. After that, methods for the measurement and modeling of thermophysical properties of colloids (nanofluids), including thermal conductivity, dynamic viscosity, specific heat capacity, and density, are presented. The main parameters affecting these properties, such as size, shape, and concentration of nanoparticles, aggregation, and sonication time are studied. Furthermore, the properties of not only simple nanofluids but also hybrid nanofluids (which are composed of more than one type of nanoparticles) are investigated. Finally, the main research gaps and challenges are listed.

    更新日期:2019-12-13
  • Dark Matter through the Higgs portal
    Phys. Rep. (IF 28.295) Pub Date : 2019-12-12
    Giorgio Arcadi; Abdelhak Djouadi; Martti Raidal

    We review scenarios in which the particles that account for the Dark Matter (DM) in the Universe interact only through their couplings with the Higgs sector of the theory, the so-called Higgs-portal models. In a first step, we use a general and model-independent approach in which the DM particles are singlets with spin 0,12 or 1, and assume a minimal Higgs sector with the presence of only the Standard Model (SM) Higgs particle observed at the LHC. In a second step, we discuss non-minimal scenarios in which the spin-12 DM particle is accompanied by additional lepton partners and consider several possibilities like sequential, singlet-doublet and vector-like leptons. In a third step, we examine the case in which it is the Higgs sector of the theory which is enlarged either by a singlet scalar or pseudoscalar field, an additional two Higgs doublet field or by both; in this case, the matter content is also extended in several ways. Finally, we investigate the case of supersymmetric extensions of the SM with neutralino DM, focusing on the possibility that the latter couples mainly to the neutral Higgs particles of the model which then serve as the main portals for DM phenomenology. In all these scenarios, we summarize and update the present constraints and future prospects from the collider physics perspective, namely from the determination of the SM Higgs properties at the LHC and the search for its invisible decays into DM, and the search for heavier Higgs bosons and the DM companion particles at high-energy colliders. We then compare these results with the constraints and prospects obtained from the cosmological relic abundance as well as from direct and indirect DM searches in astroparticle physics experiments. The complementarity between collider and astroparticle searches is investigated in all considered models.

    更新日期:2019-12-13
  • Data science applications to string theory
    Phys. Rep. (IF 28.295) Pub Date : 2019-11-20
    Fabian Ruehle

    We first introduce various algorithms and techniques for machine learning and data science. While there is a strong focus on neural network applications in unsupervised, supervised and reinforcement learning, other machine learning techniques are discussed as well. These include various clustering and anomaly detection algorithms, support vector machines, and decision trees. In addition, we review data science techniques such as genetic algorithms and topological data analysis. This first part of the review makes some reference to concepts in physics, but the explanations and examples do not assume any knowledge of string theory and should therefore be accessible to a wide variety of readers with a physics background. After that, we illustrate applications to string theory. We give an overview of existing string theory data sets and describe how they can be studied using data science techniques. We also explain the computational complexity involved in the investigation of string vacua. Example codes that illustrate the techniques introduced in this review are available from Fabian Ruehle (0000).

    更新日期:2019-11-21
  • Jet substructure at the Large Hadron Collider: A review of recent advances in theory and machine learning
    Phys. Rep. (IF 28.295) Pub Date : 2019-11-18
    Andrew J. Larkoski, Ian Moult, Benjamin Nachman

    Jet substructure has emerged to play a central role at the Large Hadron Collider (LHC), where it has provided numerous innovative new ways to search for new physics and to probe the Standard Model in extreme regions of phase space. In this article we provide a comprehensive review of state of the art theoretical and machine learning developments in jet substructure. This article is meant both as a pedagogical introduction, covering the key physical principles underlying the calculation of jet substructure observables, the development of new observables, and cutting edge machine learning techniques for jet substructure, as well as a comprehensive reference for experts. We hope that it will prove a useful introduction to the exciting and rapidly developing field of jet substructure at the LHC.

    更新日期:2019-11-18
  • Geometry of quantum phase transitions
    Phys. Rep. (IF 28.295) Pub Date : 2019-11-15
    Angelo Carollo, Davide Valenti, Bernardo Spagnolo

    In this article we provide a review of geometrical methods employed in the analysis of quantum phase transitions and non-equilibrium dissipative phase transitions. After a pedagogical introduction to geometric phases and geometric information in the characterisation of quantum phase transitions, we describe recent developments of geometrical approaches based on mixed-state generalisation of the Berry-phase, i.e. the Uhlmann geometric phase, for the investigation of non-equilibrium steady-state quantum phase transitions (NESS-QPTs ). Equilibrium phase transitions fall invariably into two markedly non-overlapping categories: classical phase transitions and quantum phase transitions, whereas in NESS-QPTs this distinction may fade off. The approach described in this review, among other things, can quantitatively assess the quantum character of such critical phenomena. This framework is applied to a paradigmatic class of lattice Fermion systems with local reservoirs, characterised by Gaussian non-equilibrium steady states. The relations between the behaviour of the geometric phase curvature, the divergence of the correlation length, the character of the criticality and the gap - either Hamiltonian or dissipative - are reviewed.

    更新日期:2019-11-15
  • k-core: Theories and applications
    Phys. Rep. (IF 28.295) Pub Date : 2019-11-07
    Yi-Xiu Kong, Gui-Yuan Shi, Rui-Jie Wu, Yi-Cheng Zhang

    With the rapid development of science and technology, the world is becoming increasingly connected. The following dire need for understanding both the relationships amongst individuals and the global structural characteristics brings forward the study of network sciences and many interdisciplinary subjects in recent years. As a result, it is crucial to have methods and algorithms that help us to unveil the structural properties of a network. Over the past few decades, many essential algorithms have been developed by scientists from many different fields. This review will focus on one of the most widely used methods called the k-core decomposition. The k-core decomposition is to find the largest subgraph of a network, in which each node has at least k neighbors in the subgraph. The most commonly used algorithm to perform k-core decomposition is a pruning process that to recursively remove the nodes that have degrees less than k. The algorithm was firstly proposed by Seidman in 1983 and soon became one of the most popular algorithms to detect the network structure due to its simplicity and broad applicability. This algorithm is widely adopted to find the densest part of a network across a broad range of scientific subjects including biology, network science, computer science, ecology, economics, social sciences, etc., so to achieve the vital knowledge under different contexts. Besides, a few physicists find that an exciting phase transition emerges with various critical behaviors during the pruning process. This review aims at filling the gap by making a comprehensive review of the theoretical advances on k-core decomposition problem, along with a review of a few applications of the k-core decomposition from many interdisciplinary perspectives.

    更新日期:2019-11-07
  • Extreme value statistics of correlated random variables: A pedagogical review
    Phys. Rep. (IF 28.295) Pub Date : 2019-11-01
    Satya N. Majumdar, Arnab Pal, Grégory Schehr

    Extreme value statistics (EVS) concerns the study of the statistics of the maximum or the minimum of a set of random variables. This is an important problem for any time-series and has applications in climate, finance, sports, all the way to physics of disordered systems where one is interested in the statistics of the ground state energy. While the EVS of ‘uncorrelated’ variables are well understood, little is known for strongly correlated random variables. Only recently this subject has gained much importance both in statistical physics and in probability theory. In this review, we will first recall the classical EVS for uncorrelated variables and discuss the three universality classes of extreme value limiting distribution, known as the Gumbel, Fréchet and Weibull distribution. We then show that, for weakly correlated random variables with a finite correlation length/time, the limiting extreme value distribution can still be inferred from that of the uncorrelated variables using a renormalisation group-like argument. Finally, we consider the most interesting examples of strongly correlated variables for which there are very few exact results for the EVS. We discuss few examples of such strongly correlated systems (such as the Brownian motion and the eigenvalues of a random matrix) where some analytical progress can be made. We also discuss other observables related to extremes, such as the density of near-extreme events, time at which an extreme value occurs, order and record statistics, etc.

    更新日期:2019-11-01
  • Saddle point approaches in strong field physics and generation of attosecond pulses
    Phys. Rep. (IF 28.295) Pub Date : 2019-10-31
    Arjun Nayak, Mathieu Dumergue, Sergei Kühn, Sudipta Mondal, Tamás Csizmadia, N.G. Harshitha, Miklós Füle, Mousumi Upadhyay Kahaly, Balázs Farkas, Balázs Major, Viktor Szaszkó-Bogár, Péter Földi, Szilárd Majorosi, Nikolaos Tsatrafyllis, Emmanuel Skantzakis, Lana Neoričić, Mojtaba Shirozhan, Giulio Vampa, Subhendu Kahaly

    Attoscience is the emerging field that accesses the fastest electronic processes occurring at the atomic and molecular length scales with attosecond (1 as = 10−18 s) time resolution having wide ranging physical, chemical, material science and biological applications. The quintessential and one of the most fundamental processes in this domain is the generation of phase locked XUV attosecond pulses. The theoretical approach to understand the process incorporates a fully quantum or semi classical or relativistic description of coherent charge dynamics in intense ultrashort electromagnetic fields driving a quantum system (an atom, a molecule, solid band gap materials or surface plasmas). Modelling of such physical and dynamical systems in science and also in many other branches often leads to equations represented in terms of complex multi-dimensional integrals. These integrals can often be solved using the stationary phase approximation, which leads to a series of equations identifying the points in the multi-dimensional space, having most significant contributions in their evaluation. These points are usually indicated as saddle points. The description of the dynamics of quantum mechanical or relativistic systems that results from such an approach enables near to classical physics intuitive perceptions of the processes under investigation. Thus, the saddle point methods are very powerful and valuable general theoretical tools to obtain asymptotic expressions of such solutions and help also to gain physical insights on the underlying phenomena. Such techniques developed in the past have been adapted to study the emission of as pulses by different physical systems and have been widely employed in calculating and estimating the response of matter to intense electromagnetic pulses on ultrafast time scales. Here we provide an extensive disposition of the saddle point approaches unifying their ubiquitous applications within the domain of attoscience valid for simple atomic to more complex condensed matter systems undergoing ultrafast dynamics and present current trends and advancements in the field. In this review we would delineate the methodology, present a synthesis of seminal works and describe the state of the art applications. Finally we also address ultrashort time dynamics of novel materials that have gained much attention recently, namely lower dimensional material systems and micro-plasma systems.

    更新日期:2019-11-01
  • Spallation processes and nuclear interaction products of cosmic rays.
    Phys. Rep. (IF 28.295) Pub Date : 1990-08-01
    R Silberberg,C H Tsao

    Most cosmic-ray nuclei heavier than helium have suffered nuclear collisions in the interstellar gas, with transformation of nuclear composition. The isotopic and elemental composition at the sources has to be inferred from the observed composition near the Earth. The source composition permits tests of current ideas on sites of origin, nucleosynthesis in stars, evolution of stars, the mixing and composition of the interstellar medium and injection processes prior to acceleration. The effects of nuclear spallation, production of radioactive nuclides and the time dependence of their decay provide valuable information on the acceleration and propagation of cosmic rays, their nuclear transformations, and their confinement time in the Galaxy. The formation of spallation products that only decay by electron capture and are relatively long-lived permits an investigation of the nature and density fluctuations (like clouds) of the interstellar medium. Since nuclear collisions yield positrons, antiprotons, gamma rays and neutrinos, we shall discuss these topics briefly.

    更新日期:2019-11-01
  • Mesoscale computational studies of membrane bilayer remodeling by curvature-inducing proteins.
    Phys. Rep. (IF 28.295) Pub Date : 2014-12-09
    N Ramakrishnan,P B Sunil Kumar,Ravi Radhakrishnan

    Biological membranes constitute boundaries of cells and cell organelles. These membranes are soft fluid interfaces whose thermodynamic states are dictated by bending moduli, induced curvature fields, and thermal fluctuations. Recently, there has been a flood of experimental evidence highlighting active roles for these structures in many cellular processes ranging from trafficking of cargo to cell motility. It is believed that the local membrane curvature, which is continuously altered due to its interactions with myriad proteins and other macromolecules attached to its surface, holds the key to the emergent functionality in these cellular processes. Mechanisms at the atomic scale are dictated by protein-lipid interaction strength, lipid composition, lipid distribution in the vicinity of the protein, shape and amino acid composition of the protein, and its amino acid contents. The specificity of molecular interactions together with the cooperativity of multiple proteins induce and stabilize complex membrane shapes at the mesoscale. These shapes span a wide spectrum ranging from the spherical plasma membrane to the complex cisternae of the Golgi apparatus. Mapping the relation between the protein-induced deformations at the molecular scale and the resulting mesoscale morphologies is key to bridging cellular experiments across the various length scales. In this review, we focus on the theoretical and computational methods used to understand the phenomenology underlying protein-driven membrane remodeling. Interactions at the molecular scale can be computationally probed by all atom and coarse grained molecular dynamics (MD, CGMD), as well as dissipative particle dynamics (DPD) simulations, which we only describe in passing. We choose to focus on several continuum approaches extending the Canham - Helfrich elastic energy model for membranes to include the effect of curvature-inducing proteins and explore the conformational phase space of such systems. In this description, the protein is expressed in the form of a spontaneous curvature field. The approaches include field theoretical methods limited to the small deformation regime, triangulated surfaces and particle-based computational models to investigate the large-deformation regimes observed in the natural state of many biological membranes. Applications of these methods to understand the properties of biological membranes in homogeneous and inhomogeneous environments of proteins, whose underlying curvature fields are either isotropic or anisotropic, are discussed. The diversity in the curvature fields elicits a rich variety of morphological states, including tubes, discs, branched tubes, and caveola. Mapping the thermodynamic stability of these states as a function of tuning parameters such as concentration and strength of curvature induction of the proteins is discussed. The relative stabilities of these self-organized shapes are examined through free-energy calculations. The suite of methods discussed here can be tailored to applications in specific cellular settings such as endocytosis during cargo trafficking and tubulation of filopodial structures in migrating cells, which makes these methods a powerful complement to experimental studies.

    更新日期:2019-11-01
  • Nonlinear dynamics of cardiovascular ageing.
    Phys. Rep. (IF 28.295) Pub Date : 2010-04-17
    Y Shiogai,A Stefanovska,P V E McClintock

    The application of methods drawn from nonlinear and stochastic dynamics to the analysis of cardiovascular time series is reviewed, with particular reference to the identification of changes associated with ageing. The natural variability of the heart rate (HRV) is considered in detail, including the respiratory sinus arrhythmia (RSA) corresponding to modulation of the instantaneous cardiac frequency by the rhythm of respiration. HRV has been intensively studied using traditional spectral analyses, e.g. by Fourier transform or autoregressive methods, and, because of its complexity, has been used as a paradigm for testing several proposed new methods of complexity analysis. These methods are reviewed. The application of time-frequency methods to HRV is considered, including in particular the wavelet transform which can resolve the time-dependent spectral content of HRV. Attention is focused on the cardio-respiratory interaction by introduction of the respiratory frequency variability signal (RFV), which can be acquired simultaneously with HRV by use of a respiratory effort transducer. Current methods for the analysis of interacting oscillators are reviewed and applied to cardio-respiratory data, including those for the quantification of synchronization and direction of coupling. These reveal the effect of ageing on the cardio-respiratory interaction through changes in the mutual modulation of the instantaneous cardiac and respiratory frequencies. Analyses of blood flow signals recorded with laser Doppler flowmetry are reviewed and related to the current understanding of how endothelial-dependent oscillations evolve with age: the inner lining of the vessels (the endothelium) is shown to be of crucial importance to the emerging picture. It is concluded that analyses of the complex and nonlinear dynamics of the cardiovascular system can illuminate the mechanisms of blood circulation, and that the heart, the lungs and the vascular system function as a single entity in dynamical terms. Clear evidence is found for dynamical ageing.

    更新日期:2019-11-01
  • First-principles modeling of electromagnetic scattering by discrete and discretely heterogeneous random media.
    Phys. Rep. (IF 28.295) Pub Date : 2016-05-16
    Michael I Mishchenko,Janna M Dlugach,Maxim A Yurkin,Lei Bi,Brian Cairns,Li Liu,R Lee Panetta,Larry D Travis,Ping Yang,Nadezhda T Zakharova

    A discrete random medium is an object in the form of a finite volume of a vacuum or a homogeneous material medium filled with quasi-randomly and quasi-uniformly distributed discrete macroscopic impurities called small particles. Such objects are ubiquitous in natural and artificial environments. They are often characterized by analyzing theoretically the results of laboratory, in situ, or remote-sensing measurements of the scattering of light and other electromagnetic radiation. Electromagnetic scattering and absorption by particles can also affect the energy budget of a discrete random medium and hence various ambient physical and chemical processes. In either case electromagnetic scattering must be modeled in terms of appropriate optical observables, i.e., quadratic or bilinear forms in the field that quantify the reading of a relevant optical instrument or the electromagnetic energy budget. It is generally believed that time-harmonic Maxwell's equations can accurately describe elastic electromagnetic scattering by macroscopic particulate media that change in time much more slowly than the incident electromagnetic field. However, direct solutions of these equations for discrete random media had been impracticable until quite recently. This has led to a widespread use of various phenomenological approaches in situations when their very applicability can be questioned. Recently, however, a new branch of physical optics has emerged wherein electromagnetic scattering by discrete and discretely heterogeneous random media is modeled directly by using analytical or numerically exact computer solutions of the Maxwell equations. Therefore, the main objective of this Report is to formulate the general theoretical framework of electromagnetic scattering by discrete random media rooted in the Maxwell-Lorentz electromagnetics and discuss its immediate analytical and numerical consequences. Starting from the microscopic Maxwell-Lorentz equations, we trace the development of the first-principles formalism enabling accurate calculations of monochromatic and quasi-monochromatic scattering by static and randomly varying multiparticle groups. We illustrate how this general framework can be coupled with state-of-the-art computer solvers of the Maxwell equations and applied to direct modeling of electromagnetic scattering by representative random multi-particle groups with arbitrary packing densities. This first-principles modeling yields general physical insights unavailable with phenomenological approaches. We discuss how the first-order-scattering approximation, the radiative transfer theory, and the theory of weak localization of electromagnetic waves can be derived as immediate corollaries of the Maxwell equations for very specific and well-defined kinds of particulate medium. These recent developments confirm the mesoscopic origin of the radiative transfer, weak localization, and effective-medium regimes and help evaluate the numerical accuracy of widely used approximate modeling methodologies.

    更新日期:2019-11-01
  • A review of snapshot multidimensional optical imaging: measuring photon tags in parallel.
    Phys. Rep. (IF 28.295) Pub Date : 2016-05-03
    Liang Gao,Lihong V Wang

    Multidimensional optical imaging has seen remarkable growth in the past decade. Rather than measuring only the two-dimensional spatial distribution of light, as in conventional photography, multidimensional optical imaging captures light in up to nine dimensions, providing unprecedented information about incident photons' spatial coordinates, emittance angles, wavelength, time, and polarization. Multidimensional optical imaging can be accomplished either by scanning or parallel acquisition. Compared with scanning-based imagers, parallel acquisition-also dubbed snapshot imaging-has a prominent advantage in maximizing optical throughput, particularly when measuring a datacube of high dimensions. Here, we first categorize snapshot multidimensional imagers based on their acquisition and image reconstruction strategies, then highlight the snapshot advantage in the context of optical throughput, and finally we discuss their state-of-the-art implementations and applications.

    更新日期:2019-11-01
  • Nonlinear and Stochastic Dynamics in the Heart.
    Phys. Rep. (IF 28.295) Pub Date : 2014-10-01
    Zhilin Qu,Gang Hu,Alan Garfinkel,James N Weiss

    In a normal human life span, the heart beats about 2 to 3 billion times. Under diseased conditions, a heart may lose its normal rhythm and degenerate suddenly into much faster and irregular rhythms, called arrhythmias, which may lead to sudden death. The transition from a normal rhythm to an arrhythmia is a transition from regular electrical wave conduction to irregular or turbulent wave conduction in the heart, and thus this medical problem is also a problem of physics and mathematics. In the last century, clinical, experimental, and theoretical studies have shown that dynamical theories play fundamental roles in understanding the mechanisms of the genesis of the normal heart rhythm as well as lethal arrhythmias. In this article, we summarize in detail the nonlinear and stochastic dynamics occurring in the heart and their links to normal cardiac functions and arrhythmias, providing a holistic view through integrating dynamics from the molecular (microscopic) scale, to the organelle (mesoscopic) scale, to the cellular, tissue, and organ (macroscopic) scales. We discuss what existing problems and challenges are waiting to be solved and how multi-scale mathematical modeling and nonlinear dynamics may be helpful for solving these problems.

    更新日期:2019-11-01
  • Local temperatures out of equilibrium
    Phys. Rep. (IF 28.295) Pub Date : 2019-10-21
    Daochi Zhang, Xiao Zheng, Massimiliano Di Ventra

    The temperature of a physical system is operationally defined in physics as “that quantity which is measured by a thermometer” weakly coupled to, and at equilibrium with the system. This definition is unique only at global equilibrium in view of the zeroth law of thermodynamics: when the system and the thermometer have reached equilibrium, the “thermometer degrees of freedom” can be traced out and the temperature read by the thermometer can be uniquely assigned to the system. Unfortunately, such a procedure cannot be straightforwardly extended to a system out of equilibrium, where local excitations may be spatially inhomogeneous and the zeroth law of thermodynamics does not hold. With the advent of several experimental techniques that attempt to extract a single parameter characterizing the degree of local excitations of a (mesoscopic or nanoscale) system out of equilibrium, this issue is making a strong comeback to the forefront of research. In this paper, we will review the difficulties to define a unique temperature out of equilibrium, the majority of definitions that have been proposed so far, and discuss both their advantages and limitations. We will then examine a variety of experimental techniques developed for measuring the non-equilibrium local temperatures under various conditions. Finally we will discuss the physical implications of the notion of local temperature, and present the practical applications of such a concept in a variety of nanosystems out of equilibrium.

    更新日期:2019-10-22
  • Implications of superrotations
    Phys. Rep. (IF 28.295) Pub Date : 2019-10-21
    Sabrina Pasterski

    A framework of connections between asymptotic symmetries, soft theorems, and memory effects has recently shed light on a universal structure associated with infrared physics. Here, we show how this pattern has been used to fill in missing elements. After the necessary groundwork, we begin by proving a Ward identity for superrotations using the subleading soft graviton theorem, thereby demonstrating a semiclassical Virasoro symmetry for scattering in quantum gravity. Next, we show there exists a new spin memory effect associated with this symmetry, explain more generally how the connections between the vertices of the infrared triangle predicted this, and describe what other examples and variations have been unveiled. Taking to heart this newly motivated Virasoro symmetry, we review how the soft theorem has been recast as a Virasoro Ward identity for a putative two dimensional conformal field theory. This derivation relies upon a map from plane wave scattering states to a conformal primary basis, which we then construct. We provide examples of familiar scattering amplitudes recast in this basis and discuss the somewhat exotic nature of the putative CFT2. We conclude by describing ongoing efforts to tame some of these features and what this change of basis in turn has taught us about the infrared limit which began our story.

    更新日期:2019-10-22
  • Quantum decoherence
    Phys. Rep. (IF 28.295) Pub Date : 2019-10-18
    Maximilian Schlosshauer

    Quantum decoherence plays a pivotal role in the dynamical description of the quantum-to-classical transition and is the main impediment to the realization of devices for quantum information processing. This paper gives an overview of the theory and experimental observation of the decoherence mechanism. We introduce the essential concepts and the mathematical formalism of decoherence, focusing on the picture of the decoherence process as a continuous monitoring of a quantum system by its environment. We review several classes of decoherence models and discuss the description of the decoherence dynamics in terms of master equations. We survey methods for avoiding and mitigating decoherence and give an overview of several experiments that have studied decoherence processes. We also comment on the role decoherence may play in interpretations of quantum mechanics and in addressing foundational questions.

    更新日期:2019-10-19
  • First-principles design of strong solids: Approaches and applications
    Phys. Rep. (IF 28.295) Pub Date : 2019-09-28
    R.F. Zhang, S.H. Zhang, Y.Q. Guo, Z.H. Fu, D. Legut, T.C. Germann, S. Veprek

    In the design of strong solids, especially hard and superhard materials, this review article attempts to critically cover an extended field of first-principles derived mechanical properties by considering both intrinsic (i.e., crystal structures, bonding nature and strength) and extrinsic (i.e., nanostructures and interface characteristics) parameters. For the intrinsic parameters, firstly, the bonding topology and nature, elastic property and ductility-brittleness criterion provide critical physics on the understanding of the mechanical response of a crystal. Secondly, the ideal strength model, the generalized stacking fault energy model, and ab initio informed Peierls-Nabarro model uniquely quantifies the facture and plastic resistance of a crystal. Taking the extrinsic parameters into further consideration, the recent progress of first-principles investigations on the mechanical behavior of nanostructured solids and heterogeneous interfaces is selectively reviewed, targeted as the origin and/or carrier of the fracture or plastic deformation. These extrinsic parameters include the work of adhesion, the critical stresses for interfacial cleavage and glide and so on. Finally, by classifying the strong solids into intrinsically and extrinsically hard/superhard materials, two different rules are proposed: (1) three-dimensional short covalent bond networks with sufficiently high ideal strength and Peierls resistance and (2) nanosized crystallites/layers glued by strongly bonded thin interfaces.

    更新日期:2019-09-29
  • Silicon strip and pixel detectors for particle physics experiments
    Phys. Rep. (IF 28.295) Pub Date : 2019-09-25
    Sally Seidel

    Following a brief introduction to the roles that a tracking detector fulfills in a particle physics experiment, the concept of a silicon tracking detector is introduced. The contributors to position resolution of the detector are described along with some technological developments that have occurred in response to them. An overview of the historical evolution of the silicon detector concept follows, with emphasis on what was learned at significant junctures. A light reminder of foundational concepts related to semiconductors and p-n junctions is provided, in order to motivate various choices that have been made in the implementation of sensor geometries; advantages and disadvantages of some key implementations are mentioned. The characteristics of an operating detector are described, as are the typical experimental goals that influence decisions on detector optimization. Due to its pervasive effect on nearly all detector characteristics, the mechanisms and vocabulary of radiation damage are introduced. Features of the classic silicon detector design that have been developed to mitigate that damage are described, and the evolution of the design toward higher radiation tolerance is indicated. The concept of the module is introduced, for strip detectors and pixel detectors. Design considerations for detector cooling, interconnections, power distribution, and support are mentioned. Various approaches to monolithic pixel detectors are described and contrasted with hybrid detectors. A look at the research frontier leads to low gain avalanche detectors and small-cell 3D detectors.

    更新日期:2019-09-26
  • Matter manipulation with extreme terahertz light: Progress in the enabling THz technology
    Phys. Rep. (IF 28.295) Pub Date : 2019-09-20
    Peter Salén, Martina Basini, Stefano Bonetti, János Hebling, Mikhail Krasilnikov, Alexey Y. Nikitin, Georgii Shamuilov, Zoltán Tibai, Vitali Zhaunerchyk, Vitaliy Goryashko

    Terahertz (THz) light has proven to be a fine tool to probe and control quasi-particles and collective excitations in solids, to drive phase transitions and associated changes in material properties, and to study rotations and vibrations in molecular systems. In contrast to visible light, which usually carries excessive photon energy for collective excitations in condensed matter systems, THz light allows for direct coupling to low-energy (meV scale) excitations of interest. The development of light sources of strong-field few-cycle THz pulses in the 2000s opened the door to controlled manipulation of reactions and processes. Such THz pulses can drive new dynamic states of matter, in which materials exhibit properties entirely different from that of the equilibrium. In this review, we first systematically analyze known studies on matter manipulation with strong-field few-cycle THz light and outline some anticipated new results. We focus on how properties of materials can be manipulated by driving the dynamics of different excitations and how molecules and particles can be controlled in useful ways by extreme THz light. Around 200 studies are examined, most of which were done during the last five years. Secondly, we discuss available and proposed sources of strong-field few-cycle THz pulses and their state-of-the-art operation parameters. Finally, we review current approaches to guiding, focusing, reshaping and diagnostics of THz pulses.

    更新日期:2019-09-21
  • Conserved charges in extended theories of gravity
    Phys. Rep. (IF 28.295) Pub Date : 2019-09-10
    Hamed Adami, Mohammad Reza Setare, Tahsin Çağrı Şişman, Bayram Tekin

    We give a detailed review of construction of conserved quantities in extended theories of gravity for asymptotically maximally symmetric spacetimes and carry out explicit computations for various solutions. Our construction is based on the Killing charge method, and a proper discussion of the conserved charges of extended gravity theories with this method requires studying the corresponding charges in Einstein’s theory with or without a cosmological constant. Hence we study the ADM charges (in the asymptotically flat case but in generic viable coordinates), the AD charges (in generic Einstein spaces, including the anti-de Sitter spacetimes) and the ADT charges in anti-de Sitter spacetimes. We also discuss the conformal properties and the behavior of these charges under large gauge transformations as well as the linearization instability issue which explains the vanishing charge problem for some particular extended theories. We devote a long discussion to the quasi-local and off-shell generalization of conserved charges in the 2+1 dimensional Chern–Simons like theories and suggest their possible relevance to the entropy of black holes.

    更新日期:2019-09-11
  • Duality between (2+1)d quantum critical points
    Phys. Rep. (IF 28.295) Pub Date : 2019-09-09
    T. Senthil, Dam Thanh Son, Chong Wang, Cenke Xu

    Duality refers to two equivalent descriptions of the same theory from different points of view. Recently there has been tremendous progress in formulating and understanding possible dualities of quantum many body theories in 2+1-spacetime dimensions. Of particular interest are dualities that describe conformally invariant quantum field theories in (2+1)d. These arise as descriptions of quantum critical points in condensed matter physics. The appreciation of the possible dual descriptions of such theories has greatly enhanced our understanding of some challenging questions about such quantum critical points. Perhaps surprisingly the same dualities also underlie recent progress in our understanding of other problems such as the half-filled Landau level and correlated surface states of topological insulators. Here we provide a pedagogical review of these recent developments from a point of view geared toward condensed matter physics.

    更新日期:2019-09-09
  • Chaos in time delay systems, an educational review
    Phys. Rep. (IF 28.295) Pub Date : 2019-08-16
    Hendrik Wernecke, Bulcsú Sándor, Claudius Gros

    The time needed to exchange information in the physical world induces a delay term when the respective system is modeled by differential equations. Time delays are hence ubiquitous, being furthermore likely to induce instabilities and with it various kinds of chaotic phases. Which are then the possible types of time delays, induced chaotic states, and methods suitable to characterize the resulting dynamics? This review presents an overview of the field that includes an in-depth discussion of the most important results, of the standard numerical approaches and of several novel tests for identifying chaos. Special emphasis is placed on a structured representation that is straightforward to follow. Several educational examples are included in addition as entry points to the rapidly developing field of time delay systems.

    更新日期:2019-08-16
  • Time-reversal-invariant topological superconductivity in one and two dimensions
    Phys. Rep. (IF 28.295) Pub Date : 2019-08-14
    Arbel Haim, Yuval Oreg

    A topological superconductor is characterized by having a pairing gap in the bulk and gapless self-hermitian Majorana modes at its boundary. In one dimension, these are zero-energy modes bound to the ends, while in two dimensions these are chiral gapless modes traveling along the edge. Majorana modes have attracted a lot of interest due to their exotic properties, which include non-abelian exchange statistics. Progress in realizing topological superconductivity has been made by combining spin–orbit coupling, conventional superconductivity, and magnetism. The existence of protected Majorana modes, however, does not inherently require the breaking of time-reversal symmetry by magnetic fields. Indeed, pairs of Majorana modes can reside at the boundary of a time-reversal-invariant topological superconductor (TRITOPS). It is the time-reversal symmetry which then protects this so-called Majorana Kramers’ pair from gapping out. This is analogous to the case of the two-dimensional topological insulator, with its pair of helical gapless boundary modes, protected by time-reversal symmetry. Realizing the TRITOPS phase will be a major step in the study of topological phases of matter. In this paper we describe the physical properties of the TRITOPS phase, and review recent proposals for engineering and detecting them in condensed matter systems, in one and two spatial dimensions. We mostly focus on extrinsic superconductors, where superconductivity is introduced through the proximity effect. We emphasize the role of interplay between attractive and repulsive electron–electron interaction as an underlying mechanism. When discussing the detection of the TRITOPS phase, we focus on the physical imprint of Majorana Kramers’ pairs, and review proposals of transport measurement which can reveal their existence.

    更新日期:2019-08-14
  • Variational and Parquet-diagram theory for strongly correlated normal and superfluid systems
    Phys. Rep. (IF 28.295) Pub Date : 2019-08-08
    H.-H. Fan, E. Krotscheck

    We develop the variational and correlated basis functions/parquet-diagram theory of strongly interacting normal and superfluid systems. The first part of this contribution is devoted to highlight the connections between the Euler equations for the Jastrow-Feenberg wave function on the one hand side, and the ring, ladder, and self-energy diagrams of parquet-diagram theory on the other side. We will show that these subsets of Feynman diagrams are contained, in a local approximation, in the variational wave function. In the second part of this work, we derive the fully optimized Fermi-Hypernetted Chain (FHNC-EL) equations for a superfluid system. Close examination of the procedure reveals that the naïve application of these equations exhibits spurious unphysical properties for even an infinitesimal superfluid gap. We will conclude that it is essential to go beyond the usual Jastrow-Feenberg approximation and to include the exact particle-hole propagator to guarantee a physically meaningful theory and the correct stability range. We will then implement this method and apply it to neutron matter and low density Fermi liquids interacting via the Lennard-Jones model interaction and the Pöschl-Teller interaction. While the quantitative changes in the magnitude of the superfluid gap are relatively small, we see a significant difference between applications for neutron matter and the Lennard-Jones and Pöschl-Teller systems. Despite the fact that the gap in neutron matter can be as large as half the Fermi energy, the corrections to the gap are relatively small. In the Lennard-Jones and Pöschl-Teller models, the most visible consequence of the self-consistent calculation is the change in stability range of the system.

    更新日期:2019-08-09
  • Coevolution spreading in complex networks
    Phys. Rep. (IF 28.295) Pub Date : 2019-07-29
    Wei Wang, Quan-Hui Liu, Junhao Liang, Yanqing Hu, Tao Zhou

    The propagations of diseases, behaviors and information in real systems are rarely independent of each other, but they are coevolving with strong interactions. To uncover the dynamical mechanisms, the evolving spatiotemporal patterns and critical phenomena of networked coevolution spreading are extremely important, which provide theoretical foundations for us to control epidemic spreading, predict collective behaviors in social systems, and so on. The coevolution spreading dynamics in complex networks has thus attracted much attention in many disciplines. In this review, we introduce recent progress in the study of coevolution spreading dynamics, emphasizing the contributions from the perspectives of statistical mechanics and network science. The theoretical methods, critical phenomena, phase transitions, interacting mechanisms, and effects of network topology for four representative types of coevolution spreading mechanisms, including the coevolution of biological contagions, social contagions, epidemic-awareness, and epidemic-resources, are presented in detail, and the challenges in this field as well as open issues for future studies are also discussed.

    更新日期:2019-07-30
  • Review of the semiclassical formalism for multiparticle production at high energies
    Phys. Rep. (IF 28.295) Pub Date : 2019-07-03
    Valentin V. Khoze, Joey Reiness

    These notes provide a comprehensive review of the semiclassical approach for calculating multiparticle production rates for initial states with few particles at very high energies. In this work we concentrate on a scalar field theory with a mass gap. Specifically, we look at a weakly-coupled theory in the high-energy limit, where the number of particles in the final state scales with energy, n∼E→∞, and the coupling λ→0 with nλ held fixed. In this regime, the semiclasical approach allows us to calculate multiparticle rates non-perturbatively.

    更新日期:2019-07-04
  • A living theory catalogue for fast radio bursts
    Phys. Rep. (IF 28.295) Pub Date : 2019-06-27
    E. Platts, A. Weltman, A. Walters, S.P. Tendulkar, J.E.B. Gordin, S. Kandhai

    At present, we have almost as many theories to explain Fast Radio Bursts as we have Fast Radio Bursts observed. This landscape will be changing rapidly with CHIME/FRB, recently commissioned in Canada, and HIRAX, under construction in South Africa. This is an opportune time to review existing theories and their observational consequences, allowing us to efficiently curtail viable astrophysical models as more data becomes available. In this article we provide a currently up to date catalogue of the numerous and varied theories proposed for Fast Radio Bursts so far. We also launched an online evolving repository for the use and benefit of the community to dynamically update our theoretical knowledge and discuss constraints and uses of Fast Radio Bursts.

    更新日期:2019-06-27
  • Network dynamics of coupled oscillators and phase reduction techniques
    Phys. Rep. (IF 28.295) Pub Date : 2019-06-25
    Bastian Pietras, Andreas Daffertshofer

    Investigating the dynamics of a network of oscillatory systems is a timely and urgent topic. Phase synchronization has proven paradigmatic to study emergent collective behavior within a network. Defining the phase dynamics, however, is not a trivial task. The literature provides an arsenal of solutions, but results are scattered and their formulation is far from standardized. Here, we present, in a unified language, a catalogue of popular techniques for deriving the phase dynamics of coupled oscillators. Traditionally, approaches to phase reduction address the (weakly) perturbed dynamics of an oscillator. They fall into three classes. (i) Many phase reduction techniques start off with a Hopf normal form description, thereby providing mathematical rigor. There, the caveat is to first derive the proper normal form. We explicate several ways to do that, both analytically and (semi-)numerically. (ii) Other analytic techniques capitalize on time scale separation and/or averaging over cyclic variables. While appealing for their more intuitive implementation, they often lack accuracy. (iii) Direct numerical approaches help to identify oscillatory behavior but may limit an overarching view how the reduced phase dynamics depends on model parameters. After illustrating and reviewing the necessary mathematical details for single oscillators, we turn to networks of coupled oscillators as the central issue of this report. We show in detail how the concepts of phase reduction for single oscillators can be extended and applied to oscillator networks. Again, we distinguish between numerical and analytic phase reduction techniques. As the latter dwell on a network normal form, we also discuss associated reduction methods. To illustrate benefits and pitfalls of the different phase reduction techniques, we apply them point-by-point to two classic examples: networks of Brusselators and a more elaborate model of coupled Wilson-Cowan oscillators. The reduction of complex oscillatory systems is crucial for numerical analyses but more so for analytical estimates and model prediction. The most common reduction is towards phase oscillator networks that have proven successful in describing not only the transition between incoherence and global synchronization, but also in predicting the existence of less trivial network states. Many of these predictions have been confirmed in experiments. As we show, however, the phase dynamics depends to large extent on the employed phase reduction technique. In view of current and future trends, we also provide an overview of various methods for augmented phase reduction as well as for phase–amplitude reduction. We indicate how these techniques can be extended to oscillator networks and, hence, may allow for an improved derivation of the phase dynamics of coupled oscillators.

    更新日期:2019-06-26
  • Rapid solidification as non-ergodic phenomenon
    Phys. Rep. (IF 28.295) Pub Date : 2019-06-18
    P.K. Galenko, D. Jou

    Rapid solidification is a relevant physical phenomenon in material sciences, whose theoretical analysis requires going beyond the limits of local equilibrium statistical physics and thermodynamics and, in particular, taking account of ergodicity breaking and of generalized formulation of thermodynamics. The ergodicity breaking is related to the time symmetry breaking and to the presence of some kinds of fluxes and gradient flows making that an average of microscopic variables along time is different that an average over some chosen statistical ensemble. In fast processes, this is due, for instance, to the fact that the system has no time enough to explore the whole region of possible microscopic states in the phase space. Similarly to this, systems submitted to strong fluxes may have no times for reaching the whole phase space in local bulks during observable macroscopic time. Rapid solidification, ergodicity breaking and extended thermodynamics actually make a conceptually novel combination in the present overview: ergodicity breaking is expressed in general terms and then extended thermodynamics is formulated as a particular phenomenological expression and applied to describe the dynamics of the phenomenon. Using the formalism of micro- and meso-scopic dynamics we introduce a general view on non-ergodic fast transitions and provide a simplest description of continual theory based on the system of hyperbolic equations applicable to rapid solidification. Analysis of non-equilibrium effects, including interface kinetics, solute trapping and solute drag, is presented with their effect on the rapidly moving solid–liquid interface. Special attention is paid to the theory predictions compared with the kinetics obtained in experiments on samples processed by electromagnetic levitation facility and in molecular dynamics simulation.

    更新日期:2019-06-18
  • Computational socioeconomics
    Phys. Rep. (IF 28.295) Pub Date : 2019-06-06
    Jian Gao, Yi-Cheng Zhang, Tao Zhou

    Uncovering the structure of socioeconomic systems and timely estimation of socioeconomic status are significant for economic development. The understanding of socioeconomic processes provides foundations to quantify global economic development, to map regional industrial structure, and to infer individual socioeconomic status. In this review, we will make a brief manifesto about a new interdisciplinary research field named Computational Socioeconomics, followed by detailed introduction about data resources, computational tools, data-driven methods, theoretical models and novel applications at multiple resolutions, including the quantification of global economic inequality and complexity, the map of regional industrial structure and urban perception, the estimation of individual socioeconomic status and demographic, and the real-time monitoring of emergent events. This review, together with pioneering works we have highlighted, will draw increasing interdisciplinary attentions and induce a methodological shift in future socioeconomic studies.

    更新日期:2019-06-07
  • Higgs physics: It ain’t over till it’s over
    Phys. Rep. (IF 28.295) Pub Date : 2019-05-27
    Sally Dawson, Christoph Englert, Tilman Plehn

    We review the theoretical underpinning of the Higgs mechanism of electroweak symmetry breaking and the experimental status of Higgs measurements from a pedagogical perspective. The possibilities and motivations for new physics in the symmetry breaking sector are discussed along with current measurements. A focus is on the implications of measurements in the Higgs sector for theoretical insights into extensions of the Standard Model. We also discuss of future prospects for Higgs physics and new analysis techniques.

    更新日期:2019-05-27
  • Nestedness in complex networks: Observation, emergence, and implications
    Phys. Rep. (IF 28.295) Pub Date : 2019-05-27
    Manuel Sebastian Mariani, Zhuo-Ming Ren, Jordi Bascompte, Claudio Juan Tessone

    The observed architecture of ecological and socio-economic networks differssignificantly from that of random networks. From a network science standpoint, non-random structural patterns observed in real networks call for an explanation of their emergence and an understanding of their potential systemic consequences. This article focuses on one of these patterns: nestedness. Given a network of interacting nodes, nestedness can be described as the tendency for nodes to interact with subsets of the interaction partners of better-connected nodes. Known since more than 80 years in biogeography, nestedness has been found in systems as diverse as ecological mutualistic systems, world trade, inter-organizational relations, among many others. This review article focuses on three main pillars: the existing methodologies to observe nestedness in networks; the main theoretical mechanisms conceived to explain the emergence of nestedness in ecological and socio-economic networks; the implications of a nested topology of interactions for the stability and feasibility of a given interacting system. We survey results from variegated disciplines, including statistical physics, graph theory, ecology, and theoretical economics. Nestedness was found to emerge both in bipartite networks and, more recently, in unipartite ones; this review is the first comprehensive attempt to unify both streams of studies, usually disconnected from each other. We believe that the truly interdisciplinary endeavor – while rooted in a complex systems perspective – may inspire new models and algorithms whose realm of application will undoubtedly transcend disciplinary boundaries.

    更新日期:2019-05-27
  • Channeling and volume reflection of high-energy charged particles in short bent crystals. Crystal assisted collimation of the accelerator beam halo
    Phys. Rep. (IF 28.295) Pub Date : 2019-05-22
    W. Scandale, A.M. Taratin

    The experimental studies of high-energy charged particle deflection due to planar and axial channeling as well as volume reflection and multi volume reflections in short bent crystals at the extracted beams of the CERN Super Proton Synchrotron (SPS) are considered. The experiments on the studies of crystal assisted collimation of the CERN SPS beam halo and the first similar experiment with the CERN Large Hadron Collider (LHC) beam of 6500 GeV/c protons are also considered.

    更新日期:2019-05-23
  • Reduction of couplings and its application in particle physics
    Phys. Rep. (IF 28.295) Pub Date : 2019-05-13
    S. Heinemeyer, M. Mondragón, N. Tracas, G. Zoupanos

    The idea of reduction of couplings in renormalizable theories will be presented and then will be applied in Particle Physics models. Reduced couplings appeared as functions of a primary one, compatible with the renormalization group equation and thus solutions of a specific set of ordinary differential equations. If these functions have the form of power series the respective theories resemble standard renormalizable ones and thus widen considerably the area covered until then by symmetries as a tool for constraining the number of couplings consistently. Still on the more abstract level reducing couplings enabled one to construct theories with beta-functions vanishing to all orders of perturbation theory. Reduction of couplings became physics-wise truly interesting and phenomenologically important when applied to the standard model and its possible extensions. In particular in the context of supersymmetric theories it became the most powerful tool known today once it was learned how to apply it also to couplings having dimension of mass and to mass parameters. Technically this all relies on the basic property that reducing couplings is a renormalization scheme independent procedure. Predictions of top and Higgs mass prior to their experimental finding highlight the fundamental physical significance of this notion.

    更新日期:2019-05-16
  • Heat transport of cuprate-based low-dimensional quantum magnets with strong exchange coupling
    Phys. Rep. (IF 28.295) Pub Date : 2019-04-12
    Christian Hess

    Transport properties provide important access to a solid’s quasiparticles, such as quasiparticle density, mobility, and scattering. The transport of heat can be particularly revealing because, in principle, all types of excitations in a solid may contribute. Heat transport is well understood for phonons and electrons, but relatively little is known about heat transported by magnetic excitations. However, during the last about two decades, the magnetic heat transport attracted increasing attention after the discovery of large and unusual signatures of it in low-dimensional quantum magnetic cuprate materials. Today it constitutes an important probe to otherwise often elusive, topological quasiparticles in a broader class of quantum magnets. This review summarizes the experimental foundation of this research, i.e. the state of the art for the magnetic heat transport in the mentioned cuprate materials which host prototypical low-dimensional antiferromagnetic S=1∕2 Heisenberg models. These comprise, in particular, the two-dimensional square lattice, and one-dimensional spin chain and two-leg ladder spin models. It is shown, how studying the heat transport provides direct access to the thermal occupation and the scattering of the already quite exotic quasiparticles of these models which range from spin-1 spin wave and triplon excitations to fractionalized spin-1/2 spinons. Remarkable transport properties of these quasiparticles have been revealed: the spin-heat transport often is highly efficient and in some cases even ballistic, in agreement with theoretical predictions.

    更新日期:2019-05-16
  • Self-interaction in classical gauge theories and gravitation
    Phys. Rep. (IF 28.295) Pub Date : 2019-03-27
    B.P. Kosyakov

    To develop a systematic treatment of the self-interaction problem in classical gauge theories and general relativity, we study tenable manifestations of self-interaction: topological phases, and rearrangements of degrees of freedom appearing in the action. We outline the occurrence of topological phases in pure field systems. We show that the rearranged Maxwell–Lorentz electrodynamics is a mathematically consistent and physically satisfactory theory which describes new entities, dressed charged particles and radiation. We extend this analysis to cover different modifications of the Maxwell–Lorentz electrodynamics and the SU(N) Yang–Mills–Wong theory. We take a brief look at a subtle mechanism of self-interaction in classical strings. Turning to general relativity, we note that the total energy and momentum of a system with nontrivial topological content, such as a black hole, are ambiguous, coordinatization-dependent quantities, which resembles the situation with paradoxical decompositions in the Banach–Tarski theorem.

    更新日期:2019-05-16
  • A high-bias, low-variance introduction to Machine Learning for physicists
    Phys. Rep. (IF 28.295) Pub Date : 2019-03-14
    Pankaj Mehta, Marin Bukov, Ching-Hao Wang, Alexandre G.R. Day, Clint Richardson, Charles K. Fisher, David J. Schwab

    Machine Learning (ML) is one of the most exciting and dynamic areas of modern research and application. The purpose of this review is to provide an introduction to the core concepts and tools of machine learning in a manner easily understood and intuitive to physicists. The review begins by covering fundamental concepts in ML and modern statistics such as the bias–variance tradeoff, overfitting, regularization, generalization, and gradient descent before moving on to more advanced topics in both supervised and unsupervised learning. Topics covered in the review include ensemble models, deep learning and neural networks, clustering and data visualization, energy-based models (including MaxEnt models and Restricted Boltzmann Machines), and variational methods. Throughout, we emphasize the many natural connections between ML and statistical physics. A notable aspect of the review is the use of Python Jupyter notebooks to introduce modern ML/statistical packages to readers using physics-inspired datasets (the Ising Model and Monte-Carlo simulations of supersymmetric decays of proton–proton collisions). We conclude with an extended outlook discussing possible uses of machine learning for furthering our understanding of the physical world as well as open problems in ML where physicists may be able to contribute.

    更新日期:2019-05-16
  • Classification, geometry and applications of supersymmetric backgrounds
    Phys. Rep. (IF 28.295) Pub Date : 2018-12-11
    U. Gran, J. Gutowski, G. Papadopoulos

    We review the remarkable progress that has been made the last 15 years towards the classification of supersymmetric solutions with emphasis on the description of the bilinears and spinorial geometry methods. We describe in detail the geometry of backgrounds of key supergravity theories, which have applications in the context of black holes, string theory, M-theory and the AdS/CFT correspondence unveiling a plethora of existence and uniqueness theorems. Some other aspects of supersymmetric solutions like the Killing superalgebras and the homogeneity theorem are also presented, and the non-existence theorem for certain smooth supergravity flux compactifications is outlined. Amongst the applications described is the proof of the emergence of conformal symmetry near black hole horizons and the classification of warped AdS backgrounds that preserve more than 16 supersymmetries.

    更新日期:2019-03-12
  • The geometry of cutting and shuffling: An outline of possibilities for piecewise isometries
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-28
    Lachlan D. Smith, Paul B. Umbanhowar, Richard M. Lueptow, Julio M. Ottino

    Cutting and shuffling is emerging as an alternative mixing mechanism for fluids and granular matter beyond the well established stretching and folding. Dynamical systems and chaos theory provided a foundation for stretching and folding which has led to applications ranging from microfluidic devices and physiological scales to many engineering and Earth science scales. Likewise, the literature of piecewise isometries (PWIs) provides a similar grounding for cutting and shuffling mechanisms. We start with one-dimensional interval exchange transformations (IETs), which are the only way to cut and shuffle in one dimension, and review and extend previous studies, connecting them in a coherent way. We introduce the concept of time-continuous piecewise isometries, i.e. PWIs that can be performed on solid bodies in a time continuous manner, without solids overlapping or the domain needing to be deformed or extended. PWIs with this property are easier to implement in experiment and applications, as we demonstrate through their connection to mixing in spherical granular tumblers and “twisty puzzles,” such as the spherical version of the Rubik’s cube.

    更新日期:2019-03-12
  • Applied nuclear physics at the new high-energy particle accelerator facilities
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-22
    Marco Durante, Alexander Golubev, Woo-Yoon Park, Christina Trautmann

    Applied nuclear physics is an essential part of the research activity at many particle accelerators. New, large accelerator facilities are currently under construction in Europe, Asia, and USA. These machines will be able to produce radioactive ion beams, and to increase the intensity and the energy of the heavy ions well beyond the limits currently available at the therapy or research facilities. The upcoming facilities open new opportunities for research in biomedical applications that require these special properties, such as particle radiography, radioactive beam imaging, ultra-high dose rates and new ions for therapy. Moreover, space radiation research and materials science can successfully exploit these new centers. The new facilities can pave the way to many future applications of nuclear physics for the benefit of the society. In this paper we will summarize the current status of applied sciences at high-energy accelerators, describe the characteristics of some of the machines under construction (FAIR, NICA, RAON, ELI) and discuss the new opportunities offered by these facilities in applied sciences.

    更新日期:2019-03-12
  • 10 years of pioneering X-ray science at the Free-Electron Laser FLASH at DESY
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-22
    Jörg Rossbach, Jochen R. Schneider, Wilfried Wurth

    Free-electron lasers produce extremely brief, coherent, and bright laser-like photon pulses that allow to image matter at atomic resolution and at timescales faster than the characteristic atomic motions. In pulses of about 50 femtoseconds duration they provide as many photons as one gets in 1 s from modern storage ring synchrotron radiation facilities. FLASH, the Free-Electron Laser at DESY in Hamburg was the first FEL in the XUV/soft X-ray spectral range, started operation as a user facility in summer 2005, and was for almost 5 years the only short wavelength FEL facility worldwide. Hence, most of the technological developments as well as the scientific experiments performed by the user community were new and unique as outlined below. FLASH was driving FEL science and technology and paved the way for many new ideas. Because of using a linear accelerator in superconducting RF technology FLASH combines the extreme peak brightness characteristic for FELs with very high average brightness. It also was the prototype for the European XFEL located in the Hamburg metropolitan area, which started user operation in summer 2017. The present review provides an overview of the progress made with accelerator science and technology at FLASH for the production of stable beams of well characterized electron pulses, reduction of the pulse jitter to the femtosecond level, generation of ultra-short photon pulses, adequate synchronization of the machine parameters with the experiment, and demonstrating advanced FEL schemes using variable gap undulators. Much of this was done in the very exciting early days of FEL science when it was even not clear if the FEL concept could be realized for X-rays. The development and the operation of the FLASH user facility is described, as well as the techniques developed to make use of the new type of X-ray beams including photon beam diagnostics and damage studies of the optical elements. The review emphasizes breakthrough experiments which demonstrated that many of the ideas collected in the world-wide discussion of the scientific case of free-electron lasers could indeed be realized and they often produced unexpected results. The first experiment on Coulomb explosion of Xe clusters performed in 2002 was a clear demonstration of the feasibility of experiments with free-electron laser beams and opened a lively discussion in the atom, molecular and optical physics community (AMO). Time resolved single-shot single-particle imaging, summarized in the slogan “Take movies instead of pictures”, was one of the most popular science drivers for the construction of free-electron X-ray lasers. As a first step in this direction experiments using a highly focused beam of FLASH demonstrated that pictures of 2 dimensional objects could be reconstructed from single-shot single-particle diffraction patterns. Explosion dynamics of nano-size particles hit by an intense FEL pulse were studied. This method, called “diffraction before destruction”, is now very successfully applied with hard X-rays and, to a large extend, solves the radiation damage problem in structural biology. A long term goal is to determine the 3 dimensional structure of a large molecule from a single-shot diffraction pattern. Along these lines the 3D architecture of free Ag nanoparticles could be determined from one diffraction pattern only using soft X-rays from FLASH. To understand light-matter interactions in this new parameter space a number of pioneering AMO experiments have been performed including non-linear interactions in atoms, molecules and clusters. Multiphoton photoionization processes in the presence of intense optical fields have been studied, as well as photo-absorption of XUV photon energies on molecular ions important for astrophysics. The nature of formation and breaking of molecular bonds was investigated in VUV pump-VUV probe experiments using a reaction microscope and a specific delay line. As an example the process of ultrafast isomerization of acetylene molecules C2 H2 triggered by single photon excitation has been studied. The structural changes during the isomerization process were visualized and an isomerization time of 52 +/- 15 fs was found. Clusters of variable size, which can be produced routinely, allow distinguish between inter- and intra-atomic effects and are considered model systems for the investigation of light-matter interactions in multi-atom objects. As an example such experimental studies provided instructive data for benchmarking theoretical models describing cluster ionization in intense short-wavelength laser pulses. The combination of single-shot single-particle imaging for determination of the cluster size with spectroscopy was crucial for success of these experiments. The investigations could later be extended to very large Xe clusters providing new insights into the nanoplasma formation and explosion dynamics of such large systems From early on, studies of high energy density plasmas and warm dense matter have been one of the most prominent research fields in building the scientific case for X-ray free-electron lasers. A good understanding of this complex regime between cold solids and hot dilute plasmas is important for high pressure studies, applied materials studies, inertial fusion, and planetary interiors. With the first observation of saturable absorption of an L-shell transition in Aluminum and pioneering studies of warm dense hydrogen FLASH kicked off research of matter in extreme conditions with free-electron lasers. In condensed matter experiments the emphasis is not so much on the peak power of the FEL beam and extreme focusing, but on beam properties like polarization and pulse duration. The sample has to stay intact in the beam over hours and the number of photons per pulse impinging on the sample has to be limited to avoid space charge effects. After demonstrating the possibility to record single-shot resonant magnetic scattering images with FELs the first time-resolved demagnetization study using a pump-probe approach with an IR-pump pulse and an XUV probe pulse to record a resonant magnetic scattering pattern as a function of pump-probe delay was also performed at FLASH. Free-electron lasers offer the possibility to extend the well-established X-ray spectroscopic techniques for the investigation of the static electronic structure of matter to probing the evolution of the electronic structure in the time domain after controlled excitation. At FLASH first time resolved core level photoemission (TR-XPS) experiments have been performed which are element specific and provide information on the dynamics of the local charge state around a specific center. Using 198 eV photons in a surface study at Ir single crystals it was possible to separate surface and bulk contributions in the Ir 4f levels with sufficient instrumental resolution. Time and angular resolved photoelectron spectroscopy (TR-ARPES) is a very powerful tool to study non-equilibrium electron dynamics of condensed matter systems, since it offers the possibility to follow the dynamics of the full band structure of a material. In another pioneering experiment the photo-induced dynamics of the Mott insulator 1T-TaS2 was studied at FLASH by investigating the dynamics of the Ta 4f photoemission. The formation of a commensurate charge density wave (CCDW) leads to a splitting of the Ta 4f level which decreases first on a sub-picosecond time scale due to electronic melting of the CCDW and afterwards on a picosecond lifetime due to electron–phonon coupling. This leads to transfer of energy from the electronic system to the lattice and a partial melting of the periodic lattice distortions accompanying the periodic charge arrangement in the CCDW phase. In materials science X-ray absorption and emission spectroscopy are among the most powerful spectroscopies to study the electronic structure of matter. The wavelength of the radiation is scanned over certain element specific resonances which at FLASH 1 can only be done by scanning the electron energy. This is time consuming and makes the experiments difficult. Nevertheless, the first time-resolved X-ray emission spectroscopy (XES) experiment was done at FLASH 1 in order to study non-thermal melting of a silicon sample. From a comparison of the observed valence electronic structure at different times after the photoexcitation it became clear that in the melting process in the first few ps a non-equilibrium low density liquid state is reached. The existence of such a metastable low density liquid state had been postulated for many systems that show tetragonal bonding in the crystalline phase like water for example, but spectroscopically the time-resolved silicon XES data taken at FLASH verified its existence for the first time. FLASH 2 has tunable undulators and it was demonstrated that scanning of the wavelength is very easy there.

    更新日期:2019-03-12
  • A primer on resurgent transseries and their asymptotics
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-22
    Inês Aniceto, Gökçe Başar, Ricardo Schiappa

    The computation of observables in general interacting theories, be them quantum mechanical, field, gauge or string theories, is a non-trivial problem which in many cases can only be addressed by resorting to perturbative methods. In most physically interesting problems these perturbative expansions result in asymptotic series with zero radius of convergence. These asymptotic series then require the use of resurgence and transseries in order for the associated observables to become nonperturbatively well-defined. Resurgence encodes the complete large-order asymptotic behaviour of the coefficients from a perturbative expansion, generically in terms of (multi) instanton sectors and for each problem in terms of its Stokes constants. Some observables arise from linear problems, and have a finite number of instanton sectors and associated Stokes constants; some other observables arise from nonlinear problems, and have an infinite number of instanton sectors and Stokes constants. By means of two very explicit examples, and with emphasis on a pedagogical style of presentation, this work aims at serving as a primer on the aforementioned resurgent, large-order asymptotics of general perturbative expansions. This includes discussions of transseries, Stokes phenomena, generalized steepest-descent methods, Borel transforms, nonlinear resonance, and alien calculus. Furthermore, resurgent properties of transseries – usually described mathematically via alien calculus – are recast in equivalent physical languages: either a “statistical mechanical” language, as motions in chains and lattices; or a “conformal field theoretical” language, with underlying Virasoro-like algebraic structures.

    更新日期:2019-03-12
  • Evaporation of a Droplet: From physics to applications
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-15
    Duyang Zang, Sujata Tarafdar, Yuri Yu. Tarasevich, Moutushi Dutta Choudhury, Tapati Dutta

    Evaporation of a drop, though a simple everyday observation, provides a fascinating subject for study. Various issues interact here, such as dynamics of the contact line, evaporation-induced phase transitions, and formation of patterns. The explanation of the rich variety of patterns formed is not only an academic challenge, but also a problem of practical importance, as applications are growing in medical diagnosis and improvement of coating/printing technology. The multi-scale aspect of the problem is emphasized in this review. The specific fundamental problem to be solved, related to the system is the investigation of the mass transfer processes, the formation and evolution of phase fronts and the identification of mechanisms of pattern formation. To understand these problems, we introduce the important forces and interactions involved in these processes, and highlight the evaporation-driven phase transitions and flows in the drop. We focus on how the deposited patterns are related to and tuned by important factors, for instance substrate properties and contents of the drop. In addition, the formation of crust and crack patterns are discussed. The simulation and modeling methods, which are often utilized in this topic, are also reviewed. Finally, we summarize the applications of drop evaporation and suggest several potential directions for future research in this area. Exploiting the full potential of this topic in basic science research and applications needs involvement and interaction between scientists and engineers from disciplines of physics, chemistry, biology, medicine and other related fields.

    更新日期:2019-03-12
  • The degree of fine-tuning in our universe — and others
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-15
    Fred C. Adams

    Both the fundamental constants that describe the laws of physics and the cosmological parameters that determine the properties of our universe must fall within a range of values in order for the cosmos to develop astrophysical structures and ultimately support life. This paper reviews the current constraints on these quantities. The discussion starts with an assessment of the parameters that are allowed to vary. The standard model of particle physics contains both coupling constants (α,αs,αw) and particle masses (mu,md,me) , and the allowed ranges of these parameters are discussed first. We then consider cosmological parameters, including the total energy density of the universe (Ω) , the contribution from vacuum energy (ρΛ) , the baryon-to-photon ratio (η) , the dark matter contribution (δ) , and the amplitude of primordial density fluctuations (Q) . These quantities are constrained by the requirements that the universe lives for a sufficiently long time, emerges from the epoch of Big Bang Nucleosynthesis with an acceptable chemical composition, and can successfully produce large scale structures such as galaxies. On smaller scales, stars and planets must be able to form and function. The stars must be sufficiently long-lived, have high enough surface temperatures, and have smaller masses than their host galaxies. The planets must be massive enough to hold onto an atmosphere, yet small enough to remain non-degenerate, and contain enough particles to support a biosphere of sufficient complexity. These requirements place constraints on the gravitational structure constant (αG) , the fine structure constant (α) , and composite parameters (C⋆) that specify nuclear reaction rates. We then consider specific instances of possible fine-tuning in stellar nucleosynthesis, including the triple alpha reaction that produces carbon, the case of unstable deuterium, and the possibility of stable diprotons. For all of the issues outlined above, viable universes exist over a range of parameter space, which is delineated herein. Finally, for universes with significantly different parameters, new types of astrophysical processes can generate energy and thereby support habitability.

    更新日期:2019-03-12
  • One-body reduced density-matrix functional theory in finite basis sets at elevated temperatures
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-12
    Klaas J.H. Giesbertz, Michael Ruggenthaler

    In this review we provide a rigorous and self-contained presentation of one-body reduced density-matrix (1RDM) functional theory. We do so for the case of a finite basis set, where density-functional theory (DFT) implicitly becomes a 1RDM functional theory. To avoid non-uniqueness issues we consider the case of fermionic and bosonic systems at elevated temperature and variable particle number, i.e, a grand-canonical ensemble. For the fermionic case the Fock space is finite-dimensional due to the Pauli principle and we can provide a rigorous 1RDM functional theory relatively straightforwardly. For the bosonic case, where arbitrarily many particles can occupy a single state, the Fock space is infinite-dimensional and mathematical subtleties (not every hermitian Hamiltonian is self-adjoint, expectation values can become infinite, and not every self-adjoint Hamiltonian has a Gibbs state) make it necessary to impose restrictions on the allowed Hamiltonians and external non-local potentials. For simple conditions on the interaction of the bosons a rigorous 1RDM functional theory can be established, where we exploit the fact that due to the finite one-particle space all 1RDMs are finite-dimensional. We also discuss the problems arising from 1RDM functional theory as well as DFT formulated for an infinite-dimensional one-particle space.

    更新日期:2019-03-12
  • The planet nine hypothesis
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-10
    Konstantin Batygin, Fred C. Adams, Michael E. Brown, Juliette C. Becker

    Over the course of the past two decades, observational surveys have unveiled the intricate orbital structure of the Kuiper Belt, a field of icy bodies orbiting the Sun beyond Neptune. In addition to a host of readily-predictable orbital behavior, the emerging census of trans-Neptunian objects displays dynamical phenomena that cannot be accounted for by interactions with the known eight-planet solar system alone. Specifically, explanations for the observed physical clustering of orbits with semi-major axes in excess of ∼250  AU, the detachment of perihelia of select Kuiper belt objects from Neptune, as well as the dynamical origin of highly inclined/retrograde long-period orbits remain elusive within the context of the classical view of the solar system. This newly outlined dynamical architecture of the distant solar system points to the existence of a new planet with mass of m9∼5–10M⊕ , residing on a moderately inclined orbit (i9∼15–25deg ) with semi-major axis a9∼400–800  AU and eccentricity between e9∼0.2–0.5 . This paper reviews the observational motivation, dynamical constraints, and prospects for detection of this proposed object known as Planet Nine.

    更新日期:2019-03-12
  • Pileup mitigation at the LHC: A theorist’s view
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-10
    Grégory Soyez

    To maximise the potential for new measurements and discoveries at CERN’s Large Hadron Collider (LHC), the machine delivers as high as possible collision rates. As a direct consequence, multiple proton–proton collisions occur whenever two bunches of protons cross. Interesting high-energy (hard) collisions are therefore contaminated by several soft, zero-bias, ones. This effect, known as pileup, pollutes the final state of the collision. It complicates the reconstruction of the objects in this final state, resulting in increased experimental measurement uncertainties. To reduce these uncertainties, and thus improve the quality and precision of LHC measurements, techniques are devised to correct for the effects of pileup. This document provides a theoretical review of the main methods employed during Run I and II of the LHC to mitigate pileup effects. I will start with anin-depth presentation of the area–median used for the vast majority of applications, including several refinements of the original idea, their practical (numerical) implementation and an assessment of their efficiency and robustness. I will then focus on several theoretical calculations that can provide both quantitative and qualitative information on the area–median approach. In the specific case of boosted jets, a field that has seen a wide interest recently, a set of methods, known as grooming techniques has also been used. I will describe these techniques, address their performance and briefly show that they are amenable to a theoretical, analytic, understanding. The last part of this review will focus on ideas oriented towards future pileup mitigation techniques. This includes a couple of new methods that have recently been proposed as well as a large series of alternative ideas. The latter are yet unpublished and have not received the same amount of investigation than the former but they have the potential to bring new developments and further improvement over existing techniques in a future where pileup mitigation will be crucial.

    更新日期:2019-03-12
  • Photonics and optoelectronics using nano-structured hybrid perovskite media and their optical cavities
    Phys. Rep. (IF 28.295) Pub Date : 2019-02-06
    Yupeng Zhang, Chang-Keun Lim, Zhigao Dai, Guannan Yu, Joseph W. Haus, Han Zhang, Paras N. Prasad

    This review focuses on the physics of optical excitation dynamics, band gap engineering and charge carrier dynamics in metal-halide perovskites and their organic hybrids as well as on their technological applications. The role of plasmonic coupling and photonic cavities in enhancing light–matter interactions and manipulating carrier dynamics is clearly presented by examples of studies of perovskite–hybrid plasmonic nanostructured perovskite cavities. Perovskite metasurface is a nascent approach to enhancing photonic device performance that is also briefly described. In addition, nonlinear optical interactions and charge carrier dynamics in (pseudo-) 2D perovskites and photonic structures are discussed. We discuss how photonic communication between a perovskite layer and an interlayer of photoactive organic material in hybrid perovskites contributes to new designs for novel devices. Applications covered are: photodetectors, solar cells, light-emitting diodes and nanolasers, displays, waveguides and modulators, and nonlinear optical devices. Device performance is enhanced by incorporating nanophotonics design concepts. The review concludes with a discussion of technical challenges. New opportunities in multiscale modeling, perovskites with epsilon near zero, perovskites–plasmonic semiconductors, perovskite sensors and quantum applications are presented also presented in the concluding outlook section.

    更新日期:2019-03-12
  • Ultra-high-energy cosmic rays
    Phys. Rep. (IF 28.295) Pub Date : 2019-01-22
    Luis A. Anchordoqui

    In this report we review the important progress made in recent years towards understanding the experimental data on ultra-high-energy (E≳109GeV ) cosmic rays. We begin with a general survey of the available data, including a description of the energy spectrum, the nuclear composition, and the distribution of arrival directions. At this point we also give a synopsis of experimental techniques. After that, we introduce the fundamentals of cosmic ray acceleration and energy loss during propagation, with a view of discussing the conjectured nearby sources. Next, we survey the state of the art regarding the high- and ultra-high-energy cosmic neutrinos which may be produced in association with the observed cosmic rays. These neutrinos could constitute key messengers identifying currently unknown cosmic accelerators, possibly in the distant universe, because their propagation is not influenced by background photon or magnetic fields. Subsequently, we summarize the phenomenology of cosmic ray air showers. We describe the hadronic interaction models used to extrapolate results from collider data to ultra-high energies and the main electromagnetic processes that govern the longitudinal shower evolution. Armed with these two principal shower ingredients and motivation from the underlying physics, we describe the different methods proposed to distinguish the primary particle species. In the end, we explore how ultra-high-energy cosmic rays can be used as probes of beyond standard model physics models.

    更新日期:2019-03-12
  • Quadratic mean field games
    Phys. Rep. (IF 28.295) Pub Date : 2019-01-21
    Denis Ullmo, Igor Swiecicki, Thierry Gobron

    Mean field games were introduced independently by J-M. Lasry and P-L. Lions, and by M. Huang, R.P. Malhamé and P.E. Caines, in order to bring a new approach to optimization problems with a large number of interacting agents. The description of such models split into two parts, one describing the evolution of the density of players in some parameter space, the other the value of a cost functional each player tries to minimize for himself, anticipating on the rational behavior of the others. Quadratic Mean Field Games form a particular class among these systems, in which the dynamics of each player is governed by a controlled Langevin equation with an associated cost functional quadratic in the control parameter. In such cases, there exists a deep relationship with the non-linear Schrödinger equation in imaginary time, connection which lead to effective approximation schemes as well as a better understanding of the behavior of Mean Field Games. The aim of this paper is to serve as an introduction to Quadratic Mean Field Games and their connection with the non-linear Schrödinger equation, providing to physicists a good entry point into this new and exciting field.

    更新日期:2019-03-12
  • A systematic approach to generalisations of General Relativity and their cosmological implications
    Phys. Rep. (IF 28.295) Pub Date : 2019-01-04
    Lavinia Heisenberg

    A century ago, Einstein formulated his elegant and elaborate theory of General Relativity, which has so far withstood a multitude of empirical tests with remarkable success. Notwithstanding the triumphs of Einstein’s theory, the tenacious challenges of modern cosmology and of particle physics have motivated the exploration of further generalised theories of space–time. Even though Einstein’s interpretation of gravity in terms of the curvature of space–time is commonly adopted, the assignment of geometrical concepts to gravity is ambiguous because General Relativity allows three entirely different, but equivalent approaches of which Einstein’s interpretation is only one. From a field-theoretical perspective, however, the construction of a consistent theory for a Lorentz-invariant massless spin-2 particle uniquely leads to General Relativity. Keeping Lorentz invariance then implies that any modification of General Relativity will inevitably introduce additional propagating degrees of freedom into the gravity sector. Adopting this perspective, we will review the recent progress in constructing consistent field theories of gravity based on additional scalar, vector and tensor fields. Within this conceptual framework, we will discuss theories with Galileons, with Lagrange densities as constructed by Horndeski and beyond, extended to DHOST interactions, or containing generalised Proca fields and extensions thereof, or several Proca fields, as well as bigravity theories and scalar–vector–tensor theories. We will review the motivation of their inception, different formulations, and essential results obtained within these classes of theories together with their empirical viability.

    更新日期:2019-03-12
  • Neutrino–nuclear responses for astro-neutrinos, single beta decays and double beta decays
    Phys. Rep. (IF 28.295) Pub Date : 2019-01-04
    H. Ejiri, J. Suhonen, K. Zuber

    Neutrino–nuclear responses associated with astro-neutrinos, single beta decays and double beta decays are crucial in studies of neutrino properties of interest for astro-particle physics. The present report reviews briefly recent studies of the neutrino–nuclear responses from both experimental and theoretical points of view in order to obtain a consistent understanding of the many facets of the neutrino–nuclear responses. Subjects discussed in this review include (i) experimental studies of neutrino–nuclear responses by means of single beta decays, charge-exchange nuclear reactions, muon- photon- and neutrino–nuclear reactions, and nucleon-transfer reactions, (ii) implications of and discussions on neutrino–nuclear responses for single beta decays, for astro-neutrinos, and for astro-neutrino nucleosynthesis, (iii) theoretical aspects of neutrino–nuclear responses for beta and double beta decays, for nuclear muon capture and for neutrino–nucleus scattering, and (iv) critical discussions on nucleonic and non-nucleonic spin–isospin correlations and renormalization (quenching or enhancement) effects on the axial weak coupling. Remarks are given on perspectives of experimental and theoretical studies of the neutrino–nuclear responses and on future experiments of double beta decays.

    更新日期:2019-03-12
  • Non-geometric backgrounds in string theory
    Phys. Rep. (IF 28.295) Pub Date : 2018-12-24
    Erik Plauschinn

    This review provides an introduction to non-geometric backgrounds in string theory. Starting from a discussion of T-duality, geometric and non-geometric torus-fibrations are reviewed, generalised geometry and its relation to non-geometric backgrounds are explained and compactifications of string theory with geometric and non-geometric fluxes are discussed. Furthermore covered are doubled geometry as well as non-commutative and non-associative structures in the context of non-geometric backgrounds.

    更新日期:2019-03-12
  • The standard model as an effective field theory
    Phys. Rep. (IF 28.295) Pub Date : 2018-11-22
    Ilaria Brivio, Michael Trott

    Projecting measurements of the interactions of the known Standard Model (SM) states into an effective field theory (EFT) framework is an important goal of the LHC physics program. The interpretation of measurements of the properties of the Higgs-like boson in an EFT allows one to consistently study the properties of this state, while the SM is allowed to eventually break down at higher energies. In this review, basic concepts relevant to the construction of such EFTs are reviewed pedagogically. Electroweak precision data is discussed as a historical example of some importance to illustrate critical consistency issues in interpreting experimental data in EFTs. A future precision Higgs phenomenology program can benefit from the projection of raw experimental results into consistent field theories such as the SM, the SM supplemented with higher dimensional operators (the SMEFT) or an Electroweak chiral Lagrangian with a dominantly JP=0+ scalar (the HEFT). We discuss the developing SMEFT and HEFT approaches, that are consistent versions of such EFTs, systematically improvable with higher order corrections, and comment on the pseudo-observable approach. We review the challenges that have been overcome in developing EFT methods for LHC studies, and the challenges that remain.

    更新日期:2019-02-26
  • Recent advances in modeling and simulation of nanofluid flows-Part I: Fundamental and theory
    Phys. Rep. (IF 28.295) Pub Date : 2018-12-06
    Omid Mahian, Lioua Kolsi, Mohammad Amani, Patrice Estellé, Goodarz Ahmadi, Clement Kleinstreuer, Jeffrey S. Marshall, Majid Siavashi, Robert A. Taylor, Hamid Niazmand, Somchai Wongwises, Tasawar Hayat, Arun Kolanjiyil, Alibakhsh Kasaeian, Ioan Pop

    It has been more than two decades since the discovery of nanofluids-mixtures of common liquids and solid nanoparticles less than 100 nm in size. As a type of colloidal suspension, nanofluids are typically employed as heat transfer fluids due to their favorable thermal and fluid properties. There have been numerous numerical studies of nanofluids in recent years (more than 1000 in both 2016 and 2017, based on Scopus statistics). Due to the small size and large numbers of nanoparticles that interact with the surrounding fluid in nanofluid flows, it has been a major challenge to capture both the macro-scale and the nano-scale effects of these systems without incurring extraordinarily high computational costs. To help understand the state of the art in modeling nanofluids and to discuss the challenges that remain in this field, the present article reviews the latest developments in modeling of nanofluid flows and heat transfer with an emphasis on 3D simulations. In part I, a brief overview of nanofluids (fabrication, applications, and their achievable thermo-physical properties) will be presented first. Next, various forces that exist in particulate flows such as drag, lift (Magnus and Saffman), Brownian, thermophoretic, van der Waals, and electrostatic double layer forces and their significance in nanofluid flows are discussed. Afterwards, the main models used to calculate the thermophysical properties of nanofluids are reviewed. This will be followed with the description of the main physical models presented for nanofluid flows and heat transfer, from single-phase to Eulerian and Lagrangian two-phase models. In part II, various computational fluid dynamics (CFD) techniques will be presented. Next, the latest studies on 3D simulation of nanofluid flow in various regimes and configurations are reviewed. The present review is expected to be helpful for researchers working on numerical simulation of nanofluids and also for scholars who work on experimental aspects of nanofluids to understand the underlying physical phenomena occurring during their experiments.

    更新日期:2018-12-07
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