• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-17
Ying Xiong; Xiaoxiao Cui; Mengmeng Zhang; Yuejiao Wang; Zhenning Lou; Weijun Shan
更新日期：2020-01-17
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-17
Jiayi Zhao; Feng Wei; Weili Xu; Xiaojun Han
更新日期：2020-01-17
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-17
Lyudmila V. Begunovich; Artem V. Kuklin; Maxim A. Visotin; Alexander A. Kuzubov; Felix N. Tomilin; Anton S. Tarasov; Yuri G. Mikhalev; Pavel V. Avramov
更新日期：2020-01-17
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Wonje Oh; Jisu Park; Chaehwan Jeong; Jinhong Park; Junsin Yi; Jaehyeong Lee
更新日期：2020-01-17
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Jing Li; Shike Hu; Zhiying Chen; Yijian Liang; He Kang; Yanhui Zhang; Yanping Sui; Shuang Wang; Guanghui Yu; Songang Peng; Zhi Jin; Xinyu Liu
更新日期：2020-01-17
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Barun Kumar Barman; Tadaaki Nagao; Karuna Kar Nanda
更新日期：2020-01-17
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Xikang Zhou; Wei Xue; Wenwen Liu; Dehua Zhu; Yu Cao
更新日期：2020-01-17
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-16
Pavel Fileviez Pérez, Clara Murgui, Alexis D. Plascencia

We discuss the possibility to predict the QCD axion mass in the context of grand unified theories. We investigate the implementation of the DFSZ mechanism in the context of renormalizable SU(5) theories. In the simplest theory, the axion mass can be predicted with good precision in the range ma = (2–16) neV, and there is a strong correlation between the predictions for the axion mass and proton decay rates. In this context, we predict an upper bound for the proton decay channels with antineutrinos, $$\tau \left(p\to {K}^{+}\overline{\nu}\right)\lesssim 4\times {10}^{37}$$ yr and $$\tau \left(p\to {\pi}^{+}\overline{\nu}\right)\lesssim 2\times {10}^{36}$$ yr. This theory can be considered as the minimal realistic grand unified theory with the DFSZ mechanism and it can be fully tested by proton decay and axion experiments.

更新日期：2020-01-17
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-16
Andrea Banfi, Barry M. Dillon, Wissarut Ketaiam, Sandra Kvedaraitė

In this paper we explore composite Higgs scenarios through the effects of light top-partners in Higgs+Jet production at the LHC. The pseudo-Goldstone boson nature of the Higgs field means that single-Higgs production via gluon fusion is insensitive to the mass spectrum of the top-partners. However in associated production this is not the case, and new physics scales may be probed. In the course of the work we consider scenarios with both one and two light top-partner multiplets in the spectrum of composite states. In compliance with perturbativity and experimental constraints, we study corrections to the Higgs couplings and the effects that the light top-partner multiplets have on the transverse momentum spectrum of the Higgs. Interestingly, we find that the corrections to the Standard Model expectation depend strongly on the representation of the top-partners in the global symmetry.

更新日期：2020-01-17
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-16
Andrea Manenti, Andreas Stergiou, Alessandro Vichi

Abstract We explore consequences of the Averaged Null Energy Condition (ANEC) for scaling dimensions ∆ of operators in four-dimensional $$\mathcal{N}$$ = 1 superconformal field theories. We show that in many cases the ANEC bounds are stronger than the corresponding unitarity bounds on ∆. We analyze in detail chiral operators in the $$\left(\frac{1}{2}j,0\right)$$ Lorentz representation and prove that the ANEC implies the lower bound $$\Delta \ge \frac{3}{2}j$$, which is stronger than the corresponding unitarity bound for j > 1. We also derive ANEC bounds on $$\left(\frac{1}{2}j,0\right)$$ operators obeying other possible shortening conditions, as well as general $$\left(\frac{1}{2}j,0\right)$$ operators not obeying any shortening condition. In both cases we find that they are typically stronger than the corresponding unitarity bounds. Finally, we elucidate operator-dimension constraints that follow from our $$\mathcal{N}$$ = 1 results for multiplets of $$\mathcal{N}$$ = 2, 4 superconformal theories in four dimensions. By recasting the ANEC as a convex optimization problem and using standard semidefinite programming methods we are able to improve on previous analyses in the literature pertaining to the nonsupersymmetric case.

更新日期：2020-01-17
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-16
Vahid Kamali

Abstract The evolution of the universe started from a hot and dense Big Bang point. Temperature fluctuation map of cosmic microwave background (CMB) radiation and initial seeds of large scale structures (LSS) are explained by an inflationary period in a very early time. Inflaton as quanta of the inflation field is responsible for the accelerated expansion of the universe. Potentials of the self-interacting single field models are constrained by observational data as well as quantum gravity. Some forms of the potential are rolled out by data of Planck satellite and some of them by quantum gravity constraints. In the standard model of inflation or cold inflation firstly universe expands where the inflaton rolls the nearly flat part of the potential and in the second part, the universe reheats where the inflaton oscillates around the minimum of the potential which leads to thermalized radiation dominated universe. String theory as the best model of quantum gravity forbids the oscillation around the minimum of the potential during the thermalized epoch of the reheating. But in the warm model of inflation thermalization happens during the accelerated expansion of the universe where the inflaton rolls nearly steep potential and the universe will be radiation dominated without any separated reheating epoch.

更新日期：2020-01-17
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-16
Martin Beneke, Mathias Garny, Sebastian Jaskiewicz, Robert Szafron, Leonardo Vernazza, Jian Wang

Abstract We sum the leading logarithms $${\alpha}_s^n{\ln}^{2n-1}\left(1-z\right)$$, n = 1, 2, . . . , near the kinematic threshold $$z={m}_H^2/\hat{s}\to 1$$ at next-to-leading power in the expansion in (1 − z) for Higgs production in gluon fusion. We highlight the new contributions compared to Drell-Yan production in quark-antiquark annihilation and show that the final result can be obtained to all orders by the substitution of the colour factor CF → CA, confirming previous fixed-order results. We also provide a numerical analysis of the next-to-leading power leading logarithms, which indicates that they are numerically relevant.

更新日期：2020-01-17
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
Alex May

As one of the results in this article, I stated a connection between bulk causal structure and boundary entanglement in the AdS/CFT correspondence.

更新日期：2020-01-17
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
Shlomo S. Razamat, Evyatar Sabag

We consider compactifications of 6d minimal (DN+3, DN+3) type conformal matter SCFTs on a generic Riemann surface. We derive the theories corresponding to three punctured spheres (trinions) with three maximal punctures, from which one can construct models corresponding to generic surfaces. The trinion models are simple quiver theories with $$\mathcal{N}$$ = 1 SU(2) gauge nodes. One of the three puncture non abelian symmetries is emergent in the IR. The derivation of the trinions proceeds by analyzing RG flows between conformal matter SCFTs with different values of N and relations between their subsequent reductions to 4d. In particular, using the flows we first derive trinions with two maximal and one minimal punctures, and then we argue that collections of N minimal punctures can be interpreted as a maximal one. This suggestion is checked by matching the properties of the 4d models such as ’t Hooft anomalies, symmetries, and the structure of the conformal manifold to the expectations from 6d. We then use the understanding that collections of minimal punctures might be equivalent to maximal ones to construct trinions with three maximal punctures, and then 4d theories corresponding to arbitrary surfaces, for 6d models described by two M5 branes probing a ℤk singularity. This entails the introduction of a novel type of maximal puncture. Again, the suggestion is checked by matching anomalies, symmetries and the conformal manifold to expectations from six dimensions. These constructions thus give us a detailed understanding of compactifications of two sequences of six dimensional SCFTs to four dimensions.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Jinlin Song; Lu Lu; Bowen Li; Bo Zhang; Run Hu; Xinping Zhou; Qiang Cheng

The diffusive nature of heat flow lays a formidable obstacle for directional heat manipulation, not akin to the wave-governed electromagnetics that can be well controlled in intensity and direction. By modulating the near-field radiative heat transfer among graphene/SiC core-shell (GSCS) nanoparticles, we propose the concept of thermal routing to address the directional heat manipulation in a particular many-body setup. The graphene shell introduces a minor polarizability peak and remarkably modifies the localized surface resonance of the particle, which plays a significant role in the radiative heat transfer within the many-body system consisting of GSCS nanoparticles. Consequently, Fermi levels of graphene shells matching allows directional radiative heat flow, thus enabling thermal routing manifested by variant designated temperature distributions. The proposed thermal routing could be used to dynamically tune heat flow in integrated nano-objects for thermal manipulation, and also opens avenues for exploiting novel thermal functionalities via radiative heat transfer at the nanoscale.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Fang Liu; Huahao Sun; Dongxiang Zhang; Qiang Chen; Jun Zhao; Liqiu Wang

This study presents numerical simulations, back propagation artificial neural networks and genetic algorithms for optimizing laminar convective heat transfer of oil-in-water nanoemulsion fluids having non-Fourier heat conduction characteristics. Firstly, a numerical study has been conducted on laminar flow and forced convective heat transfer of oil-in-water nanoemulsion fluids in toroidal ducts using Eulerian-Lagrangian two-phase approach. New correlations of drag coefficient, effective thermal conductivity and effective viscosity were adopted to improve the accuracy of simulation. Numerical results show that convective heat transfer can be enhanced by oil nanodroplets with thermal conductivity lower than that of the base fluid. Then regression models and artificial neural network models were developed based on simulation results for predicting convective heat transfer performances of nanoemulsions, considering effects of cross-sectional aspect ratio, Reynolds number, oil nanodroplet diameter and concentration. Artificial neural network models can predict mean Nusselt number and pressure drop better than the regression model. Finally, genetic algorithms was used to optimize convective heat transfer of nanoemulsions considering droplet migration. It can be found that low cross-sectional aspect ratio of width to height is beneficial for thermal performance factor. For single-objective optimization, mean Nusselt number reaches the maximum 32.3 at aspect ratio of 0.9677 and thermal performance factor reaches the maximum 1.305 at aspect ratio of 0.3935 under certain conditions. Pareto optimal set was obtained for two-objective optimization. This study would be useful for the optimal design of convective heat transfer of emulsions in toroidal ducts.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Chunrong Zhao; Michael Opolot; Ming Liu; Frank Bruno; Simone Mancin; Kamel Hooman

Application of different heat transfer augmentation techniques, including the use of fins or foams, were investigated to enhance the melting rate of a solid phase change material within an annulus where the inner and outer pipes were subjected to constant wall temperature. The carbon fibre fins as well as three commonly-used foams (made of three different materials: nickel, aluminium and copper) were simulated. Firstly, keeping the total fin volume constant, the fin number density effect on the melting rate was investigated. After an optimal fin number density was obtained, three possible strategies (unequal length, uneven intervals and tree-shaped fins) were explored aimed at a more comprehensive understanding of the induced heat transfer enhancement. It was observed that with a fixed fin thickness and volume, the melting time is not a monotonic function of the fin number density and can be optimized. Comparing pure PCM melting, the use of optimized fin number reduced over 60% of melting time, while additional 8% and 4% further time reduction could be achieved by appropriately increasing lengths and decreasing intervals of bottom fins, respectively. The use of tree-like fins resulted in a longer melting time, comparing to that of longitudinal straight fins, which indicates it is not always a good option. Finally, the results, primarily the melting rates, were compared with those obtained through the use of metal foams with different metals. It was observed that the melting time of optimized strategy-1 is rather less than those of Cu and Al foams, and approximately 2200s shorter than that of Ni foams. These results indicate that the fins, if designed properly, can be as efficient as foams.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Tian-Yu Zhang; Lin-Wei Mou; Jia-Yi Zhang; Li-Wu Fan; Jia-Qi Li

Steam condensation is a ubiquitous phenomenon of phase change that can be encountered in various industrial applications. In practice, the presence of non-condensable gases (NCG) is often inevitable, which can severely deteriorate condensation heat transfer by accumulating in the vicinity of the condensing surface as an additional thermal resistance. In this work, steam condensation heat transfer on a honeycomb-like microporous superhydrophobic surface, which has already been shown to lead to stable coalescence-induced droplet jumping with high heat flux, was studied with NCG concentrations up to ~28%. The superhydrophobic surface, having a nominal pore diameter of ~20 μm, was prepared by a rapid, cost-effective and highly scalable electrodeposition method over the outer surface of thin copper tubes. Condensation experiments were conducted in a visualized vacuum chamber maintaining at a constant pressure of 9.5 kPa. Significant enhancements of condensation heat transfer at the various NCG concentrations were exhibited on such superhydrophobic surface over a wide range of subcooling up to ~35 K, due to the successful realization of droplet jumping in spite of the presence of NCG. The adsorption of NCG into the micropores was elucidated to be a partial reason for prohibition of condensate flooding at relatively high degrees of subcooling.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Shi Tao; Ao Xu; Qing He; Baiman Chen; Frank G.F. Qin

We propose a curved lattice Boltzmann boundary scheme for thermal convective flows with Neumann boundary condition. The distribution function at the fluid-solid intersection node is obtained to accomplish the interpolation of unknown temperature distribution function at the boundary point. Specifically, the distribution function is first extrapolated from the fluid point along the lattice link; and then, the one in the opposite direction is evaluated by the anti-bounce back rule with wall temperature, which can be further determined by the specified Neumann boundary condition at the fluid-solid interface. The advantage of our scheme is that the involved inter/extrapolations are completely link-based, resulting in a quite efficient implementation procedure. Furthermore, our scheme has second-order spatial accuracy, and we verified in four numerical examples where analytical solutions are available: the heat transfer in a channel with a sinusoidal temperature gradient, the thermal diffusion in an annulus, and the conjugate heat transfer for these two cases. To further validate our scheme for thermal convective flow problems with complex geometries, we simulate the natural convection in an annulus, the thermal flow past a cylinder, and the mixed convection in a lid-driven cavity with a circular enclosure. The simulation results are consistent with existing benchmark data obtained by other methods.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Subrata Bhattacharjee; Kenneth Dong

Radiation has been found to play an important role in opposed-flow flame spread, especially in the low-velocity microgravity environment. To explore the various aspects of flame radiation, an existing comprehensive 2D computational model including gas and surface radiation as well as radiation feedback to the solid is utilized. The comprehensive radiation model is simplified into a number of sub-models: no radiation, gas losses, surface loss, uncoupled (gas and surface losses without feedback). The sub-models are evaluated over the kinetic, thermal, and radiative regimes for a thin PMMA fuel. The resulting spread rates, flame and vaporization temperatures, and flame structures are compared to the comprehensive fully coupled model. The computational results reveal that gas-to-surface feedback moderately enhances spread rate and may affect the critical burnout velocity but has little effect on flame and vaporization temperatures.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Do Yeong Lim; In Cheol Bang

To elucidate the boiling heat transfer on a biphilic surface, the bubble departure diameter and the bubble location were controlled through the variation of the size and pitch of hydrophobic patterns on the biphilic surface. We postulated that if the average bubble departure diameter can be reduced, both the critical heat flux (CHF) and heat transfer coefficient (HTC) can be enhanced owing to the reduced dry spot area and increased active bubble cycle. The bubble dynamics and boiling performance were evaluated by adjusting the hydrophobic pattern size and the pitch of the biphilic surface using a porous superhydrophobic material with high adhesion to vapor, 14.5% of CHF and 34.1% of HTC in S2P4N64 biphilic surface were enhanced over the bare surface. The bubble departure diameter decreased as the pattern size and pitch decreased, and the CHF was enhanced in inverse proportion to bubble departure diameter. This study indicates that the bubble departure diameter on biphilic surfaces can be controlled according to the intentions of the designer.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Zeyang Lei; Bin Liu; Pengzhuo Xu; Yonghai Zhang; Jinjia Wei

In this paper, the pool boiling heat transfer performance of cylindrical microstructured surfaces that were fabricated using the dry etching technique was studied. The working fluid was FC-72, and the experimental conditions included four different liquid subcooling temperatures (0, 15, 25, and 35 K). The heated microstructured surfaces consist of smooth parts and circular micropillar blocks, which are classified as single-block type (MP-1), four-block type (MP-2), 16-block type (MP-3, MP-4, MP-5) or composite-block type (MP-6). The material that was used as the substrate was P doped silicon chip. The experimental results showed that the heat transfer coefficient (HTC) and the critical heat flux (CHF) of all of the microstructured surfaces are greatly enhanced compared with the smooth surface because the block divisions and blank area could effectively prevent vapor columns from coalescing. Among the microstructured surface types, surface MP-3 has the largest CHF with different subcooling, while its actual heat transfer area of microstructured surface is relatively small. Furthermore, the mechanism and behavior of vapor column coalescence under critical heat flux conditions were analyzed. The prediction of CHF by using the critical vapor column radius (rgc) was compared and analyzed with the experimental data. Finally, the critical metastability phenomenon was demonstrated, and its occurrence mechanism was explored and explained. The experimental results show that restricting the coalescence of the vapor column is an effective method to augment CHF, and a high CHF can be obtained even when the surface area enhancement ratio is relatively low.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Xin-lin Xia; Zhen-huan Li; Chao Fan; Xiao-lei Li; Chuang Sun

Coupled radiation-convection heat transfer inside a unit metal foam layer with high-flux irradiation is studied using improved scale-integrated simulation. It integrates the discrete-scale CFD simulation with that of continuum-scale via the multi-domain concept with thermal radiation effect considered. Conservations of mass flux and energy are satisfied on these specified subdomain interfaces, and a special defined transition zone with geometry-dependent functional quantities is introduced within the continuum-scale subdomain. This zone is adjacent to the discrete-scale subdomain which ensures a reasonable transition. Absorbed radiative fluxes and radiative heat transfer within the whole domain are calculated with Monte Carlo method and treated as heat sources. The problem under consideration has been investigated via the discrete-scale simulation, the continuum-scale simulation, and the scale-integrated simulation. The accurateness of scale-integrated simulation has been fully validated for predicting both flow field and heat transfer characteristics in comparison with the outcomes of discrete-scale simulation and other investigations. Deviations between the outcomes of continuum-scale simulation and discrete-scale simulation are found to be mainly caused by inconsistent local absorbed radiative heat fluxes distribution and impinging effect around the entry region. Up to 70% and 60% reduction of computation time and memory footprints are achieved when scale-integrated strategy is employed for the CFD simulation compared with the discrete-scale simulation. Meanwhile, the detailed fluctuated characteristics of the local concerned region and overall heat transfer performance can be precisely reflected. It may break up the computation limitations of the discrete-scale simulation in studying the energy transport process in foam based solar receiver applications.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Jiansheng Wang; Jinyuan Xie; Xueling Liu

A three-dimensional closed-loop pulsating heat pipe (CLPHP), with different wettability and charged with deionized water is numerically investigated in present work. The thermal performance and bubble dynamics of CLPHP are obtained under the condition of various input heat loads. It's found that the performance of CLPHP is affected by both surface wettability and input heat load. Under lower input heat load, CLPHP with hydrophobic surface (including superhydrophobic surface) has lower thermal resistance than that with hydrophilic surface. Conversely, CLPHP with hydrophilic surface starts up earlier, and has better thermal performance under higher input heat load. Specially, compared with the CLPHP with superhydrophobic surface, the thermal resistance of CLPHP with superhydrophilic reduces by 10.8% under the input heat load of 20 W. Moreover, the reversal of flow direction is observed in CLPHP with hydrophobic surface, while the stable directional circulation is always maintained in CLPHP with hydrophilic surface. The results indicate that the difference between advancing and receding angles (dynamic contact angle hysteresis) leads to various capillary resistance. Furthermore, due to lower flow resistance and the effect of liquid film, CLPHP with hydrophilic surface can effectively raise the dry-out input heat load.

更新日期：2020-01-17
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-17
Shunsuke Hashimoto; Koichi Kurazono; Takafumi Yamauchi
更新日期：2020-01-17
• J. Comput. Phys. (IF 2.845) Pub Date : 2020-01-17
Hiroaki Nishikawa

Simple modification techniques are proposed for making numerical fluxes amenable to unrealizable states (e.g., negative density) without degrading the design order of accuracy, so that a finite-volume solver never fails with unrealizable states arising in the solution reconstruction step and continues to run. The main idea is to evaluate quantities not affecting the order of accuracy but important for stabilization, e.g., a dissipation matrix, with low-order unreconstructed solutions. For the viscous flux, the viscosity is linearly extrapolated instead of being evaluated with linearly reconstructed temperatures to avoid a failure with a negative temperature. These ideas are quite general and may be applied to a wide range of numerical fluxes. In this paper, we illustrate them with the Roe flux and the alpha-damping viscous flux and demonstrate their effectiveness for cases, where a conventional technique encounters difficulties.

更新日期：2020-01-17
• J. Comput. Phys. (IF 2.845) Pub Date : 2020-01-16
G. Chen; L. Chacón; L. Yin; B.J. Albright; D.J. Stark; R.F. Bird

Conventional explicit electromagnetic particle-in-cell (PIC) algorithms do not conserve discrete energy exactly. Time-centered fully implicit PIC algorithms can conserve discrete energy exactly, but may introduce large dispersion errors in the light-wave modes. This can lead to intolerable simulation errors where accurate light propagation is needed (e.g. in laser-plasma interactions). In this study, we selectively combine the leap-frog and Crank-Nicolson methods to produce an exactly energy- and charge-conserving relativistic electromagnetic PIC algorithm. Specifically, we employ the leap-frog method for Maxwell's equations, and the Crank-Nicolson method for the particle equations. The semi-implicit formulation still features a timestep CFL, but facilitates exact global energy conservation, exact local charge conservation, and preserves the dispersion properties of the leap-frog method for the light wave. The algorithm employs a new particle pusher designed to maximize efficiency and minimize wall-clock-time impact vs. the explicit alternative. It has been implemented in a code named iVPIC, based on the Los Alamos National Laboratory VPIC code (https://github.com/losalamos/vpic). We present numerical results that demonstrate the properties of the scheme with sample test problems: relativistic two-stream instability, Weibel instability, and laser-plasma instabilities.

更新日期：2020-01-17
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
JuYeon Kim; WonJin Kim; GeunHyung Kim

A hierarchical micro/nanoscale scaffold fabricated using a combined method involving an electric-field (E-field)-assisted printing and plasma-treatment process was proposed for myoblast alignment and differentiation. By appropriately selecting various processing conditions, including the E-field strength and printing parameters, a uniaxially aligned bundle of polycaprolactone (PCL) consisting of microsized struts (diameter = 40–50 μm) was stably obtained. After the PCL struts were printed, oxygen-plasma treatment was applied, and eventually a chemically and physically modified nanoscale structure on their surfaces was achieved. To investigate the feasibility of the struts as a biomedical scaffold for muscle tissue regeneration, in vitro C2C12 myoblast activities, including the cell proliferation, cell alignment, and myotube formation, were evaluated. The unique fabricated structure exhibited significantly higher cellular activities, including myotube formation and myogenic gene expression, than non-hierarchical and flat surfaces.

更新日期：2020-01-16
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Junxi Li; Yiyin Peng; Wendong Zhang; Xuelin Shi; Min Chen; Peng Wang; Xianming Zhang; Hailu Fu; Xiaoshu Lv; Fan Dong; Guangming Jiang
更新日期：2020-01-16
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Diego Guzmán; Mauricio Isaacs; Tatsuya Tsukuda; Seiji Yamazoe; Ryo Takahata; Ricardo Schrebler; Ana Burgos; Igor Osorio-Román; Francisco Castillo
更新日期：2020-01-16
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Tae Ho Lee; Hyunchul Jeong; Byung Hun Jeong; Jung Sik Han; Min Yeong Gim; Do Heui Kim; Sung Hyun Kim; Ki Bong Lee
更新日期：2020-01-16
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Neeraj Sharma; Mohd. Arif; Shagun Monga; Mohd. Shkir; Y.K. Mishra; Arun Singh

In the present investigation we report a comparative study of Graphene Oxide (GO) in regard to its bandgap variations arising due to different reduction methods such as thermal reduction (Heating), electrical reduction (Voltage Application) and chemical reduction (Hydrazine hydrate). This study reveals that among the GO three reduction method studied the voltage application is the most efficient one. It is found that band gap increases with decreasing carbon to oxygen (C/O) ratio and is found to be maximum, i.e. ∼ 4, for the case of GO reduced via voltage application reduction method. The GO for the present study was synthesized by modified Hummer’s Method in four batches out of which the three obtained solutions were reduced by thermal reduction, Voltage application and Hydrazine hydrate. The four resultant materials were investigated by XRD, FTIR, UV-Vis, SEM-EDX and Raman analysis. The variation of band gap of GO and reduced graphene oxide (rGO) was found to be 3.34eV (GO), HrGO (Hydrazine) 2.96eV, TrGO (Heating) 2.68 eV and VrGO (Voltage application) 2.54eV, respectively.

更新日期：2020-01-16
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Chao-Qian Guo; Song-Sheng Lin; Di Gao; Qian Shi; Chun-Bei Wei; Ming-Jiang Dai; Yi-Fan Su; Wei Xu; Peng Tang; Hong Li; Wei Wang; Xia-Gao Zhu
更新日期：2020-01-16
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-16
Hyojung Bae; Vishal Burungale; Jun-Beom Park; Seung Wan Bang; Hokyun Rho; Soon Hyung Kang; Sang-Wan Ryu; Jun-Seok Ha
更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
Harald Grosse, Alexander Hock, Raimar Wulkenhaar

Abstract Previously the exact solution of the planar sector of the self-dual Φ4-model on 4-dimensional Moyal space was established up to the solution of a Fredholm integral equation. This paper solves, for any coupling constant λ > −$$\frac{1}{\uppi}$$, the Fredholm equation in terms of a hypergeometric function and thus completes the construction of the planar sector of the model. We prove that the interacting model has spectral dimension 4 − 2 $$\frac{\arcsin \left(\uplambda \uppi \right)}{\uppi}$$ for |λ| <$$\frac{1}{\uppi}$$. It is this dimension drop which for λ > 0 avoids the triviality problem of the matricial $${\varPhi}_4^4$$-model. We also establish the power series approximation of the Fredholm solution to all orders in λ. The appearing functions are hyperlogarithms defined by iterated integrals, here of alternating letters 0 and −1. We identify the renormalisation parameter which gives the same normalisation as the ribbon graph expansion.

更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
Michael Krämer, Benjamin Summ, Alexander Voigt

Abstract We extend the known Universal One-Loop Effective Action (UOLEA) by all operators which involve scalars and fermions, not including contributions arising from open covariant derivatives. Our generic analytic expressions for the one-loop Wilson coefficients of effective operators up to dimension six allow for an application of the UOLEA to a broader class of UV-complete models. We apply our generic results to various effective theories of supersymmetric models, where different supersymmetric particles are integrated out at a high mass scale.

更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
George Georgiou, Eftychia Sagkrioti, Konstantinos Sfetsos, Konstantinos Siampos

Abstract We consider λ-deformed current algebra CFTs at level k, interpolating between an exact CFT in the UV and a PCM in the IR. By employing gravitational techniques, we derive the two-loop, in the large k expansion, β-function. We find that this is covariant under a remarkable exact symmetry involving the coupling λ, the level k and the adjoint quadratic Casimir of the group. Using this symmetry and CFT techniques, we are able to compute the Zamolodchikov metric, the anomalous dimension of the bilinear operator and the Zamolodchikov C -function at two-loops in the large k expansion, as exact func- tions of the deformation parameter. Finally, we extend the above results to λ-deformed parafermionic algebra coset CFTs which interpolate between exact coset CFTs in the UV and a symmetric coset space in the IR.

更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
T. Engel, A. Signer, Y. Ulrich

Abstract We present an extension of the FKS subtraction scheme beyond next-to-leading order to deal with soft singularities in fully differential calculations within QED with mas- sive fermions. After a detailed discussion of the next-to-next-to-leading order case, we show how to extend the scheme to even higher orders in perturbation theory. As an application we discuss the computation of the next-to-next-to-leading order QED corrections to the muon decay and present differential results with full electron mass dependence.

更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
Henry W. Lin, Leonard Susskind

A celebrated feature of SYK-like models is that at low energies, their dynamics reduces to that of a single variable. In many setups, this “Schwarzian” variable can be interpreted as the extremal volume of the dual black hole, and the resulting dynamics is simply that of a 1D Newtonian particle in an exponential potential. On the complexity side, geodesics on a simplified version of Nielsen’s complexity geometry also behave like a 1D particle in a potential given by the angular momentum barrier. The agreement between the effective actions of volume and complexity succinctly summarizes various strands of evidence that complexity is closely related to the dynamics of black holes.

更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
Thales Azevedo, Renann Lipinski Jusinskas, Matheus Lize

Abstract In this work, we investigate the bosonic chiral string in the sectorized inter- pretation, computing its spectrum, kinetic action and 3-point amplitudes. As expected, the bosonic ambitwistor string is recovered in the tensionless limit. We also consider an extension of the bosonic model with current algebras. In that case, we compute the effective action and show that it is essentially the same as the action of the mass-deformed (DF )2 theory found by Johansson and Nohle. Aspects which might seem somewhat contrived in the original construction — such as the inclusion of a scalar transforming in some real representation of the gauge group — are shown to follow very naturally from the worldsheet formulation of the theory.

更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
L. Andrianopoli, B.L. Cerchiai, R. D’Auria, A. Gallerati, R. Noris, M. Trigiante, J. Zanelli

Abstract We derive a 2+1 dimensional model with unconventional supersymmetry at the boundary of an AdS4$$\mathcal{N}$$ -extended supergravity, generalizing previous results. The (unconventional) extended supersymmetry of the boundary model is instrumental in describing, within a top-down approach, the electronic properties of graphene-like 2D materials at the two Dirac points, K and K′. The two valleys correspond to the two independent sectors of the OSp(p|2) × OSp(q|2) boundary model in the p = q case, which are related by a parity transformation. The Semenoff and Haldane-type masses entering the corresponding Dirac equations are identified with the torsion parameters of the substrate in the model.

更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-15
Sylvain Fichet, Prashant Saraswat

There are strong reasons to believe that global symmetries of quantum theories cannot be exact in the presence of gravity. While this has been argued at the qualitative level, establishing a quantitative statement is more challenging. In this work we take new steps towards quantifying symmetry violation in EFTs with gravity. First, we evaluate global charge violation by microscopic black holes present in a thermal system, which represents an irreducible, universal effect at finite temperature. Second, based on general QFT considerations, we propose that local symmetry-violating processes should be faster than black hole-induced processes at any sub-Planckian temperature. Such a proposal can be seen as part of the “swampland” program to constrain EFTs emerging from quantum gravity. Considering an EFT perspective, we formulate a con- jecture which requires the existence of operators violating global symmetry and places quantitative bounds on them. We study the interplay of our conjecture with emergent symmetries in QFT. In models where gauged U(1)’s enforce accidental symmetries, we find that constraints from the Weak Gravity Conjecture can ensure that our conjecture is satisfied. We also study the consistency of the conjecture with QFT models of emergent symmetries such as extradimensional localization, the Froggatt-Nielsen mechanism, and the clockwork mechanism.

更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-14
Sebastian Garcia-Saenz, Lucas Pinol, Sébastien Renaux-Petel

Recent studies of inflation with multiple scalar fields have highlighted the importance of non-canonical kinetic terms in novel types of inflationary solutions. This motivates a thorough analysis of non-Gaussianities in this context, which we revisit here by studying the primordial bispectrum in a general two-field model. Our main result is the complete cubic action for inflationary fluctuations written in comoving gauge, i.e. in terms of the curvature perturbation and the entropic mode. Although full expressions for the cubic action have already been derived in terms of fields fluctuations in the flat gauge, their applicability is mostly restricted to numerical evaluations. Our form of the action is instead amenable to several analytical approximations, as our calculation in terms of the directly observable quantity makes manifest the scaling of every operator in terms of the slow-roll parameters, what is essentially a generalization of Maldacena’s single-field result to non-canonical two-field models. As an important application we derive the single-field effective field theory that is valid when the entropic mode is heavy and may be integrated out, underlining the observable effects that derive from a curved field space.

更新日期：2020-01-16
• J. Comput. Phys. (IF 2.845) Pub Date : 2020-01-15
Daniil Bochkov; Frederic Gibou

We present a simple numerical algorithm for solving elliptic equations where the diffusion coefficient, the source term, the solution and its flux are discontinuous across an irregular interface. The algorithm produces second-order accurate solutions and first-order accurate gradients in the L∞-norm on Cartesian grids. The condition number is bounded, regardless of the ratio of the diffusion constant and scales like that of the standard 5-point stencil approximation on a rectangular grid with no interface. Numerical examples are given in two and three spatial dimensions.

更新日期：2020-01-16
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-14
Robin Karlsson, Manuela Kulaxizi, Andrei Parnachev, Petar Tadić

Near lightcone correlators are dominated by operators with the lowest twist. We consider the contributions of such leading lowest twist multi-stress tensor operators to a heavy-heavy-light-light correlator in a CFT of any even dimensionality with a large central charge. An infinite number of such operators contribute, but their sum is described by a simple ansatz. We show that the coefficients in this ansatz can be determined recursively, thereby providing an operational procedure to compute them. This is achieved by bootstrapping the corresponding near lightcone correlator: conformal data for any minimal­ twist determines that for the higher minimal-twist and so on. To illustrate this procedure in four spacetime dimensions we determine the contributions of double- and triple-stress tensors. We compute the OPE coefficients; whenever results are available in the literature, we observe complete agreement. We also compute the contributions of double-stress tensors in six spacetime dimensions and determine the corresponding OPE coefficients. In all cases the results are consistent with the exponentiation of the near lightcone correlator. This is similar to the situation in two spacetime dimensions for the Virasoro vacuum block.

更新日期：2020-01-15
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-13
Jan de Boer, Rik van Breukelen, Sagar F. Lokhande, Kyriakos Papadodimas, Erik Verlinde

Abstract We investigate the possibility that the geometry dual to a typical AdS black hole microstate corresponds to the extended AdS-Schwarzschild geometry, including a region spacelike to the exterior. We argue that this region can be described by the mirror operators, a set of state-dependent operators in the dual CFT. We probe the geometry of a typical state by considering state-dependent deformations of the CFT Hamiltonian, which have an interpretation as a one-sided analogue of the Gao-Jafferis-Wall traversable wormhole protocol for typical states. We argue that the validity of the conjectured bulk geometry requires that out-of-time-order correlators of simple CFT operators on typical pure states must exhibit the same chaotic effects as thermal correlators at scrambling time. This condition is related to the question of whether the product of operators separated by scrambling time obey the Eigenstate Thermalization Hypothesis. We investigate some of these statements in the SYK model and discuss similarities with state-dependent perturba- tions of pure states in the SYK model previously considered by Kourkoulou and Maldacena. Finally, we discuss how the mirror operators can be used to implement an analogue of the Hayden-Preskill protocol.

更新日期：2020-01-15
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-13
Roberto Auzzi, Stefano Baiguera, Andrea Legramandi, Giuseppe Nardelli, Pratim Roy, Nicolò Zenoni

Abstract We analytically compute subsystem action complexity for a segment in the BTZ black hole background up to the finite term, and we find that it is equal to the sum of a linearly divergent term proportional to the size of the subregion and of a term proportional to the entanglement entropy. This elegant structure does not survive to more complicated geometries: in the case of a two segments subregion in AdS3, complexity has additional finite contributions. We give analytic results for the mutual action complexity of a two segments subregion.

更新日期：2020-01-15
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-13
Luis F. Alday, Johan Henriksson, Mark van Loon

Abstract We apply the methods of modern analytic bootstrap to the critical O(N) model in a 1/N expansion. At infinite N the model possesses higher spin symmetry which is weakly broken as we turn on 1/N. By studying consistency conditions for the correlator of four fundamental fields we derive the CFT-data for all the (broken) currents to order 1/N, and the CFT-data for the non-singlet currents to order 1/N2. To order 1/N our results are in perfect agreement with those in the literature. To order 1/N2 we reproduce known results for anomalous dimensions and obtain a variety of new results for structure constants, including the global symmetry central charge CJ to this order.

更新日期：2020-01-15
• J. High Energy Phys. (IF 5.833) Pub Date : 2020-01-13
Marzia Bordone, Oscar Catà, Thorsten Feldmann

Abstract Extending the Standard Model with higher-dimensional operators in an effective field theory (EFT) approach provides a systematic framework to study new physics (NP) effects from a bottom-up perspective, as long as the NP scale is sufficiently large compared to the energies probed in the experimental observables. However, when taking into account the different quark and lepton flavours, the number of free parameters in- creases dramatically, which makes generic studies of the NP flavour structure infeasible. In this paper, we address this issue in view of the recently observed “flavour anomalies” in B-meson decays, which we take as a motivation to develop a general framework that allows us to systematically reduce the number of flavour parameters in the EFT. This framework can be easily used in global fits to flavour observables at Belle II and LHCb as well as in analyses of flavour-dependent collider signatures at the LHC. Our formalism represents an extension of the well-known minimal-flavour-violation approach, and uses Froggatt-Nielsen charges to define the flavour power-counting. As a relevant illustration of the formalism, we apply it to the flavour structures which could be induced by a U1 vector leptoquark, which represents one of the possible explanations for the recent hints of flavour non-universality in semileptonic B-decays. We study the phenomenological viability of this specific framework performing a fit to low-energy flavour observables.

更新日期：2020-01-15
• Int. J. Heat Mass Transf. (IF 4.346) Pub Date : 2020-01-15

Experiments on heat transfer over Mach 8, 15° compression corner flow affected by Görtler-like reattachment vortices of controllable intensity are carried out in the shock wind tunnel UT-1 M (TsAGI). Experiments cover two Reynolds numbers Re∞,L=(1.75±0.08) × 105 and Re∞,L=(3.90±0.15) × 105 based on the sharp flat plate length at which the reattachment flow is close to laminar or beginning transitional, respectively. The effect of streamwise vortices of different intensity on spanwise variations of the heat flux and its spanwise-averaged level at the reattachment region is investigated. The intensity of the vortices is varied by accurate controlling the height of a spanwise rake of cylindrical pins (seeding elements) placed on the plate ahead of the separation bubble.

更新日期：2020-01-15
• J. Comput. Phys. (IF 2.845) Pub Date : 2020-01-15
David Gunderman; Natasha Flyer; Bengt Fornberg

This work presents a numerical algorithm for using radial basis function-generated finite differences (RBF-FD) to solve partial differential equations (PDEs) on S2 using polyharmonic splines with added polynomials defined in a 2D plane (PHS+Poly). We introduce a novel method for calculating RBF-FD PHS+Poly differentiation weights on S2 using first a Householder reflection and then a projection onto the tangent plane. The new PHS+Poly RBF-FD method is implemented on two standard test cases: 1) solid body rotation on S2 and 2) 3D tracer transport within Earth's atmosphere. Compared to existing methods (including those in the RBF literature) at similar resolutions, this approach requires fewer degrees of freedom and is algorithmically much simpler. A MATLAB code to implement the method is included in the Appendix.

更新日期：2020-01-15
• J. Comput. Phys. (IF 2.845) Pub Date : 2020-01-15
Naveen Kumar Garg; N.H. Maruthi; S.V. Raghurama Rao; M. Sekhar

In this study, convection-pressure split Euler flux functions which contain weakly hyperbolic convective subsystems are analyzed. A system of first-order partial differential equations (PDEs) is said to be weakly hyperbolic if the corresponding flux Jacobian does not contain a complete set of linearly independent (LI) eigenvectors. Thus, the application of existing flux difference splitting (FDS) based schemes, which depend heavily on both eigenvalues and eigenvectors, are non-trivial to such systems. In the case of weakly hyperbolic systems, a required set of LI eigenvectors can be constructed through the addition of generalized eigenvectors by utilizing the theory of Jordan canonical forms. Once this is achieved for a weakly hyperbolic convective subsystem, an upwind solver can be constructed in the splitting framework. In the present work, the above approach is used for developing two new schemes. The first scheme is based on the Zha–Bilgen type splitting while the second is based on the Toro–Vázquez splitting. Both the schemes are tested on various benchmark problems in one-dimension (1-D) and two-dimensions (2-D). The concept of generalized eigenvectors based on Jordan forms is found to be useful in dealing with the weakly hyperbolic parts of the considered Euler systems.

更新日期：2020-01-15
• J. Comput. Phys. (IF 2.845) Pub Date : 2020-01-15
Jiuhua Hu; Guanglian Li

We consider the initial boundary value problem for the time-fractional diffusion equation with a homogeneous Dirichlet boundary condition and an inhomogeneous initial data a(x)∈L2(D) in a bounded domain D⊂Rd with a sufficiently smooth boundary. We analyze the homogenized solution under the assumption that the diffusion coefficient κϵ(x) is smooth and periodic with the period ϵ>0 being sufficiently small. We derive that its first order approximation measured by both pointwise-in-time in L2(D) and Lp((θ,T);H1(D)) for p∈[1,∞) and θ∈(0,T) has a convergence rate of O(ϵ1/2) when the dimension d≤2 and O(ϵ1/6) when d=3. Several numerical tests are presented to demonstrate the performance of the first order approximation.

更新日期：2020-01-15
• J. Comput. Phys. (IF 2.845) Pub Date : 2020-01-15
Hui Zheng; Chuanbing Zhou; Dong-Jia Yan; Yue-Sheng Wang; Chuanzeng Zhang

In this paper, the band structures of nanoscale phononic crystals based on the nonlocal elasticity theory are calculated by using a meshfree local radial basis function collocation method (LRBFCM). The direct method is applied to enhance the stability of the derivative calculations in the LRBFCM. A simple summation in the LRBFCM is proposed to deal with the integration related to the nonlocal stresses or tractions. The LRBFCM for the band structure calculations is validated by the results obtained with the first principle and the transfer matrix (TM) method for one-dimensional (1D) phononic crystals, as well as the comparison of the frequency responses of the two-dimensional (2D) periodical structures.

更新日期：2020-01-15
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-15
Musheng Wu; Bo Xu; Wenwei Luo; Baozhen Sun; Jing Shi; Chuying Ouyang
更新日期：2020-01-15
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-15
Juan Wang; Junru Wang; Xiaohan Song; Siyun Qi; Mingwen Zhao
更新日期：2020-01-15
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-15
Haixia Jiang; Zewen Duan; BeiBei zhang; Xiaoyu Zhao; Peng Wang
更新日期：2020-01-15
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-15
Hao Sun; Bing Liu; Dan Li; Jie Yao
更新日期：2020-01-15
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-15
Bo Gao; Xiaoye Du; Yanhuai Li; Zhongxiao Song

The synthesis of non-noble electrocatalysts for hydrogen evolution reaction (HER) is a critial challenge for practical hydrogen production applications. Molybdenum sulfide materials have been proven to be an ideal catalyst for HER due to the edge activity was close to platinum. Herein, we report a novel and facile method for Ni3B4-doped MoS2 nanosheet directly deposited on Ni foam through co-sputtering. Benefiting from the tansition of wettability from hydrophobic to hydrophilic and the existance of defects, the MoS2+Ni3B4[email protected] exhibited outstanding electrocatalytic performance compare to pure-MoS2@NF in alkaline conditions. The results revel that the mixture of Ni3B4 degrees brings the wettability tansition, which promote the contact between electrode and electrolyte, and the mixture of Ni3B4 degrees had an optimun condition. What’s more during the deposition process the bombardment and etching of ion induced defects, which expose more active sites.

更新日期：2020-01-15
• Appl. Surf. Sci. (IF 5.155) Pub Date : 2020-01-15
Dongxu Zhu; Lijin Wang; Zheming Liu; Aiwei Tang
更新日期：2020-01-15
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