The output of a laser wakefield accelerator depends strongly on the density profile of the gas target. In this work we focus on the reconstruction of 3D density profiles from tomographic measurements. We compare analytical and iterative methods, and we propose a new one, the filtered algebraic reconstruction method (FARM), which is tailored for the reconstruction of gas targets for laser wakefield

Large-scale particle image velocimetry (LSPIV) has been widely used for quantifying the velocity distribution of environmental water surfaces, especially river flows. In LSPIV, the evaluated velocity distribution of a region far from the camera tends to have a large uncertainty due to strong image distortion and reduced image resolution, especially for directions parallel to the viewing angle. This

A planarized optical fibre designed for two-dimensional bend monitoring and external refractive index sensing is presented. The approach uses two single-mode waveguides each containing a set of spectrally multiplexed Bragg gratings. To achieve sensitivity to bending and external refractive index, the cladding material of the fibre is partially removed through physical machining. This acts to offset

We reported the development of a quartz-enhanced photoacoustic sulfur hexafluoride (SF 6 ) sensor for ventilation studies using a continuous-wave distributed-feedback quantum cascade laser (QCL) at 10.5 µm. The SF 6 sensor was developed by detecting the gas-absorption induced acoustic wave using a tiny quartz tuning fork that is enclosed in a gas cell with a sample volume of 2.5 ml. By locking the

Owing to the highly dimensional nature of hyperspectral imaging datasets, waveband selection has become an important step in processing. In this work, we propose a novel weighted maximum relevance minimum redundancy waveband selection algorithm. The relative importance between redundancy and relevance is better balanced by introducing a weight coefficient. The mutual information between wavebands and

A novel approach is investigated to extend the range of measurable velocities by 3D-PTV systems. The method is specifically conceived for robotic volumetric PTV measurements, but it has applications for other similar techniques. The multi-Δ t method relies upon combining the information from two or more sets of double-frame images with pulse separation of different time duration. Measurements with

In conventional spectral domain optical coherence tomography (SD-OCT), a beam is focused to one spot on the surface of the sample to acquire depth information beneath that spot. Adjacent spots are serially scanned to obtain a tomographic image of the sample; thus, available OCT techniques can take significant time to scan large objects. This paper illustrates an SD-OCT system involving spectral-slicing

In order to obtain high-precision 3D models for 3D reconstruction of large low-texture scenes, a high-precision camera pose-estimation and optimization method is proposed in this paper. The method mainly uses a grid motion statistics feature-matching algorithm which calculates the number of matching points in the neighborhood to determine whether a match is correct or not. Therefore, this method can

We present a novel approach to the characterization of ultrafast laser–matter interaction processes in solids and liquids under extreme conditions of microplasma generation. Through the combination of three-dimensional propagation imaging, absorption measurements, shadowgraphy and photoacoustic imaging we can restore plasma electron density distribution, laser pulse fluence profile and the value of

Sensor design is important for electrical capacitance tomography (ECT) that is to be used for a particular application and for generating high-quality images from the measured data. An ECT sensor with long electrodes is commonly used to obtain stable and reliable measurement signals and to ensure the quality of 2D cross-sectional images, but it neglects the effect of electrode length on the entire

Simultaneous measurement of the straightness error and its position using a modified Wollaston-prism-sensing homodyne interferometer is proposed. In this modified interferometer, we designed a special moving sensor combining a Wollaston prism and a semi-reflective mirror being able to not only avoid the straightness measurement deviation caused by the measured object’s rotation but also simultaneously

Nanopositioning and nanomeasuring machines (NPM-machines), developed at Technische Universität Ilmenau, have provided high-precision measurement and positioning of objects across ten decades, from 20 pm resolution up to 200 mm measuring range. They work on the basis of the error-minimal, extended six degrees of freedom Abbe-comparator principle, with high-precision fibre-coupled laser interferometers

Surface patterning is widely performed in various applications, and hence high-resolution, high-throughput, and nondestructive measurement of patterned surfaces is required. The current optical methods used for such measurements are constrained, in terms of spatial resolution, by the diffraction limit. In this study, structured illumination was employed for high-resolution wide-field imaging measurements

This paper presents a novel method for uniaxial microscopic three-dimensional (3D) profilometry using a structured light system with dual-telecentric lenses in micro-scale devices. Specifically, a telecentric lens can produce an orthographic view of an object and provide the exact size of objects in the x and y directions. An electronically focus-tunable lens attached to the projector rapidly and precisely

Advance prediction about bearing remaining useful life (RUL) is a major activity which aims at scheduling proper future actions to avoid catastrophic events. However, the reliability of bearing life prediction models is subject to processes, such as construction of a robust bearing degradation health index, monotonicity and trendability of health index, uncertainty in construction of a failure threshold

This paper introduces a numerical integration method for measuring transmission line voltage using multiple D-dot electric field sensors. To date, contact measurement is mostly used for voltage measurement of transmission lines, but there are many problems with this approach, such as potentially hazardous insulation, large size and weight of measuring equipment, high cost, etc. With the development

In order to solve the problem of decreased navigation performance of the Global Navigation Satellite System (GNSS)/inertial navigation system (INS) integrated navigation systems in GNSS-denied environments, and to improve the navigation accuracy and robustness of the navigation system, a novel adaptive federated filter with a feedback scheme for a GNSS/INS/visual odometry (VO) integrated navigation

A novel approach, which utilizes astigmatism-based depth codification and discrete dual-plane illumination, is developed to provide information on the full velocity-gradient tensor in pair of planar domains by means of stereoscopic particle image velocimetry (stereo-PIV). The technique is accordingly referred to as dual-plane stereo-astigmatism (DPSA). In contrast to conventional stereo-PIV, DPSA provides

Rotational degrees of freedom (DOF) are usually indirectly derived from the measured translational DOF in structural dynamic tests by using the finite difference method. However, the noise of translational DOF measurement is easily propagated and further amplified when the finite difference method is employed to obtain the rotational DOF. Therefore, the accuracy of the obtained rotational DOF was rather

Ensemble particle tracking velocimetry (EPTV) is a method to extract high-resolution statistical information on flow fields from particle image velocimetry (PIV) images. The process is based on tracking particles and extracting the velocity probability distribution functions of the image ensemble in averaging-regions deemed to contain a sufficient number of particle pairs/tracks. The size of the averaging

As one of the most typical flow structures in hypersonic flow, the hypersonic turbulent boundary layer (TBL) is of great significance in the optimization of the aerodynamic configuration design of hypersonic vehicles. The nano-tracer-based planar laser scattering technique was utilized to obtain velocity results of the fully developed hypersonic (Mach 6.0) TBL. The scale-invariant feature transformation

Machine learning approaches work well with large labeled data sets. In the field of fault diagnosis, the need to analyze large amounts of data provides a foundation for machine learning to be applied. However, due to the changes of rotation speed, load, and other factors, data sets will be of different data distributions. Therefore, under conditions of different features and feature distributions,

Fault diagnosis plays an important role in modern rotating machinery. Recently, some deep neural network-based domain adaptation methods have been successfully applied in cross-domain fault diagnosis problems. However, most of these methods only reduce the distribution discrepancy between different domains, without considering the geometry differences and misalignments across different domains. To

Over the years, significant effort has been directed towards the development of quantitative micro-magnetic structure mapping via magneto-optical imaging (MOI). In this regard, several different approaches have been proposed to cope with different experimental environments. However, there are still open questions in the process of quantification with respect to non-uniform illumination, the resolution

The normal vectors of the free-form surface profile curve are generally not in the same plane, even if the profile curve is generated from the interaction between a plane and a surface. If the 2D compensation vector is adopted to reduce the cosine error, the accuracy is limited because the normal direction of the curve plane is not considered. In this paper, a novel radius compensation method adopts

Accurate measurements of line-width standards, sidewalls and non-spherical nanoparticles performed at the nanoscale by means of atomic force microscopy (AFM) suffer from errors due to the tip shape and size. To reduce the uncertainty, the study here presented aims to investigate a bio-plant nanostructure, namely the tobacco mosaic virus (TMV), as a candidate reference tip characterizer. The TMV has

Single-pressure refractive index gas thermometry (SPRIGT) is a novel primary thermometry technique, developed jointly by the Technical Institute of Physics and Chemistry (TIPC) of the Chinese Academy of Sciences (CAS) in China and LNE-Cnam in France. To help obtain a competitive uncertainty of 0.25 mK in thermodynamic temperature measurements, high-stability and low-uncertainty of microwave resonance

The relativistic heavy ion collider (RHIC) at BNL uses low-energy RHIC electron cooling (LEReC) to conduct experiments to search for the quantum chromodynamic critical point. The first ever electron cooling based on the RF acceleration of electron beams was experimentally demonstrated on April 5, 2019 using LEReC at BNL. The first critical step in obtaining successful 3D non-magnetized cooling of the

The NO 3 radical is one of the important indicators of atmospheric oxidation capability at night, and its accurate detection has been extensively investigated. High reflectivity cavity instruments, such as cavity ring-down spectroscopy (CRDS) and cavity-enhanced absorption spectroscopy (CEAS), are generally employed for NO 3 radical detection. However, sampling detection easily adsorbs radicals on

Modern broadband telecommunications require microelectromechanical filters which mechanically vibrate at ultra-high frequencies up to several gigahertz. Heterodyne interferometers, so-called laser-Doppler vibrometers (LDVs), provide a sensitive and contactless measurement technique for vibrations in such filters, but are limited in GHz heterodyning by the efficiency drop of acousto-optic frequency

The ratio of γ counting efficiencies is very important in trace element analysis carried out by prompt- and delayed- γ neutron activation based on k 0 standardization. Although the effect of correlation between counting efficiencies is well known and methods have been developed and adopted in prompt- γ neutron activation analysis to correctly evaluate the uncertainty, proposals and applications in

Standards ISO14687 and EN17124 set stringent limits for numerous gaseous impurities and particulates that may damage the fuel cell system in a hydrogen vehicle, as it is highly sensitive to the presence of even very low levels of impurities. However, performing the whole set of analyses is both technically challenging and time-consuming for any laboratory and will require a combination of several analytical

In the practice of clinical gastrointestinal endoscopy, precise estimation of the size of a lesion/finding, such as a polyp, is quintessential in diagnosis, e.g. risk estimation for malignancy. However, various studies confirmed that endoscopic assessment of lesion size has inherent limitations and significant measurement errors. Image-based methods proposed for in-vivo -size measurements, rely on

A new three dimensional (3D) atomic force microscopic (AFM) probe, referred to as the 3D-Nanoprobe, is introduced. The 3D-Nanoprobe is realized by introducing flexure hinge structures to the cantilever of a conventional critical dimension AFM (CD-AFM) probe. It has quasi-isotropic stiffness in 3D directions and is thus more powerful for detecting 3D tip-sample interaction forces in AFM measurements

A surface plasmon resonance optical refractive index sensor (for aqueous medium) with high angular and spectral sensitivities S, very small full width at half maxima (FWHM) w (narrow resonance), and very high quality factor, χ = S/w, is proposed, which operates in both angular and spectral interrogation modes. The structure consists of a ##IMG## [http://ej.iop.org/images/0957-0233/31/7/075204/mstab803aieqn1

Simulated and experimental molecular tagging velocimetry (MTV) images have been analyzed with a technique commonly used to process grid images on surfaces, the windowed Fourier transform with local spectrum analysis (WFT-LSA). A systematic synthetic image study of the modulation transfer function (MTF) and error tendencies of the WFT-LSA was performed and compared with a PIV-style cross-correlation

This paper presents a calibration method and an uncertainty budget for capacitance measurements performed on micrometric size capacitors at microwave frequencies and nanometric resolution using a scanning microwave microscopy (SMM). The method applies the classical one-port vector network analyzer calibration for SMM using three known capacitance standards. These standards are established from a commercial

This paper presents a new strategy for applying a piezoelectric (PZT) force sensor to the measurement of static force in a force sensor-integrated fast tool servo (FS-FTS) system for single-point diamond cutting on planar brittle material substrates. A conventional PZT force sensor unit composed of a PZT force sensor and a charge amplifier cannot be employed for measurement of static force due to the

The precise measurement of microstructures and other micron-sized materials has garnered considerable interest in recent years. However, a limited measurement region and the unavailability of miniaturized probes are the major issues in the realization of such systems. In this study, we have presented a system for microstructures based on a small-diameter optical fiber probe. In the improved measurement

A concept for the traceable calibration of magneto-optical indicator film (MOIF) based magnetic field imaging devices is presented and discussed for the example of a commercial MOIF device with a 60 × 45 mm 2 sensor. The calibration facilitates a quantitative and fast characterization of magnetic microstructures combining relatively high spatial resolution with large imaging areas. The macroscopic

Modern coordinate measuring machines (CMMs) feature high-precision scanning due to improved mechanics, electronics, control, and software. PTB’s Coordinate Metrology department therefore executed a thorough experimental comparison of the performance of scanning and discrete point probing regarding involute gear calibrations. In the last four years, PTB used scanning and discrete point probing to calibrate

In this work, a two-step damage identification method has been proposed for simply supported beam bridge local damage identification based on strain response reconstruction and statistical theory under moving loads. Damage could be identified without the response of healthy structure. Strain reconstruction equation was derived based on state space model. Strain responses were divided into two groups

A new method for accurately characterizing the tip geometry of critical dimension atomic force microscopy (CD-AFM) has been introduced. A sample type IVPS100-PTB whose line features have vertical sidewall, round corner with a radius of approx. 5 ∼ 6 nm and very low surface roughness has been applied as the tip characterizer. The geometry of the line features has been accurately and traceably calibrated

Many applications in chemistry, biology and medicine use microfluidic devices to separate, detect and analyze samples on a miniaturized size-level. Fluid flows evolving in channels of only several tens to hundreds of micrometers in size are often of a 3D nature, affecting the tailored transport of cells and particles. To analyze flow phenomena and local distributions of particles within those channels

Planar plasmonic lenses have attracted a great deal of interest over the last few years for their super-resolution focusing capabilites. These highly compact structures with dimensions of only a few micrometres allow for the focusing of light to sub-wavelength-sized spots with focal lengths reaching into the far-field. This offers opportunities for new methods in nanometrology; for example, applications

Regular inspections of bridge substructures are very important for evaluating bridge health, since early detection and assessment offer the best chances of bridge repair. However, the traditional inspection methods of checking defects with visual features cannot meet engineering needs sufficiently. Although deep-learning methods have recently demonstrated a remarkable improvement in image classification

Of paramount importance in the field of nanotechnology is the ability to measure reliably the properties of nanomaterials, especially their size. In general, just an estimate of size is not sufficient: a quantitative indication of the quality of the estimate in the form of an assessment of its uncertainty is necessary, as well. For example, standard ISO/IEC 17025:2017 ( General Requirements for the

A new measuring method for uniform scanning is proposed in this paper. This method uses a moving light field to establish the relationship between displacement and time, and the displacement is measured by the time difference of the traveling wave signal. The high-precision moving light field is configured by the time and spatial orthogonal modulation of the light intensity. Experiments verified the

Measurement of surface plasmon and surface wave propagation is important for the operation and characterization of sensors and microscope systems. One challenge is to perform these measurements both quickly and with good spatial resolution without any modification to the sample surface. This paper addresses these issues by projecting an image of the field excited from a defocused sample to a magnified

A transient spark micro-discharge in nitrogen is investigated between two sharpened electrodes at a pressure of 0.5 bar. The plasma parameters (gas temperature, electron density and reduced electric field) are determined using optical emission spectroscopy (OES) and numerical simulations. The gas temperature of 3500 ± 100 K is determined by the comparison of the measured and simulated rotational distributions

This paper proposes a novel calibration method for robot kinematic parameters by constraining a command point. At first, the profile errors derived from measuring the sphere surface by a laser displacement sensor are estimated and analyzed. A three-step measurement procedure is performed around a command point with only one single laser displacement sensor. Then, a kinematic error model including both

We designed and developed a new instrument for calibrating micro-force sensors. The calibration is traceable to the SI unit of mass and is realized from 1 µN–60 mN by means of electromagnetic force compensation of a balance. The expanded measurement uncertainty of our instrument comprises two contributions, an absolute contribution of 0.13 µN and a relative contribution of 2700 ppm. We verified our

Large-pressure-range, large-sensing-distance evanescent-mode resonator wireless passive pressure sensors were fabricated from silicon carbonitride polymer-derived ceramic (PDC-SiCN) films enhanced by the polymer-infiltration-pyrolysis (PIP) process. The properties of PIP enhanced PDC films ensure a large pressure range for the sensor. To increase the sensing distance between the interrogation antenna

Vibration monitoring using sensors mounted on machines is widely used for rotating machinery fault diagnosis. The periodic overlapping group sparsity (POGS) method has been developed in previous work of authors, and is an effective technique for detecting faults induced in rotating machines. However, the regularization parameter of the POGS problem is roughly specified via a look-up table provided

A simple Peltier cooled cold trap aperture is presented to minimize the flux of hydrocarbons on optics in vacuum UV systems. The system can be cooled down to −40 °C under vacuum. To test the effect of the cold trap, the aperture is placed in front of a high-intensity D 2 lamp used for calibration in the range of 116 nm to 300 nm which is flanged to a VUV spectrometer. The influence of the aperture

Selective two-photon absorptive resonance femtosecond laser electronic excitation tagging (STARFLEET) velocimetry is characterized for the first time at high-pressure, low-temperature conditions. Studies were carried out in the NASA Langley Research Center’s 0.3 meter transonic, cryogenic wind tunnel, with flow conditions spanning the entire operational envelope of the facility; total pressures ranging

Performing digital image correlation (DIC) at extreme temperatures has been greatly challenging due to the radiation which saturates the camera sensor. At such high temperatures, the light intensity emitted from an object is occasionally so powerful that the acquired images are overwhelmingly saturated. This induces data loss, potentially ruining the test, thus requiring the user to restart the test

In recent years, there has been growth in the development of high-speed AFMs, which offer the possibility of video rate scanning and long-range scanning over several hundred micrometres. However, until recently these instruments have been lacking full traceable metrology. In this paper traceable metrology, using optical interferometry, has been added to an open-loop contact-mode high-speed AFM to provide

The ultrasonic-based method has been proved to be a practical technique for measuring oil film thickness in the enclosed tribo-pair of a supporting bearing and under dynamic conditions. To cope with the large-scale variations of oil film thickness in engineering applications, frequency-domain based models, being adaptive for different measurement ranges, are widely used. As an improvement, the time-domain

The bearing diagnosis in industrial applications is limited because the traditional equal-time sampling strategy results in the loss of signal period and fault feature under fluctuant speed. To address these issues, a new tacholess bearing fault diagnosis method based on time-domain impulse extraction (TDIE) is proposed. With the TDIE method, the frequency fluctuant phenomenon is eliminated and fault