Arbitrary Profile Research Articles

Oновлення парку рухомого складу українських залізниць з орієнтацією на інтеграцію в європейські транспортні мережі

The strategic aim of further development of the Ukrainian railways is rolling stock and infrastructure renewal to meet the demands of the Ukrainian economy, including a rapid integration into the European transport service. The paper presents the results of recent studies conducted at the Department of Statistical Dynamics and Multidimensional Mechanical System Dynamics, the Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine, with the aim to solve important problems in the development of the Ukrainian railway transport. The studies were aimed at developing scientifically substantiated decisions on Ukrainian rolling stock renewal oriented at integration into the European railway networks. To do this, a cycle of theoretical and experimental studies was conducted at the department. Consideration was given to the problem of wheel–rail contact pair improvement by identifying a wheel profile that would offer an acceptable car ride performance and acceptable conditions of car–rail interaction both on the Ukrainian and the European railways and reduce vehicle and rail wear. The car ride performance of an articulated passenger train was simulated mathematically for its motion at different speeds along a track of arbitrary alignment and profile, and the effect of different car and track parameters on the ride performance was estimated. Energy-absorbing devices were developed to increase the passive safety of a speedy locomotive-hauled passenger train and a multiple-unit train in emergency collisions with obstacles according to the Ukrainian Standard DSTU EN 15227. Service loads on the load-bearing components of swap-body freight cars were estimated, and recommendations were developed on fasteners that would provide safe transportation of various freights in swap-body cars. Based on the results of the studies, a number of design solutions were proposed for Ukrainian railway vehicle components. Their implementation will offer a sizeable economic benefit, increase the train speed and safety, improve the vehicle–track interaction, and facilitate the formation of an up-to-date home railway complex and its integration into the European railway networks.

Dynamically variable intensity patterns projected using an optofluidic phase-shifter array

We present a concept for the dynamically variable definition of arbitrary intensity distributions using an array of optofluidic phase-shifters. These components consist of cylindrical fluidic surfaces whose interface may be controllably shaped using electrowetting-on-dielectrics actuation. Key to the generation of defined intensity distributions is the ability to calculate the required shape for this phase-shifting interface and to this end we present a novel procedure, to our knowledge, that combines a real-time optimization algorithm with an influence matrix approach to generate the required surface. We illustrate the effectiveness of this approach by reconstructing arbitrary surface profiles with one optofluidic phase-shifting component that is then used to project a desired two-dimensional intensity distribution. Using this approach, we further demonstrate the capability of a two-dimensional phase-shifter array to generate larger dynamically programmable intensity patterns by combining individual intensity distributions.

An exactly solvable model for non-Fickian transport in dynamically heterogeneous media

Abstract Diffusion, observed in various condensed phases, finds its theoretical background in Einstein’s theory of Brownian motion, characterized by the linear time-dependence of mean square displacement (MSD) denoting Fickian behavior and the Gaussian distribution of particle displacement. Nevertheless, diverse systems exhibit either non-linear, non-Fickian time-dependence of the MSD or non-Gaussian displacement distribution. Montroll and Weiss’s continuous-time random walk (CTRW) model and the stochastic diffusivity (SD) model have provided insights into anomalous diffusion phenomena and Fickian-yet-non-Gaussian transport in dynamically heterogeneous environments, respectively. Building upon these approaches, Song et al developed a generalized transport equation with an environment-dependent diffusion kernel, providing a quantitative explanation for non-Fickian MSD and non-Gaussian displacement distribution. Based on the generalized transport equation, this study introduces an exactly solvable model for a non-Gaussian displacement distribution, accommodating arbitrary time profiles in its MSD, including both Fickian and non-Fickian behaviors. Our findings confirm the model’s capability in describing such transport processes. Furthermore, the proposed model unifies the CTRW model under fast environmental fluctuations and the SD model under Fickian time dependencies, making it suitable for understanding tracer particle motion within explicit solvent or complex media.

Semiconductor optical amplifiers as an optical arbitrary waveform generator for high-energy laser systems

A simple and straightforward technique is presented as a novel temporally controllable front-end for nanosecond very-high energy laser systems. It is based on an original utilization of a semiconductor optical amplifier (SOA) used as an intensity modulator. The essential characteristics of the component are analyzed in order to evaluate potential limitations. Various parameters of interest for standard operation are displayed, demonstrating its usability and its effectiveness. We demonstrate arbitrary and controllable pulse temporal profiles with duration ranging from 1 nanosecond to 100 nanoseconds and a temporal precision of 1.1 ns. A high extinction ratio is also achieved ensuring a modulation contrast up to 53 dB. The SOA is then integrated into an existing operating system in an ultra-compact, reliable all-fibered system. It is used to seed a 2*200 J laser system, exhibiting excellent performance, and validating its usability under operation conditions without any detrimental effects.

Efficient modeling of atmospheric infrasound propagation with the Semi-Analytical-Finite-Element (SAFE) method

Downward refraction in the lower atmosphere, attributed to winds and temperature inversion, can enable infrasound to efficiently propagate over long distances inside acoustic waveguides. In this study, we use the semi-analytic finite element (SAFE) method to predict this effect in stratified, inhomogeneous, moving air for range-independent noise propagation over reflective half-planes. We present solutions for different temperature and velocity profiles and compare them to direct numerical solutions of the two-dimensional linearized Euler equations. The SAFE method separates the exact two-dimensional wave equation for a stratified, inhomogeneous, moving medium by expressing the pressure field as a sum of vertical eigenmodes propagating in the range direction. This simplifies the acoustic problem into a one-dimensional eigenvalue problem. As this problem is addressed with the finite-element method, the method can accommodate arbitrary wind and temperature profiles. For large, range-independent domains, the proposed procedure proves to be much more efficient than the tested direct numerical computations. Additionally, it converges against the exact solution of the acoustic problem if enough modes are included in the calculation. Therefore, the method offers a viable procedure for benchmarking other pressure field prediction techniques.

Accurate Ultrasonic Thickness Measurement for Arbitrary Time-Variant Thermal Profile.

Ultrasonic thickness measurement of mechanical structures is one of the most popular and commonly used nondestructive methods for various kinds of process control and corrosion monitoring. With ultrasonic propagation speed being temperature-dependent, the thickness measurement can be performed reliably only when the thermal profile is completely known. Most conventional techniques assume the temperature of the test structure is uniform and at room temperature across its thickness. Such assumptions may lead to large errors in the thickness measurement, especially when there are significant temperature variations across the thickness. State-of-the-art techniques use external temperature measurements or implement iterative methods to compensate for the unknown thermal profiles. However, such techniques produce unsatisfactory results when the heat distribution is complex or varies rapidly with time. In this work, we propose a two-sensors technique, using both compressive and shear excitations, with a non-iterative rapid data processing method for accurate thickness measurement under arbitrary time-variant thermal profile. The independent behavior of shear and compressive waves is used to formulate a real-time thickness estimation technique. The developed technique is experimentally validated on a steel plate with fixed acoustic sensors. Test results show that the error in thickness estimation can be reduced by up to 98% compared to conventional thickness gauging methods.

Estimating the Optically Pumped Threshold Fluence of Thin‐Film Gain Media Using Arbitrary Excitation Beams

Optically pumped threshold fluences are a widely reported metric to benchmark the performance of thin‐film gain media and lasers. Estimating the threshold fluence for nonhomogeneous beams, such as a circular Gaussian excitation, is not trivial since the average fluence depends on the estimated spot diameter. Using an exemplary lead halide perovskite film, the inversion volume at different pump energies is mapped. It is shown that the peak fluence of an arbitrary spatial beam profile is more relevant at the threshold, as it provides an upper bound to the threshold fluence. Also, simple conversion factors to estimate the peak fluence using Gaussian excitation beams are provided and the methodology to arbitrary profiles is extrapolated. Furthermore, it is advocated for using flat‐top or uniform stripe excitations to unambiguously extract the threshold fluence, since these excitations display minor discrepancies between the average and peak fluence, and keep the inversion volume relatively constant during the measurement.

Unified Model for Residence Time Distribution in a Recycle Reactor with Arbitrary Velocity Profiles

Unified Model for Residence Time Distribution in a Recycle Reactor with Arbitrary Velocity Profiles

Capacity and Resistance Diagnosis of Batteries with Voltage-Controlled Models

Capacity and internal resistance are key properties of batteries determining energy content and power capability. We present a novel algorithm for estimating the absolute values of capacity and internal resistance from voltage and current data. The algorithm is based on voltage-controlled models. Experimentally-measured voltage is used as an input variable to an equivalent circuit model. The simulation gives current as output, which is compared to the experimentally-measured current. We show that capacity loss and resistance increase lead to characteristic fingerprints in the current output of the simulation. In order to exploit these fingerprints, a theory is developed for calculating capacity and resistance from the difference between simulated and measured current. The findings are cast into an algorithm for operando diagnosis of batteries operated with arbitrary load profiles. The algorithm is demonstrated using cycling data from lithium-ion pouch cells operated on full cycles, shallow cycles, and dynamic cycles typical for electric vehicles. Capacity and internal resistance of a “fresh” cell was estimated with high accuracy (mean absolute errors of 0.9% and 1.8%, respectively). For an “aged” cell, the algorithm required adaptation of the model’s open-circuit voltage curve to obtain high accuracies.

Laser-induced ultrasound in multiple thin layers-An analytical solution.

Laser-induced ultrasound is based on the thermo-elastic conversion of absorbed short light pulses to pressure pulses. In the work presented here, laser-induced ultrasound in a planar structure of interconnected layers with variations in optical, thermal, and mechanical properties is studied. Layered structures can be used for generating wideband ultrasonic pulses specific to a chosen application. An analytical time-domain solution is derived for the resulting pressure transmitted from the layered structure. The solution is derived for an arbitrary number of layers with an arbitrary optical absorption profile. Free space Green's functions with image sources are used to derive the solution. A solution employing the Beer-Lambert law is also proposed. The simplification with reflections only at the boundaries is in agreement with previous published results. The spectral properties of the generated pulse are derived, where the effects of optical absorption coefficients and layer thicknesses are shown. The analytical solution is compared to one-dimensional (1D) simulations and a three-dimensional (3D) simulation, realised as a two-dimensional (2D) axially symmetric case, using the matlab toolbox k-Wave. The 3D simulation on-axis pressure agrees well with the 1D analytical solution when the diameter of the laser beam is larger by approximately 1 order of magnitude than the thickness of the planar layered structure.

Deep learning-based general beam synthesis for atmospheric propagation

Optimizing the transmit light beams unlocks the full potential of free-space optical systems. However, designing application-specific light beams remains a challenge, especially for those traversing random media. In this study, we address this gap by proposing a deep learning-based method to generate optimal beams for propagation through atmospheric turbulence. The key mechanism is approximating the receiver statistics through batch-wise computation during the training of a convolutional neural network (CNN). On that basis, statistical performance metrics including average received power, scintillation index, and mean signal-to-noise ratio (SNR) are considered for optimization. Pseudo-modes of the beam are synthesized by weighted superposition of Hermite-Gaussian eigenmodes, enabling the creation of arbitrary complex amplitude profiles, i.e., general beams. An end-to-end implementation framework is designed to facilitate self-supervised learning and eliminate the need for pre-calculated datasets. Effectiveness of the synthesized beam is validated by wave optics simulation and experiments. In particular, comparison with Gaussian Schell-model beams demonstrates that the synthesized beam can achieve lower scintillation and greater intensity at the same time, leading to markedly enhanced receiver SNR. This advantage persists in a wider range of link configurations, extending the application range of stochastic beams.

The computational method with the deformed mesh interfaces for an incompressible layer indentation by rigid indenters with arbitrary axisymmetric smooth profiles

The computational method with the deformed mesh interfaces for an incompressible layer indentation by rigid indenters with arbitrary axisymmetric smooth profiles

Techniques for solving static Klein-Gordon equation with self-interaction λϕ4 and arbitrary spherical source terms

The Klein-Gordon equation for a scalar field sourced by a static spherically symmetric background is an interesting second-order differential equation with applications in particle physics, astrophysics, and elsewhere. Here we present static solutions for generic source density profiles in the case where the scalar field has no interactions or a mass term. For a λϕ4 self-interaction term, we develop the techniques that are necessary numerical computation. We also provide code to perform the numerical calculations that can be adapted for arbitrary density profiles. ▪.

Generation and characterization of customized Laguerre–Gaussian beams with arbitrary profiles

Generation and characterization of customized Laguerre–Gaussian beams with arbitrary profiles

Procedure for the Orientation of Laser Triangulation Sensors to a Stereo Camera System for the Inline Measurement of Rubber Extrudate

Abstract. Rubber production is a labour-intensive process. In order to reduce the needed number of workers and the waste of material, the level of digitalisation should be increased. One part of the production is the extrusion to produce gaskets and similar objects. An automated observation of the continuous rubber extrudate enables an early intervention in the production process. In addition to chemical monitoring, the geometrical observation of the extrudate is an important aspect of the quality control. For this purpose, we use laser triangulation sensors (LTS) at the beginning and the end of the cooling phase of the extrudate after the extrusion. The LTS acquire two-dimensional profiles at a constant frequency. To combine these profiles into a three-dimensional model of the extrudate, the movement of the extrudate has to be tracked. Since the extrudate is moved over a conveyor belt, the conveyor belt can be tracked by a stereo camera system to deduce the movement of the extrudate. For the correct usage of the tracking, the orientation between the LTS and the stereo camera system needs to be known. A calibration object that considers the different data from the LTS and the camera system was developed to determine the orientation. Afterwards, the orientation can be used to combine arbitrary profiles. The measurement setup, consisting of the LTS, the stereo camera system and the conveyor belt, is explained. The development of the calibration object, the algorithm for evaluating the orientation data and the combination of the LTS profiles are described. Finally, experiments with real extrusion data are presented to validate the results and compare three variations of data evaluation. Two use the calculated orientation, but have different tracking approaches and one without any orientation necessary.

Geometric Design Methodology for Deployable Self-Locking Semicylindrical Structures

Due to their unique bistable characteristics, deployable self-locking structures are suitable for many engineering fields. Without changing the geometrical composition, such structures can be unfolded and locked solely by the elastic deformation of materials. However, their further applications are hampered by the lack of simple and systematic geometric design methodologies that consider arbitrary structural curvature profiles. This paper proposes such a methodology for double-layer semicylindrical grid structures to simplify their cumbersome geometric design. The proposed methodology takes joint sizes into account to ensure that the design results can be applied to actual projects without further adjustments. By introducing symmetry into the structural units (SUs) and selecting reasonable geometric parameters that describe the structural side elevation profile, a concise set of simultaneous nonlinear geometric constraint equations is established, the solution of which provides the geometric parameter values of the grid shape. On this basis, the remaining geometric parameter values, i.e., the geometric parameter values of the inner scissor-like elements (SLEs) of each SU, can be achieved from the equations derived from general SLEs. Design examples and the assembled physical grid structure indicate the feasibility and wide applicability of the proposed geometric design methodology.

Direct measurement of repulsive and attractive pair potentials using pairs of optical traps

We present a technique for measuring the interactions between pairs of colloidal particles in two optical traps. This method is particularly suitable for measuring strongly attractive potentials, an otherwise challenging task. The interaction energy is calculated from the distribution of inter-particle separations by accounting for the contribution from the optical traps with arbitrary trap profiles. The method is simple to implement and applicable to different types of pair potentials and optical trapping geometries. We apply the method to measure dipolar pair interactions in experiments with paramagnetic colloids in external magnetic fields. We obtain consistent and accurate results in all regimes, from strongly attractive to repulsive potentials. By means of computer simulations, we demonstrate that the proposed method can be successfully applied to systems with complex pair interactions characterized by multiple attractive and repulsive regimes, which are ubiquitous in soft and biological matter.

Approximating accelerator impedances with resonator networks

It is common in the accelerator community to use the impedance of accelerator components to describe wake interactions in the frequency domain. However, it is often desirable to understand such wake interactions in the time domain in a general manner for excitations that are not necessarily Gaussian in nature. The conventional method for doing this involves taking the inverse Fourier Transform of the component impedance, obtaining the Green's Function, and then convolving it with the desired excitation distribution. This method can prove numerically cumbersome, for a convolution integral must be evaluated for each individual point in time when the wake function is desired. An alternative to this method would be to compute the wake function analytically, which would sidestep the need for repetitive integration. Only a handful of cases, however, are simple enough for this method to be tenable. One of these cases is the case where the component in question is an RLC resonator, which has a closed-form analytical wake function solution. This means that a component which can be represented in terms of resonators can leverage this solution. As it happens, common network synthesis techniques may be used to map arbitrary impedance profiles to RLC resonator networks in a manner the accelerator community has yet to take advantage of. In this work, we will use Foster Canonical Resonator Networks and partial derivative descent optimization to develop a technique for synthesizing resonator networks that well approximate the impedances of real-world accelerator components. We will link this synthesis to the closed-form resonator wake function solution, giving rise to a powerful workflow that may be used to streamline beam dynamics simulations.

Reproducibility of Equatorial Kelvin Waves in a Super‐Parameterized MIROC: 2. Linear Stability Analysis of In‐Model Kelvin Waves

AbstractWhile low‐resolution climate models at present struggle to appropriately simulate convectively coupled large‐scale atmospheric disturbances such as equatorial Kelvin waves (EKWs), superparameterization helps better reproduce such phenomena. To evaluate such model differences based on physical mechanisms, a linearized theoretical framework of convectively coupled EKWs was developed in a form readily applicable to model evaluation by allowing background stability and diabatic heating to have arbitrary vertical profiles rather than assuming simplified ones. A system of linearized equations of convection‐coupled gravity waves was derived as a two‐dimensional model of the convectively coupled EKWs. In this work, the basic states are taken from observations, CTL‐MIROC and SP‐MIROC experiments introduced in Part 1. The tendency of convectively coupled gravity waves to grow faster under top‐heavy heating is confirmed for realistic stratification profiles, as found in previous studies under constant stratifications. A comparison of linear unstable solutions with basic states taken from SP‐MIROC and CTL‐MIROC shows that the top‐heavy heating profile in SP‐MIROC largely contributes to the enhancement of the EKW‐like unstable modes, while subtle differences of stratification profiles considerably affect EKW behaviors. The bottom‐heavy heating bias in the CTL‐MIROC likely originates from insufficient modeling of subgrid stratiform precipitation in tropical organized systems. It is desirable to incorporate such stratiform components in cumulus parameterizations to achieve better EKW reproducibility.

Modeling ocean eddies using exact solutions of the Charney–Obukhov equation

New exact solutions of the Charney–Obukhov equation for the ocean are obtained in the form of a partial superposition of elementary solutions with different wave numbers. The boundary conditions for the ocean are satisfied due to the presence of a carrier zonal flow in the solution. The existing arbitrariness in the choice of wave numbers and other solution parameters makes it possible to simulate an arbitrary stream function profile at a fixed ocean depth on an interval of a fixed length using a Fourier series or in a circle of a fixed radius using a Fourier–Bessel series. An example of modeling a Gaussian stream function profile on the ocean surface in the presence of circular symmetry is considered.