J. Szép

Bio: J. Szép is an academic researcher from University of Arizona. The author has contributed to research in topics: Electrostatic lens & Lens (optics). The author has an hindex of 5, co-authored 16 publications receiving 163 citations. Previous affiliations of J. Szép include Eötvös Loránd University.

Monte Carlo approach to dendritic growth

Abstract: The connection between diffusion-limited aggregation and the equations of dendritic growth is critically examined. A different type of Monte Carlo simulation is proposed and used to construct two-dimensional dendrite-like patterns. The wavelength occurring for short times is in good agreement with the linear stability analysis. The time dependence of the characteristic wavelengths is also determined.

Social determinants of eyeblinks in adult male macaques

Abstract: Videos with rich social and emotional content elicit natural social behaviors in primates. Indeed, while watching videos of conspecifics, monkeys engage in eye contact, gaze follow, and reciprocate facial expressions. We hypothesized that the frequency and timing of eyeblinks also depends on the social signals contained in videos. We monitored the eyeblinks of four male adult macaques while they watched videos of conspecifics displaying facial expressions with direct or averted gaze. The instantaneous blink rate of all four animals decreased during videos. The temporal synchrony of blinking, however, increased in response to segments depicting appeasing or aggressive facial expressions directed at the viewer. Two of the four monkeys, who systematically reciprocated the direct gaze of the stimulus monkeys, also showed eyeblink entrainment, a temporal coordination of blinking between social partners engaged in dyadic interactions. Together, our results suggest that in macaques, as in humans, blinking depends not only on the physiological imperative to protect the eyes and spread a film of tears over the cornea, but also on several socio-emotional factors.

Paralinguistic Classification of Mask Wearing by Image Classifiers and Fusion.

Abstract: In this study, we address the ComParE 2020 Paralinguistics Mask sub-challenge, where the task is the detection of wearing surgical masks from short speech segments. In our approach, we propose a computer-vision-based pipeline to utilize the capabilities of deep convolutional neural network-based image classifiers developed in recent years and apply this technology to a specific class of spectrograms. Several linear and logarithmic scale spectrograms were tested, and the best performance is achieved on linear-scale, 3-Channel Spectrograms created from the audio segments. A single model image classifier provided a 6.1% better result than the best single-dataset baseline model. The ensemble of our models further improves accuracy and achieves 73.0% UAR by training just on the ‘train’ dataset and reaches 80.1% UAR on the test set when training includes the ‘devel’ dataset, which result is 8.3% higher than the baseline. We also provide an activationmapping analysis to identify frequency ranges that are critical in the ‘mask’ versus ‘clear’ classification.

Optimum design of electrostatic lenses

Abstract: A method of design for electrostatic lenses with given source parameters, first‐order properties, and minimum aberrations is presented. It is based on constrained nonlinear optimization techniques. The variables in these procedures are spline coefficients of the axial potential distribution, or the electrode potentials of a given multielectrode lens. The optimization constraints are the minimum object‐ and image‐side working distances, maximum possible electrode potentials, and maximum allowed electrostatic fields. The parameters of the source and the final beam voltage are fixed. The goal of the design is to find an electrode configuration that would minimize the beam spot size and maximize the current density at the target. Three examples of the method’s application are presented. Keeping the given source parameters and working distances constant, essential improvements of the optical properties of three well‐known designs could be achieved by replacing the lenses with those designed by our procedures. In these examples for field ionization sources the current density at the target is increased by more than an order of magnitude.

Autonomic Management of 3D Cardiac Simulations

Abstract: Large scale scientific applications in general and especially cardiac simulations experience different execution phases at runtime and each phase has different computational and communication requirements. An optimal solution or numerical scheme for one execution phase might not be appropriate for the next phase of the application execution. We propose an autonomic management framework, which is built on the physics aware programming (PAP) paradigm for accelerating the cardiac simulations further beyond what can be achieved through traditional parallelization efforts. This approach effectively exploits the physical properties of the cardiac simulation by being smart in the development of simulation algorithms. The cardiac simulation phase is periodically monitored and analyzed to identify its current execution phase. We apply machine learning techniques to detect the phase of the simulation during each time step of the 3D model of a human ventricular epicardial myocyte simulation. For each change in the simulation phase, we exploit the spatial and temporal attributes, dynamically change the resolution of the simulation, and select the numerical algorithms/solvers that optimize its performance without sacrificing the accuracy of the simulation. We compare the performance of the PAP-based algorithm in terms of simulation accuracy and execution time with respect to the reference simulation, which is considered the high-precision implementation. We achieve an overall speedup of 28.4× with a simulation accuracy of 99.9% with the PAP-based cardiac simulations. We also couple the PAP with a multi-graphics processing units (GPU) implementation, and show up to 191× speedup on a 16-GPU system.

Flow phenomena in rocks : from continuum models to fractals, percolation, cellular automata, and simulated annealing

Abstract: In this paper, theoretical and experimental approaches to flow, hydrodynamic dispersion, and miscible and immiscible displacement processes in reservoir rocks are reviewed and discussed. Both macroscopically homogeneous and heterogeneous rocks are considered. The latter are characterized by large-scale spatial variations and correlations in their effective properties and include rocks that may be characterized by several distinct degrees of porosity, a well-known example of which is a fractured rock with two degrees of porosity---those of the pores and of the fractures. First, the diagenetic processes that give rise to the present reservoir rocks are discussed and a few geometrical models of such processes are described. Then, measurement and characterization of important properties, such as pore-size distribution, pore-space topology, and pore surface roughness, and morphological properties of fracture networks are discussed. It is shown that fractal and percolation concepts play important roles in the characterization of rocks, from the smallest length scale at the pore level to the largest length scales at the fracture and fault scales. Next, various structural models of homogeneous and heterogeneous rock are discussed, and theoretical and computer simulation approaches to flow, dispersion, and displacement in such systems are reviewed. Two different modeling approaches to these phenomena are compared. The first approach is based on the classical equations of transport supplemented with constitutive equations describing the transport and other important coefficients and parameters. These are called the continuum models. The second approach is based on network models of pore space and fractured rocks; it models the phenomena at the smallest scale, a pore or fracture, and then employs large-scale simulation and modern concepts of the statistical physics of disordered systems, such as scaling and universality, to obtain the macroscopic properties of the system. The fundamental roles of the interconnectivity of the rock and its wetting properties in dispersion and two-phase flows, and those of microscopic and macroscopic heterogeneities in miscible displacements are emphasized. Two important conceptual advances for modeling fractured rocks and studying flow phenomena in porous media are also discussed. The first, based on cellular automata, can in principle be used for computing macroscopic properties of flow phenomena in any porous medium, regardless of the complexity of its structure. The second, simulated annealing, borrowed from optimization processes and the statistical mechanics of spin glasses, is used for finding the optimum structure of a fractured reservoir that honors a limited amount of experimental data.

Viscous flows in two dimensions

Abstract: This review is an expository treatment of the displacement of one fluid by another in a two-dimensional geometry (a Hele-Shaw cell). The Saffman-Taylor equations modeling this system are discussed. They are simulated by random-walk techniques and studied by methods from complex analysis. The stability of the generated patterns (fingers) is studied by a WKB approximation and by complex analytic techniques. The primary conclusions reached are that (a) the fingers are linearly stable even at the highest velocities, (b) they are nonlinearly unstable against noise or an external perturbation, the critical amplitude for the noise being an exponential function of a power of the velocity for high velocities, (c) such exponentials seem to dominate high-velocity behavior, as can be seen from a WKB analysis, and (d) the results of the Saffman-Taylor equations disagree with experiments, apparently because they leave out film-flow phenomena.

Viscous flows in two dimensions

Abstract: This review is an expository treatment of the displacement of one Ouid by another in a two-dimensional geometry (a Hele-Shaw cell). The Saffman-Taylor equations modeling this system are discussed. They are simulated by random-walk techniques and studied by methods from complex analysis. The stability of the generated patterns (fingers) is studied by a WKB approximation and by complex analytic techniques. The primary conclusions reached are that (a) the fingers are linearly stable even at the highest velocities, (b) they are nonlinearly unstable against noise or an external perturbation, the critical amplitude for the noise being an exponential function of a power of the velocity for high velocities, (c) such exponentials seem to dominate high-velocity behavior, as can be seen from a WKB analysis, and (d) the results of the SaffmanTaylor equations disagree with experiments, apparently because they leave out film-flow phenomena.

Apparatus and method for controlled particle beam manufacturing

Abstract: A chamber for exposing a workpiece to charged particles includes a charged particle source for generating a stream of charged particles, a collimator configured to collimate and direct the stream of charged particles from the charged particle source along an axis, a beam digitizer downstream of the collimator configured to create a digital beam including groups of at least one charged particle by adjusting longitudinal spacing between the charged particles along the axis, a deflector downstream of the beam digitizer including a series of deflection stages disposed longitudinally along the axis to deflect the digital beams, and a workpiece stage downstream of the deflector configured to hold the workpiece.

Equivalence of the generalised grid and projection methods for the construction of quasiperiodic tilings

Abstract: The two main techniques for the generation of quasiperiodic tilings, de Bruijn's grid method (1981), and the projection formalism, are generalised. A very broad class of quasiperiodic tilings is obtained in this way. The two generalised methods are shown to be equivalent. The standard calculation of Fourier spectra is extended to the whole general class of tilings. Various applications are discussed.