Microscopic Physical Phenomena Research Articles

Identifying challenges and opportunities of in-memory computing on large HPC systems

With the increasing fidelity and resolution enabled by high-performance computing systems, simulation-based scientific discovery is able to model and understand microscopic physical phenomena at a level that was not possible in the past. A grand challenge that the HPC community facing is how to maintain the large amounts of analysis data generated from simulations. In-memory computing, among others, is recognized to be a viable path forward and has experienced tremendous success in the past decade. Nevertheless, there has been a lack of a complete study and understanding of in-memory computing as a whole on HPC systems. Given the enlarging disparity between compute and HPC storage I/O, it is urgent for the HPC community to assess the state of in-memory computing and understand the challenges and opportunities. This paper presents a comprehensive study of in-memory computing with regard to its software evolution, performance, usability, robustness, and portability. In particular, we conduct an indepth analysis on the evolution of in-memory computing based upon more than 3,000 commits, and use realistic workflows for two scientific workloads, i.e., LAMMPS and Laplace to quantitatively assess state-of-the-art in-memory computing libraries, including DataSpaces, DIMES, Flexpath, Decaf and SENSEI on two leading supercomputers, Titan and Cori. Our studies not only illustrate the performance and scalability, but also reveal the key aspects that are of interest to library developers and users, including usability, robustness, portability, potential design defects, etc.

Cation Composition-Dependent Device Performance and Positive Bias Instability of Self-Aligned Oxide Semiconductor Thin-Film Transistors: Including Oxygen and Hydrogen Effect.

Amorphous oxide semiconductor transistors control the illuminance of pixels in an ecosystem of displays from large-screen TVs to wearable devices. To satisfy application-specific requirements, oxide semiconductor transistors of various cation compositions have been explored. However, a comprehensive study has not been carried out where the influence of cation composition, oxygen, and hydrogen on device characteristics and stability is systematically quantified, using commercial-grade process technology. In this study, we fabricate self-aligned top-gate structure thin-film transistors with three oxide semiconductor materials, InGaZnO (In/Ga/Zn = 1:1:1), In-rich InGaZnO, and InZnO, having mobility values of 10, 27, and 40 cm2/V·s, respectively. Combinations of varied amounts of oxygen and hydrogen are incorporated into each transistor by controlling the fabrication process to study the effect of these gaseous elements on the physical nature of the channel material. Electrons can be captured by peroxy linkage (O22-) or undercoordinated In (In* to become In+), which are manifested in the extracted subgap density-of-states profile and first-principles calculations. Energy difference between electron-trapped In+ and O22- σ* is the smallest for IGZO, and In+-O22- annihilation occurs by electron excitation from the subgap In+ state to the O22- σ*. Furthermore, characteristic time constants during positive bias stress and recovery reveal the various microscopic physical phenomena within the transistor structure between different cation compositions.

Cu 기반 그래핀 나노복합재료에서 균열이 기계적 성능 및 파괴거동에 미치는 영향

The research has conducted about Cu-based graphene nanocomposites which utilize the graphene as an electronic device. It is important to evaluate the effect of cracks on mechanical performance and fracture behaviors in Cu-based graphene nanocomposites because of the possibility of performance degradation from the defects inevitably occurring interface. In this study, the mechanical properties and fracture behaviors of the multilayer Cu/graphene nanocomposite materials were evaluated about the effect of defects. The molecular dynamics evaluation method (Molecular Dynamics Simulation: MDS) was used to analyze microscopic physical phenomena. From the results, stress distributions were found depending on the position that the defect occurs. Higher stress was generated in the graphene layer even though the first delamination crack occurred in the Cu layer.

Fractal-based electric field enhancement modeling of vacuum gap electrodes

The objective of this paper is to study the characteristics of the microscopic electric field enhancement at the micro-projections on the contact surface based on the fractal modeling of the micro-projections in vacuum interrupters. In this paper, the distortions of the microscopic electric field caused by the micro-projections were studied in the case of the applied voltage 60 kV and the contact gap 2 mm. Moreover, the microscopic enhancement factor β m for the various micro-projections with the height-radius ratio being less than or equal to 50 were investigated. First, the basic Weirstrass-Mandelbrot (W-M) fractal function was introduced and simplified into the modeling of the various micro-projections with the height-radius ratio 0.2, 0.4, 1, 2, 10 and 50 respectively. Then, the electric field distributions were analyzed based on these micro-projection fractal models. The simulation results showed that the micro-projections would cause a distortion of the microscopic electric field at the micro-projections on the contact surface, especially in the case of the higher height-radius ratio. In this paper, with the height-radius ratio of the micro-projections increasing from 0.2 to 50, the microscopic enhancement factor β m based on the fractal models would increase from 16 to 3667. In comparison with the idealized ellipsoid model, to the same height-radius ratio of the micro-projection, the microscopic enhancement factor β m based on the fractal models was about four times higher than that based on the ellipsoid models. Furthermore, the microscopic electric field at the micro-projections would have a significant influence on the micro-particles impact phenomena and other microscopic physical phenomena which could give rise to the vacuum breakdown. The results could provide some useful information to understand the physical mechanism to trigger the vacuum breakdown.

Basic Interactions in Black Hole Cosmology

By highlighting the 12 major shortcomings of modern big bang cosmology and reinterpreting the cosmic redshift as a galactic atomic emission phenomenon, the authors made an attempt to develop a possible model of Black hole cosmology in a constructive way. Its validity can be well confirmed from a combined study of cosmological and microscopic physical phenomena. It can be suggested that, there exists one variable physical quantity in the presently believed atomic and nuclear physical constants and “rate of change” in its magnitude can be considered as a “standard measure” of the present “cosmic rate of expansion”. The characteristic nuclear charge radius, inverse of the Fine structure ratio, the characteristic reduced Planck’s constant seem to increase with cosmic time and there will be no change in the magnitude of Planck's constant. At any cosmic time, ’Hubble length’ can be considered as the gravitational or electromagnetic interaction range. With this idea, independent of the reduced Planck’s constant, inverse of the Fine structure ratio can be fitted in a cosmological approach. At any cosmic time, the product of ‘critical density’ and ‘Hubble volume’ gives a characteristic cosmic mass and it can be called as the ‘Hubble mass’. Schwarzschild radius of the ‘Hubble mass’ again matches with the ‘Hubble length’. Most of the cosmologists believe that this is merely a coincidence. Here the authors emphasize the fact that this coincidence is having deep connection with cosmic geometry and the cosmological and microscopic physical phenomena. In this model, forever rotating at light speed, high temperature and high angular velocity small sized primordial cosmic black hole of mass gradually transforms into a low temperature and low angular velocity large sized massive primordial cosmic black hole.

Black Hole Cosmology: A Biological Boom

In the previously published papers the authors made an attempt to develop a possible model of Black hole cosmology in a constructive way. In this model, forever rotating at light speed, high temperature and high angular velocity small sized primordial cosmic black hole of mass 2 0 4 ≅ C Me G πe gradually transforms into a low temperature and low angular velocity large sized massive primordial cosmic black hole. At any time represents the angular velocity. At its ending stage of expansion, for the whole cosmic black hole as practically remains constant, its corresponding thermal energy density will be ‘the same’ throughout its volume. This ‘sameness’ may be the reason for the observed ‘isotropic’ nature of the current CMB radiation. Observed cosmic red shift can be re-interpreted as an index of cosmological galactic atomic light emission phenomenon. Validity of this model can be well confirmed from the combined study of cosmological and microscopic physical phenomena. Finally it can be suggested that, the cosmological time is real and absolute. By interconnecting the present cosmic time with the present CMBR energy density the authors made an attempt to fit and estimate the current cosmic age and its obtained magnitude is close to 282 trillion years.

The fundamentals of modelling abrasive machining using molecular dynamics

The development of ultra-precision processes which can achieve excellent surface finish and tolerance at the nanometre level is now a critical requirement for many industrial applications. At present, it is very difficult to observe the diverse microscopic physical phenomena occurring in nanometric machining through experiments. The use of molecular dynamics (MD) simulation has proved to be an effective tool for the prediction and the analysis of these processes at the nanometre scale. The crucial task in a MD simulation is the selection of the potential function. The lack of clear understanding about the scope and the limitations of a given potential function may lead to nonsensical results. This article presents the backgrounds of popular potentials used in the modelling of materials processes and the algorithms for the solution of the equations encountered in the simulation. Current applications of MD in abrasive machining are reviewed.

Multiscale simulation of cluster growth and deposition processes by hybrid model based on direct simulation Monte Carlo method

A cluster growth and deposition model based on hybrid modeling is introduced to examine the experimental conditions of the cluster growth process in vacuum chamber and deposition process on substrate. This hybrid model is a simulation method including physical length and time scale characteristics of macro and microscale. We simulated the behavior of the cluster during the flight path by direct simulation Monte Carlo (DSMC) method and the deposition behavior on the substrate by a simple MC model. Several size distributions of the clusters and various morphologies of deposited film were obtained, and the relationship between macroscopic and microscopic physical phenomena during deposition process was examined.

Modeling of the silicon (100) thermal oxidation: from quantum to macroscopic formulation

In this paper, we investigate the modeling of dry silicon thermal oxidation in the light of the model capabilities and the trends in microelectronics. We show how a combined use of different models can be made in a way to generate process simulations that are strongly related to microscopic physical phenomena. In conjunction with experimental literature data, first principle calculations have been carried out with the objective of isolating some elementary oxidation mechanisms, i.e. basic atomic movements and their corresponding activation energies. This preliminary list of mechanisms is discussed in detail. A growth mechanism allowing the oxide defect generation is proposed. We then present Monte Carlo calculations with the implemented mechanisms where at least three silicon layers are oxidized. Finally, we introduce a macroscopic formulation of these mechanisms via the Chemical Rate Theory.

Micro‐Macroscopic Coupled Modeling of Batteries and Fuel Cells: I. Model Development

A micro‐macroscopic coupled model, aimed at incorporating solid‐state physics of electrode materials and interface morphology and chemistry, has been developed for advanced batteries and fuel cells. Electrochemical cells considered consist of three phases: a solid matrix (electrode material or separator), an electrolyte (liquid or solid), and a gas phase. Macroscopic conservation equations are derived separately for each phase using the volume averaging technique and are shown to contain interfacial terms which allow for the incorporation of microscopic physical phenomena such as solid‐state diffusion and ohmic drop, as well as interfacial phenomena such as phase transformation, precipitation, and passivation. Constitutive relations for these interfacial terms are developed and linked to the macroscopic conservation equations for species and charge transfer. A number of nonequilibrium effects encountered in high‐energy‐density and high‐power‐density power sources are assessed. Finally, conditions for interfacial chemical and electrical equilibrium are explored and their practical implications are discussed. Simplifications of the present model to previous macrohomogeneous models are examined. In a companion paper, illustrative calculations for nickel‐cadmium and nickel‐metal hydride batteries are carried out. The micro‐macroscopic model can be used to explore material and interfacial properties for desired cell performance.

Emission and capture of electrons in multiquantum-well structures

The mechanisms of unipolar emission and capture of electrons are studied in multiquantum-well structures in relation with the quantum-well infrared photoconductors (QWIP's). We clarify the roles played by the physical parameters which appear in the different QWIP photoresponse models, i.e., the photoconductive and the photoemissive ones. We then describe the experimental procedures which allow us to independently determine these different parameters: deep level optical spectroscopy for the electron emission probability, impedance spectroscopy for the quantum-well capture velocity and thermal emission time, as well as the infrared photoconductive gain for the unipolar electron capture time. The measured dependence of these parameters on photon energy and electric field sheds light on the microscopic physical phenomena which are involved in quantum-well infrared photodetection. Theoretical results on optical phonon mediated transitions in an applied electric field from barrier to well states show good agreement with experiment at low fields but less dependence on the field. Finally, this theoretical approach allows us to connect the different parameters and solve the apparent discrepancy between the QWIP photoresponse models. >

An informational process based on reversible universal cellular automata

This paper is written from the perspective of a computer scientist and addressed to theoretical physicists. As a consequence it may seem somewhat unusual, but rest assured, everything is really quite simple! The point of this paper is that the study of certain phenomena from computer science suggests that there are computer systems (cellular automata) that may be appropriate as models for microscopic physical phenomena. Cellular automata are now being used to model varied physical phenomena normally modelled by wave equations, fluid dynamics, Ising models, etc. We hypothesize that there will be found a single cellular automaton rule that models all of microscopic physics; and models it exactly. We call this field DM, for digital mechanics.

Turbulent Heating of Colliding Streams in the Solar Wind

Turbulent heating of colliding plasma streams has previously been observed in the solar wind. The original data were interpreted in terms of a fluid model. It is contended that a plasma-kinetic description is the more appropriate theoretical approach and is necessary in order to better understand the microscopic physical phenomena that underlie all fluid models. Microscopic solar-wind parameters characteristic of conditions during the observations were used, together with the quasi-linear plasma-kinetic theory, to compute the expected magnetic field and temperature enhancements in the interaction region between two counterstreaming plasma beams. The physical mechanism of excitation is the electromagnetic two-stream instability in which Alfven waves are unstable. A total field in the interaction region of about 8 gamma and a change in temperature of about 100,000 K are obtained.