Fundamental Physical Models Research Articles

Controlling the charge-transfer dynamics of two-level systems around avoided crossings.

Two-level quantum systems are fundamental physical models that continue to attract growing interest due to their crucial role as a building block of quantum technologies. The exact analytical solution of the dynamics of these systems is central to control theory and its applications, such as that to quantum computing. In this study, we reconsider the two-state charge transfer problem by extending and using a methodology developed to study (pseudo)spin systems in quantum electrodynamics contexts. This approach allows us to build a time evolution operator for the charge transfer system and to show new opportunities for the coherent control of the system dynamics, with a particular emphasis on the critical dynamic region around the transition state coordinate, where the avoided crossing of the energy levels occurs. We identify and propose possible experimental implementations of a class of rotations of the charge donor (or acceptor) that endow the electronic coupling matrix element with a time-dependent phase that can be employed to realize controllable coherent dynamics of the system across the avoided level crossing. The analogy of these rotations to reference frame rotations in generalized semiclassical Rabi models is discussed. We also show that the physical rotations in the charge-transfer systems can be performed so as to implement quantum gates relevant to quantum computing. From an exquisitely physical-mathematical viewpoint, our approach brings to light situations in which the time-dependent state of the system can be obtained without resorting to the special functions appearing in the Landau-Zener approach.

Experimental and theoretical research progress of <sup>2</sup>P<sub>1/2 </sub> – <sup>2</sup>P<sub>3/2</sub> transitions of highly charged boron-like ions

The precise measurement of the fine structure and radiative transition properties of highly charged ions (HCI) is essential for testing fundamental physical models, including strong-field quantum electrodynamics (QED) effects, electron correlation effects, relativistic effects, and nuclear effects. These measurements also provide critical atomic physics parameters for astrophysics and fusion plasma physics. Compared with the extensively studied hydrogen-like and lithium-like ion systems, boron-like ions exhibit significant contributions in terms of relativistic and QED effects in their fine structure forbidden transitions. High-precision experimental measurements and theoretical calculations of these systems provide important avenues for further testing fundamental physical models in multi-electron systems. Additionally, boron-like ions are considered promising candidates for HCI optical clocks. This paper presents the latest advancements in experimental and theoretical research on the ground state <sup>2</sup>P<sub>3/2</sub>—<sup>2</sup>P<sub>1/2</sub> transition in boron-like ions, and summarizes the current understanding of their fine and hyperfine structures. It also discusses a proposed experimental setup for measuring the hyperfine splitting of boron-like ions by using an electron beam ion trap combined with high-resolution spectroscopy. This proposal aims to provide a reference for future experimental research on the hyperfine splitting of boron-like ions, to test the QED effects with higher precision, extract the radius of nuclear magnetization distribution, and validate relevant nuclear structure models.

On the solitonic wave structures and stability analysis of the stochastic nonlinear Schrödinger equation with the impact of multiplicative noise

The nonlinear Schrödinger equation (NLSE) is a fundamental and significant physical model that plays a crucial role in demonstrating the dynamics of optical solitons in the theory optical fibers. The propagation of solitons in nonlinear optical fibers has garnered substantial interest due to its broad spectrum of applications, particularly in ultrafast signal routing systems and short light pulses for communications. This article focuses on investigating the impact of multiplicative noise on the solutions of this governing model. To achieve this, three distinct methods, namely the enhanced modified extended tanh expansion (METE) method, the generalized Kudryashov (GK) approach and the extended modified auxiliary equation mapping (EMAEM) method are employed to obtain a new variety of stochastic solutions. The perception of how noise intensity impacts the transmission of waves is a fundamental and critical issue in various fields. In the context of this study, an equation describes an exact wave pattern under the condition that s (representing noise intensity) equals zero. In such cases, the observed pattern remains undisturbed and matches the expected theoretical wave pattern. However, as the strength of noise s increases, the observed pattern begins to deviate from the ideal wave pattern and exhibits signs of damage or distortion. Furthermore, the stability analysis for the stochastic NLSE is performed, providing valuable insights into the behavior solutions as the strength of multiplicative noise increases. The validation of computational results through stability analysis enhances the confidence in the findings of the study. All the mathematical calculations, as well as graphical representations, have been meticulously achieved to present a comprehensive and detailed understanding of the impact of multiplicative on soliton propagation in nonlinear optical fibers.

Inflation and primordial gravitational waves in scale-invariant quadratic gravity with Higgs

In scale-invariant models of fundamental physics all mass scales are generated via spontaneous symmetry breaking. In this work, we study inflation in scale-invariant quadratic gravity, in which the Planck mass is generated classically by a scalar field, which evolves from an unstable fixed point to a stable one thus breaking scale-invariance. We investigate the dynamics by means of dynamical system standard techniques. By computing the spectral indices and comparing them with data, we put some constraints on the three dimensionless parameters of the theory. We show that certain regions of the parameter space will be within the range of future CMB missions like CMB-S4, LiteBIRD and STPol. The second half of the paper is dedicated to the analysis of inflationary first-order tensor perturbations and the calculation of the power spectrum of the gravitational waves. We comment on our results and compare them with the ones of mixed Starobinsky-Higgs inflation.

Development of a more accurate Geant4 quantum molecular dynamics model for hadron therapy

Objective. Although in heavy-ion therapy, the quantum molecular dynamics (QMD) model is one of the most fundamental physics models providing an accurate daughter-ion production yield in the final state, there are still non-negligible differences with the experimental results. The aim of this study is to improve fragment production in water phantoms by developing a more accurate QMD model in Geant4. Approach. A QMD model was developed by implementing modern Skyrme interaction parameter sets, as well as by incorporating with an ad hoc α-cluster model in the initial nuclear state. Two adjusting parameters were selected that can significantly affect the fragment productions in the QMD model: the radius to discriminate a cluster to which nucleons belong after the nucleus–nucleus reaction, denoted by R, and the squared standard deviation of the Gaussian packet, denoted by L. Squared Mahalanobis’s distance of fragment yields and angular distributions with 1, 2, and the higher atomic number for the produced fragments were employed as objective functions, and multi-objective optimization (MOO), which make it possible to compare quantitatively the simulated production yields with the reference experimental data, was performed. Main results. The MOO analysis showed that the QMD model with modern Skyrme parameters coupled with the proposed α-cluster model, denoted as SkM* α, can drastically improve light fragments yields in water. In addition, the proposed model reproduced the kinetic energy distribution of the fragments accurately. The optimized L in SkM* α was confirmed to be realistic by the charge radii analysis in the ground state formation. Significance. The proposed framework using MOO was demonstrated to be very useful in judging the superiority of the proposed nuclear model. The optimized QMD model is expected to improve the accuracy of heavy-ion therapy dosimetry.

Fabrication and modelling of Si3N4 ceramics with radial grain alignment generated through centripetal sinter-forging

• Textured silicon nitride (Si 3 N 4 ) ceramic, with radial grain alignment, was prepared by a novel centripetal sinter-forging using spark plasma heating at 1800 °C in 10 min. • The average values of the included angles between the c -axis of the local Si 3 N 4 grain and radial direction were as low as 16.4° and 11.0° on the section plane perpendicular to the pressing direction and parallel to both the pressing and radial directions, respectively. • A fundamental physical model was created to simulate the texture formation during the 3-dimentional strain reorientation, which revealed the rod-like grain would preferentially rotate toward the center of the sample under the flow motion in centripetal direction during sintering. Silicon nitride (Si 3 N 4 ) based ceramics are one of the most attractive advanced engineering materials, which have been widely used under high-speed rotational operation or for mechanical contacts across a curved surface. In the present study, rotationally symmetric texturing of Si 3 N 4 , with radial grain alignment, was obtained by centripetal sinter-forging (CSF) of a partially sintered sample. The average values of the included angles between the c -axis of the local Si 3 N 4 grain and radial direction were approximately 16.4° and 11.0°, on the section plane perpendicular to the pressing direction, and parallel to both the pressing and radial directions, respectively. The compressive strain in the pressing direction forced the ceramic body to flow towards the central axis, resulting in compressive strain in the tangential direction and tensile strain in the radial direction. A fundamental physical model was created to simulate the grain rotation during the 3-dimentional strain reorientation, which revealed the rod-like grain would preferentially rotate toward the center of the sample under the CSF process. In addition, due to the friction between the sample surface and the pressing punch, the increased shear strain could enhance the Si 3 N 4 grain alignment. Consequently, ceramics with rod-like grains perpendicular to the curved side surface could be anticipated by applying the centripetal forming concept in a controlled manner.

Comparison of Different Optimization Methods for the Microstructure of Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) have attracted much attention in the research and commercial sectors because they are environmental friendly and have relatively high power density compared to most other energy storage devices based on electrochemical processes. A significant part of the research on PEMFCs is related to decreasing the cost and improving the structure of PEMFCs by optimizing numerically the microstructure of these devices including the non-uniform porosity, carbon, nafion, and catalyst (i.e. platinum) distributions and the geometrical characteristics. The existing optimization techniques can generally be divided into heuristic and non-heuristic techniques. Heuristic techniques usually use stochastic approaches that search the optimization space using trial-and-error methods. Examples of such techniques include the genetic algorithm, particle swarm optimization, differential evolution, simulating annealing, harmony search, memetic algorithms, etc. These techniques can be applied to optimize a small number of design variables and often need to be used with simplified (often purely mathematic and not based on fundamental physics) models, such as compact, reduced-order models, or equivalent circuit models. On the other hand, non-heuristic techniques are deterministic and often require evaluating the gradient of the objective function. In general, these techniques have local convergence and their rate of convergence can be increased, using second-order derivatives such as the Hessian matrix, or taking advantage of the particular functional form of the objective function. Non-heuristic techniques usually require between a few tens of iterations to optimize the objective function compared to heuristic techniques which require at least tens of thousands of iterations.In this presentation we will make a thorough critical review of the different optimization methods used in the literature for PEMFCs. In additional, we will present the results of our efforts to develop a full-cell optimization algorithm for PEMFCs using the adjoint method [1-3]. The advantages and disadvantages of different methods, including the adjoint method, will be discussed in detail and examples of sample simulations results will be presented.

AUTOMATION OF DESIGN OF EDUCATIONAL PREMISES WITH SAFE WORKING CONDITIONS

When organizing the educational process in higher education institutions, safe conditions must be created that meet all the general current requirements of labor protection. The most common physical factor of adverse effects on students in classrooms are man-made electromagnetic fields around each technical means and in different configurations of the relative location of equipment. Based on the fundamental physical relations and dipole models of propagation of electric and magnetic components of electromagnetic fields using EMF LFSourse software, models of propagation of electric and magnetic fields of personal computer components were obtained. This visualized the propagation of an electric field around liquid crystal monitors, magnetic fields around personal computer system units, and uninterruptible power supplies. The result is a spatial distribution of electric and magnetic field strengths in computerized workplaces. These models allow you to streamline the relative position of personal computers in computer classrooms and other classrooms where computers are located in terms of electromagnetic safety. Detailed models of the configuration of electric and magnetic fields allow to obtain the propagation of fields around the electrical equipment of training laboratories. The example of modeling the propagation of the electric and magnetic components of the electromagnetic field of personal computer components shows the possibility of providing safe configurations of individual workplaces and many workplaces in computer classrooms. It is expedient to create models of propagation of other physical factors of technogenic origin – sound, infrasound, anomalous distribution of air ion concentrations, etc. Modeling allows you to place equipment in training laboratories at the design stage, adhering to safe conditions in the organization of the educational process.

Four-fermion operators at dimension 6: Dispersion relations and UV completions

A major task in phenomenology today is constraining the parameter space of Standard Model effective field theory and constructing models of fundamental physics from which the Standard Model derives. To this effect, we report an exhaustive list of sum rules for 4-fermion operators of dimension 6, connecting low-energy Wilson coefficients to cross sections in the UV. Unlike their dimension-8 counterparts which are amenable to a positivity bound, the discussion here is more involved due to the weaker convergence and indefinite signs of the dispersion integrals. We illustrate this by providing examples with weakly coupled UV completions leading to opposite signs of the Wilson coefficients for both convergent and nonconvergent dispersion integrals. We further decompose dispersion integrals under weak isospin and color groups, which lead to a tighter relation between IR measurements and UV models. These sum rules can become an effective tool for constructing consistent UV completions for Standard Model effective field theory following the prospective measurement of these Wilson coefficients.

Brittle Solids: From Physics and Chemistry to Materials Applications

Hard solids with predominantly covalent–ionic bonding are finding rapidly increasing usage in many modern technologies. However, this class of solids is severely limited by their intrinsic brittleness—they break easily. It is in this context that a fundamental knowledge of brittle fracture mechanisms is of practical importance. This review covers the essential features of crack behavior in characteristically brittle solids, starting with fundamental physical and chemical models, with distinctions between equilibrium and kinetic states, stability and instability, and crack propagation and initiation. Means of imparting higher strength and toughness to otherwise brittle materials are then explored along with their pros and cons. Select technological areas where fracture properties constitute a vital facet of material function—windows and display panels, structural ceramics, biomaterials, layer structures, manufacturing, and nanomechanics—are then presented as illustrative case studies. The balance between factors such as strength and toughness, scaling and threshold effects, and crack containment and crack avoidance, as well as structure at the atomic and microstructural scales, emerge as critical factors in materials design.

Cosmological Simulations and Models of Galaxy Formulation

Cosmological simulation has become the most efficient and advanced method to investigate the fundamental principle and physical model of the universe. Galaxy formulation is one of the most significant characters in this field, which attracts lots of attention. However, it is challenging to establish a proper model of galaxy simulation. Besides, a lot of investment is required to solve the problem of modelling dark matter, dark energy, and ordinary matter. This review introduces the most widely accepted cosmological models and galaxy formation procedures. Moreover, discussions and comparisons are presented for several advanced simulation methods. These results evaluate milestones in the development of cosmological numerical simulation objectively and will offer a guideline for the development of galaxy formation.

Study of Parametric Interactions in the Nuclear Reactor Control with Feedback

This article considers the principal theoretical possibility of regulating a nuclear power reactor under changing operating modes conditions when external periodic disturbances take place in conditions of changing the operating mode. By the external periodic perturbation a downward change in the conditions of the heat sink was meant. The magnitude of the changes was preliminarily calculated in such a way that the operating conditions of the power plant did not exceed the boundaries of the safe operation zone of the reactor. In the case of approaching the operation parameters to the critical ones, the heat sink was increased until the working conditions returned to their previous state. In this work the amplitude frequency response of a non-linearly enhanced system in the nuclear power plant operating conditions when non-linearly reacting to external periodic influences has been studied. The external cyclic disturbances effect produced on the reactor that initially existed under stationary operating conditions has been considered. The research was carried out by numerical simulation of the competition between processes occurring in a nuclear power plant and determined by the system’s reaction time and relaxation time while responding to periodic external influences. Calculations of the relaxation time dependence on the fixed frequency-revealing external influence’s temperature are presented. Also, the relaxation time dependence on the frequency of external influence at a fixed temperature for systems with various relaxation periods was calculated. It is determined that when the dependence between system temperature and the external influence time is calculated, there exists a wide range of possible frequency control. To evaluate the behavior of a nuclear power reactor under conditions of operating modes changes, a fundamental physical mathematical model of the reactor’s state under external harmonic influence is presented. It is based on the nonlinear Riccati equation. The external harmonic effect was simulated by changing the heat supply and heat removal conditions near the critical point.

Inflation and scale-invariant R2 gravity

In scale-invariant models of fundamental physics, mass scales are generated by spontaneous symmetry breaking. In this work, we study inflation in scale-invariant $R^2$ gravity, in which the Planck mass is generated by a scalar field, which is responsible for spontaneous breaking of scale--symmetry. If the self-interactions of the scalar field are non-zero, a cosmological constant is generated, which can be potentially quite large. To avoid fine-tuning at late times, we introduce another scalar field which drives the classical cosmological constant to zero during inflation. Working in the Einstein-frame, we find that due to a conserved Noether current the corresponding three-field inflationary model (consisting of the two scalar fields plus the scalaron) becomes effectively a two-field model. The prize to be paid for introducing the field which cancels the classical cosmological constant at the end of inflation is that the running of the spectral index and the running of the running can be quite large due to entropy perturbations during inflation, making the model testable with future cosmological experiments.

Contact line dynamics of gravity driven spreading of liquids

The spreading dynamics of the gravity-driven liquid motion on an inclined solid surface was studied by considering two fundamental physical models: the molecular kinetic theory and the hydrodynamic theory (HDT). The molecular kinetic theory is the most appropriate model to describe the gravity driven spreading mechanism investigated in this study. The gravity driven spreading which is one form of the forced spreading mechanism was compared with the spontaneous spreading for the same liquid/solid system from previous study by Mohammad Karim et al (2016 Langmuir 32 10153). Unlike the gravity driven spreading, the HDT was appropriate model to define the spontaneous spreading. This finding reveals the importance of the mechanism of spreading which are the forced and the spontaneous on the suitability of the physical model such as the molecular kinetic theory and the HDT to describe the spreading dynamics.

MFIX-Exa: A path toward exascale CFD-DEM simulations

MFIX-Exa is a computational fluid dynamics–discrete element model (CFD-DEM) code designed to run efficiently on current and next-generation supercomputing architectures. MFIX-Exa combines the CFD-DEM expertise embodied in the MFIX code—which was developed at NETL and is used widely in academia and industry—with the modern software framework, AMReX, developed at LBNL. The fundamental physics models follow those of the original MFIX, but the combination of new algorithmic approaches and a new software infrastructure will enable MFIX-Exa to leverage future exascale machines to optimize the modeling and design of multiphase chemical reactors.

Single-Conductor Transmission Line Model Incorporating Radiation Reaction

Increasing attention has been paid to the study of electromagnetic (EM) phenomena in complicated wire networks [e.g., metamaterials and EM compatibility (EMC)]. However, their lack of physical insights usually prevents systematic analysis of the phenomena. To address this, this article describes a transmission line (TL) model of a finite-length single conductor without a return current path to be applied as a fundamental physical model. The model includes radiation effects in a self-consistent way (i.e., its radiation reaction is included in an explicit way), and it is based on Sommerfeld principal wave propagation (strictly speaking, its behavior is asymptotic as the wire's conductivity approaches infinity). This formulation naturally leads to the consequence that the current flowing along a single conductor illuminated by an incident EM field is classified into three components, which are dominated by physically distinct principles, the principal wave itself (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tr</sub> , the traveling wave), the one reinduced by the traveling wave radiation (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">re</sub> , the radiation reaction), and the one that directly scatters the incident field (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> , the scattering wave). The EM energies of the traveling wave and radiation reaction components are stored in the TL and propagate, while the scattering component indicates an instantaneous scattering process. These components reveal the dynamical characteristics of a single-conductor TL model that includes radiation phenomena.

Review of Structural Health Monitoring Methods Regarding a Multi-Sensor Approach for Damage Assessment of Metal and Composite Structures.

Structural health monitoring (SHM) is the continuous on-board monitoring of a structure’s condition during operation by integrated systems of sensors. SHM is believed to have the potential to increase the safety of the structure while reducing its deadweight and downtime. Numerous SHM methods exist that allow the observation and assessment of different damages of different kinds of structures. Recently data fusion on different levels has been getting attention for joint damage evaluation by different SHM methods to achieve increased assessment accuracy and reliability. However, little attention is given to the question of which SHM methods are promising to combine. The current article addresses this issue by demonstrating the theoretical capabilities of a number of prominent SHM methods by comparing their fundamental physical models to the actual effects of damage on metal and composite structures. Furthermore, an overview of the state-of-the-art damage assessment concepts for different levels of SHM is given. As a result, dynamic SHM methods using ultrasonic waves and vibrations appear to be very powerful but suffer from their sensitivity to environmental influences. Combining such dynamic methods with static strain-based or conductivity-based methods and with additional sensors for environmental entities might yield a robust multi-sensor SHM approach. For demonstration, a potent system of sensors is defined and a possible joint data evaluation scheme for a multi-sensor SHM approach is presented.

Fast, accurate, and transferable many-body interatomic potentials by symbolic regression

The length and time scales of atomistic simulations are limited by the computational cost of the methods used to predict material properties. In recent years there has been great progress in the use of machine-learning algorithms to develop fast and accurate interatomic potential models, but it remains a challenge to develop models that generalize well and are fast enough to be used at extreme time and length scales. To address this challenge, we have developed a machine-learning algorithm based on symbolic regression in the form of genetic programming that is capable of discovering accurate, computationally efficient many-body potential models. The key to our approach is to explore a hypothesis space of models based on fundamental physical principles and select models within this hypothesis space based on their accuracy, speed, and simplicity. The focus on simplicity reduces the risk of overfitting the training data and increases the chances of discovering a model that generalizes well. Our algorithm was validated by rediscovering an exact Lennard-Jones potential and a Sutton-Chen embedded-atom method potential from training data generated using these models. By using training data generated from density functional theory calculations, we found potential models for elemental copper that are simple, as fast as embedded-atom models, and capable of accurately predicting properties outside of their training set. Our approach requires relatively small sets of training data, making it possible to generate training data using highly accurate methods at a reasonable computational cost. We present our approach, the forms of the discovered models, and assessments of their transferability, accuracy and speed.

Influence of Fundamental Model Uncertainties on Silicon Solar Cell Efficiency Simulations

We determine the uncertainties on simulated efficiencies of silicon solar cells due to uncertainties of the fundamental physical models. To determine these, we refit their parameters to the underlying measurement data. Using a metamodeling and Monte Carlo simulation approach, we then deduce how these propagate to the simulated solar cell efficiency. This is evaluated for 150- $\mu \text{m}$ -thick 1 $\Omega $ cm p-type standard and advanced silicon passivated emitter and rear cells (PERC), as well as for an ideal silicon solar cell. When sticking to the best-known set of physical models, we determine resulting efficiency uncertainties as low as 0.06%abs for usual PERC cells and 0.1%abs for an ideal cell. In a variance-based sensitivity analysis, we find the uncertainties of the bandgap and the hole density-of-states effective mass as well as the Auger recombination in the limiting case to dominate the efficiency uncertainty. In addition to these relatively low uncertainties, larger discrepancies may arise when applying different physical models for otherwise fixed device properties. We determine comparably large efficiency discrepancies of up to 0.6%abs for the two most prominent bandgap narrowing (BGN) models, and up to 0.15%abs for the two most recent parameterizations of free carrier absorption. We also show evidence that for the specific case of a strong space charge region being present at a recombining surface, Schenk’s BGN model fails to replicate experiments. Those discrepancies highlight the necessity of further research on those models. Finally, an error of up to 0.08%abs is observed by simplifying diffused regions on textured surfaces to a planar geometry.

An analytical model for characterizing the thrust performance of a Low-Pressure Micro-Resistojet

There is a clear trend towards the developments of micro-propulsion system to enhance the capabilities of nano- and pico-satellites. A promising propulsion option to meet the strict requirements of these small satellites is the Low-Pressure Micro-Resistojet (LPM) which works under rarefied gas dynamic regime. To simplify the engineering design of this propulsion system an analytical model has been developed using the fundamental physical models. This analytical model is based on the Kinetic theory of gases and the Maxwell-Boltzmann distribution of molecular velocities to describe the macroscopic flow parameters such as mass flow rate, velocity and pressure, and then to estimate the thruster performance. The equations are well known, but they are applied in this case using a particular approach in order to describe the physics behind this micro-propulsion system. Comparisons between numerical simulations using the Direct Simulation Monte Carlo method and the results of the analytical model, as well as experimental results, have been carried out. The analytical model using an accurate estimation of the transmission coefficient compared to the numerical simulation presents a maximum difference of 3%.