bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pure R2 gravity can gravitate about a flat background
Authors: Edery Ariel 
Published: July 2021

Abstract
Pure R2 gravity (R2 gravity by itself with no Einstein-Hilbert term) has attracted attention because it is different from other quadratic gravity theories. In a curved de Sitter (dS) or anti-de Sitter (AdS) background, it is equivalent to Einstein gravity with an additional massless scalar and with a cosmological constant. In contrast to other higher-derivative theories, it is therefore unitary. The equivalence with Einstein gravity is not valid for a flat background. In fact, it has been shown that linearizations of pure R2 gravity about flat spacetime does not produce a graviton. In other words, it does not gravitate about flat space. Pure R2 gravity is invariant under restricted Weyl transformations where the metric is scaled by a conformal factor that obeys a harmonic condition. In this work we consider an action composed of pure R2 gravity, a massless scalar field φ non-minimally coupled to gravity plus other terms. The entire action is invariant under restricted Weyl transformations. We show that when the scalar field φ acquires a non-zero vacuum expectation value (VEV), flat spacetime now becomes a viable gravitating background solution. The restricted Weyl symmetry becomes broken, not explicitly but spontaneously. In other words, when φ acquires a non-zero VEV, the equivalent Einstein action has now the possibility of having a zero cosmological constant and therefore solutions in a Minkowski background. The action can also have, as before, a non-zero cosmological constant, so that solutions in a dS and AdS background are still possible.
Helium as a major portion of the dark matter and the cell structure of the universe
Authors: Ben-Amots Netsivi 
Published: July 2021

Abstract
One of the unsolved problems in physics is called dark matter. It should be called non-shining matter or invisible matter in order to include transparent matter. We will review the discovery of the dark matter and various explanations, some of which state that dark matter consists of baryons. In this article, we will discuss the possibility of 4He as the transparent matter, including claims against and in favor of this idea and various implications, particularly on the evolution of galaxies, galaxy clusters, galaxy superclusters and the large cell structure of the universe. This necessitates a few paradigm shifts regarding the big bang, the black holes, rotation and more. We explain the contradictions in the paradigms accepted at present before deriving the new substitute paradigms suggested in this article. The big-bang theory is replaced with a relativistic expansion of the universe that increases the calculated time since the cosmic microwave background radiation about six times. Quasars and supermassive active galactic nuclei were and are additional factories that produce helium and disperse it in huge jets. Together these phenomena enable the production of helium in sufficient amounts to be the long time sought for transparent matter which is erroneously called dark matter.
As a result, new explanations are obtained for the cell structure of the universe, the structure of galaxies and galaxy clusters, and for their evolution.
Unruh effect and particle decay
Authors: Gaetano Luciano Giuseppe 
Published: July 2021

Abstract
We review the study of the inverse β-decay of uniformly accelerated protons in the context of neutrino flavor mixing. Letting ourselves be guided by some core theoretical principles, such as the general covariance of Quantum Field Theory and the conservation law of the family lepton numbers built into the Standard Model, we infer non-trivial results on the asymptotic nature of neutrinos.
Extended electrodynamics and SHP theory
Authors: Hively L M , Land M 
Published: July 2021

Abstract
This work shows incompleteness and inconsistency in classical electrodynamics (CED) and quantum electrodynamics (QED). Extended electrodynamics (EED) resolves these issues. Stueckelberg-Horwitz-Piron (SHP) theory is equivalent to EED with important implications.
Infrared behavior of Weyl Gravity
Authors: Rachwał Lesław , Giaccari Stefano 
Published: July 2021

Abstract
In this paper, we introduce and motivate the studies of Quantum Weyl Gravity (also known as Conformal Gravity). We discuss some appealing features of this theory both on classical and quantum level. The construction of the quantum theory is described in detail to the one-loop level. To facilitate computations we use only physical degrees of freedom, which are singled out through the York decomposition. At the one-loop level we compute the partition function around a general Einstein space. Next, the functional renormalization group of couplings in Quantum Weyl Gravity is investigated. We reproduce completely previous results obtained on maximally symmetric and Ricci-flat backgrounds. Finally, we comment on further directions and on the issue of conformal anomaly.
Does the Heisenberg uncertainty principle apply along the time dimension?
Authors: Ashmead John 
Published: July 2021

Abstract
Does the Heisenberg uncertainty principle (HUP) apply along the time dimension in the same way it applies along the three space dimensions? Relativity says it should; current practice says no. With recent advances in measurement at the attosecond scale it is now possible to decide this question experimentally.
The most direct test is to measure the time-of-arrival of a quantum particle: if the HUP applies in time, then the dispersion in the time-of-arrival will be measurably increased.
We develop an appropriate metric of time-of-arrival in the standard case; extend this to include the case where there is uncertainty in time; then compare. There is – as expected – increased uncertainty in the time-of-arrival if the HUP applies along the time axis. The results are fully constrained by Lorentz covariance, therefore uniquely defined, therefore falsifiable.
So we have an experimental question on our hands. Any definite resolution would have significant implications with respect to the role of time in quantum mechanics and relativity. A positive result would also have significant practical applications in the areas of quantum communication, attosecond physics (e.g. protein folding), and quantum computing.
Wave-particle duality and the zitterbewegung
Authors: O’Hara Paul 
Published: July 2021

Abstract
In previous work, the Hamilton-Jacobi equation has been associated with the metrics of general relativity and shown to be a generalized Dirac equation for quantum mechanics. This lends itself to a natural definition of wave-particle duality in quantum mechanics. This theory is now further developed to show that a free spinless quantum particle moving with velocity v obeys the standard wave equation of electro-magnetism. We also discuss the implications for the zitterbewegung problem and its relationship to isotropy. Moreover, it is also shown that for the theory to be consistent, the momentum defined by the Hamilton-.!acobi function presupposes the existence of a universal parameter internal to the system. In the case of particles with mass this invariant can be defined by dX = dt/m(t) where t has the units of time and m = m(t) has the units of mass.
Maxwell’s equations from spacetime geometry and the role of Weyl curvature
Authors: Lindgren J , Liukkonen J 
Published: July 2021

Abstract
This research article demonstrates how the field equations of electrodynamics can be shown to be a special case of Einstein field equations of General Relativity. By establishing a special conjecture between the electromagnetic four-potential and the metric of the spacetime, it is first shown how the relativistic wave equation of electrodynamics is a condition for the metric to be Ricci-flat. Moreover, the four-current is identified with a certain four-gradient, which allows one to conjecture that electric charge is related to the covariant divergence of the electromagnetic four-potential. These considerations allow one to understand the Einstein field equations as a nonlinear generalization of Maxwell’s equations. Finally, it is argued that the four-current induces Weyl curvature on the spacetime.
Study of the Radiation Reaction Force for a Step Electric Field and an Electromagnetic Pulse
Authors: Ares de Parga G. , Domínguez-Hernández S. , Salinas-Hernández E. , Ortiz-Domínguez M. 
Published: July 2021

Abstract
The motions of a spin-less point-like charged particle predicted by the Landau-Lifshitz equation and the Hammond method are obtained for a step electric field, a smooth step electric field and an electromagnetic pulse by using analytical and numerical solutions. In addition to Hammond method not presenting the so-called constant force paradox, using step force brings out the apparent physical contradictions of Landau-Lifshitz equation regarding energy conservation. Nevertheless, a smooth step force shows the consistency of the Landau-Lifshitz equation. Unlike other cases, the electromagnetic pulse shows another fundamental difference between the two models. Finally, an analysis of the Hammond method is made.
Influence of surface permeability on gas-dynamic characteristics of high-speed flight
Authors: Alekseeva M M , Kaun Yu V , Chernyshov M V , Yatsenko A A 
Published: July 2021

Abstract
This paper covers the use of gas-permeable materials as the outer surface of a high-speed aircraft. The gas-dynamic structures of supersonic flows are compared in the presence of blowing from the body surface and in its absence. The influence of the blowing speed on the structure of the formed gas-dynamic discontinuities is determined.
On the steady motions control of viscoelastic joined robotic manipulators
Authors: Andreev Aleksandr , Peregudova Olga 
Published: July 2021

Abstract
In this paper, the control problem of the serial multi-link robotic manipulators with rigid and viscoelastic joints is considered. The manipulators structure is such that only the rigid joints are controlled by DC motors. It is shown that such robotic manipulators can make so called stationary motions wherein the part of the generalized coordinates does’t change in time and the others change according to a linear law. The robust output feedback controllers are obtained for the robotic manipulators such that the stationary motion is locally, semi-globally, and globally asymptotically stable.
Oscillations and stability in the coupled mechanical system
Authors: Barabanov I N , Tkhai V N 
Published: July 2021

Abstract
Conservative mechanical systems are considered. Each system is supposed to admit a family of non-degenerate symmetric periodic motions. For the entire set of systems, they form a family of conditionally periodic oscillations, which is assumed to contain a symmetrical periodic motion. Universal couplings for mechanical systems are proposed such that they play the role of controls that ensure the existence, stability, and stabilization of oscillations at the same time for the whole system. Those couplings provide the natural, i.e. without involving any additional controls, stabilization of the oscillation. In addition, mechanical systems perform the synchronization in frequency and phase.
On stability of a collinear libration point in the planar circular restricted photogravitational three-body problem in the cases of first and second order resonances
Authors: Bardin B S , Avdyushkin A N 
Published: July 2021

Abstract
We deal with the planar circular photogravitational three-body problem. That is, we consider the motion of a particle under influence of gravitational and radiation forces acting from two bodies, which move in circular orbits. The stability of collinear point L1
, which located on the line between the bodies, is investigated. By using the method of normal forms and applying theorems of KAM theory we perform a nonlinear stability study for parameter values corresponding to the cases of first and second order resonances. Rigorous conclusions on instability and stability in the sense of Lyapunov have been obtained.
On the equilibriums stability in an approximate problem of the dynamics of a rigid body with a suspension point vibrating along an inclined straight line
Authors: Belichenko Mikhail 
Published: July 2021

Abstract
We consider the heavy rigid body dynamics under the assumption that one of the body points (the suspension point) performs the specified high-frequency vibrations of small amplitude along an inclined straight line, and the body mass centre lies on the principal axis of inertia for the suspension point. In the framework of an approximate autonomous system of canonical equations of motion, the question of existence, number, and stability of the body relative equilibrium positions is solved. It is shown that for all such equilibria, the mass centre radius-vector lies in the vertical plane containing the vibration axis. The number of equilibria is four, six or eight depending on the vibration intensity. Sufficient and necessary conditions for their stability are found. The existence of high-frequency periodic motions of the initial non-autonomous system, which are generated by the investigated equilibria, is justified using Poincare’s method. Conclusions about stability (in linear approximation) of these periodic motions are drawn.
Effect of the heat transfer coefficient on modelling the energy deposition of destructed meteoroid
Authors: Brykina I G , Bragin M D 
Published: July 2021

Abstract
Models of meteoroid destruction into the cloud of fragments moving with a common shock wave are considered: the two-parameter model that takes into account changes of the shape and density of the cloud, and simple models that leave these factors out of account, including those used in the literature. Models differ in equations governing the lateral expansion of the cloud. We numerically simulate the interaction of the Chelyabinsk asteroid with the Earth’s atmosphere by solving the meteor physics equations using fragment cloud models, and study the models abilities to reproduce the observational energy deposition curve. Heat transfer coefficient effect on simulating energy deposition using different models is estimated. For simple fragment cloud models, the optimal coefficient in the cloud lateral expansion equation is proposed as a function of the heat transfer coefficient (ablation parameter) to match the observational altitude of the bolide peak brightness. The optimal value of the uncertainty parameter in the expression for the heat transfer coefficient is found to match also a shape of the observational energy deposition curve. It is shown that the optimal simple and the two-parameter models give results of modelling the energy deposition of the Chelyabinsk asteroid and estimates of its entry mass, which are very close to each other and are consistent with the observational data.
On the uncertainty factor in approximation of the heat transfer coefficient in the problem of modelling the interaction of meteor body with the atmosphere
Authors: Brykina I G , Egorova L A 
Published: July 2021

Abstract
The problem of modelling the interaction of meteor body with the Earth’s atmosphere is considered. The motion, ablation, and energy deposition of the meteoroid and its fragments moving as a single body are modelled by numerically solving the meteor physics equations. For the heat transfer coefficient, which is a governing parameter in these equations, the proposed approximate expression is used, depending on the meteoroid velocity and size and the atmospheric density, as well as a constant value accepted in the literature. An uncertainty parameter is introduced into the formula for the heat transfer coefficient to make allowance for the existing uncertainty in the radiative heat flux computations in the meteoric range of flow parameters. The influence of uncertainty of the heat transfer coefficient on the meteoroid mass loss, velocity, trajectory, and energy deposition is evaluated.
Periodic body motions along a horizontal rough surface by moving two internal masses
Authors: Chekina Evgeniya A 
Published: July 2021

Abstract
The analysis of the translational motion of a body carrying two moving internal masses along a horizontal rough surface is provided. The masses perform harmonic oscillations in the vertical plane, the frequencies of which are equal, and the amplitudes and phases can be arbitrary. It is assumed that the values of the problem parameters are chosen in such a way that the body moves without separation from the surface. Friction between a body and a surface is described by Coulomb’s law. The classification of possible modes of body motion with periodically varying velocity is carried out. In the three-dimensional space of the parameters of the problem, regions in which the periodic motions are of a qualitatively different nature were constructed.
Asymptotically exact value of the distribution function of molecular pairs in a shock-compressed highly dispersed gas mixture
Authors: Demidov I V , Kuznetsov M M , Kuleshova Y D , Tikhonovets A V 
Published: July 2021

Abstract
The aim of this work is to obtain asymptotically strong expressions for the distribution functions of pairs of molecules inside the shock wave front. An asymptotically exact expression is obtained for the distribution function of the pairs of molecules of the heavy component of a binary shock-compressed gas mixture at the beginning of its translational relaxation. This result is extremely important for experimental modeling of the effect of high-speed overshoot in shock tubes.
Heat flux on streamlined body surface after local energy input
Authors: Dobrov Yu V , Renev M E , Lashkov V A , Mashek I Ch , Khoronzhuk R S 
Published: July 2021

Abstract
An experimental and numerical study of interaction between an oblique shock wave and density inhomogeneity is done. The inhomogeneity is created by interelectrode spark discharge in the oncoming flow with a Mach number of 2. As a result of the experiment, we obtained gradient heat flux sensor data and took shadow photography of the process.
3D model of deflection of an asymmetrical needle during motion in soft tissues
Authors: Druzhinin V G , Morozov V A 
Published: July 2021

Abstract
This study describes a mathematical model of deflection of a steel medical injection needle during its motion in the soft tissue phantom (imitation of human tissues). This model is necessary for adjustment of robotically assisted systems during brachytherapy procedures or similar operations where high precision needle tip positioning is prerequisite. Since the needle tip is asymmetrical, the needle will deform when moving in human tissues and consequently deflect from the rectirectilinear motion. Thus, by inserting and rotating the needle around its axis the needle tip can be led along the predetermined path. This study adopts a new approach to describe an external impact on the needle when it moves inside human tissues and also describes 2D and 3D models, a process of selection of coefficients for 3D models, and provides simulation results.
PAINeT: Implementation of neural networks for transport coefficients calculation
Authors: Istomin V , Kustova E 
Published: July 2021

Abstract
In the present study, a possibility of neural networks implementation for evaluation of transport coefficients in atomic gases taking into account electronic excitation and in molecular gases with electronic, vibrational and rotational degrees of freedom is discussed. Atomic nitrogen N and oxygen O, molecular nitrogen N
2 and oxygen O
2, as well as mixtures (N2, N, O2, O) and (N2, N, O2, O, Ar) are considered in the one-temperature approach of the kinetic theory. The results of exact calculations are compared to the neural network-based simulations. It is shown that for single-component gases, the proposed approach yields good accuracy and calculation speedup up to 3 times for atoms and up to 19 times for molecules. The speedup is significant for multi-component mixtures and increases with the mixture complexity, attaining for four- and five-component mixtures from 597 to 1196 times correspondingly. Ways to improve the accuracy of neural-network predictions of multi-component mixtures transport coefficients are discussed.
Multi-mode oscillations of a mechanical system with higher-order singularity
Authors: Kalnitsky V S 
Published: July 2021

Abstract
This article is based on earlier author’s works on the behavior of mechanical systems with a singular configuration space. We obtained exact analytical expressions for the constraints providing multi-mode oscillations of a double mathematical pendulum. It was found that there are infinitely many modes of oscillations determined by the degree of degeneracy at a singular point in the configuration space of the pendulum. The problem of a double pendulum motion with an elliptical constraint, posed by the author earlier, received a complete solution, both theoretical and experimental. For such a constraint, there are exactly two different oscillation modes: symmetric and asymmetric. Each mode can be realized by selecting the system parameters and is completely determined by the smoothness of the trajectory in the configuration space with a singularity. In the study we used only standard tools of classical analytical mechanics.
State-to-state modeling of oxygen relaxation taking into account electron kinetics
Authors: Melnik M , Kustova E 
Published: July 2021

Abstract
Coupled vibrational, chemical and electronic kinetics in oxygen is studied using the detailed state-to-state model. Simulation of zero-dimensional oxygen relaxation in the presence of free electrons in the temperature range 300 – 1000 K is carried out; the master equations for the vibrational state populations and densities of excited species are solved together with the Boltzmann equation for the electron density distribution. Different models for heavy-particle interactions are assessed. It is shown that the forced harmonic oscillator model is suitable in the entire temperature range. The effect of the initial conditions and the presence of free electrons is discussed; it is shown that including electrons modifies the main relaxation mechanisms. Recommendations are given for extending the kinetic scheme to high-temperature regimes.
Study of the hexapod dynamics using equations in redundant coordinates
Authors: Petrova Victoria 
Published: July 2021

Abstract
The dynamics of hexapods (Stewart platforms) has been extensively studied for several decades. In this problem, the equations of motion are usually constructed using the basic theorems of mechanics. Lagrange equations of the second kind are often constructed for the same purpose. In the present paper, a new form of dynamic equations is considered. These equations are a special form of equations of motion of a system of rigid bodies (equations of dynamics in redundant coordinates). This approach is used to obtain the differential equations of motion of a hexapod in redundant coordinates. In this case, the loaded Stewart platform is considered as a rigid body, whose position is determined by setting the radius vector of the center of mass and the unit vectors of the body-axes system. From the vector form of the Lagrange equations of the first kind scalar differential equations of motion of the mechanical system under consideration are obtained. The obtained equations for some standard motions of the hexapod are numerically integrated. It is noted that the stable motion of the mechanical system under consideration can be obtained only with the introduction of feedbacks.