Physics MDPI

📢 We are excited to share the good news that Physics MDPI received a new Impact Factor of 1.5, ranking Q2 in the "PHYSICS, MULTIDISCIPLINARY" category; new CiteScore of 3. 🎉 Thanks for the support of Editorial Board Members, reviewers and authors! MDPI; #OpenAccess #physics

Two New Methods in Stochastic Electrodynamics for Analyzing the Simple Harmonic Oscillator and Possible Extension to Hydrogen | Article by Daniel C. Cole https://lnkd.in/gw34R_EC This article belongs to the Special Issue Vacuum Fluctuations (https://lnkd.in/giM8cvCX) Boston University;MDPI #stochastic #electrodynamics; #classical #physical #dynamics; #hydrogen; #harmonic #oscillator; #nonlinear #physics #Abstract The position probability density function is calculated for a classical electric dipole harmonic oscillator bathed in zero-point plus Planckian electromagnetic fields, as considered in the physical theory of stochastic electrodynamics (SED). The calculations are carried out via two new methods. They start from a general probability density expression involving the formal integration over all probabilistic values of the Fourier coefficients describing the stochastic radiation fields. The first approach explicitly carries out all these integrations; the second approach shows that this general probability density expression satisfies a partial differential equation that is readily solved. After carrying out these two fairly long analyses and contrasting them, some examples are provided for extending this approach to quantities other than position, such as the joint probability density distribution for positions at different times, and for position and momentum. This article concludes by discussing the application of this general probability density expression to a system of great interest in SED, namely, the classical model of hydrogen.

The Interplay between Coronal Holes and Solar Active Regions from Magnetohydrostatic Models | Article by Jaume Terradas https://lnkd.in/gcxjNEhG Universitat de les Illes Balears; MDPI #solar #corona #magnetic #fields #magnetohydrostatic #models #physics This article belongs to the Special Issue: A Themed Issue in Honor of Professor Marcel Goossens on the Occasion of His 75th Birthday https://lnkd.in/eQhx9x5A #Abstract Coronal holes (CHs) and active regions (ARs) are typical magnetic structures found in the solar corona. The interaction of these two structures was investigated mainly from the observational point of view, but a basic theoretical understanding of how they are connected is missing. To address this problem, in this paper, magnetohydrostatic models are constructed by numerically solving a Grad–Shafranov equation in two dimensions. A common functional form for the pressure and temperature in the CH and in the AR are assumed throught the study. Keeping the parameters of the CH constant and modifying the parameters of the nearby bipolar AR, one finds essentially three types of solutions depending on the magnitude and sign of the magnetic field at the closest foot of the AR to the CH. Two of the three solutions match well with the observation, but the third solution predicts the existence of closed magnetic field lines with quite low density and temperature with opposite characteristics to those in typical ARs. Simple analytical expressions are obtained for the pressure, temperature and density at the core of the AR and their dependence upon several major physical parameters are studied. The results obtained in this paper need to be contrasted with observations.

Quantum Theory without the Axiom of Choice, and Lefschetz Quantum Physics | Article by Koen Thas https://lnkd.in/gDEMrxps UGent;MDPI #modal #quantum #theory; #axiom of choice; #Lefschetz #principle; #foundations of #quantum #theory; #thought #experiments #physics #Abstract In this paper, we discuss quantum formalisms that do not use the axiom of choice. We also consider the fundamental problem that addresses the (in)correctness of having the complex numbers as the base field for Hilbert spaces in the København interpretation of quantum theory, and propose a new approach to this problem (based on the Lefschetz principle). Rather than a theorem–proof paper, this paper describes two new research programs on the foundational level, and focuses on basic open questions that arise in these programs.

Numerical Simulations of the Decaying Transverse Oscillations in the Cool Jet | Article by Abhishek K. Srivastava and Balveer Singh from Indian Institute of Technology (Banaras Hindu University), Varanasi https://lnkd.in/gvd5-qaF This article belongs to the Special Issue A Themed Issue in Honor of Professor Marcel Goossens on the Occasion of His 75th Birthday https://lnkd.in/eQhx9x5A #physics #openaccess #Sun #atmosphere #chromosphere #magnetohydrodynamics #Abstract In the present paper, we describe a 2.5D (two-and-a-half-dimensional) magnetohydrodynamic (MHD) simulation that provides a detailed picture of the evolution of cool jets triggered by initial vertical velocity perturbations in the solar chromosphere. We implement random multiple velocity, 𝑉𝑦, pulses of amplitude 20–50 km s−1 between 1 Mm and 1.5 Mm in the Sun’s atmosphere below its transition region (TR). These pulses also consist of different switch-off periods between 50 s and 300 s. The applied vertical velocity pulses create a series of magnetoacoustic shocks steepening above the TR. These shocks interact with each other in the inner corona, leading to complex localized velocity fields. The upward propagation of such perturbations creates low-pressure regions behind them, which propel a variety of cool jets and plasma flows in the localized corona. The localized complex velocity fields generate transverse oscillations in some of these jets during their evolution. We study the transverse oscillations of a representative cool jet J1, which moves up to the height of 6.2 Mm above the TR from its origin point. During its evolution, the plasma flows make the spine of jet J1 radially inhomogeneous, which is visible in the density and Alfvén speed smoothly varying across the jet. The highly dense J1, which is triggered along the significantly curved magnetic field lines, supports the propagating transverse wave of period of approximately 195 s with a phase speed of about 125 km s−1. In the distance–time map of density, it is manifested as a transverse kink wave. However, the careful investigation of the distance–time maps of the x- and z-components of velocity reveals that these transverse waves are actually of mixed Alfvénic modes. The transverse wave shows evidence of damping in the jet. We conclude that the cross-field structuring of the density and characteristic Alfvén speed within J1 causes the onset of the resonant conversion and leakage of the wave energy outward to dissipate these transverse oscillations via resonant absorption. The wave energy flux is estimated as approximately of 1.0 × 106 ergs cm−2 s−1. This energy, if it dissipates through the resonant absorption into the corona where the jet is propagated, is sufficient energy for the localized coronal heating.

🚀#TitleStory 🔹Is the Non-Pointness of the Electron Observable in e+e− Annihilation at Center-of-Mass Energies 55–207 GeV? | Article by Yutao Chen, Chih-Hsun Lin, Minghui Liu, Alexander S. Sakharov, Jürgen Ulbricht and Jiawei Zhao https://lnkd.in/gvM_K9UJ University of Electronic Science and Technology of China; Institute of Physics, Academia Sinica; Manhattan College; CERN; ETH Zürich; MDPI #QED hashtag #model hashtag #physics

Study on the Thermodynamic Properties of Thin Film of FCC Interstitial Alloy AuSi at Zero Pressure Using the Statistical Moment Method | Article by Nguyen Thi Hoa, Nguyen Quang Hoc and Hua Xuan Dat https://lnkd.in/gRgkuTHg University of Transport and Communications;Hanoi National University of Education;MDPI #binary #interstitial #alloy; #thin #film; #thermodynamic #properties; #statistical #moment #method #physics #Abstract We built a model and proposed a theory about the thermodynamic properties of face-centered cubic (FCC) binary interstitial alloy’s thin films based on the statistical moment method and performed numerical calculations for AuSi (gold silicide). First, the statistical moment method (SMM) calculations for the thermodynamic properties of Au are compared with reported experiments and calculations that show a good agreement between the calculations in this paper and earlier studies. Additionally, the SMM calculations for thermodynamic properties of AuSi alloy films are performed, which show that the thermal expansion coefficient, the specific heat at constant volume, and the specific heat at constant pressure increases, while the isothermal elastic modulus decreases with increasing temperature and increasing interstitial atom concentration. Furthermore, when the number of layers reaches 100, the thermodynamic properties of the film are similar to those of the bulk material. The achieved theoretical results for AuSi films are novel and can be useful in designing future experiments.

Heating and Cooling in Transversely Oscillating Coronal Loops Powered by Broadband, Multi-Directional Wave Drivers | Article by Thomas Howson and Ineke De Moortel https://lnkd.in/grGaVX7u This article belongs to the Special Issue A Themed Issue in Honor of Professor Marcel Goossens on the Occasion of His 75th Birthday (https://lnkd.in/eQhx9x5A) University of St Andrews;University of Oslo;MDPI #solar #corona; #MHD (magnetohydrodynamics) #oscillations; #wave #heating; #Kelvin–Helmholtz #instability #physics #Abstract Recent studies have identified the potential for coronal wave heating to balance radiative losses in a transversely oscillating low-density loop undergoing resonant absorption, phase mixing and the Kelvin–Helmholtz instability. This result relied on a continuous, resonant oscillatory driver acting on one of the loop footpoints and similar setups with non-resonant driving produce insufficient heating. Here, we consider broadband and multi-directional drivers with power in both resonant and non-resonant frequencies. Using three-dimensional magnetohydrodynamic simulations, we impose transverse, continuous velocity drivers at the footpoints of a coronal loop, which is dense in comparison to the background plasma. We include the effects of optically thin radiation and a uniform background heating term that maintains the temperature of the external plasma but is insufficient to balance energy losses within the loop. For both broadband and multi-directional drivers, we find that the energy dissipation rates are sufficient to balance the average energy losses throughout the simulation volume. Resonant components of the wave driver efficiently inject energy into the system and these frequencies dominate the energetics. Although the mean radiative losses are balanced, the loop core cools in all cases as the wave heating rates are locally insufficient, despite the relatively low density considered here.

Advances in the Implementation of the Exactly Energy Conserving Semi-Implicit (ECsim) Particle-in-Cell Method | Article by Giovanni Lapenta https://lnkd.in/gh3gVug2 This article belongs to the Special Issue A Themed Issue in Honor of Professor Marcel Goossens on the Occasion of His 75th Birthday (https://lnkd.in/eQhx9x5A) KADOC-University of Leuven Center for mathematical Plasma Astrophysics;MDPI #particle-in-cell; #energy #conservation; #subcycling #physics #Abstract The energy-conserving semi-implicit (ECsim) method presented by the author in 2017, is a particle-in-cell (PIC) algorithm for the simulation of plasmas. Energy conservation is achieved within a semi-implicit formulation that does not require any non-linear solver. A mass matrix is introduced to linearly express the particle-field coupling. With the mass matrix, the algorithm preserves energy conservation to machine precision. The construction of the mass matrix is the central nature of the method and also the main cost of the computational cycle. Here, three methods that modify the construction of the mass matrix are analyzed. First, the paper considers how the sub-cycling of the particle motion modifies the mass matrix. Second, a form of smoothing that reduces the noise while retaining exact energy conservation is introduced. Finally, an approximation of the mass matrix is discussed that transforms the ECsim scheme to the implicit moment method.

Quantum Configuration and Phase Spaces: Finsler and Hamilton Geometries | Article by Saulo Albuquerque, Valdir B. Bezerra, Iarley P. Lobo, Gabriel Macedo, Pedro H. Morais, Ernesto Rodrigues, Luis C. N. Santos and Gislaine Varão https://lnkd.in/gWb-iwqP This article belongs to the Special Issue New Advances in Quantum Geometry (https://lnkd.in/gUDzYj3C) Universidade Federal da Paraíba;Universidade Federal de Lavras;MDPI #quantum #gravity #phenomenology; #Finsler #geometry; #Hamilton #geometry #physics #Abstract In this paper, we reviewtwo approaches that can describe, in a geometrical way, the kinematics of particles that are affected by Planck-scale departures, named Finsler and Hamilton geometries. By relying on maps that connect the spaces of velocities and momenta, we discuss the properties of configuration and phase spaces induced by these two distinct geometries. In particular, we exemplify this approach by considering the so-called q-de Sitter-inspired modified dispersion relation as a laboratory for this study. We finalize with some points that we consider as positive and negative ones of each approach for the description of quantum configuration and phases spaces.