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Collisionless tearing instability with a power-law distribution function in a relativistic pair plasma with a guide field is studied. When the current sheet is supported by plasma pressure, the tearing mode is suppressed as the particle spectrum hardens. In the force-free limit, the instability growth rate becomes independent of the particle spectrum. We apply these results to relativistic MHD turbulence, where magnetic energy greatly exceeds plasma rest energy, and derive an expression for the transverse size of turbulent eddies unstable to tearing mode. We also establish the critical plasma magnetization parameter above which charge starvation prevents the tearing instability. These results might be useful for developing more accurate models of particle acceleration in relativistic astrophysical sources. [ABSTRACT FROM AUTHOR]

On 2022 September 5, during Parker Solar Probe's (PSP) 13th encounter, a fast shock wave and a related solar energetic particle (SEP) event were observed as the spacecraft approached the perihelion of its orbit. Observations from the Integrated Science Investigation of the Sun (IS⊙IS) instrument suite show that SEPs arrived at the spacecraft with a significant delay from the onset of the parent solar eruption and that the first arriving SEPs exhibited an inverse velocity dispersion (IVD) for energetic protons above ~1 MeV. Utilizing data from multiple spacecraft, we investigate the eruption dynamics and shock wave propagation. Our analysis includes 3D shock modeling and SEP transport simulations to examine the origins of this SEP event and explore the causes of the delayed SEP onset and the observed IVD. The data-driven SEP simulation reproduces the SEP event onset observed at PSP, its evolving energy spectrum, and the IVD. This IVD is attributed to a relatively slow, ongoing particle acceleration process occurring at the flank of the expanding shock wave intercepted by PSP. This has significant implications for the role of shocks in the release of SEPs at widespread events and for methods used to infer the SEP release times. Furthermore, the match between the simulation and observations worsens when cross-field diffusion is considered, indicating that SEP diffusion had a minor effect on this event. These findings underscore the complexity of SEP events and emphasize the need for advanced modeling approaches to better understand the role of shock waves and other physical processes in SEP acceleration and release. [ABSTRACT FROM AUTHOR]

Particle acceleration is a commonly observed phenomenon at dipolarization fronts. Many studies have attempted to determine the acceleration mechanism, with betatron acceleration being a major candidate. In previous work, we attempted to match the observed change in electron energy to the change predicted by betatron acceleration, but found that although this worked in some cases, overall betatron acceleration alone could not describe the observed energy spectrum changes. In this work, we attempted to study whether ion acceleration showed similar behavior and whether a quasi-adiabatic correction would be more accurate. On average the betatron acceleration equation overestimated the observed acceleration and the quasi-adiabatic correction did not account for the difference, although there are limitations to this study due to data fidelity. We then turned to study whether our assumptions about the source population having the same phase space density as the cold pre-existing background population in the plasma sheet are valid. We indirectly studied this by comparing the relative abundances of O + and H e + + as proxies for ionospheric and solar wind populations respectively. We found the betatron acceleration equation method performs slightly better when there is a stronger ionospheric component. This suggests that when more plasma containing O + is present in the dipolarization front, it indicates that the source population is more local and therefore this method of using betatron acceleration is more valid. [ABSTRACT FROM AUTHOR]

Shocks and turbulence are ubiquitous phenomena, responsible for particle acceleration to very high energies in a large collection of astrophysical systems. Using self-consistent, hybrid-kinetic simulations with and without pre-existing turbulence, we study the transition of a shock from 'laminar' to turbulent. We show that the changes in upstream proton transport behaviour are crucial to understand this transition, which we address quantitatively with a novel Eulerian approach. This method, based on the coarse-graining of the Vlasov equation originally introduced in one of our previous studies, gives consistent results for inertial range scales. The potential applications of the coarse-graining approach beyond the shock–turbulence system are outlined. [ABSTRACT FROM AUTHOR]

Cosmic rays (CRs) are accelerated in diverse astrophysical objects like supernova remnants, massive star clusters, or pulsars. Fermi acceleration mechanisms built a power-law distribution controlled by the ratio of the acceleration to escape timescales in the acceleration site. Hence, escape is an essential mechanism to establish the particle distribution at cosmic-ray sources and to control the flux of cosmic rays injected into the galaxy. Different models have tried to account for the escape process. However, all show some limitations due to the complexity of the particle release mechanism, usually involving 3D geometry, with specific magnetic turbulence properties linked to the process itself. The escape process is also time dependent and results from the interplay of particle acceleration and injection efficiency in the astrophysical source. Once injected into the interstellar medium, freshly released particles are channelled by the ambient magnetic field, which is itself turbulent. In a simplified view, we mainly focus on the propagation of CRs along 1D magnetic flux tubes before turbulent motions start to mix them over a turbulent coherence length, and then we further question this assumption. Close to their sources, one can also expect cosmic rays to harbour higher pressure with respect to their mean value in the interstellar medium. This intermittency in the CR distribution is prone to trigger several types of kinetic and macro instabilities, among which the resonant streaming instability has been the most investigated. In this article, we review recent observational and theoretical studies treating cosmic-ray escape and propagation in the vicinity of their source. We will consider three main astrophysical contexts: association with massive star clusters, gamma-ray halos around pulsars, and, more specifically, supernova remnants. In particular, we discuss in some detail the cosmic-ray cloud (CRC) model, which has been widely used to investigate CR propagation in the environment of supernova remnants. The review also discusses recent studies on CR-induced feedback over the interstellar medium surrounding the sources associated with the release process, as well as alternative types of driven instabilities. [ABSTRACT FROM AUTHOR]

In astrophysics, one significant challenge lies in understanding the acceleration of cosmic rays, which leads to the occurrence of a power law. In this article, momentum transport generated by the combined effects of pitch-angle diffusion and background flow velocity inhomogeneities is proposed to obtain a cosmic rays acceleration mechanism, starting from the well-known focused transport equation describing particle diffusion and acceleration. The inhomogeneities of background flow velocity are ubiquitous in the astrophysical environment. The equation for the isotropic part of the distribution function of charged energetic particles is derived, and its solution is obtained, demonstrating the form of momentum power laws of cosmic rays. In addition, if it is assumed that cosmic rays penetrate compressive MHD waves or turbulence, for quasi-steady states, the spectral index δ of the momentum power law spectrum of cosmic rays is found to be in the range [−5, −3], which includes the observed power law indices of galactic cosmic rays. The results obtained in this article demonstrate that the mechanism proposed in this article, along with shock acceleration, may also contribute to the acceleration of galactic cosmic rays. Furthermore, when momentum convection effect and higher-order momentum derivative terms are considered, the indices of power laws should be smaller than −5. This may explain the power laws of solar energetic particle events. [ABSTRACT FROM AUTHOR]

Hot flow anomalies (HFAs) and foreshock bubbles (FBs) are two types of transient phenomena characterized by flow deflected and hot cores bounded by one or two compressional boundaries in the foreshock. Using conjunction observations by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, we present an MHD HFA with a core filled with magnetosheath material around the bow shock and a typical kinetic FB associated with foreshock ions upstream of the bow shock, occurring simultaneously under the same solar wind/interplanetary magnetic field (IMF) conditions. The displacements of the bow shock moving back and forth along the sun-earth line are observed. Electron energy shows enhancements from ∼50 keV in the FB to ∼100 keV in the HFA core, suggesting additional acceleration process across the bow shock within the transient structure. The magnetosheath response of an HFA core-like structure with particle heating and electron acceleration is observed by the Magnetospheric Multiscale (MMS) mission. Ultralow frequency waves in the magnetosphere modulating cold ion energy are identified by THEMIS, driven by these transient structures. Our study improves our understanding of foreshock transients and suggests that single spacecraft observations are insufficient to reveal the whole picture of foreshock transients, leading to an underestimation of their impacts (e.g., particle acceleration energy and spatial scale of disturbances). [ABSTRACT FROM AUTHOR]

Collisionless shock waves, found in supernova remnants, interstellar, stellar, and planetary environments, and laboratories, are one of nature's most powerful particle accelerators. This study combines in situ satellite measurements with recent theoretical developments to establish a reinforced shock acceleration model for relativistic electrons. Our model incorporates transient structures, wave-particle interactions, and variable stellar wind conditions, operating collectively in a multiscale set of processes. We show that the electron injection threshold is on the order of suprathermal range, obtainable through multiple different phenomena abundant in various plasma environments. Our analysis demonstrates that a typical shock can consistently accelerate electrons into very high (relativistic) energy ranges, refining our comprehension of shock acceleration while providing insight on the origin of electron cosmic rays. The mechanisms resulting in particle acceleration to relativistic energies in space plasmas are an open question. Here, the authors show a reinforced shock acceleration model which enables electrons to efficiently achieve relativistic energies and reveal a low electron injection threshold. [ABSTRACT FROM AUTHOR]

During relativistic magnetic reconnection, antiparallel magnetic fields undergo a rapid change in topology, releasing a large amount of energy in the form of non-thermal particle acceleration. This work explores the application of mesh refinement to 2D reconnection simulations to efficiently model the inherent disparity in length-scales. We have systematically investigated the effects of mesh refinement and determined necessary modifications to the algorithm required to mitigate non-physical artifacts at the coarse–fine interface. We have used the ultrahigh-order pseudo-spectral analytical time-domain Maxwell solver to analyze how its use can mitigate the numerical dispersion that occurs with the finite-difference time-domain (or "Yee") method. Absorbing layers are introduced at the coarse–fine interface to eliminate spurious effects that occur with mesh refinement. We also study how damping the electromagnetic fields and current density in the absorbing layer can help prevent the non-physical accumulation of charge and current density at the coarse–fine interface. Using a mesh refinement ratio of 8 for two-dimensional magnetic reconnection simulations, we obtained good agreement with the high-resolution baseline simulation, using only 36% of the macroparticles and 71% of the node-hours needed for the baseline. The methods presented here are especially applicable to 3D systems where higher memory savings are expected than in 2D, enabling comprehensive, computationally efficient 3D reconnection studies in the future. [ABSTRACT FROM AUTHOR]

In order to comprehend particle acceleration and transit in interplanetary space, nonlinear processes are of great importance. One process contributing to the heating of the plasmas might be the ponderomotive nonlinearity and magnetic islands that causes the localization of the parallel propagating left-handed circularly polarized dispersive Alfvén wave having a finite frequency. This study investigates the impact of nonlinearity on the creation of localized structures and current sheets formation in solar wind. Pseudo-spectral method and finite difference method with modified predictor-corrector approach are the mathematical models used for spatial integration and temporal integration, respectively, for studying the evolution of left-handed circularly polarized dispersive Alfvén wave. The findings of current study show that the nonlinearity in the system and the presence of magnetic islands are responsible for chaotic structures and turbulent state. Furthermore, to refine the physics behind the localization and current sheets formation the semi-analytical model has been used. The localized structures and current sheets obtained have the scale size of the order of ion inertial length. [ABSTRACT FROM AUTHOR]

Context. In the heliosphere, power-law particle distributions are observed, for example, upstream of interplanetary shocks, which can result from superdiffusive transport. This non-Gaussian transport regime may be due to intermittent magnetic field structures. Recently, we have shown that a Lévy flight model reproduces the observed features at shocks: power-law distributions upstream of the shock and enhanced intensities at the shock. Aims. In this work, we extend the Lévy flight model to study the impact of superdiffusive transport on particle acceleration at shocks. We compared the acceleration timescale and spectral slope to Gaussian diffusion and a Lévy walk model. Methods. We solved the fractional transport equation by sampling the number density with the corresponding stochastic differential equation that is driven by an alpha-stable Lévy distribution. For both Gaussian and superdiffusive transport, we used a modified version of the cosmic ray propagation framework CRPropa 3.2. Results. We obtained the number density and energy spectra for constant and energy-dependent anomalous diffusion, and we find, compared to the case of Gaussian diffusion, harder energy spectra at the shock as well as faster acceleration. The spectral slope is even harder than predicted for Lévy walks. Conclusions Lévy flight models of superdiffusive transport lead to observed features in the heliosphere. We further show that superdiffusive transport impacts the acceleration process by changing the probability of escaping the shock. The flexibility of the Lévy flight model allows for further studies in the future that can take the shock geometry and magnetic field structure into account. [ABSTRACT FROM AUTHOR]

The document "Pulsar Astronomy" discusses pulsars, which are fast-rotating magnetized neutron stars emitting multiwavelength electromagnetic radiation. It highlights the discovery of over 4000 pulsars since 1967 and their characteristics, such as strong magnetic fields and uncertain inner structures. The text also mentions advancements in pulsar studies in China, particularly with the Shanghai Tianma 65 m telescope and the Five-hundred-meter Aperture Spherical radio Telescope (FAST), which have led to the discovery of new radio pulsars. Additionally, the document covers topics like pulsar timing, gravitational waves, and the internal composition of pulsars, providing insights into the progress and status of pulsar observations and theories. [Extracted from the article]

Interplanetary Coronal Mass Ejections (ICMEs) and High-Speed Streams (HSSs) are significant drivers of space disturbance in interplanetary space. The interaction between these structures can lead to various phenomena, including the generation of waves, enhanced geo-effectiveness, particle acceleration, and more. However, understanding the plasma thermodynamic properties during an ICME-HSS interaction remains an open problem. In this study, we utilize observations from STEREO and WIND to investigate the thermodynamic behavior of plasma within an ICME and a HSS. Here, we used the thermal pressure ( P th ) and proton number density ( N p ) data from spacecraft. By fitting the linear model to the scattered data of ln P th vs ln N p we estimated the polytropic index (α). Our analysis reveals that the ICME observed before its interaction with the HSS by STEREO-A exhibits a polytropic index α ∼ 1.0 , indicating an isothermal process. Conversely, WIND observations of the same ICME before its interaction with the HSS show a nearly isothermal behavior, with α = 0.7. The HSS observed by WIND demonstrates α = 1.8 before its interaction with the ICME. Further analysis of WIND observations within the ICME-HSS interaction region determines a polytropic index of α = 2.5. These findings suggest that the HSS region displays a nearly adiabatic behavior, the ICME region manifests closely isothermal characteristics, and the ICME-HSS interaction region exhibits super-adiabatic behavior. We propose that the expansion of ICME increases due to its propagation in the vicinity of HSS, potentially leading to additional cooling of the observed ICME magnetic cloud, which differs from the ambient solar wind. [ABSTRACT FROM AUTHOR]

In this paper, we provide a detailed investigation of the energization processes in two-dimensional, two and a half-dimensional, and three-dimensional collapsing magnetic trap models. Using kinematic magnetohydrodynamic models of collapsing magnetic traps, we examine the importance of Fermi acceleration in comparison with betatron acceleration in these models. We extend previous work by investigating particle orbits in two-dimensional models without and with a guide field component and from full three-dimensional models. We compare the outcomes for the different models and how they depend on the chosen initial conditions. While in the literature betatron acceleration has been emphasized as the major mechanism for particle energization in collapsing magnetic traps, we find that Fermi acceleration can play a significant role as well for particle orbits with suitable initial conditions. [ABSTRACT FROM AUTHOR]

High-power pulsed lasers are used more and more as tools for particle acceleration. Characterization of the accelerated particles in real-time and monitoring of the electromagnetic pulses (EMPs) during particle acceleration are critical challenges in laser acceleration experiments. Here, we used the CETAL-PW laser facility at NILPRP for particle acceleration from different thin metallic targets, at laser intensities of the order of 3 × 10 21 W/cm2. We investigated the dependence of EMP amplitude (EMPA) and the accelerated electrons' maximal energy (AEME), on thickness, resistivity, and atomic number of the target. We have found a quasi-linear dependence between EMPA and AEME and propose an analytical model for the GHz EMP emission. The model considers the neutralization current flowing through the target stalk as the main source of the EMP in the GHz domain, the current being produced by the positive charge accumulated on the target after the electron's acceleration from the rear side of a metallic target. The data presented here support the possibility of using EMP signals to characterize the laser-accelerated particles in a real-time non-invasive way. [ABSTRACT FROM AUTHOR]

Shock waves, the interface of supersonic and subsonic plasma flows, are the primary region for charged particle acceleration in multiple space plasma systems, including Earth's bow shock, which is readily accessible for in-situ measurements. Spacecraft frequently observe relativistic electron populations within this region, characterized by energy levels surpassing those of solar wind electrons by a factor of 10,000 or more. However, mechanisms of such strong acceleration remain elusive. Here we use observations of electrons with energies up to 200 kiloelectron volts and a data-constrained model to reproduce the observed power-law electron spectrum and demonstrate that the acceleration by more than 4 orders of magnitude is a compound process including a complex, multi-step interaction between more commonly known mechanisms and resonant scattering by several distinct plasma wave modes. The proposed model of electron acceleration addresses a decades-long issue of the generation of energetic (and relativistic) electrons at planetary plasma shocks. This work may further guide numerical simulations of even more effective electron acceleration in astrophysical shocks. Mechanisms responsible for the electron acceleration to near relativistic energies in Earth's foreshock remains elusive. Here, the authors show that the combination of resonant scattering by distinct wave modes with known acceleration mechanisms explains the formation of observed electron fluxes up to and above 200 keV. [ABSTRACT FROM AUTHOR]

Jupiter's poleward (Zone II) main aurora exhibits bi‐directional electron acceleration; upward acceleration dominates but downward acceleration generates strong aurora. During Juno's first perijove (PJ1), the upward acceleration manifested as narrow electron angular beams (within ∼5° of the magnetic field) over the 30–1,200 keV energy range of Juno's Jupiter Energetic Particle Detector Investigation (JEDI). These beams can be simply connected (non‐uniquely) to >10 to perhaps 100's of MeV electrons that penetrated the radiation shielding of the camera head of the Magnetometer Investigation's Advanced Stellar Compass (ASC). The most intense of those multiple MeV populations are shown to have been highly directional and propagating upwards. How auroral processes generate such beams is unknown. With azimuthal symmetry assumed (not demonstrated here), these beams provided >1026 s−1 of >30 keV electrons to Jupiter's vast magnetosphere, a possibly critical and dominating source of energetic electrons to that region and ultimately to Jupiter's radiation belts. Plain Language Summary: Aurora at Earth and Jupiter are generated by electron acceleration processes occurring at relatively low altitude above the polar atmospheric regions emitting the auroral lights. While downward electron acceleration causes the auroral emissions, upward electron acceleration can occur in a fashion that populates the distant planetary space environments (or "magnetospheres"). We find with NASA's Juno spacecraft that upward auroral electron acceleration at Jupiter has unique features. It is often more energetic and powerful than is the downward acceleration. The resulting electron beams are unexpectedly collimated along the magnetic field lines connecting the auroral regions to the spacecraft. The beams can extend in energy to unexpectedly high values, greater than 20 million electron volts (MeV). Finally, the quantity of energetic electrons coming from Jupiter's auroral regions is possibly a major, if not dominate, source of energetic electrons for Jupiter's vast magnetosphere. Key Points: Intense, narrow (±∼5°), 30–1200 keV, upward electron beams were observed over Zone II of Jupiter's main aurora during Juno perijove‐1They can be connected simply (non‐uniquely) to previously reported >10–100 s of MeV electron populations observed over the same regionAssuming symmetry, they provided >1026/s of >30 keV electrons to Jupiter's vast magnetosphere, a possibly critical and dominant source [ABSTRACT FROM AUTHOR]

The Dungey cycle is considered from the formation of a magnetic barrier and necessary for dayside reconnection conditions till the electric field generation around the Birkeland current loop and magnetic flux circulation balance. Data-based modeling of the magnetosheath magnetic field makes it possible to quantitatively assess the main factors that control formation and destruction of the magnetospheric magnetic barrier, such as the field line draping and the field intensity increase from the bow shock to the magnetopause, as well as their dependence on the orientation of the interplanetary magnetic field (IMF). The Dungey cycle has been revised to take into account the essentially time-dependent effects of magnetic reconnection. It is shown by means of the Stokes' theorem that a powerful electric field with an effective potential difference of several tens of kV is generated around the developing substorm current system. The emerging Birkeland current loop is an important particle acceleration element in the magnetosphere, contributing to the energization of ring current protons and electrons. The electric field that arises in the dipolarization zone magnifies the already existing ring current, and the closure of its amplified part through the ionosphere generates the Region 2 field-aligned currents. The motion of the expanding partial ring current around the magnetosphere, combined with the particle drift, transfers the magnetic flux from the night side of the magnetosphere to the dayside. At the dayside magnetopause, the reconnection is also responsible for the creation of the Birkeland loop, but now the electric field in the loop area decelerates the ring current particles, and regions of weakened ring current are formed. Closure of these weakened loop currents results in a transfer of the magnetic flux from the dayside to the night side, thus ensuring its overall balance and completing the Dungey cycle. [ABSTRACT FROM AUTHOR]

This document presents a study on the deformation of bubbles in turbulent flows, focusing on the statistical properties of effective forcing and damping coefficients. The natural frequency of bubble oscillations remains constant, while the damping coefficient increases significantly in turbulent conditions. The effective forcing is independent of the Weber number, indicating one-way coupling between bubble deformations and turbulent flow. The research also delves into pressure statistics, dissipation profiles near bubble interfaces, and explores various aspects of turbulence modulation and particle behavior in reputable journals. [Extracted from the article]

Magnetic reconnection regions in space and astrophysics are known as active particle acceleration sites. There is ample evidence showing that energetic particles can take a substantial amount of converted energy during magnetic reconnection. However, there has been a lack of studies understanding the backreaction of energetic particles at magnetohydrodynamical scales in magnetic reconnection. To address this, we have developed a new computational method to explore the feedback by nonthermal energetic particles. This approach considers the backreaction from these energetic particles by incorporating their pressure into magnetohydrodynamics (MHD) equations. The pressure of the energetic particles is evaluated from their distribution evolved through Parker's transport equation, solved using stochastic differential equations (SDEs), so we coin the name MHD-SDE. Applying this method to low- β magnetic reconnection simulations, we find that reconnection is capable of accelerating a large fraction of energetic particles that contain a substantial amount of energy. When the feedback from these particles is included, their pressure suppresses the compression structures generated by magnetic reconnection, thereby mediating particle energization. Consequently, the feedback from energetic particles results in a steeper power-law energy spectrum. These findings suggest that feedback from nonthermal energetic particles plays a crucial role in magnetic reconnection and particle acceleration. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a basic particle acceleration mechanism in laboratory and astrophysical plasmas. Two-dimensional models have been critical to understanding the onset of reconnection in laboratory experiments, but are fundamentally limited in diagnosing ion acceleration along open magnetic field lines. These shortcomings have opened the way to three-dimensional (3-D) models of torsional reconnection, where localized rotational perturbations to a fan-spine magnetic null point topology have demonstrated bulk particle acceleration along open magnetic field lines. Previous computational studies of the torsional fan reconnection mode using both solar and laboratory parameters demonstrated collimated jet formation and acceleration along the spine axis, wherein the bulk particle final kinetic energy spectra were shown to fall within a relatively narrow range (${\sim }2$  keV). This paper introduces typical laboratory plasma parameters in the torsional spine mode of 3-D reconnection models to diagnose its efficacy in inducing rapid ion acceleration. Using laboratory-scale length helium plasma parameters typical of capacitive discharges (singly ionized helium), we solve for relativistic particle trajectories using solutions to the steady-state, resistive, kinematic magnetohydrodynamic equations in the fan-spine topology. We find that particle acceleration at the reconnection site is highly dependent on the injection radius, and the peak accelerated particles ($\approx$ 3 keV) are trapped about the magnetic null point. While a jet is formed by ions injected close to the peak fan plane perturbation radius, their final ion kinetic energies are an order of magnitude lower ($\approx$ 0.3 keV) than the mirrored particles. Analysing the time dependence of their limited representative energy spectra shows the torsional spine mode particles follow an evolution much different than the narrow spectra of the torsional fan mode. These results have implications for diagnostic expectations of future laboratory plasma experiments designed to induce the torsional spine reconnection mode. [ABSTRACT FROM AUTHOR]

Considering that conventional dynamic compaction (CDC) method has limitation in the effectiveness of improvement depth because the improved shallow soil layers prevent the impact energy further transmitted to the deep ground, a new technique of in-pipe deep dynamic compaction (IDDC) is proposed in which the tamper can compact soil from the deep to the shallow soil layers. In this paper, the main objective is to illustrate the work mechanism of IDDC. Firstly, main components of equipment and construction process of IDDC are introduced. Then, model tests of CDC and IDDC were conducted on loose sand to obtain the influence depth using the acceleration of soil particles during impact and the distribution of cone resistance and side friction through static cone penetration tests (CPTs) after impact. Finally, the analytical formulae of superimposed stress and settlement due to IDDC was derived based on the Mindlin's solution and equation of motion, and verified with model test results and a practical case. The results indicate that with the falling height of 1 m in model tests, the further impacts after the 6th impact of CDC could hardly improve ground, resulting in the improvement depth of around 45 cm, whereas the improvement depth of IDDC was over 80 cm. Moreover, at the falling height of 1 m, the average increment in cone resistance after IDDC is 82% greater than that after CDC. Finally, compared with experimental results, the errors of the predicted settlement and the superimposed stress are less than 26 and 14%, respectively, and the proposed formulae succeed to predict the improvement depth of IDDC applied in a coastal area of China. [ABSTRACT FROM AUTHOR]

Turbulence in astrophysical plasma transfers energy to kinetic scales, leading to proton acceleration or heating, yet the formation of suprathermal protons from such turbulence is not fully understood. While proton acceleration modeling based on the Fokker-Planck equation with diffusion through kinetic Alfvén waves (KAW) has been proposed to understand in-situ measurements of suprathermal protons in the interplanetary medium, more investigations using such modeling could help clarify the nature of particle acceleration in various astrophysical media beyond the interplanetary medium. Since the characteristics of KAW turbulence depend on the magnetization of the plasma system and the temperature anisotropy of the proton distribution function, proton acceleration mediated by KAW turbulence could also be influenced by these factors. By solving the Fokker-Planck equation, this study examines proton acceleration through KAW turbulence across strongly to weakly magnetized astrophysical plasmas, parameterized by plasma beta (β = 0.01 − 10 ), and the effects of proton temperature anisotropy. Particularly, our findings indicate that KAW turbulence significantly influences the presence of suprathermal protons in low-beta plasmas, such as the interplanetary medium, but is less impactful in high-beta environments, like the intergalactic and intracluster medium. Additionally, the proton temperature anisotropy significantly modulates the efficiency of proton diffusion in velocity space in low-beta environments. [ABSTRACT FROM AUTHOR]

Particle erosion, particularly the mechanism whereby erosion occurs under the synergy of cavitation and particle impact, is a critical area of research in hydraulic machinery. This study investigates the influence of particle size on the erosion characteristics under the synergistic action of cavitation and particle erosion through turntable erosion experiments and numerical simulations. The findings indicate that cutting erosion is dominant under these combined conditions, with a clear overlap between high-erosion-rate regions and high-speed-impact areas. For particle sizes ranging from 0.2–0.6 mm, the maximum erosion rate increases significantly. When the particles are larger than 0.6 mm, smaller-diameter particles correspond to higher impact angles, while larger-diameter particles encounter lower impact angles due to their increased inertia. Moreover, cavitation greatly influences the movement and acceleration of the particles, especially as the angle of the cavitation inducer increases, leading to a marked rise in acceleration. This study enhances the understanding of particle erosion under cavitation conditions, underscores the crucial role of cavitation in the erosion mechanism, and provides a theoretical foundation for optimizing erosion performance and guiding future research directions. [ABSTRACT FROM AUTHOR]

An abundant multi‐MeV electron population beyond the orbit of Io is required to explain the intense inner radiation belt (electrons >50 ${ >} 50$ MeV) at Jupiter and its synchrotron radiation. In order to better understand the synergistic effect of radial transport and local wave‐particle interactions driven by whistler‐mode waves on the formation of Jupiter's radiation belt, we perform 3‐D Fokker‐Planck simulations for Jovian energetic electrons with the Versatile Electron Radiation Belt code. An empirical model of Jovian whistler‐mode waves updated with measurements from the Juno extended mission is used to quantify the local acceleration and pitch angle scattering. Resonant cyclotron acceleration by whistler‐mode waves leads to significant enhancement in the intensity of electrons above 1 MeV in the middle magnetosphere. Radial diffusion is capable of transporting MeV electrons accelerated by outer‐belt whistler‐mode waves into the M<10 $M< 10$ region, where they are further accelerated adiabatically to energies of about 10 MeV. Plain Language Summary: To sustain the most intense electron radiation belt in our solar system, Jupiter's magnetosphere needs to pre‐accelerate electrons to the energy level of multi‐MeV outside the orbit of Io. How such "seed electrons" of the synchrotron radiation belt are effectively accelerated is a challenging question. Gyro‐resonance between electrons and whistler‐mode waves is believed to be a potential candidate for such pre‐acceleration process. In this study, the efficiency of particle acceleration driven by Jovian whistler‐mode waves is quantitatively evaluated. With the quasilinear scattering rate calculated with the updated Jovian whistler‐mode wave model derived from Juno measurements, 3‐D diffusion simulations show that whistler‐mode waves between 5 and 25 RJ ${R}_{J}$ are capable of accelerating electrons upto about 10 MeV in tens of days. The recently discovered outer whistler‐mode belt is found to contribute to the acceleration of multi‐MeV electrons. Key Points: Scattering rates of electrons are quantified with the latest Jovian whistler‐mode wave model from Juno PJ01‐45 dataWhistler‐mode waves are able to accelerate MeV electrons in the middle magnetosphere of Jupiter in tens of daysElectrons accelerated in the outer whistler‐mode belt are further transported inward, indicating a two‐step acceleration mechanism [ABSTRACT FROM AUTHOR]

The low energy utilization of particles in a high-speed flow field is a significant factor contributing to the inefficiency of fluidized bed opposed jet mills. To elucidate the reasons and mechanisms, this paper investigates the acceleration process of particles entrained by airflow using a combination of experimental and numerical simulations. The experimental results demonstrate that the particles are both accelerated and concentrated within the jet shear layer. Furthermore, numerical simulations indicate that turbulent kinetic energy significantly influences particle distribution within the supersonic jet flow field. The radial displacement of the particles, along with the oscillation of their acceleration direction over time and space, constitutes a key mechanical mechanism. The kinetic energy transfer between the particles and the fluid is maximized at 5.7% when the volume fraction of particles in the jet is 0.02%. These findings may offer a theoretical foundation for enhancing the grinding efficiency of fluidized bed opposed jet mill through modifications to the flow field characteristics. [ABSTRACT FROM AUTHOR]

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Wave-particle interaction plays a crucial role in the dynamics of the Earth's radiation belts. Cyclotron resonance between coherent whistler mode electromagnetic waves and energetic electrons of the radiation belts is often called a coherent instability. Coherent instability leads to wave amplification/generation and particle acceleration/scattering. The effect of wave on particle's distribution function is a key component of the instability. In general, whistler wave amplitude can grow over threshold of quasi-linear (linear) diffusion theory which analytically tracks the time-evolution of a particle distribution. Thus, a numerical approach is required to model the nonlinear wave induced perturbations on particle distribution function. A backward test particle model is used to determine the energetic electrons phase space dynamics as a result of coherent whistler wave instability. The results show the formation of a phase space features with much higher resolution than is available with forward scattering models. In the nonlinear regime the formation of electron phase space holes upstream of a monochromatic wave is observed. The results validate the nonlinear phase trapping mechanism that drives nonlinear whistler mode growth. The key differences in phase-space perturbations between the linear and nonlinear scenarios are also illustrated. For the linearized equations or for low (below threshold) wave amplitudes in the nonlinear case, there is no formation of a phase-space hole and both models show features that can be characterized as linear striations or ripples in phase-space. [ABSTRACT FROM AUTHOR]

We report the measurement of X-ray polarization in the high synchrotron peaked blazar 1ES 1959 + 650. Of the four epochs of observations from the Imaging X-ray Polarimetry Explorer, we detected polarization in the 2–8 keV band on two epochs. From the model-independent analysis of the observations on 28 October 2022, in the 2–8 keV band, we found the degree of polarization of Π X = 9.0 ± 1.6 % and an electric vector position angle of Ψ X = 53 ± 5 deg. Similarly, from the observations on 14 August 2023, we found Π X and ψ X values as 12.5 ± 0.7 % and 20 ± 2 deg, respectively. These values are also in agreement with the values obtained from spectro-polarimetric analysis of the I, Q, and U spectra. The measured X-ray polarization is larger than the reported optical values, ranging between 2.5% and 9% when observed from 2008 to 2018. Broadband spectral energy distribution constructed for the two epochs is well described by the one-zone leptonic emission model with the bulk Lorentz factor (Γ ) of the jet larger on 14 August 2023 compared to 28 October 2022. Our results favor the shock acceleration of the particles in the jet, with the difference in Π X between the two epochs being influenced by a change in the Γ of the jet. [ABSTRACT FROM AUTHOR]

Energetic GeV photons expected from the closest and the most energetic Gamma-ray bursts (GRBs) provide a unique opportunity to study the very-high-energy emission as well as the possible correlations with lower energy bands in realistic GRB afterglow models. In the standard GRB afterglow model, the relativistic homogeneous shock is usually considered to be fully adiabatic, however, it could be partially radiative. Based on the external forward-shock scenario in both stellar wind and constant-density medium, we present a radiative-adiabatic analytical model of the synchrotron self-Compton (SSC) and synchrotron processes considering an electron energy distribution with a power-law index of |$1\lt p\lt 2$| and |$2\le p$|⁠. We show that the SSC scenario plays a relevant role in the radiative parameter |$\epsilon$|⁠ , leading to a prolonged evolution during the slow cooling regime. In a particular case, we derive the Fermi /LAT light curves together with the photons with energies |$\ge 100$|  MeV in a sample of nine bursts from the second Fermi /LAT GRB catalogue that exhibited temporal and spectral indices with |$\gtrsim 1.5$| and |$\approx 2$|⁠ , respectively. These events can hardly be described with closure relations of the standard synchrotron afterglow model, and also exhibit energetic photons above the synchrotron limit. We have modelled the multiwavelength observations of our sample to constrain the microphysical parameters, the circumburst density, the bulk Lorentz factor, and the mechanism responsible for explaining the energetic GeV photons. [ABSTRACT FROM AUTHOR]

Heavy particles suspended in turbulent flow possess inertia and are ejected from violent vortical structures by centrifugal forces. Once piled up along particle paths, this small-scale mechanism leads to an effective large-scale drift. This phenomenon, known as 'turbophoresis', causes particles to leave highly turbulent regions and migrate towards calmer regions, explaining why particles transported by non-homogeneous flows tend to concentrate near the minima of turbulent kinetic energy. It is demonstrated here that turbophoretic effects are just as crucial in statistically homogeneous flows. Although the average turbulent activity is uniform, instantaneous spatial fluctuations are responsible for inertial-range inhomogeneities in the particle distribution. Direct numerical simulations are used to probe particle accelerations, specifically how they correlate to local turbulent activity, yielding an effective coarse-grained dynamics that accounts for particle detachment from the fluid and ejection from excited regions through a space- and time-dependent non-Fickian diffusion. This leads to cast fluctuations in particle distributions in terms of a scale-dependent Péclet number ${\textit {Pe}}_\ell$ , which measures the importance of turbulent advection compared with inertial turbophoresis at a given scale $\ell$. Multifractal statistics of energy dissipation indicate that $ {\textit {Pe}}_\ell \sim \ell ^\delta /\tau _{p}$ with $\delta \approx 0.84$. Numerical simulations support this behaviour and emphasise the relevance of the turbophoretic Péclet number in characterising how particle distributions, including their radial distribution function, depends on $\ell$. This approach also explains the presence of voids with inertial-range sizes, and the fact that their volumes have a non-trivial distribution with a power-law tail $p(\mathcal {V}) \propto \mathcal {V}^{-\alpha }$ , with an exponent $\alpha$ that tends to 2 as ${\textit {Pe}}_\ell \to 0$. [ABSTRACT FROM AUTHOR]

Using a classification scheme for solar-wind type based on the heliocentric distance of the observation, we look at near-perihelion observations from Parker Solar Probe Encounters 4 to 14 to study the sources of the slow Alfvénic solar wind (SASW). Through Potential Field Source Surface (PFSS) modeling and ballistic mapping, we connect streams to their solar source and find that a primary population of SASW comes from low magnetic field strength regions (low- B 0), likely small coronal holes (CHs) and their overexpanded boundaries, while a second population of high field strength (high- B 0) seems to emerge from non-CH structures potentially through interchange reconnection with nearby open field lines. This low- B 0 SASW shows larger expansion than the fast solar wind (FSW) but similar mass flux, potentially indicating additional heating below the critical point, and emergence from a cooler structure, which could lead to slower wind emerging from CH-like structures. We show that this low- B 0 SASW shows stronger preferential acceleration of alpha particles (similar to the FSW) than the high- B 0 SASW, and that this is a velocity-dependent phenomenon as found in previous studies. To have additional confidence in our mapping results, we quantify the error on both the PFSS model and ballistic mapping and discuss how additional multipoint observations of plasma parameters and composition would allow us to better constrain our models and connect the solar wind to its source. [ABSTRACT FROM AUTHOR]

Aims. Short gamma-ray bursts originate when relativistic jets emerge from the remnants of binary neutron star (BNS) mergers, as observed in the first multi-messenger event GW170817–GRB 170817A, which coincided with a gravitational wave signal. Both the jet and the remnant are believed to be magnetized, and the presence of magnetic fields is known to influence the jet propagation across the surrounding post-merger environment. In the magnetic interplay between the jet and the environment itself, effects due to a finite plasma conductivity may be important, especially in the first phases of jet propagation. We aim to investigate these effects, from jet launching to its final breakout from the post-merger environment. Methods. We used the PLUTO numerical code to perform 2D axisymmetric and full 3D resistive relativistic magnetohydrodynamic (MHD) simulations, employing spherical coordinates with spatial radial stretching. We considered and compared different models for physical resistivity, which must be small but still dominating over the intrinsic numerical dissipation (which yields unwanted smearing of structures in any ideal MHD code). Stiff terms in the current density are treated with IMplicit-EXplicit Runge Kutta algorithms for time-stepping. A Synge-like gas (Taub equation of state) is also considered. All simulations were performed using an axisymmetric analytical model for both the jet propagation environment and the jet injection; we leave the case of jet propagation in a realistic environment (i.e., imported from an actual BNS merger simulation) to a future study. Results. As expected, no qualitative differences are detected due to the effect of a finite conductivity, but significant quantitative differences in the jet structure and induced turbulence are clearly seen in 2D axisymmetric simulations, and we also compare different resistivity models. We see the formation of regions with a resistive electric field parallel to the magnetic field, and nonthermal particle acceleration may be enhanced there. The level of dissipated Ohmic power is also dependent on the various recipes for resistivity. Most of the differences arise before the breakout from the inner environment, whereas once the jet enters the external weakly magnetized environment region, these differences are preserved during further propagation despite the lower grid refinement. Finally, we show and discuss the 3D evolution of the jet within the same environment in order to highlight the emergence of nonaxisymmetric features. [ABSTRACT FROM AUTHOR]

Coronal mass ejections (CMEs) are often associated with X-ray (SXR) flares powered by magnetic reconnection in the low corona, while the CME shocks in the upper corona and interplanetary (IP) space accelerate electrons often producing the type II radio bursts. The CME and the reconnection event are part of the same energy release process as highlighted by the correlation between reconnection flux (ϕrec) that quantifies the strength of the released magnetic free energy during the SXR flare, and the CME kinetic energy that drives the IP shocks leading to type II bursts. Unlike the Sun, these physical parameters cannot be directly inferred in stellar observations. Hence, scaling laws between unresolved sun-as-a-star observables, namely SXR luminosity (LX) and type II luminosity (LR), and the physical properties of the associated dynamical events are crucial. Such scaling laws also provide insights into the interconnections between the particle acceleration processes across low-corona to IP space during solar-stellar "flare-CME-type II" events. Using long-term solar data in the SXR to radio waveband, we derived a scaling law between two novel power metrics for the flare and CME-associated processes. The metrics of "flare power" (Pflare = √(LXϕrec)) and "CME power" (PCME = √(LRVCME2)), where VCME is the CME speed, scale as Pflare ∝ PCME0.76 ± 0.04. In addition, LX and ϕrec show power-law trends with PCME with indices of 1.12 ± 0.05 and 0.61 ± 0.05, respectively. These power laws help infer the spatially resolved physical parameters, VCME and ϕrec, from disk-averaged observables, LX and LR during solar-stellar flare-CME-type II events. [ABSTRACT FROM AUTHOR]

Context. S26 is an extragalactic microquasar with the most powerful jets ever discovered. They have a kinetic luminosity of Lj ∼ 5 × 1040 erg s−1. This implies that the accretion power to the black hole should be super-Eddington, of the order of Lacc ∼ Lj. However, the observed X-ray flux of this system indicates an apparent very sub-Eddington accretion luminosity of LX ≈ 1037 erg s−1. Aims. We aim to characterize the nature of S26, explain the system emission, and study the feasibility of super-Eddington microquasars as potential PeVatron sources. Methods. We first analyze multi-epoch X-ray observations of S26 obtained with XMM-Newton and model the super-Eddington disk and its wind. We then develop a jet model and study the particle acceleration and radiative processes that occur in shocks generated near the base of the jet and in its terminal region. Results. We find that the discrepancy between the jet and the apparent disk luminosities in S26 is caused by the complete absorption of the disk radiation by the wind ejected from the super-Eddington disk. The nonthermal X-rays are produced near the base of the jet, and the thermal X-rays are emitted in the terminal regions. The radio emission observed with the Australia Telescope Compact Array can be explained as synchrotron radiation produced at the reverse shock in the lobes. We also find that S26 can accelerate protons to PeV energies in both the inner jet and the lobes. The ultra-high energy protons accelerated in the lobes of S26 are injected into the interstellar medium with a total power of ∼1036 erg s−1. Conclusions. We conclude that S26 is a super-Eddington microquasar with a dense disk-driven wind that obscures the X-ray emission from the inner disk, and that the supercritical nature of the system allows the acceleration of cosmic rays to PeV energies. [ABSTRACT FROM AUTHOR]

Laser-driven particle acceleration has attracted significant attention due to its potential for compact and cost-effective particle accelerator. Currently, the generation of highly collimated high-energy proton beams, essential for fundamental science and industry, remains a notable challenge using this technique. Here we present an effective scheme for generating such a high-quality proton beam via a circularly polarized Laguerre–Gaussian (LG) laser pulse irradiating a micro-tube foil target. Three-dimensional particle-in-cell simulations show that numerous overdense electron bunches are pulled out from the micro-tube and accelerated forward by the laser fields, inducing a strong converging sheath field at the rear side of the target. As a result, highly collimated protons are accelerated forward by this sheath field, exhibiting a high-flux of 3 × 107 protons/MeV at a cutoff energy of 125 MeV, achieved at a LG laser intensity of 1.71 × 1021 W cm−2. This high-quality proton beam is desirable for medical and biophysical applications, such as FLASH radiotherapy. [ABSTRACT FROM AUTHOR]

Fast blue optical transients (FBOTs) represent a new class of highly energetic sources observed from radio to X-rays. High luminosity, light curves and spectra of the sources can be understood if they are associated with supernova-like or tidal disruption events. Radio observations of the transient sources revealed a mildly relativistic expansion of some of the remnants. The high power and mildly relativistic shock velocities are providing favorable conditions for very high energy particle acceleration. In this paper we present a model of particle acceleration in mildly relativistic magnetohydrodynamic (MHD) outflow of the transient source. To construct the non-thermal radiation and cosmic ray spectra in a broad range of energies we combined the microscopic particle-in-cell simulations of electron and proton injection at mildly relativistic shock with Monte Carlo technique for high energy particle transport and acceleration. The model allows describing the observed non-thermal radio and X-ray emission of CSS161010, and predicts that such sources can accelerate cosmic rays to energies above 10 PeV, and possible upper limit of maximum energy is 100 PeV. With the expected event rate of FBOTs they can contribute to the very high energy cosmic rays population in galaxies. [ABSTRACT FROM AUTHOR]

In the dynamic and complex environment of the solar corona, the interaction between kinetic Alfvén waves (KAWs) and magnetic null points might play a significant role in understanding various plasma processes. Recognizing the potential role of reconnection in coronal heating, our study aims to delve into how different types of null points affect KAW dynamics and ultimately contribute to heating. We investigate the behavior of nonlinear KAWs near the more frequently occurring components-null point with a mean magnetic field in the solar corona. The nonlinearity is attributed to the ponderomotive effects due to density perturbations. We used a three-dimensional model equation that describes the dynamics of KAWs in the presence of components-null point. Numerical methods are employed to solve the model equation for solar coronal parameters. Our simulations reveal that the nonlinear interaction between KAWs and magnetic null points can lead to the generation and amplification of turbulent and chaotic structures. This formation of localized structures, progressively exhibit more chaotic behavior over time, which may efficiently contribute to energy transfer. The power spectrum analysis of these turbulent structures shows a steeper spectrum with a pronounced cascade. Turbulence implies the presence of localized plasma heating, particle acceleration, and magnetic reconnection. These phenomena have significant implications for understanding the energy transport, particle dynamics, and magnetic topology in the solar corona. We also address nonlinearity's role in promoting turbulence. This research offers insights into the dynamics of nonlinear KAWs near null points in the solar corona, suggesting their potential role in energy transfer and current sheet formation. [ABSTRACT FROM AUTHOR]

Spider pulsars are compact binary systems composed of a millisecond pulsar and a low-mass companion. Their X-ray emission – modulated on the orbital period – is interpreted as synchrotron radiation from high-energy electrons accelerated at the intrabinary shock. We perform global two-dimensional particle-in-cell simulations of the intrabinary shock, assuming that the shock wraps around the companion star. When the pulsar spin axis is nearly aligned with the orbital angular momentum, we find that the magnetic energy of the relativistic pulsar wind – composed of magnetic stripes of alternating field polarity – efficiently converts to particle energy at the intrabinary shock, via shock-driven reconnection. The highest energy particles accelerated by reconnection can stream ahead of the shock and be further accelerated by the upstream motional electric field. In the downstream, further energization is governed by stochastic interactions with the plasmoids/magnetic islands generated by reconnection. We also extend our earlier work by performing simulations that have a larger (and more realistic) companion size and a more strongly magnetized pulsar wind. We confirm that our first-principles synchrotron spectra and light curves are in good agreement with X-ray observations. [ABSTRACT FROM AUTHOR]

GRB 190829A has been widely studied due to its nature and the high-energy emission presented. Due to the detection of a very high energy component by the High Energy Stereoscopic System and the event's atypically middling luminosity, it has been categorized in a select, limited group of bursts bordering classic gamma-ray bursts (GRBs) and nearby sub-energetic events. Given the range of models utilized to adequately characterize the afterglow of this burst, it has proven challenging to identify the most probable explanation. Nevertheless, the detection of polarization data provided by the MASTER (Mobile Astronomical System of TElescope Robots) collaboration has added a new aspect to GRB 190829A that permits us to attempt to explore this degeneracy. In this paper, we present a polarization model coupled with a thin-shell synchrotron forward-shock model – a component in all models used to describe GRB 190829A's afterglow – in order to fit the polarization's temporal evolution with the existing upper limits (⁠|$\Pi < 6{{\ \rm per\, cent}}$|⁠). We find that the polarization generated from an on-axis emission is favoured for strongly anisotropic magnetic field ratios, while an off-axis scenario cannot be fully ruled out when a more isotropic framework is taken into account. [ABSTRACT FROM AUTHOR]

Tunnel #11 is one of thirteen tunnels for the first Indonesian high-speed railway (HSR) project connecting two of its biggest cities, i.e., Jakarta and Bandung. It was built using the drill-and-blast method. Since the tunnel is located in a densely populated urban area, the effect of blasting on ground vibration needs to be monitored carefully. This paper evaluates the effect of Tunnel 11 blasting on the surrounding environment through field monitoring. Four Minimate Plus units were used to monitor the blast-induced ground vibration, acceleration and air blast during the tunnel construction. Crack monitoring kits were used to measure the width of existing cracks in 61 residential houses, while 4 GPS units, 2 slope inclinometers, and 1 Robotic Total Station were used to monitor ground displacement in the residential area and slopes closest to the tunnel portal. The findings demonstrate that Tunnel 11 blasting was safe and complied with national and international standards. All monitored ground vibrations in residential areas were below PPV = 2 mm/s, while air blasts were largely maintained below 94 dB for a four-second blast duration. No structural or cosmetic damage was observed in the residential houses, as there was no noticeable widening of the existing cracks or formation of new ones in any of the inspected houses. The blasting also did not induce unwarranted ground displacement in the residential area and the monitored slopes. PPV and PPA prediction equations were developed based on 683 blast data collected, resulting in a practical blasting chart for designing future tunnel blasting. The findings of this study emphasize the vital role of monitoring ground vibration, air blast, structural damage, and ground displacement in safeguarding and controlling the adverse effects of tunnel blasting in urban areas. [ABSTRACT FROM AUTHOR]

Direct laser acceleration with radially polarized lasers is an intriguing variant of laser-based particle acceleration that has the potential of offering GeV/cm-level energy while avoiding the instabilities and complex beam dynamics associated with plasma wakefield accelerators. A major limiting factor is the difficulty of generating high-power radially polarized beams. In this paper, we propose the use of CO2-based long-wave infrared (LWIR) lasers as a driver for direct laser acceleration, as the polarization insensitivity of the gain medium allows a radially polarized beam to be amplified. Additionally, the larger waist sizes, Rayleigh lengths, and pulse lengths associated with the long wavelength could improve the injection efficiency of the electron beam. By comparing acceleration simulations using a near-infrared laser and an LWIR laser, we show that the injection efficiency is indeed improved by up to an order of magnitude with the longer wavelength. Furthermore, we show that even sub-TW peak powers with an LWIR laser can provide MeV-level energy gains. Thus, radially polarized LWIR lasers show significant promise as a driver of a direct laser-driven demonstration accelerator. [ABSTRACT FROM AUTHOR]

Recent radio observations and coincident neutrino detections suggest that some tidal disruption events (TDEs) exhibit late-time activities, relative to the optical emission peak, and these may be due to delayed outflows launched from the central supermassive black hole. We investigate the possibility that jets launched with a time delay of days to months, interact with a debris that may expand outwards. We discuss the effects of the time delay and expansion velocity on the outcomes of jet breakout and collimation. We find that a jet with an isotropic-equivalent luminosity of |$\lesssim 5 \times 10^{45}\, {\rm erg\, s}^{-1}$| is likely to be choked for a delay time of |$\sim 3$| months. We also study the observational signatures of such delayed choked jets. The jet–debris interaction preceding the breakout would lead to particle acceleration and the resulting synchrotron emission can be detected by current and near-future radio, optical and X-ray telescopes, and the expanding jet-driven debris could explain late-time radio emission. We discuss high-energy neutrino production in delayed choked jets, and the time delay can significantly alleviate the difficulty of the hidden jet scenario in explaining neutrino coincidences. [ABSTRACT FROM AUTHOR]

This study presents an implementation of a new melting layer model in the ZJU‐AERO radar observation operator (Accurate and Efficient Radar Operator designed by ZheJiang University). The proposed model utilizes a coated spheroid to represent melting snow and graupel. It consists of three stages–coating, soaking, and melting–to account for the dielectric and density effects of melting particles. The scattering properties of the melting particles are computed with the Invariant‐Imbedding T‐Matrix (IITM) method, and the results are tabulated as look‐up tables for the radar operator. Regarding the parameterization of bulk optical properties, a flux‐conservation scheme is employed to estimate the size distribution of melting particles. To demonstrate its flexibility and superiority, the single and bulk scattering properties of our multi‐stage melting model are compared against the traditional homogeneous model, which uses the effective medium approximation (EMA). The effectiveness of the multi‐stage melting model has also been assessed by mapping model states in the regional mesoscale model of the China Meteorology Administration (CMA‐MESO) to radar observations. In the microphysics package of CMA‐MESO, the melting process is not explicitly represented, and we assume that melting hydrometeors occur where solid and liquid phases overlap. When compared with observations, the present multi‐stage melting model successfully reproduces melting layer signatures, highlighting its potential for microphysic validation, quantitative precipitation estimations, and data assimilation studies. Plain Language Summary: In this study, we present a new melting particle modeling scheme for a radar observation simulator. This scheme features the representation of the melting procedure of solid precipitation particles through three stages: an initial coating stage, an intermediate soaking stage, and a final melting stage. By incorporating these stages into the simulation, this new melting model surpasses the limitation of the commonly used model that treats melting particles as homogeneous mixtures of water, air, and ice. Additionally, we calculate the probability distributions of melting particle sizes using a rigorous falling‐flux‐conservation rule that considers the acceleration of particles during melting. The scattering properties of these coated‐spheroid melting particles are computed using the Invariant‐Imbedding T‐Matrix (IITM) method. Finally, the results are compared against those obtained using the traditional melting particle model. These comparisons demonstrate the potential of this newly proposed approach for improving the accuracy and reliability of radar simulations. Key Points: A three‐stage nonspherical particle model is proposed to account for the changes of dielectric constant and density of melting hydrometeorsA rigorous flux‐conservation bulk parameterization scheme is implemented to incorporate the terminal velocity variation as particles meltThe scattering properties of melting particles are rigorously computed using the state‐of‐the‐art invariant‐imbedding T‐matrix method [ABSTRACT FROM AUTHOR]

The effect of a hypothetical maximal proper acceleration on the mass of a charged particle is investigated in the context of particle accelerators. In particular, it is shown that maximal proper acceleration implies an increase in the kinetic energy of the particle being accelerated with respect to the relativistic energy. Such an increase in kinetic energy leads to a reduction of the luminosity of the bunches with respect to the expected luminosity in the relativistic models of the bunches. This relative loss in luminosity is of the order 10−3 to 10−5 for the Large Hadron Collider (LHC) bunches and can be of order up to 10−3 for certain laser-plasma accelerator facilities. Although the effect is small, it increases with the square of the bunch population. [ABSTRACT FROM AUTHOR]

Digital microfluidic chips (DMCs) have shown the ability to flexibly manipulate droplets and particles, which is meaningful for biomedical applications in drug screening and clinical diagnostics. As a critical component of DMCs, the dielectric layer, with its key physical parameters (permittivity and thickness), directly determines the voltage distribution, thereby significantly affecting the manipulation performance. To optimize manipulation performance, simulation studies on dielectric layer parameters are essential during the DMC design. Existing simulation methods can evaluate the effect of dielectric layer parameters on droplet manipulation but encounter inherent challenges when analyzing the manipulation of particles within droplets. Here, we propose a versatile numerical analysis approach that can simultaneously analyze the effect of dielectric layer parameters on both droplet and particle manipulation, thereby optimizing the dielectric layer parameters to enhance the DMC manipulation performance. Initially, the voltage distributions corresponding to different sets of dielectric layer parameters are solved using electromagnetic field theory. Subsequently, the voltage distribution data are used to calculate the droplet and particle driving forces based on the principle of virtual work. Finally, by comparing the driving forces across different sets of dielectric layer parameters, the optimal dielectric layer parameters are determined to enhance the DMC manipulation performance. Experimental results demonstrate that the droplet and particle accelerations align with the simulated driving force trends, thereby validating our numerical analysis method. We anticipate that our method will be able to provide theoretical guidance for the optimization of dielectric layer parameters to obtain a desirable manipulation performance in more complex DMC designs. [ABSTRACT FROM AUTHOR]

The article "An analytical model for the slip velocity of particles in turbulence" in the Journal of Fluid Mechanics introduces a model to predict the slip velocity of spherical particles in turbulent flows. The model, based on the inertial filtering framework, offers equations to calculate slip velocity magnitude based on specific parameters. Validation against experimental and numerical data shows agreement across various particle properties and flow conditions, emphasizing the importance of accurate slip velocity estimation for understanding particle dynamics in turbulent environments. The document also includes references to studies on particle behavior in turbulent flows, covering topics such as particle clustering, settling, dispersion models, and bubble dynamics in high-Reynolds-number flows, providing valuable insights into the complex interactions between particles and turbulent fluid flows. [Extracted from the article]

In the Cold Spraying technology, the coatings are produced as a result of the supersonic acceleration of the particles in a gas jet, at temperatures below the melting/phase transformation point of the sprayed material. In this paper, the morphology of a Ni/CrC cold spray coating is studied, based on the identification of the particle's characteristic at various magnifications, both on cross-section and on the surface of the samples. The layer appearance is continuous, uniform and sinuous, no adhesion defects were observed at the substrate-coating interface, and the plastic deformation of the steel was highlighted. The elemental chemical analysis on the sample cross-section, together with the distribution map shows that the carbide particles have retained their sphericity to a large extent, being uniformly embedded in the Ni matrix, as a result of the plastic deformation. This allows a higher thickness of the cold spray coatings comparatively to the ones obtained with the other thermal spray methods that imply high temperatures of the gas jet and layered microstructures. [ABSTRACT FROM AUTHOR]

The University of Birmingham has a rich history in nuclear physics research dating back nearly 90 years, with key contributions to the field including the demonstration of the feasibility of an atomic bomb and the discovery of significant energy release from the fusion of light nuclei. The university operates a range of accelerators and research facilities, such as the MC40 Cyclotron and the Neutron Therapeutics BNCT accelerator, for various applications including isotope production, materials studies, and medical physics. These facilities support a wide array of research areas, from nuclear astrophysics to nuclear waste management, providing unique training opportunities for students at all levels. [Extracted from the article]