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We explore a mechanism for ionization in high-velocity (but not yet relativistic) collisions of light atomic particles, one of which being initially in an excited internal state. This mechanism is driven by the generalized Breit interaction and proceeds via radiative energy transport between the colliding particles which has an extremely long range. A comparison of this mechanism with those which are 'standard' for high-velocity collisions shows that it can play a noticeable role in collisions with excited target atoms. [ABSTRACT FROM AUTHOR]

The radiation mechanism underlying the prompt emission remains unresolved and can be resolved using a systematic and uniform time-resolved spectro-polarimetric study. In this paper, we investigated the spectral, temporal, and polarimetric characteristics of five bright gamma-ray bursts (GRBs) using archival data from AstroSat CZTI, Swift Burst Alert Telescope, and Fermi/GBM. These bright GRBs were detected by CZTI in its first year of operation, and their average polarization characteristics have been published in Chattopadhyay et al. In the present work, we examined the time-resolved (in 100–600 keV) and energy-resolved polarization measurements of these GRBs with an improved polarimetric technique such as increasing the effective area and bandwidth (by using data from low-gain pixels), using an improved event selection logic to reduce noise in the double events and extend the spectral bandwidth. In addition, we also separately carried out detailed time-resolved spectral analyses of these GRBs using empirical and physical synchrotron models. By these improved time-resolved and energy-resolved spectral and polarimetric studies (not fully coupled spectro-polarimetric fitting), we could pin down the elusive prompt emission mechanism of these GRBs. Our spectro-polarimetric analysis reveals that GRB 160623A, GRB 160703A, and GRB 160821A have Poynting flux-dominated jets. On the other hand, GRB 160325A and GRB 160802A have baryonic-dominated jets with mild magnetization. Furthermore, we observe a rapid change in polarization angle by ∼90° within the main pulse of very bright GRB 160821A, consistent with our previous results. Our study suggests that the jet composition of GRBs may exhibit a wide range of magnetization, which can be revealed by utilizing spectro-polarimetric investigations of the bright GRBs. [ABSTRACT FROM AUTHOR]

Objective. This work aims to develop a graphics processing unit (GPU)-accelerated Monte Carlo code for the coupled transport of photon, electron/positron and neutron over a broad range of energies for medical applications. Approach. By separating the MC evolution of radiation into source, transport, and interaction kernels, the branch divergence was alleviated. The memory coalescence was achieved by vectorizing the access pattern in which the secondary particles were archived. To accelerate further particle tracking, ray-tracing hardware acceleration in the Nvidia OptiXTM framework was applied. For photon and electron/positron, the EGSnrc interaction modules were ported as a GPU-optimized configuration. For neutron, a group-wised transport based on NJOY21 preprocessed data was implemented. The developed code was validated against CPU-based FLUKA. Neutron, x-ray and electron beams incident on water and ICRP phantoms were simulated. The neutron energy group and the transport parameters of photon and electron were set to be the same in both codes. A single Nvidia RTX 4090 card was used in this code while all 20 threads of a single Intel Core i9-10900K node were used in FLUKA. Main results. The number of histories was set to ensure that statistical uncertainties lower than 2% for all voxels whose doses were larger than 20% of the maximum. In all cases, the dose differences in the voxels between the codes were within 2.5%. For photons and electrons, the developed code was 150 – 300 times faster than FLUKA in both geometries. For neutrons, the code was respectively 80 and 135 times faster in the water and ICRP phantoms than FLUKA. Significance. This study offers an appropriate solution for uncoalesced memory access and branch divergence commonly encountered in coupled MC transport on the GPU architecture. The formidable acceleration in computing times and accuracy shown in this study can promise a routine clinical use of MC simulations. [ABSTRACT FROM AUTHOR]

The dispersion relation of the magnetized Kelvin–Helmholtz (KH) instability driven by shear flow with zero thickness of the shear layer is derived theoretically based on a set of magnetohydrodynamic equations in the presence of a transverse magnetic field and a radiation field. The influence of the magnetic field strength, the radiation field strength, and the density ratio of the two sides of the shear layer on KH instability is analyzed by solving the dispersion equation. The results indicate that the presence of radiation and transverse magnetic fields can destabilize the KH instability due to the resulting increase in Mach number, which in turn reduces the compressibility of the system. Also, the extent of the destabilizing effect of the magnetic field can be affected by the magnetoacoustic Mach number M 1 f and the Mach number M 2. The growth rates vary more significantly for relatively small values of both parameters. Finally, the stabilizing effect of a large density ratio is considered, and it is found that as the density ratio increases, the effect of the radiation field is more significant at larger Mach number M 2. These results can be applied to astrophysical phenomena with velocity shear, such as flows across the transition layer between an H ii region and a molecular cloud, accretion flows, and shear flows of cosmic plasmas. [ABSTRACT FROM AUTHOR]

The DIII-D tokamak has elucidated crucial physics and developed projectable solutions for ITER and fusion power plants in the key areas of core performance, boundary heat and particle transport, and integrated scenario operation, with closing the core-edge integration knowledge gap being the overarching mission. New experimental validation of high-fidelity, multi-channel, non-linear gyrokinetic turbulent transport models for ITER provides strong confidence it will achieve Q ⩾ 10 operation. Experiments identify options for easing H-mode access in hydrogen, and give new insight into the isotopic dependence of transport and confinement. Analysis of 2,1 islands in unoptimized low-torque IBS demonstration discharges suggests their onset time occurs randomly in the constant β phase, most often triggered by non-linear 3-wave coupling, thus identifying an NTM seeding mechanism to avoid. Pure deuterium SPI for disruption mitigation is shown to provide favorable slow cooling, but poor core assimilation, suggesting paths for improved SPI on ITER. At the boundary, measured neutral density and ionization source fluxes are strongly poloidally asymmetric, implying a 2D treatment is needed to model pedestal fuelling. Detailed measurements of pedestal and SOL quantities and impurity charge state radiation in detached divertors has validated edge fluid modelling and new self-consistent 'pedestal-to-divertor' integrated modeling that can be used to optimize reactors. New feedback adaptive ELM control minimizes confinement reduction, and RMP ELM suppression with sustained high core performance was obtained for the first time with the outer strike point in a W-coated, compact and unpumped small-angle slot divertor. Advances have been made in integrated operational scenarios for ITER and power plants. Wide pedestal intrinsically ELM-free QH-modes are produced with more reactor-relevant conditions, Low torque IBS with W-equivalent radiators can exhibit predator-prey oscillations in T e and radiation which need control. High- β P scenarios with q min > 2, q 95–7.9, β N > 4, β T–3.3% and H 98y2 > 1.5 are sustained with high density ( n ¯ = 7E19 m−3, f G–1) for 6 τ E, improving confidence in steady-state tokamak reactors. Diverted NT plasmas achieve high core performance with a non-ELMing edge, offering a possible highly attractive core-edge integration solution for reactors. [ABSTRACT FROM AUTHOR]

This paper presents a spatiotemporal encoding metasurface design to independently achieve the good radiation and the low scattering performances in the same frequency band. The proposed metasurface unit cell is composed of a square patch and two orthogonally placed I-shaped strips. By switching the operating states of the PIN diode inserted into each I-shaped strip between ON state and OFF state, a phase difference of 180° can be obtained in the band of 7.6–7.95 GHz for two orthogonally polarized incident waves. When a coaxial probe is introduced at the diagonal line of the square patch, the dual-polarized radiation capability is achieved within the frequency range of 7.6–7.95 GHz. With the proposed metasurface unit cell, the manipulation of the radiating wave and the scattering wave has no influence on each other. By controlling the PIN operating states by the field programmable gate array in real time, the power of the scattering wave is transferred to some higher order harmonics, thus realizing radar cross section (RCS) reduction. With optimized spatial and temporal encoding layouts, the proposed metasurface realizes the RCS reduction over 10 dB within the range of 7.3–8 GHz, with the maximum RCS reduction of 35.6 dB, while maintaining good radiation capability. [ABSTRACT FROM AUTHOR]

This paper presents a novel miniaturized ultra-wideband metamaterial absorber with a thickness of 0.069 λ L thick, engineered to suppress electromagnetic radiation in high-frequency chip packaging. The absorber's bandwidth is enhanced through the incorporation of lumped resistors and patterned metal strips. Simulation results reveal an absorption efficiency exceeding 90% across the frequency range of 17.3–33.5 GHz, while maintaining polarization insensitivity and angular stability. The absorption mechanism is investigated using equivalent circuit theory and the S -parameter inversion method, which demonstrate consistent impedance matching and advantageous loss characteristics throughout the wide band. Relevant objects were meticulously prepared and tested, yielding a high correlation between the measured and simulated results. The proposed absorber, when integrated into package chips and patch antennas, significantly reduces the far-field electric field amplitude in both applications. Specifically, the packaged chip shows up to 19.7 dB of electromagnetic radiation suppression and the patch antenna structure achieves over 10 dB of radiation suppression in the 24.2 GHz–30.4 GHz range post-integration. These results affirm the absorber's efficacy in effectively reducing unwanted electromagnetic radiation in specified frequency bands within complex electromagnetic environments. The absorber's demonstrated effectiveness provides a promising approach to address the increasing issue of electromagnetic radiation in progressively miniaturized electronic devices. [ABSTRACT FROM AUTHOR]

It has been suggested that 'transient surface currents' caused by multi-MeV fast electrons can be responsible for the emission of low frequency radiation (e.g. in THz range) from ultra-intense laser–solid interactions. This mechanism has been analyzed, and analytic upper bounds on the intensity, electric field amplitude, and normalized vector potential have been developed and tested against 1D EM Particle-in-Cell simulations. The 'transient surface current' mechanism is effective and sufficiently efficient to fully account for all radiation that has been emitted in experiments so far. [ABSTRACT FROM AUTHOR]

We consider the problem of the magnetization dynamics of a nanosized ferromagnetic sample caused by the spin–orbit interaction of electrons arising in the field of an incident electromagnetic wave. We discuss the case when the frequency of the incident electromagnetic radiation is close to the frequency of the interband transitions. We show that with the use of high-power lasers, this mechanism causes the appearance of a magnetization component perpendicular to the initial magnetization of the sample. This component shows oscillations with a frequency lower than that of incident electromagnetic waves. These dynamics make possible the magnetization reversal of the sample. [ABSTRACT FROM AUTHOR]

Flows driven by photons have been studied for almost a century, and a quantitative description of the radiative forces on atoms and ions is important for understanding a wide variety of systems with outflows and accretion disks, such as active galactic nuclei (AGN). Quantifying the associated forces is crucial to determining how these outflows enable interactive mechanisms within these environments, such as AGN feedback. The total number of spectral lines in any given ion of the outflow material must be tabulated in order to give a complete characterization of this force. Here, we provide calculations of the dimensionless line force multiplier for AGN environments. For a wide array of representative AGN sources, we explicitly calculate the photoionization balance at the proposed wind-launching region above the accretion disk, compute the strength of the line-driving force on the gas, and revisit and formalize the role of the commonly used ionization parameter ξ in ultimately determining the line-driving force. We perform these computations and analyses for a variety of AGN central source properties, such as black hole mass, initial wind velocity, and number density. We find that, while useful, the ionization parameter provides an incomplete description of the overall ionization state of the outflow material. We use these findings to provide an updated method for calculating the strength of the radiative line-driving using both the X-ray spectral index Γ X and the ionization parameter. [ABSTRACT FROM AUTHOR]

Understanding the spatial distribution of radiation levels outside of a patient undergoing 177Lu radioligand therapy is not only helpful for conducting correct tests for patient release, but also useful for estimation of its potential exposure to healthcare workers, caregivers, family members, and the general public. In this study, by mimicking the 177Lu-labeled prostate-specific membrane antigen radioligand therapy for prostate cancers in an adult male, the spatial distribution of radiation levels outside of the phantom was simulated based on the Monte Carlo software of Particle and Heavy Ion Transport System, and verified by a series of measurements. Moreover, the normalized dose rates were further formulized on the three transverse planes representing the heights of pelvis, abdomen and chest. The results showed that the distributions of radiation levels were quite complex. Multi-directional and multi-height measurements are needed to ensure the external dose rate to meet the release criteria. In general, the radiation level was higher at the horizontal plane where the source was located, and the levels in front and behind of the body were higher than those of the left and right sides at the same height. The ratio of simulated dose rates to measured ones ranged from 0.82 to 1.19 within 1 m away from the body surface in all directions. Based on the established functions, the relative root mean square deviation between the calculated and simulated values were 0.21, 0.25 and 0.23 within a radius of 1 m on the pelvis, abdomen and chest transverse planes, respectively. It is expected that the results of this study would be helpful for guiding the test of extracorporeal radiation to determine the patient's release, and of benefit to estimate the radiation exposure to others. [ABSTRACT FROM AUTHOR]

A mechanism for the ejection of relativistic jets from slim disks is studied. Since radiation pressure is dominant in the slim disk, radiative energy flows along the pressure gradient in the vertical direction. The divergence of the radiative flux tells us that the flow of radiative energy from a bottom layer near the equatorial plane is absorbed by another layer above the boundary surface. The absorbed energy accumulates in the upper layer as the matter advances inward, and calculations show that the specific energy of the flow in the upper layer can be as large as ∼ c 2 near the black hole when the accretion rate through the upper layer is relatively low. Since the specific energy ∼ c 2 is much larger than the gravitational energy, the height of the upper layer could significantly increase then. Hence, the innermost part of the upper layer after almost all the angular momentum has been removed could have a much greater height than the size of the black hole, and the flow could collide with itself around the central axis of the disk, bouncing back from the axis while simultaneously expanding along it. The flow is expected to go outward along the central axis and to become supersonic due to the change in its cross section, finally producing relativistic jets. [ABSTRACT FROM AUTHOR]

Deuterium-tritium fusion reactions produce energy in the form of 14.1 MeV neutrons, and hence fusion reactor components will be exposed to high energy neutron irradiation while also being subjected to thermal, mechanical and magnetic loads. Exposure to neutron irradiation has numerous consequences, including swelling and dimensional changes, comparable in magnitude to the peak transient thermal deformations occurring in plasma-facing components. Irradiation also dynamically alters the various thermo-mechanical properties, relating temperature, stress and swelling in a strongly non-linear way. Experimental data on the effect of neutron exposure spanning the design parameter space are very sparse and this highlights the relevance of computer simulations. In this study we explore the equivalence between the body force/surface traction approach and the eigenstrain formalism for treating anisotropic irradiation-induced swelling. We find that both commercial and massively parallelised open source software for finite element method (FEM) simulations are suitable for assessing the effect of neutron exposure on the mechanically loaded reactor components. We demonstrate how two primary effects of irradiation, radiation swelling and the degradation of thermal conductivity, affect the distributions of stress and temperature in the divertor of the ITER tokamak. Significant uncertainties characterising the magnitude of swelling and models for treating it suggest that on the basis of the presently available data, only an order of magnitude estimate can be given to the stress developing in reactor components most exposed to irradiation during service. [ABSTRACT FROM AUTHOR]

Brown dwarfs (BDs) in ultra-short-period orbits around white dwarfs (WDs) offer a unique opportunity to study the properties of tidally locked, fast-rotating (1–3 hr), and highly irradiated atmospheres. Here we present phase-resolved spectrophotometry of the WD–BD binary SDSS 1557, which is the fifth WD–BD binary in our six-object sample. Using the Hubble Space Telescope Wide Field Camera 3 Near-infrared G141 instrument, the 1.1–1.7 μ m phase curves show rotational modulations with semiamplitudes of 10.5% ± 0.1%. We observe a wavelength-dependent amplitude, with longer wavelengths producing larger amplitudes, while no wavelength-dependent phase shifts were identified. The phase-resolved extracted BD spectra exhibit steep slopes and are nearly featureless. A simple radiative energy redistribution atmospheric model re-creates the hemisphere-integrated brightness temperatures at three distinct phases and finds evidence for weak redistribution efficiency. Our model also predicts a higher inclination than previously published. We find that SDSS 1557B, the second most irradiated BD in our sample, is likely dominated by clouds on the nightside, whereas the featureless dayside spectrum is likely dominated by H− opacity and a temperature inversion, much like the other highly irradiated BD EPIC 2122B. [ABSTRACT FROM AUTHOR]

Background. Concern has been expressed regarding the risk of carcinogenesis from medical computed tomography (CT) radiation. Lowering radiation in CT without appropriate modifications often leads to severe noise-induced artifacts in the images. The utilization of deep learning (DL) techniques has achieved promising reconstruction performance in low-dose CT (LDCT) imaging. However, most DL-based algorithms require the pre-collection of a large set of image pairs (low-dose/standard-dose) and the training of networks in an end-to-end supervised manner. Meanwhile, securing such a large volume of paired, well-registered training data in clinical practice is challenging. Moreover, these algorithms often overlook the potential to utilize the abundant information in a large collection of LDCT-only images/sinograms. Methods. In this paper, we introduce a semi-supervised iterative adaptive network (SIA-Net) for LDCT imaging, utilizing both labeled and unlabeled sinograms in a cohesive network framework, integrating supervised and unsupervised learning processes. Specifically, the supervised process captures critical features (i.e. noise distribution and tissue characteristics) latent in the paired sinograms, while the unsupervised process effectively learns these features in the unlabeled low-dose sinograms, employing a conventional weighted least-squares model with a regularization term. Furthermore, the SIA-Net method is designed to adaptively transfer the learned feature distribution from the supervised to the unsupervised process, thereby obtaining a high-fidelity sinogram through iterative adaptive learning. Finally, high-quality CT images can be reconstructed from the refined sinogram using the filtered back-projection algorithm. Results. Experimental results on two clinical datasets indicate that the proposed SIA-Net method achieves competitive performance in terms of noise reduction and structure preservation in LDCT imaging, when compared to traditional supervised learning methods. [ABSTRACT FROM AUTHOR]

Solid-state single-photon emitters (SPEs) commonly encounter the limitation of quasi-omnidirectional radiation patterns, which poses challenges in utilizing their emission with conventional optical instruments. In this study, we demonstrate the tailoring of the far-field radiation patterns of SPEs based on colloidal quantum dots (QDs), both theoretically and experimentally, by employing a polymer-based dielectric antenna. We introduce a simple and cost-effective technique, namely low one-photon absorption direct laser writing, to achieve precise coupling of a QD into an all-polymer circular waveguide resonance grating. By optimizing the geometry parameters of the structure using 3D finite-difference time-domain simulations, resonance at the emission wavelength of QDs is achieved in the direction perpendicular to the substrate, resulting in photon streams with remarkably high directivity on both sides of the grating. Theoretical calculations predict beam divergence values below 2°, while experimental measurements using back focal plane imaging yield divergence angles of approximately 8°. Our study contributes to the evaluation of concentric circular grating structures employing low refractive index polymer materials, thereby expanding the possibilities for their application. [ABSTRACT FROM AUTHOR]

We propose an all-optical approach to realize a super-oscillatory longitudinal magnetization hotspot with about 0.1 λ in a 4 π focusing system using time-reversed dipole radiation and vector diffraction theory calculations. Such a magnetization behavior is induced by focal fields of opposite polarities in the central and peripheral regions based on the inverse Faraday effect. By regulating the destructive interference in the central and peripheral regions of the focal field, a super-oscillating magnetization field is generated. Moreover, two important parameters affect the size of the magnetization field are also explored. Superoscillating magnetization hotspots in the focal region can be achieved by either increasing δ (the intensity of electric field) or reducing d n (the distance of electric field). The achieved ultrasmall magnetization spot shows great prospects in high-density magnetic recording, magnetic resonance imaging, and magnetic sensors. [ABSTRACT FROM AUTHOR]

The self-force expansion allows the study of deviations from geodesic motion due to the emission of radiation and its consequent back-reaction. We investigate this scheme within the on-shell framework of semiclassical scattering amplitudes for particles emitting photons or gravitons on a static, spherically symmetric background. We first present the exact scalar two-point amplitudes for Coulomb and Schwarzschild, from which one can extract classical observables such as the change in momentum due to geodesic motion. We then present, for the first time, the three-point semiclassical amplitudes for a scalar emitting a photon in Coulomb and a graviton on linearised Schwarzschild, outlining how the latter calculation can be generalized to the fully non-linear Schwarzschild metric. Our results are proper resummations of perturbative amplitudes in vacuum but, notably, are expressed in terms of Hamilton's principal function for the backgrounds, rather than the radial action. [ABSTRACT FROM AUTHOR]

An integrated analysis is developed to determine the far-field and near-field radiation of lithography-free metal-dielectric-metal (MIM) structures. Directional spectral emissivity determined with the integrated analysis shows good agreement with the directional spectral absorptivity from verified full wave simulation. With the integrated analysis, we identified that the condition of Fabry–Perot resonance used to design broadband wide-angle perfect light absorbers/emitters with MIM structures could trigger the waveguide modes of the dielectric layer. The waveguide modes can amplify the thermal electric field for photon tunneling between two MIM structures across a 100 nm level gap. Adding an additional pair of waveguides that can amplify evanescent waves in the gap formed with two MIM structures can further enhance the strength of photon tunneling. The enhanced photon tunneling shows high-intensity quasi-monochromatic near-field radiation in TM mode across a 100 nm gap at specific wavelengths. We expect even stronger photon tunneling for high-intensity quasi-monochromatic near field radiation across a more significant gap can occur when the MIM structure made with lower loss metal is combined with structures providing stronger amplification of evanescent wave. [ABSTRACT FROM AUTHOR]

This research article, explores the influence of an inclined magnetic field on the fluid flow over a permeable stretching/shrinking surface with heat transfer. The study use water as a conventional base fluid, with graphene oxide (GO) and Aluminum oxide (Al2O3) nanoparticles submerged to create a nanofluid, the system of governing nonlinear partial differential equations converted into ordinary differential equations via suitable similarity conversions. This allow for the unique solution for stretching sheet/shrinking sheets to be obtained, along with the corresponding temperature solution in terms of the hypergeometric function, several parameters are included in the investigation and their contribution is graphically explained to examine physical characteristics such as radiation, inclined magnetic field, solution domain, volume fraction parameter, and temperature jump. Increasing the volume fraction and thermal radiation increases the thermal boundary layer, increasing the magnetic field parameter and inverse Darcy number increases the temperature and decays the velocity profile. The present work has many useful applications in engineering, biological and physical sciences, as well as in cleaning engine lubricants and thrust-bearing technologies. [ABSTRACT FROM AUTHOR]

We perform radiation hydrodynamics simulations to study the structure and evolution of a photoevaporating protoplanetary disk. Ultraviolet and X-ray radiation from the host star heats the disk surface, where H2 pumping also operates efficiently. We run a set of simulations in which we varied the number of dust grains or the dust-to-gas mass ratio, which determines the relative importance between photoelectric heating and H2 pumping. We show that H2 pumping and X-ray heating contribute more strongly to the mass loss of the disk when the dust-to-gas mass ratio is D ≤ 10 − 3 . The disk mass-loss rate decreases with a lower dust amount, but remains around 10−10−11 M ⊙yr−1. In these dust-deficient disks, H2 pumping enhances photoevaporation from the inner disk region and shapes the disk mass-loss profile. We thus argue that the late-stage disk evolution is affected by the ultraviolet H2 pumping effect. The mass-loss rates derived from our simulations can be used in the study of long-term disk evolution. [ABSTRACT FROM AUTHOR]

In this study, electrical measurements on ferroelectric random-access memory by prior x-ray irradiation are conducted. Compared with an unirradiated device, parameters such as current leakage and remnant polarization of the irradiated device were unexpectedly improved. Besides, better reliabilities including the number of endurance times and retention time have also been demonstrated. To clarify the underlying physical mechanism, the electrical properties are analyzed. The current–voltage curve (I–V) implies a change in the grain size in the ferroelectric layer (FL), and the capacitance–voltage curve (C – V) profile indicates that the FL undergoes a phase change during irradiation. Finally, according to the electrical results, a physical model is proposed as an explanation. [ABSTRACT FROM AUTHOR]

We present a comparative study on the heavy quarks energy loss through medium polarization and gluon radiation in the quark-gluon plasma. To do so, we investigated the energy loss per unit length and drag coefficient for both cases. To have better contrast, we also obtained the nuclear modification factor employing Langevin dynamics. The comparison shows that the polarization effect dominates at lower momentum. The medium temperature also plays an important role in the comparison. [ABSTRACT FROM AUTHOR]

This paper presents a novel view of the impact of electron collision off-axis positions on the dynamic properties and relativistic nonlinear Thomson inverse scattering of excited electrons within tightly focused, circularly polarized laser pulses of varying intensities. We examine the effects of the transverse ponderomotive force, specifically how the deviation angle and speed of electron motion are affected by the initial off-axis position of the electron and the peak amplitude of the laser pulse. When the laser pulse intensity is low, an increase in the electron's initial off-axis distance results in reduced spatial radiation power, improved collimation, super-continuum phenomena generation, red-shifting of the spectrum's harmonic peak, and significant symmetry in the radiation radial direction. However, in contradiction to conventional understandings, when the laser pulse intensity is relatively high, the properties of the relativistic nonlinear Thomson inverse scattering of the electron deviate from the central axis, changing direction in opposition to the aforementioned effects. After reaching a peak, these properties then shift again, aligning with the previous direction. The complex interplay of these effects suggests a greater nuance and intricacy in the relationship between laser pulse intensity, electron position, and scattering properties than previously thought. [ABSTRACT FROM AUTHOR]

Károlyházy's original proposal, suggesting that space-time fluctuations could be a source of decoherence in space, faced a significant challenge due to an unexpectedly high emission of radiation (13 orders of magnitude more than what was observed in the latest experiment). To address this issue, we reevaluated Károlyházy's assumption that the stochastic metric fluctuation must adhere to a wave equation. By considering more general correlation functions of space-time fluctuations, we resolve the problem and consequently revive the aforementioned proposal. [ABSTRACT FROM AUTHOR]

We study the formation of Population III stars by performing radiation hydrodynamic simulations for three different initial clouds extracted from cosmological hydrodynamic simulations. Starting from the cloud collapse stage, we follow the growth of protostars by accretion for ∼105 yr until the radiative feedback from the protostars suppresses the accretion and the stellar properties are nearly fixed. We find that Population III stars form in massive and wide binary/small-multiple stellar systems, with masses >30 M ⊙ and separations >2000 au. We also find that the properties of the final stellar system correlate with those of the initial clouds: the total mass increases with the cloud-scale accretion rate, and the angular momentum of the binary orbit matches that of the initial cloud. While the total mass of the system in our simulations is consistent with our previous single-star formation simulations, individual masses are lower due to mass sharing, suggesting potential modification in the extent of feedback from Population III stars in the subsequent evolution of the Universe. We also identify such systems as mini-binaries embedded in a wider outer multiple-star system, which could evolve into progenitors for observed gravitational wave events. [ABSTRACT FROM AUTHOR]

Objective. To investigate biological effectiveness of 252Cf brachytherapy source using Monte Carlo-calculated microdosimetric distributions. Approach. 252Cf source capsule was placed at the center of the spherical water phantom and phase-space data were scored as a function of radial distance in water (R = 1–5 cm) using TOPAS Monte Carlo code. The phase-space data were used to calculate microdosimetric distributions at 1 μ m site size. Using these distributions, Relative Biological Effectiveness (RBE), mean quality factor ( Q ̅ ) and Oxygen Enhancement Ratio (OER) were calculated as a function of R. Main results. The overall shapes of the microdosimetric distributions are comparable at all the radial distances in water. However, slight variation in the bin-wise yield is observed with R. RBE, Q ̅ and OER are insensitive to R over the range 1–5 cm. Microdosimetric kinetic model based RBE values are about 2.3 and 2.8 for HSG tumour cells and V79 cells, respectively, whereas biological weighting function-based RBE is about 2.8. ICRP 60 and ICRU 40 recommendation-based Q ̅ values are about 14.5 and 16, respectively. Theory of dual radiation action based RBE is 11.4. The calculated value of OER is 1.6. Significance. This study demonstrates the relative insensitivity of RBE, Q ̅ and OER radially away from the 252Cf source along the distances of 1–5 cm in water. [ABSTRACT FROM AUTHOR]

We report the serendipitous discovery of a giant mid-infrared outburst from a previously unknown source near a star-forming region in the constellation Monoceros. The source gradually brightened by a factor of 5 from 2014–2016 before an abrupt rise by a factor of more than 100 in 2017. A total amplitude increase of >500 at 4.5 μ m has since faded by a factor of about 10. Prior to the outburst, it was only detected at wavelengths longer than 1.8 μ m in UKIDSS, Spitzer, and Herschel with a spectral energy distribution of a Class I young stellar object (YSO). It has not been detected in recent optical surveys, suggesting that it is deeply embedded. With a minimum distance of 3.5 kpc, the source has a bolometric luminosity of at least 9 L ☉ in the quiescent state and 400 L ☉ at the peak of the eruption. The maximum accretion rate is estimated to be at least a few 10−5 M ☉ yr−1. It shares several common properties with another eruptive event, WISE J142238.82-611553.7: exceptionally large amplitude, featureless near-infrared spectrum with the exception of H2 lines, intermediate eruption duration, an embedded Class I YSO, and a low radiative temperature (<600–700 K) in outburst. We interpret that the radiation from the inner accretion disk and young star is obscured and reprocessed by either an inflated outer disk or thick dusty outflow on scales >6.5 au during the outburst. [ABSTRACT FROM AUTHOR]

HFO-1336mzz(E) is proposed as a novel alternative to SF6 due to its low greenhouse effect and high insulation strength. Typically, it is mixed with CO2 or Air to lower its boiling point to meet the minimum operating temperature. To better understand the thermophysical properties of the gases' arcing plasma, the composition, thermodynamic properties, transport properties, and net emission coefficient of 30% molar fraction of HFO-1336mzz(E) mixed with CO2 or Air at temperatures from 300 K to 30 000 K at 0.12 MPa are calculated. It is found that HFO-1336mzz(E) mixtures have similar turbulent energy dissipation and thermal interruption capability to the pure SF6. Analysis of radiation characteristics demonstrates that the HFO-1336mzz(E) mixtures at 0.12 MPa exhibit stronger radiation emission compared to SF6 at 0.1 MPa, which indicates good arc radiation dissipation capabilities within such mixtures. This study reports the properties of thermal plasma of HFO-1336mzz(E) mixtures for the first time. These findings not only provide fundamental data for further magneto-hydro-dynamic calculations for arcing process but also put forward the potential application of these mixtures as arc interruption medium in medium voltage switchgears. [ABSTRACT FROM AUTHOR]

We did 194 epochs of simultaneous 2.25/8.60 GHz observations of XTE J1810−197 in 926 days shortly following its reactivation in 2018 with Shanghai Tian Ma Radio Telescope (TMRT). Although its integrated profiles changed with both time and frequency during this period, they could be classified into 12 types according to phase areas of active radiation components. After MJD 59015, XTE J1810−197 turned from the normal emission state into the spiky emission state that was manifesting as a series of bright narrow sub-pulse bursts at both 2.25 and 8.60 GHz. Due to its variable integrated profiles and unsteady rotations, we got the spin frequency ν and spin-frequency derivatives ν ̇ with the piecewise fitting method. In addition, its long-term declining trend of ν was also obtained as ν ̇ = − 3.2 (1) × 10 − 13 s−2 with the linear fitting method based on our observations spanning a comparatively longer period. We found its flux densities went through three stages: sharp decrease, stabilization, and day-to-day fluctuations in our dual-frequency observations. Although the flux density showed different stages, XTE J1810−197 showed a relatively flat spectrum (α > –1) in most observations. Assuming an ideal dipole magnetic field as some previous research works, we obtained the emission heights of XTE J1810−197 were about 7.5(9) × 104 km and 2.38(7) × 104 km at 2.25 and 8.60 GHz, respectively. We also found that its emission heights would decrease rapidly with the degree of magnetic field twisting. [ABSTRACT FROM AUTHOR]

Far-ultraviolet (FUV) emission lines from dwarf stars are important driving sources of photochemistry in planetary atmospheres. Properly interpreting spectral features of planetary atmospheres critically depends on the emission of its host star. While the spectral energy distributions (SEDs) of K- and M-type stars have been extensively characterized by previous observational programs, the full X-ray to infrared SED of F-type stars has not been assembled to support atmospheric modeling. On the second flight of the Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SISTINE-2) rocket-borne spectrograph, we successfully captured the FUV spectrum of Procyon A (F5 IV-V) and made the first simultaneous observation of several emission features across the FUV bandpass (1010–1270 and 1300–1565 Å) of any cool star. We combine flight data with stellar models and archival observations to develop the first SED of a mid-F star. We model the response of a modern Earth-like exoplanet's upper atmosphere to the heightened X-ray and extreme UV radiation within the habitable zone of Procyon A. These models indicate that this planet would not experience significant atmospheric escape. We simulate observations of the Ly α transit signal of this exoplanet with the Hubble Space Telescope (HST) and the Habitable Worlds Observatory (HWO). While marginally detectable with HST, we find that H i Ly α transits of potentially habitable exoplanets orbiting high radial velocity F-type stars could be observed with HWO for targets up to 150 pc away. [ABSTRACT FROM AUTHOR]

The toroidal dipole excitation is important for metamaterial research because of its low-loss attribute. In this study, we demonstrate numerically and experimentally, a unique toroidal metasurface that modulates a broad resonance into a sharp mode, independent of the polarization of the incident terahertz (THz) radiation, by coupling the inherent toroidal dipole excitation to the lattice mode of the metasurface. The advantage of polarization independence enables the excitation of 'lattice-coupled toroidal mode' for both the orthogonally polarized states of the incident THz radiation in the metasurface. The interaction of the two resonances results in the enhancement of the quality factor of the metasurface at the point of resonance matching. The surface current profile as well as multipole analysis of scattered powers by electric, magnetic, and toroidal dipoles confirm the domineering effect of toroidal dipole excitation for both the polarization states of incident THz radiation. Such a lattice-matched toroidal excitation-based device has the potential to impact the development of polarization-independent THz components for ultrasensitive sensors, lattice-enhanced equipment, and slow light devices for light–matter interaction. [ABSTRACT FROM AUTHOR]

Observations of supernovae (SNe) Ic occurring after the prompt emission of long gamma-ray bursts (GRBs) are addressed within the binary-driven hypernova (BdHN) model where GRBs originate from a binary composed of a ∼10 M ⊙ carbon–oxygen (CO) star and a neutron star (NS). The CO core collapse gives the trigger, leading to a hypernova with a fast-spinning newborn NS (ν NS) at its center. The evolution depends strongly on the binary period, P bin. For P bin ∼ 5 min, BdHNe I occur with energies 1052–1054 erg. The accretion of SN ejecta onto the NS leads to its collapse, forming a black hole (BH) originating the MeV/GeV radiation. For P bin ∼ 10 min, BdHNe II occur with energies 1050–1052 erg and for P bin ∼ hours, BdHNe III occur with energies below 1050 erg. In BdHNe II and III, no BH is formed. The 1–1000 ms ν NS originates, in all BdHNe, the X-ray-optical-radio afterglows by synchrotron emission. The hypernova follows an independent evolution, becoming an SN Ic, powered by nickel decay, observable after the GRB prompt emission. We report 24 SNe Ic associated with BdHNe. Their optical peak luminosity and time of occurrence are similar and independent of the associated GRBs. From previously identified 380 BdHN I comprising redshifts up to z = 8.2, we analyze four examples with their associated hypernovae. By multiwavelength extragalactic observations, we identify seven new episodes, theoretically explained, fortunately not yet detected in Galactic sources, opening new research areas. Refinement of population synthesis simulations is needed to map the progenitors of such short-lived binary systems inside our galaxy. [ABSTRACT FROM AUTHOR]

The chromospheric Ly α line of neutral hydrogen (1216 Å) is the most intense emission line in the solar spectrum, yet until recently observations of flare-related Ly α emission have been scarce. Here, we examine the relationship between nonthermal electrons accelerated during the impulsive phase of three M3 flares that were co-observed by RHESSI, GOES, and the Solar Dynamics Observatory, and the corresponding response of the chromosphere in Ly α. Despite having identical X-ray magnitudes, these flares showed significantly different Ly α responses. The peak Ly α enhancements above the quiescent background for these flares were 1.5%, 3.3%, and 6.4%. However, the predicted Ly α enhancements from FISM2 were consistently <2.5%. By comparing the properties of the nonthermal electrons derived from spectral analysis of hard X-ray observations, flares with a "harder" spectral index were found to produce a greater Ly α enhancement. The percentage of nonthermal energy radiated by the Ly α line during the impulsive phase was found to range from 2.0% to 7.9%. Comparatively, the radiative losses in He ii (304 Å) were found to range from 0.6% to 1.4% of the nonthermal energy while displaying enhancements above the background of 7.3% to 10.8%. FISM2 was also found to underestimate the level of He ii emission in two of the three flares. These results may have implications for space weather studies and for modeling the response of the terrestrial atmosphere to changes in the solar irradiance, and will guide the interpretation of flare-related Ly α observations that will become available during Solar Cycle 25. [ABSTRACT FROM AUTHOR]

This work presents an experimental study of the influence of radiation on structural health monitoring systems based on the electromechanical impedance method using low-cost piezoelectric diaphragms. For application of the method, the baseline was obtained without radiation and then compared by damage indices after application of radiation. Considering applications in nuclear power plants, the irradiation and calculation of damage indices were performed in the range of 10 kGy–60 kGy at 10 kGy intervals. Impedance measurements were performed in seven frequency bands between 0 and 65 kHz. The results show that, due to the change in the impedance signatures, the damage indices values increase according to the total applied radiation dose, which may indicate a false indication of damage. Besides, results indicate that there are frequency bands less sensitive to radiation and a threshold can be defined to distinguish radiation from structural damage. [ABSTRACT FROM AUTHOR]

Relativistic jets from (supermassive) black holes are typically observed in nonthermal emission, caused by highly relativistic electrons. Here, we study the interrelation between three-dimensional (special) relativistic magnetohydrodynamics, and particle acceleration in these jets. We inject Lagrangian particles into the jet that are accelerated through diffusive shock acceleration and radiate energy via synchrotron and inverse Compton processes. We investigate the impact of different injection nozzles on the jet dynamics, propagation, and the spectral energy distribution of relativistic particles. We consider three different injection nozzles—injecting steady, variable, and precessing jets. These jets evolve with substantially different dynamics, driving different levels of turbulence and shock structures. The steady jet shows a strong, stationary shock feature, resulting from a head-on collision with an inner back-flow along the jet axis—a jet inside a jet. This shock represents a site for highly efficient particle acceleration for electrons up to a few tens of TeV and should be visible in emission as a jet knot. Overall, we find that the total number of shocks is more essential for particle acceleration than the strength of the shocks. The precessing jet is most efficient in accelerating electrons to high energies reaching even few hundred TeVs, with power-law index ranging from 2.3 to 3.1. We compare different outflow components, such as the jet and the entrained material concerning particle acceleration. For the precessing nozzle, the particle acceleration in the entrained material is as efficient as that in the jet stream. This is due to the higher level of turbulence induced by the precession motion. [ABSTRACT FROM AUTHOR]

Experiments in DIII-D document the ITER Baseline Scenario (IBS) at q _95 ∼ 3 and P _IN / P _LH ∼ 1–2, in both deuterium and hydrogen utilizing Kr and Xe as Tungsten-equivalent radiators. The power threshold for H-mode operation ( P _LH ) was determined experimentally without added impurities and found to be about a factor of two higher than the scaling law. In recent IBS experiments in deuterium, intrinsic levels of metals such as Tungsten (W) or molybdenum and inconel are present that reduce the pedestal pressure by 20%–25%. A complete radiative collapse of deuterium IBS plasmas occurs at W core concentrations C _W = 10 ^−5 . Simulations show that for core temperatures expected for ITER, the plasmas would not have a radiative collapse at C _W = 1 × 10 ^−5 , moreover Q = 8–10 would still be achieved for C _W up to 3 × 10 ^−5 . In contrast to deuterium, the IBS in hydrogen is not affected by intrinsic high-Z impurities, indicating that hydrogen H-modes in ITER may not inform the D-T phase with respect to W accumulation and discharge survival. Compared to deuterium, the pedestal pressure in hydrogen is ∼25% lower, with much higher ELM frequency of 150 Hz, decreasing with input power. Krypton was injected in a matrix scan of input power and impurity flow in IBS hydrogen discharges. Krypton impurity density profiles in hydrogen are similar to deuterium plasmas, but at Kr flows that are 2–3 times higher for the same input power. Krypton is transported into the core and affects the whole radius; at the highest injection rates a radiative collapse occurs at core radiation fractions of 0.3–0.35, consistent with the expected maximum W radiation fraction for ITER core plasmas. Comparing the results with previous International Tokamak Physics Activity database studies of the IBS confirms that at higher radiation fraction due to high-Z impurities, a drop in H _98 of >10% is observed. On the other hand, the results using Kr as a W-equivalent radiator indicate that metal (W) devices at lower core temperatures than ITER may provide overly pessimistic performance extrapolations to ITER for deuterium-tritium operation. The new DIII-D results support a more attractive option for the ITER Research Plan with a short hydrogen phase for system commissioning, transitioning to deuterium operations as soon as possible to provide relevant conditions for deuterium-tritium operations.

Present work analyze the ionizing radiations attenuation behaviour, photon trajectories and dose rate reduction properties of silver tellurite glasses to investigate their potential application in radiation shielding. The shielding capability of five glass systems with different elemental compositions have been calculated with the help of theoretical software: Phy-X/PSD and NIST XCOM. For the photon energy range of 1.00 keV to 100.00 GeV, various shielding parameters are calculated, including attenuation coefficients ( MAC , LAC ), mean free path, half value layer, tenth value layer, effective atomic number, effective electron density, energy build up factors, energy absorption buildup factors, and fast neutron removal cross section. While the energy stopping potentials, projected range of ions (H ^+ , He ^+ , and C ^+ ) has been presented with the help of SRIM software. Additionally photon trajectories and dose rate attenuating behavior of 10 ^5 photons generated from ^137 Cs and ^60 Co sources with activity 200.00 GBq has been studied with the help of particle and heavy ion transport (PHITS) code. It is observed that at both low and high energy levels, the glass composition, labelled S _4 , (70TeO _2 -25Ag _2 O-2Nb _2 O _5 -2BaO-1PbO), exhibits comparable attenuation coefficients to previously recommended glass samples for radiation shielding applications. In addition to S _4 , nine different types of glass samples and polymers with comparable densities to our glass sample, along with water, were included for comparison. The findings indicate that among all the samples tested, S _4 demonstrates the highest and comparable radiation-protective performance, positioning it favourably for such applications.

With chemical stability under high temperatures, dielectric materials can be idealized thermal emitters for different energy applications. However, dielectric materials do not support surface waves at near-infrared ranges for longer-distance thermal photon tunneling, which limits their applications in near-field thermal radiation. It is demonstrated in this study that thermal field amplification at near-infrared wavelengths at dielectric surfaces could be achieved through asymmetric Fabry–Perot resonance with anti-reflection coatings or 1D photonic crystal type structures. ⩾100 nm near-infrared thermal photon tunneling can be achieved when these thin film structures are added to the emitter and the collector surfaces. Among these two thin film structures, 1D photonic crystal type periodic structures constructed with the same high refractive index material as the emitter/collector material allow near-field thermal photon tunneling at large parallel wavenumbers. Moreover, the field amplification can be increased by adding more 1D photonic crystal layers to achieve even longer distances near field thermal photon tunneling. [ABSTRACT FROM AUTHOR]

We perform 3D radiation hydrodynamic local shearing-box simulations to study the outcome of gravitational instability (GI) in optically thick active galactic nuclei (AGNs) accretion disks. GI develops when the Toomre parameter Q T ≲ 1, and may lead to turbulent heating that balances radiative cooling. However, when radiative cooling is too efficient, the disk may undergo runaway gravitational fragmentation. In the fully gas-pressure-dominated case, we confirm the classical result that such a thermal balance holds when the Shakura–Sunyaev viscosity parameter (α) due to the gravitationally driven turbulence is ≲0.2, corresponding to dimensionless cooling times Ω t cool ≳ 5. As the fraction of support by radiation pressure increases, the disk becomes more prone to fragmentation, with a reduced (increased) critical value of α (Ω t cool). The effect is already significant when the radiation pressure exceeds 10% of the gas pressure, while fully radiation-pressure-dominated disks fragment at t cool ≲ 50 Ω−1. The latter translates to a maximum turbulence level α ≲ 0.02, comparable to that generated by magnetorotational instability. Our results suggest that gravitationally unstable (Q T ∼ 1) outer regions of AGN disks with significant radiation pressure (likely for high/near-Eddington accretion rates) should always fragment into stars, and perhaps black holes. [ABSTRACT FROM AUTHOR]

With infrared flux contrasts larger than typically seen in hot Jupiter, tidally locked white dwarf–brown dwarf binaries offer a superior opportunity to investigate atmospheric processes in irradiated atmospheres. NLTT5306 is such a system, with a M BD = 52 ± 3 M Jup brown dwarf, orbiting a T eff = 7756 ± 35 K white dwarf with an ultra-short period of ∼102 minutes. We present Hubble Space Telescope/Wide Field Camera 3 spectroscopic phase curves of NLTT5306, consisting of 47 spectra from 1.1 to 1.7 μ m with an average signal-to-noise ratio ∼ 65 per wavelength. We extracted the phase-resolved spectra of the brown dwarf NLTT5306B, finding a small <100 K day–night temperature difference (∼5% of the average day-side temperature). Our best-fit model phase curves revealed a complex wavelength-dependence on amplitudes and relative phase offsets, suggesting longitudinal–vertical atmospheric structure. The night-side spectrum was well fit by a cloudy, nonirradiated atmospheric model while the day side was best matched by a cloudy, weakly irradiated model. Additionally, we created a simple radiative energy redistribution model of the atmosphere and found evidence for efficient day-to-night heat redistribution and a moderately high Bond albedo. We also discovered an internal heat flux much higher than expected given the published system age, leading to an age reassessment that resulted in NLTT5306B most likely being much younger. We find that NLTT5306B is the only known significantly irradiated brown dwarf where the global temperature structure is not dominated by external irradiation, but rather its own internal heat. Our study provides an essential insight into the drivers of global circulation and day-to-night heat transport as a function of irradiation, rotation rate, and internal heat. [ABSTRACT FROM AUTHOR]

At the end of its evaporation, a black hole may leave a remnant where a large amount of information is stored. We argue that the existence of an area gap as predicted by loop quantum gravity removes a main objection to this scenario. Remnants should radiate in the low-frequency spectrum. We model this emission and derive properties of the diffuse radiation emitted by a population of such objects. We show that the frequency and energy density of this radiation, which are measurable in principle, suffice to estimate the mass of the parent holes and the remnant density, if the age of the population is known. [ABSTRACT FROM AUTHOR]

We present numerical models from the field-aligned HYDrodynamics and RADiation code (HYDRAD) of a highly asymmetric closed coronal loop with near-singular expansion factor. This loop was chosen to simulate a coronal magnetic flux tube that passes close to a null point, as in the last set of closed loops under the fan surface of a coronal jet or a pseudostreamer. The loop has a very large cross section localized near the coronal null. The coronal heating was assumed to be uniform and steady. A siphon flow establishes itself within 4 hr of simulation time, flowing from the smaller-area footpoint to the larger-area footpoint, with high initial speeds dropping rapidly as the plasma approaches the null region. Observationally, this would translate to strong upflows on the order of 10 km s−1 from the footpoint rooted in the localized minority polarity, and weak downflows from the fan-surface footpoint on the order of a few kilometers per second, along with near-stationary plasma near the null region. We present the model results for two heating rates. In addition, we analyzed analogous Hinode EUV Imaging Spectrometer observations of null-point topologies, which show associated Doppler shifts in the plasma that correlate well with the simulation results in both direction and magnitude of the bulk velocity. We discuss the implications of our results for determining observationally the topology of the coronal magnetic field. [ABSTRACT FROM AUTHOR]

Nonlinear waveguides with two distinct domains of anomalous dispersion can support the formation of molecule-like two-color pulse compounds. They consist of two tightly bound subpulses with frequency loci separated by a vast frequency gap. Perturbing such a two-color pulse compound triggers periodic amplitude and width variations, reminiscent of molecular vibrations. With increasing strength of perturbation, the dynamics of the pulse compound changes from harmonic to nonlinear oscillations. The periodic amplitude variations enable coupling of the pulse compound to dispersive waves, resulting in the resonant emission of multi-frequency radiation. We demonstrate that the location of the resonances can be precisely predicted by phase-matching conditions. If the pulse compound consists of a pair of identical subpulses, inherent symmetries lead to degeneracies in the resonance spectrum. Weak perturbations lift existing degeneracies and cause a splitting of the resonance lines into multiple lines. Strong perturbations result in more complex emission spectra, characterized by well separated spectral bands caused by resonant Cherenkov radiation and additional four-wave mixing processes. [ABSTRACT FROM AUTHOR]

It is extremely difficult to simulate the details of coronal heating and also make meaningful predictions of the emitted radiation. Thus, testing realistic models with observations is a major challenge. Observational signatures of coronal heating depend crucially on radiation, thermal conduction, and the exchange of mass and energy with the transition region and chromosphere below. Many magnetohydrodynamic simulation studies do not include these effects, opting instead to devote computational resources to the magnetic aspects of the problem. We have developed a simple method of accounting approximately for the missing effects. It is applied to the simulation output ex post facto and therefore may be a valuable tool for many studies. We have used it to predict the emission from a model corona that is driven by vortical boundary motions meant to represent photospheric convection. We find that individual magnetic strands experience short-term brightenings, both scattered throughout the computational volume and in localized clusters. The former may explain the diffuse component of the observed corona, while the latter may explain bright coronal loops. Several observed properties of loops are reproduced reasonably well: width, lifetime, and quasi-circular cross section (aspect ratio not high). Our results lend support to the idea that loops are multistranded structures heated by "storms" of nanoflares. [ABSTRACT FROM AUTHOR]

The jet composition in gamma-ray bursts (GRBs) is still an unsolved issue. We try to provide some clues to the issue by analyzing the spectral properties of GRB 160509A and GRB 130427A with a main burst and a postburst. We first perform Bayesian time-resolved spectral analysis and compare the spectral components and spectral properties of the main bursts and postbursts of the two bursts and find that both bursts have the thermal components, and the thermal components are mainly found in the main bursts, while the postbursts are mainly dominated by the nonthermal components. We also find that the low-energy spectral indices of some time bins in the main bursts of these two GRBs exceed the so-called synchronous dead line, and in the postburst, only GRB 160509A has four time bins exceeding the dead line, while none of GRB 130427A exceed the dead line. We then constrain the outflow properties of both bursts and find that the main bursts is consistent with the typical properties of photosphere radiation. Therefore, our results support the transition of the GRB jet component from the fireball to the Poynting-flux-dominated jet. Finally, after analyzing the correlation and parameter evolution of the spectral parameters of the two bursts, we find that the correlations of the spectral parameters have different behaviors in the main bursts and postbursts. The parameter evolution trends of the main bursts and postbursts also show consistent and inconsistent behavior; therefore, we currently cannot determine whether the main bursts and postbursts come from the same origin. [ABSTRACT FROM AUTHOR]

Dynamics and radiation of a relativistic charged particle moving in a linear restoring force field is studied. Solutions to the equations of motion are presented in a compact form in terms of Jacobi elliptic functions. The intensity of radiation, its angular distribution and radiation spectrum of a relativistic oscillator are investigated. It is shown that, unlike a non-relativistic oscillator, the maximum intensity is emitted not at the turning points, but at some intermediate points of the particle’s trajectory. The emission spectrum consists of lines at frequencies that are multiples of the oscillation frequency of the oscillator. As the oscillator energy increases, the number of harmonics in the spectrum increases. The maximum in the spectrum of highly relativistic oscillator occurs on high numbers of harmonics. [ABSTRACT FROM AUTHOR]

We present a detailed study of the 2019 outburst of the cataclysmic variable V1047 Cen, which hosted a classical nova eruption in 2005. The peculiar outburst occurred 14 yr after the classical nova event and lasted for more than 400 days, reaching an amplitude of around 6 magnitudes in the optical. Early spectral follow-up revealed what could be a dwarf nova (accretion disk instability) outburst. However, the outburst duration, high-velocity (>2000 km sâˆ'1) features in the optical line profiles, luminous optical emission, and presence of prominent long-lasting radio emission together suggest a phenomenon more exotic and energetic than a dwarf nova outburst. The outburst amplitude, radiated energy, and spectral evolution are also not consistent with a classical nova eruption. There are similarities between V1047 Cen’s 2019 outburst and those of classical symbiotic stars, but pre-2005 images of the field of V1047 Cen indicate that the system likely hosts a dwarf companion, implying a typical cataclysmic variable system. Based on our multiwavelength observations, we suggest that the outburst may have started with a brightening of the disk due to enhanced mass transfer or disk instability, possibly leading to enhanced nuclear shell burning on the white dwarf, which was already experiencing some level of quasi-steady shell burning. This eventually led to the generation of a wind and/or bipolar, collimated outflows. The 2019 outburst of V1047 Cen appears to be unique, and nothing similar has been observed in a typical cataclysmic variable system before, hinting at a potentially new astrophysical phenomenon. [ABSTRACT FROM AUTHOR]

Objective. Image guidance and precise irradiation are fundamental to ensure the reliability of small animal oncology studies. Accurate positioning of the animal and the in-beam monitoring of the delivered radio-therapeutic treatment necessitate several imaging modalities. In the particular context of proton therapy with a pulsed beam, information on the delivered dose can be retrieved by monitoring the thermoacoustic waves resulting from the brief and local energy deposition induced by a proton beam (ionoacoustics). The objective of this work was to fabricate a multimodal phantom (x-ray, proton, ultrasound, and ionoacoustics) allowing for sufficient imaging contrast for all the modalities. Approach. The phantom anatomical parts were extracted from mouse computed tomography scans and printed using polylactic acid (organs) and a granite/polylactic acid composite (skeleton). The anatomical pieces were encapsulated in silicone rubber to ensure long term stability. The phantom was imaged using x-ray cone-beam computed tomography, proton radiography, ultrasound imaging, and monitoring of a 20 MeV pulsed proton beam using ionoacoustics. Main results. The anatomical parts could be visualized in all the imaging modalities validating the phantom capability to be used for multimodal imaging. Ultrasound images were simulated from the x-ray cone-beam computed tomography and co-registered with ultrasound images obtained before the phantom irradiation and low-resolution ultrasound images of the mouse phantom in the irradiation position, co-registered with ionoacoustic measurements. The latter confirmed the irradiation of a tumor surrogate for which the reconstructed range was found to be in reasonable agreement with the expectation. Significance. This study reports on a realistic small animal phantom which can be used to investigate ionoacoustic range (or dose) verification together with ultrasound, x-ray, and proton imaging. The co-registration between ionoacoustic reconstructions of the impinging proton beam and x-ray imaging is assessed for the first time in a pre-clinical scenario. [ABSTRACT FROM AUTHOR]

Theoretical and experimental data is presented for the application of an injection-seeded frequency-shifted feedback (FSF) laser for high accuracy ranging. Previous work discussed such a ranging scheme with a phase-modulated single-frequency laser where the phase modulation is done by an electro-optical modulator driven by a single frequency Ω which is swept over a certain bandwidth depending on the given experimental situation. In the present theoretical and experimental work, the phase modulation of the injection laser is done by a frequency comb with temporally fixed frequency components at intervals Ω d spanning a bandwidth adapted to the geometry of the object to be measured. It is shown that the superposition of such FSF radiation returning from the object and a reference surface on a detector leads to a train of sinusoidal pulses with an instantaneous frequency Ωinst in the radio-frequency range. The repetition rate of these pulses is Ω d and their duration is < 2 π / Ω d . The central result of this work is the observation that the path length difference between reference and object surface can be deduced from Ωinst, e.g. by frequency counting. The benefit of this approach lies in the fact that active frequency variation is not needed; all features of the entire system (FSF laser plus phase-modulated injected radiation) are constant in time. Proof-of-concept results using an FSF-laser ranging scheme based on a semiconductor laser are presented. [ABSTRACT FROM AUTHOR]