bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulations of two-temperature jets in galaxy clusters
Authors: Ohmura T. , Machida M.
Published: October 2023

Context. Non-radiating protons in the radio lobes play an essential role in shaping the jet morphology, as demonstrated in recent radio and X-ray observations. However, since protons and electrons are not always in energy equilibrium due to weak Coulomb coupling, it is difficult to estimate the energy contribution of protons for the inflation of radio lobes.

Aims. The focus of this study is to examine the effect of the variable model for electron heating by turbulence and shock waves on the thermal energy distribution of electrons and protons.

Methods. We performed two-temperature three-dimensional magnetohydrodynamic (3D MHD) simulations of sub-relativistic jets in the galaxy cluster, while varying the jet magnetization parameters. Because the energy partition rate between electrons and protons in shock and turbulence is determined by plasma kinetic scale physics, our global simulations include electron instantaneous heating sub-grid models for shock waves and turbulence.

Results. We find that most of the bulk kinetic energy of the jet is converted into the thermal energy of protons through both shocks and turbulence. Thus, protons are energetically dominant. Meanwhile, thermal electrons stored in the lobe evolve toward energy equipartition with magnetic energy through turbulent dissipation. We further estimated the radio power and the mechanical jet power of radio lobes following the same method used for radio and X-ray observations, then we compared these powers with that of the observed radio jets. The two-temperature model quantitatively explains the radiatively inefficient radio cavities, but it cannot reproduce the radiatively efficient cavity, even for strongly magnetized jets. This implies that a significant population of pair-plasma is needed to explain radiatively efficient radio cavities.
Self-consistent modeling of the energetic storm particle event of November 10, 2012
Authors: Afanasiev A. , Vainio R. , Trotta D. , Nyberg S. , Talebpour Sheshvan N. , Hietala H. , Dresing N.
Published: October 2023

Context. It is thought that solar energetic ions associated with coronal and interplanetary shock waves are accelerated to high energies by the diffusive shock acceleration mechanism. For this mechanism to be efficient, intense magnetic turbulence is needed in the vicinity of the shock. The enhanced turbulence upstream of the shock can be produced self-consistently by the accelerated particles themselves via streaming instability. Comparisons of quasi-linear-theory-based particle acceleration models that include this process with observations have not been fully successful so far, which has motivated the development of acceleration models of a different nature.

Aims. Our aim is to test how well our self-consistent quasi-linear SOLar Particle Acceleration in Coronal Shocks (SOLPACS) simulation code, developed earlier to simulate proton acceleration in coronal shocks, models the particle foreshock region.

Methods. We applied SOLPACS to model the energetic storm particle (ESP) event observed by the STEREO A spacecraft on November 10, 2012.

Results. All but one main input parameter of SOLPACS are fixed by the in situ plasma measurements from the spacecraft. By comparing a simulated proton energy spectrum at the shock with the observed one, we were able to fix the last simulation input parameter related to the efficiency of particle injection to the acceleration process. A subsequent comparison of simulated proton time-intensity profiles in a number of energy channels with the observed ones shows a very good correspondence throughout the upstream region.

Conclusions. Our results strongly support the quasi-linear description of the foreshock region.
Gas phase Elemental abundances in Molecular cloudS (GEMS)
Authors: Rodríguez-Baras M. , Esplugues G. , Fuente A. , Spezzano S. , Caselli P. , Loison J. C. , Roueff E. , Navarro-Almaida D. , Bachiller R. , Martín-Doménech R. , Jiménez-Serra I. , Beitia-Antero L. , Le Gal R.
Published: October 2023

Context. H2S is predicted to form by hydrogenation of atomic sulphur on grains and is thought to be the main sulphur reservoir in interstellar ice, being therefore a key molecule to understanding sulphur chemistry in the star formation process and to solving the missing sulphur problem in molecular clouds and star-forming regions. The study of the H2S deuterium fraction can be used to constrain its molecule formation pathways.

Aims. The aim of this work is to investigate for the first time the deuteration of H2S in a large sample of starless cores.

Methods. We used observations of the GEMS IRAM 30 m Large Program and complementary IRAM 30 m telescope observations. We considered a sample of 19 starless cores located in the Taurus, Perseus, and Orion molecular clouds, detecting HDS in ten of these starless cores, and D2S in five. The single and double H2S deuterium fractions were analysed with regard to their relation with the cloud physical parameters, comparisons with values obtained for other interstellar sources, and comparisons with deuterium fractions in early-stage star-forming sources of abundant molecules: c-C3H2, H2CS, H2O, H2CO, and CH3OH.

Results. We obtain a range of X(HDS)/X(H2S) ~ 0.025–0.2 in the starless cores with HDS detections. The five starless cores with D2S detections show values of X(D2S)/X(HDS) ~ 0.05–0.3. H2S single deuteration shows an inverse relation with the cloud kinetic temperature, but no trend is found with molecular hydrogen density or visual extinction. H2S deuteration values in starless cores are similar to those observed in Class 0, although this may be a consequence of an observational bias due to the limited spatial resolution. Comparison with c-C3H2, H2CS, H2O, H2CO, and CH3OH in other interstellar sources reveals a general trend of decreasing deuteration with increasing temperature, with lower values for Class I and massive star-forming sources. In starless cores and Class 0 objects, H2CS and H2CO present higher deuteration fractions than c-C3H2, H2S, H2O, and CH3OH. H2O shows single and double deuteration values one order of magnitude lower than those of H2S and CH3OH.

Conclusions. Differences between c-C3H2, H2CS and H2CO deuterium fractions and those of H2S, H2O, and CH3OH are related to deuteration processes produced in gas or solid phases, respectively. We interpret the differences between H2S and CH3OH deuterations and that of H2O as a consequence of differences in the formation routes in the solid phase, which can particularly be explained in terms of the different occurrence of the D-H and H-D substitution reactions in the ice, together with the chemical desorption processes. Further interferometric observations and laboratory experiments are needed to understand the deuteration processes.
Modelling the interaction of Alfvénic fluctuations with coronal mass ejections in the low solar corona
Authors: Sishtla Chaitanya Prasad , Pomoell Jens , Vainio Rami , Kilpua Emilia , Good Simon
Published: October 2023

Context.Alfvénic fluctuations of various scales are ubiquitous in the corona; their non-linear interactions and eventual turbulent cascade result in an important heating mechanism that accelerates the solar wind. These fluctuations may be processed by large-scale, transient, and coherent heliospheric structures such as coronal mass ejections (CMEs). In this study we investigate the interactions between Alfvénic solar wind fluctuations and CMEs using magnetohydrodynamic (MHD) simulations.

Aims.We study the transmission of upstream solar wind fluctuations into the CME leading to the formation of CME sheath fluctuations. Additionally, we investigate the influence of the fluctuation frequencies on the extent of the CME sheath.

Methods.We used an ideal MHD model with an adiabatic equation of state. An Alfvén pump wave is injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components, and a CME is injected by inserting a flux-rope modelled as a magnetic island into the quasi-steady solar wind.

Results.The upstream Alfvén waves experience a decrease in wavelength and change in the wave vector direction due to the non-radial topology of the CME shock front. The CME sheath inhibits the transmission of long-wavelength fluctuations due to the presence of non-radial flows in this region. The frequency of the solar wind fluctuations also affects the steepening of MHD fast waves causing the CME shock propagation speed to vary with the solar wind fluctuation frequencies.
Hydrogen production from coke oven gas using pressure swing adsorption process − a mathematical modelling approach
Authors: Ramani Balan , van der Stel Jan , Jagers Gerard , Buijs Wim
Published: October 2023

Coal is playing a major role as a reductant and as an energy source in the present world steel production due to its low cost and widespread distribution around the world. At the same time, being the largest contributor to global CO2 emissions, coal faces significant environmental challenges in terms of air pollution and global warming. Hydrogen is a promising alternative for coal in lowering the steel industry’s CO2 footprint, but the availability of green hydrogen is currently limited by its high production cost. This research study focuses on developing a pressure swing adsorption (PSA) technology that will allow for continued use of coal for a smooth transition towards green hydrogen-based steel production, by better utilisation of its by-product coke oven gas to produce high purity hydrogen. A generic, fast and robust simulation tool for simulating a variety of PSA processes considering both equilibrium and kinetic effects using a detailed non-isothermal and non-isobaric model is developed in the study. The adsorption equilibrium data required for the model are calculated from experimental results using the non-linear regression data fitting method. A series of rigorous parametric studies and breakthrough tests are performed using the developed mathematical model for better understanding of the effects of different factors on the PSA process performance. With the better understanding obtained from the above-mentioned parametric studies, the model is optimised by performing several simulation tests to achieve a high process performance in terms of purity and recovery of the H2 product, productivity of the adsorbents and energy consumption for compression of gases. The optimised 14-step multi-bed PSA cycle developed in this study allows for an improved energy efficiency of coal usage by better utilisation of its by-product coke oven gas by converting it into valuable high purity (>99.999%) hydrogen product with a recovery of over 75%.
Isotope effects in dynamics of water isotopologues induced by core ionization at an x-ray free-electron laser
Authors: Guillemin R. , Inhester L. , Ilchen M. , Mazza T. , Boll R. , Weber Th. , Eckart S. , Grychtol P. , Rennhack N. , Marchenko T. , Velasquez N. , Travnikova O. , Ismail I. , Niskanen J. , Kukk E. , Trinter F. , Gisselbrecht M. , Feifel R. , Sansone G. , Rolles D. , Martins M. , Meyer M. , Simon M. , Santra R. , Pfeifer T. , Jahnke T. , Piancastelli M. N.
Published: October 2023

Dynamical response of water exposed to x-rays is of utmost importance in a wealth of science areas. We exposed isolated water isotopologues to short x-ray pulses from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we identify significant structural dynamics with characteristic isotope effects in H2O2+, D2O2+, and HDO2+, such as asymmetric bond elongation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. A method to disentangle the sequences of events taking place upon the consecutive absorption of two x-ray photons is described. The obtained deep look into structural properties and dynamics of dissociating water isotopologues provides essential insights into the underlying mechanisms.
Effect of initial phase on the ablative Rayleigh–Taylor instability
Authors: Kuang Yuanyuan , Lu Yan , Lin Zhi , Yang Ming
Published: October 2023

The effect of initial perturbation phase on the ablative Rayleigh–Taylor instability is investigated by numerical simulations. We aim at the growth of harmonic amplitudes and the formation of spikes and bubbles in single- and two-mode coupling cases, respectively. In the two-mode coupling case, two kinds of simulations are performed: two modes with relatively small linear growth rate difference and two modes with relatively large linear growth rate difference. The initial relative phase between the original two modes has a significant effect on the growth of harmonic amplitudes, and in different initial relative phases, the structures of spikes and bubbles begin to show great differences in the nonlinear stage. Fortunately, the harmonic amplitudes are weakened at a specific initial relative phase. This has a certain enlightening significance for the stabilization of ablative Rayleigh–Taylor instability.
In search of a precursor for crystal nucleation of hard and charged colloids
Authors: de Jager Marjolein , Smallenburg Frank , Filion Laura
Published: October 2023

The interplay between crystal nucleation and the structure of the metastable fluid has been a topic of significant debate over recent years. In particular, it has been suggested that even in simple model systems such as hard or charged colloids, crystal nucleation might be foreshadowed by significant fluctuations in local structure around the location where the nucleus first arises. We investigate this using computer simulations of spontaneous nucleation events in both hard and charged colloidal systems. To detect local structural variations, we use both standard and unsupervised machine learning methods capable of finding hidden structures in the metastable fluid phase. We track numerous nucleation events for the face-centered cubic and body-centered cubic crystals on a local level and demonstrate that all signs of crystallinity emerge simultaneously from the very start of the nucleation process. We thus conclude that we observe no precursor for the crystal nucleation of hard and charged colloids.
THz-range cyclotron super-radiance from photoinjector-formed dense bunch of rotating electrons
Authors: Ginzburg N. S. , Yurovskiy L. A. , Zotova I. V. , Kocharovskaya E. R. , Sergeev A. S. , Malkin A. M. , Rozental R. M.
Published: October 2023

We study the possibility of terahertz pulse generation based on cyclotron super-radiance (SR) of an extended (in the scale of the wavelength) bunch of rotating electrons, which moves in a cylindrical waveguide with a translational velocity close to the wave's group velocity. In the rest frame, this group synchronism regime corresponds to radiation of an unmoving bunch of excited cyclotron oscillators at a quasi-cutoff frequency of a waveguide mode. We develop the generalized self-consistent model of cyclotron SR in the group synchronism regime describing both the azimuthal self-bunching of rotating electrons and their longitudinal displacements under the action of Coulomb repulsive forces and recoil effects caused by high-frequency magnetic fields of the generated SR pulse. Within the framework of the developed analytical model and based on direct PIC simulations, we demonstrate the feasibility of generating picosecond SR pulses with a central frequency of 1 THz and a peak power of 90 MW by photoinjector-formed electron bunches guided in a strong magnetic field of 10.5 T. Simulations show that in the group synchronism regime, the SR pulse is less affected by longitudinal forces, as compared to the case of mismatched velocities. In addition, the Lorentz force can provide partial self-compression of the electron bunch with the formation of electron density filaments.
Effect of high-frequency jet velocity perturbations on impinging jets atomization characteristics
Authors: Li Yuan , Tang Chenglong , Zhang Peng
Published: October 2023

The atomization characteristics of impinging jets with high-frequency jet velocity perturbations is studied numerically based on the volume of fluid method. Three typical perturbation modes are considered to mimic the velocity discrepancies of jet flow in real engine conditions. Both the perturbation amplitude and frequency are investigated independently. Results show that the liquid sheet structure and atomization characteristics are significantly changed under the intrinsic perturbation frequency. The spectrum analysis is performed to reveal the specific phenomenon and explore the mechanism of different velocity perturbation modes. The analyses show that the atomization process is sensitive to perturbation frequency but its effectiveness diminishes significantly at excessively high frequencies. Additionally, when the frequency of velocity perturbation approaches the natural intrinsic frequency of sheet waves, resonance occurs within the liquid sheet for certain perturbation mode, leading to dramatic varies in breakup length and spray angle because the velocity superposition of the intrinsic and perturbed flow and its dynamics.
Spatial and temporal evolution of laser plasma produced using a double-stream gas puff target
Authors: Bartnik Andrzej , Jach Karol , Świerczyński Robert , Fok Tomasz , Węgrzyński Łukasz , Wachulak Przemysław , Fiedorowicz Henryk
Published: October 2023

Laser plasma produced using a double-stream gas puff target is an intense source of soft x-ray (SXR) and extreme ultraviolet (EUV) radiation, however, without the harmful emission of debris associated with a solid target. Debris-free laser plasma x-ray and EUV sources have been applied in many various applications, including metrology, imaging in a nanoscale, tomography, processing materials, emission and absorption spectroscopy, laboratory astrophysics and astrochemistry, radiobiology, and radiochemistry. In this work, the results of the experimental and theoretical studies on the spatial and temporal evolution of laser plasma produced as a result of irradiation of an argon/helium gas puff target with laser pulses of 1.3 or 6 ns time duration generated with an Nd:YAG laser system are presented. Imaging and spectral measurements of SXR emission from the plasma, created in the double-stream gas puff target, have been performed with the use of an x-ray streak camera. The analysis of the results of spectral measurements, supported by numerical simulations of plasma x-ray emission, allowed the estimation of the plasma electron temperature and its changes over time. Experimental data were compared with the results of theoretical studies performed using a computer model of plasma hydrodynamics. It was shown that plasma expansion is fast enough to reduce the plasma density in the laser focus area during the laser–plasma interaction.
Spectral widths and Stokes shifts in InP-based quantum dots
Authors: Cavanaugh Paul , Wang Xudong , Bautista Maria J. , Jen-La Plante Ilan , Kelley David F.
Published: October 2023

InP-based quantum dots (QDs) have Stokes shifts and photoluminescence (PL) line widths that are larger than in II–VI semiconductor QDs with comparable exciton energies. The mechanisms responsible for these spectral characteristics are investigated in this paper. Upon comparing different semiconductors, we find the Stokes shift decreases in the following order: InP > CdTe > CdSe. We also find that the Stokes shift decreases with core size and decreases upon deposition of a ZnSe shell. We suggest that the Stokes shift is largely due to different absorption and luminescent states in the angular momentum fine structure. The energy difference between the fine structure levels, and hence the Stokes shifts, are controlled by the electron–hole exchange interaction. Luminescence polarization results are reported and are consistent with this assignment. Spectral widths are controlled by the extent of homogeneous and inhomogeneous broadening. We report PL and PL excitation (PLE) spectra that facilitate assessing the roles of homogeneous and different inhomogeneous broadening mechanisms in the spectra of zinc-treated InP and InP/ZnSe/ZnS particles. There are two distinct types of inhomogeneous broadening: size inhomogeneity and core–shell interface inhomogeneity. The latter results in a distribution of core–shell band offsets and is caused by interfacial dipoles associated with In–Se or P–Zn bonding. Quantitative modeling of the spectra shows that the offset inhomogeneity is comparable to but somewhat smaller than the size inhomogeneity. The combination of these two types of inhomogeneity also explains several aspects of reversible hole trapping dynamics involving localized In3+/VZn2− impurity states in the ZnSe shells.
Airfoil optimization for rotors operating in the ultra-low Reynolds number regime
Authors: Carreño Ruiz M. , Renzulli L. , D'Ambrosio D.
Published: October 2023

Ultra-low Reynolds number aerodynamics has gained significant attention in recent times, primarily due to the proliferation of micro-aerial vehicles and their utilization in low-density environments such as the Martian atmosphere and high altitudes in Earth's atmosphere. The Martian atmosphere presents a unique combination of low Reynolds numbers and high subsonic Mach numbers, necessitating the use of unconventional airfoil designs in this regime. This study focuses on optimizing airfoils for rotors operating in the compressible ultra-low Reynolds number regime. We demonstrate the capability of XFOIL, a panel method code incorporating an integral boundary layer formulation, to accurately predict airfoil loads when the flow remains attached. We determine the optimal camber and maximum camber positions by analyzing the four digits, two percent thickness, National Advisory Committee for Aeronautics XX02 airfoil family using XFOIL. Subsequently, we employ a multi-objective optimization approach, utilizing a Class Shape Transformation airfoil parameterization to maximize lift and minimize drag. We select several points from the resulting Pareto front and evaluate their performance through unsteady compressible Navier–Stokes simulations. Our findings reveal that incorporating sharp leading-edge variations in these airfoil designs enhances the peak efficiency by over 10%, primarily attributable to the development of laminar separation bubbles on the suction side of the airfoils. Importantly, these modified airfoils maintain favorable performance at low angles of attack.
Evidence for liquid-liquid phase separation during the early stages of Mg-struvite formation
Authors: Karafiludis Stephanos , Scoppola Ernesto , Wolf Stephan E. , Kochovski Zdravko , Matzdorff David , Van Driessche Alexander E. S. , Hövelmann Jörn , Emmerling Franziska , Stawski Tomasz M.
Published: October 2023

The precipitation of struvite, a magnesium ammonium phosphate hexahydrate (MgNH4PO4 · 6H2O) mineral, from wastewater is a promising method for recovering phosphorous. While this process is commonly used in engineered environments, our understanding of the underlying mechanisms responsible for the formation of struvite crystals remains limited. Specifically, indirect evidence suggests the involvement of an amorphous precursor and the occurrence of multi-step processes in struvite formation, which would indicate non-classical paths of nucleation and crystallization. In this study, we use synchrotron-based in situ x-ray scattering complemented by cryogenic transmission electron microscopy to obtain new insights from the earliest stages of struvite formation. The holistic scattering data captured the structure of an entire assembly in a time-resolved manner. The structural features comprise the aqueous medium, the growing struvite crystals, and any potential heterogeneities or complex entities. By analysing the scattering data, we found that the onset of crystallization causes a perturbation in the structure of the surrounding aqueous medium. This perturbation is characterized by the occurrence and evolution of Ornstein-Zernike fluctuations on a scale of about 1 nm, suggesting a non-classical nature of the system. We interpret this phenomenon as a liquid-liquid phase separation, which gives rise to the formation of the amorphous precursor phase preceding actual crystal growth of struvite. Our microscopy results confirm that the formation of Mg-struvite includes a short-lived amorphous phase, lasting >10 s.
HORTENSIA, a program package for the simulation of nonadiabatic autoionization dynamics in molecules
Authors: Issler Kevin , Mitrić Roland , Petersen Jens
Published: October 2023

We present a program package for the simulation of ultrafast vibration-induced autoionization dynamics in molecular anions in the manifold of the adiabatic anionic states and the discretized ionization continuum. This program, called HORTENSIA (Hopping Real-time Trajectories for Electron-ejection by Nonadiabatic Self-Ionization in Anions), is based on the nonadiabatic surface-hopping methodology, wherein nuclei are propagated as an ensemble along classical trajectories in the quantum-mechanical potential created by the electronic density of the molecular system. The electronic Schrödinger equation is numerically integrated along the trajectory, providing the time evolution of electronic state coefficients, from which switching probabilities into discrete electronic states are determined. In the case of a discretized continuum state, this hopping event is interpreted as the ejection on an electron. The derived diabatic and nonadiabatic couplings in the time-dependent electronic Schrödinger equation are calculated from anionic and neutral wavefunctions obtained from quantum-chemical calculations with commercially available program packages interfaced with our program. Based on this methodology, we demonstrate the simulation of autoionization electron kinetic energy spectra that are both time- and angle-resolved. In addition, the program yields data that can be interpreted easily with respect to geometric characteristics, such as bonding distances and angles, which facilitate the detection of molecular configurations important for the autoionization process. Furthermore, several useful extensions are included, namely, tools for the generation of initial conditions and input files as well as for the evaluation of output files, all of this both through console commands and a graphical user interface.
Parallel water entry: Experimental investigations of hydrophobic/hydrophilic spheres
Authors: Akbarzadeh Pooria , Krieger Michael , Hofer Dominik , Thumfart Maria , Gittler Philipp
Published: October 2023

This study aims to experimentally investigate the vertical parallel water entry of two identical spheres (in geometry and material) with different surface wettability (hydrophilic or hydrophobic) pairings. The spheres simultaneously impact the water surface with velocities ranging from 1.71 to 4.32 m s−1. The corresponding ranges of the impact Froude, Weber, and Reynolds numbers are 3.87–9.75, 816–5167, and 38.5×103 to 96.8×103, respectively. The spheres' lateral distances vary from 1.0 to 5.0 times the diameter. A high-speed photography system and image processing technique analyze the event dynamics, focusing on air-entrainment cavity behavior (shapes, closure, shedding), water flow features (Worthington jets, splashes), and sphere kinetics. Results for hydrophobic/hydrophobic cases show that even at the maximum lateral distance, a slightly asymmetric cavity forms, but deep-seal pinching occurs at a single point, similar to a single water entry scenario. As the lateral distance decreases, the spheres significantly influence each other's behavior, leading to the formation of a highly asymmetric air cavity and an oblique Worthington jet. In the case of a hydrophobic/hydrophilic pairing, vortices generated behind the hydrophilic sphere influence the air cavity development of the hydrophobic sphere. This can cause a secondary pinch-off, especially at low lateral distances. This effect becomes more pronounced at higher impact velocities. Additionally, at higher impact velocities and minimum lateral distance (direct contact between the spheres), a smaller cavity detaches from the hydrophobic sphere's cavity, attaches to the hydrophilic sphere, and moves with it. These different regimes result in varying descent velocities for the spheres.
The impacts of material acoustic impedance and thickness on single laser-induced bubble dynamics and determining factors in resulting pressure
Authors: Zhao Ben , Coutier-Delgosha Olivier
Published: October 2023

The objective of this paper is to experimentally identify the primary sources of pressure when a laser-induced cavitation bubble is collapsing to a wall with specific emphases on the material acoustic impedance and thickness. Both high-speed videos and local wall pressure measurements were performed for various standoff ratios γ, bubble diameters, and wall materials. In the case of a rigid wall, in addition to the known high pressure for γ<0.6 where the bubble attaches and collapses on the wall (ring collapse), at γ≈1.12 where the jet is dominant, and low pressure obtained at γ≈0.913, where neither effect is significant, we further captured similar pressure profiles during the collapse after the first rebound at γ≈1.16 for the ring collapse, γ≈1.79 for the jet, and γ≈1.41 for the minimal, respectively. This indicates a strong jet is typically followed by a strong ring collapse. Generally, the pressure from the second collapse increases faster with the bubble size than that of the first collapse. For walls featuring smaller acoustic impedance or thickness, which cannot be approximated as rigid bodies or accessed by pressure sensor, our unique bubble edge analyzing tool shows that the ring collapse and jet effects are moved to smaller values of γ. The maximum pressure exerted on the wall in these cases is smaller than that on the rigid wall. Finally, we summarized the asymptotic evolution curves of each edge which bound the bubble dynamics at different standoff ratios.
The Debye’s model for the dielectric relaxation of liquid water and the role of cross-dipolar correlations. A MD-simulations study
Authors: Alvarez Fernando , Arbe Arantxa , Colmenero Juan
Published: October 2023

By means of massive (more than 1.2 · 106 molecules) molecular dynamics simulations at 300 K we have disentangled self- and cross-dipolar contributions to the dielectric relaxation of liquid water that cannot be experimentally resolved. We have demonstrated that cross dipolar correlations are of paramount importance. They amount for almost a 60% of the total dielectric amplitude. The corresponding relaxation function is a one-step Debye-like function with a characteristic time, τcross, of the order of the phenomenological Debye time, τD. In contrast, the relaxation function corresponding to the self-contribution is rather complex and contains a fast decay related to dipolar librations and a second relaxation step that can be well described by two exponentials: a low-amplitude fast process (τ0 = 0.31 ps) and a main slow process (τself = 5.4 ps) that fully randomizes the dipolar orientation. In addition to dipolar relaxation functions, we have also calculated scattering-like magnitudes characterizing translation and rotation of water molecules. Although these processes can be considered as “jump” processes in the short time range, at the time scale of about τD–τcross, at which the cross-dipolar correlations decay to zero, the observed behavior cannot be distinguished from that corresponding to uncoupled Brownian translational and rotational diffusion. We propose that this is the reason why the Debye model, which does not consider intermolecular dipolar interactions, seems to work at time t ≳ τD.
Photonic nanojets generated by microfabricated dielectric cylinders using proton beam writing
Authors: Kosumsupamala Kunpisit , Tobe Keito , Tsuji Akihiro , Seya Daiya , Seki Hironori , Puttaraksa Nitipon , Matsui Tatsunosuke , Nishikawa Hiroyuki
Published: October 2023

Photonic nanojet (PNJ) is an optical phenomenon that focuses incident light to a sub-wavelength beam waist/width and several wavelength long beam length by scattering with a microstructure. Here, we report on the PNJs directly generated along the axial axis of poly(methyl methacrylate) (PMMA) micro-cylinders of 2, 4, 6, and 8 μm diameters fabricated by proton beam writing approach. Experimental results reveal that the PMMA micro-cylinders were produced with smooth surfaces, which are appropriate to form the PNJs. Accordingly, the PNJs were measured by using an in-house confocal microscope apparatus. The results show that the larger micro-cylinder diameters led to wider and longer PNJs, which agree well with the finite-difference time-domain simulation. This fabrication of micro-cylinders could offer specific PNJ properties for advancing sub-wavelength applications.
Injection-limited and space-charge-limited conduction in wide bandgap semiconductors with velocity saturation effect
Authors: Lee Kok Wai , Ang Yee Sin
Published: October 2023

Carrier conduction in wide bandgap semiconductors (WBS) often exhibits velocity saturation at the high-electric field regime. How such effects influence the transition between contact-limited and space-charge-limited current (SCLC) in a two-terminal device remains largely unexplored thus far. Here, we develop a generalized carrier transport model that includes contact-limited field-induced carrier injection, space charge, carrier scattering, and velocity saturation effect. The model reveals various transitional behaviors in the current–voltage characteristics, encompassing Fowler–Nordheim emission, trap-free Mott–Gurney (MG) SCLC, and velocity-saturated SCLC. Using GaN, 6H–SiC and 4H–SiC WBS as examples, we show that the velocity-saturated SCLC completely dominates the high-voltage (102–104 V) transport for typical sub-μm GaN and SiC diodes, thus unraveling velocity-saturated SCLC as a central transport mechanism in WBG electronics.
Enhanced terahertz magneto-optical performance in substrate-free ultra-thick TbErBi:RIG crystal films
Authors: Xue Qiang , Zhang Yuan-Jing , Zhao Dan , Yang Qing-Hui , Zhang Huai-Wu , Fan Fei , Wen Qi-Ye
Published: October 2023

A wafer-scale single crystal thick film of rare-earth iron garnet (RIG) has been successfully produced on a 3-in. gadolinium gallium garnet (GGG) substrate using the liquid phase epitaxy method. The RIG crystal's thickness measures ∼550 μm. By removing the GGG substrate through polishing, we improved the terahertz (THz) transmittance of the RIG crystal. In the frequency range of 0.1–1.0 THz, the RIG material exhibits a large refractive index of around 4.50, with a transmittance of ∼60% and an absorption rate of only 10–50 cm−1. Furthermore, we investigated the THz magneto-optical effect in the RIG material through THz time-domain spectroscopy. The observed results demonstrate the presence and significance of the magneto-optical effect in the RIG crystal. To provide further insights, we measured the THz Faraday rotation angle of the 550 μm-thick RIG crystal using the THz-TDS system under an external magnetic field of 0.17 T. The measured Faraday rotation angle reached 22°, and the calculated Verdet constant for the RIG sample was ∼120°/mm/T. Considering these findings, our study highlights the unique properties of this wafer-scale single crystal thick film of RIG, including its low loss, high transmission, and strong magneto-optical effect in the THz range. These characteristics make it a promising candidate for various applications, such as THz magnetic polarization conversion, non-reciprocal phase shifters, and isolators.
The effect of initial electrons generation approaches on nanosecond pulsed breakdown characteristics
Authors: Wang Yongliang , Li Junna , Jiang Ming , Li Shiji , Shi Haoliang , Cui Guangxi , Liu Jian , Qiu Aici
Published: October 2023

In this paper, the effects of initial electrons generation approaches on nanosecond pulsed breakdown characteristics are analyzed. Based on the numerical simulations with a 3D PIC-MCC model, the impacts of field-enhancement factor and initial electron concentration on nanosecond pulsed breakdown characteristics are investigated. Three types of switches are designed and subjected to testing under pulse voltages with rise times of 40, 70, and 120 ns, respectively. The results can be summarized as follows. First, the field-enhancement factor and initial electron concentration have significant influences on the development of the discharge channel. Second, the cathode-grooved self-triggered switch exhibits lower breakdown time delay jitter than the hemispherical self-breakdown switch at low pressure, while the differences in jitter between the two switches become negligible at high pressure. Third, the cathode-grooved self-triggered switch shows a lower breakdown time delay jitter compared to the pre-ionization self-triggered switch for pulse voltages with rise times of 40 and 70 ns. Conversely, this trend reverses for pulse voltage with a rise time of 120 ns. Finally, the breakdown time delay jitter for both the cathode-grooved self-triggered switch and the pre-ionization self-triggered switch has been reduced, and both switches are suitable for different operating requirements and conditions.
Dielectric relaxation in open circuit: Theory, simulations, and some experiments
Authors: Molinié Philippe
Published: October 2023

Static charge on insulating material surfaces may be a source of nuisance and an operational requirement in many devices. It induces a potential that evolves with time due to conduction and polarization processes in the dielectric. Here, we analyze, from a theoretical and experimental point of view, the response of an insulator subjected to a charging pulse, within the frame of linear system theory. The surface potential decay and the return voltage after a brief neutralization, which can be easily measured using an electrostatic probe, usually follow time power laws. We consider here a dielectric following the classical Cole–Cole response function in the frequency domain and derive an exact analytic formula for the potential decay, which involves a Mittag–Leffler function. The relationship between the potential decay and the absorption current when a constant voltage is applied on the dielectric is also analyzed. Experiments on several common insulating materials are analyzed according to this theory, using a numerical simulation with a two-cell model. Return voltage measurements are used to check which materials behave according to the linear model. We underline that an equivalent circuit using constant-phase elements, corresponding to several cells following the Cole–Cole response, can also represent dipolar motions in the dielectric as charge hopping between energy-distributed traps.
A thermodynamic analysis of CLC transporter dimerization in lipid bilayers
Authors: Chadda Rahul , Lee Taeho , Mahoney-Kruszka Robyn , Kelley Elizabeth G. , Bernhardt Nathan , Sandal Priyanka , Robertson Janice L.
Published: October 2023

The CLC-ec1 chloride/proton antiporter is a membrane-embedded homodimer with subunits that can dissociate and associate, but the thermodynamic driving forces favor the assembled dimer at biological densities. Yet, the physical reasons for this stability are confounding as dimerization occurs via the burial of hydrophobic interfaces away from the lipid solvent. For binding of nonpolar surfaces in aqueous solution, the driving force is often attributed to the hydrophobic effect, but this should not apply in the membrane since there is very little water. To investigate this further, we quantified the thermodynamic changes associated with CLC dimerization in membranes by carrying out a van ‘t Hoff analysis of the temperature dependency of the free energy of dimerization, Δ
G°
. To ensure that the reaction reached equilibrium at different temperatures, we utilized a Förster resonance energy transfer assay to report on relaxation kinetics of subunit exchange as a function of temperature. Equilibration times were then applied to measure CLC-ec1 dimerization isotherms at different temperatures using the single-molecule subunit-capture photobleaching analysis approach. The results demonstrate that the dimerization free energy of CLC in
Escherichia coli
–like membranes exhibits a nonlinear temperature dependency corresponding to a large, negative change in heat capacity, a signature of solvent ordering effects such as the hydrophobic effect. Consolidating this with our previous molecular analyses suggests that the nonbilayer defect required to solvate the monomeric state is one source of the observed change in heat capacity and indicates the existence of a generalizable driving force for protein association in membranes.
Analysis of the risk and pre-emptive control of viral outbreaks accounting for within-host dynamics: SARS-CoV-2 as a case study
Authors: Hart William S. , Park Hyeongki , Jeong Yong Dam , Kim Kwang Su , Yoshimura Raiki , Thompson Robin N. , Iwami Shingo
Published: October 2023

In the era of living with COVID-19, the risk of localised SARS-CoV-2 outbreaks remains. Here, we develop a multiscale modelling framework for estimating the local outbreak risk for a viral disease (the probability that a major outbreak results from a single case introduced into the population), accounting for within-host viral dynamics. Compared to population-level models previously used to estimate outbreak risks, our approach enables more detailed analysis of how the risk can be mitigated through pre-emptive interventions such as antigen testing. Considering SARS-CoV-2 as a case study, we quantify the within-host dynamics using data from individuals with omicron variant infections. We demonstrate that regular antigen testing reduces, but may not eliminate, the outbreak risk, depending on characteristics of local transmission. In our baseline analysis, daily antigen testing reduces the outbreak risk by 45% compared to a scenario without antigen testing. Additionally, we show that accounting for heterogeneity in within-host dynamics between individuals affects outbreak risk estimates and assessments of the impact of antigen testing. Our results therefore highlight important factors to consider when using multiscale models to design pre-emptive interventions against SARS-CoV-2 and other viruses.
The duplication of genomes and genetic networks and its potential for evolutionary adaptation and survival during environmental turmoil
Authors: Ebadi Mehrshad , Bafort Quinten , Mizrachi Eshchar , Audenaert Pieter , Simoens Pieter , Van Montagu Marc , Bonte Dries , Van de Peer Yves
Published: October 2023

The importance of whole-genome duplication (WGD) for evolution is controversial. Whereas some view WGD mainly as detrimental and an evolutionary dead end, there is growing evidence that polyploidization can help overcome environmental change, stressful conditions, or periods of extinction. However, despite much research, the mechanistic underpinnings of why and how polyploids might be able to outcompete or outlive nonpolyploids at times of environmental upheaval remain elusive, especially for autopolyploids, in which heterosis effects are limited. On the longer term, WGD might increase both mutational and environmental robustness due to redundancy and increased genetic variation, but on the short—or even immediate—term, selective advantages of WGDs are harder to explain. Here, by duplicating artificially generated Gene Regulatory Networks (GRNs), we show that duplicated GRNs—and thus duplicated genomes—show higher signal output variation than nonduplicated GRNs. This increased variation leads to niche expansion and can provide polyploid populations with substantial advantages to survive environmental turmoil. In contrast, under stable environments, GRNs might be maladaptive to changes, a phenomenon that is exacerbated in duplicated GRNs. We believe that these results provide insights into how genome duplication and (auto)polyploidy might help organisms to adapt quickly to novel conditions and to survive ecological uproar or even cataclysmic events.
Global, glocal or local?
Authors: Li Xiangdong
Published: October 2023

Local (peripheral) social sciences and humanities journals are underrepresented in major indexes due to
linguistic, ideological, and disciplinary bias. To seek international visibility without sacrificing their local identity, they
are adopting translation-mediated bilingual publishing to construct a new identity. Since bilingual publishing is a new trend,
what identity is being constructed is rarely investigated. This article aims to explore the linguistic, content, and communicated
identity of those journals. Content analysis was used to review the language policies (websites, article abstracts, and full
articles), the composition of editorial teams, pools of contributors, instructions to authors, journal overviews, and website
logos or journal covers of sixty-eight peripheral social sciences and humanities journals. The results indicate that the majority
are attempting to construct a glocal identity, a hybrid identity to maintain their unique status as a local journal and
simultaneously strive for better recognition in the international community. Another finding is that the journals are divided in
terms of communicated identity, causing obstacles to the successful construction of a new identity. This study provides evidence
on the construction of a glocal identity by bilingually published peripheral journals and has implications for the strategic use
of linguistic and non-linguistic resources in identity construction.
Threshold and surface potential-based sensitivity analysis of symmetrical double gate AlGaN/GaN MOS-HEMT including capacitance effects for label-free biosensing
Authors: Sriramani P , Mohankumar N , Prasamsha Y , Sarkar Angsuman , Chanda Manash
Published: October 2023

This paper presents an analytical framework, based on the surface potential for a symmetrical double-gate AlGaN/GaN Metal oxide semiconductor high electron mobility transistor (DG-MOSHEMT) equipped with an embedded nanocavity tailored for biomedical sensing applications. The proposed model operates on the dielectric modulation principle and meticulously scrutinizes the device’s performance using critical sensing metrics such as threshold voltage shift (ΔVth), threshold voltage sensitivity (SVth), surface potential shift (ΔΨs,0), and surface potential sensitivity (SΨs,0). The model demonstrates remarkable sensitivity in detecting minute biomolecule variations, explicitly focusing on streptavidin, uricase, protein, and ChOx as the target biomolecules. Additionally, analytical equations based on surface potential are established to accurately determine gate charges (QG), gate-to-drain capacitance (CGD), and gate-to-source capacitance (CGS). The thorough investigation of biomolecule effects on gate capacitance holds paramount significance as it plays a vital and profound role in dictating device performance. Furthermore, variations in nanocavity length, AlGaN layer thickness, and oxide layer thickness are explored to understand their influence on ΔVth and SVth. The proposed model exhibits a remarkable improvement in both threshold voltage shift and sensitivity compared to the single MOS-HEMT. Notably, it demonstrates substantial enhancements of 2.06, 1.72, 1.49, and 1.5 times for the uricase, streptavidin, protein, and ChOx biomolecules, in terms of threshold voltage shift, and impressive improvements of 10.7%, 14.5%, 18.2%, and 50% for the same biomolecules, respectively, in terms of threshold voltage sensitivity, surpassing the previous findings. Uricase exhibited the most significant shift in surface potential (ΔΨs,0) among the analyzed biomolecules, with a value of 100 mV mm−1 and a sensitivity (SΨs,0) of 0.44. In contrast, ChOx showed a modest (ΔΨs,0) of 24 mV mm−1 with a relative sensitivity (SΨs,0) value of 0.108. Increasing nanocavity length and oxide layer thickness positively contribute to ΔVth and SVth. Moreover, while an increase in AlGaN layer thickness enhances ΔVth performance, its impact on SVth is minimal.