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A rotating black hole can be clouded by light bosons via superradiance and thus acquire an atom-like structure. If such a gravitational atom system is accompanied by a pulsar, the pulsar can trigger transitions between energy levels of the gravitational atom, and these transitions can be detected by pulsar timing. We show that in such pulsar–black hole systems, fine and hyperfine structure transitions are more likely to be probed than the Bohr transition. Also, the calculation of these fine and hyperfine structure transitions are under better analytic control. Thus, these fine and hyperfine structure transitions are more ideal probes in the search for gravitational collider signals in pulsar–black hole systems. [ABSTRACT FROM AUTHOR]

The behavior of the axial group speeds of trapped sausage modes plays an important role in determining impulsively generated wave trains, which have often been invoked to account for quasi-periodic signals with quasi-periods of the order of seconds in a considerable number of coronal structures. We conduct a comprehensive eigenmode analysis, both analytically and numerically, on the dispersive properties of sausage modes in pressureless tubes with three families of continuous radial density profiles. We find a rich variety of the dependence on the axial wavenumber k of the axial group speed . Depending on the density contrast and profile steepness as well as on the detailed profile description, the curves either possess or do not possess cutoff wavenumbers, and they can behave in either a monotonical or non-monotonical manner. With time-dependent simulations, we further show that this rich variety of the group speed characteristics heavily influences the temporal evolution and Morlet spectra of impulsively generated wave trains. In particular, the Morlet spectra can look substantially different from the “crazy tadpoles” found for the much-studied discontinuous density profiles. We conclude that it is necessary to re-examine available high-cadence data to look for the rich set of temporal and spectral features that can be employed to discriminate between the unknown forms of the density distributions transverse to coronal structures. [ABSTRACT FROM AUTHOR]

The frequency dependence of the longitudinal group speeds of trapped sausage waves plays an important role in determining impulsively generated wave trains, which have often been invoked to account for quasi-periodic signals in coronal loops. We examine how the group speeds () depend on angular frequency (ω) for sausage modes in pressureless coronal tubes with continuous transverse density distributions by solving the dispersion relation pertinent to the case where the density inhomogeneity of arbitrary form occurs in a transition layer of arbitrary thickness. We find that in addition to the transverse lengthscale l and density contrast , the group speed behavior also depends on the detailed form of the density inhomogeneity. For parabolic profiles, always decreases with ω first before increasing again, as happens for the much studied top-hat profiles. For linear profiles, however, the behavior of the curves is more complex. When , the curves become monotonical for large values of l. On the other hand, for higher density contrasts, a local maximum exists in addition to a local minimum when coronal tubes are diffuse. With time-dependent computations, we show that the different behavior of group speed curves, the characteristic speeds and in particular, is reflected in the temporal evolution and Morlet spectra of impulsively generated wave trains. We conclude that the observed quasi-periodic wave trains not only can be employed to probe such key parameters as density contrasts and profile steepness, but also have the potential to discriminate between the unknown forms of the transverse density distribution. [ABSTRACT FROM AUTHOR]

Kilonovae are approximately thermal transients, produced by the mergers of binary neutron stars (BNSs) and neutron star (NS)–black hole binaries. As the optical counterpart of the gravitational-wave event GW170817, AT2017gfo is the first kilonova detected with smoking-gun evidence. Its observation offers vital information for constraining the Hubble constant, the sources of cosmic r -process enrichment, and the equation of state of NSs. The 2.5 m Wide-Field Survey Telescope (WFST) operates in six bands (u, g, r, i, z, w), spanning from 320 to 925 nm. It will be completed in the first half of 2023, and with a field-of-view diameter of 3°, aims to detect kilonovae in the near future. In this article, considering the influence of the host galaxies and sky brightness, we generate simulated images to investigate WFST's ability to detect AT2017gfo-like kilonovae. Due to their spectra, host galaxies can significantly impact kilonova detection at longer wavelengths. When kilonovae are at peak luminosity, we find that WFST performs better in the g and r bands and can detect 90% (50%) of kilonovae at a luminosity distance of 248 Mpc (338 Mpc) with 30 s exposures. Furthermore, to reflect the actual efficiency under target-of-opportunity observations, we calculate the total time of follow up under various localization areas and distances. We find that if the localization areas of most BNS events detected during the fourth observing (O4) run of LIGO and Virgo are hundreds of deg2, WFST is expected to find ∼30% of kilonovae in the first two nights following the detection of a GW event produced by a BNS during the O4 period. [ABSTRACT FROM AUTHOR]

We examine the influence of a continuous density structuring transverse to coronal slabs on the dispersive properties of fundamental standing kink and sausage modes supported therein. We derive generic dispersion relations (DRs) governing linear fast waves in pressureless straight slabs with general transverse density distributions, and focus on cases where the density inhomogeneity takes place in a layer of arbitrary width and in arbitrary form. The physical relevance of the solutions to the DRs is demonstrated by the corresponding time-dependent computations. For all profiles examined, the lowest order kink modes are trapped regardless of longitudinal wavenumber k. A continuous density distribution introduces a difference to their periods of ≲13% when k is the observed range relative to the case where the density profile takes a step function form. Sausage modes and other branches of kink modes are leaky at small k, and their periods and damping times are heavily influenced by how the transverse density profile is prescribed, in particular the length scale. These modes have sufficiently high quality to be observable only for physical parameters representative of flare loops. We conclude that while the simpler DR pertinent to a step function profile can be used for the lowest order kink modes, the detailed information on the transverse density structuring needs to be incorporated into studies of sausage modes and higher order kink modes. [ABSTRACT FROM AUTHOR]

The shielding property of cylinder with circular, square, and equilateral triangle holes was investigated by finite element analysis (FEA). The hole area (Shole) plays an important role in magnetic circuit on the surface of cylinder. When Shole is less than the critical area (SH), cylinder with three shapes of holes obtained the same remanent magnetization inside, indicating that the shielding property is unaffected by the shape of the hole. Hence, high-permeability material is the major path of the magnetic field. On the condition of Shole > SH, the sequence of the shielding property is equilateral triangle > square > circular, resulting from magnetoresistance of leakage flux in air dielectric. Besides, the anisotropy of shielding property caused by hole structural differences of the cylinder is evaluated. We find that a good shielding effectiveness is gained in the radial direction, compared with the axis direction. This research focuses on providing a theoretical support for the design of magnetic shield and improvement on the magnetic shielding ability. [ABSTRACT FROM AUTHOR]

The diamond anvil cell-based high-pressure technique is a unique tool for creating new states of matter and for understanding the physics underlying some exotic phenomena. In situ sensing of spin and charge properties under high pressure is crucially important but remains technically challenging. While the nitrogen-vacancy (NV) center in diamond is a promising quantum sensor under extreme conditions, its spin dynamics and the quantum control of its spin states under high pressure remain elusive. In this study, we demonstrate coherent control, spin relaxation, and spin dephasing measurements for ensemble NV centers up to 32.8 GPa. With this in situ quantum sensor, we investigate the pressure-induced magnetic phase transition of a micron-size permanent magnet Nd2Fe14B sample in a diamond anvil cell, with a spatial resolution of ∼2 μm, and sensitivity of ∼20 μT/Hz1/2. This scheme could be generalized to measure other parameters such as temperature, pressure and their gradients under extreme conditions. This will be beneficial for frontier research of condensed matter physics and geophysics. [ABSTRACT FROM AUTHOR]

Impulsively generated sausage wave trains in coronal structures are important for interpreting a substantial number of observations of quasi-periodic signals with quasi-periods of order seconds. We have previously shown that the Morlet spectra of these wave trains in coronal tubes depend crucially on the dispersive properties of trapped sausage waves, the existence of cutoff axial wavenumbers, and the monotonicity of the dependence of the axial group speed on the axial wavenumber in particular. This study examines the difference a slab geometry may introduce, for which purpose we conduct a comprehensive eigenmode analysis, both analytically and numerically, on trapped sausage modes in coronal slabs with a considerable number of density profiles. For the profile descriptions examined, coronal slabs can trap sausage waves with longer axial wavelengths, and the group speed approaches the internal Alfvén speed more rapidly at large wavenumbers in the cylindrical case. However, common to both geometries, cutoff wavenumbers exist only when the density profile falls sufficiently rapidly at distances far from coronal structures. Likewise, the monotonicity of the group speed curves depends critically on the profile steepness right at the structure axis. Furthermore, the Morlet spectra of the wave trains are shaped by the group speed curves for coronal slabs and tubes alike. Consequently, we conclude that these spectra have the potential for inferring the subresolution density structuring inside coronal structures, although their detection requires an instrumental cadence of better than ∼1 s. [ABSTRACT FROM AUTHOR]

Standing sausage modes in flare loops are important for interpreting quasi-periodic pulsations (QPPs) in solar flare light curves. We propose an inversion scheme that consistently uses their periods P and damping times τ to diagnose flare loop parameters. We derive a generic dispersion relation governing linear sausage waves in pressure-less straight tubes, for which the transverse density inhomogeneity takes place in a layer of arbitrary width l and is of arbitrary form. We find that P and τ depend on the combination of where R is the loop radius, L is the looplength, vAi is the internal Alfvén speed, and ρi/ρe is the density contrast. For all the density profiles examined, P and τ experience saturation when L/R ≫ 1, yielding an inversion curve in the space with a specific density profile when L/R is sufficiently large. When applied to a spatially unresolved QPP event, the scheme yields that R/vAi is the best constrained, whereas l/R corresponds to the other extreme. For spatially resolved QPPs, while L/R ≫ 1 cannot be assumed beforehand, an inversion curve remains possible due to additional geometrical constraints. When a spatially resolved QPP event involves another mode, as is the case for a recent event, the full set of can be inferred. We conclude that the proposed scheme provides a useful tool for magneto-seismologically exploiting QPPs. [ABSTRACT FROM AUTHOR]

Electrocatalytic production of hydrogen from water is considered to be a promising and sustainable strategy. In this work, the low-cost nanostructured MoO2/MoS2/MoP heterojunction is successfully synthesized by phosphorization of the pre-prepared urchin-like MoO2/MoS2 nanospheres as the stable, highly efficient electrocatalysis for the hydrogen evolution reaction (HER). The MoO2/MoS2/MoP-800 (MoO2/MoS2 nanospheres are phosphated at 800 °C) displays a catalytic ability for the HER with an overpotential of 135 mV to achieve 10 mA cm−2 and a Tafel slope of 67 mV dec−1 in 0.5 M H2SO4, which is superior to MoO2/MoS2 nanospheres (200 °C; 24 h), MoO2/MoS2/MoP-700 (MoO2/MoS2 nanospheres are phosphated at 700 °C) and MoO2/MoS2/MoP-900 (MoO2/MoS2 nanospheres are phosphated at 900 °C). Meanwhile, the catalyst exhibits superior properties for HER with an overpotential of 145 mV to achieve 10 mA cm−2 and a Tafel slope of 71 mV dec−1 in 1 M KOH solution. Detailed characterizations reveal that the improved HER performances are significantly related to P-doping and the spherical nanostructure. This work not only provides a low-cost selective for electrocatalytic production of hydrogen, but also serves as a guide to optimize the composition and structure of nanocomposites. [ABSTRACT FROM AUTHOR]

In order to efficiently select a specific electrospinning technology to construct multifunctional nanomaterials according to their actual demands, herein, we utilize the same spinning dopes to construct fluorescent-conductive-magnetic trifunctional array. This is a case study to compare the advantages and disadvantages of four electrospinning technologies including conjugate electrospinning (CJE), parallel electrospinning (PE), coaxial electrospinning (CAE) and traditional electrospinning (TE) technologies, and further systematically investigate the differences in structure and properties of the electrospun products. The results indicate that CAE technology is more suitable to prepare multifunctional materials with fluorescent property, and PE technology is more beneficial for the fabrication of Janus-structured multifunctional materials with conductive anisotropy. Janus-structured materials can be constructed by PE and CJE technologies, but CJE technology is a better choice to prepare high pairing-rate Janus structure. TE technology is more suitable for fabricating ordinary nanobelt or nanofiber owing to its easy operation and simple equipment. CAE, PE and CJE technologies are used to construct 1D nanostructures with two functional partitions, and these partitioned nanostructures can help to reduce adverse influences among various starting materials to obtain better multifunctionalities. The research results have important guiding significance for researchers to fabricate multifunctional nanomaterials via selecting a specific electrospinning technology. Highlights • Four electrospinning techniques are comparatively studied using the same spinning dopes. • Merits and demerits of the four electrospinning techniques are exhibited in detail. • Differences in structure and properties of the electrospun products are compared. • Electrospun product has fluorescent-anisotropic conductive-magnetic trifunctionality. • Result can guide the selection of specific electrospinning towards multifunctional material. [ABSTRACT FROM AUTHOR]

There has been considerable interest in sausage modes in photospheric waveguides such as pores and sunspots, and slow surface sausage modes (SSSMs) have been suggested to damp sufficiently rapidly to account for chromospheric heating. Working in the framework of linear resistive magnetohydrodynamics, we examine how efficient electric resistivity and resonant absorption in the cusp continuum can be for damping SSSMs in a photospheric waveguide with equilibrium parameters compatible with recent measurements of a photospheric pore. For SSSMs with the measured wavelength, we find that the damping rate due to the cusp resonance is substantially less strong than theoretically expected with the thin-boundary approximation. The damping-time-to-period ratio (τ/P) we derive for standing modes, equivalent to the damping-length-to-wavelength ratio for propagating modes given the extremely weak dispersion, can reach only ∼180. However, the accepted values for electric resistivity (η) correspond to a regime where both the cusp resonance and resistivity play a role. The values for τ/P attained at the largest allowed η may reach ∼30. We conclude that electric resistivity can be considerably more efficient than the cusp resonance for damping SSSMs in the pore in question, and needs to be incorporated into future studies on the damping of SSSMs in photospheric waveguides in general. [ABSTRACT FROM AUTHOR]

We examine the dispersive properties of linear fast standing modes in transversely nonuniform solar coronal slabs with finite gas pressure, or, equivalently, finite plasma beta. We derive a generic dispersion relation governing fast waves in coronal slabs, for which the continuous transverse distributions of the physical parameters comprise a uniform core, a uniform external medium, and a transition layer (TL) in between. The profiles in the TL are allowed to be essentially arbitrary. Restricting ourselves to the first several branches of fast modes, which are mostly interesting from an observational standpoint, we find that a finite plasma beta plays an at most marginal role in influencing the periods (P), damping times (τ), and critical longitudinal wavenumbers (), when both P and τ are measured in units of the transverse fast time. However, these parameters are in general significantly affected by how the TL profiles are described. We conclude that, for typical coronal structures, the dispersive properties of the first several branches of fast standing modes can be evaluated with the much simpler theory for cold slabs, provided that the transverse profiles are properly addressed and the transverse Alfvén time in cold MHD is replaced with the transverse fast time. [ABSTRACT FROM AUTHOR]

Photoelectric properties of CdZnTe:In samples with distinctive defect distributions are investigated using various techniques. Samples cut from the head (T04) and tail (W02) regions of a crystal ingot show distinct differences in Te inclusion distribution. Obvious difference is not observed in Fourier transform infrared (FTIR) spectra, UV–Vis–NIR transmittance spectra, and I–V measurements. However, carrier mobility of the tip sample is higher than that of the tail according to the laser beam induced current (LBIC) measurements. Low temperature photoluminescence (PL) measurement presents sharp emission peaks of D0X and A0X, and relatively large peak of D0X (or A0X) / Dcomplex for T04, indicating a better crystalline quality. Thermally stimulated current (TSC) spectrum shows higher density of shallow point defects, i.e., Cd vacancies, , etc., in W02 sample, which could be responsible for the deterioration of electron mobility. [ABSTRACT FROM AUTHOR]

High temperature superconducting (HTS) coils are key parts of many AC applications, such as generators, superconducting magnetic energy storage and transformers. AC loss reduction in HTS coils is essential for the commercialization of these HTS devices. Magnetic material is generally used as the flux diverter in an effort to reduce the AC loss in HTS coils. To achieve the greatest reduction in the AC loss of the coils, the flux diverter should be made of a material with low loss and high saturated magnetic density, and the optimization of the geometric size and location of the flux diverter is required. In this paper, we chose Ni-alloy as the flux diverter, which can be processed into a specific shape and size. The influence of the shape and location of the flux diverter on the AC loss characteristics of stacked (RE)BCO tapes is investigated by use of a finite element method. Taking both the AC loss of the (RE)BCO coils and the ferromagnetic loss of the flux diverter into account, the optimal geometry of the flux diverter is obtained. It is found that when the applied current is at half the value of the critical current, the total loss of the HTS stack with the optimal flux diverter is only 18% of the original loss of the HTS stack without the flux diverter. Besides, the effect of the flux diverter on the critical current of the (RE)BCO stack is investigated. [ABSTRACT FROM AUTHOR]

An asymmetric embedded microring resonant system is proposed and fabricated on a silicon-on-insulator (SOI) to achieve slope tunable Fano resonances. The Fano resonances originate from the nonlinear phase shift produced by adding an inner ring coupling with the outer ring. The slope of the Fano resonance can be well tuned to be ultra-high by controlling the microheaters to adjust the phase condition. Experimentally, we observe Fano resonance with a maximum extinction ratio of about 40 dB, and the slope can be tuned from −35 dB nm−1 to −93 dB nm−1, which shows good agreement with the theoretical analysis. This device could find potential applications in ultra-high sensitivity sensing systems. [ABSTRACT FROM AUTHOR]

While standing fast sausage modes in flare loops are often invoked to interpret quasi-periodic pulsations (QPPs) in solar flares, it is unclear as to how they are influenced by the combined effects of a continuous transverse structuring and a finite internal plasma beta (). We derive a generic dispersion relation governing linear sausage waves in straight magnetic tubes for which plasma pressure is not negligible, and the density and temperature inhomogeneities of essentially arbitrary form take place in a layer of arbitrary width. Focusing on fast modes, we find that only weakly influences , the critical longitudinal wavenumber separating the leaky from trapped modes. Likewise, for both trapped and leaky modes, the periods P in units of the transverse fast time depend only weakly on , which is compatible with the fact that the effective wave vectors of fast sausage modes are largely perpendicular to the background magnetic field. However, a weak dependence of the damping times τ is seen only when the length-to-radius ratio L/R is ∼50% larger than some critical value , which itself rather sensitively depends on the density contrast, profile steepness, as well as on how the transverse structuring is described. In the context of QPPs, we conclude that the much simpler zero-beta theory can be employed for trapped modes, as long as one sees the deduced internal Alfvén speed as actually being the fast speed. In contrast, effects due to a finite beta in flare loops should be considered when leaky modes are exploited. [ABSTRACT FROM AUTHOR]

To accomplish their functions, proteins have to achieve different conformations accompanied by conformational transitions. However, the relationship between the preference of amino acids and the stability of the secondary structure is still unclear. Here we perform molecular simulations on a series of helical structures. Our data show that the dissociation energy of the helical structure is related to the preference of amino acids, and the electrostatic repulsion of the residue i and i + 3/4 with the same sign of charge destabilizes the alpha helix. [ABSTRACT FROM AUTHOR]

The measurable wavelength range and the resolution of the ratio-metric wavelength monitor are limited by each other in a conventional structure. To solve this problem we designed and fabricated a high-performance integrated double ratio-metric wavelength measurement device on glass by the method of ion-exchange. It consists of four unbalanced Mach–Zehnder interferometers (MZIs) to form a rough wavelength measurement with a wide range and a fine wavelength measurement with high resolution. The highest measured resolution can reach 10 pm in a 1.6 nm-wide wavelength range for the fine wavelength measurement together with a 45 nm-wide wavelength range for the rough measurement. By heating the unbalanced MZI, the performance of the fine wavelength monitor can be improved. [ABSTRACT FROM AUTHOR]