分类： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间： 2021-12-18
摘要： True random number generator (TRNG) is an important component for modern information security technologies. Among the candidates, TRNG with spin-orbit torque (SOT)-induced probabilistic magnetization switching is competitive for its advantages in anti-radiation, unlimited endurance, robust stability, and broad temperature range. However, realization of a SOT-TRNG requires intensive understanding of the magnetic dynamic process under a spin-orbit current. Here, we performed micromagnetic simulation of the SOT-induced probabilistic magnetization switching by using Mumax 3. Without thermal noise, identical magnetic moment precessions were found between repeated simulation cycles, resulting in deterministic magnetization switching. When thermal noises were taken into account, stochastic precession trails and thereby probabilistic magnetization switching were finally obtained. Our results suggest the Mumax 3 to be a practical tool for simulating the probabilistic magnetization switching behavior of a SOT-TRNG, as well as highlighting the crucial role of thermal noise during the during the simulation.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： At a fixed frequency, a general wave field in an open optical waveguide is a sum of finite number of guided modes and an integral of radiation modes. Most studies on open lossless dielectric waveguides are concerned with regular guided modes which are confined around the waveguide core, have a real propagation constant, and propagate along the waveguide axis without attenuation. However, there may be guided modes with a complex propagation constant even though the waveguide consists of lossless isotropic dielectric materials, and they are the so-called complex modes. The complex modes are proper modes confined around the waveguide core, and are different from the leaky modes which have divergent wave fields in the transverse plane. For waveguides with discontinuities and defects, the complex modes can be excited and must be included in eigenmode expansions. However, existing studies on complex modes in open lossless dielectric waveguides are very limited. In this Letter, we consider circular fibers and silicon waveguides, study the formation mechanism of complex modes, and calculate the dispersion relations for several complex modes in each waveguide. For circular fibers, we also determine the minimum refractive-index ratio for the existence of complex modes. Our study fills a gap in optical waveguide theory and provides a basis for realizing potential applications of complex modes.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： We study the possibility that the long term red timing-noise in pulsars originates from the evolution of the magnetic inclination angle χ. The braking torque under consideration is a combination of the dipole radiation and the current loss. We find that the evolution of χ can give rise to extra cubic and fourth-order polynomial terms in the timing residuals. These two terms are determined by the efficiency of the dipole radiation, the relative electric-current density in the pulsar tube and χ. The following observation facts can be explained with this model: a) young pulsars have positive ν¨; b) old pulsars can have both positive and negative ν¨; c) the absolute values of ν¨ are proportional to −ν˙; d) the absolute values of the braking indices are proportional to the characteristic ages of pulsars. If the evolution of χ is purely due to rotation kinematics, then it can not explain the pulsars with braking index less than 3, and thus the intrinsic change of the magnetic field is needed in this case. Comparing the model with observations, we conclude that the drift direction of χ might oscillate many times during the lifetime of a pulsar. The evolution of χ is not sufficient to explain the rotation behavior of the Crab pulsar, because the observed χand χ˙ are inconsistent with the values indicated from the timing residuals using this model.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： The Wilkinson Microwave Anisotropy Probe (WMAP) team subtracted template-based foreground models to produce foreground-reduced maps, and masked point sources and uncertain sky regions directly; however, whether foreground residuals exist in the WMAP foreground-reduced maps is still an open question. Here, we use Pearson correlation coefficient (PCC) analysis with AS-γ TeV cosmic ray (CR) data to probe possible foreground residuals in the WMAP nine-year data. The correlation results between the CR and foreground-contained maps (WMAP foreground-unreduced maps, WMAP template-based and MEM foreground models) suggest that: (1) CRs can trace foregrounds in the WMAP data; (2) at least some TeV CRs originate from the Milky Way; (3) foregrounds may be related to the existence of CR anisotropy (loss-cone and tail-in structures); (4) there exist differences among different types of foregrounds in the declination range of <15∘. Then, we generate 10,000 mock CMB sky maps to describe the cosmic variance, which is used to measure the effect of the fluctuations of all possible CMB maps to the correlations between CR and CMB maps. Finally, we do correlation analysis between the CR and WMAP foreground-reduced maps, and find that: (1) there are significant anticorrelations; and (2) the WMAP foreground-reduced maps are credible. However, the significant anticorrelations may be accidental, and the higher signal-to-noise ratio (SNR) Planck SMICA map cannot reject the hypothesis of accidental correlations. We therefore can only conclude that the foreground residuals exist with ∼ 95\% probability.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： The orientations of the red galaxies in a filament are aligned with the orientation of the filament. We thus develop a location-alignment-method (LAM) of detecting filaments around clusters of galaxies, which uses both the alignments of red galaxies and their distributions in two-dimensional images. For the first time, the orientations of red galaxies are used as probes of filaments. We apply LAM to the environment of Coma cluster, and find four filaments (two filaments are located in sheets) in two selected regions, which are compared with the filaments detected with the method of \cite{Falco14}. We find that LAM can effectively detect the filaments around a cluster, even with 3σ confidence level, and clearly reveal the number and overall orientations of the detected filaments. LAM is independent of the redshifts of galaxies, and thus can be applied at relatively high redshifts and to the samples of red galaxies without the information of redshifts. We also find that the images of background galaxies (interlopers) which are lensed by the gravity of foreground filaments are amplifiers to probe the filaments.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： Precise spectra of 3C 279 in the 0.5-70 keV range, obtained during two epochs of \emph{Swift} and \emph{NuSTAR} observations, are analyzed using a near-equipartition model. We apply a one-zone leptonic model with a three-parameter log-parabola electron energy distribution (EED) to fit the \emph{Swift} and \emph{NuSTAR} X-ray data, as well as simultaneous optical and \emph{Fermi}-LAT γ-ray data. The Markov Chain Monte Carlo (MCMC) technique is used to search the high-dimensional parameter space and evaluate the uncertainties on model parameters. We show that the two spectra can be successfully fit in near-equipartition conditions, defined by the ratio of the energy density of relativistic electrons to magnetic field ζe being close to unity. In both spectra, the observed X-rays are dominated by synchrotron-self Compton photons, and the observed γ rays are dominated by Compton scattering of external infrared photons from a surrounding dusty torus. Model parameters are well constrained. From the low state to the high state, both the curvature of the log-parabola width parameter and the synchrotron peak frequency significantly increase. The derived magnetic fields in the two states are nearly identical (∼1\ G), but the Doppler factor in the high state is larger than that in the low state (∼28 versus ∼18). We derive that the gamma-ray emission site takes place outside the broad-line region, at ≳ 0.1 pc from the black hole, but within the dusty torus. Implications for 3C 279 as a source of high-energy cosmic-rays are discussed.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： We model the evolution of the spin frequency's second derivative ν¨ and the braking index n of radio pulsars with simulations within the phenomenological model of their surface magnetic field evolution, which contains a long-term power-law decay modulated by short-term oscillations. For the pulsar PSR B0329+54, a model with three oscillation components can reproduce its ν¨ variation. We show that the "averaged" n is different from the instantaneous n, and its oscillation magnitude decreases abruptly as the time span increases, due to the "averaging" effect. The simulated timing residuals agree with the main features of the reported data. Our model predicts that the averaged ν¨ of PSR B0329+54 will start to decrease rapidly with newer data beyond those used in Hobbs et al.. We further perform Monte Carlo simulations for the distribution of the reported data in |ν¨| and |n| versus characteristic age τc diagrams. It is found that the magnetic field oscillation model with decay index α=0 can reproduce the distributions quite well. Compared with magnetic field decay due to the ambipolar diffusion (α=0.5) and the Hall cascade (α=1.0), the model with no long term decay (α=0) is clearly preferred for old pulsars by the p-values of the two-dimensional Kolmogorov-Smirnov test.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： We re-estimate the surface magnetic fields of neutron stars (NSs) in Be X-ray binaries (BeXBs) with different models of torque, improved beyond Klus et al. (2014). In particular, a new torque model (Dai \& Li 2006) is applied to three models of magnetosphere radius. Unlike the previous models, the new torque model does not lead to divergent results for any fastness parameter. The inferred surface magnetic fields of these NSs for the two compressed magnetosphere models are much higher than that for the uncompressed magnetosphere model. The new torque model using the compressed-magnetosphere radius (Shi, Zhang \& Li 2014) leads to unique solutions near spin equilibrium in all cases, unlike other models that usually give two branches of solutions. Although our conclusions are still affected by the simplistic assumptions about the magnetosphere radius calculations, we show several groups of possible surface magnetic field values with our new models when the interaction between the magnetosphere and the infalling accretion plasma is considered. The estimated surface magnetic fields for NSs BeXBs in the Large Magellanic Cloud, the Small Magellanic Cloud and the Milk Way are between the quantum critical field and the maximum "virial" value by the spin equilibrium condition.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： We study the dynamic changes of electron energy distribution (EED) through systematically analysing the quasi-simultaneous spectral energy distributions (SEDs) of the flat spectrum radio quasar 3C 279 in different states. With Markov chain Monte Carlo (MCMC) technique we model fourteen SEDs of 3C 279 using a leptonic model with a three-parameter log-parabola electron energy distribution (EED). The 14 SEDs can be satisfactorily fitted with the one-zone leptonic model. The observed γ rays in 13 states are attributed to Compton scattering of external infrared photons from a surrounding dusty torus. The curved γ-ray spectrum observed during 2-8 April 2014 is well explained by the external Compton of dust radiation. It is found that there is a clear positive correlation between the curvature parameter b of the EED and the electron peak energy γ′pk. No clear correlation between b and the synchrotron peak frequency νs is found, due to the varied product of Doppler factor and fluid magnetic field from state to state. We interpret the correlation of b−γ′pk in a stochastic acceleration scenario. This positive correlation is in agreement with the prediction in the stage when the balance between acceleration and radiative cooling of the electrons is nearly established in the case of the turbulence spectral index q=2.
分类： 物理学 >> 核物理学 提交时间： 2016-09-01
摘要： Context: The LIGO consortium announced the first direct detection of gravitation wave event GW150914 from two merging black holes; however the nature of the black holes are still not clear. Aims: We study whether electromagnetic radiation can be detected from merging stellar mass black binaries like GW150914. Methods: We briefly investigate the possible growth and merging processes of the two stellar mass black holes in the merging event of GW150914 detected by aLIGO, as clocked by a distant external observer. Our main results are: (1) The description of the black hole growth using stationary metric of a pre-existing black hole predicts strong electromagnetic radiation from merging black holes, which is inconsistent with GW150914; (2) Only gravitational wave radiation can be produced in the coalescence of two black holes such as that in the GW150914 event, if the black hole growth is described using time-dependent metric considering the influence of the in-falling matter onto a pre-existing black hole, as clocked by a distant external observer. Conclusions: Future high sensitivity detections of gravitational waves from merging black holes might be used to probe matter distribution and space-time geometry in the vicinity of the horizon. Perhaps the GW150914-like events can be identified with traditional astronomy observations only if the black holes are embedded in extremely dense medium before their final merge, when very strong electromagnetic radiation is produced and can escape from the system.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the late inspiral phase of a double neutron star (NS) or NS-black hole system in which one NS is a magnetar, the tidal force on the magnetar arisen from its companion will increase dramatically as the binary approaches. The tidal-induced deformation may surpass the maximum that the magnetar's crust can sustain just seconds or subseconds before the coalescence. A catastrophic global crust destruction may thus occur, and the magnetic energy stored in the magnetar's interior will have the opportunity to be released, which would be observed as a superflare with energy 100s of times larger than giant flares of magnetars. Such a mechanism can naturally explain the recently observed precursor of GRB 211211A, including its quasiperiodic oscillation. We predict that in the coming gravitational wave O4/O5 period, there could be a fraction of detected double NS mergers associated with such super flares. If observed, copious information on the structure and magnetic field in an NS interior can be obtained, which is hard to study elsewhere.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Scientific Complementary Metal Oxide Semiconductor (sCMOS) sensors are finding increasingly more applications in astronomical observations, thanks to their advantages over charge-coupled devices (CCDs) such as a higher readout frame rate, higher radiation tolerance, and higher working temperature. In this work, we investigate the performance at the individual pixel level of a large-format sCMOS sensor, GSENSE1516BSI, which has 4096 * 4096 pixels, each of 15 {\mu}m in size. To achieve this, three areas on the sCMOS sensor, each consisting of 99 * 99 pixels, are chosen for the experiment. The readout noise, conversion gain and energy resolutions of the individual pixels in these areas are measured from a large number (more than 25,000) of X-ray events accumulated for each of the pixels through long time exposures. The energy resolution of these pixels can reach 140 eV at 6.4 keV at room temperature and shows a significant positive correlation with the readout noise. The accurate gain can also be derived individually for each of the pixels from its X-ray spectrum obtained. Variations of the gain values are found at a level of 0.56% statistically among the 30 thousand pixels in the areas studied. With the gain of each pixel determined accurately, a precise gain correction is performed pixel by pixel in these areas, in contrast to the standardized ensemble gain used in the conventional method. In this way, we could almost completely eliminate the degradation of energy resolutions caused by gain variations among pixels. As a result, the energy resolution at room temperature can be significantly improved to 124.6 eV at 4.5 keV and 140.7 eV at 6.4 keV. This pixel-by-pixel gain correction method can be applied to all kinds of CMOS sensors, and is expected to find interesting applications in X-ray spectroscopic observations in the future.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Scientific Complementary Metal Oxide Semiconductor (sCMOS) sensors are finding increasingly more applications in astronomical observations, thanks to their advantages over charge-coupled devices (CCDs) such as a higher readout frame rate, higher radiation tolerance, and higher working temperature. In this work, we investigate the performance at the individual pixel level of a large-format sCMOS sensor, GSENSE1516BSI, which has 4096 * 4096 pixels, each of 15 {\mu}m in size. To achieve this, three areas on the sCMOS sensor, each consisting of 99 * 99 pixels, are chosen for the experiment. The readout noise, conversion gain and energy resolutions of the individual pixels in these areas are measured from a large number (more than 25,000) of X-ray events accumulated for each of the pixels through long time exposures. The energy resolution of these pixels can reach 140 eV at 6.4 keV at room temperature and shows a significant positive correlation with the readout noise. The accurate gain can also be derived individually for each of the pixels from its X-ray spectrum obtained. Variations of the gain values are found at a level of 0.56% statistically among the 30 thousand pixels in the areas studied. With the gain of each pixel determined accurately, a precise gain correction is performed pixel by pixel in these areas, in contrast to the standardized ensemble gain used in the conventional method. In this way, we could almost completely eliminate the degradation of energy resolutions caused by gain variations among pixels. As a result, the energy resolution at room temperature can be significantly improved to 124.6 eV at 4.5 keV and 140.7 eV at 6.4 keV. This pixel-by-pixel gain correction method can be applied to all kinds of CMOS sensors, and is expected to find interesting applications in X-ray spectroscopic observations in the future.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the late inspiral phase of a double neutron star (NS) or NS-black hole system in which one NS is a magnetar, the tidal force on the magnetar arisen from its companion will increase dramatically as the binary approaches. The tidal-induced deformation may surpass the maximum that the magnetar's crust can sustain just seconds or subseconds before the coalescence. A catastrophic global crust destruction may thus occur, and the magnetic energy stored in the magnetar's interior will have the opportunity to be released, which would be observed as a superflare with energy 100s of times larger than giant flares of magnetars. Such a mechanism can naturally explain the recently observed precursor of GRB 211211A, including its quasiperiodic oscillation. We predict that in the coming gravitational wave O4/O5 period, there could be a fraction of detected double NS mergers associated with such super flares. If observed, copious information on the structure and magnetic field in an NS interior can be obtained, which is hard to study elsewhere.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In recent years, scientific Complementary Metal Oxide Semiconductor (sCMOS) devices have been increasingly applied in X-ray detection, thanks to their attributes such as high frame rate, low dark current, high radiation tolerance and low readout noise. We tested the basic performance of a backside-illuminated (BSI) sCMOS sensor, which has a small pixel size of 6.5 um * 6.5 um. At a temperature of -20C, The readout noise is 1.6 e, the dark current is 0.5 e/pixel/s, and the energy resolution reaches 204.6 eV for single-pixel events. The effect of depletion depth on the sensor's performance was also examined, using three versions of the sensors with different deletion depths. We found that the sensor with a deeper depletion region can achieve a better energy resolution for events of all types of pixel splitting patterns, and has a higher efficiency in collecting photoelectrons produced by X-ray photons. We further study the effect of depletion depth on charge diffusion with a center-of-gravity (CG) model. Based on this work, a highly depleted sCMOS is recommended for applications of soft X-ray spectroscop.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In recent years, scientific Complementary Metal Oxide Semiconductor (sCMOS) devices have been increasingly applied in X-ray detection, thanks to their attributes such as high frame rate, low dark current, high radiation tolerance and low readout noise. We tested the basic performance of a backside-illuminated (BSI) sCMOS sensor, which has a small pixel size of 6.5 um * 6.5 um. At a temperature of -20C, The readout noise is 1.6 e, the dark current is 0.5 e/pixel/s, and the energy resolution reaches 204.6 eV for single-pixel events. The effect of depletion depth on the sensor's performance was also examined, using three versions of the sensors with different deletion depths. We found that the sensor with a deeper depletion region can achieve a better energy resolution for events of all types of pixel splitting patterns, and has a higher efficiency in collecting photoelectrons produced by X-ray photons. We further study the effect of depletion depth on charge diffusion with a center-of-gravity (CG) model. Based on this work, a highly depleted sCMOS is recommended for applications of soft X-ray spectroscop.
分类： 天文学 >> 天文学 提交时间： 2024-02-28 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： We conduct a statistical analysis of the hardness ratio (HR) for bright sources in the 4 yr Galactic Plane Scanning Survey catalog of Insight-HXMT. Depending on the stable (variable) flux Fs (Fv) or spectrum Ss(Sv) of each source, the bright sources are classified into three groups: Fv&Sv, Fv&Ss, and Fs&Ss. Our study of the HR characteristics in different types of sources reveals that accretion-powered neutron star (NS) low-mass X-ray binaries (LMXBs) exhibit softer energy spectra than NS high-mass X-ray binaries (HMXBs), but harder energy spectra than black hole binaries in most cases. This difference is probably due to their different magnetic field strengths. Additionally, Fv&Sv LMXBs tend to be harder than Fv&Ss LMXBs below 7 keV, while the opposite is true for HMXBs. Our results suggest that LMXBs may dominate unclassified sources, and NS binaries are likely to be the primary type of X-ray binaries with ambiguous compact stars. By comparing the HR of transient sources in their outburst and low-flux states, it is found that the averaged HR of four sources in the two states are roughly comparable within uncertainties. We also investigate the spatial properties of the three groups and find that Fv&Sv sources are mainly located in the longitude of −20° < l < 9°, Fv&Ss sources cross the Galactic Plane, and Fs&Ss sources are predominantly concentrated in 19° < l < 42°. In addition, analyzing the HR spatial distributions shows the absorption of soft X-rays (primarily below 2 keV) in the Galactic Plane.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Jiewei Guo
Zhi Zhang
Nan Zhang
Binpeng Shang
Jiayun Xue
Yuezheng Wang
Shishi Tao
Bofu Xie
Lanjun Guo
Lie Lin
Weiwei Liu
摘要： In this work, sub-ppb aerosol detection is achieved by femtosecond laser filament with a single pulse energy of 4 mJ at a distance of 30 m. A concave mirror with an open aperture of 41.4 cm is employed in an off-axis optical system to focus the femtosecond laser beam and collect the fluorescence of NaCl aerosol. The simulation and experimental results show that the astigmatism can be greatly reduced when femtosecond laser beam is incident non-symmetrically on the concave mirror. Compared with the case that femtosecond laser strikes at the center of the concave mirror, the intensity of the optical filament is increased by 69.5 times, and the detection of limit of sodium chloride aerosol is reduced by 86%, which is down to 0.32 ppb. The improved excitation scheme in this work utilizes the nonsymmetrical beam spot on the concave mirror to compensate the non-symmetry induced by the off-axis setup, reducing the astigmatism of the focusing laser beam and improving the aerosol's detection of limit.
分类： 物理学 >> 核物理学 提交时间： 2016-08-30
Xue-Feng Wu
He Gao
Jun-Jie Wei
Xi-Long Fan
Peter M´esz´aros
Bing Zhang
Zi-Gao Dai
Shuang-Nan Zhang
Zong-Hong Zhu
摘要： A conservative constraint on the Einstein Equivalence Principle (EEP) can be obtained under the assumption that the observed time delay between correlated particles from astronomical sources is dominated by the gravitational fields through which they move. Current limits on the EEP are mainly based on the observed time delays of photons with different energies, and it is highly desirable to develop more accurate tests involving different types of particles. The detection by the advanced LIGO/VIRGO systems of gravitational waves (GWs) will provide attractive candidates for constraining the EEP, which would further extend the tested particle species to the gravitons, with potentially higher accuracy. Considering the capabilities of the advanced LIGO/VIRGO network and the source direction uncertainty, we show that the joint detection of GWs and electromagnetic signals can potentially probe the EEP to an accuracy of 10−11, which is several orders of magnitude tighter than previous limits.
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