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Showing papers in "Science China-physics Mechanics & Astronomy in 2022"


Journal ArticleDOI
TL;DR: In this paper, two different inverse design schemes were proposed to study phononic crystal beams using reinforcement learning algorithm to effectively and inversely design the structural parameters to maximize the bandgap width and employ the tandem-architecture neural network to solve the training-difficulty problem caused by inconsistent data.
Abstract: The development of phononic crystals, especially their interaction with topological insulators, allows exploration of the anomalous properties of acoustic/elastic waves for various applications. However, rapidly and inversely exploring the geometry of specific targets remains a major challenge. In this work, we show how machine learning can address this challenge by studying phononic crystal beams using two different inverse design schemes. We first develop the theory of phononic beams using the transfer matrix method. Then, we use the reinforcement learning algorithm to effectively and inversely design the structural parameters to maximize the bandgap width. Furthermore, we employ the tandem-architecture neural network to solve the training-difficulty problem caused by inconsistent data and complete the task of inverse structure design with the targeted topological properties. The two inverse-design schemes have different adaptabilities, and both are characterized by high efficiency and stability. This work provides deep insights into the combination of machine learning, topological property, and phononic crystals and offers a reliable platform for rapidly and inversely designing complex material and structure properties.

16 citations


Journal ArticleDOI
TL;DR: In this paper, the cosmological parameter estimation with the standard siren observations from the LISA-Taiji network was analyzed and it was shown that the standard Siren data from LISA and Taiji can provide much tighter constraints on cosmology parameters, e.g., the constraint precision of w reaches about 4%.
Abstract: LISA and Taiji are expected to form a space-based gravitational-wave (GW) detection network in the future. In this work, we make a forecast for the cosmological parameter estimation with the standard siren observation from the LISA-Taiji network. We simulate the standard siren data based on a scenario with configuration angle of 40° between LISA and Taiji. Three models for the population of massive black hole binary (MBHB), i.e., pop III, Q3d, and Q3nod, are considered to predict the events of MBHB mergers. We find that, based on the LISA-Taiji network, the number of electromagnetic (EM) counterparts detected is almost doubled compared with the case of single Taiji mission. Therefore, the LISA-Taiji network’s standard siren observation could provide much tighter constraints on cosmological parameters. For example, solely using the standard sirens from the LISA-Taiji network, the constraint precision of H0 could reach 1.3%. Moreover, combined with the CMB data, the GW-EM observation based on the LISA-Taiji network could also tightly constrain the equation of state of dark energy, e.g., the constraint precision of w reaches about 4%, which is comparable with the result of CMB+BAO+SN. It is concluded that the GW standard sirens from the LISA-Taiji network will become a useful cosmological probe in understanding the nature of dark energy in the future.

4 citations


Journal ArticleDOI
TL;DR: In this article, the authors presented a detailed spectral analysis of AT2019wey in the low/hard state during its X-ray outburst on the basis of Nuclear Spectroscopic Telescope Array (NSTA) observations.
Abstract: AT2019wey is a new galactic X-ray binary that was first discovered as an optical transient by the Australia Telescope Large Area Survey (ATLAS) on December 7, 2019. AT2019wey consists of a black hole candidate as well as a low-mass companion star ($M_{\text {star }} \lesssim 0.8 M_{\odot}$) and is likely to have a short orbital period ($P_{\text {orb }} \lesssim 8$ h). Although AT2019wey began activation in the X-ray band during almost the entire outburst on March 8, 2020, it did not enter the soft state during the entire outburst. In this study, we present a detailed spectral analysis of AT2019wey in the low/hard state during its X-ray outburst on the basis of Nuclear Spectroscopic Telescope Array \emph observations. We obtain tight constraints on several of its important physical parameters by applying the State-of-art \texttt{relxill} relativistic reflection model family. In particular, we determine that the measured inner radius of the accretion disk is most likely to have extended to the innermost stable circular orbit (ISCO) radius, i.e., $R_{\text{in}}=1.38^{+0.23}_{-0.16}~R_{\text{ISCO}}$. Hence, assuming $R_{\text{in}}$=$R_{\text{ISCO}}$, we find the spin of AT2019wey to be $a_{*}\sim$$0.97$, which is close to the extreme and an inner disk inclination angle of ~$i\sim$$22 ^{\circ}$. Additionally, according to our adopted models, AT2019wey tends to have a relatively high iron abundance of $A_{\mathrm{Fe}}\sim$ 5 $A_{\mathrm{Fe}, \odot}$ and a high disk ionization state of $\log \xi\sim$ 3.4.

3 citations


Journal ArticleDOI
TL;DR: In this paper, a super-radiant maser with a linewidth below millihertz can be achieved with moderate kilohertz incoherent pumping of over 1014 spins at room temperature.
Abstract: Recent experiments have demonstrated Rabi-oscillations, superradiant pulses and stimulated emission from negatively-charged nitrogen-vacancy (NV−) center spins in microwave resonators. These phenomena witness the kind of collective and strong coupling which has been the prerequisite for observation of superradiant lasing in the optical frequency regime. In this article, we investigate the possibility to employ coherence, present in both the collective NV− spin ensemble and the microwave field, to achieve a superradiant maser. Our calculations show that a superradiant maser with a linewidth below millihertz can be achieved with moderate kilohertz incoherent pumping of over 1014 spins at room temperature. We show that the superradiant masing prevails in the presence of inhomogeneous broadening, and we present numerical and analytical studies of the dependence of the phenomenon on the various physical parameters.

3 citations


Journal ArticleDOI
TL;DR: In this article, a resistors, inductors and capacitors (RLC) electrical circuit is proposed to theoretically analyze and fully simulate a non-Hermitian Su-Schrieffer-Heeger (SSH) model with complex hoppings.
Abstract: We propose an resistors, inductors and capacitors (RLC) electrical circuit to theoretically analyze and fully simulate a new type of non-Hermitian Su-Schrieffer-Heeger (SSH) model with complex hoppings. We formulate its construction and investigate its properties by taking advantage of the circuits versatility. Rich physical properties can be identified in this system from the normal modes of oscillation of the RLC circuit, including the highly tunable bulk-edge correspondence between topological winding numbers and edge states and the non-Hermitian skin phenomenon originating from a novel complex energy plane topology. The present study is able to show the wide and appealing topological physics inherent to electric circuits, which is readily generalizable to a plenty of both Hermitian and non-Hermitian nontrivial systems.

3 citations


Journal ArticleDOI
TL;DR: In this paper, the ultrathin photoexcited carriers and coherent phonons in Bi2Te3 thermoelectric films were studied through transient differential transmission spectroscopy, and an ultralow frequency coherent optical phonon at 0.16 THz was ascribed to interlayer breathing modes.
Abstract: The ultrafast dynamics of photoexcited carriers and coherent phonons in ultrathin Bi2Te3 thermoelectric films are studied through transient differential transmission spectroscopy. An ultralow frequency coherent optical phonon at 0.16 THz emerges, especially in ultrathin films, and it is ascribed to interlayer breathing modes. It can divide the ultrathin films into two groups which have out-of-phase vibration along the normal of a film plane, causing a destructive interference between in-plane propagating thermal waves in the two groups of quintuple layers, and thus possibly reducing the thermal conductivity of the ultrathin films. The excitation power dependence of ultrafast dynamics reveals carrier-carrier scattering dominating thermalization, which provides a microscopic understanding of the reported high electrical conductivity and anomalously high power factor of ultrathin Bi2Te3 films at room temperature.

2 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of different Gaussian priors and detector configurations on distance measurement and cosmological research were investigated for short gamma-ray bursts, where the cosine of inclination follows a Gaussian distribution, which may act as a prior in the Bayes analysis.
Abstract: Gravitational waves from binary neutron stars associated with short gamma-ray bursts have drawn considerable attention due to their prospect in cosmology. For such events, the sky locations of sources can be pinpointed with techniques such as identifying the host galaxies. However, the cosmological applications of these events still suffer from the problem of degeneracy between luminosity distance and inclination angle. To address this issue, a technique was proposed in previous study, i.e., using the collimation property of short gamma-ray bursts. Based on the observations, we assume that the cosine of inclination follows a Gaussian distribution, which may act as a prior in the Bayes analysis to break the degeneracy. This paper investigates the effects of different Gaussian priors and detector configurations on distance measurement and cosmological research. We first derive a simplified Fisher information matrix for demonstration, and then conduct quantitative analyses via simulation. By varying the number of third-generation detectors and the scale of prior, we generate four catalogs of 1000 events. It is shown that, in the same detecting period, a network of detectors can recognize more and farther events than a single detector. Besides, adopting tighter prior and employing multiple detectors both decrease the error of luminosity distance. Also considered is the performance of a widely adopted formula in the error budget, which turns out to be a conservative choice in each case. As for cosmological applications, for the ΛCDM model, 500, 200, 600, and 300 events are required for the four configurations to achieve 1% H0 accuracy. With all 1000 events in each catalog, H0 and Ωm can be constrained to (0.66%, 0.37%, 0.76%, 0.49%), and (0.010, 0.006, 0.013, 0.010), respectively. The results of the Gaussian process also show that the gravitational wave standard siren can serve as a probe of cosmology at high redshifts.

2 citations




Journal ArticleDOI
TL;DR: In this article, the surface brightness radial profile of extended gamma-ray sources illuminated by both cosmic ray protons and electrons was investigated, taking into account the radiation mechanisms and projection effects, as well as the response of instruments.
Abstract: The morphologies of the extended $\gamma$-ray sources are governed by the propagation process of parent relativistic particles. In this paper, we investigate the surface brightness radial profile of extended $\gamma$-ray sources illuminated by both cosmic ray protons and electrons, taking into account the radiation mechanisms and projection effects, as well as the response of instruments. We found that the parent particle species as well as the propagation process can cause significant differences in the observed radial profiles. Thus the surface brightness profile can be used as a unique tool to identify the radiation mechanism as well as the propagation process of the parent particles. We also discuss the possible implications regarding the latest discoveries from very/ultra high energy $\gamma$-ray instruments such as LHAASO and HAWC.