The Cauchy Problem for a Class of Semilinear Wave Equations with Piecewise Constants Data

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一次强沙尘暴长距离输送的数值模拟研究

利用HYSPLIT-4传输,扩散模式对2003年4月9日发生在我国西北的强沙尘暴进行长距离输送的数值模拟研究,并进行轨迹和浓度分析.研究结果表明:(1)2003年4月9日强沙尘暴过程的沙尘来源并非某单一地区;(2)此次沙尘暴长距离输送过程中,主要有两个高浓度中心向东传输.一个在北纬35度附近,主要在1 500～3000m高空传输,另一个在北纬40度附近,且主要在1 500m以下传输.后期两者合二为一.     

Gain Assisted Raman Induced Classical and Quantum Talbot Imaging

2D Raman generated classical and quantum Talbot imaging is proposed in a three-level gain assisted system. First, a 2D Raman induced grating (RIG) will be constructed by modulating transmission function in the weak probe channel using a strong control standing wave field. Furthermore, RIG will diffract a probe field, by shining a probing light beam on an optically generated lattice within a rubidium vapor cell. This study uses gain assisted Raman medium [Nature 406 , 277 (2000)] to examine classical and quantum Talbot imaging. In the case of Raman-induced classical imaging, the diffraction pattern repeats itself at planes with integer multiple Talbot lengths. Additionally, by taking into account entangled photon pairs, the scenario of Raman-induced quantum imaging is investigated. This study also looks at the RIG's amplitude and phase information with adjustable image size variation. As a result of the gain feature and zero absorption, this system is anticipated to be more suitable from the perspective of application. This analysis may pave the way for further research into the Talbot effect's nonlinear and quantum dynamical properties. Also, it provide a non-destructive, lensless method for imaging very cold atoms or molecules.     

Polarimetric-Spectral-Sensitive Compressed Ultrafast Photography Enables Real-Time Intensity Visualization of Time-Varying Polarized Ultrafast Laser Pulses

Ultrafast laser pulses with complex spatiotemporal and polarization couplings have shown great application prospects in coherent control, particle acceleration, molecular dynamics excitation, and chiral or anisotropic detection. It is very important to observe the polarization-coupled ultrafast laser pulses for characterizing the performance of laser source and understanding the laser-matter interaction, but there is currently no detection technique that can completely characterize them, including the spatio-, spectral-, and polarimetric-temporal information. In this work, a polarimetric-spectral-sensitive has been compressed ultrafast photography (PS-CUP) to realize the real-time intensity visualization of time-varying polarized (TP) ultrafast laser pulses. PS-CUP can not only distinguish the polarization state of a TP pulse, but also realize the spatio-, spectral- and polarimetric-temporal measurement. To demonstrate the ability of polarization resolving detection, PS-CUP is used to successfully distinguish between the sinistral and dextral TP pulses and measure the angle and degree of linear polarization of a dextral TP pulse, respectively, and the experimental results are highly consistent with theoretical simulations. Owing to the unprecedented multidimensional detection ability, PS-CUP is prospected to provide a powerful tool for the diagnosis of various complex ultrafast laser pulses and the detection of ultrafast chiral optics.     

Enhanced Terahertz Phonon Polariton in Lithium Niobate Chip

Terahertz (THz) phonon polaritons, fundamental quasi-particles that couple lattice vibrations with electromagnetic fields at THz frequencies, are found in a variety of materials that offer the potential for a wide range of THz optoelectronic devices and on-chip integrated systems. However, these compact devices and on-chip systems are hampered by the absence of on-chip powerful THz phonon polariton sources. In this study, the efficient generation and amplification of THz phonon polaritons are proposed and directly visualized on a lithium niobate (LN) chip via a tilted pulsefront phase matching technique. By combining lateral pumping and phase matching schemes, two orders of magnitude are successfully attained in the interaction distance between the pump light and the LN chip, accompanied by a substantial amplification of generated THz phonon polariton. The results of this study may lead to abundant potential applications in chip scale THz photonic devices and systems based on LN materials and its integrated heterostructures.     

Neural network representations of quantum many-body states

Machine learning is currently the most active interdisciplinary field having numerous applications;additionally,machine-learning techniques are used to research quantum many-body problems.In this study,we first propose neural network quantum states(NNQSs)with general input observables and explore a few related properties,such as the tensor product and local unitary operation.Second,we determine the necessary and sufficient conditions for the representability of a general graph state using normalized NNQS.Finally,to quantify the approximation degree of a given pure state,we define the best approximation degree using normalized NNQSs.Furthermore,we observe that some 7V-qubit states can be represented by a normalized NNQS,such as separable pure states,Bell states and GHZ states.     

Dark energy versus modified gravity: Impacts on measuring neutrino mass

In this paper,we make a comparison for the impacts of smooth dynamical dark energy,modified gravity,and interacting dark energy on the cosmological constraints on the total mass of active neutrinos.For definiteness,we consider theΛCDM model,the w CDM model,the f(R)model,and two typical interacting vacuum energy models,i.e.,the IΛCDM1 model with Q=βHρc and the IΛCDM2 model with Q=βHρΛ.In the cosmological fits,we use the Planck 2015 temperature and polarization data,in combination with other low-redshift observations including the baryon acoustic oscillations,the type Ia supernovae,the Hubble constant measurement,and the large-scale structure observations,such as the weak lensing as well as the redshift-space distortions.Besides,the Planck lensing measurement is also employed in this work.We find that,the w CDM model favors a higher upper limit on the neutrino mass compared to theΛCDM model,while the upper limit in the f(R)model is similar with that in theΛCDM model.For the interacting vacuum energy models,the IΛCDM1 model favors a higher upper limit on neutrino mass,while the IΛCDM2 model favors an identical neutrino mass with the case ofΛCDM.     

An improved evaluation of the neutron background in the PandaX-Ⅱ experiment

In dark matter direct detection experiments,neutron is a serious source of background,which can mimic the dark matter-nucleus scattering signals.In this paper,we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach.Instead of fully relying on the Monte Carlo simulation,the overall neutron background is determined from the neutron-induced high energy signals in the data.In addition,the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator,where the correlated emission of neutron(s)andγ(s)in the(α,n)reactions and spontaneous fissions is taken into consideration.With this method,the neutron backgrounds in the Run 9(26-ton-day)and Run 10(28-ton-day)data sets of PandaX-II are estimated to be(0.66±0.24)and(0.47±0.25)events,respectively.     

CaPtAs: A new noncentrosymmetric superconductor

We report the discovery of a new noncentrosymmetric superconductor CaPtAs.It crystallizes in a tetragonal structure(space group I41md,No.109),featuring three dimensional honeycomb networks of Pt-As and a much elongated c-axis(a=b=4.18?,and c=43.70?).The superconductivity of CaPtAs with Tc=1.47 K was characterized by means of electrical resistivity,specific heat,and ac magnetic susceptibility.The electronic specific heat Ce(T)/T shows evidence for a deviation from the behavior of a conventional BCS superconductor,and can be reasonably fitted by a p-wave model.The upper critical fieldμ0Hc2 of CaPtAs exhibits a moderate anisotropy,with an in-plane value of around 204 mT and an out-of-plane value of 148 mT.Density functional theory calculations indicate that the Pt-5 d and As-4 p orbitals mainly contribute to the density of states near the Fermi level,showing that the Pt-As honeycomb networks may significantly influence the superconducting properties.     

The High Energy X-ray telescope (HE) onboard the Insight-HXMT astronomy satellite

The Insight-Hard X-ray Modulation Telescope(Insight-HXMT) is a broadband X-ray and γ-ray(1-3000 ke V) astronomy satellite. One of its three main telescopes is the High Energy X-ray telescope(HE). The main detector plane of HE comprises 18 Na I(Tl)/Cs I(Na) phoswich detectors, where Na I(Tl) is used as the primary detector to measure ~ 20-250 ke V photons incident from the field of view(FOV) defined by collimators, and Cs I(Na) is used as the active shielding detector to Na I(Tl) by pulse shape discrimination. Additionally, Cs I(Na) is used as an omnidirectional γ-ray monitor. The HE collimators have a diverse FOV,i.e. 1.1°×5.7°(15 units), 5.7°×5.7°(2 units), and blocked(1 unit). Therefore, the combined FOV of HE is approximately5.7°×5.7°. Each HE detector has a diameter of 190 mm resulting in a total geometrical area of approximately 5100 cm2, and the energy resolution is ~15% at 60 ke V. For each recorded X-ray event by HE, the timing accuracy is less than 10 μs and the deadtime is less than 10 μs. HE is used for observing spectra and temporal variability of X-ray sources in the 20-250 ke V band either by pointing observations for known sources or scanning observations to unveil new sources. Additionally, HE is used for monitoring the γ-ray burst in 0.2-3 Me V band. This paper not only presents the design and performance of HE instruments but also reports results of the on-ground calibration experiments.