A Novel Clutter Suppression Algorithm for Low-Slow-Small Targets Detecting Based on Sparse Adaptive Filtering

Passive detection of low-slow-small(LSS)targets is easily interfered by direct signal and multipath clutter,and the traditional clutter suppression method has the contradiction between step size and convergence rate.In this paper,a frequency domain clutter suppression algorithm based on sparse adaptive filtering is proposed.The pulse compression operation between the error signal and the input reference signal is added to the cost function as a sparsity constraint,and the criterion for filter weight updating is improved to obtain a purer echo signal.At the same time,the step size and penalty factor are brought into the adaptive iteration process,and the input data is used to drive the adaptive changes of parameters such as step size.The proposed algorithm has a small amount of calculation,which improves the robustness to parameters such as step size,reduces the weight error of the filter and has a good clutter suppression performance.

Dzyaloshinskii–Moriya interaction and field-free sub-10 nm topological magnetism in Fe/bismuth oxychalcogenides heterostructures

Topological magnetism with strong robustness,nanoscale dimensions and ultralow driving current density(106 A/m^(2))is promising for applications in information sensing,storage,and processing,and thus sparking widespread research interest.Exploring candidate material systems with nanoscale size and easily tunable properties is a key for realizing practical topological magnetism-based spintronic devices.Here,we propose a class of ultrathin heterostructures,Fe/Bi_(2)O_(2)X(X=S,Se,Te)by deposing metal Fe on quasi-two-dimensional(2D)bismuth oxychalcogenides Bi_(2)O_(2)X(X=S,Se,Te)with excellent ferroelectric/ferroelastic properties.Large Dzyaloshinskii–Moriya interaction(DMI)and topological magnetism can be realized.Our atomistic spin dynamics simulations demonstrate that field-free vortex–antivortex loops and sub-10 nm skyrmions exist in Fe/Bi_(2)O_(2)S and Fe/Bi_(2)O_(2)Se interfaces,respectively.These results provide a possible strategy to tailor topological magnetism in ultrathin magnets/2D materials interfaces,which is extremely vital for spintronics applications.

Exciton Bose–Einstein Condensation in Transition Metal Dichalcogenide Monolayer under In-Plane Magnetic Fields

Based on the Gross–Pitaevskii equation,we theoretically investigate exciton Bose–Einstein condensation(BEC)in transition metal dichalcogenide monolayers(TMDC-MLs)under in-plane magnetic fields.We observe that the in-plane magnetic fields exert a strong influence on the exciton BEC wave functions in TMDC-MLs because of the mixing of the bright and dark exciton states via Zeeman effect.This leads to the brightening of the dark exciton BEC states.The competition between the dipole–dipole interactions caused by the long-range Coulomb interaction and the Zeeman effect induced by the in-plane magnetic fields can effectively regulate dark exciton BEC states.Our findings emphasize the utility of TMD-MLs as platforms for investigating collective phenomenon involving excited states.

大数据时代高校在线教学现状、问题及提升策略研究

随着国家大数据战略的实施以及师生被动分离的学习需要,高校在线教学规模不断滋养壮大,诸多问题也在发展运用之中逐渐显露。基于在线教学平台,从学习者、教学组织者、教学管理者三个层面深度剖析在线教学从规划设计到动态使用再到教学评价全过程所存在的问题,基于问题从不同视角寻求对应的提升策略,通过数据挖掘及学习分析技术,多层次多维度地分析学生的行为数据,合理调整平台的功能模块、学习资源的类型,更好地调动学习者的积极主动性;而教学管理相关人员在此大环境下,以“终身学习、不断提升”的教育理念促使学习者在相互协作、资源共享、反复沟通之中,加深对在线学习体系的认同感和信念感,为大数据环境下在线教学的长远发展及构建在线教育生态体系提出建议。

MoS_(2) on topological insulator Bi_(2)Te_(3) thin films:Activation of the basal plane for hydrogen reduction

2H-MoS_(2) is a well-studied and promising non-noble metal electrocatalyst for heterogeneous reactions,such as the hydrogen evolution reaction(HER).The performance is largely limited by the chemically inert basal plane,which is unfavorable for surface adsorption and reactions.Herein,we report a facile method to boost the HER activities of 2H-MoS_(2) by coupling with epitaxial Bi2Te3 topological insulator films.The as-obtained MoS_(2)/Bi2Te3/SrTiO3 catalyst exhibits prominent HER catalytic activities compared to that of pure MoS_(2) structures,with a 189 mV decrease in the overpotential required to reach a current density of 10 mA cm^(−2) and a low Tafel slope of 58 mV dec−1.Theoretical investigations suggest that the enhanced catalytic activity originates from the charge redistribution at the interface between the Bi2Te3topological insulator films and the MoS_(2) layer.The delocalized sp-derived topological surface states could denote electrons to the MoS_(2) layer and activate the basal plane for hydrogen adsorption.This study demonstrates the potential of manipulating topological surface states to design high-performance electrocatalysts.

Exciton Vortices in Two-Dimensional Hybrid Perovskite Monolayers

We study theoretically the exciton Bose–Einstein condensation and exciton vortices in a two-dimensional(2 D)perovskite(PEA)2 Pb I4 monolayer.Combining the first-principles calculations and the Keldysh model,the exciton binding energy of in a(PEA)2 Pb I4 monolayer can approach hundreds of me V,which make it possible to observe the excitonic effect at room temperature.Due to the large exciton binding energy,and hence the high density of excitons,we find that the critical temperature of the exciton condensation could approach the liquid nitrogen regime.In the presence of perpendicular electric fields,the dipole-dipole interaction between excitons is found to drive the condensed excitons confined in(PEA)2 Pb I4 monolayer flakes into patterned vortices,as the evolution time of vortex patterns is comparable to the exciton lifetime.

Peripheral CD4^(+)CD8^(+) double positive T cells:A potential marker to evaluate renal impairment susceptibility during systemic lupus erythematosus

Lupus nephritis(LN) has a high incidence in systemic lupus erythematosus(SLE) patients, but there is a lack of sensitive predictive markers. The purpose of the study was to investigate the association between the CD4^(+)CD8^(+)double positive T(DPT) lymphocytes and LN. The study included patients with SLE without renal impairment(SLE-NRI), LN, nephritic syndrome(NS), or nephritis. Peripheral blood lymphocyte subsets were analyzed by flow cytometry. Biochemical measurements were performed with peripheral blood in accordance with the recommendations proposed by the National Center for Clinical Laboratories. The proportions of DPT cells in the LN group were significantly higher than that in the SLE-NRI group(t=4.012, P<0.001), NS group(t=3.240,P=0.001), and nephritis group(t=2.57, P=0.011). In the LN group, the risk of renal impairment increased significantly in a DPT cells proportion-dependent manner. The risk of LN was 5.136 times(95% confidence interval, 2.115–12.473) higher in cases with a high proportion of DPT cells than those whose proportion of DPT cells within the normal range. These findings indicated that the proportion of DPT cells could be a potential marker to evaluate LN susceptibility, and the interference of NS and nephritis could be effectively excluded when assessing the risk of renal impairment during SLE with DPT cell proportion.

Atomic Heterointerface Engineering of Nickel Selenide Confined Nickel Molybdenum Nitride for High-Performance Solar-Driven Water Splitting

A heterostructured electrocatalyst of small NiSe_(2) nanoparticles confined NiMoN nanorods(NiSe_(2)-NPs/NiMoN-NRs)is prepared to accelerate both the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in a same alkaline medium.The synergistic effects caused by the combination of merits derived from NiSe_(2) and NiMoN phases trigger an optimum electronic structure with high density of state at near Fermi level and enhance adsorption free energy,thereby resulting in excellent catalytic activities and strengthened working stability.The catalyst requires a low overpotential of 58 mV for HER and 241 mV for OER to reach 10 mA cm^(−2) in 1.0 M KOH electrolyte.A twoelectrode electrolyzer based on the developed catalyst shows outstanding cell voltage of 1.51 and 1.46 V to reach 10 mA cm^(−2) in 1.0 M and 30 wt%KOH solution at 25℃ for overall water splitting,respectively.In addition,the solardriven water splitting process delivers a high solar-to-H_(2) conversion efficiency of∼18.4%,impressively unveiling that the developed bifunctional catalyst is highly potential for overall water splitting to produce green hydrogen fuel.

Chiral Anomaly-Enhanced Casimir Interaction between Weyl Semimetals

We theoretically study the Casimir interaction between Weyl semimetals.When the distance a between semiinfinite Weyl semimetals is in the micrometer regime,the Casimir attraction can be enhanced by the chiral anomaly.The Casimir attraction depends sensitively on the relative orientations between the separations(b1,b2)of Weyl nodes in the Brillouin zone and show anisotropic behavior for the relative orientation of these separations(b1,b2)when they orient parallel to the interface.This anisotropy is quite larger than that in conventional birefringent materials.The Casimir force can be repulsive in the micrometer regime if the Weyl semimetal slabs are sufficiently thin and the direction of Weyl nodes separations(b1,b2)is perpendicular to the interface.The Casimir attraction between Weyl semimetal slabs decays slower than 1/a4 when the Weyl nodes separations b1 and b2 are both parallel to the interface.

Molybdenum Carbide:A Stable Topological Semimetal with Line Nodes and Triply Degenerate Points

We propose that the hexagonal crystal form of MoC is a stable and new type of topological semimetal. It hosts an exotic Fermi surface consisting of two concentric nodal rings in the presence of spin-orbit coupling, and possesses four pairs of triply degenerate points （TDPs） in the vicinity of the Fermi energy. The coexistence of the nodal ring Fermi surface and TDPs in MoC leads to extraordinary properties such as distinguishable drumhead surface states and manipulatable new fermions, which make MoC a fertile platform for in-depth understanding of topological phenomena and a potential candidate material for topological electronic devices.

Spin-orbit interaction induced Casimir-Lifshitz torque between two-dimensional electron gases

We investigate theoretically the Casimir interaction between two parallel two-dimensional electron gases(2DEGs)with Rashba and Dresselhaus spin-orbit interactions(SOIs),based on the quantum field theory.We derive an analytical expression for the polarization tensor and obtain the solution to the motion equation of the electromagnetic(EM)field.We calculate the CasimirLifshitz torque(CLT)between two parallel 2DEGs with Rashba and Dresselhaus SOIs,which can be tuned by changing the relative strength between two SOIs.The anisotropic Casimir energy between 2DEGs caused by the interplay between the SOIs of 2DEGs offers a new origin of CLT and a new type of optoelectronic device.

Clinical features and the traditional Chinese medicine therapeutic characteristics of 293 COVID-19 inpatient cases

Coronavirus disease 2019 (COVID-19) is now pandemic worldwide and has heavily overloaded hospitals in Wuhan City, China during the time between late January and February. We reported the clinical features and therapeutic characteristics of moderate COVID-19 cases in Wuhan that were treated via the integration of traditional Chinese medicine (TCM) and Western medicine. We collected electronic medical record (EMR) data, which included the full clinical profiles of patients, from a designated TCM hospital in Wuhan. The structured data of symptoms and drugs from admission notes were obtained through an information extraction process. Other key clinical entities were also confirmed and normalized to obtain information on the diagnosis, clinical treatments, laboratory tests, and outcomes of the patients. A total of 293 COVID-19 inpatient cases, including 207 moderate and 86 (29.3%) severe cases, were included in our research. Among these cases, 238 were discharged, 31 were transferred, and 24 (all severe cases) died in the hospital. Our COVID-19 cases involved elderly patients with advanced ages (57 years on average) and high comorbidity rates (61%). Our results reconfirmed several well-recognized risk factors, such as age, gender (male), and comorbidities, as well as provided novel laboratory indications (e.g., cholesterol) and TCM-specific phenotype markers (e.g., dull tongue) that were relevant to COVID-19 infections and prognosis. In addition to antiviral/antibiotics and standard supportive therapies, TCM herbal prescriptions incorporating 290 distinct herbs were used in 273 (93%) cases. The cases that received TCM treatment had lower death rates than those that did not receive TCM treatment (17/273= 6.2% vs. 7/20= 35%, P = 0.0004 for all cases;17/77= 22% vs. 7/9= 77.7%, P = 0.002 for severe cases). The TCM herbal prescriptions used for the treatment of COVID-19 infections mainly consisted of Pericarpium Citri Reticulatae, Radix Scutellariae, Rhizoma Pinellia, and their combinations, which reflected the practical TCM principles (e.g., clearing heat and dampening phlegm). Lastly, 59% of the patients received treatment, including antiviral, antibiotics, and Chinese patent medicine, before admission. This situation might have some effects on symptoms, such as fever and dry cough. By using EMR data, we described the clinical features and therapeutic characteristics of 293 COVID-19 cases treated via the integration of TCM herbal prescriptions and Western medicine. Clinical manifestations and treatments before admission and in the hospital were investigated. Our results preliminarily showed the potential effectiveness of TCM herbal prescriptions and their regularities in COVID-19 treatment.

Excellent photothermal conversion of core/shell CdSe/ Bi2Se3 quantum dots

Water-dispersed CdSe/Bi2Se3 core/shell QDs with a photothermal conversion coefficient of 27.09% have been synthesized by a cation exchange reaction. The microstructure and crystal structure of the QDs, which were confirmed by TEM and XRD, showed that partial cation exchange occurred inside the CdSe QDs. Two main mechanisms are responsible for the excellent photothermal conversion： inhibition of radiative recombination of carriers due to the formation of type-II semiconductor heterostructures, and the large surface-to-volume ratio of the QDs. Photothermal conversion experiments indicated that the CdSe/Bi2Se3 QDs showed high photothermal conversion efficiency and excellent NIR photostability.

From two-to multi-state vertical spin valves without spacer layer based on Fe3GeTe2 van der Waals homo-junctions

Different than covalently bonded magnetic multilayer systems,high-quality interfaces without dangling bonds in van der Waals(vd W)junctions of two-dimensional(2D)layered magnetic materials offer opportunities to realize novel functionalities.Here,we report the fabrication of multi-state vertical spin valves without spacer layers by using vd W homo-junctions in which exfoliated Fe3GeTe2 nanoflakes act as ferromagnetic electrodes and/or interlayers.We demonstrate the typical behavior of two-state and threestate magnetoresistance for devices with two and three Fe3GeTe2 nanoflakes,respectively.Distinct from traditional spin valves with sandwich structures,our novel homo-junction-based spin-valve structure allows the straightforward realization of multi-state magnetic devices.Our work demonstrates the possibility of extend multi-state,non-volatile spin information to 2 D magnetic homo-junctions,and it emphasizes the utility of vd W interface as a fundamental building block for spintronic devices.

A multiplexed circulating tumor DNA detection platform engineered from 3D-coded interlocked DNA rings

Circulating tumor DNA(ctDNA)is a critical biomarker not only important for the early detection of tumors but also invaluable for personalized treatments.Currently ctDNA detection relies on sequencing.Here,a platform termed three-dimensional-coded interlocked DNA rings(3D-coded ID rings)was created for multiplexed ctDNA identification.The ID rings provide a ctDNA recognition ring that is physically interlocked with a reporter ring.The specific binding of ctDNA to the recognition ring initiates target-responsive cutting via a restriction endonuclease;the cutting then triggers rolling circle amplification on the reporter ring.The signals are further integrated with internal 3D codes for multiplexed readouts.ctDNAs from non-invasive clinical specimens including plasma,feces,and urine were detected and validated at a sensitivity much higher than those obtained through sequencing.This 3D-coded ID ring platform can detect any multiple DNA fragments simultaneously without sequencing.We envision that our platform will facilitate the implementation of future personalized/precision medicine.

Even-odd-dependent optical transitions of zigzag monolayer black phosphorus nanoribbons

We analytically study the electronic structure and optical properties of zigzag-edged phosphorene nanoribbons(ZPNRs) using the tight-binding Hamiltonian and Kubo formula. By directly solving the discrete Schrodinger equation, we obtain the energy spectra and wavefunctions for N-ZPNR(where N is the number of transverse zigzag atomic chains) and classify the eigenstates according to the lattice symmetry. Then, we obtain the optical transition selection rule of ZPNRs on the basis of symmetry analysis and analytical expressions of optical transition matrix elements. Under incident light that is linearly polarized along the ribbon, we determine that the optical transition selection rule for N-ZPNR with even-or odd-N is qualitatively different. Specifically, for even-N ZPNRs, the inter-(intra-) band selection rule is ?n =odd(even) because the parity of the wavefunction corresponding to the n-th subband in the conduction(valence) band is(-1)~n[(-1)~((n+1))] owing to the presence of C(2x) symmetry. However, the optical transitions between any subbands are possible owing to the absence of C(2x) symmetry. Our results provide a further understanding on the electronic states and optical properties of ZPNRs, which are useful for explaining the optical experiment data on ZPNR samples.

Validation and Refinement of Two Interpretable Models for Coronavirus Disease 2019 Prognosis Prediction

Objective:To validate two proposed coronavirus disease 2019(COVID-19)prognosis models,analyze the characteristics of different models,consider the performance of models in predicting different outcomes,and provide new insights into the development and use of artificial intelligence(AI)predictive models in clinical decision-making for COVID-19 and other diseases.Materials and Methods:We compared two proposed prediction models for COVID-19 prognosis that use a decision tree and logistic regression modeling.We evaluated the effectiveness of different model-building strategies using laboratory tests and/or clinical record data,their sensitivity and robustness to the timings of records used and the presence of missing data,and their predictive performance and capabilities in single-site and multicenter settings.Results:The predictive accuracies of the two models after retraining were improved to 93.2% and 93.9%,compared with that of the models directly used,with accuracies of 84.3% and 87.9%,indicating that the prediction models could not be used directly and require retraining based on actual data.In addition,based on the prediction model,new features obtained by model comparison and literature evidence were transferred to integrate the new models with better performance.Conclusions:Comparing the characteristics and differences of datasets used in model training,effective model verification,and a fusion of models is necessary in improving the performance of AI models.

Electrically pumped terahertz laser based on a topological insulator quantum dot array

The energy level separation between the edge states in topological insulator quantum dots lies in the terahertz(THz) range.Quantum confinement ensures the nonuniformity of the energy level separation near the Dirac point. Based on these features, we propose that a topological insulator quantum dot array can be operated as an electrically pumped continuous-wave THz laser. The proposed device can operate at room temperature, with power exceeding 10 mW and quantum efficiency reaching ~50%. This study may promote the usage of topological insulator quantum dots as an important source of THz radiation.