Statistical moment-based structural damage detection method in time domain

A novel structural damage detection method with a new damage index,i.e.,the statistical moment-based damage detection（SMBDD） method in the frequency domain,has been recently proposed.The aim of this study is to extend the SMBDD method in the frequency domain to the time domain for building structures subjected to non-Gaussian and non-stationary excitations.The applicability and effectiveness of the SMBDD method in the time domainis verified both numerically and experimentally.Shear buildings with various damage scenarios are first numerically investigated in the time domain taking into account the effect of measurement noise.The applicability of the proposed method in the time domain to building structures subjected to non-Gaussian and non-stationary excitations is then experimentally investigated through a series of shaking table tests,in which two three-story shear building models with four damage scenarios aretested.The identified damage locations and severities are then compared with the preset values.The comparative results are found to be satisfactory,and the SMBDD method is shown to be feasible and effective for building structures subjected to non-Gaussian and non-stationary excitations.

Future Physics Programme of BESⅢ

There has recently been a dramatic renewal of interest in hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like XYZ states at BESⅢ and B factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related X(1835) meson state at BESⅢ, as well as the threshold measurements of charm mesons and charm baryons. We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESⅢ during the remaining operation period of BEPCⅡ. This survey will help in the optimization of the data-taking plan over the coming years, and provides physics motivation for the possible upgrade of BEPCⅡ to higher luminosity.

Artifact analysis of a far-field coded-aperture gamma camera extended to partially coded field-of-view

Purpose Coded-aperture gamma cameras play an important role for homeland security nowadays.They have limitedfield-of-view(FOV)which is a critical parameter for many applications.The FOV can be potentially increased by extending it to the penumbra area(partially coded FOV).Methods In this study,we analyzed this artifact phenomenon based on simulating a commercial coded-aperture gamma camera.The camera uses a modified uniformly redundant array(MURA)mask with a basic pattern of rank 11.Its opening angle of the basic pattern to the detector center is 26.36◦which is the commonly used non-artifact FOV(NAFOV).In some applications,the radiation source is a far-field single-point source.Thus,we extend its FOV to 40◦by including a part of the partially coded area,which is a trade-off between the FOV and image quality.Analytical calculations and simulation studies were carried out.The system matrix was calculated using the Sidden’s algorithm.The maximum likelihood expectation maximization(MLEM)reconstruction method was employed.Projections and reconstruction results of the point source at different positions were compared.The second moment of inertia was used as thefigure of merit.Results Results show that projections have periodic similarity with a period of NAFOV,and reconstructions also have periodic artifacts,i.e.,fromθtoθ+NAFOV.Artifacts are the most serious at the edge of the NAFOV.The upper and lower artifacts are more serious than the left and right artifacts due to the difference between the horizontal centerline(tungsten)and vertical centerline(holes expect the center unit)of the mask.Conclusions For a point source with high activity,artifacts can be reduced by increasing the iteration number of the MLEM reconstruction.Even at the edge of NAFOV,the point source can be possibly reconstructed thanks to the large size of the position sensitive detector(PSD)used.The noise will significantly increase artifacts,which may lead to error locate the point source with low activity at some specific positions.

Application Prospect of Fission-Powered Spacecraft in Solar System Exploration Missions

Fission power is a promising technology,and it has been proposed for several future space uses.It is being considered for highpower missions whose goal is to explore the solar system and even beyond.Space fission power has made great progress when NASA’s 1 kWe Kilowatt Reactor Using Stirling TechnologY(KRUSTY)prototype completed a full power scale nuclear test in 2018.Its success stimulated a new round of research competition among the major space countries.This article reviews the development of the Kilopower reactor and the KRUSTY system design.It summarizes the current missions that fission reactors are being considered as a power and/or propulsion source.These projects include visiting Jupiter and Saturn systems,Chiron,and Kuiper belt object;Neptune exploration missions;and lunar and Mars surface base missions.These studies suggest that the Fission Electric Propulsion(FEP)/Fission Power System(FPS)is better than the Radioisotope Electric Propulsion(REP)/Radioisotope Power System(RPS)in the aspect of cost for missions with a power level that reaches~1 kWe,and when the power levels reaches~8 kWe,it has the advantage of lower mass.For a mission that travels further than~Saturn,REP with plutonium may not be cost acceptable,leaving FEP the only choice.Surface missions prefer the use of FPS because it satisfies the power level of 10’s kWe,and FPS vastly widens the choice of possible landing location.According to the current situation,we are expecting a flagship-level fission-powered space exploration mission in the next 1-2 decades.

Observation of e^+e^-→D_s^+■^((*)0)K^- and study of the P-wave D_s mesons

Studies of e^+e~→D_s^+■^((*)0)K^-and the P-wave charmed-strange mesons are performed based on an e^+e^-collision data sample corresponding to an integrated luminosity of 567 pb^(-1) collected with the BESIII detector at s^(1/2)=4.600 GeV. The processes of e^+e^-→D_s^+■^(*0)K^- and D_s^+■~0K^- are observed for the first time and are found to be dominated by the modes D_s^+D_(s1)(2536)^-and D_s^+D_(s2)~*(2573)^-, respectively. The Born cross sections are measured to be σ~B(e^+e^-→D_s^+■^(*0)K^-) =(10.1±2.3±0.8) pb and σ~B(e^+e^-→D_s^+■~0K^-) =(19.4±2.3± 1.6) pb, and the products of Born cross section and the decay branching fraction are measured to be σ~B(e^+e^-→D_s^+D_(s1)(2536)^-+c.c.)·B(D_(s1)(2536)^-→■^(*0)K^-)=(7.5±1.8±0.7) pb and σ~B(e^+e^-→D_s^+D_(s2)~*(2573)^-+ c.c.)·B(D_(s2)~*(2573)^-→■~0 K^-)=(19.7 ± 2.9 ±2.0) pb. For the D_(s1)(2536)^-and D_(s2)~*(2573)^-mesons, the masses and widths are measured to be M(D_(s1)(2536)^-)=(2537.7±0.5 ±3.1) MeV/c2, Γ(D_(s1)(2536)^-) =(1.7 ±1.2 ±0.6)MeV, and M(D_(s2)~*(2573)^-)=(2570.7±2.0 ±1.7) MeV/c^2, Γ(D_(s2)~*(2573)^-)=(17.2 ±3.6 ±1.1) MeV. The spin-parity of the D_(s2)~*(2573)^-meson is determined to be J^p= 2^+. In addition, the processes e^+e^-→D_s^+■^((*)0)K^-are searched for using the data samples taken at four(two) center-of-mass energies between 4.416(4.527) and 4.575 GeV, and upper limits at the 90% confidence level on the cross sections are determined.

Evidence for the decays of ∧_c^+→∑^+η and ∑^+η’

We study the hadronic decays of ∧c+ to the final states ∑+η and ∑+η’,using an e+e-annihilation data sample of 567 pb-1 taken at a center-of-mass energy of 4.6 GeV with the BESIII detector at the BEPCⅡ collider.We find evidence for the decays ∧c+→∑+η and ∑+η’ with statistical significance of 2.5σ and 3.2σ,respectively.Normalizing to the reference decays ∧c+→∑+π0 and ∑+ω,we obtain the ratios of the branching fractions■and ■to be 0.35±0.16±0.02 and 0.86±0.34±0.04,respectively.The upper limits at the 90% confidence level are set to be■and■.Using BESIII measurements of the branching fractions of the reference decays,we determine B（∧c+→∑+η）=（0.41±0.19±0.05）%（<0.68%）and B（∧c+→∑+η’）=（1.34±0.53 ±0.19）%（<1.9%）.Here,the first uncertainties are statistical and the second systematic.The obtained branching fraction of ∧c+→∑+η is consistent with the previous measurement,and the branching fraction of ∧c+→∑+η’ is measured for the first time.