Statics, vibration, and buckling of sandwich plates with metamaterial cores characterized by negative thermal expansion and negative Poisson's ratio

This paper proposes a three-dimensional(3D)Maltese cross metamaterial with negative Poisson’s ratio(NPR)and negative thermal expansion(NTE)adopted as the core layers in sandwich plates,and aims to explore the relations between the mechanical responses of sandwich composites and the NPR or NTE of the metamaterial.First,the NPR and NTE of the metamaterial are derived analytically based on energy conservation.The effective elastic modulus and mass density of the 3D metamaterial are obtained and validated by the finite element method(FEM).Subsequently,the general governing equation of the 3D sandwich plate under thermal environments is established based on Hamilton’s principle with the consideration of the von Kármán nonlinearity.The differential quadrature(DQ)FEM(DQFEM)is utilized to obtain the numerical solutions.It is shown that NPR and NTE can enhance the global stiffness of sandwich structures.The geometric parameters of the Maltese cross metamaterial significantly affect the responses of the thermal stress,natural frequency,and critical buckling load.

Theoretical analysis on quasi-static lateral compression of elliptical tube between two rigid plates

Based on the rigid plastic theory; the load-deflection functions with and without considering the effect of strain hardening are respectively derived for an elliptical tube under quasi-static compression by two parallel rigid plates. The non-dimensional load-deflection responses predicted by the present theory and the finite element simula- tions are compared, and the favorable agreement is found. The results show that strain hardening may have a noticeable influence on the load-deflection curves of an elliptical tube under quasi-static compression. Compared with the circular counterpart, the ellip- tical tube exhibits different energy absorption behavior due to the difference between the major axis and the minor axis. When loaded along the major axis of a slightly oval tube, a relative even and long plateau region of the load-deflection curve is achieved, which is especially desirable for the design of energy absorbers.

Theoretical model for elliptical tube laterally impacted by two parallel rigid plates

An analytical model is developed to study the crushing behavior and energy absorption capability of a single elliptical tube impacted by two parallel rigid plates, with and without consideration of the strain hardening effect. The four-hinge collapse mechanism is used, and the governing equation is derived from Lagrange equations of the second kind. The numerical simulation of the dynamic response of the elliptical tube under impact using the finite element explicit code LS-DYNA is performed. The reaction force-displacement curve and displacement-time curve of the plate obtained from the two methods are in good agreement.

Evaluation of outcomes reported in randomized controlled trials for herbal remedies for adults with chronic hepatitis C

Background:Herbal remedies have been widely utilized in treating chronic hepatitis C (CHC) worldwide.Selecting appropriate outcomes to reflect both beneficial and harmful effects is a crucial step in designing randomized controlled trials (RCTs).This study evaluated the outcomes reported in RCTs on herbal remedies for CHC with comparison to the core outcomes recommended by the Cochrane Hepato-Biliary Group (CHBG),to check the consistency of the outcomes and to provide recommendation for future researches.Methods:A systematic literature search was conducted in Western and Chinese databases to identify RCTs on herbal remedies for adults with CHC.For each trial,all the outcomes reported in the results section were collected.Comparison between trial outcomes and CHBG core outcomes were evaluated and summarized with descriptive statistics.Results:A total of 116 RCTs involving 9154 participants were included;27 outcomes were identified.Commonly reported outcomes included alanine aminotransferase (64 trials,55.2%),adverse events (58 trials,50.0%),and end-of-treatment virological response (50 trials,43.1%).All trials indicated that the herbal remedies under investigation had a positive effect and was markedly more effective than the control.Nearly half of the trials reported that the combination of herbal medicine and antiviral drugs could ameliorate adverse events.Very few trials reported primary core outcomes relating survival and quality of life.The most frequently reported core outcomes are non-serious adverse events (54 trials,46.6%),viral response (27 trials,23.3%),and biochemical response (24 trials,20.7%).Conclusion:The variation and inconsistency in trial outcomes impedes research synthesis efforts,and indicate the need for comparable outcomes through the development of core outcome sets in CHC.The low concordance of outcome reporting could be improved by following CHBG core outcomes recommendation.

A Theoretical Analysis of Thermoelastic Damping Model in Laminated Trilayered Circular Plate Resonators

Thermoelastic damping of the axisymmetric vibration of laminated circular plate resonators is discussed in this paper. Based on the classical laminated plate theory assumptions, the governing equations of coupled thermoelastic problems are established for axisymmetric out-of-plane vibration of trilayered circular plate. The analytical expression for thermoelastic damping is obtained and the accuracy is verified through comparison with finite element analysis results. Then some simplifications are made on the theoretical model.

Controlled synthesis of Mn_(x)Cd_(1-x)S for enhanced visible-light driven photocatalytic hydrogen evolution

Ternary sulfide solid solutions have garnered great attention in photocatalytic water splitting due to their tunable electronic property,low cost,and sufficient light-absorption performance.Herein,a series of Mn_(x)Cd_(1-x)S samples with different Mn/Cd molar ratios were synthesized by solvothermal method and used for photocatalytic hydrogen production under visible light.The Mn_(0.2)Cd_(0.8)S and Mn_(0.4)Cd_(0.6)S are demonstrated to be the solid so-lutions,while Mn_(0.6)Cd_(0.4)S and Mn_(0.8)Cd_(0.2)S consist of Mn_(x)Cd_(1-x)S solid solution and MnS.In addition,the Mn_(0.4)Cd_(0.6)S exhibits the highest photocatalytic performance with the H_(2) production rate of 185.95μmol·h^(-1),which is 4.7 times higher than that of CdS.Without cocatalyst,the quantum efficiency of Mn_(0.4)Cd_(0.6)S reaches 2.04%at 400 nm.In addition,the Mn_(0.4)Cd_(0.6)S solid solution also shows high stability during the photocatalytic H_(2) production reaction.The effect of Mn/Cd molar ratio on the microstructure,band gap structure,and photo-catalytic hydrogen production performance of Mn_(x)Cd_(1-x)S was revealed systematically.The excellent photo-catalytic H_(2) production performance of Mn_(0.4)Cd_(0.6)S solid solution is mainly due to its enhanced reducing potential and high charge separation efficiency.

Tetrabromobisphenol A and hexabromocyclododecane in sediments from the Zhujiang(Pearl) River Estuary and South China Sea

Marine sediments collected from the Zhujiang(Pearl) River Estuary(ZRE) and South China Sea(SCS) were utilized to study the occurrence and spatial distribution of tetrabromobisphenol A(TBBPA) and hexabromocyclododecane(HBCDD).The levels of TBBPA and HBCDD in sediments ranged from not detected(nd) to 6.14 ng/g dry weight(dw) and nd to 0.42 ng/g dw.TBBPA concentrations in marine sediments were substantially higher than HBCDD.The concentrations of TBBPA and HBCDD in the ZRE sediments were significantly greater than those in the SCS.α-HBCDD(48.7%) and γ-HBCDD(46.2%) were the two main diastereoisomers of HBCDD in sediments from the ZRE,with minor contribution of β-HBCDD(5.1%).HBCDD were only found in one sample from the northern SCS.The enantiomeric fraction of α-HBCDD in sediments from the ZRE was obviously greater than 0.5,indicating an accumulation of(+)-α-HBCDD.The enantiomers of HBCDD were not measured in sediments from the SCS.This work highlighted the environmental behaviors of TBBPA and HBCDD in marine sediments.

直拉硅单晶的杂质工程:微量掺锗的效应

直拉硅单晶是集成电路的基础材料,因而在过去几十年来被广泛而深入研究.直拉硅单晶的缺陷以及机械强度对集成电路制造的成品率有显著的影响.传统上,人们认为直拉硅单晶中除了掺杂所需的电活性杂质以及不可避免的氧杂质以外,其他杂质越少越好.在此情形下,直拉硅单晶的缺陷控制和机械强度的改善几乎只能依赖于晶体生长工艺的优化.为了打破这种限制,我们提出在直拉硅单晶中掺入特定的非电活性杂质,既可以通过这些杂质原子与点缺陷的相互作用来调控维度更高的缺陷的行为,又可以发挥增强机械强度的作用,这就是直拉硅单晶的杂质工程.本文首先阐述直拉硅单晶的杂质工程的研究背景与意义,随后综述作为直拉硅单晶的杂质工程的一个范本——微量掺锗的效应,包括掺锗对氧沉淀和空洞等缺陷形成的影响及其对集成电路制造的有益作用,以及掺锗对硅片机械强度的增强作用.

Zeeman slowing atoms using the magnetic field from a magneto-optical trap

We study a Zeeman slower using the magnetic field generated by a pair of coils for a magneto-optical trap. The efficiency of the Zeeman slower is shown to be dependent on the intensity and frequency detuning of the laser light for slowing the atoms. With the help of numerical analysis, optimal experimental parameters are explored.Experimentally, the optimal frequency detuning and intensity of the slowing beam are explored, and 4 × 10~7 ytterbium atoms are trapped in the magneto-optical trap.

Retrieval and validation of long-term aerosol optical depth from AVHRR data over China

Advanced Very High Resolution Radiometer(AVHRR)onboard National Oceanic and Atmospheric Administration(NOAA)satellites can provide over 40 years of global remote sensing observations,which can be used to retrieve long-term aerosol optical depth(AOD).This is of great significance to the study of global climate change.In this paper,we proposed an algorithm to jointly calculate AOD and land surface properties from AVHRR observations.With assumptions that AOD doesn’t vary in adjacent space and earth surface property doesn’t vary in two days,the algorithm considered non-Lambertian surface reflection based on the shape of bidirectional reflectance distribution function(BRDF shape)and obtained AOD and surface property by optimal estimation(OE)method.The algorithm has been applied to NOAA-7,9,11,14,16,18,and 19 satellites and AVHRR-retrieved AOD with 5×10 km over China(15°–60°N,70°–140°E)has been obtained from 1982 to 2016.Comparisons of AVHRR-retrieved AOD against AErosol RObotic NETwork(AERONET)(in and around China)and China Aerosol Remote Sensing Network(CARSNET)AOD show good consistency with 62.62%points within the uncertainty ofΔτ=±(0.05+0.25τ)and root-mean-square error(RMSE)of 0.26.Further comparison of the monthly mean AOD of multiple AOD datasets in the‘Beijing’,‘Dalanzadgad’,‘NCU_Taiwan’and‘Kanpur’stations shows that the results of the algorithm are stable.The yearly averaged AOD data also has similar agreements with MERRA-2(The Modern-Era Retrospective analysis for Research and Applications,Version 2)and AVHRRDB data(AVHRR‘Deep Blue’aerosol data set).The multi-year mean correlation coefficient is 0.70 and 0.61 and the percentages within the uncertainty are 80.01%and 67.29%compared with MERRA-2 AOD and AVHRRDB AOD respectively.

Laser stabilizing to ytterbium clock transition with Rabi and Ramsey spectroscopy

A cavity-stabilized 578 nm laser is used to probe the clock transition of ytterbium atoms trapped in optical lattice sites.We obtain a Fourier-limited 4.2-Hz-linewidth Rabi spectrum and a Ramsey spectrum with fringe linewidth of 3.3 Hz.Based on one of the spectra,the 578 nm laser light is frequency-stabilized to the center of the transition to achieve a closed-loop operation of an optical clock.Based on interleaved measurement,the frequency instability of a single optical clock is demonstrated to be 5.4×10-16/pτ.

INFLUENCE OF THE MIDDLE WEAK LAYER ON THE IMPACT BEHAVIOR OF LAMINATED STRUCTURES

In this paper, a calculation model based on the subsection displacement theory and the large deflection analysis is developed to describe the dynamic response of isotropic laminated circular plates impacted by a soft body. The model takes into account the interlaminar shear effect induced by the middle weak layer. It is proved by numerical examples that the difference between the model developed in this paper and that based on the classical laminated theory mainly depends on three factors, the elastic modulus of the glue, the radius of the circular plate and the impact force.