Energy dissipation mechanism and ballistic characteristic optimization in foam sandwich panels against spherical projectile impact

This study systematically examines the energy dissipation mechanisms and ballistic characteristics of foam sandwich panels(FSP)under high-velocity impact using the explicit non-linear finite element method.Based on the geometric topology of the FSP system,three FSP configurations with the same areal density are derived,namely multi-layer,gradient core and asymmetric face sheet,and three key structural parameters are identified:core thickness(t_(c)),face sheet thickness(t_(f))and overlap face/core number(n_(o)).The ballistic performance of the FSP system is comprehensively evaluated in terms of the ballistic limit velocity(BLV),deformation modes,energy dissipation mechanism,and specific penetration energy(SPE).The results show that the FSP system exhibits a significant configuration dependence,whose ballistic performance ranking is:asymmetric face sheet>gradient core>multi-layer.The mass distribution of the top and bottom face sheets plays a critical role in the ballistic resistance of the FSP system.Both BLV and SPE increase with tf,while the raising tcor noleads to an increase in BLV but a decrease in SPE.Further,a face-core synchronous enhancement mechanism is discovered by the energy dissipation analysis,based on which the ballistic optimization procedure is also conducted and a design chart is established.This study shed light on the anti-penetration mechanism of the FSP system and might provide a theoretical basis for its engineering application.

Static recrystallization and grain growth during annealing of an extruded Mg-Zn-Zr-Er magnesium alloy

Microstructure stability is essential to maintain a fine grain structure for an alloy throughout its processing.The effects of Er addition and its existing form on the static recrystallization and grain growth during annealing of an extruded Mg-1.5Zn-0.6Zr magnesium alloy were studied in this paper.The results showed that microstructure stability was much improved by Er addition and the best thermability was obtained in 2 wt.%Er-containing alloy.For the incomplete dynamic recrystallization(DRX)microstructures extruded at a lower temperature of 350℃,Er addition increased the resistance of static recrystallization;and for the complete DRX microstructures extruded at a relatively high temperature of 420℃,Er addition suppressed grain growth.The difference in microstructure stability was then correlated with the microstructure features.Both the intermetallic phase and the solute atoms of Er inα-Mg matrix contributed to the microstructure stability.Moreover,it is believed that the existing form of Er-Zn atom pairs in theα-Mg solid solution favored the most to improve the thermal stability of the alloy.

Temperature-Dependent Tearing Behavior of Rubber Materials:Characterization and Modeling

With the increasingly widespread application of rubber in many fields,there is a growing demand for quantitative characterization of temperature-dependent mechanical properties in high-temperature service environments.The critical tearing energy is an important criterion for determining whether rubber materials will experience tearing instability,while tear strength is a key parameter for rubber materials to resist tearing.It is necessary to quantitatively characterize their evolution with temperature.Current theoretical research mainly relies on fitting a large amount of experimental data,which is not convenient for engineering applications.Therefore,in this work,a temperature-dependent critical tearing energy model is firstly developed based on the force-heat equivalence energy density principle.This model considers the equivalent relationship between the critical tearing energy required for crack instability propagation and the thermal energy stored in the rubber material.It is demonstrated that our model has higher prediction accuracy when compared to other models.Furthermore,combining with the Griffith fracture theory,temperature-dependent tear strength models applicable to three different crack modes are separately established.These models are validated using experimental data for Mode I opening cracks and ModeⅢtearing cracks,and good consistency is achieved.Additionally,a quantitative analysis of the influence of elastic modulus on tear strength at different temperatures is conducted.This work provides a reliable way for predicting temperature-dependent tearing instability behavior and offers beneficial suggestions for improving the tear strength of rubber materials at different temperatures.

Extraordinary mechanical properties of AZ61 alloy processed by ECAP with 160° channel angle and EPT

AZ61 Mg alloy with homogeneous refined microstructure and exceptional mechanical properties was obtained by the combined technology of equal-channel angular pressing(ECAP)and electropulsing treatment(EPT)in this paper.Based on an ECAP die with an intersection angle of 160,the lower temperature is particularly adapted for AZ61 alloy to be deformed,in which accompanied by high accumulated defects density.The recrystallization of EPTed samples during different stages indicated that the recrystallization behavior of the deformed Mg alloy was mainly affected by the processing time and duration of EPT.Compared to those of the as-received samples,the average grain size of the EPTed samples was refined from 89μm to 1.0μm,accordingly the yields stress(YS)and ultimate tensile strength(UTS)were increased from 100 MPa and 260 MPa to 330 MPa and 448 MPa,respectively.The mechanisms of microstructure transformation and the reinforced mechanical properties were analyzed based on the strain of single ECAP,cumulative storage energy and the athermal effect of EPT.

The temperature-dependent fracture strength model for ultra-high temperature ceramics

Breaking down the entire structure of a material implies severing all the bonds between its atoms either by applying work or by heat transfer. Because bond-breaking is indifferent to either means, there is a kind of equivalence between heat energy and strain energy. Based on this equivalence, we assume the existence of a constant maximum storage of energy that includes both the strain energy and the corresponding equivalent heat energy. A temperaturedependent fracture strength model is then developed for ultrahigh temperature ceramics （UHTCs）. Model predictions for UHTCs, HfB2, TiC and ZrB2, are presented and compared with the experimental results. These predictions are found to be largely consistent with experimental results.

中国汉族人群66个InDel基因座的遗传多态性

插入/缺失多态性(insertion/deletion polymorphism,InDel)遗传标记是一类由DNA片段的插入或者缺失形成的变异形式,在降解检材身份识别领域展现出优势。本文从dbSNP数据库中自主筛选66个InDel基因座,基于高通量测序系统建立了一套多重复合扩增体系(66-plex InDels)。通过评估66-plex InDels在251名中国汉族人群的群体遗传学参数,分析其法医学应用价值。研究结果表明:经过Bonferroni法校正,66个InDel基因座在中国汉族人群中均符合Hardy-Weinberg平衡定律(P>0.000758),各基因座间处于连锁平衡状态。各基因座平均观测杂合度(Ho)为0.482,平均期望杂合度(He)为0.483,平均个体识别力(DP)为0.612,平均多态性信息含量(PIC)为0.365,累计个体识别率(TDP)为0.99999999999999999999999999942818。66个InDel基因座的二联体累计非父排除概率(CPE_(duo))为0.999739,三联体累计非父排除概率(CPE_(trio))为0.999999999417。结果表明:66个InDel基因座在中国汉族人群中具有良好的遗传多态性,可独立应用于法医个体识别和亲权鉴定研究。

Analysis of Spectral Characteristics Based on Optical Remote Sensing and SAR Image Fusion

Because of cloudy and rainy weather in south China, optical remote sens-ing images often can＇t be obtained easily. With the regional trial results in Baoying, Jiangsu province, this paper explored the fusion model and effect of ENVISAT/SAR and HJ-1A satel ite multispectral remote sensing images. Based on the ARSIS strat-egy, using the wavelet transform and the Interaction between the Band Structure Model （IBSM）, the research progressed the ENVISAT satel ite SAR and the HJ-1A satel ite CCD images wavelet decomposition, and low/high frequency coefficient re-construction, and obtained the fusion images through the inverse wavelet transform. In the light of low and high-frequency images have different characteristics in differ-ent areas, different fusion rules which can enhance the integration process of self-adaptive were taken, with comparisons with the PCA transformation, IHS transfor-mation and other traditional methods by subjective and the corresponding quantita-tive evaluation. Furthermore, the research extracted the bands and NDVI values around the fusion with GPS samples, analyzed and explained the fusion effect. The results showed that the spectral distortion of wavelet fusion, IHS transform, PCA transform images was 0.101 6, 0.326 1 and 1.277 2, respectively and entropy was 14.701 5, 11.899 3 and 13.229 3, respectively, the wavelet fusion is the highest. The method of wavelet maintained good spectral capability, and visual effects while improved the spatial resolution, the information interpretation effect was much better than other two methods.

Characteristics of long-gap AC streamer discharges under low pressure conditions

The generation and propagation of a streamer is a significant physical process of air gap discharge. Research on the mechanism of streamers under low-pressure conditions is helpful for understanding the process of long-gap discharge in a high-altitude area. This paper describes laboratory investigations of streamer discharge under alternating current（AC） voltage in a low pressure test platform for a 60 cm rod–plane gap at 30 kPa, and analyzes the characteristics of streamer generation and propagation. The results show that the partial streamer and breakdown streamer all occur in the positive half-cycle of AC voltage near the peak voltage at 30 kPa. The partial streamer could cause the distortion of current and voltage waveform, and it appears as the branching characteristic at the initial stage. With the extension of the streamer, the branching and tortuosity phenomena become gradually obvious, but the branching is suppressed when the streamer crosses the gap. The low-pressure condition has little influence on the tortuosity length and the tortuosity number of the streamer, but affect the diameter of streamer obviously.

Diversity and community structure of eukaryotic microalgae in surface sediments in the central Bohai Sea,China,based on a metabarcoding approach

Sediment samples were collected at 17 stations in the central Bohai Sea,China,and the diversity and community structure of eukaryotic microalgae were assessed by metabarcoding the V4 region of 18S r DNA.A total of 930 operational taxonomic units(OTUs)were detected for microeukaryotes,including 98algal OTUs.The algal communities comprised 42 genera belonging to 19 classes of six phyla,and they were dominated by chrysophytes and dinoflagellates.Dinoflagellates were also the most diverse microalgal group.The nano-sized dinoflagellates Biecheleria halophila and Azadinium trinitatum occurred abundantly in the study area;however,they have not been reported previously,as they may be overlooked or misidentified in light microscopy.Many pico-sized chlorophytes were detected in the sediment samples.Sixteen of the detected OTUs were assigned to potentially harmful and/or bloom-forming microalgae,suggesting some potential risks of harmful algal blooms in the central Bohai Sea.The capacity of metabarcoding to detect morphologically cryptic and small species makes this method a sufficiently sensitive means of detection for assessing eukaryotic microalgae in sediments.

Comparison in diversity of eukaryotic algae in surface sediments from different functional sea areas of Qingdao coast,the Yellow Sea,China:a metabarcoding approach

Surface sediment samples were collected in three different functional sea areas in Qingdao coast,East China,including the inner Jiaozhou Bay,the Laoshan Coast,and the Amphioxus Reserve area.Diversity and community structure of eukaryotic algae especially those of phytoplankton resting stages were assessed by metabarcoding V4 region of the 18S rDNA.Biogenic elements including total organic carbon(TOC),organic matter(OM),total nitrogen(TN),total phosphorus(TP),and biogenic silicon(BSi)were analyzed.A total of 1496 eukaryotic operational taxonomic units(OTUs)were measured,including 207algal OTUs,which contributed to 13.84%of the total OTUs.Ninety-eight species in 8 phyla,24 classes of eukaryotic algae were detected.Among them,47 species have been reported to form resting stages,and 12 species are firstly recorded in Chinese coastal waters.Dinofl agellates dominated in both DNA reads and OTU richness,which contributed to 73.02%and 61.35%of the eukaryotic algal sequences and OTU richness,respectively.DNA reads,OTU richness and alpha diversity indexes of eukaryotic algae were higher in the Laoshan Coast,and lower in Jiaozhou Bay.Eukaryotic algal community differed in the three sea areas,which was dominated by chrysophytes in Jiaozhou Bay,by dinofl agellates in the Laoshan Coast,and co-dominated by dinoflagellates and chrysophytes in the Amphioxus Reserve area.Clustering analysis showed that the Laoshan Coast and the Amphioxus Reserve area are clustered together,while Jiaozhou Bay is clustered separately.Thirty-six harmful algal bloom(HAB)species were detected,and 10 species have been reported to form blooms in Jiaozhou Bay and the Qingdao coast before.Some of these species occurred widely and dominantly in this study,suggesting high potential risk of HABs in the Qingdao coastal area.

Effects of mechanical boundary conditions on thermal shock resistance of ultra-high temperature ceramics

The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance（TSR） of ultra-high temperature ceramics（UHTCs） are studied by investigating the TSR of a UHTC plate with various types of constraints under the first, second, and third type of thermal boundary conditions. The TSR of UHTCs is strongly dependent on the heat transfer modes and severity of the thermal environments. Constraining the displacement of the lower surface in the thickness direction can significantly decrease the TSR of the UHTC plate, which is subject to the thermal shock at the upper surface. In contrast, the TSR of the UHTC plate with simply supported edges or clamped edges around the lower surface is much better.

Self-organized pattern on the surface of a metal anode in low-pressure DC discharge

Self-organization phenomena on the surface of a metal electrode in low-pressure DC discharge is studied. In this paper, we carry out laboratory investigations of self-organization in a lowpressure test platform for 100–200 mm rod-plane gaps with a needle tip, conical tip and hemispherical tip within 1–10 k Pa. The factors influencing the pattern profile are the pressure value, gap length and shape of the electrode, and a variety of pattern structures are observed by changing these factors. With increasing pressure, first the pattern diameter increases and then decreases. With the needle tip, layer structure, single-ring structure and double-ring structure are displayed successively with increasing pressure. With the conical tip, the ring-like structure gradually forms separate spots with increasing pressure. With the hemispherical tip, there are anode spots inside the ring structure. With the increase of gap length, the diameter of the selforganized pattern increases and the profile of the pattern changes. The development process of the pattern contains three key stages： pattern enlargement, pattern stabilization and pattern shrink.

Algorithms for mesh repairing to represent automobile parts

In representing automobile parts with mesh in the field of reverse engineering or finite element generation, the mesh reconstruction and data exchanging between different CAD/CAM systems often introduce many invisible topological and geometrical errors into mesh. These artifacts can cause serious problems in subsequent operations such as finite element analysis, reverse engineering, animation, and simulation. In this study we propose a practical method for repairing topological and geometrical errors on mesh. First, coincident vertices during mesh input are removed, fol- lowed by the identification of non-manifold vertices and edges. The non-manifold vertices are modified, and the facets having non-manifold edges are removed. Finally, faces that have the wrong orientations in the mesh are re-oriented. Experiments show that our methods can eliminate most common mesh errors quickly and effectively. The refined mesh can be properly used in subsequent operations.

Effect of electropulsing treatment on static recrystallization behavior of cold-rolled magnesium alloy ZK60 with different reductions

Effect of electropulsing treatment(EPT) on recrystallization behavior of cold-rolled Mg alloy ZK60 strips was investigated. It was found that EPT significantly improved nucleation rate and migration ability of grain boundaries, leading to accelerated recrystallization of the deformed metals at relatively low temperature. After the recrystallization induced by EPT, the average grain size of 20% rolling reduction samples decreased from 113 um to around 10 um, meanwhile the typical basal-type texture of the coldrolled sample was weakened. EPT was normally accompanied with a thermal and an athermal effects. The athermal effect played a dominated role in increasing nucleation rate, while the thermal effect promoted grain growth. A fewer recrystallized grains originated along the grain boundaries in the 10% reduction samples, while most of the recrystallization took place inside the twins in the 20% reduction samples.

A Three-phase Integrated Power Electronic Transformer with the Capability of DC Fault Clearance

This paper presents a three-phase integrated power electronic transformer(PET)topology with the capability of DC fault clearance based on the investigation of PET topology.The proposed PET has three ports of high-voltage AC,high-voltage DC and low-voltage DC,which can achieve the flexible access of distributed energy resources・The power unit of the PET adopts a three-phase integrated topology,and the single-phase fluctuating power in the DC-link capacitor is reduced by a 4-port DC/DC converter,thereby reducing the capacitance of the DC-link capacitor;Meanwhile,the power unit uses the clamp double sub-module(CDSM)to allow for self-clearing of the short-circuit fault on the high-voltage DC side.Finally,this paper verifies the proposed PET through an EMT simulation and experimental prototype.

Feasibility and physics potential of detecting ^(8)B solar neutrinos at JUNO

The Jiangmen Underground Neutrino Observatory(JUNO)features a 20 kt multi-purpose underground liquid scintillator sphere as its main detector.Some of JUNO's features make it an excellent location for^8B solar neutrino measurements,such as its low-energy threshold,high energy resolution compared with water Cherenkov detectors,and much larger target mass compared with previous liquid scintillator detectors.In this paper,we present a comprehensive assessment of JUNO's potential for detecting^8B solar neutrinos via the neutrino-electron elastic scattering process.A reduced 2 MeV threshold for the recoil electron energy is found to be achievable,assuming that the intrinsic radioactive background^(238)U and^(232)Th in the liquid scintillator can be controlled to 10^(-17)g/g.With ten years of data acquisition,approximately 60,000 signal and 30,000 background events are expected.This large sample will enable an examination of the distortion of the recoil electron spectrum that is dominated by the neutrino flavor transformation in the dense solar matter,which will shed new light on the inconsistency between the measured electron spectra and the predictions of the standard three-flavor neutrino oscillation framework.IfDelta m^(2)_(21)=4.8times10^(-5);(7.5times10^(-5))eV^(2),JUNO can provide evidence of neutrino oscillation in the Earth at approximately the 3sigma(2sigma)level by measuring the non-zero signal rate variation with respect to the solar zenith angle.Moreover,JUNO can simultaneously measureDelta m^2_(21)using^8B solar neutrinos to a precision of 20% or better,depending on the central value,and to sub-percent precision using reactor antineutrinos.A comparison of these two measurements from the same detector will help understand the current mild inconsistency between the value of Delta m^2_(21)reported by solar neutrino experiments and the KamLAND experiment.

Off-label drug use in children over the past decade: a scoping review

To the Editor:Off-label drug use(OLDU)refers to the use of a drug outside of the age,indication,weight,dose,formulation,or route of administration indicated on the label.It is a major concern and a common practice for clinicians around the globe,especially for pediatricians,owing to the lack of pediatric-specific drug information.[1]Research showed that US office-based physicians had ordered 41.2 million off-label orders per year for children and the trend had been increasing from 2006 to 2015.

JUNO sensitivity on proton decay p→νK^(+)searches

The Jiangmen Underground Neutrino Observatory(JUNO)is a large liquid scintillator detector designed to explore many topics in fundamental physics.In this study,the potential of searching for proton decay in the p→νK^(+)mode with JUNO is investigated.The kaon and its decay particles feature a clear three-fold coincidence signature that results in a high efficiency for identification.Moreover,the excellent energy resolution of JUNO permits suppression of the sizable background caused by other delayed signals.Based on these advantages,the detection efficiency for the proton decay via p→νK^(+)is 36.9%±4.9%with a background level of 0.2±0.05(syst)±0.2(stat)events after 10 years of data collection.The estimated sensitivity based on 200 kton-years of exposure is 9.6×1033 years,which is competitive with the current best limits on the proton lifetime in this channel and complements the use of different detection technologies.

Effect of Sintering Time on the Mechanical and Corrosion Behavior of Zn-Mg Composites with a Core-Shell Structure Prepared by SPS

Zn-10 Mg composite with a core-shell structure was prepared by spark plasma sintering(SPS)technology,and a systematic study of the microstructure and properties has been conducted for different sintering times.The shell layer dominated by the hard MgZn2 phase thickens with the increase in sintering time,which has a positive effect on the mechanical and degradation properties of the material.The sample sintered for 20 min(T-20)has the best mechanical properties,with a compressive strength of 226 MPa and a compression rate of 6.5%.The corrosion resistance of samples increases as the sintering time prolongs,while the hydrogen evolution volume and pH value decrease in the immersion experiment.Furthermore,the increase in the shell thickness significantly reduces the corrosion rate,which is attributed to the weakening of the galvanic corrosion reaction between the Mg core and the MgZn2 shell.Therefore,composite with unique core-shell structure provides an advanced design idea for degradable biomaterials,and a reasonable control of sintering time can provide the optimal design strategy.

Search for Majoron at the COMET experiment

A new Goldstone particle named Majoron is introduced in order to explain the origin of neutrino mass via some new physics models assuming that neutrinos are Majorana particles.By expanding the signal region and using likelihood analysis,it becomes possible to search for Majoron using experiments originally designed to search forμ-e conversion.For the COMET experiment,the sensitivity of processμ→eJ is able to reach B(μ→eJ)=2.3×10-5in Phase-I and O(10-8)in Phase-II.Meanwhile,the sensitivities to search for Majoron in future experiments are also discussed in this article.