Effect of desorbed gas on microwave breakdown on vacuum side of dielectric window

The gas desorbed from the dielectric surface has a great influence on the characteristics of microwave breakdown on the vacuum side of the dielectric window. In this paper, the dielectric surface breakdown is described by using the electromagnetic particle-in-cell-Monte Carlo collision(PIC-MCC) model. The process of desorption of gas and its influence on the breakdown characteristics are studied. The simulation results show that, due to the accumulation of desorbed gas, the pressure near the dielectric surface increases in time, and the breakdown mechanism transitions from secondary electron multipactor to collision ionization. More and more electrons generated by collision ionization drift to the dielectric surface, so that the amplitude of self-organized normal electric field increases in time and sometimes points to the dielectric surface. Nevertheless, the number of secondary electrons emitted in each microwave cycle is approximately equal to the number of primary electrons. In the early and middle stages of breakdown, the attenuation of the microwave electric field near the dielectric surface is very small. However, the collision ionization causes a sharp increase in the number density of electrons,and the microwave electric field decays rapidly in the later stage of breakdown. Compared with the electromagnetic PIC-MCC simulation results, the mean energy and number of electrons obtained by the electrostatic PIC-MCC model are overestimated in the later stage of breakdown because it does not take into account the attenuation of microwave electric field. The pressure of the desorbed gas predicted by the electromagnetic PIC-MCC model is close to the measured value,when the number of gas atoms desorbed by an incident electron is taken as 0.4.

Rapid printing of 3D porous scaffolds for breast reconstruction

Prosthesis implantation and fat transplantation are common breast reconstructionmethods.In general,prosthesis implantation alone does not achieve a realistic enough appearance,and fat transplantation alone is difficult to achieve in the correct capacity.To date,no reports have focused on methods of combining fat with implanted prostheses for breast reconstruction.Using a newly designed bionic ink(i.e.,polyether F127 diacrylate(F127DA)&poly(ethylene glycol)diacrylate(PEGDA))and projection-based three-dimensional bioprinting(PBP),we report the development of a new method for printing porous prostheses.PEGDA was used to improve the printing precision of the prosthesis by increasing the gel point of F127DA and reducing the impact of external temperature.The compression modulus of the printed prosthesis was very close to that of prostheses currently used in clinical practice and to that of natural breasts.Finally,stromal vascular fraction gel(SVF-gel),a human fat extract,was injected into the pores of the synthesized prostheses to prepare a prosthesis mixed with adipose tissue.These were implanted subcutaneously in nude mice to observe their biological performance.After 14 and 28 days of observation,the prosthesis showed good biocompatibility,and adipose tissues grew well in and around the prosthesis.This result shows that a porous prosthesis containing pre-placed adipose tissues is a promising breast reconstruction material.

Multi-resonator coupled metamaterials for broadband vibration suppression

In this study,multi-resonator coupled metamaterials(MRCMs)with local resonators are proposed to obtain the multiple and wide band gaps.Kinetic models of the MRCMs are established,and the boundary conditions of the unit cell are obtained with Bloch's theorem.The effects of structural parameters,including the mass of the resonator and the spring stiffness,on the distributions of the band gaps are studied.Furthermore,the frequency domain responses and the time domain responses are calculated for analyzing the structural vibration characteristics and the effects of damping on structural vibration.The results show that the frequency domain response can accurately express the distributions of the band gaps of the MRCMs,and we can increase the number and the width of the band gaps by using the MRCMs for the superior vibration suppression capability.

Micrometer-sized ferrosilicon composites wrapped with multi-layered carbon nanosheets as industrialized anodes for high energy lithium-ion batteries

Various nanostructured architectures have been demonstrated to be effective to address the issues of high capacity Si anodes. However, the scale-up of these nano-Si materials is still a critical obstacle for commercialization. Herein, we use industrial ferrosilicon as low-cost Si source and introduce a facile and scalable method to fabricate a micrometer-sized ferrosilicon/C composite anode, in which ferrosilicon microparticles are wrapped with multi-layered carbon nanosheets. The multi-layered carbon nanosheets could effectively buffer the volume variation of Si as well as create an abundant and reliable conductivity framework, ensuring fast transport of electrons. As a result, the micrometer-sized ferrosilicon/C anode achieves a stable cycling with 805.9 m Ah g-1 over 200 cycles at 500 mA g-1 and a good rate capability of455.6 mAh g-1 at 10 A g-1. Therefore, our approach based on ferrosilicon provides a new opportunity in fabricating cost-effective, pollution-free, and large-scale Si electrode materials for high energy lithium-ion batteries.

Dependence of plasma structure and propagation on microwave amplitude and frequency during breakdown of atmospheric pressure air

The structure and propagation of the plasma in air breakdown driven by high-power microwave have attracted great interest.This paper focuses on the microwave amplitude and frequency dependence of plasma formation at atmospheric pressure using one two-dimensional model,which is based on Maxwell’s equations coupled with plasma fluid equations.In this model,we adopt the effective electron diffusion coefficient,which can describe well the change from free diffusion in a plasma front to ambipolar diffusion in the bulk plasma.The filamentary plasma arrays observed in experiments are well reproduced in the simulations.The density and propagation speed of the plasma from the simulations are also close to the corresponding experimental data.The size of plasma filament parallel to the electric field decreases with increasing frequency,and it increases with the electric field amplitude.The distance between adjacent plasma filaments is close to one-quarter wavelength under different frequencies and amplitudes.The plasma propagation speed shows little change with the frequency,and it increases with the amplitude.The variations of plasma structure and propagation with the amplitude and frequency are due to the change in the distribution of the electric field.

Analysis of Reflection Properties of High Power Microwave Propagation in Mixture-Atmosphere

A simple theoretical modeling is made to describe the reflection features of the high power microwave (HPM) in the mixture-atmosphere. The time-space dependent mixture-atmosphere is generated by ionization of the neutral molecules in atmosphere. Reflection will occur when HPM propagates in such mixture-atmosphere. The reflection characteristic of the HPM propagation in the mixture-atmosphere is investigated by FDTD numerical experiments in inhomogeneous medium, the influence on the reflection for different HPM parameters is concluded. An additional stability conditions for the FDTD difference scheme of the HPM mixture-atmosphere propagation model are presented.

Effect of air breakdown on microwave pulse energy transmission

The energy transmission of the long microwave pulse for the frequency of 2.45 GHz and 5.8 GHz is studied by using the electron fluid model, where the rate coefficients are deduced from the Boltzmann equation solver named BOLSIG＋. The breakdown thresholds for different air pressures and incident pulse parameters are predicted, which show good agreement with the experimental data. Below the breakdown threshold, the transmitted pulse energy is proportional to the square of the incident electric field amplitude. When the incident electric field amplitude higher than the breakdown threshold increases,the transmitted pulse energy decreases monotonously at a high air pressure, while at a low air pressure it first decreases and then increases. We also compare the pulse energy transmission for the frequency of 2.45 GHz with the case of 5.8 GHz.

Experimental Investigation of Boundary Layer Characteristics on Blade Surface under Different Inlet Flow Conditions

In this paper, an experimental study is conducted on cascade boundary layer under different inlet conditions. New method is used to measure the total pressure in blade surface boundary layer directly using total pressure probe. Total pressure in both suction and pressure surfaces are acquired at different inlet conditions by changing incidence angle and inlet Mach number. In addition, a series of parameters related to boundary layer characteristics are calculated. The objective of the experiment is to investigate the influence of inlet flow conditions on them. The results indicate that influence of incidence angle is significant when other conditions are the same. Displacement thickness, momentum thickness as well as other parameters display some disciplines for variation. In contrast, inlet Mach number has only a small influence in that boundary layer becomes a litter thinner with increasing Mach number. Comparisons of experimental results with theoretical expectations demonstrate that the method in this experiment is effective and reliable.

A Hybrid Key Management Scheme Based on Clustered Wireless Sensor Networks

According to the weakness of session key construction based on node’s own location, we propose a hybrid key management scheme which based on clustered wireless sensor networks. The use of hierarchical thinking, reducing the amount of key storage and computing, while supporting network topology, dynamic key management for which aims to prevent leakage. Through analyzing, it shows that the scheme have certain advantages in key connectivity, security, communication and energy consumption.

染料负载型MOFs材料在荧光传感检测中的应用研究进展

随着新型传感材料的需求持续增长,染料负载型金属有机框架(MOFs)材料因其独特的物理化学性质和丰富的结构多样性而引起了广泛关注.本综述旨在全面审视染料负载型MOFs材料作为荧光传感器的潜力和应用,主要总结了染料负载型MOFs材料在荧光传感检测方面的研究进展,详细讨论了其在环境监测、生物医学检测和水资源痕量水检测等领域中的应用案例.之后,本综述总结了目前研究开发的工作重点,并提出了未来研究的发展方向.最后,强调了染料负载型MOFs材料在快速、准确和可视化检测领域的广阔应用前景,并对未来的研究方向进行了展望.

miR-133a-3p修饰的间充质干细胞外泌体促进心肌梗死后大鼠心肌修复

目的探讨miR-133a-3p修饰的人源脐带血间充质干细胞(ucMSC)衍生的外泌体对急性心肌梗死(AMI)后大鼠心肌修复的作用。方法体外扩增培养ucMSC,将携带miR-133a-3p的慢病毒载体及阴性对照载体分别转染至ucMSC,分别提取其分泌的外泌体,命名为miR-133a-3p-Exo及miR-NC-Exo。采用冠状动脉左前降支结扎术构建大鼠AMI模型,分别于梗死区边缘原位注射miR-133a-3p-Exo或miR-NC-Exo进行干预。干预后28 d,采用超声心动图检测大鼠心功能;采用Masson染色检测大鼠梗死后心肌纤维化面积;采用TUNEL染色评估梗死后大鼠心肌凋亡情况;采用免疫荧光染色评估梗死后大鼠血管新生情况。结果与miR-NC-Exo组相比,miR-133a-3p-Exo组在AMI后28 d左心室射血分数较高[(64.2%±8.9%)比(47.4%±9.8%),P<0.05],心肌纤维化面积[(18.0%±1.5%)比(31.2%±7.3%),P<0.01]和凋亡率[(15.1%±4.4%)比(25.6%±3.6%),P<0.05]较低;梗死边缘区血小板-内皮黏附因子(CD31)及平滑肌肌动蛋白(α-SMA)阳性血管的数量均较多[CD31:(13.9±2.0)条比(2.9±0.9)条,α-SMA:(11.0±1.6)条比(3.5±0.9)条,P均<0.0001]。结论miR-133a-3p修饰的ucMSC分泌的外泌体可有效抑制梗死后心肌凋亡、促进梗死后血管新生,从而改善AMI后大鼠的心功能。

Targeting CD47-SIRPα axis for Hodgkin and non-Hodgkin lymphoma immunotherapy

The interaction between cluster of differentiation 47(CD47)and signal regulatory proteinα(SiRPa)protects healthy cells from macrophage attack,which is crucial for maintain-ing immune homeostasis.Overexpression of CD47 occurs widely across various tumor cell types and transmits the"don't eat me"signal to macrophages to avoid phagocytosis through binding to SIRPa.Blockade of the CD47-SIRPa axis is therefore a promising approach for cancer treat-ment.Lymphoma is the most common hematological malignancy and is an area of unmet clin-ical need.This review mainly described the current strategies targeting the CD47-SIRPa axis,including antibodies,SiRPaFc fusion proteins,small molecule inhibitors,and peptides both in preclinical studies and clinical trials with Hodgkin lymphoma and non-Hodgkin lymphoma.

Development of a potent benzonitrile-based inhibitor of glutaminyl-peptide cyclotransferase-like protein(QPCTL)with antitumor efficacy

Dear Editor,Immune checkpoint therapies manipulating the immune system to eliminate tumor cells have shown remarkable clinical efficacy in treating various cancers.CD47,an emerging efficient immune checkpoint,is crucial for cancer cells to evade macrophagemediated phagocytosis by interaction with signal-regulatory proteinα(SIRPα).Antibodies blocking the CD47/SIRPαinteraction have been effective to promote macrophage-mediated phagocytosis in various types of cancer in mice and humans.CD47 is not only highly expressed in tumor cells,but also normal cells,such as red blood cells(RBCs).Thus,during clinical trials involving cancer patients,anti-CD47 antibodies may promote the macrophagesmediated phagocytosis of RBCs,ultimately inducing undesirable anemia side effects.In contrast,small molecule inhibitors interrupting CD47/SIRPαaxis have shown potential to overcome the anemia,possibly due to their lower immunogenicity and shorter half-life compared to antibodies.1 Hence,developing the novel strategies,especially those without the anemia side effect,to intervene in CD47/SIRPαinteraction will benefit cancer immunotherapy.

Emerging phagocytosis checkpoints in cancer immunotherapy

Cancer immunotherapy,mainly including immune checkpoints-targeted therapy and the adoptive transfer of engineered immune cells,has revolutionized the oncology landscape as it utilizes patients’own immune systems in combating the cancer cells.Cancer cells escape immune surveillance by hijacking the corresponding inhibitory pathways via overexpressing checkpoint genes.Phagocytosis checkpoints,such as CD47,CD24,MHC-I,PD-L1,STC-1 and GD2,have emerged as essential checkpoints for cancer immunotherapy by functioning as“don’t eat me”signals or interacting with“eat me”signals to suppress immune responses.Phagocytosis checkpoints link innate immunity and adaptive immunity in cancer immunotherapy.Genetic ablation of these phagocytosis checkpoints,as well as blockade of their signaling pathways,robustly augments phagocytosis and reduces tumor size.Among all phagocytosis checkpoints,CD47 is the most thoroughly studied and has emerged as a rising star among targets for cancer treatment.CD47-targeting antibodies and inhibitors have been investigated in various preclinical and clinical trials.However,anemia and thrombocytopenia appear to be formidable challenges since CD47 is ubiquitously expressed on erythrocytes.Here,we review the reported phagocytosis checkpoints by discussing their mechanisms and functions in cancer immunotherapy,highlight clinical progress in targeting these checkpoints and discuss challenges and potential solutions to smooth the way for combination immunotherapeutic strategies that involve both innate and adaptive immune responses.

A time sequential microfluid sensor with Tesla valve channels

The concentration of biomarkers in sweat can be used to evaluate human health,making efficient sweat sensing a focus of research.While flow channel design is often used to detect sweat velocity,it is rarely incorporated into the sensing of biomarkers,limiting the richness of sensing results.In this study,we report a time sequential sensing scheme for uric acid in sweat through a sequential design of Tesla valve channels.Graphene electrodes for detecting uric acid and directional Tesla valve flow channels were fabricated using laser engraving technology to realize time sequential sensing.The performance of the channels was verified through simulation.The time sequential detection of uric acid concentration in sweat can help researchers improve the establishment of human health management systems through flexible wearable devices.

Analysis of COVID-19 clusters involving vertical transmission in residential buildings in Hong Kong region

Multiple clusters of coronavirus disease 2019(COVID-19)in Hong Kong have involved vertical transmissions in residential buildings,wherein the flats of confirmed cases were often vertically aligned.Data on the buildings and cases associated with 19 such clusters were retrieved and compared with the corresponding data on the entirety of Hong Kong region.Vertical transmissions usually occurred in old high-rise buildings with small flat areas and low estate prices during winter.In addition,infection occurred frequently among the elderly and among upstairs neighbours of index cases.Virus-laden aerosols may have been transmitted between flats mostly via shared drainpipes,and the vertical distribution of the confirmed cases in a building varied by its drainage system design.For buildings with their entire drainpipes installed indoors,both the upstairs and downstairs neighbours of the index case flats could be infected.By comparison,buildings with their drainage stacks installed outdoors had lower infection risks and demonstrated a clearer pattern of vertical transmission:most infected cases resided upstairs from the index case flats,indicating that the virus spread could be dominated by the stack effect.This study provides valuable data and analysis for developing epidemic control strategies for residential buildings.

Effects of post annealing on the microstructure,precipitation behavior,and mechanical property of a(CoCrNi)_(94)Al_(3)Ti_(3)medium-entropy alloy fabricated by laser powder bed fusion

The additive manufacturing of multi-principal element alloys has remarkable potential for industrial ap-plications.In this study,a(CoCrNi)_(94)Al_(3)Ti_(3)medium-entropy alloy(MEA)with adequate strength-ductility synergy was prepared via laser powder bed fusion.The microstructural evolution,mechanical property,and deformation mechanisms of the MEA were investigated after post annealing for a short period(0.5 h)at a temperature range of 773-1373 K using various microstructural characterization techniques and quantitative analysis.The static recrystallization temperature of the(CoCrNi)_(94)Al_(3)Ti_(3)MEA ranged from 973 to 1073 K.The average grain size first decreased and then increased,while the dislocation den-sity persistently decreased and texture gradually weakened with increasing annealing temperature.Cr-richσ-phase precipitates formed after 1073 K and then gradually dissolved at 1373 K,while Ni,Al,and Ti elements were aggregated to form a small amount of fine L1_(2)coherent precipitates with an aver-age diameter of approximately 70 nm at 1373 K.The evolution of the dislocation density,grain size,and precipitates significantly influenced the propensity of deformation twins and stacking faults,which consequently affected the strain hardening behavior and mechanical properties.The quantitative calcu-lation of strengthening mechanisms showed that dislocation strengthening played a dominant role at annealing temperatures below 1073 K,and it significantly weakened at 1373 K.Precipitation and grain boundary strengthening both markedly increased owing to the formation of precipitation particles and recrystallization-induced grain refinement after annealing at 1073 K.

Elastic Wave Propagation in Lattice Metamaterials with Koch Fractal

In this study,the wave propagation properties of lattice metamaterials with Koch fractal structures are investigated in terms of band structures and directional wave propagation.The analytical models of lattice metamaterials are established using the finite element method,and the dispersion relation is solved using the Bloch’s theorem.The band structures of the lattice metamaterials with different numbers of iterations are studied,and the group velocities at a selected frequency are calculated to analyze the directional wave propagation characteristics.Furthermore,dynamic responses of the finite structures are calculated using commercial finite element software to verify the band gaps and directional wave propagation behaviors in the lattice metamaterials.The results show that multiple and low band gaps are present in the lattice materials with various geometric parameters of the Koch fractal,and the position of the lowest band gap decreases as the number of iterations increases.The results indicate the potential applications of lattice metamaterials with Koch fractals for vibration isolation and multi-functional design.

Numerical Simulation of the Dynamic Behaviors of a Gas Tungsten Welding Arc for Joining Magnesium Alloy AZ61A

Based on the Magneto-Hydro-Dynamic（MHD） theory, a united three-dimensional（3D） transient numerical model is developed to investigate the dynamic behaviors of arc plasma for a magnesium alloy AZ61A gas tungsten arc welding（GTAW） arc. The arc, electrode and workpiece are integrated into one calculation domain to avoid both presumed distribution of the current density at the electrode tip and the assumption of constant conditions of interface between welding arc and workpiece. The distributions of electric potential, current density, magnetic flux density, electromagnetic force, velocity, temperature, and pressure of the arc plasma in the 3D space are analyzed by using the numerical model. Results indicate that the maximum gradient of the electric potential in the whole arc space exists around the electrode tip, where the electric current density, electromagnetic force, and temperature are also the maximum. However, maximum pressure is found at the velocity stagnation, which is above the workpiece.Comparison between predicted temperature and measured one in arc region shows a good agreement.

Recent Advances in Spectroscopic Gas Sensing With Micro/Nano-Structured Optical Fibers

With micro-and nano-structured optical fibers,parts-per-million to parts-per-trillion level gas detection has been demonstrated for a range of gases such as methane,acetylene,ethane,carbon monoxide,hydrogen,and oxygen.We review the recent development in optical fiber gas cells and gas detection systems based on direct absorption,photothermal,photoacoustic,and stimulated Raman spectroscopies.