不同城市道路工况下重型商用车侧风气动特性研究

依托动网格技术,并采用局部节点位移方式,研究城市道路方案分别为重型商用车经过位于其背风侧的单个建筑物、经过位于其迎风侧的单个建筑物和连续经过位于其迎风侧的2个建筑物3种情况下的瞬态气动特性。方案中网格节点位移速度即重型商用车行驶速度定为15 ms,侧风速度为10 m/s。结果显示,建筑物对重型商用车瞬态气动特性的影响较为明显,行驶过程中侧向力系数与横摆力矩系数在1 s内变化值达到5.0之多,相应的侧向力和横摆力矩变化值约为12 kN和30 kN·m,变化率峰值可达-12kN·s^-1和35 kN·m·s^-1,并且方向在行驶过程中发生改变。

Formation and characterization of core-shell CL-20/TNT composite prepared by spray-drying technique

The core-shell 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/2,4,6-Trinitrotoluene(CL-20/TNT)composite was prepared by spray-drying method in which sensitive high energy explosive(CL-20)was coated with insensitive explosive(TNT).The structure and properties of different formulations of CL-20/TNT composite and CL-20/TNT mixture were characterized by scanning electron microscopy(SEM),Transmission electron microscopy(TEM),Laser particle size analyzer,X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),differential scanning calorimetry(DSC),impact sensitivity test and detonation performance.The results of SEM,TEM,XPS and XRD show that e-CL-20 particles are coated by TNT.When the ratio of CL-20/TNT is 75/25,core-shell structure is well formed,and thickness of the shell is about 20e30 nm.And the analysis of heat and impact show that with the increase of TNT content,the TNT coating on the core-shell composite material can not only catalyze the thermal decomposition of core material(CL-20),but also greatly reduce the impact sensitivity.Compared with the CL-20/TNT mixture(75/25)at the same ratio,the characteristic drop height of core-shell CL-20/TNT composite(75/25)increased by 47.6%and the TNT coating can accelerate the nuclear decomposition in the CL-20/TNT composites.Therefore,the preparation of the core-shell composites can be regarded as a unique means,by which the composites are characterized by controllable decomposition rate,high energy and excellent mechanical sensitivity and could be applied to propellants and other fields.

Direct ink writing of 3D-Honeycombed CL-20 structures with low critical size

3D-Honeycombed CL-20 structures with low critical size of detonation have been fabricated successfully for intelligent weapon systems using a micro-flow direct ink writing(DIW) technology.The CL-20-based explosive ink for DIW technology was prepared by a two-component adhesive system with waterborne polyurethane(WPU) and ethyl cellulose(EC).Not only the preparation of the explosive ink but also the principle of DIW process have been investigated systematically.The explosive ink displayed stro ng shea rthinning behavior that permitted layer-by-laye r deposition from a fine nozzle onto a substrate to produce complex shapes.The EC content was varied to alter the pore structure distribution and rheological behavior of ink samples after curing.The deposited explosive composite materials are of a honeycombed structure with high porosity,and the pore size distribution increases with the increase of EC content.No phase change was observed during the preparation process.Both WPU and EC show good compatibility with CL-20 particles.Apparently high activation energy was realized in the CL-20-based composite ink compared with that of the refined CL-20 due to the presence of non-energetic but stable WPU.The detonation performance of the composite materials can be precisely controlled by an adjustment in the content of binders.The 3D honeyco mbed CL-20 structures,which are fabricated by DIW technology,have a very small critical detonation size of less than 69 μm,as demonstrated by wedge shaped charge test.The ink can be used to create 3D structures with complex geometries not possible with traditional manufacturing techniques,which presents a bright future for the development of intelligent weapon systems.

Insensitive energetic microspheres DAAF/RDX fabricated by facile molecular self-assembly

Insensitive energetic materials are promising in the defense weapons field.However,energetic materials still suffer from great challenges and the concern about their safety limits their utilization.In this work,insensitive energetic explosive 3,30-diamino-4,40-azoxyfurazan/hexahydro-1,3,5-trinitro-1,3,5-triazine(DAAF/RDX)microspheres were fabricated by self-assembly method.Rod-like DAAF/RDX was prepared by mechanical ball milling for comparison.DAAF/RDX composites with different mass ratios(90:10,80:20,and 70:30)were obtained.The morphologies and structures of as-obtained DAAF/RDX composites were characterized by scanning electron microscopy(SEM),powder x-ray diffraction(PXRD)and fourier transform infrared spectroscopy(FT-IR).The results showed that DAAF/RDX microspheres exhibited regular shaped microspheres with sizes from 0.5 to 1.2 mm.There was no crystal transition during the modification process.The thermal properties of as-obtained materials were then evaluated by differential scanning calorimetry(DSC)and materials studio software.DAAF/RDX microspheres showed an advanced decomposition peak temperature compared with rod-like DAAF/RDX.The binding energy and peak temperature values at zeroβ_(i)(T_(P0))of DAAF/RDX(90:10)increased by 36.77 kJ/mol,1.6℃,and 58.11 kJ/mol,12.3℃compared to DAAF/RDX(80:20)and DAAF/RDX(70:30),indicating the better thermal stability of DAAF/RDX(90:10).The characteristic drop height(H_(50))of DAAF/RDX(higher than 100 cm)composites was higher than that of raw RDX(25 cm),suggesting significant improvements in mechanical safety.The preparation of DAAF/RDX microspheres is promising for the desensitization of RDX and useful for the formation of other materials and future wide applications.

Preparation and characterization of HMX/EVA/hBNNSs microcomposites with improved thermal stability and reduced sensitivity

Hexagonal boron nitride nanosheets(HBNNSs)have huge potential in the field of coating materials owing to their remarkable chemical stability,mechanical strength and thermal conductivity.Thin-layer hBNNSs were obtained by a liquid-phase exfoliation of h-BN powders and incorporated into EVA coatings for improving the safety performance of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX).HBNNSs and ethylene-vinyl acetate copolymer(EVA)were introduced to HMX by a solvent-slurry process.For comparison,the HMX/EVA and HMX/EVA/graphene(HMX/EVA/G)composites were also prepared by a similar process.The morphology,crystal form,surface element distribution,thermal decomposition property and impact sensitivity of HMX/EVA/hBNNSs composites were contrastively investigated.Results showed that as prepared HMX/EVA/hBNNSs composites were well coated with hBNNSs and EVA,and exhibited better thermal stability and lower impact sensitivity than that of HMX/EVA and HMX/EVA/G composites,suggesting superior performance of desensitization of hBNNSs in explosives.

Performances and direct writing of CL-20 based ultraviolet curing explosive ink

A new type of explosive ink formulation that can be quickly cured was prepared with unsaturated polyester as binder,styrene as active monomer,2,4,6-trimethylbenzoyl-diphenylphosphine oxide as photoinitiator,and hexanitrohexaazaisowurtzitane(CL-20)as the main explosive.Then the explosive inkdirect writing technology was used to charge the micro-sized energetic devices,the curing mechanism of the explosive ink was discussed,and the microstructure,safety performance and explosive transfer performance of the explosive ink molded samples were tested and analyzed.Results indicate that the composite material has a fast curing molding speed,its hardness can reach 2H within 8 min.The crystal form of CL-20 in the molded sample is still type.The CL-20 based UV-curing explosive ink formulation has good compatibility,its apparent activation energy is increased by about 3.5 kj/mol.The composite presents a significant reduction in impact sensitivity and its characteristic drop height can reach 39.8 cm,whichis about 3 times higher than the raw material.When the line width of charge is 1.0 mm,the critical thickness of the explosion can reach 0.015 mm,and the explosion velocity is 7129 m/s when the charge density is 1.612 g/cm^(3).

Contrast-enhanced ultrasound using SonoVue mixed with oral gastrointestinal contrast agent to evaluate esophageal hiatal hernia: Report of three cases and a literature review

BACKGROUND Due to a thicker abdominal wall in some patients,ultrasound artifacts from gastrointestinal gas and surrounding tissues can interfere with routine ultrasound examination,precluding its ability to display or clearly show the structure of a hernial sac(HS)and thereby diminishing diagnostic performance for esophageal hiatal hernia(EHH).Contrast-enhanced ultrasound(CEUS)imaging using an oral agent mixture allows for clear and intuitive identification of an EHH sac and dynamic observation of esophageal reflux.CASE SUMMARY In this case series,we report three patients with clinically-suspected EHH,including two females and one male with an average age of 67.3±16.4 years.CEUS was administered with an oral agent mixture(microbubble-based SonoVue and gastrointestinal contrast agent)and identified a direct sign of supradiaphragmatic HS(containing the hyperechoic agent)and indirect signs[e.g.,widening of esophageal hiatus,hyperechoic mixture agent continuously or intermittently reflux flowing back and forth from the stomach into the supradiaphragmatic HS,and esophagus-gastric echo ring(i.e.,the“EG”ring)seen above the diaphragm].All three cases received a definitive diagnosis of EHH by esophageal manometry and gastroscopy.Two lesions resolved upon drug treatment and one required surgery.The recurrence rate in follow-up was 0%.The data from these cases suggest that the new non-invasive examination method may greatly improve the diagnosis of EHH.CONCLUSION CEUS with the oral agent mixture can facilitate clear and intuitive identification of HS and dynamic observation of esophageal reflux.

ELEMENTAL CONTENTS IN ORGANS AND TISSUES OF CHINESE ADULT MEN

Objective To provide basis of reference values for relevant parameters of Chinese Reference Man. Methods Eighteen kinds of major organ or tissue samples, including muscle, rib, liver, and so on, were obtained from 4 areas (Hebei, Shanxi, Jiangsu, and Sichuan provinces) with different dietary patterns in China in autopsy of 16 healthy adult men, who had just encountered sudden deaths. At the same time, whole blood samples were collected from 10 volunteers living in each of these areas. The concentrations of 56 elements in these samples were detected by using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), and Graphite Furnace Atomic Absorption Spectrometry (GF-AAS) techniques. Based on obtained concentrations and reference values of these organ or tissue weights for Chinese Reference Man, the relative elemental burdens in these organs or tissues as well whole body were also estimated. Results The concentrations of 56 elements in 18 main organs or tissues were determined all together and their elemental organ or tissue and whole body burdens were estimated. Furthermore, the distributions of important elements for radiation protection in these organs or tissues were emphatically discussed. Conclusion By summing with past related results, the total results obtained from the series of research may provide more reliable and better representative basis of these reference values for Chinese Reference Man than before.

Fabrication and characterization of mussel-inspired layer-by-layer assembled CL-20-based energetic films via micro-jet printing

Three-dimensional(3D)micro-jet printing is a droplet deposition technique based on liquid-phase materials.To improve the deposition density and performance of energetic films with micro/nanoscale on an energetic chip,polydopamine(PDA)was utilized as a linker bridge to induce the in-situ self-assembly of CL-20-based energetic film via 3D micro-jet printing.The self-assembly was extensively characterized by confocal laser scanning microscopy(CLSM),SEM,power-XRD,XPS,and DSC.The performance of the self-assembled film was verified by the mechanical properties and detonation properties,and a possible self-assembly mechanism in the layer-by-layer micro-jet printing process was proposed.The results indicated PDA-induced self-assembly enhanced the physical entanglement between the binders and energetic crystal,reduced the porosity from 15.87%to 11.28%,and improved the elastic modulus and the detonation performance of the CL-20-based energetic film.This work proposes a novel and promising energetic film design and fabrication strategy to enhance the interaction between the energetic composite layers in the micro-jet printing process.

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

Plasmonic optical manipulation has emerged as an affordable alternative to manipulate single chemical and biological molecules in nanoscience.Although the theoretical models of sub-5 nm single-molecule trapping have been considered promising,the experimental strategies remain a challenge due to the Brownian motions and weak optical gradient forces with significantly reduced molecular polarizability.Herein,we address direct trapping and in situ sensing of single molecules with unprecedented size,down to∼5Åin solution,by employing an adjustable plasmonic optical nanogap and single-molecule conductance measurement.The theoretical simulations demonstrate that local fields with a high enhancement factor,over 103,were generated at such small nanogaps,resulting in optical forces as large as several piconewtons to suppress the Brownian motion and trap a molecule of length sub-1 nm.This work demonstrates a strategy for directly manipulating the small molecule units,promising a vast multitude of applications in chemical,biological,and materials sciences at the single-molecule level.

Electron transition manipulation under graphene-mediated plasmonic engineering nanostructure

Monolayer graphene has attracted enormous attention owing to its unique electronic and optical properties.However,achieving an effective approach without applying electrical bias for manipulating the charge transfer based on graphene is elusive to date.Herein,we realized the manipulation of excitons’transition from emitter to the graphene surface with plasmonic engineering nanostructures and firstly obtained large enhancements for photon emission on the graphene surface.The localized plasmons generated from the plasmonic nanostructures of shell-isolated nanoparticle coupling to ultra-flat Au substrate would dictate a consistent junction geometry while enhancing the optical field and dominating the electron transition pathways,which may cause obvious perturbations for molecular radiation behaviors.Additionally,the three-dimensional finite-difference time-domain and time-dependent density functional theory were also carried out to simulate the distributions of electromagnetic field and energy levels of hybrid nanostructure respectively and the results agreed well with the experimental data.Therefore,this work paves a novel approach for tunning graphene charge/energy transfer processes,which may hold great potential for applications in photonic devices based on graphene.

S, N co-doped carbon nanotube-encapsulated core-shelled CoS2@Co nanoparticles： efficient and stable bifunctional catalysts for overall water splitting

Hydrogen, serving as a clean, sustainable energy source, may be mainly produced from electrolysis water.Herein, we report cobalt disulphide encapsulated in self-catalyzed carbon nanotubes(S,N-CNTs/CoS_2@Co) serving as a bifunctional catalyst, which exhibits excellent hydrogen evolution reaction performance(10.0 mA cm^(-2) at 0.112 V, and low Tafel slope for 104.9 mV dec^(-1)) and oxygen evolution reaction performance(10.0 mA cm^(-2) at 1.57 V, and low Tafel slope for 76.1 mV dec^(-1)), meanwhile with a strong stability at various current densities. In-depth study reveals that the excellent catalytic properties can be mainly attributed to the increased catalytic sites induced by S, N co-doping, the improved electronic conductivity derived from the carbon nanotubes, and Mott-Schottky effect between the metal cobalt and semiconductive cobalt disulfide. Notably, when the bifunctional catalysts are applied to overall water splitting, a low potential of 1.633 V at the current density of 10.0 mA cm^(-2) is achieved, which can compete with the precious metal catalyst benchmarks in alkaline media, demonstrating its promising practicability in the realistic water splitting application. This work elucidates a practicable way to the design of transition metal and nano-carbon composite catalysts for a broad application in the fields of energy chemistry.

Application of Omega vortex identification method in cavity buffeting noise

The cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding,where weak vortices coexist with strong vortices and the strong shear phenomenon also exists at the opening of the cavity.Therefore,it is of great significance to accurately capture vortices at the opening for the control of the cavity buffeting noise.This paper first compares the Omega vortex identification method with the Q andλ2criteria based on the large eddy simulation(LES)of the backward-facing step flow,and it is found that the Omega method enjoys the following advantages:it is not sensitive to a moderate threshold change andΩ=0.52 can be used as a fixed threshold,it can capture both the strong and weak vortices at the same time;and it will not be contaminated by the shear.Then the Omega(Ω)method is applied to the LES of the cavity buffeting noise:the mechanism of the cavity buffeting noise is studied based on a simple cavity model firstly,and then the effects of the incoming boundary layer thicknesses and the incoming boundary layer shapes on the cavity buffeting noise are analyzed.The results show that:theΩmethod clearly captures the processes of the vortex generation,development,collision and fragmentation,verifying that the generation of the cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding;as the thickness of the incoming boundary layer increases,the free shear layer becomes more stable and the Helmholtz resonance is avoided effectively,thereby the cavity buffeting noise is reduced effectively,adding a convexity upstream of the cavity opening to interfere the shape of the incoming boundary layer to reduce the acoustic feedback effect can reduce the cavity buffeting noise effectively.

Clinical and immunological features of convalescent pediatric patients infected with the SARS-CoV-2 Omicron variant in Tianjin, China

COVID-19 has spread surprisingly fast worldwide, and new variants continue to emerge. Recently, the World Health Organization acknowledged a new mutant strain “Omicron”, with children were accounting for a growing share of COVID-19 cases compared with other mutant strains. However, the clinical and immunological characteristics of convalescent pediatric patients after Omicron infection were lacking. In this study, we comparatively analyzed the clinical data from pediatric patients with adult patients or healthy children and the effects of SARSCoV-2 vaccine on the clinical and immune characteristics in convalescent pediatric patients. Our results indicated that convalescent pediatric patients had unique clinical and immune characteristics different from those of adult patients or healthy children, and SARS-CoV-2 vaccination significantly affected on the clinical and immune characteristics and the prevention of nucleic acid re-detectable positive(RP) in convalescent patients. Our study further deepens the understanding of the impact of Omicron on the long-term health of pediatric patients and provides a valuable reference for the prevention and treatment of children infected with Omicron.

Manipulating the light-matter interactions in plasmonic nanocavities at 1 nm spatial resolution

The light-matter interaction between plasmonic nanocavity and exciton at the sub-diffraction limit is a central research field in nanophotonics.Here,we demonstrated the vertical distribution of the light-matter interactions at~1 nm spatial resolution by coupling A excitons of MoS2 and gap-mode plasmonic nanocavities.Moreover,we observed the significant photoluminescence(PL)enhancement factor reaching up to 2800 times,which is attributed to the Purcell effect and large local density of states in gap-mode plasmonic nanocavities.Meanwhile,the theoretical calculations are well reproduced and support the experimental results.

Preparation and characterization of Cu2ZnSn(S,Se)4 film by drop-coating of Cu2ZnSnS4 nanoink

In this work,a simple and facile one-pot oleylamine solvothermal synthetic method was developed to synthesize Cu2ZnSnS4（CZTS） nanocrystals.And the Cu2ZnSn（S,Se）4（CZTSSe） thin films were prepared by selenizing CZTS nanocrystals.The obtained CZTS nanocrystals and CZTSSe films were studied using X-ray diffraction（XRD）,transmission electron microscopy（TEM）,scanning electron microscopy（SEM）,energy-dispersive X-ray spectroscopy（EDX）,and ultraviolet–visible spectrophotometer（UV–Vis）.TEM results show that the sphere–like CZTS nanoparticles with diameter between 12 and 35 nm are polydispersed.XRD studies indicate that the prepared CZTS nanocrystals form kesterite crystal structure,and the CZTSSe films with kesterite crystal structure are also obtained at the annealing temperatures of 500 and550 °C.In particular after annealing at 500 °C for 20 min,the CZTSSe film exhibits a smooth,uniform,crack-free,and large-grained topography and possesses Cu-poor and Sn-rich composition.Moreover,it shows strong optical absorption from visible to near-infrared（IR） region,and its optical band gap（Eg） is found to be about 1.44 e V.

Control of water contamination on side window of road vehicles by A-pillar section parameter optimization

The water contamination on the side windows of moving vehicles is a crucial issue in improving the driving safety and the comfort.In this paper,an effective optimization method is proposed to reduce the water contamination on the side windows of automobiles.The accuracy and the efficiency of the numerical simulation are improved by using the lattice Boltzmann method,and the Lagrangian particle tracking method.Optimized parameters are constructed on the basis of the occurrence of the water deposition on a vehicle’s side window.The water contamination area of the side window and the aerodynamic drag are considered simultaneously in the design process;these two factors are used to form the multi-objective optimization function in the genetic algorithm(GA)method.The approximate model,the boundary-seeded domain method,and the GA method are combined in this study to enhance the optimization efficiency.After optimization,the optimal parameters for the A-pillar section are determined by setting the boundary to an area of W=7.77 mm,L=1.27 mm and H=11.22 mm.The side window’s soiling area in the optimized model is reduced by 66.93%,and the aerodynamic drag is increased by 0.41%only,as compared with the original model.It is shown that the optimization method can effectively solve the water contamination problem of side windows.