A joint optimization algorithm for focused energy delivery in precision electronic warfare

Focused energy delivery(FED) is a technique that can precisely bring energy to the specific region,which arouses wide attention in precision electronic warfare(PREW).This paper first proposes a joint optimization model with respect to the locations of the array and the transmitted signals to improve the performance of FED.As the problem is nonconvex and NP-hard,particle swarm optimization(PSO) is adopted to solve the locations of the array,while designing the transmitted signals under a feasible array is considered as a unimodular quadratic program(UQP) subproblem to calculate the fitness criterion of PSO.In the PSO-UQP framework established,two methods are presented for the UQP subproblem,which are more efficient and more accurate respectively than previous works.Furthermore,a threshold value is set in the framework to determine which method to adopt to take full advantages of the methods above.Meanwhile,we obtain the maximum localization error that FED can tolerate,which is significant for implementing FED in practice.Simulation results are provided to demonstrate the effectiveness of the joint optimization algorithm,and the correctness of the maximum localization error derived.

Discussion of 90°stopband in low-energy superconducting linear accelerators

Superconducting linear accelerators(SCL)have a high acceleration gradient and are capable of operating in a high-duty factor mode.For high-power and high-intensity SCL,the design of beam dynamics generally follows the principle that the zero-current periodic phase advance(σ0)of each degree of freedom is less than 90°to avoid envelope instability caused by space charge.However,this principle is obtained under the condition of a completely periodic focusing channel,and it is ambiguous for pseudoperiodic structures,such as linear accelerators.Although transverse beam dynamics without acceleration have been studied by other researchers,it appears that there are some connections between pure 2D and 3D beam dynamics.Based on these two points,five focusing schemes for the solenoid and quadrupole doublet channels were designed to simulate the beam behavior with non-constantσ0.Among them,the four schemes follow the characteristics of variation in the zero-current longitudinal phase advance(σ0l)under a constant acceleration gradient and synchronous phase.The zero-current transverse phase advance(σ0t)is consistent withσ0l,based on the equipartition requirement.The initialσ0twas set to 120°,110°,100°,and 90°,and was then gradually decreased to approximately 40°at the end of the channel.The last scheme maintains the maximumσ0tof88°by reducing the acceleration gradient of the corresponding cavities,until the point at whichσ0tequals88°with a normal gradient.Using the stopbands obtained from the linearized envelope equations and multiparticle particle-in-cell(PIC)simulations,the transport properties of both continuous and 3D-bunched beams with the acceleration of the five focusing schemes were studied.It was found that for a CW beam,when tune depression>0.7,σ0tcan break through 90°when the beams were transported in both solenoid and quadrupole doublet periodic focusing channels.When tune depression<0.7,the conclusions were different.For the solenoid focusing system,σ0tcan partially break through 90°,and the beam quality is not significantly affected.For the quadrupole doublet focusing system,a partial breakthrough of 90°has a greater impact on the beam quality.The same conclusions were obtained for a bunched beam with acceleration.

Protective effects of combined treatment with ciprofol and mild therapeutic hypothermia during cerebral ischemia-reperfusion injury

Despite improvement in cardiopulmonary resuscitation(CPR)performance,cardiac arrest(CA)is still associated with poor prognosis.The high mortality rate is due to multi-organ dysfunction caused by cerebral ischemia and reperfusion injury(I/R).The guidelines for CPR suggest the use of therapeutic hypothermia(TH)as an effective treatment to decrease mortality and the only approach confirmed to reduce I/R injury.During TH,sedative agents(propofol)and analgesia agents(fentanyl)are commonly used to prevent shiver and pain.However,propofol has been associated with a number of serious adverse effects such as metabolic acidosis,cardiac asystole,myocardial failure,and death.In addition,mild TH alters the pharmacokinetics of agents(propofol and fentanyl)and reduces their systemic clearance.For CA patients undergoing TH,propofol can be overdosed,leading to delayed awakening,prolonged mechanical ventilation,and other subsequent complications.Ciprofol(HSK3486)is a novel anesthetic agent that is convenient and easy to administer intravenously outside the operating room.Ciprofol is rapidly metabolized and accumulates at low concentrations after continuous infusion in a stable circulatory system compared to propofol.Therefore,we hypothesized that treatment with HSK3486 and mild TH after CA could protect the brain and other organs.

High-pressure new phases of V–N compounds

The high-pressure diagram of V–N compounds is enriched by proposed seven new stable high-pressure phases.The P-1-VN_4with the armchair N-rich structure may be quenched to ambient conditions.The formed N–N covalent bond plays an important role for the structural stability of N-chain.The charge transfer results in a V–N ionic bond interaction,which further improves the stability of N-chain structure.The P-1-VN_4,P4mnc-VN_8,and Immm-VN_(10)with the outstanding detonation properties have potential application in explosive field.

A meta-analysis of the success rates of heartbeat restoration within the platinum 10min among outpatients suffering from sudden cardiac arrest in China

Background:The optimal time to save a person who has had a sudden cardiac arrest is within the first few minutes of the incident.Early compression and early defibrillation should be performed at this time.Timeliness is the key to successful CPR; as such,Prof.He proposed the 'platinum 10 min' system to study early CPR issues.This paper systematically evaluates the success rates of heartbeat restoration within the 'platinum 10min' among patients suffering from sudden cardiac arrest.Methods:The clinical data of outpatients suffering from a cardiac arrest were retrieved from the China Knowledge Network(January 1975-January 2015),the Chongqing VIP database(January 1989-January 2015),and the Wanfang database(January 1990-January 2015).The success of the cardiopulmonary resuscitation(CPR) performed at different times after the patients had cardiac arrests was analyzed.Two researchers screened the literature and extracted the data independently.A meta-analysis was conducted using Stata 12.0.A total of 57 papers met the inclusion criteria,including 29,269 patients.Of these patients,1,776 had their heartbeats successfully restored.The results showed high heterogeneity(χ~2=3428.85,P<0.01,I2=98.4%).The meta-analysis was conducted using a random-effects model.The combined effect size was 0.171(0.144-0.199).Results:1) The success rate of heartbeat restoration did not differ among the four emergency treatment methods that patients received:the methods described in the 2000 Guidelines for CPR and Emergency Cardiovascular Care,that described in the 2005 version,2010 version,and another CPR method.2) The patients were divided into five groups based on the time when CPR was performed:the ?1min group,the 1-5min group,the 5-10 min group,the 10-15 min group and the >15min group.The CPR success rates of these five groups were 0.247(0.15-0.344),0.353(0.250-0.456),0.136(0.109-0.163),0.058(0.041-0.075),and 0.011(0.004-0.019),respectively.The CPR success rates did not differ between the patients in the ?1min group and the 1-5min group.This success rate was higher for the patients in the 1-5min group than those in the 10-15 min group,those in the 10-15 min group,and those in the >15min group.The CPR success rate was higher for the patients in the 5-10 min group than those in the 10-15 min group and those in the >15min group.The CPR success rate was higher for the patients in the 10-15 min group than those in the >15min group.In addition,the patients were divided into two groups based on whether CPR was performed within the first 10 min after the cardiac arrest occurred:the ?10min group and the >10min group.The CPR success rate was higher for the patients in the ?10min group [0.189(0.161-0.218)] than those in the >10min group [0.044(0.032-0.056)].3) Differences were not found between the CPR success rates among the patients in the telephone guidance group [0.167(0.016-0.351)] and those in the ?1min,1-5min,5-10 min,10-15 min,and >15min groups.4) The CPR success rates did not differ among in the patients in the witness + public group [0.329(0.221-0.436)],those in the ?1min group,and those in the 1-5min group.However,this success rate was higher in the patients in the witness + public group than those in the 5-10 min,10-15 min,and >15min groups.Conclusion:The success rate of heartbeat restoration did not differ among patients receiving CPR based on different guidelines.The success rate of CPR lies in its timeliness.The participation of the general population is the cornerstone of improving CPR.Providing complete emergency treatment equipment and perfecting comprehensive measures can improve the success rate of CPR among patients within the platinum 10 min.CPR research in China must be improved.

Meta-analysis of the success rate of heartbeat recovery in patients with prehospital cardiac arrest in the past 40 years in China

Background:Systematic evaluation of the successful heartbeat recovery rate(HRR)in patients during the platinum ten minutes after cardiac arrest.Methods:The databases of CNKI(January 1979–March 2019),Chongqing VIP(January 1989–March 2019),Wanfang(January 1990–March 2019)and Web of Science(January 1900-May 2020)were searched.To collect the clinical data of patients with cardiac arrest before hospitalization and analyze the cardiopulmonary resuscitation(CPR)at different times.Literature selection and data extraction were carried out by two researchers independently,and the meta package of R software(version 3.61)was used for analysis.Results:A total of 116 papers met the inclusion criteria,including 37,181 patients.Of these patients,3367 had their heartbeats successfully restored.The results showed a high degree of heterogeneity(χ2=6999.21,P<0.01,I2=97.6%).The meta-analysis was conducted using a random-effects model.The combined effect size was 0.199(0.157–0.250).(1)According to the five CPR groups(International Cardiopulmonary Resuscitation Guide 2000,2005,2010,2015 and other versions),the HRR of other versions[0.264(0.176–0.375)]was higher than the International Cardiopulmonary Resuscitation 2005 edition[0.121(0.092–0.158)].(2)The rescue time was divided into the 0 to≤5 min group,the 5 to≤10 min group,the 10 to≤15 min group,and the>15 min group.The HRR were 0.417(0.341–0.496),0.143(0.104–0.193),0.049(0.034–0.069),and 0.022(0.009–0.051),respectively.The HRR was higher in the 0 to≤5 min group than in the 5 to≤10 min group,the 10 to≤15 min group and the>15 min group.There was no difference between the 10 to≤15 min group and the>15 min group.(3)When the groups were stratified with the cutoff of 10 min,the≤10 min group HRR[0.250(0.202–0.306)]was higher than the>10 min group rate[0.041(0.029–0.057)].(4)The HRR of the telephone guidance group was[0.273(0.227–0.325)]lower than that of the 0 to≤5 min group[0.429(0.347–0.516)]but higher than that of the 5 to≤10 min group,the 10 to≤15 min group,and the>15 min group.(5)The HRR of the witness group[0.325(0.216–0.458)]was not different from that of the 0 to≤5 min group,but it was higher than those of the 5 to≤10 min group,the 10 to≤15 min group and the>15 min group.(6)There was no significant difference HRR between the witnessed group,the telephone guidance group and the≤10 min group.Conclusions:(1)The HRR is time-sensitive,and early rescue can improve it.(2)CPR performed within the platinum ten minutes must be executed by the public,and other forces are auxiliary.(3)The concept of peri-cardiac arrest period(PCAP)should be established and improved to guide CPR.

Microstructural characterization of as-cast and homogenized 2D70 aluminum alloy

The microstructure of the as-cast 2D70 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, X-ray diffraction （XRD）, and differential scanning calorimetry （DSC） analysis. The results indicate that the microstructure of the as-cast 2D70 aluminum alloy mainly consists of the dendritic network of aluminum solid solution and intermetallic compounds （Al2CuMg, Al2Cu, Al9FeNi, Cu2FeAl7, and Al7Cu4Ni）. After conventional homogenization, Al/Al2CuMg eutectic phases are dissolved into the matrix, and a small amount of high melting-point eutectic Al/Al2Cu phases exist in the matrix, resulting in an increase in the starting melting temperature. Under double homogenization, the high melting point Al/Al2Cu phases are dissolved, and no obvious change is observed for the size and morphology of Al9FeNi, Cu2FeAl7, and Al7CuaNi compounds.

孙氏镜联合输尿管硬镜同期治疗同侧输尿管结石和肾结石的疗效观察

目的评估孙氏镜联合输尿管硬镜同期治疗同侧输尿管结石和肾结石的安全性和有效性。方法选取需手术治疗的输尿管中下段结石合并肾结石患者56例作为研究对象,采用随机数字化法分为实验组(同期31例)和对照组(不同期25例),统计两组患者一般资料(年龄、性别、结石负荷、结石位置和肾结石CT值)、上镜成功率、结石寻及率、碎石成功率、总手术时间、手术并发症、术后住院天数、住院总费用和结石清除率(SFR)。结果两组患者上镜成功率[93.55%(29/31)和100.00%(25/25)]、结石寻及率[90.32%(28/31)和100.00%(25/25)]、碎石成功率[87.10%(27/31)和92.00%(23/25)]、手术并发症发生率[20.69%(6/29)和12.00%(3/25)]和术后第4周SFR[74.19%(23/31)和80.00%(20/25)]比较,差异均无统计学意义(P>0.05);手术总时间[(91.46±15.33)和(108.03±10.26)min]、术后住院天数[(3.54±1.08)和(6.02±2.06)d]和住院总费用[(17235.48±1352.36)和(21537.05±1036.27)元]比较,差异均有统计学意义(P<0.05)。结论孙氏镜联合输尿管硬镜同期治疗同侧输尿管中下段结石合并肾结石安全、有效。

Optimization of the S-band side-coupled cavities for proton acceleration

The proton beam with energy around 100 MeV has seen wide applications in modern scientific research and in various fields.However,proton sources in China fall short for meeting experimental needs owing to the vast size and expensive traditional proton accelerators.The Institute of Nuclear Science and Technology of Sichuan University proposed to build a 3 GHz side-coupled cavity linac(SCL)for re-accelerating a 26 MeV proton beam extracted from a CS-30 cyclotron to 120 MeV.We carried out investigations into several vital factors of S-band SCL for proton acceleration,such as optimization of SCL cavity geometry,end cell tuning,and bridge coupler design.Results demonstrated that the effective shunt impedance per unit length ranged from 22.5 to 59.8 MX/m throughout the acceleration process,and the acceleration gradient changed from 11.5 to 15.7 MV/m when the maximum surface electric field was equivalent to Kilpatrick electric field.We obtained equivalent circuit parameters of the biperiodic structures and applied them to the end cell tuning;results of the theoretical analysis agreed well with the 3D simulation.We designed and optimized a bridge coupler based on the previously obtained biperiodic structure parameters,and the field distribution un-uniformness was\1.5%for a two-tank module.The radio frequency power distribution system of the linac was obtained based on the preliminary beam dynamics design.

Pressure-induced isostructural phase transition in α-Ni（OH）2 nanowires

High pressure structural phase transition of monoclinic paraotwayite type α-Ni(OH)2 nanowires with a diameter of15 nm–20 nm and a length of several micrometers were studied by synchrotron x-ray diffraction(XRD) and Raman spectra.It is found that the α-Ni(OH)2 nanowires experience an isostructural phase transition associated with the amorphization of the H-sublattice of hydroxide in the interlayer spaces of the two-dimensional crystal structure at 6.3 GPa–9.3 GPa. We suggest that the isostructural phase transition can be attributed to the amorphization of the H-sublattice. The bulk moduli for the low pressure phase and the high pressure phase are 41.2(4.2) GPa and 94.4(5.6) GPa, respectively. Both the pressure-induced isostructural phase transition and the amorphization of the H-sublattice in the α-Ni(OH)2 nanowires are reversible upon decompression. Our results show that the foreign anions intercalated between the α-Ni(OH)2 layers play important roles in their structural phase transition.

Effect of void size and Mg contents on plastic deformation behaviors of Al-Mg alloy with pre-existing void:Molecular dynamics study

The plastic deformation properties of cylindrical pre-void aluminum-magnesium(Al-Mg)alloy under uniaxial tension are explored using molecular dynamics simulations with embedded atom method(EAM)potential.The factors of Mg content,void size,and temperature are considered.The results show that the void fraction decreases with increasing Mg in the plastic deformation,and it is almost independent of Mg content when Mg is beyond 5%.Both Mg contents and stacking faults around the void affect the void growth.These phenomena are explained by the dislocation density of the sample and stacking faults distribution around the void.The variation trends of yield stress caused by void size are in good agreement with the Lubarda model.Moreover,temperature effects are explored,the yield stress and Young’s modulus obviously decrease with temperature.Our results may enrich and facilitate the understanding of the plastic mechanism of Al-Mg with defects or other alloys.

Analysis of corneal morphologic and pathologic changes in early-stage congenital aniridic keratopathy

AIM：To determine typical corneal changes of congenital aniridic keratopathy（CAK）using corneal topography and confocal systems,and to identify characteristics that might assist in early diagnosis.METHODS：Patients with CAK and healthy control subjects underwent detailed ophthalmic examinations including axial length,corneal thickness,tear film condition,corneal topography,and laser-scanning in vivo confocal microscopy（IVCM）. RESULTS：In early stage aniridic keratopathy,Schirmer I test（SIT）,break-up time（BUT）,mean keratometry（mean K）and simulated keratometry（sim K）were reduced relative to controls（P〈0.05）,while simulation of corneal astigmatism（sim A）and corneal thickness were increased（P〈0.05）. In addition,significantly more eyes exhibited flat cornea compared with the control group. Inflammatory dendritic cells were present in the aniridic epithelium,with significantly increased density relative to controls（P〈0.05）. Palisade ridge-like features and abnormal cell morphology were observed in six out of sixteen CAK cases. In central cornea area,the aniridic corneas had the increased subbasal nerve density. CONCLUSION：These changes in corneal morphology in borderline situations can be useful to confirm the diagnosis of CAK.

Debris falling forecast method for spacecraft disintegrating separation

Large spacecraft fall out of orbit and re-enter the atmosphere at the end of their lifetime,and they can break up into small debris upon re-entry.The spacecraft debris generated by the disintegration may lead to high risk when the surviving debris reaches the ground.One way to reduce the damage risk of spacecraft is to simulate the spacecraft disintegration process and accurately predict the falling area.Aerodynamics seriously affects the reentering process,especially in the continuous flow regime.Aerodynamic force and heat are the main factors leading to debris disintegration.High dynamic pressure leads to sharp changes in attitude and complex trajectories during debris fall.A numerical method based on an unstructured Cartesian grid was developed to simulate the disintegrating separation problem by coupling the Navier-Stokes equation and the six-degree-of-freedom trajectory equation.A method combining the numerical method for dynamic processes with numerical simulation based on a static aerodynamic/dynamic characteristic database was developed for forecasting the falling area.Spacecraft disintegrating separation from 60 km was simulated using the method,and the multibody aerodynamic interference and the separation trajectory were predicted.The falling process was forecast by a numerical simulation method based on the static aerodynamic database/dynamic characteristic database when the debris went out of the influence domain.This method has good forecasting efficiency while considering the aerodynamic interference,making it a valuable method for forecasting disintegrating separation and falling debris.

Gas-kinetic unified algorithm for computable modeling of Boltzmann equation and application to aerothermodynamics for falling disintegration of uncontrolled Tiangong-No.1 spacecraft

How to solve the hypersonic aerothermodynamics around large-scale uncontrolled spacecraft during falling disintegrated process from outer space to earth,is the key to resolve the problems of the uncontrolled Tiangong-No.1 spacecraft reentry crash.To study aerodynamics of spacecraft reentry covering various flow regimes,a Gas-Kinetic Unified Algorithm(GKUA)has been presented by computable modeling of the collision integral of the Boltzmann equation over tens of years.On this basis,the rotational and vibrational energy modes are considered as the independent variables of the gas molecular velocity distribution function,a kind of Boltzmann model equation involving in internal energy excitation is presented by decomposing the collision term of the Boltzmann equation into elastic and inelastic collision terms.Then,the gas-kinetic numerical scheme is constructed to capture the time evolution of the discretized velocity distribution functions by developing the discrete velocity ordinate method and numerical quadrature technique.The unified algorithm of the Boltzmann model equation involving thermodynamics non-equilibrium effect is presented for the whole range of flow regimes.The gas-kinetic massive parallel computing strategy is developed to solve the hypersonic aerothermodynamics with the processor cores 500~45,000 at least 80%parallel efficiency.To validate the accuracy of the GKUA,the hypersonic flows are simulated including the reentry Tiangong-1 spacecraft shape with the wide range of Knudsen numbers of 220~0.00005 by the comparison of the related results from the DSMC and N-S coupled methods,and the low-density tunnel experiment etc.For uncontrolling spacecraft falling problem,the finite-element algorithm for dynamic thermalforce coupling response is presented,and the unified simulation of the thermal structural response and the hypersonic flow field is tested on the Tiangong-1 shape under reentry aerodynamic environment.Then,the forecasting analysis platform of end-of-life largescale spacecraft flying track is established on the basis of ballistic computation combined with reentry aerothermodynamics and deformation failure/disintegration.

Fracture mechanism of a laminated aluminum alloy plate during ballistic impact

The multilayered 7XXX series aluminum alloy was impacted by 7.62 mm ogival projectiles at velocities ranging from 787 to 851m·s^（-1）. The deformed microstructure under various impacting velocities and fracture surfaces of different sections were investigated at different physical scales to determine the process of failure.Optical microscopy（OM）,electron back-scattered diffraction（EBSD） and scanning electron microscopy（SEM） were used in the investigation. The results show that crater is constrained in the 7B52 front layer and two types of adiabatic shear bands which are transformed bands and deformed bands and different types of cracks are observed.Spall fracture is the significant failure mode of 7B52 front layer, and the resulting delamination leads to the presence of bending tensile fracture instead of the shear plugging.The ductile 7A01 layer blunts and deflects the spall crack tips, preventing the targets from full spall, and induces a constraint of 7A52 rear layer. The level of the constraint determines different fracture modes of 7A52 layer,accounting for the asymmetry of damage.

Mechanical properties,microstructure and surface quality of Al-1.2Mg-0.6Si-0.2Cu alloy after solution heat treatment

The effect of solution heat treatment （SHT） on mechanical properties, microstructure and surface quality of Al-1.2Mg-0.6Si-0.2Cu-0.6Zn alloy was investigated by tensile test, Erichsen test, surface topography, scanning electron microscope （SEM） and electron back-scattered diffraction （EBSD）. The results indicate that with the increase in SHT temperature, yield strength and cupping test value （IE） of the sheets increase greatly and reach a peak value, then decrease. Meanwhile, intermetallic com- pounds dissolve into matrix gradually. The grains grow up as SHT temperature increases, and abnormal grain growth leads to the surface defects after solution-treated above 560 ~C. Considering mechanical properties, IE value, residual phases, grain size and surface quality of the sheets, SHT temperature for the alloy should not be higher than 550 ℃.

Processing maps and microstructural evolution of Al-Cu-Li alloy during hot deformation

The hot deformation behavior of Al-Cu-Li alloy was investigated by hot compression tests in the temperature range of 340-500℃ with strain rate of 0.001-10.000 s^(-1).Based on the dynamic materials model(DMM),processing maps of the test alloy were developed for optimizing hot processing parameters.The optimum parameters of hot deformation for Al-Cu-Li alloy are at temperature of 400-430℃and strain rate of about 0.100 s^(-1),with efficiency of power dissipation of around 30%.The microstructural manifestation of the alloy deformed in instability domains is flow localization,and dynamic softening first occurs in flow localizations structure.In stable domains,dynamic recovery(DRV) and dynamic recrystallization(DRX) are the main microstructural evolution mechanism.DRX is gradually strengthened with the increase in deformation temperature and the decrease in strain rate.During hot deformation,the DRX mechanism of Al-Cu-Li alloy is dominated by continuous DRX(CDRX).A DRX model of Al-Cu-Li alloy is proposed based on the microstructural evolution process of the test alloy.

Effect of the Addition of High Li Concentration on the Microstructure and Mechanical Properties of Al-Mg-Si Alloys with Different Mg Contents

In the present work,the microstructural characteristics and mechanical properties of Al-1.5 Mg-0.6Si and Al-3.0 Mg-0.6Si alloy containing 3 wt%Li were investigated by optical microscopy(OM),X-ray diffraction analysis(XRD),scanning electron microscopy(SEM),time of flight-secondary ion mass spectrometry(SIMS),transmission electron microscopy(TEM),and mechanical performance testing.The addition of Li reduces the density of the base alloy by up to 8.4%.The residual second phases contain Mg and Si in the hot-rolled condition,but the Mg/Si atomic ratio decreases after quenching,which means that Li substitute some of the Mg and convert Mg_(2)Si into a(Mg,Li)_(2)Si phase during solution treatment.The results of SIMS observations confirm this.The high Mg-containing alloy has a more rapid hardening response compared to the low Mg-containing alloy.TEM observation reveals that theδ′-Al3Li+β′′-Mg_(2)Si dual phases can be observed in the high Mg-containing alloy after aging for 100 h at 170°C.The higher Mg content enhances the precipitation of theδ′phase,which results in the high Mg-containing alloy having a larger average diameter size ofδ′particles and widerδ′-precipitate-free zones(δ′-PFZs).The mechanical properties are significantly improved with the elastic modulus increasing by more than 16.5%.However,the existence of large second phases and wideδ′-PFZs in Li-containing alloys is detrimental to their ductility;as a result,their elongation is much lower than that of the base alloy.

DSMC modeling of rarefied ionization reactions and applications to hypervelocity spacecraft reentry flows

The DSMC modeling is developed to simulate three-dimensional(3D)rarefied ionization flows and numerically forecast the communication blackout around spacecraft during hypervelocity reentry.A new weighting factor scheme for rare species is introduced,whose key point is to modify the corresponding chemical reaction coefficients involving electrons,meanwhile reproduce the rare species in resultants and preserve/delete common species in reactants according to the weighting factors.The resulting DSMC method is highly efficient in simulating weakly inhomogeneous flows including the Couette shear flow and controlling statistical fluctuation with high resolution.The accurate reliability of the present DSMC modeling is also validated by the comparison with a series of experimental measurements of the Shenzhou reentry capsule tested in a low-density wind tunnel from the HAI of CARDC.The obtained electron number density distribution for the RAM-C II vehicle agrees well with the flight experiment data,while the electron density contours for the Stardust hypervelocity reentry match the reference data completely.In addition,the present 3D DSMC algorithm can capture distribution of the electron,N+and O+number densities better than the axis-symmetric DSMC model.The introduction of rare species weighting factor scheme can significantly improve the smoothness of the number density contours of rare species,especially for that of electron in weak ionization case,while it has negligible effect on the macroscopic flow parameters.The ionization characteristics of the Chinese lunar capsule reentry process are numerically analyzed and forecasted in the rarefied transitional flow regime at the flying altitudes between 80 and 97 km,and the simulations predict communication blackout altitudes which are in good agreement with the actual reentry flight data.For the spacecraft reentry with hypervelocity larger than the second cosmic speed,it is forecasted and verified by the present DSMC modeling that ionization reactions will cover the windward capsule surface,leading to reentry communication blackout,and the communication interruption must be considered in the communication design during reentry in rarefied flow regimes.

A Gas-Kinetic Unified Algorithm for Non-Equilibrium Polyatomic Gas Flows Covering Various Flow Regimes

In this paper,a gas-kinetic unified algorithm(GKUA)is developed to investigate the non-equilibrium polyatomic gas flows covering various regimes.Based on the ellipsoidal statistical model with rotational energy excitation,the computable modelling equation is presented by unifying expressions on the molecular collision relaxing parameter and the local equilibrium distribution function.By constructing the corresponding conservative discrete velocity ordinate method for this model,the conservative properties during the collision procedure are preserved at the discrete level by the numerical method,decreasing the computational storage and time.Explicit and implicit lower-upper symmetric Gauss-Seidel schemes are constructed to solve the discrete hyperbolic conservation equations directly.Applying the new GKUA,some numerical examples are simulated,including the Sod Riemann problem,homogeneous flow rotational relaxation,normal shock structure,Fourier and Couette flows,supersonic flows past a circular cylinder,and hypersonic flow around a plate placed normally.The results obtained by the analytic,experimental,direct simulation Monte Carlo method,and other measurements in references are compared with the GKUA results,which are in good agreement,demonstrating the high accuracy of the present algorithm.Especially,some polyatomic gas non-equilibrium phenomena are observed and analysed by solving the Boltzmann-type velocity distribution function equation covering various flow regimes.