Laser-assisted Simulation of Dose Rate Effects of Wide Band Gap Semiconductor Devices

Laser-assisted simulation technique has played a crucial role in the investigation of dose rate effects of silicon-based devices and integrated circuits,due to its exceptional advantages in terms of flexibility,safety,convenience,and precision.In recent years,wide band gap materials,known for their strong bonding and high ionization energy,have gained increasing attention from researchers and hold significant promise for extensive applications in specialized environments.Consequently,there is a growing need for comprehensive research on the dose rate effects of wide band gap materials.In response to this need,the use of laser-assisted simulation technology has emerged as a promising approach,offering an effective means to assess the efficacy of investigating these materials and devices.This paper focused on investigating the feasibility of laser-assisted simulation to study the dose rate effects of wide band gap semiconductor devices.Theoretical conversion factors for laser-assisted simulation of dose rate effects of GaN-based and SiC-based devices were been provided.Moreover,to validate the accuracy of the conversion factors,pulsed laser and dose rate experiments were conducted on GaN-based and SiC-based PIN diodes.The results demonstrate that pulsed laser radiation andγ-ray radiation can produce highly similar photocurrent responses in GaN-based and SiC-based PIN diodes,with correlation coefficients of 0.98 and 0.974,respectively.This finding reaffirms the effectiveness of laser-assisted simulation technology,making it a valuable complement in studying the dose rate effects of wide band gap semiconductor devices.

Single-Channel Speech Enhancement Using Critical-Band Rate Scale Based Improved Multi-Band Spectral Subtraction

This paper addresses the problem of single-channel speech enhancement in the adverse environment. The critical-band rate scale based on improved multi-band spectral subtraction is investigated in this study for enhancement of single-channel speech. In this work, the whole speech spectrum is divided into different non-uniformly spaced frequency bands in accordance with the critical-band rate scale of the psycho-acoustic model and the spectral over-subtraction is carried-out separately in each band. In addition, for the estimation of the noise from each band, the adaptive noise estimation approach is used and does not require explicit speech silence detection. The noise is estimated and updated by adaptively smoothing the noisy signal power in each band. The smoothing parameter is controlled by a-posteriori signal-to-noise ratio (SNR). For the performance analysis of the proposed algorithm, the objective measures, such as, SNR, segmental SNR, and perceptual evaluations of the speech quality are conducted for the variety of noises at different levels of SNRs. The speech spectrogram and objective evaluations of the proposed algorithm are compared with other standard speech enhancement algorithms and proved that the musical structure of the remnant noise and background noise is better suppressed by the proposed algorithm.

厚夹矸顶煤放出率计算方法研究

针对含厚夹矸放顶煤开采的顶煤放出率难以计算的现状,本文以淮北朱仙庄煤矿Ⅱ863工作面为研究背景,采用散体介质流相似模拟试验以及顶煤放出率现场测定试验,研究了不同层位的顶煤回收率,并分析其运动规律,研究结果表明:相似模拟试验中顶煤平均放出率78%,现场试验顶煤平均放出率77.8%;不同层位顶煤放出率呈现“两头低中间高”的规律;该研究不仅实现了含厚夹矸顶煤放出率的计算,还为结构复杂的厚夹矸顶煤开采提供了科学依据。

广义频分复用系统峰均功率比抑制算法

为了降低广义频分复用系统存在着多载波系统中固有的高峰均功率比问题,本文提出了一种适用于广义频分复用系统的子载波抑制高峰均功率比算法。该算法以限幅法为基础,降低了系统的高峰均功率比,但与限幅法不同的是,该算法几乎不会对带外性能及误码率性能造成影响。由于子载波抑制高峰均功率比算法的峰均功率比抑制性能略差于限幅法,因此本文进一步提出将部分序列传输与子载波抑制高峰均功率比结合来进一步抑制系统高峰均功率比的算法。仿真表明:本文提出的算法的高峰均功率比抑制性能与限幅法相同,且不会对系统的带外与误码率性能造成影响。

冷轧压下率对高强无取向电工钢变形组织和磁性能的影响

借助场发射扫描电镜(SEM+EBSD)、快速升温管式炉和交流磁性能测量仪研究高强无取向电工钢冷轧变形组织和磁性能随冷轧压下率的变化规律。结果表明:冷轧高强无取向电工钢中形成含有大量亚结构的粗糙条带和变形量较小的光滑条带。粗糙条带具有γ取向,主要为{111}〈110〉,光滑条带具有{112}〈110〉和{001}〈110〉取向。粗糙条带中存在大量宽度约为2~3μm的剪切带,与轧向呈20°~35°夹角,且随压下率增大,数量逐渐增多。剪切带与基体间具有一定取向差,随压下率增大,剪切带逐渐从{111}〈110〉取向转向{223}〈110〉取向,与基体间取向差逐渐增大。退火后Goss和{111}面织构增多,{001}面织构减少;轧向磁感应强度增大,横向磁感应强度减小,各向异性显著,铁损下降。

应变速率对TB6钛合金绝热剪切敏感性的影响

在室温下采用分离式霍普金森压杆对TB6钛合金帽型试样进行动态加载,研究了应变速率对TB6钛合金绝热剪切敏感性的影响。结果表明,应变速率1950~2510 s^(-1)时,4组试样均表现出明显的应变硬化效应;在绝热温升作用下,4组试样均发生热塑失稳形成绝热剪切带;受冲击载荷和材料晶粒尺寸影响,基体和绝热剪切带之间的过渡区域变形梯度不明显;热剪切带内100 nm等轴晶的形成是旋转动态再结晶机制作用的结果。通过观察金相、表征绝热剪切敏感性及计算扩展能发现,TB6钛合金绝热剪切敏感性随应变速率增加而增加。

1.27 μm O_(2)(a^(1)Δ g)气辉临边观测辐射传 输特性

1.27μm波段的O_(2)(a^(1)Δg)气辉辐射具有辐射信号强、空间跨度大、自吸收效应弱等诸多内禀优势,是临近空间大气遥感的重要目标源,对于中高层大气的动力学及热学特性研究,全球温室气体探测,以及臭氧浓度三维层析等卫星遥感具有重要的科学意义和应用价值。首先基于O_(2)(a^(1)Δg)光化学反应模型,研究了O_(2)(a^(1)Δg)气辉的产生机制及湮灭机理,在此基础上,计算得到了O_(2)(a^(1)Δg)气辉体辐射率廓线,并基于HITRAN数据库给出的谱线强度及爱因斯坦系数,提出了两种计算O_(2)(a^(1)Δg)气辉光谱分布的方法。采用最新的分子光谱参数、光化学反应速率常数及F10.7太阳紫外通量等参数,结合光化学反应模型计算得到的O_(2)(a^(1)Δg)气辉体辐射率廓线信息,借助逐线积分算法,建立了1.27μm O_(2)(a^(1)Δg)气辉临边观测辐射传输理论模型,并分析了自吸收效应对不同临边观测高度处气辉辐射光谱强度的影响。然后,利用剥洋葱算法,对大气图像扫描成像吸收光谱仪(SCIAMACHY)在临边观测模式下测得的O_(2)分子近红外大气带的气辉辐射信号进行处理得到了目标层O_(2)(a^(1)Δg)气辉辐射光谱,并通过谱积分算法反演得到了O_(2)(a^(1)Δg)气辉的体辐射率廓线信息。最后通过对比气辉临边观测辐射传输理论模型计算得到的以及SCIAMACHY仪器测量反演得到的1.27μm O_(2)(a^(1)Δg)辐射光谱及体辐射率廓线信息,验证1.27μm O_(2)(a^(1)Δg)气辉临边观测辐射传输理论模型的可靠性与合理性。基于比对结果,对O_(2)(a^(1)Δg)气辉临边辐射强度和体辐射率的影响因素进行了分析。分析结果表明,在50 km以上的高空区域,理论计算结果与卫星实测结果吻合性较好,而随着海拔高度的降低,两者的偏差逐渐增大,这是因为在临边观测模式下,中低空区域的卫星遥感信号受自吸收效应及大气散射效应影响严重。此外,与HITRAN数据库给出的谱线强度参数相比,基于爱因斯坦系数建立的O_(2)(a^(1)Δg)气辉临边辐射模型与卫星实测结果更加吻合。1.27μm O_(2)(a^(1)Δg)气辉临边观测辐射传输理论模型的建立,对于临近空间大气遥感,奠定了理论基础。

正火冷却速度对20CrNiMo钢组织和性能的影响

利用扫描电镜、金相显微镜和硬度计等检测手段研究不同正火冷却速度对20CrNiMo钢组织和性能的影响。结果表明:经炉冷的20CrNiMo钢组织中主要为珠光体和铁素体;经风冷的20CrNiMo钢组织中主要为珠光体和铁素体,此外还发现少量的马氏体;经空冷+风冷的20CrNiMo钢组织中除了珠光体和铁素体外,还发现一定量的马氏体。随着正火冷却速度的增加,容易诱发马氏体相变。此外还发现,随着正火冷却速度的增加,20CrNiMo钢的洛氏硬度基本保持平稳,显微硬度部分区域有所上升,这与组织变化趋势相一致。

液压弹簧式准零刚度隔振系统特性分析

针对车载精密仪器低频隔振,文章将两个液压弹簧作为负刚度元件,并与竖直弹簧并联构造了一种新型准零刚度隔振系统。通过对系统进行静力学分析,得到了实现准零刚度特性的参数条件;利用平均法求解了系统在简谐力激励下的幅频响应;采用马蒂厄方程判别法对系统的稳定性进行了分析;又分析了线性刚度参数和非线性刚度参数对力传递率的影响。研究结果表明,相较于线性系统,准零刚度系统的起始隔振频率降低了54%左右。该研究使得车载精密仪器在低频乃至超低频工况下也不会轻易损坏,具有广泛的应用前景。

Formation of adiabatic shearing band for high-strength Ti-5553 alloy:A dramatic thermoplastic microstructural evolution

By using split Hopkinson pressure bar, optical microscopy and electronic microscopy, we investigate the influence of initial microstructures on the adiabatic shear behavior of high-strength Ti-5Al-5V-5Mo-3Cr(Ti-5553) alloy with lamellar microstructure and bimodal microstructure. Lamellar alloy tends to form adiabatic shearing band(ASB) at low compression strain, while bimodal alloy is considerably ASBresistant. Comparing with the initial microstructure of Ti-5553 alloy, we find that the microstructure of the ASB changes dramatically. Adiabatic shear of lamellar Ti-5553 alloy not only results in the formation of recrystallized β nano-grains within the ASB, but also leads to the chemical redistribution of the alloying elements such as Al, V, Cr and Mo. As a result, the alloying elements distribute evenly in the ASB.In contrast, the dramatic adiabatic shear of bimodal alloy might give rise to the complete lamination of the globular primary a grain and the equiaxial prior β grain, which is accompanied by the dynamic recrystallization of a lamellae and β lamellae. As a result, ASB of bimodal alloy is composed of a/β nanomultilayers. Chemical redistribution does not occur in ASB of bimodal alloy. Bimodal Ti-5553 alloy should be a promising candidate for high performance armors with high mass efficiency due to the processes high dynamic flow stress and excellent ASB-resistance.

Mathematical Modelling and 3D FEM Analysis of the Influence of Initial Stresses on the ERR in a Band Crack’s Front in the Rectangular Orthotropic Thick Plate

This paper deals with the mathematical modelling and 3D FEM study of the energy release rate(ERR)in the band crack’s front contained in the orthotropic thick rectangular plate which is stretched or compressed initially before the loading of the crack's edge planes.The initial stretching or compressing of the plate causes uniformly distributed normal stress to appear acting in the direction which is parallel to the plane on which the band crack is located.After the appearance of the initial stress in the plate it is assumed that the crack's edge planes are loaded with additional uniformly distributed normal forces and the ERR caused with this additional loading is studied.The corresponding boundary value problem is formulated within the scope of the so-called 3D linearized theory of elasticity which allows the initial stress on the values of the ERR to be taken into consideration.Numerical results on the influence of the initial stress,anisotropy properties of the plate material,the crack’s length and its distance from the face planes of the plate on the values of the ERR,are presented and discussed.In particular,it is established that for the relatively greater length of the crack’s band,the initial stretching of the plate causes a decrease,but the initial compression causes an increase in the values of the ERR.

Characteristics of Growth Rate of Coral Porites from Sanya Bay,Hainan Island and its Relationship to Environmental Variables

The time series of annual and seasonal growth rate of two coral Porites, collected at different sites of fringe reef in the Sanya Bay, Hainan Island have been obtained by analyzing X-radiograph of skeletal band. There are obvious seasonal variations of the growth rate in two corals, the average low rate in winter and the average high rate from spring to autumn. Compared with the time series of environmental variables, the coral growth rate is only correlated statistically with seawater temperature and not related to rainfall and sunshine. Furthermore, the growth rate in spring and summer is correlated directly with seawater temperature of the winter-early spring ( between December and March ) and the other seasonal growth rate has no relationship with seasonal variations of seawater temperature. We propose that seawater temperature is one of the factors affecting the coral growth rate in the area and the low seawater temperature is a primary control of the seasonal growth rate.

Analysis of damage localization for ductile metal in process of shear band propagation

Distribution of localized damage in shear band can’ t be predicted theoretically based on classical elastoplastic theory. The average damage variable in shear band was considered to be a non-local variable. Based on non-local theory, an analytical expression for the localized damage in strain-softening region of shear band in the process of shear band propagation was presented using boundary condition and symmetry of local damage variable, etc. The results show that dynamic shear softening modulus, dynamic shear strength and shear elastic modulus influence the distribution of the localized damage in shear band. Internal length of ductile metal only governs the thickness of shear band. In the strain-softening region of shear band, the local damage variable along shear band’s tangential and normal directions is non-linear and highly non-uniform. The non-uniformities in the normal and tangential directions of shear band stem from the interactions and interplaying among microstructures and the non-uniform distribution of shear stress, respectively. At the tail of the strain-softening region, the maximum value of local damage variable reaches 1. This means that material at this position fractures completely. At the tip of shear band and upper as well as lower boundaries, no damage occurs. Local damage variable increases as dynamic shear softening modulus decreases or shear elastic modulus increases, leading to difficulty in identification or detection of damage for less ductile metal material at higher strain rates.

LOCALIZED SUPERPLASTIC BEHAVIOUR INα-TITANIUM AT HIGH STRAIN RATE

The microstructure of x-Ti/ mild steel composite fabricated by using constant stand-off cladding technique was observed with optical microscopy, SEM and TEM analyses. Very fine equiaxed grains (<0.1um) with a low dislocation density were observed in the adiabatic shear bands (ASB) this enables a thermomechanical response that may lead to a super plastic de formation.

Analyses of Adiabatic Shear in Some Metals from Calculations of the Temperature Distribution and the Cooling Rate

The temperature distribution under shear with a high strain rate and the cooling rate of the shear bands of Al, Cu and 0.06C steel have been calculated using a computer. The results show that the temperature of shear band increases with the increase of the average strain rate (_o). When _o is in the range 8×10~5 to 10~6 1/s, the structure of the adiabatic shear band in a 0.06C steel is martensite but it becomes metallic glass if _o=10~6 1/s. As to A1 and Cu, the structure of the adiabatic shear bands can also be of metallic glass if _o is greater than 1.8×10~6 and 5.5×10~7 1/s respectively. It explains that Cu tends most difficultly to form adiabatic shear band, while 0.06C steel most readily among the three metals.

A method for calculating damage evolution in adiabatic shear band of titanium alloy

A method for calculating the evolution of the local damage variable at the adiabatic shear band(ASB)center was proposed.In the present method,the JOHNSON-COOK model and the nonlocal theory were adopted,and the damage variable formula applicable for the bilinear(linearly elastic and strain-softening)constitutive relation was further generalized to consider the plastic deformation occurring in the strain-hardening stage.Aiming at Ti-6Al-4V,the effect of strain rate on the evolution of the local damage variable at the ASB center was investigated.In addition,a parametric study was carried out,including the effects of strain-hardening exponent,strain rate sensitive coefficient,thermal-softening exponent,static shear strength,strain-hardening modulus,shear elastic modulus,work to heat conversion factor,melting temperature and initial temperature.The damage extent at the ASB center in the radial collapse experiment was assessed.It is found that at higher strain rates the damage in the ASB becomes more serious at the same average plastic shear strain of the ASB.

Microstructural Characterization of the Shear Bands in Fe-Cr-Ni Single Crystal by EBSD

An investigation has been made into the microstructural characterization of the shear bands generated under high-strain rate （≈10^4 s^-1） deformation in Fe-15%Cr-15%Ni single crystal by EBSD-SEM （electron backscatter diffraction-scanning electron microscopy）, TEM （transmission electron in microscopy） and HREM （high- resolution electron microscopy）. The results reveal that the propagation of the shear band exhibits an asymmetrical behavior arising from inhomogenous distribution in plasticity in the bands because of different resistance to the collapse in different crystallographic directions; The γ-ε-α′phase transformations may take place inside and outside the bands, and these martensitic phases currently nucleate at intersections either between the twins and deformation bands or between the twins and ε-sheet. Investigation by EBSD shows that recrystallization can occur in the bands with a grain size of an average of 0.2μm in diameter. These nano-grains are proposed to attribute to the results of either dynamic or static recrystallization, which can be described by the rotational recrystallization mechanism. Calculation and analysis indicate that the strain rate inside the shear band can reach 2.50×10^6 s^-1, which is higher, by two or three orders of magnitude, than that exerted dynamically on the specimen tested.

Self-Adaptive Control System for Additive Manufacturing Using Double Electrode Micro Plasma Arc Welding

Wire arc additive manufacturing(WAAM)has been investigated to deposit large-scale metal parts due to its high deposition efficiency and low material cost.However,in the process of automatically manufacturing the high-quality metal parts by WAAM,several problems about the heat build-up,the deposit-path optimization,and the stability of the process parameters need to be well addressed.To overcome these issues,a new WAAM method based on the double electrode micro plasma arc welding(DE-MPAW)was designed.The circuit principles of different metal-transfer models in the DE-MPAW deposition process were analyzed theoretically.The effects between the parameters,wire feed rate and torch stand-off distance,in the process of WAAM were investigated experimentally.In addition,a real-time DE-MPAW control system was developed to optimize and stabilize the deposition process by self-adaptively changing the wire feed rate and torch stand-off distance.Finally,a series of tests were performed to evaluate the control system’s performance.The results show that the capability against interferences in the process of WAAM has been enhanced by this self-adaptive adjustment system.Further,the deposition paths about the metal part’s layer heights in WAAM are simplified.Finally,the appearance of the WAAM-deposited metal layers is also improved with the use of the control system.

Circulation Retrieval of Wake Vortices under Rainy Conditions with an X Band Radar

At airports, runway operation is the limiting factor for the overall throughput; specifically the fixed and overly conservative ICAO wake turbulence separation minima. The wake turbulence hazardous flows can dissipate quicker because of decay due to air turbulence or be transported out of the way on oncoming traffic by cross-wind, yet wake turbulence separation minima do not take into account wind conditions. Indeed, for safety reasons, most airports assume a worst-case scenario and use conservative separations; the interval between aircraft taking off or landing therefore often amounts to several minutes. However, with the aid of accurate wind data and precise measurements of wake vortex by radar sensors, more efficient intervals can be set, particularly when weather conditions are stable. Depending on traffic volume, these adjustments can generate capacity gains, which have major commercial benefits. This paper presents the use of Electronic scanning radar for detecting wake vortices. In this method, the raindrops Doppler spectrogram is used to retrieve the strength of the wake vortex. Numerical simulation are performed to establish an empirical model used during the retrieval method. This paper presents also the results obtained during the trials of the PARIS-CDG data set recorded from October 2014 to November 2015 with an X-band RADAR developed and deployed by THALES.