爆炸粉末烧结颗粒间摩擦引起的界面温升研究

 针对爆炸粉末烧结过程中颗粒间的摩擦效应提出了一种无夹角斜碰撞模型,分析了烧结过程中颗粒间摩擦力随温度的变化规律,借助于LS-DYNA有限元程序研究了冲击压力、颗粒大小、材料强度等因素对孔隙闭合时间的影响,给出了颗粒界面温升的表达式。研究结果表明,由摩擦引起的颗粒界面的温升与材料特性、颗粒度、冲击角度、冲击压力等因素有关,随材料的蓄热能力、传热能力和材料强度的增加而减小,并随着材料疏松程度、颗粒直径、冲击压力的增加而增加;在粉末颗粒直径和冲击压力不是太小的情况下,颗粒表面温度将达到材料的熔点。     

刚热粘塑性轴对称一维流的解法

 根据轴对称一维流动的控制方程，采用刚塑性流体假设，将偏微分方程组化为一阶常微分方程组，从而可引入热粘塑性本构关系。利用成熟的一阶常微分方程组解法求解。文中还对厚壁圆管承受外压作用下塌缩运动情况、应力分布、温度分布进行了计算。     

爆炸烧结制备W-Al含能结构材料及其准静态压缩特性研究

通过爆炸烧结法,采用不同粒度的W、Al混合粉末,成功制备了近乎致密的W-Al含能结构材料(ESM)。研究发现:冲击波压力是粉末致密化的主导因素,粉末粒径对烧结密度和微观结构的影响显著,W的粒径越小,颗粒团聚越明显,从而阻碍致密化,在致密块体中形成连续分布的W相。所制备样品的最大抗压强度和失效应变分别达到288 MPa和20%,材料的力学性能和断裂模式主要取决于连续相,Al相连续的ESM抗压强度低、塑性较好,呈轴向劈裂破坏;而W相连续的ESM则表现出脆性和高抗压强度,破坏模式为剪切破坏,与Al的低强度高塑性和W高强度脆性特性一致。     

纳米陶瓷粉末在爆炸压实过程中的破碎行为研究

 在爆炸压实过程中，纳米颗粒所受冲击载荷发生显著变化的时间远远大于应力波传过颗粒特征长度所用时间；同时，陶瓷颗粒在爆炸冲击过程中主要表现为脆性。基于以上两个事实提出了弹性假设，推导了颗粒在压实过程中的受力状态。回顾了判断脆性材料破坏的三个准则，即Hugonoit弹性极限、动态屈服强度和理论剪切强度，并从这三种判据的交集值出发来判断爆炸压实过程中陶瓷颗粒是否有发生破碎的可能。通过具体计算得出颗粒内存在两个最大剪应力的位置：一个位置发生在距颗粒接触面0.5 nm范围以内，此处剪应力最大；另一个位置发生在距接触面较远处。这一结果为解释陶瓷粉末颗粒在爆炸压实过程中存在塑性行为和破碎行为提供了理论依据。     

复板静载弯曲挠度对爆炸焊接参数的影响

 爆炸焊接是利用炸药爆轰压力工作的固态焊接技术,广泛应用于制造层状金属复合材料。但对薄复板施焊安装过程中,薄板在自重及炸药重量作用下将发生弯曲。基于弹性力学薄板理论,得出了复板受均布载荷作用下产生的挠度及转角表达式;又通过分析爆炸焊接过程中的基、复板的运动参数,结合再入射流形成的声速限条件、流动限条件,推导出爆炸焊接时射流形成的预置角范围;最后将两者结合推导出在给定复板材料及长、宽的条件下,成功施焊所要求的复板最小厚度。     

A Model of Wavefunction Collapse in Discrete Space-Time

We give a new argument supporting a gravitational role in quantum collapse. It is demonstrated that the discreteness of space-time, which results from the proper combination of quantum theory and general relativity, may inevitably result in the dynamical collapse of the wave function. Moreover, the minimum size of discrete space-time yields a plausible collapse criterion consistent with experiments. By assuming that the source to collapse the wave function is the inherent random motion of particles described by the wave function, we further propose a concrete model of wavefunction collapse in the discrete space-time. It is shown that the model is consistent with the existing experiments and macroscopic experiences. PACS numbers: 0365B 0460     

Null Fluid Collapse in Rastall Theory of Gravity

A Vaidya spacetime is considered for gravitational collapse of a type II fluid in the context of the Rastall theory of gravity. For a linear equation of state for the fluid profiles, the conditions under which the dynamical evolution of the collapse can give rise to the formation of a naked singularity are examined. It is shown that depending on the model parameters, strong curvature, naked singularities would arise as exact solutions to the Rastall's field equations. The allowed values of these parameters satisfy certain conditions on the physical reliability, nakedness, and the curvature strength of the singularity. It turns out that Rastall gravity, in comparison to general relativity, provides a wider class of physically reasonable spacetimes that admit both locally and globally naked singularities.     

卵石材料在中子场下的次级放射性分析

由中国科学院近代物理研究所负责设计和建设的加速器驱动嬗变研究装置（CiADS）将建于广东省惠州市。作为一个核装置,CiADS在运行过程中会对环境造成次级放射性影响,因此评估CiADS对环境造成的次级放射性影响水平不仅对公众健康有重要意义,对屏蔽设计也具有一定的指导作用。利用241Am-Be中子源对兰州重离子加速器研究装置（HIRFL）附近的卵石材料进行了辐照实验,测量和分析了辐照后卵石样品内产生的24Na,54Mn,56Mn和27Mg的比活度等相关信息。通过对实验数据与利用蒙特卡罗程序Geant4模拟得到的各放射性核素比活度的比较,验证了Geant4模拟分析中子场下环境介质次级放射性这一方法的可靠性。进而利用Geant4模拟研究了CiADS质子加速器HEBT隧道底部屏蔽层外的中子能谱以及隧道底部屏蔽层外卵石层因中子活化产生的主要放射性核素的饱和比活度。分析结果表明,在合理的屏蔽设计条件下,CiADS运行期间泄露到屏蔽层外的中子活化环境中卵石材料造成的环境影响几乎可以忽略。The China initiative Accelerator Driven System (CiADS) is the first integrated ADS facility designed to study the safety disposal of nuclear waste. As a nuclear facility, it will cause radiological impact on the environment. Therefore, the assessment of radiological impact on the environment around this facility will not only meaningful to the public health, but also offers significant guides to the shielding design of CiADS. Pebble samplings were collected around the campus of the Heavy Ion Research Facility in Lanzhou (HIRFL) and irradiated by a 241Am-Be neutron source. Based on the γ-spectrum measured by a HPGe detector before and after the neutron irradiation, the specific activities of induced radionuclides 24Na,54Mn,56Mn and 27Mg in these samples were analyzed and compared with the Monte-Carlo simulation values obtained with the Geant4 toolkit. The comparison between the experimental and simulated results indicates that Geant4 toolkit is feasible for radiation impact assessment of nuclear facilities, such as CiADS. Then the neutron spectrum outside the concrete shielding of HEBT tunnel of the CiADS have been simulated by the Geant4 toolkit, and the saturation activities of the induced nuclides in the first 10 cm pebble layer have been predicted. The results show that the saturation activities of induced radionuclides in pebbles outside the CiADS shielding are much lower than their exemption values and their radiation impacts to the environment could be ignored.     

低能电子径迹中能量沉积频率分布

根据我们建立的径迹结构Monte Carlo计算模型,计算了低能电子在液态水中径迹范围内DNA分子片段模型和染色质丝片段模型区域内的能量沉积频率分布,结果与OREC和CPA程序结果进行了比较,这些计算结果为解释低能重离子注入生物体造成深部生物效应而提出的一种物理机制──软X射线机制提供了理论依据.     

Sensitivity of run-to-detonation distance in practical explosives

The dynamics of detonation in a granular explosive following a piston impact is examined computationally for a two-phase model. Different choices are considered for equations of state and reaction rate. Of special interest is the behaviour of the run-to-detonation distance as a function of the initial porosity of the explosive, for which new experimental information has recently become available. It is found that this response can vary both qualitatively and quantitatively depending upon the constitutive input to the model. Computations based upon up-to-date equation-of-state and reaction-rate information for the explosive PBX-9501 show that the response of the run-to-detonation distance as a function of the initial porosity is in the shape of an inverted U, which is in qualitative agreement with the latest experiments. Mechanisms responsible for this behaviour are identified.     

Chemical Analysis of Hydroxyapatite Artificial Bone Powders by Energy Dispersive X-Ray Fluorescence Spectrometry(EDXRF)

Stoichiometric hydroxyapatite (HA) nanoparticles were synthesized by a wet chemical method. Calcium nitrate tetra hydrate used as calcium source and dibasic ammonium phosphate used as phosphorous source. Calcium nitrate tetra hydrate and dibasic ammonium phosphate solutions were prepared by dissolving the salts in distilled water. Stoichiometric hydroxyapatite nanoparticles used by artificial bone powders and synthesized by a wet chemical method were analyzed using EDXRF method.The concentrations of K, Ca, Ti, V, Cr, Fe, Ni, Cu, Sr and Pb for artificial bone powders have been determined. Besides, Calcium contents were evaluated according to the agitation time and temperature in the production process.     

半干旱采煤塌陷不同应力区典型植物高光谱特征分析

利用高光谱反演、监测植被生长状况的基础是光谱特征识别。以半干旱采煤塌陷区为样地，利用Field Spec 3地物光谱仪与SPAD-502叶绿素仪同步采集采煤地表塌陷形成的不同应力区(非采区、中性区、拉伸区、压缩区)典型植物叶片光谱反射率与叶绿素含量(SPAD值)，分析典型植物相同应力区SPAD值升高其光谱特征的变化，对比不同应力区典型植物SPAD值较高与较低时光谱特征的差异，并借助Matlab软件深入研究不同应力区典型植物SPAD值与差值指数、归一化指数的相关关系。结果表明：(1)不同应力区同种植物光谱曲线随着SPAD值不同变化规律相异，可见光波段区分明显，其余波段受应力影响的区域样本SPAD值不同，反射率比非采区波动更为剧烈与无序。可见光波段，糙隐子草、柠条、杨树、油蒿SPAD值低的样本光谱曲线绿峰缺失，SPAD值升高，绿峰出现但位置红移，SPAD值高于30时，为典型植被光谱曲线，油松样本SPAD值越高反射峰值越小；受应力影响的区域SPAD值低的样本谷、峰、边特征参数缺失更多，光谱变化规律不强。(2)400～700 nm波段，不同应力区糙隐子草、油蒿、油松、柠条样本SPAD值较低组反射率显著高于较高组，杨树样本相反；780～1 350 nm波段，拉伸区的糙隐子草、非采区的油蒿和柠条、压缩区的油松和杨树样本SPAD值较高组与较低组的反射率差异小；相较于非采区，受应力影响的糙隐子草、油蒿、柠条样本在所测波段SPAD值较高组与较低组的同波段反射率差值显著减小。(3)受应力影响的区域样本SPAD值与光谱指数相关性较之非采区在某些波段大面积增强。与非采区相比，中性区的油蒿、油松、柠条、杨树样本SPAD值与光谱指数的最大相关系数值均增大，糙隐子草相反；非采区植物SPAD值与NDVI最大相关系数均高于DI，波段组合多位于近红外，受应力影响区域的样本最大相关系数多数位于可见光波段。本研究为矿区不同应力区典型植物高光谱波段识别与植物健康状态监测、矿区生态环境精准治理提供了理论支撑。