SiC过渡层对氟化类金刚石薄膜附着特性的影响

采用射频反应磁控溅射法在316L不锈钢基片上分别沉积了两种薄膜:一种是氟化类金刚石薄膜(F-DLC),另一种是先镀上一定厚度的SiC过渡层再沉积F-DLC.着重研究了薄膜的附着力随过渡层制备条件的变化规律.结果显示,增加SiC过渡层后薄膜的附着力明显增加,且附着力随SiC过渡层的制备条件有所变化,在射频输入功率为200 W,沉积时间5min制备出的SiC过渡层上再沉积F-DLC时,附着力可达8.7 N,远高于未加过渡层时F-DLC膜的附着力(4 N).通过研究SiC的沉积速率曲线、表面形貌和红外光谱,探讨了SiC过渡层及其制备条件影响薄膜附着力的相关机制.     

Li掺杂对MgH2(001)表面H2分子扩散释放影响的第一性原理研究

本文利用基于密度泛函理论的第一性原理分别研究了MgH₂(001)表面H原子扩散形成H₂分子释放出去的可能路径及金属Li原子掺杂对其影响. 研究结果表明: 干净MgH₂(001)表面第一层释放H原子形成H₂分子有两种可能路径, 其释放能垒分别为2.29和2.50 eV; 当将Li原子替代Mg原子时, 两种H原子扩散释放路径的能垒分别降到了0.31和0.22 eV, 由此表明Li原子掺杂使MgH₂(001)表面H原子扩散形成H₂释放更加容易.     

SiC空间反射镜材料及其表面改性技术现状分析

SiC材料具有良好的物理特性和机械特性,是制备大口径空间反射镜的主要候选材料之一,而SiC反射镜的制名加工及其表面改性技术是推动高水平空间光学系统应用的重要条件.本文从实际工程应用的角度出发,分析了几种用SiC基底反射镜材料的特性,介绍了4种SiC的制备工艺.研究了目前国内外SiC基底反射镜的应用现状及其表面性情况,对改性层的性能指标、制备工艺和发展趋势进行了深入讨论.针对目前国内反射镜材料应用现状,认为加快性能SiC基底材料研发工作步伐,并找到一种利用现有大口径PVD设备低温制备优质SiC改性层的方法是今后工程用的发展方向.     

热熔胶和橡胶关节止痛膏中的挥发油成分体外释放对比研究

对比研究热熔胶和橡胶关节止痛膏中挥发油成分的释放情况.按2010版《中国药典》透皮贴剂释放度测定法的要求,用气相色谱法对两种剂型中挥发油成分的释放度进行测定.研究表明两种剂型中挥发油的释放均随时间为一递增过程,符合Higuchi方程.在累积释药百分含量方面,热熔胶贴膏中挥发油的释放百分含量明显高于橡胶膏中挥发油的释放百分含量.在释放速率方面,热熔胶贴膏中挥发油的释放速率高于橡胶膏中挥发油成分的释放速率,在前8h释放较快,之后释放曲线斜率变小,释放趋于平缓.两种剂型中热熔胶关节止痛膏的挥发油成分释药速率快,累积释放总量多.     

空间反射镜基底材料碳化硅表面改性研究

直接抛光后的SiC反射镜表面光学散射仍较大,无法满足高质量空间光学系统的心用需求.为此必须对SiC反射镜进行表而改性,以获得高质量的光学表面.目前国际上较为流行的足制备Si或SiC改性层进行表面改性.分别采用离子辅助电子束蒸发方法制备Si和SiC改性层进行改性,相关测试结果表明:Si改性层结构为立方相,改性后基底表面粗糙度(rms)降到0.620 nm,散射系数减小到1.52%;SiC改性层结构为非晶相,改性后基底表面粗糙度(rms)降到0.743 nm,散射系数减小到2.79%.两种改性层均与基底结合牢固,温度稳定性较高.从可靠性方面考虑,目前在国内第一种方法更适于实际工程应用.该工艺改性后SiC基底表面散射损耗大大降低,表面质量得到明显改善.镀Ag后表面反射率接近于抛光良好的微晶玻璃的水平,已能够满足高质量空间光学系统的应用需要.     

石墨烯/AZO/SiC复合结构的近场辐射换热特性

由于倏逝波贡献,近场辐射换热可以远超黑体辐射定律给出的极限换热热流,对近场辐射换热的调控在近场热光伏及热管理方面有重要的应用前景。石墨烯是一种有潜力的可用于近场辐射换热调控的功能材料。本文研究了由石墨烯、铝掺杂氧化锌(aluminum-doped zinc-oxide,AZO)及SiC构成的多层复合薄膜的近场辐射换热特性。研究发现:"AZO薄膜+SiC基底"结构的频谱辐射热流在SiC的SPhP频域出现谷值,而"SiC薄膜+AZO基底"结构同时在两种表面极化激元的共振频率处出现峰值;覆盖单层石墨烯薄膜对"AZO薄膜+SiC基底"结构的近场辐射换热基本没有影响;而"石墨烯/SiC薄膜/AZO基底"结构却可以同时支持三种表面极化激元,并在调控石墨烯化学势到适当值时,可以有效增强近场换热。本研究有助于理解石墨烯对近场辐射换热的调控特性。     

牙齿组织光学穿透深度有限元仿真分析

利用有限元方法对光在二维牙齿双层有限尺寸模型中传输的扩散方程进行求解,获取了光能在组织体内部的分布情况,并对牙釉质和牙本质在不同光学参量模型下的光学穿透深度进行仿真分析.结果发现,穿透深度随牙釉质散射系数的增大而减小,随牙本质的散射系数增大而增大.但牙釉质的穿透深度随散射系数的变化率(βe=0.00797)要远远大于牙本质(βd=0.000828).采用MonteCarlo随机统计方法验证了本文有限元求解扩散方程的正确性.     

霍尔推进器壁面材料二次电子发射及鞘层特性

霍尔推进器放电通道等离子体与壁面相互作用形成鞘层,不同壁面材料的二次电子发射对推进器鞘层特性具有重要影响,本文针对推进器壁面鞘层区域建立二维物理模型,研究了氮化硼(BN)、碳化硅(SiC)和三氧化二铝(Al_2O_3)三种不同壁面材料的二次电子发射特性,在改进SiC材料二次电子发射模型的基础上,采用粒子模拟方法,讨论了壁面二次电子发射系数与电子温度和磁场强度的关系,研究了三种材料(BN,SiC和Al_2O_3)的鞘层特性,结果表明:修正的二次电子发射模型拟合曲线与实验曲线几乎一致;在相同电子温度下,三种材料(BN,SiC和Al_2O_3)的二次电子发射系数和壁面电子数密度依次增大,而鞘层电场和鞘层电势降依次减小,BN材料具有合适的二次电子发生射系数,使得霍尔推进器能在低电流下稳态工作。     

多组分液滴汽化的一个模型

本文导出在对流运动介质中多组分液滴汽化的通量公式,并给出描述液滴汽化历史的微分方程组.同时作了各种多组分液滴汽化历史的计算,计算结果与实验结果较好地吻合. 一、通量积分式和有效扩散系数 研究一个多组分理想溶液液滴在隋性气体(液滴溶液不吸收也不释放的气体),I中的汽化.设溶液由n种组分构成,则在液滴表面形成n+1种组分的多元气体混合物轴对称扩散膜层,第n+1种组分指的是隋性气体I.用假想膜层理论将轴对称扩散膜层折合为等效的球对称假想膜层,则可按stewart通量公式写出在该膜层中任意半径r处的稳态扩散方程,即:     

非均匀混合下氘氚聚变反应速率的理论研究

激光驱动惯性约束聚变中壳层材料和聚变燃料的混合是影响聚变点火燃烧性能的关键物理问题,聚变过程中混合物形态的演化及相应热核反应速率的物理建模直接影响数值模拟的置信度,具有重要的科学意义和应用价值.本文以扩散混合机制下混合形态随时间的演化规律及其对热核反应速率的影响为研究对象,基于热力学平衡与理想气体物态方程假设,通过解析分析与一维球几何扩散方程数值解的对比研究,揭示了扩散混合主导下热核反应速率随混合形态演化的物理规律.研究发现,混合量主要通过影响燃料的体积份额直接影响热核反应速率,由混合非均匀尺度和扩散系数共同决定的扩散时间直接影响热核反应速率的时间演化行为.进一步利用蒙特卡罗方法直接模拟扩散过程得到的互扩散系数,定量分析了燃料中混入低Z、高Z材料时热核反应速率随时间演化的差异,通过与美国非均匀混合效应实验典型数值模拟结果进行对比分析,验证了理论评估的可靠性.本工作对我国惯性约束聚变混合效应实验的设计和改进具有重要参考意义.     

Radiochemical studies in the development of deep geological repository in the Czech Republic

In this contribution the main achievements of radiochemical studies performed within the framework of the Czech DGR development programme are summarized and further plans outlined. The results of selection of the most dangerous radionuclides in spent fuel assemblies from VVER 440 reactors, based on spent fuel inventory calculations and analyses of migration rate of radionuclides to the environment, are presented in the first part of the contribution. It is shown that ¹⁴C, ¹²⁹I, ¹²⁶Sn, ¹³⁵Cs, ³⁶Cl, ⁷⁹Se, ²²⁶Ra, ²³⁷Np, ²²⁹Th, and ²⁴²Pu belong among the most dangerous radionuclides in the Czech disposal concept. Problems with the determination of migration parameters of radionuclides are described in the second part of this contribution.     

Radiochemical studies in the development of deep geological repository in the Czech Republic

In this contribution the main achievements of radiochemical studies performed within the framework of the Czech DGR development programme are summarized and further plans outlined. The results of selection of the most dangerous radionuclides in spent fuel assemblies from VVER 440 reactors, based on spent fuel inventory calculations and analyses of migration rate of radionuclides to the environment, are presented in the first part of the contribution. It is shown that ¹⁴C, ¹²⁹I, ¹²⁶Sn, ¹³⁵Cs, ³⁶Cl, ⁷⁹Se, ²²⁶Ra, ²³⁷Np, ²²⁹Th, and ²⁴²Pu belong among the most dangerous radionuclides in the Czech disposal concept. Problems with the determination of migration parameters of radionuclides are described in the second part of this contribution.     

Studies of the radionuclide content of fuel particles sampled from the chernobyl nuclear power plant’s No. 4 reactor unit

Spectroscopic studies are performed of the L _x , K _x , and ?? emanations from fuel particles sampled in 2011 inside the Chernobyl Nuclear Power Plant??s (ChNPP??s) No. 4 reactor unit. The isotope ratios for ^134,135Cs, ^154,155Eu, Pu isotopes, ^241,243Am, and ²⁴³Cm are measured. The data on ?? emitters for all radionuclides above ²⁴¹Am exhibit considerable inconsistency with the theoretically calculated values. A systematic deviation of the ⁹⁰Sr and ¹³⁷Cs ratios for the fuel component from the 1986 data is observed. Zirconium is shown to be the main radionuclide in the fuel particles.     

The production and isolation of Cu-64 and Cu-67 from zinc target material and other radionuclides

A two-stage method is described for the purification of Cu radionuclides from up to 5 g of ^natZn and other radionuclides. After proton bombardment, co-produced ^66,67Ga is removed by passing the dissolved zinc in 7 M HCl through a 2.5 ml column of AmberChrom CG-71, a methacrylate-based polymeric resin. This first column eluate, which contains ⁶⁵Zn, ^64,67Cu, and ^56,57,58Co, is taken to incipient dryness and reconstituted in 300 ml 0.05 M HCl. This solution is then pumped through a novel 10 ml column of dithizone impregnated AmberChrom CG-71, where Cu radionuclides are efficiently retained with no breakthrough. Zinc and Co radionuclides elute smoothly during washing with no tailing. More than 97% Cu is eluted by washing with 40 ml 5 M HNO₃ warmed to 50 °C. No dithizone is detected in this eluate.     

Mathematical Modeling of Drug Release in a Phase-Transient Temperature-Responsive Drug Delivery System in Spherical Coordinates

Abstract

A sphere-shaped drug delivery system responsive to temperature, as a unique external stimulus, was introduced and its performance mathematically studied at the pseudo-steady state. The system is composed of three individual sections, including the drug core, phase-transient intermediate shell, and protective polymeric shell. An ON-OFF release of drug could be achieved by increasing or decreasing the environmental temperature around the melting point of the intermediate shell and the smartness of system is due to the solid-liquid phase transition of this shell. The ON-OFF response of the system was mathematically modeled by solving the governing heat and mass transfer equations at the pseudo-steady state. The results showed the lag time of the system in the ON state, the cumulative released drug in the ON state and the fractional undesired release of drug in the OFF state are strongly under the influences of different kinds of factors, including the geometrical characteristics of the system (e.g., the radius of the drug core and the thicknesses of the intermediate and polymeric shells), the physical properties of the system (e.g., the thermal conductivities and diffusion coefficients of the intermediate and polymeric shells), and the environmental and operation conditions.     

Simulation of Fission Product Release from Microfuel Particles Taking into Account the Effects of Trapped Fraction and Concentration Jumps at the Interfaces

A modification of the FP Kinetics code [1] has been performed to calculate the fission product release from HTGR microfuel particles, allowing for chemical binding, limited solubility effects, and component concentration jumps at the interfaces of the coating layers. A comparison is made of the release curves of Cs from microfuel particles calculated using the FP Kinetics and PARFUME codes [2]. It is shown that taking into account the concentration jumps at the interfaces of the silicon carbide layer makes it possible to give a noncontradictory explanation of the experimental data obtained for Cs release in post-reactor thermal testing. The need for performing experiments to determine the limits of solubility in coating materials is noted.

     

Implementation of the thermonuclear process in D<Superscript>3</Superscript>He-<Superscript>9</Superscript>Be plasma on the basis of a Z pinch with an ultrafast laser ignition

A new concept of inertial-magnetic confinement fusion is proposed. This concept is based on a high-current Z pinch combined with a femtosecond laser. The fusion target is composed of a D³He fuel contained under a high pressure inside a sealed cylindrical capsule made from metallic ⁹Be. An electric discharge along the capsule preheats the target and transforms it into a state of compressed liner. A subsequent TW femtosecond-laser pulse focused on a target end face causes ultrafast cold ignition of a small portion of the D³He fuel. This laser impact generates energetic electrons and ions, which trigger a nuclear-physics mechanism of a catalytic heating of the fuel and also creates a detonation shock wave capable of propagating along the plasma filament. It is shown that the self-sustaining fusion burn wave can appear in the D³He-⁹Be plasma, in which case the bulk of the energy release is carried by nonradioactive ions, with the energy gain being in excess of 50. The possibility of probing the fusion process by means of gamma-ray spectroscopy is also discussed. The radiative-capture reactions ³He(d, γ), D(d, γ), and ³He(³He, γ) naturally accompanying the burning of the D³He fuel are shown to serve as a convenient diagnostic tool. A nuclear “marker” of D³He fusion on the basis of the detection of monochromatic gamma rays produced in the reaction ⁹Be(α, γn), which is induced in the liner beryllium shell by energetic fusion alpha particles, is also examined.     

A study of fractional Schrödinger equation composed of Jumarie fractional derivative

In this paper we have derived the fractional-order Schrödinger equation composed of Jumarie fractional derivative. The solution of this fractional-order Schrödinger equation is obtained in terms of Mittag–Leffler function with complex arguments, and fractional trigonometric functions. A few important properties of the fractional Schrödinger equation are then described for the case of particles in one-dimensional infinite potential well. One of the motivations for using fractional calculus in physical systems is that the space and time variables, which we often deal with, exhibit coarse-grained phenomena. This means infinitesimal quantities cannot be arbitrarily taken to zero – rather they are non-zero with a minimum spread. This type of non-zero spread arises in the microscopic to mesoscopic levels of system dynamics, which means that, if we denote x as the point in space and t as the point in time, then limit of the differentials dx (and dt) cannot be taken as zero. To take the concept of coarse graining into account, use the infinitesimal quantities as (Δx) ^α (and (Δt) ^α ) with 0 < α < 1; called as ‘fractional differentials’. For arbitrarily small Δx and Δt (tending towards zero), these ‘fractional’ differentials are greater than Δx (and Δt), i.e. (Δx) ^α > Δx and (Δt) ^α > Δt. This way of defining the fractional differentials helps us to use fractional derivatives in the study of dynamic systems.     

基于VHTRC的棱柱式高温气冷堆核设计程序验证北大核心CSCD

高温气冷堆是国际公认的固有安全性高的反应堆堆型。针对高温气冷堆包覆颗粒燃料引入的燃料组件的双重非均匀性以及棱柱式堆芯布置的非均匀性和强空间耦合效应,提出基于蒙特卡罗均匀化-确定论输运方法的RMC-SaraGR程序系统作为棱柱式高温气冷堆的核设计程序。基于日本棱柱式高温气冷堆临界实验装置VHTRC基准题,针对此套核设计程序系统开展了均匀化模型研究和初步验证。研究结果表明,基于蒙特卡罗均匀化方法,采用全堆模型、合适的能群结构和分区方式产生组件群常数,并经过超级等效均匀化方法进行等效均匀化修正,可以保证堆芯多群均匀计算具有较高的计算精度。     

Exposure assessment of process by-product nanoparticles released during the preventive maintenance of semiconductor fabrication facilities

This study characterized the process by-product particles (mostly nanoparticles) released during the preventive maintenance of semiconductor fabrication facilities, such as chemical mechanical planarization (CMP), plasma-enhanced chemical vapor deposition (PECVD), and ion implantation. Manual sampling and real-time measurements with direct reading instruments were conducted to assess the exposure levels of nanoparticles and their physical and chemical properties. Significant amount of nanoparticles were observed in the breathing zone of the workers during the maintenance of the PECVD and ion implanters with the peak number concentrations as high as 6,470,000 and 65,444 #/cm³, respectively, indicating that the deposited residual chemicals in the reaction chambers were released as airborne nanoparticles by the maintenance activities. In contrast, nanoparticles released during the maintenance of the local scrubber, CMP, and replacing CMP slurry drums were insignificant. Causes of the particle release were discussed and suggestions were made to mitigate the nanoparticle release and reduce the exposure levels.