Radiophotosynthesis of some 14C-labelled Amino Acids using the Unicellular Green Alga Scenedesmus acutus

Radiophotosynthesis has been carried out using the unicellular green algea Scenedesmus acutus grown, as a substrate for preparing some carbon-14 labelled amino acids. Gaseous ¹⁴CO₂, in an air tight photosynthesis chamber or NaH¹⁴CO₃ solution, in an ordinary photosynthesis chamber, were used as radioactive carbon sources. The yields, radiochemical yields and specific activities of the formed radioactive products are reported in both cases. The results obtained clearly showed the advantages of using the NaH¹⁴CO₃ method. In that case the process was by far less tedious. Moreover, the chemical and radiochemical yields of the formed amino acids were relatively much more higher than the values obtained on using ¹⁴CO₂ in the tight photosynthesis chamber.     

Indpeendent Yields of Iodine and Tellurium Isotopes in Fission of 232 Thorium with 30.5 MeV Alpha Particles

Iodine and tellurium isotopes produced in the fission of ²³²Th with 30.5 MeV alpha particles were separated using a method of sublimation in an air stream and the independent yields of ¹³⁰I, ¹³¹I, ^132m,gI, ¹³³I ¹³⁴I, ^134m,gTe, ^133mTe and ¹³⁴Te (cumulative) were determined by means of high resolution Ge(Li) γ-ray spectrometry. A Gaussian fit to the experimental data was used to obtain the width parameter σ_z and the most probable charge Z_p of the nuclear charge distribution in the isobaric chains 130 – 131. The most probable masses for fission fragments with Z = 52 and Z = 53 were also deduced from the measured fission yields.     

用于位置灵敏型中子探测器的6LiF/ZnS（Ag）闪烁体性能研究

研究了掺杂6LiF的ZnS(Ag)闪烁体对中子、γ射线的发光特性和EJ426闪烁体样品的热中子探测效率、出射光产额和γ灵敏度。EJ426的热中子探测效率为32.4%,出射光产额为8.01×103光子/中子,70 mV阈值时的γ灵敏度小于10-7,表明EJ426是较理想的闪烁体型位置灵敏中子探测器材料。     

Z箍缩软X射线辐射能量薄膜量热计改进技术

薄膜量热计是进行Z箍缩辐射总能量测量的主要手段之一,准确可信的总能量参数对Z箍缩研究具有重要意义。对薄膜量热计装置进行技术改进,采用脉冲恒流源代替脉冲恒压源驱动镍薄膜量热计,撤除了回路中的串接电阻,可直接测量薄膜探测器的电阻变化,从而有效提高了辐射总能量测量的精度,拓宽了该设备的适用范围,使其可对目前强光一号加速器Z箍缩实验中所有典型负载进行测量。改进后平面型铝丝阵负载实验中总能量测量的相对不确定度由49.0%降低为19.6%。与闪烁探测系统功率测量结果积分值进行了对比,二者比值在0.87~1.04之间。     

超二代像增强器多碱阴极光电发射特性研究

通过测量超二代像增强器多碱阴极的光谱反射率和透射率,根据能量守恒定律计算得到了多碱阴极的光谱吸收率.结果表明,只有当光子的能量大于1.333 eV以后,多碱阴极的吸收率才开始快速增大.这说明多碱阴极的光谱吸收存在一个1.333 eV的长波吸收限,入射光的光子能量如果小于该吸收限,多碱阴极将不吸收.在多碱阴极的表面电子亲合势进一步降低的情况下,多碱阴极光电发射的长波理论阈值由长波吸收限所决定.多碱阴极在吸收光子之后的电子跃迁过程中,跃迁电子的能量增加小于所吸收入射光子的能量,即存在一个"能量损失".光子的能量越高,所激发的跃迁电子所处的能级越高,能量损失越大.同时光子的能量越高,跃迁电子所处的能级越高,电子跃迁的几率越低.多碱阴极的量子效率由吸收率、跃迁几率和跃迁能级、扩散过程中的能量损失等因素共同决定,因此多碱阴极的量子效率存在长波阈的同时也存在短波阈.多碱阴极的量子效率在2.11 eV达到最大值之后,随着光子能量的增加而单调减小,在3.6 eV时,量子效率减小到零.多碱阴极在3.6 eV时的吸收系数仍然很高,但由于电子跃迁的几率低,同时电子扩散过程中的能量损失大,导致尽管多碱阴极对短波具有较高的吸收系数,但量子效率仍然较低.因此对多碱阴极所吸收的光子能量中,转换成为光电导、晶格热振动等其他非光电发射形式能量的比例而言,短波较长波高,对光电发射的贡献率而言,短波较长波低.     

Bonds and Options in Exponentially Affine Bond Models

Abstract

In this article we apply the Flesaker–Hughston approach to invert the yield curve and to price various options by letting the randomness in the economy be driven by a process closely related to the short rate, called the abstract short rate. This process is a pure deterministic translation of the short rate itself, and we use the deterministic shift to calibrate the models to the initial yield curve. We show that we can solve for the shift needed in closed form by transforming the problem to a new probability measure. Furthermore, when the abstract short rate follows a Cox–Ingersoll–Ross (CIR) process we compute bond option and swaption prices in closed form. We also propose a short-rate specification under the risk-neutral measure that allows the yield curve to be inverted and is consistent with the CIR dynamics for the abstract short rate, thus giving rise to closed form bond option and swaption prices.     

基于具有LR型模 糊输出回归模型的上证指数预测

以对称二次型模糊回归模型为基础,引入一般二次模糊回归模型,利用模糊最小二乘法估计未知参数．构建评价标准考察两模型的拟合效果,在样本期内和样本期外分别评价模型的实际拟合与预测能力．     

Which stresses affect the glide of screw dislocations in bcc metals?

By direct application of stress in molecular statics calculations we identify the stress components that affect the glide of 1/2?111? screw dislocations in bcc tungsten. These results prove that the hydrostatic stress and the normal stress parallel to the dislocation line do not play any role in the dislocation glide. Therefore, the Peierls stress of the dislocation cannot depend directly on the remaining two normal stresses that are perpendicular to the dislocation but, instead, on their combination that causes an equibiaxial tension-compression (and thus shear) in the plane perpendicular to the dislocation line. The Peierls stress of 1/2?111? screw dislocations then depends only on the orientation of the plane in which the shear stress parallel to the Burgers vector is applied and on the magnitude and orientation of the shear stress perpendicular to the slip direction.     

Open critical area model and extraction algorithm based on the net flow-axis

In the integrated circuit manufacturing process, the critical area extraction is a bottleneck to the layout optimization and the integrated circuit yield estimation. In this paper, we study the problem that the missing material defects may result in the open circuit fault. Combining the mathematical morphology theory, we present a new computation model and a novel extraction algorithm for the open critical area based on the net flow-axis. Firstly, we find the net flow-axis for different nets. Then, the net flow-edges based on the net flow-axis are obtained. Finally, we can extract the open critical area by the mathematical morphology. Compared with the existing methods, the nets need not to divide into the horizontal nets and the vertical nets, and the experimental results show that our model and algorithm can accurately extract the size of the open critical area and obtain the location information of the open circuit critical area.     

Numerical simulation of flat-tip micro-indentation of glassy polymers: Influence of loading speed and thermodynamic state

Flat-tip micro-indentation tests were performed on quenched and annealed polymer glasses at various loading speeds. The results were analyzed using an elasto-viscoplastic constitutive model that captures the intrinsic deformation characteristics of a polymer glass: a strain-rate dependent yield stress, strain softening and strain hardening. The advantage of this model is that changes in yield stress due to physical aging are captured in a single parameter. The two materials studied (polycarbonate (PC) and poly(methyl methacrylate) (PMMA)) were both selected for the specific rate-dependence of the yield stress that they display at room temperature. Within the range of strain rates experimentally covered, the yield stress of PC increases linearly with the logarithm of strain rate, whereas, for PMMA, a characteristic change in slope can be observed at higher strain rates. We demonstrate that, given the proper definition of the viscosity function, the flat-tip indentation response at different indentation speeds can be described accurately for both materials. Moreover, it is shown that the model captures the mechanical response on the microscopic scale (indentation) as well as on the macroscopic scale with the same parameter set. This offers promising possibilities of extracting mechanical properties of polymer glasses directly from indentation experiments.