HL-1装置硬x射线辐射剂量测量

一、引言 多年来,从事受控核聚变的研究人员相继对环形磁约束装置的硬X射线辐射做了许多深入的实验研究,因为逃逸电子是高温等离子体的必然产物,通过逃逸电子产物——硬X射线的研究,便可得知等离子体的行为。但是,装置的硬X射线辐射剂量却直接影响到周围环境及工作人员的身体健康。高能X射线通过物质时,主要以光电效应,康普顿散射和电子对效应损失能量,进入生物组织后,X射线能量在其中转移、吸收乃至最终导致组织损伤。随着实验的进展,人们对硬X射线辐射剂量日益关心。为此,1987年,我们在HL-1装置实验运行期间(近旁的电子回旋共振加热系统未投入工作),测量了装置的硬X射线辐射剂量。     

A Mehrotra-type predictor-corrector algorithm with polynomiality andQ-subquadratic convergence

Mehrotra's predictor-corrector algorithm [3] is currently considered to be one of the most practically efficient interior-point methods for linear programming. Recently, Zhang and Zhang [18] studied the global convergence properties of the Mehrotra-type predictor-corrector approach and established polynomial complexity bounds for two interior-point algorithms that use the Mehrotra predictor-corrector approach. In this paper, we study the asymptotic convergence rate for the Mehrotra-type predictor-corrector interior-point algorithms. In particular, we construct an infeasible-interior-point algorithm based on the second algorithm proposed in [18] and show that while retaining a complexity bound ofO(n ^1.5 t)-iterations, under certain conditions the algorithm also possesses aQ-subquadratic convergence, i.e., a convergence ofQ-order 2 with an unboundedQ-factor.Research supported in part by NSF DMS-9102761 and DOE DE-FG02-93ER25171.     

适用于量子阱激光器的速率方程

首次在理论上用量子阱激光器增益与载流子密度的对数关系替代了原有速率方程中的线性关系，得到了改进了速率方程，分析了稳态和调制特性，从理论上得到了获得最低阈值的最佳阱数和最大调制带宽的最佳腔长。     

Some comments on the hazard gradient

For random variables T₁,…,T_n, the gradient of $\text{R(t) = ?log}\text{P}\text{{T}{}_1\text{> t}{}_1\text{,…,T}{}_{\mathrm{n}}\text{> t}{}_{\mathrm{n}}\text{}}$ is called the hazard gradient. Some properties of this multivariate version of the hazard rate are demonstrated, and some examples are given to show the usefulness of the hazard gradient in characterizing distributions or families of distributions.     

Characterization of proton NMR relaxation times in normal and pathological tissues by correlation with other tissue parameters

To help understand which tissue parameters best account for the water proton NMR relaxation times, the longitudinal relaxation time (T₂), the transverse relaxation time (T₂), and the water content of 16 tissues from normal adult rats were measured at 10.7 MHz and 29°C. Regression analyses between the above and other tissue parameters were performed. These other tissue parameters included: the amounts of various organic and inorganic components, protein synthetic rate, oxygen consumption rate, and morphological composition. In addition, the differences in T₁, T₂, and water content values between normal liver and malignant tumor (Morris #7777 a transplantable hepatoma) were studied to help understand how a disease state can be detected and characterized by NMR spectroscopy. The results of this study and information from the literature allow the following generalizations to be made about tissue T₁ and T₂ values: (1) Each normal tissue has rather consistent and characteristic T₁ and T₂ relaxation times which are always shorter than the T₁ and T₂ of bulk water; (2) tissues with higher water content tend to have longer T₁ relaxation times; (3) tissue T₂ values are not, however, as well correlated with water content as T₁ values; (4) tissues with shorter T₁ values have higher calculated hydration fractions, greater amounts of rough endoplasmic reticulum, and a greater rate of protein synthetic activity; (5) tissues with higher lipid content, associated with intracellular non-membrane bounded lipid droplets, tend to have longer T₂ values; (6) tissues with greater overall surface area, whether in the form of cellular membranes or intracellular or extracellular fibrillar macromolecules, tend to have shorter T₂ values; (7) the differences between T₁ and T₂ values between tumor and normal tissues correlated with differences in the volume fraction (amounts) of extracellular fluid volumes and in the amounts of membrane and fibrillar surface area in the cells. The above generalizations should be useful in predicting T₁ and T₂ changes associated with specific tissue pathologies.     

An algorithm for the minimization of convex,nondifferentiable functionals in Hilbert space

In this paper, an algorithm for minimizing a convex functionalF(x), defined by the maximum of convex smooth functionalsF _i (x), is described. The sequence of valuesF(x _n ) is monotonically decreasing, the algorithm is convergent, and it attains quadratic convergence near the solution.This work was supported by the National Research Council of Italy.     

On the distribution of the number of packets in the fluid flow approximation of packet arrival streams

Fluid flow approximations are widely used for approximating models of communication systems where packet arrival streams are generated in a regular manner over certain intervals (constant rate). The appropriate mathematical model for describing those bursty arrival streams in the fluid flow framework are the well-known Markov modulated rate processes (MMRP). The paper deals with the distribution of the numberN(t) of packets in the interval [0,t] of MMRP. For two-state MMRPs and their superpositions we derive formulas for the distribution ofN(t) and its density. Further we give asymptotic results. The presented numerical results and simulation studies illustrate the goodness of the fluid flow approximation and show that the proposed numerical algorithms work well even in the case of multiplexing a large number of burst silence sources.This work was partially supported by a grant from the Deutsche Bundespost TELEKOM.     

Plasma-maser interaction of langmuir wave with kinetic Alfvén wave turbulence

A theoretical study is made on the generation mechanism of Langmuir mode wave in the presence of kinetic Alfvén wave turbulence in a magnetized plasma on the basis of plasma-maser interaction. It is shown that a test high frequency Langmuir mode wave is unstable in the presence of low frequency kinetic Alfvén wave turbulence. The growth of the Langmuir wave occurs due to direct and polarization coupling terms. Because of the universal existence of the kinetic Alfvén waves in large scale plasmas, the results have potential importance in space and astrophysical radiation processes.     

微生物量对印染废水中的基质去除速率的影响

基于Monod方程,引入微生物量函数,建立了考虑微生物量作用的基质去除速率方程,并利用基质去除的零级反应速率求解有关参数.活性污泥好氧处理印染废水时,所需要的微生物量与反应时间密切相关,当HRT为24h,MLSS为2.2g·L-1,基质去除率为83%;而当HRT为12h,要达到相同的基质去除率,MLSS须维持在4.0g·L-1.当MLSS≤2.5g·L-1,基质去除速率与微生物量成正比;当MLSS为4.0g·L-1,基质去除速率约为最大值的86.2%,而且MLSS≥4.0g·L-1,基质去除速率随MLSS的变化不明显.所建立的基质去除速率方程能够较好地反映微生物量对基质去除速率的影响.     

磁绝缘传输线振荡器中辐射场的非线性行为

 导出了磁绝缘传输线振荡器(MILO)中辐射场的非线性演化方程，并讨论了在临界值点附近可能出现非线性不稳定解的条件。结论是：(1)非线性增长速率与线性增长速率的比值g<1.2，且远离g+γ=1(γ为非线性相位增长率与线性相位增长率的比值)点时，出现非稳定解的失谐量临界值很小，而线性增长速率临界值临界值很大，容易出现非稳定解；(2)当g≥1.2时，任意小的失谐量都可以使场出现非稳定解；(3)线性增长速率越大，越不容易出现非稳定解。