On the spectral analysis of quantum field Hamiltonians

We define C^∗-algebras on a Fock space such that the Hamiltonians of quantum field models with positive mass are affiliated to them. We describe the quotient of such algebras with respect to the ideal of compact operators and deduce consequences in the spectral theory of these Hamiltonians: we compute their essential spectrum and give a systematic procedure for proving the Mourre estimate.     

混合分布的识别性及其应用

设(Y_1,Y_2)是非负的二维随机变量,有联合分布函数F(y_1,y_2),设Z=min(Y_1,Y_2),定义随机变量I=1;2;3,分别对应于Y_1Y_2;Y_1=Y_2时.记p_i=P(I=i),f_i(·)为给定I=i时Z的条件密度(i=1;2;3).给定可识最小值(Z,I)的联合密度函数P_iJ_i(·)(i=1;2;3),得到F(·,·)是混合分布时,F(·,·)用P_if_i(·)来表示的一个显式表达式.对三维及以上情形,得到类似的结果.特别,把识别基本定理应用于多元Marshall-Olkin型指数分布的参数估计,得到了基于观察值(Z_jI_j)(j=1,2,…,n)的参数的极大似然估计及矩估计,并且证明了极大似然估计具有联合完备充分的,渐近无偏的,均方误差一致的,及渐近正态性特性,修正估计恰好是Arnold估计,它是唯一的一致最小方差无偏估计,且同时是渐近有效估计,本文还指出了矩估计方法的不唯一性.     

综述180°回转型弯头对U型管内的气液两相流流型压降与传热的影响

从流型,压降和传热三个方面综述了以前研究者在U型管中所做的研究。指出了180°弯头对整个U型管的流型及其流型转变,压降损失及其预测方法和增强换热的影响。同时提出了今后关于U型管可能的研究方向:(1)细化曲率比等几何因素对流型压降传热的影响;(2)关注低温介质的U型管中的流动与传热;(3)以180°弯头加上距其一定距离的上下游为一个单元考虑其整体的压降损失;(4)量化气液两相流在U型管中的传热。     

用于监控系统的鱼眼镜头光学设计

为了满足监控系统中单镜头可实现全景监控的需求,运用仿生学原理,在原有鱼眼镜头的基础上结合监控系统的需求,运用ZEMAX软件设计了一款视场为180°,相对孔径为1/1.6的鱼眼镜头.该镜头由9片透镜组成,总长度为68.5mm,采用1/3英寸CCD作为图像接收器件.在120lp/mm时,其MTF曲线在轴上大于0.4,在80...     

不同重力下90°弯管内气液两相流流型及流动特性研究

研究了不同重力条件下90°弯管内气液两相流流型分布形态及流动特性. 通过建立90°弯管内气液两相流流动的三维数学物理模型,采用VOF 方法,对10-6g₀, 10-4g₀, 10-2g₀, 1g₀ (g₀= 9.8m/s2) 重力下的90°弯管内气液两相流流型分布特征、截面空隙率、滑速比及气相尾部最大斜向角进行了比较分析. 研究结果表明:所建立的模型能够正确模拟不同重力条件下90°弯管内气液两相流流型和截面空隙率,并得到气液两相弯管二次流与单相二次流的不同特性. 随着重力水平的提高,90°弯管对气相流型的影响作用减弱,气相整体向弯管内侧积聚靠拢,弯管对尾部的斜向作用减弱.      

A magnetic resonance study on the structure of amorphous networks in the Si–B–N(–C) system

The amorphous networks Si₃B₃N₇ and ‘SiBN₃C' are studied by solid-state nuclear magnetic resonance (NMR), continuous-wave and pulse electron paramagnetic resonance (EPR), and by one- and two-dimensional electron nuclear double resonance spectroscopy. In both compounds, boron is found to be coordinated exclusively by nitrogen with close to trigonal planar geometry and close to equal bond lengths. Silicon is four-coordinated by nitrogen with the coordination tetrahedra being distorted to accommodate the coordination preferences of boron. REDOR measurements demonstrate that boron resides in the second coordination sphere of silicon. Carbon incorporation into the Si–B–N network does not lead to any observable changes in NMR parameters including the average dipolar coupling between ¹¹B nuclei which depends on the average distance of the boron atoms. Only spin–lattice relaxation of the nuclei is accelerated due to the generation of paramagnetic centers. The unpaired electrons appear to be delocalized over several carbon atoms and exhibit significant hyperfine couplings to boron, silicon, nitrogen, and some residual protons. In contrast to electron spectroscopic imaging experiments, the magnetic resonance results suggest formation of carbon clusters.     

鼠S180肉瘤的体内31P MRS研究

利用表面线圈³¹P NMR研究了小鼠S180肉瘤生长过程中能量代谢和磷脂类变化的特点.结果发现:随着肿瘤体积的增大,(1)Pi和PME升高;(2)PCr降低,在肿瘤体积较大时常检测不到;(3)β-NTP(通常用来表示ATP的量)变化较小;(4)PDE波动性较大;(5)PCr/Pi和β-NTP/Pi比值均下降,且PCr/Pi比β-NTP/Pi下降得快;(6)PME/β-NTP比值升高;(7)肿瘤pH下降,且与PCr/Pi、β-NTP/Pi或(PCr+β-NTP)/Pi比值有相关性.讨论了与这些参数变化相关联的生物学意义.     

周视彩虹全息图中共轭像的抑制

本文从理论和实验两方面分析了共轭像的干扰问题,求得了共轭像强度对记录介质厚度及物光—参考光夹角的依赖关系,并对普通6μm干板给出了抑制共轭像的条件.     

An easy and economic method for preparing completely reduced basalt glass

Four basalt glass samples were prepared by fusing basalt rock (powder) with different amounts of sulfur in a platinum crucible at 1550 °C for 30 min. Each melt was quenched in air. Sulfur addition to the basalt powder was changed from 0 to 5, 10 and 15 wt%. The prepared glass samples were pulverized for measuring the Mössbauer spectra by the constant acceleration method. The basalt rock spectrum can be analyzed into four peaks; two sites due to Fe³⁺ with octahedral (Oh) and tetrahedral (Td) symmetry, and the other two due to Fe²⁺ with Oh and Td symmetry. Pure basalt glass (sulfur-free) consists of four doublets; two of them represent Fe²⁺(Oh) sites and the third represents Fe²⁺(Td); while the fourth doublet belongs to Fe³⁺(Td). The sample containing 5 wt% sulfur has four iron sites also, although there is a slight difference in the relative absorption area when compared with sulfur-free sample. The fraction of Fe³⁺ in the 5% sulfur sample was estimated to be only 7.1%; i.e., the fraction of Fe²⁺ was 92.9%. Three iron sites present in the 10% sulfur sample, two of them represent Fe²⁺ with (Oh) symmetry, while the third one represents Fe²⁺(Td) site. Mössbauer spectrum of 15 wt% sulfur sample is essentially the same as that of the sample which contains 10 wt%. It is noteworthy that the sulfur content shows a linear relationship with the Fe²⁺ fraction which is calculated from the Mössbauer spectra of basalt glasses. 7.5 wt% of sulfur is large enough to completely reduce the iron in basalt glass. The reduction of glasses could occur easily and economically using sulfur as a reducing agent. This method is a very easy and economic method for the preparation of completely reduced oxide glass.     

Recent developments in manufacturing emulsions and particulate products using membranes

Membrane emulsification (ME) is a relatively new technique for the highly controlled production of particulates. This review focuses on the recent developments in this area, ranging from the production of simple oil-in-water (O/W) or water-in-oil (W/O) emulsions to multiple emulsions of different types, solid-in-oil-in-water (S/O/W) dispersions, coherent solids (silica particles, solid lipid microspheres, solder metal powder) and structured solids (solid lipid microcarriers, gel microbeads, polymeric microspheres, core-shell microcapsules and hollow polymeric microparticles). Other emerging technologies that extend the capabilities into different membrane materials and operation methods (such as rotating membranes, repeated membrane extrusion of coarsely pre-emulsified feeds) are introduced. The results of experimental work carried out by cited researchers in the field together with those of the current authors are presented in a tabular form in a rigorous and systematic manner. These demonstrate a wide range of products that can be manufactured using different membrane approaches. Opportunities for creation of new and novel entities are highlighted for low throughput applications (medical diagnostics, healthcare) and for large-scale productions (consumer and personal products).