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11.
The subject of spectral distribution methods where one derives and applies the locally smoothed forms of observables in nuclei
is briefly reviewed. It is well understood that the local forms (with respect to energy) of the level density function, expectation
values and strength densities are Gaussian, linear (or ratio of Gaussians) and a bivariate Gaussian respectively. To accomodate
symmetries in the above forms, one has to deal with multivariate distributions in general; for example the angular-momentum
(J) decomposition leads to a bivariate Gaussian form for the level density. These results extend to indefinitely large spaces
by method of partitioning and they generate convolution forms. The origin of these remarkable spectral properties is discussed
and shell model examples are given to substantiate their applicability to nuclear systems. Spectral distribution theory is
a practical, usable theory because the smoothed forms are defined in terms of traces of low particle-rank operators, and the
trace information propagates. Finally we discuss the application of the spectral methods for a wide range of nuclear problems;
these include binding energies, orbit occupancies, electromagnetic andβ-decay sum rule quantities, analysis of operators, symmetry breaking, numerical level densities, and determination of bounds
on time-reversal non-invariant part of nucleon-nucleon interaction. 相似文献
12.
环形线电荷的电场分布 总被引:30,自引:10,他引:20
给出了圆环形线电荷电场分布的理论公式,并利用计算机计算出其具体分布规律。 相似文献
13.
14.
Stretch-dominated truss and plate microstructures are contenders in the quest for realizing architected materials with extreme stiffness and strength. In the low volume fraction limit, closed-cell isotropic plate microstructures meet theoretical upper bounds on stiffness but have low buckling strength, whereas open-cell truss microstructures have high buckling strength at the cost of significantly reduced stiffness. At finite volume fractions, the picture becomes less clear but both are outperformed by hollow truss lattice and hierarchical microstructures in terms of buckling strength. Despite significant advances in manufacturing methods, hollow and multi-scale hierarchical microstructures are still challenging to build. The question is if there exist realizable microstructures providing stiffness and strength matching or even beating hard-to-realize hollow or hierarchical microstructures? Herein, single-scale non-hierarchical (first order) microstructures that beat the buckling strength of hollow truss lattice structures by a factor of 2.4 and first- and second-order plate microstructures by factors of 5 and 1.4, respectively, are systematically designed, built, and tested. Stiffness of the microstructures is within 40% of theoretical bounds and beats both truss and second order plate microstructures. The microstructures are realized with 3D printing. Experiments validate theoretical predictions and additional insight is provided through numerical modeling of a CT-scanned sample. 相似文献
15.
Vinyl-containing poly(acrylic acid-co-itaconic acid) copolymers were synthesized and used to formulate light-curable cements containing reactive glass fillers (Fuji II LC). The conditions for light curing were studied and optimized. Effects of molecular weight (MW), grafting ratio, comonomer, liquid composition, powder/liquid (P/L) ratio, glass powder and aging were evaluated. The results show that the vinyl-containing glass-ionomer cements (GICs) prepared in this study exhibit higher compressive strength (CS, 225.6 MPa), diametral tensile strength (DTS, 28.4 MPa) and much higher flexural strength (FS, 116.4 MPa), as compared to commercial Fuji II LC GIC (186.6 in CS, 19.1 in DTS and 57.1 in FS). The optimal light-exposure time was found to be around 10 min, and concentrations of CQ and DC were 0.5% (by weight) and 1.0%, respectively. Effects of MW, grafting ratio, P/L ratio and content of polymer in the liquid formulation were significant. The highest strengths were found for the optimal formulations where the MW was 15,000 (weight average), grafting ratio 25 mol%, P/L ratio 2.7 and liquid composition 50:20:30. During aging, the cement showed an increase of strength over the first week and then no change for a month. SEM analysis suggests that more integrated microstructures and smaller glass particles can lead to higher FS and higher polymer content in GICs leads to tough fracture surface and plastic deformation. 相似文献
16.
17.
Julie L. S. Bell David J. Wesolowski Donald A. Palmer 《Journal of solution chemistry》1993,22(2):125-136
The dissociation quotients of formic acid were measured potentiometrically from 25 to 200°C in NaCl solutions at ionic strengths of 0.1, 0.3 1.0, 3.0, and 5.0 mol-kg–1. The experiments were carried out in a concentration cell with hydrogen electrodes. The resulting molal acid dissociation quotients for formic acid, as well as a set of infinite dilution literature values and a calorimetrically-determined enthalpy of reaction, were fitted by an empirical equation involving an extended Debye Hückel term and seven adjustable parameters involving functions of temperature and ionic strength. This regressional analysis yielded the following thermodynamic quantities for 25°C: logK=–3.755±0.002, Ho=–0.09±0.15 kJ-mol–1, So=–72.2±0.5 J-K–1-mol–1, and C
p
o
=–147±4 J-K–1-mol–1. The isocoulombic form of the equilibrium constant is recommended for extrapolation to higher temperatures. 相似文献
18.
19.
以去离子水与乙二醇的混合液(体积分数分别为36.5%,48.7%,59.0%及71.2%,以下简称混合液)作为同轴传输线的绝缘介质,进行了μs级高电压负充电条件下的正电极击穿实验,研究了混合液的击穿电压、击穿时间、相对介电常数及电阻率与体积分数的关系。实验结果表明:在充电电压为20kV时,71.2%的混合液比36.5%的混合液的平均击穿电压提高25.1%,平均击穿时间延长10.49%,而相对介电常数减小868%。同时,随着充电时间的缩短,混合液的击穿电压提高。 相似文献
20.
探头对共聚焦内窥成像系统层析能力的影响 总被引:2,自引:1,他引:1
根据透镜成像规律和单模光纤的传输特性,获得基于单模光纤的共聚焦内窥成像系统轴向光强分布,发现系统的成像过程由于单模光纤的介入呈现非线性,照明光路系统和接收光路系统仅影响系统接收信号的总强度,系统层析能力取决于探头和单模光纤性能.通过建立的共聚焦内窥成像实验装置,测量出在三组不同物镜组合情况下系统的归一化轴向光强分布.结果显示已建立的共聚焦内窥成像系统的理论模型是正确的,扫描光点的定位精度对系统层析能力影响很大,系统设计应该综合考虑光学、机械和电子方面的性能要求. 相似文献