利用MCNPX模拟研究不同中子源对有源符合中子法的影响

利用MCNPX软件建立了有源井型符合计数器(简称AWCC)测量模型,模拟了诱发中子源分别为Am-Li源和Am-Be源时AWCC测量贫化铀的中子符合计数率,研究了两种诱发中子源下AWCC测量贫化铀质量的精度.研究表明,Am-Be源引起的诱发中子符合计数率低于Am-Li源引起的诱发中子符合计数率,Am-Be源下的质量刻度曲...     

Coriolis流量计在油水两相流中的误差特性研究

在油水两相流实验回路上,用Coriolis质量流量计对油水两相流中的流量和含水率的误差特性进行了实验研究。实测了含水率的相对误差随含水率的变化特性。实验结果也证明质量流量和体积流量的相对误差在含水率0-100％范围内都较小,且在同一含水率下,流量越大,精度越高。实验所用的Coriolis质量流量计通径为25 mm,实验范围为:体积流量1.2 m3/h～2.4 m3/h,含水率0-100％。     

Systematics on fission fragment mass distribution of neutron induced 235U fission

Based on the neutron induced fission fragment mass distribution data up to     

Systematics on fission fragment mass distribution of neutron induced 235U fission

Based on the neutron induced fission fragment mass distribution data up to neutron energy 20 MeV measured with the double kinetic energy method (KEM) and the radio active method (RAM), the systematics of fission fragment mass distribution was investigated by using 5 Gaussian model and the systematics parameters were obtained by fitting the experimental data. With the systematics, the yields of any mass A and at any energy in the region from 0 to 20 MeV of neutron energy can be calculated. The calculated results could well reproduce the experimental data measured with KEM, but show some systematical deviation from the data measured by RAM, which reflects some systematical deviations between the two kinds of measured data.The error of systematics yield was calculated in an exact error transformation way, including from the error of the experimental yield data to the error of the discrete parameters, then to the systematics parameters,and at last to the yield calculated with systematics.     

Errata

A numerical error was made in estimating an El transition strength in ⁶⁴Ge. Correction of the error indicates isospin mixing is similar to that found in beta decay experiments in this mass region.     

A novel observer design method for neural mass models

Neural mass models can simulate the generation of electroencephalography(EEG) signals with different rhythms,and therefore the observation of the states of these models plays a significant role in brain research. The structure of neural mass models is special in that they can be expressed as Lurie systems. The developed techniques in Lurie system theory are applicable to these models. We here provide a new observer design method for neural mass models by transforming these models and the corresponding error systems into nonlinear systems with Lurie form. The purpose is to establish appropriate conditions which ensure the convergence of the estimation error. The effectiveness of the proposed method is illustrated by numerical simulations.     

Mass measurements of few-electron systems in Penning traps

The accuracy of the SMILETRAP mass spectrometer has been verified by a number of mass comparisons involving well-known masses. Our results for H₂ ⁺,Ne⁶⁺,Ne^{9+ ,10+},Si^{12+ ,13+ ,14+},and Ar^{14+ ,16+} all agree within the statistical errors (0.3–1 ppb) with previous determinations. However, all measurements involving He give a deviation. The combined He^1+,2+ data results in a mass deviation of +1.9 ±0.23 ppb. The uncertainty of the accepted He mass is 0.25 ppb, thus this represents a significant deviation. High statistics comparisons (statistical uncertainty <0.5 × 10^-9utilizing different species (excluding He) and charge states agree within ±0.5 ppb. An analysis estimating the contribution from individual systematic error sources and other auxiliary tests does not allow a systematic error larger than ± 0.85 ppb. We conclude that for now we cannot rule out the presence of an unknown systematic error which in the He comparison results in a near 2 ppb deviation. Thus, as a safety measure we should exclude the He data when calculating the proton mass. The He discrepancy also forces us to give a larger limit of the systematic error of the proton mass than motivated by high statistics comparisons. However, due to the consistency of all other measurements and tests, it appears unlikely that this deviation should be present to the same extent in other comparisons. Thus, for now, after a preliminary analysis we report a proton mass = 1.007 276 466 72 ± 16 ± 85 u, where the errors are the weighted statistical errors and the estimated maximal systematical error, respectively. After a complete analysis we expect the systematic error to be reduced below ±0.5 ppb. This revised version was published online in July 2006 with corrections to the Cover Date.     

多孔介质对流干燥外部传热传质的非平衡热力学理论

从非平衡热力学理论出发,以广义热力学力作为传质过程驱动势,建立了描述多孔介质恒速干燥阶段外部对流传热传质过程的热力学理论模型,并进行了数值计算,计算值与已有的实验数据吻合较好;同时,还将计算结果与传统的理论进行了比较,结果表明,非平衡热力学理论更能反映过程的物理本质。     

The Measurement of Particles Suspended in a stirred vessel using microphotography and digital image analysis

A novel technique to determine the size of particles suspended in a stirred vessel is investigated. The method uses microphotography to obtain a still image of the particles in situ. The equivalent circular diameter of the particles is obtained from the photographs using digital image analysis. The particles used for the test were certified particle size standards of a very small tolerance in diameter deviation. The size comparison was determined as a percent error between the measured particle diameter (equivalent circular diameter) and the diameter established by the particle manufacturer. To determine the limiting ranges of particle size and concentrations, spherical particles in a size range of approximately 1 to 10.0 μm (microns) in diameter were employed in the test. Concentrations varied from 0.00005% to 0.1% (mass basis). For each particle size, an aqueous solution of the particles was prepared at the desired concentration and placed in a stirred vessel. Photographs of the solutions were made at 25.5x, 40x, 60x and 80x magnification. For all sizes of particles, the entire range of concentration was examined. The results indicate a minimum size resolution of approximately 3μm, in a corresponding concentration range of 0.0001% to 0.05%. Similar limits on concentration were found for the larger diameter particles, although a true upper limit for the largest particle sizes was not established. The functional concentration range appears to shift towards higher mass concentrations with increasing particle size. For 2.92 μm diameter particles, the error in size measurement was found to be below 10% for a concentration range of 0.0005% to 0.05%. Additionally, a relationship between turbidity and the error was seen at low particle concentration levels where decreasing levels of turbidity generated increasing levels of error.     

Estimation of the Dynamics of the Drift of Spectral Lines and Computer Correction of the Scan of a Mass Spectrum

This article describes the technique used to estimate the temporal positions of spectral lines of a quadrupole mass spectrometer and to automatically determine mass numbers without resorting to reference substances, as well as the algorithms of digital registration of mass spectra and the technical means of an experimental automated system based on a serial MX-7304A mass spectrometer and a personal computer. The results of experimental investigations of the dynamics of the drift of peaks and the results of tests of the technique under real conditions are given. The error in determining the atomic mass unit (u) by the technique developed was not higher than 0.01%.     

激光诱导击穿光谱技术定量分析钢铁合金中痕量Mo元素实验研究

探索在内标物谱线选择受限情况下利用激光诱导击穿光谱(LIBS)技术进行定量分析的可行方案,并应用到复杂钢铁合金中痕量金属元素钼(Mo)的检测分析中.实验中烧蚀激光波长为532 nm,LIBS信号的采集通过光栅单色仪、(2CD、Boxcar和PMT来完成.对Mo的550.649,553.305和557.045 nm三条原...     

古代计时器——水钟

通过对中国古代计时器水钟的原理研究,利用现代的技术和材料制作了水钟.采用2种方式将匀速的水流转化为其他形式变量:一种是水滴计数法,水钟计时时长15min,累计误差6s;另一种是将匀速的水流转换成质量信号,计时时长10min,累计误差2～3s.     

夸克模型下的轻介子质量谱

最近,文献[1]将辅助场方法应用于准相对论性夸克模型中,获得了一个解析的非奇异轻介子质量公式。本文将这种方法推广到奇异轻介子的情况,得到了一个味道依赖的轻介子质量公式。结果表明,质量公式预言的低激发态质量谱与实验值吻合良好,平均误差在30 MeV左右。质量公式预言的高激发态质量谱和其他文献（特别是弦模型）的计算相比,也符合较好。Recently, with the help of auxiliary field method, Ref.[1] obtains an analytical mass formula for nonstrange light mesons in quasi-relativistic quark model. In this work, we generalize this method to the case of strange light mesons, and obtain a mesonic mass formula which is flavor-dependent. The results show that the mass of low excitations given by the mass formula are in good agreement with the experimental data and the average error is around 30 MeV. Our mass predictions for the high states also agree well with the other calculations in the literatures, particularly, the string model calculations.     

基于SVM的混合气体红外光谱分析关键技术研究

为了解决海量混合气体光谱数据样本无法获取、混合气体组分气体特征吸收谱线重叠、混合气体组分浓度分布的随意性等问题,将支持向量机用于混合气体红外光谱分析中.提出了光谱数据样本特征选择、数据预处理、SVM校正模型参量优化及层次式混合气体光谱分析结构等关键技术.实验分析了上述4项关键技术对分析结果的影响.实验结果显示,采用关键技术的混合气体组分浓度分析的最大绝对误差为2.93%,最大平均绝对误差为0.73%.     

Molecular mass estimation by PFG NMR spectroscopy

A simplified PFG NMR diffusion analysis method was developed to estimate the molecular mass of small molecules in dilute aqueous and organic solutions. Internal referencing was utilized to improve the experimental robustness and simplify the data analysis. Specifically, tetramethylsilane (TMS) and HDO were chosen for the organic and aqueous reference molecules, respectively. Relative diffusivity-molecular mass correlations were empirically developed in the range of 2-1280 g/mol for dilute CDCl3 and D2O solutions. The median error in the predicted molecular mass was found to be 10 rel%. The utility of the method was demonstrated by analyzing the major and minor components in olive oil.     

Physical nucleon properties from lattice QCD

We investigate various resummations of the chiral expansion and fit to the extremely accurate lattice QCD data for the mass of the nucleon recently obtained by the CP-PACS group. Using a variety of finite-range regulators, we demonstrate a remarkably robust chiral extrapolation of the nucleon mass. The systematic error associated with the chiral extrapolation alone is estimated to be less than 1%.     

物质比热容测定实验的改进

用混合法测定物质比热容中通常把高温物质放入低温的水中，这时损失大量的热量，增加了测量误差，为减少这部分误差，提出了把低温物质放进高温物质的实验方法和步骤。     

不同质量含水量的土壤反射率光谱模拟模型

土壤含水量的时空分布与变化情况对土壤温度变化、陆地—大气间热量平衡以及陆面大气环流产生显著的影响,因此,对大范围内土壤含水量进行实时动态监测,获得某段时间内土壤含水量的连续变化情况具有重要的意义。研究目的是借助高光谱遥感手段,通过构建不同质量含水量的土壤反射率光谱模拟模型,深入了解土壤质量含水量与土壤反射率光谱之间的关系,为监测土壤含水量提供有效手段。利用ASD Field Spectral FR野外光谱仪和加水称重法获得北京市8个采样点的土壤样品不同质量含水量下的土壤反射率光谱实测数据,利用其中2个土壤样品不同质量含水量下的光谱数据构建含水土壤反射率光谱模拟模型,并利用未参与建模的另外6个土壤样品数据对该模型的模拟效果进行了检验。通过数据验证发现,当土壤质量含水量小于田间持水量时,该模型的模拟精度较高;而且对于不同的土壤样品,模型的模拟效果都比较好。最后又利用北京大学校园内三个采样点的实地测量光谱数据对模型进行了验证,光谱的模拟值与实测值之间的均方根误差最小可达0.005 8。因此该模型可实现对质量含水量小于田间持水量的不同类型土壤的反射率光谱进行较高精度的模拟。     

Neutrino mass and dark energy from weak lensing

Weak gravitational lensing of background galaxies by intervening matter directly probes the mass distribution in the Universe. This distribution is sensitive to both the dark energy and neutrino mass. We examine the potential of lensing experiments to measure features of both simultaneously. Focusing on the radial information contained in a future deep 4000 deg(2) survey, we find that the expected (1-sigma) error on a neutrino mass is 0.1 eV, if the dark-energy parameters are allowed to vary. The constraints on dark-energy parameters are similarly restrictive, with errors on w of 0.09.     

基于狭义相对论转动质量效应的X-ray光谱分析

基于狭义相对论的基本观点,研究了特征X-ray的产生机理,分析了在狭义相对论下转动质量效应对X-ray光谱的影响,导出了一个计算X-ray特征波长的公式,同时对计算推导的特征波长值做了系统的误差分析,得到了相对误差的规律。结果表明,计算推导的波长值与实验的波长值相比是非常的接近的,并且随着原子序数的增加,转动质量效应对特征波长的影响越来越明显,研究结果在实际应用中对分析特征X-ray光谱具有一定的参考意义。