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71.
The emission of radiation from relativistic positrons moving in the 〈110〉 axial channels of an f.c.c. (diamond) crystal has
been studied. An expression for the radiation intensity has been obtained for the general case of positron motion. This expression
has been simplified for the particular case of well-collimated incident beam. Enhancement of the radiation over (ordinary)
bremsstrahlung has been discussed. 相似文献
72.
Osamu Ohtaka Naoyuki Ohnishi Katsuyuki Kubo Hiroshi Arima Hiroshi Fukui Takamitsu Yamanaka 《高压研究》2013,33(1):11-15
Using a hot isostatic pressing (HIP) technique, we synthesized diamond/SiC composites from diamond and Si powders. At an HIP condition of 1450 °C and 100 MPa, a pressure much lower than that of the diamond stability field, diamond powders react with molten Si to form well-sintered diamond/SiC composites. Cubes of the composites with 15 mm edge length were thereby fabricated, and an application to the second stage anvils in a Kawai-type high-pressure apparatus was attempted. A hybrid anvils system using four cubes of the composites and four of the conventional WC was introduced and heating experiments up to 1600 °C became possible. Because the diamond/SiC composites are transparent to X-rays, the present system is applicable not only to diffraction studies but also to radiographic studies that need a larger window for an X-ray image. 相似文献
73.
74.
75.
2×2列联表中二属性相关的假设检验是定性数据分析中的热点问题,针对此问题的研究频率学派已做过大量的工作,其理论方法已趋于成熟.利用Bayes检验研究2×2列联表中二属性的相关性迄今为止国内外的相关文献还为数不多.将依据Bayes理论对此问题提出新的检验方法,推出其Bayes因子计算公式,利用正态近似研究三项假设计算出有关的后验概率,不仅解决了频率学派难以处理的问题,并且为吸烟有害健康提供了理论支撑. 相似文献
76.
We construct a generalization of Maxwell's equations associated with the proper-time of the source which accounts for radiation reaction without any assumptions concerning the nature of the source. The theory leads to a new invariance group, related to the Lorentz group, which leaves the proper-time of the source fixed for all observers. 相似文献
77.
在70-300K温度范围内测量了组分x为0.01和0.04的Cd1-xFexTe及CdTe的法拉第效应随入射光子能量的变化,首次获得了Cd1-xFexTe在布里渊区Γ点和L点的有效g因子及其与温度的关系。给出了Fe2+离子与载流子间的sp-d交换作用常数N0(β-α)=(-1.57±0.03)eV。 相似文献
78.
甲状腺内^(131)I放射性活度与辐射探测结果的比例关系与甲状腺几何尺寸、探测距离等因素相关,是估算甲状腺内^(131)I含量与其可能造成的辐照损伤的关键参数。基于MCPT辐射输运数值模拟算法器库开发了用于开展NaI探测器伽马辐射测量模拟的应用程序,进而建立了多组具有不同容积的甲状腺型容器和不同探测距离的物理模型,最终通过蒙特卡罗数值计算得到了不同测量状态下探测器的探测效率。在甲状腺型容器与探测器距离较远时,数值模拟给出的结果与理论计算结果一致,证明此应用程序可用于定量分析NaI的探测效率。数值模拟结果表明,小距离模型的结果受甲状腺样容器的大小和距离的显著影响,模拟给出的探测效率表为开展深入细致的实验研究奠定了基础。 相似文献
79.
Linear regression (LR) is a core model in supervised machine learning performing a regression task. One can fit this model using either an analytic/closed-form formula or an iterative algorithm. Fitting it via the analytic formula becomes a problem when the number of predictors is greater than the number of samples because the closed-form solution contains a matrix inverse that is not defined when having more predictors than samples. The standard approach to solve this issue is using the Moore–Penrose inverse or the L2 regularization. We propose another solution starting from a machine learning model that, this time, is used in unsupervised learning performing a dimensionality reduction task or just a density estimation one—factor analysis (FA)—with one-dimensional latent space. The density estimation task represents our focus since, in this case, it can fit a Gaussian distribution even if the dimensionality of the data is greater than the number of samples; hence, we obtain this advantage when creating the supervised counterpart of factor analysis, which is linked to linear regression. We also create its semisupervised counterpart and then extend it to be usable with missing data. We prove an equivalence to linear regression and create experiments for each extension of the factor analysis model. The resulting algorithms are either a closed-form solution or an expectation–maximization (EM) algorithm. The latter is linked to information theory by optimizing a function containing a Kullback–Leibler (KL) divergence or the entropy of a random variable. 相似文献
80.
The effects of Co-60 gamma-rays and about 25-MeV pulsed electrons have been investigated on CR-39 plastic nuclear track detector. The bulk etch rate was measured as a function of the absorbed dose under three different irradiation conditions; gamma-ray exposure in air at the dose rate of 6 kGy/h, that in vacuum and electron shower in air at 126 kGy/h on average. It was found that the bulk etch rate (V) increased nearly exponentially with the dose (D); V=V0exp(kD), and the characteristic parameter (k) was 35, 9 and 12 MGy−1, respectively. It is considered that a lack of oxygen in damage formation processes could occur momentarily during a short electron pulse, just similarly to the vacuum effect of reduction in track etch rates in outgassed CR-39 plastic. 相似文献