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假设能量低于3×10l8eV的宇宙线主要起源于银河系超新星爆发,用各向同性弥散传播模型详细研究了铁核的非定态空间密度分布,考虑到原初宇宙线的成份和河外宇宙线的影响,以及银河系超新星在空间和时间上的一个合理分布,该统计模型能很好解释1012—1020eV宇宙线的观测谱. 相似文献
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怀柔EAS阵列对初级宇宙线“膝”区能谱的测定 总被引:5,自引:2,他引:5
仔细分析了近年来怀柔广延大气簇射阵列记录的65万个大气簇射事例,得到了簇射Size(即荷电总粒子数)谱和1015—5×1016eV能段的初级宇宙线微分能谱.此谱呈明显的、平滑过渡的“膝”样结构,拐点在3×1015eV附近.除了“膝”较平滑不象明野谱那样尖锐拐折而外,怀柔谱在绝对流强和“膝”的位置上都与日本明野组吻合得很好.在银河磁场刚度截止模型框架下,怀柔实验Size谱界定的宇宙线质子谱拐折能量Ec的取值范围在160到240TeV之间. 相似文献
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μ子动量谱的精确测量是L3C宇宙线实验最重要的目标之一.事例重建的好坏是该测量的关键,而能量确定的衰变为双μ子的事例是检验重建程序的最好手段.该数据分析利用在2000年中获取的数据作为样本,筛选出了LEP在2000年4月、5月、8月和9月等Z0能量运行期间L3C宇宙线实验数据中记录的Z0→μ+μ-事例数据,得到通过重建程序后动量为45GeV的μ子动量分辨率为(5.4?7±0.25)%. 相似文献
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宇宙线超高能相互作用的QCD部分子模型产生器 总被引:1,自引:1,他引:0
在pQCD的部分子模型和独立碎裂方案的部分子强子化模型基础上,建立了用于超高能宇宙线与空气核相互作用的产生器.通过拟合PP散射和e+e-对撞实验数据来决定产生器中的参数.再现了从s=546GeV到1800GeVpp散射中喷注的产生和从s=14GeV到91GeV e+e-对撞等实验的基本特征,并外推到≤22TeV的超高能区. 相似文献
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The prevalence of neurodegenerative diseases (NDD) has grown rapidly in recent years and NDD screening receives much attention. NDD could cause gait abnormalities so that to screen NDD using gait signal is feasible. The research aim of this study is to develop an NDD classification algorithm via gait force (GF) using multiscale sample entropy (MSE) and machine learning models. The Physionet NDD gait database is utilized to validate the proposed algorithm. In the preprocessing stage of the proposed algorithm, new signals were generated by taking one and two times of differential on GF and are divided into various time windows (10/20/30/60-sec). In feature extraction, the GF signal is used to calculate statistical and MSE values. Owing to the imbalanced nature of the Physionet NDD gait database, the synthetic minority oversampling technique (SMOTE) was used to rebalance data of each class. Support vector machine (SVM) and k-nearest neighbors (KNN) were used as the classifiers. The best classification accuracies for the healthy controls (HC) vs. Parkinson’s disease (PD), HC vs. Huntington’s disease (HD), HC vs. amyotrophic lateral sclerosis (ALS), PD vs. HD, PD vs. ALS, HD vs. ALS, HC vs. PD vs. HD vs. ALS, were 99.90%, 99.80%, 100%, 99.75%, 99.90%, 99.55%, and 99.68% under 10-sec time window with KNN. This study successfully developed an NDD gait classification based on MSE and machine learning classifiers. 相似文献
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为了实现车载γ谱仪巡测系统对辐射剂量率的准确测定,提出基于快速傅里叶变换(FFT)本底扣除法的改进型BP神经网络模型(FFT-BP神经网络模型)。实验采用γ射线能谱分析法,对不同间距处的137Cs放射源进行车载γ能谱测试,将得到的谱数据通过快速傅里叶变换(FFT)扣除本底,获得新的谱线数据。应用FFT-BP神经网络模型对未知剂量的车载γ谱线作辐射剂量率的定量预测,将预测结果同3个函数模型的拟合结果比较,验证FFT-BP神经网络模型的预测效果。结果表明,FFT扣除法能较好的削弱散射本底对γ谱线的影响,能有效的降低谱线本底。通过新谱线获得的特征峰面积和净谱线面积与辐射剂量率的相关系数均为0.99(p<0.05),相关性显著。模型拟合分析过程中,FFT-BP神经网络模型表现出较强的学习泛化能力,预测较理想,相对误差和累计误差分别低于0.6%和9%,效果明显优于数学模型和γ能谱全能峰法,可显著降低γ能谱分析辐射剂量率的误差,且能有效提升工作效率。因此,FFT-BP神经网络模型适用于γ能谱辐射剂量的预测分析,为车载γ谱仪巡测系统测量辐射剂量提供了一种新型有效的分析方法。 相似文献
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Meng X Nguyen BD Ridge C Shaka AJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,196(1):12-22
High-dimensional (HD) NMR spectra have poorer digital resolution than low-dimensional (LD) spectra, for a fixed amount of experiment time. This has led to "reduced-dimensionality" strategies, in which several LD projections of the HD NMR spectrum are acquired, each with higher digital resolution; an approximate HD spectrum is then inferred by some means. We propose a strategy that moves in the opposite direction, by adding more time dimensions to increase the information content of the data set, even if only a very sparse time grid is used in each dimension. The full HD time-domain data can be analyzed by the filter diagonalization method (FDM), yielding very narrow resonances along all of the frequency axes, even those with sparse sampling. Integrating over the added dimensions of HD FDM NMR spectra reconstitutes LD spectra with enhanced resolution, often more quickly than direct acquisition of the LD spectrum with a larger number of grid points in each of the fewer dimensions. If the extra-dimensions do not appear in the final spectrum, and are used solely to boost information content, we propose the moniker hidden-dimension NMR. This work shows that HD peaks have unmistakable frequency signatures that can be detected as single HD objects by an appropriate algorithm, even though their patterns would be tricky for a human operator to visualize or recognize, and even if digital resolution in an HD FT spectrum is very coarse compared with natural line widths. 相似文献
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Recent observations of a direct reaction between adsorbates and hydrogen atoms incident from the gas phase are interpreted in terms of an Eley-Rideal reaction. A detailed comparison of the experimental data for the HD/Cu(111) system with quantum mechanical model calculations corroborates such an interpretation. The peculiar isotope effect observed can be understood from the different dynamical implications of appropriately rescaled potential energy surfaces. The width of the measured time-of-flight spectrum is explained from the overlapping contributions of the populated vibrational levels. The angular distributions are rationalized by contributions both from 'indirect' events, where the incident atoms make several bounces in the surface well prior to reaction, and 'direct' reactive events. 相似文献
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Molecular beam techniques are employed to study the adsorption and desorption of H2 on the (100), (110), and stepped (310) crystal faces of copper. Each crystal is exposed simultaneously to a supersonic molecular beam of H2 (energy variable from 1.6 to 10.7 kcal/mole) and a highly dissociated beam of deuterium. The majority of the H2 molecules are scattered from the surface (i.e., are not adsorbed), while a portion of the remaining molecules adsorb dissociatively and react catalytically with adsorbed deuterium atoms to form HD molecules. These HD molecules desorb, and their angular distribution is measured by a rotatable mass spectrometer. For all three crystal faces, the distributions of desorbed HD deviate significantly from diffuse emission and are in excellent agreement with the results of our previous permeation study. From the dependence of the HD signal on the energy and incident angle of the H2 beam, it appears that there are substantial energy barriers to adsorption, with these barriers depending on crystallographic orientation and acting essentially perpendicular to the surfaces. Both the energy dependence of the dissociative adsorption probability and the shapes of the HD angular distributions are nearly identical for the stepped (310) and (100) surfaces, thereby suggesting that ledge sites are not the principal regions responsible for adsorption of hydrogen on copper. The estimated adsorption probabilities versus energy are “S” shaped curves which appear to level off at values considerably less than unity. A comparison of our results with a very simple model with a single energy barrier to adsorption is qualitatively but not quantitatively satisfactory. An interpretation which includes a distribution of energy barriers is suggested. 相似文献
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Recent observations of a direct reaction between adsorbates and hydrogen atoms incident from the gas phase are interpreted in terms of an Eley-Rideal reaction. A detailed comparison of the experimental data for the HD/Cu(111) system with quantum mechanical model calculations corroborates such an interpretation. The peculiar isotope effect observed can be understood from the different dynamical implications of appropriately rescaled potential energy surfaces. The width of the measured time-of-flight spectrum is explained from the overlapping contributions of the populated vibrational levels. The angular distributions are rationalized by contributions both from ‘indirect’ events, where the incident atoms make several bounces in the surface well prior to reaction, and ‘direct’ reactive events. 相似文献
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Quasielectron electron scattering from gaseous H2, D2, a 50:50 mixture of H2 and D2, and HD is investigated with 2.25 keV impact energy and a momentum transfer variant Planck's over 2piq of 19.7 a.u. The energy transfer is less than the dissociation energy. The spectral positions of the H and D recoil peaks agree with Rutherford scattering theory. Surprisingly, in the spectrum of the 50:50 H2-D2 mixture, the integrated intensity of the H peak is 31%+/-4% lower (as compared to that of D) than predicted by Rutherford scattering, despite equal screening of nuclear charges by the electrons. In contrast, the ratio of scattering intensities from H and D in HD agrees with the predictions of Rutherford scattering. Comparison is made with neutron Compton scattering results from the same systems, but at higher energy transfers causing bond breaking. Possible theoretical explanations are outlined. 相似文献
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Caroline Vandeputte Jean-Marc Taymans Cindy Casteels Frea Coun Yicheng Ni Koen Van Laere Veerle Baekelandt 《BMC neuroscience》2010,11(1):92