Multistep direct emission from nucleon-induced reactions

Unbound 1p1h states are excited together with the bound ones in one-step direct processes induced by nucleons of energy greater than the particle binding energy. The cross-sections of the one-step direct reactions to bound final states are folded into a convolution integral to obtain the multistep cross-sections. This is done in the framework of the theory of Feshbach, Kerman and Koonin (FKK) that describes the emission of one particle. The processes to unbound 1p1h final states give rise to more complicated direct reactions, that are evaluated by an approximate method. The comparison of the theory with inclusive proton inelastic scattering by iron and with the charge exchange (p,n) reaction on zirconium is revised, at energies from 25 MeV to 120 MeV. It is shown that in the case of the (p,n) reaction the theory of FKK does not account for approximately 35% of the direct processes.Received: 11 November 2003, Published online: 10 August 2004PACS: 25.40.Kv Charge-exchange reactions - 25.40.Ep Inelastic proton scattering - 24.60.Gv Statistical multistep direct reactions     

Investigation of the 60Ni(n,p) reaction mechanism at 18.5 MeV

The differential cross sections of the ⁶⁰Ni(n, p) reaction are measured at 18.5 MeV. The reaction mechanism has been discussed in the framework of the Geramb model and of the FKK statistical multistep emission theory. Special attention is paid to the excitation of the GDR as a doorway state in ⁶⁰Ni and as a parent analog in ⁶⁰Co. The total proton emission cross section is estimated.     

The statistical theory of multi-step compound and direct reactions

The theory of nuclear reactions is extended so as to include a statistical treatment of multi-step processes. Two types are distinguished, the multi-step compound and the multi-step direct. The wave functions for the system are grouped according to their complexity. The multi-step direct process involves explicitly those states which are open, while the multi-step compound involves those which are bound. In addition to the random phase assumption which is applied differently to the multi-step direct and to the multi-step compound cross-sections, it is assumed that the residual interaction will have non-vanishing matrix elements between states whose complexities differ by at most one unit. This is referred to as the chaining hypothesis. Explicit expressions for the double differential cross-section giving the angular distribution and energy spectrum are obtained for both reaction types. The statistical multi-step compound cross-sections are symmetric about 90°. The classical statistical theory of nuclear reactions is a special limiting case. The cross-section for the statistical multi-step direct reaction consists of a set of convolutions of single-step direct cross-sections. For the many step case it is possible to derive a diffusion equation in momentum space. Application is made to the reaction ¹⁸¹Ta(p, n)¹⁸¹W using the statistical multi-step compound formalism.     

在Feshbach-Kerman-Koonin多步理论中P及Q空间的跃迁

存在直接作用时, 在哈密顿量中将包括非对角元, 并导致Feshbach,Kerman和Koonin预平衡反应多步复合理论中P和Q空间的耦合, 得到了理论上更严格的Feshbach, Kerman和Koonin预平衡反应多步复合理论与复合核反应Hauser-Feshbach理论的统一表示, 也改进了与实验结果的符合.     

FKK多步复合核模型发射模式分析

本文分析了FKK多步复合核理论中,考虑模型空间限制在束缚态空间情况下,对能谱形状的影响及各种可能发射模式对能谱贡献的相对重要性,得出了能谱的高能硬尾,主要由不改变反应初始阶段总激子数的两激子散射过程v=0的发射模式决定的结论。 Relative contributions of possible threee exit modes to the spectrum of FKK multistepcompound process are analysed with considering effects caused by the restriction of model space tobound configurations. It has been found that high-energy tail of the spectrum is mainly dominated bythe emission through ν=0 mode i. e. through the scattering of two excitons without changing totalexciton number.     

Statistical multi-step compound emission in (n, 2n) reactions

The multi-step compound-emission (MSC) theory has been used to analyse the preequilibrium effects in the neutron-emission spectra and excitation curves of the (n, 2n) reactions. Cross sections for the ¹⁹¹Ir(n, 2n) and ¹⁹³Ir(n, 2n) reactions are reported in the neutron-energy range from 13 MeV to 18 MeV and analysed in terms of combined compound-nucleus and MSC theory.     

钡原子6p3/2ns自电离里德伯态的研究

用激光多步激发技术研究了处于6p1/2电离限以下的6p3/2ns自电离态的光谱。 并利用最新的R矩阵的计算结果, 结合多通道量子亏损理论进行了理论分析。 理论结果与实验光谱相符合。     

Multi-step-direct-reaction analysis of continuum spectra of (p, α) reaction

Application of multi-step direct reaction theory to transfer reactions is demonstrated by successfully fitting continuous spectra of the ⁵³Fe(p, α)⁵¹Mn reaction taken as an example.     

基于混沌算子网络的时间序列多步预测研究

结合相空间重构理论和时间序列分析理论,提出一种用于时间序列多步预测的网络模型.网络采用多个混沌算子加权求和的形式构成.网络各层单元采用固定权值连接,混沌算子的控制参数利用混沌优化算法进行训练调节,从而控制预测网络的动力学行为.利用已知时间序列数据构造出训练样本,训练样本在网络训练过程中仅使用一次,促使网络的动力学特性随时间的推移而变化,并逐渐逼近被预测系统的动力学特性,最终完成对未来时刻数据的预测.在对理论数据进行预测分析时,通过计算预测序列的Lyapunov指数验证了预测网络的有效性.在对实际时间序列的预测过程中,该网络表现出了良好的预测性能.仿真结果表明,该预测网络可对多种时间序列在一定的预测步长范围内实现有效的预测.     

Multi-step structure of side-polished fiber sensor to enhance SPR effect

A multi-step side-polished multi-mode fiber sensor structure based on the surface plasmon resonance (SPR) and transverse magnetic (TM)-field-mode coupling phenomena is proposed. The multi-step structure with single-step, two-step, and three-step SPR fiber sensors are demonstrated via the difference in the SPR response for DI water. The time dependence of the measured intensity of transmitted light with the multi-step structure is observed as the variation increased. The structure with the advantages of no bulky components and no complicated signal processing gives an obvious SPR response and provides a two-fold increase for the sensitivity of intensity measurement.     

短时交通流复杂动力学特性分析及预测

为揭示短时交通流的内在动态特性,利用非线性方法对交通流混沌特性进行识别,为短时交通流的预测提供基础.基于混沌理论对交通流时间序列进行相空间重构,利用C-C算法计算时间延迟和嵌入维数,采用Grassberger-Procaccia算法计算吸引子关联维数,通过改进小数据量法计算最大Lyapunov指数来判别交通流时间序列的混沌特性.针对局域自适应预测方法在交通流多步预测中预测器系数无法调节的问题,提出了交通流多步自适应预测方法.通过实测数据计算,结果表明:2,4和5 min三种统计尺度的交通流时间序列均具有混沌特性;改进的小数据量法能够准确地计算出最大Lyapunov指数;构建的交通流多步自适应预测模型能够有效地预测交通流量的变化.为智能交通系统诱导和控制提供了依据.     

Evaluation of eigenvalues of a smooth potential via Schroedinger transmission across multi-step potential

In a one-dimensional quantal solution of Schroedinger equation, the general expressions for reflection and transmission coefficients are derived for a potential constituting n number of rectangular wells and barriers. These expressions are readily used for the estimation of eigenvalues of a smooth potential which is simulated by a multi-step potential. The applicability of this method is demonstrated with success in potentials with different forms including the most versatile Ginocchio potential where the widely used numerical method like Runge-Kutta integration algorithm fails to yield the result. Accurate evaluation of eigenvalues free from numerical problem for any form of potentials, whether analytically solvable or not, is the highlight of the present multi-step approximation method in the theory of potential scattering.      

Multi-step geoacoustic inversion with a towed line array

Geoacoustic inversion is important for acoustic field predictions and matched field localizations in shallow water.Combing the Matched-field inversion(MFI) and the Reflectionloss inversion,a multi-step Bayesian inversion for geoacoustic parameters was presented.This method applied the posterior probability density(PPD) or inversion results from one inversion as prior information for subsequent inversion.First,the sensitive parameters were determined by the MFI.Second,the insensitive parameters were determined by the Reflection-loss inversion based on the PPD and inversion results from the MFI.The PPD results indicated that the multi-step inversion method was performed better than direct matched-field inversion,and the inversion results of some parameters were improved significantly.To demonstrate the advantages of the multi-step inversion method on the sound field prediction,the statistical properties of transmission loss based on the posterior probability were introduced.The transmission loss distribution showed that the predicted acoustic fields based on the multi-step inversion method had smaller errors.     

混沌时间序列多步自适应预测方法

针对混沌时间序列局域自适应预测方法在多步预测中预测器系数无法调节的问题，根据混沌时间序列的短期可预测性及自适应算法的自适应跟踪混沌运动轨迹的特点，提出了混沌时间序列多步自适应预测方法.仿真结果表明，此方法的多步预测性能明显好于局域自适应预测方法的多步预测性能. 关键词： 多步自适应预测方法 局域自适应预测方法 混沌时间序列     

基于多核最小二乘支持向量机的永磁同步电机混沌建模及其实时在线预测

提出了多核最小二乘支持向量机的永磁同步电机混沌系统建模方法. 通过不同核函数的线性加权组合构造新的等价核,降低建模精度对核函数及其参数选择的依赖性. 理论上给出多核最小二乘支持向量机回归参数和模型输出值的求解方法. 采用关联积分计算方法对永磁同步电机混沌系统进行相空间重构,以窗式移动的在线学习方式对重构后的永磁同步电机混沌序列进行一步和多步实时在线预测,并讨论了不同测量噪声对该方法的影响. 仿真结果表明,该方法能有效提高永磁同步电机混沌系统的建模精度,具有良好的抗噪能力.     

基于多核最小二乘支持向量机的永磁同步电机混沌建模及其实时在线预测

提出了多核最小二乘支持向量机的永磁同步电机混沌系统建模方法. 通过不同核函数的线性加权组合构造新的等价核,降低建模精度对核函数及其参数选择的依赖性. 理论上给出多核最小二乘支持向量机回归参数和模型输出值的求解方法. 采用关联积分计算方法对永磁同步电机混沌系统进行相空间重构,以窗式移动的在线学习方式对重构后的永磁同步电机混沌序列进行一步和多步实时在线预测,并讨论了不同测量噪声对该方法的影响. 仿真结果表明,该方法能有效提高永磁同步电机混沌系统的建模精度,具有良好的抗噪能力. 关键词： 永磁同步电机 多核学习 最小二乘支持向量机 混沌预测     

Improvement in crystalline quality and surface smoothness of ZnO film by multi-step deposition process

The effect of multi-step deposition process on the crystalline quality and surface smoothness of ZnO film was investigated. ZnO films were composed of multi-layers, in which each layer was deposited at different temperatures. The maximum intensity and the smallest FWHM of (0 0 2) diffraction peak in XRD spectrum were observed for the multi-layered ZnO film of which each layer was deposited at progressively higher temperatures. In addition, the smoothest film surface was also observed for the ZnO film deposited through multi-step process in which deposition temperatures gradually increase. On the other hand, the large difference between the deposition temperatures in multi-step process did not result in the significant improvement of the crystalline quality of ZnO film. The ZnO film prepared by using multi-step process had high transmittance over 70% in visible region and the optical band gap of 3.22 eV.     

状态方程实验用铜多台阶靶制备工艺

 采用单点金刚石切削技术,通过合理的刀具设计、夹具设计及工艺过程设计,确定了加工工艺参数,完成了厚度几μm至几十μm的无氧铜多台阶靶的制备。通过触针式轮廓仪,台阶仪,白光干涉仪对表面轮廓及粗糙度进行了测量。结果表明：通过单点金刚石切削技术加工成形的铜多台阶靶,各台阶表面均方根粗糙度小于50 nm,工件表面轮廓平直,台阶垂直度较好。采用阿基米德原理对材料密度进行测量,加工成形后密度为(8.945±0.074) g/cm3,接近材料理论密度。     

Mechanism of H2 desorption from monohydride Si(100)2 × 1H

Most recent experimental work on H₂ desorption from the monohydride Si(100) surface seems to point to a pairwise desorption mechanism involving the concerted desorption of two hydrogen atoms on different Si atoms of a single dimer. Using ab initio SCF and CI theory and a cluster model of the surface, the present work finds that the lowest energy pathway is symmetric rather than asymmetric. The desorption energy barrier is calculated to be 3.7 eV. Compared with an experimental value of 2.6 eV, the large barrier suggests that this direct desorption mechanism is not applicable. A multi-step desorption mechanism which involves a delocalized process in the formation of dihydride SiH₂ and a localized desorption of H₂ is proposed and is shown to explain the experimental observations.