Electron scattering from a tensor polarized2H internal target

An experiment (NIKHEF 91-12) is described which measures the spin dependence of the (e,e) and (e,ep) reactions for polarized deuterium and unpolarized electrons, using the Internal Target Hall facility at the Amsterdam Pulse Stretcher Ring at NIKHEF. Tensor polarized deuterium is produced in an atomic beam source and injected into a storage cell target. Polarimeters are used to monitor the target polarization. A large acceptance non-magnetic detector system is used for the electron-proton (deuteron) coincidence measurement. It is demonstrated that these techniques result in low backgrounds due to scattering from species other than the polarized target gas and allow for fast and flexible orientation of the target spin. Specific issues such as interfacing the experiment to the storage ring and monitoring the performance of the target system are discussed in detail.Lectures given at the Indian-Summer school on Electron Scattering of Nucleons and Nuclei, Prague (Czech Republic), September 1994.The author thanks the entire 91-12 collaboration and acknowledges interesting discussions with Henk Jan Bulten. The research is supported by the National Science Foundation under Contract No. PHY-9316221 and under a NATO Grant No. CRG920219.     

Novel internal target for electron scattering off unstable nuclei

A novel internal target has been developed, which will make electron scattering off short-lived radioactive nuclei possible in an electron storage ring. An "ion trapping" phenomenon in the electron storage ring was successfully utilized for the first time to form the target for electron scattering. Approximately 7 x 10(6) stable 133Cs ions were trapped along the electron beam axis for 85 ms at an electron beam current of 80 mA. The collision luminosity between the stored electrons and trapped Cs ions was determined to be 2.4(8) x 10(25) cm(-2) s(-1) by measuring elastically scattered electrons.     

Electron momentum density distribution in iridium by Compton scattering technique

The isotropic Compton profile of iridium, measured using 59.54 keVγ-rays, is reported in this paper. The results are compared with the theoretical Compton profiles from APW method with and without incorporating electron correlation effects. It is seen that correlation effects improve the agreement between the experiment and theory. Comparison with the renormalized-free-atom (RFA) model calculations has also been made. Behaviour ofd-band electrons in Ir and some other 5d transition metals is discussed in terms of broadening in their Compton profiles.     

基于颜色传递的双波段目标跟踪算法研究

针对复杂背景下Camshift算法容易丢失目标的情况,提出一种基于YCBCR空间将红外与可见光融合图像与彩色参考图像进行颜色传递后,采用Camshift进行目标跟踪的算法。该算法在颜色传递时充分利用双波段图像信息,得到的目标对比度高并且颜色空间较其周围背景突出,增强了目标的颜色概率图,提高了Camshift算法效率。实验表明,通过对可见光图像、经颜色传递后的红外图像以及传统颜色传递方法得到的图像采用相同跟踪算法进行定性分析,在该算法得到的图像中,跟踪窗口中心相对于目标质心仅有3个像素的误差,跟踪精度远远优于对比实验图像的跟踪结果,并且算法的跟踪时间为每帧20.6 ms,达到了实时性的要求。     

Compton scattering on a target with degeneracy states

An additional pole term and the contributions to it from intermediate states with the same mass but with different spins is calculated for the Compton scattering amplitude on a two-particle system with zero total angular momentum. It is shown that the decomposition of invariant amplitudes on the generalized polarizabilities of the system does not take place if this term is taken into account.     

A novel FOCAL technique based on BP-ANN

In this paper, the feed-forward back-propagation artificial neural network (BP-ANN) algorithm is introduced in the traditional Focus Calibration using Alignment procedure (FOCAL) technique, and a novel FOCAL technique based on BP-ANN is proposed. The effects of the parameters, such as the number of neurons on the hidden-layer and the number of training epochs, on the measurement accuracy are analyzed in detail. It is proved that the novel FOCAL technique based on BP-ANN is more reliable and it is a better choice for measurement of the image quality parameters.     

High coercivity powders based on Sm-Fe-Ta-N prepared by a novel technique

Nitrided Sm₂Fe₁₇-based materials possess excellent intrinsic magnetic properties. In this study, we investigate two compositions, Sm_13.7Fe_86.3 and Sm_13.8Fe_82.2Ta_4.0. The stoichiometry of each phase was determined and the SmFeTa material was found to include Ta₃Fe₇, in addition to the Sm₂Fe₁₇, SmFe₂, and SmFe₃ phases observed in the SmFe alloy, but without the α-iron dendrites characteristic of the binary material. SEM and TEM studies revealed that in the cast structure, approximately 2.0% Ta is initially dissolved in the Sm₂(FeTa)₁₇ phase; however, HDDR processing causes the formation of Ta-based precipitates, leaving a 2: 17 phase with much less dissolved Ta. The HDDR process, with subsequent nitrogenation, was used to prepare coercive powders. The coercivities of these powders were found to be very dependent on the HDDR conditions and Ta addition. The highest coercivity achieved was 1280 kA/m for the composition with Ta.     

Deeply virtual Compton scattering on a virtual pion target

We study deeply virtual Compton scattering on a virtual pion that is emitted by a proton. Using a range of models for the generalized parton distributions of the pion, we evaluate the cross section, as well as the beam spin and beam charge asymmetries in the leading-twist approximation. Studying Compton scattering on the pion in suitable kinematics puts high demands on both beam energy and luminosity, and we find that the corresponding requirements will first be met after the energy upgrade at Jefferson Laboratory. As a by-product of our study, we construct a parameterization of pion generalized parton distributions that has a non-trivial interplay between the x and t dependence and is in good agreement with form factor data and lattice calculations.     

A new technique for fluid velocimetry based on near field scattering

We show that the time evolution of near-field scattering speckles, originated by a fluid suspension of particles, provides information about the velocity field in the fluid. This information can be extracted from a statistical analysis of speckle fields taken at different times, either by measuring their cross-correlation function or by recovering the power spectrum corresponding to the difference between the two speckle fields. Experimental data are in accordance to the expected behaviors. The results are independent of the scatterer's size, allowing one to exploit the technique also with sub-wavelength tracking particles.     

Liquids microprinting through a novel film-free femtosecond laser based technique

Laser-induced forward transfer (LIFT) is a high resolution microprinting technique in which small amounts of material are transferred from a previously prepared donor thin film to a receptor substrate. The application of LIFT to liquid donor films allows depositing complex and fragile materials in solution or suspension without compromising the integrity of the deposited material. However, the main drawback of LIFT is the preparation of the donor material in thin film form, being difficult to obtain reproducible thin films with thickness uniformity and good stability.In this work we present a laser microprinting technique that is able to overcome the drawbacks associated with the preparation of the liquid film, allowing the deposition of well-defined uniform microdroplets with high reproducibility and resolution. The droplet transfer mechanism relies on the highly localized absorption of strongly focused femtosecond laser pulses underneath the free surface of the liquid contained in a reservoir.An analysis of the influence of laser pulse energy on the morphology of the printed droplets is carried out, revealing a clear correlation between the printed droplet dimensions and the laser pulse energy. Such correlation is interpreted in terms of the dynamics of the liquid displaced by a laser-generated cavitation bubble close to the free surface of the liquid. Finally, the feasibility of the technique for the production of miniaturized biosensors is tested.     

On the technique of absolutization of diffuse scattering intensity measurements based on thermal diffuse scattering measurements

Features of microdefect (MD) formation in GaAs(Si) single crystals grown by horizontally oriented crystallization were studied by X-ray diffuse scattering (XRDS). Measurements were performed at room temperature (∼298 K) and near the liquid nitrogen evaporation temperature (∼85 K) using an open-flow cooling nitrogen cryostat. A practical technique for measuring XRDS using a triple-axis X-ray diffractometer was developed and applied to separate scattering on defects and thermal diffuse scattering. For a crystal with n = 2.0 × 10¹⁸ cm⁻³, the radius of detected nonspherical MDs was determined as ∼0.2 μm; thermal diffuse scattering (TDS) was experimentally separated. For a crystal with n = 3.9 × 10¹⁸ cm⁻³, nonspherical MDs ∼0.5 μm in radius were detected; TDS was found to be a negligible fraction of total XRDS. At the same time, in the case of coinciding crystal orientations and identical experimental conditions, TDS measurement data for one crystal can be used for other GaAs(Si) crystals with the same orientation.     

Electron Raman scattering of a two-dimensional pseudodot system

We have carried out the theoretical investigation of the differential cross section for the electron Raman scattering process, which is associated with intersubband transitions in a two-dimensional quantum pseudodot system. The great advantage of our methodology is that it enables confinement regimes by varying two parameters in the model potential. It is found that the differential cross section is affected by the external magnetic field, the geometrical size and the chemical potential of the pseudodot system.     

海杂波背景下的目标检测新方法

提出了一种基于分形布朗运动模型的S波段雷达海杂波分形维数提取方法.分析了基于记忆库混沌时间序列预测方法，引入一种改进核函数的支持向量机分类器.在此基础上，提出了一种新的海杂波背景下目标检测方法.应用S波段雷达实测海杂波数据，计算得到了该信号的分形维数与Lyapunov指数，验证了S波段雷达海杂波的混沌分形特性.仿真实验结果验证了该方法具有较强的检测能力和抗杂波性能. 关键词： 分形布朗运动 分形维数 记忆库预测方法 支持向量机分类器     

Double N-N scattering on polarized proton target

The triple scattering depolarization transfer parameterD _t in elastic p-p scattering was measured at an energy of 660 MeV using a polarzied proton target. All measurements have been carried out with the help of an optical spark chamber.The following results have been obtained:D _t (90)=D(90)=0·54±0·10.D _t (130)=D(130)=0·72±0·11.Devoted to Professor V. Petrílka on his sixty-fifth birthday.On leave of absence from theInstitute for Computing Technique of the Czechoslovak Academy of Sciences, Prague.On leave of absence from theNuclear Research Institute of the Czechoslovak Academy of Sciences, e.On leave of absence from theFaculty of Nuclear Science and Physical Engineering of the Technical University, Prague.In conclusion the authors express their deep gratitude to S. M. Bilenky, G. Gozzika, M. Hansroul, L. Lapidus, M. Odehnal, M. Maly, B. S. Neganov, R. M. Ryndin and P. Winternitz for helpful discussions and J. Cechová, E. Dudová and H. Sternová for help in the work.     

Electron scattering on two-neutron halo nuclei: The case of He

The formalism to describe electron scattering reactions on two-neutron halo nuclei is developed. The halo nucleus is described as a three-body system (core +n + n), and the wave function is obtained by solving the Faddeev equations in coordinate space. We discuss elastic and quasielastic scattering using the impulse approximation to describe the reaction mechanism. We apply the method to investigate the case of electron scattering on ⁶He. Spectral functions, response functions, and differential cross sections are calculated for both neutron knockout and knockout by the electron.     

Electron scattering in a point contact of one-dimensional conductors

The scattering matrix of a point contact between one-dimensional coherent conductors is considered. It is shown that the flux conservation law, time-reversal symmetry, and an hypothesis of continuity of the wave function lead to parametrization of the scattering matrix by a single real parameter, regardless of the number of conductors connected by the contact. The condition of maximum transmission fixes this parameter and thereby uniquely defines the scattering matrix. The condition of flux conservation then reduces to the condition that the sum of the derivatives of the wave function with respect to the directions of the conductors vanish. Possible applications of the model considered to experimentally feasible arrays of one-dimensional elements are discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 2070–2074 (November 1999)     

Electron scattering by a ring-shaped barrier in magnetic fields

We investigate the transport phenomena through a region containing a ring-shaped barrier in a quasi-one-dimensional quantum wire in magnetic fields. The calculated magnetoconductance curve shows a periodic dip structure, which is superimposed upon by another quasi-periodic dip structure. The current distributions for resonant states and the magnetoconductance features are well explained on the basis of the magnetic field dependence of the eigenvalue in the two-dimensional system.