大入射能量范围内重离子输运过程的动力学性质研究

基于一个改进的微观动力学输运模型——极端相对论量子分子动力学（UrQMD）, 较为系统地研究了从SIS能区到AGS和SPS能区, 再到RHIC能区, 入射能量跨5个数量级的重离子核反应及多个人们感兴趣的实验观测量, 如粒子产额、 集体流、 核阻止以及两粒子HBT关联等。研究表明, 不论单粒子观测量, 还是两粒子关联观测量, 都能自洽地由同一个输运模型加以描述。Based on one updated microscopic transport model Ultra relativistic Quantum Molecular Dynamics (UrQMD) with modifications of both potentials and two body scattering cross sections, quite a few interesting observables, such as yields, collective flows, the nuclear stopping, and the HBT two particle interferometry, are systematically investigated for heavy ion collisions within a large beam energy regime of five orders of magnitude (from SIS, AGS, SPS up to RHIC). It is shown that a consistent explanation can be received from both single particle and two particle related observables.     

A microscopic calculation of secondary Drell-Yan production in heavy ion collisions

A study of secondary Drell-Yan production in nuclear collisions is presented for SPS energies. In addition to the lepton pairs produced in the initial collisions of the projectile and target nucleons, we consider the potentially high dilepton yield from hard valence antiquarks in produced mesons and antibaryons. We calculate the secondary Drell-Yan contributions taking the collision spectrum of hadrons from the microscopic model URQMD. The contributions from meson-baryon interactions, small in hadron-nucleus interactions, are found to be substantial in nucleus-nucleus collisions at low dilepton masses. Preresonance collisions of partons may further increase the yields. Received: 9 July 1997 / Revised version: 17 December 1997 / Published online: 10 March 1998     

Novel mechanism of H0 dibaryon production in proton-proton interactions from parton-based Gribov-Regge theory

A novel mechanism of H0 and strangelet production in hadronic interactions within the Gribov-Regge approach is presented. In this approach the H0 is produced by the same mechanism as usual hadrons, namely, by disintegration of the remnant formed by the exchange of pomerons between the two protons. Rapidity and transverse momentum spectra of the observed hadrons are well described in this approach. In contrast to traditional distillation approaches, here the production of multiple (strange) quark bags does not require large baryon densities or a quark gluon plasma. We calculate the rapidity and transverse momentum distributions as well as the 4pi multiplicity of the H0 for sqrt[s]=17 GeV (Super Proton Synchrotron) and 200 GeV (Relativistic Heavy Ion Collider). In both cases the H0, if it exists, should be observable by the present experiments.     

Ultrasensitive 3He magnetometer for measurements of high magnetic fields

We describe a ³He magnetometer capable to measure high magnetic fields (B> 0.1 T) with a relative accuracy of better than 10^-12. Our approach is based on the measurement of the free induction decay of gaseous, nuclear spin polarized ³He following a resonant radio frequency pulse excitation. The measurement sensitivity can be attributed to the long coherent spin precession time T₂ ^? being of order minutes which is achieved for spherical sample cells in the regime of “motional narrowing” where the disturbing influence of field inhomogeneities is strongly suppressed. The ³He gas is spin polarized in situ using a new, non-standard variant of the metastability exchange optical pumping. We show that miniaturization helps to increase T₂ ^? further and that the measurement sensitivity is not significantly affected by temporal field fluctuations of order 10^-4.     

Learning the Learning Cycle: The Differential Effect on Elementary Preservice Teachers

This study examined the difficulties and factors that led to understanding the learning cycle teaching strategy. Participants included 83 preservice elementary teachers (PTs) enrolled in multiple sections of a science methods course taught by the same professor, one of the authors of this study. Analysis revealed that there were four categories of PTs, ranging from Enthusiastic to Fearful students, distinguished by their science content background and attitudes to science. High achieving students, successful in science courses, felt confused by the learning cycle that was so different from their previous science learning experiences and formed mindsets against learning it. Average students who expressed disinterest or even fear of science embraced it as their first successful science learning experience. Multiple exposures to the learning cycle were necessary to overcome these mindsets. Most PTs in all categories increased in their understanding of the learning cycle and perceived it as an effective method for allowing students to construct their understanding of science.     

Mass spectral fragmentation of metal dithiocarbamate complex salts

A summary of the mass spectra of metal dithiocarbamate complex salts (ML₂ and ML₃) is presented. Only divalent metal dithiocarbamate ions without an electronic configuration containing an inert s-orbital electron pair exhibited both expulsion of a ligand radical (L) and the neutral even electron species (L–H) generated from the ligand via hydrogen transfer to the metal-containing fragment ion. Divalent metal dithiocarbamate ions can be generated either by direct electron impact ionization of gas phase ML₂ molecules or ionization of ML₃ molecules followed by loss of a ligand radical. A highly stable sp² hybridized, gas phase ion of a monobidentate lead dithiocarbamate complex is proposed.     

Pulsed ion beam parameters to ensure maximum coefficients of metal surface erosion

Erosion of metal surface under pulsed ion beams is investigated using a two-phase evaporation model. The coefficients of erosion due to evaporation are calculated for aluminum, iron and copper under irradiation by submicrosecond ion beams of carbon with the initial particle energy within the range 10–1000 keV. The ion energy and ion beam current density values of the most efficient erosive impact are determined. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 31–36, May, 2007.     

Resonant tunneling of spin-wave packets via quantized states in potential wells

We have studied the tunneling of spin-wave pulses through a system of two closely situated potential barriers. The barriers represent two areas of inhomogeneity of the static magnetic field, where the existence of spin waves is forbidden. We show that for certain values of the spin-wave frequency corresponding to the quantized spin-wave states existing in the well formed between the barriers, the tunneling has a resonant character. As a result, transmission of spin-wave packets through the double-barrier structure is much more efficient than the sequent tunneling through two single barriers.     

The Reactions of Zn(CF3)Br · 2 CH3CN with Phenol,Pentafluorophenol, their Potassium and Ammonium Salts

Triphenoxymethane, tris(pentafluorophenoxy)methane, phenyl(difluoromethyl)ethers, and tetrakis(pentafluorophenoxy)ethene were prepared via carbenoid reactions of Zn(CF₃)Br · 2 CH₃CN and the corresponding phenol or the potassium or ammonium salts in the presence of the auxiliary acid BF₃ · O(CH₃)₂. The products were identified by their melting and boiling points and in part by their NMR and mass spectra as well as elemental analysis.