Geometry of Σ9 and Σ11 asymmetrical grain boundaries

It is shown how the decomposition scheme into structural units can be developed for rational asymmetrical tilt grain boundaries without computer simulations. The method is illustrated on the 9 and 11 grain boundaries in the f.c.c. lattice for which experimental observations of the boundary structures are available. Besides short-period boundaries, which may serve as elementary structural units, the irrational aperiodic asymmetrical boundaries are also considered. There are clear experimental indications that some of them, namely those composed of dense-packed atomic planes, and called special asymmetrical boundaries, behave differently from the other more general boundaries.     

On the structure of Σ-hypernuclei

We investigate the-nucleus potential in the framework of a relativistic mean field approximation. As input for the elementaryN interaction we supplement the-repulsion by the exchange of an effective, complex-meson to account for theN N conversion. As the main result we find that the strength of ths absorptive central potential is smaller than the corresponding real part, whereas in the spin-orbit interaction, which is expected to be much weaker than for a nucleon, the imaginary component dominates.This work was partially supported by CNPq, FINEP (Brazil) and by the Bilateral Cooperation W. Germany — Brazil (KFA — CNPq).     

Analysis of the strong coupling form factors of Σ_bNB and Σ_cND in QCD sum rules

In this article, we study the strong interaction of the vertices Σ_bNB and Σ_cND using the three-point QCD sum rules under two different Dirac structures. Considering the contributions of the vacuum condensates up to dimension 5 in the operation product expansion, the form factors of these vertices are calculated. Then, we fit the form factors into analytical functions and extrapolate them into time-like regions, which gives the coupling constants. Our analysis indicates that the coupling constants for these two vertices are G_(Σ_bNB)= 0.43±0.01 GeV~(-1) and G_(Σ_cND)=3.76±0.05 GeV~(-1).     

Light Σ hypernuclei and Σ− atoms

The structures of ⁴ He and ⁷ Li are investigated within the frame of the [³H + ⁺] + + [³He + ^o] model and the microscopic cluster model +2N+, respectively. The different binding mechanism between ⁴ He and ⁷ Li is emphasized together with a brief discussion on the ⁴ Be hypernucleus. It is clarified that the ⁴ He hypernucleus is bound due to the cooperative contribution from the and terms of -N interaction, while the ⁷ Li hypernucleus is bound mainly due to the term of -N interaction. The combined analysis of ^– atoms and ⁴ He hypernucleus is shown to be useful to reveal the characteristic differences among the model D, model F and soft core versions of the Nijmegen OBE potentials.The authors would like to express their sincere thanks to J. ofka, O. Richter, M. Sotona, L. Majling, A. Cieply and other colleagues in Nuclear Physics Institute (e/Prague), and H. Band, Y. Yamamoto and T. Motoba, for collaboration and useful discussions. We dedicate this article to the memory of the excellent activities of the late Prof. Jan ofka.     

The production of narrow Σ-hypernuclear states

It has been suggested that some of the observed narrow Σ hypernuclear states may be “bound states in the continuum” of the Σ interacting with the host nucleus formed when that interaction is strongly absorptive. It is shown that the S matrix for such a process vanishes at the complex energy of such a bound state. Some general properties of the S matrix in the presence of absorption are derived.     

Σ- atoms and the ΣN interaction

It is shown that among four models of the Nijmegen baryon-baryon interaction only model F --which leads to a repulsive potential felt by the Σ hyperon inside the nucleus-- is consistent both with the analysis of Σ^- atoms and of the (K ^-,π) reactions. The Nijmegen models are used to determine the strong complex single-particle (s.p.) potential of Σ^-, and to calculate the strong-interaction shifts and widths of the lowest observed levels of Σ^- atoms. The results obtained with model F are in best agreement with the experimental data. Received: 15 January 2002 / Accepted: 14 March 2002     

Study of Σ~*-Δ Interactions

We study the Σ~*-Δ interaction in the chiral SU(3) quark model and in the extended chiral SU(3) quark model.In these two models,the short-range interaction mechanism are totally different,one is from the one-gluon exchange and another is from the vector meson exchange.The possible reasons of forming strangeness-1 bound states are given.Comparisons between the cases with and without quark exchange effect are made.The results show the quark exchange effect does give attractions to (Σ~*Δ)_(ST)=0 5/2 and (Σ~*Δ)_(ST)=3 1/2 systems,which means the special symmetry is important.Also,we make some analysis on chiral field effect,our results show that the σ exchange dominantly provides the attractive interaction for these two states.     

ΛN and ΣN Interactions from Lattice QCD

We present our recent study on ΛN and ΣN (isospin I = 3/2) interactions by measuring Nambu–Bethe–Salpeter wave functions on the Lattice QCD. The lattice QCD calculation is performed by using the N _f  = 2 + 1 gauge configurations generated by PACS-CS collaboration together with employing an improved method to obtain potentials in lattice QCD simulations. For the ¹ S ₀ channel, the central ΣN (I = 3/2) potential and the central ΛN (¹ S ₀) potential are found to be very similar. For the spin triplet (³ S ₁?³ D ₁) channels, the central ΛN(³ S ₁?³ D ₁) potential is attractive while the central ΣN(I = 3/2, ³ S ₁?³ D ₁) potentials is repulsive. Tensor potentials, on the other hand, are rather weak in both ΛN and ΣN(I = 3/2) systems.     

Leading/nonleading charm-production asymmetry in Σ− p interactions

The asymmetry between the spectra of leading and nonleading charmed mesons that was measured in Σ^? A interactions at p _L=340 GeV/c in the WA89 experiment is described within the Model of Quark-Gluon Strings (QGS model also known as QGSM) under the assumption that there is a fraction of charmed sea quark-antiquark pairs (intrinsic charm) in an interacting hyperon. It is shown that the asymmetries between D ^?-and D ⁺-meson spectra and between D _s ^? -and D _s ⁺ -meson spectra can be approximated by QGSM curves obtained with the same string-fragmentation parameter, a ₁=10, and the same intrinsic-charm fraction, $\delta _{c,\bar c} = 0.01$ , as those that were used in describing D _s ^? /D _s ⁺ -meson asymmetry of π^? A experiments in previous studies. The asymmetry between the spectra of Λ_c and $\bar \Lambda _c $ that was measured in Σ^? A collisions at p _L=600 GeV/c in the E781 experiment is also described within this scheme. The QGSM results are compared with the results of the calculations in the next-to-leading approximation of perturbative QCD that were performed by other authors.     

Supersymmetry and geometry in D < 4 nonlinear Σ-models

We discuss the augmentation of D < 4 supersymmetric σ-models by the addition of higher derivative terms, such as the Skyrme and Wess-Zumino actions. These terms must satisfy differential constraints so that they preserve the symmetries of the usual kinetic action. In two dimensions, we explicitly construct the gauged WZ action for group manifolds. Some difficulties with the analogous four dimensional theories are noted.     

Deviation from Reference Planes and Reference Misorientation for Σ3 Boundaries

The purpose of the present work is to study the crystallography of a particular family of interfaces, 3 boundaries in copper, in the context of the relationships between 3 plane indices, their deviation from reference planes, and the deviation from exact 3 matching, v/v_m. The relatively high values of v/v_m recorded were considered to be the result of texture development during annealing and various back twinning and 3ⁿ impingement interactions. The results show that there is a reasonable correlation between the deviation from a reference misorientation (v/v_m) and the deviation from reference interface plane (R). Measurement of v/v_m alone provides an indirect estimate of the plane type and hence energy of the boundary, at least for 3 boundaries, and moreover is more germane to the experimental mode of data collection. The effect of intragrain orientation variations on the interface parameters was also studied, and it was shown that there is a 20% difference between misorientations calculated near the interface compared with displaced from the interface.     

Binding energy and rates of Σ-hyperon decays of double hypernuclei

The binding energies of double hypernuclei are calculated as a function of mass number. Estimates are made for the width of the -hyperon decay channel of double hypernuclei. Significant suppression of this channel due to -to- conversion is found in heavy hypernuclei.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 70–73, April, 1989.     

C_2^+ (X^4 Σ_g^-,1^4 Σ_u^+)离子体系解析势能函数、光谱常数和振动能级研究

采用多参考组态相互作用(MRCI)方法,结合aug-cc-pV6Z(AV6Z)基组,计算了C₂⁺(X⁴Σ_g^-,1⁴Σ_u⁺)的势能曲线,计算过程中考虑了Davidson修正和相对论效应,并将结果外推至完备基组(CBS)的极限.基于得到的单点能量,用最小二乘法方法进行了Murrell-Sorbie函数拟合,得到了势能函数解析式(APEF).基于APEF,计算了C₂⁺(X⁴Σ_g^-,1⁴Σ_u⁺)离子体系的离解能D_e,平衡核间距R_e,光谱常数ω_e,ω_eχ_e,B_e,α_e,结果与实验和其他理论计算值符合...     

Study of Σ* Resonances from K − N → πΛ Reactions

In order to know more about some Σ resonances and distinguish various models of hadron structures, an analysis is performed for the reactions K ^? n → π ^? Λ and K ^? p → π ⁰ Λ, using an effective Lagrangian approach. The differential cross sections and Λ polarizations from two experiments are analyzed with the c.m. energy between 1,550 and 1,676 MeV. Our study strongly support the existence of a ${J^P = {1\over 2}^+ \Sigma}$ resonance with mass near 1,633 MeV and width about 120 MeV, which is compatible with the three-star ${\Sigma(1660){1\over 2}^+}$ in PDG. Meanwhile, no evidence is found for the two-star ${\Sigma(1620){1\over 2}^-}$ listed in PDG.     

A model for temperature-dependent collisional quenching of NO A2 Σ+

A model for the temperature-dependent electronic quenching of NO A ^{2 +} is presented. The model is appropriate for collision partners having stable negative ions, which are predicted to have large quenching cross-sections. Colliders with relatively large negative electron affinities are predicted to have cross-sections that are near-zero at room temperature and can increase dramatically at very high temperatures. A negligibly small electronic quenching cross-section is predicted for collision partners having negative ions that are unstable on a collisional timescale. Results of the model are compared to experimentally measured cross-sections for a number of species of interest in combustion and aerothermodynamic applications.     

Infrared emission spectroscopy of a new Σ-Σ system of TiCl

The spectra of TiCl have been reinvestigated in the 4200-8500 cm⁻¹ region using the 1-m Fourier transform spectrometer associated with the National Solar Observatory at Kitt Peak. The molecules were excited in a microwave discharge lamp operated with 3.0 Torr of He and a trace of TiCl₄ vapor, and the spectra were recorded at a resolution of 0.01 cm⁻¹. Three new bands with origins near 6938.9, 6900.2, and 6861.7 cm⁻¹ have been assigned as the 0-0, 1-1, and 2-2 bands of a new - transition. This assignment is supported by our recent ab initio calculations on TiCl and ZrCl [J. Chem. Phys. 114 (2001) 3977]. A rotational analysis of these bands has been carried out and spectroscopic constants have been extracted for the states.     

Structure and stability of Σ3 grain boundaries in face centered cubic metals

Σ3 grain boundaries form as a result of either growth twinning or deformation twinning in face centered cubic (fcc) metals and play a crucial role in determining the mechanical and electrical properties and microstructural stability. We studied the structure and stability of Σ3 grain boundaries (GBs) in fcc metals by using topological analysis and atomistic simulations. Atomistic simulations were performed for Cu and Al with empirical interatomic potentials to reveal the influence of stacking fault energy on the morphology of the twinned grains. Three sets of tilt Σ3 GBs were studied with respect to the tilt axis parallel to ?111?, ?112?, and ?110?, respectively. We showed that Σ3{111} and Σ3{112} GBs are thermodynamically stable and the others will dissociate into terraced interfaces regardless of the stacking fault energy. The morphology of the nano-twinned grains in Cu is predicted from the above analysis and found to match with experiments.     

The sub-millimeter and Fourier transform microwave spectrum of HZnCl (X Σ)

The pure rotational spectrum of HZnCl (X ¹Σ⁺) has been recorded using sub-millimeter direct-absorption methods in the range of 439-540 GHz and Fourier transform microwave (FTMW) techniques from 9 to 39 GHz. This species was produced by the reaction of zinc vapor and chlorine gas with H₂ or D₂ in a d.c. glow discharge for the sub-millimeter studies. In the FTMW measurements, HZnCl was created in a discharge nozzle from Cl₂ and (CH₃)₂Zn. Between 5 and 10 rotational transitions were measured in the sub-millimeter regime for four zinc and two chlorine isotopologues; four transitions were recorded with the FTMW machine for the main isotopologue, each consisting of several chlorine hyperfine components. The data are consistent with a linear molecule and a ¹Σ⁺ ground electronic state. Rotational and chlorine quadrupole constants were established from the spectra, as well as an r_m⁽²⁾ structure. The Zn-Cl and Zn-H bond lengths were determined to be 2.0829 and 1.5050 Å, respectively; in contrast, the Zn-Cl bond distance in ZnCl is 2.1300 Å, longer by ∼0.050 Å. The zinc-chlorine bond distance therefore shortens with the addition of the H atom. The ³⁵Cl electric quadrupole coupling constant of eQq = −27.429 MHz found for HZnCl suggests that this molecule is primarily an ionic species with some covalent character for the Zn-Cl bond.