Partial structures and compressibilities of ions in fused potassium bromide

Treating the coulomb interaction between ion species as a perturbation on the Waisman-Lebowitz solution for direct correlation function within the hard core region, the total direct correlation function in K-space has been formulated, which gives a direct method of evaluating the partial structure factors between different ion species of the fused salts through the use of Pearson-Rushbrooke equations. The partial structure factors so obtained have been applied to evaluate the partial radial distribution functions of ion pairs. In addition, many other important associated functions such as the static correlations of total number, mass and charge densities have been computed by particular linear combination of partial structure factors. The charge neutrality relate the partial structure factors to the isothermal compressibility for the wavevectorK → 0 and hence the evaluation of the compressibilities of ions in fused KBr is possible, which agrees well with the observed value. As such the present method is very useful in investigating the structure of molten salts since only the parametersσ _ij , the distances of closest approach between ions andɛ, the effective dielectric constant (which can be estimated from the literature) are enough for this work.     

Electromagnetic form factors of bound nucleons revisited

We investigate the possible modifications of the nucleons' electromagnetic form factors in the framework of a modified Skyrme model allowing for nucleon deformation and using realistic nuclear mass distributions. We show that such effects are small in light nuclei Received: 19 November 2002 / Accepted: 3 December 2002 / Published online: 18 March 2003 RID="a" ID="a"Address after January 1st, 2003: Helmholtz Institut für Strahlen- und Kernphysik (Theorie), Universit?t Bonn, Nu?allee 14-16, D-53115 Bonn, Germany; e-mail: meissner@itkp.uni-bonn.de RID="b" ID="b"Present address: Helmholtz Institut für Strahlen- und Kernphysik (Theorie), Universit?t Bonn, D-53115 Bonn, Germany. Communicated by V. Vento     

Nucleon form factors from a covariant quark core: Limits in their description

In treating the relativistic 3-quark problem, a dressed-quark propagator parameterization is used which is compatible with recent lattice data and pion observables. Furthermore 2-quark correlations are modeled as a series of quark loops in the scalar and axialvector channel. The resulting reduced Faddeev equations are solved for nucleon and delta. Nucleon electromagnetic form factors are calculated in a fully covariant and gauge-invariant scheme. Whereas the proton electric form factor G _E and the nucleon magnetic moments are described correctly, the neutron electric form factor and the ratio G _E/G _M for the proton appear to be quenched. The influence of vector mesons on the form factors is investigated which amounts to a 25% modification of the electromagnetic proton radii within this framework. Received: 16 April 2002 / Accepted: 29 August 2002 / Published online: 17 January 2003 RID="a" ID="a"Supported by a Feodor-Lynen fellowship of the Alexander-von-Humboldt foundation and the Australian Research Council. RID="b" ID="b"Address after April 30: MPI für Metallforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany. RID="c" ID="c"e-mail: Reinhard.Alkofer@uni-tuebingen.de Communicated by A. Sch?fer     

The D state of I2: a case study of statistical error propagation in the computation of RKR potential curves, spectroscopic constants, and Franck-Condon factors

Existing spectroscopic data for the ion-pair state of I₂ are reanalyzed with the primary goal of improving and extending to higher υ the rotational constants B_υ. To this end, data for several precisely known (υ,J) levels in the υ=203-207 region are analyzed together with vibrational and rotational data from a number of sources. The lack of rotational data for the υ=130-200 region makes the structure of this data set unusual, and has prompted a thorough study of the propagated statistical error in the directly fitted spectroscopic constants, T_υ and B_υ, and in the RKR potential curve calculated therefrom. For the first time, such error propagation computations have been extended to properties computed by numerical solution of the Schrödinger equation for the state in question: the quantum vibrational energy G_υ and rotational constant B_υ, centrifugal distortion constants D_υ and H_υ, and Franck-Condon factors for the D-X transition.     

The finite images of finitely generated groups

Given any sequence of non-abelian finite simple primitive permutationgroups S_n, we construct a finitely generated group G whose profinitecompletion is the infinite permutational wreath product ...S_n S_n–1 ... S₀. It follows that the upper compositionfactors of G are exactly the groups S_n. By suitably choosingthe sequence S_n we can arrange that G has any one of a continuousrange of slow, non-polynomial subgroup growth types. We alsoconstruct a 61-generator perfect group that has every non-abelianfinite simple group as a quotient. 2000 Mathematics SubjectClassification: 20E07, 20E08, 20E18, 20E32.     

Adsorption of Methanol From the Liquid Mobile Phase on the Column Packing Surface

The adsorption isotherms of methanol in water solutions which were used as mobile phase in RP HPLC on adsorbents modified with dimethyloctadecylchlorosilane were measured. On the basis of these isotherms the chemical composition of the stationary phase as a function of the mobile phase concentration was determined. The influence of both those phases on retention factors k′ of alkyl derivatives of benzene was discussed. It was stated that k′ of benzene and its derivatives decreases with the various rate together with the increase of the methanol concentration in both phases. Quotient of volume coefficient corresponding to a unit of adsorbed methanol (logk′/n^s _Me) decreases linearly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Charge form factor and cluster structure of the 6Li nucleus

The charge form factor of the 6Li nucleus is considered on the basis of its cluster structure. The charge density of ⁶Li is presented as a superposition of two terms. One of them is a folded density and the second one is a sum of the ⁴He and deuteron densities. Using the available experimental data for ⁴He and deuteron charge form factors, a satisfactory agreement of the calculations within the suggested scheme is obtained with the experimental data for the charge form factor of ⁶Li, including those in the region of large transferred momenta.      

Low-frequency fluctuation in multimode semiconductor laser subject to optical feedback

Dynamics of a semiconductor laser subject to moderate optical feedback operating in the low-frequency fluctuation regime is numerically investigated.Multimode Lang-Kobayashi(LK)equations show that the low-frequency intensity dropout including the total intensity and sub-modes intensity is accompanied by sudden dropout simultaneously,which is in good agreement with experimental observation.The power fluctuation is quite annoying in practical applications,therefore it becomes important to study the mechanism of power fluctuation.It is also shown that many factors,such as spontaneous emission noise and feedback parameter,may influence power fluctuation larger than previously expected.     

Flavor content of nucleon form factors in a VMD approach

The strange form factors of the nucleon are studied in a two-component model consisting of a three-quark intrinsic structure surrounded by a meson cloud. A comparison with the available experimental world data from the SAMPLE, PVA4, HAPPEX and G0 Collaborations shows a good overall agreement. It is shown that the strangeness contribution to the electric and magnetic form factors is of the order of a few percent. In particular, the strange quark contribution to the charge radius is small 〈r ² _s〉_E = 0.005 fm^2 and to the magnetic moment it is positive μ_s = 0.315 μ_N .     

Logarithmic corrections and soft photon phenomenology in the multipole model of the nucleon form factors

We analyzed the presently available experimental data on nucleon electromagnetic form factors within a multipole model based on dispersion relations. A good fit of the data is achieved by considering the coefficients of the multipole expansions as logarithmic functions of the momentum transfer squared. The superconvergence relations, applied to this coefficients, makes the model agree with unitary constraints and pQCD asymptotics for the Dirac and Pauli form factors. The soft photon emission is proposed as a mechanism responsible for the difference between the Rosenbluth, polarization and beam-target asymmetry data. It is shown that the experimentally measured cross-sections depend not only on the Dirac and Pauli form factors, but also on the average number of the photons emitted. For the proton this number is shown to be different for different types of experimental measurements and then estimated phenomenologically. For the neutron the same mechanism predicts that the data form different types of experiments must coincide with high accuracy. A joint fit of all the experimental data reproduce the Q²-dependence with the accuracy χ²/dof = 0.86 . Predictions of the model, that 1) the ratios of the proton form factors G _E/G _M are different for Rosenbluth, polarization and beam-target asymmetry experiments and 2) similar ratios are nearly the same for neutron, can be used for experimental verification of the model.