Lambda-nucleon interaction potentials

Two-body S-wave, spin dependent, central Λ-N interaction potentials of the form first given by Ram and Downs are constructed to fit the zero energy scattering lengths a_s = −2.25 fm, a_t = −2.08 fm of Herndon and Tang. When assumed to be effective in even-parity states with full strength and in odd-parity states with zero strength, these potentials fit the Λ-p scattering cross section data very well. The binding energy D of the Λ-particle in nuclear matter using these potentials is calculated by the method of independent pair approximation. The potentials that best fit the scattering data give values for D which are only 3–4 MeV lower than that obtained previously with a potential of Hemdon and Tang. It is concluded that the three-body ΛNN forces may be quite important in the calculations of D.     

Surface properties of semi-infinite Fermi systems

A functional relation between the kinetic-energy density and the total density is used to analyze the surface properties of semi-infinite Fermi systems. We find an explicit expression for the surface thickness in which the role of the infinite matter compressibility, binding energy and non-locality effects is clearly shown. The method, which holds both for nuclear and electronic systems (liquid metals), yields a very simple relation between the surface thickness and the surface energy.     

The Brueckner-Hartree-Fock Equation of State for Nuclear Matter and Neutron Skin

The equation of state for nuclear matter is presented within the Brueckner-Hartree-Fock(BHF) scheme,by using the realistic Argonne V18 or Bonn B two-nucleon potentials plus their corresponding microscopic three-nucleon forces.It is then applied to calculate the properties of finite nuclei within a simple liquid-drop model,and we compare the calculated volume,surface,and Coulomb parameters with the empirical ones from the liquid drop model.Nuclear density distributions and charge radii in good agreement with the experimental data are obtained,and we predict the neutron skin thickness of various nuclei.     

Nuclear matter equation of state and three-body forces

The energy per particle, symmetry energy, pressure, and free energy are calculated for symmetric nuclear matter using BHF approach with modern nucleon-nucleon CD-Bonn, Nijm1, Argonne v₁₈, and Reid 93 potentials. To obtain saturation in nuclear matter we add three-body interaction terms which are equivalent to a density-dependent two-nucleon interaction a la Skyrme force. Good agreement is obtained in comparison with previous theoretical estimates and experimental data.     

核物质的对称能与中子皮厚度(英文)

在现有的平均场模型中引入同位旋相关的高阶修正项．研究了核物质对称能的密度依赖性和。^208Pb的中子皮厚度。采用新提出的PK1相互作用以及NL3．S271和Z271相互作用．得到核物质饱和点对称能的范围为29-38MeV以及相应的^208Pb中子皮厚度为0．17—0.28fm．在所有相互作用中，核物质饱和点的对称能与^208Pb的中子皮厚度近似呈线性关系。After adding isospin dependent high order correction terms to existing relativistic mean field models (RMF), the density dependence of symmetry energy and the neutron skin thickness S for 208Pb are studied. Using the new effective interaction PK1, together with NL3, S271 and Z271, a range of 29—38 MeV for the symmetry energy for nuclear matter at saturation point and the corresponding neutron skin thickness S = 0.14—0.28 fm for 208Pb are obtained. For all effective interactions, a linear relation between the symmetry energy at saturation point and the neutron skin thickness for 208Pb is observed.     

One-boson-exchange potential and the ground state of 16O

Two one-boson-exchange potentials (OBEP), which fit two-nucleon data and give reasonable results in nuclear matter, are tested in ¹⁶O. Ground state properties are calculated in the framework of the Brueckner-Hartree-Fock approach. The density dependence of the reaction matrix elements stemming from the Pauli operator and starting energy are carefully taken into account.     

η in the nuclear medium within a chiral unitary approach

The s-wave η self-energy in the nuclear medium is calculated in a chiral unitary approach. A coupled channel Bethe–Salpeter equation is solved to obtain the effective ηN interaction in the medium. The base model reproduces well the free space πN elastic and inelastic scattering at the ηN threshold or N^*(1535) region. The Pauli blocking on the nucleons, binding potentials for the baryons and self-energies of the mesons are incorporated, including the η self-energy in a self-consistent way. Our calculation predicts about −54−i29 MeV for the optical potential at normal nuclear matter for an η at threshold but also shows a strong energy dependence of the potential.     

The tensor force in nuclear saturation

One-term separable potentials in the ³S-³D channel are constructed which fit the following low-energy nucleon-nucleon data: the triplet effective range and scattering length, deuteron binding energy and quadrupole moment. They also yield ³D₁ phase shifts which have the correct sign. These potentials differ, however, in the amount of deuteron D-state probability, P_D, which they predict, where P_D ranges from 1 % to 9 %. Binding energy calculations of infinite nuclear matter and ⁴He are performed in order to test the effect of the tensor force on nuclear saturation properties. It is found that the larger the D-state probability, the smaller the energy per particle and saturation density. Detailed comparisons with local potentials in nuclear matter are also presented.

In nuclear matter no single-particle potential in intermediate states is used; in ⁴He, , where f is varied such that the absolute value of the diagram with a single potential insertion in a particle line is minimized. It is found in ⁴He that f= 0.75 and that this result is almost independent of both the potential employed and of ω. Furthermore, for 0 f 1.5, the total energy is independent of f.     

Surface diffusion of dysprosium on the W(1 1 1) facet

Diffusion of dysprosium on the (1 1 1) facet of a tungsten micromonocrystal was investigated by means of spectral analysis of field emission current fluctuations. The experimental spectral density functions of the current fluctuations were analysed by using Gesley and Swanson’s theoretical spectral density function, which enables to determine the surface diffusion coefficient D for dysprosium. Derived from the temperature dependence of D, the diffusion activation energy E is presented for some Dy coverages θ_(1 1 1). In the temperature range 400–600 K, the E first drops from 1.25 eV per atom at θ₍₁₁₁₎≈0.25 ML to 0.48 eV per atom at θ₍₁₁₁₎≈1 ML (corresponding to the minimum of the work function of the system), then increases to 1.03 eV per atom at θ₍₁₁₁₎≈1.3 ML. The results are discussed from the aspects of the substrate structure and interaction in the adsorbed layer.     

Morphometry in temporal lobe epilepsy

We demonstrate a method for quantitating changes in volume and morphology of the temporal lobe in epilepsy. The temporal lobes of 10 neurologically normal subjects and six subjects with well defined left-sided mesial temporal epilepsy were studied. From high resolution T₁-weighted magnetic resonance images, the grey and white matter were manually segmented over a predetermined extent. The volumes of the grey and white matter were determined. Using the segmented images, the grey matter/CSF surface and the white matter/grey matter surface were reconstructed, allowing estimates of the surface area and calculation of indices of curvature for the two surfaces. The index of curvature was calculated for each vertex of a polygonal mesh that was fitted to the surfaces. An index of grey matter thickness (grey matter volume/white matter surface area) was also calculated. There was a significant bilateral decrease in the total volume (p < .01), grey matter volume (p < .001) and grey matter thickness index (p < .05) in epileptic subjects. In addition, there was a bilateral decrease in white matter surface area (p < .05) and a small left-sided decrease in white matter volume (p < .05) in epileptic subjects. The average distributions of indices of curvature for both surfaces differed significantly (p < .05) between normal and epileptic subjects. In the grey matter/CSF surface of normal subjects, a large peak corresponding to surface concavity was present. The amplitude of this peak was significantly lower in epileptic subjects (p < .05 for the right hemisphere; p < .001 for the left hemisphere).     

Monte Carlo calculation of thermal desorption spectra: Application to CO/Ru(001)

The thermal desorption spectrum and phase diagram for the triangular lattice gas model with strong repulsive 1NN and weak attractive 2NN interaction are calculated using Monte Carlo method and the transition state rate theory. Starting from an extreme case of the hard hexagon model, the magnitudes of the interactions are varied to reach a good coincidence with the experimental desorption spectrum of CO/Ru(001). The calculated spectrum describes well the characteristic zero-order (-like) behavior and asymmetric sharp peak observed in experiment, which are known to arise from the critical point in the model. Also, calculation of the phase diagram confirms that the tricritical temperature appears in the same magnitude with the 2NN interaction, kT_t ≈ ¦ε₂¦. The determined 1NN and 2NN interaction energies, ε₁ ≈ 8 to 10 kJ/mol, ε₂ ≈ −1.6 to −1.2 kJ/mol, are about t than those estimated previously by the isosteric Arrhenius analysis of the experimental desorption spectrum.     

The contribution of 2N photon absorption in C(γ,2N) reactions for Eγ = 150–400 MeV

The ¹²C(γ,pn) and ¹²C(γ,pp) reactions have been studied using tagged photons of energy E_γ = 150–400 MeV. Recoil momentum distributions are compared to the results of Monte Carlo calculations based on a two-nucleon photon absorption model and two different phase space models. The ¹²C(γ,pn) data at low missing energy are consistent with absorption on 1p² and 1s1p nucleon pairs.     

A remark on the saturation of nuclear forces in nuclear matter

The paper deals with the problem of saturation in nuclear matter, when the two-nucleon interaction is described by the soft core potentials acting in a limited number of orbital states. The potentials used belong to the class of the realistic potentials.     

Etch pits and tunnel barrier in chemically etched YBa2Cu3O7−δ crystals by scanning tunneling microscopy

By imaging in air the (001) surfaces of YBa₂Cu₃O_7−δ single crystals etched in dilute CH₃OH : Br₂ solution with scanning tunneling microscopy we have observed etch pits and followed their modification with time. The current-voltage characteristics of the junction are measured and described in terms of electron tunneling through a trapezoidal potential barrier of average thickness (≈ 25 Å). Such a barrier results from the passivated layer formed on the superconductor surface exposed to room air after the etching. The superconductor surface is metallic. The normalized conductance G(V) measured at room temperature is that of a metal-insulator-metal junction except at small bias. Sharp peaks assigned to local density-of-states features within 1 eV from the Fermi level are observed.     

Study of the magnetic properties of single-crystal Ba0.6K0.4BiO3

The magnetic properties of single-crystal Ba_0.6K_0.4BiO₃ were studied. The results show that this isotropic superconductor (cubic structure with T_c ≈ 32 K) exhibits irreversibility and relaxation properties similar to those observed in the layered, high temperature superconductors. For fields above 0.1 T, an irreversibility line B_irr = B_irr (0) (1 − t)ⁿ with n = 3/2 and B_irr (0) = 20 T is observed. The comparison among several superconducting systems with different anisotropies suggests that the irreversibility line is unlikely to be the melting line for the YBa₂Cu₃O_7−δ.     

Scaling probability, key to the equilibrium statistical volume distribution in foams

The equilibrium statistical volume distribution in foams, which has been previously demonstrated to be the so-called log-normal, is accounted on probability grounds by a scaling law on the bubble's volume time-evolution. This law states that the conditional probability for a given bubble to have the volume v(t + Δt), he assumption that it was v(t), to depend solely on the relationship v(t + Δt)/v(t), and in particular, to be independent of the time t. The theoretical results, however, allow to go further. Indeed, since the time dependece of its parameters (expectation and variance) are given functions of time, only two parameters are necessary to describe completely the foam.     

Dynamical energy equipartition of the Toda model with additional on-site potentials

We study the dynamical energy equipartition properties in the integrable Toda model with additional uniform or disordered on-site energies by extensive numerical simulations. The total energy is initially equidistributed among some of the lowest frequency linear modes. For the Toda model with uniform on-site potentials, the energy spectrum keeps its profile nearly unchanged in a relatively short time scale. On a much longer time scale, the energies of tail modes increase slowly with time. Energy equipartition is far away from being attached in our studied time scale. For the Toda model with disordered on-site potentials, the energy transfers continuously to the high frequency modes and eventually towards energy equipartition. We further perform a systematic study of the equipartition time teq depending on the energy density εand the nonlinear parameter α in the thermodynamic limit for the Toda model with disordered on-site potentials. We find teq∝(1/ε)~a(1/α)~b, where b ≈ 2 a. The values of a and b are increased when increasing the strengths of disordered on-site potentials or decreasing the number of initially excited modes.     

Intergranular properties of YBCO and BSCCO ceramic superconductors at low fields

Isothermal low-field AC susceptibility measurements have been used to analyze the intergranular critical current density J_c(T) on sintered, non-oriented YBa₂Cu₃O_7−δ and Bi₂Sr₂CaCu₂O_8+δ ceramic samples at zero field. Below the critical temperature, potential variations, J_c(T) ≈ (1−t_j)^m with t_j = T/T_j, have been found, T_j being the onset of grain's coherence, but with different exponents, supporting that different mechanisms limit the intergranular J_c values. Moreover, the effect of texture has been also considered on Bi₂Sr₂CaCu₂O_8+δ ceramics grown by the laser floating zone method, which have stronger intergranular junctions. Their high-temperature behaviour is limited by intrinsic effects, while at low temperatures the quality of the junctions is the limiting factor. The temperature dependence of the χ′(h₀) extrapolation at zero filed has also been correlated with the evolution of the intergranular penetration depth, λ_J(T).     

Glueballs as bound states of massive gluons

Recent work in both lattice and continuum QCD shows that the gauge field is massive. We investigate the bound states of massive gluons with a Schrödinger equation and find M(0⁺⁺) ≈ 2.3 m, M(0⁻⁺) ≈ 2.7 m, M(2⁺⁺) ≈ 3.2 m, where m is the gluon mass; we expect from this as well as earlier work that m ≈ 500 MeV. These glueballs have widths typical of allowed hadronic decays.