Quasi-Moessbauer effect in two dimensions

Expressions for the absorption spectrum of a nucleus in a three- and a two-dimensional crystal respectively are obtained analytically at zero and at finite temperature respectively. It is found that for finite temperature in two dimensions the Moessbauer effect vanishes but is replaced by what we call a Quasi-Moessbauer effect. Possibilities to identify two-dimensional elastic behavior are discussed.Comment: 18 pages, 5 figures, notation simplifie

A cluster theory for a Janus fluid

Recent Monte Carlo simulations on the Kern and Frenkel model of a Janus fluid have revealed that in the vapour phase there is the formation of preferred clusters made up of a well-defined number of particles: the micelles and the vesicles. A cluster theory is developed to approximate the exact clustering properties stemming from the simulations. It is shown that the theory is able to reproduce the micellisation phenomenon.Comment: 27 pages, 8 figures, 6 table

Electron Mean-Free Paths in the Alkali Metals

Photoemission data in which the signal from the first atomic layer is well resolved from that of the bulk are used to determine accurately the kinetic-energy dependence of the inelastic-electron mean free path in the alkali metals. At the higher kinetic energies, the data are in very good agreement with the theory of Penn. Below about 10 eV, the mean free path in the heavier alkali metals drops markedly below the theoretical values. This is attributed to electron decay processes involving the unoccupied d bands

Thermal and Surface Core-Electron Binding-Energy Shifts in Metals

High-resolution photoemission spectra from the shallow core levels of alkali metals and of In have been obtained between 78 K and room temperature. The data yield values for the alkali-metal surface-atom core-level shift and show thermal shifts of comparable size for bulk and surface. The positive surface shifts are due to the spill-out of conduction-electron charge, which is responsible for the surface dipole layer. The surface shifts are in good agreement with values obtained from a Born-Haber cycle expressed in terms of surface energies. The thermal shifts are proportional to the lattice expansion, and arise from both initial-state and final-state effects. As the lattice expands, the Fermi level decreases, decreasing the core-electron binding energy. At the same time, the expansion of the conduction-electron charge increases rs, thereby decreasing the potential at the core level and increasing the binding energy. The expansion also decreases the relaxation energy, further increasing the core-electron binding energy. In the alkali metals, the combined potential- and relaxation-energy terms dominate the Fermi-level term, making the shifts positive. In divalent metals the three terms tend to cancel, while in trivalent metals it is the Fermi-level term that dominates, making the shifts negative

Effective Magnetic Hamiltonian and Ginzburg Criterion for Fluids

We develop further the approach of Hubbard and Schofield (Phys.Lett., A40 (1972) 245), which maps the fluid Hamiltonian onto a magnetic one. We show that all coefficients of the resulting effective Landau-Ginzburg-Wilson (LGW) Hamiltonian may be expressed in terms of the compressibility of a reference fluid containing only repulsive interactions, and its density derivatives; we calculate the first few coefficients in the case of the hard-core reference fluid. From this LGW-Hamiltonian we deduce approximate mean-field relations between critical parameters and test them on data for Lennard-Jones, square-well and hard-core-Yukawa fluids. We estimate the Ginzburg criterion for these fluids.Comment: 4 pages, LaTeX, To appear in Phys.Rev.

Self-diffusion coefficients of charged particles: Prediction of Nonlinear volume fraction dependence

We report on calculations of the translational and rotational short-time self-diffusion coefficients $D^t_s$ and $D^r_s$ for suspensions of charge-stabilized colloidal spheres. These diffusion coefficients are affected by electrostatic forces and many-body hydrodynamic interactions (HI). Our computations account for both two-body and three-body HI. For strongly charged particles, we predict interesting nonlinear scaling relations $D^t_s\propto 1-a_t\phi^{4/3}$ and $D^r_s\propto 1-a_r\phi^2$ depending on volume fraction $\phi$, with essentially charge-independent parameters $a_t$ and $a_r$. These scaling relations are strikingly different from the corresponding results for hard spheres. Our numerical results can be explained using a model of effective hard spheres. Moreover, we perceptibly improve the known result for $D^t_s$ of hard sphere suspensions.Comment: 8 pages, LaTeX, 3 Postscript figures included using eps

A Local Moment Approach to magnetic impurities in gapless Fermi systems

A local moment approach is developed for the single-particle excitations of a symmetric Anderson impurity model (AIM), with a soft-gap hybridization vanishing at the Fermi level with a power law r > 0. Local moments are introduced explicitly from the outset, and a two-self-energy description is employed in which the single-particle excitations are coupled dynamically to low-energy transverse spin fluctuations. The resultant theory is applicable on all energy scales, and captures both the spin-fluctuation regime of strong coupling (large-U), as well as the weak coupling regime. While the primary emphasis is on single particle dynamics, the quantum phase transition between strong coupling (SC) and (LM) phases can also be addressed directly; for the spin-fluctuation regime in particular a number of asymptotically exact results are thereby obtained. Results for both single-particle spectra and SC/LM phase boundaries are found to agree well with recent numerical renormalization group (NRG) studies. A number of further testable predictions are made; in particular, for r < 1/2, spectra characteristic of the SC state are predicted to exhibit an r-dependent universal scaling form as the SC/LM phase boundary is approached and the Kondo scale vanishes. Results for the `normal' r = 0 AIM are moreover recovered smoothly from the limit r -> 0, where the resultant description of single-particle dynamics includes recovery of Doniach-Sunjic tails in the Kondo resonance, as well as characteristic low-energy Fermi liquid behaviour.Comment: 52 pages, 19 figures, submitted to Journal of Physics: Condensed Matte

Donor Kidney Recovery Methods and the Incidence of Lymphatic Complications in Kidney Transplant Recipients

Background: Lymphatic leak and lymphocele are well-known complications after kidney transplantation. Objective: To determine the incidence of lymphatic complications in recipients of living donor kidneys. Methods: Among 642 kidney transplants performed between 1999 and 2007, the incidence of lymphatic complications was retrospectively analyzed in recipients of living donor kidneys procured by laparoscopic nephrectomy (LP, n=218) or by open nephrectomy (OP, n=127) and deceased donor kidneys (DD, n=297). A Jackson-Pratt drain was placed in the retroperitoneal space in all recipients and was maintained until the output became less than 30 mL/day. Results: Although the incidence of symptomatic lymphocele, which required therapeutic intervention, was comparable in all groups, the duration of mean±SD drain placement was significantly longer in the LP group—8.6±2.7 days compared to 5.6±1.2 days in the OP group and 5.4±0.7 days in the DD group (p<0.001). Higher output of lymphatic drainage in recipients of LP kidneys could lead to a higher incidence of lymphocele if wound drainage is not provided. Conclusion: More meticulous back table preparation may be required in LP kidneys to decrease lymphatic complications after kidney transplantation. These observations also support the suggestion that the major source of persistent lymphatic drainage following renal transplantation is severed lymphatics of the allograft rather than those of the recipient’s iliac space

Unoccupied Band Structure of NbSe2 by Very-Low-Energy Electron Diffraction: Experiment and Theory

A combined experimental and theoretical study of very-low-energy electron diffraction at the (0001) surface of 2H-NbSe2 is presented. Electron transmission spectra have been measured for energies up to 50 eV above the Fermi level with k|| varying along the GammaK line of the Brillouin zone. Ab initio calculations of the spectra have been performed with the extended linear augmented plane wave k-p method. The experimental spectra are interpreted in terms of three-dimensional one-electron band structure. Special attention is paid to the quasi-particle lifetimes: by comparing the broadening of the spectral structures in the experimental and calculated spectra the energy dependence of the optical potential Vi is determined. A sharp increase of Vi at 20 eV is detected, which is associated with a plasmon peak in the Im(-1/epsilon) function. Furthermore, the electron energy loss spectrum and the reflectivity of NbSe2 are calculated ab initio and compared with optical experiments. The obtained information on the dispersions and lifetimes of the unoccupied states is important for photoemission studies of the 3D band structure of the valence band.Comment: 17 pages, 11 Postscript figures, submitted to Phys. Rev.