Strong energy dependence of the electron-phonon coupling strength on Bi(100)

We have studied the energy dependence of the electron-phonon coupling strength on Bi(100). A fit of the temperature-dependent surface state linewidth results in a change of the coupling parameter lambda from 0.20+/-0.02 to 0.72+/-0.05 as the binding energy of the surface state increases from 70 to 330 meV. This result cannot be reconciled with the usual interpretation of lambda as the electron-phonon mass enhancement parameter at the Fermi energy. We suggest that this behavior is mainly caused by the strong energy dependence of the bulk density of states in this region.     

Experimental investigation of the energy and depth dependence of flux peaking

The yield of helium ions backscattered from Yb implanted in silicon crystals has been studied as a function of the angle between the incident beam direction and various symmetry axes of the silicon crystal. The depth of the implanted Yb has been varied by using different implantation energies, and the analyzing beam energy has been varied from 0.5 to 2 MeV in an effort to obtain information about the energy and depth dependence of the flux-peaking phenomenon. The results are compared with those of Andersen and coworkers. We have observed the oscillation with depth of the flux in the center of a channel predicted by Van Vliet.     

Experimental determination of the effective strong coupling constant

We present a first attempt to experimentally extract an effective strong coupling constant that we define to be a low Q²$Q^2$ extension of a previous definition by S. Brodsky et al. following an initial work of G. Grunberg. Using Jefferson Lab data and sum rules, we establish its Q²$Q^2$-behavior over the complete Q²$Q^2$-range. The result is compared to effective coupling constants inferred from different processes and to calculations based on Schwinger–Dyson equations, hadron spectroscopy or lattice QCD. Although the connection between the experimentally extracted effective coupling constants and the calculations is not established it is interesting to note that their behaviors are similar.     

Parton energy loss at strong coupling and the universal bound

The apparent universality of jet quenching observed in heavy-ion collisions at RHIC for light and heavy quarks, as well as for quarks and gluons, is very puzzling and calls for a theoretical explanation. Recently, it has been proposed that synchrotron-like radiation at strong coupling gives rise to a universal bound on the energy of a parton escaping from the medium. Since this bound appears to be quite low, almost all of the observed particles at high transverse momentum have to originate from the surface of the hot fireball. Here I make a first attempt of checking this scenario against the RHIC data and formulate a “universal-bound model” of jet quenching that can be further tested at RHIC and LHC.     

The zero temperature energy gap of strong coupling superconductors

A simple equation for the zero temperature energy gap of a superconductor is derived which enables one to calculate Δ₀ very quickly with only a modest loss of accuracy. This equation is used to calculate the relative effectiveness of phonons of different frequencies in enhancing Δ₀. It predicts that the optimum phonon frequency for enhancing Δ₀ is close to Δ₀ for any material.     

Experimental investigation of the magnetic configuration dependence of turbulent transport

The dependence of turbulent transport on magnetic field properties is measured in detail on a plasma in a stellarator configuration. Pronounced poloidal asymmetries of fluctuation amplitudes and turbulent transport are observed. The transport maximum is located in regions where normal curvature of the magnetic field is negative and simultaneously the geodesic curvature has positive values. A major role of the local magnetic shear cannot be confirmed. The results can have important implications for the optimization of stellarators and the power influx into the scrape-off layer.     

Prediction of averaged energy for moderately damped systems with strong coupling

In this paper, the prediction of averaged energy of damped structural-acoustic systems is investigated. A simplified energy finite element method, referred to as EFEM⁰, is developed based on the energy flow analysis (EFA) equations and implemented using the finite volume method. The resulting formulations can be incorporated into statistical energy analysis (SEA) software and extends SEA application to moderately damped systems with strong coupling. The formulations are verified against analytical solutions for a single beam and coupled beams with both strong and weak coupling. A hybrid technique consisting of the EFEM⁰ approximation superimposed on a direct field is used to model moderately damped plates. For lightly damped systems, both methods produce acceptable results. For moderately damped two-dimensional systems, the EFEM⁰ method augmented with the direct field component produces significantly improved results.     

Vortex free energy and string tension at strong and intermediate coupling

We present results of high temperature expansions up to order g^?24 for the vortex free energy respectively string tension in pure lattice gauge theories with gauge groups SU(2) and Z₂ in 3 and 4 dimensions. For SU(2) in 4 dimensions the result is compared with Monte Carlo calculations of Creutz and is in good agreement. An intermediate coupling region is seen, where the string tension smoothly interpolates between strong coupling and weak coupling behaviour.     

Measurement of the energy dependence of hadronic jet rates and the strong coupling $\alpha_s$ from the four-jet rate with the DELPHI detector at LEP

Hadronic events from the data collected with the DELPHI detector at LEP within the energy range from 89 Gev to 209 Gev are selected, their jet rates are determined and compared to predictions of four different event generators. One of them is the recently developed APACIC + + generator which performs a massive matrix element calculation matched to a parton shower followed by string fragmentation. The four-jet rate is used to measure in the next-to-leading-order approximation yielding The running of determined by using four-jet events has been tested. The logarithmic energy slope is measured to be Since the analysis is based on four-jet final states it represents an alternative approach to previous DELPHI measurements using event shape distributions.Received: 4 August 2004, Revised: 1 October 2004, Published online: 7 December 2004     

Experimental study of the energy dependence of transmission in photoelectron spectrometers

The present study describes an experiment which allows determination of the transmission of any photoelectron spectrometer using AlKα radiation. The procedure is based on the energy independence of transmission in an iron-free, magnetic-type spectrometer. The relative line intensifies for Ag measured using such an instrument are used as a reference data set. The transmission of a VG ESCALAB-5 spectrometer has been determined and found to be proportional to E in the constant retarding ratio mode, and proportional to E^?q, with q = 0.4 ± 0.05, in the constant analyser-energy mode, for energies usually encountered in XPS.     

Experimental verification of thin-beam wandering dependence on distance in strong indoor turbulence

Abstract

The dependence of beam wandering (random lateral displacement) on distance of a thin beam propagating through strong indoor turbulence is investigated experimentally. In the case of small fluctuations and within the limits of the geometrical-optics approximation, the transverse displacement variance is expected to follow a third-power law dependence on distance. Here we present the results of measurements made over paths of a few metres, both in the laboratory and in a large corridor. Inner scale measured values are also reported.     

Experimental investigation of coupling impedances of the VEPP-4M electron-positron collider

The interaction of a beam with vacuum chamber elements via induced electromagnetic field is analyzed in the frequency domain using frequency-dependent coupling impedances. The knowledge of the impedances makes it possible to estimate the stability conditions for propagation of the beam. The calculation of impedances of accelerators like the VEPP-4M electron-positron collider with a large number of inhomogeneities in the vacuum chamber is a complicated and time-consuming problem. However, the impedances can be studied in such cases experimentally by analyzing the propagation of the beam. The results of experiments on the longitudinal and transverse impedances of VEPP-4M are considered. We describe a method for measuring the local transverse impedance ensuring a higher sensitivity as compared to the methods used earlier.     

Experimental investigation of the concentration dependence of the permittivity in ternary disordered systems

The concentration dependence of the complex permittivity in a model insulator-semiconductor-conductor ternary system is studied. A maximum in the real part of the permittivity is found, and a qualitative explanation of this finding is suggested.     

About the connection between the transition temperature and the energy gap for superconductors with strong coupling

A theoretical relation between Δ(0) and T_c for superconductors with strong coupling is compared with experimental data. We note the essential role of the lower phonon-peak. The agreement is rather good.