A hierarchical phase space generator for QCD antenna structures

We present a ``hierarchical'' strategy for phase space generation in order to efficiently map the antenna momentum structures, typically occurring in QCD amplitudes.Comment: 21 pages, few typos corrected, figure added, to appear in Eur.Phys.J.

The Mass Function and Average Mass Loss Rate of Dark Matter Subhaloes

We present a simple, semi-analytical model to compute the mass functions of dark matter subhaloes. The masses of subhaloes at their time of accretion are obtained from a standard merger tree. During the subsequent evolution, the subhaloes experience mass loss due to the combined effect of dynamical friction, tidal stripping, and tidal heating. Rather than integrating these effects along individual subhalo orbits, we consider the average mass loss rate, where the average is taken over all possible orbital configurations. This allows us to write the average mass loss rate as a simple function that depends only on redshift and on the instantaneous mass ratio of subhalo and parent halo. After calibrating the model by matching the subhalo mass function (SHMF) of cluster-sized dark matter haloes obtained from numerical simulations, we investigate the predicted mass and redshift dependence of the SHMF.We find that, contrary to previous claims, the subhalo mass function is not universal. Instead, both the slope and the normalization depend on the ratio of the parent halo mass, M, and the characteristic non-linear mass M*. This simply reflects a halo formation time dependence; more massive parent haloes form later, thus allowing less time for mass loss to operate. We analyze the halo-to-halo scatter, and show that the subhalo mass fraction of individual haloes depends most strongly on their accretion history in the last Gyr. Finally we provide a simple fitting function for the average SHMF of a parent halo of any mass at any redshift and for any cosmology, and briefly discuss several implications of our findings.Comment: Replaced to match version accepted for publication in MNRAS. Small section added that discusses higher-order moments of subhalo occupation distribution (including a new figure). Otherwise, few small change

Universal conductance fluctuations and low temperature 1/f noise in mesoscopic AuFe spin glasses

We report on intrinsic time-dependent conductance fluctuations observed in mesoscopic AuFe spin glass wires. These dynamical fluctuations have a 1/f-like spectrum and appear below the measured spin glass freezing temperature of our samples. The dependence of the fluctuation amplitude on temperature, magnetic field, voltage and Fe concentration allows a consistent interpretation in terms of quantum interference effects which are sensitive to the slowly fluctuating spin configuration.Comment: 4 pages, 4 figure

Photo-ionization modelling of planetary nebulae -- II. Galactic bulge nebulae, a comparison with literature results

We have constructed photo-ionization models of five galactic bulge planetary nebulae using our automatic method which enables a fully self-consistent determination of the physical parameters of a planetary nebula. The models are constrained using the spectrum, the IRAS and radio fluxes and the angular diameter of the nebula. We also conducted a literature search for physical parameters determined with classical methods for these nebulae. Comparison of the distance independent physical parameters with published data shows that the stellar temperatures generally are in good agreement and can be considered reliable. The literature data for the electron temperature, electron density and also for the abundances show a large spread, indicating that the use of line diagnostics is not reliable and that the accuracy of these methods needs to be improved. Comparison of the various abundance determinations indicates that the uncertainty in the electron temperature is the main source of uncertainty in the abundance determination. The stellar magnitudes predicted by the photo-ionization models are in good agreement with observed values.Comment: Accepted for publication in MNRA

A Comparative Study Of The Double Motor Innervation In Marine Crustaceans

A double motor innervation has been shown for several muscles of marine crustaceans. The adductors of the claws of Randallia and Blepharipoda and the adductor of the dactylopodite of the walking leg of Cancer were studied physiologically. The two motor axons which innervate these muscles have a different diameter (ratio 1.4:1). Stimulation of the thick fibre causes a response, which, though it is not always faster than the response of the thin fibre, must be considered as a "fast" contraction. In Randallia and in Blepharipoda the slow contraction is higher than the fast with frequencies of less than ± 50 per sec., in Cancer with frequencies less than 100 per sec. The action currents of the two kinds of contraction are different. Both show facilitation, but under the same conditions of stimulation the fast-action currents are higher. The first stimulus of the thick fibre causes an action current top which is clearly distinguishable, the action currents of the slow contraction show up only after a number of stimuli. Even when the mechanical reaction on stimulation of the thick fibre is smaller than on similar stimulation of the thin fibre, the action currents are higher in the first case. A single impulse in the thick fibre does not cause a contraction, but sets up a muscle-action current. The chronaxie of this action current in Blepharipoda and Randallia is 0.8{sigma} and is about the same as that found for the action current of the nerve. Two impulses in the thick fibre may cause a mechanical response, as is shown by summation experiments. The pseudo-chronaxie of this contraction was measured as 3.5 {sigma}. The second action current shows facilitation, when it follows the first within 1 sec.; a mechanical reaction results with summation intervals of two stimuli of less than 10{sigma}. The facilitation of the action current increases with decrease of the time interval between the two impulses; with the shortest intervals that give summation the resulting action current is a smooth high spike

Role of defects and impurities in doping of GaN

We have calculated formation energies and position of the defect levels for all native defects and for a variety of donor and acceptor impurities employing first-principles total-energy calculations. An analysis of the numerical results gives direct insight into defect concentrations and impurity solubility with respect to growth parameters (temperature, chemical potentials) and into the mechanisms limiting the doping levels in GaN. We show how compensation and passivation by native defects or impurities, solubility issues, and incorporation of dopants on other sites influence the acceptor doping levels.Comment: 8 pages, 3 figures, to appear in "The Physics of Semiconductors