sunbeds and carcinogenesis the need for new regulations and restrictions in europe from the euromelanoma perspective

n/

Quasiparticle spectrum of the cuprate BiSrCaCuO: Possible connection to the phase diagram

We previously introduced [T. Cren et al., Europhys. Lett. 52, 203 (2000)] an energy-dependant gap function, $\Delta(E)$, that fits the unusual shape of the quasiparticle (QP) spectrum for both BiSrCaCuO and YBaCuO. A simple anti-resonance in $\Delta(E)$ accounts for the pronounced QP peaks in the density of states, at an energy $\Delta_p$, and the dip feature at a higher energy, $E_{dip}$. Here we go a step further : our gap function is consistent with the ($T, p$) phase diagram, where $p$ is the carrier density. For large QP energies ($E >> \Delta_p$), the total spectral gap is $\Delta(E) \simeq \Delta_p + \Delta_\phi$, where $\Delta_\phi$ is tied to the condensation energy. From the available data, a simple $p$-dependance of $\Delta_p$ and $\Delta_\phi$ is found, in particular $\Delta_\phi(p) \simeq 2.3 k_B T_c(p)$. These two distinct energy scales of the superconducting state are interpreted by comparing with the normal and pseudogap states. The various forms of the QP density of states, as well as the spectral function $A(k,E)$, are discussed

Absence of the zero bias peak in vortex tunneling spectra of high temperature superconductors?

The c-axis tunneling matrix of high-Tc superconductors is shown to depend strongly on the in-plane momentum of electrons and vanish along the four nodal lines of the d(x^2-y^2)-wave energy gap. This anisotropic tunneling matrix suppresses completely the contribution of the most extended quasiparticles in the vortex core to the c-axis tunneling current and leads to a spectrum similar to that of a nodeless superconductor. Our results give a natural explanation of the absence of the zero bias peak as well as other features observed in the vortex tunneling spectra of high-Tc cuprates.Comment: 4 pages 3 figures, minor corrections, to appear in Phys Rev

Laser Cooling of Trapped Fermi Gases deeply below the Fermi Temperature

We study the collective Raman cooling of a polarized trapped Fermi gas in the Festina Lente regime, when the heating effects associated with photon reabsorptions are suppressed. We predict that by adjusting the spontaneous Raman emission rates and using appropriately designed anharmonic traps, temperatures of the order of 2.7% of the Fermi temperature can be achieved in 3D.Comment: 4 pages, 3 figures; final versio

Congested Traffic States in Empirical Observations and Microscopic Simulations

We present data from several German freeways showing different kinds of congested traffic forming near road inhomogeneities, specifically lane closings, intersections, or uphill gradients. The states are localized or extended, homogeneous or oscillating. Combined states are observed as well, like the coexistence of moving localized clusters and clusters pinned at road inhomogeneities, or regions of oscillating congested traffic upstream of nearly homogeneous congested traffic. The experimental findings are consistent with a recently proposed theoretical phase diagram for traffic near on-ramps [D. Helbing, A. Hennecke, and M. Treiber, Phys. Rev. Lett. {\bf 82}, 4360 (1999)]. We simulate these situations with a novel continuous microscopic single-lane model, the ``intelligent driver model'' (IDM), using the empirical boundary conditions. All observations, including the coexistence of states, are qualitatively reproduced by describing inhomogeneities with local variations of one model parameter. We show that the results of the microscopic model can be understood by formulating the theoretical phase diagram for bottlenecks in a more general way. In particular, a local drop of the road capacity induced by parameter variations has practically the same effect as an on-ramp.Comment: Now published in Phys. Rev. E. Minor changes suggested by a referee are incorporated; full bibliographic info added. For related work see http://www.mtreiber.de/ and http://www.helbing.org

A two-species model of a two-dimensional sandpile surface: a case of asymptotic roughening

We present and analyze a model of an evolving sandpile surface in (2 + 1) dimensions where the dynamics of mobile grains ({\rho}(x, t)) and immobile clusters (h(x, t)) are coupled. Our coupling models the situation where the sandpile is flat on average, so that there is no bias due to gravity. We find anomalous scaling: the expected logarithmic smoothing at short length and time scales gives way to roughening in the asymptotic limit, where novel and non-trivial exponents are found.Comment: 7 Pages, 6 Figures; Granular Matter, 2012 (Online

Spin-polarized transport and Andreev reflection in semiconductor/superconductor hybrid structures

We show that spin-polarized electron transmission across semiconductor/superconductor (Sm/S) hybrid structures depends sensitively on the degree of spin polarization as well as the strengths of potential and spin-flip scattering at the interface. We demonstrate that increasing the Fermi velocity mismatch in the Sm and S regions can lead to enhanced junction transparency in the presence of spin polarization. We find that the Andreev reflection amplitude at the superconducting gap energy is a robust measure of the spin polarization magnitude, being independent of the strengths of potential and spin-flip scattering and the Fermi velocity of the superconductor.Comment: 4 pages, 2 figure

Kinetics and Jamming Coverage in a Random Sequential Adsorption of Polymer Chains

Using a highly efficient Monte Carlo algorithm, we are able to study the growth of coverage in a random sequential adsorption (RSA) of self-avoiding walk (SAW) chains for up to 10^{12} time steps on a square lattice. For the first time, the true jamming coverage (theta_J) is found to decay with the chain length (N) with a power-law theta_J propto N^{-0.1}. The growth of the coverage to its jamming limit can be described by a power-law, theta(t) approx theta_J -c/t^y with an effective exponent y which depends on the chain length, i.e., y = 0.50 for N=4 to y = 0.07 for N=30 with y -> 0 in the asymptotic limit N -> infinity.Comment: RevTeX, 5 pages inclduing figure

Demagnetization via Nucleation of the Nonequilibrium Metastable Phase in a Model of Disorder

We study both analytically and numerically metastability and nucleation in a two-dimensional nonequilibrium Ising ferromagnet. Canonical equilibrium is dynamically impeded by a weak random perturbation which models homogeneous disorder of undetermined source. We present a simple theoretical description, in perfect agreement with Monte Carlo simulations, assuming that the decay of the nonequilibrium metastable state is due, as in equilibrium, to the competition between the surface and the bulk. This suggests one to accept a nonequilibrium "free-energy" at a mesoscopic/cluster level, and it ensues a nonequilibrium "surface tension" with some peculiar low-T behavior. We illustrate the occurrence of intriguing nonequilibrium phenomena, including: (i) Noise-enhanced stabilization of nonequilibrium metastable states; (ii) reentrance of the limit of metastability under strong nonequilibrium conditions; and (iii) resonant propagation of domain walls. The cooperative behavior of our system may also be understood in terms of a Langevin equation with additive and multiplicative noises. We also studied metastability in the case of open boundaries as it may correspond to a magnetic nanoparticle. We then observe burst-like relaxation at low T, triggered by the additional surface randomness, with scale-free avalanches which closely resemble the type of relaxation reported for many complex systems. We show that this results from the superposition of many demagnetization events, each with a well- defined scale which is determined by the curvature of the domain wall at which it originates. This is an example of (apparent) scale invariance in a nonequilibrium setting which is not to be associated with any familiar kind of criticality.Comment: 26 pages, 22 figure