A compact spectroradiometer for solar simulator measurements

Compact spectral irradiance probe has been designed and built which uses wedge filter in conjunction with silicon cell and operational amplifier. Probe is used to monitor spectral energy distribution of solar simulators and other high intensity sources

Fluctuations in the level density of a Fermi gas

We present a theory that accurately describes the counting of excited states of a noninteracting fermionic gas. At high excitation energies the results reproduce Bethe's theory. At low energies oscillatory corrections to the many--body density of states, related to shell effects, are obtained. The fluctuations depend non-trivially on energy and particle number. Universality and connections with Poisson statistics and random matrix theory are established for regular and chaotic single--particle motion.Comment: 4 pages, 1 figur

Energy dissipation and equivalent damping of RC columns subjected to biaxial bending: an investigation based in experimental results

The cyclic behaviour of reinforced concrete columns have been object of many experimental studies in the recent past years. However, the experimental studies on the biaxial response of RC columns are still limited. In this paper are presented the main results of an experimental study of 24 full-scale rectangular building columns tested for different loading paths under uniaxial and biaxial conditions. The experimental results are presented and discussed in terms of global behaviour, particularly focusing on the stiffness and strength degradation due to the increasing cyclic demand, and energy dissipation evolution. The equivalent viscous damping was estimated based on the experimental results of the RC columns tested under biaxial loading and empirical expressions are proposed

Spontaneous ignition characteristics of gaseous hydrocarbon-air mixtures

Experiments are conducted to determine the spontaneous ignition delay times of gaseous propane, kerosine vapor, and n-heptane vapor in mixtures with air, and oxygen-enriched air, at atmospheric pressure. Over a range of equivalence ratios from 0.2 to 0.8 it is found that ignition delay times are sensibly independent of fuel concentration. However, the results indicate a strong dependence of delay times on oxygen concentration. The experimental data for kerosine and propane demonstrate very close agreement with the results obtained previously by Mullins and Lezberg respectively

3D hydrodynamical CO5BOLD model atmospheres of red giant stars: I. Atmospheric structure of a giant located near the RGB tip

We investigate the character and role of convection in the atmosphere of a prototypical red giant located close to the red giant branch (RGB) tip with atmospheric parameters, Teff=3660K, log(g)=1.0, [M/H]=0.0. Differential analysis of the atmospheric structures is performed using the 3D hydrodynamical and 1D classical atmosphere models calculated with the CO5BOLD and LHD codes, respectively. All models share identical atmospheric parameters, elemental composition, opacities and equation-of-state. We find that the atmosphere of this particular red giant consists of two rather distinct regions: the lower atmosphere dominated by convective motions and the upper atmosphere dominated by wave activity. Convective motions form a prominent granulation pattern with an intensity contrast (~18%) which is larger than in the solar models (~15%). The upper atmosphere is frequently traversed by fast shock waves, with vertical and horizontal velocities of up to Mach ~2.5 and ~6.0, respectively. The typical diameter of the granules amounts to ~5Gm which translates into ~400 granules covering the whole stellar surface. The turbulent pressure in the giant model contributes up to ~35% to the total (i.e., gas plus turbulent) pressure which shows that it cannot be neglected in stellar atmosphere and evolutionary modeling. However, there exists no combination of the mixing-length parameter and turbulent pressure that would allow to satisfactorily reproduce the 3D temperature-pressure profile with 1D atmosphere models based on a standard formulation of mixing-length theory.Comment: 13 pages, 18 figures, accepted for publication in A&

Color, Spin and Flavor Diffusion in Quark-Gluon Plasmas

In weakly interacting quark-gluon plasmas diffusion of color is found to be much slower than the diffusion of spin and flavor because color is easily exchanged by the gluons in the very singular forward scattering processes. If the infrared divergence is cut off by a magnetic mass, $m_{mag}\sim \alpha_sT$, the color diffusion is $D_{color}\sim (\alpha_s\ln(1/\alpha_s)T)^{-1}$, a factor $\alpha_s$ smaller than spin and flavor diffusion. A similar effect is expected in electroweak plasmas above $M_W$ due to $W^\pm$ exchanges. The color conductivity in quark-gluon plasmas and the electrical conductivity in electroweak plasmas are correspondingly small in relativistic heavy ion collisions and the very early universe.Comment: 5 pages, no figure