CI emission in Ultra Luminous Infrared Galaxies as a molecular gas mass tracer

We present new sensitive wide-band measurements of the fine structure line 3^P_1 -> 3^P_0 (J=1-0, 492GHz) of neutral atomic carbon (CI) in the two typical Ultra Luminous Infrared Galaxies NGC6240 and Arp220. We then use them along with several other CI measurements in similar objects found in the literature to estimate their global molecular gas content under the assumption of a full CI-H_2 concomitance. We find excellent agreement between the H_2 gas mass estimated with this method and the standard methods using 12^CO. This may provide a new way to measure H_2 gas mass in galaxies, and one which may be very valuable in ULIRGs since in such systems the bright 12^CO emission is known to systematically overestimate the gas mass while their 13^CO emission is usually very weak. At redshifts z>=1 the CI J=1-0 line shifts to much more favorable atmospheric windows and can become a viable alternative tracer of the H_2 gas fueling starburst events in the distant Universe.Comment: 11 pages, 2 figures. Accepted for publication in ApJ Letter

Shear buckling of square perforated plates

The behavior of thin square perforated plates under the action of uniform shear deformation is studied experimentally and analytically using finite element analysis. Elastic Shear buckling strength is established as a function of the diameter of a round, centrally located hole in the plate. Post buckling behavior and the behavior of perforated plates with various ring stiffeners are also studied experimentally

Plasmon-enhanced internal photoemission for photovoltaics: Theoretical efficiency limits

Plasmon-enhanced internal photoemission in metal-semiconductor Schottky junctions has recently been proposed as an alternative photocurrent mechanism for solar cells. Here, we identify and discuss the requirements for efficient operation of such cells and analyze their performance limits under standard solar illumination. We show that the maximum efficiency limit is 20%.We acknowledge the Australian Research Council and the Australian Solar Institute for financial support

The Absolute Abundance of Iron in the Solar Corona

We present a measurement of the abundance of Fe relative to H in the solar corona using a technique which differs from previous spectroscopic and solar wind measurements. Our method combines EUV line data from the CDS spectrometer on SOHO with thermal bremsstrahlung radio data from the VLA. The coronal Fe abundance is derived by equating the thermal bremsstrahlung radio emission calculated from the EUV Fe line data to that observed with the VLA, treating the Fe/H abundance as the sole unknown. We apply this technique to a compact cool active region and find Fe/H = 1.56 x 10^{-4}, or about 4 times its value in the solar photosphere. Uncertainties in the CDS radiometric calibration, the VLA intensity measurements, the atomic parameters, and the assumptions made in the spectral analysis yield net uncertainties of order 20%. This result implies that low first ionization potential elements such as Fe are enhanced in the solar corona relative to photospheric values.Comment: Astrophysical Journal Letters, in pres

The transition between hole-pairs and four-hole clusters in four-leg tJ ladders

Holes weakly doped into a four-leg \tj ladder bind in pairs. At dopings exceeding a critical doping of $\delta_c\simeq {1/8}$ four hole clusters are observed to form in DMRG calculations. The symmetry of the ground state wavefunction does not change and we are able to reproduce this behavior qualitatively with an effective bosonic model in which the four-leg ladder is represented as two coupled two-leg ladders and hole-pairs are mapped on hard core bosons moving along and between these ladders. At lower dopings, $\delta<\delta_c$, a one dimensional bosonic representation for hole-pairs works and allows us to calculate accurately the Luttinger liquid parameter \krho, which takes the universal value \krho=1 as half-filling is approached