Exciton-exciton scattering: Composite boson versus elementary boson

This paper introduces a new quantum object, the ``coboson'', for composite particles, like the excitons, which are made of two fermions. Although commonly dealed with as elementary bosons, these composite bosons -- ``cobosons'' in short -- differ from them due to their composite nature which makes the handling of their many-body effects quite different from the existing treatments valid for elementary bosons. Due to this composite nature, it is not possible to correctly describe the interaction between cobosons as a potential $V$. Consequently, the standard Fermi golden rule, written in terms of $V$, cannot be used to obtain the transition rates between exciton states. Through an unconventional expression for this Fermi golden rule, which is here given in terms of the Hamiltonian only, we here give a detailed calculation of the time evolution of two excitons. We compare the results of this exact approach with the ones obtained by using an effective bosonic exciton Hamiltonian. We show that the relation between the inverse lifetime and the sum of transition rates for elementary bosons differs from the one of composite bosons by a factor of 1/2, whatever the mapping from composite bosons to elementary bosons is. The present paper thus constitutes a strong mathematical proof that, in spite of a widely spread belief, we cannot forget the composite nature of these cobosons, even in the extremely low density limit of just two excitons. This paper also shows the (unexpected) cancellation, in the Born approximation, of the two-exciton transition rate for a finite value of the momentum transfer

Photometric Observations of Star Formation Activity in Early Type Spirals

We observationally study the current star formation activities of early type spiral galaxies. We construct a complete sample of 15 early type spirals having far-infrared (FIR) to optical B band luminosity ratios, L(FIR)/L(B), larger than the average of the type, and make their CCD imaging of the R and H-alpha bands. The equivalent widths of H-alpha emission increase with increasing L(FIR)/L(B), indicating that L(FIR)/L(B) can be an indicator of star formation for such early type spirals with star formation activities higher than the average. For all of the observed early type spirals, the extended HII regions exist at the central regions with some asymmetric features. H-alpha emission is more concentrated to the galactic center than the R band light, and the degree of the concentration increases with the star formation activity. We also analyze the relation between the star formation activities and the existence of companion galaxies in the sample galaxies and other bright early type spirals. No correlation is found and this suggests that the interaction is not responsible for all of the star formation activities of early type spirals.Comment: LaTex, 23 pages (2 tables included), plus 9 Postscript figures & 1 table. To be published in AJ (November issue

Why holes are not like electrons. II. The role of the electron-ion interaction

In recent work, we discussed the difference between electrons and holes in energy band in solids from a many-particle point of view, originating in the electron-electron interaction, and argued that it has fundamental consequences for superconductivity. Here we discuss the fact that there is also a fundamental difference between electrons and holes already at the single particle level, arising from the electron-ion interaction. The difference between electrons and holes due to this effect parallels the difference due to electron-electron interactions: {\it holes are more dressed than electrons}. We propose that superconductivity originates in 'undressing' of carriers from $both$ electron-electron and electron-ion interactions, and that both aspects of undressing have observable consequences.Comment: Continuation of Phys.Rev.B65, 184502 (2002) = cond-mat/0109385 (2001

Effects of telmisartan and ramipril on adiponectin and blood pressure in patients with type 2 diabetes

<b>Background:</b> Adiponectin is secreted by adipose tissue and may play a role in cardiovascular disease. We examined adiponectin levels in patients with type 2 diabetes who participated in the Telmisartan vs. Ramipril in Renal Endothelial Dysfunction (TRENDY) study. <b>Methods</b> A total of 87 patients were assessed at baseline and following 9 weeks treatment with the angiotensin-receptor blocker telmisartan (final dose, 80 mg; n = 45) or the angiotensin-converting enzyme inhibitor ramipril (final dose, 10 mg; n = 42). Adiponectin levels were measured in plasma by radioimmunoassay. <b>Results:</b> Adiponectin levels were inversely correlated with systolic (SBP; r = -0.240, P < 0.05) and diastolic (DBP; r = -0.227, P < 0.05) blood pressure at baseline and following treatment with telmisartan or ramipril (SBP: r = -0.228, P < 0.05; DBP: r = -0.286, P < 0.05). Changes in adiponectin levels were related to changes in SBP (r = -0.357, P < 0.01) and DBP (r = -0.286, P < 0.01). There was a significant increase in adiponectin levels in the telmisartan (0.68 (95% confidence interval (CI), 0.27 to 1.10) <sup>µ</sup>g/ml, P < 0.01) but not in the ramipril group (0.17 (95% CI, -0.56 to 0.90) <sup>µ</sup>g/ml, P = 0.67). Blood pressure reduction in the telmisartan group (DeltaSBP: -13.5 (95% CI, -17.0 to -10.0) mm Hg; ΔDBP: -7.6 (95% CI, -9.8 to -5.3) mm Hg, each P < 0.001) was significantly (P less than or equal to 0.01 for SBP and P < 0.01 for DBP) greater than in the ramipril group (ΔSBP: -6.1 (95% CI, -6.2 to -2.0) mm Hg; ΔDBP: -2.7 (95% CI, -5.0 to -0.5) mm Hg; P < 0.01 and P < 0.05, respectively). <b>Conclusion:</b> Adiponectin is correlated with blood pressure in patients with type 2 diabetes. Whether increased adiponectin contributes to the blood pressure–lowering effect of telmisartan needs further study

Slowly varying envelope kinetic simulations of pulse amplification by Raman backscattering

A numerical code based on an eikonal formalism has been developed to simulate laser-plasma interactions, specifically Raman backscatter(RBS). In this code, the dominant laser modes are described by their wave envelopes, avoiding the need to resolve the laser frequency; appropriately time-averaged equations describe particle motion. The code is fully kinetic, and thus includes critical physics such as particle trapping and Landau damping which are beyond the scope of the commonly used fluid three-wave equations. The dominant forces on the particles are included: the ponderomotive force resulting from the beat wave of the forward and backscattered laser fields and the self-consistent plasma electric field. The code agrees well, in the appropriate regimes, with the results from three-wave equations and particle-in-cell simulations. The effects of plasma temperature on RBS amplification are studied. It is found that increasing the plasma temperature results in modification to particle trapping and the saturation of RBS, even before the onset of Landau damping of the plasma wave. This results in a reduction in the coupling efficiency compared to predictions based on the three-wave equations.open192

Relativistic Models for Binary Neutron Stars with Arbitrary Spins

We introduce a new numerical scheme for solving the initial value problem for quasiequilibrium binary neutron stars allowing for arbitrary spins. The coupled Einstein field equations and equations of relativistic hydrodynamics are solved in the Wilson-Mathews conformal thin sandwich formalism. We construct sequences of circular-orbit binaries of varying separation, keeping the rest mass and circulation constant along each sequence. Solutions are presented for configurations obeying an n=1 polytropic equation of state and spinning parallel and antiparallel to the orbital angular momentum. We treat stars with moderate compaction ((m/R) = 0.14) and high compaction ((m/R) = 0.19). For all but the highest circulation sequences, the spins of the neutron stars increase as the binary separation decreases. Our zero-circulation cases approximate irrotational sequences, for which the spin angular frequencies of the stars increases by 13% (11%) of the orbital frequency for (m/R) = 0.14 ((m/R) = 0.19) by the time the innermost circular orbit is reached. In addition to leaving an imprint on the inspiral gravitational waveform, this spin effect is measurable in the electromagnetic signal if one of the stars is a pulsar visible from Earth.Comment: 21 pages, 14 figures. A few explanatory sentences added and some typos corrected. Accepted for publication in Phys. Rev.

Physical Properties of Asteroid (308635) 2005 YU55 derived from multi-instrument infrared observations during a very close Earth-Approach

The near-Earth asteroid (308635) 2005 YU55 is a potentially hazardous asteroid which was discovered in 2005 and passed Earth on November 8th 2011 at 0.85 lunar distances. This was the closest known approach by an asteroid of several hundred metre diameter since 1976 when a similar size object passed at 0.5 lunar distances. We observed 2005 YU55 from ground with a recently developed mid-IR camera (miniTAO/MAX38) in N- and Q-band and with the Submillimeter Array (SMA) at 1.3 mm. In addition, we obtained space observations with Herschel/PACS at 70, 100, and 160 micron. Our thermal measurements cover a wide range of wavelengths from 8.9 micron to 1.3 mm and were taken after opposition at phase angles between -97 deg and -18 deg. We performed a radiometric analysis via a thermophysical model and combined our derived properties with results from radar, adaptive optics, lightcurve observations, speckle and auxiliary thermal data. We find that (308635) 2005 YU55 has an almost spherical shape with an effective diameter of 300 to 312 m and a geometric albedo pV of 0.055 to 0.075. Its spin-axis is oriented towards celestial directions (lam_ecl, beta_ecl) = (60 deg +/- 30deg, -60 deg +/- 15 deg), which means it has a retrograde sense of rotation. The analysis of all available data combined revealed a discrepancy with the radar-derived size. Our radiometric analysis of the thermal data together with the problem to find a unique rotation period might be connected to a non-principal axis rotation. A low to intermediate level of surface roughness (r.m.s. of surface slopes in the range 0.1 - 0.3) is required to explain the available thermal measurements. We found a thermal inertia in the range 350-800 Jm^-2s^-0.5K^-1, very similar to the rubble-pile asteroid (25143) Itokawa and indicating a mixture of low conductivity fine regolith with larger rocks and boulders of high thermal inertia on the surface.Comment: Accepted for publication in Astronomy & Astrophysics, 12 pages, 10 figure

Terrestrial exposure of a fresh Martian meteorite causes rapid changes in hydrogen isotopes and water concentrations

Determining the hydrogen isotopic compositions and H2O contents of meteorites and their components is important for addressing key cosmochemical questions about the abundance and source(s) of water in planetary bodies. However, deconvolving the effects of terrestrial contamination from the indigenous hydrogen isotopic compositions of these extraterrestrial materials is not trivial, because chondrites and some achondrites show only small deviations from terrestrial values such that even minor contamination can mask the indigenous values. Here we assess the effects of terrestrial weathering and contamination on the hydrogen isotope ratios and H2O contents of meteoritic minerals through monitored terrestrial weathering of Tissint, a recent Martian fall. Our findings reveal the rapidity with which this weathering affects nominally anhydrous phases in extraterrestrial materials, which illustrates the necessity of sampling the interiors of even relatively fresh meteorite falls and underlines the importance of sample return missions