Collision-induced hyper-Rayleigh spectrum of H2–Ar gas mixture

The collision-induced hyper-Rayleigh (CIHR) spectra of the gaseous H 2 – Ar mixture are discussed in the binary regime on the basis of our ab initio computed H 2 – Ar collision-induced (CI) first dipole hyperpolarizability tensor Δ β ( R ) . A method for the computation of the spherical, rotationally adapted components Δ β λ L ( s , K ) ( R ) of Δ β ( R ) needed for spectroscopic line shape analysis is proposed. Both the vector and the septor parts of the H 2 – Ar CIHR spectrum are evaluated at room ( T = 295 K ) temperature. The spectra are calculated assuming the full quantum computations based on the Schrödinger equation of the relative translational motion of H 2 – Ar as well as semiclassical methods (classical trajectory approach and Birnbaum–Cohen model translational profiles). The H 2 – Ar pair CIHR septor spectrum has been found stronger than the vector one

Multi-property isotropic intermolecular potentials and predicted spectral lineshapes of collision-induced absorption (CIA), collision-induced light scattering (CILS) and collision-induced hyper-Rayleigh scattering (CIHR) for H2 –Ne, −Kr and −Xe

Quantum mechanical lineshapes of collision-induced absorption (CIA), collision-induced light scattering (CILS) and collision-induced hyper-Rayleigh scattering (CIHR) at room temperature (295 K) are computed for gaseous mixtures of molecular hydrogen with neon, krypton and xenon. The induced spectra are detected using theoretical values for induced dipole moment, pair-polarizability trace and anisotropy, hyper-polarizability and updated intermolecular potentials. Good agreement is observed for all spectra when the literature and the present potentials which are constructed from the transport and thermo-physical properties are used

Theoretical study of dislocation nucleation from simple surface defects in semiconductors

Large-scale atomistic calculations, using empirical potentials for modeling semiconductors, have been performed on a stressed system with linear surface defects like steps. Although the elastic limits of systems with surface defects remain close to the theoretical strength, the results show that these defects weaken the atomic structure, initializing plastic deformations, in particular dislocations. The character of the dislocation nucleated can be predicted considering both the resolved shear stress related to the applied stress orientation and the Peierls stress. At low temperature, only glide events in the shuffle set planes are observed. Then they progressively disappear and are replaced by amorphization/melting zones at a temperature higher than 900 K

The origin of variability of the intermediate-mass black-hole ULX system HLX-1 in ESO 243-49

The ultra-luminous intermediate-mass black-hole system HLX-1 in the ESO 243-49 galaxy exhibits variability with a possible recurrence time of a few hundred days. Finding the origin of this variability would constrain the still largely unknown properties of this extraordinary object. Since it exhibits an intensity-hardness behavior characteristic of black-hole X-ray transients, we have analyzed the variability of HLX-1 in the framework of the disk instability model that explains outbursts of such systems. We find that the long-term variability of HLX-1 is unlikely to be explained by a model in which outbursts are triggered by thermal-viscous instabilities in an accretion disc. Possible alternatives include the instability in a radiation-pressure dominated disk but we argue that a more likely explanation is a modulated mass-transfer due to tidal stripping of a star on an eccentric orbit around the intermediate-mass black hole. We consider an evolutionary scenario leading to the creation of such a system and estimate the probability of its observation. We conclude, using a simplified dynamical model of the post-collapse cluster, that no more than 1/100 to 1/10 of Mbh < 10^4 Msun IMBHs - formed by run-away stellar mergers in the dense collapsed cores of young clusters - could have a few times 1 Msun Main-Sequence star evolve to an AGB on an orbit eccentric enough for mass transfer at periapse, while avoiding collisional destruction or being scattered into the IMBH by 2-body encounters. The finite but low probability of this configuration is consistent with the uniqueness of HLX-1. We note, however, that the actual response of a standard accretion disk to bursts of mass transfer may be too slow to explain the observations unless the orbit is close to parabolic (and hence even rarer) and/or additional heating, presumably linked to the highly time-dependent gravitational potential, are invoked.Comment: 8 pages, 2 figures. Additional figure, extended discussion. To be published in ApJ, June 10, 2011, v734 -

Collision-induced hyperpolarizability and hyper-Rayleigh spectra in the He–Ar heterodiatom

The ab initio interatomic distance dependent collision induced dipole moment, polarizability and the vector b1 (R) and an irreducible 3rd rank tensor b3 (R) components of the first hyperpolarizability tensor b of He–Ar pair are obtained. The hyperpolarizability data are applied in order to calculate the collision induced He–Ar hyper-Rayleigh spectra both quantum-mechanically and semiclassically for the frequency shifts up to 1200 cm-1. Computations were carried out for two temperature values – T = 295 K and T = 95 K. Spectral features of both vector and the irreducible 3rd rank tensor parts of CIHR spectra are analyzed. The frequency dependent behavior of the HR depolarization ratio is discussed

Modelling the spectral response of the Swift-XRT CCD camera: Experience learnt from in-flight calibration

(Abbreviated) We show that the XRT spectral response calibration was complicated by various energy offsets in photon counting (PC) and windowed timing (WT) modes related to the way the CCD is operated in orbit (variation in temperature during observations, contamination by optical light from the sunlit Earth and increase in charge transfer inefficiency). We describe how these effects can be corrected for in the ground processing software. We show that the low-energy response, the redistribution in spectra of absorbed sources, and the modelling of the line profile have been significantly improved since launch by introducing empirical corrections in our code when it was not possible to use a physical description. We note that the increase in CTI became noticeable in June 2006 (i.e. 14 months after launch), but the evidence of a more serious degradation in spectroscopic performance (line broadening and change in the low-energy response) due to large charge traps (i.e. faults in the Si crystal) became more significant after March 2007. We describe efforts to handle such changes in the spectral response. Finally, we show that the commanded increase in the substrate voltage from 0 to 6V on 2007 August 30 reduced the dark current, enabling the collection of useful science data at higher CCD temperature (up to -50C). We also briefly describe the plan to recalibrate the XRT response files at this new voltage.Comment: 27 pages, 29 figures (many in colour), accepted for publication in A&

External Validation of the “Walking Estimated Limitation Calculated by History” (WELCH) Questionnaire in Patients with Claudication

ObjectiveTo externally validate the recently proposed “Walking Estimated Limitation Calculated by History” (WELCH) questionnaire.MethodsA prospective study was performed on 450 new patients referred to our laboratory for treadmill testing (constant load 3.2 km/h and 10% slope for 15 minutes and then incremental increases). Results are presented as mean ± SD or median [25th–75th percentiles] or number (percentage). An ankle brachial index <0.90 defined the presence of peripheral artery disease (PAD). Typical “vascular-type claudication” is a lower-limb pain or discomfort that is absent at rest, appears at exercise, forces stopping, and disappears within 10 minutes of exercise stopping. The Spearman r coefficient of correlation between maximal walking time (MWT) on treadmill and WELCH scores was calculated for patients with (PAD+) or without (PAD−) PAD, and reporting typical vascular-type claudication (VTC+) or not (VTC−).ResultsThe WELCH score was obtained in all included patients. The number (%) of patients with a WELCH score <25 was 37 (54%), 198 (65%), 14 (44%), and 18 (38%), and the Spearman correlation coefficient between WELCH score and treadmill MWT was 0.588, 0.609, 0.581, and 0.591 in the VTC−/PAD+, VTC+/PAD+, VTC−/PAD−, and VTC+/PAD− groups respectively (all p < .001). In PAD+/VTC+ patients, the WELCH positive predictive value for the inability to walk for 5 minutes on the treadmill was 79%.ConclusionThe WELCH score correlates moderately with treadmill-walking capacity in patients with or without PAD, and with or without typical VTC. It appears to be a simple to complete and easily scored instrument to help clinicians standardise the subjective estimation of walking capacity in their patients

The four modes of thinking framed by utopian discursivity. Or why we need Utopia

This article stands for the idea that Thomas More was a founder of discursivity. Based on this notion (which Michel Foucault applied to Karl Marx and Sigmund Freud), the article examines the four modes of thinking prospective thinking, critical thinking, holistic thinking and creative thinking that are framed by utopian discursivity. Ultimately, the description of these modes of thinking aim to ground the authors conviction that, because of the way they organise our reflection on the possibilities for the development of our society, they are the tools we need to construct a better future