On the relevance of polyynyl-substituted PAHs to astrophysics

We report on the absorption spectra of the polycyclic aromatic hydrocarbon (PAH) molecules anthracene, phenanthrene, and pyrene carrying either an ethynyl (-C2H) or a butadiynyl (-C4H) group. Measurements were carried out in the mid infrared at room temperature on grains embedded in CsI pellets and in the near ultraviolet at cryogenic temperature on molecules isolated in Ne matrices. The infrared measurements show that interstellar populations of polyynyl-substituted PAHs would give rise to collective features in the same way non-substituted PAHs give rise to the aromatic infrared bands. The main features characteristic of the substituted molecules correspond to the acetylenic CH stretching mode near 3.05 mum and to the almost isoenergetic acetylenic CCH in- and out-of-plane bending modes near 15.9 mum. Sub-populations defined by the length of the polyynyl side group cause collective features which correspond to the various acetylenic CC stretching modes. The ultraviolet spectra reveal that the addition of an ethynyl group to a non-substituted PAH molecule results in all its electronic transitions being redshifted. Due to fast internal energy conversion, the bands at shorter wavelengths are significantly broadened. Those at longer wavelengths are only barely affected in this respect. As a consequence, their relative peak absorption increases. The substitution with the longer butadiynyl chain causes the same effects with a larger magnitude, resulting in the spectra to show a prominent if not dominating pi-pi* transition at long wavelength. After discussing the relevance of polyynyl-substituted PAHs to astrophysics, we conclude that this class of highly conjugated, unsaturated molecules are valid candidates for the carriers of the diffuse interstellar bands.Comment: 29 pages, 9 figures, accepted for publication in ApJ 2 April 201

A phenomenological theory giving the full statistics of the position of fluctuating pulled fronts

We propose a phenomenological description for the effect of a weak noise on the position of a front described by the Fisher-Kolmogorov-Petrovsky-Piscounov equation or any other travelling wave equation in the same class. Our scenario is based on four hypotheses on the relevant mechanism for the diffusion of the front. Our parameter-free analytical predictions for the velocity of the front, its diffusion constant and higher cumulants of its position agree with numerical simulations.Comment: 10 pages, 3 figure

Two dimensional anisotropic non Fermi-liquid phase of coupled Luttinger liquids

We show using bosonization techniques, that strong forward scattering interactions between one dimensional spinless Luttinger liquids (LL) can stabilize a phase where charge-density wave, superconducting and transverse single particle hopping perturbations are irrelevant. This new phase retains its LL like properties in the directions of the chains, but with relations between exponents modified by the transverse interactions, whereas, it is a perfect insulator in the transverse direction. The mechanism that stabilizes this phase are strong transverse charge density wave fluctuations at incommensurate wavevector, which frustrates crystal formation by preventing lock-in of the in-chain density waves.Comment: (4 pages, 2 figures

Absence of Two-Dimensional Bragg Glasses

The stability to dislocations of the elastic phase, or ``Bragg glass'', of a randomly pinned elastic medium in two dimensions is studied using the minimum-cost-flow algorithm for a disordered fully-packed loop model. The elastic phase is found to be unstable to dislocations due to the quenched disorder. The energetics of dislocations are discussed within the framework of renormalization group predictions as well as in terms of a domain wall picture.Comment: 5 pages, REVTEX, 3 figures included. Further information can be obtained from [email protected]

Treatment of Low-flow Vascular Malformations by Ultrasound-guided Sclerotherapy with Polidocanol Foam: 24 Cases and Literature Review

AbstractObjectivesTreatment by sclerotherapy has been suggested as a first-line treatment of low-flow vascular malformations. This study reports our experience in treating low-flow vascular malformations by ultrasound-guided sclerosis with polidocanol foam at the Vascular Medicine Department in Grenoble, France.DesignRetrospective single-centre consecutive series.Materials and methodsBetween January 2006 and December 2009, we analysed the complete records of patients with symptomatic low-flow vascular malformations of venous, lymphatic or complex type (Klippel–Trenaunay syndrome, KTS) treated by ultrasound-guided sclerosis. The therapeutic indication was always validated by the Consultative Committee for vascular malformations of the University Hospital of Grenoble. All vascular malformations were classified according to the Hamburg Classification. The sclerosing agent was polidocanol used as foam.ResultsA total of 24 patients between 7 and 78 years were treated (19 venous malformations, three KTSs and two venous-lymphatic malformations). The concentrations of polidocanol used ranged from 0.25% to 3%. The average number of sessions was 2.3 (1–16). After a median follow-up at 5 months after the last session, 23 out of 24 patients reported a decrease in pain; in nine cases (37.5%), over 50% reduction in size was observed, and in 14 cases (58.3%), a reduction of less than 50% of the original size was obtained. Two minor side effects were reported.ConclusionsTreatment by ultrasound-guided sclerosis using polidocanol foam seems to be well tolerated and can improve the symptoms of low-flow malformations without the risks of more aggressive sclerosing agents, such as ethanol