Piezospectroscopy of the I Lines of Gallium in Germanium

Piezospectra have been obtained for the closely spaced I lines of Ga in Ge. Small, homogeneous stresses have been obtained by abrading the optical faces. The symmetries of the final states of some of these lines have been deduced

Bleaching in foraminifera with algal symbionts: implications for reef monitoring and risk assessment

Abstrac

Non-linear Response of the trap model in the aging regime : Exact results in the strong disorder limit

We study the dynamics of the one dimensional disordered trap model presenting a broad distribution of trapping times $p(\tau) \sim 1/\tau^{1+\mu}$, when an external force is applied from the very beginning at $t=0$, or only after a waiting time $t_w$, in the linear as well as in the non-linear response regime. Using a real-space renormalization procedure that becomes exact in the limit of strong disorder $\mu \to 0$, we obtain explicit results for many observables, such as the diffusion front, the mean position, the thermal width, the localization parameters and the two-particle correlation function. In particular, the scaling functions for these observables give access to the complete interpolation between the unbiased case and the directed case. Finally, we discuss in details the various regimes that exist for the averaged position in terms of the two times and the external field.Comment: 27 pages, 1 eps figur

Theory of Double-Sided Flux Decorations

A novel two-sided Bitter decoration technique was recently employed by Yao et al. to study the structure of the magnetic vortex array in high-temperature superconductors. Here we discuss the analysis of such experiments. We show that two-sided decorations can be used to infer {\it quantitative} information about the bulk properties of flux arrays, and discuss how a least squares analysis of the local density differences can be used to bring the two sides into registry. Information about the tilt, compressional and shear moduli of bulk vortex configurations can be extracted from these measurements.Comment: 17 pages, 3 figures not included (to request send email to [email protected]

Towards a Formal Verification Methodology for Collective Robotic Systems

We introduce a UML-based notation for graphically modeling systems’ security aspects in a simple and intuitive way and a model-driven process that transforms graphical specifications of access control policies in XACML. These XACML policies are then translated in FACPL, a policy language with a formal semantics, and the resulting policies are evaluated by means of a Java-based software tool

Disordered Boson Systems: A Perturbative Study

A hard-core disordered boson system is mapped onto a quantum spin 1/2 XY-model with transverse random fields. It is then generalized to a system of spins with an arbitrary magnitude S and studied through a 1/S expansion. The first order 1/S expansion corresponds to a spin-wave theory. The effect of weak disorder is studied perturbatively within such a first order 1/S scheme. We compute the reduction of the speed of sound and the life time of the Bloch phonons in the regime of weak disorder. Generalizations of the present study to the strong disordered regime are discussed.Comment: 27 pages, revte

Transport Properties near the z=2 Insulator-Superconductor Transition

We consider here the fluctuation conductivity near the point of the insulator-superconductor transition in a system of regular Josephson junction arrays in the presence of particle-hole asymmetry or equivalently homogeneous charge frustration. The transition is characterised by the dynamic critical exponent $z=2$, opening the possibility of the perturbative renormalization-group (RG) treatment. The quartic interaction in the Ginzburg-Landau action and the coupling to the Ohmic heat bath, giving the finite quasiparticle life-time, lead to the non-monotonic behavior of the dc conductivity as a function of temperature in the leading logarithmic approximation.Comment: Revised version for publication. To appear in PR

Localization properties of the anomalous diffusion phase x tμx ~ t^{\mu} in the directed trap model and in the Sinai diffusion with bias

We study the anomalous diffusion phase $x ~ t^{\mu}$ with $0<\mu<1$ which exists both in the Sinai diffusion at small bias, and in the related directed trap model presenting a large distribution of trapping time $p(\tau) \sim 1/\tau^{1+\mu}$. Our starting point is the Real Space Renormalization method in which the whole thermal packet is considered to be in the same renormalized valley at large time : this assumption is exact only in the limit $\mu \to 0$ and corresponds to the Golosov localization. For finite $\mu$, we thus generalize the usual RSRG method to allow for the spreading of the thermal packet over many renormalized valleys. Our construction allows to compute exact series expansions in $\mu$ of all observables : at order $\mu^n$, it is sufficient to consider a spreading of the thermal packet onto at most $(1+n)$ traps in each sample, and to average with the appropriate measure over the samples. For the directed trap model, we show explicitly up to order $\mu^2$ how to recover the diffusion front, the thermal width, and the localization parameter $Y_2$. We moreover compute the localization parameters $Y_k$ for arbitrary $k$, the correlation function of two particles, and the generating function of thermal cumulants. We then explain how these results apply to the Sinai diffusion with bias, by deriving the quantitative mapping between the large-scale renormalized descriptions of the two models.Comment: 33 pages, 3 eps figure

Interstitials, Vacancies and Dislocations in Flux-Line Lattices: A Theory of Vortex Crystals, Supersolids and Liquids

We study a three dimensional Abrikosov vortex lattice in the presence of an equilibrium concentration of vacancy, interstitial and dislocation loops. Vacancies and interstitials renormalize the long-wavelength bulk and tilt elastic moduli. Dislocation loops lead to the vanishing of the long-wavelength shear modulus. The coupling to vacancies and interstitials - which are always present in the liquid state - allows dislocations to relax stresses by climbing out of their glide plane. Surprisingly, this mechanism does not yield any further independent renormalization of the tilt and compressional moduli at long wavelengths. The long wavelength properties of the resulting state are formally identical to that of the ``flux-line hexatic'' that is a candidate ``normal'' hexatically ordered vortex liquid state.Comment: 21 RevTeX pgs, 7 eps figures uuencoded; corrected typos, published versio

Differential Regulation of Tyrosinase Activity in Skin of White and Black Individuals In Vivo by Topical Retinoic Acid

Tyrosinase activity is a key determinant of melanin production in skin. Because retinoic acid regulates tyrosinase activity in melanoma cells, we analyzed modulation of pigmentation in vivo by retinoic acid. Black and white subjects were either not treated, or treated topically for 4 d under occlusion with vehicle, retinoic acid (0.1%), or the irritant sodium lauryl sulfate (2%). In untreated skin, tyrosinase activity and melanin content were significantly greater (2.3 times, and 3.2 times, respectively) in blacks versus whites. Four days of treatment with topical retinoic acid did not alter tyrosinase activity or melanin content in black skin. In contrast, retinoic acid treatment significantly induced (2.7 times, n = 8) tyrosinase activity, compared to vehicle treatment, in white skin. Melanin content, however, remained unchanged at 4 d. In separate experiments, tyrosinase activity in white subjects (n = 25) was increased 16% (p = 0.01) in sodium lauryl sulfate – treated skin, and 77% (p = 0.0005) in retinoic acid – treated skin, compared to vehicle-treated skin. The effect of retinoic acid on tyrosinase activity could be differentiated from non-specific irritation, because tyrosinase activity in retinoic acid – treated skin was significantly greater (52%, p = 0.004) than sodium lauryl sulfate-treated skin. Similar results were obtained with the dihydroxyphenylalanine reaction done on vehicle, sodium lauryl sulfate-, and retinoic acid – treated white skin. Northern analysis (n = 6) and semi-quantitative polymerase chain reaction (n = 6) demonstrated that retinoic acid treatment did not alter tyrosinase mRNA levels in white skin. Western analysis revealed that induction of tyrosinase activity by retinoic acid also was not associated with increased tyrosinase protein content (n = 9), indicating that regulation of tyrosinase activity by retinoic acid occurs through a post-translational mechanism. These data demonstrate that low tyrosinase activity in white skin in vivio is retinoic acid inducible and high tyrosinase activity in black skin in vivo is neither further induced nor reduced by retinoic aci