Metal-insulator transitions in an expanding metallic fluid: particle formation kinetics

Core-level photoemission spectroscopy provides a local probe of expansion dynamics and associated transient chemical properties as a highly pressurized, metallic fluid expands into vacuum following impulsive heating of a semiconductor by an intense, ultrashort laser pulse. Transient photoemission peak shifts reveal that metal-insulator transitions occur rapidly following laser heating. These experiments probe constituents species and solidification kinetics occurring in the early moments of material ejection and provide insight into how particles arise in the current laser ablation regime.     

Weak versus strong harmonic-expansion analyses of self-pulsing lasers: II—the inhomogeneously broadened system

A simple harmonic expansion method is applied to investigate some aspects of the dynamic properties of the integro-differential ‘Maxwell-Bloch’ equations that describe the self-pulsing regime of a single-mode inhomogeneously broadened laser. First, we show that the usual small perturbative methods only describe the transient relaxation oscillations, characteristic of the signal relaxing towards its permanent state, either stable or unstable. Second, we show that an adapted strong harmonic expansion analysis applied to the permanent pulsing solutions yields an accurate evaluation of the pulsing frequencies.     

Effect of metal diffusion into polycrystalline 6H–SiC prior to its anodization on luminescence response

p-Type porous SiC layers were fabricated by anodization of resistive p-type 6H–SiC samples using HF/ethylene glycol solution. Thin films of lithium (Li) and aluminum (Al) as donor and acceptor elements were vacuum deposited and diffused onto SiC substrates prior to anodization. The aim of this work is to investigate the properties of the nanoporous SiC layer formed by this method and to deduce the effect of diffused lithium as donor and Al as acceptor atoms on their photoluminescence response (PL). The profile distribution of lithium and aluminum diffused atoms was carried out using secondary ion mass spectrometry (SIMS). The photoluminescence spectra of the anodized Al-diffused samples exhibit a broad emission band centered at about 475 nm, while the Li-diffused samples exhibit luminescence with one broad peak located at 655 nm, attributed to Li-related defect centers. In addition, the PL intensity of lithium diffused samples varies with varying the etching time. Finally, the results are expected to have important applications in modern optoelectronic devices and electrode materials of lithium batteries.     

On the wave equation with semilinear porous acoustic boundary conditions

The goal of this work is to study a model of the wave equation with semilinear porous acoustic boundary conditions with nonlinear boundary/interior sources and a nonlinear boundary/interior damping. First, applying the nonlinear semigroup theory, we show the existence and uniqueness of local in time solutions. The main difficulty in proving the local existence result is that the Neumann boundary conditions experience loss of regularity due to boundary sources. Using an approximation method involving truncated sources and adapting the ideas in Lasiecka and Tataru (1993) [28], we show that the existence of solutions can still be obtained. Second, we prove that under some restrictions on the source terms, then the local solution can be extended to be global in time. In addition, it has been shown that the decay rates of the solution are given implicitly as solutions to a first order ODE and depends on the behavior of the damping terms. In several situations, the obtained ODE can be easily solved and the decay rates can be given explicitly. Third, we show that under some restrictions on the initial data and if the interior source dominates the interior damping term and if the boundary source dominates the boundary damping, then the solution ceases to exists and blows up in finite time. Moreover, in either the absence of the interior source or the boundary source, then we prove that the solution is unbounded and grows as an exponential function.     

Ultrafast extreme ultraviolet induced isomerization of acetylene cations

Ultrafast isomerization of acetylene cations ([HC=CH](+)) in the low-lying excited A(2)Σ(g)(+) state, populated by the absorption of extreme ultraviolet (XUV) photons (38 eV), has been observed at the Free Electron Laser in Hamburg, (FLASH). Recording coincident fragments C(+) + CH2(+) as a function of time between XUV-pump and -probe pulses, generated by a split-mirror device, we find an isomerization time of 52±15 fs in a kinetic energy release (KER) window of 5.8相似文献   

Idempotent et cohomologie de Hochschild

Any idempotent element e of an (associative) algebra T defines an algebra $A=eTe$ with unit e. We show that the morphism which compares their Hochschild cohomology algebras is a Gerstenhaber algebras morphism. Moreover, this morphism factorizes through the cohomological algebras of many triangular algebras. To cite this article: B. Bendiffalah, D. Guin, C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Sulfur-capped cyclodextrins: a new class of cavitands with extroverted as well as introverted donor functionalities

Ansa-cyclodextrins were obtained in high yields by reaction of sodium sulfide with A,B-di- or A,B,D,E-tetramesylated alpha-CD precursors; the resulting thiocavitands are suitable for forming nanotubular molecules, as well as for hosting metal-organic fragments.     

The Bresse system in thermoelasticity

In this paper, we consider the Bresse system coupled with the Fourier law of heat conduction. We prove that the decay rate of the solution is very slow. In fact, we show that the L²‐norm of the solution decays with the rate of (1 + t)^?1/12 similar to the one obtained for the Timoshenko system. In addition, we found that the wave speed of the first two equations still control the decay rate of the solution with respect to the regularity of the initial data. This seems to be the first result dealing with the behavior of the Cauchy problem in the Bresse–Fourier model. Copyright © 2014 John Wiley & Sons, Ltd.     

Shape Selectivity in Enol Thioether Synthesis Catalyzed by Zeolites

The competitive reaction catalyzed by solid acid catalyst between two cyclohexanones (1a) and (1b) with thiophenol (2) has been studied. No selectivity was observed with the lamellar montmorillonite in contrast with microporous aluminosilicates (zeolites) where shape selectivity was observed, in particularly when the zeolites were saturated by thiophenol (2) before a competitive reaction.     

Existence and asymptotic stability of a viscoelastic wave equation with a delay

In this paper, we consider the viscoelastic wave equation with a delay term in internal feedbacks; namely, we investigate the following problem