Temperature suppression of STM-induced desorption of hydrogen on Si(100) surfaces

The temperature dependence of hydrogen (H) desorption from Si(100) H-terminated surfaces by a scanning tunneling microscope (STM) is reported for negative sample bias. It is found that the STM induced H desorption rate ($R$) decreases several orders of magnitude when the substrate temperature is increased from 300 K to 610 K. This is most noticeable at a bias voltage of -7 V where $R$ decreases by a factor of ~200 for a temperature change of 80 K, whilst it only decreases by a factor of ~3 at -5 V upon the same temperature change. The experimental data can be explained by desorption due to vibrational heating by inelastic scattering via a hole resonance. This theory predicts a weak suppression of desorption with increasing temperature due to a decreasing vibrational lifetime, and a strong bias dependent suppression due to a temperature dependent lifetime of the hole resonance.Comment: 5 pages, RevTeX, epsf files. Accepted for surface science letter

Benefits derived from capturing consumable supply costs by DRG as an input to physician practice pattern programs in military treatment facilities

The study examines the benefits that can be derived by Military Treatment Facilities from capturing consumable supply costs by Diagnostic Related Groups. Civilian hospitals are capturing supply costs at the patient level using physician and Diagnostic Related Grouped specific cost accounting methods. Cost data captured in this manner can be combined with severity of illness adjusted clinical performance data, available through the facility's utilization management program, thus providing data required to execute a physician practice pattern program. Direct financial benefits can be derived from a physician practice pattern program. Indirect benefits to product line decisions and materials management can be derived from this type of program as well. Military Treatment Facilities can derive the same benefits as civilian hospitals by adopting a physician and Diagnostic Related Grouped specific cost accounting system. When this type of accounting system is combined with existing utilization management programs an effective physician practice pattern program can be executed and the benefits of this type of program may be realized.http://archive.org/details/benefitsderivedf1094542808U.S. Navy (USN) authorApproved for public release; distribution is unlimited

Nouveautés sur les débits monstrueux de l'Amazone...

Après une première étude sur les variations saisonnières de l'Amazone, Maurice Pardé proposait en 1954 à la communauté hydrologique la valeur de 100000 à 110000 m3/s comme module de ce fleuve géant qui draine un bassin de plus de 6000000 km2. Ce résultat, que certains jugeaient alors excessif, était basé sur les observations de son compatriote Paul Le Cointe, et sur le calcul d'un bilan hydrique rudimentaire, du fait du très petit nombre de données hydroclimatiques disponibles à cette époque. Après les premiers jaugeages de l'Amazone à Obidos par l'USGS en 1963-64, le module de plus puissant fleuve du monde était alors estimé à 170000-190000 m3/s, attestant ainsi que la première estimation de Pardé n'était absolument pas surestimée... Les résultats obtenus dans le cadre du programme HIBAM (Hidrologia de Bacia Amazonica, DNAEE/CNPq-ORSTOM) ont permis de préciser le régime de l'Amazone et de ses principaux tributaires. Les apports des différents sous-bassins et le module de l'Amazone à son embouchure ont pu être estimés avec une assez bonne précision, ce qui a rendu possible la régionalisation des débits annuels. (Résumé d'auteur

Solving the riddle of codon usage preferences: a test for translational selection

Translational selection is responsible for the unequal usage of synonymous codons in protein coding genes in a wide variety of organisms. It is one of the most subtle and pervasive forces of molecular evolution, yet, establishing the underlying causes for its idiosyncratic behaviour across living kingdoms has proven elusive to researchers over the past 20 years. In this study, a statistical model for measuring translational selection in any given genome is developed, and the test is applied to 126 fully sequenced genomes, ranging from archaea to eukaryotes. It is shown that tRNA gene redundancy and genome size are interacting forces that ultimately determine the action of translational selection, and that an optimal genome size exists for which this kind of selection is maximal. Accordingly, genome size also presents upper and lower boundaries beyond which selection on codon usage is not possible. We propose a model where the coevolution of genome size and tRNA genes explains the observed patterns in translational selection in all living organisms. This model finally unifies our understanding of codon usage across prokaryotes and eukaryotes. Helicobacter pylori, Saccharomyces cerevisiae and Homo sapiens are codon usage paradigms that can be better understood under the proposed model

Spectroscopic properties of Er3+-doped antimony oxide glass

International audienceSpectroscopic properties of Er3+ ions have been studied in the 60Sb2O3-20WO3-19Na2O-1Bi2O3 (SWNB) glasses doped with 0.25 and 0.50 mol% Er2O3 respectively. The Judd-Ofelt parameters measured from the absorption spectra have been used to calculate the radiative life-time (τr) and the stimulated emission cross section. The low phonon energy, a reduced quenching effect and a high quantum efficiency of 90% for the 1.53 μm expected laser emission into pumping at 980 nm are in favor of promising material laser application

Multiple plasmon resonances in naturally-occurring multiwall nanotubes: infrared spectra of chrysotile asbestos

Chrysotile asbestos is formed by densely packed bundles of multiwall hollow nanotubes. Each wall in the nanotubes is a cylindrically wrapped layer of $Mg_3 Si_2 O_5 (OH)_4$. We show by experiment and theory that the infrared spectrum of chrysotile presents multiple plasmon resonances in the Si-O stretching bands. These collective charge excitations are universal features of the nanotubes that are obtained by cylindrically wrapping an anisotropic material. The multiple plasmons can be observed if the width of the resonances is sufficiently small as in chrysotile.Comment: 4 pages, 5 figures. Revtex4 compuscript. Misprint in Eq.(6) correcte

Decaying shock studies of phase transitions in MgOSiO2 systems: implications for the Super-Earths interiors

We report an experimental study of the phase diagrams of periclase (MgO), enstatite (MgSiO3) and forsterite (Mg2SiO4) at high pressures. We investigated with laser driven decaying shocks the pressure/temperature curves of MgO, MgSiO3 and Mg2SiO4 between 0.2-1.2 TPa, 0.12-0.5 TPa and 0.2-0.85 TPa respectively. A melting signature has been observed in MgO at 0.47 TPa and 9860 K, while no phase changes were observed neither in MgSiO3 nor in Mg2SiO4. An increasing of reflectivity of MgO, MgSiO3 and Mg2SiO4 liquids have been detected at 0.55 TPa -12 760 K, 0.15 TPa - 7540 K, 0.2 TPa - 5800 K, respectively. In contrast to SiO2, melting and metallization of these compounds do not coincide implying the presence of poor electrically conducting liquids close to the melting lines. This has important implications for the generation of dynamos in Super-earths mantles

Electron-Phonon Interacation in Quantum Dots: A Solvable Model

The relaxation of electrons in quantum dots via phonon emission is hindered by the discrete nature of the dot levels (phonon bottleneck). In order to clarify the issue theoretically we consider a system of $N$ discrete fermionic states (dot levels) coupled to an unlimited number of bosonic modes with the same energy (dispersionless phonons). In analogy to the Gram-Schmidt orthogonalization procedure, we perform a unitary transformation into new bosonic modes. Since only $N(N+1)/2$ of them couple to the fermions, a numerically exact treatment is possible. The formalism is applied to a GaAs quantum dot with only two electronic levels. If close to resonance with the phonon energy, the electronic transition shows a splitting due to quantum mechanical level repulsion. This is driven mainly by one bosonic mode, whereas the other two provide further polaronic renormalizations. The numerically exact results for the electron spectral function compare favourably with an analytic solution based on degenerate perturbation theory in the basis of shifted oscillator states. In contrast, the widely used selfconsistent first-order Born approximation proves insufficient in describing the rich spectral features.Comment: 8 pages, 4 figure

Scattering defect in large diameter titanium-doped sapphire crystals grown by the Kyropoulos technique

International audienceThe Kyropoulos technique allows growing large diameter Ti doped sapphire for Chirped pulse amplification laser. A scattering defect peculiar to Kyropoulos grown crystals is presented. This defect is characterized by different techniques: luminescence, absorption measurement, X-ray rocking curve. The impact of this defect to the potential application in chirped pulse amplification CPA laser is evaluated. The nature of this defect is discussed. Modified convexity of the interface is proposed to avoid the formation of this defect and increase the quality of the Ti sapphire crystal

The Unique Origin of Colors of Armchair Carbon Nanotubes

The colors of suspended metallic colloidal particles are determined by their size-dependent plasma resonance, while those of semiconducting colloidal particles are determined by their size-dependent band gap. Here, we present a novel case for armchair carbon nanotubes, suspended in aqueous medium, for which the color depends on their size-dependent excitonic resonance, even though the individual particles are metallic. We observe distinct colors of a series of armchair-enriched nanotube suspensions, highlighting the unique coloration mechanism of these one-dimensional metals.Comment: 4 pages, 3 figure