Growth dynamics of chemical composition gratings in fluorine-doped silica optical fibers

The refractive-index modulation of chemical composition gratings in fluorine-germanium-doped silica fibers as a function of thermal treatment during manufacturing has been studied. The final grating strength was found to depend strongly on an intermediate annealing step, with an optimum temperature near 600-700 degrees C, before development at a fixed temperature of 1000 degrees C. Low-temperature treatment, aimed at removing any remaining hydrogen from the fiber, performed at 100 degrees C for 20 h before the annealing step, also significantly increased the final refractive-index modulation.     

Isotope composition of Zelkova serrata leaves as an indicator of atmospheric pollution in Japan

In spite of increasing concern regarding the effects of greenhouse gases, atmospheric CO2 concentration continues to increase, with current levels now as high as 370 ppm. This elevated CO2 concentration influences not only atmospheric characteristics, but also ground vegetation: leaf structure, chemical composition and carbon-isotope composition are all affected. It was with this in mind that we investigated the viability of coupling an isotopic and a botanical approach to determine leaf interaction in relation to atmospheric pollution levels. Results show that, among the botanical indexes considered, the most reliable proxy of atmospheric CO2 levels would appear to be leaf mass per area (LMA), which increases with pollution. Our study also shows that LMA determination coupled with carbon-isotope compositions is a sensitive tracer of the local pollution-level variations.     

Formation of fully pearlitic microstructure in medium carbon steel

Pearlitic microstructure can be obtained when austenite of eutectoid composition is slowly cooled from high temperature to below the Ae₃ temperature. It is also possible to induce such structure in hypo-eutectoid composition of austenite through proper heat treatment as well. However, in the current work, one hypo-eutectoid steel during very slow cooling only produced completely pearlitic microstructure which was not expected from a steel with such composition. The calculations carried out considering orthoequilibrium condition actually predicted the presence of about 37% ferrite in the microstructure. Further calculations considering different equilibrium modes and kinetics of transformation indicates that the composition and thermal condition of the steel under consideration was such that proeutectoid ferrite formation could not start before the composition reaches to the Negligible Partitioning Local Equilibrium phase boundary which further coincides with the area described by Hultgren extrapolation and thus, the steel completely transforms to pearlite even with hypo-eutectoid composition during very slow cooling.     

In situ Raman study of mineral phases formed as by‐products in a rotary kiln for clinker production

Portland clinker production consists essentially in the burning of material with defined composition in a rotary kiln at temperatures around 1450 °C. The main fuel used in this process is coal, even though in the last few years the use of alternative fuels has been increasing. Four main minerals are formed, namely, tricalcium and dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite. Along with these main phases, variations in burning conditions of fuels or in the local composition of raw materials can lead to the formation of relatively high amounts of secondary by‐products, which can negatively affect the quality of the final material. Characterization of these by‐products allows not only optimization of the process of clinker production but also the design of special refractory materials for the wall of kilns and preheaters. Being found as particles included in (or alternating to) a hard solid clinker matrix, a detailed characterization of these extra phases could be achieved only via microscopic techniques. In this work, micro‐Raman spectroscopy has been successfully tested as a highly selective method for characterization and localization of included minerals that formed as overlapped crusts deposited on the internal wall of a conventional rotary kiln for cement production, without any manipulation of the sample. Understanding the chronological order of deposition of these overlapped layers is extremely important, as it is the only way to go back up to the production process and to individuate the problem. Copyright © 2008 John Wiley & Sons, Ltd.     

Isotope composition of Zelkova serrata leaves as an indicator of atmospheric pollution in Japan

In spite of increasing concern regarding the effects of greenhouse gases, atmospheric CO₂ concentration continues to increase, with current levels now as high as 370?ppm. This elevated CO₂ concentration influences not only atmospheric characteristics, but also ground vegetation: leaf structure, chemical composition and carbon-isotope composition are all affected. It was with this in mind that we investigated the viability of coupling an isotopic and a botanical approach to determine leaf interaction in relation to atmospheric pollution levels. Results show that, among the botanical indexes considered, the most reliable proxy of atmospheric CO₂ levels would appear to be leaf mass per area (LMA), which increases with pollution. Our study also shows that LMA determination coupled with carbon-isotope compositions is a sensitive tracer of the local pollution-level variations.     

Magnetic Nanocomposites Formed by FeNi3 Nanoparticles Embedded in Graphene. Application as Supercapacitors

A general family of magnetic nanocomposites formed by FeNi₃ ferromagnetic nanoparticles (NPs) embedded in a graphitized carbon matrix is reported. The soft chemical approach used relies on the catalytic effect of the NPs resulting from the thermal decomposition of the layered double hydroxide precursor, which acts as a multilayered nanoreactor enabling the formation of a range of carbon nanoforms (CNFs). This is followed by acid treatment of the as‐prepared nanocomposites to isolate the different CNFs formed. These range from carbon nano‐onions to graphene depending on the temperature of the thermal decomposition. This synthetic process paves the way for the rational design of metal–carbon nanocomposites with controllable composition as precursors of nanocarbons or even graphene. The coexistence of metal NPs and nanostructured carbon is a major source of applications. As a proof of concept, the electrochemical performance of these metal–carbon hybrid supercapacitors is studied under high discharging current densities and they exhibit high values of specific capacitance and excellent rate capabilities.     

BNCT中子源用RFQ加速器

 分析了加速器作为硼中子俘获治疗(BNCT)中子源的优势，提出以射频四极场（RFQ）加速器作为BNCT用中子源的首选机型。对该RFQ的参数进行了选择，利用质子轰击锂靶近阈反应产生的前冲中子束能散低、散角小的优势，设定RFQ最终能量为1.9 MeV。采用“匹配均温”设计方法进行了此强流质子RFQ的束流动力学设计，并对设计方案进行了传输模拟，在入口归一化均方根发射度为0.25 mm·mrad、流强为100 mA时，束流传输效率为99.3％。选择合适厚度的锂靶，经过整形即可得到满足BNCT治疗需要的中子束。     

Preparation and properties of Fe and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles in ZrO<Subscript>2</Subscript> matrix

Iron and magnetite nanoparticles in zirconium oxide matrix have been prepared by a heat treatment of a mixture of nanocrystalline iron oxide and zirconium oxide or zirconium hydride powders. Changes in the phase composition of the as-mixed powders during annealing in vacuum or in hydrogen were monitored using thermomagnetic curves. Structure and phase composition of the final products were characterized by X-ray powder diffraction and ⁵⁷Fe Mössbauer spectroscopy. Influence of the composition of the original mixture and quality of the annealing atmosphere on the final properties of the composites are discussed.     

Elementary processes at semiconductor/electrolyte interfaces: perspectives and limits of electron spectroscopy

Semiconductor device properties based on electrolyte contacts or modified by electrochemical reactions are dominated by the electronic structure of the interface. Electron spectroscopy as e.g. photoemission is the most appropriate surface science techniques to investigate elementary processes at semiconductor/electrolyte interfaces. For such investigations a specific experimental set-up (SoLiAS) has been built-up which allows performing model experiments as well as surface analysis after emersion under different experimental conditions. The experimental approach is presented by a number of experiments performed during the last years with GaAs as substrate material. Model experiments by adsorption and coadsorption of electrolyte species give information on fundamental aspects of semiconductor/electrolyte interactions. Emersion experiments give information on a final composition and the related electronic structure of electrodes after electrochemical reactions. The use of frozen electrolytes will help to bridge the gap between these two approaches. With the combination of the experimental procedures one may expect a detailed analysis of electrolyte (modified) interfaces covering chemical composition, electronic structure of surfaces/interfaces as well as surface/interface potentials.     

Diffusion coefficients of gases from the rate of approach to the steady state in thermal diffusion

The rate of approach to the steady state in a convection-free two-bulb thermal diffusion experiment is treated in a more rigorous manner than previously available, in order that reliable ordinary diffusion coefficients may be derived from thermal diffusion measurements. The final results are of the same form as in the original simplified Jones and Furry treatment, but the parameters are now interpreted somewhat differently and a new correction term appears. Application to Nettley's measurements on H₂-N₂ mixtures removes an apparent discrepancy with the kinetic theory prediction of the composition dependence of the diffusion coefficient for this system.     

Les premières étoiles

The oldest stars of the Galaxy are quite different from common stars, like our Sun. Understanding why it is so, requires to open the question in a cosmological perspective. After the Big Bang, and for at least 300 000 years, the Universe was nearly uniform, and had a very simple chemical composition formed during the hot phase of the Big Bang: only hydrogen, helium and traces of other light elements, deuterium, ³ He, and ⁷ Li. This composition is known as “primordial”. At a later time, about one or two billion years after the Big Bang, condensations developped at all scales, the smallest ones being stars. The most massive stars, reaching very high temperatures at their center, transformed their initial composition by thermonuclear reactions, producing all common elements observed in the solar system, carbon, nitrogen, oxygen, etc. These elements were dispersed into the interstellar medium by mass-ejection at the final stage of evolution of these massive stars, and recycled by subsequent generations of stars. The first stars must have been formed with the primordial composition, whereas later generations had an increasing proportion of elements produced by stellar nucleosynthesis. Intensive searches of stars with no, or very little elements produced by stellar nucleosynthesis have been performed during the last 20 years. Actually more than 100 stars were discovered with a very low proportion of such elements, one thousandth of the proportion in the Sun (in which they amount to about 1.7% by mass), or less. But no star was found with less that 1/10,000 of the solar proportion. So no “primordial” star has been observed yet. The reason why is still an open question.     

Calculation of diffusion effect for arbitrary pulse sequences

A method is presented for calculating the nuclear spin magnetization created by an arbitrary number of short radio frequency pulses and of piecewise constant gradient applied in a selected direction. The isotropic diffusion, the transverse and longitudinal relaxations as well as the global transport are taken into account. A thorough analysis of the magnetization density evolution results in an algorithm for the analytical calculation of final NMR signal. Computationally, it requires only accumulating numerical coefficients in the found analytical structure. For arbitrary sequences this is done with a computer program. This approach, which can be classified as symbolical computations, results in a high performance and in a practically unlimited accuracy. Results for sample pulse sequences are presented.     

Supercritical Fluid Extraction as a Method of Thermochemical Activation of Wood Cell Walls

The thermochemical activation of the lignocarbohydrate matrix by supercritical (SC) fluid extraction was studied. Labile and stable regions of lignocarbohydrate formations distributed in the cell wall were revealed. Changes in the composition and morphology of the wood substance during the treatment were determined. Supercritical fluid extraction with carbon dioxide was shown to be a useful method for selective treatment of the weak H-bonds of the lignocarbohydrate complex to obtain new data on the structure and composition of the wood substance and its components.     

An Infinitesimal Deformation Approach to the Crystallographic Theory of the Martensite Phase Transformation: Application to Au-Cd,Fe-Ni AND In-Tl Alloys

Using the infinitesimal deformation approach, a crystallographic analysis of the austenite-martensite transformation from the cubic to orthorhombic phase - which predicts crystallographic parameters such as habit plane, orientation relationship between austenite and martensite, rotation matrix and total shape deformation matrix - is derived from a knowledge of the crystal structures of the initial and final phase only. The numerical values coming from orientation relationships obtained for Au-47.5 Cd Fe-Ni and In--Tl alloys are compared with predictions of the phenomenological crystallographic theory, infinitesimal deformation approach and experimental data.     

A simple non-perturbative approach of atom ionisation by intense and ultra-short laser pulses

A simple theoretical approach based on Coulomb-Volkov states is introduced to predict ionisation of atoms by intense laser pulses in cases where the effective interaction time does not exceed one or two optical cycles [M. Nisoli et al., Opt. Lett. 22, 522 (1997)]. Under these conditions, the energy distributions of ejected electrons predicted by this non-perturbative approach are in very good agreement with “exact" results obtained by a full numerical treatment. The agreement is all the better that the principal quantum number of the initial state is high. For very strong fields, most electrons are ejected at an energy which is close to the classical kinetic energy that would be transferred to free electrons by the electromagnetic field during the pulse. The power of the present approach appears when keV. In this region, full numerical treatments become very lengthy and finally do not converge. However, the present Coulomb-Volkov theory still makes reliable predictions in very short computer times. Received 19 November 1999 and Received in final form 19 January 2000     

A Miniaturized XeCl Dielectric Barrier Discharge as a Source of Short Lived,Fast Decaying UV Radiation

A dielectric barrier discharge (DBD) of coaxial geometry has been examined as source of intensive, short‐lived UV radiation. A binary gas mixture consisting of 98% Xe + 2% Cl₂ and a ternary composition of 96% Ne + 6% Xe + 0.2% HCl were investigated in the pressure range between 10 and 750 mbar. The discharge was excited by unipolar high voltage square pulses with amplitudes of 3 to 7 kV at a repetition rate of 100 Hz. UV radiation intensity is increased by combining 5 square pulses with a period of 1 μs each in one train (burst). Radiation decay on three orders of magnitude within 10 μs was obtained for both gas mixtures in burst mode. Maximum energy of the light pulse was the same for both gas mixtures and estimated as 40 nJ. It is shown that the optimum gas pressure for highest radiation intensity depends not only on gas composition but also on applied voltage and number of pulses in the train. A variation of the spectral band shape of XeCl emission during the pulse is detected (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spider silk as a model biomaterial

Spider silk combines strength and extensibility, and a wide range of mechanical properties can be achieved with only minute (if any) changes in chemical structure. It appears that the full range of thermo-mechanical properties of such silk fibres can be predicted by examining the energy imparted during stretching with the theoretical framework provided by Mean Field Theory for Polymers. This approach attempts to integrate strain and tensile stress with a range of relevant energetic and mechanical parameters such as the loss tangent and potential energy of atomic inter-chain bonding as well as the tensile and bulk elastic moduli. The model reveals that the underlying design principle of silks seems to share an inherent and surprising simplicity at the macromolecular level. We conclude that our modelling approach allows in-depth analysis of natural silks as well as a comparison with synthetic fibres.     

Hydrothermal synthesis of highly nitrogen-doped carbon powder

Nitrogen-doped carbon powder (NCP) with high and controllable dopant concentration was facilely synthesized via hydrothermal treatment of sucrose under ammonia followed by calcination. The dopant concentration of the as-synthesized carbon powder can be easily adjusted in the range of 4.37-17.82 wt.% by careful choice of the reaction conditions. The precursor with high nitrogen content was prepared by aminization reaction between sucrose and ammonia in hydrothermal condition, amine groups are successfully introduced into the precursor molecule, which groups convert finally to pyridinic-like and graphitic-like structure in the followed heat-treatment process. Various techniques, including the elemental analysis, TG-DTA, XPS, XRD, SEM and FTIR, were employed to characterize and assess the compositional and structural properties of the precursor and final nitrogen-doped materials. The present work propose a novel method for synthesis of highly nitrogen-doped carbon materials.     

The Influence of Powder Properties and Tabletting Conditions on the Surface Roughness of Tablets

Tablets of five different compression formulations were investigated for their surface roughness using scanning electron microscopy and non-contact laser profilometry. It was found that the composition of a formulation not only influenced the tabletting properties of the powder mixtures, but also the surface properties of the final product. The addition of larger quantities of very brittle materials such as dibasic calcium phosphate dihydrate increased the surface roughness of tablets. An increase in tabletting pressure reduced the tablet surface roughness. Tablets were found to have smoother edges than faces, presumably due to the comparatively higher shear stress at the die walls and a polishing effect during tablet ejection. The assessment of surface roughness in three dimensions appeared more powerful than a simple line profile measurement.