非腔长匹配相干叠加脉冲锁模激光器的理论研究

提出了一个新的非腔长匹配相干叠加脉冲锁模激光器的物理模型,建立了它的数学方程,并进行了模拟计算.计算结果给出了各个参数对相干叠加脉冲锁模激光器运转的影响,以及脉冲宽度压缩速度和各参数之间的关系,获得了实现非腔长匹配相干叠加脉冲锁模激光器运转的最佳条件.     

Analysis of longitudinal multispin orders in strongly coupled spin systems

Longitudinal multispin orders provide an effective way for measurement of scalar couplings and also to probe molecular interactions and dynamics. Analysis of longitudinal orders has been made in strongly coupled AB and ABX spin systems to determine the dependence of strong coupling parameter on these orders. Experimental and simulated spectra of various longitudinal orders are illustrated for these spin systems. This general procedure can be extended to broad range of spin systems to understand the influence of strong coupling on longitudinal orders.     

Marked length rigidity of rank one symmetric spaces and their product

In this paper we show that if two Zariski dense representations, from a group G into Iso(X) where X is rank one symmetric space, have the proportional marked length spectrum, then they are conjugate. As a generalization we show that a Zariski dense representation into the isometry group of the product of rank one symmetric spaces is determined by the marked cross ratio.     

Development of new apertures for coherent X‐ray experiments

When one performs a coherent small‐angle X‐ray scattering experiment, the incident beam must be spatially filtered by slits on a length scale smaller than the transverse coherence length of the source which is typically around 10 µm. The Fraunhofer diffraction pattern of the slit is one of the important sources of background in these experiments. New slits which minimize this parasitic background have been designed and tested. The slit configuration apodizes the beam by the use of partially transmitting inclined slit jaws. A model is presented which predicts that the high wavevector tails of the diffraction pattern fall as the inverse fourth power of the wavevector instead of the inverse second power that is observed for standard slits. Using cleaved GaAs single‐crystal edges, Fraunhofer diffraction patterns from 3 and 5.5 keV X‐rays were measured, in agreement with the theoretical model proposed. A novel phase‐peak diffraction pattern associated with phase variations of the transmitted electric field was also observed. The model proposed adequately accounts for this phenomenon.     

An investigation of the accelerated thermal degradation of different epoxy resin composites using X-ray microcomputed tomography and optical coherence tomography

Epoxy resin composites reinforced with hollow glass microspheres, microlight microspheres, 3D parabeam glass, and E-Glass individually were subjected to accelerated thermal degradation conditions. X-ray microcomputed tomography (XμCT) was used to evaluate density changes, reinforcement filler damage, homogeneity, cracks and microcracks in the bulk of the different epoxy resin composites. XμCT 3D images, 2D reconstructed images and voids calculations revealed microspheres damage, filler distributions and showed cracks in all composites with different shapes and volume in response to the thermal degradation conditions. In addition, expansion of air bubbles/voids was observed and recorded in the microsphere and microlight epoxy composite samples. In a complementary way, optical coherence tomography (OCT) was used as a novel optical characterisation technique to study structural changes of the surface and near-surface regions of the composites, uncovering signs of surface shrinkage caused by the thermal treatment. Thus, combining XμCT and OCT proved useful in examining epoxy resin composites' structure, filler-resin interface and surface characteristics.     

Characteristic lengths and the structure of salt free polyelectrolyte solutions. A small angle neutron scattering study

We have studied salt free semi dilute polyelectrolyte solutions by small angle neutron scattering. Specific labelling associated with an extrapolation method has allowed the separation of the form factor of a single polyelectrolyte chainS ₁(q) and the structure factorS ₂(q). Two lengths are deduced from these two factors: the persistence lengthb _t which characterizes the electrostatic interactions along the chain by a fitting ofS ₁(q) with calculation of the scattering function for a wormlike chain, and fromS ₂(q),q _m ^–1 which characterizes the interactions between chains. These two lengths vary in the same way with the concentration of polyions (b _t C _p ^–1/2 ,q _m ^–1 C _p ^–1/2 ) and a constant relation exists between them: only one length is then necessary to describe the structure of polyelectrolyte soltuion on this semidilute concentration range.Laboratoire Commun CEA-CNRS.     

Experimental study on equilibrium deviations in atmospheric pressure argon/helium surface wave discharges

Atmospheric pressure surface wave discharges generated with Ar–He mixtures with He concentrations up to 99% were studied using spectroscopic techniques. The variation of electron density and linear power density with He concentration and along the plasma column is discussed together with the excitation temperatures derived from the Boltzmann plot of the excited states of Ar I and the values of the b(p) parameters to derive the thermodynamic equilibrium state of the discharge. Important deviations with respect to Local Thermodynamic Equilibrium were observed for He concentrations over 50% as the discharge shifts from a recombining to an ionizing behaviour. Furthermore, the discharge kinetic variations behind these changes are discussed.     

Determination of ppt levels of atmospheric volatile organic compounds in Yakushima, a remote south-west island of Japan

An analytical method was utilized to detect ppt levels of VOCs in air. The method was based on the US-EPA method TO-14, consisting of canister sampling, three module enrichment and GC/MS analysis. Target compounds included chlorofluorocarbons (four kinds), benzene and its derivatives (14), halogenated hydrocarbons (20), and others (three). The minimum detection limits of the method for the target compounds ranged from 0.016 to 0.040 ppb (0.06–0.23 μg/m³). The recoveries of the target compounds ranged from 77 to 113% and relative coefficients of variation (n=4) were 3.0–9.0%. The sampled air was stable for at least 14 days after pressurizing with humidified nitrogen gas at 200 kPa (absolute pressure). The method was applied to analyze the VOCs in the air of Yakushima, a remote island of south-west Japan where no distinct local pollution source is considered.     

Determination of photoelectron attenuation lengths in calcium phosphate ceramic films using XPS and RBS

Calcium phosphate (CaP) coatings are used to improve the biological performance of an implant. A technique that is often used to measure the composition of this material is XPS. When extremely thin coatings are measured, for example to study the interface between CaP and a substrate, the quantification of the XPS results is complicated by the varying attenuation lengths (ALs) of the photoelectrons at different energies. To correct for this, AL data are needed. In this work we measured these ALs by comparing XPS yields with the coating coverage (as measured by Rutherford backscattering spectrometry). We were able to determine the AL for several calcium and phosphorus peaks. Determination of the oxygen ALs was not possible owing to diffusion of oxygen into the polymeric substrates. For the peaks that are most often used for quantification of XPS yields (the Ca 2p and the P 2p peak), we found ALs of 21.8 × 10¹⁵ atoms cm^?2 and 26.8 × 10¹⁵ atoms cm^?2, respectively. Concentration profiles near the interface, growth mode and interfacial roughness appeared to have no measurable effect on the measured ALs. For the ALs, an energy dependence with an exponent of 0.55 was found. The measured ALs are best predicted by the empirical CS1 equation of Cumpson and Seah. Copyright © 2003 John Wiley & Sons, Ltd.     

An optimized method for the determination of volatile and semi-volatile aldehydes and ketones in ambient particulate matter

A method has been developed to measure aldehydes and ketones associated with atmospheric particles. Carbonyl compounds from particulate material collected on Teflon-coated glass-fiber filters were simultaneously extracted and derivatized with an appropriate 2,4-dinitrophenylhydrazine (2,4-DNPH) solution. The efficiency of this procedure utilizing various 2,4-DNPH concentrations and solvent compositions was studied for 13 carbonyl compounds of atmospheric importance. These include formaldehyde, acetaldehyde, acetone, dicarbonyls such as glyoxal and methylglyoxal, and biogenic carbonyls such as pinonaldehyde and nopinone. An extraction solution containing 3 × 10^?2 M 2,4-DNPH, in 60% acetonitrile/40% water, and pH 3 was most efficient in extracting and derivatizing these aldehydes and ketones (83-100% recovery). Improved sample enrichment and 2,4-DNPH purification methods were developed that afforded detection limits of 0.009-5.6 ng m^?3. The relative standard deviation for replicate analyses were 1.9-10.1%. Carbonyl compounds in ambient particulate samples were quantified during a recent field study. Median values for nine carbonyl species ranged from 0.01-33.9 ng m^?3 during the study.