排序方式: 共有157条查询结果,搜索用时 15 毫秒
131.
Edmund R. Malinowski Michael J. Barber Graham T. Whitaker Eugene T. Smith 《Journal of Chemometrics》2007,21(12):520-528
The free flavin adenine dinucleotide (FAD) cofactor is known to exhibit a pH‐dependent midpoint potential involving a simultaneous two‐electron transfer step (n = 2). Uv‐vis spectroelectrochemical reductions of FAD at constant pH, ranging from 5 to 9, were recorded and analyzed by factor analysis. Principal factor analysis was used to determine the number of species present at each pH. The results indicate that only two composite forms of FAD are present: the oxidized and the reduced forms. Window factor analysis was used to extract the concentration profiles of the controlling species. The oxidized form was found to be a single pH‐independent species, whereas the reduced form consists of two species. The pH‐dependent spectroscopic changes of reduced FAD were best modeled by a single proton transfer step involving two different ionization states with an apparent pKa = 6.3. This value compares favorably with those obtained from NMR and from midpoint potential measurements. At pH 6, the reduction of FAD was found to be first order, whereas at pH 9 the reduction is zero order; these observations are explained in terms of the reaction pathway involving xanthine oxidase, its substrate, and the pH. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
132.
A new variety of the “soliton management” in heterogeneous optical media is proposed. The system is composed as a periodic chain of nonlinear fibers with negligible intrinsic group-velocity dispersion (GVD), alternating with sections of unchirped fiber Bragg gratings (FBGs) operating in the reflection regime. Losses due to incomplete reflection are compensated by linear amplifiers. The model may apply to fiber-optic telecommunication links with periodically installed FBG modules, and it may be used for the design of laser setups. By means of extended simulations, we identify small regions in the underlying parameter space where this model, featuring the periodic separation of the Kerr nonlinearity and FBG-induced GVD (hence the name of the “split-step” system), supports stable transmission of RZ (return-to-zero) pulses, i.e., quasi-solitons. The effect of nonzero fiber’s GVD on the stable transmission regime is considered too. Moderately unstable (partly usable) transmission regimes are found in larger regions of the parameter space; they may be of two different types, with the average nonlinearity either undercompensating or overcompensating the GVD. Interactions between the stable RZ pulses are also studied, leading to the identification of a minimum separation between them necessary for the suppression of interaction effects. 相似文献
133.
G. F. Gribakin C. M.R. Lee 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(1):51-61
We analyse the process of rapid positron annihilation in large polyatomic molecules due to positron capture into vibrational
Feshbach resonances. Resonant annihilation occurs in molecules which can bind positrons, and we analyse positron binding to
alkanes using zero-range potentials. Related questions of spectra of annihilation gamma quanta and molecular fragmentation
following annihilation, are discussed briefly. 相似文献
134.
J.M. Cao 《Applied Surface Science》2006,253(5):2460-2464
Three-step raising temperature process was employed to fabricate carbon nanotubes by pyrolysis of ferrocene/melamine mixtures on silica and single crystalline silicon wafers respectively. Then the morphologies, structures and compositions of obtained carbon nanotubes are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscope (EDX) and electron energy-loss spectroscopy (EELS). TEM and SEM observation shows that on silica substrate, high-oriented carbon nanotube can grow compactly to form continuous film on both frontal and cross-section surfaces, but on silicon substrate, only can form on cross-section surface. These carbon nanotubes have much irregular cup-like structure, and with outer diameter varying from 25 nm to 35 nm. At the top end of carbon nanotube there is a catalyst particle. EDX analysis reveals that the particle are iron cluster, and EELS spectrum indicates that the nanotube is composed of pure carbon. Finally, the effect of substrate surface roughness on the growth behavior of carbon nanotubes has been discussed. 相似文献
135.
Organic modification of TEOS based silica aerogels using hexadecyltrimethoxysilane as a hydrophobic reagent 总被引:2,自引:0,他引:2
Nagaraja D. Hegde 《Applied Surface Science》2006,253(3):1566-1572
The experimental results on the synthesis and characterization of tetraethoxysilane (TEOS) based hydrophobic silica aerogels using hexadecyltrimethoxysilane (HDTMS) as a hydrophobic reagent by two step sol-gel process, are described. The molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), acidic water (0.001 M, oxalic acid) and basic water (10 M, NH4OH) was kept constant at 1:55:3.25:1.25 and the molar ratio of HDTMS/TEOS (M) was varied from 0 to 28.5 × 10−2. The organic modification was confirmed by infrared spectroscopic studies, and the hydrophobicity of the aerogels was tested by the contact angle measurements. The maximum contact angle of 152° was obtained for M = 22.8 × 10−2. The aerogels retained the hydrophobicity up to a temperature of 240 °C and above this temperature the aerogels became hydrophilic. The aerogels were characterized by the thermal conductivity, density, contact angle measurements, optical transmission and scanning electron micrographs. 相似文献
136.
K. Moritani M. Okada T. Fukuyama Y. Teraoka A. Yoshigoe T. Kasai 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(1):111-115
We report a study on the oxidation process induced by a hyperthermal oxygen
molecular beam (HOMB) on Cu(110) using X-ray photoemission spectroscopy in
conjunction with a synchrotron radiation source. The oxidation process
induced by energetic O2 beams on Cu(110), depending on the azimuthal
angle of incidence, suggests that the –Cu–O– added row structure has a role
in inhibiting adsorption as a steric obstacle for incident O2
molecules. 相似文献
137.
We demonstrate that a thin marker layer, sandwiched in the guiding medium of a thin film planner X-ray waveguide structure, can be used to determine X-ray compression efficiency for a particular excitation mode. It can also be used in evaluating the transmission efficiency of waveguide structure and for the determination of X-ray intensities reaching the waveguide exit. This approach has been applied for determining X-ray compression and transmission efficiency of a Mo/B4C/Mo based X-ray waveguide structure, by inserting a thin Fe marker layer. 相似文献
138.
B.N. Mavrin V.N. Denisov D.M. Popova M.S. Kuznetsov S.A. Terentiev 《Physics letters. A》2008,372(21):3914-3918
For the first time investigations of the boron distribution in the subsurface region of HPHT boron-doped diamond that is promising for applications in electronics were carried out by X-ray photoelectron (XPS) and Raman spectroscopy. It was found from XPS data that the boron content decreased gradually more than one order of magnitude in depth of surface. The first-principle calculations have shown that the Raman polarizability in the crossed polarization configuration should increase considerably with boron doping. The Raman spectra from as-grown and polished surfaces of heavily boron-doped diamond are discussed in the context of theoretical results. 相似文献
139.
An analytical method of quantitative phase identification and mapping on the nanoscale is presented based on correlative similarity mapping from spectrum images within electron energy loss spectroscopy across the low‐loss plasmon region. The method is applied to map the reaction layer formation for heat treated Cu–Al–Al2O3 thin films. Coexistence of residual Al pockets next to polycrystalline but epitaxial CuAl2 as main reaction product is found as well as a distinctive interfacial plasmon region. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
140.
Gene delivery process in a single animal cell after femtosecond laser microinjection 总被引:1,自引:0,他引:1
Yoichiroh Hosokawa Seriya Iguchi Yuji Hiraki Chisa Shukunami 《Applied Surface Science》2009,255(24):9880-9884
Microinjection of extracellular molecules into a single animal cell was performed by an amplified femtosecond laser irradiation. When a single-shot laser pulse was focused on the plasma membrane of a single fibroblast from the mouse cell line NIH3T3 with a high-numerical aperture objective lens, a transient hole with a diameter of 1 μm was formed. The delivery process of extracellular molecules immediately after the hole formation was monitored by a fluorescence staining with fluoresceinisothiocyanate-dextran (FITC-dextran). Then the gene expression was confirmed using a DNA plasmid of an enhanced green fluorescent protein (EGFP). The gene expression was observed when the laser pulse was focused first on the cellular membrane and then on the nuclear membrane, while the gene was not expressed when the laser was focused only on the cellular membrane. On the basis of these results, the efficiency of gene delivery by the femtosecond laser microinjection and the subsequent gene expression were clarified. 相似文献