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排序方式: 共有761条查询结果,搜索用时 15 毫秒
51.
Bel R Behnia K Proust C van der Linden P Maude D Vedeneev SI 《Physical review letters》2004,92(17):177003
We present a study of heat and charge transport in Bi(2+x)Sr(2-x)CuO(6+delta) focused on the size of the low-temperature linear term of the thermal conductivity at optimal-doping level. In the superconducting state, the magnitude of this term implies a d-wave gap with an amplitude close to what has been reported. In the normal state, recovered by the application of a magnetic field, measurement of this term and residual resistivity yields a Lorenz number L=kappa(N)rho(0)/T=1.3+/-0.2L(0). The departure from the value expected by the Wiedemann-Franz law is thus slightly larger than our estimated experimental resolution. 相似文献
52.
This study was designed to evaluate changes in erythrocyte contents during endurance moderate intensity exercise, a model of physiological oxidative stress. 16 endurance-trained subjects cycled 2 h at 55% of maximal aerobic capacity and blood was collected every 15 min. Transmission FT-IR spectrometry was used to analyze separately plasma and erythrocyte content changes during oxidative stress. Erythrocyte FT-IR spectra were corrected for hemoconcentration (Hc) before spectral areas integration of main IR absorbances belonging to phospholipids [nu(as)(CH(3)), [nu(as)(CH(2)), and nu(P=O)], proteins [nu(C=O) and delta(N-H)], and lactate [nu(C-O)] were used to determine erythrocyte content changes. Changes in nu(as)(CH(2)) and nu(P=O) absorbances while nu(as)(CH(3)) remained stable showed the magnitude of free radical attacks on phospholipids bilayer. Decrease in nu(C=O) and delta(N-H) absorbances while plasma and intracellular lactate, O(2) consumption, and Hc rose were linked to hemoglobin, and possibly spectrin, denaturation. Finally, the synergistic changes found between physiological, plasmatic and erythrocyte parameters showed that FT-IR spectrometry was a sufficiently accurate and sensitive method to determine acute changes in erythrocytes during moderate, physiological, oxidative stress. 相似文献
53.
Poriel C Ferrand Y Le Maux P Rault-Berthelot J Simonneaux G 《Inorganic chemistry》2004,43(16):5086-5095
Anodic oxidation of free base and manganese complexes of tetraspirobifluorenylporphyrins leads to the coating of the working electrode by insoluble electroactive poly(9,9'-spirobifluorene-free and manganese porphyrin) films which electrochemical behavior and physicochemical properties are described. After removal from the electrode, the manganese-complexed polymers were evaluated as catalysts for the oxidation of alkenes by iodobenzene diacetate or iodosylbenzene. The results show that the reactions proceeded very efficiently at room temperature with good yields. The electrosynthesized polymer catalysts can be recycled by simple filtration and reused even up to the eighth cycle without loss of activity and selectivity. These results represent an important improvement over those previously described for manganese-porphyrin-catalyzed epoxidation reactions. 相似文献
54.
Solladié N Walther ME Gross M Duarte TM Bourgogne C Nierengarten JF 《Chemical communications (Cambridge, England)》2003,(19):2412-2413
In addition to the ammonium-crown ether recognition, pi-stacking interactions between the C60 sphere and the porphyrin moiety have been evidenced in a supramolecular complex obtained from a porphyrin-crown ether conjugate and a fullerene derivative bearing an ammonium unit. 相似文献
55.
Godard C Duckett SB Parsons S Perutz RN 《Chemical communications (Cambridge, England)》2003,(18):2332-2333
UV irradiation of a solution of (eta5-C5H5)bis(ethene)rhodium in the presence of 2,2'-dipyridylketone yields (eta5-C5H5)Rh(kappa2-N,O-2,2'-dipyridylketone) which inserts ethene to yield a bicyclic oxametallacyclopentane. 相似文献
56.
Rainer Cremer Mirjam Witthaut Dieter Neuschütz Cyril Trappe Martin Laurenzis Olaf Winkler Heinrich Kurz 《Mikrochimica acta》2000,133(1-4):299-302
Cu3N films for optical data storage were deposited on Si(100) wafers and 0.6 mm thick polycarbonate DVD base material discs at
a temperature of 50 °C by reactive magnetron sputtering. A copper target was sputtered in rf mode in a nitrogen plasma. For
basic investigations concerning the composition and structure of Cu3N, Si wafers were used as substrate material. To study the suitability of Cu3N as an optical data storage medium under technical conditions, Cu3N/Al bilayers were deposited on polycarbonate discs. The composition and structure of the films were investigated by X-ray
photoelectron spectroscopy (XPS) and X-ray diffraction (XRD).
The decomposition of Cu3N into metallic copper and nitrogen was induced and characterized with a dynamic tester consisting of an optical microscope
with an integrated high power laser diode. The change in reflectivity induced by the laser pulses was measured by a high sensitivity
photo detector. Optimized Cu3N films could be decomposed into metallic copper at pulse lengths of 200 ns. The reflectivity change from 3.2% to 33.2% for
completely transformed areas and to 12% for single bits as well as the maximum write data rate of 3.3 Mbit/s demonstrated
the suitability of Cu3N for write once optical data storage. Especially the carrier to noise ratio of 41 dB shows an increase of a factor of 3 for
this novel material as compared to conventional optical data storage media. 相似文献
57.
Cyril Girardin Daniel P. Rasse Philippe Biron Jaleh Ghashghaie Claire Chenu 《Rapid communications in mass spectrometry : RCM》2009,23(12):1792-1800
The molecular composition of plant residues is suspected to largely govern the fate of their constitutive carbon (C) in soils. Labile compounds, such as metabolic carbohydrates, are affected differently from recalcitrant and structural compounds by soil‐C stabilisation mechanisms. Producing 13C‐enriched plant residues with specifically labeled fractions would help us to investigate the fate in soils of the constitutive C of these compounds. The objective of the present research was to test 13C pulse chase labeling as a method for specifically enriching the metabolic carbohydrate components of plant residues, i.e. soluble sugars and starch. Bean plants were exposed to a 13CO2‐enriched atmosphere for 0.5, 1, 2, 3 and 21 h. The major soluble sugars were then determined on water‐soluble extracts, and starch on HCl‐hydrolysable extracts. The results show a quick differential labeling between water‐soluble and water‐insoluble compounds. For both groups, 13C‐labeling increased linearly with time. The difference in δ13C signature between water‐soluble and insoluble fractions was 7‰ after 0.5 h and 70‰ after 21 h. However, this clear isotopic contrast masked a substantial labeling variability within each fraction. By contrast, metabolic carbohydrates on the one hand (i.e. soluble sugars + starch) and other fractions (essentially cell wall components) on the other hand displayed quite homogeneous signatures within fractions, and a significant difference in labeling between fractions: δ13C = 414 ± 3.7‰ and 56 ± 5.5‰, respectively. Thus, the technique generates labeled plant residues displaying contrasting 13C‐isotopic signatures between metabolic carbohydrates and other compounds, with homogenous signatures within each group. Metabolic carbohydrates being labile compounds, our findings suggest that the technique is particularly appropriate for investigating the effect of compound lability on the long‐term storage of their constitutive C in soils. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
58.
Fractal First-Order Partial Differential Equations 总被引:1,自引:0,他引:1
The present paper is concerned with semi-linear partial differential equations involving a particular pseudo-differential
operator. It investigates both fractal conservation laws and non-local Hamilton–Jacobi equations. The idea is to combine an
integral representation of the operator and Duhamel's formula to prove, on the one hand, the key a priori estimates for the scalar conservation law and the Hamilton–Jacobi equation and, on the other hand, the smoothing effect of
the operator. As far as Hamilton–Jacobi equations are concerned, a non-local vanishing viscosity method is used to construct
a (viscosity) solution when existence of regular solutions fails, and a rate of convergence is provided. Turning to conservation
laws, global-in-time existence and uniqueness are established. We also show that our formula allows us to obtain entropy inequalities
for the non-local conservation law, and thus to prove the convergence of the solution, as the non-local term vanishes, toward
the entropy solution of the pure conservation law. 相似文献
59.
Seydou Yao Giancarlo DellaVentura Cyril Petibois 《Analytical and bioanalytical chemistry》2010,397(6):2079-2089
Asbestos is a fiber causing lung diseases such as asbestosis and mesothelioma. Although the process involving these diseases
remains to be elucidated for developing drugs and treatments, direct consequences of fiber exposure in humans have been clearly
demonstrated. These diseases are first characterized by histological heterogeneity and combine chronic inflammation with fibrosis
and cellular alterations. As a consequence, asbestosis is usually diagnosed at advanced stages of the disease and treatments
are usually inefficient to cure the patients. Here, we review the links established between asbestos fiber chemistry and morphology
with the occurrence of associated lung diseases. Cytological and histological aspects of diseases are described with respect
to current analytical capabilities, notably for microscopy techniques. 相似文献
60.
Cyril Petibois 《Analytical and bioanalytical chemistry》2010,397(6):2051-2065
Combining elemental, chemical, molecular, and morphological imaging information from individual cells with a lateral resolution well below 1?×?1 μm2 is the current technological challenge for investigating the smallest dimensions of living systems. In the race for such analytical performance, several techniques have been successfully developed; some use probes to determine given cellular contents whereas others use possible interactions between cellular matter with light or elements for characterization of contents. Morphological techniques providing information about cell dimensions have, when combined with other techniques, also opened the way to quantitative studies. New analytical opportunities are now being considered in cell biology, combining top-performance imaging techniques, applied to the same biosystem, with microscopy (nm–μm range) techniques providing elemental (micro-X-ray fluorescence, particle-induced X-ray emission, secondary-ion mass spectrometry), chemical (Raman, coherent anti-stokes Raman, Fourier-transform infrared, and near-field), molecular (UV–visible confocal and multiphoton), and morphological (AFM, ellipsometry, X-ray phase contrast, digital holography) information. Dedicated cell-culture methods have been proposed for multimodal imaging in vitro and/or ex vivo. This review shows that in addition to UV–fluorescent techniques, the imaging modalities able to provide interesting information about a cell, with high spatial and time resolution, have grown sufficiently to envisage quantitative analysis of chemical species inside subcellular compartments. 相似文献