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排序方式: 共有356条查询结果,搜索用时 15 毫秒
71.
The effect of repeated cycles of water adsorption/desorption on the structural stability of ordered mesoporous silica SBA-15 is studied by small-angle x-ray scattering (SAXS). In?situ sorption measurements are conducted using a custom-built sorption apparatus in connection with a laboratory SAXS setup. Two striking irreversible changes are observed in the sorption isotherms as derived from the integrated SAXS intensity. First, the capillary condensation pressure shifts progressively to lower relative pressure values with increasing number of sorption cycles. This effect is attributed to chemisorption of water at the silica walls, resulting in a change of the fluid-wall interaction. Second, the sorption cycles do not close completely at vanishing vapour pressure, suggesting that progressively more water remains trapped within the porous material after each cycle. This effect is interpreted to be the result of an irreversible collapse of parts of mesopores, originating from pore wall deformation due to the large Laplace pressure of water acting on the pore walls at capillary condensation and capillary evaporation. 相似文献
72.
A quantitative method, using LC/ESI-MS(n) with a quadrupole linear ion trap mass analyzer, has been developed for the analysis of ipratropium cation in horse plasma and urine. The method applies solid-phase extraction with WCX cartridges for plasma and MM2 cartridges for urine, prior to analysis by LC/ESI-MS(n). The efficiency of extraction combined with the sensitivity and the selectivity of MS(n) allows for the quantification of ipratropium cation at picogram per milliliter levels. The analytical capabilities of the method have been successfully checked by the quantitative analysis of ipratropium cation in post-administration samples collected from horses treated by nebulization. 相似文献
73.
Balsells JM Jurado-Navas A Paris JF Castillo-Vázquez M Puerta-Notario A 《Optics letters》2012,37(4):719-721
In this paper, the performance of the variable weight multiple pulse-position modulation (MPPM) coding technique in an atmospheric optical communication environment under gamma-gamma optical scintillation is analyzed, proposing a closed-form expression for the average bit error rate (BER). This study is based on a hyperexponential fitting of the conditional BER in absence of turbulence fluctuations, leading to closed-form expressions that characterize the behavior of this nonlinear coding scheme. Finally, conditional and average BER expressions proposed here are corroborated with Monte Carlo simulations results. 相似文献
74.
The effects of aluminium substitution in In2S3 are investigated by single crystal XRD, 27Al NMR spectroscopy, and DFT calculations. 相似文献
75.
Vladimir Vinogradov Richard B. Paris Olga Yanushkevichiene 《Lithuanian Mathematical Journal》2012,52(4):444-461
We derive new Wright-function representations for the densities of the generating measures of most representatives of the power-variance family of distributions. For all members of this family, we construct new saddlepoint-type approximations having an arbitrary fixed number of refining terms. To this end, we derive new, ??exponentially small,?? Poincaré series for a subclass of the Wright functions whose coefficients are expressed in terms of the Zolotarev polynomials. 相似文献
76.
A. Gizon J. Genevey C.F. Liang P. Paris D. Barnéoud J. Inchaouh I. Penev A. Plochocki 《The European Physical Journal A - Hadrons and Nuclei》2001,12(3):309-316
An investigation of low-lying energy levels of 130Pr and 130Ce has been made via β-decay. The radioactive parent nuclei were produced via 94,96Mo + 40Ca reactions at 6.8 MeV/nucleon and transported by a He-jet system. Gamma-γ-t, γ-X-t, γ-e--t coincidence measurements were performed. Internal conversion coefficients have been measured with a magnetic spectrometer.
The new β-decay half-life of 130Nd has been determined to be 21(3) s. A partial level scheme of 130Pr at low-spin has been constructed. The β-decay of 130Pr to 130Ce suggests the existence of three β-instable isomeric states in 130Pr, while only one half-life T
1/2 = 40(4) s has been measured. Based on the present work and low-lying excited states in neighbouring odd-mass nuclei, the
spins and parities of isomeric states in 130Pr are proposed to be 2+, (4,5)+ and (7,8±). The ground state in 130Pr is still undetermined.
Received: 20 August 2001 / Accepted: 6 November 2001 相似文献
77.
C. F. Liang P. Paris M. G. Porquet J. Obert J. C. Putaux 《Zeitschrift für Physik A Hadrons and Nuclei》1985,320(4):695-696
A new 12s activity has been produced via the35C1+112Sn reaction at 191 MeV and ascribed to the143Tb EC/β+ decay. A decay scheme is derived from γ-γ and γ-X-ray coincidence measurements. 相似文献
78.
Low molecular weight venom constituents of the spider Scodra griseipes have been derivatized using bis(trimethylsilyl)-trifluoroacetamide and pentafluoropropionic anhydride. Examination of these derivatives by coupled gas chromatography/mass spectrometry using electron ionization or ammonia- or isobutane-chemical ionization allows their structural identification. Comparisons have also been made with retention time and mass spectra of the pure compounds. Four acids: phosphoric, lactic, citric, gamma-aminobutyric (neurotransmitter) and four basic biogenic amines: putrescine, cadaverine, spermidine and spermine have been found. 相似文献
79.
80.