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排序方式: 共有77条查询结果,搜索用时 31 毫秒
1.
Raynald Gauvin Eric Lifshin Hendrix Demers Paula Horny Helen Campbell 《Microscopy and microanalysis》2006,12(1):49-64
A new Monte Carlo program, Win X-ray, is presented that predicts X-ray spectra measured with an energy dispersive spectrometer (EDS) attached to a scanning electron microscope (SEM) operating between 10 and 40 keV. All the underlying equations of the Monte Carlo simulation model are included. By simulating X-ray spectra, it is possible to establish the optimum conditions to perform a specific analysis as well as establish detection limits or explore possible peak overlaps. Examples of simulations are also presented to demonstrate the utility of this new program. Although this article concentrates on the simulation of spectra obtained from what are considered conventional thick samples routinely explored by conventional microanalysis techniques, its real power will be in future refinements to address the analysis of sample classifications that include rough surfaces, fine structures, thin films, and inclined surfaces because many of these can be best characterized by Monte Carlo methods. The first step, however, is to develop, refine, and validate a viable Monte Carlo program for simulating spectra from conventional samples. 相似文献
2.
The essential oils from bark and leaves of Cedrelopsis grevei Baill (Ptaeroxylaceae), an aromatic and medicinal plant from Madagascar, are widely used in folk medicine. These two commercially available oils have been examined separately by means of GC-MS. The oil constituents were identified according to their mass spectra and their relative retention indices determined on both polar and non-polar stationary phase capillary columns. A total of 55 compounds have been identified constituting 76.7% (bark) and 91.6% (leaves) of the volatile constituents. Both oils were found to have a similar composition; however the relative percentages of some compounds notably differed. The bark essential oil contained beta-pinene (17.1%), cis-sesquisabinene hydrate (12.8%) and caryophyllene oxide (7.0%) as the main components whereas the leaf essential oil was largely dominated by trans-beta-farnesene (35.6%); beta-pinene (12.8%), cis-sesquisabinene hydrate (9.8%) and ar-curcumene (8.6%) were also present as major components. As far as we know, this is the first report on the Cedrelopsis grevei bark and leaf essential oils which therapeutic properties may be attractive for aromatherapy. 相似文献
3.
Persephone Canonne Raynald Boulanger Bernard Chantegrel 《Journal of heterocyclic chemistry》1989,26(1):113-117
A one-step synthesis of spiro[cycloalkane-1,4′-2H-3′,1-benzoxazin]-2′-ones and spiro[cycloalkane-1,4′-1H-pyrido[2′,3′-d][1,3′]oxazin]-2′-ones, obtained in good yield from the corresponding 1-(o-aminophenyl) and 1-(2′-amino-3′-pyridinyl)cycloalkanols is described using ethyl carbonate in presence of n-butyllithium. 相似文献
4.
S. Della Negra H. Gauvin H. Jungclas Y. Le Beyec M. Lefort 《Zeitschrift für Physik A Hadrons and Nuclei》1977,282(1):65-73
Excitation functions have been drawn for evaporation residues issued from150Gd, a compound nucleus produced either by16O ions on134Ba, or by40Ar on110Pd. Absolute cross sections were measured for145–147Gd,145–147Eu,141m Sm,143m Sm,140m Pm and139m Nd. Complete fusion cross sections have been obtained and compared to calculated estimations based, at low energies, on the simple expressionσ CF=πR Fuss 2 (1?V Fus/E) whereR Fus andV Fus are respectively the distance and the potential for fusion atdV/dr=0. For high energies σCF=πR cr 2 (1?Vcr/E) with the model of critical distanceR cr and critical potentialV cr. Thresholds energies have been determined with a particular care. The analysis of the shape and the width of excitation functions, particularly for the emission of 4 and 5 neutrons, has been carried out and compared to calculated values. The difference between argon and oxygen induced reactions has been attributed to the difference inl population in the entrance channel. 相似文献
5.
A specially designed plasma chamber was constructed to study the operating characteristics of a dc plasma-transferred arc of argon, struck between a fluid convective cathode and a water-cooled anode. The arc voltage increased markedly with arc length and with an increase in the inlet velocity of the argon flow past the cathode tip, and much less with an increase in current. Radiation from the plasma column to the chamber walls and transfer of energy to the anode were the two principal modes of transfer of the arc energy. The former was dominant in the case of long arcs and at high inlet argon velocities. At the anode, the major contribution was from electron transfer, which occurred on a very small area of the anode (~5 mm in diameter). Convective heat transfer from the plasma was somewhat less. In all cases, the arc energy contributions to cathode cooling and to the exit gas enthalpy were small. From total heat flux and radiative heat transfer measurements, it was estimated that the plasma temperature just above the anode was in the range 10,000–12,000 K. Preliminary experiments with an anode consisting of molten copper showed that the arc root was no longer fixed but moved around continuously. The arc was othwewise quite stable, and its operating characteristics differed little from those reported for solid anodes, in spite of the greater extent of metal vaporization. 相似文献
6.
Carmona AT Fuentes J Robina I García ER Demange R Vogel P Winters AL 《The Journal of organic chemistry》2003,68(10):3874-3883
A new route for the preparation of four new indolizidines, (1R,2S,6S,7S,8aS)- and (1R,2S,6R,7R,8aS)-1,2,6,7-tetrahydroxyindolizidine (30 and 32) and (1S,2R,7S,8S,8aR)- and (1S,2R,7R,8R,8aR)-1,2,7,8-tetrahydroxyindolizidine (44 and 46), is reported. The synthesis is based on Knoevenagel homologation of the readily available enantiomerically pure pyrrolidin-carbaldehydes 13 and 37followed by asymmetric dihydroxylation of the subsequent alkenyl pyrrolidines and cyclization of the corresponding imino-octitols. The new indolizidines and their precursors (imino-octitols 20, 25, 26) and indolizidinones 28a and 28b have been tested for inhibitory activities toward 26 glycosidases. The enzymatic inhibition of trans-7-hydroxy-d-(-)-swainsonine (44) toward alpha-mannosidases is similar to that described for trans-7-hydroxy-l-(+)-swainsonine (11b) toward naringinase (alpha-l-rhamnosidase from Penicillium decumbens). 相似文献
7.
Gandelman M Naing KM Rybtchinski B Poverenov E Ben-David Y Ashkenazi N Gauvin RM Milstein D 《Journal of the American Chemical Society》2005,127(43):15265-15272
A new general, synthetically simple, and safe method for the preparation of metal carbene complexes, which is based on diphenyl sulfonium salts as carbenoid precursors, has been developed, and its scope and applications were studied. In general, deprotonation of a sulfonium salt with a base results in a sulfur ylide, which, in turn, reacts with an appropriate metal precursor to give the corresponding metal carbene complex. Thus, starting from benzyldiphenylsulfonium salt, the complexes (PCX)Rh=CHPh (X = P, N) were prepared in quantitative yield. Syntheses of Grubbs' catalyst, (PCy(3))(2)Cl(2)Ru=CHPh, and of Werner's carbene, [Os(=CHPh)HCl(CO)(P(i)Pr(3))(2)], were achieved by this method. Novel trans-bisphosphine Rh and Ir carbenes, ((i)Pr(3)P)(2)(Cl)M=CHPh, which could not be prepared by other known methods, were synthesized by the sulfur ylide approach. The method is not limited to metal benzylidenes, as demonstrated by the preparation of the Ru vinyl-alkylidene, (PCy(3))(2)Cl(2)Ru=CH-CH=CH(2), methoxycarbonyl-alkylidene, (PCy(3))(2)Cl(2)Ru=CH(CO(2)Me), and alkylidene (PCy(3))(2)Cl(2)Ru=CH(CH(3)), (PCy(3))(2)Cl(2)Ru=CH(2) compounds. The problem of recycling of starting materials as well as the issue of facile purification of the product metal carbene complex were addressed by the synthesis of a polymer-supported diarylsulfide, the carrier of the carbenoid unit in the process. Based on the sulfur ylide route, a methodology for the synthesis of metallocarbenes anchored to a polymer via the carbene ligand, using a commercial Merrifield resin, was developed. 相似文献
8.
S. Della Negra H. Gauvin H. Jungclas Y. Le Beyec M. Lefort 《Zeitschrift für Physik A Hadrons and Nuclei》1977,282(1):75-82
The deexcitation of the compound nucleus150Gd formed by156O+134Ba and40Ar+110Pd have been studied. Excitation functions were determined for various exit channels: (HI, × n) withx=3, 4, 5 (HI, pxn) withx=2, 3, 4 (HI, axn) withx=3 and 5. A systematic comparison has been made between these experimental data and the results of evaporation calculation using the ALI CE code. The very good agreement obtained for the total residue cross section disappears completely when a more detailed analysis of the different contributions is performed. Absolute and relative cross sections are not reproduced; excitation functions of each individual channel (HI, 3n), (HI, 4n) etc. ... are not found at the right place in energy. A very preliminary explanation for such a shift towards higher energies is suggested. 相似文献
9.
10.