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排序方式: 共有49条查询结果,搜索用时 187 毫秒
1.
A. Malki J. P. Coffin G. Guillaume F. Jundt K. Krishan F. Rami P. Wagner P. Fintz M. Zahar M. Gonin B. Heusch M. Ohta B. Rastegar D. Rebreyend F. Merchez J. Mistretta S. Kox 《Zeitschrift für Physik A Hadrons and Nuclei》1991,339(2):283-292
In an attempt to separate preequilibrium and thermalised emissions of light particles in low impact parameter heavy-ion collisions, the40Ar+24Mg reaction has been studied at 27.5 MeV/nucleon. Exclusive measurements have permitted us to examine, in some detail, heavy fragments and charged particles (p, d, t,-particle). The fragments recognized as evaporation residues have been selected and, due to inverse kinematic conditions, the related preequilibrium and statistical emissions of light particles resulting from incomplete fusion reaction appear to be distinguishable to a fair extent. This separation is fully supported by Monte Carlo calculations. Some experimental characteristics of the light particles have been examined and compared to the predictions of dynamical calculations. These calculations, associating a preequilibrium (interpreted as prompt emitted particles) model with a statistical-decay model, follow the evolution of the collision from the point of contact between the projectile and the target to the final evaporation-residue formation on an event by event basis. The predictions of these calculations have been compared to experimental data and satisfactory agreement is achieved for fragment-mass distribution, proton-energy spectra, and proton-angular distribution. 相似文献
2.
Olenik ID Kim MW Rastegar A Rasing T 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):3120-3128
Surface optical second-harmonic generation measurements were used to determine the change in the surface density and the surface orientational order parameter of the trans-cinnamoyl side groups of unidirectionally photopolymerized poly(vinyl cinnamate) (PVCN) films. The observed surface features were compared to the bulk properties of the films, which were probed by their UV absorption spectra and birefringence measurements. We found that the surface and the bulk photoreaction kinetics of the trans cinnamoyl side groups of the PVCN are very similar. The two photoreaction processes (trans-cis photoisomerization and photo-induced cross linking) appear to affect the linear and nonlinear optical properties of the polymer differently. This may explain the discrepancy between the birefringence and the azimuthal anchoring force of the unidirectionally photopolymerized PVCN. 相似文献
3.
Experiments by Gittings, Bandyopadhyay and Durian (Europhys. Lett. 65, 414 (2004)) demonstrate that light possesses a higher probability to propagate in the liquid phase of a foam due to total
reflection. The authors term this observation photon channelling which we investigate in this article theoretically. We first
derive a central relation in the work of Gitting et al. without any free parameters. It links the photon's path-length fraction f in the liquid phase to the liquid fraction ɛ. We then construct two-dimensional Voronoi foams, replace the cell edges by
channels to represent the liquid films and simulate photon paths according to the laws of ray optics using transmission and
reflection coefficients from Fresnel's formulas. In an exact honeycomb foam, the photons show superdiffusive behavior. It
becomes diffusive as soon as disorder is introduced into the foams. The dependence of the diffusion constant on channel width
and refractive index is explained by a one-dimensional random-walk model. It contains a photon channelling state that is crucial
for the understanding of the numerical results. At the end, we shortly comment on the observation that photon channelling
only occurs in a finite range of ɛ. 相似文献
4.
Saeed?Rastegar Naser?MohammadiEmail author Reza?Bagheri 《Colloid and polymer science》2004,283(2):145-153
The morphology of a quaternary blend containing a diglycidyl ether of bisphenol-A (DGEBA), a thermoplastic modifier (PMMA), a phase-separating curing agent (diaminodiphenylmethane, DDM), and a non-phase-separating curing agent (methylenebis(3-chloro-2,6-diethylaniline, MCDEA) was studied as a function of volume fraction of the thermoplastic modifier and fractional concentration of the curing agents in their mixture. It was found that using mixtures of curing agents a co-continuous morphology could be obtained at PMMA concentrations as low as 2.5 volume percent. Using FTIR spectroscopy it was proved that specific interactions are present between PMMA and individual amine curing agents. On the other hand, there was no detectable specific interaction between PMMA and DGEBA. By analyzing the micro-indentation hardness data of the cryo-fractured samples and putting forward the intrinsic hardness concept, it was proposed that the co-continuous morphology is inherently more effective than the other morphologies in changing the mechanical properties of the above-mentioned multi-component blends. 相似文献
5.
M. Torshabi M. Badiee M. A. Faramarzi H. Rastegar H. Forootanfar E. Mohit 《Chemistry of Natural Compounds》2011,47(1):59-63
Fungi have proved to be powerful biocatalysts in steroid biotransformations. In the present study, the soil isolate filamentous
fungus Mucor racemosus was applied for bioconversion of methyltestosterone (1), an anabolic steroid, in a five-day fermentation. Microbial metabolites were purified chromatographically and identified
on the basis of their spectral data as 7α-hydroxymethyltestosterone (2), 15α-hydroxymethyltestosterone (3), and 12,15α-dihydroxymethyltestosterone (4). Observed modifications were hydroxylations at C-7α, C-12, and 15α-positions. Best fermentation condition for production of hydroxylated derivatives was found to be 25°C at 150 rpm for 5 days
with a substrate concentration of 1 mg/mL. 相似文献
6.
In order to develop a sensor for the detection of toxic N2O molecules, the interaction of pristine and Aldoped BN nanosheets with an N2O molecule was investigated using density functional theory calculations. It was found that unlike the pristine sheet, the Al-doped sheet can effectively interact with the N2O molecule so that its electronic properties and conductivity are dramatically changed. Webelieve that replacing a B atom of the BN sheet with an Al atom may be a good strategy for improving the sensitivity of these nanosheets toward N2O, which cannot be trapped and detected by the pristine sheet. 相似文献
7.
M. Zahar A. Malki M. Bozin P. Wagner F. Rami J. P. Coffin G. Guillaume F. Jundt P. Fintz B. Rastegar D. Rebreyend F. Merchez J. Mistretta S. Kox 《Zeitschrift für Physik A Hadrons and Nuclei》1991,339(4):465-473
Protons, deuterons, tritons,α-particles and Li have been studied in coincidence with evaporation residues produced at low impact parameter for the40Ar(1100 MeV)+13C reaction. Experimental characteristics of the light particle — heavy residue correlations, and among them an effect of left-right asymmetry, are analyzed and discussed in some detail on the basis of Monte Carlo simulations. This reaction appears to be governed by an incomplete fusion process. Due to transverse emission of preequilibrium particles, the compound nuclei associated with light-particle-evaporation-residue coincidence events recoil at a non-zero degree lab. angle with some dispersion around this direction. When these effects are introduced into statistical decay calculations, it is then possible to reproduce various experimental results and to understand features like the asymmetry effect. Discrimination of light particles of preequilibrium and of evaporative origin appears possible. 相似文献
8.
E. A. Maier M. L. Sargentini-Maier F. Rastegar C. Christophe C. Ruch R. Heimburger M. J. F. Leroy 《Fresenius' Journal of Analytical Chemistry》1988,331(1):58-60
Summary The energy dispersive X-ray fluorescence spectrometer (EDXRF) developped together with the Siemens Company (FRG) allows to perform rapid multi-elemental analysis of biological fluids without pretreatment of the samples. The performance of this technique and its features are reported in two different fields: blood analysis and pulmonary investigations. Blood and plasma analysis were performed for more than 2500 patients and a statistical treatment of the data lead to the normal concentrations of trace elements Se, Rb, Cu, Zn, Fe, Ca, Br, K. Toxic elements such as Hg or Pb and also drugs like Au and Pt compounds can be detected even after a long period after treatment. To illustrate the performance of the spectrometer we report the influence of Cis-Pt treatment on the trace element concentrations in plasma of patients with anemia.The EDXRF spectrometry was also used to investigate the inorganic composition of the broncho-alveolar lavage fluids. After determination of the normal concentration range, it was possible to characterize some typical pulmonary diseases due to occupational exposure. Some examples of detected pneumoconiosis and for some patients the presence in the alveoli of elements due to special medication (Amiodarone, Aurothiopropanol-sulfonate) are mentioned.Other fields are being investigated such as: follow-up of Mn dependent enzymes in neuronal and glial cells in culture; origin of lead in dental tissues or composition of lyophilized food powders. They will be briefly discussed.
Energie-dispersive Röntgenfluorescenz in der biomedizinischen Analyse相似文献
9.
MF Miller IA Franchi AS Sexton CT Pillinger 《Rapid communications in mass spectrometry : RCM》1999,13(13):1211-1217
The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd. 相似文献
10.
CM Silva MF Duarte ML Mira MH Florêncio K Versluis AJ Heck 《Rapid communications in mass spectrometry : RCM》1999,13(12):1098-1103
Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd. 相似文献