排序方式: 共有43条查询结果,搜索用时 15 毫秒
1.
Catalytic properties of silica-supported heteropolyacids (HPA) in a mechanical mixture with reduced Me-Ce oxides (Me = Ni,
Pd) in n-hexane isomerization are studied. The role of each component of the mixed oxides (Ce and, typically, Ni and Pd) and their
optimum content has been illuminated: cerium is not only beneficial for eliminating or preventing coke deposition but is also
effective for maintaining the Keggin structure of the highly-organized HPA during the reaction and probably allows a better
dispersion of the second metal species. Nickel and palladium, present as Ni0 and Pd0, reinforce the activation of the alkane, which is difficult to obtain by means of a direct attack by an acid, and, thus,
enhance noticeably the activity of the catalyst. The best mechanical mixtures are obtained with 30–70 wt % NiCeO-HPW/SiO2 and 50–50 wt % Pd0.1CeO-HPW/SiO2. These mixtures have the highest efficiency for a Ni/(Ni + W) atomic ratio of 0.66 and a Pd/(Pd + W) ratio of 0.40, respectively.
Finally, the conversion of n-hexane is in the order HPW > HSiW > HBW, which seems to be consistent with the order of their acid strength as per the literature,
but the isomerization selectivity appears to be slightly higher on HSiW.
Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 1, pp. 24–28.
The text was submitted by the authors in English. 相似文献
2.
A rapid and simple reversed-phase (using muBondapak C18 as the stationary phase) liquid chromatographic method with fluorimetric detection is described for the quantitation of 5-hydroxytryptamine in whole blood. The rapidity and simplicity of the method are explained by the absence of a pretreatment. 5-Fluoro-dl-tryptophan was used as internal standard. The mobile phase was 0.01 M phosphate buffer (pH 4.5) with 0.0025 M 1-heptanesulfonic acid and 20% methanol. The detection wavelength were 302 nm for excitation and 340 nm for emission. Analysis time was 10 min with retention times for 5-hydroxytryptamine of 9 min and for 5-fluoro-dl-tryptophan of 7 min. This method is proposed for biological exploration of psychiatric disorders involving 5-hydroxytryptamine and would be useful for tryptophan. 相似文献
3.
Abolhassan Mohammadi Tayeb Golanbari Haidar Sheikhahmadi Kosar Sayar Lila Akhtari M. A. Rasheed Khaled Saaidi 《中国物理C(英文版)》2020,44(9):095101-095101-13
In this study, the scenario of a two-component warm tachyon inflation is considered, where the tachyon field plays the role of the inflaton by driving the inflation. During inflation, the tachyon scalar field interacts with the other component of the Universe, which is assumed to be photon gas, i.e., radiation. The interacting term contains a dissipation coefficient, and the study is modeled based on two different and familiar choices of the coefficient that were studied in the literature. By employing the latest observational data, the acceptable ranges for the free parameters of the model are obtained. For any choice within the estimated ranges, there is an acceptable concordance between the theoretical predictions and observations. Although the model is established based on several assumptions, it is crucial to verify their validity for the obtained values of the free parameters of the model. It is found that the model is not self-consistent for all values of the ranges, and for some cases, the assumptions are violated. Therefore, to achieve both self-consistency and agreement with the data, the parameters of the model must be constrained. Subsequently, we consider the recently proposed swampland conjecture, which imposes two conditions on the inflationary models. These criteria rule out some inflationary models; however, warm inflation is among those that successfully satisfy the swampland criteria. We conduct a precise investigation, which indicates that the proposed warm tachyon inflation cannot satisfy the swampland criteria for some cases. In fact, for the first case of the dissipation coefficient, in which, there is dependency only on the scalar field, the model agrees with observational data. However, it is in direct tension with the swampland criteria. Nevertheless, for the second case, wherein the dissipation coefficient has a dependency on both the scalar field and temperature, the model exhibits acceptable agreement with observational data, and suitably satisfies the swampland criteria. 相似文献
4.
This paper deals with the diffusion approximation of a semiconductor Boltzmann–Poisson system. The statistics of collisions we are considering here, is the Fermi–Dirac operator with the Pauli exclusion term and without the detailed balance principle. Our study generalizes, the result of Goudon and Mellet [11], to the multi-dimensional case. 相似文献
5.
Tanguy Pier Khalid Kandoussi Claude Simon Nathalie Coulon Tayeb Mohammed-Brahim Hervé Lhermite 《Journal of Non》2008,354(19-25):2300-2304
Microcrystalline silicon (μc-Si) films have been deposited on PDMS as well as on PEN substrate. Excimer laser annealing was used to improve the crystalline structure and so to obtain high mobility TFTs. The effect of the laser annealing on the crystalline structure of silicon films is studied using different characterization techniques and discussed. Mobility values of 60 cm2/V s with PDMS and 46 cm2/V s with PEN are obtained. 相似文献
6.
Olivier Bonnaud Tayeb Mohammed-Brahim 《Applied Physics A: Materials Science & Processing》2009,96(1):259-269
This paper is a review of technological process evolution associated to electrical performance improvement of silicon-based
thin-film transistors (TFTs) that were performed mainly in the GM/IETR laboratory. The main objective in agreement with the
fields of applications is to fabricate TFTs at a temperature low enough to be compatible with the substrates, glass substrates
in a first place and flexible substrates in a second one, which implies several approaches. In fact, the electrical properties
of the TFTs, mainly field-effect mobility of carriers in the channel, I
on/I
off drain current ratio, and subthreshold slope, are strongly dependent on the quality and the nature of the channel material,
on the material quality and thus on the density of states at the interface with the gate insulator, and on the quality of
the gate insulator itself. All the improvements are directly linked to all these aspects, which means an actual combination
of the efforts. For the glass substrate, compatible technology processes such as deposition techniques, or solid phase, or
laser crystallizations of active layers were studied and compared. The paper details all these approaches and electrical performances.
In addition, some results about the use of a silicon–germanium compound as channel active layer and airgap transistors for
which the insulator is released, complete the presentation of the evolution of the silicon-based TFTs during the last twenty
years. 相似文献
7.
Mahdi Sadeghi Zeanab Ansari Tayeb Kakavand 《Journal of Radioanalytical and Nuclear Chemistry》2012,293(1):7-12
The radionuclide vanadium-48 (T 1/2?=?16?d, ?? +=?49.5?%) could be employed to positron emission tomography. In this Study, 48V excitation function for the nat/49/48Ti(p,x)48V and the 48Ti(d,2n)48V nuclear reactions were calculated by ALICE/ASH code. Then recommended thickness of the targets according to the SRIM-2010 code was calculated; consequently, the theoretical integral yields were computed for all reactions by the computer software. As a result, the 48Ti(p,n)48V reaction was determined as the best reaction. Ti target was prepared by sedimentation method to produce 48V throughout accelerator proton bombardment. 相似文献
8.
The synthesis of methyl 14α-methyl-15-oxo-5β-chol-8-en-24-oate derivatives from cholic acid is described, as are the spectroscopic data of the various intermediates. A route to tetracyclic triterpene acids related to polyporenic acid is thus opened. 相似文献
9.
Homogenization and Hydrodynamic Limit for Fermi‐Dirac Statistics Coupled to a Poisson Equation
下载免费PDF全文
![点击此处可从《纯数学与应用数学通讯》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper deals with the diffusion approximation of a Boltzmann‐Poisson system modeling Fermi‐Dirac statistics in the presence of an extra external oscillating electrostatic potential. Here we extend the analysis done in [19] to the case of a nonlinear collision operator. In addition to the averaging lemma and control from entropy dissipation used in [19], here we use two‐scale Young measures and renormalization techniques to prove the convergence. This result rigorously justifies the formal analysis of [3]. © 2015 Wiley Periodicals, Inc. 相似文献
10.
S. Guenneau S. Anantha Ramakrishna S. Enoch Sangeeta Chakrabarti G. Tayeb B. Gralak 《Photonics and Nanostructures》2007,5(2-3):63-72
Negative refractive index materials are known to be able to support a host of surface plasmon states for both polarizations of light. This makes possible unique effects such as a perfect lens. Checkerboards consisting of alternating cells of positive and negative refractive index represent a very singular situation in which the density of modes diverges at the corners. This raises the question as to whether such effects will still be observed in a real dissipative system of finite size. We have considered several aspects of such structures including these and symmetry aspects (rectangular against triangular checkerboards). We have also studied silver checkerboards whose transverse extent is finite. Negative refractive index checkerboards bring new electromagnetic paradigms both through the intriguing possibilities they appear to offer, and the challenges they present to our understanding of the diffraction process. Most intriguing of all is the possibility of a triangular checkerboard lens whose resolution is limited not by wavelength, but only by the losses in the constituent materials, while a ray picture suggests it behaves as a perfect mirror. The resolution of this lens increases without limit as the losses tend to zero as shown by the generalized lens theorem. We finally show that light confinement can be achieved to certain extent using dielectric triangular photonic crystal (PC) checkerboards displaying the all-angle-negative-refraction (AANR) within the Bragg regime in p polarization. Effectively even a single rectangular or triangular PC can act as an open resonator that confines light in its neighborhood. This cloaking effect has been previously observed in PC slabs displaying the AANR effect. We show that the cloaking is enhanced for three triangular PC wedges sharing a vertex and further improved for 12 triangular PC wedges arranged in a checkerboard fashion. 相似文献