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41.
Multiwall carbon nanotubes (MWNTs) were synthesized in supercritical toluene at 600 degrees C and approximately 12.4 MPa using ferrocene, Fe, or FePt nanocrystals as growth catalysts. Toluene serves as both the carbon source for nanotube formation and the solvent. In contrast to vapor-phase synthetic routes, the supercritical solvent provides high precursor concentration and a homogeneous reaction environment with dispersed growth catalyst particles. Both carbon filaments and MWNTs are produced by this approach, and a growth mechanism is proposed to explain the factors that determine the nanotube versus filament morphology. The plasmon energies of the pi and pi + sigma valence electrons were measured using electron energy-loss spectroscopy (EELS) of individual carbon fibers and MWNTs as a characterization tool to complement the imaging data obtained from electron microscopy. 相似文献
42.
Buldygin Valery Utzet Frederic Zaiats Vladimir 《Statistical Inference for Stochastic Processes》2004,7(1):1-34
The problem of estimation of an unknown response function of a time-invariant continuous linear system is considered. Discrete-time sample input–output cross-correlograms are taken as estimates of the response function. The inputs are supposed to be zero-mean stationary Gaussian processes close, in some sense, to a white noise. Both asymptotic normality of finite-dimensional distributions of the estimates and their asymptotic normality in spaces of continuous functions are studied. Our basic tool is a new integral representation for cumulants of the estimate as a finite sum of integrals involving cyclic products of kernels. Some inequalities for these integrals are obtained and their asymptotic behaviour is studied. 相似文献
43.
Samira Ouardad Sergei V. Kostjuk François Ganachaud Judit E. Puskas Alain Deffieux Frederic Peruch 《Journal of polymer science. Part A, Polymer chemistry》2011,49(23):4948-4954
The polymerization of isoprene initiated by dimethylallyl alcohols (DMAOH) in the presence of Lewis acids (LAs) as coinitiators has been selected as a potential model of the proposed cationic mechanisms involved in natural rubber (NR) biosynthesis. In view to investigate the activation/ionization mechanism of the allyl alcohol chain terminus (PIAllOH), which was shown to exist in NR, different isomers of DMAOH were used as simple models of polyisoprene chain‐end structures in the presence of tris(pentafluorophenyl)borane (BLA) as a LA. It is shown that cationation of 3,3‐DMAOH by BLA proceeds by direct OH abstraction. However, this process is strongly retarded in the presence of 2,6‐di‐tert‐butylpyridine (dtBP), due to the formation of different BLA complexes, one with 3,3‐DMAOH, active for cationation, and a dormant one involving its ionized form 3,3‐DMAO?. The monomer generated in situ by ionization/proton elimination steps subsequently adds on the primary allylic carbocation form, then resulting in the formation of oligoisoprenes, whereas the tertiary carbocation form of the allylic carbocation yields exclusively to proton elimination and isoprene formation, a possible mechanism of chain‐end termination. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011. 相似文献
44.
We present a general result of transverse nonlinear instability of 1d solitary waves for Hamiltonian PDE's for both periodic or localized transverse perturbations. Our main structural assumption is that the linear part of the 1-d model and the transverse perturbation “have the same sign”. Our result applies to the generalized KP-I equation, the Nonlinear Schrödinger equation, the generalized Boussinesq system and the Zakharov–Kuznetsov equation and we hope that it may be useful in other contexts. 相似文献
45.
Frederic Y. M. Wan Hubertus J. Weinitschke 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1987,38(1):79-91
Summary The method of matched asymptotic expansions is used to describe finite axisymmetric deformations of two thin elastic membrane problems: a circular membrane with a small radial traction at the edge, an annular membrane with a small circular hole at the center. In both problems, the surface load is assumed to be an axial pressure. There is a boundary layer at the outer edge in the first problem, and at the hole in the second problem.
Zusammenfassung Mit Hilfe der in der singulären Störungsrechnung benutzten Methode einer inneren und äußeren asymptotischen Entwicklung werden endliche, axialsymmetrische Deformationen bei zwei Membranproblemen beschrieben: eine dünne elastische Kreismembran mit kleiner radialer Zugspannung am Rande, und eine Kreisringmembran mit einem kleinen konzentrischen Loch. In beiden Problemen wird die Belastung als ein axial gerichteter Oberflächendruck angenommen. Im ersten Problem zeigt die Lösung am äußeren Rand Grenzschichtverhalten, welches im zweiten Problem am Lochrand vorliegt.相似文献
46.
Fluorine occupies an original and strategic position in modern optics. The F2 excimer lasers are unrivaled sources of deep UV light for semiconductors, microphotolithography and micromachining which has brought on the development of single crystal calcium fluoride optics. Due to the weak polarisability of the fluoride ion, fluoride materials have low refractive index suitable for thin film antireflective coatings specially in IR optics. Transparent magnesium fluoride ceramics, prepared by fine grains hot pressing, are transparent in the mid IR where the transparency windows of the atmosphere are located. They are used as IR domes for missiles guidance. Fluoride glasses when elaborated as optical fibers or channel waveguides and when doped with appropriate lanthanides, are original optical devices for laser operations lying from the mid IR to the UV region where light emission is characterized by up-conversion phenomena. The same devices have also found industrial applications in telecommunications as a new generation of optical amplifiers operating in the ultra-transparency window of the silica fiber. 相似文献
47.
Ohne Zusammenfassung 相似文献
48.
The design and testing of kinetically-appropriate operando spectroscopic cells for investigating heterogeneous catalytic reactions 总被引:1,自引:0,他引:1
Meunier FC 《Chemical Society reviews》2010,39(12):4602-4614
This tutorial review discusses some of the current designs of reaction cells used for operando spectroscopy (X-ray absorption, UV-vis, Raman, transmission FTIR and DRIFTS) and the relation to the apparent reaction kinetics. Beam effects, the control of the catalyst bed temperature and bed by-pass are some of the potential problems that may lead to flawed activity measurements. Finally, four examples are given in which a good agreement was obtained between the activity of a powdered catalyst measured in a conventional reactor and in a spectroscopic cell. It is proposed that such comparison between reactors should become a standard procedure, to ensure the correctness of the data collected over typically non-ideal spectroscopic reaction cells. 相似文献
49.
Saoussen Turki Atef Ayed Néjib Chalghoumi Frederic Weekers Philippe Thonart Héla Kallel 《Applied biochemistry and biotechnology》2010,160(5):1371-1385
Yarrowia lipolytica LgX64.81 is a non-genetically modified mutant that was previously identified as a promising microorganism for extracellular
lipase production. In this work, the development of a fed-batch process for the production of this enzyme in this strain was
described. A lipolytic activity of 2,145 U/mL was obtained after 32 h of batch culture in a defined medium supplemented with
10 g/L of tryptone, an enhancer of lipase expression. To maximize the volumetric productivity, two different fed-batch strategies
had been investigated. In comparison to batch process, the intermittent fed-batch strategy had not improved the volumetric
lipase productivity. In contrast, the stepwise feeding strategy combined with uncoupled cell growth and lipase production
phases resulted in a 2-fold increase in the volumetric lipase productivity, namely, the lipase activity reached 10,000 U/mL
after 80 h of culture. Furthermore, this lipase was purified to homogeneity by anion exchange chromatography on MonoQ resin
followed by gel filtration on Sephacryl S-100. This process resulted in an overall yield of 72% and a 3.5-fold increase of
the specific lipase activity. The developed process offers a great potential for an economic production of Lip2 at large scale
in Y. lipolytica LgX64.81. 相似文献
50.
Briggs BN McMillin DR Todorova TK Gagliardi L Poineau F Czerwinski KR Sattelberger AP 《Dalton transactions (Cambridge, England : 2003)》2010,39(47):11322-11324
The emission spectra of the solids [n-Bu(4)N](2)Tc(2)X(8) (X = Cl, Br) have been investigated at room temperature and 77 K. In each case, the emission originates in the (1)δ-δ* excited state, as with the rhenium homologues, but has a shorter lifetime. 相似文献