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1.
Nonlinear Dynamics - Nonlinear flutter of variable stiffness composite plates—using a reduced-order model benefiting from a large-enough number of modes or degrees of freedom—is the... 相似文献
2.
Analysis Mathematica - We introduce and study the k-Hankel Gabor transform. We investigate the localization operators for this transform. In particular, we study their trace class properties and we... 相似文献
3.
Ben Jadi S. El Guerraf A. Bazzaoui E.A. Wang R. Martins J.I. Bazzaoui M. 《Journal of Solid State Electrochemistry》2019,23(8):2423-2433
Journal of Solid State Electrochemistry - Due to their distinctive chemical, electronic, and environmental properties, polypyrrole is used as a blocking barrier for methanol leakage in direct... 相似文献
4.
Claudia Poloni Marc C. A. Stuart Pieter van der Meulen Wiktor Szymanski Ben L. Feringa 《Chemical science》2015,6(12):7311-7318
The external photocontrol over peptide folding, by the incorporation of molecular photoswitches into their structure, provides a powerful tool to study biological processes. However, it is limited so far to switches that exhibit only a rather limited geometrical change upon photoisomerization and that show thermal instability of the photoisomer. Here we describe the use of an overcrowded alkene photoswitch to control a model β-hairpin peptide. This photoresponsive unit undergoes a large conformational change and has two thermally stable isomers which has major influence on the secondary structure and the aggregation of the peptide, permitting the phototriggered formation of amyloid-like fibrils. 相似文献
5.
We consider the problem of estimating a large rank-one tensor u ⊗k ∈ (ℝn)⊗k , k ≥ 3 , in Gaussian noise. Earlier work characterized a critical signal-to-noise ratio λ Bayes = O(1) above which an ideal estimator achieves strictly positive correlation with the unknown vector of interest. Remarkably, no polynomial-time algorithm is known that achieved this goal unless λ ≥ Cn(k − 2)/4 , and even powerful semidefinite programming relaxations appear to fail for 1 ≪ λ ≪ n(k − 2)/4 . In order to elucidate this behavior, we consider the maximum likelihood estimator, which requires maximizing a degree-k homogeneous polynomial over the unit sphere in n dimensions. We compute the expected number of critical points and local maxima of this objective function and show that it is exponential in the dimensions n , and give exact formulas for the exponential growth rate. We show that (for λ larger than a constant) critical points are either very close to the unknown vector u or are confined in a band of width Θ(λ−1/(k − 1)) around the maximum circle that is orthogonal to u . For local maxima, this band shrinks to be of size Θ(λ−1/(k − 2)) . These “uninformative” local maxima are likely to cause the failure of optimization algorithms. © 2019 Wiley Periodicals, Inc. 相似文献
6.
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
7.
Generation of UV laser light by stimulated Raman scattering in D2, D2/Ar and D2/He using a pulsed Nd:YAG laser at 355nm
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A pulsed Nd:YAG laser at 355nm is used to pump Raman cell filled with D_2, D_2/Ar and D_2/He. With adequately adjusted parameters, the maximum photon conversion efficiency of the first-order Stokes light (S_1, 396.796nm) reaches 33.33% in D_2/Ar and the stability of S_1 in pure D_2 is fairly high, the energy drift being less than 10% when the pump energy drifts in the range of 5%. The conversion efficiency and stability, which are functions of the composition and pressure of the Raman medium and the energy of pump laser, are investigated. The result has been used to optimize the laser transmitter system for a differential absorption lidar system to measure NO_2 concentration profiles. 相似文献
8.
Alberto Plaza Sonia Piacente Angela Perrone Arafa Hamed Cosimo Pizza Giuseppe Bifulco 《Tetrahedron》2004,60(52):12201-12209
Stemmosides C and D, two novel pregnane glycosides characterized by an unusual C-17 side chain were isolated from the pericarps of Solenostemma argel. In addition, stemmoside D displays an uncommon 14β proton configuration, apparently being the first pregnane isolated from plants known to have a 15 keto, cis CD ring junction. Their structures have been established by ESIMS and NMR experiments. The relative configuration of the molecules was determined using a strategy based on the simulation of 1H, 13C, and J coupling NMR parameters. DFT calculations of 1H and 13C chemical shifts, and of the 1H homonuclear spin–spin coupling constants were performed with the mPW1PW91 functional using the 6-31G(d,p) basis set on the fully optimized geometries of all the possible stereoisomers. 相似文献
9.
Richard Kotek Kyeong Pang Ben Schmidt Alan Tonelli 《Journal of Polymer Science.Polymer Physics》2004,42(23):4247-4254
Poly(ethylene isophthalate) (PEI) was synthesized for this research with essentially a condensation polymerization of isophthalic acid and ethylene glycol catalyzed by zinc acetate and antimony trioxide. Several samples were obtained, and their characteristics were observed and compared with poly(ethylene terephthalate) (PET). The synthesized PEI samples were chemically identified by 1H NMR. Thermal analysis with differential scanning calorimetry (DSC) yielded results that indicate the samples were primarily amorphous, with a glass‐transition temperature of 55–60 °C. Molecular weights of these PEI samples were also obtained through intrinsic viscosity measurements (Mark–Houwink equation). Molecular weights varied with conditions of the polymerization, and the highest molecular weight achieved was 21,000 g/mol. Finally, the diffusion coefficient, solubility, and permeability of CO2 gas in PEI were measured and found to be substantially lower than in PET, as anticipated from their isomeric chemical structures. This is because in PET the phenyl rings are substituted in the para (1,4) positions, which allows for their facile flipping, effectively permitting gases to pass through. However, the meta‐substituted phenyl rings in PEI do not permit such ring flipping, and thus PEI may be more suitable for barrier applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4247–4254, 2004 相似文献
10.