排序方式: 共有35条查询结果,搜索用时 15 毫秒
11.
M Pattabiraman G Rangarajan Kwang-Yong Choi P Lemmens G Guentherodt G Balakrishnan DMcK Paul MR Lees 《Pramana》2002,58(5-6):1013-1017
We report polarized Raman scattering in single crystals of Nd0.7Sr0.3MnO3. The temperature dependence of the MnO6 octahedral bending and stretching modes observed in the XX spectra points to the existence of local lattice distortions,
possibly polarons. The XY spectra have been analyzed using a collision-dominated model, which allows the extraction of the
carrier scattering rate. 相似文献
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Beulen MW Bugler J de Jong MR Lammerink B Huskens J Schonherr H Vancso GJ Boukamp BA Wieder H Offenhauser A Knoll W van Veggel FC Reinhoudt DN 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(7):1176-1183
We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of alpha-, beta-, and gamma-cyclodextrins. Monolayers of these cyclodextrin adsorbates were characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM). The differences in thickness and polarity of the outerface of the monolayers were measured by electro-chemistry and wettability studies. On average about 70% of the sulfide moieties were used for binding to the gold, as measured by XPS. Tof-SIMS measurements showed that the cyclodextrin adsorbates adsorb without any bond breakage. AFM measurements revealed for beta-cyclodextrin monolayers a quasi-hexagonal lattice with a lattice constant of 20.6 A, which matches the geometrical size of the adsorbate. The alpha-cyclodextrin and gamma-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2,6-TNS) and the highly ordered monolayers of heptapodant beta-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a beta-cyclodextrin monolayer and 1,8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations (< or = 5 microM). The association constant for the binding of 1,8-ANS (K = 289,000 +/- 13,000M-1) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the beta-cyclodextrin strongly decreases the binding. 相似文献
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The needs for automated assistance in the simulation task are undeniable. The size and complexity of current modelling efforts far exceed the bounds considered challenging only a decade ago. A research prototype of a simulation model development environment (SMDE) has been developed to provide an integrated and comprehensive collection of computer-based tools to (1) offer cost-effective, integrated and automated support of model development throughout its entire life cycle, (2) improve the model quality by effectively assisting in the quality assurance of the model, (3) significantly increase the efficiency and productivity of the project team, and (4) substantially decrease the model development time. The prototype SMDE is composed of four layers: (0) hardware and operating system, (1) kernel SMDE, (2) minimal SMDE, and (3) SMDEs. Currently, a SUN 3/160 colour computer workstation and the UNIX operating system constitute layer 0, upon which an advanced prototype SMDE is being developed. The objectives of this paper are to: (1) describe the current state of research on simulation support environments; (2) use the SMDE research prototype as an example for describing concepts and principles employed, experiences gained, and guidelines (potential principles) derived in the design and creation of the prototype; and (3) identify and speculate on future research directions. 相似文献
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Carson W. Reed Mark G. Fulton Kellie D. Nance Craig W. Lindsley 《Tetrahedron letters》2019,60(10):743-745
This communication details the first total synthesis of the 13-membered macrolide, (?)-Melearoride A, as well as unnatural (+)-Melearoride A. The synthesis features a concise 13 step synthesis (11 steps longest linear sequence) that offers flexible stereo-control and multiple opportunities for unnatural analog synthesis to delve into antifungal SAR. The route features a cuprate addition, an Evans asymmetric alkylation, and a ring-closing metathesis (RCM) to close the 13-membered macrocyclic core. 相似文献
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The propagation of an explosive blast wave containing inert metal particles is investigated numerically using a robust two-phase
methodology with appropriate models to account for real gas behavior, inter-phase interactions, and inter-particle collisions
to study the problem of interest. A new two-phase Eulerian–Lagrangian formulation is proposed that can handle the dense nature
of the flow-field. The velocity and momentum profiles of the gas and particle phases are analyzed and used to elucidate the
inter-phase momentum transfer, and its effect on the impulsive aspects of heterogeneous explosive charges. The particles are
found to pick up significant amounts of momentum and kinetic energy from the gas, and by virtue of their inertia, are observed
to sustain it for a longer time. The impulse characteristics of heterogeneous explosives are compared with a homogeneous explosive
containing the same amount of high explosive, and it is observed that the addition of solid particles augments the impulsive
loading significantly in the near-field, and to a smaller extent in the far-field. The total impulsive loading is found to
be insensitive to the particle size added to the explosive charge above a certain cut-off radius, but the individual impulse
components are found to be sensitive, and particles smaller than this cut-off size deliver about 8% higher total impulse than
the larger ones. Overall, this study provides crucial insights to understand the impulsive loading characteristics of heterogeneous
explosives. 相似文献
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A new robust numerical methodology is used to investigate the propagation of blast waves from homogeneous explosives. The
gas-phase governing equations are solved using a hybrid solver that combines a higher-order shock capturing scheme with a
low-dissipation central scheme. Explosives of interest include Nitromethane, Trinitrotoluene, and High-Melting Explosive.
The shock overpressure and total impulse are estimated at different radial locations and compared for the different explosives.
An empirical scaling correlation is presented for the shock overpressure, incident positive phase pressure impulse, and total
impulse. The role of hydrodynamic instabilities to the blast effects of explosives is also investigated in three dimensions,
and significant mixing between the detonation products and air is observed. This mixing results in afterburn, which is found
to augment the impulse characteristics of explosives. Furthermore, the impulse characteristics are also observed to be three-dimensional
in the region of the mixing layer. This paper highlights that while some blast features can be successfully predicted from
simple one-dimensional studies, the growth of hydrodynamic instabilities and the impulsive loading of homogeneous explosives
require robust three-dimensional investigation. 相似文献
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A new approach to variable selection in least squares problems 总被引:9,自引:0,他引:9
The title Lasso has been suggested by Tibshirani (1996) as acolourful name for a technique of variable selection which requiresthe minimization of a sum of squares subject to an l1 bound on the solution. This forces zero components in the minimizingsolution for small values of . Thus this bound can functionas a selection parameter. This paper makes two contributionsto computational problems associated with implementing the Lasso:(1) a compact descent method for solving the constrained problemfor a particular value of is formulated, and (2) a homotopymethod, in which the constraint bound becomes the homotopyparameter, is developed to completely describe the possibleselection regimes. Both algorithms have a finite terminationproperty. It is suggested that modified Gram-Schmidt orthogonalizationapplied to an augmented design matrix provides an effectivebasis for implementing the algorithms. 相似文献
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RM. Murugappan M. Karthikeyan A. Aravinth MR. Alamelu 《Applied biochemistry and biotechnology》2012,168(8):2170-2183
In the present study, siderophore produced by the marine yeast Aureobasidium pullulans was characterized as hydroxamate by chemical and bioassays. The hydroxamate assignment was supported by the appearance of peaks at 1,647.21?C1,625.99?cm?1 and at 1,435.04?cm?1 in the infrared spectrum. The purified siderophore exhibited specific growth-promoting activity under iron-limited conditions for siderophore auxotrophic probiotic bacteria. Cross-utilization of siderophore indicates a symbiotic relationship between the yeast A. pullulans and the selected probiotic bacterial strains. Statistical optimization of medium components for improved siderophore production in A. pullulans was depicted by response surface methodology. The shift in UV?CVis spectroscopy indicates the photoreactive property and subsequent oxidative cleavage of purified siderophore on exposure to sunlight. 相似文献