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991.
The pressure dependence of the experimental 7Li NMR spectra is reported for first stage lithium graphite (LiC6) intercalation compound at temperatures T = 232 and 293 K. This experiment together with the presented point charge model calculation of the 7Li quadrupole coupling constant allows an unambiguous determination of the sign of e2qQ/h which is negative: at p = 1 bar and T = 232 K. The averaged location of the electrons transferred from the Li intercalant to the graphite layers, as estimated in this study, is in excellent agreement with earlier theoretical energy-band calculations. The compressibility of LiC6 in the c-direction is predicted to be kc = 1.7 × 10-12cm2dyn-1, it agrees with estimates derived from the available phonon dispersion relations. 相似文献
992.
S. M. J. Kelly 《Optics Communications》1989,70(6):495-501
The effect of incorporating an empty external cavity into the feedback loop of a mode-locked laser is investigated. Particular attention is paid to the response of the mode-locking as the external cavity is detuned by a fraction of a wavelength from the round trip transit time associated with the laser. The results for two regimes of operation are presented. In the first case a series of short lived transients develop whereas the other case leads to a persistent intermittent Q-switching scenario, where mode-locking fails. The role of coupling between the cavities and the laser's memory time in relation to the results is discussed. A mechanism for the improved mode-locking observed with non-linear external cavities is suggested. 相似文献
993.
Simple and convenient methods for determining surface chemical composition of lignocellulosic materials are described. The
methods are based on vapor phase fluorine surface derivatization with either trifluoro acetic anhydride (TFAA), tri-fluoro
ethanol (TFE) or pentafluorophenyl hydrazine (PFPH) and subsequent Electron Spectroscopy for Chemical Analysis (ESCA). Model
cellulosic surfaces with well defined functionalities were used to optimize the derivatization reaction conditions. Detection
and accessibility of surface hydroxyl functional groups were investigated in cotton and regenerated cellulose as models. Carboxymethyl
cellulose (CMC) was used as a model surface for detection and quantification of carboxylic acid groups. Theoretical conversion
curves for derivatization reactions were calculated and used to evaluate the extent of the reactions on the model surfaces.
It was found that the conversion was higher for the regenerated cellulose and CMC than for cotton. The protocols developed
using the model surfaces were applied to a case study on wood fibers with different degrees of complexity, namely dissolving
and chemithermomechanical (CTMP) pulp. Untreated and oxygen-plasma modified pulps were compared with respect to the surface
composition of functional groups. According to the derivatization reactions, functionalities containing oxygen were significantly
increased on the plasma-treated samples. The effect of the treatment was found to be dependent on the type of pulp. Fluorine
derivatization is shown to be an unambiguous method for clear assessment of the chemical functionalities of cellulosic surfaces. 相似文献
994.
Cluster ions have been recognized as a superb primary species in time of flight secondary ion mass spectroscopy (ToF-SIMS) compared with monatomic primary ions, as they significantly enhance the secondary ion yields from bulk samples. Self-assembled monolayers provide an important system for studying the fundamental mechanism involved in the yield enhancement.We used a gold cluster ion source to analyze a new type of self-assembled monolayer: a fluorocarbon-grafted polyethylene terephthalate. In addition to the structure details, which helped to understand the grafting mechanism, ToF-SIMS analysis revealed that fluorocarbon secondary ion yield enhancements by cluster ions were due to the enhanced sputter efficiency. A larger information depth may also be expected from the enhancement. Both mathematical definitions of damage cross-section and disappearance cross-section were revisited under a new context. Another cross-section parameter, sputter cross-section, was introduced to differentiate the beam induced sputter process from damage process. 相似文献
995.
This paper presents the development and laboratory evaluation of a PM10/2.5/1.0 trichotomous sampling inlet that consists of two main parts: a previously designed PM10 size‐selective inlet part and a PM2.5/1.0 two‐stage virtual impactor, which was newly fabricated and attached serially to the PM10 size selective inlet part. Particles are collected in three locations through the trichotomous sampling inlet to provide for not only particle concentration measurements of PM10, PM2.5 and PM1.0, but also those of PM2.5–10 and PM1.0–2.5. 相似文献
996.
In this paper, a locally computed suboptimal control strategy for a class of interconnected systems is introduced. First, optimal statefeedback control equations are derived for a finite-horizon quadratic cost. Then, the control for each subsystem is separated into two portions. The first portion stabilizes the isolated subsystem, and the second portion corresponds to the interactions. To achieve a locally calculable control, an approximation to the optimal control equations is introduced, and two iterative suboptimal control algorithms are developed. In the first algorithm, the initial conditions of subsystems are assumed to be known; in the second algorithm, this information is replaced by statistical distributions. The orders of errors in the iterations of the algorithm and in the suboptimality are given in terms of interconnections. An example with comparisons is also included to show the performance of the approach. 相似文献
997.
We construct division algebras with involution containing a Baer ordering with noninvariant order ring. This gives a negative
answer to a question of Holland, whether the order ring is always invariant under inner automorphisms. Furthermore, we give
examples of any index. Previously, the only known examples of division algebras containing Baer orderings were of index 2
n
or of indexp forp a prime of the form 4m + 3.
Supported in part by the National Science Foundation. 相似文献
998.
Buckling of sandwich wide columns 总被引:2,自引:0,他引:2
The paper deals with the theoretical prediction of buckling loads for sandwich columns with metallic and laminated facings and foam or honeycomb core. The loading is a uniform axial compression, applied statically (very slowly) and suddenly with constant magnitude and infinite duration (step loading). The effect of length and boundary conditions is assessed and results are presented for the following cases: for a cantilever column, a simply supported column and a clamped column, for several lengths. Several fiber materials are used in the laminated facings. Two types of core were examined: alloy-foam or hexagonal glass/phenolic honeycomb. The facings are Boron/Epoxy, Graphite/Epoxy and Kevlar/Epoxy laminates with 0° orientation with respect to the column axis and a metallic one made out of aluminum. These various materials are employed to provide comparative data that can be used in design. Results, for the static case are generated by computer codes as well as by the use of closed form theoretical solutions. For the dynamic case, results are generated by the DYNA3D code. 相似文献
999.
J A Bennell C N Potts J D Whitehead 《The Journal of the Operational Research Society》2002,53(10):1109-1117
In the min-max loop layout problem, machines are to be arranged around a loop of conveyor belt. The ordering of the machines dictates the number of circuits of the conveyor belt required to manufacture each of several products. The goal is to find an ordering of the machines that minimises the maximum number of circuits required for the manufacture of any of the products. Since the problem is strongly NP-hard, the study of heuristic methods is of interest. This paper proposes iterated descent and tabu search algorithms, and a randomised insertion algorithm. Results of extensive computational tests show that all of our algorithms outperform a previously known algorithm that applies a greedy heuristic to the solution of a linear programming relaxation. The best quality solutions are obtained with iterated descent. This adds further evidence to the belief that iterated descent can produce high quality solutions to a variety of combinatorial optimisation problems. Moreover, unlike some other local search algorithms, iterated descent does not require much tuning in order to be competitive. 相似文献
1000.
M. Le Vassor D’yerville D. Monge D. Cassagne J. P. Albert 《Optical and Quantum Electronics》2002,34(5-6):445-454
We present here a tight-binding-like modelling of two-dimensional (2D) photonic crystals (PCs). Adopted from solid-state physics,
the concept of generalized Wannier functions is used to construct a localized state basis that allows a parameter-free ab
initio study of defects in PCs. We demonstrate here for a 2D triangular lattice of dielectric rods in air, the existence of
this localized basis and the possibility to study large scale complex dielectric structures deviating from periodicity. Specific
numerical simulations on a split waveguide embedded in this triangular lattice are performed, and they demonstrate the superiority
of this method over plane wave based techniques. 相似文献