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961.
Summary It is shown that in the presence of a crossed electric and magnetic field the electronic states of a semiconductor in the
effective-mass approximation are described by a Hamiltonian containing a non-local potential. In order to preserve the gauge
invariance of the two-photon interband transition rate, the interaction Hamiltonian between the electrons and the incident
radiation has to be generalized. For GaAs, the transition rate between two particular levels is evaluated in both length and
velocity gauges demonstrating the correctness of our approach.
Work partially supported by the European Community Programme ESPRIT, Basic research, action n. 6878, EASI. 相似文献
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Andrea Galtarossa Luca Palmieri 《Journal of Optical and Fiber Communications Reports》2004,1(2):150-179
Polarization sensitive reflectometric techniques can be effectively used to
perform spatially resolved measurements of polarization properties of fiber optic link
— such as birefringence, polarization mode dispersion and polarization dependent
loss. In particular, this contribution is focused on polarization sensitive OTDR and
provides a survey of its theory and main applications. Special emphasis is given to
the characterization of fiber birefringence, that allows to inspect the fiber while cabled
and, consequently, to test and improve the cabling process. In addition, the analysis
of the birefringence also allows to define reliable mathematical models, which are
essential for the design of low polarization mode dispersion fibers. Reflectometric
measurements of polarization mode dispersion and polarization dependent loss are
also discussed. 相似文献
965.
Chlorella vulgaris was cultivated in a growth medium containing arsenate concentration of <0.01, 10, 100 and 1000 mg l?1. Illumination was carried out in 12 h cycles for 5 days. The health status of the culture was monitored by continuous pH and dissolved oxygen (DO) readings. Destructive sampling was used for the determination of biomass, chlorophyll, total arsenic and arsenic species. The chlorophyll a content, the DO and pH cycles were not significantly different for the different arsenate concentrations in the culture. In contrast, biomass production was significantly (p < 0.05) increased for the arsenic(V) treatment at 1000 mg l?1 compared with 100 mg l?1. The arsenic concentration in the algae increased with the arsenate concentration in the culture. However, the bioconcentration factor decreased a hundred‐fold with increase of arsenate from the background level to 1000 mg l?1. The arsenic species were identified by using strong anion‐exchange high‐performance liquid chromatography–inductively coupled plasma mass spectrometry analysis after methanol/water (1 : 1) extraction. The majority (87–100%) of the extractable arsenic was still arsenate; arsenite was found to be between 1 and 6% of total extractable arsenic in the algae. In addition to dimethylarsinic acid, one unknown arsenical (almost co‐eluting with methylarsonic acid) and three different arsenosugars have been identified for the first time in C. vulgaris growing in a culture containing a mixture of antibiotics and believed to be axenic. The transformation to arsenosugars in the algae is not dependent on the arsenate concentration in the culture and varies between 0.2 and 5% of total accumulated arsenic. Although no microbiological tests for bacterial contamination were made, this study supports the hypothesis that algae, and not associated bacteria, produce the arsenosugars. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
966.
Andrea Cappelli Maurizio Anzini Salvatore Vomero Alessandro Donati Lucia Zetta Raniero Mendichi Mario Casolaro Pietro Lupetti Paolo Salvatici Gianluca Giorgi 《Journal of polymer science. Part A, Polymer chemistry》2005,43(15):3289-3304
The macromolecular and aggregate structures of poly[ethyl 1‐methylene‐3‐(4‐methylphenyl)‐1H‐indene‐2‐carboxylate] (poly‐ BF1 ; a new polymer based on a functionalized benzofulvene moiety showing interesting properties, i.e., thermoreversible polymerization/depolymerization behavior, high solubility in the most common organic solvents, and susceptibility to molecular manipulation) have been investigated with NMR spectroscopy, absorption and emission spectrophotometry, and transmission electron microscopy (TEM). Moreover, the polymerization mechanism has been studied to obtain further information on the polymer structure. The collected evidence is consistent in indicating for poly‐ BF1 a vinyl (1,2) polymer structure stabilized by means of aromatic stacking interactions. Furthermore, TEM studies performed on metal replicas have shown that the polymer is liable to give nanostructured aggregates. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3289–3304, 2005 相似文献
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We study the partition function for the low-energy edge excitations of the incompressible electron fluid. On an annular geometry, these excitations have opposite chiralities on the two edges; thus, the partition function takes the standard form of rational conformal field theories. In particular, it is invariant under modular transformations of the toroidal geometry made by the angular variable and the compact Euclidean time. The Jain series of plateaus have been described by two types of edge theories: the minimal models of the W1+∞ algebra of quantum area-preserving diffeomorphisms, and their non-minimal version, the theories with
affine algebra. We find modular invariant partition functions for the latter models. Moreover, we relate the Wen topological order to the modular transformations and the Verlinde fusion algebra. We find new, non-diagonal modular invariants which describe edge theories with extended symmetry algebra; their Hall conductivities match the experimental values beyond the Jain series. 相似文献
970.
We show that a small perturbation of the evolution law of chaotic dynamical systems is practically equivalent to the finite precision on the knowledge of the initial condition. In spite of the short predictability time tp on a single trajectory we found that the statistical properties are not sensitive to small changes in the evolution law or initial probability distribution. This feature holds also for correlation functions at a delay larger than tp. We discuss the roundoff effects on integrable systems. 相似文献