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781.
The features of the Entity-Relationship model are examined, as a means for representing both the conceptual schema and the external schema in a database system. In order to serve in this dual capacity, its modelling features are extended to support multiple user views. We show how to represent a model and present a suitable diagrammatic technique. To represent these concepts at the user level we propose a data definition language with a concise and simple structure. Furthermore, guidelines are given for interfacing the E-E-R schema with existing DBTG-like systems. 相似文献
782.
The dynamic properties of the order parameter and the quasiparticle distribution function in short superconducting weak links are investigated. The corresponding equations recently derived by Schmid, Schön, and Tinkham are solved numerically in a wide range of parameters. The complete low-voltage part of the current-voltage characteristic is determined, which shows a foot structure observed in many experiments. The frequency spectrum of the emitted Josephson radiation is also calculated. 相似文献
783.
Recent advances in laser technology now allow us to study the ultrafast primary photochemical events in rhodopsin, bacteriorhodopsin, and halorhodopsin in real time. The results of various ultrafast studies of rhodopsins are reviewed with an emphasis on (1) the relationship between the reaction rate and reaction efficiency and its implications for the mechanism of isomerization, (2) the homogeneity of the reaction pathways, and (3) the role of the protein in the reaction dynamics. The results mandate the introduction of a new paradigm to describe these ultrafast reactions that specifically considers the importance of the timescale of vibrational dephasing and relaxation relative to the reactive motion and the contribution of vibrational coherence to the reaction mechanism. 相似文献
784.
785.
786.
Hongbin Zhang Gerd Mrozynski Amir Wallrabenstein Juergen Schrage Elmar Griese 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(3):377-389
A self-consistent model of vertical-cavity surface-emitting lasers (VCSEL's) is presented in this paper, in which the carrier diffusion rate equation, the photon density rate equation, and the thermal conduction equation are considered simultaneously. The nonuniform heat flux density distribution in the active region due to the current-spreading effect is taken into account. The effects of temperature on gain and transparency carrier density are also included in this model. It is nonlinearly and self-consistently solved in the Matlab environment. The transient and lateral distribution characteristics of the carrier and photon densities and the junction temperature are investigated. Some interesting results are gotten and analyzed. 相似文献
787.
Yuriy Makhlin Gerd Schön Alexander Shnirman 《Applicable Algebra in Engineering, Communication and Computing》2000,10(4-5):375-382
Among the physical realizations of the elements required for quantum computation nano-scale electronic devices [2, 10, 12,
16] are very promising. They can be easily integrated into electronic circuits and scaled up to large numbers of qubits. Here
we describe qubits based on low-capacitance Josephson junctions. In these systems Coulomb blockade effects allow the control
of the charge on a superconducting island. They constitute quantum bits, with logical states differing by the charge on one
island. Single- and two-bit operations can be performed by manipulating applied gate voltages. The phase coherence time is
sufficiently long to allow a series of these steps. In addition to the manipulation of qubits, the resulting quantum state
can be read out by coupling a single-electron transistor capacitively to the qubit.
Received: October 23, 1998; revised version: September 21, 1999 相似文献
788.
789.
Kritische Erörterung von Schrifttumsangaben über den Verlauf der Schmelzgleichgewichte im Zustandsschaubild FeO–Fe2O3–CaO. Beschreibung eigener Versuche zur Ermittlung des Verlaufs der Liquidusflächen und der Linien doppelter Sättigung. Nachweis der Gültigkeit des quasibinären Schnittes Eisen-Dicalciumferrit mit Angaben über das ternäre Eutektikum und ternäre Peritektikum. Geschlossene Darstellung der Schmelzgleichgewichte des ternären Zustandsschaubildes. 相似文献
790.