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991.
For the multivariate ℓ1-norm symmetric distributions, which are generalizations of the n-dimensional exponential distribution with independent marginals, a geometric representation formula is given, together with some of its basic properties. This formula can especially be applied to a new developed and statistically well motivated system of sets. From that the distribution of a t-statistic adapted for the two-parameter exponential distribution and its generalizations is determined. Asymptotic normality of this adapted t-statistic is shown under certain conditions. 相似文献
992.
W. Richter 《Applied Physics A: Materials Science & Processing》2002,75(1):129-140
Metal organic vapour phase epitaxy (MOVPE) is nowadays one of the leading techniques for epitaxial growth. While the processes
in the gas phase of MOVPE are reasonably well understood, the processes on the growing surface are not. This situation is
in contrast to molecular beam epitaxy (MBE), where considerable knowledge about growth processes on the surface could be gained.
The main reason is that all the UHV-based classical surface-science tools (using electrons and ions), especially reflection
high-energy electron diffraction, can be applied in the vacuum-based MBE but not under the gas-phase conditions of MOVPE.
This situation has changed in the last decade since optical surface-science tools have been developed. Especially, with the
linear optical techniques like reflectance anisotropy spectroscopy and spectroscopic ellipsometry, there is now a quasi-standard
tool at hand which allows for the study of all kinds of pregrowth and growth situations in MOVPE (in MBE of course, as well).
These optical methods give, moreover, chemical information also.
In this article we will describe shortly the features of these optical techniques and then concentrate on III-V-semiconductor
growth. The spectral definition of surface reconstructions and time-resolved studies of phase transitions between them (adsorption/desorption
kinetics of group-III and group-V elements) are discussed next. Under growth, the surfaces can be classified and defined according
to their optical surface response into a pressure versus temperature phase diagram. The regions of such a phase diagram correspond
to different geometrical and chemical surface structures and consequently lead to different growth modes. Finally, as an example
of modern nanogrowth, monitoring of the growth of quantum-dot structures is presented.
Received: 2 August 2001 / Accepted: 23 October 2001 / Published online: 3 April 2002 相似文献
993.
994.
Franz‐Josef K. Rehmann Laurence P. Cuffe Oscar Mendoza Dilip K. Rai Nigel Sweeney Katja Strohfeldt William M. Gallagher Matthias Tacke 《应用有机金属化学》2005,19(3):293-300
Starting from 2‐furylfulvene (1a) , 2‐thiophenylfulvene (1b) , and 1‐methyl‐2‐pyrrolylfulvene (1c), [1,2‐di(cyclopentadienyl)‐1,2‐di‐(2‐furyl)ethanediyl] titanium dichloride (2a) , [1,2‐di(cyclopentadienyl)‐1,2‐di‐(2‐thiophenyl)ethanediyl] titanium dichloride (2b) , and [1,2‐di(cyclopentadienyl)‐1,2‐bis‐(1‐methyl‐2‐pyrrolyl)ethanediyl] titanium dichloride (2c) were synthesized. When titanocenes (2a–c) were tested against pig kidney carcinoma cells (LLC‐PK), inhibitory concentrations (50%) of 4.5 × 10?4 M , 2.9 × 10?4 M and 2.0 × 10?4 M respectively were observed. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
995.
This paper concerns Floer homology for periodic orbits and for a Lagrangian intersection problem on the cotangent bundle T* M of a compact orientable manifold M. The first result is a new L∞ estimate for the solutions of the Floer equation, which allows us to deal with a larger—and more natural—class of Hamiltonians. The second and main result is a new construction of the isomorphism between the Floer homology and the singular homology of the free loop space of M in the periodic case, or of the based loop space of M in the Lagrangian intersection problem. The idea for the construction of such an isomorphism is to consider a Hamiltonian that is the Legendre transform of a Lagrangian on T M and to construct an isomorphism between the Floer complex and the Morse complex of the classical Lagrangian action functional on the space of W1,2 free or based loops on M. © 2005 Wiley Periodicals, Inc. 相似文献
996.
Let K be a finitely generated field of transcendence degree 1 over a finite field, and set GK?Gal(Ksep/K). Let φ be a Drinfeld A-module over K in special characteristic. Set E?EndK(φ) and let Z be its center. We show that for almost all primes p of A, the image of the group ring Ap[GK] in EndA(Tp(φ)) is the commutant of E. Thus, for almost all p it is a full matrix ring over Z⊗AAp. In the special case E=A it follows that the representation of GK on the p-torsion points φ[p] is absolutely irreducible for almost all p. 相似文献
997.
998.
The question whether a polynomial time recognition algorithm for the class of perfectly orderable graphs exists was posed by Chvátal in 1981 when he introduced the notion of perfect orders. Since then several classes of perfectly orderable graphs have been identified. In this note we prove that recognizing perfectly orderable graphs is NP-complete. 相似文献
999.
1000.
Computing shortest paths with two or more conflicting optimization criteria is a fundamental problem in transportation and
logistics. We study the problem of finding all Pareto-optimal solutions for the multi-criteria single-source shortest-path
problem with nonnegative edge lengths. The standard approaches are generalizations of label-setting (Dijkstra) and label-correcting
algorithms, in which the distance labels are multi-dimensional and more than one distance label is maintained for each node.
The crucial parameter for the run time and space consumption is the total number of Pareto optima. In general, this value
can be exponentially large in the input size. However, in various practical applications one can observe that the input data
has certain characteristics, which may lead to a much smaller number—small enough to make the problem efficiently tractable
from a practical viewpoint. For typical characteristics which occur in various applications we study in this paper whether
we can bound the size of the Pareto set to a polynomial size or not. These characteristics are also evaluated (1) on a concrete
application scenario (computing the set of best train connections in view of travel time, fare, and number of train changes)
and (2) on a simplified randomized model. It will turn out that the number of Pareto optima on each visited node is restricted
by a small constant in our concrete application, and that the size of the Pareto set is much smaller than our worst case bounds
in the randomized model.
A preliminary short version of this paper appeared in the Proceedings of the 5th Workshop on Algorithm Engineering (WAE 2001),
LNCS 2141, Springer Verlag, pp. 185–197 (2001) under the title “Pareto shortest paths is often feasible in practice.” 相似文献