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991.
Kenji Fujito Shuichi Kubo Hirobumi Nagaoka Tae Mochizuki Hideo Namita Satoru Nagao 《Journal of Crystal Growth》2009,311(10):3011-3014
We succeeded in preparing very thick c-plane bulk gallium nitride (GaN) crystals grown by hydride vapor phase epitaxy. Growth of the bulk GaN crystals was performed on templates with 3 μm GaN layer grown by metal organic chemical vapor deposition on (0 0 0 1) sapphire substrates. Colorless freestanding bulk GaN crystals were obtained through self-separation processes. The crystal's diameter and thickness were about 52 and 5.8 mm, respectively. No surface pits were observed within an area of 46 mm diameter of the bulk GaN crystal. The dislocation density decreased with growth direction (from N-face side to Ga-face side) and ranged from 5.1×106 cm−2 near the N-face surface to 1.2×106 cm−2 near the Ga-face. A major impurity was Si, and other impurities (O, C, Cl, H, Fe, Ni and Cr) were near or below the detection limits by SIMS measurements. 相似文献
992.
We study positive linear Volterra integro-differential equations in Banach lattices. A characterization of positive equations
is given. Furthermore, an explicit spectral criterion for uniformly asymptotic stability of positive equations is presented.
Finally, we deal with problems of robust stability of positive systems under structured perturbations. Some explicit stability
bounds with respect to these perturbations are given. 相似文献
993.
994.
Dielectric relaxation measurements were made on methyl methacrylate—styrene and methyl methacrylate–p-chlorostyrene copolymers at temperatures higher than the glass transition temperature Tg. It was found that the temperature dependence of the relaxation time can be described satisfactorily by an expression derived recently for chain motion in amorphous polymers. The temperature Tg obtained from the expression agrees well with that determined by differential thermal analysis. 相似文献
995.
Naoya Ogata Kohei Sanui Yoshikazu Hosoda Hiroyuki Nakamura 《Journal of polymer science. Part A, Polymer chemistry》1976,14(4):783-792
Polycondensation of diethyl 2,3,4,5-tetrahydroxyadipate with various diamines was carried out in solutions under mild conditions. The polycondensation reaction occurred rapidly even at room temperature in polar solvents such as alcohols, and in aqueous solution a cyclic product was obtained instead of linear polymers although the reaction with diamines was completed within several minutes. Polymers obtained from diethyl 2,3,4,5-tetrahydroxyadipate were a linear polyamide having pendant hydroxyl groups, which decomposed on heating at around 200°C. A solid-phase polycondensation of the precursor polyamide yielded a high molecular weight polyamide. 相似文献
996.
A bisubmodular polyhedron is defined in terms of a so-called bisubmodular function on a family of ordered pairs of disjoint
subsets of a finite set. We examine the structures of bisubmodular polyhedra in terms of signed poset and exchangeability
graph. We give a characterization of extreme points together with an O(n
2) algorithm for discerning whether a given point is an extreme point, wheren is the cardinality of the underlying set, and we assume a function evaluation oracle for the bisubmodular function. The algorithm
also determines the signed posetructure associated with the given point if it is an extreme point. We reveal the adjacency
relation of extreme points by means of the Hasse diagrams of the associated signed posets. Moreover, we investigate the connectivity
and the decomposition of a bisubmodular system into its connected components. 相似文献
997.
Satoru Toyooka Nobuaki Hayasaka Munehide Kataguchi Fumio Kobayashi 《Optical Review》1998,5(4):207-211
A spectral intensity distribution of interference colors which is a function of optical path difference (OPD) is represented as a pattern vector on a subspace. A new algorithm to design a color scale on the subspace to estimate OPD values is proposed. In experiments, interference colors generated by a differential interference microscope (DIM) were examined. A subspace spanned by four orthogonal bases was constructed to make a color scale to determine OPD values in the range between 0 nm and 1000 nm. Estimated OPD values almost coincided with these expected. In an experiment on two-dimensional interference colors obtained by a spherical surface of a ballbearing observed by DIM, the resultant OPD distribution coincided well with that expected within a standard deviation of 12.8 nm. 相似文献
998.
We determine the values attained by the rank of the Gauss map of a projective model for a fixed algebraic variety in positive characteristic p. In particular, it is shown that any variety in p>0 has a projective model such that the differential of the Gauss map is identically zero. On the other hand, we prove that there exists a product of two or more projective spaces admitting an embedding into a projective space such that the differential of the Gauss map is identically zero if and only if p=2. 相似文献
999.
1000.
We describe an O(n
4
hmin{logU,n
2logn}) capacity scaling algorithm for the minimum cost submodular flow problem. Our algorithm modifies and extends the Edmonds–Karp
capacity scaling algorithm for minimum cost flow to solve the minimum cost submodular flow problem. The modification entails
scaling a relaxation parameter δ. Capacities are relaxed by attaching a complete directed graph with uniform arc capacity
δ in each scaling phase. We then modify a feasible submodular flow by relaxing the submodular constraints, so that complementary
slackness is satisfied. This creates discrepancies between the boundary of the flow and the base polyhedron of a relaxed submodular
function. To reduce these discrepancies, we use a variant of the successive shortest path algorithm that augments flow along
minimum cost paths of residual capacity at least δ. The shortest augmenting path subroutine we use is a variant of Dijkstra’s
algorithm modified to handle exchange capacity arcs efficiently. The result is a weakly polynomial time algorithm whose running
time is better than any existing submodular flow algorithm when U is small and C is big. We also show how to use maximum mean cuts to make the algorithm strongly polynomial. The resulting algorithm is the
first capacity scaling algorithm to match the current best strongly polynomial bound for submodular flow.
Received: August 6, 1999 / Accepted: July 2001?Published online October 2, 2001 相似文献