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171.
F. Soška F. Beneš S. Jura B. Gross Z. šimša F. Kosek J. Horák J. Kašpar K. čermák J. Lipták M. Ryba E. F. Holländer A. Havránek E. Havránková A. Kochanovská J. Sommer F. Vilím P. Lukáš C. Rumler S. Kadečková F. Vávra M. Matyáš J. Beneš J. Kučera L. DvoŘák Z. KudĚlásek J. Hájek A. Marek Z. Malec J. Janků B. Sojka L. Karmazin M. Ryšavá L. Janko K. Huml 《Czechoslovak Journal of Physics》1961,11(11):852-862
172.
Cai YQ Chow PC Restrepo OD Takano Y Togano K Kito H Ishii H Chen CC Liang KS Chen CT Tsuda S Shin S Kao CC Ku W Eguiluz AG 《Physical review letters》2006,97(17):176402
A sharp feature in the charge-density excitation spectra of single-crystal MgB2, displaying a remarkable cosinelike, periodic energy dispersion with momentum transfer (q) along the c* axis, has been observed for the first time by high-resolution nonresonant inelastic x-ray scattering (NIXS). Time-dependent density-functional theory calculations show that the physics underlying the NIXS data is strong coupling between single-particle and collective degrees of freedom, mediated by large crystal local-field effects. As a result, the small-q collective mode residing in the single-particle excitation gap of the B pi bands reappears periodically in higher Brillouin zones. The NIXS data thus embody a novel signature of the layered electronic structure of MgB2. 相似文献
173.
Broniatowski M Vila Romeu N Dynarowicz-Łatka P 《The journal of physical chemistry. B》2006,110(7):3078-3087
This work presents the results of phase behavior studies of two-dimensional (2D) binary systems involving semifluorinated alkanes (SFAs) and fatty alcohols. Four different SFAs were selected for investigations: (i) with a short and branched perfluorinated moiety (iF3H20), (ii) with a short and normal perfluorinated chain (F4H20), (iii) with a long and branched perfluorinated fragment (iF9H20), and (iv) with a long and normal perfluorinated group (F10H20). Two alcohols were selected to mix with the above-mentioned SFAs: tetradecanol and docosanol. The measurements were based on surface pressure/area isotherms in addition to Brewster angle microscope (BAM) imaging. Dependencies of the collapse surface pressure and the compression modulus vs the monolayer composition together with the excess free energy of mixing values, complemented with BAM images, enabled us to draw some general conclusions regarding the phase behavior of the investigated mixed systems. Generally, it has been noticed that the addition of docosanol into an SFA monolayer exerts a condensing effect, contrary to tetradecanol. Moreover, SFAs with a long perfluorinated segment mix to a larger extent with alcohols as compared to their analogues having a short perfluorinated moiety. The resultant phase diagrams for all the investigated eight mixtures are presented and discussed. 相似文献
174.
Biing-Feng Wang Shietung Peng Hong-Yi Yu Shan-Chyun Ku 《Journal of Algorithms in Cognition, Informatics and Logic》2006,59(2):107-124
Let T=(V,E) be a free tree in which each vertex has a weight and each edge has a length. Let n=|V|. Given T and parameters k and l, a (k,l)-tree core is a subtree X of T with diameter l, having k leaves, which minimizes the sum of the weighted distances from all vertices in T to X. In this paper, two efficient algorithms are presented for finding a (k,l)-tree core of T. The first algorithm has O(n2) time complexity for the case that each edge has an arbitrary length. The second algorithm has O(lkn) time complexity for the case that the lengths of all edges are 1. The (k,l)-tree core problem has an application in distributed database systems. 相似文献
175.
176.
Herng TS Qi DC Berlijn T Yi JB Yang KS Dai Y Feng YP Santoso I Sánchez-Hanke C Gao XY Wee AT Ku W Ding J Rusydi A 《Physical review letters》2010,105(20):207201
We report direct evidence of room-temperature ferromagnetic ordering in O-deficient ZnO:Cu films by using soft x-ray magnetic circular dichroism and x-ray absorption. Our measurements have revealed unambiguously two distinct features of Cu atoms associated with (i) magnetically ordered Cu ions present only in the oxygen-deficient samples and (ii) magnetically disordered regular Cu2+ ions present in all the samples. We find that a sufficient amount of both oxygen vacancies (V(O)) and Cu impurities is essential to the observed ferromagnetism, and a non-negligible portion of Cu impurities is uninvolved in the magnetic order. Based on first-principles calculations, we propose a microscopic "indirect double-exchange" model, in which alignments of localized large moments of Cu in the vicinity of the V(O) are mediated by the large-sized vacancy orbitals. 相似文献
177.
Non-Gaussian photoluminescence peaks observed in a-Si:H-based structures at 6 K are interpreted as a consequence of the presence of different phases in material. Thin films of amorphous silicon deposited on glass substrate have been analyzed.The main aims of the contribution are (i) analysis of numerical data obtained by fitting procedure and (ii) formulation of corresponding conclusions in terms of structural properties of sample. Spectrum of a-Si:H-based samples can be interpreted as superposition of photoluminescence signals arising from two domains with different degrees of structural disordering. By our knowledge this result corresponds to real situation from view of structural properties of amorphous hydrogenated silicon. Under certain circumstances, decomposition of photoluminescence spectrum can give information of geometrical structure of sample. 相似文献
178.
Jaeun Ku 《BIT Numerical Mathematics》2010,50(3):609-630
Highly localized pointwise error estimates for a stabilized Galerkin method are provided for second-order non-selfadjoint
elliptic partial differential equations. The estimates show a local dependence of the error on the derivative of the solution
u and weak dependence on the global norm. The results in this paper are an extension of the previous pointwise error estimates
for the self-adjoint problems. In order to provide pointwise error estimates in the presence of the first-order term in the
differential equations, we prove that the stabilized Galerkin solution is higher order perturbation to the Ritz projection
of the true solutions. Then, we proceed to obtain pointwise estimates using the so-called discrete Green’s function. Application
to error expansion inequalities and a posteriori error estimators are briefly discussed. 相似文献
179.
Let B(k,0,n) denote the group with k generators which is free in the group variety defined by the identity x
n
=1. Let B
slo
(k,1,n) denote the semilattice-ordered semigroup with k generators which is free in the semilattice-ordered semigroup variety defined by the identity x
n
=x. We prove a generalization of the Green-Rees theorem: B
slo
(k,1,n) is finite for all k≥1 if and only if B(k,0,n−1) is finite for all k≥1. We find a formula for card(B
slo
(1,1,n)). We construct B
slo
(k,1,n) for some concrete values of k and n. 相似文献
180.
Let [n] denote the set of positive integers {1,2,…,n}. An r-partial permutation of [n] is a pair (A,f) where A⊆[n], |A|=r and f:A→[n] is an injective map. A set A of r-partial permutations is intersecting if for any (A,f), (B,g)∈A, there exists x∈A∩B such that f(x)=g(x). We prove that for any intersecting family A of r-partial permutations, we have .It seems rather hard to characterize the case of equality. For 8?r?n-3, we show that equality holds if and only if there exist x0 and ε0 such that A consists of all (A,f) for which x0∈A and f(x0)=ε0. 相似文献