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941.
Alexandre Pinlou 《Discrete Mathematics》2006,306(24):3281-3289
A directed star forest is a forest all of whose components are stars with arcs emanating from the center to the leaves. The acircuitic directed star arboricity of an oriented graph G (that is a digraph with no opposite arcs) is the minimum number of arc-disjoint directed star forests whose union covers all arcs of G and such that the union of any two such forests is acircuitic. We show that every subcubic graph has acircuitic directed star arboricity at most four. 相似文献
942.
944.
Let G be an (m+2)-graph on n vertices, and F be a linear forest in G with |E(F)|=m and ω1(F)=s, where ω1(F) is the number of components of order one in F. We denote by σ3(G) the minimum value of the degree sum of three vertices which are pairwise non-adjacent. In this paper, we give several σ3 conditions for a dominating cycle or a hamiltonian cycle passing through a linear forest. We first prove that if σ3(G)≥n+2m+2+max{s−3,0}, then every longest cycle passing through F is dominating. Using this result, we prove that if σ3(G)≥n+κ(G)+2m−1 then G contains a hamiltonian cycle passing through F. As a corollary, we obtain a result that if G is a 3-connected graph and σ3(G)≥n+κ(G)+2, then G is hamiltonian-connected. 相似文献
945.
Yun Zhang Hua Wang Jinfang Nie Hui Zhou Guoli Shen Ruqin Yu 《Electrochemistry communications》2009,11(10):1936-1939
Encoded polymer films for electrochemical identification have been achieved by embedding different semiconductor nanocrystals into self-polymerized dopamine films. Such encoded polydopamine films based on mussel-inspired surface chemistry show high adhesive ability and can be created on a wide range of inorganic and organic materials, including noble metals, oxides, ceramics, and synthetic polymers. By incorporating different predetermined levels of various redox nanomarkers, the use of multi-film system composed of multiple, sequenced polydopamine identification films could theoretically generate nearly unlimited (>1012) distinct voltammetric signatures (electric codes). 相似文献
946.
基于最小特权原理,从分析进程的访问权限出发,提出了一种防御恶意程序攻击的数据保护模型.该模型对DAC访问控制机制进行了增强,当进程实际访问用户数据时,进程必须先获得操作用户的意愿,用户根据进程的任务赋予进程访问系统最小必需数据集的权限,使进程无法访问任务之外的数据集,防止进程因权限过大破坏用户数据.测试结果表明,该模型可以有效地阻止进程的非法访问而确保数据不被窃取或破坏. 相似文献
947.
Bescher Eric Piqué Francesca Stulik Dusan Mackenzie J.D. 《Journal of Sol-Gel Science and Technology》2000,19(1-3):215-218
A sol-gel coating was used in the long-term protection of the 14th Century mosaic situated above the gates of St. Vitus cathedral, in the center of Prague Castle. The choice of a sol-gel coating is the result of a research effort involving both on-site testing in Prague and accelerated ageing of various polymers and sol-gel materials in the laboratory. The coating selected for treatment of the entire 13 m × 10 m mosaic is a multi-layer system in which an organic-inorganic sol-gel layer is placed between the glass substrate and a fluoropolymer coating. This coating combination performed very well in an accelerated weathering chamber as well as during onsite testing. Since the top layer is scheduled to be removed and re-applied periodically, it is hoped that this concept will allow long term protection to the largest outdoors mosaic north of the Alps. On-site application of the coatings on the entire mosaic started in 1998 and will be completed in 2000. 相似文献
948.
949.
Andrew N. Lowell 《Tetrahedron》2010,66(30):5573-5582
Syntheses of an isocoumarin subunit suitable for the completion of purpuromycin are outlined. Specifically, work targeting an orthogonally protected isocoumarin (eventually 12% yield over 12 steps) and an improved synthesis of a symmetrically protected isocoumarin (18% over 10 steps) are described. A new modification for selective catechol protection as mediated by potassium bicarbonate is also presented along with insights into oxidative and reductive functionalization of isocoumarins. 相似文献
950.
D Montecchio O Francioso P Carletti D Pizzeghello S Chersich F Previtali S Nardi 《Journal of Thermal Analysis and Calorimetry》2006,83(2):393-399
Humic
acids (HAs) extracted from soils developed under two Norwegian spruce (Picea
abies, (L.) Karst) subalpine forests of northern Italy were characterized
using chemical, thermal (TG-DTA) and spectroscopic (DRIFT) analyses. The samples
were taken from five sites which differed in orientation (northern and southern
exposure) and vegetal cover at different old age: grassland, regeneration,
immature and mature stands. In general, the thermal patterns of HAs were similar
(three exothermic reactions appeared around at 300, 400 and 500°C) in
both sites in grasslands and regeneration while a considerable modification
appeared in HA from stands of different age at northern and southern exposure
site. DRIFT spectroscopy confirmed the differences observed through TG-DTA
analysis. In particular the main structural changes were ascribed to modification
of carbonyl group and of CH stretching in aliphatic components in each HAs
from different sites. 相似文献