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81.
In this paper we study the classical problem of finding disjoint paths in
graphs. This problem has been studied by a number of authors both for specific
graphs and general classes of graphs. Whereas for specific graphs many
(almost) matching upper and lower bounds are known for the competitiveness of
on-line algorithms, not much is known about how well on-line algorithms can
perform in the general setting. The best results obtained so far use the
expansion of a network to measure the algorithms performance. We use a
different parameter called the routing number that, as we will show, allows
more precise results than the expansion. It enables us to prove tight upper and
lower bounds for deterministic on-line algorithms. The upper bound is obtained
by surprisingly simple greedy-like algorithms. Interestingly, our upper bound
on the competitive ratio is even better than the best previous approximation
ratio for off-line algorithms. Furthermore, we introduce a refined variant of
the routing number and show that this variant allows us, for some classes of
graphs, to construct on-line algorithms with a competitive ratio significantly
below the best possible upper bound that could be obtained using the routing
number or the expansion of a network only. We also show that our on-line
algorithms can be transformed into efficient algorithms for the more general
unsplittable flow problem. 相似文献
82.
Toxicity increases in ice containing monochlorophenols upon photolysis: environmental consequences 总被引:4,自引:0,他引:4
Bláha L Klánová J Klán P Janosek J Skarek M Růzicka R 《Environmental science & technology》2004,38(10):2873-2878
The toxic effects of photoproducts formed upon the photolysis of 2- and 4-chlorophenol (CP) frozen solutions in polycrystalline ice phase were determined with a bacterial luminescence test (Vibrio fisheri), and in vitro biomarker assay for dioxin-like effects (inductions of AhR-dependent luciferase in H4IIE-luc cells) and compared to the toxic effects of products of the same photoreaction in aquatic phase. Coupling photoproducts formed in ice samples (3'-chlorobiphenyl-2,4'-diol and 3-chlorobiphenyl-2,2'-diol from 2-CP photolysis and 5-chlorobiphenyl-2,4'-diol from 4-CP photolysis) were found to be more toxic to V. fisheri than parent CPs and elicited significant inductions of dioxin-like effects (the effective concentrations EC50 approximately 3 x 10(-5) mol L(-1) corresponded to known weaker ligands of AhR, such as nonplanar polychlorinated biphenyls or polycyclic aromatic hydrocarbons). To complete the picture, a photoproduct formed from 4-CP (5-chlorobiphenyl-2,4'-diol) was synthesized, and a detailed toxicity assessment with purified compound confirmed the results obtained with irradiated samples. Our findings support a recently proposed model according to which solar radiation can trigger the formation of new types of organic pollutants in polar ice or tropospheric ice cloud particles, presenting possibly greater risk to the environment than the parent compounds. 相似文献
83.
Hoops and Fuzzy Logic 总被引:4,自引:0,他引:4
Esteva Francesc; Godo Lluis; Hajek Petr; Montagna Franco 《Journal of Logic and Computation》2003,13(4):532-555
84.
n-Alkane content of intramuscular lipids (Biceps femoris muscle) of the Iberian pig have been determined. Thirty-four pigs, divided into four groups, based in the feeding system (Montanera, fed on acorns and pasture; and Pienso, fed on a concentrate feed) and in the genotype (Iberian pure pigs; and Iberian crossbred with Duroc 50%) were studied. n-Alkane content of intramuscular lipids has not been affected by neither crossbreeding nor feeding, although the analysis of feeds administered to the pigs showed greater n-alkane values in pasture (consumed by animals in montanera), than in acorns and concentrate feed. 相似文献
85.
Enhancement of magnetic losses in hybrid polymer composites with MnZn-ferrite and conductive fillers
Robert Moučka Alexander V. Lopatin Natalia E. Kazantseva Jarmila Vilčáková Petr Sáha 《Journal of Materials Science》2007,42(22):9480-9490
Polymer composites (PCs) with a polyurethane (PU) matrix filled with magnetic filler (MnZn ferrite) and hybrid polymer composites
(HPCs) consisting of this magnetic filler and various types of conductive fillers (carbon black, carbon fibers, aluminum powder,
polypyrrole) are prepared. The matrix structure of a HPC is formed (i) by a polymer filled with conductive filler, which forms
the skeleton of an infinite cluster, and (ii) by ferrite particles that are larger than conductive particles. Thus, an HPC
represents an ensemble of ferrite particles each of which is surrounded by a conductive medium and can be considered as a
“core–shell” structure. The development of a core–shell structure is evidenced by the lower electric percolation threshold
in an HPC compared with that in PU filled with conductive filler. Magnetic and dielectric spectra of PCs and HPCs are studied
in the frequency range from 1 MHz to 10 GHz. Hybrid systems exhibit a considerable enhancement of magnetic losses compared
with PCs. The enhancement of magnetic losses in HPCs is due to the conduction currents that are induced in the conductive
shell by a microwave magnetic field. 相似文献
86.
Petr Holub Martin Šrom Martin Pulec Jiří Matela Martin Jirman 《Future Generation Computer Systems》2013,29(8):1991-2006
Low-latency transmissions of high resolution video such as HD, 2K, or 4K over both Internet and private IP networks have found a foothold in many interactive applications, ranging from collaborative environments in science and medicine to the arts and entertainment industry. In this paper we demonstrate how the power of commodity graphics processing units can be used for efficient implementation of JPEG and DXT compression. We propose an approach to fine-grained parallelization of JPEG compression and the use of auxiliary indexes for efficient decompression, which are backward compatible with the JPEG standard. In-depth performance analysis is provided to show various aspects of the proposed parallelization including the dependency on image content and on various settings of the compression algorithm, as well as the impact of compression for interactive applications in terms of end-to-end latency. The applicability of these compression schemes in medicine and cinematography has also been evaluated using double-blind ABX tests compared with uncompressed video. We describe selected successful real-world deployment use cases based on our open-source implementation within the UltraGrid framework, such as trans-Atlantic 4K interactive video streaming during the CineGrid 2011 workshop. As discussed in the paper, the proposed approaches to parallelization provide sufficient performance even for the future generation of 8K video processing systems, currently limited by availability of camera and display hardware. 相似文献
87.
We present a case study in identification of taxa in paleobiological data. Our approach utilizes formal concept analysis and is based on conceiving a taxon as a group of individuals sharing a collection of attributes. In addition to the incidence relation between individuals and their attributes, the method uses expert background knowledge regarding importance of attributes which helps to filter out correctly formed but paleobiologically irrelevant taxa. We present results of experiments carried out with belemnites—a group of extinct cephalopods which seems particularly suitable for such a purpose. We demonstrate that the methods are capable of revealing taxa and relationships among them that are relevant from a paleobiological point of view. 相似文献
88.
Petr Kellnhofer Tobias Ritschel Karol Myszkowski Hans‐Peter Seidel 《Computer Graphics Forum》2013,32(4):143-152
Beyond the careful design of stereo acquisition equipment and rendering algorithms, disparity post‐processing has recently received much attention, where one of the key tasks is to compress the originally large disparity range to avoid viewing discomfort. The perception of dynamic stereo content however, relies on reproducing the full disparity‐time volume that a scene point undergoes in motion. This volume can be strongly distorted in manipulation, which is only concerned with changing disparity at one instant in time, even if the temporal coherence of that change is maintained. We propose an optimization to preserve stereo motion of content that was subject to an arbitrary disparity manipulation, based on a perceptual model of temporal disparity changes. Furthermore, we introduce a novel 3D warping technique to create stereo image pairs that conform to this optimized disparity map. The paper concludes with perceptual studies of motion reproduction quality and task performance in a simple game, showing how our optimization can achieve both viewing comfort and faithful stereo motion. 相似文献
89.
Ji?í Jeništa Hidemasa Takana Hideya Nishiyama Milada Bartlová Vladimír Aubrecht Petr K?enek Viktor Sember Alan Mašláni 《Computer Physics Communications》2011,182(9):1776-1783
The paper presents numerical simulations of the discharge and the near-outlet regions of the hybrid-stabilized argon–water electric arc. Two different numerical methods for solving the set of conservative equations for the continuity, momentum and energy have been applied. The major difference between the results using the two methods occurs in the temperature distribution in arc fringes within the discharge chamber. This fact influences the potential drop, overpressure, reabsorption of radiation and arc efficiency. It is shown that the radial profiles of temperature at the exit nozzle are less influenced by different temperature distribution within the discharge chamber. Comparison with chosen experimental temperature profiles shows very good agreement. 相似文献
90.
Marc García-Arnau David Pérez Alfonso Rodríguez-Patón Petr Sosík 《Natural computing》2008,7(4):471-483
Since their first publication in 2006, spiking neural (SN) P systems have already attracted the attention of a lot of researchers.
This might be owing to the fact that this abstract computing device follows basic principles known from spiking neural nets,
but its implementation is discrete, using membrane computing background. Among the elementary properties which confer SN P
systems their computational power one can count the unbounded fan-in (indegree) and fan-out (outdegree) of each “neuron”,
synchronicity of the whole system, the possibility of delaying and/or removing spikes in neurons, the capability of evaluating
arbitrary regular expressions in neurons in constant time and some others. In this paper we focus on the power of these elementary
features. Particularly, we study the power of the model when some of these features are disabled. Rather surprisingly, even
very restricted SN P systems keep their universal computational power. Certain important questions regarding this topic still
remain open. 相似文献