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71.
We propose a uniform method to encode various types of trees succinctly. These families include ordered (ordinal), k-ary (cardinal), and unordered (free) trees. We will show the approach is intrinsically suitable for obtaining entropy-based encodings of trees (such as the degree-distribution entropy). Previously-existing succinct encodings of trees use ad hoc techniques to encode each particular family of trees. Additionally, the succinct encodings obtained using the uniform approach improve upon the existing succinct encodings of each family of trees; in the case of ordered trees, it simplifies the encoding while supporting the full set of navigational operations. It also simplifies the implementation of many supported operations. The approach applied to k-ary trees yields a succinct encoding that supports both cardinal-type operations (e.g. determining the child label i) as well as the full set of ordinal-type operations (e.g. reporting the number of siblings to the left of a node). Previous work on succinct encodings of k-ary trees does not support both types of operations simultaneously (Benoit et al. in Algorithmica 43(4):275–292, 2005; Raman et al. in ACM-SIAM Symposium on Discrete Algorithms (SODA), pp. 233–242, 2002). For unordered trees, the approach achieves the first succinct encoding. The approach is based on two recursive decompositions of trees into subtrees. Recursive decomposition of a structure into substructures is a common technique in succinct encodings and has even been used to encode (ordered) trees (Geary et al. in ACM Trans. Algorithms 2(4):510–534, 2006; He et al. in ICALP, pp. 509–520, 2007) and dynamic binary trees (Munro et al. in ACM-SIAM Symposium on Discrete Algorithms (SODA), pp. 529–536, 2001; Storm in Representing dynamic binary trees succinctly, Master’s thesis, 2000). The main distinction of the approach in this paper is that a tree is decomposed into subtrees in a manner that the subtrees are maximally isolated from each other. This intermediate decomposition result is interesting in its own right and has proved useful in other applications (Farzan et al. in ICALP (1), pp. 451–462, 2009; Farzan and Munro in ICALP (1), pp. 439–450, 2009; Farzan and Kamali in ICALP, 2011). 相似文献
72.
Carl Yuheng Ren Victor Prisacariu Ian Reid 《International Journal of Computer Vision》2014,106(3):269-281
We propose a novel regression based framework that uses online learned shape information to reconstruct occluded object contours. Our key insight is to regress the global, coarse, properties of shape from its local properties, i.e. its details. We do this by representing shapes using their 2D discrete cosine transforms and by regressing low frequency from high frequency harmonics. We learn this regression model using Locally Weighted Projection Regression which expedites online, incremental learning. After sufficient observation of a set of unoccluded shapes, the learned model can detect occlusion and recover the full shapes from the occluded ones. We demonstrate the ideas using a level-set based tracking system that provides shape and pose, however, the framework could be embedded in any segmentation-based tracking system. Our experiments demonstrate the efficacy of the method on a variety of objects using both real data and artificial data. 相似文献
73.
UAV Path Following in Windy Urban Environments 总被引:2,自引:0,他引:2
Mangal Kothari Ian Postlethwaite Da-Wei Gu 《Journal of Intelligent and Robotic Systems》2014,74(3-4):1013-1028
This paper considers UAV path following in cluttered environments under windy conditions. Unstructured wind patterns in cluttered environments can make path following difficult resulting in high errors and possibly collisions with buildings. Combining a pursuit guidance law philosophy with a line-of-sight guidance law, we develop a novel guidance law that has low computational complexity and can track straight line paths, circular paths, a combination of both and waypaths accurately in the presence of wind blowing as high as fifty percent of the UAV’s air speed. Performance of the guidance law is demonstrated through numerical simulations. 相似文献
74.
75.
These investigations are concerned with water-polymer interactions in polymer latices. It is known that water can act as a plasticizer for many solid polymers and cause a reduction in the glass transition temperature, Tg, of the amorphous regions. Experiments were carried out to determine whether pulsed n.m.r. techniques could be used to study the Tg of a polymer suspension and hence the influence of water and electrolyte on it. From T1 and T2 proton relaxation measurements as a function of temperature on polystyrene latex systems it was shown that the presence of water lowers the Tg of the polymer particles (by about 10°C), the effect being slightly greater in the presence of concentrated electrolyte. The extent of electrolyte penetration into the particles was deduced by studying relaxation as a function of particle diameter in latices containing paramagnetic Mn2+ ions. Using simple theories of relaxation and spin diffusion it was concluded that for all but the smallest particles electrolyte penetration is restricted to a very thin shell of the order of 1 nm. These conclusions were supported by the results of similar measurements on PTFE particles. 相似文献
76.
The strength, S , of ceramic and glass fibers often can be estimated from fractographic investigation using the fracture mirror radius, r m , and the relationship S = A m /( r m )1/2 , where A m is the "mirror constant." The present work estimates the value of A m for Tyranno® Si-Ti-C-O fibers in situ in a three-dimensional woven SiC/SiC-based composite to be 2.50 ± 0.09 MPa·m1/2 . This value is within the range of 2–2.51 MPa·m1/2 previously obtained for nominally similar Nicalon® Si-C-O fibers. 相似文献
77.
Ingvarsdóttir A Birkett MA Duce I Mordue W Pickett JA Wadhams LJ Mordue Luntz AJ 《Journal of chemical ecology》2002,28(10):2107-2117
The role of olfaction and diffusible pheromones in mate location behavior of sea lice, Lepeophtheirus salmonis, was assessed with Y-tube behavioral bioassays. The pheromone emitting animals were located in a chamber in one arm of a Y-tube arena, with artificial seawater flowing through both arms. Adult male sea lice displayed both activation and directional responses to seawater conditioned with preadult II virgin females, but were only activated by mated adult female conditioned water. Further, when males were given the choice of preadult II virgin females or mated adult females, a significant number of males chose the arm with the preadult II virgin females. Adult males showed activation responses when presented with water conditioned with adult males but were not attracted to them. When presented with adult males, preadult II virgin females showed only directional responses, but not activation responses. Preadult II virgin female conditioned water was extracted using solid-phase extraction (SPE) protocols pioneered for semiochemical isolation. Adult male sea lice showed significant directional responses to the preadult II virgin female SPE extract. Distillation under vacuum was performed on the extract to give a distillate comprising components with a molecular weight range and physical properties comparable to those of compounds utilized as volatile semiochemicals by terrestrial organisms and a residue comprising components with higher molecular weight range comparable to those utilized as involatile semiochemicals. Adult males were found to be both significantly activated and attracted to the distillate, but not to the residue. This research provides evidence that small, lipophilic organic molecules are used by sea lice as sex pheromone signals to locate a member of the opposite sex. 相似文献
78.
Durability of lingo‐cellulosic fiber composites under environmental conditions such as moisture, freezing and thawing, and UV exposure needs to be determined prior to the use of these composite materials in outdoor applications. Dimensional stability and changes in the flexural strength and stiffness of extruded rice husk filled high‐density polyethylene composites with and without processing additives such as compatibilizers and processing aid were examined after exposing the composites to water, conditions of freeze–thaw cycles, and UV light. Water absorption results indicated a decrease in the rate of penetration of water in the composites in the presence of compatibilizers. The reduction in strength and stiffness after water absorption was lower for composites with compatibilizers than for the composites without any additives. Freezing and thawing experiments also showed the dimensional changes and degradation of strength and stiffness were less in composites with compatibilizers. Presence of processing aid in the composite showed a similar or enhanced water absorption and loss of mechanical properties, compared with those of the composite without processing additives. Although the composites showed a discoloration of the surface after the UV exposure time (745 h) studied, it was found that within this period of UV exposure the flexural strength and stiffness of the composites did not show significant change. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3619–3625, 2006 相似文献
79.
80.
Bioremediation of polycyclic aromatic hydrocarbons: current knowledge and future directions 总被引:1,自引:0,他引:1
Selina M Bamforth Ian Singleton 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(7):723-736
Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds that have accumulated in the natural environment mainly as a result of anthropogenic activities such as the combustion of fossil fuels. Interest has surrounded the occurrence and distribution of PAHs for many decades due to their potentially harmful effects to human health. This concern has prompted researchers to address ways to detoxify/remove these organic compounds from the natural environment. Bioremediation is one approach that has been used to remediate contaminated land and waters, and promotes the natural attenuation of the contaminants using the in situ microbial community of the site. This review discusses the variety of fungi and bacteria that are capable of these transformations, describes the major aerobic and anaerobic breakdown pathways, and highlights some of the bioremediation technologies that are currently available. Copyright © 2005 Society of Chemical Industry 相似文献