973 resultados para uncertain polynomials


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With 210 genera and 2010 species, Cyprinidae is the largest freshwater fish family in the world. Several papers, based on morphological and molecular data, have been published and have led to some solid conclusions, such as the close relationships between North American phoxinins and European leuciscins. However, the relationships among major subgroups of this family are still not well resolved, especially for those East Asian groups. In the present paper, the mitochondrial DNA (mtDNA) control region, 896-956 base pairs, of 17 representative species of East Asian cyprinids was sequenced and compared with those of 21 other cyprinids to study their phylogenetic relationships. After alignment, there were 1051 sites. The comparison between pairwise substitutions and HKY distances showed that the mtDNA control region was suitable for phylogenetic study. Phylogenetic analysis indicated that there are two principal lineages in Cyprinidae: Cyprinine and Leuciscine. In Cyprinine, the relationships could be a basal Labeoinae, an intermediate Cyprininae, and a diversified Barbinae (including Schizothroaxinae). In Leuciscine, Rasborinae is at the basal position; Gobioninae and Leuciscinae are sister groups; the East Asian cultrin-xenocyprinin taxa form a large monophyletic group with some small affiliated groups; and the positions of Acheilognathinae and Tincinae are still uncertain.

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The largest damming project to date, the Three Gorges Dam has been built along the Yangtze River (China), the most species-rich river in the Palearctic region. Among 162 species of fish inhabiting the main channel of the upper Yangtze, 44 are endemic and are therefore under serious threat of global extinction from the dam. Accordingly, it is urgently necessary to develop strategies to minimize the impacts of the drastic environmental changes associated with the dam. We sought to identify potential reserves for the endemic species among the 17 tributaries in the upper Yangtze, based on presence/absence data for the 44 endemic species. Potential reserves for the endemic species were identified by characterizing the distribution patterns of endemic species with an adaptive learning algorithm called a "self-organizing map" (SOM). Using this method, we also predicted occurrence probabilities of species in potential reserves based on the distribution patterns of communities. Considering both SOM model results and actual knowledge of the biology of the considered species, our results suggested that 24 species may survive in the tributaries, 14 have an uncertain future, and 6 have a high probability of becoming extinct after dam filling.

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Optical waveguide propagation loss measurement method based on optical multiple reflections detection is presented in this paper. By using a precision reflectometer, uncertain influence on waveguide propagation loss measurement caused by fiber-waveguide coupling can be eliminated effectively and the waveguide net propagation loss can be measured accurately. To demonstrate this, the propagation loss of a Silicon-on-Insulator (SOI) rib waveguide fabricated by RIE is measured with the obtained value being 4.3 dB/cm. This method provides a non-destructive means for evaluating waveguide propagation loss. (c) 2005 Elsevier B.V. All rights reserved.

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Almost free-standing single crystal mesoscale and nanoscale dots of ferroelectric BaTiO(3) have been made by direct focused ion beam patterning of bulk single crystal material. The domain structures which appear in these single crystal dots, after cooling through the Curie temperature, were observed to form into quadrants, with each quadrant consisting of fine 90 degrees stripe domains. The reason that these rather complex domain configurations form is uncertain, but we consider and discuss three possibilities for their genesis: first, that the quadrant features initially form to facilitate field-closure, but then develop 90 degrees shape compensating stripe domains in order to accommodate disclination stresses; second, that they are the result of the impingement of domain packets which nucleate at the sidewalls of the dots forming "Forsbergh" patterns (essentially the result of phase transition kinetics); and third, that 90 degrees domains form to conserve the shape of the nanodot as it is cooled through the Curie temperature but arrange into quadrant packets in order to minimize the energy associated with uncompensated surface charges (thus representing an equilibrium state). While the third model is the preferred one, we note that the second and third models are not mutually exclusive.

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We present a class of indecomposable polynomials of non prime-power degree over the finite field of two elements which are permutation polynomials on infinitely many finite extensions of the field. The associated geometric monodromy groups are the simple ...

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近年来,人们对于如何表示和处理移动对象的不确定性进行了研究,提出了一些较为有效的模型和算法。但是,在如何索引移动对象的不确定时空轨迹方面,相关的研究工作十分有限。为了解决上述问题,本文提出了一种网络受限移动对象不确定轨迹的索引结构(UTIi—Tree),并给出了相关的索引更新及查询算法。在该索引结构的支持下,移动对象数据库不仅可以快速地处理对移动对象过去可能位王的查询,而且能够对其现在及将来的可能位置进行高效的查询处理。

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移动对象的轨迹预测研究已成为当前移动对象研究中关注的热点,移动对象的轨迹预测技术具有高度的研究价值及广阔的应用前景.目前移动对象的轨迹预测方法主要是针对历史轨迹确定的欧氏空间轨迹预测,但有相当一部分的应用要求预测历史轨迹存在不确定性的移动对象在受限路网中的轨迹.为了解决这一问题,首先提出了不确定性轨迹的生成方法及其表示形式,然后提出了一种基于路网的不确定性轨迹频繁模式挖掘算法,最后给出了利用索引快速查找轨迹模式并进行预测的方法.实验结果表明该方法具有较高的预测准确率、较好的查询效率以及较低的存储空间.

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A critical Biot number, which determines both the sensitivity of spherical ceramics to quenching and the durations of the temperature-wave propagation and the thermal stresses in the ceramics subjected to thermal shock, is theoretically obtained. The results prove that once the Biot number of a ceramic sphere is greater than the critical number, its thermal shock failure will be such a rapid process that the failure only occurs in the initial regime of heat conduction, whereas the thermal shock failure of the ceramic sphere is uncertain in the course of heat conduction. The presented results provide a guide to the selection of the ceramics applied in the thermostructural engineering with thermal shock.

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High-speed free-space optical communication systems have recently used fiber-optical components. The coupling efficiency with which the received laser beam can be coupled into a single-mode fiber is noticeably limited by atmospheric turbulence due to the degradation of its spatial coherence. Fortunately, adaptive optics (AO) can alleviate this limitation by partially correcting the turbulence-distorted wavefront. The coupling efficiency improvement provided by Zernike modal AO correction is numerically evaluated. It is found that the first 3-20 corrected polynomials can considerably improve the fiber-coupling efficiency. The improvement brought by AO is compared with that brought by a coherent fiber array. Finally, a hybrid technique that integrates AO and a coherent fiber array is proposed. Results show that the hybrid technique outperforms each of the two above-mentioned techniques. (C) 2009 Elsevier GmbH. All rights reserved.

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The nuclear symmetry energy E-sym(rho) is the most uncertain part of the Equation of State (EOS) of dense neutron-rich nuclear matter. In this talk, we discuss the underlying physics responsible for the uncertain E-sym(rho) especially at supra-saturation densities, the circumstantial evidence for a super-soft E-sym(rho) from analyzing pi(-)/pi(+) ratio in relativistic heavy-ion collisions and its impacts on astrophysics and cosmology.

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Ligand-to-metal charge transfer energies of YBO3:Eu have been investigated from the chemical bond viewpoint. The chemical bond parameters, such as the covalency, the polarizability of the chemical bond volume, and the presented charge of the ligands in the chemical bond have been quantitatively determined based on the dielectric theory of complex crystal. We calculated the environmental factor (h(e)), which is the major factor influencing the charge transfer energy in the compounds. The calculated results show that the suitable group space of YBO3 is C2/c. The method provides us with a supplementary tool to judge the proper structure when the structure of the crystal has many uncertain space groups.

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The major protein component of the amyloid deposition in Alzheimer's disease is a 39-43 residue peptide, amyloid beta (A beta). A beta is toxic to neurons, although the mechanism of neurodegeneration is uncertain. Evidence exists for non-B DNA conformation in the hippocampus of Alzheimer's disease brains, and A beta was reportedly able to transform DNA conformation in vitro. In this study, we found that DNA conformation was altered in the presence of A beta, and A beta induced DNA condensation in a time-dependent manner. Furthermore, A beta sheets, serving as condensation nuclei, were crucial for DNA condensation, and Cu2+ and Zn2+ ions inhibited A beta sheet-induced DNA condensation. Our results suggest DNA condensation as a mechanism of A beta toxicity.

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Based on the data analysis, this study further explores the characteristics of East Asian winter monsoon (hereafter, EAWM, for brevity) as well as the related air-sea-land system, and illustrates how and to what degree anomalous signals of the subsequent Asian summer monsoon are rooted in the preceding EAWM activity. We identified an important air-sea coupled mode, i.e., the EAWM mode illustrated in Section 3. In cold seasons, strong EAWM-related air-sea two-way interaction is responsible for the development and persistence of the SSTA pattern of EAWM mode. As a consequence, the key regions, i.e., the western Pacific and South China Sea (hereafter, SCS, for brevity), are dominated by such an SSTA pattern from the winter to the following summer. In the strong EAWM years, the deficient snow cover dominates eastern Tibetan Plateau in winter, and in spring, this anomaly pattern is further strengthened and extended to the northwestern side of Tibetan Plateau. Thus, the combined effect of strong EAWM-related SSTA and Tibetan snow cover constitutes an important factor in modulating the Asian monsoon circulation. The active role of the EAWM activity as well as the related air-sea-land interaction would, in the subsequent seasons, lead to: 1) the enhancement of SCS monsoon and related stronger rainfall; 2) the northward displacement of subtropical high during Meiyu period and the related deficient rainfall over Meiyu rainband; 3) above-normal precipitation over the regions from northern Japan to northeastern China in summer; 4) more rainfall over the Arabian Sea and Northeast India, while less rainfall over southwest India and the Bay of Bengal. The strong EAWM-related air-sea interaction shows, to some degree, precursory signals to the following Asian summer monsoon. However, the mechanism for the variability of Indian summer monsoon subsequent to the strong EAWM years remains uncertain.

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The Ludox-QPS method is a newly developed technique, which combines the Ludox HS 40 density centrifugation and quantitative protargol stain, to enumerate marine ciliates with good taxonomic resolution. We tested the method for simultaneous enumeration of diatoms, protozoa and meiobenthos and compared its extraction efficiency for meiobenthos with that of the routine Ludox-TM centrifugation and a modified protocol using Ludox HS 40. We conducted the evaluation with a sample size of 8.3 ml each from sandy, muddy-sand and muddy sediments collected from the intertidal area of the Yellow Sea in summer 2006 and spring 2007. The Ludox-QPS method not only produced high extraction efficiencies of 97 +/- 1.3% for diatoms and 97.6 +/- 0.8% for ciliates, indicating a reliable enumeration for eukaryotic microbenthos, but also produced excellent extraction efficiencies of on average 97.3% for total meiobenthos, 97.9% for nematodes and 97.8% for copepods from sands, muddy sands and mud. By contrast, the routine Ludox-TM centrifugation obtained only about 74% of total meiobenthos abundance with one extraction cycle, and the modified Ludox HS 40 centrifugation yielded on average 93% of total meiobenthos: 89.4 +/- 2.0% from sands, 93 +/- 4.1% from muddy sands and 97.1 +/- 3.0% from mud. Apart from the sediment type, sample volume was another important factor affecting the extraction efficiency for meiobenthos. The extraction rate was increased to about 96.4% when using the same modified Ludox centrifugation for a 4 ml sediment sample. Besides the excellent extraction efficiency, the Ludox-QPS method obtained higher abundances of meiobenthos, in particular nematodes, than the routine Ludox centrifugation, which frequently resulted in an uncertain loss of small meiobenthos during the sieving process. Statistical analyses demonstrated that there were no significant differences between the meiobenthos communities revealed by the Ludox-QPS method and the modified Ludox HS 40 centrifugation, showing the high efficiency of the Ludox-QPS method for simultaneous enumeration of diatom, protozoa and meiobenthos. Moreover, the comparatively high taxonomic resolution of the method, especially for diatoms and ciliates, makes it feasible to investigate microbial ecology at community level.