999 resultados para 465


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雌雄异熟和异型花在一些被子植物中的共同存在被认为是一种有效避免两性花植物自交并促进异交的机制。本文报道青藏高原特有植物祁连獐牙菜Swertia przewalskii pissjauk.的花同时具有雌雄异熟和异型花这两种特征。在此基础上,我们详细观察了该植物访花昆虫的访花行为,主要探讨这种促进异花传粉的机制是否能完全避免株内异花传粉的自交。繁育系统试验证明祁连獐牙菜单花套袋不结实,说明雌雄异熟和异型花的花特征完全避免了单花的自花传粉,自然结实必须依赖昆虫传粉才能完成。然而,该植物却是高度自交亲和的,因为人工株内异花自交具有较高的种子结实率。每个植株在盛花期开放1-6朵,平均具有3朵开放的雄性期或者雌性期的花,二者的比例为2:1,在植株上的分布没有规律。我们观察到多种昆虫访问该植物的花,其中,克什米尔熊蜂Bumbuskeshimirensis Friese和蜜蜂如Apis mellifera L.是该植物最常见与最有效的传粉者。进一步的观察发现,这两类传粉昆虫对雌性阶段和雄性阶段的花的访问没有选择,但在一个植株上访花顺序的总体趋势是由下向上的。它们在同一植株上访花数超过1朵的访问比例约占37.1%。因此可以初步推断,祁连獐牙菜中异型花和雌雄异熟现象的共同存在并没有完全避免同株异花传粉导致的自交。结果支持两性花中的这种雌雄异熟和异型花现象可能在避免两性冲突上具有更为重要的功能。

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石灰土是广泛分布于亚热带喀斯特山区的一种非地带性土壤,近几十年来,位于西南喀斯特分布中心的贵州石灰土地区石漠化扩张速度明显加快,已经对该地区数千万群众的基本生存条件构成严重威胁。本文从地质学角度详细分析了这一地区石灰土土壤侵蚀和土地石漠化的形成原因,分析结果表明:石灰土本身的矿物学特征和基本理化性质较好,并不是造成土壤侵蚀和石漠化的主要原因。石灰土成土速率慢,土壤允许流失量小;作为土壤营养库的富含有机质和矿质养分的表土层一旦被剥蚀,土壤结构迅速退化,土壤侵蚀愈演愈烈;喀斯特独特的二元结构和地形地

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云南白马寨镍矿区煌斑岩全部为云煌岩.两个样品的^40Ar/^39Ar定年结果分别为32.46±0.62Ma和32.01±0.60Ma,表明矿区煌斑岩为哀牢山断裂带新生代早期高钾岩浆活动的产物.在化学组成上,矿区煌斑岩具有高M值[100×Mg/(Mg+Fe^2+)](67.42~86.35)、高ALK(K2O+Na2O为7.01%~9.81%)、富钾(K2O/Na2O为1.66~2.64)、富大离子亲石元素(如Sr、Rb、Ba等)和LREE、明显的Ta、Nb、Ti负异常的特征.Sr-Nd同位素具有高(^87Sr/^86Sr)0比值(0.70625~0.70912)和低εNd(-5.22~-3.68)的特征,位于EM1和EM2地幔端元之间,有更靠近EM2的趋势.元素和同位素地球化学特征表明矿区煌斑岩的源区为交代富集地幔,进一步判别表明源岩处于尖晶石相方辉橄榄岩和石榴石相二辉橄榄岩的混合线上,以尖晶石相方辉橄榄岩为主.源区交代富集的矿物既有金云母,也有角闪石.岩浆演化过程中经历了橄榄石+斜长石±磷灰石±铁钛氧化物的结晶分异.岩浆形成于大陆弧的构造背景,俯冲的陆壳和古特提斯洋壳对富集的源区均有贡献.白马寨镍矿区煌斑岩和哀牢山断裂带新生代早期其它高钾岩浆岩具有相近的年代、一致的地球化学特征,表明它们具有相似的源区,受控于相同的构造背景.

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Wilson, M.S. and Neal, M.J., 'Diminishing Returns of Engineering Effort in Telerobotic Systems', IEEE Transactions on Systems, Man and Cybernetics - Part A:Systems and Humans, 2001, September, volume 31, number 5, pp 459-465, IEEE Robotics and Automation Society, ed. Dautenhahn,K., Special Issue on Socially Intelligent Agents - The Human in the Loop

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IEEE Transactions on Knowledge and Data Engineering, vol. 15, no. 5, pp. 1338-1343, 2003.

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Davison, G. and Gleeson, M. (2005). Influence of Acute Vitamin C and/or Carbohydrate Ingestion on Hormonal, Cytokine, and Immune Responses to Prolonged Exercise. International Journal of Sport Nutrition and Exercise Metabolism. 15(5), pp.465-479 RAE2008

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This thesis is focused on the design and development of an integrated magnetic (IM) structure for use in high-power high-current power converters employed in renewable energy applications. These applications require low-cost, high efficiency and high-power density magnetic components and the use of IM structures can help achieve this goal. A novel CCTT-core split-winding integrated magnetic (CCTT IM) is presented in this thesis. This IM is optimized for use in high-power dc-dc converters. The CCTT IM design is an evolution of the traditional EE-core integrated magnetic (EE IM). The CCTT IM structure uses a split-winding configuration allowing for the reduction of external leakage inductance, which is a problem for many traditional IM designs, such as the EE IM. Magnetic poles are incorporated to help shape and contain the leakage flux within the core window. These magnetic poles have the added benefit of minimizing the winding power loss due to the airgap fringing flux as they shape the fringing flux away from the split-windings. A CCTT IM reluctance model is developed which uses fringing equations to accurately predict the most probable regions of fringing flux around the pole and winding sections of the device. This helps in the development of a more accurate model as it predicts the dc and ac inductance of the component. A CCTT IM design algorithm is developed which relies heavily on the reluctance model of the CCTT IM. The design algorithm is implemented using the mathematical software tool Mathematica. This algorithm is modular in structure and allows for the quick and easy design and prototyping of the CCTT IM. The algorithm allows for the investigation of the CCTT IM boxed volume with the variation of input current ripple, for different power ranges, magnetic materials and frequencies. A high-power 72 kW CCTT IM prototype is designed and developed for use in an automotive fuelcell-based drivetrain. The CCTT IM design algorithm is initially used to design the component while 3D and 2D finite element analysis (FEA) software is used to optimize the design. Low-cost and low-power loss ferrite 3C92 is used for its construction, and when combined with a low number of turns results in a very efficient design. A paper analysis is undertaken which compares the performance of the high-power CCTT IM design with that of two discrete inductors used in a two-phase (2L) interleaved converter. The 2L option consists of two discrete inductors constructed from high dc-bias material. Both topologies are designed for the same worst-case phase current ripple conditions and this ensures a like-for-like comparison. The comparison indicates that the total magnetic component boxed volume of both converters is similar while the CCTT IM has significantly lower power loss. Experimental results for the 72 kW, (155 V dc, 465 A dc input, 420 V dc output) prototype validate the CCTT IM concept where the component is shown to be 99.7 % efficient. The high-power experimental testing was conducted at General Motors advanced technology center in Torrence, Los Angeles. Calorific testing was used to determine the power loss in the CCTT IM component. Experimental 3.8 kW results and a 3.8 kW prototype compare and contrast the ferrite CCTT IM and high dc-bias 2L concepts over the typical operating range of a fuelcell under like-for-like conditions. The CCTT IM is shown to perform better than the 2L option over the entire power range. An 8 kW ferrite CCTT IM prototype is developed for use in photovoltaic (PV) applications. The CCTT IM is used in a boost pre-regulator as part of the PV power stage. The CCTT IM is compared with an industry standard 2L converter consisting of two discrete ferrite toroidal inductors. The magnetic components are compared for the same worst-case phase current ripple and the experimental testing is conducted over the operation of a PV panel. The prototype CCTT IM allows for a 50 % reduction in total boxed volume and mass in comparison to the baseline 2L option, while showing increased efficiency.

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Recent years have witnessed a rapid growth in the demand for streaming video over the Internet and mobile networks, exposes challenges in coping with heterogeneous devices and varying network throughput. Adaptive schemes, such as scalable video coding, are an attractive solution but fare badly in the presence of packet losses. Techniques that use description-based streaming models, such as multiple description coding (MDC), are more suitable for lossy networks, and can mitigate the effects of packet loss by increasing the error resilience of the encoded stream, but with an increased transmission byte cost. In this paper, we present our adaptive scalable streaming technique adaptive layer distribution (ALD). ALD is a novel scalable media delivery technique that optimises the tradeoff between streaming bandwidth and error resiliency. ALD is based on the principle of layer distribution, in which the critical stream data are spread amongst all packets, thus lessening the impact on quality due to network losses. Additionally, ALD provides a parameterised mechanism for dynamic adaptation of the resiliency of the scalable video. The Subjective testing results illustrate that our techniques and models were able to provide levels of consistent high-quality viewing, with lower transmission cost, relative to MDC, irrespective of clip type. This highlights the benefits of selective packetisation in addition to intuitive encoding and transmission.

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β-arrestins are versatile adapter proteins that form complexes with most G-protein-coupled receptors (GPCRs) following agonist binding and phosphorylation of receptors by G-protein-coupled receptor kinases (GRKs). They play a central role in the interrelated processes of homologous desensitization and GPCR sequestration, which lead to the termination of G protein activation. β-arrestin binding to GPCRs both uncouples receptors from heterotrimeric G proteins and targets them to clathrincoated pits for endocytosis. Recent data suggest that β-arrestins also function as GPCR signal transducers. They can form complexes with several signaling proteins, including Src family tyrosine kinases and components of the ERK1/2 and JNK3 MAP kinase cascades. By recruiting these kinases to agonist-occupied GPCRs, β-arrestins confer distinct signaling activities upon the receptor. β-arrestin-Src complexes have been proposed to modulate GPCR endocytosis, to trigger ERK1/2 activation and to mediate neutrophil degranulation. By acting as scaffolds for the ERK1/2 and JNK3 cascades, β-arrestins both facilitate GPCR-stimulated MAP kinase activation and target active MAP kinases to specific locations within the cell. Thus, their binding to GPCRs might initiate a second wave of signaling and represent a novel mechanism of GPCR signal transduction.

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The Computer Aided Parallelisation Tools (CAPTools) [Ierotheou, C, Johnson SP, Cross M, Leggett PF, Computer aided parallelisation tools (CAPTools)-conceptual overview and performance on the parallelisation of structured mesh codes, Parallel Computing, 1996;22:163±195] is a set of interactive tools aimed to provide automatic parallelisation of serial FORTRAN Computational Mechanics (CM) programs. CAPTools analyses the user's serial code and then through stages of array partitioning, mask and communication calculation, generates parallel SPMD (Single Program Multiple Data) messages passing FORTRAN. The parallel code generated by CAPTools contains calls to a collection of routines that form the CAPTools communications Library (CAPLib). The library provides a portable layer and user friendly abstraction over the underlying parallel environment. CAPLib contains optimised message passing routines for data exchange between parallel processes and other utility routines for parallel execution control, initialisation and debugging. By compiling and linking with different implementations of the library, the user is able to run on many different parallel environments. Even with today's parallel systems the concept of a single version of a parallel application code is more of an aspiration than a reality. However for CM codes the data partitioning SPMD paradigm requires a relatively small set of message-passing communication calls. This set can be implemented as an intermediate `thin layer' library of message-passing calls that enables the parallel code (especially that generated automatically by a parallelisation tool such as CAPTools) to be as generic as possible. CAPLib is just such a `thin layer' message passing library that supports parallel CM codes, by mapping generic calls onto machine specific libraries (such as CRAY SHMEM) and portable general purpose libraries (such as PVM an MPI). This paper describe CAPLib together with its three perceived advantages over other routes: - as a high level abstraction, it is both easy to understand (especially when generated automatically by tools) and to implement by hand, for the CM community (who are not generally parallel computing specialists); - the one parallel version of the application code is truly generic and portable; - the parallel application can readily utilise whatever message passing libraries on a given machine yield optimum performance.

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In this paper, coupled fire and evacuation simulation tools are used to simulate the Station Nightclub fire. This study differs from the analysis conducted by NIST in three key areas; (1)an enhanced flame spread model and (2)a toxicity generation model are used, (3)the evacuation is coupled to the fire simulation. Predicted early burning locations in the full-scale fire simulation are in line with photographic evidence and the predicted onset of flashover is similar to that produced by NIST. However, it is suggested that both predictions of the flashover time are approximately 15 sec earlier than actually occurred. Three evacuation scenarios are then considered, two of which are coupled with the fire simulation. The coupled fire and evacuation simulation suggests that 180 fatalities result from a building population of 460. With a 15 sec delay in the fire timeline, the evacuation simulation produces 84 fatalities which are in good agreement with actual number of fatalities. An important observation resulting from this work is that traditional fire engineering ASET/RSET calculations which do not couple the fire and evacuation simulations have the potential to be considerably over optimistic in terms of the level of safety achieved by building designs.

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