708 resultados para 1054


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Monodisperse rare-earth ion (Eu3+, Ce3+, Tb3+) doped LaPO4 particles with oval morphology were successfully prepared through a facile solvothermal process without further hear treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) spectra and the kinetic decays were performed to characterize these samples. The XRD results reveal that all the doped samples are well crystalline at 180 degrees C and assigned to the monoclinic monazite-type structure of the LaPO4 phase. It has been shown that all the as-synthesized samples show perfectly oval morphology with narrow size distribution. The possible growth mechanism of the LapO(4):Ln has been investigated as well.

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提取量子化学参数来表征苯甲酸类化合物的结构 ,应用多元回归方法和人工神经网法在该类化合物的结构和 p Ka 值间构造了二维空间的数学模型 ,并进一步运用 Co MFA法在三维空间进行研究。人工神经网络法和 Co MFA法获得了比较好的结果 ,同时 ,讨论了空间作用和静电作用对 p Ka值的影响。

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Large amplitude internal solitary waves (ISWs) often exhibit highly nonlinear effects and may contribute significantly to mixing and energy transporting in the ocean. We observed highly nonlinear ISWs over the continental shelf of the northwestern South China Sea (19A degrees 35'N, 112A degrees E) in May 2005 during the Wenchang Internal Wave Experiment using in-situ time series data from an array of temperature and salinity sensors, and an acoustic Doppler current profiler (ADCP). We summarized the characteristics of the ISWs and compared them with those of existing internal wave theories. Particular attention has been paid to characterizing solitons in terms of the relationship between shape and amplitude-width. Comparison between theoretical prediction and observation results shows that the high nonlinearity of these waves is better represented by the second-order extended Korteweg-de Vries (KdV) theory than the first-order KdV model. These results indicate that the northwestern South China Sea (SCS) is rich in highly nonlinear ISWs that are an indispensable part of the energy budget of the internal waves in the northern South China Sea.

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铁吸收调节蛋白(Fur)是革兰氏阴性菌中普遍存在的重要的转录调控因子,它调控着不同的生命活动,包括铁的吸收,细胞的新陈代谢,应激反应以及毒力因子的合成。因此,对于许多病原菌来说,Fur在侵染和致病的过程中起到了关键性的作用。本研究从一株分离自患病牙鲆的荧光假单胞菌TSS中克隆得到了fur基因,并且发现TSS Fur能够与fur基因突变的大肠杆菌部分互补。本研究构建了一株TSS fur基因的缺失突变体TFM。研究发现与TSS相比,TFM的生长能力和抵抗宿主血清杀菌能力减弱,外膜蛋白表达异常,在宿主血液和组织中的扩散能力显著降低,并且在以牙鲆为模型的感染实验中发现TFM的毒力较TSS大幅下降。将TFM作为减毒疫苗通过注射、浸泡和口服的途径免疫牙鲆后,发现其对荧光假单胞菌和嗜水气单胞菌皆有很好的保护效应。为了进一步扩展TFM的交叉保护范围,本研究进一步构建了表达哈维氏弧菌抗原AgaV-DegQ的质粒pJAQ,并将其转入TFM中得到TFM/pJAQ。研究发现TFM/pJAQ是一种高效交叉保护疫苗,能同时保护牙鲆抵抗荧光假单胞菌、嗜水气单胞菌以及哈维氏弧菌感染。

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青藏高原特殊的气候变化特征,在区域生态系统碳动态平衡起着重要作用。本文就青藏高原不同生态系统CO_2通量的时空变化及其影响因子和控制途径进行综述,以明确青藏高原植草地生态系统的碳源汇状况及时空变化特征,为全球变化的研究提供依据。

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Previous research in force control has focused on the choice of appropriate servo implementation without corresponding regard to the choice of mechanical hardware. This report analyzes the effect of mechanical properties such as contact compliance, actuator-to-joint compliance, torque ripple, and highly nonlinear dry friction in the transmission mechanisms of a manipulator. A set of requisites for high performance then guides the development of mechanical-design and servo strategies for improved performance. A single-degree-of-freedom transmission testbed was constructed that confirms the predicted effect of Coulomb friction on robustness; design and construction of a cable-driven, four-degree-of- freedom, "whole-arm" manipulator illustrates the recommended design strategies.

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Y. Zhu, S. Williams and R. Zwiggelaar, 'A hybrid ASM approach for sparse volumetric data segmentation', Pattern Recognition and Image Analysis 17 (2), 252-258 (2007)

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Shears, J. (2006). A tale untold: The Search for a Story in Byron's Lara. The Byron Journal. 34(1), pp.1-8. RAE2008

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8 hojas : fotografías baja calidad.

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http://www.archive.org/details/acrosstheprairie00haseuoft

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PURPOSE: To develop a mathematical model that can predict refractive changes after Descemet stripping endothelial keratoplasty (DSEK). METHODS: A mathematical formula based on the Gullstrand eye model was generated to estimate the change in refractive power of the eye after DSEK. This model was applied to four DSEK cases retrospectively, to compare measured and predicted refractive changes after DSEK. RESULTS: The refractive change after DSEK is determined by calculating the difference in the power of the eye before and after DSEK surgery. The power of the eye post-DSEK surgery can be calculated with modified Gullstrand eye model equations that incorporate the change in the posterior radius of curvature and change in the distance between the principal planes of the cornea and lens after DSEK. Analysis of this model suggests that the ratio of central to peripheral graft thickness (CP ratio) and central thickness can have significant effect on refractive change where smaller CP ratios and larger graft thicknesses result in larger hyperopic shifts. This model was applied to four patients, and the average predicted hyperopic shift in the overall power of the eye was calculated to be 0.83 D. This change reflected in a mean of 93% (range, 75%-110%) of patients' measured refractive shifts. CONCLUSIONS: This simplified DSEK mathematical model can be used as a first step for estimating the hyperopic shift after DSEK. Further studies are necessary to refine the validity of this model.

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In this paper the results obtained from the parallelisation of some 3D industrial electromagnetic Finite Element codes within the ESPRIT Europort 2 project PARTEL are presented. The basic guidelines for the parallelisation procedure, based on the Bulk Synchronous Parallel approach, are presented and the encouraging results obtained in terms of speed-up on some selected test cases of practical design significance are outlined and discussed.