989 resultados para 762
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海洋设施长期处于恶劣的腐蚀环境中,如不加以防护,一旦发生应力腐蚀开裂(SCC),损失就会极为惨重。海底泥土区环境十分重要,因为管线和平台桩腿等都埋在海底泥中。海底泥中硫酸盐还原菌(SRB)十分活跃,而且为了防止腐蚀,海泥中的设施无一例外地采取了阴极保护,相当于设施处在长期稳定的充氢状态。因此非常有必要研究海泥中的活性SRB和极化电位对海洋结构用钢在海泥中的氢渗透行为和SCC敏感性造成的影响,弄清SCC发生和发展的过程以便采取相应的措施减缓或防止SCC。 本文通过慢应变速率拉伸实验(SSRT)、电化学阻抗谱(EIS)技术、动电位扫描极化曲线测定实验和氢渗透实验等研究了海泥中SRB和极化电位对16Mn钢和管线钢X56(API X56)的SCC敏感性造成的影响。 从渤海海泥中富集得到SRB菌种,并做出了SRB在海泥中的生长曲线;在荧光显微镜下观察SRB为弧状,可以归为脱硫弧菌属,为革兰氏阴性菌;海泥中活性SRB数量与硫电位等主要腐蚀环境因子具有一定的对应关系。 SSRT结果表明,施加阴极极化电位可以使试样断裂脆性特征明显,SCC敏感性增大;海泥中活性SRB浓度越高,断裂脆性特征越明显,SCC敏感性越大。在含SRB海泥中或阴极极化电位条件下,两种钢都容易发生SCC,氢脆(HIC)起主要作用。 随着浸泡天数的增加,试样在灭菌海泥中的Rp一直增大;在含SRB海泥中Rp先增大,又变小,并呈现出显著的Warburg阻抗特征;在灭菌海泥中,两种试样在阳极电位范围内无SCC敏感区,而在阴极电位范围内有明显的SCC敏感区;在含SRB海泥中,在阳极电位范围和阴极电位范围内均有SCC敏感区;SRB代谢产物既有阳极去极化作用,又有阴极去极化作用,能使腐蚀电流密度增加。 活性SRB的存在能够促进试样在海泥中的氢渗透;在实海工程应用中,两种钢在含SRB海泥中的氢渗透电流密度大约是在不含SRB海泥中的3~4倍。阴极极化电位能够促进试样在灭菌海泥中的氢渗透。在含SRB海泥中对试样施加阴极极化电位,氢渗透电流密度大于不加阴极极化电位时的氢渗透电流密度,也大于在不含SRB的海泥中的氢渗透电流密度。
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Suspended particulate matter (SPM), sediments and clams were collected at three sites in Jiaozhou Bay to assess the magnitude of trace metal pollution in the area. Metal concentrations in SPM (Cu: 40.11-203; Zn: 118-447; Pb: 50.1-132; Cd: 0.55-4.39; Cr: 147.6-288; Mn: 762-1670 mu g/g), sediments (Cu: 17.64-34.26; Zn: 80.79-110; Pb: 24.57-49.59; Cd: 0.099-0.324; Cr: 41.6-88.1; Mn: 343-520 mu g/g) and bivalves (Cu: 6.41-19.76; Zn: 35.5-85.5; Pb: 0.31-1.01; Cd: 0.51-0.67; Mn: 27.45-67.6 mu g/g) are comparable to those reported for other moderately polluted world environments. SPM showed a less clear pattern. Metal concentrations in sediments displayed a clear geographical trend with values increasing with proximity to major urban centers. The clams (on dry weight) showed a complex pattern due to the variability introduced by age-related factors. Cd showed an apparent reverse industrial trend with higher concentrations in clams collected at distant stations. Zn, Pb and Mn showed no clear geographical pattern, whereas Cu increased in the clams collected in the most industrialized area. In addition, the bioaccumulation factors (BAF) were calculated. The result indicated that the studied Ruditapes philippinarum in Jiaozhou Bay possessed different bioaccumulation capacities for Cd, Zn, Cu, Pb and Mn, and Cd, Zn had a relatively high assimilation of those metals from sediment particles. A significant relationship with clam age was observed for Zn (positive) and Cu (negative) suggesting different physiological requirements for both metals with age. Trace metal concentrations measured in the tissue of the investigated clam were in the range considered safe by the WHO for human use.
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唐古特白刺(Nitraria tangutorum Bohr.)是蒺藜科白刺属的一个品种,在柴达木盆地的沙漠绿洲边缘,盐碱沙滩地大量分布,生境海拔1900—3500m,分布面积约25万km^2。据我们调查,盆地相对集中成片具有开发价值的天然白刺林约50-60万亩,每年产白刺鲜果5—10万吨。具有较高的经济和药用价值.
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目的建立了青海地区唐古特大黄药材的HPLC指纹图谱.方法采用反相高效液相色谱法,乙腈-水(0.04%的磷酸)为流动相,梯度洗脱,体积流量1.0 mL/min,检测波长为280 nm,柱温为40 C.结果精密度、重现性、稳定性试验中共有峰面积和保留时间的RSD均小于5%.青海不同采集地唐古特大黄的平均相似度为0.925.结论该方法简便、实用、可靠,可用于以青海果洛地区为主产地不同海拔唐古特大黄药材质量标准的分析检测,也为栽培大黄代替野生大黄提供理论基础.
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在Y字型选择箱中进行3种不同熟悉处理的配偶选择实验以检验动情雌性根田鼠配偶选择时的亲属识别和近交回避。(1)动情雌鼠在熟悉雄性同胞和陌生非同胞之间嗅添频次和时间、及自我修饰时间的差异非常显著(P<0.01),所作的脊柱前凸反应时间也有显著差异(P<0.05),这些行为均多针对于陌生非同胞雄性。结果提示动情雌性根田鼠在熟知雄性同胞身份的条件下对陌生非亲属雄性的气味更感兴趣,在择偶中与非亲属雄性交配来实现近交回避。(2)动情雌鼠对陌生雄性非同胞的嗅添频次和时间及所作的脊柱前凸反应时间显著大于陌生同胞雄性(P<0.05),而针对陌生雄性非同胞自我修饰时间非常显著地大于针对陌生雄性同胞(P<0.01)。这说明动情雌性根田鼠在择偶时可以识别断奶后分离不熟悉的雄性亲属,而在交配行为上偏向于非亲属雄性。(3)动情雌鼠在熟悉雄性同胞和非同胞之间跃添时间差异明显(P<0.05),嗅添频次的差异更甚(P<0.01);所作的脊柱前凸反应时间和社交后自我修饰时间差异也非常显著(P<0.01),这些行为也均都偏向于非同胞雄性;结果提示断奶后继续熟悉可维持动情雌鼠对雄性亲属的嗅觉识别记忆力,在交配行为上主动回避亲属雄性。故认为:断奶后嗅觉识别持久力是发情雌性根田鼠亲属识别的机制,亲属识别是最初发情的雌性根田鼠配偶选择中近交回避的首要途径和机制,熟悉性是维持雌性根田鼠配偶选择实现近交回避的机制和特征。
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Metagentiana striata is an alpine annual herbaceous plant endemic to the east of the Qinghai-Tibet (Q-T) Plateau and adjacent areas. The phylogeography of M. striata was studied by sequencing the chloroplast DNA (cpDNA) trnS-trnG intergenic spacer. Ten haplotypes were identified from an investigation of 232 individuals of M. striata from 14 populations covering the entire geographical range of this species. The level of differentiation amongst populations was very high (G(ST) = 0.746; N-ST = 0.774) and a significant phylogeographical structure was observed (P < 0.05). An analysis of molecular variance found a high variation amongst populations (76%), with F-ST = 0.762 (highly significant, P < 0.001), indicating that little gene flow occurred amongst the different regions; this was explained by the isolation of populations by high mountains along the Q-T Plateau and adjacent areas (N-m = 0.156). Only one ancestral haplotype (A) was common and widespread throughout the distributional range of M. striata. The populations of the Hengduan Mountains region of the south-eastern Q-T Plateau showed high diversity and uniqueness of haplotypes. It is suggested that this region was the potential refugium of M. striata during the Quaternary glaciation, and that interglacial and postglacial range expansion occurred from this refugium. This scenario was in good agreement with the results of nested clade analysis, which inferred that the current spatial distribution of cpDNA haplotypes and populations resulted from range expansion, together with past allopatric fragmentation events. (c) 2008 The Linnean Society of London.
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Olusanya, O. (2004). Double Jeopardy Without Parameters: Re-characterization in International Criminal Law. Series Supranational Criminal Law: Capita Selecta, volume 2. Antwerp: Intersentia. RAE2008
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Wilkinson, Jane, 'The Place of the European Foreigner in Contemporary German Drama', Third Text (2006) 20(6) pp.753-762 RAE2008 Special Issue: FORTRESS EUROPE: Migration, Culture and Representation
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http://www.archive.org/details/callqualificatio00studuoft
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The trend towards miniaturization of electronic products leads to the need for very small sized solder joints. Therefore, there is a higher reliability risk that too large a fraction of solder joints will transform into Intermetallic Compounds (IMCs) at the solder interface. In this paper, fracture mechanics study of the IMC layer for SnPb and Pb-free solder joints was carried out using finite element numerical computer modelling method. It is assumed that only one crack is present in the IMC layer. Linear Elastic Fracture Mechanics (LEFM) approach is used for parametric study of the Stress Intensity Factors (SIF, KI and KII), at the predefined crack in the IMC layer of solder butt joint tensile sample. Contrary to intuition, it is revealed that a thicker IMC layer in fact increases the reliability of solder joint for a cracked IMC. Value of KI and KII are found to decrease with the location of the crack further away from the solder interfaces while other parameters are constant. Solder thickness and strain rate were also found to have a significant influence on the SIF values. It has been found that soft solder matrix generates non-uniform plastic deformation across the solder-IMC interface near the crack tip that is responsible to obtain higher KI and KII.
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Granular air-borne particles generally carry very small amounts of electric charge as a consequence of charging by the triboelectric effect. The presence of such particles induces charge of opposite polarity on a stationary conducting electrode. The amount of charge carried by the particles and the trajectories of the particles have significant random components and the signals produced are of very low level. The signal processing is further complicated by the random variation in the concentration of particles, i.e. the solid/gas ratio. This paper compares the results obtained from the electrostatic modelling of such sensors with those obtained from experiments.
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El presente estudio tiene el objetivo de ofrecer una visión general sobre los Modelos de Desarrollo y Organización Territorial desde la perspectiva de las relaciones entre el medio urbano, “rururbano” y rural, en España. Para ello, tras conocer y valorar los enfoque conceptuales y temáticos, se estudia el crecimiento urbano en nuestro país en las últimas décadas, analizando de manera pormenorizada la importancia que ha cobrado y cobra la aplicación legislativa de leyes, planes y normas, tanto en el propio crecimiento urbano como en la demanda de viviendas en las ciudades españolas y, de igual modo, la vinculación de ambas con el precio de las viviendas, relacionándolo con la problemática de la “rururbanización”, y del medio rural.
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La Cadena Datos-Información-Conocimiento (DIC), denominada “Jerarquía de la Información” o “Pirámide del Conocimiento”, es uno de los modelos más importantes en la Gestión de la Información y la Gestión del Conocimiento. Por lo general, la estructuración de la cadena se ha ido definiendo como una arquitectura en la que cada elemento se levanta sobre el elemento inmediatamente inferior; sin embargo no existe un consenso en la definición de los elementos, ni acerca de los procesos que transforman un elemento de un nivel a uno del siguiente nivel. En este artículo se realiza una revisión de la Cadena Datos-Información-Conocimiento examinando las definiciones más relevantes sobre sus elementos y sobre su articulación en la literatura, para sintetizar las acepciones más comunes. Se analizan los elementos de la Cadena DIC desde la semiótica de Peirce; enfoque que nos permite aclarar los significados e identificar las diferencias, las relaciones y los roles que desempeñan en la cadena desde el punto de vista del pragmatismo. Finalmente se propone una definición de la Cadena DIC apoyada en las categorías triádicas de signos y la semiosis ilimitada de Peirce, los niveles de sistemas de signos de Stamper y las metáforas de Zeleny.
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Background: In order to isolate the â??bestâ?? sperm for assisted conception a discontinuous two-step density gradient centrifugation is usually employed. This technique is known to isolate a subpopulation with good motility, morphology and nuclear DNA (nDNA) integrity. As yet its ability to isolate sperm with unfragmented mitochondrial DNA (mtDNA) is unknown. Methods: Semen was obtained from men (n=28) attending our Regional Fertility Centre for infertility investigations. We employed a modified long polymerase chain reaction to study mtDNA and a modified alkaline Comet assay to determine nDNA fragmentation. Results: The high- density fraction displayed significantly more wild type mtDNA (75% of samples) than that of the low- density fraction (25% of samples). In the high-density fraction, there was a higher incidence of single, rather than double or multiple deletions and the deletions were predominantly small scale (0.1-4.0kb). There was a strong correlation between nDNA fragmentation, the number of mtDNA deletions (r=0.7, p