Individual growth rates and movement of juvenile white shrimp (Litopenaeus setiferus) in a tidal marsh nursery

We measured growth and movements of individually marked free-ranging juvenile white shrimp (Litopenaeus setiferus) in tidal creek subsystems of the Duplin River, Sapelo Island, Georgia. Over a period of two years, 15,974 juvenile shrimp (40−80 mm TL) were marked internally with uniquely coded microwire tags and released in the shallow upper reaches of four salt marsh tidal creeks. Subsequent samples were taken every 3−6 days from channel segments arranged at 200-m intervals along transects extending from the upper to lower reach of each tidal creek. These collections included 201,384 juvenile shrimp, of which 184 were marked recaptures. Recaptured shrimp were at large an average of 3−4 weeks (range: 2−99 days) and were recovered a mean distance of <0.4 km from where they were initially marked. Mean residence times in the creek subsystems ranged from 15.2 to 25.5 days and were estimated from exponential decay functions describing the proportions of marked individuals recaptured with increasing days at large. Residence time was not significantly correlated with creek length (Pearson=−0.316, P=0.684 ), but there was suggestive evidence of positive associations with either intertidal (Pearson r=0.867, P=0.133) or subtidal (Pearson r=0.946, P=0.054) drainage area. Daily mean specific growth rates averaged 0.009 to 0.013 among creeks; mean absolute growth rates ranged from 0.56−0.84 mm/d, and were lower than those previously reported for juvenile penaeids in estuaries of the southeastern United States. Mean individual growth rates were not significantly different between years (t-test, P>0.30) but varied significantly during the season, tending to be greater in July than November. Growth rates were size-dependent, and temporal changes in size distributions rather than temporal variation in physical environmental factors may have accounted for seasonal differences in growth. Growth rates differed between creeks in 1999 (t-test, P<0.015), but not in 1998 (t-test, P>0.5). We suggest that spatial variation in landscape structure associated with access to intertidal resources may have accounted for this apparent interannual difference in growth response.

塔里木河下游植被和景观格局变化及其驱动力分析

利用RS和GIS手段相结合的方法研究了塔里木河下游的植被和景观变化，并分析了由于历史时期塔里木河水流量的变化而导致的地下水位变化、环境因子和人类活动对植被及景观格局的影响。 对环境因子与植被覆盖变化关系的分析结果发现： ⑴在1987年至2004年占研究区总面积26％的景观发生变化；而植被和水体的变化最大；植被的变化中荒漠化和转化为农田是其主要的变化类型。1987年至2004年，仅有占总面积39％的植被没有发生变化，而发生荒漠化和盐碱化的植被仅有少数能够恢复。 ⑵在选取的环境因子中，植被缀块的起始NDVI和植被缀块距河道的距离对植被变化的影响最大，其次为海拔、坡度、缀块形状和缀块距离居民点的距离；而坡向和缀块面积与植被变化的关系较小。发生荒漠化的植被缀块距离河道较远且自身的NDVI较低，表明这些植被缀块的变化主要是受到水资源的限制；而转化为农田的植被缀块自身的NDVI较高且距河道较近，表明人类的开垦活动主要在植被生长较好的地区进行。研究期间内能够保持的植被距河道较近且NDVI较低，这与能够保留的植被主要是较稀疏的胡杨林有关。 ⑶植被缀块距河道的距离在1987年至1999年间与植被的变化显著相关，而在1999年至2004年相关不显著，这表明影响植被变化的影响环境因子随时间变化。 ⑷虽然所选取的环境因子对植被变化的解释力偏低，但在某些时间段对植被变化的解释力可以达到40％。如果增加环境因子，使用梯度分析的方法可以较好的解释环境及其它因子对植被变化的影响。 对地下水位变化对植被及景观时空格局变化的研究结果发现： ⑴在地下水水位剧烈下降的1986年至1999年，植被面积减少30％，距离河道最近的区域减少最多，植被占总面积的比例和植被的减少随距离河道距离的增加而减小；平均NDVI降低；荒漠面积增加4.8％，年均增加1338公顷；盐碱地面积增加。由于生态应急输水工程的实施，1999年至2004年期间沿塔里木河道地下水位回升，植被面积增加48％，距离河道最近的区域面积增加最明显，植被面积增加的增幅随距离河道距离的增加而减小；荒漠面积减少8.3％，年均减少6280公顷；平均NDVI升高；荒漠面积减少；盐碱地面积在某些区段增加，某些区段减少。 ⑵1986年至1999年胡杨林、柽柳灌丛和盐生草甸缀块密度增加，植被趋于破碎化；总体上胡杨林、柽柳灌丛和盐生草甸的缀块形状变得规则，而盐生草甸在某些区段趋于不规则；景观的聚集度在河道左侧增加而右侧减小；景观多样性和均匀性均下降。1999年至2004年，总体上胡杨林、柽柳灌丛和盐生草甸的缀块密度减小，植被趋于整合；胡杨林、柽柳灌丛和盐生草甸缀块形状变得不规则，但盐生草甸在某些区段变得相对规则；景观聚集度指数变化没有明显的规律；景观多样性和均匀性均增加。 ⑶除植被占总面积的比例在沿河道由上段到中断到下段方向上呈现减少的趋势，其它植被及景观特性在沿河道纵向上变化规律不明显；而在沿河道垂直方向上，植被及景观特性的变化表现出与距离河道的距离相关，表明该地区的植被及景观特性是受到地下水控制的。 ⑷在塔里木河实施的生态应急输水工程对当地植被的恢复起到了一定的作用，但主要局限在沿河道附近的区域。对于干旱区植物的保护，合理使用径流水资源，保证水资源的供应畅通是更好和更长远的发展策略。 对人类活动对景观的影响的研究发现： ⑴1987年至1999年，农田面积增加4240公顷，年均增加353公顷；植被面积减少4884公顷，年均减少407公顷。1999年至2004年，农田面积增加4568公顷，年均增加913公顷；植被面积减少8487公顷，年均减少1697公顷，远大于农田面积的增加。 ⑵农田平均缀块面积和农田最大缀块面积从1987年至1999年至2004年增加；聚集度指数在1987年至1999年降低，而1999年至2004年升高。最大植被缀块面积、平均形状指数和聚集指数从1987年至1999年至2004年均下降；其它植被及农田景观指数在1987年至1999年和1999年至2004年间变化不一致。在距河道1km的范围内，农田缀块数、农田面积、最大农田缀块面积、平均缀块面积、平均形状指数以及聚集度指数在从1987年至1999年至2004年一直升高；距河道1km范围内的景观多样性和均匀度指数和平均形状指数在1987年至1999年至2004年增加，而聚集度指数和最大缀块指数在1987年至1999年至2004年一直减小。 ⑶研究结果表明人类活动-主要是开垦农田-导致了当地植被面积的减少，并导致植被破碎化。受到径流来水量减少的影响，人类开垦活动正在逐渐向距离河道近的区域转移，并导致植被向退化的方向发展，河道附近的区域是塔里木河下游植被分布的主要区域，这对该地区植被的维持和保护非常不利。 在塔里木河下游，地下水位的下降和人类活动都导致植被趋于退化，人工输水虽然能够恢复植被，但其效应主要集中在河道附近的地区，对于该生态关键地区植被的保护，合理的使用水资源并适当的进行人类活动才是植被及生态保护的根本。

ABRASIVE WEAR OF LUBRICATED CONTACTS.

A foil bearing arrangement has been used to investigate the wear of carbon graphite materials running against 316 stainless steel in the presence of a hydrodynamic film of fluid contaminated with particulate material. As the thickness of the fluid film is reduced so the wear rate of the carbon reaches a maximum value, further reductions in thickness actually producing reduced wear rates. Possible mechanisms and implications of this behaviour are discussed.

Negligible penalty all-optical routing using a 12 × 12 passive InP wavelength-selective router

This work demonstrates transmission at 2.5 Gbit/s across two wavelength-division multiplexing (WDM) network nodes, constructed using counter-propagating semiconductor optical amplifier (SOA) wavelength converters and an integrated wavelength-selective router separated by 45 km of fiber, with an overall penalty of 0.6 dB. Minimal degradation of the eye diagram is evident across the whole system. Full utilization of the capacity of the router would allow an aggregate 360-Gbit/s node capacity for a WDM channel of 2.5 Gb/s.

Friction and material transfer in micro-scale sliding contact between aluminium alloy and steel

A ball-on-flat reciprocating micro-tribometer has been used to measure the friction coefficient between aluminium alloy strip and a steel ball. A relatively small ball and correspondingly low contact load is used to give a contact width of the order of 100μm, closer to asperity contact widths than generally found for this type of test. The effects of load, initial strip surface roughness, lubricants and boundary additives are investigated. It is found that the friction coefficient is significantly reduced by the addition of a lubricant. Observations of the wear tracks and ball surface show that the material transfer from aluminium to the ball is reduced in the presence of the lubricant. The initial friction coefficient is further reduced by the addition of a boundary additive, but the friction coefficient after 8 cycles is unchanged. Copyright © 2004 by Springer Science+Business Media, Inc.

滇蛙抗氧化肽及其基因和应用

本发明涉及一种滇蛙抗氧化肽及其基因和应用，属于生物医学技术领域。滇蛙抗氧化肽是中国两栖类动物滇蛙基因编码的一种单链多肽，分子量为1653.88 道尔顿，等电点8.22，滇蛙抗氧化肽全序列为：NH2-GIRPTYNRQCEIGF-COOH。编码的基因由316个核苷酸组成，其中编码成熟部分的为第130-171位核苷酸。人工合成的滇蛙抗氧化肽具有强烈的抗氧化活性，能作为制备皮肤抗氧化保护和体内自由基清除药物的应用，并且还具有序列简单、合成方便的优点。