Variations in strength and slip rate along the san andreas fault system

Convergence across the San Andreas fault (SAF) system is partitioned between strike-slip motion on the vertical SAF and oblique-slip motion on parallel dip-slip faults, as illustrated by the recent magnitude M(s) = 6.0 Palm Springs, M(s) = 6.7 Coalinga, and M(s) = 7.1 Loma Prieta earthquakes. If the partitioning of slip minimizes the work done against friction, the direction of slip during these recent earthquakes depends primarily on fault dip and indicates that the normal stress coefficient and frictional coefficient (micro) vary among the faults. Additionally, accounting for the active dip-slip faults reduces estimates of fault slip rates along the vertical trace of the SAF by about 50 percent in the Loma Prieta and 100 percent in the North Palm Springs segments.     

Microorganisms from the late precambrian of the grand canyon, Arizona

An assemblage of cellularly well-preserved, filamentous and spheroidal plant microfossils has been detected in a cherty pisolite bed of the late Precambrian Chuar Group from the eastern Grand Canyon of the Colorado River. This newly discovered microflora, probably among the youngest Precambrian biological communities now known, appears to be of both evolutionary and biostratigraphic significance.     

Nile delta: the defunct pelusiac branch identified

The course of the ancient Pelusiac branch of the Nile River has been traced on a deltaic plain east of the Suez Canal, between the El Baqar Canal and Tell el Farama (ancient Pelusium). Two minor distributaries branched northward. The critical stage in the process of the silting up of the lower reaches of the Pelusiac branch, due to prograding beach accretion, occurred around A.D. 25. Ancient ruins in the area are closely associated with the courses.     

二硫代磷酸酯类对尼罗罗非鱼和鲮体内AChE酶活性的影响

为探明二硫代磷酸酯类对尼罗罗非鱼(Oreochromis niloticus)的特异性毒性机理,以尼罗罗非鱼和土鲮(Cirrhinus molitorella)为试验对象,研究暴露在不同药物质量浓度(0.05、0.1 mg/L)和不同时间下2种鱼的生存状况以及体内乙酰胆碱酯酶(ACh E)活性的变化。结果表明:在急性毒性试验及清水恢复的整个过程中,暴露在0.05、0.1 mg/L药液中的尼罗罗非鱼和鲮的死亡率分别为100%和0;尼罗罗非鱼和鲮的脑及肝脏中的ACh E酶活性呈现出随药物暴露浓度和时间的增加而显著降低的趋势,但尼罗罗非鱼体内ACh E酶活性的下降幅度显著高于鲮(P<0.05),且呈现不可逆的趋势;在10 d清水恢复后,暴露在0.05、0.1 mg/L药液中的鲮脑中的ACh E酶活性复原度高达96.25%、79.33%。由此得出,低剂量的二硫代磷酸酯类对尼罗罗非鱼具有高毒性,而对鲮的毒害作用较小,其特异性的毒杀机制可能源于2种鱼体内ACh E酶活性对二硫代磷酸酯类敏感性的显著性差异。     

Chitinozoans from the late precambrian chuar group of the grand canyon, Arizona

Carbonaceous shales of the late Precambrian Chuar Group of the Grand Canyon, Arizona, contain abundant and well-preserved chitinozoans. The occurrence of these distinctive, tear- and flask-shaped microfossils, the oldest chitinozoans now known and the first to be reported from the Precambrian, seems to suggest that heterotrophic protists (or primitive metaozoans) were extant at least as early as about 750 +/- 100 million years ago.     

The 1990 to 1991 Sudan earthquake sequence and the extent of the East african rift system

One of the largest earthquakes ever recorded in Africa (surface wave magnitude M(s) = 7.2) occurred about 50 kilometers east of the Upper River Nile on 20 May 1990. Four days later, two more large earthquakes (M(s) = 6.4 and 7.0) occurred about 50 kilometers to the northwest in the Nile Valley. In the following months, a further 60 events were recorded by seismic stations worldwide. The earthquakes are associated with two fault systems: one east of the Nile with azimuth southeast and one along the Nile Valley with azimuth north-northeast. The activity alternated between the two fault systems and indicates that the northern extremity of the western branch of the East African Rift System extends at least 350 kilometers north of Lake Albert.     

光照周期对尼罗罗非鱼幼鱼昼夜节律调节的作用

为了研究尼罗罗非鱼幼鱼游泳行为在不喂食时是否存在昼夜节律和光照周期的调节作用,设计了光周期为光照(L)∶黑暗(D)=12 h∶12 h,持续的黑暗(DD),持续的光照(LL),光周期为L∶D=6 h∶6 h和光周期为L∶D=2 h∶2 h。结果表明:(1)光周期为L∶D=12 h∶12 h时,尼罗罗非鱼具有明显的昼夜节律,昼夜节律周期为(24. 3±0. 2) h;(2)尼罗罗非鱼的昼夜节律在持续的黑暗和光照下仍然存在,分别为(25. 1±1. 1) h和(25. 6±1. 0) h;(3)光周期为L∶D=6 h∶6 h时,尼罗罗非鱼仍具有明显的昼夜节律(12. 6±0. 5) h;(4)在光周期为L∶D=2 h∶2 h时,尼罗罗非鱼的昼夜游泳行为仍具有明显的昼夜节律,节律周期为(4. 0±2. 0) h。这些结果表明,尼罗罗非鱼具有以24 h为周期的内源性生物钟,但相比与外源性光照调控,内源性的生物钟对罗非鱼的调控较弱,外源性的光照周期才是调节尼罗罗非鱼幼鱼昼夜行为节律的主要因素。     

Drifting organisms in the precambrian sea

Drag marks in the Upper Precambrian Winnall Beds of central Australia were made by semibuoyant flexible objects at least 15 centimeters long, which presumably were algae. This find extends the range of such marks into the Precambrian era and supplements the discovery of microflora in the same Sedimentary Sequence.     

Historical nile floods and their implications for climatic change

Analysis of Nile flood stages from A.D. 640 to 1921 reveals major episodes of low Nile discharge during the years 930 to 1070 and 1180 to 1350 and major episodes of high Nile floods during 1070 to 1180 and 1350 to 1470. Examination of Nile flood maxima and minima and comparison with water levels in Lake Chad reveal a correlation between high Nile discharge and greater rainfall in equatorial East Africa. There is also apparently a correlation between low Nile discharge and cold climate in Europe.     

Composition of the ancient north american crust

Geochemical studies of Wyoming Precambrian graywackes derived from continental crust older than 3.2 x 10(9) years indicate that their source area was at least as highly differentiated as most younger Precambrian crust. The composition of this early crust (approximately that of calcium-rich granite) is not unlike that of the 2.5 to 3.2 x 10(9) year old North American crust. Limited geochemical data suggest that the composition of North America may not have changed significantly during the last 3.0 to 3.5 x 10(9) years.     

室内水生动物对蓝藻生长的抑制效果

在室内模拟小水体中,开展了不同密度尼罗罗非鱼和鲢鱼抑制蓝藻生长的对比试验.结果表明:尼罗罗非鱼和鲢鱼对水体中蓝藻绿藻过量增长均有不同程度的抑制作用,其中尼罗罗非鱼抑制消除蓝藻的效果优于鲢鱼,且尼罗罗非鱼的密度越高抑制消除蓝藻的速度越快;尼罗罗非鱼对水体中营养盐水平消除无明显贡献,但能有效提高水体的透明度,降低水体的pH值.     

Microfossils in conophyton from the soviet union and their bearing on precambrian biostratigraphy

Silicified specimens of the Vendian (late Precambrian) "index fossil" Conophyton gaubitza from South Kazakstan contain a diverse assemblage of well-preserved cyanophytic and apparently eukaryotic algae, the first stromatolitic microbiota to be reported from the Soviet Union. Unlike the stromatolites in which they occur, the microorganisms that apparently built this form of Conophyton did not become extinct at the end of the Precambrian.     

Geochronology of wadi tushka: lost tributary of the nile

The Sadat Canal, now under construction, is designed to drain excess water from Lake Nasser to the Western Desert by way of Wadi Tushka, a sand-filled, dry-wash tributary of the Nile 34 kilometers north of Abu Simbel. Core-drilling logs made by the Aswan High Dam Authority prior to excavation of the Sadat Canal and along 48 kilometers of its axis reveal as much as 33 meters of unconsolidated sand and gravel over Mesozoic bedrock and under surficial dune sand and playa muds of Holocene age. Excavation of the canal revealed Acheulean artifacts 6.7 meters below the surface in fluvial sediments capped by a buried, red calcic paleosol. These data are interpreted as evidence for the existence of a major tributary of the Nile during the late middle Pleistocene. The tributary drained the Kiseiba-Dungul Depression and possibly the Kharga Depression as well. Chalcedony-armored mudstones in the depressions are believed to be saline lake deposits possibly related to a lake that drained to the Nile by way of Wadi Tushka, thus entrenching the divide between the depression and the valley. Gross correlations with Pleistocene deposits of the Nile Valley and the Kharga Depression are based upon archeological evidence only until more precise geochronology can be applied to the problem.     

不同热处理对脆化罗非鱼肉挥发性成分的影响

为了比较脆化养殖尼罗罗非鱼和普通尼罗罗非鱼肌肉中挥发性风味物质的组成和含量,采纳固相微萃取-气相色谱-质谱技术,对两种尼罗罗非鱼肌肉中的挥发性风味物质进行检测.结果表明,两种尼罗罗非鱼生肉样品所含有的挥发性风味物质组成和含量不完全相同,确定了尼罗罗非鱼主体风味物质是：庚醛、辛醛、癸醛、壬醛、2,4-癸二烯醛、1-辛烯-3-醇和2,3-辛二酮等化合物,且脆化养殖尼罗罗非鱼的主要风味物质如庚醛、辛醛、壬醛和1-辛烯-3-醇较普通尼罗罗非鱼多,而癸醛以及2,3-辛二酮较普通尼罗罗非鱼少,2,4-癸二烯醛无明显差异.脆化养殖尼罗罗非鱼经不同烹饪方法处理后样品之间的风味差异主要来源于其所含的比例不同.然而,对两种尼罗罗非鱼鱼肉进行热处理均能降低腥味物质的含量并改变挥发性物质的化学组成.其中,烤制处理能增加鱼肉的奶油香味和产生清香味物质柠檬烯,赋予鱼肉特殊的香气.探究两种尼罗罗非鱼以及不同热处理对鱼肉挥发性风味物质的影响,为食品加工及储藏技术提供一定理论指导,为脆化养殖罗非鱼预制菜的开发,加工工艺选择,产品后续推广提供风味相关的研究数据.     

西尼罗病毒研究进展

 在最近20年以来西尼罗病毒不断感染人畜,导致相关西尼罗河疾病暴发流行,给人类带来危害并造成畜牧业严重的经济损失。通过对西尼罗病毒的病原学、流行特征、临床表现、诊断以及疫苗的研究进行概括,为进一步了解和研究该病毒提供依据。     

新形势下大学生就业指导课程建设创新研究

大学生就业指导课程建设是高校进行大学生就业、创业教育的基础,是一项长期而艰巨的任务。贯彻＂以学生为本＂教育理念是课程建设的重要前提;提升大学生职业道德品质、求职技能和职业发展水准是课程建设的重要内涵;开展专题教学,创新教学方法是课程建设的重要环节;加强师资队伍建设,开展教学内容专项研究是课程建设的重要保障。     

水库鲮和罗非鱼谷胱甘肽转移酶基因表达量与水中蓝藻含量的关系

采用荧光定量的方法对不同季节广州显岗水库鲮(Cirrhinus molitorella)和尼罗罗非鱼(Oreochro-mis niloticu)肝脏中去毒酶基因谷胱甘肽转移酶GST基因的表达情况,并结合不同季节鱼类摄入蓝藻量进行研究,旨在了解鱼体中GST基因的表达量与水体中蓝藻含量的内在联系。结果表明,4月份水库蓝藻暴发,也是鲮和尼罗罗非鱼摄食产毒蓝藻量最多的月份。GST基因的表达情况是:4月份鲮GST基因表达量比其他月份低,可能与鲮对有毒蓝藻的敏感性和耐受力有关,4月份尼罗罗非鱼GSTA及GSTR2表达量最高;其他月份,鲮GSTT表达量最高,而GSTK表达量较低,尼罗罗非鱼GSTA及GSTR2表达量相对较低。结果表明鲮GSTT在去毒过程中起重要作用,但作为环境检测的生物标记,仅适用于环境中藻毒素较低的情况。尼罗罗非鱼GSTA和GSTR2的表达量与食物中的产毒蓝藻生物量多少成正比,因此,尼罗罗非鱼GSTA及GSTR2可作为环境中藻毒素的生物标记,且尼罗罗非鱼可摄入大量有毒蓝藻,通过GST基因去除有毒蓝藻毒性,可用于生物控藻,改善水质。     

尼罗罗非鱼幼鱼氮收支与饲料组成关系

用生物学方法测定和比较了三种饲料喂养的"吉富"品系尼罗罗非鱼的氮收支,同时用化学方法估算和比较了三种饲料组的含氮排泄废物。结果表明,饲料种类对尼罗罗非鱼的特定生长率及饲料转化效率有显著影响(P<0.01),饲喂欧洲料的鱼的特定生长率最快;饲料种类对尼罗罗非鱼的氮收支分配也有显著影响(P<0.01),饲喂大江料的鱼用于生长的氮的比例最高;饲料蛋白源的质量、含能量以及营养平衡状况直接影响鱼的氮代谢,提高饲料质量是从源头控制养殖污染的关键。     

Ediacaran (precambrian) fossils from the wernecke mountains, northwestern Canada

Fossil medusoids identified as Cyclomedusa davidi?, Beltanelliformis brunsae, and cf. Sekwia excentrica are reported from Late Precambrian strata in the Wernecke Mountains. They are representatives of the Ediacaran fauna, the oldest assemblage of cosmopolitan metazoans, and are only the third such occurrence in Canada. In addition, specimens broadly resembling the problematic structure Rugoinfractus ovruchensis, previously known only from the Precambrian of the Ukraine, are reported from the Lower Cambrian of the nearby Mackenzie Mountains.     

吉富罗非鱼对低温持续胁迫的死亡反应

为探讨罗非鱼对不同低温胁迫及其持续期的耐受性,采用人工降温持续胁迫吉富罗非鱼,统计不同低温协迫致死亡历时。结果表明：7.0、8.0、9.0、10.0℃低温持续胁迫条件下,吉富罗非鱼的半致死历时分别为12.25、17.00、25.00和31.50 h（P〈0.05）,即持续低温胁迫水平越低,半致死历时越短;而相同低温胁迫持续期内,温度越低,死亡率越高。拟合低温持续胁迫下吉富罗非鱼死亡率和死亡历时的回归方程,发现在7.0、8.0℃持续胁迫下,死亡率与死亡历时呈幂函数相关,分别为y=0.0024x^2.2453（R^2=0.9667）和y=0.0013x^2.0554（R^2=0.9516）;在9.0、10.0℃持续胁迫下,死亡率与死亡历时呈线性相关,分别为y=0.0552x-0.6854（R^2=0.9535）和y=0.0288x-0.2875（R^2=0.9523）。