A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes

The first Cenozoic ice sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling ～34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving Antarctic circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of ice-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. Ice-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of Antarctic topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5?km of ice, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from ice-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of ice-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East Antarctic Ice Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1?km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.     

A new species of Phrynobatrachus (Amphibia: Anura: Phrynobatrachidae) from the Northern Mountains of Tanzania

ABSTRACT

Using integrative approaches, a new large-bodied species of Phrynobatrachus is described from a series of 48 specimens from the montane forests of the West Usambara and North Pare Mountains of Tanzania. The most distinguishing morphological feature separating Phrynobatrachus ambanguluensis sp. nov from similar species is the markedly overhanging and pointed upper jaw and snout. Mitochondrial 16S rRNA indicates that the new species differs from all other species with published sequence data by a minimum distance of 4.75% and is sister to P. krefftii, with which it has been confused in the past. The new species is known from two forest reserves and is of high conservation concern given these areas are highly impacted by anthropogenic change.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:E0C82A87-47A5-426B-978D-96D27FA7A3B7     

半胱氨酸亚金铵的合成、理化性质及电镀金应用

以半胱氨酸为配体合成一种新型亚金配合物NH4Au(Cys)2,对该配合物进行元素分析、红外光谱、紫外光谱、热失重分析和导电性测量等理化性质研究;以该亚金配合物为金源开展相关的电镀金工艺探索,并通过四因素三水平的正交试验获得其最佳条件参数;采用扫描电子显微镜(SEM)和X线衍射(XRD)对镀金层的表面质量进行探讨。研究结果表明:该目标产物的分子式为NH4Au(Cys)2·2H2O,该配合物中以半胱氨酸的巯基和金配位为成健特征,在170℃以下热稳定性较好,该亚金配合物是一个典型的离子化合物。在电流密度为200~300 A/m2,p H为10.5~12.0,温度为35~45℃,金质量浓度为15~25 g/L的电镀工艺条件下,得到粒度为0.5~1.0μm的单质金,且主要沿着(111)面进行生长。     

随机纳米碳管网络及其渗流性质

数值模拟了实验上构造纳米碳管网络的溶液沉积方法.与一般的随机网络模型不同,将碳管的长度计算在内,而且考虑了不同的空间相交位形.数值模拟发现网络的度分布为高斯分布,平均集聚系数约为0.11.当网络中碳管平均面密度取值在σ0=179 200根/cm2附近时,网络系综达到渗流.在临界点附近,网络的连通概率p、两极之间电导G、...     

十六位微机教学实验系统分析与改进

本文在分析CCT－88／51／98教学实验系统监控程序的基础上，对该教学实验系统监控程序中存在的问题作出了一些改进。     

用脸谱图对太子河本溪市区段河流沉积物中重金属污染进行评价的研究

本文将沉积学原理及国际上新发展的两种重金属污染评价方法与多变量的图表示法——脸谱图相结合,对太子河本溪市区段河道沉积物中重金属的污染状况及潜在生态危害进行了综合性的评价研究。从脸谱图上可以直观地看出各采样点重金属的污染情况和潜在生态危害程度。从研究结果可以看出,太子河本溪市区段河道沉积物中重金属的污染是很严重的。     

用模糊综合评判法评价变电所所址

变电所选址是电力系统规划的一个重要环节。但与变电所所址有关的因素错综复杂,很难仅凭经验就能确定最佳所址。本文采用模糊综合评判方法对备选所址进行评判,确定其优先次序。在模糊综合评判中,各因素的权重分配对结果起决定性作用,用层次分析法确定与所址密切相关的各个因素相对总体目标而言的权重,使得权重的确定更科学。算例表明该方法是可行的。     

Somatic activation of the K-ras oncogene causes early onset lung cancer in mice

About 30% of human tumours carry ras gene mutations. Of the three genes in this family (composed of K-ras, N-ras and H-ras), K-ras is the most frequently mutated member in human tumours, including adenocarcinomas of the pancreas ( approximately 70-90% incidence), colon ( approximately 50%) and lung ( approximately 25-50%). To construct mouse tumour models involving K-ras, we used a new gene targeting procedure to create mouse strains carrying oncogenic alleles of K-ras that can be activated only on a spontaneous recombination event in the whole animal. Here we show that mice carrying these mutations were highly predisposed to a range of tumour types, predominantly early onset lung cancer. This model was further characterized by examining the effects of germline mutations in the tumour suppressor gene p53, which is known to be mutated along with K-ras in human tumours. This approach has several advantages over traditional transgenic strategies, including that it more closely recapitulates spontaneous oncogene activation as seen in human cancers.     

寻找四元域上n维线性空间中n/2维自对偶子空间的方法

本文讨论F4上n维线性空间的k维子空间W，这些子空间都有特定的自同构群(实际上是典型群GLn(F4)的一个子群)，根据群中元素形式的不同可将子空间W分为两类，并对寻找n维空间中形如这两类的n／2维自对偶子空间提供了一种采用降低维数寻找的方法。