A lamprey from the Devonian period of South Africa

Lampreys are the most scientifically accessible of the remaining jawless vertebrates, but their evolutionary history is obscure. In contrast to the rich fossil record of armoured jawless fishes, all of which date from the Devonian period and earlier, only two Palaeozoic lampreys have been recorded, both from the Carboniferous period. In addition to these, the recent report of an exquisitely preserved Lower Cretaceous example demonstrates that anatomically modern lampreys were present by the late Mesozoic era. Here we report a marine/estuarine fossil lamprey from the Famennian (Late Devonian) of South Africa, the identity of which is established easily because many of the key specializations of modern forms are already in place. These specializations include the first evidence of a large oral disc, the first direct evidence of circumoral teeth and a well preserved branchial basket. This small agnathan, Priscomyzon riniensis gen. et sp. nov., is not only more conventionally lamprey-like than other Palaeozoic examples, but is also some 35 million years older. This finding is evidence that agnathans close to modern lampreys had evolved before the end of the Devonian period. In this light, lampreys as a whole appear all the more remarkable: ancient specialists that have persisted as such and survived a subsequent 360 million years.     

论高等教育多样化办学的发展趋势

随着高等教育大众化时代的到来，高等教育呈现出日益多样化的办学特征与发展趋势，主要表现在办学形式、办学类型、办学性质、办学层次、办学特色以及人才培养目标、定位、规格等多个方面。高等教育办学的多样化，也要求有科学多样化的高等教育质量观与之相适应。     

A lamprey from the Cretaceous Jehol biota of China

Widespread nowadays in freshwater and coastal seas of the cold and temporal zones, lampreys are a jawless vertebrate group that has been in existence for more than 300 million years but left a meagre fossil record. Only two fossil lamprey species, namely Mayomyzon pieckoensis and Hardistiella montanensis, have been recognized with certainty from North American Carboniferous marine deposits. Here we report a freshwater lamprey from the Early Cretaceous epoch (about 125 million years ago) of Inner Mongolia, China. The new taxon, Mesomyzon mengae, has a long snout, a well-developed sucking oral disk, a relatively long branchial apparatus showing branchial basket, seven gill pouches, gill arches and impressions of gill filaments, about 80 myomeres and several other characters that are previously unknown or ambiguous. Our finding not only indicates Mesomyzon's closer relationship to extant lampreys but also reveals the group's invasion into a freshwater environment no later than the Early Cretaceous. The new material furthers our understanding of ancient lampreys, bridges the gap between the Carboniferous ones and their recent relatives, and adds to our knowledge of the evolutionary history of lampreys.     

Viruses in the sea

Viruses exist wherever life is found. They are a major cause of mortality, a driver of global geochemical cycles and a reservoir of the greatest genetic diversity on Earth. In the oceans, viruses probably infect all living things, from bacteria to whales. They affect the form of available nutrients and the termination of algal blooms. Viruses can move between marine and terrestrial reservoirs, raising the spectre of emerging pathogens. Our understanding of the effect of viruses on global systems and processes continues to unfold, overthrowing the idea that viruses and virus-mediated processes are sidebars to global processes.     

Evolutionary biology: lamprey Hox genes and the origin of jaws

The development of jaws was a critical event in vertebrate evolution because it ushered in a transition to a predatory lifestyle, but how this innovation came about has been a mystery. In the embryos of jawed vertebrates (gnathostomes), the jaw cartilage develops from the mandibular arch, where none of the Hox genes is expressed; if these are expressed ectopically, however, jaw development is inhibited. Here I show that in the lamprey, a primitively jawless (agnathan) fish that is a sister group to the gnathostomes, a Hox gene is expressed in the mandibular arch of developing embryos. This finding, together with outgroup comparisons, suggests that loss of Hox expression from the mandibular arch of gnathostomes may have facilitated the evolution of jaws.     

变权综合决策中变权向量的构造

为了构造符合人类决策思维和决策偏好的综合决策模型,采用理论推导和实验的方法,引入了一个变权因子,构造了一组变权公式。构造的变权公式满足变权的三个公理条件,当用于加权综合分析时,也满足可加型综合函数的定义。通过实例对提出的变权综合决策模型进行了验证。结果表明,选择不同的变权因子,构造不同的变权综合决策模型,可实现对综合决策结果的不同偏好要求。研究结果可用于多指标综合决策与评价应用中,决策结果更加符合人类决策思维和决策偏好。     

浅谈小学数学教学方法的多元化

我国义务教育的数学课程教学目标是促进学生的全面可持续和谐发展.本着这一出发点,针对数学学科特点,结合儿童的身心发展规律和教学实际,探索小学数学的教学方法.分析小学数学多元化教学的必要性,探讨如何运用多元学科知识和创新手段推进小学数学教学方法的多元化.     

防风（Saposchnikovia divaricata）体细胞在继代培养过程中的染色体变异

对防风（Ｓａｐｏｓｃｈｉｋｏｖｉａｄｉｖａｒｉｃａｔａ）体细胞在组织培养过程中遗传物质的稳定性进行了研究，结果发现防风体细胞在继代培养过程中染色体变异显著，有亚倍体、超倍体、单倍体、多倍体和微核细胞出现，并发生染色体的形态变异。培养半年以上亚倍体和微核细胞出现并开始增多，超倍体和多倍体细胞极少；随着培养时间的延长，亚倍体和微核细胞消失，而多倍体和超倍体细胞显著增多。对于这种规律性的变化，认为是培养基成分对不同的变异类型加以选择的结果，推测培养后期超倍体的大量出现与微核细胞的消失可能有着某种因果联系。微核可能有其它的形成途径。     

低温对动物体细胞的损伤影响

低温保存细胞是最常见的长期保存方法,但低温保存是有条件的,降温过快或过慢及其复温速率都直接影响细胞的存活。综述了降温与复温对动物体细胞的损伤。     

试论古代帝王贤圣的身体叙事

东汉永平十年（67）之前，中国历史典籍与文学作品中，古代帝王贤圣的身体叙事有一个共同的特点，即以奇形怪状为神异，以畸形、病态或异形合体为神奇，并以之作为神化他们的依据。其原因似在于中国古人的神话思维方式。此一身体叙事的功能在于为其君权神授或圣人天生论张目。东汉永平十年之后，法相说随着佛教而传入东土，并被社会舆论所崇奉，从而对帝王贤圣的身体叙事有着深远的影响。史书以及通俗小说对帝王贤圣的形貌描述，大多依据法相说进行撰述，目的也是从身体方面证明他们是“见在佛”或神仙的化身，从而不言而喻地表明他们法统的正当性。     

水稻悬浮体细胞胚胎发生及其特异蛋白

以水稻优良品种吉农大８号成熟种子为实验材料,建立了悬浮体细胞胚胎发生体系,并获得再生植株,对其发生过程中特异蛋白的变化,以及诱导中胚性与非胚性愈伤组织的差异等问题进行了探讨,为将来深入研究体细胞胚胎发生机理奠定了基础,实验结果表明,不同培养偌上诱导的胚性愈伤组织的发生频率是不同的,基本培养基ＮＭＢ诱导形成的愈伤组织在适当激素浓度下,可由悬浮培养产生体细胞胚,转移到固体培养基上后,得到再生植株,对这一过程进行的组织学观察证实该形态发生途径是单细胞起源的体细胞胚胎发生,利用ＳＤＳ－聚合烯酰胺凝胶电泳比较体细胞胚胎发生中不同时期可溶性蛋白组分的差异,发现相对分子质量为５９０００的蛋白组分存在于分化初期的球形胚中,相对分子质量为５６０００的蛋白组分仅在早期成熟胚中出现;在分化出幼叶的晚期成熟胚中具有相对分子质量为３２０     

Somatic and germline activating mutations of the ALK kinase receptor in neuroblastoma

Neuroblastoma, a tumour derived from the peripheral sympathetic nervous system, is one of the most frequent solid tumours in childhood. It usually occurs sporadically but familial cases are observed, with a subset of cases occurring in association with congenital malformations of the neural crest being linked to germline mutations of the PHOX2B gene. Here we conducted genome-wide comparative genomic hybridization analysis on a large series of neuroblastomas. Copy number increase at the locus encoding the anaplastic lymphoma kinase (ALK) tyrosine kinase receptor was observed recurrently. One particularly informative case presented a high-level gene amplification that was strictly limited to ALK, indicating that this gene may contribute on its own to neuroblastoma development. Through subsequent direct sequencing of cell lines and primary tumour DNAs we identified somatic mutations of the ALK kinase domain that mainly clustered in two hotspots. Germline mutations were observed in two neuroblastoma families, indicating that ALK is a neuroblastoma predisposition gene. Mutated ALK proteins were overexpressed, hyperphosphorylated and showed constitutive kinase activity. The knockdown of ALK expression in ALK-mutated cells, but also in cell lines overexpressing a wild-type ALK, led to a marked decrease of cell proliferation. Altogether, these data identify ALK as a critical player in neuroblastoma development that may hence represent a very attractive therapeutic target in this disease that is still frequently fatal with current treatments.     

热特性参数可变时变截面环肋的传热研究

本文导出了热特性参数不为常数时变截面环肋的控制微分方程,并对导热系数是温度的线性函数,放热系数沿肋片长度变化时的情形进行数值求解. 该控制微分方程是一个非线性的微分方程,用四阶龙格库塔法和牛顿拉伐森迭代法求解,得到沿肋片长度方向上的温度分布曲线,接着又探讨了导热系数变化因子a.几何形状因子D_b,肋片因子N的影响问题.所得结果对于肋片的设计和选型以及进一步研究肋片的换热问题,都具有重要的意义.     

Evolutionary diversification of TTX-resistant sodium channels in a predator-prey interaction

Understanding the molecular genetic basis of adaptations provides incomparable insight into the genetic mechanisms by which evolutionary diversification takes place. Whether the evolution of common traits in different lineages proceeds by similar or unique mutations, and the degree to which phenotypic evolution is controlled by changes in gene regulation as opposed to gene function, are fundamental questions in evolutionary biology that require such an understanding of genetic mechanisms. Here we identify novel changes in the molecular structure of a sodium channel expressed in snake skeletal muscle, tsNa(V)1.4, that are responsible for differences in tetrodotoxin (TTX) resistance among garter snake populations coevolving with toxic newts. By the functional expression of tsNa(V)1.4, we show how differences in the amino-acid sequence of the channel affect TTX binding and impart different levels of resistance in four snake populations. These results indicate that the evolution of a physiological trait has occurred through a series of unique functional changes in a gene that is otherwise highly conserved among vertebrates.     

The role of parasites in sympatric and allopatric host diversification

Exploiters (parasites and predators) are thought to play a significant role in diversification, and ultimately speciation, of their hosts or prey. Exploiters may drive sympatric (within-population) diversification if there are a variety of exploiter-resistance strategies or fitness costs associated with exploiter resistance. Exploiters may also drive allopatric (between-population) diversification by creating different selection pressures and increasing the rate of random divergence. We examined the effect of a virulent viral parasite (phage) on the diversification of the bacterium Pseudomonas fluorescens in spatially structured microcosms. Here we show that in the absence of phages, bacteria rapidly diversified into spatial niche specialists with similar patterns of diversity across replicate populations. In the presence of phages, sympatric diversity was greatly reduced, as a result of phage-imposed reductions in host density decreasing competition for resources. In contrast, allopatric diversity was greatly increased as a result of phage-imposed selection for resistance, which caused populations to follow divergent evolutionary trajectories. These results show that exploiters can drive diversification between populations, but may inhibit diversification within populations by opposing diversifying selection that arises from resource competition.     

医用蝉鸣声多样化合成的一种新方法

耳鸣掩蔽疗法是根据耳鸣的频谱和响度来调节掩蔽声, 使之与耳鸣感知类型相匹配, 以达到掩蔽耳鸣的目的. 蝉鸣声是最为常见的耳鸣感知类型, 但不同患者的耳鸣感知类型不一样, 因此研究蝉鸣声的多样化合成方法显得至关重要. 针对耳鸣匹配声源不够丰富的问题, 本文将近年来迅速发展起来的希尔伯特 黄变换法和非线性调幅 调频模型(AM FM)相结合的方法来合成蝉鸣声. 首先, 利用总体平均经验模态分解法的自适应带通滤波特性, 将不同共振峰分离出来; 然后通过归一化希尔伯特算法计算出各自的瞬时频率和瞬时幅度; 最后利用AM FM合成蝉鸣声. 实验结果表明, 该方法合成效果较理想, 具有一定的医用参考价值.