Mammal-like muscles power swimming in a cold-water shark

Effects of temperature on muscle contraction and powering movement are profound, outwardly obvious, and of great consequence to survival. To cope with the effects of environmental temperature fluctuations, endothermic birds and mammals maintain a relatively warm and constant body temperature, whereas most fishes and other vertebrates are ectothermic and conform to their thermal niche, compromising performance at colder temperatures. However, within the fishes the tunas and lamnid sharks deviate from the ectothermic strategy, maintaining elevated core body temperatures that presumably confer physiological advantages for their roles as fast and continuously swimming pelagic predators. Here we show that the salmon shark, a lamnid inhabiting cold, north Pacific waters, has become so specialized for endothermy that its red, aerobic, locomotor muscles, which power continuous swimming, seem mammal-like, functioning only within a markedly elevated temperature range (20-30 degrees C). These muscles are ineffectual if exposed to the cool water temperatures, and when warmed even 10 degrees C above ambient they still produce only 25-50% of the power produced at 26 degrees C. In contrast, the white muscles, powering burst swimming, do not show such a marked thermal dependence and work well across a wide range of temperatures.     

一个本原图的scrambling指数

若存在非负整数k（k〉0）,D中的每一对顶点（u,v）都存在另一顶点w,使得从w到u和v都有长为k的途径,且这个k是所有满足上述条件中的最小的整数,就是D的scram-bling指数,记作k（D）.文章给出了一个特殊的本原图的scrambling指数.     

一个本原图的scrambling指数

若存在非负整数k（k〉0）,D中的每一对顶点（u,v）都存在另一顶点w,使得从w到u和v都有长为k的途径,且这个k是所有满足上述条件中的最小的整数,就是D的scram-bling指数,记作k（D）.文章给出了一个特殊的本原图的scrambling指数.     

一类特殊本原有向图的广义的scrambling指数

文章研究一类含有3个圈的本原有向图的广义scrambling指数,其中2个圈的长度相同,通过运用本原有向图的scrambling指数和广义scrambling指数的概念,分析图中点的特点,得出此类特殊的本原有向图的scrambling指数和广义scrambling指数.     

一类特殊本原不可幂定号有向图的local基

对一类特殊的含有3个圈的本原不可幂定号有向图的local基进行了研究.运用异圈对、Frobenius集及本原指数等讨论图中是否有相应的SSSD途径对,得到了这类图的local基与基.     

Complete nucleotide sequence of an immunoglobulin VH gene homologue from Caiman, a phylogenetically ancient reptile

Immunoglobulin variable (V) gene regions typify extensive multigenic families in terms of overall size, chromosomal arrangement and presence of large numbers of apparent pseudogenes. A unique mechanism of somatic reorganization involving recombination of VH, D and JH or VL and JL segments accompanies the differentiation of lymphoid cells and together with somatic mutation and other types of recombination accounts for V-region diversity. Although these processes have been well characterized in higher mammals, little is known concerning their origin and diversification during phylogenetic time. Previously, we described the blot-hybridization characteristics of murine VHIII probes with restriction enzyme-digested genomic DNA isolated from several phylogenetically critical species, including Caiman crocodylus, a modern representative of an ancient reptilian subclass. Here we have used a murine probe, S107V, to select homologous clones from a library of Caiman genomic DNA constructed in a lambda bacteriophage. The complete nucleotide sequence of a Caiman gene homologous to the murine VH gene and its adjacent 5' and 3' region is described. Comparison of the sequence with mammalian prototypes shows evidence of considerable organizational and structural homology extending outside the presumed VH-coding region and including elements believed to be involved in somatic recombination. Inferences about the evolution of this multigenic family can now be extended to the level of phylogenetic class.     

一类n阶本原图的广义Competition指数

根据图论、数论的相关知识,对本原图中每一点经过k长途径所到达点的集合进行分析,再结合广义Competition 指数的定义,确定了一类n阶本原图的广义 Competition 指数。当m≤s＋1且s＋m为奇数时,km（D）=1＋〔s＋m-1/2〕s;当m≤s且s＋m为偶数时,km（D）=1＋〔s＋m-2/2〕（s＋1）;当m≥s＋2时,km（D）=1＋s2.     

一类本原有向图的m-competition指数及广义scrambling指数

根据图论、数论和集合的相关知识,对本原图中任一点经过k长途径所到达点的集合进行分析,结合广义competition指数和广义scrambling指数的定义,研究了一类特殊本原有向图(含有2个s-1圈和s个s圈)。得到了这一类本原有向图的m-competition指数以及广义scrambling指数。     

关中地区的贫水化探讨

关中地区水资源贫乏，供需矛盾尖锐，存在严重贫水化问题，这阻碍着陕西经济的进一步发展．本文主要论述了这一地区贫水化的表现，提出解决贫水化问题的措施和对策     

审视科技信用缺失现象

剖析科技信用缺失现象 ,有利于全面治理社会信用缺失。科技信用缺失 ,存在于科技成果研究、开发和转让的全过程。就研究过程来说 ,主要表现为学术论著、实验报告、技术文件和情报文献造假。就开发过程来说 ,主要表现为技术鉴定和经济评价做假。就转让过程来说 ,主要表现为技术成果转让和技术咨询中的失信行为 ,以及用假冒的高科技产品行骗 ,窃取别人的科技成果等     

Hilbert C*-模中本原理想子模的一些性质

给出了Hilbert C*-模中本原理想子模的定义,研究了Hilbert C*-模的本原理想子模空间以及谱空间的一些性质,所得结果推广和改进了已有的结果。     

浅谈英语语篇中照应缺省的修辞理据

前后照应可以使语篇表达准确完整,是文章写作应该遵守的一种规范,属于消极修辞;有时为了表达的特殊需要,作者有意使上下文照应不周,形成修辞缺省,从而制造出意想不到的幽默,诙谐的调侃,或启人心智的效果。     

Defective ability to self-renew in vitro of highly purified primitive haematopoietic cells

Stromal cells play a critical role in haematopoiesis, both in a permissive and, probably, in a directive manner. Study of the interactions between stromal cells and haematopoietic stem cells, however, is difficult to perform using whole bone marrow, in which stem cells are indistinguishable from precursor cells and maturing haematopoietic cells, and where stromal and haematopoietic cells co-exist in a heterogeneous mixture. We have purified primitive haematopoietic spleen colony-forming cells (CFU-S) using fluorescence-activated cell sorting (FACS) and produced CFU-S populations which approach 100% purity (ref. 6 and B.I.L. and E.S., in preparation). This cell population is devoid of significant stromal cells and mature haematopoietic cells. Here, we report that when purified CFU-S are seeded onto a stromal adherent layer in vitro, foci of haematopoietic cells develop within the stroma followed by production of a wave of maturing and mature progeny. However, self-renewal of CFU-S does not occur and haematopoietic activity rapidly declines, indicating that caution should be applied in the use of highly purified stem cells for human bone marrow transplantation.     

我国社会诚信缺失问题研究

我国社会的整体信用环境向好,但公众评价堪忧。社会诚信缺失是个人的一种利益博弈选择,这种选择造成目前一部分人的失信,对社会的健康成长与发展非常有害。在构建诚信社会过程中,我们要遵循诚信教化是基础、政府诚信是重点、立法惩戒是关键、建章立制是保障的路径选择。     

Haemangioblast commitment is initiated in the primitive streak of the mouse embryo

Haematopoietic and vascular cells are thought to arise from a common progenitor called the haemangioblast. Support for this concept has been provided by embryonic stem (ES) cell differentiation studies that identified the blast colony-forming cell (BL-CFC), a progenitor with both haematopoietic and vascular potential. Using conditions that support the growth of BL-CFCs, we identify comparable progenitors that can form blast cell colonies (displaying haematopoietic and vascular potential) in gastrulating mouse embryos. Cell mixing and limiting dilution analyses provide evidence that these colonies are clonal, indicating that they develop from a progenitor with haemangioblast potential. Embryo-derived haemangioblasts are first detected at the mid-streak stage of gastrulation and peak in number during the neural plate stage. Analysis of embryos carrying complementary DNA of the green fluorescent protein targeted to the brachyury locus demonstrates that the haemangioblast is a subpopulation of mesoderm that co-expresses brachyury (also known as T) and Flk-1 (also known as Kdr). Detailed mapping studies reveal that haemangioblasts are found at highest frequency in the posterior region of the primitive streak, indicating that initial stages of haematopoietic and vascular commitment occur before blood island development in the yolk sac.