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.     

一类本原有向图的m-competition指数

设D是一个n阶本原有向图, 对于正整数m及n(1≤m≤n), 定义本原有向图D的m competition指数为最小正整数k, 满足对于任意一对顶点x和y, 在D中都存在m个不同的顶点v1,v2,…,vm,使得xkvi且ykvi(i=1,2,…,m).文中讨论了一个含有两个n-2圈和一个n-3圈的n阶本原有向图D。由D的结构得到本原有向图Dn-2和Dn-3, 再根据m-competition指数的定义, 得到这个本原有向图D的m-competition指数。     

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.     

关于模P原根分布的一个推广

利用Kloostermann和估计、三角和估计及其解析方法研究推广的模P原根的分布性质M（p,k,δ，a)=1/2^k∑w1∈A a1…ak=1(p) |ai-ai^-|≤δp∑ak∈A∏j=1^k|aj-a^-j|^a并且给出一个分布的渐近公式。     

从诚信缺失看大学生就业

大学生在就业过程中出现的诚信缺失现象已经成为社会关注的重要问题,建立高校毕业生诚信体系、畅通就业信息渠道、加强媒体舆论监督等是解决这一问题的有效对策。     

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。