A Cretaceous terrestrial snake with robust hindlimbs and a sacrum

It has commonly been thought that snakes underwent progressive loss of their limbs by gradual diminution of their use. However, recent developmental and palaeontological discoveries suggest a more complex scenario of limb reduction, still poorly documented in the fossil record. Here we report a fossil snake with a sacrum supporting a pelvic girdle and robust, functional legs outside the ribcage. The new fossil, from the Upper Cretaceous period of Patagonia, fills an important gap in the evolutionary progression towards limblessness because other known fossil snakes with developed hindlimbs, the marine Haasiophis, Pachyrhachis and Eupodophis, lack a sacral region. Phylogenetic analysis shows that the new fossil is the most primitive (basal) snake known and that all other limbed fossil snakes are closer to the more advanced macrostomatan snakes, a group including boas, pythons and colubroids. The new fossil retains several features associated with a subterranean or surface dwelling life that are also present in primitive extant snake lineages, supporting the hypothesis of a terrestrial rather than marine origin of snakes.     

Assembly of the inner rod determines needle length in the type III secretion injectisome

Assembly of multi-component supramolecular machines is fundamental to biology, yet in most cases, assembly pathways and their control are poorly understood. An example is the type III secretion machine, which mediates the transfer of bacterial virulence proteins into host cells. A central component of this nanomachine is the needle complex or injectisome, an organelle associated with the bacterial envelope that is composed of a multi-ring base, an inner rod, and a protruding needle. Assembly of this organelle proceeds in sequential steps that require the reprogramming of the secretion machine. Here we provide evidence that, in Salmonella typhimurium, completion of the assembly of the inner rod determines the size of the needle substructure. Assembly of the inner rod, which is regulated by the InvJ protein, triggers conformational changes on the cytoplasmic side of the injectisome, reprogramming the secretion apparatus to stop secretion of the needle protein.     

基于逻辑选择脉冲时滞动力系统的稳定性分析

为了使动力系统在稳定性分析上更具有一般化,能更加精确实际地刻画自然现象;针对具有逻辑选择脉冲效应的时滞动力系统,提出此系统的全局指数稳定性分析问题,可在一定程度上推广一般脉冲时滞动力系统的稳定性分析;通过引入具有逻辑选择脉冲效应的时滞非线性动力系统,并利用半张量积将该动力系统中的逻辑函数转换为代数状态空间表示,再建立脉冲型 Halanay 微分不等式来估计该动力系统中线性系统部分的 Cauchy 矩阵; 基于此,对向量和函数给出了4个假设条件,得到在逻辑选择脉冲控制下的非线性时滞系统的零解全局指数稳定性判定依据,且证明了此动力系统的指数收敛率为 λ-η。     

Problem Structuring Methods: A Review of Advances Over the Last Decade

Systemic Practice and Action Research - The Problem Structuring Methods (PSMs) are a set of interactive and participatory modeling approaches for dealing with unstructured complex problems, which...     

基于数据素养的数据库系列课程教学改革研究

新工科背景下高等工程教育改革进入新阶段,数据素养日显重要。传统的数据库课程体系不够完善,培养意识不够明确。基于此,根据新工科背景下应用型本科人才培养目标,提出结合数据素养理念进行教学改革的思路和具体实践措施。根据“二线并行、逐层递进”的模式重新规划课程体系结构,加大实践教学的比重,形成以数据素养指标体系和评价体系来指导教学的方法,并完善课程教学资源,设计多样性实践考核方式,有效地促进学生学习的积极性,实现数据素养与数据库系列课程相融合的教学改革新模式,为提升应用型本科课程教学质量提供借鉴和方法。