STABILITY OF STEADY－STATE SOLUTIONS OF THE COMPETITION MODEL IN THE CHEMOSTAT

ＳＴＡＢＩＬＩＴＹＯＦＳＴＥＡＤＹ－ＳＴＡＴＥＳＯＬＵＴＩＯＮＳＯＦＴＨＥＣＯＭＰＥＴＩＴＩＯＮＭＯＤＥＬＩＮＴＨＥＣＨＥＭＯＳＴＡＴ￥ＷＵＪｉａｎｈｕａ（Ｘｉ＇ａｎＩｎｓｔｉｔｕｔｅｏｆＨｉｇｈｗａｙ，Ｘｉ，ａｎ７１００６４，Ｃｈｉｎａ）ＬＩＹａｎ...     

Paracrine Wingless signalling controls self-renewal of Drosophila intestinal stem cells

In the Drosophila midgut, multipotent intestinal stem cells (ISCs) that are scattered along the epithelial basement membrane maintain tissue homeostasis by their ability to steadily produce daughters that differentiate into either enterocytes or enteroendocrine cells, depending on the levels of Notch activity. However, the mechanisms controlling ISC self-renewal remain elusive. Here we show that a canonical Wnt signalling pathway controls ISC self-renewal. The ligand Wingless (Wg) is specifically expressed in the circular muscles next to ISCs, separated by a thin layer of basement membrane. Reduced function of wg causes ISC quiescence and differentiation, whereas wg overexpression produces excessive ISC-like cells that express high levels of the Notch ligand, Delta. Clonal analysis shows that the main downstream components of the Wg pathway, including Frizzled, Dishevelled and Armadillo, are autonomously required for ISC self-renewal. Furthermore, epistatic analysis suggests that Notch acts downstream of the Wg pathway and a hierarchy of Wg/Notch signalling pathways controls the balance between self-renewal and differentiation of ISCs. These data suggest that the underlying circular muscle constitutes the ISC niche, which produce Wg signals that act directly on ISCs to promote ISC self-renewal. This study demonstrates markedly conserved mechanisms regulating ISCs from Drosophila to mammals. The identification of the Drosophila ISC niche and the principal self-renewal signal will facilitate further understanding of intestinal homeostasis control and tumorigenesis.     

A new micro programmable blazed grating (μPBG) and its application to multispectral imaging

A new micro programmable blazed grating (μPBG) was designed, fabricated and characterized using the two-layer polysilicon surface micromachining process. The μPBG presented is simple in structure and has the capability of continuous spectral tuning for a wide wavelength range. To maximize the operational blazed angle, dimple structure was adopted as the key component for grating slats, and its height was close to the air gap. By the measurements, the developed μPBG sample can reach a maximum blazed angle of...     

Quadrature Kalman particle fitler

In order to resolve the state estimation problem of nonlinear/non-Gaussian systems,a new kind of quadrature Kalman particle filter (QKPF) is proposed.In this new algorithm,quadrature Kalman filter (QKF) is used for generating the importance density function.It linearizes the nonlinear functions using statistical linear regression method through a set of GaussianHermite quadrature points.It need not compute the Jacobian matrix and is easy to be implemented.Moreover,the importantce density function integrates the latest measurements into system state transition density,so the approximation to the system posterior density is improved.The theoretical analysis and experimental results show that,compared with the unscented partcle filter (UPF),the estimation accuracy of the new particle filter is improved almost by 18%,and its calculation cost is decreased a little.So,QKPF is an effective nonlinear filtering algorithm.     

公路工程项目管理分析及对策

管理在公路项目中具有至关重要的作用,管理的好坏不仅关系到公路工程的质量,而且关系到公路工程在以后使用中的寿命及维护.本文就公路工程项目管理存的问题进行了分析,提出了具体时策和应对措施.     

多孔陶瓷管基膜上合成ZSM-5沸石膜新方法

采用喷涂晶种法在多孔α -Al2 O3基膜上引入一晶种层后 ,再用水热法一次可合成出渗透量大、选择性高的 ZSM-5沸石膜 .XRD、SEM及气体渗透性对所合成膜的结构、形态和分离性能表征表明 :所合成的膜是典型的 ZSM-5沸石膜 ,膜表面晶粒排列有序 ,整齐地连成一致密层 ,未发现有裂缝、针孔等缺陷 .H2 的渗透率很大 ,在常温下可达 2 .70× 1 0 - 6 mol.m- 2 .Pa- 1 .s- 1 ,H2 /C3H8的分离因数达 1 4以上     

Adaptive neural network tracking control for a class of unknown nonlinear time-delay systems

1 .INTRODUCTIONNeural network (NN) control has made great pro-gress in past decades[1 ~4]. In Ref .[1] , adaptivebounding design technique was applied to adaptiveneural control for a class of strict-feedback nonlin-ear systems . The requirement of a known boundon the network reconstruction error was removed.By introducing an integral Lyapunov function,anadaptive NN control approach was proposed forunknown strict-feedback nonlinear systems[2],where the controller singularity problem was …     

Algorithm for multi-constrained path selection based on experimental analysis

1. INTRODUCTION It is a challenging problem to provide quality-of-servi- ce (QoS) guarantees in next generation high-speed network, and the QoS routing is one of the key issues of the problem. The problem of routing optimization for different QoS requirements has attracted more and more attention and has becomes a hot issue in this field[1~6]. The QoSR problem deals with the metric parameters including bandwidth, delay, delay jitter, loss probability, reliability and hop count. Based o…     

Magnetostratigraphy of Late Cenozoic fossil mammals in the northeastern margin of the Tibetan Plateau

~~Magnetostratigraphy of Late Cenozoic fossil mammals in the northeastern margin of the Tibetan Plateau~~~~