Mechanisms of axon guidance in the developing nervous system

The human brain assembles an incredible network of over a billion neurons. Understanding how these connections form during development in order for the brain to function properly is a fundamental question in biology. Much of this wiring takes place during embryonic development. Neurons are generated in the ventricular zone, migrate out, and begin to differentiate. However, neurons are often born in locations some distance from the target cells with which they will ultimately form connections. To form connections, neurons project long axons tipped with a specialized sensing device called a growth cone. The growing axons interact directly with molecules within the environment through which they grow. In order to find their targets, axonal growth cones use guidance molecules that can either attract or repel them. Understanding what these guidance cues are, where they are expressed, and how the growth cone is able to transduce their signal in a directionally specific manner is essential to understanding how the functional brain is constructed. In this chapter, we review what is known about the mechanisms involved in axonal guidance. We discuss how the growth cone is able to sense and respond to its environment and how it is guided by pioneering cells and axons. As examples, we discuss current models for the development of the spinal cord, the cerebral cortex, and the visual and olfactory systems. (c) 2005, Elsevier Inc.

The novel cytoskeleton-associated protein Neuronal protein 22: Elevated expression in the developing rat brain

Neuronal development and process targeting is mediated by proteins of the cytoskeleton. However, the signaling pathways underlying these mechanisms are complex and have not yet been fully elucidated. Neuronal protein 22 (NP22) has been identified as a cytoskeleton-associated protein. It colocalizes with microtubules and actin, the two major components of the cytoskeleton. It contains numerous signaling motifs and induces process formation in non-neuronal cells. Expression of rat NP22 (rNP22) rises incrementally at specific time points during brain development, with the greatest elevation occurring during synaptogenesis in the rat brain. its neuronal localization is primarily at the plasma membrane of the soma in the embryonic brain and progresses into homogeneous expression in the postnatal rat brain. Data suggest that NP22 may play a role in mediating the molecular events governing development of the neuronal architecture. Furthermore, its sustained expression in postnatal brain implies a function in the maintenance of neuronal morphology.

A combined spectrophotometric and morphometric study of the lunar mare dome fields near Cauchy, Arago, Hortensius, and Milichius

In this Study we examine the spectral and morphometric properties of the four important lunar mare dome fields near Cauchy, Arago, Hortensius. and Milichius. We utilize Clementine UV vis mulfispectral data to examine the soil composition of the mare domes while employing telescopic CCD imagery to compute digital elevation maps in order to determine their morphometric properties, especially flank slope, height, and edifice Volume. After reviewing previous attempts to determine topographic data for lunar domes, we propose an image-based 3D reconstruction approach which is based on a combination of photoclinometry and shape from shading. Accordingly, we devise a classification scheme for lunar Marc domes which is based on a principal component analysis of the determined spectral and morphometric features. For the effusive mare domes of the examined fields we establish four Classes, two of which are further divided into two subclasses, respectively, where each class represents distinct combinations of spectral and morphometric dome properties. As a general trend, shallow and steep domes formed out of low-TiO2 basalts are observed in the Hortensius and Milichius dome fields, while the domes near Cauchy and Arago that consist of high-TiO2 basalts are all very shallow. The intrusive domes of our data set cover a wide continuous range of spectral and morphometric quantities, generally characterized by larger diameters and shallower flank slopes than effusive domes. A comparison to effusive and intrusive mare domes in other lunar regions, highland domes, and lunar cones has shown that the examined four mare dome fields display Such a richness in spectral properties and 3D dome shape that the established representation remains valid in a more global context. Furthermore, we estimate the physical parameters of dome formation for the examined domes based on a rheologic model. Each class of effusive domes defined in terms of spectral and morphometric properties is characterized by its specific range of values for lava viscosity, effusion rate, and duration of the effusion process. For our data set we report lava viscosities between about 10(2) and 10(8) Pas, effusion rates between 25 and 600 m(3) s(-1), and durations of the effusion process between three weeks and 18 years. Lava viscosity decreases with increasing R-415/R-750 spectral ratio and thus TiO2 content; however, the correlation is not strong, implying an important influence of further parameters like effusion temperature on lava viscosity.

Cone photoreceptor oil droplet pigmentation is affected by ambient light intensity

The cone photoreceptors of many vertebrates contain spherical organelles called oil droplets. In birds, turtles, lizards and some lungfish the oil droplets are heavily pigmented and function to filter the spectrum of light incident upon the visual pigment within the outer segment. Pigmented oil droplets are beneficial for colour discrimination in bright light, but at lower light levels the reduction in sensitivity caused by the pigmentation increasingly outweighs the benefits generated by spectral tuning. Consequently, it is expected that species with pigmented oil droplets should modulate the density of pigment in response to ambient light intensity and thereby regulate the amount of light transmitted to the outer segment. In this study, microspectrophotometry was used to measure the absorption spectra of cone oil droplets in chickens (Gallus gallus domesticus) reared under bright (unfiltered) or dim (filtered) sunlight. Oil droplet pigmentation was found to be dependent on the intensity of the ambient light and the duration of exposure to the different lighting treatments. In adult chickens reared in bright light, the oil droplets of all cone types (except the violet-sensitive single cones, whose oil droplet is always non-pigmented) were more densely pigmented than those in chickens reared in dim light. Calculations show that the reduced levels of oil droplet pigmentation in chickens reared in dim light would increase the sensitivity and spectral bandwidth of the outer segment significantly. The density of pigmentation in the oil droplets presumably represents a trade-off between the need for good colour discrimination and absolute sensitivity. This might also explain why nocturnal animals, or those that underwent a nocturnal phase during their evolution, have evolved oil droplets with low pigment densities or no pigmentation or have lost their oil droplets altogether.

Morphology, characterization, and distribution of retinal photoreceptors in the Australian lungfish Neoceratodus forsteri (Krefft, 1870)

The Australian lungfish Neoceratodus forsteri (Dipnoi) is an ancient fish that has a unique phylogenetic relationship among the basal Sarcopterygii. Here we examine the ultrastructure, histochemistry, and distribution of the retinal photoreceptors using a combination of light and electron microscopy in order to determine the characteristics of the photoreceptor layer in this living fossil. Similar proportions of rods (53%) and cones (47%) reveal that N. forsteri optimizes both scotopic and photopic sensitivity according to its visual demands. Scotopic sensitivity is optimized by a tapetum lucidum and extremely large rods (18.62 +/- 2.68 mu m ellipsoid diameter). Photopic sensitivity is optimized with a theoretical spatial resolving power of 3.28 +/- 0.66 cycles degree(-1), which is based on the spacing of at least three different cone types: a red cone containing a red oil droplet, a yellow cone containing a yellow ellipsoidal pigment, and a colorless cone containing multiple clear oil droplets. Topographic analysis reveals a heterogeneous distribution of all photoreceptor types, with peak cone densities predominantly found in temporal retina (6,020 rods MM 2, 4,670 red cones mm(-2), 900 yellow cones mm(-2), and 320 colorless cones mm(-2)), but ontogenetic changes in distribution are revealed. Spatial resolving power and the diameter of all photoreceptor types (except yellow cones) increases linearly with growth. The presence of at least three morphological types of cones provides the potential for color vision, which could play a role in the clearer waters of its freshwater environment.

Microvertebrate assemblages from the Upper Silurian of Cornwallis Island, Arctic Canada

Microvertebrate assemblages from four Upper Silurian (?Ludlow-Pridoli) localities on Cornwallis Island, Arctic Canada, comprise mainly scales, plus dentition cones and jaw fragments from ischnacanthid acanthodians, with rare scales assigned to heterostracan Lepidaspis? sp., ?chondrichthyan Arauzia? sp., and Placodermi? gen. et sp. indet. Most of the scales in sample C-11460 are assigned to the poracanthodid acanthodian Poracanthodes canadensis sp.nov., which shows closest affinity to Poracanthodes punctatus Brotzen variants from the Baltic Pridoli. The flank scales of the new species resemble those of P. punctatus s.s. (Silurian variant; the zone fossil for the late Pridoli in the Standard Silurian microvertebrate scheme), with their superposed crown growth zones, rows of small pores aligned with the underlying zones, number of radial canals, and arcade canals connecting these radial canals. They differ in having numerous anterior crown riblets, zig-zag rather than straight crown pore rows, and V-shaped arcade canals.

Rastros e rostos do protestantismo brasileiro: uma historiografia de mulheres

Esta pesquisa abrange mulheres atuantes no chamado protestantismo histórico, principalmente vinculadas à Igreja Metodista do Brasil. O trabalho pretende visibilizar especialmente mulheres leigas e suas redes, geralmente informais, de articulação e chamar a atenção para seu papel na constituição destas comunidades de fé. Trata-se de um aspecto pouco explorado nas investigações sobre o protestantismo no Brasil que, quando abordado, se restringe a alguns ícones femininos. O foco principal do trabalho se restringe ao período de 1930, ano em que a Igreja Metodista do Brasil se constituiu como instituição autônoma, desvinculando-se formalmente de sua congênere nos EUA, até 1970/71, quando mulheres metodistas passam a ser admitidas no presbiterato, ou seja, podem solicitar a ordenação ao pastorado. Além de discutir a produção bibliográfica principalmente no âmbito da história do protestantismo, a pesquisa se baseia em fontes primárias, como boletins e jornais denominacionais, relatórios de eventos, correspondências e informações dispersas em diferentes materiais. Como referencial teórico a pesquisa se valeu da micro-história, procurando assim dar vida a personagens esquecidos e desvelar enredos ocultados pela história oficial. Portanto, além de demonstrar aspectos da atuação de mulheres no protestantismo brasileiro, silenciados tanto na memória institucional como na historiografia em suas diferentes matizes, a pesquisa pretende contribuir para uma avaliação crítica da mentalidade de mulheres sobre sua atuação no campo religioso, entre a adequação aos padrões culturais dominantes e os indícios de autonomia de pensamento diante de demandas específicas.(AU)

INTERSEÇÕES ENTRE PUBLICIDADE E CULTURA: UMA ANÁLISE DA PRESENÇA DO RELIGIOSO EM COMERCIAIS TELEVISIVOS

Este trabalho buscou entender as composições provindas das interações atuais entre consumo, publicidade e a religião, com vistas a compreender as formas de confluência/interseções entre a cultura publicitária e a religiosa. Assim, colocam-se como objetivos revelar quais as relações de interseções entre os fazeres religioso e o capitalista/publicitário quando o símbolo religioso passa a ser utilizado pela publicidade/propaganda em peças publicitárias televisivas. Dessa forma, são analisados os recursos utilizados para que a publicidade consiga aproximar religião e consumo. Para tanto, logo após uma discussão hermenêutica, se analisou sete diferentes peças publicitárias televisivas, todas veiculadas em rede nacional aberta brasileira entre 2000 e 2009, as quais se utilizavam de ícones religiosos como instrumento para comunicação mercadológica. A base para este estudo são os instrumentais teóricos dos Estudos Culturais e da matriz religiosa brasileira. Com isso, obtivemos uma compreensão mais clara acerca dos processos de confluência/interseções dos fazeres em questão, entendendo, assim, parte de seus funcionamento dentro da sociedade atual.

Estratégias de Comunicação e Ativismo Feminino na Esfera Pública Midiática: Estudo sobre a participação de jovens negras no hip-hop, a construção de identidades e sua presença na internet.

Estudo sobre as experiências vividas por mulheres negras que participam do movimento cultural hip-hop. Em particular, buscou-se discutir sobre a organização dos arranjos interativos e as relações de pertencimento, presença e empoderamento, tendo como elo a produção musical e as Tecnologias da Informação e Comunicação (TICs).Desvendar as implicações que as TICs têm com as práticas culturais juvenis contemporâneas de periferia, que funcionam como referência no combate às desigualdades de gênero e do racismo. Investigar as conexões entre as interações sociais, a cultura e ação política na esfera pública. A experiência de identidade, gênero e participação no universo on-line foi construída a partir de leituras sobre as políticas identitárias, teorias feministas e das interações sociais proporcionadas pelas TICs. Os procedimentos metodológicos incluem a pesquisa bibliográfica, entrevistas semi-estruturadas, aplicação de formulários, observação a partir da participação em eventos, além de estudo de sites dos grupos estudados e participação nas redes sociais. Entre os resultados, destaca-se que há o fortalecimento das ações e de ícones na disseminação da cultura hip-hop e que a proposição sobre o ativismo político e social das jovens envolvidas no hip-hop.

Estratégias de Comunicação e Ativismo Feminino na Esfera Pública Midiática: Estudo sobre a participação de jovens negras no hip-hop, a construção de identidades e sua presença na internet

Estudo sobre as experiências vividas por mulheres negras que participam do movimento cultural hip-hop. Em particular, buscou-se discutir sobre a organização dos arranjos interativos e as relações de pertencimento, presença e empoderamento, tendo como elo a produção musical e as Tecnologias da Informação e Comunicação (TICs).Desvendar as implicações que as TICs têm com as práticas culturais juvenis contemporâneas de periferia, que funcionam como referência no combate às desigualdades de gênero e do racismo. Investigar as conexões entre as interações sociais, a cultura e ação política na esfera pública. A experiência de identidade, gênero e participação no universo on-line foi construída a partir de leituras sobre as políticas identitárias, teorias feministas e das interações sociais proporcionadas pelas TICs. Os procedimentos metodológicos incluem a pesquisa bibliográfica, entrevistas semi-estruturadas, aplicação de formulários, observação a partir da participação em eventos, além de estudo de sites dos grupos estudados e participação nas redes sociais. Entre os resultados, destaca-se que há o fortalecimento das ações e de ícones na disseminação da cultura hip-hop e que a proposição sobre o ativismo político e social das jovens envolvidas no hip-hop.

The Kinematics of interference mechanisms in certain machining operations

The mechanism of "Helical Interference" in milled slots is examined and a coherent theory for the geometry of such surfaces is presented. An examination of the relevant literature shows a fragmented approach to the problem owing to its normally destructive nature, so a complete analysis is developed for slots of constant lead, thus giving a united and exact theory for many different setting parameters and a range of cutter shapes. For the first time, a theory is developed to explain the "Interference Surface" generated in variable lead slots for cylindrical work and attention is drawn to other practical surfaces, such as cones, where variable leads are encountered. Although generally outside the scope of this work, an introductory analysis of these cases is considered in order to develop the cylindrical theory. Special emphasis is laid upon practical areas where the interference mechanism can be used constructively and its application as the rake face of a cutting tool is discussed. A theory of rake angle for such cutting tools is given for commonly used planes, and relative variations in calculated rake angle between planes is examined. Practical tests are conducted to validate both constant lead and variable lead theories and some design improvements to the conventional dividing head are suggested in order to manufacture variable lead workpieces, by use of a "superposed" rotation. A prototype machine is manufactured and its kinematic principle given for both linear and non-linearly varying superposed rotations. Practical workpieces of the former type are manufactured and compared with analytical predictions,while theoretical curves are generated for non-linear workpieces and then compared with those of linear geometry. Finally suggestions are made for the application of these principles to the manufacture of spiral bevel gears, using the "Interference Surface" along a cone as the tooth form.

Ion plating

Under ideal conditions ion plating produces finely grained dense coatings with excellent adhesion. The ion bombardment induced damage initiates a large number of small nuclei. Simultaneous coating and sputtering stimulates high rates of diffusion and forms an interfacial region of graded composition responsible for good adhesion. To obtain such coatings on components far industrial applications, the design and construction Of an ion plater with a 24" (O.6rn) diameter chamber were investigated and modifications of the electron beam gun were proposed. A 12" (O.3m) diameter ion plater was designed and constructed. The equipment was used to develop surfaces for solar energy applications. The conditions to give extended surfaces by sputter etching were studied. Austenitic stainless steel was sputter etched at 20 and 30 mTorr working pressure and at 3, 4 and 5 kV. Uniform etching was achieved by redesigning the specimen holder to give a uniform electrostatic field over the surfaces of the specimens. Surface protrusions were observed after sputter etching. They were caused by the sputter process and were independent of grain boundaries, surface contaminants and inclusions. The sputtering rate of stainless steel was highly dependent on the background pressure which should be kept below 10-5 Torr. Sputter etching improved the performance of stainless steel used as a solar selective surface. A twofold improvement was achieved on sputter etching bright annealed stainless steel. However, there was only slight improvement after sputter etching stainless steel which had been mechanically polished to a mirror finish. Cooling curves Were used to measure the thermal emittance of specimens.The deposition rate of copper was measured at different levels of power input and was found to be a maximum at 9.5 kW. The diameter of the copper feed rod was found to be critical for the maintenance of a uniform evaporation rate.

Size dependent enhancement of helium ion irradiation tolerance in sputtered Cu/V nanolaminates

We have investigated the evolution of radiation damage and changes in hardness of sputter-deposited Cu/V nanolaminates upon room temperature helium ion irradiation. As the individual layer thickness decreases from 200 to 5 nm, helium bubble density and radiation hardening both decrease. The magnitude of radiation hardening becomes negligible for individual layer thickness of 2.5 nm or less. These observations indicate that nearly immiscible Cu/V interface can effectively absorb radiation-induced point defects and reduce their concentrations.

Pupil responses associated with coloured afterimages are mediated by the magno-cellular pathway

Sustained fixation of a bright coloured stimulus will, on extinction of the stimulus and continued steady fixation, induce an afterimage whose colour is complementary to that of the initial stimulus; an effect thought to be caused by fatigue of cones and/or of cone-opponent processes to different colours. However, to date, very little is known about the specific pathway that causes the coloured afterimage. Using isoluminant coloured stimuli recent studies have shown that pupil constriction is induced by onset and offset of the stimulus, the latter being attributed specifically to the subsequent emergence of the coloured afterimage. The aim of the study was to investigate how the offset pupillary constriction is generated in terms of input signals from discrete functional elements of the magno- and/or parvo-cellular pathways, which are known principally to convey, respectively, luminance and colour signals. Changes in pupil size were monitored continuously by digital analysis of an infra-red image of the pupil while observers viewed isoluminant green pulsed, ramped or luminance masked stimuli presented on a computer monitor. It was found that the amplitude of the offset pupillary constriction decreases when a pulsed stimulus is replaced by a temporally ramped stimulus and is eliminated by a luminance mask. These findings indicate for the first time that pupillary constriction associated with a coloured afterimage is mediated by the magno-cellular pathway. © 2003 Elsevier Science Ltd. All rights reserved.

Directions De Majoration D'une Fonction Quasiconvexe Et Applications

We introduce the convex cone constituted by the directions of majoration of a quasiconvex function. This cone is used to formulate a qualification condition ensuring the epiconvergence of a sequence of general quasiconvex marginal functions in finite dimensional spaces.