974 resultados para Organization of space


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The segregation of thalamocortical inputs into eye-specific stripes in the developing cat or monkey visual cortex is prevented by manipulations that perturb or abolish neural activity in the visual pathway. Such findings show that proper development of the functional organization of visual cortex is dependent on normal patterns of neural activity. The generalisation of this conclusion to other sensory cortices has been questioned by findings that the segregation of thalamocortical afferents into a somatotopic barrel pattern in developing rodent primary somatosensory cortex (S1) is not prevented by activity blockade. We show that a temporary block of N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptors in rat S1 during the critical period for barrel development disrupts the topographic refinement of thalamocortical connectivity and columnar organization. These effects are evident well after the blockade is ineffective and thus may be permanent. Our findings show that neural activity and specifically the activation of postsynaptic cortical neurons has a prominent role in establishing the primary sensory map in S1, as well as the topographic organization of higher order synaptic connections.

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We examined the effects of eye position on saccades evoked by electrical stimulation of the intraparietal sulcus (IPS) of rhesus monkeys. Microstimulation evoked saccades from sites on the posterior bank, floor, and the medial bank of the IPS. The size and direction of the eye movements varied as a function of initial eye position before microstimulation. At many stimulation sites, eye position affected primarily the amplitude and not the direction of the evoked saccades. These "modified vector saccades" were characteristic of most stimulation-sensitive zones in the IPS, with the exception of a narrow strip located mainly on the floor of the sulcus. Stimulation in this "intercalated zone" evoked saccades that moved the eyes into a particular region in head-centered space, independent of the starting position of the eyes. This latter response is compatible with the stimulation site representing a goal zone in head-centered coordinates. On the other hand, the modified vector saccades observed outside the intercalated zone are indicative of a more distributed representation of head-centered space. A convergent projection from many modified vector sites onto each intercalated site may be a basis for a transition from a distributed to a more explicit representation of space in head-centered coordinates.

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Predictions of earthquakes that are based on observations of precursory seismicity cannot depend on the average properties of the seismicity, such as the Gutenberg-Richter (G-R) distribution. Instead it must depend on the fluctuations in seismicity. We summarize the observational data of the fluctuations of seismicity in space, in time, and in a coupled space-time regime over the past 60 yr in Southern California, to provide a basis for determining whether these fluctuations are correlated with the times and locations of future strong earthquakes in an appropriate time- and space-scale. The simple extrapolation of the G-R distribution must lead to an overestimate of the risk due to large earthquakes. There may be two classes of earthquakes: the small earthquakes that satisfy the G-R law and the larger and large ones. Most observations of fluctuations of seismicity are of the rate of occurrence of smaller earthquakes. Large earthquakes are observed to be preceded by significant quiescence on the faults on which they occur and by an intensification of activity at distance. It is likely that the fluctuations are due to the nature of fractures on individual faults of the network of faults. There are significant inhomogeneities on these faults, which we assume will have an important influence on the nature of self-organization of seismicity. The principal source of the inhomogeneity on the large scale is the influence of geometry--i.e., of the nonplanarity of faults and the system of faults.

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In this article we present a model of organization of a belief system based on a set of binary recursive functions that characterize the dynamic context that modifies the beliefs. The initial beliefs are modeled by a set of two-bit words that grow, update, and generate other beliefs as the different experiences of the dynamic context appear. Reason is presented as an emergent effect of the experience on the beliefs. The system presents a layered structure that allows a functional organization of the belief system. Our approach seems suitable to model different ways of thinking and to apply to different realistic scenarios such as ideologies.

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Thesis (Master's)--University of Washington, 2016-06

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What are the components that control the assembly of subcellular organelles in eukaryotic cells? Although membranes can clearly be distorted by cytosolic factors, very little is known about the intrinsic mechanisms that control the biogenesis, shape, and organization of organellar membranes. Here, we found that the unconventional phospholipid lysobisphosphatidic acid (LBPA) could induce the formation of multivesicular liposomes that resembled the multivesicular endosomes that exist where this lipid is found in vivo. This process depended on the same pH gradient that exists across endosome membranes in vivo and was selectively controlled by Alix. In turn, Alix regulated the organization of LBPA-containing endosomes in vivo.

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In this paper, we review evidence from comparative studies of primate cortical organization, highlighting recent findings and hypotheses that may help us to understand the rules governing evolutionary changes of the cortical map and the process of formation of areas during development. We argue that clear unequivocal views of cortical areas and their homologies are more likely to emerge for 'core' fields, including the primary sensory areas, which are specified early in development by precise molecular identification steps. In primates, the middle temporal area is probably one of these primordial cortical fields. Areas that form at progressively later stages of development correspond to progressively more recent evolutionary events, their development being less firmly anchored in molecular specification. The certainty with which areal boundaries can be delimited, and likely homologies can be assigned, becomes increasingly blurred in parallel with this evolutionary/developmental sequence. For example, while current concepts for the definition of cortical areas have been vindicated in allowing a clarification of the organization of the New World monkey 'third tier' visual cortex (the third and dorsomedial areas, V3 and DM), our analyses suggest that more flexible mapping criteria may be needed to unravel the organization of higher-order visual association and polysensory areas.

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Background. The secondary structure of folded RNA sequences is a good model to map phenotype onto genotype, as represented by the RNA sequence. Computational studies of the evolution of ensembles of RNA molecules towards target secondary structures yield valuable clues to the mechanisms behind adaptation of complex populations. The relationship between the space of sequences and structures, the organization of RNA ensembles at mutation-selection equilibrium, the time of adaptation as a function of the population parameters, the presence of collective effects in quasispecies, or the optimal mutation rates to promote adaptation all are issues that can be explored within this framework. Results. We investigate the effect of microscopic mutations on the phenotype of RNA molecules during their in silico evolution and adaptation. We calculate the distribution of the effects of mutations on fitness, the relative fractions of beneficial and deleterious mutations and the corresponding selection coefficients for populations evolving under different mutation rates. Three different situations are explored: the mutation-selection equilibrium (optimized population) in three different fitness landscapes, the dynamics during adaptation towards a goal structure (adapting population), and the behavior under periodic population bottlenecks (perturbed population). Conclusions. The ratio between the number of beneficial and deleterious mutations experienced by a population of RNA sequences increases with the value of the mutation rate µ at which evolution proceeds. In contrast, the selective value of mutations remains almost constant, independent of µ, indicating that adaptation occurs through an increase in the amount of beneficial mutations, with little variations in the average effect they have on fitness. Statistical analyses of the distribution of fitness effects reveal that small effects, either beneficial or deleterious, are well described by a Pareto distribution. These results are robust under changes in the fitness landscape, remarkably when, in addition to selecting a target secondary structure, specific subsequences or low-energy folds are required. A population perturbed by bottlenecks behaves similarly to an adapting population, struggling to return to the optimized state. Whether it can survive in the long run or whether it goes extinct depends critically on the length of the time interval between bottlenecks. © 2010 Stich et al; licensee BioMed Central Ltd.

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This study was a critical reassessment of the problematics of mestizaje in three representative texts pertaining to the Indigenist Peruvian narrative: Yawar Fiesta (1941) by José María Arguedas; El mundo es ancho y ajeno (1941) by Ciro Alegría; and Los ríos profundos (1958) by José María Arguedas. As this investigation demonstrated, Alegría's and Arguedas' writings went beyond the reach of Indianism and orthodox Indigenism, which were prevalent during the first decades of the twentieth century, to emphasize, the values of the Indian peasantry as well as those of the mestizo and mestiza: the products of Indian and white unions, who were also considered representatives of the Peruvian culture. ^ The first chapter traced the historical process of mestizaje and demonstrated how the discursive practice of this mestizaje was expressed in the Indigenist Peruvian narrative. The chronological organization of the chapters in this dissertation paralleled the evolution of this narrative.^ The relevance of my research lies on the important contribution it makes to the field of Indigenist literature, by seeing mestizaje as both a reconstruction and a reinterpretation of the idea of nation, identity and cultural interchange. In Alegría's and Arguedas' novels, the Indigenous reality was not only seen as an isolated phenomenon, but also as the dichotomy of European versus Indian values. As a result, Indigenist narrative presented a true and all encompassing world; therefore, Alegría's and Arguedas' narrative deepened our understanding of the aspects of a multicultural society.^ In order to accomplish this analysis, research was conducted in areas such as history, languages, ethnology, ethnography, anthropology, folklore, religion, and syncretism. My study was based on works such as Antonio Cornejo Polar's heterogeneous literatures, Mijail Bajtín's conception of dialogism and polyphony, Benedict Anderson's Imagined Communities, Angel Rama's notion of transculturation, Homi Bhabha's liminal space, Walter Ong's study of orality and literacy, and Julia Kristeva's theory of abjection, among others.^

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The study examines the thought of Yanagita Kunio (1875–1962), an influential Japanese nationalist thinker and a founder of an academic discipline named minzokugaku. The purpose of the study is to bring into light an unredeemed potential of his intellectual and political project as a critique of the way in which modern politics and knowledge systematically suppresses global diversity. The study reads his texts against the backdrop of the modern understanding of space and time and its political and moral implications and traces the historical evolution of his thought that culminates in the establishment of minzokugaku. My reading of Yanagita’s texts draws on three interpretive hypotheses. First, his thought can be interpreted as a critical engagement with John Stuart Mill’s philosophy of history, as he turns Mill’s defense of diversity against Mill’s justification of enlightened despotism in non-Western societies. Second, to counter Mill’s individualistic notion of progressive agency, he turns to a Marxian notion of anthropological space, in which a laboring class makes history by continuously transforming nature, and rehabilitates the common people (jomin) as progressive agents. Third, in addition to the common people, Yanagita integrates wandering people as a countervailing force to the innate parochialism and conservatism of agrarian civilization. To excavate the unrecorded history of ordinary farmers and wandering people and promote the formation of national consciousness, his minzokugaku adopts travel as an alternative method for knowledge production and political education. In light of this interpretation, the aim of Yanagita’s intellectual and political project can be understood as defense and critique of the Enlightenment tradition. Intellectually, he attempts to navigate between spurious universalism and reactionary particularism by revaluing diversity as a necessary condition for universal knowledge and human progress. Politically, his minzokugaku aims at nation-building/globalization from below by tracing back the history of a migratory process cutting across the existing boundaries. His project is opposed to nation-building from above that aims to integrate the world population into international society at the expense of global diversity.

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This paper discusses the importance of space in today’s space driven world, the current space activities of Turkey, its space organizations with legislation background information and calls for the necessity for the establishment of the Turkish Space Agency (TSA). Firstly, the importance of space is given which is followed by a brief background and current space activities in Turkey. Then, the answers to why Turkey needs a National Space Agency are outlined by stating its expected role and duties. Additionally, the framework for space policy for Turkey is proposed and the findings are compared with other developing regional space actors. Lastly, it is proposed and demonstrated that Turkey is on the right track with its space policy and it is suggested that the establishment of the TSA is critical both for a coherent space policy and progress as well as the successful development of its national space industry, security and international space relations.

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Research on women’s employment has proliferated over recent decades, often under a perspective that conceptualizes female labour market activity as independent of male presences and absences in the productive and reproductive spheres. In the face of these approaches, the article argues the need to focus on the couple as the unit of analysis of work-life articulation. After referring to the main theoretical arguments that, from a gender perspective within labour studies, have pointed out the relevance of placing the household as the central space for the analysis of the sexual division of labour, the article reviews different empirical contributions that have incorporated such perspective in the international literature. Next, the state of the art in the Spanish literature is presented, before arguing the desirability of applying such framework of analysis to the study of employment and care work in Spanish households, which are at present undergoing major transformations.

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Care has come to dominate much feminist research on globalized migrations and the transfer of labor from the South to the North, while the older concept of reproduction had been pushed into the background but is now becoming the subject of debates on the commodification of care in the household and changes in welfare state policies. This article argues that we could achieve a better understanding of the different modalities and trajectories of care in the reproduction of individuals, families, and communities, both of migrant and nonmigrant populations by articulating the diverse circuits of migration, in particular that of labor and the family. In doing this, I go back to the earlier North American writing on racialized minorities and migrants and stratified social reproduction. I also explore insights from current Asian studies of gendered circuits of migration connecting labor and marriage migrations as well as the notion of global householding that highlights the gender politics of social reproduction operating within and beyond households in institutional and welfare architectures. In contrast to Asia, there has relatively been little exploration in European studies of the articulation of labor and family migrations through the lens of social reproduction. However, connecting the different types of migration enables us to achieve a more complex understanding of care trajectories and their contribution to social reproduction.