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Search Results: 1 - 10 of 192376 matches for " Larry D. Wittie "
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Application of a “Staggered Walk” Algorithm for Generating Large-Scale Morphological Neuronal Networks
Jack Zito,Heraldo Memelli,Kyle G. Horn,Irene C. Solomon,Larry D. Wittie
Computational Intelligence and Neuroscience , 2012, DOI: 10.1155/2012/876357
Abstract: Large-scale models of neuronal structures are needed to explore emergent properties of mammalian brains. Because these models have trillions of synapses, a major problem in their creation is synapse placement. Here we present a novel method for exploiting consistent fiber orientation in a neural tissue to perform a highly efficient modified plane-sweep algorithm, which identifies all regions of 3D overlaps between dendritic and axonal projection fields. The first step in placing synapses in physiological models is neurite-overlap detection, at large scales a computationally intensive task. We have developed an efficient “Staggered Walk” algorithm that can find all 3D overlaps of neurites where trillions of synapses connect billions of neurons. 1. Introduction Simulating brain structures with large-scale neuronal models lets researchers precisely manipulate features of simulated neural tissues and observe both local and global properties of neural systems. During the last decade, large-scale brain modeling has risen in prominence, with a wide range of publications on brain-scale models[1–3]. Most large-scale modeling research groups focus either on networks that are highly realistic down to the individual axon collaterals and dendrite branches of each neuron [4] or on systems simplified enough to simulate in near real-time on massively parallel hardware [1, 2]. Rather than emphasizing details or simulation speed, our group is more interested in a balanced approach that capitalizes on general structural connectivity and data acquired through multiunit electrode experiments, diffusion tensor imaging, and connectomics studies with stacked slices of brain tissues stained for scanning [4–6]. To develop and test our model-creation code, we have derived parameters for cerebellar models from the detailed connection and density data for the cerebellar cortex in the compendium by Eccles et al. [7]. Large-scale neuronal models range in accuracy from simple, randomly probabilistic networks [8, 9] to realistic neuronal mappings [4]. The level of detail we need for our models is roughly at the tissue level [10], where probabilities of connectivity between distinct volumes of neural tissue and specified neuronal groups can be derived well enough to create alternative models for comparison. The resulting parameters allow for the generation of microcircuitry for particular areas of the brain. The microcircuits can be repeated, with small changes, up to millions of times in some brain regions [10, 11]. A critical and complex part of large-scale neuronal modeling is the
Analyzing the Effects of Gap Junction Blockade on Neural Synchrony via a Motoneuron Network Computational Model
Heraldo Memelli,Kyle G. Horn,Larry D. Wittie,Irene C. Solomon
Computational Intelligence and Neuroscience , 2012, DOI: 10.1155/2012/575129
Analyzing the Effects of Gap Junction Blockade on Neural Synchrony via a Motoneuron Network Computational Model
Heraldo Memelli,Kyle G. Horn,Larry D. Wittie,Irene C. Solomon
Computational Intelligence and Neuroscience , 2012, DOI: 10.1155/2012/575129
Abstract: In specific regions of the central nervous system (CNS), gap junctions have been shown to participate in neuronal synchrony. Amongst the CNS regions identified, some populations of brainstem motoneurons are known to be coupled by gap junctions. The application of various gap junction blockers to these motoneuron populations, however, has led to mixed results regarding their synchronous firing behavior, with some studies reporting a decrease in synchrony while others surprisingly find an increase in synchrony. To address this discrepancy, we employ a neuronal network model of Hodgkin-Huxley-style motoneurons connected by gap junctions. Using this model, we implement a series of simulations and rigorously analyze their outcome, including the calculation of a measure of neuronal synchrony. Our simulations demonstrate that under specific conditions, uncoupling of gap junctions is capable of producing either a decrease or an increase in neuronal synchrony. Subsequently, these simulations provide mechanistic insight into these different outcomes. 1. Introduction Gap junctions are found in a number of areas in the mammalian CNS and are believed to play a significant role in neuronal synchrony [1, 2]. Gap junctions link the intracellular space of two neurons, permitting ions and metabolic molecules to pass between neighboring cells, resulting in a coupling of both electrical and metabolic behavior [3, 4]. These junctions are formed from a hexameric assembly of structural proteins called connexins (Cx), and a number of Cx isoforms, including Cx26, Cx32, Cx36, Cx30.2, Cx45, and Cx50, have been identified in some populations of neurons [5–15]. Of these Cx isoforms, Cx26, Cx32, and Cx36 have been reported to be expressed in neurons and/or motoneurons in respiratory-related CNS regions [9, 11, 12, 14, 16–20]. While many CNS regions have been shown to express Cx proteins or functional gap junction coupling, gap junctions are often present in areas where synchronized firing activity is important. Amongst these CNS regions, brainstem areas associated with central respiratory control (including respiratory-related hypoglossal and phrenic motoneurons), have been shown to express Cx proteins [12, 14, 16–18, 20] or functional coupling [21–23]. Moreover, blockade of gap junctions has been shown to alter not only respiratory activity but also inspiratory-phase neuronal synchrony [24, 25], an observation that is consistent with the idea that the conductance and opening or closing of gap junctions has a direct effect on synchrony of neuronal networks [26]. Intuitively, one
Students’ Estimates of Others’ Mental Health Demonstrate a Cognitive Bias  [PDF]
Larry D. Reid
Psychology (PSYCH) , 2011, DOI: 10.4236/psych.2011.25067
Abstract: Students of five USA-campuses were surveyed concerning their use of prescription drugs to improve mental health. They were asked whether they had ever been prescribed medicines to treat various disorders and if they were currently taking the prescribed medicines and to estimate the percent of the students on their campus responding similarly. The incidence of being prescribed and currently taking medicines for the disorders was not markedly different than what might be expected from knowing published incidence rates. The students’ estimates of their fellow students’ rates of being prescribed and currently taking the medicines was considerably, sometimes dramatically, larger than the actual rates. Further testing rejected some potential explanations of the tendency to make overestimations. The conclusion was eventually drawn that the tendency to overestimate the mental distress of fellow students was a special case of superiority bias and had features of an implicit social cognition enhancing their own self-esteem.
Larry D. Yore
L1 Educational Studies in Language and Literature , 2008,
Abstract: It is important that the first, native, home, or mother tongue language (L1), cultural and personal beliefs, ontological assumptions, and epistemological beliefs of students be explicitly considered in teaching and learning environments where a different language of instruction (L2) and an English-dominated scientific enterprise (L3) are commonplace. Teaching in today’s multicultural classrooms in most countries requires understanding of the three-language issue. Research inquiries into language, literacy, and science issues must consider the values, beliefs, and practices and the traditional knowledge about nature and naturally occurring events embedded in language and culture. This introductory piece provides a reference frame for the roles of the nature of western science, language, and culture for these considerations in an attempt to produce insights for culturally sensitive curricula and effective constructivist teaching. Some authors will question the explicit and implicit values of western science as outlined here, which is the central purpose of this special issue. Cultural restoration, environmental literacy to survive, and other priorities are competing goals with acculturation into western science discourse communities for some peoples.
Los estudiantes y el significado acerca de los estudios universitarios: reflexión y propuesta metodológica
Larry D. Andrade
Perfiles educativos , 2002,
Philosophy Incarnate
Larry D. Harwood
Analytic Teaching and Philosophical Praxis , 2000,
Abstract: Book Review
Sagely Wisdom in Confucianism
Larry D. Harwood
Analytic Teaching and Philosophical Praxis , 2011,
Abstract: Though Westerners may count Chinese Confucianism as a religion, some are skeptical that Confucianism is indeed religious, while others see in Confucianism a kind of ethical humanism. Huston Smith noted the Chinese proverb that as a people the Chinese admit to being extraordinarily flatfooted, that is, with an eye toward the earth. By contrast, the West in general has derived much of its ethical framework from an overt theological and religious background. This is decidedly less so in China and in Confucianism. As the Sages of the Chinese people, neither Confucius nor Lao-Tzu is conceived of as a Savior, as Christ is in the Christian religion. There are of course differences between Taoism and Confucianism. Lao-Tzu is reported to have said, “Banish sageliness, discard wisdom, and the people will benefit a hundredfold.” However, in Confucianism, sageliness is the personification of an acquired wisdom that benefits the people in a way denied by Lao-Tzu. In this paper I will examine the Confucian notion of the sage, with some comparisons made along the way to Taoism and finally to Western thought.
Bulletin of the Texas Archeological Society, Volume 71 (2000), Austin, Paper.
Larry D. Banks
Bulletin of the History of Archaeology , 2000, DOI: 10.5334/bha.10203
Abstract: This annual bulletin of the Texas Archeological Society is a unique contribution specifically focused upon the history of Texas archaeology in a format that no others have done previously. The volume contains 150 pages, the majority of which consists of interviews (146 pages) conducted by the first State Archaeologist of Texas, Curtis Tunnell. In 1968 Tunnell conceived of the idea of obtaining personal interviews from individuals whom he considered his heroes for their pioneering efforts in Texas archeology. This volume entails the first publication of such information, but more will certainly follow. The remaining four pages comprise two different reviews of other publications important in their own right to those interested in Southern Plains archeology of Texas. These two reviews by Timothy K Pertulla and David T. Hughes, respectively, are of The Coronado Expedition to Tierra Nueva: The 1540·1542 Route Across the Southwest by Richard Flint and Shirley Cushing flint, and GaffCreek: Artifact Collection Strategy and Occupation Prehistory on the Southern High Plains, Texas County. Oklahoma. The section by Tunnell titled "In Their Own Words: Stories from Some Pioneer Texas Archeologists" contains numerous previously unpublished photographs of people, sites and artifacts referred to the texts.
Phases of Dense Quarks at Large N_c
McLerran, Larry;Pisarski, Robert D.
High Energy Physics - Phenomenology , 2007, DOI: 10.1016/j.nuclphysa.2007.08.013
Abstract: In the limit of a large number of colors, N_c, we suggest that gauge theories can exhibit several distinct phases at nonzero temperature and quark density. Two are familiar: a cold, dilute phase of confined hadrons, where the pressure is ~ 1, and a hot phase of deconfined quarks and gluons, with pressure ~ N_c^2. When the quark chemical potential mu ~ 1, the deconfining transition temperature, T_d, is independent of mu. For T < T_d, as mu increases above the mass threshold, baryons quickly form a dense phase where the pressure is ~ N_c. As illustrated by a Skyrme crystal, chiral symmetry can be both spontaneously broken, and then restored, in the dense phase. While the pressure is ~ N_c, like that of (non-ideal) quarks, the dense phase is still confined, with interactions near the Fermi surface those of baryons, and not of quarks. Thus in the chirally symmetric region, baryons near the Fermi surface are parity doubled. We suggest possible implications for the phase diagram of QCD.
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