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Search Results: 1 - 10 of 232 matches for " Ty Hedrick "
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Aerodynamics of the Smallest Flying Insects
Laura A. Miller,Steven Harenber,Ty Hedrick,Alice Robinson,Arvind Santhanakrishnan,Audrey Lowe
Physics , 2011,
Abstract: We present fluid dynamics videos of the flight of some of the smallest insects including the jewel wasp, \textit{Ampulex compressa}, and thrips, \textit{Thysanoptera} spp. The fruit fly, \textit{Drosophila melanogaster}, is large in comparison to these insects. While the fruit fly flies at $Re \approx 120$, the jewel wasp flies at $Re \approx 60$, and thrips flies at $Re \approx 10$. Differences in the general structures of the wakes generated by each species are observed. The differences in the wakes correspond to changes in the ratio of lift forces (vertical component) to drag forces (horizontal component) generated.
Physiological Properties of Cholinergic and Non-Cholinergic Magnocellular Neurons in Acute Slices from Adult Mouse Nucleus Basalis
Tristan Hedrick,Jack Waters
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0011046
Abstract: The basal forebrain is a series of nuclei that provides cholinergic input to much of the forebrain. The most posterior of these nuclei, nucleus basalis, provides cholinergic drive to neocortex and is involved in arousal and attention. The physiological properties of neurons in anterior basal forebrain nuclei, including medial septum, the diagonal band of Broca and substantia innominata, have been described previously. In contrast the physiological properties of neurons in nucleus basalis, the most posterior nucleus of the basal forebrain, are unknown.
Resistance to malaria in humans: the impact of strong, recent selection
Hedrick Philip W
Malaria Journal , 2012, DOI: 10.1186/1475-2875-11-349
Abstract: Malaria is one of the leading causes of death worldwide and has been suggested as the most potent type of selection in humans in recent millennia. As a result, genes involved in malaria resistance are excellent examples of recent, strong selection. In 1949, Haldane initially suggested that infectious disease could be a strong selective force in human populations. Evidence for the strong selective effect of malaria resistance includes the high frequency of a number of detrimental genetic diseases caused by the pleiotropic effects of these malaria resistance variants, many of which are “loss of function” mutants. Evidence that this selection is recent comes from the genetic dating of the age of a number of these malaria resistant alleles to less than 5,000 years before the present, generally much more recent than other human genetic variants. An approach to estimate selection coefficients from contemporary case–control data is presented. In the situations described here, selection is much greater than 1%, significantly higher than generally observed for other human genetic variation. With these selection coefficients, predictions are generated about the joint change of alleles S and C at the β-globin locus, and for α-thalassaemia haplotypes and S, variants that are unlinked but exhibit epistasis. Population genetics can be used to determine the amount and pattern of selection in the past and predict selection in the future for other malaria resistance variants as they are discovered.
Effect of temperature on spiking patterns of neocortical layer 2/3 and layer 6 pyramidal neurons
Tristan Hedrick,Jack Waters
Frontiers in Neural Circuits , 2012, DOI: 10.3389/fncir.2012.00028
Abstract: The spiking patterns of neocortical pyramidal neurons are shaped by the conductances in their apical dendrites. We have previously shown that the spiking patterns of layer 5 pyramidal neurons change with temperature, probably because temperature modulates the electrical coupling between somatic and dendritic compartments. Here we determine whether temperature has similar effects on the spiking patterns of layer 2/3 and layer 6 pyramidal neurons in acute slices of mouse primary motor cortex. In both cell types, decreasing temperature led to more irregular spiking patterns. Our results indicate that a decrease in spiking regularity with decreasing temperature, probably mediated by increased electrical coupling between soma and dendrites, is common to all pyramidal neurons in motor cortex.
Spiking Patterns of Neocortical L5 Pyramidal Neurons in Vitro Change with Temperature
Tristan Hedrick,Jack Waters
Frontiers in Cellular Neuroscience , 2011, DOI: 10.3389/fncel.2011.00001
Abstract: A subset of pyramidal neurons in layer 5 of the mammalian neocortex can fire action potentials in brief, high-frequency bursts while others fire spikes at regularly spaced intervals. Here we show that individual layer 5 pyramidal neurons in acute slices from mouse primary motor cortex can adopt both regular and burst spiking patterns. During constant current injection at the soma, neurons displayed a regular firing pattern at 36–37°C, but switched to burst spiking patterns upon cooling the slice to 24–26°C. This change in firing pattern was reversible and repeatable and was independent of the somatic resting membrane potential. Hence these spiking patterns are not inherent to discrete populations of pyramidal neurons and are more interchangeable than previously thought. Burst spiking in these neurons is the result of electrical interactions between the soma and distal apical dendritic tree. Presumably the interactions between soma and distal dendrite are temperature-sensitive, suggesting that the manner in which layer 5 pyramidal neurons translate synaptic input into an output spiking pattern is fundamentally altered at sub-physiological temperatures.
Composition of the Invasive Macrophyte Community in three river basins in the Okyeman Area, Southern Ghana
TY Annang
West African Journal of Applied Ecology , 2012,
Abstract: A survey was carried out to study the composition of the invasive aquatic macrophyte community including submerged forms, in three river basins the Okyeman area namely the Ayensu, Birim and Densu basins. Of prime interest was the presence of any one of these four species, Pistia stratiotes (water lettuce), Eichhornia crassipes (water hyacinth), Azolla species (fairy fern) and Salvinia molesta (Kariba weed), a floating water fern, which are alien to Africa. The number of invasive macrophytes encountered in the survey of the macrophytes was low with Eichhornia crassipes (water hyacinth) conspicuously missing. A concerted effort to exclude these species from our freshwater bodies is suggested as the presence of any of these four is regarded as detrimental to aquatic life, because once they become established they tend to prevent the growth of native ones.
A Check-list of Some Elements of the Vegetation in three river basins in the Okyeman Area, Southern Ghana
TY Annang
West African Journal of Applied Ecology , 2012,
Abstract: The composition of some elements of the aquatic flora was determined in three river basins namely Ayensu, Birim and Densu, in the Okyeman area in Southern Ghana. Samples of these vegetation types, namely bryophytes, podostemonads and rhodophytes, in the three river basins were taken at 16 sites as follows: 4 sampling sites from the Ayensu basin, 7 sampling sites within the Birim and 5 sites were sampled in the Densu basin. Two species of rhodophytes were identified inconclusively. However no bryophyte species and podostemonads were encountered due to stated factors. Issues concerning detailed update of these members of the aquatic flora in Ghana are discussed.
Appendix H: Focus Group Summary of the Cambodian and Lao Student Union
Kanara Ty
Journal of Southeast Asian American Education and Advancement , 2011,
Fourth-order flows in surface modelling
Ty Kang
Computer Science , 2013,
Abstract: This short article is a brief account of the usage of fourth-order curvature flow in surface modelling.
Partition Learning for Multiagent Planning
Jared Wood,J. Karl Hedrick
Journal of Robotics , 2012, DOI: 10.1155/2012/590479
Abstract: Automated surveillance of large geographic areas and target tracking by a team of autonomous agents is a topic that has received significant research and development effort. The standard approach is to decompose this problem into two steps. The first step is target track estimation and the second step is path planning by optimizing directly over target track estimation. This standard approach works well in many scenarios. However, an improved approach is needed for the scenario when general, nonparametric estimation is required, and the number of targets is unknown. The focus of this paper is to present a new approach that inherently handles the task to search for and track an unknown number of targets within a large geographic area. This approach is designed for the case when the search is performed by a team of autonomous agents and target estimation requires general, nonparametric methods. There are consequently very few assumptions made. The only assumption made is that a time-changing target track estimation is available and shared between the agents. This estimation is allowed to be general and nonparametric. Results are provided that compare the performance of this new approach with the standard approach. From these results it is concluded that this new approach improves search and tracking when the number of targets is unknown and target track estimation is general and nonparametric. 1. Introduction The advancement of computing technology has enabled the practical development of intelligent autonomous systems. Intelligent autonomous systems can be used to perform difficult sensing tasks. One such sensing task is to search for and track targets over large geographic areas. Much research has gone into this task resulting in a standard approach. This standard approach decomposes the problem into two steps. (1)Target track estimation. (2)Agent path optimization based on target track estimation. Significant research has been accomplished for each of these steps. Target track estimation has largely been solved [1–5] and this paper proposes no new methods for target track estimation. Agent path optimization based on target track estimation has been solved for many scenarios. However, the general scenario of when the number of targets is unknown still requires more development. The standard approach in general works particularly well when it can be assumed that there is a single target [6–14]. And in many scenarios the standard approach works well even when there are multiple targets [15, 16]. However, when there are multiple targets, methods following
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