Descomposición de potenciales de campo local en sus fuentes presinápticas y su aplicación al estudio de dinámica de redes neuronales en el hipocampo

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Biológicas, Departamento de Biología Celular, leída el 16-11-2012Depto. de Biología CelularFac. de Ciencias BiológicasTRUEunpu

Stirling Convertor Fasteners Reliability Quantification

Onboard Radioisotope Power Systems (RPS) being developed for NASA s deep-space science and exploration missions require reliable operation for up to 14 years and beyond. Stirling power conversion is a candidate for use in an RPS because it offers a multifold increase in the conversion efficiency of heat to electric power and reduced inventory of radioactive material. Structural fasteners are responsible to maintain structural integrity of the Stirling power convertor, which is critical to ensure reliable performance during the entire mission. Design of fasteners involve variables related to the fabrication, manufacturing, behavior of fasteners and joining parts material, structural geometry of the joining components, size and spacing of fasteners, mission loads, boundary conditions, etc. These variables have inherent uncertainties, which need to be accounted for in the reliability assessment. This paper describes these uncertainties along with a methodology to quantify the reliability, and provides results of the analysis in terms of quantified reliability and sensitivity of Stirling power conversion reliability to the design variables. Quantification of the reliability includes both structural and functional aspects of the joining components. Based on the results, the paper also describes guidelines to improve the reliability and verification testing

Experimental Creep Life Assessment for the Advanced Stirling Convertor Heater Head

The United States Department of Energy is planning to develop the Advanced Stirling Radioisotope Generator (ASRG) for the National Aeronautics and Space Administration (NASA) for potential use on future space missions. The ASRG provides substantial efficiency and specific power improvements over radioisotope power systems of heritage designs. The ASRG would use General Purpose Heat Source modules as energy sources and the free-piston Advanced Stirling Convertor (ASC) to convert heat into electrical energy. Lockheed Martin Corporation of Valley Forge, Pennsylvania, is integrating the ASRG systems, and Sunpower, Inc., of Athens, Ohio, is designing and building the ASC. NASA Glenn Research Center of Cleveland, Ohio, manages the Sunpower contract and provides technology development in several areas for the ASC. One area is reliability assessment for the ASC heater head, a critical pressure vessel within which heat is converted into mechanical oscillation of a displacer piston. For high system efficiency, the ASC heater head operates at very high temperature (850 C) and therefore is fabricated from an advanced heat-resistant nickel-based superalloy Microcast MarM-247. Since use of MarM-247 in a thin-walled pressure vessel is atypical, much effort is required to assure that the system will operate reliably for its design life of 17 years. One life-limiting structural response for this application is creep; creep deformation is the accumulation of time-dependent inelastic strain under sustained loading over time. If allowed to progress, the deformation eventually results in creep rupture. Since creep material properties are not available in the open literature, a detailed creep life assessment of the ASC heater head effort is underway. This paper presents an overview of that creep life assessment approach, including the reliability-based creep criteria developed from coupon testing, and the associated heater head deterministic and probabilistic analyses. The approach also includes direct benchmark experimental creep assessment. This element provides high-fidelity creep testing of prototypical heater head test articles to investigate the relevant material issues and multiaxial stress state. Benchmark testing provides required data to evaluate the complex life assessment methodology and to validate that analysis. Results from current benchmark heater head tests and newly developed experimental methods are presented. In the concluding remarks, the test results are shown to compare favorably with the creep strain predictions and are the first experimental evidence for a robust ASC heater head creep life

Reliability of Radioisotope Stirling Convertor Linear Alternator

Onboard radioisotope power systems being developed and planned for NASA s deep-space missions would require reliable design lifetimes of up to 14 years. Critical components and materials of Stirling convertors have been undergoing extensive testing and evaluation in support of a reliable performance for the specified life span. Of significant importance to the successful development of the Stirling convertor is the design of a lightweight and highly efficient linear alternator. Alternator performance could vary due to small deviations in the permanent magnet properties, operating temperature, and component geometries. Durability prediction and reliability of the alternator may be affected by these deviations from nominal design conditions. Therefore, it is important to evaluate the effect of these uncertainties in predicting the reliability of the linear alternator performance. This paper presents a study in which a reliability-based methodology is used to assess alternator performance. The response surface characterizing the induced open-circuit voltage performance is constructed using 3-D finite element magnetic analysis. Fast probability integration method is used to determine the probability of the desired performance and its sensitivity to the alternator design parameters

Can pathway-specific LFPs be obtained in cytoarchitectonically complex structures?

[Abstract] Deciphering how the brain encodes the continuous flow of information contained in natural stimuli requires understanding the spontaneous activity of functional assemblies in multiple neuronal populations. A promising integrative approach that combines multisite recordings of local field potentials (LFP) with an independent component analysis (ICA) enables continuous readouts of population specific activities of functionally different neuron groups to be obtained. We previously used this technique successfully in the hippocampus, a single-layer neuronal structure. Here we provide numerical evidence that the cytoarchitectonic complexity of other brain structures does not compromise the value of the ICA-separated LFP components, given that spatial sampling of LFP is representative. The spatial distribution of an LFP component may be quite complex due to folded and multilayered structure of the neuronal aggregate. Nevertheless, the time course of each LFP component is still a reliable postsynaptic convolution of spikes fired by a homogeneous afferent population. This claim is supported by preliminary experimental data obtained in the lateral geniculate nucleus of the awake monkey.Ministerio de Ciencia e Innovación; BFU2010-19192Ministerio de Ciencia e Innovación; BFU2009-08169Ministerio de Ciencia e Innovación; FIS2010-2005

Constitutive hippocampal cholesterol loss underlies poor cognition in old rodents

Cognitive decline is one of the many characteristics of aging. Reduced long-term potentiation (LTP) and long-term depression (LTD) are thought to be responsible for this decline, although the precise mechanisms underlying LTP and LTD dampening in the old remain unclear. We previously showed that aging is accompanied by the loss of cholesterol from the hippocampus, which leads to PI3K/Akt phosphorylation. Given that Akt de-phosphorylation is required for glutamate receptor internalization and LTD, we hypothesized that the decrease in cholesterol in neuronal membranes may contribute to the deficits in LTD typical of aging. Here, we show that cholesterol loss triggers p-Akt accumulation, which in turn perturbs the normal cellular and molecular responses induced by LTD, such as impaired AMPA receptor internalization and its reduced lateral diffusion. Electrophysiology recordings in brain slices of old mice and in anesthetized elderly rats demonstrate that the reduced hippocampal LTD associated with age can be rescued by cholesterol perfusion. Accordingly, cholesterol replenishment in aging animals improves hippocampal-dependent learning and memory in the water maze test.publishedVersionFil: Martín, Mauricio Gerardo. Consejo Superior de Investigaciones Científicas. Centro de Biología Molecular Severo Ochoa; España.Fil: Martín, Mauricio Gerardo. Universidad Autónoma de Madrid. Centro de Biología Molecular Severo Ochoa; España.Fil: Martín, Mauricio Gerardo. Katholieke Universiteit Leuven. Center for Human Genetics. VIB Center for the Biology of Disease; Bélgica.Fil: Ahmed, Tariq. Katholieke Universiteit Leuven. Faculty of Psychology and Educational Sciences. Laboratory of Biological Psychology; Bélgica.Fil: Korovaichuk, Alejandra. Consejo Superior de Investigaciones Científicas. Instituto Cajal. Departamento de Neurobiología Funcional y de Sistemas; España.Fil: Venero, César. Universidad Nacional de Educación a Distancia. Facultad de Psicología. Departamento de Psicobiología; España.Fil: Menchón, Silvia Adriana. Katholieke Universiteit Leuven. Center for Human Genetics. VIB Center for the Biology of Disease; Bélgica.Fil: Menchón, Silvia Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Menchón, Silvia Adriana. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Salas, Isabel. Consejo Superior de Investigaciones Científicas. Centro de Biología Molecular Severo Ochoa; España.Fil: Salas, Isabel. Universidad Autónoma de Madrid. Centro de Biología Molecular Severo Ochoa; España.Fil: Salas, Isabel. Consejo Superior de Investigaciones Científicas. Centro de Biología Molecular Severo Ochoa; España.Fil: Munck, Sebastian. Katholieke Universiteit Leuven. Center for Human Genetics. VIB Center for the Biology of Disease; Bélgica.Fil: Herreras, Oscar. Consejo Superior de Investigaciones Científicas. Instituto Cajal. Departamento de Neurobiología Funcional y de Sistemas; España.Fil: Balschun, Detlef. Katholieke Universiteit Leuven. Faculty of Psychology and Educational Sciences. Laboratory of Biological Psychology; Bélgica.Fil: Dotti, Carlos Gerardo. Consejo Superior de Investigaciones Científicas. Centro de Biología Molecular Severo Ochoa; España.Fil: Dotti, Carlos Gerardo. Universidad Autónoma de Madrid. Centro de Biología Molecular Severo Ochoa; España.Fil: Dotti, Carlos Gerardo. Katholieke Universiteit Leuven. Center for Human Genetics. VIB Center for the Biology of Disease; Bélgica.Biofísic

Teaching Hospital Five-Year Mortality Trends in the Wake of Duty Hour Reforms

Background The Accreditation Council for Graduate Medical Education (ACGME) implemented duty hour regulations for residents in 2003 and again in 2011. While previous studies showed no systematic impacts in the first 2 years post-reform, the impact on mortality in subsequent years has not been examined. OBJECTIVE To determine whether duty hour regulations were associated with changes in mortality among Medicare patients in hospitals of different teaching intensity after the first 2 years post-reform. DESIGN Observational study using interrupted time series analysis with data from July 1, 2000 to June 30, 2008. Logistic regression was used to examine the change in mortality for patients in more versus less teaching-intensive hospitals before (2000–2003) and after (2003–2008) duty hour reform, adjusting for patient comorbidities, time trends, and hospital site. PATIENTS Medicare patients (n  = 13,678,956) admitted to short-term acute care non-federal hospitals with principal diagnoses of acute myocardial infarction (AMI), gastrointestinal bleeding, or congestive heart failure (CHF); or a diagnosis-related group (DRG) classification of general, orthopedic, or vascular surgery. MAIN MEASURE All-location mortality within 30 days of hospital admission. KEY RESULTS In medical and surgical patients, there were no consistent changes in the odds of mortality at more vs. less teaching intensive hospitals in post-reform years 1–3. However, there were significant relative improvements in mortality for medical patients in the fourth and fifth years post-reform: Post4 (OR 0.88, 95 % CI [0.93–0.94]); Post5 (OR 0.87, [0.82–0.92]) and for surgical patients in the fifth year post-reform: Post5 (OR 0.91, [0.85–0.96]). CONCLUSIONS Duty hour reform was associated with no significant change in mortality in the early years after implementation, and with a trend toward improved mortality among medical patients in the fourth and fifth years. It is unclear whether improvements in outcomes long after implementation can be attributed to the reform, but concerns about worsening outcomes seem unfounded

The Biomedical Model in Practice: NGO-Administered Healthcare in Rural Guatemala

Mentor: Peter Benson From the Washington University Undergraduate Research Digest: WUURD, Volume 7, Issue 1, Fall 2011. Published by the Office of Undergraduate Research, Joy Zalis Kiefer Director of Undergraduate Research and Assistant Dean in the College of Arts & Sciences; Kristin Sobotka, Editor

Spatial Modules of Coherent Activity in Pathway-Specific LFPs in the Hippocampus Reflect Topology and Different Modes of Presynaptic Synchronization

Ongoing network activity often manifests as irregular fluctuations in local field potentials (LFPs), a complex mixture of multicellular synaptic currents of varying locations and extensions. Among other conditions, for synchronously firing presynaptic units to generate sizable postsynaptic LFPs, their axonal territories should overlap. We have taken advantage of anatomical regularity of the rat hippocampus and combined multiple linear recordings and spatial discrimination techniques to separate pathway-specific LFPs with enough spatial resolution to discriminate postsynaptic regions of varying activation, and to investigate their presynaptic origin, chemical nature, and spatial extension. We identified 6 main excitatory and inhibitory LFP generators with different synaptic territories in principal cells and hippocampal subfields matching anatomical pathways. Some recognized pathways did not contribute notably to LFPs. Each showed different septo-temporal spatial modules over which the field potential fluctuations were synchronous. These modules were explained by either the strong overlap of synaptic territories of coactivated afferent neurons (e.g., CA3 clusters for CA1 Schaffer LFPs), or widespread coalescence of postsynaptic territories (granule cell somatic inhibition). We also show evidence that distinct modes of afferent synchronization generate stereotyped spatial patterns of synchronous LFPs in one pathway. Thus, studying spatial coherence of pathway-specific LFPs provides remote access to the dynamics of afferent populations