2,651 research outputs found

    Population Health and AHEOR at JSPH

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    Noncooperatively Optimized Tolerance: Decentralized Strategic Optimization in Complex Systems

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    We introduce noncooperatively optimized tolerance (NOT), a generalization of highly optimized tolerance (HOT) that involves strategic (game theoretic) interactions between parties in a complex system. We illustrate our model in the forest fire (percolation) framework. As the number of players increases, our model retains features of HOT, such as robustness, high yield combined with high density, and self-dissimilar landscapes, but also develops features of self-organized criticality (SOC) when the number of players is large enough. For example, the forest landscape becomes increasingly homogeneous and protection from adverse events (lightning strikes) becomes less closely correlated with the spatial distribution of these events. While HOT is a special case of our model, the resemblance to SOC is only partial; for example, the distribution of cascades, while becoming increasingly heavy-tailed as the number of players increases, also deviates more significantly from a power law in this regime. Surprisingly, the system retains considerable robustness even as it becomes fractured, due in part to emergent cooperation between neighboring players. At the same time, increasing homogeneity promotes resilience against changes in the lightning distribution, giving rise to intermediate regimes where the system is robust to a particular distribution of adverse events, yet not very fragile to changes

    Generation of Circular Polarization of the Cosmic Microwave Background

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    The standard cosmological model, which includes only Compton scattering photon interactions at energy scales near recombination, results in zero primordial circular polarization of the cosmic microwave background. In this paper we consider a particular renormalizable and gauge-invariant standard model extension coupling photons to an external vector field via a Chern-Simons term, which arises as a radiative correction if gravitational torsion couples to fermions. We compute the transport equations for polarized photons from a Boltzmann-like equation, showing that such a coupling will source circular polarization of the microwave background. For the particular coupling considered here, the circular polarization effect is always negligible compared to the rotation of the linear polarization orientation, also derived using the same formalism. We note the possibility that limits on microwave background circular polarization may probe other photon interactions and related fundamental effects such as violations of Lorentz invariance.Comment: 20 pages. Revised version includes an explicit calculation of gauge invariance. Text reorganized to improve clarity, and references adde

    Chronicity and Mental Health Service Utilization for Anxiety, Mood, and Substance Use Disorders among Black Men in the United States; Ethnicity and Nativity Differences.

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    This study investigated ethnic and nativity differences in the chronicity and treatment of psychiatric disorders of African American and Caribbean Black men in the U.S. Data were analyzed from the National Survey of American Life, a population-based study which included 1859 self-identified Black men (1222 African American, 176 Caribbean Black men born within the U.S., and 461 Caribbean Black men born outside the U.S.). Lifetime and twelve-month prevalence of DSM-IV mood, anxiety, and substance use disorders (including Bipolar I and Dysthmia), disorder chronicity, and rate of mental health services use among those meeting criteria for a lifetime psychiatric disorder were examined. Logistic regression models were employed to determine ethnic differences in chronicity, and treatment utilization for disorders. While rates of DSM-IV disorders were generally low in this community sample of Black men, their disorders were chronic and remained untreated. Caribbean Black men born in the U.S. had higher prevalence of Post-Traumatic Stress Disorder, Major Depressive Disorder, and Alcohol Abuse Disorder compared with African American men. Foreign born Caribbean Black men experienced greater chronicity in Social Phobia and Generalized Anxiety Disorder compared to other Black Men. Utilization of mental health service was low for all groups of Black Men, but lowest for the foreign born Caribbean Black men. Results underscore the large unmet needs of both African American and Caribbean Black men in the United States. Results also highlight the role of ethnicity and nativity in mental disorder chronicity and mental health service utilization patterns of Black men

    Nucleus-Nucleus Bremsstrahlung from Ultrarelativistic Collisions

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    The bremsstrahlung produced when heavy nuclei collide is estimated for central collisions at the Relativistic Heavy Ion Collider. Soft photons can be used to infer the rapidity distribution of the outgoing charge. An experimental design is outlined.Comment: 12 pages, 7 figures, uses revte

    Synthesis of Nm-PHB (nanomelanin-polyhydroxy butyrate) nanocomposite film and its protective effect against biofilm-forming multi drug resistant Staphylococcus aureus

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    Melanin is a dark brown ubiquitous photosynthetic pigment which have many varied and ever expanding applications in fabrication of radio-protective materials, food packaging, cosmetics and in medicine. In this study, melanin production in a Pseudomonas sp. which was isolated from the marine sponge Tetyrina citirna was optimized employing one-factor at a time experiments and characterized for chemical nature and stability. Following sonication nucleated nanomelanin (Nm) particles were formed and evaluated for antibacterial and antioxidant properties. Nanocomposite film was fabricated using combinations (% w/v) of polyhydroxy butyrate-nanomelanin (PHB: Nm) blended with 1% glycerol. The Nm was found to be spherical in shape with a diameter of 100-140 nm and showed strong antimicrobial activity against both Gram positive and Gram negative bacteria. The Nm-PHB nanocomposite film was homogeneous, smooth, without any cracks, and flexible. XRD and DSC data indicated that the film was crystalline in nature, and was thermostable up to 281.87 degrees C. This study represents the first report on the synthesis of Nm and fabrication of Nm-PHB nanocomposite film which show strong protective effect against multidrug resistant Staphyloccoccus aureus. Thus this Nm-PHB nanocomposite film may find utility as packaging material for food products by protecting the food products from oxidation and bacterial contamination

    Inadequacies in the conventional treatment of the radiation field of moving sources

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    There is a fundamental difference between the classical expression for the retarded electromagnetic potential and the corresponding retarded solution of the wave equation that governs the electromagnetic field. While the boundary contribution to the retarded solution for the {\em potential} can always be rendered equal to zero by means of a gauge transformation that preserves the Lorenz condition, the boundary contribution to the retarded solution of the wave equation governing the {\em field} may be neglected only if it diminishes with distance faster than the contribution of the source density in the far zone. In the case of a source whose distribution pattern both rotates and travels faster than light {\em in vacuo}, as realized in recent experiments, the boundary term in the retarded solution governing the field is by a factor of the order of R1/2R^{1/2} {\em larger} than the source term of this solution in the limit that the distance RR of the boundary from the source tends to infinity. This result is consistent with the prediction of the retarded potential that part of the radiation field generated by a rotating superluminal source decays as R1/2R^{-1/2}, instead of R1R^{-1}, a prediction that is confirmed experimentally. More importantly, it pinpoints the reason why an argument based on a solution of the wave equation governing the field in which the boundary term is neglected (such as appears in the published literature) misses the nonspherical decay of the field

    Space Shuttle Program: Automatic rendezvous, proximity operations, and capture (category 3)

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    The NASA Johnson Space Center is actively pursuing the development and demonstration of capabilities for automatic rendezvous, proximity operations, and capture (AR&C) using the Space Shuttle as the active vehicle. This activity combines the technologies, expertise, tools, and facilities of the JSC Tracking and Communications Division (EE), Navigation, Control and Aeronautics Division (EG), Automation and Robotics Division (ER), and Structures and Mechanics Division (ES) of the Engineering Directorate and the Flight Design and Dynamics Division (DM) of the Mission Operations Directorate. Potential benefits of AR&C include more efficient and repeatable rendezvous, proximity operations, and capture operations; reduced impacts on the target vehicles (e.g., Orbiter RCS plume loads); reduced flight crew work loads; reduced ground support requirements; and reduced operational constraints. This paper documents the current JSC capabilities/tools/facilities for AR&C and describes a proposed plan for a progression of ground demonstrations and flight tests and demonstrations of AR&C capabilities. This plan involves the maturing of existing technologies in tracking and communications; guidance, navigation and control; mechanisms; manipulators; and systems management and integrating them into several evolutionary demonstration stages
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