60,331 research outputs found

    Tate (co)homology via pinched complexes

    Full text link
    For complexes of modules we study two new constructions, which we call the pinched tensor product and the pinched Hom. They provide new methods for computing Tate homology and Tate cohomology, which lead to conceptual proofs of balancedness of Tate (co)homology for modules over associative rings. Another application we consider is in local algebra. Under conditions of vanishing of Tate (co)homology, the pinched tensor product of two minimal complete resolutions yields a minimal complete resolution.Comment: Final version; 23 pp. To appear in Trans. Amer. Math. So

    Development of a 200 W CW High Efficiency Traveling Wave Tube at 12 GHz

    Get PDF
    The design, development, and test results are reported for an experimental PPM focused, traveling-wave tube that produces 235 watts of CW RF power over 85 MHz centered at 12.080 GHz. The tube uses a coupled cavity RF circuit with a velocity taper for greater than 30 percent basic efficiency. Overall efficiency of 51 percent is achieved by means of a nine stage depressed collector designed at NASA Lewis Research Center. This collector is cooled by direct radiation to deep space

    Myocardial Architecture and Patient Variability in Clinical Patterns of Atrial Fibrillation

    Get PDF
    Atrial fibrillation (AF) increases the risk of stroke by a factor of four to five and is the most common abnormal heart rhythm. The progression of AF with age, from short self-terminating episodes to persistence, varies between individuals and is poorly understood. An inability to understand and predict variation in AF progression has resulted in less patient-specific therapy. Likewise, it has been a challenge to relate the microstructural features of heart muscle tissue (myocardial architecture) with the emergent temporal clinical patterns of AF. We use a simple model of activation wavefront propagation on an anisotropic structure, mimicking heart muscle tissue, to show how variation in AF behaviour arises naturally from microstructural differences between individuals. We show that the stochastic nature of progressive transversal uncoupling of muscle strands (e.g., due to fibrosis or gap junctional remodelling), as occurs with age, results in variability in AF episode onset time, frequency, duration, burden and progression between individuals. This is consistent with clinical observations. The uncoupling of muscle strands can cause critical architectural patterns in the myocardium. These critical patterns anchor micro-re-entrant wavefronts and thereby trigger AF. It is the number of local critical patterns of uncoupling as opposed to global uncoupling that determines AF progression. This insight may eventually lead to patient specific therapy when it becomes possible to observe the cellular structure of a patient's heart.Comment: 5 pages, 4 figures. For supplementary materials please contact Kishan A. Manani at [email protected]

    ECONOMIC IMPACTS OF EPA'S MANURE APPLICATION REGULATIONS ON DAIRY FARMS IN THE SOUTHWEST REGION

    Get PDF
    We estimate that EPA's CAFO final rule on manure application would have different impacts on dairy farms in the region, assuming that the farms would maintain the same herd size and same crop production practices. Some farms in the region would be able to comply it on their current land base, but other would need to lease additional land for land application of manure. Less than 30 percent of those affected farms would have a lower farm income. Most of these affected farms could have no income reduction or a higher income as a result of reduced feed cost from expanding homegrown feed production.Environmental Economics and Policy,

    Isotropic magnetometry with simultaneous excitation of orientation and alignment CPT resonances

    Full text link
    Atomic magnetometers have very high absolute precision and sensitivity to magnetic fields but suffer from a fundamental problem: the vectorial or tensorial interaction of light with atoms leads to "dead zones", certain orientations of magnetic field where the magnetometer loses its sensitivity. We demonstrate a simple polarization modulation scheme that simultaneously creates coherent population trapping (CPT) in orientation and alignment, thereby eliminating dead zones. Using 87^{87}Rb in a 10 Torr buffer gas cell we measure narrow, high-contrast CPT transparency peaks in all orientations and also show absence of systematic effects associated with non-linear Zeeman splitting.Comment: 4 pages, 4 figure

    Identification and evaluation of educational uses and users for the STS. Educational planning for utilization of space shuttle ED-PLUSS

    Get PDF
    A planning and feasibility study to identify and document a methodology needed to incorporate educational programs into future missions and operations of the space transportation system was conducted. Six tasks were identified and accomplished during the study. The task statements are as follows: (1) potential user identification, (2) a review of space education programs, (3) development of methodology for user involvement, (4) methods to encourage user awareness, (5) compilation of follow-on ideas, and (6) response to NASA questions. Specific recommendations for improving the educational coverage of space activities are provided
    corecore