741 research outputs found

    Characterization of On-Orbit GPS Transmit Antenna Patterns for Space Users

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    The GPS Antenna Characterization Experiment (GPS ACE) has made extensive observations of GPS L1 signals received at geosynchronous (GEO) altitude, with the objective of developing comprehensive models of the signal levels and signal performance in the GPS transmit antenna side lobes. The experiment was originally motivated by the fact that data on the characteristics and performance of the GPS signals available in GEO and other high Earth orbits was limited. The lack of knowledge of the power and accuracy of the side lobe signals on-orbit added risk to missions seeking to employ the side lobes to meet navigation requirements or improve performance. The GPS ACE Project lled that knowledge gap through a collaboration between The Aerospace Corporation and NASA Goddard Space Fight Center to collect and analyze observations from GPS side lobe transmissions to a satellite at GEO using a highly-sensitive GPS receiver installed at the ground station. The GPS ACE architecture has been in place collecting observations of the GPS constellation with extreme sensitivity for several years. This sensitivity combined with around-the-clock, all-in-view processing enabled full azimuthal coverage of the GPS transmit gain patterns over time to angles beyond 90 degrees off-boresight. Results discussed in this paper include the reconstructed transmit gain patterns, with comparisons to available pre-fight gain measurements from the GPS vehicle contractors. For GPS blocks with extensive ground measurements, the GPS ACE results show remarkable agreement with ground based measurements. For blocks without extensive ground measurements, the GPS ACE results provide the only existing assessments of the full transmit gain patterns. The paper also includes results of pseudorange deviation analysis to assess systematic errors associated with GPS side lobe signals

    A note on monopole moduli spaces

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    We discuss the structure of the framed moduli space of Bogomolny monopoles for arbitrary symmetry breaking and extend the definition of its stratification to the case of arbitrary compact Lie groups. We show that each stratum is a union of submanifolds for which we conjecture that the natural L2L^2 metric is hyperKahler. The dimensions of the strata and of these submanifolds are calculated, and it is found that for the latter, the dimension is always a multiple of four.Comment: 17 pages, LaTe

    I-Brane Inflow and Anomalous Couplings on D-Branes

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    We show that the anomalous couplings of DD-brane gauge and gravitational fields to Ramond-Ramond tensor potentials can be deduced by a simple anomaly inflow argument applied to intersecting DD-branes and use this to determine the eight-form gravitational coupling.Comment: 8 pages, harvmac, no figure

    Stability and BPS branes

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    We define the concept of Pi-stability, a generalization of mu-stability of vector bundles, and argue that it characterizes N=1 supersymmetric brane configurations and BPS states in very general string theory compactifications with N=2 supersymmetry in four dimensions.Comment: harvmac, 18 p

    Vaccination against Foot-and-mouth disease : do initial conditions affect its benefit?

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    When facing incursion of a major livestock infectious disease, the decision to implement a vaccination programme is made at the national level. To make this decision, governments must consider whether the benefits of vaccination are sufficient to outweigh potential additional costs, including further trade restrictions that may be imposed due to the implementation of vaccination. However, little consensus exists on the factors triggering its implementation on the field. This work explores the effect of several triggers in the implementation of a reactive vaccination-to-live policy when facing epidemics of foot-and-mouth disease. In particular, we tested whether changes in the location of the incursion and the delay of implementation would affect the epidemiological benefit of such a policy in the context of Scotland. To reach this goal, we used a spatial, premises-based model that has been extensively used to investigate the effectiveness of mitigation procedures in Great Britain. The results show that the decision to vaccinate, or not, is not straightforward and strongly depends on the underlying local structure of the population-at-risk. With regards to disease incursion preparedness, simply identifying areas of highest population density may not capture all complexities that may influence the spread of disease as well as the benefit of implementing vaccination. However, if a decision to vaccinate is made, we show that delaying its implementation in the field may markedly reduce its benefit. This work provides guidelines to support policy makers in their decision to implement, or not, a vaccination-to-live policy when facing epidemics of infectious livestock disease

    Mindfulness-Oriented Recovery Enhancement vs Supportive Group Therapy for Co-occurring Opioid Misuse and Chronic Pain in Primary Care: A Randomized Clinical Trial

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    Importance: Successful treatment of opioid misuse among people with chronic pain has proven elusive. Guidelines recommend nonopioid therapies, but the efficacy of mindfulness-based interventions for opioid misuse is uncertain. Objective: To evaluate the efficacy of Mindfulness-Oriented Recovery Enhancement (MORE) for the reduction of opioid misuse and chronic pain. Design, Setting, and Participants: This interviewer-blinded randomized clinical trial enrolled patients from primary care clinics in Utah between January 4, 2016, and January 16, 2020. The study included 250 adults with chronic pain receiving long-term opioid therapy who were misusing opioid medications. Interventions: Treatment with MORE (comprising training in mindfulness, reappraisal, and savoring positive experiences) or supportive group psychotherapy (control condition) across 8 weekly 2-hour group sessions. Main Outcomes and Measures: Primary outcomes were (1) opioid misuse assessed by the Drug Misuse Index (self-report, interview, and urine screen) and (2) pain severity and pain-related functional interference, assessed by subscale scores on the Brief Pain Inventory through 9 months of follow-up. Secondary outcomes were opioid dose, emotional distress, and ecological momentary assessments of opioid craving. The minimum intervention dose was defined as 4 or more completed sessions of MORE or supportive group psychotherapy. Results: Among 250 participants (159 women [63.6%]; mean [SD] age, 51.8 [11.9] years), 129 were randomized to the MORE group and 121 to the supportive psychotherapy group. Overall, 17 participants (6.8%) were Hispanic or Latino, 218 (87.2%) were White, and 15 (6.0%) were of other races and/or ethnicities (2 American Indian, 3 Asian, 1 Black, 2 Pacific Islander, and 7 did not specify). At baseline, the mean duration of pain was 14.7 years (range, 1-60 years), and the mean (SD) morphine-equivalent opioid dose was 101.0 (266.3) mg (IQR, 16.0-90.0 mg). A total of 203 participants (81.2%) received the minimum intervention dose (mean [SD], 5.7 [2.2] sessions); at 9 months, 92 of 250 participants (36.8%) discontinued the study. The overall odds ratio for reduction in opioid misuse through the 9-month follow-up period in the MORE group compared with the supportive psychotherapy group was 2.06 (95% CI, 1.17-3.61; P = .01). At 9 months, 36 of 80 participants (45.0%) in the MORE group were no longer misusing opioids compared with 19 of 78 participants (24.4%) in the supportive psychotherapy group. Mixed models demonstrated that MORE was superior to supportive psychotherapy through 9 months of follow-up for pain severity (between-group effect: 0.49; 95% CI, 0.17-0.81; P = .003) and pain-related functional interference (between-group effect: 1.07; 95% CI, 0.64-1.50; P < .001). Participants in the MORE group reduced their opioid dose to a greater extent than those in the supportive psychotherapy group. The MORE group also had lower emotional distress and opioid craving. Conclusions and Relevance: In this randomized clinical trial, among adult participants in a primary care setting, the MORE intervention led to sustained improvements in opioid misuse and chronic pain symptoms and reductions in opioid dosing, emotional distress, and opioid craving compared with supportive group psychotherapy. Despite attrition caused by the COVID-19 pandemic and the vulnerability of the sample, MORE appeared to be efficacious for reducing opioid misuse among adults with chronic pain. Trial Registration: ClinicalTrials.gov Identifier: NCT0260253

    The social value of a QALY : raising the bar or barring the raise?

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    Background: Since the inception of the National Institute for Health and Clinical Excellence (NICE) in England, there have been questions about the empirical basis for the cost-per-QALY threshold used by NICE and whether QALYs gained by different beneficiaries of health care should be weighted equally. The Social Value of a QALY (SVQ) project, reported in this paper, was commissioned to address these two questions. The results of SVQ were released during a time of considerable debate about the NICE threshold, and authors with differing perspectives have drawn on the SVQ results to support their cases. As these discussions continue, and given the selective use of results by those involved, it is important, therefore, not only to present a summary overview of SVQ, but also for those who conducted the research to contribute to the debate as to its implications for NICE. Discussion: The issue of the threshold was addressed in two ways: first, by combining, via a set of models, the current UK Value of a Prevented Fatality (used in transport policy) with data on fatality age, life expectancy and age-related quality of life; and, second, via a survey designed to test the feasibility of combining respondents’ answers to willingness to pay and health state utility questions to arrive at values of a QALY. Modelling resulted in values of £10,000-£70,000 per QALY. Via survey research, most methods of aggregating the data resulted in values of a QALY of £18,000-£40,000, although others resulted in implausibly high values. An additional survey, addressing the issue of weighting QALYs, used two methods, one indicating that QALYs should not be weighted and the other that greater weight could be given to QALYs gained by some groups. Summary: Although we conducted only a feasibility study and a modelling exercise, neither present compelling evidence for moving the NICE threshold up or down. Some preliminary evidence would indicate it could be moved up for some types of QALY and down for others. While many members of the public appear to be open to the possibility of using somewhat different QALY weights for different groups of beneficiaries, we do not yet have any secure evidence base for introducing such a system

    Numerical Calabi-Yau metrics

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    We develop numerical methods for approximating Ricci flat metrics on Calabi-Yau hypersurfaces in projective spaces. Our approach is based on finding balanced metrics, and builds on recent theoretical work by Donaldson. We illustrate our methods in detail for a one parameter family of quintics. We also suggest several ways to extend our results.Comment: 23 pages, 3 figure

    The spectrum of BPS branes on a noncompact Calabi-Yau

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    We begin the study of the spectrum of BPS branes and its variation on lines of marginal stability on O_P^2(-3), a Calabi-Yau ALE space asymptotic to C^3/Z_3. We show how to get the complete spectrum near the large volume limit and near the orbifold point, and find a striking similarity between the descriptions of holomorphic bundles and BPS branes in these two limits. We use these results to develop a general picture of the spectrum. We also suggest a generalization of some of the ideas to the quintic Calabi-Yau.Comment: harvmac, 45 pp. (v2: added references
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