298 research outputs found

    Efficient Heralding of Photonic Qubits with Apllications to Device Independent Quantum Key Distribution

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    We present an efficient way of heralding photonic qubit signals using linear optics devices. First we show that one can obtain asymptotically perfect heralding and unit success probability with growing resources. Second, we show that even using finite resources, we can improve qualitatively and quantitatively over earlier heralding results. In the latte r scenario, we can obtain perfect heralded photonic qubits while maintaining a finite success probability. We demonstrate the advantage of our heralding scheme by predicting key rates for device independent quantum key distribution, taking imperfections of sources and detectors into account

    New Applications of Satellite-Measured Tropical Cyclone Wind Speeds

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    Major hurricanes are becoming more frequent due to climate change and the warming of the oceans. Now more than ever, the ability to model hurricanes accurately and provide advanced warning to affected areas is crucial. However, while hurricane track forecasting has greatly improved, there has been little improvement in intensity forecasting, partly due to inadequate observations and modeling of the inner core of the storm. CYGNSS, an experimental NASA satellite mission launched in December 2016, is designed to frequently measure surface wind speeds in hurricanes via GPS reflections. These additional measurements should improve forecasting of hurricane rapid intensification. This dissertation looks at new ways to use and interpret remotely sensed wind speeds in hurricanes. First, we look at how estimated storm intensity is affected by the spatial resolution of the satellite. Satellite-measured wind speeds are not point measurements—a single measurement is of a broad area on the surface where contributions from each part of the surface are given weight according to the antenna pattern. Hurricane intensity is usually determined by the maximum wind speed (Vm). Because satellite-measured wind speeds are effectively averages over a large area, the satellite-measured Vm is lower than the true Vm. Unless this is corrected for, hurricane wind fields from satellites will systematically underestimate storm intensity. This work explores how information from any satellite-measured wind field can be used to improve the estimated storm intensity via a scale factor correction. Next, hurricane parametric wind speed models are examined. Parametric wind models are established using meteorological principles combined with simplifying assumptions about the environment or storm structure. These models tune several free parameters to wind speed measurements by minimizing the difference between the measurements and the wind field “seen” by the model. Parametric wind models are especially useful for filling in gaps between measurements—once the free parameters are optimized, the model can report a wind speed estimate everywhere in the storm. Hurricane wind field characteristics such as Vm, radial distance to Vm, azimuthal information, and more are easily determined from a full wind field but are more difficult to estimate from a gap-filled wind field. Also, many modeling applications are enabled by having a full wind field. This dissertation discusses limitations of existing parametric wind models, and new parameters are added to allow for improved representation of a wider variety of storms. A parametric wind model is then used to find the center location of a hurricane using the principle that the model fit is best when the correct storm center is assumed. The storm center is the location that optimizes the model fit. Most storm center fixes are done manually—this is one of few automated storm center fix techniques and the only one not using cloud structure seen in satellite imagery. Accurate storm center locations are necessary for forecasting hurricanes, hurricane research, and historical record keeping. Lastly, a new CYGNSS data product is described which reports gridded surface wind speeds with increased convenience and reliability for users of hurricane-specific data. This product, which will be released to the public in early 2021, processes the CYGNSS wind speeds in a way that allows for self-consistency checks of the data. This new CYGNSS hurricane wind speed product is shown to be in excellent agreement with wind speeds from models and a well-established satellite.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/168082/1/drmayers_1.pd

    Security Trade-offs in Ancilla-Free Quantum Bit Commitment in the Presence of Superselection Rules

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    Security trade-offs have been established for one-way bit commitment in quant-ph/0106019. We study this trade-off in two superselection settings. We show that for an `abelian' superselection rule (exemplified by particle conservation) the standard trade-off between sealing and binding properties still holds. For the non-abelian case (exemplified by angular momentum conservation) the security trade-off can be more subtle, which we illustrate by showing that if the bit-commitment is forced to be ancilla-free an asymptotically secure quantum bit commitment is possible.Comment: 7 pages Latex; v2 has 8 pages and additional references and clarifications, this paper is to appear in the New Journal of Physic

    Effect of short-stay service use on stay-at-home duration for elderly with certified care needs: Analysis of long-term care insurance claims data in Japan

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    ObjectiveHome independence is an important issue for the elderly in many countries and cultures. The aim of this study was to examine the effect of short-stay service use on stay-at-home duration for elderly people by level of care need under the Japanese long-term care insurance system.MethodsWe analyzed anonymous, Ministry of Health, Labour and Welfare of Japan Long-Term Care Insurance claims data from Ibaraki Prefecture. All participants were certified as eligible for long-term care insurance and had moved into a facility under long-term care insurance after certification between April 2006 and March 2012. Data was analyzed for 2,454 participants aged 65 years or older who entered residential care at least 1 month after initial use of care services. The participants were divided into 2 groups (low- and high-care need), depending on their required level of care. Cox proportional hazard modeling was used to calculate the adjusted hazard ratio (HR) of residential care admission after initial use of care services.ResultsUse of short-stay services was positively correlated to delay of residential care admission compared to non-use in the low-care need group (HR; 0.834, 95% confidence interval (CI); 0.740–0.939). In the high-care need group, however, use of short-stay services was somewhat correlated with earlier admission (HR; 1.254, 95% CI; 1.084–1.451).ConclusionsThe results of this study show that appropriate timing short-stay service use is necessary for the elderly to stay at home longer

    One future or many? November 14, 15, and 16, 2002

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    This repository item contains a single issue of the Pardee Conference Series, a publication series that began publishing in 2006 by the Boston University Frederick S. Pardee Center for the Study of the Longer-Range Future. This was the Center's 2nd annual Conference that took place during November 14, 15, and 16, 2002.The conference brought together some 30 experts from various disciplines to discuss whether the trajectories of the future will be ‘global’ or ‘regional’ in nature. Different panels looks at the future trajectories for Europe, the Western Hemisphere, Central Asia and the Former Soviet Union, and on Asia and in each case the discussion looked at the relative importance of the regional and of global dynamics on teh forces shaping the future of these regions.Carnegie Council on Ethics and International Affair

    Eavesdropper's Optimal Information in Variations of Bennett-Brassard 1984 Quantum Key Distribution in the Coherent Attacks

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    We calculate eavesdropper's optimal information on raw bits in Bennett-Brassard 1984 quantum key distribution (BB84 QKD) and six-state scheme in coherent attacks, using a formula by Lo and Chau [Science 283 (1999) 2050] with single photon assumption. We find that eavesdropper's optimal information in QKD without public announcement of bases [Phys. Lett. A 244 (1998) 489] is the same as that of a corresponding QKD WITH it in the coherent attack. We observe a sum-rule concerning each party's information.Comment: no correction, 7 pages, 1 figure, RevTe

    Analysis and Application of an efficient line solver based upon the Symmetrical Coupled Gauss-Seidel Scheme

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    This paper describes an efficient line solver for the coupled equations. The calculation procedure, called SCGS/LS (Symmetrical Coupled Gauss-Seidel/Line Solver), is based on the SCGS scheme. The technique is applied to the driven cavity problem for the incompressible Navier-Stokes equations. A Fourier analysis of this technique is carried out. The scheme is simple and easy to programme. The rates of convergence and the computational times are reported for the test case

    Efficacy of Short-Course AZT Plus 3TC to Reduce Nevirapine Resistance in the Prevention of Mother-to-Child HIV Transmission: A Randomized Clinical Trial

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    Neil Martinson and colleagues report a randomized trial of adding short-course zidovudine+lamivudine to reduce drug resistance from single-dose nevirapine used to prevent mother-to-child transmission of HIV
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