9,059 research outputs found

    Predicting magnetopause crossings at geosynchronous orbit during the Halloween storms

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    [1] In late October and early November of 2003, the Sun unleashed a powerful series of events known as the Halloween storms. The coronal mass ejections launched by the Sun produced several severe compressions of the magnetosphere that moved the magnetopause inside of geosynchronous orbit. Such events are of interest to satellite operators, and the ability to predict magnetopause crossings along a given orbit is an important space weather capability. In this paper we compare geosynchronous observations of magnetopause crossings during the Halloween storms to crossings determined from the Lyon-Fedder-Mobarry global magnetohydrodynamic simulation of the magnetosphere as well to predictions of several empirical models of the magnetopause position. We calculate basic statistical information about the predictions as well as several standard skill scores. We find that the current Lyon-Fedder-Mobarry simulation of the storm provides a slightly better prediction of the magnetopause position than the empirical models we examined for the extreme conditions present in this study. While this is not surprising, given that conditions during the Halloween storms were well outside the parameter space of the empirical models, it does point out the need for physics-based models that can predict the effects of the most extreme events that are of significant interest to users of space weather forecasts

    A profile of children with complex chronic conditions at end of life among Medicaid beneficiaries: Implications for health care reform

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    Background: As the United States braces for full implementation of health care reform, the eyes of the nation are on Medicaid. The large number of newly eligible Medicaid beneficiaries may challenge health care resources and ultimately impact quality of care. This is a special concern among current Medicaid beneficiaries such as children with complex chronic conditions (CCCs) who have significant health care needs, especially at end of life (EOL). Yet, a comprehensive profile of these children is lacking. Objective: To understand the demographic and health characteristics, health care utilization, and expenditures among Medicaid children with CCCs at EOL. Methods: Our study used a retrospective cohort design with data from the 2007 and 2008 California Medicaid data files. Descriptive statistics were used to profile children in the last year of life. Results: We found a diverse group of children who suffered with serious, multiple chronic conditions, and who accessed comprehensive, multidisciplinary care. Most children had neuromuscular conditions (54%), cardiovascular conditions (46%), and cancer (30%). A majority (56%) had multiple CCCs. Children with CCCs received comprehensive care including hospital inpatient (67%), primary (82%), ancillary (87%), and other acute care services (83%); however, few children utilized hospice and home health care services (26%). Significant age differences existed among the children. Conclusions: The current California Medicaid system appears to provide comprehensive care for children at EOL. The underutilization of hospice and home health services, however, represents an opportunity to improve the quality of EOL care while potentially reducing or remaining budget neutral

    Low-frequency noise reduction of spacecraft structures

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    Low frequency noise reduction of spacecraft structure

    Oxygen isotopes implanted in the LDEF spacecraft

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    Secondary ion mass spectrometry was used to study oxygen implanted in the surface of copper from the Long Duration Exposure Facility (LDEF). Oxidation that occurred in orbit shows a characteristic oxygen isotope composition, depleted in O-18. The measured depletion is comparable to the predicted depletion (45 percent) based on a model of the gravitational separation of the oxygen isotopes. The anomalous oxygen was contained within 10nm of the surface. Tray E10 was calculated to have received 5.14 x 10(exp 21) atoms of oxygen cm(sup -2) during the LDEF mission and so there is sufficient anomalous implanted oxygen present in the surface to obtain a reliable isotopic profile

    Fatigue risk assessment of a Helicopter Emergency Medical Service crew working a 24/7 shift pattern:results of a prospective service evaluation

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    Background: The work of Helicopter Emergency Medical Services (HEMS) teams crosses the boundaries of several high-risk occupations including medicine, aviation, and transport. Working conditions can be challenging and operational demands requires a 24-h rota, resulting in disruption of the normal circadian rhythm. HEMS crews are therefore prone to both mental and physical fatigue. As fatigue in medical providers is linked to poor cognitive performance, degradation of psychomotor skills and error, this study aimed to explore the existence of predictable patterns of crew-fatigue in a HEMS service.Methods: HEMS medical crew members working a 3-on 3-off forward rotating rota with a 5-week shift cycle were asked to do psychomotor vigilance tests (PVT) as an objective measure of fatigue. PVT testing was undertaken at the start, mid- and at the end of every shift during a full 5-week shift cycle. In addition, they were asked to score subjective tiredness with the Samn-Perelli Fatigue Scale (SPFS), and to keep a Transport Fatigue Assessment shift log, wherein they noted shift characteristics potentially related to fatigue. Primary outcome of interest was defined as the change in PVT and SPFS scores over time.Results: Mean baseline resting PVT in milliseconds at the start of the study period was 427 [390–464]. There was an overall trend towards higher PVT-scores with shift progression mean [95% CI] PVT at the start of shifts 447 [433–460]; halfway through the shift 452 [440–463]; end of the shift 459 [444–475], p = 0.10), whereas SPFS scores remained constant. Within a 5 week forward-rotating cycle, an overall trend towards a gradual increase in both average PVT (from 436 [238–454] to 460 [371–527, p = 0.68] ms;) and SPFS (from 2.9 [2.6–3.2] to 3.6 [3.1–4.0], p = 0.38) was observed, although significant interindividual variation was present. Reported SPFS scores ≥ 4 (moderate fatigue) were mainly related to workload (number of jobs) and transport mode (car-based shifts).Conclusion: An overall trend towards a decline in psychomotor vigilance and an increase in self-reported tiredness was found for HEMS crew over a 5-week shift cycle. Using a bespoke predictive fatigue tool on a day-to-day basis could increase fatigue awareness and provide a framework to which relevant mitigating options can be applied.</p

    Anomalous Spin Polarization of GaAs Two-Dimensional Hole Systems

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    We report measurements and calculations of the spin-subband depopulation, induced by a parallel magnetic field, of dilute GaAs two-dimensional (2D) hole systems. The results reveal that the shape of the confining potential dramatically affects the values of in-plane magnetic field at which the upper spin subband is depopulated. Most surprisingly, unlike 2D electron systems, the carrier-carrier interaction in 2D hole systems does not significantly enhance the spin susceptibility. We interpret our findings using a multipole expansion of the spin density matrix, and suggest that the suppression of the enhancement is related to the holes' band structure and effective spin j=3/2.Comment: 6 pages, 4 figures, substantially extended discussion of result

    High fidelity quantum memory via dynamical decoupling: theory and experiment

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    Quantum information processing requires overcoming decoherence---the loss of "quantumness" due to the inevitable interaction between the quantum system and its environment. One approach towards a solution is quantum dynamical decoupling---a method employing strong and frequent pulses applied to the qubits. Here we report on the first experimental test of the concatenated dynamical decoupling (CDD) scheme, which invokes recursively constructed pulse sequences. Using nuclear magnetic resonance, we demonstrate a near order of magnitude improvement in the decay time of stored quantum states. In conjunction with recent results on high fidelity quantum gates using CDD, our results suggest that quantum dynamical decoupling should be used as a first layer of defense against decoherence in quantum information processing implementations, and can be a stand-alone solution in the right parameter regime.Comment: 6 pages, 3 figures. Published version. This paper was initially entitled "Quantum gates via concatenated dynamical decoupling: theory and experiment", by Jacob R. West, Daniel A. Lidar, Bryan H. Fong, Mark F. Gyure, Xinhua Peng, and Dieter Suter. That original version split into two papers: http://arxiv.org/abs/1012.3433 (theory only) and the current pape

    Electrical activation and electron spin resonance measurements of implanted bismuth in isotopically enriched silicon-28

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    We have performed continuous wave and pulsed electron spin resonance measurements of implanted bismuth donors in isotopically enriched silicon-28. Donors are electrically activated via thermal annealing with minimal diffusion. Damage from bismuth ion implantation is repaired during thermal annealing as evidenced by narrow spin resonance linewidths (B_pp=12uT and long spin coherence times T_2=0.7ms, at temperature T=8K). The results qualify ion implanted bismuth as a promising candidate for spin qubit integration in silicon.Comment: 4 pages, 4 figure

    Electron spin relaxation of N@C60 in CS2

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    We examine the temperature dependence of the relaxation times of the molecules N@C60 and N@C70 (which comprise atomic nitrogen trapped within a carbon cage) in liquid CS2 solution. The results are inconsistent with the fluctuating zero field splitting (ZFS) mechanism, which is commonly invoked to explain electron spin relaxation for S > 1/2 spins in liquid solution, and is the mechanism postulated in the literature for these systems. Instead, we find a clear Arrhenius temperature dependence for N@C60, indicating the spin relaxation is driven primarily by an Orbach process. For the asymmetric N@C70 molecule, which has a permanent non-zero ZFS, we resolve an additional relaxation mechanism caused by the rapid reorientation of its ZFS. We also report the longest coherence time (T2) ever observed for a molecular electron spin, being 0.25 ms at 170K.Comment: 6 pages, 6 figures V2: Updated to published versio
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