4,977 research outputs found

    Early life-history studies of nearshore rockfishes and lingcod off Central California, 1987-92

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    This study focused on the physical and biological processes that influence the distribution, abundance, growth, and survival of young-of-the-year (YOY) rockfishes and lingcod along the central California coast. The annual somatic and reproductive condition of adult female blue rockfish corresponded to annual upwelling. Resulting larval production may correspond to the reproductive potential of adults; however, ultimate recruitment success of YOY is also effected by oceanographic conditions during their planktonic stage. Within a year, each species of settled YOY was observed concurrently and in relatively similar abundances at all study dive sites along the central coast. Most species of YOY exhibited similar growth patterns among stations and years. We found a high degree of interannual variability in the condition of adults and relative abundances of YOY. We believe a large part of this variability is due to annual oceanographic conditions, specifically upwelling. Marine reserves, which would protect populations of reproductively mature rockfishes and lingcod and insure 1arval production, have been suggested as an alternative to present management strategies for these species. However, a crucial question is whether or not larvae from adult fish in reserves would significantly contribute to replenishing stocks in other areas. This study was undertaken to assist in determining the feasibility of reserves to enhance nearshore rockfish and lingcod populations. (78pp.

    Pediatric Hand Surgery Training in Nicaragua: A Sustainable Model of Surgical Education in a Resource-Poor Environment.

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    Recent reports have demonstrated that nearly two-thirds of the world's population do not have access to adequate surgical care, a burden that is borne disproportionately by residents of resource-poor countries. Although the reasons for limited access to surgical care are complex and multi-factorial, among the most substantial barriers is the lack of trained surgical providers. This is particularly true in surgical subspecialties that focus on life-improving, rather than life-saving, treatments, such as pediatric hand and upper extremity surgery, which manages such conditions as congenital malformations, trauma and post-traumatic deformities including burns, and neuromuscular conditions (brachial plexus birth palsy, spinal cord injury, and cerebral palsy). Many models of providing surgical care in resource-limited environments have been described and implemented, but few result in sustainable models of health-care delivery. We present our experience developing a pediatric hand and upper extremity surgery training program in Nicaragua, a resource-limited nation, that grew out of a collaboration of American and Nicaraguan orthopedic surgeons. We compare this experience to that of surgeons undergoing subspecialty training in pediatric upper limb surgery in the US, highlighting the similarities and differences of these training programs. Finally, we assess the results of this training program and identify areas for further growth and development

    Towards the Future of Supernova Cosmology

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    For future surveys, spectroscopic follow-up for all supernovae will be extremely difficult. However, one can use light curve fitters, to obtain the probability that an object is a Type Ia. One may consider applying a probability cut to the data, but we show that the resulting non-Ia contamination can lead to biases in the estimation of cosmological parameters. A different method, which allows the use of the full dataset and results in unbiased cosmological parameter estimation, is Bayesian Estimation Applied to Multiple Species (BEAMS). BEAMS is a Bayesian approach to the problem which includes the uncertainty in the types in the evaluation of the posterior. Here we outline the theory of BEAMS and demonstrate its effectiveness using both simulated datasets and SDSS-II data. We also show that it is possible to use BEAMS if the data are correlated, by introducing a numerical marginalisation over the types of the objects. This is largely a pedagogical introduction to BEAMS with references to the main BEAMS papers.Comment: Replaced under married name Lochner (formally Knights). 3 pages, 2 figures. To appear in the Proceedings of 13th Marcel Grossmann Meeting (MG13), Stockholm, Sweden, 1-7 July 201

    Extending BEAMS to incorporate correlated systematic uncertainties

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    New supernova surveys such as the Dark Energy Survey, Pan-STARRS and the LSST will produce an unprecedented number of photometric supernova candidates, most with no spectroscopic data. Avoiding biases in cosmological parameters due to the resulting inevitable contamination from non-Ia supernovae can be achieved with the BEAMS formalism, allowing for fully photometric supernova cosmology studies. Here we extend BEAMS to deal with the case in which the supernovae are correlated by systematic uncertainties. The analytical form of the full BEAMS posterior requires evaluating 2^N terms, where N is the number of supernova candidates. This `exponential catastrophe' is computationally unfeasible even for N of order 100. We circumvent the exponential catastrophe by marginalising numerically instead of analytically over the possible supernova types: we augment the cosmological parameters with nuisance parameters describing the covariance matrix and the types of all the supernovae, \tau_i, that we include in our MCMC analysis. We show that this method deals well even with large, unknown systematic uncertainties without a major increase in computational time, whereas ignoring the correlations can lead to significant biases and incorrect credible contours. We then compare the numerical marginalisation technique with a perturbative expansion of the posterior based on the insight that future surveys will have exquisite light curves and hence the probability that a given candidate is a Type Ia will be close to unity or zero, for most objects. Although this perturbative approach changes computation of the posterior from a 2^N problem into an N^2 or N^3 one, we show that it leads to biases in general through a small number of misclassifications, implying that numerical marginalisation is superior.Comment: Resubmitted under married name Lochner (formally Knights). Version 3: major changes, including a large scale analysis with thousands of MCMC chains. Matches version published in JCAP. 23 pages, 8 figure

    Large Payload Transportation and Test Considerations

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    Ironically, the limiting factor to a national heavy lift strategy may not be the rocket technology needed to throw a heavy payload, but rather the terrestrial infrastructure - roads, bridges, airframes, and buildings - necessary to transport, acceptance test, and process large spacecraft. Failure to carefully consider how large spacecraft are designed, and where they are manufactured, tested, or launched, could result in unforeseen cost to modify/develop infrastructure, or incur additional risk due to increased handling or elimination of key verifications. During test and verification planning for the Altair project, a number of transportation and test issues related to the large payload diameter were identified. Although the entire Constellation Program - including Altair - was canceled in the 2011 NASA budget, issues identified by the Altair project serve as important lessons learned for future payloads that may be developed to support national "heavy lift" strategies. A feasibility study performed by the Constellation Ground Operations (CxGO) project found that neither the Altair Ascent nor Descent Stage would fit inside available transportation aircraft. Ground transportation of a payload this large over extended distances is generally not permitted by most states, so overland transportation alone would not have been an option. Limited ground transportation to the nearest waterway may be permitted, but water transportation could take as long as 66 days per production unit, depending on point of origin and acceptance test facility; transportation from the western United States would require transit through the Panama Canal to access the Kennedy Space Center launch site. Large payloads also pose acceptance test and ground processing challenges. Although propulsion, mechanical vibration, and reverberant acoustic test facilities at NASA s Plum Brook Station have been designed to accommodate large spacecraft, special handling and test work-arounds may be necessary, which could increase cost, schedule, and technical risk. Once at the launch site, there are no facilities currently capable of accommodating the combination of large payload size and hazardous processing (which includes hypergolic fuels, pyrotechnic devices, and high pressure gasses)

    Modeling the Optical-X-ray Accretion Lag in LMC X-3: Insights Into Black-Hole Accretion Physics

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    The X-ray persistence and characteristically soft spectrum of the black hole X-ray binary LMC X-3 make this source a touchstone for penetrating studies of accretion physics. We analyze a rich, 10-year collection of optical/infrared (OIR) time-series data in conjunction with all available contemporaneous X-ray data collected by the ASM and PCA detectors aboard the Rossi X-ray Timing Explorer. A cross-correlation analysis reveals an X-ray lag of ~2 weeks. Motivated by this result, we develop a model that reproduces the complex OIR light curves of LMC X-3. The model is comprised of three components of emission: stellar light; accretion luminosity from the outer disk inferred from the time-lagged X-ray emission; and light from the X-ray-heated star and outer disk. Using the model, we filter a strong noise component out of the ellipsoidal light curves and derive an improved orbital period for the system. Concerning accretion physics, we find that the local viscous timescale in the disk increases with the local mass accretion rate; this in turn implies that the viscosity parameter alpha decreases with increasing luminosity. Finally, we find that X-ray heating is a strong function of X-ray luminosity below ~50% of the Eddington limit, while above this limit X-ray heating is heavily suppressed. We ascribe this behavior to the strong dependence of the flaring in the disk upon X-ray luminosity, concluding that for luminosities above ~50% of Eddington, the star lies fully in the shadow of the disk.Comment: Accepted in ApJ (12 pages long in emulateapj format

    Psoriasis vulgaris flare during efalizumab therapy does not preclude future use: a case series

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    BACKGROUND: Severe psoriasis vulgaris can be extremely difficult to treat in some patients, even with the newer biological therapies available today. CASE PRESENTATIONS: We present two patients with severe chronic plaque psoriasis who received numerous systemic anti-psoriatic therapies with varied results. Both responded well to initial treatment with efalizumab (anti-CD11a), but then experienced a flare of their disease after missing a dose. However, after disease stablization, both patients responded well to re-introduction of efalizumab, one patient requiring concurrent treatment with infliximab (anti-TNF-α). CONCLUSION: These cases are presented to characterize this "flare" reaction, and to inform health care providers that efalizumab can still be administered after disease flare, and again may be a successful therapy
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