775 research outputs found

    User's manual for PRESTO: A computer code for the performance of regenerative steam turbine cycles

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    Standard turbine cycles for baseload power plants and cycles with such additional features as process steam extraction and induction and feedwater heating by external heat sources may be modeled. Peaking and high back pressure cycles are also included. The code's methodology is to use the expansion line efficiencies, exhaust loss, leakages, mechanical losses, and generator losses to calculate the heat rate and generator output. A general description of the code is given as well as the instructions for input data preparation. Appended are two complete example cases

    VLBI astrometry of PSR J2222-0137: a pulsar distance measured to 0.4% accuracy

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    The binary pulsar J2222-0137 is an enigmatic system containing a partially recycled millisecond pulsar and a companion of unknown nature. Whilst the low eccentricity of the system favors a white dwarf companion, an unusual double neutron star system is also a possibility, and optical observations will be able to distinguish between these possibilities. In order to allow the absolute luminosity (or upper limit) of the companion object to be properly calibrated, we undertook astrometric observations with the Very Long Baseline Array to constrain the system distance via a measurement of annual geometric parallax. With these observations, we measure the parallax of the J2222-0137 system to be 3.742 +0.013 -0.016 milliarcseconds, yielding a distance of 267.3 +1.2 -0.9 pc, and measure the transverse velocity to be 57.1 +0.3 -0.2 km/s. Fixing these parameters in the pulsar timing model made it possible to obtain a measurement of Shapiro delay and hence the system inclination, which shows that the system is nearly edge-on (sin i = 0.9985 +/- 0.0005). Furthermore, we were able to detect the orbital motion of J2222-0137 in our VLBI observations and measure the longitude of ascending node. The VLBI astrometry yields the most accurate distance obtained for a radio pulsar to date, and is furthermore the most accurate parallax for any radio source obtained at "low" radio frequencies (below ~5 GHz, where the ionosphere dominates the error budget). Using the astrometric results, we show the companion to J2222-0137 will be easily detectable in deep optical observations if it is a white dwarf. Finally, we discuss the implications of this measurement for future ultra-high-precision astrometry, in particular in support of pulsar timing arrays.Comment: 22 pages, 7 figures, accepted for publication in Ap

    Pulsar J1411+2551: A Low Mass New Double Neutron Star System

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    In this work, we report the discovery and characterization of PSR J1411+2551, a new binary pulsar discovered in the Arecibo 327 MHz Drift Pulsar Survey. Our timing observations of the radio pulsar in the system span a period of about 2.5 years. This timing campaign allowed a precise measurement of its spin period (62.4 ms) and its derivative (9.6 ±\pm 0.7) ×10−20 s s−1\times 10^{-20}\, \rm s\, s^{-1}; from these, we derive a characteristic age of ∼10 \sim 10\,Gyr and a surface magnetic field strength of 2.5 ×109\times 10^{9} G. These numbers indicate that this pulsar was mildly recycled by accretion of matter from the progenitor of the companion star. The system has an eccentric (e = 0.17e\, = \, 0.17) 2.61 day orbit. This eccentricity allows a highly significant measurement of the rate of advance of periastron, ω˙=0.07686±0.00046∘ yr−1\dot{\omega} = 0.07686 \pm 0.00046 ^{\circ}~{\rm yr}^{-1}. Assuming general relativity accurately models the orbital motion, this implies a total system mass M = 2.538±0.022M⊙2.538 \pm 0.022 M_{\odot}. The minimum companion mass is 0.92 M⊙0.92\, M_{\odot} and the maximum pulsar mass is 1.62 M⊙1.62\, M_{\odot}. The large companion mass and the orbital eccentricity suggest that PSR J1411+2551 is a double neutron star system; the lightest known to date including the DNS merger GW 170817. Furthermore, the relatively low orbital eccentricity and small proper motion limits suggest that the second supernova had a relatively small associated kick; this and the low system mass suggest that it was an ultra-stripped supernova.Comment: Accepted for publication in APJ letter

    Fungal infections and antifungal prophylaxis in pediatric cardiac extracorporeal life support

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    ObjectiveInfections acquired by children during extracorporeal membrane oxygenation (ECMO) increase mortality. Our aim was to evaluate the effectiveness of prophylactic fluconazole on the incidence of fungal infections and to assess whether hospital-acquired fungal infection is associated with increased in-hospital mortality in pediatric cardiac patients requiring ECMO.MethodsWe retrospectively reviewed a prospectively maintained database and collected data on all hospital-acquired infections in patients supported for cardiac indications at a tertiary children’s hospital from 1989 to 2008.ResultsECMO was deployed 801 times in 767 patients. After exclusion criteria were applied, 261 pediatric patients supported for cardiac indications were studied. Fungal infection (blood, urine, or surgical site) occurred in 12% (31/261) of patients, 9 (7%) of 127 patients receiving fluconazole prophylaxis versus 22 (16.4%) of 134 without antifungal prophylaxis (P = .02). Using a multivariable logistic regression model, the absence of fluconazole prophylaxis was associated with an increased risk of fungal infection (odds ratio [OR] = 2.8; 95% confidence intervals [CI], 1.2, 6.7; P = .016). In a multivariable logistic regression model for in-hospital mortality, the presence of fungal infection was associated with increased odds (OR = 3.8; 95% CI, 1.5, 9.6; P = .005) of in-hospital mortality among cardiac patients requiring ECMO, and the absence of antifungal prophylaxis showed a trend toward the same (OR = 1.6; 95% CI, 0.96, 2.8; P = .072).ConclusionsChildren with cardiac disease supported with ECMO who acquire fungal infections have increased mortality. Routine fluconazole prophylaxis is associated with lower rates of fungal infections in these patients
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