2,359 research outputs found

    Multiple cyclotron line-forming regions in GX 301-2

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    We present two observations of the high-mass X-ray binary GX 301-2 with NuSTAR, taken at different orbital phases and different luminosities. We find that the continuum is well described by typical phenomenological models, like a very strongly absorbed NPEX model. However, for a statistically acceptable description of the hard X-ray spectrum we require two cyclotron resonant scattering features (CRSF), one at ~35 keV and the other at ~50 keV. Even though both features strongly overlap, the good resolution and sensitivity of NuSTAR allows us to disentangle them at >=99.9% significance. This is the first time that two CRSFs are seen in GX 301-2. We find that the CRSFs are very likely independently formed, as their energies are not harmonically related and, if it were a single line, the deviation from a Gaussian shape would be very large. We compare our results to archival Suzaku data and find that our model also provides a good fit to those data. We study the behavior of the continuum as well as the CRSF parameters as function of pulse phase in seven phase bins. We find that the energy of the 35 keV CRSF varies smoothly as function of phase, between 30-38 keV. To explain this variation, we apply a simple model of the accretion column, taking the altitude of the line-forming region, the velocity of the in-falling material, and the resulting relativistic effects into account. We find that in this model the observed energy variation can be explained simply due to a variation of the projected velocity and beaming factor of the line forming region towards us.Comment: 18 pages, 10 figures, accepted for publication in A&

    Poulty Manure Impacts on Water Quality

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    Iowa\u27s egg industry continues to grow each year. In 2001, Iowa became the number one egg producing state in the US, producing 8.69 billion eggs (USDA, 2003; USDA 2002). Iowa broke its record the following year producing 10.1 billion eggs which it topped again in 2003 producing 10.1 billion eggs, thus maintaining its position as number one egg producing state in the US (USDA, 2003; USDA, 2004). With this success comes the added weight of maintaining this status, as well as, managing for all the manure that is generated by being the number one producer. Poultry manure can be a valuable soil amendment for adding organic matter and nutrients to farm fields, but if not managed properly, it can also impact the environment by deteriorating water quality. Lakes, rivers, and streams can receive excessive nutrient loads and be contaminated by surface runoff and subsurface drain water. It is the purpose of this study to gain a better understanding on how poultry manure applied to Iowa soils impacts crop growth, soil nutrients, and water quality

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    Using Lysimeters and Tile Drained Field Plots to Study the Leaching of Field Applied Poultry Manure and UAN into Tile Water

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    Six lysimeters and eleven tile drained field plots were used to determine if the amount of contaminants leaching into tile water would increase after the application of poultry manure and urea ammonium nitrate fertilizer (UAN). There were three nitrogen based treatments applied to the lysimeters and fields: 168 kg N/ha of UAN, 168 kg N/ha of poultry manure, and 336 kg N/ha of poultry manure. (One treatment per lysimeter/field plot.) Corn was planted in the lysimeters and field plots, as well as soybeans in the field plots, in order to simulate field conditions. Tile water samples were collected once a week and after rain events and tested for nitrate, total phosphate, orthophosphate, E. coli, and total coliform. Results thus far indicate that larger amounts of manure/fertilizer applied to lysimeters/field plots appear to predispose the lysimeters and field plot soils to greater contaminate leaching potential. E. coli, total coliform, and total phosphate leaching increased when heavy rain events occurred, while nitrate and orthophosphate leaching decreased

    Cyclotron resonant scattering feature simulations. I. Thermally averaged cyclotron scattering cross sections, mean free photon-path tables, and electron momentum sampling

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    Electron cyclotron resonant scattering features (CRSFs) are observed as absorption-like lines in the spectra of X-ray pulsars. A significant fraction of the computing time for Monte Carlo simulations of these quantum mechanical features is spent on the calculation of the mean free path for each individual photon before scattering, since it involves a complex numerical integration over the scattering cross section and the (thermal) velocity distribution of the scattering electrons. We aim to numerically calculate interpolation tables which can be used in CRSF simulations to sample the mean free path of the scattering photon and the momentum of the scattering electron. The tables also contain all the information required for sampling the scattering electron's final spin. The tables were calculated using an adaptive Simpson integration scheme. The energy and angle grids were refined until a prescribed accuracy is reached. The tables are used by our simulation code to produce artificial CRSF spectra. The electron momenta sampled during these simulations were analyzed and justified using theoretically determined boundaries. We present a complete set of tables suited for mean free path calculations of Monte Carlo simulations of the cyclotron scattering process for conditions expected in typical X-ray pulsar accretion columns (0.01<B/B_{crit}<=0.12, where B_{crit}=4.413x10^{13} G and 3keV<=kT<15keV). The sampling of the tables is chosen such that the results have an estimated relative error of at most 1/15 for all points in the grid. The tables are available online at http://www.sternwarte.uni-erlangen.de/research/cyclo.Comment: A&A, in pres

    Prospective Study Examining Clinical Outcomes Associated with a Negative Pressure Wound Therapy System and Barker’s Vacuum Packing Technique

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    Background The open abdomen has become a common procedure in the management of complex abdominal problems and has improved patient survival. The method of temporary abdominal closure (TAC) may play a role in patient outcome. Methods A prospective, observational, open-label study was performed to evaluate two TAC techniques in surgical and trauma patients requiring open abdomen management: Barker’s vacuum-packing technique (BVPT) and the ABTheraTM open abdomen negative pressure therapy system (NPWT). Study endpoints were days to and rate of 30-day primary fascial closure (PFC) and 30-day all-cause mortality. Results Altogether, 280 patients were enrolled from 20 study sites. Among them, 168 patients underwent at least 48 hours of consistent TAC therapy (111 NPWT, 57 BVPT). The two study groups were well matched demographically. Median days to PFC were 9 days for NPWT versus 12 days for BVPT (p = 0.12). The 30-day PFC rate was 69 % for NPWT and 51 % for BVPT (p = 0.03). The 30-day all-cause mortality was 14 % for NPWT and 30 % for BVPT (p = 0.01). Multivariate logistic regression analysis identified that patients treated with NPWT were significantly more likely to survive than the BVPT patients [odds ratio 3.17 (95 % confidence interval 1.22–8.26); p = 0.02] after controlling for age, severity of illness, and cumulative fluid administration. Conclusions Active NPWT is associated with significantly higher 30-day PFC rates and lower 30-day all-cause mortality among patients who require an open abdomen for at least 48 h during treatment for critical illness

    Two-level system with a thermally fluctuating transfer matrix element: Application to the problem of DNA charge transfer

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    Charge transfer along the base-pair stack in DNA is modeled in terms of thermally-assisted tunneling between adjacent base pairs. Central to our approach is the notion that tunneling between fluctuating pairs is rate-limited by the requirement of their optimal alignment. We focus on this aspect of the process by modeling two adjacent base pairs in terms of a classical damped oscillator subject to thermal fluctuations as described by a Fokker-Planck equation. We find that the process is characterized by two time scales, a result that is in accord with experimental findings.Comment: original file is revtex4, 10 pages, three eps figure
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