5,120 research outputs found

    The Influence of Tidal Heating on the Habitability of Planets Orbiting White Dwarfs

    Full text link
    In recent years, there have been a growing number of observations indicating the presence of rocky material in short-period orbits around white dwarfs. In this Letter, we revisit the prospects for habitability around these post-main-sequence star systems. In addition to the typically considered radiative input luminosity, potentially habitable planets around white dwarfs are also subjected to significant tidal heating. The combination of these two heating sources can, for a narrow range of planetary properties and orbital parameters, continuously maintain surface temperatures amenable for habitability for planets around white dwarfs over time scales up to 10 Gyr. We show that for a specific locus of orbital parameter space, tidal heating can substantially extend the timescale of continuous habitability for a planet around a white dwarf.Comment: Accepted to ApJ

    Cladding mode coupling in highly localized fiber Bragg gratings: modal properties and transmission spectra

    Full text link
    The spectral characteristics of a fiber Bragg grating (FBG) with a transversely inhomogeneous refractive index profile, differs con- siderably from that of a transversely uniform one. Transmission spectra of inhomogeneous and asymmetric FBGs that have been inscribed with focused ultrashort pulses with the so-called point-by-point technique are investigated. The cladding mode resonances of such FBGs can span a full octave in the spectrum and are very pronounced (deeper than 20dB). Using a coupled-mode approach, we compute the strength of resonant coupling and find that coupling into cladding modes of higher azimuthal order is very sensitive to the position of the modification in the core. Exploiting these properties allows precise control of such reflections and may lead to many new sensing applications.Comment: Submission to OE, 16 pages, 6 figure

    The Nearby Neutron Star RX J0720.4-3125 from Radio to X-rays

    Full text link
    We present radio, optical, ultraviolet, and X-ray observations of the isolated, thermally-emitting neutron star RX J0720.4-3125 using the Parkes radio telescope, the Very Large Array, the Hubble Space Telescope, and the Chandra X-ray Observatory. From these data we show that the optical/UV spectrum of RX J0720.4-3125 is not well fit by a Rayleigh-Jeans tail as previously thought, but is instead best fit by either a single non-thermal power-law or a combination of a Rayleigh-Jeans tail and a non-thermal power-law. Taken together with the X-ray spectrum, we find the best model for RX J0720.4-3125 to be two blackbodies plus a power-law, with the cool blackbody implying a radius of 11-13 km at an assumed distance of 300 pc. This is similar to many middle aged (10^{5-6} yr) radio pulsars such as PSR B0656+14, evidence supporting the hypothesis that RX J0720.4-3125 is likely to be an off-beam radio pulsar. The radio data limit the flux at 1.4 GHz to be <0.24 mJy, or a luminosity limit of 4*pi*d^2*F < 3e25*d_300^2 ergs/s, and we see no sign of extended nebulosity, consistent with expectations for a pulsar like RX J0720.4-3125.Comment: 13 pages, 9 figures. Uses emulateapj5.sty and onecolfloat5.sty. Accepted for publication in Ap

    Difference Image Analysis of Galactic Microlensing II. Microlensing Events

    Full text link
    The MACHO collaboration has been carrying out Difference Image Analysis (DIA) since 1996 with the aim of increasing the sensitivity to the detection of gravitational microlensing. This is a preliminary report on the application of DIA to galactic bulge images in one field. We show how the DIA technique significantly increases the number of detected lensing events, by removing the positional dependence of traditional photometry schemes and lowering the microlensing event detection threshold. This technique, unlike PSF photometry, gives the unblended colours and positions of the microlensing source stars. We present a set of criteria for selecting microlensing events from objects discovered with this technique. The 16 pixel and classical microlensing events discovered with the DIA technique are presented.Comment: 13 pages, 6 figures, uses AAS LaTEX 4.0, To appear in ApJ

    Difference Image Analysis of Galactic Microlensing I. Data Analysis

    Full text link
    This is a preliminary report on the application of Difference Image Analysis (DIA) to galactic bulge images. The aim of this analysis is to increase the sensitivity to the detection of gravitational microlensing. We discuss how the DIA technique simplifies the process of discovering microlensing events by detecting only objects which have variable flux. We illustrate how the DIA technique is not limited to detection of so called ``pixel lensing'' events, but can also be used to improve photometry for classical microlensing events by removing the effects of blending. We will present a method whereby DIA can be used to reveal the true unblended colours, positions and light curves of microlensing events. We discuss the need for a technique to obtain the accurate microlensing time scales from blended sources, and present a possible solution to this problem using the existing HST colour magnitude diagrams of the galactic bulge and LMC. The use of such a solution with both classical and pixel microlensing searches is discussed. We show that one of the major causes of systematic noise in DIA is differential refraction. A technique for removing this systematic by effectively registering images to a common airmass is presented. Improvements to commonly used image differencing techniques are discussed.Comment: 18 pages, 8 figures, uses AAS LaTEX 4.0, To appear in Astrophysical Journa

    Patient Medication Instruction and Provider Interactions: Effects on Knowledge and Attitudes

    Full text link
    This prospective study examines whether a patient medication instruction sheet (PMI) given to clinic patients by their health care provider affects knowledge and/or attitudes with thiazide diuretic use as part of an antihypertensive regimen. Adult male patients ( N = 285) in a general medicine clinic were assigned to groups receiving the American Medical Association PMI describing their diuretic. Patients getting the PMI obtained it either directly from their provider or at the pharmacy dispensing window. All patients were surveyed by phone 1 week following the clinic visit with regard to the PMI, knowledge of medication use, and attitudes toward drug use. Results indicate that a provider-dispensed PMI results in higher levels of drug knowledge and greater patient satisfaction with their knowledge than a pharmacy-dispensed PMI. In addition, the PMIs educational value may be lessened by an incomplete verbal consult. This study demonstrates that the AMA PMI is an effective educational tool when distributed by a provider and can promote better understanding and use of prescribed medications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66928/2/10.1177_109019818601300106.pd

    A Global Diatom Database- Abundance, Biovolume and Biomass in the World Ocean

    Get PDF
    Phytoplankton identification and abundance data are now commonly feeding plankton distribution databases worldwide. This study is a first attempt to compile the largest possible body of data available from different databases as well as from individual published or unpublished datasets regarding diatom distribution in the world ocean. The data obtained originate from time series studies as well as spatial studies. This effort is supported by the Marine Ecosystem Model Inter-Comparison Project (MAREMIP), which aims at building consistent datasets for the main plankton functional types (PFTs) in order to help validate biogeochemical ocean models by using carbon (C) biomass derived from abundance data. In this study we collected over 293 000 individual geo-referenced data points with diatom abundances from bottle and net sampling. Sampling site distribution was not homogeneous, with 58% of data in the Atlantic, 20% in the Arctic, 12% in the Pacific, 8% in the Indian and 1% in the Southern Ocean. A total of 136 different genera and 607 different species were identified after spell checking and name correction. Only a small fraction of these data were also documented for biovolumes and an even smaller fraction was converted to C biomass. As it is virtually impossible to reconstruct everyone\u27s method for biovolume calculation, which is usually not indicated in the datasets, we decided to undertake the effort to document, for every distinct species, the minimum and maximum cell dimensions, and to convert all the available abundance data into biovolumes and C biomass using a single standardized method. Statistical correction of the database was also adopted to exclude potential outliers and suspicious data points. The final database contains 90 648 data points with converted C biomass. Diatom C biomass calculated from cell sizes spans over eight orders of magnitude. The mean diatom biomass for individual locations, dates and depths is 141.19 ╬╝g Cl-1, while the median value is 11.16 ╬╝g Cl-1. Regarding biomass distribution, 19% of data are in the range 0-1 ╬╝g Cl-1, 29% in the range 1-10 ╬╝g Cl-1, 31% in the range 10-100 ╬╝g Cl-1, 18% in the range 100-1000 ╬╝g Cl-1, and only 3% \u3e 1000 ╬╝g Cl-1. Interestingly, less than 50 species contributed to \u3e90% of global biomass, among which centric species were dominant. Thus, placing significant efforts on cell size measurements, process studies and C quota calculations of these species should considerably improve biomass estimates in the upcoming years. A first-order estimate of the diatom biomass for the global ocean ranges from 444 to 582 Tg C, which converts to 3 to 4 Tmol Si and to an average Si biomass turnover rate of 0.15 to 0.19 d-1. Link to the dataset: doi:10.1594/PANGAEA.777384
    • ÔÇŽ
    corecore