42,182 research outputs found

    Defining the original extent and floristic composition of the naturally-treeless grasslands of the Liverpool Plains, North Western Slopes, New South Wales

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    A study was conducted on the Liverpool Plains (30o 43’–31o 44’S; 149o 40’–150o 41’E), North Western Slopes of NSW, to determine the original boundaries of the naturally-treeless grasslands, to determine reasons for the lack of woody vegetation on these areas, and to assess the status of Austrostipa aristiglumis (Plains Grass), a species that is today commonly dominant on the few remaining remnant grassland areas and is commonly assumed to characterise the original grassland community. The original tree line boundaries were reconstructed using NSW Lands Department survey portion plans and other historical records. The lack of woody vegetation was attributed primarily to a combination of fine-textured soil, climate and topography restricting the availability of water below the grass root zone, with waterlogging and deep soil cracking possibly playing minor roles. Published and anecdotal evidence and landholder experience indicate that the Austrostipa aristiglumis dominated remnants are probably a relatively recent anthropogenic feature, a consequence of post-settlement management practices. The pre-settlement grasslands appear to have been composed of a wide range of grasses, possibly dominated by species such as Themeda avenacea (Native Oatgrass) and Eulalia aurea (Silky Browntop), with a range of forbs occupying the interstitial spaces. Management implications are discussed

    Social ties and the job search of recent immigrants

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    This article highlights a specific mechanism through which social networks help in job search. The authors characterize the strength of a network by its likelihood of providing a job offer. Using a theoretical model, they show that the difference between wages in jobs found using networks versus those found using formal channels decreases as the network becomes stronger. The authors verify this result for recent immigrants to Canada for whom a strong network is captured by the presence of a “close tie.” Furthermore, structural estimates confirm that the presence of a close tie operates by increasing the likelihood of generating a job offer from the network rather than by altering the network wage distribution.Accepted manuscrip

    GTOSS: Generalized Tethered Object Simulation System

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    GTOSS represents a tether analysis complex which is described by addressing its family of modules. TOSS is a portable software subsystem specifically designed to be introduced into the environment of any existing vehicle dynamics simulation to add the capability of simulating multiple interacting objects (via multiple tethers). These objects may interact with each other as well as with the vehicle into whose environment TOSS is introduced. GTOSS is a stand alone tethered system analysis program, representing an example of TOSS having been married to a host simulation. RTOSS is the Results Data Base (RDB) subsystem designed to archive TOSS simulation results for future display processing. DTOSS is a display post processors designed to utilize the RDB. DTOSS extracts data from the RDB for multi-page printed time history displays. CTOSS is similar to DTOSS, but is designed to create ASCII plot files. The same time history data formats provided for DTOSS (for printing) are available via CTOSS for plotting. How these and other modules interact with each other is discussed

    A Laplace Transform Method for Molecular Mass Distribution Calculation from Rheometric Data

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    Polydisperse linear polymer melts can be microscopically described by the tube model and fractal reptation dynamics, while on the macroscopic side the generalized Maxwell model is capable of correctly displaying most of the rheological behavior. In this paper, a Laplace transform method is derived and different macroscopic starting points for molecular mass distribution calculation are compared to a classical light scattering evaluation. The underlying assumptions comprise the modern understanding on polymer dynamics in entangled systems but can be stated in a mathematically generalized way. The resulting method is very easy to use due to its mathematical structure and it is capable of calculating multimodal molecular mass distributions of linear polymer melts

    Telescopes don't make catalogues!

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    Astronomical instruments make intensity measurements; any precise astronomical experiment ought to involve modeling those measurements. People make catalogues, but because a catalogue requires hard decisions about calibration and detection, no catalogue can contain all of the information in the raw pixels relevant to most scientific investigations. Here we advocate making catalogue-like data outputs that permit investigators to test hypotheses with almost the power of the original image pixels. The key is to provide users with approximations to likelihood tests against the raw image pixels. We advocate three options, in order of increasing difficulty: The first is to define catalogue entries and associated uncertainties such that the catalogue contains the parameters of an approximate description of the image-level likelihood function. The second is to produce a K-catalogue sampling in "catalogue space" that samples a posterior probability distribution of catalogues given the data. The third is to expose a web service or equivalent that can re-compute on demand the full image-level likelihood for any user-supplied catalogue.Comment: presented at ELSA 2010: Gaia, at the frontiers of astrometr
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