9,778 research outputs found

    Optical signatures of molecular particles via mass-selected cluster spectroscopy

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    A new molecular beam apparatus was developed to study optical absorption in cold (less than 100 K) atomic clusters and complexes produced by their condensation with simple molecular gases. In this instrument, ionized clusters produced in a laser vaporization nozzle source are mass selected and studied with photodissociation spectroscopy at visible and ultraviolet wavelengths. This new approach can be applied to synthesize and characterize numerous particulates and weakly bound complexes expected in planetary atmospheres and in comets

    Improved Pseudofermion Approach for All-Point Propagators

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    Quark propagators with arbitrary sources and sinks can be obtained more efficiently using a pseudofermion method with a mode-shifted action. Mode-shifting solves the problem of critical slowing down (for light quarks) induced by low eigenmodes of the Dirac operator. The method allows the full physical content of every gauge configuration to be extracted, and should be especially helpful for unquenched QCD calculations. The method can be applied for all the conventional quark actions: Wilson, Sheikoleslami-Wohlert, Kogut-Susskind, as well as Ginsparg-Wilson compliant overlap actions. The statistical properties of the method are examined and examples of physical processes under study are presented.Comment: LateX, 26 pages, 10 eps figure

    RGtk2: A Graphical User Interface Toolkit for R

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    Graphical user interfaces (GUIs) are growing in popularity as a complement or alternative to the traditional command line interfaces to R. RGtk2 is an R package for creating GUIs in R. The package provides programmatic access to GTK+ 2.0, an open-source GUI toolkit written in C. To construct a GUI, the R programmer calls RGtk2 functions that map to functions in the underlying GTK+ library. This paper introduces the basic concepts underlying GTK+ and explains how to use RGtk2 to construct GUIs from R. The tutorial is based on simple and pratical programming examples. We also provide more complex examples illustrating the advanced features of the package. The design of the RGtk2 API and the low-level interface from R to GTK+ are discussed at length. We compare RGtk2 to alternative GUI toolkits for R.

    Forage seed quality in Ethiopia: Issues and opportunities

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    Parallel Lives: Birth, Childhood and Adolescent Influences on Career Paths

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    This paper uses sequence methods and cluster analysis to create a typology of career paths for a cohort of British 29 year olds born in 1970. There are clear ‘types’ identified by these techniques including several paths dominated by various forms of non-employment. These types are strongly correlated with individual characteristics and parental background factors observed at birth, age ten and age sixteen. By estimating a multinomial logit model of career types we show how policy makers might identify early those young people likely to experience long term non-employment as adults, enabling better targeted preventative policy intervention.careers, cluster analysis, optimal matching

    A wall-function approach to incorporating Knudsen-layer effects in gas micro flow simulations

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    For gas flows in microfluidic configurations, the Knudsen layer close to the wall can comprise a substantial part of the entire flow field and has a major effect on quantities such as the mass flow rate through micro devices. The Knudsen layer itself is characterized by a highly nonlinear relationship between the viscous stress and the strain rate of the gas, so even if the Navier-Stokes equations can be used to describe the core gas flow they are certainly inappropriate for the Knudsen layer itself. In this paper we propose a "wall-function" model for the stress/strain rate relations in the Knudsen layer. The constitutive structure of the Knudsen layer has been derived from results from kinetic theory for isothermal shear flow over a planar surface. We investigate the ability of this simplified model to predict Knudsen-layer effects in a variety of configurations. We further propose a semi-empirical Knudsen-number correction to this wall function, based on high-accuracy DSMC results, to extend the predictive capabilities of the model to greater degrees of rarefaction
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