23,863 research outputs found

    Home-based self-employment: combining personal, household and employment influences

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    Despite the significant economic, innovative and social contributions of home-based self-employment, it is an under-researched and under-theorised area. We address this gap by drawing from established entrepreneurial theory to propose and validate a more complete theoretical model that combines personal, household and employment influences. We validate our proposed model by drawing on quantitative data from a large-scale, longitudinal, UK-based, social studies dataset. Our validated model demonstrates how and why antecedent and current household and employment factors, but not personal factors, associated with being home-based interact and provide constitutive affordances that result in a setting for self-employment that is unique in more fundamental ways than simply the home location of the business. Despite being responsible for some of the world’s most innovative and successful businesses, home-based businesses are often denigrated as lacking ambition or growth potential. The results of our analysis vindicate the choices of the home-based self-employed, by demonstrating that basing a business in the home is a rational choice based on an intersection of household and employment characteristics. The data used in this study predates the COVID-19 pandemic. However, it is expected that home-based self-employment will grow significantly following the pandemic in response to increasing acceptance of home-working. It therefore behoves entrepreneurship scholars to have a robust understanding of this previously overlooked type of self-employment if we are to be able to provide guidance to policymakers and self-employment support services

    The Final Remnant of Binary Black Hole Mergers: Multipolar Analysis

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    Methods are presented to define and compute source multipoles of dynamical horizons in numerical relativity codes, extending previous work from the isolated and dynamical horizon formalisms in a manner that allows for the consideration of horizons that are not axisymmetric. These methods are then applied to a binary black hole merger simulation, providing evidence that the final remnant is a Kerr black hole, both through the (spatially) gauge-invariant recovery of the geometry of the apparent horizon, and through a detailed extraction of quasinormal ringing modes directly from the strong-field region.Comment: 12 pages, 13 figures. Published version. Some references have been added and reordered, and the figures cleaned up

    Ion-tracer anemometer

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    Gas velocity measuring instrument measures transport time of ion-trace traveling fixed distance between ionization probe and detector probe. Electric field superimposes drift velocity onto flow velocity so travel times can be reduced to minimize ion diffusion effects

    Inside-Out Planet Formation. V. Structure of the Inner Disk as Implied by the MRI

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    The large population of Earth to super-Earth sized planets found very close to their host stars has motivated consideration of inin situsitu formation models. In particular, Inside-Out Planet Formation is a scenario in which planets coalesce sequentially in the disk, at the local gas pressure maximum near the inner boundary of the dead zone. The pressure maximum arises from a decline in viscosity, going from the active innermost disk (where thermal ionization of alkalis yields high viscosities via the magneto-rotational instability (MRI)) to the adjacent dead zone (where the MRI is quenched). Previous studies of the pressure maximum, based on α\alpha-disk models, have assumed ad hoc values for the viscosity parameter α\alpha in the active zone, ignoring the detailed physics of the MRI. Here we explicitly couple the MRI criteria to the α\alpha-disk equations, to find steady-state (constant accretion rate) solutions for the disk structure. We consider the effects of both Ohmic and ambipolar resistivities, and find solutions for a range of disk accretion rates (M˙\dot{M} = 101010^{-10} - 10810^{-8} M{\rm M}_{\odot}/yr), stellar masses (MM_{\ast} = 0.1 - 1 M{\rm M}_{\odot}), and fiducial values of the nonnon-MRI α\alpha-viscosity in the dead zone (αDZ=105\alpha_{\rm {DZ}} = 10^{-5} - 10310^{-3}). We find that: (1) A midplane pressure maximum forms radially outsideoutside the inner boundary of the dead zone; (2) Hall resistivity dominates near the midplane in the inner disk, which may explain why close-in planets do notnot form in \sim50% of systems; (3) X-ray ionization can be competitive with thermal ionization in the inner disk, because of the low surface density there in steady-state; and (4) our inner disk solutions are viscously unstable to surface density perturbations.Comment: 34 pages, 28 figures, 3 appendices. Accepted by the Astrophysical Journa

    The absolute photometry of the zodiacal light

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    Absolute photometry of zodiacal ligh

    Technical note: a new method for the Lagrangian tracking of pollution plumes from source to receptor using gridded model output

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    Lagrangian particle dispersion models (LPDMs) are powerful and popular tools used for the analysis of atmospheric trace gas measurements. However, it can be difficult to determine the transport pathway of emissions from their source to a receptor using the standard gridded model output, particularly during complex meteorological scenarios. In this paper we present a method to clearly and easily identify the pathway taken by only those emissions that arrive at a receptor at a particular time, by combining the standard gridded output from forward (e.g., concentration) and backward (e.g., residence time) LPDM simulations. By comparing the pathway determined from this method with particle trajectories from both the forward and backward models, we show that this method successfully restores much of the Lagrangian information that is lost when the data are gridded. A sample analysis is presented, demonstrating that the sourceto-receptor pathway determined from this method is more accurate and easier to use than existing methods using standard LPDM products (gridded fields of, e.g., concentrations and residence time). As demonstrated in an evaluation and an example application, the method requires agreement between the transport described by the forward and backward simulations and thus provides a means to assess the quality and reversibility of the simulation. Finally, we discuss the potential for combining the backward LPDM simulation with gridded data from other sources (e.g., chemical transport models) to obtain a Lagrangian sampling of the air that will eventually arrive at a receptor. Based on the advantages presented here, this new method can complement or even replace many of the standard uses of backward LPDM simulations

    Matched filters for coalescing binaries detection on massively parallel computers

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    We discuss some computational problems associated to matched filtering of experimental signals from gravitational wave interferometric detectors in a parallel-processing environment. We then specialize our discussion to the use of the APEmille and apeNEXT processors for this task. Finally, we accurately estimate the performance of an APEmille system on a computational load appropriate for the LIGO and VIRGO experiments, and extrapolate our results to apeNEXT.Comment: 19 pages, 6 figure

    The Motion of a Body in Newtonian Theories

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    A theorem due to Bob Geroch and Pong Soo Jang ["Motion of a Body in General Relativity." Journal of Mathematical Physics 16(1), (1975)] provides the sense in which the geodesic principle has the status of a theorem in General Relativity (GR). Here we show that a similar theorem holds in the context of geometrized Newtonian gravitation (often called Newton-Cartan theory). It follows that in Newtonian gravitation, as in GR, inertial motion can be derived from other central principles of the theory.Comment: 12 pages, 1 figure. This is the version that appeared in JMP; it is only slightly changed from the previous version, to reflect small issue caught in proo

    Mathematical analysis of a model for the growth of the bovine corpus luteum

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    The corpus luteum (CL) is an ovarian tissue that grows in the wound space created by follicular rupture. It produces the progesterone needed in the uterus to maintain pregnancy. Rapid growth of the CL and progesterone transport to the uterus require angiogenesis, the creation of new blood vessels from pre-existing ones, a process which is regulated by proteins that include fibroblast growth factor 2 (FGF2).\ud \ud In this paper we develop a system of time-dependent ordinary differential equations to model CL growth. The dependent variables represent FGF2, endothelial cells (ECs), luteal cells, and stromal cells (like pericytes), by assuming that the CL volume is a continuum of the three cell types. We assume that if the CL volume exceeds that of the ovulated follicle, then growth is inhibited. This threshold volume partitions the system dynamics into two regimes, so that the model may be classified as a Filippov (piecewise smooth) system.\ud \ud We show that normal CL growth requires an appropriate balance between the growth rates of luteal and stromal cells. We investigate how angiogenesis influences CL growth by considering how the system dynamics depend on the dimensionless EC proliferation rate, p5. We find that weak (low p5) or strong (high p5) angiogenesis leads to ‘pathological’ CL growth, since the loss of CL constituents compromises progesterone production or delivery. However, for intermediate values of p5, normal CL growth is predicted. The implications of these results for cow fertility are also discussed. For example, inadequate angiogenesis has been linked to infertility in dairy cows
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