388 research outputs found

    Geotail and LFM comparisons of plasma sheet climatology: 2. Flow variability

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    [1] We characterize the variability of central plasma sheet bulk flows with a 6-year Geotail data set and a 2-month Lyon-Fedder-Mobarry (LFM) global MHD simulation at two spatial resolutions. Comparing long databases of observed and simulated parameters enable rigorous statistical tests of the model\u27s ability to predict plasma sheet properties during routine driving conditions and represent a new method of global MHD validation. In this study, we use probability density functions (PDFs) to compare the statistics of plasma sheet velocities in the Geotail observations with those in the LFM simulations. We find that the low-resolution model grossly underestimates the occurrence of fast earthward and tailward flows. Increasing the simulation resolution inherently changes plasma sheet mass transport in the model, allowing the development of fast, bursty flows. These flows fill out the wings of the velocity distribution and bring the PDF into closer agreement with observations

    Geotail and LFM comparisons of plasma sheet climatology: 1. Average values

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    [1] We compare the statistics of central plasma sheet properties from 6 years of Geotail observations with 2 months of Lyon-Fedder-Mobarry (LFM) global MHD simulations. This statistical validation effort represents an inherently new method of systematically characterizing and quantifying global MHD model performance. For our comparison, we identify the central plasma sheet in the observations and simulation by identical criteria and select the simulation interval to ensure statistically similar distributions of solar wind conditions in both studies. After verifying our plasma sheet selection by inspecting the magnetic signatures of both studies, we compare the resultant number densities, thermal pressures, thermal energies, and bulk flows as functions of position across the equatorial plane. We find that the LFM model successfully reproduces the gross features of the global plasma sheet in a statistical sense. However, our comparison also reveals certain systematic discrepancies between the model and the observations. The LFM predicts a plasma sheet which is too dense, too cool, and exhibits faster globally averaged bulk flows than the observed plasma sheet. By quantifying the LFM overestimate of ionospheric transpolar potential and showing that ΊPC correlates with plasma sheet flow speed, we demonstrate that 15% of the plasma sheet velocity discrepancy is reflected in a ΊPC overestimate. This statistical validation effort represents an essential first step toward the rigorous, quantitative evaluation of a global MHD model in the plasma sheet

    AE9, AP9 and SPM: New Models for Specifying the Trapped Energetic Particle and Space Plasma Environment

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    The radiation belts and plasma in the Earth’s magnetosphere pose hazards to satellite systems which restrict design and orbit options with a resultant impact on mission performance and cost. For decades the standard space environment specification used for spacecraft design has been provided by the NASA AE8 and AP8 trapped radiation belt models. There are well-known limitations on their performance, however, and the need for a new trapped radiation and plasma model has been recognized by the engineering community for some time. To address this challenge a new set of models, denoted AE9/AP9/SPM, for energetic electrons, energetic protons and space plasma has been developed. The new models offer significant improvements including more detailed spatial resolution and the quantification of uncertainty due to both space weather and instrument errors. Fundamental to the model design, construction and operation are a number of new data sets and a novel statistical approach which captures first order temporal and spatial correlations allowing for the Monte-Carlo estimation of flux thresholds for user-specified percentile levels (e.g., 50th and 95th) over the course of the mission. An overview of the model architecture, data reduction methods, statistics algorithms, user application and initial validation is presented in this paper.United States. Air Force (e contracts FA8718-05-C-0036, FA8718-10-C-001, FA8721-05-C-0002 and FA8802-09-C-0001)United States. National Aeronautics and Space Administration (grant NNG05GM22G

    Comparing nuclear power trajectories in Germany and the UK: from ‘regimes' to ‘democracies’ in sociotechnical transitions and Discontinuities

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    This paper focuses on arguably the single most striking contrast in contemporary major energy politics in Europe (and even the developed world as a whole): the starkly differing civil nuclear policies of Germany and the UK. Germany is seeking entirely to phase out nuclear power by 2022. Yet the UK advocates a ‘nuclear renaissance’, promoting the most ambitious new nuclear construction programme in Western Europe.Here,this paper poses a simple yet quite fundamental question: what are the particular divergent conditions most strongly implicated in the contrasting developments in these two countries. With nuclear playing such an iconic role in historical discussions over technological continuity and transformation, answering this may assist in wider understandings of sociotechnical incumbency and discontinuity in the burgeoning field of‘sustainability transitions’. To this end, an ‘abductive’ approach is taken: deploying nine potentially relevant criteria for understanding the different directions pursued in Germany and the UK. Together constituted by 30 parameters spanning literatures related to socio-technical regimes in general as well as nuclear technology in particular, the criteria are divided into those that are ‘internal’ and ‘external’ to the ‘focal regime configuration’ of nuclear power and associated ‘challenger technologies’ like renewables. It is ‘internal’ criteria that are emphasised in conventional sociotechnical regime theory, with ‘external’ criteria relatively less well explored. Asking under each criterion whether attempted discontinuation of nuclear power would be more likely in Germany or the UK, a clear picture emerges. ‘Internal’ criteria suggest attempted nuclear discontinuation should be more likely in the UK than in Germany– the reverse of what is occurring. ‘External’ criteria are more aligned with observed dynamics –especially those relating to military nuclear commitments and broader ‘qualities of democracy’. Despite many differences of framing concerning exactly what constitutes ‘democracy’, a rich political science literature on this point is unanimous in characterising Germany more positively than the UK. Although based only on a single case,a potentially important question is nonetheless raised as to whether sociotechnical regime theory might usefully give greater attention to the general importance of various aspects of democracy in constituting conditions for significant technological discontinuities and transformations. If so, the policy implications are significant. A number of important areas are identified for future research, including the roles of diverse understandings and specific aspects of democracy and the particular relevance of military nuclear commitments– whose under-discussion in civil nuclear policy literatures raises its own questions of democratic accountability

    Mid-Infrared Imaging of Candidate Vega-Like Systems

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    We have conducted deep mid-infrared imaging of a relatively nearby sample of candidate Vega-like stars using the OSCIR instrument on the CTIO 4-meter and Keck II 10-meter telescopes. Our discovery of a spatially-resolved disk around HR 4796A has already been reported (Jayawardhana et al. 1998). Here we present imaging observations of the other members of the sample, including the discovery that only the primary in the HD 35187 binary system appears to harbor a substantial circumstellar disk and the possible detection of extended disk emission around 49 Ceti. We derive global properties of the dust disks, place constraints on their sizes, and discuss several interesting cases in detail. Although our targets are believed to be main sequence stars, we note that several have large infrared excesses compared to prototype Vega-like systems, and may therefore be somewhat younger. The disk size constraints we derive, in many cases, imply emission from relatively large (≳\gtrsim 10ÎŒ\mum) particles at mid-infrared wavelengths.Comment: 15 pages and 2 PostScript figures, accepted for publication in The Astronomical Journa

    The governance of justice and internal security in Scotland: Between the Scottish independence referendum and British decisions on the EU

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    This article examines how the governance of justice and internal security in Scotland could be affected by the outcome of the Scottish independence referendum in September 2014. The article argues that it is currently impossible to equate a specific result in the referendum with a given outcome for the governance of justice and internal security in Scotland. This is because of the complexities of the current arrangements in that policy area and the existence of several changes that presently affect them and are outside the control of the government and of the people of Scotland. This article also identifies an important paradox. In the policy domain of justice and internal security, a ‘no’ vote could, in a specific set of circumstances, actually lead to more changes than a victory of the ‘yes’ camp

    Reconsidering the Tribal-State Compact Process

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    This essay evaluates the tribal‐state compact process, as one of several alternative, nonadversarial processes, warranting attention. It argues that, because of its binding character and relatively low cost (in contrast to litigation), and because it is based in the idea of tribes and states exhibiting mutual respect, the compact process is an advanced version of negotiation and bargaining that tribes and states should consider where appropriate

    Genome sequences of four cluster P mycobacteriophages

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    Four bacteriophages infecting Mycobacterium smegmatis mc2155 (three belonging to subcluster P1 and one belonging to subcluster P2) were isolated from soil and sequenced. All four phages are similar in the left arm of their genomes, but the P2 phage differs in the right arm. All four genomes contain features of temperate phages
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