20,660 research outputs found

    Investigation of sputtering effects on the moon's surface Eleventh quarterly status report, 25 Oct. 1965 - 24 Jan. 1966

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    Implications of Lunar 9 moon probe, sputtering yield reduction due to surface roughness, water formation by solar wind bombardment, photometric function of moon, and chemical sputterin

    A comparison of spectral element and finite difference methods using statically refined nonconforming grids for the MHD island coalescence instability problem

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    A recently developed spectral-element adaptive refinement incompressible magnetohydrodynamic (MHD) code [Rosenberg, Fournier, Fischer, Pouquet, J. Comp. Phys. 215, 59-80 (2006)] is applied to simulate the problem of MHD island coalescence instability (MICI) in two dimensions. MICI is a fundamental MHD process that can produce sharp current layers and subsequent reconnection and heating in a high-Lundquist number plasma such as the solar corona [Ng and Bhattacharjee, Phys. Plasmas, 5, 4028 (1998)]. Due to the formation of thin current layers, it is highly desirable to use adaptively or statically refined grids to resolve them, and to maintain accuracy at the same time. The output of the spectral-element static adaptive refinement simulations are compared with simulations using a finite difference method on the same refinement grids, and both methods are compared to pseudo-spectral simulations with uniform grids as baselines. It is shown that with the statically refined grids roughly scaling linearly with effective resolution, spectral element runs can maintain accuracy significantly higher than that of the finite difference runs, in some cases achieving close to full spectral accuracy.Comment: 19 pages, 17 figures, submitted to Astrophys. J. Supp

    Video Conversations - The Future of the Colorado River

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    This video series explores key Colorado River management issues with key managers across the basin. Video discussions in the table on the next page are presented in the order they were recorded. Topics include river ecosystems, California, Upper Basin, Tribal, and Federal perspectives, as well as future hydrology and climate. Each video runs for 60 to 90 minutes. Speakers start by describing how they got to the place they are professionally. There are prepared remarks and questions and answers from participants who attended at the time the video was recorded. Links to suggested readings are provided. Click the VIDEO url to access the video. Several early videos are no longer available but slides are provided. Asynchronous discussion prompts for select videos are noted in the far right column of the table and appear below the table. This series was produced during April and early May 2020 as part of the courses CEE 6490 Integrated River Basins Watershed Planning and Management and WATS 6330/5330 Large River Management at Utah State University co-taught by David Rosenberg and Jack Schmidt. The video series was produced as an alternative to a multi-day field trip to Glen Canyon Dam and Lees Ferry and face-to-face meetings with stakeholders that was canceled because of university travel restrictions imposed on March 11, 2020. Additional videos have been produced after May 2020 and are available at https://qcnr.usu.edu/coloradoriver/learn/

    Beta lives - some statistical perspectives on the capital asset pricing model

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    This note summarizes some technical issues relevant to the use of the idea of excess return in empirical modelling. We cover the case where the aim is to construct a measure of expected return on an asset and a model of the CAPM type is used. We review some of the problems and show examples where the basic CAPM may be used to develop other results which relate the expected returns on assets both to the expected return on the market and other factors

    The effects of nitrogen and carbon sources on the ability of two microbial isolates to produce bioemulsifiers

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    Pseudomonas mallei and Pseudomonas pseudomallei were isolated from produced water samples collected from Escravos Tankfarm, Nigeria. The two bacterial isolates were found to produce very high emulsion turbidities when grown on hydrocarbon culture medium. The bioemulsifier produced by these two isolates were found to be related as they contain both protein and carbohydrate moieties of very close molecular weight and no trace of lipid. The bioemulsifier produced emulsified both aliphatic and aromatic hydrocarbons and also a variety of hydrocarbon mixtures such as olive oil, kerosene, diesel oil and crude oil. A combination of acetate and diesel oil seemed to be the preferred carbon source for bioemulsification while Ammonium sulfate was the preferred nitrogen source. Bioemulsifier production was highest at pH 7.05 while a pH greater than 7.25 inhibited bacterial growth and emulsifying activity

    Pfleiderer2: identification of a new globular cluster in the Galaxy

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    We provide evidence that indicate the star cluster Pfleiderer 2, which is projected in a rich field, as a newly identified Galactic globular cluster. Since it is located in a crowded field, core extraction and decontamination tools were applied to reveal the cluster sequences in B, V and I Color-Magnitude Diagrams (CMDs). The main CMD features of Pfleiderer 2 are a tilted Red Giant Branch, and a red Horizontal Branch, indicating a high metallicity around solar. The reddening is E(B-V)=1.01. The globular cluster is located at a distance from the Sun d⊙_{\odot} = 16±\pm2 kpc. The cluster is located at 2.7 kpc above the Galactic plane and at a distance from the Galactic center of RGC_{\rm GC}=9.7 kpc, which is unusual for a metal-rich globular cluster.Comment: Accepted by The Astronomical Journa

    Adaptive mesh refinement with spectral accuracy for magnetohydrodynamics in two space dimensions

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    We examine the effect of accuracy of high-order spectral element methods, with or without adaptive mesh refinement (AMR), in the context of a classical configuration of magnetic reconnection in two space dimensions, the so-called Orszag-Tang vortex made up of a magnetic X-point centered on a stagnation point of the velocity. A recently developed spectral-element adaptive refinement incompressible magnetohydrodynamic (MHD) code is applied to simulate this problem. The MHD solver is explicit, and uses the Elsasser formulation on high-order elements. It automatically takes advantage of the adaptive grid mechanics that have been described elsewhere in the fluid context [Rosenberg, Fournier, Fischer, Pouquet, J. Comp. Phys. 215, 59-80 (2006)]; the code allows both statically refined and dynamically refined grids. Tests of the algorithm using analytic solutions are described, and comparisons of the Orszag-Tang solutions with pseudo-spectral computations are performed. We demonstrate for moderate Reynolds numbers that the algorithms using both static and refined grids reproduce the pseudo--spectral solutions quite well. We show that low-order truncation--even with a comparable number of global degrees of freedom--fails to correctly model some strong (sup--norm) quantities in this problem, even though it satisfies adequately the weak (integrated) balance diagnostics.Comment: 19 pages, 10 figures, 1 table. Submitted to New Journal of Physic

    Solar Physics - Plasma Physics Workshop

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    A summary of the proceedings of a conference whose purpose was to explore plasma physics problems which arise in the study of solar physics is provided. Sessions were concerned with specific questions including the following: (1) whether the solar plasma is thermal or non-themal; (2) what spectroscopic data is required; (3) what types of magnetic field structures exist; (4) whether magnetohydrodynamic instabilities occur; (5) whether resistive or non-magnetohydrodynamic instabilities occur; (6) what mechanisms of particle acceleration have been proposed; and (7) what information is available concerning shock waves. Very few questions were answered categorically but, for each question, there was discussion concerning the observational evidence, theoretical analyses, and existing or potential laboratory and numerical experiments
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