363,792 research outputs found

    Multifluid, Magnetohydrodynamic Shock Waves with Grain Dynamics II. Dust and the Critical Speed for C Shocks

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    This is the second in a series of papers on the effects of dust on multifluid, MHD shock waves in weakly ionized molecular gas. We investigate the influence of dust on the critical shock speed, v_crit, above which C shocks cease to exist. Chernoff showed that v_crit cannot exceed the grain magnetosound speed, v_gms, if dust grains are dynamically well coupled to the magnetic field. We present numerical simulations of steady shocks where the grains may be well- or poorly coupled to the field. We use a time-dependent, multifluid MHD code that models the plasma as a system of interacting fluids: neutral particles, ions, electrons, and various ``dust fluids'' comprised of grains with different sizes and charges. Our simulations include grain inertia and grain charge fluctuations but to highlight the essential physics we assume adiabatic flow, single-size grains, and neglect the effects of chemistry. We show that the existence of a phase speed v_phi does not necessarily mean that C shocks will form for all shock speeds v_s less than v_phi. When the grains are weakly coupled to the field, steady, adiabatic shocks resemble shocks with no dust: the transition to J type flow occurs at v_crit = 2.76 v_nA, where v_nA is the neutral Alfven speed, and steady shocks with v_s > 2.76 v_nA are J shocks with magnetic precursors in the ion-electron fluid. When the grains are strongly coupled to the field, v_crit = min(2.76 v_nA, v_gms). Shocks with v_crit < v_s < v_gms have magnetic precursors in the ion-electron-dust fluid. Shocks with v_s > v_gms have no magnetic precursor in any fluid. We present time-dependent calculations to study the formation of steady multifluid shocks. The dynamics differ qualitatively depending on whether or not the grains and field are well coupled.Comment: 43 pages with 17 figures, aastex, accepted by The Astrophysical Journa

    Benefits to be derived from meteorological satellite technology

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    The benefits derived from satellite technology in educational communication and meteorology are cited

    Protein Import Into Chloroplasts: An Ever-Evolving Story

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    Chloroplasts are but one type of a diverse group of essential organelles that distinguish plant cells and house many critical biochemical pathways, including photosynthesis. The biogenesis of plastids is essential to plant growth and development and relies on the targeting and import of thousands of nuclear-encoded proteins from the cytoplasm. The import of the vast majority of these proteins is dependent on translocons located in the outer and inner envelope membranes of the chloroplast, termed the Toc and Tic complexes, respectively. The core components of the Toc and Tic complexes have been identified within the last 12 years; however, the precise functions of many components are still being elucidated, and new components are still being identified. In Arabidopsis thaliana (and other species), many of the components are encoded by more than one gene, and it apperas that the isoforms differentially associate with structurally distinct import complexes. Furthermore, it appears that these complexes represent functionally distinct targeting pathways, and the regulation of import by these separate pathways may play a role in the differentiation and specific functions of distinct plastid types during plant growth and development. This review summarizes these recent discoveries and emphasizes the mechanisms of differential Toc complex assembly and substrate recognition

    MS-050: Robert B. Arms Collection

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    The Robert B. Arms collection consists largely of papers regarding quarterly returns, receipts, and letters from the ordnance office; along with muster rolls, descriptive lists and state of Vermont orders. There is a section on the 16th Regimental Reunions, as well as documents pertaining to Arms’ role as Deputy Collector. There is extensive paperwork regarding George Stannard’s account, including at testimony made by Arms on the matter of Stannard’s bankruptcy. The researcher will find a hefty amount of correspondence between Arms and William A. Scott concerning the sale of property in North Dakota. Although this is a Civil War collection, it is not a rich Civil War resource. There are a few orders to Arms from his commander Colonel Veazey, as well as detailed letter from Arms to his parents describing the raid on headquarters that resulted in the capture of General Stoughton. The most intriguing item is a letter from Arms to his son written in October 1889 describing his trip to Gettysburg, and the possibility of a misunderstanding of what his Company actually did in the battle. The majority of the collection, however, is the basic paperwork of an officer. The post-war documents demonstrate how Arms served his state after the war, specifically his men in aiding with their pension claims. Special Collections and College Archives Finding Aids are discovery tools used to describe and provide access to our holdings. Finding aids include historical and biographical information about each collection in addition to inventories of their content. More information about our collections can be found on our website http://www.gettysburg.edu/special_collections/collections/.https://cupola.gettysburg.edu/findingaidsall/1045/thumbnail.jp