2,675 research outputs found

    Research into the feasibility of thin metal and oxide film capacitors

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    Feasibility of thin metal and oxide film capacitor

    Two-fluid and magnetohydrodynamic modelling of magnetic reconnection in the MAST spherical tokamak and the solar corona

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    Twisted magnetic flux ropes are ubiquitous in space and laboratory plasmas, and the merging of such flux ropes through magnetic reconnection is an important mechanism for restructuring magnetic fields and releasing free magnetic energy. The merging-compression scenario is one possible start up scheme for spherical tokamaks, which has been used on the Mega Amp Spherical Tokamak MAST. Two current-carrying plasma rings, or flux ropes, approach each other through the mutual attraction of their like currents, and merge, through magnetic reconnection, into a single plasma torus, with substantial plasma heating. 2D resistive MHD and Hall MHD simulations of this process are reported, and new results for the temperature distribution of ions and electrons are presented. A model of the based on relaxation theory is also described, which is now extended to tight aspect ratio geometry. This model allows prediction of the final merged state and the heating. The implications of the relaxation model for heating of the solar corona are also discussed, and a model of the merger of two or more twisted coronal flux ropes is presented, allowing for different senses of twist

    Effects of creep feeding and its interactions with other factors on the performance of meat goat kids and dams when managed on pasture

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    Creep feeding and its possible interactions with other influential factors (genetics, litter type, and sex) for weaning traits were studied in meat goat kids and their dams. Kids across 3 yr were creep fed (254 kids; 5 pens) or not creep fed (255 kids; 5 pens) from 30 to 90 d of age. Creep-fed kids had higher (P ≤ 0.05) preweaning average daily weight gain and weaning weights (113.1 ± 13.0 g/d; 15.0 ± 0.8 kg) than kids not creep fed (99.8 ± 13.1 g/d; 14.0 ± 0.8 kg). However, financial returns were not higher (P \u3e 0.05) for creep-fed kids compared with kids not creep fed. There was no difference (P \u3e 0.05) in kid conformation score or survival rates between the treatment groups. The only important interaction among kid traits was treatment × litter type (P \u3c 0.05) for FAMACHA scores. Within noncreep pens, single kids had lower (better; P \u3c 0.05) FAMACHA scores (2.9 ± 0.3) than twin kids (3.9 ± 0.3). There was no litter-type effect on FAMACHA scores for kids within the creep feed pens. Dams of the creep-fed (n = 175) and noncreep (n = 178) kids were also evaluated. Treatment did not affect (P \u3e 0.05) litter weights, dam weight change, gross revenue for weaned litters, or fecal egg counts. Treatment interacted with litter type (P \u3c 0.05) to effect packed cell volume (PCV). In the noncreep group, dams raising singles had higher (better; P \u3c 0.05) PCV (18.7 ± 1.3%) than dams rearing twin kids (15.7 ± 1.3%). The litter-type effect on dam PCV was not evident (P \u3e 0.05) in the creep-fed group. Creep feeding improved some kid growth traits but did not improve dam traits or financial returns. Interactions of creep treatment with other factors were minimal for doe-kid traits

    The atomic structure of large-angle grain boundaries Σ5\Sigma 5 and Σ13\Sigma 13 in YBa2Cu3O7−δ{\rm YBa_2Cu_3O_{7-\delta}} and their transport properties

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    We present the results of a computer simulation of the atomic structures of large-angle symmetrical tilt grain boundaries (GBs) Σ5\Sigma 5 (misorientation angles \q{36.87}{^{\circ}} and \q{53.13}{^{\circ}}), Σ13\Sigma 13 (misorientation angles \q{22.62}{^{\circ}} and \q{67.38}{^{\circ}}). The critical strain level ϵcrit\epsilon_{crit} criterion (phenomenological criterion) of Chisholm and Pennycook is applied to the computer simulation data to estimate the thickness of the nonsuperconducting layer hn{\rm h_n} enveloping the grain boundaries. The hn{\rm h_n} is estimated also by a bond-valence-sum analysis. We propose that the phenomenological criterion is caused by the change of the bond lengths and valence of atoms in the GB structure on the atomic level. The macro- and micro- approaches become consistent if the ϵcrit\epsilon_{crit} is greater than in earlier papers. It is predicted that the symmetrical tilt GB Σ5\Sigma5 \theta = \q{53.13}{^{\circ}} should demonstrate a largest critical current across the boundary.Comment: 10 pages, 2 figure

    Induction of Germinal Centers by MMTV Encoded Superantigen on B Cells

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    It has not been established whether an endogenous superantigen (SAg) expressed on B cells can induce germinal centers (GCs). An interesting model is that of mammary tumor virus encoded viral SAgs, which induce vigorous T cell proliferation and are predominantly expressed on activated B cells. We have used this model to analyze the possibility that direct stimulation of Mtv7+ DBA/2 B cells by vSAg-responsive (Vβ6+) BALB/c T cells can give rise to GCs. Injection of BALB/c SCID mice iv with 2 × 106 DBA/2 B cells, together with LPS, followed by 2 × 106 BALB/c T cells induces numerous large splenic GCs within 3–5 days. The GCs are still large on day 7, but are very much reduced by day 10. B cell activation with LPS is needed for this effect. These GCs form in spite of the apparent absence of follicular dendritic cells (FDCs) as judged by staining for several FDC surface markers. Control mice receiving either BALB/c T or DBA/2 B cells + LPS alone or DBA/2 T + B cells + LPS fail to exhibit any GCs on days 3–7. Numerous small clusters of PNA+ cells, but few large GCs are observed when TNF-R(p55)-Ig is also injected, whereas LTβR-Ig treatment impeded the formation of aggregations of these cells even further, leaving scattered PNA+ single cells and very small clumps throughout the white pulp of the spleens. Anti-TNFα had no effect. These results suggest that endogenous vSAg mediated GC formation is independent of antigen trapping by FDCs

    One-Step Processing of Spinel Ferrites via the High-Energy Ball Milling of Binary Oxides

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    MnZn ferrites have been produced via the high-energy ball milling of binary oxide precursors. The milled ferrites have a nonequilibrium cation site distribution, with an unusually high population of Zn cations on the octahedral sites. The particle size distribution drops precipitously with milling time from 60±1 to ∼14±1 nm at 10 h, but increases to 18.5±1 nm after long durations (20–40 h) concurrent with the formation of nearly pure ferrite. A 1 h anneal at 673 K facilitates a redistribution of cations to their near equilibrium sites. This processing approach circumvents the need for deleterious high-temperature heat treatments that often lead to nonstoichiometries in the resulting ferrites

    Simulations of core convection in rotating A-type stars: Differential rotation and overshooting

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    We present the results of 3--D simulations of core convection within A-type stars of 2 solar masses, at a range of rotation rates. We consider the inner 30% by radius of such stars, thereby encompassing the convective core and some of the surrounding radiative envelope. We utilize our anelastic spherical harmonic (ASH) code, which solves the compressible Navier-Stokes equations in the anelastic approximation, to examine highly nonlinear flows that can span multiple scale heights. The cores of these stars are found to rotate differentially, with central cylindrical regions of strikingly slow rotation achieved in our simulations of stars whose convective Rossby number (R_{oc}) is less than unity. Such differential rotation results from the redistribution of angular momentum by the nonlinear convection that strongly senses the overall rotation of the star. Penetrative convective motions extend into the overlying radiative zone, yielding a prolate shape (aligned with the rotation axis) to the central region in which nearly adiabatic stratification is achieved. This is further surrounded by a region of overshooting motions, the extent of which is greater at the equator than at the poles, yielding an overall spherical shape to the domain experiencing at least some convective mixing. We assess the overshooting achieved as the stability of the radiative exterior is varied, and the weak circulations that result in that exterior. The convective plumes serve to excite gravity waves in the radiative envelope, ranging from localized ripples of many scales to some remarkable global resonances.Comment: 48 pages, 16 figures, some color. Accepted to Astrophys. J. Color figures compressed with appreciable loss of quality; a PDF of the paper with better figures is available at http://lcd-www.colorado.edu/~brownim/core_convectsep24.pd
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