209,322 research outputs found

    Operators between subspaces and quotients of L1

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    We provide an unified approach of results of L. Dor on the complementation of the range, and of D. Alspach on the nearness from isometries, of small into isomorphisms of L1. We introduce the notion of small subspace of L1 and show lifting theorems for operators between quotients of L1 by small subspaces. We construct a subspace of L1 which shows that extension of isometries from subspaces of L1 to the whole space are no longer true for isomorphisms, and that nearly isometric isomorphisms from subspaces of L1 into L1 need not be near from any isometry.Comment: 35 page

    Fluorine Abundances of Galactic Low-Metallicity Giants

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    With abundances and 2{\sigma} upper limits of fluorine (F) in seven metal-poor field giants, nucleosynthesis of stellar F at low metallicity is discussed. The measurements are derived from the HF(1-0) R9 line at 23358{\AA} using nearinfrared K-band high-resolution spectra obtained with CRIRES at the Very Large Telescope. The sample reaches lower metallicities than previous studies on F of field giants, ranging from [Fe/H] = -1.56 down to -2.13. Effects of three-dimensional model atmospheres on the derived F and O abundances are quantitatively estimated and shown to be insignificant for the program stars. The observed F yield in the form of [F/O] is compared with two sets of Galactic chemical evolution models, which quantitatively demonstrate the contribution of Type II supernova (SN II) {\nu}-process and asymptotic giant branch/Wolf-Rayet stars. It is found that at this low-metallicity region, models cannot well predict the observed distribution of [F/O], while the observations are better fit by models considering an SN II {\nu}-process with a neutrino energy of E_{\nu} = 3 x 10^53 erg. Our sample contains HD 110281, a retrograde orbiting low-{\alpha} halo star, showing a similar F evolution as globular clusters. This supports the theory that such halo stars are possibly accreted from dwarf galaxy progenitors of globular clusters in the halo.Comment: 8 pages, 8 figures, 2 tables, published in The Astrophysical Journa

    Functional repair of the corticospinal tract by delayed transplantation of olfactory ensheathing cells in adult rats

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    Adult rats were trained to use their forepaws to retrieve a piece of food. Destruction of the dorsal corticospinal tract on one side at the level of the first cervical segment abolished the use of the ipsilateral forepaw for retrieval for at least 6 months after operation. Where a variable amount of the corticospinal tract was spared, there was a proportionate persistence of retrieval. In lesioned rats that had shown no retrieval for 8 weeks after operation, a suspension of olfactory ensheathing cells was injected into the lesion site. Starting between 1 and 3 weeks after transplantation, all rats with transplants bridging the lesion site resumed retrieval by the ipsilateral forepaw. Biotin dextran anterograde tracing shows regenerating corticospinal axons crossing the bridge, traveling caudally for ~10 mm in the distal part of the corticospinal tract and forming terminal arborizations in the spinal gray matter. Functional recovery can occur when only ~1% of the corticospinal tract axons are present

    Engineering a Conformant Probabilistic Planner

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    We present a partial-order, conformant, probabilistic planner, Probapop which competed in the blind track of the Probabilistic Planning Competition in IPC-4. We explain how we adapt distance based heuristics for use with probabilistic domains. Probapop also incorporates heuristics based on probability of success. We explain the successes and difficulties encountered during the design and implementation of Probapop

    The zero-energy state in graphene in a high magnetic field

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    The fate of the charge-neutral Dirac point in graphene in a high magnetic field HH has been investigated at low temperatures (T∼T\sim 0.3 K). In samples with small V0V_0 (the gate voltage needed to access the Dirac point), the resistance R0R_0 at the Dirac point diverges steeply with HH, signalling a crossover to an insulating state in intense field. The approach to the insulating state is highly unusual. Despite the steep divergence in R0R_0, the profile of R0R_0 vs. TT in fixed HH saturates to a TT-independent value below 2 K, consistent with charge carrying gapless excitations.Comment: 4 pages, 4 figures. Four new sub-figures have been added. Text expanded to discuss data from more sample

    Unusual Nernst effect suggestive of time-reversal violation in the striped cuprate La2−x_{2-x}Bax_xCuO4_4

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    The striped cuprate La2−x_{2-x}Bax_xCuO4_4 (x=18)x=\frac18) undergoes several transitions below the charge-ordering temperature TcoT_{co} = 54 K. From Nernst experiments, we find that, below TcoT_{co}, there exists a large, anomalous Nernst signal eN,even(H,T)e_{N,even}(H,T) that is symmetric in field HH, and remains finite as H→0H\to 0. The time-reversal violating signal suggests that, below TcoT_{co}, vortices of one sign are spontaneously created to relieve interlayer phase frustration.Comment: 5 pages, 4 figure
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