2,177 research outputs found
A tunable radiation source by coupling laser-plasma-generated electrons to a periodic structure
Near-infrared radiation around 1000 nm generated from the interaction of a high-density MeV electron beam, obtained by impinging an intense ultrashort laser pulse on a solid target, with a metal grating is observed experimentally. Theoretical modeling and particle-in-cell simulation suggest that the radiation is caused by the Smith-Purcell mechanism. The results here indicate that tunable terahertz radiation with tens GV=m field strength can be achieved by using appropriate grating parameter
Topological Charge Fluctuations and Low-Lying Dirac Eigenmodes
We discuss the utility of low-lying Dirac eigenmodes for studying the nature
of topological charge fluctuations in QCD. The implications of previous results
using the local chirality histogram method are discussed, and the new results
using the overlap Dirac operator in Wilson gauge backgrounds at lattice
spacings ranging from a~0.04 fm to a~0.12 fm are reported. While the degree of
local chirality does not change appreciably closer to the continuum limit, we
find that the size and density of local structures responsible for chiral
peaking do change significantly. The resulting values are in disagreement with
the assumptions of the Instanton Liquid Model. We conclude that the
fluctuations of topological charge in the QCD vacuum are not locally quantized.Comment: 3 pages, 4 figures, Lattice2001(confinement
Tumor suppressor in lung cancer-1 (TSLC1) functions as a glioma tumor suppressor
Tumor suppressor in lung cancer-1 (TSLC1) loss is common in many human cancers, including meningioma. In this study, we demonstrate that TSLC1 protein and RNA expression is lost in 60% to 65% of high-grade gliomas, and that TSLC1 reintroduction into glioma cells results in growth suppression. Moreover, Tslc1 loss in mice results in increased astrocyte proliferation in vivo and in vitro. These data indicate that TSLC1 functions as a glioma tumor suppressor. ©2006AAN Enterprises, Inc.Fil: Houshmandi, S.S.. Washington University in St. Louis; Estados UnidosFil: Surace, Ezequiel Ignacio. Washington University in St. Louis; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; ArgentinaFil: Zhang, H.B.. Washington University in St. Louis; Estados UnidosFil: Fuller, G.N.. University of Texas; Estados UnidosFil: Gutmann, D.H.. Washington University in St. Louis; Estados Unido
Low-dimensional long-range topological structure in the QCD vacuum
Lattice topological charge associated with Ginsparg-Wilson fermions exhibits
generic topological stability over quantum ensemble of configurations
contributing to the QCD path integral. Moreover, the underlying chiral symmetry
leads to the suppression of ultraviolet noise in the associated topological
charge densities ("chiral smoothing"). This provides a solid foundation for the
direct study of the role of topological charge fluctuations in the physics of
QCD vacuum. Using these tools it was recently demonstrated that: (a) there is a
well-defined space-time structure (order) in topological charge density
(defined through overlap fermions) for typical configurations contributing to
QCD path integral; (b) this fundamental structure is low-dimensional,
exhibiting sign-coherent behavior on subsets of dimension less than four and
not less than one; (c) the structure has a long-range global character
(spreading over maximal space-time distances) and is built around the locally
one-dimensional network of strong fields (skeleton). In this talk we elaborate
on certain aspects and implications of these results.Comment: 3 pages, 1 figure; Lattice2003(topology
Effects of Allelic Variation in Glutenin Subunits and Gliadins on Baking-Quality in Near-isogenic Lines of Common Wheat cv. Longmai 19
Two lines, L-19-613 and L-19-626, were produced from the common wheat cultivar Longmai 19 (L-19) by six consecutive backcrosses using biochemical marker-assisted selection. L-19 (Glu-D1a, Glu-A3c/Gli-A1?; Gli-A1? is a gene coding for unnamed gliadin) and L-19-613 (Glu-D1d, Glu-A3c/Gli-A1?) formed a set of near-isogenic lines (NILs) for HMW-GS, while L-19-613 and L-19-626 (Glu-D1d, Glu-A3e/Gli-A1m) constituted another set of NILs for the LMW-GS/gliadins. The three L-19 NILs were grown in the wheat breeding nursery in 2007 and 2008. The field experiments were designed using the three-column contrast arrangement method with four replicates. The three lines were ranked as follows for measurements of gluten strength, which was determined by the gluten index, Zeleny sedimentation, the stability and breakdown time of the farinogram, the maximum resistance and area of the extensogram, and the P andWvalues of the alveogram: L-19-613 > L-19-626 > L-19. The parameters listed above were significantly different between lines at the 0.05 or 0.01 level. The Glu-D1 and Glu-A3/Gli-A1 loci had additive effects on the gluten index, Zeleny sedimentation, stability, breakdown time, maximum resistance, area, P and W values. Although genetic variation at the Glu-A3/Gli-A1 locus had a great influence on wheat quality, the genetic difference between Glu-D1d and Glu-D1a at the Glu-D1 locus was much larger than that of Glu-A3c/Gli-A1? and Glu-A3e/Gli-A1m at the Glu-A3/Gli-A1 locus. Glu-D1d had negative effects on the extensibility and the L value compared with Glu-D1a. In contrast, Glu-A3c/Gli-A1? had a positive effect on these traits compared with Glu-A3e/Gli-A1m
Reduction of three-band model for copper oxides to single-band generalized t~-~J model
A three-band model for copper oxides in the region of parameters where the
second hole on the copper has energy close to the first hole on the oxygen is
considered. The exact solution for one hole on a ferromagnetic background of
the ordered copper spins is obtained. A general procedure for transformation of
the primary Hamiltonian to the Hamiltonian of singlet and triplet excitations
is proposed. Reduction of the singlet-triplet Hamiltonian to the single-band
Hamiltonian of the generalized t~-~J model is performed. A comparison of the
solution for the generalized t~-~J model on a ferromagnetic background with the
exact solution shows a very good agreement.Comment: 20 pages (LATEX
Spin tunnelling in mesoscopic systems
We study spin tunnelling in molecular magnets as an instance of a mesoscopic
phenomenon, with special emphasis on the molecule Fe8. We show that the tunnel
splitting between various pairs of Zeeman levels in this molecule oscillates as
a function of applied magnetic field, vanishing completely at special points in
the space of magnetic fields, known as diabolical points. This phenomena is
explained in terms of two approaches, one based on spin-coherent-state path
integrals, and the other on a generalization of the phase integral (or WKB)
method to difference equations. Explicit formulas for the diabolical points are
obtained for a model Hamiltonian.Comment: 13 pages, 5 figures, uses Pramana style files; conference proceedings
articl
Integrating HDAd5/35++ vectors as a new platform for HSC gene therapy of hemoglobinopathies
We generated an integrating, CD46-targeted, helper-dependent adenovirus HDAd5/35++ vector system for hematopoietic stem cell (HSC) gene therapy. The ∼12-kb transgene cassette included a β-globin locus control region (LCR)/promoter driven human γ-globin gene and an elongation factor alpha-1 (EF1α)-mgmtP140K expression cassette, which allows for drug-controlled increase of γ-globin-expressing erythrocytes. We transduced bone marrow lineage-depleted cells from human CD46-transgenic mice and transplanted them into lethally irradiated recipients. The percentage of γ-globin-positive cells in peripheral blood erythrocytes in primary and secondary transplant recipients was stable and greater than 90%. The γ-globin level was 10%–20% of adult mouse globin. Transgene integration, mediated by a hyperactive Sleeping Beauty SB100x transposase, was random, without a preference for genes. A second set of studies was performed with peripheral blood CD34+ cells from mobilized donors. 10 weeks after transplantation of transduced cells, human cells were harvested from the bone marrow and differentiated ex vivo into erythroid cells. Erythroid cells expressed γ-globin at a level of 20% of adult α-globin. Our studies suggest that HDAd35++ vectors allow for efficient transduction of long-term repopulating HSCs and high-level, almost pancellular γ-globin expression in erythrocytes. Furthermore, our HDAd5/35++ vectors have a larger insert capacity and a safer integration pattern than currently used lentivirus vectors
Tunneling conductance in strained graphene-based superconductor: Effect of asymmetric Weyl-Dirac fermions
Based on the BTK theory, we investigate the tunneling conductance in a
uniaxially strained graphene-based normal metal (NG)/ barrier
(I)/superconductor (SG) junctions. In the present model, we assume that
depositing the conventional superconductor on the top of the uniaxially
strained graphene, normal graphene may turn to superconducting graphene with
the Cooper pairs formed by the asymmetric Weyl-Dirac electrons, the massless
fermions with direction-dependent velocity. The highly asymmetrical velocity,
vy/vx>>1, may be created by strain in the zigzag direction near the transition
point between gapless and gapped graphene. In the case of the highly
asymmetrical velocity, we find that the Andreev reflection strongly depends on
the direction and the current perpendicular to the direction of strain can flow
in the junction as if there was no barrier. Also, the current parallel to the
direction of strain anomalously oscillates as a function of the gate voltage
with very high frequency. Our predicted result is found as quite different from
the feature of the quasiparticle tunneling in the unstrained graphene-based
NG/I/SG conventional junction. This is because of the presence of the
direction-dependent-velocity quasiparticles in the highly strained graphene
system.Comment: 18 pages, 7 Figures; Eq.13 and 14 are correcte
- …