704 research outputs found
Simulations of “tunnelling of the 3rd kind”
We consider the phenomenon of ``tunnelling of the 3rd kind" \cite{third}, whereby a magnetic field may traverse a classically impenetrable barrier by pair creation of unimpeded quantum fermions. These propagate through the barrier and generate a magnetic field on the other side. We study this numerically using quantum fermions coupled to a classical Higgs-gauge system, where we set up a magnetic field outside a box shielded by two superconducting barriers. We examine the magnitude of the internal magnetic field, and find agreement with existing perturbative results within a factor of two
Dinitrogen Activation in the Gas Phase: Spectroscopic Characterization of C–N Coupling in the V<sub>3</sub>C<sup>+</sup> + N<sub>2</sub> Reaction
We report on cluster-mediated C–N bond formation in the gas phase using N2 as a nitrogen source. The V3C+ + N2 reaction is studied by a combination of ion-trap mass spectrometry with infrared photodissociation (IRPD) spectroscopy and complemented by electronic structure calculations. The proposed reaction mechanism is spectroscopically validated by identifying the structures of the reactant and product ions. V3C+ exhibits a pyramidal structure of C1 symmetry. N2 activation is initiated by adsorption in an end-on fashion at a vanadium site, followed by spontaneous cleavage of the N≡N triple bond and subsequent C−N coupling. The IRPD spectrum of the metal nitride product [NV3(C=N)]+ exhibits characteristic C=N double bond (1530 cm-1) and V-N single bond (770, 541 and 522 cm-1) stretching bands
Turbulence and Multiscaling in the Randomly Forced Navier Stokes Equation
We present an extensive pseudospectral study of the randomly forced
Navier-Stokes equation (RFNSE) stirred by a stochastic force with zero mean and
a variance , where is the wavevector and the dimension . We present the first evidence for multiscaling of velocity structure
functions in this model for . We extract the multiscaling exponent
ratios by using extended self similarity (ESS), examine their
dependence on , and show that, if , they are in agreement with those
obtained for the deterministically forced Navier-Stokes equation (NSE). We
also show that well-defined vortex filaments, which appear clearly in studies
of the NSE, are absent in the RFNSE.Comment: 4 pages (revtex), 6 figures (postscript
Interleukin-10 inhibits tumor metastasis through an NK-cell dependent mechanism
Interleukin-10 (IL-10) is a recently described pleiotropic cytokine secreted mainly by type 2 helper T cells. Previous studies have shown that IL-10 suppresses cytokine expression by natural killer (NK) and type 1 T cells, thus down-regulating cell-mediated immunity and stimulating humoral responses. We here report that injected IL-10 protein is an efficient inhibitor of tumor metastasis in experimental (B16-F10) and spontaneous (M27 and Lox human melanoma) metastasis models in vivo at doses that do not have toxic effects on normal or cancer cells. Histological characterization after IL-10 treatment confirmed the absence of CD8+ and CD4+ T cells and macrophages at the sites of tumor growth, but abundant NK cells were localized at these sites. This unexpected finding was confirmed by showing that IL-10 inhibits most B16-F10 and Lox metastases in mice deficient in T or B cells (SCID and nu/nu mice), but not in those deficient in NK cells (beige mice or NK cell-depleted mice). However, IL-10 downregulation of pro-inflammatory cytokine production and/or recruitment of additional effector cells may also be involved in the anti-tumor effect at higher local concentrations of IL-10, since transfected B16 tumor cells expressing high amounts of IL-10 were rejected by normal, nu/nu, or SCID mice at the primary tumor stage, and there was still a 33% inhibition of tumor metastasis in beige mice
A minimum single-band model for low-energy excitations in superconducting KFeSe
We propose a minimum single-band model for the newly discovered iron-based
superconducting KFeSe. Our model is found to be numerically
consistent with the five-orbital model at low energies. Based on our model and
the random phase approximation, we study the spin fluctuation and the pairing
symmetry of superconducting gap function. The spin excitation
and the pairing symmetry are revealed. All of the results can
well be understood in terms of the interplay between the Fermi surface topology
and the local spin interaction, providing a sound picture to explain why the
superconducting transition temperature is as high as to be comparable to those
in pnictides and some cuprates. A common origin of superconductivity is
elucidated for this compound and other high-T materials.Comment: 5 pages, 4 figure
Structural, Magnetic and Electronic Properties of the Iron-Chalcogenide AFeSe (A=K, Cs, Rb, Tl and etc.) Superconductors
The latest discovery of a new iron-chalcogenide superconductor
AFeSe(A=K, Cs, Rb, Tl and etc.) has attracted much attention
due to a number of its unique characteristics, such as the possible insulating
state of the parent compound, the existence of Fe-vacancy and its ordering, a
new form of magnetic structure and its interplay with superconductivity, and
the peculiar electronic structures that are distinct from other Fe-based
superconductors. In this paper, we present a brief review on the structural,
magnetic and electronic properties of this new superconductor, with an emphasis
on the electronic structure and superconducting gap. Issues and future
perspectives are discussed at the end of the paper.Comment: 45 pages, 19 figure
Analytical methods in wineries: is it time to change?
A review of the methods for the most common parameters determined in wine—namely, ethanol, sulfur dioxide, reducing sugars, polyphenols, organic acids, total and volatile acidity, iron, soluble solids, pH, and color—reported in the last 10 years is presented here. The definition of the given parameter, official and usual methods in wineries appear at the beginning of each section, followed by the methods reported in the last decade divided into discontinuous and continuous methods, the latter also are grouped in nonchromatographic and chromatographic methods because of the typical characteristics of each subgroup. A critical comparison between continuous and discontinuous methods for the given parameter ends each section. Tables summarizing the features of the methods and a conclusions section may help users to select the most appropriate method and also to know the state-of-the-art of analytical methods in this area
The Identification of Lymphocyte-Like Cells and Lymphoid-Related Genes in Amphioxus Indicates the Twilight for the Emergency of Adaptive Immune System
To seek evidence of a primitive adaptive immune system (AIS) before vertebrate, we examined whether lymphocytes or lymphocyte-like cells and the related molecules participating in the lymphocyte function existed in amphioxus. Anatomical analysis by electron microscopy revealed the presence of lymphocyte-like cells in gills, and these cells underwent morphological changes in response to microbial pathogens that are reminiscent of those of mammalian lymphocytes executing immune response to microbial challenge. In addition, a systematic comparative analysis of our cDNA database of amphioxus identified a large number of genes whose vertebrate counterparts are involved in lymphocyte function. Among these genes, several genes were found to be expressed in the vicinity of the lymphocyte-like cells by in situ hybridization and up-regulated after exposure to microbial pathogens. Our findings in the amphioxus indicate the twilight for the emergency of AIS before the invertebrate-vertebrate transition during evolution
Persistence of Topological Order and Formation of Quantum Well States in Topological Insulators Bi2(Se,Te)3 under Ambient Conditions
The topological insulators represent a unique state of matter where the bulk
is insulating with an energy gap while the surface is metallic with a Dirac
cone protected by the time reversal symmetry. These characteristics provide a
venue to explore novel quantum phenomena in fundamental physics and show
potential applications in spintronics and quantum computing. One critical issue
directly related with the applications as well as the fundamental studies is
how the topological surface state will behave under ambient conditions (1
atmosphere air and room temperature). In this paper, we report high resolution
angle-resolved photoemission measurements on the surface state of the
prototypical topological insulators, Bi2Se3, Bi2Te3 and Bi2(Se0.4Te2.6), upon
exposing to ambient conditions. We find that the topological order persists
even when the surface is exposed to air at room temperature. However, the
surface state is strongly modified after such an exposure. Particularly, we
have observed the formation of two-dimensional quantum well states near the
surface of the topological insulators after the exposure which depends
sensitively on the original composition, x, in Bi2(Se3-xTex). These rich
information are crucial in utilizing the surface state and in probing its
physical properties under ambient conditions.Comment: 15 Pages, 4 Figure
Statistical Properties of Turbulence: An Overview
We present an introductory overview of several challenging problems in the
statistical characterisation of turbulence. We provide examples from fluid
turbulence in three and two dimensions, from the turbulent advection of passive
scalars, turbulence in the one-dimensional Burgers equation, and fluid
turbulence in the presence of polymer additives.Comment: 34 pages, 31 figure
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