14,597 research outputs found
Transport properties of a two impurity system: a theoretical approach
A system of two interacting cobalt atoms, at varying distances, was studied
in a recent scanning tunneling microscope experiment by Bork et. al.[Nature
Phys. 7, 901 (2011)]. We propose a microscopic model that explains, for all
experimentally analyzed interatomic distances, the physics observed in these
experiments. Our proposal is based on the two-impurity Anderson model, with the
inclusion of a two-path geometry for charge transport. This many-body system is
treated in the finite-U slave boson mean-field approximation and the
logarithmic-discretization embedded-cluster approximation. We physically
characterize the different charge transport regimes of this system at various
interatomic distances and show that, as in the experiments, the features
observed in the transport properties depend on the presence of two impurities
but also on the existence of two conducting channels for electron transport. We
interpret the splitting observed in the conductance as the result of the
hybridization of the two Kondo resonances associated with each impurity.Comment: 5 pages, 5 figure
New results for the t-J model in ladders: Changes in the spin liquid state with applied magnetic field. Implications for the cuprates
Exact Diagonalization calculations are presented for the t-J model in the
presence of a uniform magnetic field. Results for 2xL ladders (L=8,10,12) and
4x4 square clusters with 1 and 2 holes indicate that the diamagnetic response
to a perpendicular magnetic field tends to induce a spin liquid state in the
spin background. The zero-field spin liquid state of a two-leg ladder is
reinforced by the magnetic field: a considerable increase of rung
antiferromagnetic correlations is observed for J/t up to 0.6, for 1 and 2
holes. Pair-breaking is also clearly observed in the ladders and seems to be
associated in part with changes promoted by the field in the spin correlations
around the zero-field pair. In the 4x4 cluster, the numerical results seem to
indicate that the field-induced spin liquid state competes with the zero-field
antiferromagnetic short-range-order, the spin liquid state being favored by
higher doping and smaller values of J/t. It is interesting to note that the
field-effect can also be observed in a 2x2 plaquette with 1 and 2 holes. This
opens up the possibility of gaining a qualitative understanding of the effect.Comment: 16 pages, 7 figures, latex New results adde
A constant dark matter halo surface density in galaxies
We confirm and extend the recent finding that the central surface density
r_0*rho_0 galaxy dark matter halos, where r_0 and rho_0 are the halo core
radius and central density, is nearly constant and independent of galaxy
luminosity. Based on the co-added rotation curves of about 1000 spiral
galaxies, mass models of individual dwarf irregular and spiral galaxies of late
and early types with high-quality rotation curves and, galaxy-galaxy weak
lensing signals from a sample of spiral and elliptical galaxies, we find that
log(r_0*rho_0) = 2.15 +- 0.2, in units of log(Msol/pc^2). We also show that the
observed kinematics of Local Group dwarf spheroidal galaxies are consistent
with this value. Our results are obtained for galactic systems spanning over 14
magnitudes, belonging to different Hubble Types, and whose mass profiles have
been determined by several independent methods. In the same objects, the
approximate constancy of rho_0*r_0 is in sharp contrast to the systematical
variations, by several orders of magnitude, of galaxy properties, including
rho_0 and central stellar surface density.Comment: Accepted for publication in MNRAS. 9 pages, 4 figure
Electron Transport through a Molecular Conductor with Center-of-Mass Motion
The linear conductance of a molecular conductor oscillating between two
metallic leads is investigated numerically both for Hubbard interacting and
noninteracting electrons. The molecule-leads tunneling barriers depend on the
molecule displacement from its equilibrium position. The results present an
interesting interference which leads to a conductance dip at the electron-hole
symmetry point, that could be experimentally observable. It is shown that this
dip is caused by the destructive interference between the purely electronic and
phonon-assisted tunneling channels, which are found to carry opposite phases.
When an internal vibrational mode is also active, the electron-hole symmetry is
broken but a Fano-like interference is still observed
Effect of Electrolyte Balance in Low-Protein Diets on Broiler Performance and Tibial Dyschondroplasia Incidence
A proper dietary electrolyte balance (DEB) is essential to ensure an optimum acid-base equilibrium and broiler performance. In low-CP diets, this balance can be affected by reduction of soybean meal and inclusion of high levels of synthetic amino acids. Although, some studies have related low-protein diets supplemented with amino acids and DEB, these relations are not well explained, because some research demonstrates confusion about the deficiency and balance of nutrients. The objective of these experiments was to evaluate the DEB effects of diets with low levels of protein supplemented with amino acids on broiler performance and bone development. Results indicated that DEB and CP content influenced broiler chick performance in the starter and growing periods. There was no significant effect due to the interaction between DEB and CP content for tibial dyschondroplasia incidence (TD) or in bone breaking resistance during the growing period of either experiment. The incidence of TD was reduced with 253 mEq/kg DEB in the starter period
Effects of Urban Sprawl on Meningococcal Meningitis Incidence in Kaduna Urban Area, Nigeria
Meningococcal meningitis is an airborne disease that has overwhelmed the lives of many people for over a century now. There are factors that are connected to the spread of the disease. They include level of income, social behavior, housing condition, climate, environment and urbanization. The “African meningitis belt” which is a region located around west Africa is the most plagued by the disease. This study aims at exploring the deviational distribution and standard distance in relation to the effects that the urban sprawl has on the spatial pattern of the spread of the disease in Kaduna urban area. The Meningococcal meningitis reported cases (confirmed and unconfirmed) were used for the study and it was sourced from the public and private hospitals within Kaduna urban area. For each of those years, satellite images (quick bird) were used by digitizing the urban lands and comparing all the years together. Directional distribution and standard distance analysis were conducted using spatial statistical tools in ArcGIS 10.1. The results of the digitized imageries, the directional distribution, and the standard distance were analyzed so as to determine the relationship between urbanization and the disease spread. It was observed from the result that those years that had higher sprawl are more affected by the disease. Keywords: Spatial Pattern, Meningococcal meningitis, Urban sprawl, Directional Distribution, Standard Distanc
Of?p stars: a class of slowly rotating magnetic massive stars
Only 5 Of?p stars have been identified in the Galaxy. Of these, 3 have been
studied in detail, and within the past 5 years magnetic fields have been
detected in each of them. The observed magnetic and spectral characteristics
are indicative of organised magnetic fields, likely of fossil origin, confining
their supersonic stellar winds into dense, structured magnetospheres. The
systematic detection of magnetic fields in these stars strongly suggests that
the Of?p stars represent a general class of magnetic O-type stars.Comment: Proceedings of IAUS 272: Active OB star
Transport and Strong-Correlation Phenomena in Carbon Nanotube Quantum Dots in a Magnetic Field
Transport through carbon nanotube (CNT) quantum dots (QDs) in a magnetic
field is discussed. The evolution of the system from the ultraviolet to the
infrared is analyzed; the strongly correlated (SC) states arising in the
infrared are investigated. Experimental consequences of the physics are
presented -- the SC states arising at various fillings are shown to be
drastically different, with distinct signatures in the conductance and, in
particular, the noise. Besides CNT QDs, our results are also relevant to double
QD systems.Comment: 5 pages, 5 figure
Economic and environmental analysis of citrus based intercropping systems in costal tablelands.
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