12,864 research outputs found
Exact Results for 1D Kondo Lattice from Bosonization
We find a solvable limit to the problem of the 1D electron gas interacting
with a lattice of Kondo scattering centers. In this limit, we present exact
results for the problems of incommensurate filling, commensurate filling,
impurity vacancy states, and the commensurate-incommensurate transition.Comment: 4 pages, two columns, Latex fil
Stripe phases in high-temperature superconductors
Stripe phases are predicted and observed to occur in a class of
strongly-correlated materials describable as doped antiferromagnets, of which
the copper-oxide superconductors are the most prominent representative. The
existence of stripe correlations necessitates the development of new principles
for describing charge transport, and especially superconductivity, in these
materials.Comment: 5 pp, 1 color eps fig., to appear as a Perspective in Proc. Natl.
Acad. Sci. US
Dimerization in a half-filled one-dimensional extended Hubbard model
We use a density matrix renormalization group method to study quantitatively
the phase diagram of a one-dimensional extended Hubbard model at half-filling
by investigating the correlation functions and structure factors. We confirm
the existence of a novel narrow region with long-rang bond-order-wave order
which is highly controversial recently between the charge-density-wave phase
and Mott insulator phase. We determined accurately the position of the
tricritical point , which is quite different
from previous studies
Combined Analysis of Numerical Diagonalization and Renormalization Group methods for the One-Dimensional - Model at Quarter filling
The one-dimensional extended Hubbard model with both the on-site and the
nearest neighbor interactions at quarter filling is studied by using a
novel finite size scaling. We diagonalize finite size systems numerically and
calculate the Luttinger-liquid parameter which is substituted into
the renormalization group equation as an initial condition. It leads
in the infinite size system and the result agrees very well with the available
exact result with . This approach also yields the charge gap in the
insulating state near the metal-insulator transition where the characteristic
energy becomes exponentially small and the usual finite size scaling is not
applicable.Comment: 7 pages, 8 figures,submitted to PR
Sea surface velocities from visible and infrared multispectral atmospheric mapping sensor imagery
High resolution (100 m), sequential Multispectral Atmospheric Mapping Sensor (MAMS) images were used in a study to calculate advective surface velocities using the Maximum Cross Correlation (MCC) technique. Radiance and brightness temperature gradient magnitude images were formed from visible (0.48 microns) and infrared (11.12 microns) image pairs, respectively, of Chandeleur Sound, which is a shallow body of water northeast of the Mississippi delta, at 145546 GMT and 170701 GMT on 30 Mar. 1989. The gradient magnitude images enhanced the surface water feature boundaries, and a lower cutoff on the gradient magnitudes calculated allowed the undesirable sunglare and backscatter gradients in the visible images, and the water vapor absorption gradients in the infrared images, to be reduced in strength. Requiring high (greater than 0.4) maximum cross correlation coefficients and spatial coherence of the vector field aided in the selection of an optimal template size of 10 x 10 pixels (first image) and search limit of 20 pixels (second image) to use in the MCC technique. Use of these optimum input parameters to the MCC algorithm, and high correlation and spatial coherence filtering of the resulting velocity field from the MCC calculation yielded a clustered velocity distribution over the visible and infrared gradient images. The velocity field calculated from the visible gradient image pair agreed well with a subjective analysis of the motion, but the velocity field from the infrared gradient image pair did not. This was attributed to the changing shapes of the gradient features, their nonuniqueness, and large displacements relative to the mean distance between them. These problems implied a lower repeat time for the imagery was needed in order to improve the velocity field derived from gradient imagery. Suggestions are given for optimizing the repeat time of sequential imagery when using the MCC method for motion studies. Applying the MCC method to the infrared brightness temperature imagery yielded a velocity field which did agree with the subjective analysis of the motion and that derived from the visible gradient imagery. Differences between the visible and infrared derived velocities were 14.9 cm/s in speed and 56.7 degrees in direction. Both of these velocity fields also agreed well with the motion expected from considerations of the ocean bottom topography and wind and tidal forcing in the study area during the 2.175 hour time interval
Geometric phase for a dimerized disordered continuum: Topological shot noise
Geometric phase shift associated with an electron propagating through a
dimerized-disordered continuum is shown to be 0, or (modulo 2),
according as the associated circuit traversed in the two-dimensional parameter
space excludes, or encircles a certain singularity. This phase-shift is a
topological invariant. Its discontinuous dependence on the electron energy and
disorder implies a statistical spectral and conductance fluctuation in a
corresponding mesoscopic system. Inasmuch as the fluctuation derives from the
discreteness of the phase shift, it may aptly be called a topological
shot-noise.Comment: 10 pages(LATEX) + 1 figure, (revised version). Will appear in
Europhys. Let
Science materials for the gifted in grades two and three
Thesis (Ed.M.)--Boston Universit
Rotationally resolved spectroscopy of (20000) Varuna in the near-infrared
Models of the escape and retention of volatiles by minor icy objects exclude
any presence of volatile ices on the surface of TNOs smaller than ~1000km in
diameter at the typical temperature in this region of the solar system, whereas
the same models show that water ice is stable on the surface of objects over a
wide range of diameters. Collisions and cometary activity have been used to
explain the process of surface refreshing of TNOs and Centaurs. These processes
can produce surface heterogeneity that can be studied by collecting information
at different rotational phases. The aims of this work are to study the surface
composition of (20000)Varuna, a TNO with a diameter ~650km and to search for
indications of rotational variability. We observed Varuna during two
consecutive nights in January 2011 with NICS@TNG obtaining a set of spectra
covering the whole rotation period of Varuna. After studying the spectra
corresponding to different rotational phases, we did not find any indication of
surface variability. In all the spectra, we detect an absorption at 2{\mu}m,
suggesting the presence of water ice on the surface. We do not detect any other
volatiles on the surface, although the S/N is not high enough to discard their
presence. Based on scattering models, we present two possible compositions
compatible with our set of data and discuss their implications in the frame of
the collisional history of the Kuiper Belt. We find that the most probable
composition for the surface of Varuna is a mixture of amorphous silicates,
complex organics, and water ice. This composition is compatible with all the
materials being primordial. However, our data can also be fitted by models
containing up to a 10% of methane ice. For an object with the characteristics
of Varuna, this volatile could not be primordial, so an event, such as an
energetic impact, would be needed to explain its presence on the surface.Comment: 6 pages, 5 figures, to be published in A&
Cytokinin Accumulation and an Altered Ethylene Response Mediate the Pleiotropic Phenotype of the Pea Nodulation Mutant R50 (\u3cem\u3esym16\u3c/em\u3e)
R50 (sym16), a pleiotropic mutant of Pisum sativum L., is short, has thickened internodes and roots, and has a reduced number of lateral roots and nodules. Its low nodule phenotype can be restored with the application of ethylene inhibitors; furthermore, it can be mimicked by applying cytokinins (CKs) to the roots of the parent line #8216;Sparkle’. Here, we report on the etiolation phenotypes of R50 and ‘Sparkle’, and on the interactive roles of ethylene and CKs in these lines. R50 displayed an altered etiolation phenotype, as it was shorter and thicker, and had more developed leaves than dark-grown ‘Sparkle’. Shoot morphological differences induced by exogenous ethylene or CKs were found to be less severe for R50. Ethylene inhibitor application induced root and shoot elongation and encouraged apical hook opening in both etiolated lines. Liquid chromatography–tandem mass spectrometry analysis indicated that CK concentrations in R50 were higher than in ‘Sparkle’, particularly in mature shoots where the levels were maintained at elevated concentrations. These differences indicate a reduction in the CK catabolism of R50. The accumulation of CKs can be directly related to several traits of R50, with the reduced number of nodules and altered shoot ethylene response being likely indirect effects
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