1,565 research outputs found
Enhanced Pairing in the "Checkerboard" Hubbard Ladder
We study signatures of superconductivity in a 2--leg "checkerboard" Hubbard
ladder model, defined as a one--dimensional (period 2) array of square
plaquettes with an intra-plaquette hopping and inter-plaquette hopping
, using the density matrix renormalization group method. The highest
pairing scale (characterized by the spin gap or the pair binding energy,
extrapolated to the thermodynamic limit) is found for doping levels close to
half filling, and . Other forms of modulated
hopping parameters, with periods of either 1 or 3 lattice constants, are also
found to enhance pairing relative to the uniform two--leg ladder, although to a
lesser degree. A calculation of the phase stiffness of the ladder reveals that
in the regime with the strongest pairing, the energy scale associated with
phase ordering is comparable to the pairing scale.Comment: 9 pages, 9 figures; Journal reference adde
Restrained Shrinkage of Fly Ash Based Geopolymer Concrete and Analysis of Long Term Shrinkage Prediction Models
The research presented in this manuscript describes the procedure to quantify the restrained shrinkage of geopolymer concrete (GPC) using ring specimen. Massive concrete structures are susceptible to shrinkage and thermal cracking. This cracking can increase the concrete permeability and decrease the strength and design life. This test is comprised of evaluating geopolymer concrete of six different mix designs including different activator solution to fly ash ratio and subjected to both restrained and free shrinkage. Test results obtained from this experimental setup was plotted along with the available empirical equation to observe the shrinkage strain of GPC and a model was suggested to predict the shrinkage strain of GPC. It was found from this study that along with activator solution to fly ash ratio the final compressive strength of GPC plays an important role on shrinkage strai
Superconductivity in zigzag CuO chains
Superconductivity has recently been discovered in
PrBaCuO with a maximum of about 15K.
Since the CuO planes in this material are believed to be insulating, it has
been proposed that the superconductivity occurs in the double (or zigzag) CuO
chain layer. On phenomenological grounds, we propose a theoretical
interpretation of the experimental results in terms of a new phase for the
zigzag chain, labelled by CS. This phase has a gap for some of the
relative spin and charge modes but no total spin gap, and can have a divergent
superconducting susceptibility for repulsive interactions. A microscopic model
for the zigzag CuO chain is proposed, and on the basis of density matrix
renormalization group (DMRG) and bosonization studies of this model, we adduce
evidence that supports our proposal.Comment: 10 pages, 5 figures; Journal-ref. adde
Ethical Perspectives and Practice Behaviors Involving Computer-Based Test Interpretation
The debates of the 1980s regarding responsible use of computer-based test interpretation (CBTI) software have mostly disappeared, as CBTI use has become common practice. We surveyed 364 members of the Society for Personality Assessment to determine how they use CBTI software in their work and their perspectives on the ethics of using CBTI in various ways. Psychologists commonly use CBTI software for test scoring and to provide a complementary source of input for case formulations. Most do not use CBTI software as the primary way to formulate a case, nor as an alternative to a written report. Controversy and uncertainty were expressed about importing sections of CBTI narratives into psychological reports. We distinguish between support and replacement functions of CBTI use, arguing that adequate research evidence should be present before using CBTI as a replacement for established assessment procedures
Phases of the infinite U Hubbard model
We apply the density matrix renormalization group (DMRG) to study the phase
diagram of the infinite U Hubbard model on 2-, 4-, and 6-leg ladders. Where the
results are largely insensitive to the ladder width, we consider the results
representative of the 2D square lattice model. We find a fully polarized
ferromagnetic Fermi liquid phase when n, the density of electrons per site, is
in the range 1>n>n_F ~ 4/5. For n=3/4 we find an unexpected commensurate
insulating "checkerboard" phase with coexisting bond density order with 4 sites
per unit cell and block spin antiferromagnetic order with 8 sites per unit
cell. For 3/4 > n, the wider ladders have unpolarized groundstates, which is
suggestive that the same is true in 2D
Possible way out of the Hawking paradox: Erasing the information at the horizon
We show that small deviations from spherical symmetry, described by means of
exact solutions to Einstein equations, provide a mechanism to "bleach" the
information about the collapsing body as it falls through the aparent horizon,
thereby resolving the information loss paradox. The resulting picture and its
implication related to the Landauer's principle in the presence of a
gravitational field, is discussed.Comment: 11 pages, Latex. Some comments added to answer to some raised
questions. Typos corected. Final version, to appear in Int. J. Modern. Phys.
Theory of the striped superconductor
We define a distinct phase of matter, a "pair density wave" (PDW), in which
the superconducting order parameter varies periodically as a function of
position such that when averaged over the center of mass position, all
components of vanish identically. Specifically, we study the simplest,
unidirectional PDW, the "striped superconductor," which we argue may be at the
heart of a number of spectacular experimental anomalies that have been observed
in the failed high temperature superconductor, La BaCuO. We
present a solvable microscopic model with strong electron-electron interactions
which supports a PDW groundstate. We also discuss, at the level of Landau
theory, the nature of the coupling between the PDW and other order parameters,
and the origins and some consequences of the unusual sensitivity of this state
to quenched disorder.Comment: 16 pages, 3 figures, 1 table; Journal ref. adde
Preferential attachment in the protein network evolution
The Saccharomyces cerevisiae protein-protein interaction map, as well as many
natural and man-made networks, shares the scale-free topology. The preferential
attachment model was suggested as a generic network evolution model that yields
this universal topology. However, it is not clear that the model assumptions
hold for the protein interaction network. Using a cross genome comparison we
show that (a) the older a protein, the better connected it is, and (b) The
number of interactions a protein gains during its evolution is proportional to
its connectivity. Therefore, preferential attachment governs the protein
network evolution. The evolutionary mechanism leading to such preference and
some implications are discussed.Comment: Minor changes per referees requests; to appear in PR
The ground states of the two-component order parameter superconductor
We show that in presence of an applied external field the two-component order
parameter superconductor falls in two categories of ground states, namely, in
the traditional Abrikosov ground state or in a new ground state fitted to
describe a superconducting layer with texture, that is, patched regions
separated by a phase difference of . The existence of these two kinds of
ground states follows from the sole assumption that the total supercurrent is
the sum of the two individual supercurrents and is independent of any
consideration about the free energy expansion. Uniquely defined relations
between the current density and the superfluid density hold for these two
ground states, which also determine the magnetization in terms of average
values of the order parameters. Because these ground state conditions are also
Bogomolny equations we construct the free energy for the two-component
superconductor which admits the Bogomolny solution at a special coupling value.Comment: 5 page
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