102,227 research outputs found
Spin Gaps in a Frustrated Heisenberg model for CaVO
I report results of a density matrix renormalization group (DMRG) study of a
model for the two dimensional spin-gapped system CaVO. This study
represents the first time that DMRG has been used to study a two dimensional
system on large lattices, in this case as large as , allowing
extrapolation to the thermodynamic limit. I present a substantial improvement
to the DMRG algorithms which makes these calculations feasible.Comment: 10 pages, with 4 Postscript figure
Comment on ``Density-matrix renormalization-group method for excited states''
In a Physical Review B paper Chandross and Hicks claim that an analysis of
the density-density correlation function in the dimerised Hubbard model of
polyacetylene indicates that the optical exciton is bound, and that a previous
study by Boman and Bursill that concluded otherwise was incorrect due to
numerical innacuracy. We show that the method used in our original paper was
numerically sound and well established in the literature. We also show that,
when the scaling with lattice size is analysed, the interpretation of the
density-density correlation function adopted by Chandross and Hicks in fact
implies that the optical exciton is unbound.Comment: RevTeX, 10 pages, 4 eps figures fixed and included now in tex
Energetics of Domain Walls in the 2D t-J model
Using the density matrix renormalization group, we calculate the energy of a
domain wall in the 2D t-J model as a function of the linear hole density
\rho_\ell, as well as the interaction energy between walls, for J/t=0.35. Based
on these results, we conclude that the ground state always has domain walls for
dopings 0 < x < 0.3. For x < 0.125, the system has (1,0) domain walls with
\rho_\ell ~ 0.5, while for 0.125 < x < 0.17, the system has a possibly
phase-separated mixture of walls with \rho_\ell ~ 0.5 and \rho_\ell =1. For x >
0.17, there are only walls with \rho_\ell =1. For \rho_\ell = 1, diagonal (1,1)
domain walls have very nearly the same energy as (1,0) domain walls.Comment: Several minor changes. Four pages, four encapsulated figure
How do galactic winds affect the Lyalpha forest?
We investigate the effect of galactic winds on the Lyalpha forest in
cosmological simulations of structure and galaxy formation. We combine high
resolution N-body simulations of the evolution of the dark matter with a
semi-analytic model for the formation and evolution of galaxies which includes
detailed prescriptions for the long-term evolution of galactic winds. This
model is the first to describe the evolution of outflows as a two-phase process
(an adiabatic bubble followed by a momentum--driven shell) and to include
metal--dependent cooling of the outflowing material. We find that the main
statistical properties of the Lyalpha forest, namely the flux power spectrum
P(k) and the flux probability distribution function (PDF), are not
significantly affected by winds and so do not significantly constrain wind
models. Winds around galaxies do, however, produce detectable signatures in the
forest, in particular, increased flux transmissivity inside hot bubbles, and
narrow, saturated absorption lines caused by dense cooled shells. We find that
the Lyalpha flux transmissivity is highly enhanced near strongly wind-blowing
galaxies, almost half of all high-redshift galaxies in our sample, in agreement
with the results of Adelberger et al. (2005). Finally, we propose a new method
to identify absorption lines potentially due to wind shells in the Lyalpha
forest: we calculate the abundance of saturated regions in spectra as a
function of region width and we find that the number with widths smaller than
about 1 Angstrom at z=3 and 0.6 Angstrom at z=2 may be more than doubled. This
should be detectable in real spectra.Comment: 14 pages, 11 figures. Minor changes in the text. Accepted for
publication in MNRA
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Transgressions and expressions: Affective facial muscle activity predicts moral judgments
Recent investigations into morality suggest that affective responses may precede moral judgments. The present study investigated, first, whether individuals show specific facial affect in response to moral behaviors and, second, whether the intensity of facial affect predicts subsequent moral judgments. Muscle activity relating to disgust (levator labii), anger (corrugator supercilii), and positive affect (zygomaticus major) was recorded while participants considered third-person statements describing good and bad behaviors across five foundations of morality (purity, fairness, harm, authority, and ingroup). Facial disgust was highest in response to purity violations, followed by fairness violations. In contrast, harm violations evoked anger expressions. Importantly, the extremity of subsequent moral judgments was predicted by facial affect, such that judgments about purity and fairness correlated with facial disgust, harm correlated with facial anger, and ingroup correlated with positive facial affect. These results demonstrate that individuals spontaneously exhibit domain-specific moral affect that allows inferences about their moral judgments. </jats:p
Conditions implying the uniqueness of the weak*-topology on certain group algebras
We investigate possible preduals of the measure algebra M(G) of a locally compact group and the Fourier algebra A(G) of a separable compact group. Both of these algebras are canonically dual spaces and the canonical preduals make the multiplication separately weak*-continuous so that these algebras are dual Banach algebras. In this paper we find additional conditions under which the preduals
C0(G) of M(G) and C*(G) of A(G) are uniquely determined. In both cases we consider a natural comultiplication and show that the canonical predual gives rise to the unique weak*-topology making both the multiplication separately weak*-continuous and the comultiplication weak*-continuous. In particular, dual cohomological properties of these algebras are well defined with this additional structure
Control System Design Philosophy for Effective Operations and Maintenance
A well-designed control system facilitates the functions of machine
operation, maintenance and development. In addition, the overall effectiveness
of the control system can be greatly enhanced by providing reliable mechanisms
for coordination and communication, ensuring that these functions work in
concert. For good operability, the information presented to operators should be
consistent, easy to understand and customizable. A maintainable system is
segmented appropriately, allowing a broken element to be quickly identified and
repaired while leaving the balance of the system available. In a research and
development environment, the control system must meet the frequently changing
requirements of a variety of customers. This means the system must be flexible
enough to allow for ongoing modifications with minimal disruptions to
operations. Beyond the hardware and software elements of the control system,
appropriate workflow processes must be in place to maximize system uptime and
allow people to work efficiently. Processes that provide automatic electronic
communication ensure that information is not lost and reaches its destination
in a timely fashion. This paper discusses how these control system design and
quality issues have been applied at the Thomas Jefferson National Accelerator
Facility.Comment: ICALEPCS 200
Influence of cell surface characteristics on adhesion of Saccharomyces cerevisiae to the biomaterial hydroxylapatite
The influence of the physicochemical properties of biomaterials on microbial cell adhesion is well known, with the extent of adhesion depending on hydrophobicity, surface charge, specific functional groups and acid–base properties. Regarding yeasts, the effect of cell surfaces is often overlooked, despite the fact that generalisations may not be made between closely related strains. The current investigation compared adhesion of three industrially relevant strains of Saccharomyces cerevisiae (M-type, NCYC 1681 and ALY, strains used in production of Scotch whisky, ale and lager, respectively) to the biomaterial hydroxylapatite (HAP). Adhesion of the whisky yeast was greatest, followed by the ale strain, while adhesion of the lager strain was approximately 10-times less. According to microbial adhesion to solvents (MATS) analysis, the ale strain was hydrophobic while the whisky and lager strains were moderately hydrophilic. This contrasted with analyses of water contact angles where all strains were characterised as hydrophilic. All yeast strains were electron donating, with low electron accepting potential, as indicated by both surface energy and MATS analysis. Overall, there was a linear correlation between adhesion to HAP and the overall surface free energy of the yeasts. This is the first time that the relationship between yeast cell surface energy and adherence to a biomaterial has been described
Effect of the W-term for a t-U-W Hubbard ladder
Antiferromagnetic and d_{x2-y2}-pairing correlations appear delicately
balanced in the 2D Hubbard model. Whether doping can tip the balance to pairing
is unclear and models with additional interaction terms have been studied. In
one of these, the square of a local hopping kinetic energy H_W was found to
favor pairing. However, such a term can be separated into a number of simpler
processes and one would like to know which of these terms are responsible for
enhancing the pairing. Here we analyze these processes for a 2-leg Hubbard
ladder
The interaction region of high energy protons
The spatial view of the interaction region of colliding high energy protons
(in terms of impact parameter) is considered. It is shown that the region of
inelastic collisions has a very peculiar shape. It saturates for central
collisions at an energy of 7 TeV. We speculate on the further evolution with
energy, which is contrasted to the "black disk" picture.Comment: 9 pages, 1 figure. arXiv admin note: text overlap with
arXiv:1406.215
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