1,170 research outputs found
Qualitative understanding of the sign of t' asymmetry in the extended t-J Model and relevance for pairing properties
Numerical calculations illustrate the effect of the sign of the next
nearest-neighbor hopping term t' on the 2-hole properties of the t-t'-J model.
Working mainly on 2-leg ladders, in the -1.0 < t'/t < 1.0 regime, it is shown
that introducing t' in the t-J model is equivalent to effectively renormalizing
J, namely t' negative (positive) is equivalent to an effective t-J model with
smaller (bigger) J. This effect is present even at the level of a 2x2 plaquette
toy model, and was observed also in calculations on small square clusters.
Analyzing the transition probabilities of a hole-pair in the plaquette toy
model, it is argued that the coherent propagation of such hole-pair is enhanced
by a constructive interference between both t and t' for t'>0. This
interference is destructive for t'<0.Comment: 5 pages, 4 figures, to appear in PRB as a Rapid Communicatio
The spin and charge gaps of the half-filled N-leg Kondo ladders
In this work, we study N-leg Kondo ladders at half-filling through the
density matrix renormalization group. We found non-zero spin and charge gaps
for any finite number of legs and Kondo coupling . We also show evidence
of the existence of a quantum critical point in the two dimensional Kondo
lattice model, in agreement with previous works. Based on the binding energy of
two holes, we did not find evidence of superconductivity in the 2D Kondo
lattice model close to half-filling.Comment: 4 pages, 1 table, 3 fig
Potential bio-activity of whey fermented extract as sanitizer of organic grown lettuce
Short CommunicationConsumption of vegetables is increasing due to demand for healthy products in peoples' diets. To reduce
microbial contamination and maintain freshness, industrial processes in Portugal rely on minimally
processing of vegetables with hypochlorite as sanitizer. Formation of toxic chlorine derivatives has raised
concern restrictions to its use and alternatives with whey permeate as a disinfection agent has been
attempted. The aim of this work was to evaluate the bio potential of fermented cheese whey, for use on
disinfection of minimally processed lettuce organically grown.
Assays were made with whey obtained from inoculated milk during cheese processing, fermented for
120 h at 37 C, after which, among other carbohydrates, lactic acid was measured by HPLC, giving average
yields of 18 g L 1.
The sanitizing effect of whey, undiluted, 75 and 50% solutions, was compared with 110 ppm sodium
hypochlorite, after rinsing. Aerobic Microorganisms (AM), Psychrotrophic Microorganisms (PM) and
Enterobacteriaceae (ENT), were used as indicators for hygiene quality. For a level of significance of
P < 0.05, the hygiene quality standards of lettuce samples, were better using 75% whey solution (AM 6.62,
PM 7.48 cfu g 1), than using sodium hypochlorite (AM 7.48, PM 8.15 cfu g 1), for the 7 days of shelf life
studied. Evaluation of Enterobacteriaceae showed significant differences after 3 days, betweenwater (ENT
4.98 cfu g 1) sodium hypochlorite (ENT 4.81 cfu g 1) and 75% solution of whey (ENT 4.63 cfu g 1).
Considering the actual limitations imposed to chlorine sanitation, these results point a good alternative
to the food industry, especially for organic fresh vegetables, which are chemical free brandsinfo:eu-repo/semantics/publishedVersio
Recent progress in the truncated Lanczos method : application to hole-doped spin ladders
The truncated Lanczos method using a variational scheme based on Hilbert
space reduction as well as a local basis change is re-examined. The energy is
extrapolated as a power law function of the Hamiltonian variance. This
systematic extrapolation procedure is tested quantitatively on the two-leg t-J
ladder with two holes. For this purpose, we have carried out calculations of
the spin gap and of the pair dispersion up to size 2x15.Comment: 5 pages, 4 included eps figures, submitted to Phys. Rev. B; revised
versio
Dietary Patterns Associated with Alzheimer?s Disease and Related Chronic Disease Risk: A Review
The world’s population is growing older due to improved healthcare and nutrition. As a result, Alzheimer’s disease (AD) prevalence is rapidly increasing. The focus of the current research climate is shifting from understanding AD pathology and diagnosis to primary prevention and intervention strategies. Diet represents one potential intervention strategy accessible to all. Accumulating evidence suggests diet plays a major role in risk and development of AD and AD-related chronic diseases of the periphery like cardiovascular disease (CVD) and diabetes. This paper reviews studies that have explored the relationship between “a priori” dietary patterns, AD and AD-related chronic disease risk. The dietary patterns we will review are the healthy eating index, healthy diet indicator, recommended food score, and the Mediterranean diet (MeDi). Our review of the literature suggests a generally positive association between healthy diet patterns, AD and AD-related chronic disease risk; however the magnitude of the protective effect is modest in many studies. Consequently, we can only confidently conclude that the MeDi is associated with reduced AD risk, and further studies on the remaining indices need to be carried out. It is our opinion that a combination of dietary scores could predict overall dietary quality and chronic disease risk to a greater extent than one score individually. Analysis in multi-ethnic cohorts, investigating combinations of scores must be completed before firm conclusions can be reached on the ideal combination of scores. Obtaining further insight into the association between dietary patterns, AD and AD-related chronic disease risk may help in prioritizing public health efforts and provide a stronger basis for recommendations to improve dietary patterns
Intake of products containing anthocyanins, flavanols, and flavanones, and cognitive function: A narrative review
The purpose of this review is to examine human research studies published within the past 6 years which evaluate the role of anthocyanin, flavanol, and flavanone consumption in cognitive function, and to discuss potential mechanisms of action underlying any observed benefits. Evidence to date suggests the consumption of flavonoid-rich foods, such as berries and cocoa, may have the potential to limit, or even reverse, age-related declines in cognition. Over the last 6 years, the flavonoid subgroups of anthocyanins, flavanols, and flavanones have been shown to be beneficial in terms of conferring neuroprotection. The mechanisms by which flavonoids positively modulate cognitive function are yet to be fully elucidated. Postulated mechanisms include both direct actions such as receptor activation, neurotrophin release and intracellular signaling pathway modulation, and indirect actions such as enhancement of cerebral blood flow. Further intervention studies conducted in diverse populations with sufficient sample sizes and long durations are required to examine the effect of consumption of flavonoid groups on clinically relevant cognitive outcomes. As populations continue to focus on adopting healthy aging strategies, dietary interventions with flavonoids remains a promising avenue for future research. However, many questions are still to be answered, including identifying appropriate dosage, timeframes for intake, as well as the best form of flavonoids, before definitive conclusions can be drawn about the extent to which their consumption can protect the aging brain
Impurity corrections to the thermodynamics in spin chains using a transfer-matrix DMRG method
We use the density matrix renormalization group (DMRG) for transfer matrices
to numerically calculate impurity corrections to thermodynamic properties. The
method is applied to two impurity models in the spin-1/2 chain, namely a weak
link in the chain and an external impurity spin. The numerical analysis
confirms the field theory calculations and gives new results for the crossover
behavior.Comment: 9 pages in revtex format including 5 embedded figures (using epsf).
To appear in PRB. The latest version in PDF format can be found at
http://fy.chalmers.se/~eggert/papers/DMRGimp.pd
Differences Between Hole and Electron Doping of a Two-Leg CuO Ladder
Here we report results of a density-matrix-renormalization-group (DMRG)
calculation of the charge, spin, and pairing properties of a two-leg CuO
Hubbard ladder. The outer oxygen atoms as well as the rung and leg oxygen atoms
are included along with near-neighbor and oxygen-hopping matrix elements. This
system allows us to study the effects of hole and electron doping on a system
which is a charge transfer insulator at a filling of one hole per Cu and
exhibits power law, d-wave-like pairing correlations when doped. In particular,
we focus on the differences between doping with holes or electrons.Comment: REVTEX 4, 10 pages, 13 figure
Suppression of static stripe formation by next-neighbor hopping
We show from real-space Hartree-Fock calculations within the extended Hubbard
model that next-nearest neighbor (t') hopping processes act to suppress the
formation of static charge stripes. This result is confirmed by investigating
the evolution of charge-inhomogeneous corral and stripe phases with increasing
t' of both signs. We propose that large t' values in YBCO prevent static stripe
formation, while anomalously small t' in LSCO provides an additional reason for
the appearance of static stripes only in these systems.Comment: 4 pages, 5 figure
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