3,884 research outputs found
Magnetic and Transport Properties of a Coupled Hubbard Bilayer with Electron and Hole Doping
The single band, two dimensional Hubbard Hamiltonian has been extensively
studied as a model for high temperature superconductivity. While Quantum Monte
Carlo simulations within the dynamic cluster approximation are now providing
considerable evidence for a d-wave superconducting state at low temperature,
such a transition remains well out of reach of finite lattice simulations
because of the "sign problem". We show here that a bilayer Hubbard model, in
which one layer is electron doped and one layer is hole doped, can be studied
to lower temperatures and exhibits an interesting signal of d-wave pairing. The
results of our simulations bear resemblance to a recent report on the magnetic
and superconducting properties of BaCaCuOF which contains
both electron and hole doped CuO planes. We also explore the phase diagram
of bilayer models in which each sheet is at half-filling
Quantum Monte Carlo Study of an Interaction-Driven Band Insulator to Metal Transition
We study the transitions from band insulator to metal to Mott insulator in
the ionic Hubbard model on a two dimensional square lattice using determinant
Quantum Monte Carlo. Evaluation of the temperature dependence of the
conductivity demonstrates that the metallic region extends for a finite range
of interaction values. The Mott phase at strong coupling is accompanied by
antiferromagnetic (AF) order. Inclusion of these intersite correlations changes
the phase diagram qualitatively compared to dynamical mean field theory.Comment: 4 pages, 6 figure
Attractive Hubbard Model on a Honeycomb Lattice
We study the attractive fermionic Hubbard model on a honeycomb lattice using
determinantal quantum Monte Carlo simulations. By increasing the interaction
strength U (relative to the hopping parameter t) at half-filling and zero
temperature, the system undergoes a quantum phase transition at 5.0 < U_c/t <
5.1 from a semi-metal to a phase displaying simultaneously superfluid behavior
and density order. Doping away from half-filling, and increasing the
interaction strength at finite but low temperature T, the system always appears
to be a superfluid exhibiting a crossover between a BCS and a molecular regime.
These different regimes are analyzed by studying the spectral function. The
formation of pairs and the emergence of phase coherence throughout the sample
are studied as U is increased and T is lowered
Depletion induced isotropic-isotropic phase separation in suspensions of rod-like colloids
When non-adsorbing polymers are added to an isotropic suspension of rod-like
colloids, the colloids effectively attract each other via depletion forces. We
performed Monte Carlo simulations to study the phase diagram of such
rod-polymer mixture. The colloidal rods were modelled as hard spherocylinders;
the polymers were described as spheres of the same diameter as the rods. The
polymers may overlap with no energy cost, while overlap of polymers and rods is
forbidden.
Large amounts of depletant cause phase separation of the mixture. We
estimated the phase boundaries of isotropic-isotropic coexistence both, in the
bulk and in confinement. To determine the phase boundaries we applied the grand
canonical ensemble using successive umbrella sampling [J. Chem. Phys. 120,
10925 (2004)], and we performed a finite-size scaling analysis to estimate the
location of the critical point. The results are compared with predictions of
the free volume theory developed by Lekkerkerker and Stroobants [Nuovo Cimento
D 16, 949 (1994)]. We also give estimates for the interfacial tension between
the coexisting isotropic phases and analyse its power-law behaviour on approach
of the critical point
Australian Sphingidae â DNA Barcodes Challenge Current Species Boundaries and Distributions
Š 2014 Rougerie et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article
Selective substitution in orbital domains of a low doped manganite : an investigation from Griffiths phenomenon and modification of glassy features
An effort is made to study the contrast in magnetic behavior resulting from
minimal disorder introduced by substitution of 2.5% Ga or Al in Mn-site of
LaSrMnO. It is considered that Ga or Al selectively
creates disorder within the orbital domains or on its walls, causing
enhancement of Griffiths phase (GP) singularity for the former and
disappearance of it in the later case. It is shown that Ga replaces Mn
which is considered to be concentrated within the domains, whereas Al replaces
Mn which is segregated on the hole-rich walls, without causing any
significant effect on structure or ferromagnetic transition temperatures. Thus,
it is presumed that the effect of disorder created by Ga extend across the bulk
of the domain having correlation over similar length-scale resulting in
enhancement of GP phenomenon. On the contrary, effect of disorder created by Al
remains restricted to the walls resulting in the modification of the dynamics
arising from the domain walls and suppresses the GP. Moreover contrasting
features are observed in the low temperature region of the compounds; a
re-entrant spin glass like behavior is observed in the Ga doped sample, while
the observed characteristics for the Al doped sample is ascribed only to
modified domain wall dynamics with the absence of any glassy phase. Distinctive
features in third order susceptibility measurements reveals that the magnetic
ground state of the entire series comprises of orbital domain states. These
observations bring out the role of the nature of disorder on GP phenomenon and
also reconfirms the character of self-organization in low-doped manganites
U.S. adolescent and adult women\u27s experiences accessing and using toilets in schools, workplaces, and public spaces: A multi-site focus group study to inform future research in bladder health
The World Health Organization recognizes access to clean and safe toilets as crucial for public health. This study explored U.S. adolescent and adult cisgender women\u27s lived experiences accessing toilets in schools, workplaces, and public spaces. As part of the Prevention of Lower Urinary Tract Symptoms (PLUS) Research Consortium, we conducted 44 focus groups with female participants (n = 360; ages 11-93). Focus groups were stratified by age (11-14, 15-17, 18-25, 26-44, 45-64, 65+) and conducted across 7 geographically diverse U.S. sites from July 2017-April 2018. Using a transdisciplinary approach, we conducted conventional qualitative coding informed by our PLUS conceptual framework and used content analysis processes to identify salient themes. Across settings, toilet access was restricted by gatekeepers (i.e., individuals who control access to toilets). In contrast, self-restricting toilet use (deciding not to use the toilet despite biologic need to urinate) was based on internalized norms to prioritize school and job responsibilities over urination. In public spaces, self-restricting use was largely in response to lack of cleanliness. Across the life course, participants perceived gender disparities in the ability to easily access public toilets. Further research is needed to determine if and how these factors impact bladder health across the life course
Experimental Limit on the Cosmic Diffuse Ultra-high Energy Neutrino Flux
We report results from 120 hours of livetime with the Goldstone Lunar
Ultra-high energy neutrino Experiment (GLUE). The experiment searches for <10
ns microwave pulses from the lunar regolith, appearing in coincidence at two
large radio telescopes separated by 22 km and linked by optical fiber. Such
pulses would arise from subsurface electromagnetic cascades induced by
interactions of >= 100 EeV neutrinos in the lunar regolith. No candidates are
yet seen, and the implied limits constrain several current models for
ultra-high energy neutrino fluxes.Comment: 4 pages, 4 figures, revtex4 style. New intro section, Fig. 2, Fig 4;
in final PRL revie
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Carbon and nitrogen isotopic ratios of urine and faeces as novel nutritional biomarkers of meat and fish intake
Purpose
Meat and fish consumption are associated with changes in the risk of chronic diseases. Intake is mainly assessed using self-reporting, as no true quantitative nutritional biomarker is available. The measurement of plasma fatty acids, often used as an alternative, is expensive and time-consuming. As meat and fish differ in their stable isotope ratios, δ13C and δ15N have been proposed as biomarkers. However, they have never been investigated in controlled human dietary intervention studies.
Objective
In a short-term feeding study, we investigated the suitability of δ13C and δ15N in blood, urine and faeces as biomarkers of meat and fish intake.
Methods
The dietary intervention study (n = 14) followed a randomised cross-over design with three eight-day dietary periods (meat, fish and half-meatâhalf-fish). In addition, 4 participants completed a vegetarian control period. At the end of each period, 24-h urine, fasting venous blood and faeces were collected and their δ13C and δ15N analysed.
Results
There was a significant difference between diets in isotope ratios in faeces and urine samples, but not in blood samples (KruskalâWallis test, p < 0.0001). In pairwise comparisons, δ13C and δ15N were significantly higher in urine and faecal samples following a fish diet when compared with all other diets, and significantly lower following a vegetarian diet. There was no significant difference in isotope ratio between meat and half-meatâhalf-fish diets for blood, urine or faecal samples.
Conclusions
The results of this study show that urinary and faecal δ13C and δ15N are suitable candidate biomarkers for short-term meat and fish intake
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