1,852 research outputs found
Critical behavior of the S=3/2 antiferromagnetic Heisenberg chain
Using the density-matrix renormalization-group technique we study the
long-wavelength properties of the spin S=3/2 nearest-neighbor Heisenberg chain.
We obtain an accurate value for the spin velocity v=3.8+- 0.02, in agreement
with experiment. Our results show conclusively that the model belongs to the
same universality class as the S=1/2 Heisenberg chain, with a conformal central
charge c=1 and critical exponent eta=1Comment: RevTeX (version 3.0), 4 twocolumn pages with 4 embedded figure
Spin-charge separation in Aharonov-Bohm rings of interacting electrons
We investigate the properties of strongly correlated electronic models on a
flux-threaded ring connected to semi-infinite free-electron leads. The
interference pattern of such an Aharonov-Bohm ring shows sharp dips at certain
flux values, determined by the filling, which are a consequence of spin-charge
separation in a nanoscopic system.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let
Spin-spin correlations between two Kondo impurities coupled to an open Hubbard chain
In order to study the interplay between Kondo and
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, we calculate the spin-spin
correlation functions between two Kondo impurities coupled to different sites
of a half-filled open Hubbard chain. Using the density-matrix renormalization
group (DMRG), we re-examine the exponents for the power-law decay of the
correlation function between the two impurity spins as a function of the
antiferromagnetic coupling J, the Hubbard interaction U, and the distance R
between the impurities. The exponents for finite systems obtained in this work
deviate from previously published DMRG calculations. We furthermore show that
the long-distance behavior of the exponents is the same for impurities coupled
to the bulk or to both ends of the chain. We note that a universal exponent for
the asymptotic behavior cannot be extracted from these finite-size systems with
open boundary conditions.Comment: 8 pages, 10 figures; v2: final version, references and Fig. 8 adde
Spin-charge separation in strongly interacting finite ladder rings
We study the conductance through Aharonov-Bohm finite ladder rings with
strongly interacting electrons, modelled by the prototypical t-J model. For a
wide range of parameters we observe characteristic dips in the conductance as a
function of magnetic flux, predicted so far only in chains which are a
signature of spin and charge separation. These results open the possibility of
observing this peculiar many-body phenomenon in anisotropic ladder systems and
in real nanoscopic devices.Comment: 4 pages, 6 figure
Detection of topological transitions by transport through molecules and nanodevices
We analyze the phase transitions of an interacting electronic system weakly
coupled to free-electron leads by considering its zero-bias conductance. This
is expressed in terms of two effective impurity models for the cases with and
without spin degeneracy. We demonstrate using the half-filled ionic Hubbard
ring that the weight of the first conductance peak as a function of external
flux or of the difference in gate voltages between even and odd sites allows
one to identify the topological charge transition between a correlated
insulator and a band insulator.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
Spin order in the one-dimensional Kondo and Hund lattices
We study numerically the one-dimensional Kondo and Hund lattices consisting
of localized spins interacting antiferro or ferromagnetically with the
itinerant electrons, respectively. Using the Density Matrix Renormalization
Group we find, for both models and in the small coupling regime, the existence
of new magnetic phases where the local spins order forming ferromagnetic
islands coupled antiferromagnetically. Furthermore, by increasing the
interaction parameter we find that this order evolves toward the
ferromagnetic regime through a spiral-like phase with longer characteristic
wave lengths. These results shed new light on the zero temperature magnetic
phase diagram for these models.Comment: PRL, to appea
Estimation of Dietary Iron Bioavailability from Food Iron Intake and Iron Status
Currently there are no satisfactory methods for estimating dietary iron absorption (bioavailability) at a population level, but this is essential for deriving dietary reference values using the factorial approach. The aim of this work was to develop a novel approach for estimating dietary iron absorption using a population sample from a sub-section of the UK National Diet and Nutrition Survey (NDNS). Data were analyzed in 873 subjects from the 2000–2001 adult cohort of the NDNS, for whom both dietary intake data and hematological measures (hemoglobin and serum ferritin (SF) concentrations) were available. There were 495 men aged 19–64 y (mean age 42.7±12.1 y) and 378 pre-menopausal women (mean age 35.7±8.2 y). Individual dietary iron requirements were estimated using the Institute of Medicine calculations. A full probability approach was then applied to estimate the prevalence of dietary intakes that were insufficient to meet the needs of the men and women separately, based on their estimated daily iron intake and a series of absorption values ranging from 1–40%. The prevalence of SF concentrations below selected cut-off values (indicating that absorption was not high enough to maintain iron stores) was derived from individual SF concentrations. An estimate of dietary iron absorption required to maintain specified SF values was then calculated by matching the observed prevalence of insufficiency with the prevalence predicted for the series of absorption estimates. Mean daily dietary iron intakes were 13.5 mg for men and 9.8 mg for women. Mean calculated dietary absorption was 8% in men (50th percentile for SF 85 µg/L) and 17% in women (50th percentile for SF 38 µg/L). At a ferritin level of 45 µg/L estimated absorption was similar in men (14%) and women (13%). This new method can be used to calculate dietary iron absorption at a population level using data describing total iron intake and SF concentration
Repeatability and reproducibility of applanation resonance tonometry: a cross-sectional study
Long-term effects of a novel continuous remote care intervention including nutritional ketosis for the management of type 2 diabetes: A 2-year non-randomized clinical trial
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