1,074 research outputs found
Tunnelling matrix elements with antiferromagnetic Gutzwiller wave functions
We use a generalized Gutzwiller Approximation (GA) elaborated to evaluate
matrix elements with partially projected wave functions and formerly applied to
homogeneous systems.
In the present paper we consider projected single-particle (hole) excitations
for electronic systems with antiferromagnetic (AFM) order and obtain the
corresponding tunnelling probabilities. The accuracy and the reliability of our
analytical approximation is tested using the Variational Monte Carlo (VMC).
Possible comparisons with experimental results are also discussed.Comment: 16 pages, 10 figure
Optical conductivity of the half-filled Hubbard chain
We combine well-controlled analytical and numerical methods to determine the
optical conductivity of the one-dimensional Mott-Hubbard insulator at zero
temperature. A dynamical density-matrix renormalization group method provides
the entire absorption spectrum for all but very small coupling strengths. In
this limit we calculate the conductivity analytically using exact
field-theoretical methods. Above the Lieb-Wu gap the conductivity exhibits a
characteristic square-root increase. For small to moderate interactions, a
sharp maximum occurs just above the gap. For larger interactions, another weak
feature becomes visible around the middle of the absorption band.Comment: 4 pages with 3 eps figures, published version (changes in text and
references
Excitons in one-dimensional Mott insulators
We employ dynamical density-matrix renormalization group (DDMRG) and
field-theory methods to determine the frequency-dependent optical conductivity
in one-dimensional extended, half-filled Hubbard models. The field-theory
approach is applicable to the regime of `small' Mott gaps which is the most
difficult to access by DDMRG. For very large Mott gaps the DDMRG recovers
analytical results obtained previously by means of strong-coupling techniques.
We focus on exciton formation at energies below the onset of the absorption
continuum. As a consequence of spin-charge separation, these Mott-Hubbard
excitons are bound states of spinless, charged excitations (`holon-antiholon'
pairs). We also determine exciton binding energies and sizes. In contrast to
simple band insulators, we observe that excitons exist in the Mott-insulating
phase only for a sufficiently strong intersite Coulomb repulsion. Furthermore,
our results show that the exciton binding energy and size are not related in a
simple way to the strength of the Coulomb interaction.Comment: 15 pages, 6 eps figures, corrected typos in labels of figures 4,5,
and
Exact analytic results for the Gutzwiller wave function with finite magnetization
We present analytic results for ground-state properties of Hubbard-type
models in terms of the Gutzwiller variational wave function with non-zero
values of the magnetization m. In dimension D=1 approximation-free evaluations
are made possible by appropriate canonical transformations and an analysis of
Umklapp processes. We calculate the double occupation and the momentum
distribution, as well as its discontinuity at the Fermi surface, for arbitrary
values of the interaction parameter g, density n, and magnetization m. These
quantities determine the expectation value of the one-dimensional Hubbard
Hamiltonian for any symmetric, monotonically increasing dispersion epsilon_k.
In particular for nearest-neighbor hopping and densities away from half filling
the Gutzwiller wave function is found to predict ferromagnetic behavior for
sufficiently large interaction U.Comment: REVTeX 4, 32 pages, 8 figure
Gender-related differences in patients presenting with suspected acute coronary syndromes: clinical presentation, biomarkers and diagnosis
Objectives: Gender differences in patients presenting with suspected acute coronary syndromes (ACS) have not yet been fully characterized. The aim of this study was to assess gender-related disparities in clinical profiles, biomarkers and diagnoses of patients with suspected ACS. Methods: This single-centre, prospective cohort study included 377 consecutive patients presenting with suspected ACS to the emergency department. Suspected ACS was defined as a request for conventional troponin T (c-cTnT) measurements on clinical grounds. Results: Women were older than men (p = 0.004), and had a lower prevalence of known coronary artery and peripheral vascular disease (p < 0.05). c-cTnT was positive in 8% of female and in 14% of male patients (p = 0.16), TIMI risk score and cardiac biomarkers including c-cTnT, hs-cTnT, myoglobin, creatine kinase, N-terminal pro-brain natriuretic peptide, myeloid-related protein 8/14 and pregnancy-associated plasma protein A were lower in women (p < 0.05). Women were less frequently diagnosed with ACS (30 vs. 51%), and were not referred for urgent coronary angiography as often as men (p < 0.001). In multivariate analysis, female gender was associated with a lower referral for coronary angiography (HR 0.41, 95% CI 0.23-0.78, p = 0.006). Conclusions: In patients with suspected ACS, women presented with different biomarker profiles, and were less often diagnosed with ACS and referred to coronary angiography
Exact Solution of the strong coupling t-V model with twisted boundary conditions
We present the solution of the one-dimensional t-V model with twisted
boundary conditions in the strong coupling limit, t<<V and show that this model
can be mapped onto the strong coupling Hubbard chain threaded by a fictitious
flux proportional to the total momentum of the charge carriers. The high energy
eigenstates are characterized by a factorization of degrees of freedom
associated with configurations of soliton and antisoliton domains and degrees
of freedom associated with the movement of ``holes'' through these domains. The
coexistence of solitons and antisolitons leads to a strange flux dependence of
the eigenvalues. We illustrate the use of this solution, deriving the full
frequency dependence of the optical conductivity at half-filling and zero
temperature.Comment: 11 pages, 1 figure; to be published in Physical Review
Spectrum and Thermodynamics of the one-dimensional supersymmetric t-J model with exchange and hopping
We derive the spectrum and the thermodynamics of the one-dimensional
supersymmetric t-J model with long range hopping and spin exchange using a set
of maximal-spin eigenstates. This spectrum confirms the recent conjecture that
the asymptotic Bethe-ansatz spectrum is exact. By empirical determining the
spinon degeneracies of each state, we are able to explicitly construct the free
energy.Comment: 13 pages, Latex, (published in PRB46, 6639 (1992)
Two-particle photoemission from strongly correlated systems: A dynamical-mean field approach
We study theoretically the simultaneous, photo-induced two-particle
excitations of strongly correlated systems on the basis of the Hubbard model.
Under certain conditions specified in this work, the corre- sponding transition
probability is related to the two-particle spectral function which we calculate
using three different methods: the dynamical-mean field theory combined with
quantum Monte Carlo (DMFT- QMC) technique, the first order perturbation theory
and the ladder approximations. The results are analyzed and compared for
systems at the verge of the metal-insulator transitions. The dependencies on
the electronic correlation strength and on doping are explored. In addition,
the account for the orbital degeneracy allows an insight into the influence of
interband correlations on the two particle excitations. A suitable experimental
realization is discussed.Comment: 25 pp, 10 figs. to be published in PR
The basophil activation test differentiates between patients with wheat-dependent exercise-induced anaphylaxis and control subjects using gluten and isolated gluten protein types
Background: Oral food challenge using gluten and cofactors is the gold standard to diagnose wheat-dependent exercise-induced anaphylaxis (WDEIA), but this procedure puts patients at risk of an anaphylactic reaction. Specific IgE to ω5-gliadins as major allergens and skin prick tests to wheat may yield negative results. Thus, we designed a proof-of-principle study to investigate the utility of the basophil activation test (BAT) for WDEIA diagnosis. Methods: Different gluten protein types (GPT; α-, γ-, ω1,2- and ω5-gliadins, high-molecular-weight glutenin subunits [HMW-GS] and low-molecular-weight glutenin subunits [LMW-GS]) and gluten were used in different concentrations to measure basophil activation in 12 challenge-confirmed WDEIA patients and 10 control subjects. The results were compared to routine allergy diagnostics. Parameters analyzed include the percentage of CD63+ basophils, the ratio of %CD63+ basophils induced by GPT/gluten to %CD63+ basophils induced by anti-FcεRI antibody, area under the dose-response curve and test sensitivity and specificity. Results: GPT and gluten induced strong basophil activation for %CD63+ basophils and for %CD63+/anti-FcɛRI ratio in a dose-dependent manner in patients, but not in controls (p < 0.001, respectively). BAT performance differed from acceptable (0.73 for LMW-GS) to excellent (0.91 for ω5-gliadins) depending on the specific GPT as evaluated by the area under the receiver operating characteristic curve. Patients showed individual sensitization profiles. After determination of the best cut-off points, ω5-gliadins and HMW-GS showed the best discrimination between patients and controls with a sensitivity/specificity of 100/70 and 75/100, respectively. Conclusion: This study shows the alternative role of BAT in better defining WDEIA and the causative wheat allergens. The best BAT parameters to distinguish WDEIA patients from controls were %CD63+ basophil values for ω5-gliadins and HMW-GS
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