91 research outputs found
SU(\nu) Generalization of Twisted Haldane-Shastry Model
The SU() generalized Haldane-Shastry spin chain with interaction
is studied with twisted boundary conditions. The exact wavefunctions of Jastrow
type are obtained for every rational value of the twist angle in unit of
. The spectral flow of the ground state is then discussed as a function
of the twist angle. By resorting to the motif picture in the Bethe ansatz
method, we show that the period of the spectral flow is , which is
determined by the statistical interaction in exclusion statistics.Comment: 23 pages, revtex, To appear in Nucl. Phys.
Spectral flow in the supersymmetric - model with a interaction
The spectral flow in the supersymmetric {\it t-J} model with
interaction is studied by analyzing the exact spectrum with twisted boundary
conditions. The spectral flows for the charge and spin sectors are shown to
nicely fit in with the motif picture in the asymptotic Bethe ansatz. Although
fractional exclusion statistics for the spin sector clearly shows up in the
period of the spectral flow at half filling, such a property is generally
hidden once any number of holes are doped, because the commensurability
condition in the motif is not met in the metallic phase.Comment: 8 pages, revtex, Phys. Rev. B54 (1996) August 15, in pres
Low-Energy Properties of Regularly Depleted Spin Ladders
We investigate a model for the regularly depleted two-leg spin ladder
systems. By using Lieb-Schultz-Mattis theorem, it is rigorously shown that this
model realizes massless excitations or, alternatively, a degenerate ground
state, although the original spin ladder system has a spin gap and a unique
ground state. The ground state of the depleted model is either a spin singlet
or partially ferromagnetic reflecting topological properties of the depleted
sites. In order to show that the low-energy excitations are indeed massless, we
proceed our analysis in two different ways by resorting to effective field
theories. We first investigate an effective weak-coupling model in terms of
renormalization group methods. Although the tendency to massless spin
excitations is seen in the strong coupling regime, it turns out that the model
is still massive for any finite coupling, implying that a conventional
weak-coupling approach is not efficient to describe massless modes in our
model. To overcome this difficulty, we further study low-energy properties of
the depleted spin model by mapping on the non-linear sigma model, and confirm
that the massless spin excitation indeed occur.Comment: 13 pages, revtex, 7 figures, to appear in PRB. A new section is
added, in which we derived the spin-wave dispersion relation and analyzed the
quantum fluctuation around it by means of the O(3) nonlinear sigma mode
Elementary Excitations and Dynamical Correlation Functions of the Calogero-Sutherland Model with Internal Symmetry
We consider the physical properties of elementary excitations of the
Calogero-Sutherland (CS) model with SU(K) internal symmetry. From the results
on the thermodynamics of this model, we obtain the charge, spin, and statistics
of elementary excitations. Combining this knowledge and the known results on
the dynamics in the spinless CS model, we propose the expression for the
dynamical correlation functions of the SU(K) CS model. In the asymptotic
region, we confirm the consistency of our results with predictions from
conformal field theory.Comment: 22 pages, REVTe
Physics and Mathematics of Calogero particles
We give a review of the mathematical and physical properties of the
celebrated family of Calogero-like models and related spin chains.Comment: Version to appear in Special Issue of Journal of Physics A:
Mathematical and Genera
Extended Aharonov-Bohm period analysis of strongly correlated electron systems
The `extended Aharonov-Bohm (AB) period' recently proposed by Kusakabe and
Aoki [J. Phys. Soc. Jpn (65), 2772 (1996)] is extensively studied numerically
for finite size systems of strongly correlated electrons. While the extended AB
period is the system length times the flux quantum for noninteracting systems,
we have found the existence of the boundary across which the period is halved
or another boundary into an even shorter period on the phase diagram for these
models. If we compare this result with the phase diagram predicted from the
Tomonaga-Luttinger theory, devised for low-energy physics, the halved period
(or shorter periods) has a one-to-one correspondence to the existence of the
pairing (phase separation or metal-insulator transition) in these models. We
have also found for the t-J model that the extended AB period does not change
across the integrable-nonintegrable boundary despite the totally different
level statistics.Comment: 26 pages, RevTex, 16 figures available on request from
[email protected], to be published in J. Phys. Soc. Jpn 66 No.
7(1997), We disscus the extended AB period of strongly correlated systems
more systematically by performing numerical calculation for the t-J-J' model
and the extended Hubbard model in addition to the 1D t-J model and the t-J
ladde
Symmetry and Topology in Superconductors - Odd-frequency pairing and edge states -
Superconductivity is a phenomenon where the macroscopic quantum coherence
appears due to the pairing of electrons. This offers a fascinating arena to
study the physics of broken gauge symmetry. However, the important symmetries
in superconductors are not only the gauge invariance. Especially, the symmetry
properties of the pairing, i.e., the parity and spin-singlet/spin-triplet,
determine the physical properties of the superconducting state. Recently it has
been recognized that there is the important third symmetry of the pair
amplitude, i.e., even or odd parity with respect to the frequency. The
conventional uniform superconducting states correspond to the even-frequency
pairing, but the recent finding is that the odd-frequency pair amplitude arises
in the spatially non-uniform situation quite ubiquitously. Especially, this is
the case in the Andreev bound state (ABS) appearing at the surface/interface of
the sample. The other important recent development is on the nontrivial
topological aspects of superconductors. As the band insulators are classified
by topological indices into (i) conventional insulator, (ii) quantum Hall
insulator, and (iii) topological insulator, also are the gapped
superconductors. The influence of the nontrivial topology of the bulk states
appears as the edge or surface of the sample. In the superconductors, this
leads to the formation of zero energy ABS (ZEABS). Therefore, the ABSs of the
superconductors are the place where the symmetry and topology meet each other
which offer the stage of rich physics. In this review, we discuss the physics
of ABS from the viewpoint of the odd-frequency pairing, the topological
bulk-edge correspondence, and the interplay of these two issues. It is
described how the symmetry of the pairing and topological indices determines
the absence/presence of the ZEABS, its energy dispersion, and properties as the
Majorana fermions.Comment: 91 pages, 38 figures, Review article, references adde
Expression and biological-clinical significance of hTR, hTERT and CKS2 in washing fluids of patients with bladder cancer
<p>Abstract</p> <p>Background</p> <p>at present, pathogenesis of bladder cancer (BC) has not been fully elucidated. Aim of this study is to investigate the role of human telomerase RNA (<it>hTR</it>), human telomerase reverse transcriptase (<it>hTERT</it>) and CDC28 protein kinase regulatory subunit 2 (<it>CKS2</it>) in bladder carcinogenesis and their possible clinical significance;</p> <p>Methods</p> <p>the transcript levels of <it>hTR</it>, <it>hTERT </it>and <it>CKS2 </it>were quantified by Real time reverse transcriptase chain reaction in exfoliated cells from bladder washings of 36 patients with BC and 58 controls. The statistical significance of differences between BC bearing patients and control groups, in the general as well as in the stratified analysis (superficial or invasive BC), was assessed by Student's t test. Non parametric Receiver Operating Characteristics analysis (ROC) was performed to ascertain the accuracy of study variables to discriminate between BC and controls. The clinical value of concomitant examination of <it>hTR</it>, <it>hTERT </it>and <it>CKS2 </it>was evaluated by logistic regression analysis;</p> <p>Results</p> <p>a significant decrease in <it>hTR </it>and a significant increase in <it>hTERT </it>or <it>CKS2 </it>gene expression were found between BC bearing patients and controls, as well as in the subgroups analysis. The area under the curve (AUC) indicated an average discrimination power for the three genes, both in the general and subgroups analysis, when singularly considered. The ability to significantly discriminate between superficial and invasive BC was observed only for <it>hTR </it>transcript levels. A combined model including <it>hTR </it>and <it>CKS2 </it>was the best one in BC diagnosis;</p> <p>Conclusions</p> <p>our results, obtained from a sample set particularly rich of exfoliated cells, provide further molecular evidence on the involvement of <it>hTR, hTERT </it>and <it>CKS2 </it>gene expression in BC carcinogenesis. In particular, while <it>hTERT </it>and <it>CKS2 </it>gene expression seems to have a major involvement in the early stages of the disease, <it>hTR </it>gene expression, seems to be more involved in progression. In addition, our findings suggest that the studied genes have a clinical role in discriminating between BC and controls in the general as well as in the stratified analysis, when singularly considered. A combined model improved over the single marker BC diagnosis.</p
Why Are Outcomes Different for Registry Patients Enrolled Prospectively and Retrospectively? Insights from the Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF).
Background: Retrospective and prospective observational studies are designed to reflect real-world evidence on clinical practice, but can yield conflicting results. The GARFIELD-AF Registry includes both methods of enrolment and allows analysis of differences in patient characteristics and outcomes that may result. Methods and Results: Patients with atrial fibrillation (AF) and ≥1 risk factor for stroke at diagnosis of AF were recruited either retrospectively (n = 5069) or prospectively (n = 5501) from 19 countries and then followed prospectively. The retrospectively enrolled cohort comprised patients with established AF (for a least 6, and up to 24 months before enrolment), who were identified retrospectively (and baseline and partial follow-up data were collected from the emedical records) and then followed prospectively between 0-18 months (such that the total time of follow-up was 24 months; data collection Dec-2009 and Oct-2010). In the prospectively enrolled cohort, patients with newly diagnosed AF (≤6 weeks after diagnosis) were recruited between Mar-2010 and Oct-2011 and were followed for 24 months after enrolment. Differences between the cohorts were observed in clinical characteristics, including type of AF, stroke prevention strategies, and event rates. More patients in the retrospectively identified cohort received vitamin K antagonists (62.1% vs. 53.2%) and fewer received non-vitamin K oral anticoagulants (1.8% vs . 4.2%). All-cause mortality rates per 100 person-years during the prospective follow-up (starting the first study visit up to 1 year) were significantly lower in the retrospective than prospectively identified cohort (3.04 [95% CI 2.51 to 3.67] vs . 4.05 [95% CI 3.53 to 4.63]; p = 0.016). Conclusions: Interpretations of data from registries that aim to evaluate the characteristics and outcomes of patients with AF must take account of differences in registry design and the impact of recall bias and survivorship bias that is incurred with retrospective enrolment. Clinical Trial Registration: - URL: http://www.clinicaltrials.gov . Unique identifier for GARFIELD-AF (NCT01090362)
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