4,748 research outputs found
Mott transitions in two-orbital Hubbard systems
We investigate the Mott transitions in two-orbital Hubbard systems. Applying
the dynamical mean field theory and the self-energy functional approach, we
discuss the stability of itinerant quasi-particle states in each band. It is
shown that separate Mott transitions occur at different Coulomb interaction
strengths in general. On the other hand, if some special conditions are
satisfied for the interactions, spin and orbital fluctuations are equally
enhanced at low temperatures, resulting in a single Mott transition. The phase
diagrams are obtained at zero and finite temperatures. We also address the
effect of the hybridization between two orbitals, which induces the Kondo-like
heavy fermion states in the intermediate orbital-selective Mott phase.Comment: 21 Pages, 17 Figures, to appear in Progress of Theoretical Physics
(YKIS2004 Proceedings
Zero-temperature Phase Diagram of Two Dimensional Hubbard Model
We investigate the two-dimensional Hubbard model on the triangular lattice
with anisotropic hopping integrals at half filling. By means of a self-energy
functional approach, we discuss how stable the non-magnetic state is against
magnetically ordered states in the system. We present the zero-temperature
phase diagram, where the normal metallic state competes with magnetically
ordered states with and structures. It is shown
that a non-magnetic Mott insulating state is not realized as the ground state,
in the present framework, but as a meta-stable state near the magnetically
ordered phase with structure.Comment: 4 pages, 4 figure
Finite-temperature Mott transitions in multi-orbital Hubbard model
We investigate the Mott transitions in the multi-orbital Hubbard model at
half-filling by means of the self-energy functional approach. The phase
diagrams are obtained at finite temperatures for the Hubbard model with up to
four-fold degenerate bands. We discuss how the first-order Mott transition
points and as well as the critical temperature depend
on the orbital degeneracy. It is elucidated that enhanced orbital fluctuations
play a key role to control the Mott transitions in the multi-orbital Hubbard
model.Comment: 8 pages, 7 figure
Role of infrainguinal bypass in Buerger's disease: An eighteen-year experience
Objectives:The role of bypass to the distal arteries for patients with Buerger's disease (thromboangiitis or TAO) remains controversial because of the high incidence of graft failure. We retrospectively reviewed the results of 71 bypasses to evaluate their efficacy.Materials and methods:We performed 71 autogenous vein bypasses in 61 patients with TAO. Of the patients, 97% were heavy smokers. The indications for surgery were claudication in 41%, and ischaemic ulcer or gangrene in 59%. Of the bypasses 85% were to the crural arteries or to the arteries below the ankle. The grafts used were 53 single saphenous veins, and 18 venovenous composite grafts.Results:There were 38 graft failures, the main causes including anastomosis to a diseased artery, disease progression (which occurred in smokers after surgery), and vein graft stenosis. Of 38, 10 were restored to patency by revision surgery. Primary and secondary patency rates were 48.8% and 62.5% at 5 years, and 43.0% and 56.3% at 10 years, respectively. The patency rates of the postoperative non-smoking group was significantly higher than that of the smoking group (66.8% vs. 34.7%, p < 0.05). Thirty-six patients (59%) had successful revascularisation and returned to full-time work. However, of 28 with secondary failure, 11 underwent amputation, while 14 had persistent disabling claudication.Conclusion:Bypass to the distal arteries is an effective treatment for TAO patients, and the long-term patency is quite satisfactory as long as patients stop smoking
An antigen-independent contact mechanism as an early step in T cell-proliferative responses to dendritic cells.
The administration ofan antigen to the immune system can lead to the selection and expansion of clones precommitted to respond to that antigen. Antigens are not presented directly to T lymphocytes. Instead, antigens are processed and complexed to transmembrane products of genes in the MHC. The antigen-MHC complexes then are presented on the surface of APC (1-4). How might antigen-MHC complexes on the surface ofAPC find and select clones of T cells that are specific to that antigen, since neither the ligand nor the TCR are free to diffuse in solution? Also, the amount of peptide/MHC complex and the frequency of antigen-specificTcell clones both may be small. Nonetheless, it is evident that antigens on dendritic cells are capable of selecting specificTlymphocytes from a pool of lymphocytes in culture. For example, on the first day of a primary MLR, most of the antigen-specific T cells have formed clusters with dendritic cells (5, 6). The clustered lymphocytes then proliferate and release lymphokines. The specificity of the dendriticT cell binding is evident by the facts that (a) the nonclustered population is selectively depleted of antigen-reactive T cells; and (b) th
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