Star Unfolding Convex Polyhedra via Quasigeodesic Loops

We extend the notion of star unfolding to be based on a quasigeodesic loop Q rather than on a point. This gives a new general method to unfold the surface of any convex polyhedron P to a simple (non-overlapping), planar polygon: cut along one shortest path from each vertex of P to Q, and cut all but one segment of Q.Comment: 10 pages, 7 figures. v2 improves the description of cut locus, and adds references. v3 improves two figures and their captions. New version v4 offers a completely different proof of non-overlap in the quasigeodesic loop case, and contains several other substantive improvements. This version is 23 pages long, with 15 figure

Colossal magnetooptical conductivity in doped manganites

We show that the current carrier density collapse in doped manganites, which results from bipolaron formation in the paramagnetic phase, leads to a colossal change of the optical conductivity in an external magnetic field at temperatures close to the ferromagnetic transition. As with the colossal magnetoresistance (CMR) itself, the corresponding magnetooptical effect is explained by the dissociation of localized bipolarons into mobile polarons owing to the exchange interaction with the localized Mn spins in the ferromagnetic phase. The effect is positive at low frequencies and negative in the high-frequency region. The present results agree with available experimental observations.Comment: 4 pages, REVTeX 3.0, two eps-figures included in the tex

Autoantibodies to adenozine deaminase as marker of immunological disorders in systemic lupus erythematosus

Conferinţa naţională în medicina internă din Republica Moldova cu participare internaţională, 19-20 mai 2011, Chişinău, Republica MoldovaObjectives. The autoantibodies to various enzymes are often found out in sera of systemic lupus erythematosus (SLE) patients, but clinical value of such antibodies often is not understood. Purpose. The purpose of work was to study the of antibodies generation to the basic enzyme of purine metabolism – Adenozine Deaminase (ADA) in SLE and to reveal the relationship of studied antibodies with clinical and laboratory features of pathological process. Methods. 30 healthy persons have been included in our study and 71 SLE patients (66 women and 5 men) with various clinical signs (44 persons had 1st degree of disease activity, 27 persons – 2nd degree of pathological process activity). 18 women had habitual noncarrying of pregnancy (HNP) in anamnesis. Antibodies of IgG class to ADA (anti- ADA) determined by technique of indirect ELISA developed by us with the use of immobilized form of ADA as an antigenic matrix. β2-glicoprotein-I-dependent antiphospholipids (aPhL) of IgG and IgМ classes were determined using commercial „Anti- Phospholipid Screen IgG/IgM” test set (Orgentec Diagnostica). Results. At admission an anti-ADA was revealed in 36,6%, aPhL of IgG class – in 45,1%, and aPhL of IgМ class – in 23 (32,4%) SLE patients. It has been noted that IgG- aPhL were found out in anti-ADA-positive patients more often and in higher antibody titer, than in anti-ADA-negative SLE patients (χ2 =6,4; р <0,02). Development of cytopenic syndrome was noted reliable more often in SLE patients with associated presence of IgGaPhL and an anti-ADA in comparison with patients who has not the combinations of these antibodies in blood (χ2 = 3,9; р <0,05). The increased levels of anti-ADA were revealed in 11 of 18 women with HNP, and the combination of anti-ADA and aPhL (9/18) was found out more often than isolated anti-ADA (2/18, χ2 =6,5; р <0,02) or isolated aPhL (3/18, χ2 =4,5; р <0,05). Conclusion. Taking into account the imbalance of immunoregulatory functions in SLE, the further studying of autoantibodies to ADA generation seems to be very promising. Presence of HNP in anamnesis is the evidence of necessity of careful biochemical monitoring of aPhL and anti-ADA in women for the prevention of abortus fetus and administration of adequate therapy

Semiclassical action based on dynamical mean-field theory describing electrons interacting with local lattice fluctuations

We extend a recently introduced semiclassical approach to calculating the influence of local lattice fluctuations on electronic properties of metals and metallic molecular crystals. The effective action of electrons in degenerate orbital states coupling to Jahn-Teller distortions is derived, employing dynamical mean-field theory and adiabatic expansions. We improve on previous numerical treatments of the semiclassical action and present for the simplifying Holstein model results for the finite temperature optical conductivity at electron-phonon coupling strengths from weak to strong. Significant transfer of spectral weight from high to low frequencies is obtained on isotope substitution in the Fermi-liquid to polaron crossover regime.Comment: 10 pages, 7 figure

Semiclassical approach to calculating the influence of local lattice fluctuations on electronic properties of metals

We propose a new semiclassical approach based on the dynamical mean field theory to treat the interactions of electrons with local lattice fluctuations. In this approach the classical (static) phonon modes are treated exactly whereas the quantum (dynamical) modes are expanded to second order and give rise to an effective semiclassical potential. We determine the limits of validity of the approximation, and demonstrate its usefulness by calculating the temperature dependent resistivity in the Fermi liquid to polaron crossover regime (leading to `saturation behavior') and also isotope effects on electronic properties including the spectral function, resistivity, and optical conductivity, problems beyond the scope of conventional diagrammatic perturbation theories.Comment: 11 pages, 7 figure

Magnetic field - temperature phase diagram of quasi-two-dimensional organic superconductor lambda-(BETS)_2 GaCl_4 studied via thermal conductivity

The thermal conductivity kappa of the quasi-two-dimensional (Q2D) organic superconductor lambda-(BETS)_2 GaCl_4 was studied in the magnetic field H applied parallel to the Q2D plane. The phase diagram determined from this bulk measurement shows notable dependence on the sample quality. In dirty samples the upper critical field H_{c2} is consistent with the Pauli paramagnetic limiting, and a sharp change is observed in kappa(H) at H_{c2 parallel}. In contrast in clean samples H_{c2}(T) shows no saturation towards low temperatures and the feature in kappa(H) is replaced by two slope changes reminiscent of second-order transitions. The peculiarity was observed below ~ 0.33T_c and disappeared on field inclination to the plane when the orbital suppression of superconductivity became dominant. This behavior is consistent with the formation of a superconducting state with spatially modulated order parameter in clean samples.Comment: 10 pages, 8 figures, new figure (Fig.5) and references added, title change

Challenges of Matrix Models

Brief review of concepts and unsolved problems in the theory of matrix models.Comment: Contribution to Proceedings of Cargese 200

Carrier relaxation, pseudogap, and superconducting gap in high-Tc cuprates: A Raman scattering study

We describe results of electronic Raman-scattering experiments in differently doped single crystals of Y-123 and Bi-2212. The comparison of AF insulating and metallic samples suggests that at least the low-energy part of the spectra originates predominantly from excitations of free carriers. We therefore propose an analysis of the data in terms of a memory function approach. Dynamical scattering rates and mass-enhancement factors for the carriers are obtained. In B2g symmetry the Raman data compare well to the results obtained from ordinary and optical transport. For underdoped materials the dc scattering rates in B1g symmetry become temperature independent and considerably larger than in B2g symmetry. This increasing anisotropy is accompanied by a loss of spectral weight in B2g symmetry in the range between the superconducting transition at Tc and a characteristic temperature T* of order room temperature which compares well with the pseudogap temperature found in other experiments. The energy range affected by the pseudogap is doping and temperature independent. The integrated spectral loss is approximately 25% in underdoped samples and becomes much weaker towards higher carrier concentration. In underdoped samples, superconductivity related features in the spectra can be observed only in B2g symmetry. The peak frequencies scale with Tc. We do not find a direct relation between the pseudogap and the superconducting gap.Comment: RevTeX, 21 pages, 24 gif figures. For PostScript with embedded eps figures, see http://www.wmi.badw-muenchen.de/~opel/k2.htm