Contemporary Methods of Treating Children with Autoimmune Nephric Diseases

The review is dedicated to the analysis of contemporary therapies and efficacy thereof for treating children autoimmune nephric diseases. The authors describe peculiarities of using the conventional therapy in children and discuss alternative treatments using cyclosporine, tacrolimus, budesonide and ursodeoxycholic acid, as well as the need in using the second-line drugs for treating patients with resistant autoimmune nephric diseases. The review touches upon the promising approaches to the treatment of this category of patients

Effective action for Superconductors and BCS-Bose crossover

A standard perturbative expansion around the mean-field solution is used to derive the low-energy effective action for superconductors at T=0. Taking into account the density fluctuations at the outset we get the effective action where the density $\rho$ is the conjugated momentum to the phase $\theta$ of the order parameter. In the hydrodynamic regime, the dynamics of the superconductor is described by a time dependent non-linear Schr\"odinger equation (TDNLS) for the field $\Psi(x)=\sqrt{\rho/2} e^{i\theta}$. The evolution of the density fluctuations in the crossover from weak-coupling (BCS) to strong-coupling (Bose condensation of localized pairs) superconductivity is discussed for the attractive Hubbard model. In the bosonic limit, the TDNLS equation reduces to the the Gross-Pitaevskii equation for the order parameter, as in the standard description of superfluidity. The conditions under which a phase-only action can be derived in the presence of a long-range interaction to describe the physics of the superconductivity of ``bad metals'' are discussed.Comment: 13 pages, accepted for publication on Phys. Rev.

Современные методы лечения детей с аутоиммунными заболеваниями печени

The review is dedicated to the analysis of contemporary therapies and efficacy thereof for treating children autoimmune nephric diseases. The authors describe peculiarities of using the conventional therapy in children and discuss alternative treatments using cyclosporine, tacrolimus, budesonide and ursodeoxycholic acid, as well as the need in using the second-line drugs for treating patients with resistant autoimmune nephric diseases. The review touches upon the promising approaches to the treatment of this category of patients. В обзоре проанализированы современные схемы терапии и их эффективность у детей с аутоиммунными заболеваниями печени. Описаны особенности применения стандартного режима терапии у детей, рассмотрены альтернативные схемы лечения с использованием циклоспорина, такролимуса, будесонида и урсодезоксихолевой кислоты, а также необходимость применения препаратов второй линии для лечения больных с резистентными случаями аутоиммунных заболеваний печени. Освещены перспективные направления лечения этой категории больных.

Real space inhomogeneities in high temperature superconductors: the perspective of two-component model

The two-component model of high temperature superconductors in its real space version has been solved using Bogoliubov-de Gennes equations. The disorder in the electron and boson subsystem has been taken into account. It strongly modifies the superconducting properties and leads to local variations of the gap parameter and density of states. The assumption that the impurities mainly modify boson energies offers natural explanation of the puzzling positive correlation between the positions of impurities and the values of the order parameter found in the scanning tunnelling microscopy experiments.Comment: 19 pages, IOPP style include

Berezinskii-Kosterlitz-Thouless transition and BCS-Bose crossover in the two-dimensional attractive Hubbard model

We study the two-dimensional attractive Hubbard model using the mapping onto the half-filled repulsive Hubbard model in a uniform magnetic field coupled to the fermion spins. The low-energy effective action for charge and pairing fluctuations is obtained in the hydrodynamic regime. We recover the action of a Bose superfluid where half the fermion density is identified as the conjugate variable of the phase of the superconducting order parameter. By integrating out charge fluctuations, we obtain a phase-only action. In the zero-temperature superconducting state, this action describes a collective phase mode smoothly evolving from the Anderson-Bogoliubov mode at weak coupling to the Bogoliubov mode of a Bose superfluid at strong coupling. At finite temperature, the phase-only action can be used to extract an effective XY model and thus obtain the Berezinskii-Kosterlitz-Thouless (BKT) phase transition temperature. We also identify a renormalized classical regime of superconducting fluctuations above the BKT phase transition, and a regime of incoherent pairs at higher temperature. Special care is devoted to the nearly half-filled case where the symmetry of the order parameter is enlarged to SO(3) due to strong ${\bf q}=(\pi,\pi)$ charge fluctuations. The low-energy effective action is then an SO(3) non-linear sigma model with a (symmetry breaking) magnetic field proportional to the doping. In the strong-coupling limit, the attractive Hubbard model can be mapped onto the Heisenberg model, from which we recover the Gross-Pitaevskii equation in the low-density limit.Comment: 31 pages, 12 figures, RevTex4; (v2) changes following referees' comments, references adde

The Phonon Drag Effect in Single-Walled Carbon Nanotubes

A variational solution of the coupled electron-phonon Boltzmann equations is used to calculate the phonon drag contribution to the thermopower in a 1-D system. A simple formula is derived for the temperature dependence of the phonon drag in metallic, single-walled carbon nanotubes. Scattering between different electronic bands yields nonzero values for the phonon drag as the Fermi level varies.Comment: 8 pages, 4 figure

Superfluid transition temperature in a trapped gas of Fermi atoms with a Feshbach resonance

We investigate strong coupling effects on the superfluid phase transition in a gas of Fermi atoms with a Feshbach resonance. The Feshbach resonance describes a composite quasi-Boson, which can give rise to an additional pairing interaction between the Fermi atoms. This attractive interaction becomes stronger as the threshold energy of the Feshbach resonance two-particle bound state is lowered. In a recent paper, we showed that in the uniform Fermi gas, this tunable pairing interaction naturally leads to a BCS-BEC crossover of the Nozi`eres and Schmitt-Rink kind, in which the BCS-type superfluid phase transition continuously changes into the BEC-type as the threshold energy is decreased. In this paper, we extend our previous work by including the effect of a harmonic trap potential, treated within the local density approximation (LDA). We also give results for both weak and strong coupling to the Feshbach resonance. We show that the BCS-BEC crossover phenomenon strongly modifies the shape of the atomic density profile at the superfluid phase transition temperature Tc, reflecting the change of the dominant particles going from Fermi atoms to composite Bosons. In the BEC regime, these composite Bosons are shown to first appear well above Tc. We also discuss the "phase diagram" above Tc as a function of the tunable threshold energy. We introduce a characteristic temperature T* describing the effective crossover in the normal phase from a Fermi gas of atoms to a gas of stable molecules.Comment: 43 pages, 13 figures (submitted to PRA

Non-linear feedback effects in coupled Boson-Fermion systems

We address ourselves to a class of systems composed of two coupled subsystems without any intra-subsystem interaction: itinerant Fermions and localized Bosons on a lattice. Switching on an interaction between the two subsystems leads to feedback effects which result in a rich dynamical structure in both of them. Such feedback features are studied on the basis of the flow equation technique - an infinite series of infinitesimal unitary transformations - which leads to a gradual elimination of the inter-subsystem interaction. As a result the two subsystems get decoupled but their renormalized kinetic energies become mutually dependent on each other. Choosing for the inter - subsystem interaction a charge exchange term (the Boson-Fermion model) the initially localized Bosons acquire itinerancy through their dependence on the renormalized Fermion dispersion. This latter evolves from a free particle dispersion into one showing a pseudogap structure near the chemical potential. Upon lowering the temperature both subsystems simultaneously enter a macroscopic coherent quantum state. The Bosons become superfluid, exhibiting a soundwave like dispersion while the Fermions develop a true gap in their dispersion. The essential physical features described by this technique are already contained in the renormalization of the kinetic terms in the respective Hamiltonians of the two subsystems. The extra interaction terms resulting in the process of iteration only strengthen this physics. We compare the results with previous calculations based on selfconsistent perturbative approaches.Comment: 14 pages, 16 figures, accepted for publication in Phys. Rev.

Pi excitation of the t-J model

In this paper, we present analytical and numerical calculations of the pi resonance in the t-J model. We show in detail how the pi resonance in the particle-particle channel couples to and appears in the dynamical spin correlation function in a superconducting state. The contribution of the pi resonance to the spin excitation spectrum can be estimated from general model-independent sum rules, and it agrees with our detailed calculations. The results are in overall agreement with the exact diagonalization studies of the t-J model. Earlier calculations predicted the correct doping dependence of the neutron resonance peak in the YBCO superconductor, and in this paper detailed energy and momentum dependence of the spin correlation function is presented. The microscopic equations of motion obtained within current formalism agree with that of the SO(5) nonlinear sigma model, where the pi resonance is interpreted as a pseudo Goldstone mode of the spontaneous SO(5) symmetry breaking.Comment: 33 pages, LATEX, 14 eps fig

Aharonov-Bohm spectral features and coherence lengths in carbon nanotubes

The electronic properties of carbon nanotubes are investigated in the presence of disorder and a magnetic field parallel or perpendicular to the nanotube axis. In the parallel field geometry, the $\phi_{0}(=hc/e)$-periodic metal-insulator transition (MIT) induced in metallic or semiconducting nanotubes is shown to be related to a chirality-dependent shifting of the energy of the van Hove singularities (VHSs). The effect of disorder on this magnetic field-related mechanism is considered with a discussion of mean free paths, localization lengths and magnetic dephasing rate in the context of recent experiments.Comment: 22 pages, 6 Postscript figures. submitted to Phys. Rev.