Vibrational properties of phonons in random binary alloys: An augmented space recursive technique in the k-representation

We present here an augmented space recursive technique in the k-representation which include diagonal, off-diagonal and the environmental disorder explicitly : an analytic, translationally invariant, multiple scattering theory for phonons in random binary alloys.We propose the augmented space recursion (ASR) as a computationally fast and accurate technique which will incorporate configuration fluctuations over a large local environment. We apply the formalism to $Ni_{55}Pd_{45}$, Ni_{88}Cr_12} and $Ni_{50}Pt_{50}$ alloys which is not a random choice. Numerical results on spectral functions, coherent structure factors, dispersion curves and disordered induced FWHM's are presented. Finally the results are compared with the recent itinerant coherent potential approximation (ICPA) and also with experiments.Comment: 20 pages, LaTeX, 23 figure

Statins: Old drugs as new therapy for liver diseases?

In addition to lowering cholesterol levels, statins have pleiotropic effects, particularly anti-inflammatory, antiangiogenic, and antifibrotic, that may be beneficial in some chronic inflammatory conditions. Statins have only recently been investigated as a potential treatment option in chronic liver diseases because of concerns related to their safety in patients with impaired liver function. A number of experimental studies in animal models of liver diseases have shown that statins decrease hepatic inflammation, fibrogenesis and portal pressure. In addition, retrospective cohort studies in large populations of patients with cirrhosis and pre-cirrhotic conditions have shown that treatment with statins, with the purpose of decreasing high cholesterol levels, was associated with a reduced risk of disease progression, hepatic decompensation, hepatocellular carcinoma development, and death. These beneficial effects persisted after adjustment for disease severity and other potential confounders. Finally, a few randomised controlled trials have shown that treatment with simvastatin decreases portal pressure (two studies) and mortality (one study). Statin treatment was generally well tolerated but a few patients developed severe side effects, particularly rhabdomyolysis. Despite these promising beneficial effects, further randomised controlled trials in large series of patients with hard clinical endpoints should be performed before statins can be recommended for use in clinical practice

A first-principles thermodynamic approach to ordering in Ni-Mo alloys

There is a competition between several face centered cubic (FCC)-based ordered inter-metallic phases in Ni-Mo alloys containing 8-33 at% Mo. The transformation behavior of these alloys in terms of ordering instabilities has been studied. First-principles tight-binding-linear muffin-tin orbital (TB-LMTO) method coupled with augmented space recursion (ASR) in conjunction with orbital peeling (OP) technique has been employed to extract the concentration dependent effective pair interactions. Further, the mean-field statistical mechanics based static concentration wave (SCW) model has been used to determine the free energies of these ordered phases as functions of temperature, composition and order parameter. This ASR-OP-SCW approach, applied to Ni-Mo alloy system, gives the correct ground state stability sequence as observed experimentally. Furthermore, it has been shown that such an approach can be used to study the complex transformation behavior involving several competing superstructures as well as competing first order and second order ordering processes

Study of Phase Stability in NiPt Systems

We have studied the problem of phase stability in NiPt alloy system. We have used the augmented space recursion based on the TB-LMTO as the method for studying the electronic structure of the alloys. In particular, we have used the relativistic generalization of our earlier technique. We note that, in order to predict the proper ground state structures and energetics, in addition to relativistic effects, we have to take into account charge transfer effects with precision.Comment: 22 pages, 7 figures. Accepted for publication in JPC

Optical properties of perovskite alkaline earth titanates : a formulation

In this communication we suggest a formulation of the optical conductivity as a convolution of an energy resolved joint density of states and an energy-frequency labelled transition rate. Our final aim is to develop a scheme based on the augmented space recursion for random systems. In order to gain confidence in our formulation, we apply the formulation to three alkaline earth titanates CaTiO_3, SrTiO_3 and BaTiO_3 and compare our results with available data on optical properties of these systems.Comment: 19 pages, 9 figures, Submitted to Journal of Physics: Condensed Matte

Spectral statistics near the quantum percolation threshold

The statistical properties of spectra of a three-dimensional quantum bond percolation system is studied in the vicinity of the metal insulator transition. In order to avoid the influence of small clusters, only regions of the spectra in which the density of states is rather smooth are analyzed. Using finite size scaling hypothesis, the critical quantum probability for bond occupation is found to be $p_q=0.33\pm.01$ while the critical exponent for the divergence of the localization length is estimated as $\nu=1.35\pm.10$. This later figure is consistent with the one found within the universality class of the standard Anderson model.Comment: REVTeX, 4 pages, 5 figures, all uuencoded, accepted for publication in PRB (Rapid Communication

Influence of s-d interfacial scattering on the magnetoresistance of magnetic tunnel junctions

We propose the two-band s-d model to describe theoretically a diffuse regime of the spin-dependent electron transport in magnetic tunnel junctions (MTJ's) of the form F/O/F where F's are 3d transition metal ferromagnetic layers and O is the insulating spacer. We aim to explain the strong interface sensitivity of the tunneling properties of MTJ's and investigate the influence of electron scattering at the nonideal interfaces on the degradation of the TMR magnitude. The generalized Kubo formalism and the Green's functions method were used to calculate the conductance of the system. The vertex corrections to the conductivity were found with the use of "ladder" approximation combined with the coherent-potential approximation (CPA) that allowed to consider the case of strong electron scattering. It is shown that the Ward identity is satisfied in the framework of this approximation that provides the necessary condition for a conservation of a tunneling current. Based on the known results of ab-initio calculations of the TMR for ballistic junctions, we assume that exchange split quasi-free s-like electrons with the density of states being greater for the majority spin sub-band give the main contribution to the TMR effect. We show that, due to interfacial inter-band scattering, the TMR can be substantially reduced even down to zero value. This is related to the fact that delocalized quasi-free electrons can scatter into the strongly localized d sub-band with the density of states at the Fermi energy being larger for minority spins compared to majority spins. It is also shown that spin-flip electron scattering on the surface magnons within the interface leads to a further decrease of the TMR at finite temperature.Comment: REVTeX4, 20 pages, 9 figures, 1 table, submitted to Phys.Rev.B; In Version 2 the text is substantially improved, the main results and conclusions left the sam

Magnetic properties of X-Pt (X=Fe,Co,Ni) alloy systems

We have studied the electronic and magnetic properties of Fe-Pt, Co-Pt and Ni-Pt alloy systems in ordered and disordered phases. The influence of various exchange-correlation functionals on values of equilibrium lattice parameters and magnetic moments in ordered Fe-Pt, Co-Pt and Ni-Pt alloys have been studied using linearized muffin-tin orbital method. The electronic structure calculations for the disordered alloys have been carried out using augmented space recursion technique in the framework of tight binding linearized muffin-tin orbital method. The effect of short range order has also been studied in the disordered phase of these systems. The results show good agreements with available experimental values.Comment: 21 pages, 4 eps figures, accepted for publication in Journal of Physics Condensed Matte

Antiviral Responses following L-Leucyl-L-Leucine Methyl Esther (LLME)-Treated Lymphocyte Infusions: Graft-versus-Infection without Graft-versus-Host Disease

Although allogeneic hematopoietic progenitor cell transplant (HPCT) is curative therapy for many disorders, it is associated with significant morbidity and mortality, which can be related to graft-versus-host disease (GVHD) and the immunosuppressive measures required for its prevention and/or treatment. Whether the immunosuppression is pharmacologic or secondary to graft manipulation, the graft recipient is left at increased risk of the threatening opportunistic infection. Refractory viral diseases in the immunocompromised host have been treated by infusion of virus-specific lymphotyces and by unmanipulated donor lymphocyte infusion (DLI) therapy. L-leucyl-L-leucine methyl ester (LLME) is a compound that induces programmed cell death of natural killer (NK) cells, monocytes, granulocytes, most CD8+ T cells, and a small fraction of CD4+ T cells. We have undertaken a study of the use of LLME-treated DLI following T cell-depleted allogeneic HPCT, specifically to aid with immune reconstitution. In this ongoing clinical trial, we have demonstrated the rapid emergence of virus-specific responses following LLME DLI with minimal associated GVHD. This paper examines the pace of immune recovery and the rapid development of antiviral responses in 6 patients who developed viral infections during the time period immediately preceding or coincident with the administration of the LLME DLI