ABSTRACT
We present here a quantitative analysis of the ground state and magnetic properties of Ce3Pt23Si11, based on a crystalline electric field description within the mean-field approximation. In this face-centered cubic compound, the point group symmetry at the Ce site is orthorhombic. One main difficulty in this low symmetry case is that the CEF potential for Ce3+ ions is determined by five independent parameters, while only two magnetic excitations are observed by inelastic neutron scattering. Moreover the anisotropy of the magnetic susceptibility of the Ce ion, that permits an independent determination of the second-order CEF parameters is hidden by the cubic symmetry of the compound. A specific procedure is developed for this purpose that combines genetic algorithms and more conventional optimization methods. A set of CEF parameters is found that best reproduces the different experimental observations in both the paramagnetic and ferromagnetic phases of Ce3Pt23Si11. The analysis accounts for two seemingly contradictory properties: a strong local anisotropy that aligns the moment along a fourfold axis and a rather weak anisotropy of the bulk magnetization with an easy threefold magnetization axis. Ce3Pt23Si11 is shown to be a model system where single site anisotropies compete within a crystal structure of overall high symmetry.
ABSTRACT
We explore the magnetic anisotropy of GaMnAs ferromagnetic semiconductor by Planar Hall Effect (PHE) measurements. Using low magnitude of applied magnetic field (i.e., when the magnitude H is smaller than both cubic Hc and uniaxial Hu anisotropy field), we have observed various shapes of applied magnetic field direction dependence of Planar Hall Resistance (PHR). In particular, in two regions of temperature. At T < Tc/2, the "square-shape" signal and at T > Tc/2 the "zigzag-shape" signal of PHR. They reflect different magnetic anisotropy and provide information about magnetization reversal process in GaMnAs ferromagnetic semiconductor. The theoretical model calculation of PHR based on the free energy density reproduces well the experimental data. We report also the temperature dependence of anisotropy constants and magnetization orientations. The transition of easy axis from biaxial to uniaxiale axes has been observed and confirmed by SQUID measurements.
Subject(s)
Metal Nanoparticles/chemistry , Models, Chemical , Semiconductors , Anisotropy , Computer Simulation , Magnetics , Materials Testing , TemperatureABSTRACT
Magnetic susceptibility anisotropy and high sensitivity magnetostriction measurements are used to investigate the symmetry of CeB(6) ordered states. The antiferromagnetic state is confirmed as tetragonal, but no deviation from the cubic symmetry is observed in the so-called antiferroquadrupolar phase, where only volume effects are detected. In this phase, the temperature dependence of the strain field susceptibilities is typical of nonordered quadrupoles. Moreover, while an antiferroquadrupolar order should be cubic, this symmetry is incompatible with the (½½½) ordering wave vector. The antiferroquadrupolar description of CeB(6) phase II is clearly inconsistent, and an alternative model, based on a unidimensional representation of the cube, has to be sought.
Subject(s)
Cat's Claw , HIV Protease Inhibitors , Herb-Drug Interactions , Plant Preparations , Atazanavir Sulfate , Cat's Claw/adverse effects , Female , HIV Protease Inhibitors/administration & dosage , HIV Protease Inhibitors/blood , HIV Protease Inhibitors/pharmacokinetics , HIV Protease Inhibitors/therapeutic use , Humans , Metabolic Clearance Rate , Middle Aged , Oligopeptides/administration & dosage , Oligopeptides/blood , Oligopeptides/pharmacokinetics , Oligopeptides/therapeutic use , Plant Preparations/administration & dosage , Plant Preparations/adverse effects , Pyridines/administration & dosage , Pyridines/blood , Pyridines/pharmacokinetics , Pyridines/therapeutic use , Ritonavir/administration & dosage , Ritonavir/blood , Ritonavir/pharmacokinetics , Ritonavir/therapeutic use , Saquinavir/administration & dosage , Saquinavir/blood , Saquinavir/pharmacokinetics , Saquinavir/therapeutic useABSTRACT
La incorporación de los inhibidores de la proteasa (saquinavir, ritonavir, indinavir, nelfinavir) en la terapia antirretroviral ha supuesto un importante descenso en la morbilidad y mortalidad provocada por el SIDA. Son compuestos no peptídicos que inhiben de forma potente y selectiva la proteasa del VIH-1. Se caracterizan por tener en común un metabolismo de eliminación hepático y una semivida de eliminación corta, con diferencias en el ámbito de absorción y distribución. Excepto el indinavir, deben administrarse con comidas. Poseen distintos perfiles de toxicidad, siendo el ritonavir el que presenta una mayor incidencia de reacciones adversas. La extensa metabolización por la isoenzima CYP3A4 del citocromo P450 puede originar interacciones de interés clínico. Actualmente, la carga viral y linfocitos T CD4 son los marcadores de evolución clínica de la enfermedad. Recientes estudios sugieren que la monitorización de las concentraciones plasmáticas pueden ser de utilidad en casos de no-adherencia, interacciones farmacocinéticas y fracaso virológico (AU)
Subject(s)
Humans , Antiviral Agents/therapeutic use , Antiviral Agents/pharmacokinetics , HIV Infections/drug therapy , HIV Infections/blood , Protease Inhibitors/therapeutic use , Protease Inhibitors/pharmacokinetics , Protease Inhibitors/adverse effectsABSTRACT
A cross-sectional study was designed to determine whether plasma concentrations of glutathione and cysteine in HIV-infected hemophiliacs vary according to the progression of the disease and to compare them with those obtained in HIV negative hemophiliacs. Cysteine, total glutathione and glutathione disulphide were measured in plasma of HIV-infected hemophiliacs at different stages of HIV infection and in plasma of HIV-negative hemophiliacs. CD4 and CD8 T-cell counts, leukocyte and lymphocyte counts, beta 2-microglobulin and p24 antigen values were recorded for HIV positive hemophiliacs at the time of the study. The hemophiliac HIV-positive group showed a decrease in total glutathione levels (-18%) and an increase of glutathione disulphide (8.18 vs. 14.90%) compared to the HIV-negative group. The cysteine levels found in HIV-positive hemophiliacs were not different from those found in the HIV-negative group. There were no differences with statistical significance in total glutathione, glutathione disulphide and cysteine among HIV-infected hemophiliacs according to the different clinical stage of the disease (AIDS vs. non-AIDS). The interest of evaluating plasma concentrations of glutathione and cysteine in HIV-infected patients is limited from the point of view of considering them as markers of progression of the disease. Interest in a therapeutic strategy designed to replenish or normalize glutathione plasma levels is also limited.
