Magnetic properties of a helical spin chain with alternating isotropic and anisotropic spins: magnetization plateaus and finite entropy

We study a model which could explain some of the unusual magnetic properties observed for the one-dimensional helical spin system Co(hfac)_2 NITPhOMe. One of the properties observed is that the magnetization shows plateaus near zero and near one-third of the saturation value if a magnetic field is applied along the helical axis, but not if the field is applied in the plane perpendicular to that axis. The system consists of a spin-1/2 chain in which cobalt ions (which are highly anisotropic with an easy axis e_i) and organic radicals (which are isotropic) alternate with each other. The easy axis of the cobalts e_i lie at an angle theta_i with respect to the helical axis, while the projection of e_{i+1} - e_i on the plane perpendicular to the helical axis is given by 2 pi /3. For temperatures and magnetic fields which are much smaller than the coupling between the nearest-neighbor cobalts and radicals, one can integrate out the radicals to obtain an Ising model for the cobalts; this enables one to compute the thermodynamic properties of the system using the transfer matrix approach. We consider a model in which the tilt angles theta_i are allowed to vary with i with period three; we find that for certain patterns of theta_i, the system shows the magnetization plateaus mentioned above. At the ends of the plateaus, the entropy is finite even at very low temperatures, while the magnetic susceptibility and specific heat also show some interesting features.Comment: Revtex, 7 pages including 7 figure

DEVELOPMENT AND VALIDATION OF RP-CHIRAL HPLC METHOD FOR QUANTIFICATION OF (S)-ISOMER IN TENOFOVIR DISOPROXIL FUMARATE

Objective: The main objective of present study was to develop and validate a reverse phase enantioselective chiral high performance liquid chromatographic method was developed for enantiomeric resolution of Tenofovir disoproxil fumarate; it decreases the HIV infection in human body. The method is specific, rapid, precise and accurate for the separation and determination of (S)-isomer in tenofovir disoproxil fumarate drug substance form.Methods: The S-Isomer of Tenofovir disoproxil fumarate was resolved on a Chiral AGP (150 × 4.0 mm, 5 µm) column (L-41) using a mobile phase system containing 0.1 M ammonium acetate in water pH 6.8 with ammonia solution and methanol in the ratio of (85:15 v/v). The mobile phase was set at a flow rate of 0.8 ml/min and the volume injected was 10μl for every injection. The detection wavelength was set at 260 nm and the column temperature was set at 15 °C.Results: The proposed method was productively applied for the quantitative determination of (S)-isomer in Tenofovir disoproxil fumarate drug substance form. The linear regression analysis data for calibration plots showed a good linear relationship over a concentration range of 0.125 to 3.75 µg/ml for (S)-isomer, 0.125-3.75 µg/ml for Tenofovir disoproxil fumarate. The mean values of the correlation coefficient were 0.999 and 0.999 for (S)-isomer and Tenofovir disoproxil fumarate. The method was validated as per the ICH guidelines. The detection limit (LOD) was about 0.05 µg/ml and quantitation limit (LOQ) was about 0.125 µg/ml for (S)-isomer and Tenofovir disoproxil fumarate. The relative standard deviation was found to be 0.78 % for (S)-isomer in Tenofovir disoproxil fumarate.Conclusion: The developed and validated HPLC method and the statistical analysis showed that the method is repeatable and selective for the estimation of the (S)-isomer of the Tenofovir disoproxil fumarate drug substance

A multi-channel fixed point for a Kondo spin coupled to a junction of Luttinger liquids

We study a system of an impurity spin coupled to a junction of several Tomonaga-Luttinger liquids using a renormalization group scheme. For the decoupled S-matrix at the junction, there is a range of Kondo couplings which flow to a multi-channel fixed point for repulsive inter-electron interactions; this is associated with a characteristic temperature dependence of the spin-flip scatterings. If the junction is governed by the Griffiths S-matrix, the Kondo couplings flow to a strong coupling fixed point where all the wires are decoupled.Comment: 7 pages including 3 figures; the RG equations have been corrected, and the discussion of the muti-channel fixed point has been suitably modifie

ISOLATION, CHARACTERIZATION AND VALIDATION OF HPLC METHOD FOR QUANTIFICATION OF BIS-[10-(2-METHYL-4H-3-THIA-4,9-DIAZABENZO[F]AZULENE)]-1,4-PIPERAZINE IN AN ANTI-PSYCHOTIC DRUG SUBSTANCE, OLANZAPINE

Objective: The main objective of present study was to Isolate, characterize and validate a reverse phase high performance liquid chromatographic method was validated for quantification of bis-[10-(2-methyl-4H-3-thia-4,9-diazabenzo[f]azulene)]-1,4-piperazine in Olanzapine drug substance; it decreases the mental disorders in human body. The method is specific, rapid, precise and accurate for the separation and determination of bis-[10-(2-methyl-4H-3-thia-4,9-diazabenzo[f]azulene)]-1,4-piperazine in Olanzapine drug substance form.Methods: The bis-[10-(2-methyl-4H-3-thia-4,9-diazabenzo[f]azulene)]-1,4-piperazine of Olanzapine was resolved on a Zorbax RX-C 8, 250 mm X 4.6 mm, 5 micron column (L-1) using a mobile phase system containing 0.03 M sodium dodecyl sulphate in water pH 2.5 with 1 N sodium hydroxide solution and acetonitrile in the ratio of (Mobile phase A-52:48 v/v) and (Mobile phase B-buffer and Acetonitrile 30:70 v/v) by using the gradient program. The mobile phase was set at a flow rate of 1.5 ml/min and the volume injected was 20μl for every injection. The detection wavelength was set at 220 nm and the column temperature was set at 35 °C.Results: The proposed method was productively applied for the quantitative determination of bis-[10-(2-methyl-4H-3-thia-4,9-diazabenzo [f]azulene)]-1,4-piperazine in Olanzapine drug substance form. The linear regression analysis data for calibration plots showed a good linear relationship over a concentration range of 0.025to 0.903 µg/ml for bis-[10-(2-methyl-4H-3-thia-4,9-diazabenzo[f]azulene)]-1,4-piperazine, 0.081-0.608 µg/ml for Olanzapine. The mean values of the correlation coefficient were 0.999 and 0.999 for bis-[10-(2-methyl-4H-3-thia-4,9-diazabenzo[f]azulene)]-1,4-piperazine and Olanzapine. The method was validated as per the ICH guidelines. The detection limit (LOD) was about 0.007 µg/ml, 0.024 µg/ml and quantitation limit (LOQ) was about 0.024 µg/ml, 0.081 µg/ml for bis-[10-(2-methyl-4H-3-thia-4,9-diazabenzo[f]azulene)]-1,4-piperazine and Olanzapine. The relative standard deviation was found to be 1.64 % and 2.18 % for bis-[10-(2-methyl-4H-3-thia-4,9-diazabenzo[f]azulene)]-1,4-piperazine and Olanzapine.Conclusion: The validated HPLC method and the statistical analysis showed that the method is repeatable and selective for the estimation of the bis-[10-(2-methyl-4H-3-thia-4,9-diazabenzo[f]azulene)]-1,4-piperazine of the Olanzapine drug substance

Screening for sexually transmitted infections at a DeAddictions service in South India

Objectives To estimate the lifetime prevalence of four sexually transmitted infections (STIs) and to identify correlates of these infections among patients seeking care for a substance use disorder at a specialized DeAddictions Unit in southern India. Methods Consecutive inpatients (n = 361; 98% male; M age = 36.7 years) admitted to DeAddictions Unit of the National Institute of Mental Health and Neuro Sciences in Bangalore, India, participated in a structured interview to obtain demographic, psychiatric, sexual behavior, and substance use data; each patient also provided a blood sample for serologic testing for HIV, chlamydia, syphilis, and hepatitis B. Results One-quarter of all patients tested positive for at least one STI. Lifetime seroprevalence rates were 12.9% for syphilis, 10.3% for chlamydia, 3.1% for hepatitis B, and 1.1% for HIV. Analyses did not reveal any consistent pattern of associations between STI status and sociodemographic, psychiatric, and sexual behavioral characteristics. Conclusions All patients should receive a comprehensive sexual assessment during standard care; for those patients who report risky sexual practices, we recommend voluntary counseling and testing for STIs. Although we do not recommend universal testing for STIs at this time, this should be revisited based upon national surveillance data

A new validated stability-indicating gradient RP-HPLC method for the determination of pemetrexed disodium and its process related substances

Pemetrexed disodium is used for the treatment of malignant pleural mesothelioma and lung cancer. In the present study a simple stability indicating RP-HPLC method was developed and validated for the determination of Pemetrexed disodium. The process related substances such as Dimer-1 impurity, Dimer-2 impurity, N-Methyl Pemetrexed, Pemetrexed diethyl ester, Alanine derivative of Pemetrexed, DMF derivative of Pemetrexed, Acid intermediate, Oxidation impurity and D-isomer were separated on gradient mode and quantified. Forced degradation studies were performed to prove the specificity. Hypersil BDS C18 100 x 4.6mm, 3µm was used for the separation (at 27°C) with mobile phase mixture consisting of (0.02M sodium dihydrogen phosphate with 0.1% HCOOH and pH 3.8 with dilute sodium hydroxide): Acetonitrile (40:60 v/v) (pH 3.8) with a flow rate of 1.2 mL/min. Methanol: water (1:1) was used as diluent and the eluted compounds were monitored at 240 nm. 0.5-1500 µg/mL with linear regression equation y = 20588x - 9294.1 (R2=0.9999). The degradation products observed during the forced degradation studies were well resolved from the drug peak and proving that the method is a stability-indicating method. The method was validated as per ICH guidelines. Keywords: Pemetrexed disodium, RP-HPLC, gradient mode, Related substances, Stability indicating, Validation

Renormalization group study of the Kondo problem at a junction of several Luttinger wires

We study a system consisting of a junction of N quantum wires, where the junction is characterized by a scalar S-matrix, and an impurity spin is coupled to the electrons close to the junction. The wires are modeled as weakly interacting Tomonaga-Luttinger liquids. We derive the renormalization group equations for the Kondo couplings of the spin to the electronic modes on different wires, and analyze the renormalization group flows and fixed points for different values of the initial Kondo couplings and of the junction S-matrix (such as the decoupled S-matrix and the Griffiths S-matrix). We generally find that the Kondo couplings flow towards large and antiferromagnetic values in one of two possible ways. For the Griffiths S-matrix, we study one of the strong coupling flows by a perturbative expansion in the inverse of the Kondo coupling; we find that at large distances, the system approaches the ferromagnetic fixed point of the decoupled S-matrix. For the decoupled S-matrix with antiferromagnetic Kondo couplings and weak inter-electron interactions, the flows are to one of two strong coupling fixed points in which all the channels are strongly coupled to each other through the impurity spin. But strong inter-electron interactions, with K_\rho < N/(N+2), stabilize a multi-channel fixed point in which the coupling between different channels goes to zero. We have also studied the temperature dependence of the conductance at the decoupled and Griffiths S-matrices.Comment: Revtex4, 16 pages including 6 figure