Experimental observation of quantum corrections to electrical resistivity in nanocrystalline soft magnetic alloys

X-ray diffraction patterns of nanocrystalline Fe-Cu-Nb-Si-B (FINEMET) alloys reveal that bcc α-Fe/α-FeSi crystallites with the average grain size of 20(5) nm are dispersed in amorphous matrix. Enhanced electron—electron interaction (EEI) and quantum interference (QI) effects as well as electron-magnon (and/or electron-spin fluctuation) scattering turn out to be the main mechanisms that govern the temperature dependence of resistivity. Of all the inelastic scattering processes, inelastic electron-phonon scattering is the most effective mechanism to destroy phase coherence of electron wave functions. The diffusion constant, density of states at the Fermi level and the inelastic scattering time have been estimated, for the first time, for the alloys in question Article presented at the International Symposium on Advances in Superconductivity and Magnetism: Materials, Mechanisms and Devices, ASMM2D-2001, 25–28 September 2001, Mangalore, India.     

Magnetic and martensitic transitions in Ni-Fe-Ga alloy

The ferromagnetic shape memory alloy with nominal composition Ni₅₄Fe₁₉Ga₂₇ is investigated by Ac susceptibility and resistivity measurements. The alloy shows long-range ferromagnetic order below 290 K. The anomaly due to the martensitic transition is observed in the susceptibility and resistivity data in the temperature range around 220 K, which is associated with clear thermal hysteresis. Minor hysteresis loop technique was used to investigate the phase coexistence across the martensitic transition, and our analysis indicate that both martensite and austenite phases mutually coexist in the region of hysteresis.     

HPTLC Determination of Swertiamarin and Amarogentin in Swertia Species from the Western Himalayas

JPC – Journal of Planar Chromatography – Modern TLC - A high-performance thin-layer chromatographic (HPTLC) method has been established for simple and rapid quantification of two...     

Crystal and magnetic structure of the Sm0.55Sr0.45MnO3 and (Nd0.545Tb0.455)0.55Sr0.45MnO3 manganites

Neutron diffraction data are presented for the ¹⁵²Sm_0.55Sr_0.45MnO₃ (SSM) and (Nd_0.545Tb_0.455)_0.55Sr_0.45MnO₃ (NTSM) manganites. The Nd and Tb contents in the latter composition are such that the average radius of the A cation 〈r _A 〉 in these two compounds is the same. The difference in local tolerance factor fluctuations was about 10%. It was found that replacement of a rare-earth cation with leaving 〈r _A 〉 unchanged has practically no effect on the structural and transport properties; indeed, both compounds are metals at low temperatures, have the same crystal structure from liquid-helium to room temperature, and exhibit the same pattern of structural distortions at the onset of magnetic ordering. Magnetic moments of Mn ions in both compositions are ferromagnetically ordered at low temperatures, with T _C =122 and 90 K for the SSM and NTSM, respectively. Below 80 K, the rare-earth cation moments in NTSM undergo additional ordering. In contrast to compositions that are close in Sr concentration (x _Sr=0.4, 0.5), which feature a phase-separated state with a mixture of the ferromagnetic metallic and antiferromagnetic insulator phases, the ground state of both studied compositions with x _Sr=0.45 is uniformly ferromagnetic and metallic. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 9, 2004, pp. 1650–1656. Original Russian Text Copyright ? 2004 by Kurbakov, Trounov, Balagurov, Pomyakushin, Sheptyakov, Gorbenko, Kaul.     

Quantification of Valerenic Acid in Valeriana jatamansi and Valeriana officinalis by HPTLC

A simple, rapid, cost-effective and accurate high performance thin layer chromatographic method has been developed for quantification of valerenic acid in Valeriana jatamansi and Valeriana officinalis which is one of the stable compounds of Valeriana officinalis and designated as a key marker compound. Valerenic acid makes substantial contribution to the sedative and spasmolytic activity of the essential oil and extract of Valeriana officinalis. Separation and quantification was achieved by HPTLC using ternary mobile phase of hexane: ethyl acetate: acetic acid (80:20:0.5 v/v) on precoated silica gel 60F₂₅₄ aluminium plates and densitometric determination was carried out after derivatization with anisaldehyde-sulphuric acid reagent at 700 nm, in absorption-reflectance mode. The calibration curves were linear in the range of (500 ng–2.5 μg). This is the first HPTLC report for the identification and quantification of valerenic acid in Valeriana jatamansi and Valeriana officinalis.     

Synthesis of a negatively charged dibenzofuran-based beta-turn mimetic and its incorporation into the WW miniprotein-enhanced solubility without a loss of thermodynamic stability

A versatile synthesis has been developed to functionalize the 4-(2-aminoethyl)-6-dibenzofuran propionic acid residue (1a) at the 2 and 8 positions with a variety of different substructures. The unfunctionalized version of this peptidomimetic (1a) is known to facilitate beta-hairpin formation in a variety of small peptides and proteins in aqueous solution when incorporated in place of the i + 1 and i + 2 residues of a beta-turn. In this study, we append propionate substituents on 1a at the 2 and 8 positions to successfully overcome solubility problems encountered with the incorporation of 1a in place of the i + 1 and i + 2 residues of the beta-turn in loop 1 of the WW domain. The thermodynamic stability of several WW domain analogues incorporating residues 1a and 1b was compared to that of the wild-type sequence revealing comparable DeltaG(H(2)O) unfolding values at 4 degrees C ranging from 3 to 3.6 kcal/mol. WW domains incorporating residue 1b exhibit improved solubility (exceeding 100 microM) and resistance to aggregation without compromising thermodynamic stability.     

Simultaneous densitometric determination of artemisinin, artemisinic acid and arteannuin-B in Artemisia annua using reversed-phase thin layer chromatography

A rapid and simple RP-TLC method for simultaneous quantification of pharmacologically important sesquiterpene artemisinin (AM) together with its precursors arteannuin-B (AB) and artemisinic acid (AA) in the inflorescence part of Artemisia annua plant has been developed. The RP-TLC of sesquiterpenes was performed on RP-18 F254 S thin-layer chromatographic plates by developing in mobile phase, containing 0.2% TFA in water/ACN (35:65, v/v). The densitometric determination of AM, AB and AA was carried out after derivatization with anisaldehyde reagent at 426 nm in absorption-reflectance mode.     

Stability-Indicating HPLC Method for the Determination of Metadoxine as Bulk Drug and in Pharmaceutical Dosage Form

A sensitive and reproducible method is described for the quantitative determination of metadoxine in the presence of its degradation products. The method was based on high performance liquid chromatographic separation of the drug from its degradation products on the reversed phase, kromasil column [C₁₈ (5-micron, 25 cm × 4.6 mm, i.d.)] at ambient temperature using a mobile phase consisting of methanol and water (50: 50, v/v). Flow rate was 1.0 mL min^?1 with an average operating pressure of 180 kg cm^?2 and t _R was found to be 2.85 ± 0.05 min. Quantitation was achieved with UV detection at 286 nm based on peak area with linear calibration curves at concentration range 10–100 μg mL^?1. This method has been successively applied to pharmaceutical formulation. No chromatographic interference from the tablet excipients was found. The method was validated in terms of precision, robustness, recovery and limits of detection and quantitation. Drug was subjected to acid, alkali and neutral hydrolysis, oxidation, dry heat, wet heat treatment and photo and UV degradation. As the proposed method could effectively separate the drug from its degradation products, it can be employed as stability indicating one. Moreover, the proposed HPLC method was utilized to investigate the kinetics of the acidic, alkaline and oxidative degradation processes at different temperatures and their respective apparent pseudo first order rare constant, half-life and activation energy was calculated with the help of Arrhenius plot. In addition the pH-rate profile of degradation of metadoxine in constant ionic strength buffer solutions with in the pH range 2–11 was studied.