Stability-Indicating LC Method for Assay of Cholecalciferol

This paper discusses the development of a stability-indicating reversed-phase LC method for analysis of cholecalciferol as the bulk drug and in formulations. The mobile phase was acetonitrile–methanol–water 50:50:2 (v/v). The calibration plot for the drug was linear in the range 0.4–10 μg mL⁻¹. The method was accurate and precise with limits of detection and quantitation of 64 and 215 ng, respectively. Mean recovery was 100.71%. The method was used for analysis of cholecalciferol in pharmaceutical formulations in the presence of its degradation products and commonly used excipients.

     

Colorimetric Procedure for the Microdetermination of the Antibilharzial Drug Praziquantel and its Applications to Pharmaceutical Formulations

 A procedure for the colorimetric assay of praziquantel has been developed. The method is based on the formation of charge-transfer complexes with p-chloranil (I), dichloronitrophenol (II), 2,3-dichloro-5,6 dicyano-p-benzoquinone (III), 7,7,8,8-tetracyanoquinodimethane (IV) and tetracyanoethylene (V) as π-acceptors to give highly coloured species. The coloured products are measured spectrophotometrically at 550, 425, 460, 844 and 393 nm for I, II, III, IV and V, respectively. Optimization of the different reaction conditions is described. The colour system obeyed Beer’s law in non-aqueous media in the concentration range 2.0–48 μg ml⁻¹. It was stable for at least 4.0 h. The detection limit was found to be 0.6 μg ml⁻¹. Applications of the procedure to the analysis of various pharmaceutical samples gave reproducible and accurate results. Further, the validity of the procedure was confirmed by applying the standard addition technique. The total average recovery was 100.2%. Received June 10, 2000. Revision December 23, 2000.     

Mechanical response of proton beam irradiated nitinol

The present investigation deals with the study of mechanical behavior of proton beam irradiated nitinol at room temperature. The specimens in austenitic phase were irradiated over periods of 15, 30, 45 and 60 min at room temperature using 2 MeV proton beam obtained from Pelletron accelerator. The stress-strain curves of both unirradiated and irradiated specimens were obtained using a universal testing machine at room temperature. The results of the experiment show that an intermediate rhombohedral (R) phase has been introduced between austenite and martensite phase, which resulted in the suppression of direct transformation from austenite to martensite (A-M). Stresses required to start R-phase (σ_RS) and martensitic phase (σ_MS) were observed to decrease with increase in exposure time. The hardness tests of samples before and after irradiation were also carried out using Vickers hardness tester. The comparison reveals that the hardness is higher in irradiated specimens than that of the unirradiated one. The increase in hardness is quite sharp in specimens irradiated for 15 min, which then increases linearly as the exposure time is increased up to 60 min. The generation of R-phase, variations in the transformation stresses σ_RS and σ_MS and increase in hardness of irradiated nitinol may be attributed to lattice disorder and associated changes in crystal structure induced by proton beam irradiation.     

Von Neumann Regularity and Quadratic Conorms in JB^＊-triples and C^＊-algebras

We revise the notion of von Neumann regularity in JB^＊-triples by finding a new characterisation in terms of the range of the quadratic operator Q（a）. We introduce the quadratic conorm of an element a in a JB^＊-triple as the minimum reduced modulus of the mapping Q（a）. It is shown that the quadratic conorm of a coincides with the infimum of the squares of the points in the triple spectrum of a. It is established that a contractive bijection between JBW^＊-triples is a triple isomorphism if, and only if, it preserves quadratic conorms. The continuity of the quadratic conorm and the generalized inverse are discussed. Some applications to C^＊-algebras and von Neumann algebras are also studied.     

Effects of a small length scale on vibrations of an embedded double-walled carbon nanotube

Extensive continuum analyses are carried out to estimate the influence of matrix stiffness, a small length scale, and intertubular radial displacements on free vibrations of an individual double-walled carbon nanotybe. The analyses are based on both local and classical Euler–Bernoulli and Timoshenko elasticity theories with concentricity and nonconcentricity assumptions. The effect of a small length scale is incorporated in the formulations. New intertubular resonant frequencies are calculated based on these theories. Detailed results are demonstrated for the resonant frequencies as functions of matrix stiffness and the small length scale. The results indicate that the internal radial displacement and the stiffness of the surrounding matrix can greatly affect the resonant frequencies, especially at higher frequencies, and thus the latter does not keep the otherwise concentric structure at ultrahigh frequencies. More over, at high frequencies and small aspect ratios, the effect of the small length scale be comes more significant.     

Septic spline solutions of sixth-order boundary value problems

Septic spline is used for the numerical solution of the sixth-order linear, special case boundary value problem. End conditions for the definition of septic spline are derived, consistent with the sixth-order boundary value problem. The algorithm developed approximates the solution and their higher-order derivatives. The method has also been proved to be second-order convergent. Three examples are considered for the numerical illustrations of the method developed. The method developed in this paper is also compared with that developed in [M. El-Gamel, J.R. Cannon, J. Latour, A.I. Zayed, Sinc-Galerkin method for solving linear sixth order boundary-value problems, Mathematics of Computation 73, 247 (2003) 1325–1343], as well and is observed to be better.     

Spatial-dependent probe transmission based high-precision two-dimensional atomic localization

Herein, we propose a scheme for the realization of two-dimensional atomic localization in aλ-type three-level atomic medium such that the atom interacts with the two orthogonal standing-wave fields and a probe field. Because of the spatially dependent atom-field interaction, the information about the position of the atom can be obtained by monitoring the probe transmission spectra of the weak probe field for the first time. A single and double sharp localized peaks are observed in the one-wavelength domain. We have theoretically archived high-resolution and high-precision atomic localization within a region smaller thanλ/25×λ/25. The results may have potential applications in the field of nano-lithography and advance laser cooling technology.     

Efficient two-dimensional atom localization in a five-level conductive chiral atomic medium via birefringence beam absorption spectrum

We have theoretically investigated two-dimensional atom localization using the absorption spectra of birefringence beams of light in a single wavelength domain.The atom localization is controlled and modified through tunneling effect in a conductive chiral atomic medium with absorption spectra of birefringent beams.The significant localization peaks are investigated in the left and right circularly polarized beam.Single and double localized peaks are observed in different quadrants with minimum uncertainty and significant probability.The localized probability is modified by controlling birefringence and tunneling conditions.These results may be useful for the capability of optical microscopy and atom imaging.     

Effect of quantization and positron concentration on shielding potentials in electron-positron-ion plasma

The kinetic theory of plasma has been employed to compute the test-charge potential distributions accounting for quantization effects in magnetized electron-positron-ion (EPI) plasmas. In this regard, the degenerate positrons and electrons are assumed to follow the Fermi-Dirac distribution, while inertial ions are modelled by Maxwellian velocity distribution. By solving the Fourier-transformed Vlasov–Poisson equations, a modified dielectric function and electrostatic potential is obtained. By imposing various constraints on the test-charge speed, the potential profile has been analysed in terms of Debye–Hückel (DH), far-field (FF), and wake-field (WF) potentials. It has been found that the amplitude of DH and FF potentials increases by the inclusion of quantization effects, and it becomes the opposite for the WF potential profile. Furthermore, the variation of positron concentration significantly affects the DH, FF, and WF potentials. The present findings are important to understand the shielding phenomenon in degenerate multi-species plasmas.