A stability-indicating HPLC method to determine cyproterone acetate in tablet formulations

A simple and accurate liquid chromatographic method was developed to estimate cyproterone acetate (CA) in pharmaceuticals. The drug was chromatographed on a reversed-phase C18 column. Eluents were monitored at a wavelength of 254 nm utilizing a mixture (60:40) of acetonitrile and water. Solution concentrations were measured on a weight basis to avoid the use of an internal standard. The method was statistically validated for linearity, accuracy, precision, and selectivity. Due to its simplicity and accuracy, we believe that the method can be used for routine quality control analysis. No specific sample preparation is required except for the use of a column guard and a suitable prefilter attached to the syringe.     

Phase-reversal broad-band traveling-wave LiNbO/sub 3/ electrooptic modulator optimized for time-domain applications by a genetic algorithm

Several new nonperiodic spatial codes for phase-reversal coplanar waveguides (CPWs) used in the framework of the quasi-phase match technique (QPM) for broadening the optical response of z-cut LiNbO/sub 3/ electrooptic modulators (EOMs) are presented. The peculiarity of the codes is that they open the possibility for time-domain applications of EOMs based on nonperiodic QPM structures. They were obtained by using a specialized version of the genetic algorithm that generates an optimal length and number of the phase-reversal sections. The codes provide both flat amplitude and nearly linear phase frequency responses of the EOM within several frequency ranges important for fiber-optical/radio systems: from dc to 25, 40, and 90 GHz. The phase-reversal structures described here were optimized taking into account the CPW electrode losses and under the matching condition with 50 /spl Omega/-sources. They possess as low value of the drive voltage (V/sub /spl pi//, required for realization of 100% EO modulation efficiency) as possible for EOMs based on QPM, under the above conditions.     

Linear estimation for discrete-time systems in the presence oftime-correlated disturbances and uncertain observations

This note considers optimum linear recursive estimation for linear discrete-time systems with uncertain observations in cases where state and measurement noises are correlated. The different kinds of estimation problems treated include one-stage prediction and filtering     

Etude structurale des phases Sc5,5Nb1,5O12 et Sc5,5Ta1,5O12. Ordre des cations dans les composes (A,B)7O12 de type Y6UO12

New phases Sc_5,5Nb_1,5O₁₂ and Sc_5,5Ta_1,5O₁₂ were prepared. Their structure is rhombohedral (space group R3, Z = 1) ($\text{a}\text{= 6,080}\text{A}\text{?}\text{α = 99°16}$ (niobate), $\text{a}\text{= 6,084}\text{A}\text{?}\text{α = 99°18}$ (tantalate). Many (A,B)₇O₁₂ ternary oxides have the same fluorite-related structure, the distortion from the cubic lattice depending upon ordering of cations on non-equivalent atomic positions. A sensitive influence of the degree of ordering is observed in the vibrational spectra of those phases.     

Properties of sodium caseinate film-forming dispersions and films

The flow properties of sodium caseinate (NaCAS) film-forming dispersions were studied as a function of protein and glycerol concentration. Apparent viscosity vs. concentration profiles showed a disruption at about 10% (wt/wt) NaCAS. This was interpreted in terms of protein-water and protein-protein interactions. The presence of glycerol in the NaCAS film-forming suspensions reduced the viscosity of aqueous NaCAS as a consequence of decreasing protein-protein and protein-solvent interactions through the hydrogen bonding formation between the glycerol, the polypeptide chain of NaCAS, and water molecules. For higher concentration of glycerol, viscosity of NaCAS dispersions increased as a result of increasing total solid content. The glass transition temperature for solid films of 10% (wt/wt) NaCAS decreased with the glycerol content. The glycerol-protein interactions reduced the protein-protein interaction and, thus, increased the intermolecular spacing, leading to higher protein chain mobility and water vapor permeability.     

Infrared multiphoton dissociation with a hollow fiber waveguide

A novel scheme for performing infrared multiphoton dissociation (IRMPD) is presented in which a hollow fiber waveguide (HFWG) is used to transmit IR radiation into the ion storage region of a mass spectrometer. Efficient dissociation of oligonucleotide and protein ions is demonstrated on an ESI-FTICR instrument in which IRMPD is performed in the external ion reservoir and on a quadrupole ion trap. Using a simple optical scheme consisting of a single focusing lens and an x, y translator, the 10.6-microm IR laser beam, initially 3.5 mm in diameter, is focused into the vacuum-sealed HFWG. The small internal diameter and the high transfer efficiency of the waveguide allow IR radiation of high power density to be employed for IRMPD. In studies performed on a quadrupole ion trap, a 500-microm-i.d. waveguide was used as a medium to transmit IR radiation directly through a 700-microm orifice in the ring electrode. Efficient IRMPD of both a 12-mer oligonucleotide and the protein melittin were performed at laser powers of 0.5 and 3.2 W, respectively.     

Oxidation Behavior of Al-Alloyed ZrSi2

The oxidation resistance of ZrSi₂–4 at.% Al prepared by reactive sintering was evaluated in air between 600 and 1100°C. The microstructure of the intermetallic consists of equiaxed ZrSi₂ grains of about 10 m with isolated nonreacted silicon and aluminum particles at grain boundaries. The oxidation rate of the alloy shows an anomalous dependence with the temperature. Mass-gain curves can be divided in an initial transient state and a subsequent steady state. Although the mass gain in both stages is very low, it is negligible during the steady state. Oxidation during the transient stage is determined by inward oxygen diffusion in the intermetallic substrate. The subsequent decrease in the oxidation rate during the steady stage is caused by the formation of a protective alumina layer. Grain boundaries contribute to the fast inward oxygen transport into the alloy, leading to internal oxidation of nonreacted silicon and aluminum particles.     

The formation of an apatite coating on carboxylated polyphosphazenes via a biomimetic process

The biomimetic deposition of an apatite coating on polyphosphazene was investigated. A polyphosphazene having carboxylatophenoxy side groups was synthesized as a candidate polymer with heterogeneous nucleation sites for apatite deposition. Poly[bis(carboxylatophenoxy)phosphazene] (PCPP) was synthesized by a two-step synthetic route involving the synthesis of poly(dichlorophosphazene) (PDP) followed by nucleophilic replacement of the chlorine atoms of PDP with carboxylatophenoxy groups. The surface of the carboxylated polyphosphazene induced the formation of a dense layer of apatite on the surface after incubation in simulated body fluid at 37 °C with an ionic concentration approximately the same as that of human blood plasma. The results suggested an early precipitation of octacalcium phosphate and calcium phosphate intermediates on the surface, both of which are known to promote osteoblast differentiation and proliferation.     

Tight closed-form approximation for the ergodic capacity of orthogonal STBC

In this letter we derive a simple and tight closed-form approximation for the ergodic capacity of orthogonal space-time block coding in arbitrary fading channels. The expression is an analytical function of the power covariance matrix of the channel. In the case of uncorrelated channels the expression only depends on the variances of the channel power gains. These channel statistics can be easily obtained from both analytical and physical fading channel models. Simulations results show the accuracy of the proposed expression     

Performance Evaluation of a Multicell Topology Implemented With Single-Phase Nonregenerative Cells Under Unbalanced Supply Voltages

The analysis of a multicell topology that is implemented with single-phase nonregenerative cells under an unbalanced ac mains is presented. The study shows that the topology naturally compensates most of the voltage unbalance; for instance, for a 100% voltage unbalance in the ac mains, just 32% reaches the load. For critical applications, a feedforward control technique is proposed in order to compensate the remaining unbalance at the load side. The resulting topology, in combination with the proposed strategy, reduces near to zero the load fundamental voltage unbalance, while the input current unbalance and distortion are also improved. A theoretical analysis that is based on symmetrical components and the experimental results confirm the theoretical considerations.