In vitro evaluation of commercially available theophylline sustained release tablets in Pakistan

The dissolution behavior of five commercially available brands of sustained release theophylline tablets was studied in phosphate buffer solutions of pH 1.2, 4.5, 5.5, 6.0 and 7.5 at 37 °C using the USP dissolution apparatus II (paddle method). Drug concentration in the samples was determined spectrophotometrically at 272 nm. For predicting the release characteristics of theophylline from selected commercially available tablets the data obtained in the dissolution studies was fitted into various mathematic models defining kinetic parameters of drug release like zero-order rate equation, first-order rate equation, Hixen-crowell cube root law, Higuchi equation and Korsemeyer-Peppas model. Tablets were subjected to weight variation test, hardness, drug content and in vitro release studies. The present study revealed that drug release increases with the increase of pH of the dissolution medium and also varies from brand to brand. Among the five selected brands, B1 and B4 showed better pH dependency and drug release behaviour. It has been suggested that possible reasons for difference in dissolution or drug release behaviour are the difference in the manufacturing techniques and the quantity of hydrophobic excepients used by different manufacturers, which retard the penetration of dissolution medium and ultimately decreases availability of drug in the solution.Colegio de Farmacéuticos de la Provincia de Buenos Aire

In vitro evaluation of commercially available theophylline sustained release tablets in Pakistan

The dissolution behavior of five commercially available brands of sustained release theophylline tablets was studied in phosphate buffer solutions of pH 1.2, 4.5, 5.5, 6.0 and 7.5 at 37 °C using the USP dissolution apparatus II (paddle method). Drug concentration in the samples was determined spectrophotometrically at 272 nm. For predicting the release characteristics of theophylline from selected commercially available tablets the data obtained in the dissolution studies was fitted into various mathematic models defining kinetic parameters of drug release like zero-order rate equation, first-order rate equation, Hixen-crowell cube root law, Higuchi equation and Korsemeyer-Peppas model. Tablets were subjected to weight variation test, hardness, drug content and in vitro release studies. The present study revealed that drug release increases with the increase of pH of the dissolution medium and also varies from brand to brand. Among the five selected brands, B1 and B4 showed better pH dependency and drug release behaviour. It has been suggested that possible reasons for difference in dissolution or drug release behaviour are the difference in the manufacturing techniques and the quantity of hydrophobic excepients used by different manufacturers, which retard the penetration of dissolution medium and ultimately decreases availability of drug in the solution.Colegio de Farmacéuticos de la Provincia de Buenos Aire

Second Order Power Corrections in the Heavy Quark Effective Theory I. Formalism and Meson Form Factors

In the heavy quark effective theory, hadronic matrix elements of currents between two hadrons containing a heavy quark are expanded in inverse powers of the heavy quark masses, with coefficients that are functions of the kinematic variable $v\cdot v'$. For the ground state pseudoscalar and vector mesons, this expansion is constructed at order $1/m_Q^2$. A minimal set of universal form factors is defined in terms of matrix elements of higher dimension operators in the effective theory. The zero recoil normalization conditions following from vector current conservation are derived. Several phenomenological applications of the general results are discussed in detail. It is argued that at zero recoil the semileptonic decay rates for $B\to D\,\ell\,\nu$ and $B\to D^*\ell\,\nu$ receive only small second order corrections, which are unlikely to exceed the level of a few percent. This supports the usefulness of the heavy quark expansion for a reliable determination of $V_{cb}$.Comment: (34 pages, REVTEX, two postscript figures available upon request), SLAC-PUB-589

Efficacy of fertilizing method for different potash sources in cotton (Gossypium hirsutum L.) nutrition under arid climatic conditions

Precise choice of potassium (K) source and application method does matter for its cost-effectiveness. This study was aimed to evaluate the best source and method of K fertilizer application to improve cotton productivity and profitability under an arid climate. Three different K sources (KNO3, K2SO4 and KCl) were applied at 100 kg ha-1 by four methods, i.e. a) basal application, b) side dressing, c) fertigation and d) foliar application of 2% K2SO4. The highest productivity and profitability were recorded with K2SO4 applied as foliar application. Total boll weight per plant was similar in foliar applied K2SO4 and basal application of KNO3. Better boll opening in foliar applied K2SO4, perhaps, played decisive role for increased seed-cotton yield. For basal application and side dressing, KNO3 produced the highest seed-cotton yield, but the benefit cost ratio was better for foliar applied K2SO4. In crux, foliar application of K2SO4 might be opted to improve the seed cotton yield, fiber quality and net returns under the arid climate. However, soil K application through K2SO4 and/or KNO3 is essential to balance the K removal from soil

Axial behavior of reinforced concrete short columns strengthened with wire rope and T-shaped steel plate units.

yesThis paper presents a relatively simple column strengthening procedure using unbonded wire rope and T-shaped steel plate units. Twelve strengthened columns and an unstrengthened control column were tested to failure under concentric axial load to explore the significance and shortcomings of the proposed strengthening technique. The main variables investigated were the volume ratio of wire ropes as well as geometrical size and configuration of T-shaped steel plates. Axial load capacity and ductility ratio of columns tested were compared with predictions obtained from the equation specified in ACI 318-05 and models developed for conventionally tied columns, respectively. The measured axial load capacities of all strengthened columns were higher than predictions obtained from ACI 318-05, indicating that the ratio of the measured and predicted values increased with the increase of volume ratio of wire ropes and flange width of T-shaped steel plates. In addition, at the same lateral reinforcement index, a much higher ductility ratio was exhibited by strengthened columns having a volume ratio of wire ropes above 0·0039 than tied columns. The ductility ratio of strengthened columns tested increased with the increase of flange width, thickness, and web height of T-shaped steel plates. A mathematical model for the prediction of stress–strain characteristics of confined concrete using the proposed strengthening technique is developed, that was in good agreement with test results

One-pion transitions between heavy baryons in the constituent quark model

Single pion transitions of S wave to S wave, P wave to S wave and P wave to P wave heavy baryons are analyzed in the framework of the Heavy Quark Symmetry limit (HQS). We use a constituent quark model picture for the light diquark system with an underlying SU(2N_{f}) X O(3) symmetry to reduce the number of the HQS coupling factors required to describe these transitions. We also use the quantum theory of angular momentum to rewrite the one-pion transitions constituent quark model results in a more general form using the 6j- and 9j-symbols. We finally estimate the decay rates of some single pion transitions between charm baryon states.Comment: Latex, 33 pages including 2 figures (Postscript). Some typos are corrected with minor changes. Two references were added to the final version which will appear in Phy. Rev.

Excited heavy baryon masses to order Lambda_{QCD}/m_Q from QCD sum rules

Masses of the p-wave excited heavy baryons have been calculated to the Lambda_{QCD}/m_Q order using QCD sum rule method within the framework of heavy quark effective theory. Numerical results for kinetic energy lambda_1 and chromo-magnetic interaction lambda_2 are presented. The splitting between spin 1/2 and 3/2 doublet derived from our calculation is given, for which the agreement with the current experiment is desirable.Comment: RevTeX4, 10 pages, to appear in Phys. Rev.

Direct characterization of photo-induced lattice dynamics in BaFe₂As₂

Ultrafast light pulses can modify electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved X-ray scattering to measure the lattice dynamics of photoexcited BaFe$_{2}$As$_{2}$. On optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A$_{1g}$ mode that modulates the Fe–As–Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photoinduced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands

Leptonic and Semileptonic Decays of Charm and Bottom Hadrons

We review the experimental measurements and theoretical descriptions of leptonic and semileptonic decays of particles containing a single heavy quark, either charm or bottom. Measurements of bottom semileptonic decays are used to determine the magnitudes of two fundamental parameters of the standard model, the Cabibbo-Kobayashi-Maskawa matrix elements $V_{cb}$ and $V_{ub}$. These parameters are connected with the physics of quark flavor and mass, and they have important implications for the breakdown of CP symmetry. To extract precise values of $|V_{cb}|$ and $|V_{ub}|$ from measurements, however, requires a good understanding of the decay dynamics. Measurements of both charm and bottom decay distributions provide information on the interactions governing these processes. The underlying weak transition in each case is relatively simple, but the strong interactions that bind the quarks into hadrons introduce complications. We also discuss new theoretical approaches, especially heavy-quark effective theory and lattice QCD, which are providing insights and predictions now being tested by experiment. An international effort at many laboratories will rapidly advance knowledge of this physics during the next decade.Comment: This review article will be published in Reviews of Modern Physics in the fall, 1995. This file contains only the abstract and the table of contents. The full 168-page document including 47 figures is available at http://charm.physics.ucsb.edu/papers/slrevtex.p

Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory

Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle Physic