ENHANCEMENT OF SOLUBILITY AND DISSOLUTION RATE OF ACETYLSALICYLIC ACID VIA CO-CRYSTALLIZATION TECHNIQUE: A NOVEL ASA-VALINE COCRYSTAL

Objective: This study aims to synthesize acetylsalicylic acid (ASA) cocrystals using valine as a coformer via a co-crystallization technique to increase the solubility and dissolution rate of ASA. Methods: The ASA-valine cocrystal (1:1 molar ratio) was prepared using the solvent evaporation technique with ethanol: water (50:50). The cocrystal was characterized using Fourier transform infrared spectroscopy (FT-IR), Differential scanning calorimetry (DSC), Powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM), melting point to confirm the formation of cocrystal. The evaluation of cocrystal was done by drug content determination, solubility and dissolution studies. Results: The prepared cocrystal was successfully confirmed for the formation of a hydrogen bond. The melting point of prepared cocrystal was decreased compared to pure ASA and valine, which indicated the formation of a new crystalline form. The FT-IR studies showed the formation of a new hydrogen bond by shifting the-O-H,-C=O and-N-H functional groups. SEM studies ensured that the prepared cocrystals were in needle-like appearance. Finally, DSC and PXRD studies were also indicated the successful formation of ASA-valine cocrystal. The drug release of cocrystal was found to be 100% at 60th min. Where in the case of pure ASA and marketed product of ASA exhibited the dissolution rate of 59% and 69% at 60th min respectively. Conclusion: The co-crystallization technique can be adopted as the best strategy to increase the solubility and dissolution rate of BCS class 2 drugs. Therefore the prepared ASA-valine cocrystal can be a greater alternative to increase the solubility and dissolution rate compared with pure and marketed ASA

Phase Diffusion in Localized Spatio-Temporal Amplitude Chaos

We present numerical simulations of coupled Ginzburg-Landau equations describing parametrically excited waves which reveal persistent dynamics due to the occurrence of phase slips in sequential pairs, with the second phase slip quickly following and negating the first. Of particular interest are solutions where these double phase slips occur irregularly in space and time within a spatially localized region. An effective phase diffusion equation utilizing the long term phase conservation of the solution explains the localization of this new form of amplitude chaos.Comment: 4 pages incl. 5 figures uucompresse

The Conical Point in the Ferroelectric Six-Vertex Model

We examine the last unexplored regime of the asymmetric six-vertex model: the low-temperature phase of the so-called ferroelectric model. The original publication of the exact solution, by Sutherland, Yang, and Yang, and various derivations and reviews published afterwards, do not contain many details about this regime. We study the exact solution for this model, by numerical and analytical methods. In particular, we examine the behavior of the model in the vicinity of an unusual coexistence point that we call the ``conical'' point. This point corresponds to additional singularities in the free energy that were not discussed in the original solution. We show analytically that in this point many polarizations coexist, and that unusual scaling properties hold in its vicinity.Comment: 28 pages (LaTeX); 8 postscript figures available on request ([email protected]). Submitted to Journal of Statistical Physics. SFU-DJBJDS-94-0

Non-Gaussian Distributions in Extended Dynamical Systems

We propose a novel mechanism for the origin of non-Gaussian tails in the probability distribution functions (PDFs) of local variables in nonlinear, diffusive, dynamical systems including passive scalars advected by chaotic velocity fields. Intermittent fluctuations on appropriate time scales in the amplitude of the (chaotic) noise can lead to exponential tails. We provide numerical evidence for such behavior in deterministic, discrete-time passive scalar models. Different possibilities for PDFs are also outlined.Comment: 12 pages and 6 figs obtainable from the authors, LaTex file, OSU-preprint-

Finite-size scaling and the toroidal partition function of the critical asymmetric six-vertex model

Finite-size corrections to the energy levels of the asymmetric six-vertex model transfer matrix are considered using the Bethe ansatz solution for the critical region. The non-universal complex anisotropy factor is related to the bulk susceptibilities. The universal Gaussian coupling constant $g$ is also related to the bulk susceptibilities as $g=2H^{-1/2}/\pi$, $H$ being the Hessian of the bulk free energy surface viewed as a function of the two fields. The modular covariant toroidal partition function is derived in the form of the modified Coulombic partition function which embodies the effect of incommensurability through two mismatch parameters. The effect of twisted boundary conditions is also considered.Comment: 19 pages, 5 Postscript figure files in the form of uuencoded compressed tar fil

On the Finite Size Scaling in Disordered Systems

The critical behavior of a quenched random hypercubic sample of linear size $L$ is considered, within the ``random-$T_{c}$'' field-theoretical mode, by using the renormalization group method. A finite-size scaling behavior is established and analyzed near the upper critical dimension $d=4-\epsilon$ and some universal results are obtained. The problem of self-averaging is clarified for different critical regimes.Comment: 21 pages, 2 figures, submitted to the Physcal Review

Five-loop renormalization-group expansions for the three-dimensional n-vector cubic model and critical exponents for impure Ising systems

The renormalization-group (RG) functions for the three-dimensional n-vector cubic model are calculated in the five-loop approximation. High-precision numerical estimates for the asymptotic critical exponents of the three-dimensional impure Ising systems are extracted from the five-loop RG series by means of the Pade-Borel-Leroy resummation under n = 0. These exponents are found to be: \gamma = 1.325 +/- 0.003, \eta = 0.025 +/- 0.01, \nu = 0.671 +/- 0.005, \alpha = - 0.0125 +/- 0.008, \beta = 0.344 +/- 0.006. For the correction-to-scaling exponent, the less accurate estimate \omega = 0.32 +/- 0.06 is obtained.Comment: 11 pages, LaTeX, no figures, published versio