The evolution of interstellar clouds in a streaming hot plasma including heat conduction

To examine the evolution of giant molecular clouds in the stream of a hot plasma we performed two-dimensional hydrodynamical simulations that take full account of self-gravity, heating and cooling effects and heat conduction by electrons. We use the thermal conductivity of a fully ionized hydrogen plasma proposed by Spitzer and a saturated heat flux according to Cowie & McKee in regions where the mean free path of the electrons is large compared to the temperature scaleheight. Significant structural and evolutionary differences occur between simulations with and without heat conduction. Dense clouds in pure dynamical models experience dynamical destruction by Kelvin-Helmholtz (KH) instability. In static models heat conduction leads to evaporation of such clouds. Heat conduction acting on clouds in a gas stream smooths out steep temperature and density gradients at the edge of the cloud because the conduction timescale is shorter than the cooling timescale. This diminishes the velocity gradient between the streaming plasma and the cloud, so that the timescale for the onset of KH instabilities increases, and the surface of the cloud becomes less susceptible to KH instabilities. The stabilisation effect of heat conduction against KH instability is more pronounced for smaller and less massive clouds. As in the static case more realistic cloud conditions allow heat conduction to transfer hot material onto the cloud's surface and to mix the accreted gas deeper into the cloud.Comment: 19 pages, 12 figures, accepted in Astronomy and Astrophysic

Formulation and Evaluation of Fast Dissolving Films for Delivery of Triclosan to the Oral Cavity

The present investigation was undertaken with the objective of formulating TC containing fast dissolving films for local delivery to oral cavity. Various film forming agents, film modifiers and polyhydric alcohols were evaluated for optimizing the composition of fast dissolving films. The potential of poloxamer 407 and hydroxypropyl-β- cyclodextrin (HPBCD) to improve solubility of TC was investigated. Fast dissolving films containing hydroxypropyl methylcellulose (HPMC), xanthan gum, and xylitol were formulated. Use of poloxamer 407 and HPBCD resulted in significant improvement in the solubility of TC. Fast dissolving films containing TC-HPBCD complex and TC-Poloxamer 407 were formulated and were evaluated for the in vitro dissolution profile and in vitro microbiological assay. Films containing TC-Poloxamer 407 exhibited better in vitro dissolution profile and in vitro antimicrobial activity as compared to the films containing TC-HPBCD complex. Effect of incorporation of eugenol on the in vivo performance of TC-Poloxamer 407 containing films was evaluated in human volunteers. Eugenol containing films improved the acceptability of TC-Poloxamer 407 films with respect to taste masking and mouth freshening without compromising the in vivo dissolution time

Development and evaluation of Cetirizine HCl taste-masked oral disintegrating tablets

The purpose of the current study was to mask the taste of cetirizine HCl and to incorporate the granules produced in oral disintegrating tablets (ODT). The bitter, active substance was coated by fluidized bed coating using Eudragit® RL30-D at levels between 15% and 40% w/w. The ODTs were developed by varying the ratio of superdisintegrants such as sodium croscarmellose, crospovidone grades and low substituted hydroxypropyl cellulose (L-HPC). A direct compression process was used to compress the ODTs under various compaction forces to optimize tablet robustness. The properties of the compressed tablets including porosity, hardness, friability and dissolution profiles were further investigated. The in vitro and in vivo evaluation of the tablet disintegration times showed almost identical rapid disintegration below 10 s at the optimal levels of each superdisintegrant. Finally, the taste and sensory evaluation in human volunteers demonstrated excellence in masking the bitter active and tablet palatability

Nonlinear model-based control of thin-film drying for continuous pharmaceutical manufacturing

This paper considers the model-based control of composition and thickness for a thin-film drying process used in the continuous manufacturing of pharmaceutical tablets. In this nonlinear distributed dynamical system, a drug formulation solution is coated onto a moving surface and then dried to form thin films of approximately 250 μm in thickness. A dynamic optimizer is designed that employs a first-principles process model to simulate the spatial distribution of solvent concentration in the film and the thin film shrinkage during drying. A critical parameter to describe the highly nonlinear dynamics of the thin-film drying is the mutual polymer-solvent diffusion coefficient, which strongly depends on solvent concentration and film temperature. Two optimal control problems are studied for set point tracking of solvent concentration and minimization of energy consumption in the dryer while satisfying various operational and product quality constraints. An unscented Kalman filter is designed to facilitate the output feedback implementation of the dynamic optimizer and to estimate unmeasured thin-film quality attributes such as the film thickness. The performance of the model-based controller is compared to that of a proportional integral controller in two simulation case studies. The nonlinear model-based control strategy has improved versatility and the potential to reduce production of off spec material. © 2013 American Chemical Society