Yuriy Gulak

Inversion of Andersen Cascade Impactor Data using the Maximum Entropy Method

The problem of the Andersen cascade impactor data inversion is studied using the maximum entropy method to recover the particle size distribution function from a set of measured masses collected on the impactor stages. The classical entropy maximization and its modification to accommodate data errors are reviewed using the techniques of convex optimization. Numerical experiments were performed to test the method on several unimodal and multimodal distributions commonly observed in practice. The Maximum Entropy Method for data inversion produced excellent agreement between the recovered and test Particle Size Distribution Functions without the need for a priori assumptions.

Numerical calibration of the Andersen cascade impactor using a single jet model

A single jet model is described and used to analyze the performance of an 8-stage Andersen cascade impactor (ACI). The two-dimensional axisymmetric jet flow field was calculated numerically by solving the Navier-Stokes equations and particle trajectories were then analyzed to obtain the collection efficiency curves at different flow rates. The resulting efficiency curves and corresponding cutoff diameters were compared and found to be in good agreement with the available experimental data. We also examined the effect of gravity on impactor performance and discuss the limitations of the single jet model.

Solvent Penetration Rate in Tablet Measurement Using Video Image Processing

We describe a simple technique for the measurement of solvent penetration rates into spray-dried lactose (DCL) tablets and tablets made of blended materials using digital video image processing. The results of the experimental study show that the penetration rate in some cases appears to be close to linear with time, which corresponds to non-Fickian or Case II-type diffusion. We discuss relevant capillary invasion models in order to explain the observed penetration rate. The proposed technique allows fast diffusion rate acquisition/processing and can be useful when designing immediate release tablets that require a large number of measurements corresponding to different formulations and processing parameters.

Transient Temperature Monitoring of Pharmaceutical Tablets During Compaction Using Infrared Thermography

Manufacturing of pharmaceutical tablets from powders is always accompanied by the conversion of irreversible mechanical work of compaction into heat. The heat is generated due to friction between powder particles, particles and the die wall, plastic deformation of particles, bonding, and other irreversible processes. The resulting temperature increase potentially might have significant effects on a tablet’s mechanical properties, disintegration time, and drug release. In the present work, we show that using infrared thermography as a nondestructive and noncontact process analytical technology (PAT) tool to measure the tablet’s rate of cooling, in contrast to the temperature evolution, can be directly related to the tablet’s thermal diffusivity. Results show the potential capabilities of this technique to discriminate and toward predicting tensile strength of tablets between same formulations produced at same compaction force but experienced different process shear conditions. Correlation of the tablet’s tensile strength, relative density, and rate of cooling at regular regime with respect to different process shear is also discussed.

On Elementary and Algebraic Cellular Automata

In this paper we study elementary cellular automata from an algebraic viewpoint. The goal is to relate the emergent complex behavior observed in such systems with the properties of corresponding algebraic structures. We introduce algebraic cellular automata as a natural generalization of elementary ones and discuss their applications as generic models of complex systems.

Stress Distribution and Tomographic Profiling with Energy Dispersive X-Ray Scattering

Two novel and potentially powerful, x-ray scattering techniques for tomographic profiling of composite materials and for profiling residual strain variation, versus depth, in a specimen are presented. The techniques utilize a high intensity/energy “white” beam synchrotron source and monitor the energy dispersive scattering from a fixed micro-volume as the specimen is scanned through it. The tomographic profiles based on the net scattered intensity and exploiting absorption coefficient/scattering-power variations, can be contrast enhanced by selectively monitoring scattering from specific crystal structures in a composite material. The strain profiling technique is shown to chronicle the detailed internal the stress variation over several mm’s of steel. The initial state residual stresses, the effect of a cantilever spring imposed external stress, and their interplay in elastic/plastic deformation are discussed.