The Merck Index of Chemicals and Drugs An Encyclopedia for the Chemist, Pharmacist, Physician and Allied Professions Sixth edition Pp xiv + 1167 (Rahway, NJ: Merck and Company, Inc, 1952) 750 dollars; thumb-indexed, 8 dollars

The Merck Index

Fluid film lubrication

In addition to a number of highly soluble drugs, most new chemical entities under development are poorly water-soluble drugs generally characterized by an insufficient dissolution rate and a small absorption window, leading to the low bioavailability. Controlled-release (CR) formulations have several potential advantages over conventional dosage forms, such as providing a uniform and prolonged therapeutic effect to improve patient compliance, reducing the frequency of dosing, minimizing the number of side effects, and reducing the strength of the required dose while increasing the effectiveness of the drug. Solid dispersions (SD) can be used to enhance the dissolution rate of poorly water-soluble drugs and to sustain the drug release by choosing an appropriate carrier. Thus, a CR-SD comprises both functions of SD and CR for poorly water-soluble drugs. Such CR dosage forms containing SD provide an immediately available dose for an immediate action followed by a gradual and continuous release of subsequent doses to maintain the plasma concentration of poorly water-soluble drugs over an extended period of time. This review aims to summarize all currently known aspects of controlled release systems containing solid dispersions, focusing on the preparation methods, mechanisms of action and characterization of physicochemical properties of the system.

Controlled Release Systems Containing Solid Dispersions: Strategies and Mechanisms

Internet education in mathematics is developing as a new mode of teaching with its own characteristics and possibilities, different from the traditional way of teaching. In a study presented in two parts, we attempt to capture the world of Internet teaching of undergraduate mathematics. In the first part of the study (Engelbrecht, J. and Harding, A.: 2004, ‘Teaching undergraduate mathematics on the web 1: Technologies and taxonomy’), we attempt to create some order in the huge number of activities that are available on the web with a graphical classification of the different types of web courses and discuss some of the technologies involved. In this, the second part of the study, we discuss attributes and implications of this mode of teaching/learning mathematics, also mentioning some of the benefits and concerns. Speculation about the future in such a fluid environment is both risky and fascinating but we nevertheless envisage some possible future trends. Research on this mode of teaching is sparse and open research questions are plentiful. We list possible research issues.

Teaching Undergraduate Mathematics on the Internet.

Pharmaceutical applications of confocal laser scanning microscopy: The physical characterisation of pharmaceutical systems

Ice accretion is a problematic natural phenomenon that affects a wide range of engineering applications including power cables, radio masts, and wind turbines. Accretion on aircraft wings occurs when supercooled water droplets freeze instantaneously on impact to form rime ice or runback as water along the wing to form glaze ice. Most models to date have ignored the accretion of mixed ice, which is a combination of rime and glaze. A parameter we term the “freezing fraction” is defined as the fraction of a supercooled droplet that freezes on impact with the top surface of the accretion ice to explore the concept of mixed ice accretion. Additionally we consider different “packing densities” of rime ice, mimicking the different bulk rime densities observed in nature. Ice accretion is considered in four stages: rime, primary mixed, secondary mixed, and glaze ice. Predictions match with existing models and experimental data in the limiting rime and glaze cases. The mixed ice formulation however provides additio...

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Mixed ice accretion on aircraft wings

Steady Stokes flow driven by gravity down an inclined plane over and around an attached obstacle is considered. The effects of the obstacle are examined for various flow configurations and results produced for flow over hemispherical obstacles. Comparison is made with previously published papers that assume that the obstacle is small and/or the free surface deflection and disturbance velocity are small. Values for the unit normal and curvature of the free surface are found using both finite difference approximations and Hermitian radial basis function interpolations, with the resulting solutions compared. Free surface profiles for thin film flows over hemispherical obstacles that approach the film surface are produced and the effects of near point singularities considered. All free surface profiles indicate an upstream peak, followed by a trough downstream of the obstacle with the peak decaying in a “horseshoe” shaped surface deformation. Flow profiles are governed by the plane inclination, the Bond numbe...

Three-dimensional thin film flow over and around an obstacle on an inclined plane

Purpose. pH modifiers are often used to promote drug solubility/stability in dosage forms, but predicting the extent and duration of internal pH modification is difficult. Here, a noninvasive technique is developed for the spatial and temporal mapping of pH in a hydrated pharmaceutical pellet, within a pH range appropriate for microenvironmental pH control by weak acids.

Measurement and mapping of pH in hydrating pharmaceutical pellets using confocal laser scanning microscopy.

The work presented forms part of an ongoing investigation, focusing on modeling the motion of a wall oil film present in a bearing chamber and comparison to existing experimental data. The film is generated through the impingement of oil droplets shed from a roller bearing. Momentum resulting from the impact of oil droplets, interfacial shear from the airflow, and gravity cause the film to migrate around the chamber. Oil and air exit the chamber at scavenge and vent ports. A previously reported numerical approach to the simulation of steady-state two-phase flow in a bearing chamber, which includes in-house submodels for droplet-film interaction and oil film motion, has been extended. This paper includes the addition of boundary conditions for the vent and scavenge together with a comparison to experimental results obtained from ITS, University of Karlsruhe. The solution is found to be sensitive to the choice of boundary conditions applied to the vent and scavenge.

A Numerical Model for Oil Film Flow in an Aeroengine Bearing Chamber and Comparison to Experimental Data

An understanding and optimization of three-dimensional air/oil flows in aero-engine transmission systems forms an integral part of future designs. This especially applies to bearing chambers, which contain a complex two-phase flow formed by the interaction of sealing airflows and lubrication oil. A critical design quantity is the composition of the liquid (oil) and gas (air) phases in the exit flows. Using a previously validated numerical model, the air/oil flow in a commercial bearing chamber is computed with particular focus on the flow exiting the chamber. The division of oil exiting the chamber through the vent and scavenge ports is determined for three shaft speeds and two configurations of the vent port. Comparison with available experimental data shows that consistent trends are predicted, but further model development is necessary in the vicinity of the scavenge port.

Stephen Hibberd

Papers

Mixed ice accretion on aircraft wings

Three-dimensional thin film flow over and around an obstacle on an inclined plane

Measurement and mapping of pH in hydrating pharmaceutical pellets using confocal laser scanning microscopy.

A Numerical Model for Oil Film Flow in an Aeroengine Bearing Chamber and Comparison to Experimental Data

Prediction of air/oil exit flows in a commercial aero-engine bearing chamber