A study of the problems presented by the foster mothers of adolescent boys to the placement worker.

Thesis (M.S.)--Boston Universit

Individuals' insight into intrapersonal externalities

An intrapersonal externality exists when an individual's decisions affect the outcomes of her future decisions. It can result in decreasing or increasing average returns to the rate of consumption, as occurs in addiction or exercise. Experimentation using the Harvard Game, which models intrapersonal externalities, has found differences in decision making between drug users and control subjects, leading to the argument that these externalities influence the course of illicit drug use. Nevertheless, it is unclear how participants who behave optimally conceptualise the problem. We report two experiments using a simplified Harvard Game, which tested the differences in contingency knowledge between participants who chose optimally and participants who did not. Those who demonstrated optimal performance exhibited both a pattern of correct responses and systematic errors to questions about the payoff schedules. The pattern suggested that they learned explicit knowledge of the change in reinforcement on a trail-by-trial basis. They did not have, or need, a full knowledge of the historical interaction leading to each payoff. We also found no evidence of choice differences between participants who were given a guaranteed payment and participants who were paid contingent on their performance, but those given a guaranteed payment were able to report more contingency knowledge as the experiment progressed, suggesting that they explored more rather than settling into a routine. Experiment 2 showed that using a fixed inter-trial interval did not change the results

NACA Research Memorandums

Report presenting testing regarding the Bell X-2 supersonic research airplane, which is equipped with a skid main landing gear and nose wheel, to determine the low-speed handling qualities and landing characteristics. Results regarding the landing approach pattern, time histories, and final resting position of the airplane at landing are provided

Low pressure microfilter design aspects and filtration performance

A microfilter should retain micron sized material yet provide minimal resistance to liquid flow. A slotted pore surface microfilter was oscillated whilst filtering yeast cells under constant rate. At shear rates over 7760 s-1, a pore blocking model fitted the data. The operating pressure was very low (<1000 Pa), but particle retention was limited by the 4 micron pore slot width. A sintered glass micro-bead coating improved yeast rejection: 95% at 1.7 microns at a shear rate of 5000 s-1, with a 1.2 kPa transmembrane pressure. Two models were validated to assist with the design of future micro-bead coatings constructed from spherical particles

Production of porous silica microparticles by membrane emulsification

A method for the production of near-monodispersed spherical silica particles with controllable porosity based on the formation of uniform emulsion droplets using membrane emulsification is described. A hydrophobic metal membrane with a 15 μm pore size and 200 μm pore spacing was used to produce near-monodispersed droplets, with a mean size that could be controlled between 65 and 240 μm containing acidified sodium silicate solution (with 4 and 6 wt % SiO2) in kerosene. After drying and shrinking, the final silica particles had a mean size in the range between 30 and 70 μm. The coefficient of variation for both the droplets and the particles did not exceed 35%. The most uniform particles had a mean diameter of 40 μm and coefficient of variation of 17%. By altering the pH of the sodium silicate solution and aging the gel particles in water or acetone, the internal structure of the silica particles was successfully modified, and both micro- and mesoporous near-monodispersed spherical particles were produced with an average internal pore size between 1 and 6 nm and an average surface area between 360 and 750 m2 g–1. A material balance and particle size analysis provided identical values for the internal voidage of the particles, when compared to the voidage as determined by BET analysis

Preparation and characterization of PLGA particles for subcutaneous controlled drug release by membrane emulsification

Uniformly sized microparticles of poly(DL, lactic-co-glycolic) (PLGA) acid, with controllable median diameters within the size range 40 to 140 microns, were successfully prepared by membrane emulsification of an oil phase injected into an aqueous phase, followed by solvent removal. Initially, simple particles were produced as an oil-in-water emulsion, where dichloromethane (DCM) and PLGA were the oil phase and water with stabiliser was the continuous phase. The oil was injected into the aqueous phase through an array type microporous membrane, which has very regular pores equally spaced apart, and two different pore sizes were used: 20 and 40 microns in diameter. Shear was provided at the membrane surface, causing the drops to detach, by a simple paddle stirrer rotating above the membrane. Further tests involved the production of a primary water-in-oil emulsion, using a mechanical homogeniser, which was then subsequently injected into a water phase through the microporous membrane to form a water-in-oil-in-water emulsion. These tests used a water soluble model drug (blue dextran) and encapsulation efficiencies of up to 100% were obtained for concentrations of 15% PLGA dissolved in the DCM and injected through a 40 micron membrane. Solidification of the PLGA particles followed by removal of the DCM through the surrounding aqueous continuous phase. Different PLGA concentrations, particle size and osmotic pressures were considered in order to find their effect on encapsulation efficiency. Osmotic pressure was varied by changing the salt concentration in the external aqueous phase whilst maintaining a constant internal aqueous phase salt concentration. Osmotic pressure was found to be a significant factor on the resulting particle structure, for the tests conducted at lower PLGA concentrations (10 and 5% PLGA). The PLGA concentration and particle size distribution influence the time to complete the solidification stage and a slow solidification, formed by stirring gently overnight, provided the most monosized particles and highest encapsulation efficiency

Novel membrane emulsification method of producing highly uniform silica particles using inexpensive silica sources

A membrane emulsification method for production of monodispersed silica-based ion exchange particles through water-in-oil emulsion route is developed. A hydrophobic microsieve membrane with 15 :m pore size and 200 :m pore spacing was used to produce droplets, with a mean size between 65 and 240 :m containing acidified sodium silicate solution (with 4 and 6% wt. SiO2) in kerosene. After drying, the final silica particles had a mean size in the range between 30 and 70 :m. Coefficient of variation for both the droplets and particles did not exceed 35%. The most uniform particles had a mean diameter of 40 :m and coefficient of variation of 17%. The particles were functionalised with 3-aminopropyltrimethoxysilane and used for chemisorption of Cu(II) from an aqueous solution of CuSO4 in a continuous flow stirred cell with slotted pore microfiltration membrane. Functionalised silica particles showed a higher binding affinity toward Cu(II) than non-treated silica particles

Stirred cell membrane emulsification and factors influencing dispersion drop size and uniformity

Water-in-oil (w/o) and oil-in-water (o/w) emulsions were generated using 30-μm pore diameter surface membranes to investigate the factors influencing drop size, and the degree of uniformity of drop size distribution, using a stirred cell employing a simple paddle mounted above a circular disc membrane. The importance of the transitional radius, which is the radius at which the vortex around the unbaffled paddle stirrer changes from a forced vortex to a free vortex and the shear stress at the membrane surface below the stirrer is at its greatest, is demonstrated. Monosized emulsions were produced, with drop size distribution coefficient of variation values of 10% for o/w emulsions and 13.5% for w/o emulsions. These tests demonstrated that a membrane of reduced annular operating area (ringed membrane) produced a more monosized o/w emulsion than a membrane where the full area was used to generate the emulsion, without affecting the mean drop size. The improved size distribution was achieved while the transitional radius was located within the ringed annular section of the membrane. The force balance model, applied to drops formed at the surface of the membrane during emulsification, predicted the droplet diameter provided further drop break up within the stirred cell did not occur. Drop break up occurred at Reynolds numbers below 300 for both oil-in-water and water-in-oil dispersions. Therefore, for Reynolds numbers greater than this, an annular radial ring membrane can be designed to produce monosized droplets using the stirred cell at known continuous phase viscosities with predictable mean droplet size. This knowledge can be used as a design tool to produce monosized droplets of a specified size for various applications using simple stirred cell emulsification

Novel method of producing highly uniform silica particles using inexpensive silica sources

Novel method of producing highly uniform silica particles using inexpensive silica source

Liquid-liquid membrane dispersion in a stirred cell with and without controlled shear

Oil was passed through membranes into a continuous water phase containing a surfactant (Tween 20) to form oil dispersions with drop diameters between 40 and 400 μm. Two types of stirred equipment were used:  a Weissenberg rheometer (cone and plate geometry) providing constant shear stress at all radial positions which was modified to include a membrane instead of the plate and a simple stirred cell, with a paddle rotating above the membrane, providing variable shear with radial position. Experiments show that the simple paddle-stirred cell provided an oil drop dispersion that was as monosized as that produced by the controlled shear device, if not better. An analysis indicated that only the section of the membrane close to the radius of the highest shear under the paddle stirred membrane produced oil drops. The membranes used in the experiments contained a regular array of nontortuous pores uniformly spaced and provided oil injection rates up to 1000 L m-2 h-1, which is much higher than reported fluxes for the alternative tortuous pore channel membranes made by sintering