No description available.

No description available.

No description available.

Cindy Sherman’s photographic series, Untitled Film Stills, is an icon of postmodern art. The series is comprised of discrete single-frame narratives, which Sherman rendered in the visual vocabulary of mid-century cinematic publicity photography. One of the series’ most unifying features is its pervasive ambiguity, which Sherman has described as a conscious motivation behind the series. Despite the Stills’ continuous, international success, not every photograph in the series has merited uniform popularity, and some are largely absent from the greater circulation of popular and critical discourse. There is, in fact, significant variation in the circulation of individual Stills. I suggest that there is a spectrum of ambiguity in the photographs, and that this spectrum converges with the range of circulation. Within these spectra there are limits to the effectiveness of ambiguity. Therefore, the question that has governed my research is, “What is the threshold of ambiguity in Untitled Film Stills?” / text

Thesis (PhD)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The use of solar distillation as a means of desalination to provide potable water to communities in remote and arid regions has often been discarded on economic grounds mainly because of the inherent low efficiency of relatively expensive solar distillation units (solar stills). Closer analysis of this constraint showed that by following a mainly Physical Chemistry approach (rather than the traditional engineering one), the technology could be made more economically attractive through (1) lowering the construction cost of the solar still and / or (2) increasing its operational life and / or (3) increasing its efficiency. The study into different solar still designs showed that, despite its limitations, the basin solar still is preferred due to its simplicity, ease of operation and low maintenance. Given the solar distillation process as formulated in this study, substitute durable components could be identified and optimised for this design. A basin solar still that costs about 80% less than a reference unit without an apparent drop in performance was consequently developed and successfully tested up to full plant scale. An in-house experimental facility that simulates solar still behaviour under controlled environmental conditions was developed to simulate conditions of lower radiation intensity and productivity, which enabled research into performance enhancement and microbiological water quality. It was found that (a) absorption of the radiation by the water plays an important part in productivity and that a productivity decrease of up to 33% can be expected as the black interior lining becomes contaminated, (b) the simulated winter productivity of the basin still was about 25% of the summer value due to the lesser amount of solar radiation hours, the lower angles of radiation incidence onto the cover and the decrease in water area receiving direct radiation, (c) an annual productivity increase of about 10% can be obtained when a particular reflector configuration is fixed behind the basin, and (d) the microbiological pasteurisation temperature is less than the distillation onset temperature. This study played an important role in making solar still technology affordable for use by poor, rural communities, as was demonstrated by the successful use of the research product (basin solar still) in a pilot drinking water plant at a typical target community. This was made possible through the use of evaluation models developed as part of this research, which addressed relevant construction and performance factors influencing the economic viability of the specific solar still. The following outcomes of this study can be regarded as new contributions to the field of solar distillation technology, namely (a) a test matrix that can be used to screen solar still construction materials at component level, (b) an evaluation model that can be used to determine the economic viability of solar stills at a given location, (c) a laboratory testing facility to study solar still behaviour under controlled conditions and (d) a solar still design that has been optimised and tested for local field application. / AFRIKAANSE OPSOMMING: Die gebruik van son-energie om brakwater deur middel van distillasie te ontsout en sodoende drinkwater aan afgeleë gemeenskappe te verskaf, is herhaaldelik in die verlede as ekonomies nie-lewensvatbaar aangetoon. Dit is hoofsaaklik toeskryfbaar aan die inherente lae effektiwiteit van sodanige stelsels, asook die hoë kapitaalkoste daaraan verbonde. Die hoofsaaklike faktore wat die tegnologie bekostigbaar kan maak, is egter hieruit afgelei en volgens 'n Fisiese Chemie benadering geoptimeer, naamlik (1) vermindering van die konstruksiekoste van die sondistilleerder-eenhede, en / of (2) verlenging van die operasionele leeftyd daarvan, en / of (3) verhoging van effektiwiteit van die stelsel. Die literatuurstudie het aangetoon dat die pan-tipe sondistilleerder-eenheid verkieslik as navorsingsbasis is omdat dit eenvoudig en maklik bedryf- en onderhoudbaar is. Vanuit die geformuleerde beskrywing van die sondistillasie-proses kon plaasvervangende komponente vir die sondistilleerder-eenheid geïdentifiseer en getoets word, wat daartoe gelei het dat 'n eenheid met dieselfde funksioneringseienskappe vir sowat 80% goedkoper ontwikkel kon word. 'n Laboratoriumopstelling waarmee lae bestralingskondisies gesimuleer kan word, is ontwikkel om navorsing op produktiwiteitsverbetering en mikrobiologiese produkwaterkwaliteit te doen. Dit is aangetoon dat (a) absorpsie van die inkomende bestraling deur die water belangrik is en dat 'n sondistilleerder-eenheid tot 33% minder produktief kan wees indien die swart voering binne die eenheid besoedel sou word, (b) winterproduktiwiteit daal tot 25% van somerproduktiwiteit as gevolg van die verminderde sonlig-ure, die laer invalshoek van die bestraling op die glasdeksel, en die gepaardgaande verkleining van die blootgestelde water-oppervlakte, (c) 'n gemiddelde produktiwiteitsverhoging van 10% deur weerkaatsers agter die sondistilleerder-eenheid teweeggebring kan word, en (d) die distillasie-temperatuur die water-ontsmettingstemperatuur oorskry. Hierdie navorsmg het 'n belangrike rol gespeelom sondistilleerder-tegnologie bekostigbaar vir behoeftge gemeenskappe in landelike gebiede te maak. Dit is gedemonstreer deur die suksesvolle toepassing van die navorsingsproduk (sondistilleerder-eenheid) in 'n drinkwatervoorsieningsprojek by 'n tipiese teikengemeenskap. Dit is vermag deur die gebruikmaking van evaluasie-modelle wat gedurende hierdie studie ontwikkel is, en wat die toepaslike konstruksie- en funksioneringsfaktore wat die ekonomiese lewensvatbaarheid van die eenheid beïnvloed, aanspreek. Die volgende navorsingsprodukte kan beskou word as nuut in die veld van sondistillasie-tegnologie, naamlik (a) 'n toetsmatriks wat gebruik kan word om komponente vir sondistilleeerders te evalueer, (b) 'n ekonomiese evalueringsmodel wat gebruik kan word om die bekostigbaarheid van sondistilleerders in 'n bepaalde gebied te bepaal, (c) 'n laboratorium-toetsfasiliteit om die werking van sondistilleerders onder beheerde kondisies te ondersoek en (d) 'n sondistilleerdereenheid wat doelgeskik vir plaaslike omstandighede ontwikkel en getoets is.

No description available.

No description available.

Molecular or short-path distillation is one form of high vacuum distillation, and offers a means of separating heat-sensitive, high-boiling materials which cannot be separated by conventional methods. Many of the so-called "undistillables," which include the natural fats and waxes, sugar derivatives, petroleum residues, plasticizers, dyes, and a host of other substances now fall within the scope of molecular distillation. The use or the process is limited, however, due to the high costs involved and the poor separatoey powers which are still characteristic of this method or distillation. Although there have been many mechanical improvements in the constructional designs of the molecular stills since the early beginnings of the crude pot stills, they still remain too inflexible in design and too compact in construction to allow the proper study or the fundamental factors affecting their performance. One of the problems yet to be solved satisfactorily is the prevention of leaks through the bearings and packings of the rotor shaft. It was the purpose of this investigation to redesign and reconstruct a five-inch magnetically-driven centrifugal molecular still, and by so doing to eliminate leaks around the rotor shaft by enclosing the rotor within the still head, and to gain flexibility by the use of a high-form bell jar, and a water-cooled condenser. The still head assembly consisted of a number of integrated units, many of which were of the same design and construction as the units used in other stills by previous investigators. Some of the more important changes were; a magnetic drive, consisting or an inner flange of magnets connected to the rotor shaft, and an outer flange of magnets connected to the drive shaft of the motor, a nitralloy rotary gear feed pump, especially fitted and constructed as a vacuum tight unit, and a water-cooled copper condenser, so constructed that its distance from the rotor surface could be varied. The feed, residue, and distillate tanks, as well as all flow lines for the feed, were constructed of aluminum or aluminum tubing; the vacuum lines were constructed of copper tubing, and all joints on the vacuum lines were either bronzed or silver-soldered to minimize the possibilities of leaks. All other constructional features of the still, such as electrical connections, vacuum connections to the base plate, bell jar seal, and thermocouple construction, were the same as used by previous investigators. / Master of Science

The vacuum distillation of heat-sensitive substances such as organic oils, dyes, and drugs requires special equipment from that available for atmospheric distillation. Study in the resulting field, high vacuum distillation, has subsequently led to the development of such equipment. Three types of high vacuum distillation and distillation equipment are recognized: conventional distillation, unobstructed-path distillation, and molecular distillation. Conventional vacuum distillation employs standard equipment under relatively high vacuum conditions. For unobstructed-path distillation, the equipment is modified so that the vapor path between the evaporating and condensing surfaces is clear. When the vapor path is unobstructed and the condenser is separated from the evaporator by a distance less than the mean free path of the evaporating molecules, the phenomenon is called molecular distillation. Molecular distillation is the limiting type of high vacuum distillation with the absolute pressure range approximately 1 to 7 microns of mercury. The use of the centrifugal molecular still permits the distillation of organic substances which might suffer thermal decomposition even under the conditions of the conventional high vacuum still. Against the advantages of prevention of thermal decomposition and shorter time requirements must be placed the poor separatory power of distillation and the necessity of numerous redistillations. The molecular still is valuable not because it gives good separation but because distillation is accomplished 50 to 250 degrees centigrade below temperatures of conventional atmospheric distillation. In ideal molecular distillation, equilibrium does not exist between the vapor and the liquid, no molecules re-enter the distilland after once being vaporized. Under these ideal conditions, Langmuir's equation predicts that the quantity of a given material distilling at a given temperature is proportional to P/√M where P is the vapor pressure and M is the molecular weight. Previous investigations at the Virginia Polytechnic Institute and other laboratories substantiate the importance of molecular weight and structure. Since most of these investigations have been only exploratory, insufficient work has been done to permit any conclusions of major importance. The purpose of this investigation was to determine the effects of various molecular structures of fatty acids on their distillation characteristics when distilled in a laboratory-size centrifugal molecular still. Saturated (C₁₅, C₁₆, C₁₇, C₁₈, C₁₉, and C₂₀) and unsaturated (C₁₈ with one, two, and three double bonds) fatty acids were used in the study. Such effects as the chain length, presence of double bonds and their position in the molecule, and cis-trans and positional isomerism were studied. / Ph. D.

The three basic requirements for unobstructed, short path distillation are: a surface over which a think layer of distilland is distributed, a cooler condensing surface in close proximity to the evaporating surface, and a suitable system for evacuating the space between the two surfaces. When the distance of transfer between the evaporating and condensing surfaces is comparable to the mean free path of the vapor molecules in the residual gas, the process is known as molecular distillation. [Continued in document] / Ph. D.