Effect of constant temperatures, darkness and light on the secretion of melatonin by pineal explants and retinas in the gecko Christinus marmoratus

The effects of temperature and lighting conditions on the secretion of melatonin by the pineal organ of the nocturnal gecko Christinus marmoratus was studied using in vitro perifusion. In a 12L:12D lighting regime, a high-amplitude melatonin rhythm was detectable at a constant temperature of 20 and 30 degrees C but not at 10 or 37 degrees C. There were sustained high levels of melatonin in constant darkness and sustained low levels in constant light. No retinal melatonin was detected using static and perifusion culture techniques. These results show that the pineal organ of C. marmoratus maintains light sensitivity in vitro but does not contain an oscillator coupled to the melatonin synthetic pathway.     

Control of film defects in solventborne high-solids coatings: The non-additives vs. a new additives approach

Acetylenic based surfactants have long found utility in compliant coatings such as waterborne systems and are demonstrated here to enhance performance of solventborne high solids systems. Three new additives are shown to reduce surface defects such as craters and orange peel in conventionally spray applied polyester and epoxy paints. Important to this new additive technology is the lack of adverse effect on physical properties, recoatability, and durability of the applied coating. Also discussed are the theory and background of the origins of surface defects with emphasis on the influence of additives on paint rheology, compatibility, and surface tension. Presented at the Latin American Coatings Show, August 27–28, 1997, Mexico City, Mexico by Joel Schwartz and the 5th International Exhibition of Paint Industry Suppliers, September 15–17, 1997, Sao Paulo, Brazil, by Frank Lee. 7201 Hamilton Blvd., Allentown, PA 18195. 109 Lukens Dr., New Castle, DE 19720.     

Intravenous gestational cocaine in rats: effects on offspring development and weanling behavior

Pregnant rats were injected with cocaine (CN; 6 mg/kg) or an equal volume of saline (SAL), via the tail vein, on gestation days 8-20. A third group was untreated (UT). Maternal weight gain was not affected by dam treatment despite slight differences in food intake. Litter characteristics (e.g., litter size, pup weight) did not differ among groups. Indices of fetal mortality were not affected by the treatments. Developmental tests, initiated on postnatal day (PND) 2, indicated slight delays in the negative geotaxic response and eye opening in cocaine-exposed pups. Open-field and tail-flick tests were performed on PND 21. Pups were acutely injected with cocaine (10 mg/kg, IP), saline, or received no treatment before placement in a novel open field; morphine (1.5 mg/kg, SC) or saline was injected prior to the tail flick test. Pups from CN dams exhibited a significant decrease in spontaneous exploratory behavior compared to both controls, and a time-dependent increase in rearing compared to pups from UT dams. The acute cocaine injection prior to placement in the open field did not alter locomotion or rearing among dam treatment groups. However, the acute cocaine injection did increase stereotypy ratings for female pups from CN dams compared to similarly treated males, and females from SAL and UT dams. No differences were observed among groups in the tail-flick test. These data suggest that the IV route of administration provides a viable method of cocaine delivery in pregnant rats, and provides further evidence of the developmental and behavioral teratogenicity of prenatal cocaine exposure.     

A near optimal crack tip mesh

The near optimal crack tip mesh obtained by the authors in a previous paper is tested for a set of problems. The accuracy is maintained within the desired values. The direct displacement extrapolation method for SIF estimation is compared to the virtual crack extension. The methodology for crack tip mesh design discussed previously is validated.     

Hierarchical mesh adaptation of 2D quadrilateral elements

In this paper, we present some examples which illustrate the use of adaptive finite element analysis using a new hierarchical refinement algorithm for 2D quadrilateral elements. Projection type a posteriori error estimators based on a global stress smoothing and a simple stress averaging scheme have been used. The algorithm produces well refined meshes for some simple examples which contain stress singularities and stress concentrations. The convergence of the energy norm error has been found to be improved over a previous simple splitting algorithm.     

Vibration response of geometrically nonlinear elastic beams subjected to pulse and impact loading

The governing equations for the geometrically non-linear deformation of elastic beams subjected to dynamic bending loads are developed and solved for various initial conditions. Of primary interest is the response to pulse loading and simulated impact. Both transient and several cycle solutions are generated for the free vibration response to pulse loading. The results obtained are compared to a first mode analysis approximation.A new model is developed to simulate impact loading by the distribution of additional mass to the elastic system and subjecting it to a velocity pulse. The governing equations are solved using second order finite differences in space and time. The solutions obtained are in reasonable agreement with experimental results previously obtained [1].     

Energy conservation in the transient response of nonlinear beam vibration problems subjected to pulse loading—a numerical approach

The nonlinear vibration response of a double cantilevered beam subjected to pulse loading over a central sector is studied. The initial response is generated in detail to ascertain the energetics of the response. The total energy is used as a gauge of the stability and accuracy of the solution. It is shown that to obtain accurate and stable initial solutions an extremely high spatial and time resolution is required. This requirement was only evident through an examination of the energy of the system. It is proposed, therefore, to use the total energy of the system as a necessary stability and accuracy criterion for the nonlinear response of conservative systems. The results also demonstrate that even for moderate nonlinearities, the effects of membrane forces have a significant influence on the system. It is also shown that while the fundamental response is contained in a first mode envelope, the fluctuations caused by the higher order modes must be resolved.     

A Catalytic Process for Mullite Whiskers

Mixtures of alumina and silica react with SiF₄ above 600°C to form fluorotopaz. Pyrolysis of fluorotopaz gives a stoichiometric yield of interlocked whiskers of mullite and SiF₄, which is recovered for reuse. The diameter of whiskers (aspect ratio ∼15) can be controlled from a maximum of ∼100 μm to less than 1 μm.     

Imprinting of Local Metallic States into VO2 with Ultraviolet Light

Materials exhibiting electronic phase transitions have attracted widespread attention. By switching between metallic and insulating states under external stimuli, the accompanying changes in the electrical and optical properties can be harnessed in novel electronic and optical applications. In this work, a laterally confined conductive pattern is inscribed into an otherwise insulating VO₂ thin film using ultraviolet light, inducing an almost four orders of magnitude decrease in electrical resistivity of the exposed area. The metallic imprint remains in VO₂ after ultraviolet light exposure and can be completely erased by a short low temperature anneal. The ability to optically pattern confined metallic structures provides new opportunities for reconfigurable photonic and plasmonic structures, as well as re‐writable electric circuitry.