Modifications in the Structure of the Dish of the Morehead Radio Telescope to Facilitate Greater Resolution of Radio Signals

A report submitted by Letitia L. Crisp to the Research and Creative Productions Committee on May 19, 1994 on modifications to the Morehead Radio Telescope

Intersection of three-dimensional geometric surfaces

Calculating the line of intersection between two three-dimensional objects and using the information to generate a third object is a key element in a geometry development system. Techniques are presented for the generation of three-dimensional objects, the calculation of a line of intersection between two objects, and the construction of a resultant third object. The objects are closed surfaces consisting of adjacent bicubic parametric patches using Bezier basis functions. The intersection determination involves subdividing the patches that make up the objects until they are approximately planar and then calculating the intersection between planes. The resulting straight-line segments are connected to form the curve of intersection. The polygons in the neighborhood of the intersection are reconstructed and put back into the Bezier representation. A third object can be generated using various combinations of the original two. Several examples are presented. Special cases and problems were encountered, and the method for handling them is discussed. The special cases and problems included intersection of patch edges, gaps between adjacent patches because of unequal subdivision, holes, or islands within patches, and computer round-off error

Bimodal Distribution of Sulfuric Acid Aerosols in the Upper Haze of Venus

The upper haze (UH) of Venus is variable on the order of days and it is populated by two particle modes. We use a 1D microphysics and vertical transport model based on the Community Aerosol and Radiation Model for Atmospheres to evaluate whether interaction of upwelled cloud particles and sulfuric acid particles nucleated in situ on meteoric dust are able to generate the two size modes and whether their observed variability are due to cloud top vertical transient winds. Nucleation of photochemically produced sulfuric acid onto polysulfur condensation nuclei generates mode 1 cloud droplets that then diffuse upwards into the UH. Droplets generated in the UH from nucleation of sulfuric acid onto meteoric dust coagulate with the upwelled cloud particles and cannot reproduce the observed bimodal size distribution. The mass transport enabled by cloud top transient winds are able to generate a bimodal size distribution in a time scale consistent with observations. Sedimentation and convection in the middle and lower clouds causes the formation of large mode 2 and mode 3 particles. Evaporation of these particles below the clouds creates a local sulfuric acid vapor maximum that causes upwelling of sulfuric acid back into the clouds. If the polysulfur condensation nuclei are small and their production rate is high, coagulation of small droplets onto larger droplets in the middle cloud may result in sulfuric acid "rain" below the clouds once every few Earth months. Reduction of the polysulfur condensation nuclei production rate destroys this oscillation and reduces the mode 1 particle abundance in the middle cloud by two orders of magnitude, though it better reproduces the sulfur-to-sulfuric-acid mass ratio in the cloud and haze droplets. In general we find satisfactory agreement between our results and observations, though improvements could be made by incorporating sulfur microphysics.Comment: 62 pages, 18 figures, 1 table. Accepted for publication in Icaru

Solvent-mediated polymorphism and characterisation of inhaled pharmaceuticals

The use of polar anti-solvents for the crystallisation of lactose from 10% (w/v) aqueous solutions has been investigated. Crystal growth was observed at 50-65% antisolvent content and showed a morphological transition from polyhedral to needle-like habit with increasing antisolvent content, which coincided with a polymorphic transition from alpha lactose monohydrate (LαH2O) to beta lactose (Lβ). Where anhydrous dehydrating antisolvents were employed such as methanol and ethanol, evidence of Lα.H2O dehydration to form stable anhydrous alpha lactose (LαS) was also observed at 95% antisolvent content. Powder X-ray diffraction (PXRD) analysis of the samples highlighted the preferred orientation effects exhibited by large crystals of this kind, indicating the difficulties experienced by the non-specialist when performing phase identification of lactose polymorphs by PXRD. Application of the same crystallisation procedures to a racemic mixture of the active pharmaceutical ingredient (API) salbutamol sulfate (SS) indicated that some conditions can promote the formation of solvated SS.....

First year student expectations: Results from a university-wide student survey

Although much has been written on the first-year experience of students at higher education institutions, less attention has been directed to the expectations of students when they enter an institution for the first time. This paper provides additional insights into the expectations of students at an Australian university and highlights areas in which students’ expectations may not necessarily align with the realities of common university practices. By providing opportunities for students to articulate their expectations, staff are able to use the responses for a constructive dialogue and work towards a more positive alignment between perceived expectations and levels of student satisfaction with their experience.Geoffrey Crisp, Edward Palmer, Deborah Turnbull, Ted Nettelbeck, Lynn Ward, Amanda LeCouteur, Aspa Sarris, Peter Strelan, and Luke Schneide