Theoretical studies of positronium formation in positron collisions with lithium and hydrogen atoms

The Kohn variational method has been used to study elastic scattering and positronium (Ps) formation in positron collisions with atomic hydrogen and lithium, in the energy region where only these two channels are open. In common with other alkali metals, lithium is interesting in that its valence electron is sufficiently weakly bound that positronium formation is exothermic, and hence an open channel for incident positrons of zero energy. For such a process, Wigner's threshold theory predicts an s-wave cross section which has an inverse dependence on the wavenumber, k, of the projectile as k→0. Using a model potential and very elaborate trial functions, a detailed investigation of s- and p-wave positron-lithium scattering has been made in the energy range 0-1.84eV, and preliminary results have also been obtained for d-wave scattering. The s-wave Ps formation cross section, as calculated variationally, appears to be in accordance with the Wigner theory, although this partial wave contributes negligibly to the Ps channel across most of the energy range considered. The p and d partial waves make a much more substantial contribution to the rearrangement process. New cross sections for positron-hydrogen scattering have been calculated for the energy region close to the positronium formation threshold, and results have been compared with the predictions of R-matrix threshold theory

Current Market Value of a 40-acre Residential Tract - Palmdale, California

A letter report by Stephen Watts of the Harrison Price Company (HPC) to Stephen Hinchliffe, Jr. of The Leisure Group, Inc. that summarizes HPC’s findings and conclusions relative to the fair market value of The Leisure Group’s 40-acre tract of undeveloped land near Palmdale, California. The report also includes commentary on the merits of a pending purchase offer

Evaluation of Oliver Properties, Jackson, Wyoming

Mr. Steven Bonnett, Vice President, Trust Division of Pittsburgh National Bank served as executor of the estate of the late Henry Oliver, Jr. Mr. Bonnett retained Vern Englehorn and Frank Kemp of Denver to appraise the fair market value of two assets owned by Mr. Oliver, the Poodle Ranch and the Four Lazy F Ranch in Teton County, Wyoming. Mr. Bonnett subsequently retained the Harrison Price Company to critique the Englehorn/Kemp appraisal and the subsequent IRS appraisal based on that report, with particular reference to establishing the cash equivalent value associated with the comparable sales cited in the Englehorn/Kemp appraisal. HPC research program included a physical inspection of each comparable sale, a review of their development entitlements, confirmation of terms of sale, and interviews with appropriate investing institutions to determine the discount rate they would have employed at the relevant valuation date of January 11, 1978 if they were to purchase those notes at that date. The report was prepared by Stephen S. Watts, Director of Real Estate for the Harrison Price Company. Appendix A contains a resume of Mr. Watts as well as his qualifications statement relative to the HPC

Experimental Heat Transfer Supporting Simulated Water Well Performance on Mars

Favorable indications of massive quantities of water on Mars have initiated studies of potential changes to human Mars missions. Using a technique known as a Rodriguez Well to melt the ice, store the resulting water in a subsurface ice cavity until needed, and then pump water to the surface for use is one potential means to effect these changes. A computer simulation of the Rodriguez Well in a terrestrial environment is one of the engineering tools being used to characterize the performance of this type of well on Mars. An experiment at the NASA Johnson Space Center is gathering data for convective heat transfer and evaporation rates at Mars surface conditions so that this computer simulation can be properly modified to predict performance on Mars. While quantitative results await processing, tests have indicated that a pool of water can be maintained at 1C to 2 C while at Mars surface temperatures and pressures

An Optimized Integrator Windup Protection Technique Applied to a Turbofan Engine Control

This paper introduces a new technique for providing memoryless integrator windup protection which utilizes readily available optimization software tools. This integrator windup protection synthesis provides a concise methodology for creating integrator windup protection for each actuation system loop independently while assuring both controller and closed loop system stability. The individual actuation system loops' integrator windup protection can then be combined to provide integrator windup protection for the entire system. This technique is applied to an H(exp infinity) based multivariable control designed for a linear model of an advanced afterburning turbofan engine. The resulting transient characteristics are examined for the integrated system while encountering single and multiple actuation limits

A Comparison of Multivariable Control Design Techniques for a Turbofan Engine Control

This paper compares two previously published design procedures for two different multivariable control design techniques for application to a linear engine model of a jet engine. The two multivariable control design techniques compared were the Linear Quadratic Gaussian with Loop Transfer Recovery (LQG/LTR) and the H-Infinity synthesis. The two control design techniques were used with specific previously published design procedures to synthesize controls which would provide equivalent closed loop frequency response for the primary control loops while assuring adequate loop decoupling. The resulting controllers were then reduced in order to minimize the programming and data storage requirements for a typical implementation. The reduced order linear controllers designed by each method were combined with the linear model of an advanced turbofan engine and the system performance was evaluated for the continuous linear system. Included in the performance analysis are the resulting frequency and transient responses as well as actuator usage and rate capability for each design method. The controls were also analyzed for robustness with respect to structured uncertainties in the unmodeled system dynamics. The two controls were then compared for performance capability and hardware implementation issues

Simulated Water Well Performance on Mars

The surface of Mars once had abundant water flowing on its surface, but now there is a general perception that this surface is completely dry. Several lines of research have shown that there are sources of potentially large quantities of water at many locations on the surface, including regions considered as candidates for future human missions. Recent discovery of exposed water ice scarps in Martian mid-latitudes has bolstered the evidence for massive amounts of almost pure water in these regions. These favorable indications of massive quantities of water have initiated studies of changes that could be made to human Mars missions if a means could be devised that would make this water available to these crews. The proposed paper will describe progress towards developing one approach for accessing and extracting water from these mid-latitude sources. This approach relies on mechanical drills to access the water ice through overlying debris. Once the ice has been accessed, a technique known as a Rodriguez Well is used to melt the ice, store the resulting water until it is needed, and then pump the water to the surface for use. Previous work in this area has utilized a computer simulation to predict the performance of the Rodriguez Well. This simulation was developed originally to predict performance in terrestrial polar regions. While the basic approach used in this model is appropriate for a similar well on Mars, several parameters were known to require a change to correctly model the Martian environment. Some of these parameters are empirical and require experiments simulating the Martian environment to determine their value. The proposed paper will describe the experiments set up to determine the value of these parameters and compare their numerical value to the terrestrial equivalent. Finally, the proposed paper will show results from the updated computer simulation and compare results with those determined from the original version of the simulation

Mars Surface Systems Common Capabilities and Challenges for Human Missions

This paper describes the current status of common systems and operations as they are applied to actual locations on Mars that are representative of Exploration Zones (EZ) - NASA's term for candidate locations where humans could land, live and work on the martian surface. Given NASA's current concepts for human missions to Mars, an EZ is a collection of Regions of Interest (ROIs) located within approximately 100 kilometers of a centralized landing site. ROIs are areas that are relevant for scientific investigation and/or development/maturation of capabilities and resources necessary for a sustainable human presence. An EZ also contains a habitation site that will be used by multiple human crews during missions to explore and utilize the ROIs within the EZ. The Evolvable Mars Campaign (EMC), a description of NASA's current approach to these human Mars missions, assumes that a single EZ will be identified within which NASA will establish a substantial and durable surface infrastructure that will be used by multiple human crews. The process of identifying and eventually selecting this single EZ will likely take many years to finalized. Because of this extended EZ selection process it becomes important to evaluate the current suite of surface systems and operations being evaluated for the EMC as they are likely to perform at a variety of proposed EZ locations and for the types of operations - both scientific and development - that are proposed for these candidate EZs. It is also important to evaluate proposed EZs for their suitability to be explored or developed given the range of capabilities and constraints for the types of surface systems and operations being considered within the EMC

The Fourth North American Echinoderm Conference, 22-26 August 2001

Friends of Echinoderms Share Their Research and Renew Their Enthusiasm John H. Dearborn NAEC History and Commentary John M. Lawrence Papers on Sea Urchin Fisheries and Aquaculture at the NAEC 2001: A PerspectiveJohn M. Lawrence and Stephen A. Watts Plenary Abstract

Effect of Temperature on Gamete Production and Biochemical Composition of Gonads in the Sea Urchin Lytechinus variegatus

Temperature is one of the most important proximate factors affecting the biology of ectothermal organisms. In the sea urchin, Lytechimus variegatus, the reproductive cycle in wild populations is correlated with changing water temperature, suggesting that reproduction may be dependent, in part, on temperature. Adult L. variegatus (ca. 35.63 ± 1.24 g wet weight, 40-mm diameter) were collected in October 2001 from St. Joseph Bay, FL (30°N, 85.5°W) and transported to the University of Alabama at Birmingham. Sea urchins were placed into nine 80-liter aquaria (n = eight sea urchins per aquarium) maintained in enclosed incubators (n = three aquaria per incubator) at a specific constant temperature of 16, 22, or 28°C and 32 ppt salinity synthetic seawater (Instant Ocean). Within each aquarium, individuals were maintained in 1-liter containers with recirculation and were fed daily a formulated feed ad libitum for 8 wk. At the end of week 8, final measurements of each individual were recorded, individuals were dissected, gonads were measured, and gonad histology and biochemistry were analyzed. Gonad weights were highest for individuals held at the 22°C treatment, but did not vary between individuals held at 16 or 28°C. The acinus volume in the gonad was occupied primarily by nutritive phagocytes at all temperature treatments. In females, gamete volumes were highest for females held at 22°C, whereas gamete volumes were not different for females held at 16 or 28°C. In males, gamete volumes were significantly lower at 28°C, and gamete volumes were not different between males held at 16 or 22°C. Gamete volumes were small in all temperature treatments, suggesting that gamete production had not substantially advanced within the 8-wk study period. The cellular ultrastructure of the nutritive phagocytes varied with temperature. Vacuolated nutritive phagocytes were common in the acini of individuals held at 16°C, and globulated nutritive phagocytes were common in the acini of individuals held at 28°C, Females held at 22°C had the highest protein content in the gonad, and protein content was not different between females held at 16 or 28°C. The amount of lipid was highest for males held at 16°C and did not differ between males held at 22 or 28°C. These data lead us to suggest that L. variegatus utilize different nutrient allocation strategies in the gonad in response to temperature, which could affect the reproductive success of the species if subjected to long-term changes in seawater temperature