Domino tilings with barriers

In this paper, we continue the study of domino-tilings of Aztec diamonds. In particular, we look at certain ways of placing ``barriers'' in the Aztec diamond, with the constraint that no domino may cross a barrier. Remarkably, the number of constrained tilings is independent of the placement of the barriers. We do not know of a combinatorial explanation of this fact; our proof uses the Jacobi-Trudi identity.Comment: 5 pages (two-column format), 1 figur

The History Major and Undergraduate Liberal Education

Argues that the study of history integrates disciplinary knowledge, methods, and principles into a broad education and civic engagement. Recommends that departments set goals for student outcomes, diversify course requirements, and emphasize teaching

Estimation of Apartment Submarkets

The analysis of apartment sub-markets and the modelling of such markets have attracted a considerable degree of attention recently. This study compares apartment submarkets within a major European city. The price behaviour of the Dublin, Ireland apartment market is tested using hedonic models and aggregate and disaggregate data. The results strongly indicate that the modelling of apartment markets at the disaggregate level does result in significant improvements in estimation in comparison to estimations undertaken at an aggregate level. This particular apartment market is especially interesting, due to the introduction of fiscal incentives in inner-city locations. In order to fully understand the Dublin apartment market requires an appreciation of the role played by tax breaks for owner-occupiers and investors in urban renewal locations. The results show that different submarkets responded differently. The central city apartment market [urban renewal locations] saw a short-term stabilization of prices in the months following the fiscal changes, with price increases accelerating again shortly afterwards.

Ceramics for engines

The NASA Lewis Research Center's Ceramic Technology Program is focused on aerospace propulsion and power needs. Thus, emphasis is on high-temperature ceramics and their structural and environmental durability and reliability. The program is interdisciplinary in nature with major emphasis on materials and processing, but with significant efforts in design methodology and life prediction

GRAIN EXPORTS AS A SOURCE OF AGRICULTURAL INSTABILITY

International Relations/Trade,

The NASA cryogenic fluid management technology program plan

During the past three decades, NASA has been designing and using large quantities of cryogenic fluids for propulsion system propellants, coolants for experiments, and for environmental control systems. As a consequence, an erroneous conclusion has been drawn that the technology exists for using large quantities of cryogens in space for long periods of time. The attempt here is to dispel that myth and to present the technology needs that require development in order to support the NASA programs of the future. A NASA program, developed through the impetus of the Marshall Space Flight Center and the Lewis Research Center and supported by all NASA centers is outlined. The current state of the art is discussed along with specific needs for near future missions. Then, using the Space Exploration Initiative mission set, cost/benefit projections are made for the development of advanced cryogenic fluid management techniques. Earth based and space based test programs are discussed relative to the technology requirements for liquid storage, supply, and transfer for fluid transfer and advanced instrumentation

Ceramics for engines

Structural ceramics were under nearly continuous development for various heat engine applications since the early 1970s. These efforts were sustained by the properties that ceramics offer in the areas of high-temperature strength, environmental resistance, and low density and the large benefits in system efficiency and performance that can result. The promise of ceramics was not realized because their brittle nature results in high sensitivity to microscopic flaws and catastrophic fracture behavior. This translated into low reliability for ceramic components and thus limited their application in engines. For structural ceramics to successfully make inroads into the terrestrial heat engine market requires further advances in low cost, net shape fabrication of high reliability components, and improvements in properties such as toughness, and strength. These advances will lead to very limited use of ceramics in noncritical applications in aerospace engines. For critical aerospace applications, an additional requirement is that the components display markedly improved toughness and noncatastrophic or graceful fracture. Thus the major emphasis is on fiber-reinforced ceramics

The propagator for the step potential using the path decomposition expansion

We present a direct path integral derivation of the propagator in the presence of a step potential. The derivation makes use of the Path Decomposition Expansion (PDX), and also of the definition of the propagator as a limit of lattice paths.Comment: To appear in DICE 2008 conference proceeding

Laying Out the Future of Cryogenics

NASA has developed a family of thermal test cryostats at the Cryogenics Test Laboratory at NASA’s Kennedy Space Center. The lab is a one-of-a-kind capability for research, development, and application of cross-cutting technologies to meet the needs of aerospace and other industry, government, and research institutions. Provided are experimental testing, prototype construction, engineering evaluation, and practical problem-solving for technology development with government and commercial partners worldwide. Technology focus areas include thermal insulation systems, cryogenic components, propellant process systems, and low-temperature applications. Our overall objective is to develop materials, produce new technology, and promote engineering for energy-efficient storage, transfer, and use of cryogens and cryogenic propellants on Earth and in space. Qinetiq North America recently licensed one of the cryostat patents for manufacturing and selling these units to industry. Based on the family of cryostat instruments, we will discuss the future of sub-ambient temperature thermal conductivity measurement and market application trends. Through task groups under ASTM International, these cryostat instruments are a key part of the development of technical standards for cryogenic insulation materials, systems, and test methods. We will also emphasize that cryogenic boil-off calorimetry is not just for cryogenic work but can be a cost-effective, better solution for a wide range of sub-ambient work (refrigeration, food, medical, transportation, buildings, etc.)