An Analysis of Pricing Strategy and Price Dispersion on the Internet

Using prices obtained from shopbots, we test several hypotheses regarding the economics of information and optimal search. We find that price dispersion is positively (negatively) related to product price and the number of sellers in cross-sectional (time series) analysis. Price dispersion increases over time when the sample includes new entrants, but decreases in the absence of entry. Controlling for shipping charges and seller heterogeneity reduces, but does not eliminate, price dispersion. Finally, prices appear to be correlated across products and over time – low price sellers for one product (time period) generally charge low prices for all items (time periods).

PIV Measurements of the CEV Hot Abort Motor Plume for CFD Validation

NASA s next manned launch platform for missions to the moon and Mars are the Orion and Ares systems. Many critical aspects of the launch system performance are being verified using computational fluid dynamics (CFD) predictions. The Orion Launch Abort Vehicle (LAV) consists of a tower mounted tractor rocket tasked with carrying the Crew Module (CM) safely away from the launch vehicle in the event of a catastrophic failure during the vehicle s ascent. Some of the predictions involving the launch abort system flow fields produced conflicting results, which required further investigation through ground test experiments. Ground tests were performed to acquire data from a hot supersonic jet in cross-flow for the purpose of validating CFD turbulence modeling relevant to the Orion Launch Abort Vehicle (LAV). Both 2-component axial plane Particle Image Velocimetry (PIV) and 3-component cross-stream Stereo Particle Image Velocimetry (SPIV) measurements were obtained on a model of an Abort Motor (AM). Actual flight conditions could not be simulated on the ground, so the highest temperature and pressure conditions that could be safely used in the test facility (nozzle pressure ratio 28.5 and a nozzle temperature ratio of 3) were used for the validation tests. These conditions are significantly different from those of the flight vehicle, but were sufficiently high enough to begin addressing turbulence modeling issues that predicated the need for the validation tests

Evaluating Ornamental Grasses for the Challenging Rain Garden Environment

Four experiments were conducted to determine the growth and survival of seven species of perennial ornamental grasses, tufted hairgrass [Deschampsia cespitosa (L.) P. Beauv.], switchgrass (Panicum virgatum L.), big bluestem (Andropogan gerardii Vitman), Chinese silvergrass (Miscanthus sinensis Andersson), little bluestem [Schizachyrium scoparium (Michx.) Nash], blue grama grass [Bouteloua gracilis (Kunth) Lag. ex Griffiths], and feather reed grass [Calamagrostis x acutiflora (Schrad.) Rchb.], when subjected to cyclical flood and drought, varying submergence depths and durations, NaCl, and NaCl with petroleum hydrocarbons. Chinese silvergrass and switchgrass survived cyclical soil flooding and drought and submergence for 7-d at a depth of 30 cm while maintaining an acceptable amount of foliar damage. All grasses survived cyclical flood and drought when the soil VWC was maintained at 14% suggesting all seven grasses can withstand periodic soil flooding as long as the water is not too deep. As water depth and duration increased from 4-d to 7-d, little bluestem, blue grama grass, and feather reed grass suffered significant foliar damage. Tufted hair grass and big bluestem suffered significant foliar damage when submerged for 2-d. Switchgrass and feather reed grass survived NaCl loads of up to 6.7 Mg?ha-1 and maintained a visual damage rating less than three making them suitable for planting in rain gardens or bioretention systems receiving NaCl runoff. Switchgrass also tolerated motor oil at rates up to 5% in combination with NaCl at rates up to 6.7 Mg?ha-1. Switchgrass would be an ideal grass for planting in areas receiving both contaminates. Tufted hair grass has limited tolerance to NaCl or motor oil and should not be planted in areas that may receive those contaminates in stormwater runoff. Big bluestem and little bluestem have limited tolerance to NaCl but some tolerance to motor oil and may be candidates for planting in areas receiving only motor oil in stormwater runoff. Chinese silvergrass and blue grama grass can tolerate moderate levels of NaCl and motor oil while maintaining a visual damage rating of four or less and would be candidates for planting in areas that receive moderate amounts of both pollutants in stormwater runoff

Human Selection and Digitized Archival Collections: an Exploratory Research Project About Choice of Archival Materials Digitized for Online Public Availability

Our collective memory, the history that is cultivated through reflection, documentation, and consensus of historical data, is predicated upon the citizenry having access to the historical materials that society has created. Digitization has enabled greater public access to those materials. However, are items being scanned or digitally photographed to create surrogates that are then not made available to the world? The impetus for this study is to delve into whether or not intentional or unintentional personal choices play a role in determining which items archivists transform into digital surrogates; both in the decision of what to digitize and what to make available to the public on the World Wide Web. When one archival collection is prioritized over another or when it is not possible to digitize an entire collection, what rationale is used to determine which items will be digitized and published online? Do intentional or unintentional personal choices come into play in the decision-making? To answer these questions, four case studies were conducted, involving the random sampling of online collections and concomitant interviews of archivists. The purpose of this study is to enhance archivists’ understanding of the reasons that guide the digitization decision-making process. Through such understanding, archivists can be more proactive in the decision-making process to realize the benefit of digitizing and publishing archival materials that ultimately affect collective memory. The findings of this research revealed that in the case of the four institutions assessed, archivists do use personal choice to determine which materials within an archive are digitized

A Fuzzy Logic Optimal Control Law Solution to the CMMCA Tracking Problem

The Air Force uses the C-18 Cruise Missile Mission Control Aircraft (CMMCA) to radar track cruise missiles (CM) during test flights. Because of the complexity of the CM flight profiles, maintaining radar coverage at all times is very difficult. This thesis attempted to apply optimal control theory to construct a simulation providing 100% radar coverage. The simulation was divided into ten second intervals, and fuzzy logic was used at the start of each interval to determine the set point, i.e., that point in space where the CMMCA should be in ten seconds. The set point calculation\u27s fuzzy logic balanced CMMCA maneuvering based on present and future CM positions. Three different future times were used: 60, 90 and 120 seconds ahead, and the performance for each time was compared. The simulation was performed on an IBM compatible PC with Matlab and Simulink (both by The MathWorks). The final form of the fuzzy logic provided varying radar coverage at each look ahead time for a complex CM flight path (CM in 20 degrees of bank) 1850 seconds long. At 120 seconds look ahead time, the coverage was 100%. When the same profile was performed with the CM in 30 degrees of bank, coverage was degraded, and 60 seconds look ahead performed best

Identification and analysis of gene families from the duplicated genome of soybean using EST sequences

BACKGROUND: Large scale gene analysis of most organisms is hampered by incomplete genomic sequences. In many organisms, such as soybean, the best source of sequence information is the existence of expressed sequence tag (EST) libraries. Soybean has a large (1115 Mbp) genome that has yet to be fully sequenced. However it does have the 6th largest EST collection comprised of ESTs from a variety of soybean genotypes. Many EST libraries were constructed from RNA extracted from various genetic backgrounds, thus gene identification from these sources is complicated by the existence of both gene and allele sequence differences. We used the ESTminer suite of programs to identify potential soybean gene transcripts from a single genetic background allowing us to observe functional classifications between gene families as well as structural differences between genes and gene paralogs within families. The identification of potential gene sequences (pHaps) from soybean allows us to begin to get a picture of the genomic history of the organism as well as begin to observe the evolutionary fates of gene copies in this highly duplicated genome. RESULTS: We identified approximately 45,000 potential gene sequences (pHaps) from EST sequences of Williams/Williams82, an inbred genotype of soybean (Glycine max L. Merr.) using a redundancy criterion to identify reproducible sequence differences between related genes within gene families. Analysis of these sequences revealed single base substitutions and single base indels are the most frequently observed form of sequence variation between genes within families in the dataset. Genomic sequencing of selected loci indicate that intron-like intervening sequences are numerous and are approximately 220 bp in length. Functional annotation of gene sequences indicate functional classifications are not randomly distributed among gene families containing few or many genes. CONCLUSION: The predominance of single nucleotide insertion/deletions and substitution events between genes within families (individual genes and gene paralogs) is consistent with a model of gene amplification followed by single base random mutational events expected under the classical model of duplicated gene evolution. Molecular functions of small and large gene families appear to be non-randomly distributed possibly indicating a difference in retention of duplicates or local expansion