System reduction and the accuracy of solutions of DSGE models: A note

Many algorithms that provide approximate solutions for dynamic stochastic general equilibrium (DSGE) models employ the generalized Schur factorization since it allows for a flexible formulation of the model and exempts the researcher from identifying equations that give raise to infinite eigenvalues. We show, by means of an example, that the policy functions obtained by this approach may differ from those obtained from the solution of a properly reduced system. As a consequence, simulation results may depend on the numeric values of parameters that are theoretically irrelevant. The source of this inaccuracy are ill-conditioned matrices as they emerge, e.g., in models with strong habits. Therefore, researchers should always cross-check their results and test the accuracy of the solution

A note on the uniqueness of solutions to rational expectations models

Klein (2000) advocates the use of the Schur decomposition of a matrix pencil to solve linear rational expectations (RE) models. Meanwhile his algorithm has become a center piece in several computer codes that provide approximate solutions to (non-linear) dynamic stochastic general equilibrium (DSGE) models. A subtlety not resolved by Klein is whether or not a certain Schur decompostion could fail to solve the model while a second one would provide a solution. We show that this cannot happen

Results of winglet development studies for DC-10 derivatives

The results of investigations into the application of winglets to the DC-10 aircraft are presented. The DC-10 winglet configuration was developed and its cruise performance determined in a previous investigation. This study included high speed and low speed wind tunnel tests to evaluate aerodynamic characteristics, and a subsonic flutter wind tunnel test with accompanying analysis and evaluation of results. Additionally, a configuration integration study employed the results of the wind tunnel studies to determine the overall impact of the installation of winglets on the DC-10 aircraft. Conclusions derived from the high speed and low speed tests indicate that the winglets had no significant effects on the DC-10 stability characteristics or high speed buffet. It was determined that winglets had a minimal effect on aircraft lift characteristics and improved the low speed aircraft drag under high lift conditions. The winglets affected the DC-10 flutter characteristics by reducing the flutter speed of the basic critical mode and introducing a new critical mode involving outer wing torsion and longitudinal bending. The overall impact of winglets was determined to be of sufficient benefit to merit flight evaluation

The diverse nature of island isolation and its effect on land bridge insular faunas

Aim: Isolation is a key factor in island biology. It is usually defined as the distance to the geographically nearest mainland, but many other definitions exist. We explored how testing different isolation indices affects the inference of impacts of isolation on faunal characteristics. We focused on land bridge islands and compared the relationships of many spatial and temporal (i.e., through time) isolation indices with community‐, population‐ and individual‐level characteristics (species richness, population density and body size, respectively). Location: Aegean Sea islands, Greece. Time period: Current. Taxon: Many animal taxa. Methods: We estimated 21 isolation indices for 205 islands and recorded species richness data for 15 taxa (invertebrates and vertebrates). We obtained body size data for seven lizard species and population density data for three. We explored how well indices predict each characteristic, in each taxon, by conducting a series of ordinary least squares regressions (controlling for island area when needed) and a meta‐analysis. Results: Isolation was significantly (and negatively) associated with species richness in 10 of 15 taxa. It was significantly (and positively) associated with body size in only one of seven species and was not associated with population density. The effect of isolation on species richness was much weaker than that of island area, regardless of the index tested. Spatial indices generally out‐performed temporal indices, and indices directly related to the mainland out‐performed those related mainly to neighbouring islands. No index was universally superior to others, including the distance to the geographically nearest mainland. Main conclusions: The choice of index can alter our perception of the impacts of isolation on biological patterns. The nearly automatic, ubiquitous use of distance to the geographically nearest mainland misrepresents the complexity of the effects of isolation. We recommend the simultaneous testing of several indices that represent different aspects of isolation, in order to produce more constructive and thorough investigations and avoid imprecise inference

Social media in the curriculum and co-curriculum: pre-service teachers and their collegiate peers

2013 Fall.Includes bibliographical references.Although use of social media by students has been shown to be nearly ubiquitous, many K-12 school systems have banned its use on their campuses or use between their teachers and students. In contrast, many collegiate faculty have utilized social media in their teaching. Social media has been shown to assist faculty in engaging with students, helping students engage with content outside of class and sound implementation into the curriculum has been show to have positive educational impacts. Data from a sample of two thousand and fifty-six college students across two land-grant institutions is compared between pre-service teachers and their collegiate peers. Pre-service teachers reported using Twitter in the curriculum more, were more inspired by the use of social media use by their faculty, used social media more on their own for educational purposes and had a stronger belief that social media can be used for educationally relevant purposes than their collegiate peers

Master of Science

thesisBioretention is a structure which captures runoff from small catchments and stores it in porous vegetated areas with the intent of infiltrating all or a large fraction of the annual runoff volume. The effects of bioretention on potential groundwater recharge are oftentimes unknown because of variable infiltration rates. This study examined the performance of a field site on the University of Utah campus in Salt Lake City, Utah. Data were collected between March, 2012 and November, 2012. The site demonstrated improvement in volume retention and infiltration over the preexisting conditions. The average storm event produced 5.6 mm (0.22 in) of precipitation. For all storm events examined, nearly all inflow volume was retained and either infiltrated, lost through evapotranspiration, or utilized by plants. Average vertical and horizontal infiltration rates ranged between 0.5 cm/hr and 20 cm/hr for the sandy loam subsoils. The wetting front took 1 to 2 days (24 to 48 hrs) to reach the 1.8 m (6 ft) depth and 7 to 14 days to reach the 3.7 m (12 ft) depth depending on the spatial location. At depths of 1.8 m (6 ft), 3.7 m (12 ft) and 4.6 m (15 ft) outside the basin, the wetting front progressed at least 3 m (10 ft) laterally in three days (72 hrs), but without additional sensors located at larger lateral distances, it remains unclear exactly where the lateral extent of the wetting front ceases. Without additional engineering to protect infrastructure such as building foundations and retaining walls, it is recommended that bioretention cells constructed in semiarid climates and with similar subsoils be located at least 6.1 m (20 ft) from infrastructure. Overall, this research indicates that bioretention is a viable stormwater best management practice in Utah. It was shown that with proper design and sizing, nearly all annual runoff volume can be controlled on site and either infiltrated or utilized by native plant species. As measured infiltration data were limited to the vadose zone, the infiltrated volume was considered potential recharge; future work may include modeling and installation of deeper sensors as a means of approximating recharge