UNT Theses and Dissertations - 3 Matching Results

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Forest Landscape Dynamics: a Semi-Markov Modeling Approach

Description: A transition model (MOSAIC) is used to describe forest dynamics at the landscape scale. The model uses a semi-Markov framework by considering transition probabilities and Erlang distributed holding times in each transition. Parameters for the transition model are derived from a gap model (ZELIG). This procedure ensures conceptual consistency of the landscape model with the fine scale ecological detail represented by the forest gap model. Spatial heterogeneity in the transition model is driven by maps of terrain with characteristics contained in a Geographic Information System (GIS) database. The results of the transition model simulations, percent cover forest type maps, are exported to grid-maps in the GIS. These cover type maps can be classified and used to describe forest dynamics using landscape statistics metrics. The linkage model-GIS enhances the transition model spatial analytical capabilities. A parameterization algorithm was developed that takes as input gap model tracer files which contain the percent occupation of each cover type through time. As output, the algorithm produces a file that contains the parameter values needed for MOSAIC for each one of the possible transitions. Parameters for the holding time distribution were found by calculating an empirical estimate of the cumulative probability function and using a non-linear least squares method to fit this estimate to an Erlang distribution. The algorithm provided good initial estimates of the transitions parameters that can be refined with few additional simulations. A method for deriving classification criteria to designate cover types is presented. The method uses cluster analysis to detect the number and type of forest classes and Classification and Regression Tree (CART) analysis to explain the forest classes in term of stand attributes. This method provided a precise and objective approach for forest cover type definition and classification. The H. J. Andrews forest in Oregon was used to demonstrate the ...
Date: August 1997
Creator: Ablan, Magdiel
Partner: UNT Libraries

Conception and Design of Constructed Wetland Systems to Treat Wastewater at the Biosphere 2 Center with Use of Reaction Rate Models and the Habitat Evaluation Procedure to Determine the Effects of Designing for Wildlife Habitat on Treatment Efficiency

Description: A study was undertaken to explore relationships between wetland characteristics which make them efficient water purifiers versus their ability to serve as wildlife habitat. The effects of designing constructed wetlands for improved habitat on water treatment efficiencies were quantified. Results indicate that some sacrifice in treatment efficiency is required and that the degree of efficiency reduction is dependant upon pollutant loading rates. However, sacrifice in efficiency is much smaller than increase in habitat quality, and can be offset by increasing wetland area. A practical, theoretical application was then attempted.
Date: May 1998
Creator: Clingenpeel, Glenn C. (Glenn Christopher)
Partner: UNT Libraries

Identification of a Potential Factor Affecting Graduation Rates in STEM for Hispanic Students at the University of North Texas, via Analysis of Nonfiction Science Books in Spanish Language for ELLs in the Dallas ISD Schools

Description: Latinos are the largest minority group in the U.S.; however despite the continuous growth of the Hispanic population, Latinos are severely underrepresented in STEM fields. One of the reasons that might explain why Latinos do not major in STEM is the way they encounter science curriculum in primary school. Students' limited proficiency in English may constrain their science achievement when instruction is delivered exclusively in English. A quantitative analysis with graduation rates in STEM from 2009 to 2014 at the University of North Texas was conducted, finding that there is a significant difference (p<0.05) in the number of bachelor's degrees in STEM between Hispanic, White, African American and other student populations. Interviews with teachers, librarians and publishing companies were performed to describe the limited science literature in Spanish at the Dallas ISD schools. Improving science literacy by teaching according to ELLs' linguistic skills and culture may lead to a better understanding of science curriculum throughout their education, which may translate into higher college graduation rates by Hispanic recipients in STEM.
Date: August 2016
Creator: Garcia Colin, Monica
Partner: UNT Libraries