Master of Science

thesisModeling the relationships between climate and crop growth is an important tool to study agriculture in the past and future. Agricultural suitability models, which estimate the probability of rain-fed cultivation in a particular location, provide an opportunity to predict agricultural conditions for multiple scenarios in space and time. This thesis presents a methodological approach to developing a simple agricultural suitability model with machine learning techniques and applying it to two scenarios. First, to predict the potential impacts of climate change, the model was used to project agricultural suitability at the end of the 21st century at the global scale. Second, the model was used to predict agricultural suitability in Range Creek Canyon, an important archeological site in east-central Utah, in the 10th -13th centuries. The agricultural suitability model was supplemented with a streamflow model of Range Creek to address the potential for irrigation. The predictive power of random forest and XGBoost were compared and random forest was found to build the stronger model in this application. Applied to the future, this model predicts a net increase of 13.8-28.2% of agriculturally suitable land by AD 2100. The broad patterns agree with past suitability models, with the largest gains of suitability distributed in the high-northern latitudes. Decreases in suitability are projected in some regions, particularly in the current most intensely cultivated regions including Midwestern America. A sensitivity analysis revealed that the main driver of these shifts was changing growing season length and intensity, while changing soil moisture had a limited effect. Applied to the past in Range Creek Canyon, the model predicted very low agricultural suitability, providing evidence that rain-fed agriculture in Range Creek Canyon from AD 900-1200 was nearly impossible. Modeled Range Creek streamflow predicted that mean streamflow from AD 900-1200 was 6.34% greater than modern streamflow. The area of maize fields that could be irrigated with this amount of streamflow was approximately 30.6 hectares. The agricultural suitability model applied to two scenarios differing in scales of time and space demonstrate how it can provide meaningful insights to a broad range of past and future scenarios

Enhanced cardiac-specific differentiation of mouse embryonic stem cells via electrical stimulation

Cardiovascular diseases account for more deaths than any other disease. Cardiac tissue engineering has turned to stem cells as a renewable source of myocytes for use in tissue replacements. Existing methods for stem cell differentiation are non-specific, yielding low numbers of myocytes, with varying contraction frequencies and strengths. The goals of this project are to design novel experimental approaches, utilizing an electrical stimulation regimen, aimed at increasing the efficiency of cardiac differentiation from embryonic stem cells and generating cardiac myocytes/scyncithia with functional characteristics that more closely resemble native tissues. It has been found that parameters such as amplitude, duration and frequency of the electrical stimulus and the timing of its onset are critical factors for enhancement of cardiac differentiation. Embryonic stem cells, subjected to an optimum regime of embryoid body formation via the hanging drop method followed by suspension culture and subsequent post plating on conductive slides with stimulation exhibit nearly 50% more cells differentiating toward the cardiac lineage compared to non-stimulated controls, as determined by microscopical analysis of the expression of ventricular marker myosin light chain-2v via immunohistochemistry. The spontaneous contractions in the stimulated cells begin up to one day earlier and have an average beat frequency close to that of the stimulus applied during differentiation. The spontaneously contracting regions have larger areas of contraction, which beat more rhythmically, as determined by videographic analysis. Data suggests that these improved myocytes may be better suited for applications in tissue engineered constructs, direct implantation into an ailing heart and for use in drug development models than those from other methods.Ph.D., Biomedical Engineering -- Drexel University, 200

Occupant Dynamics in Rollover Crashes: Influence of Roof Deformation and Seat Belt Performance on Probable Spinal Column Injury

Motor vehicle crashes are the leading cause of death in the United States for people ages 3–33, and rollover crashes have a higher fatality rate than any other crash mode. At the request and under the sponsorship of Ford Motor Company, Autoliv conducted a series of dynamic rollover tests on Ford Explorer sport utility vehicles (SUV) during 1998 and 1999. Data from those tests were made available to the public and were analyzed in this study to investigate the magnitude of and the temporal relationship between roof deformation, lap–shoulder seat belt loads, and restrained anthropometric test dummy (ATD) neck loads

Organic electrode coatings for next-generation neural interfaces

Traditional neuronal interfaces utilize metallic electrodes which in recent years have reached a plateau in terms of the ability to provide safe stimulation at high resolution or rather with high densities of microelectrodes with improved spatial selectivity. To achieve higher resolution it has become clear that reducing the size of electrodes is required to enable higher electrode counts from the implant device. The limitations of interfacing electrodes including low charge injection limits, mechanical mismatch and foreign body response can be addressed through the use of organic electrode coatings which typically provide a softer, more roughened surface to enable both improved charge transfer and lower mechanical mismatch with neural tissue. Coating electrodes with conductive polymers or carbon nanotubes offers a substantial increase in charge transfer area compared to conventional platinum electrodes. These organic conductors provide safe electrical stimulation of tissue while avoiding undesirable chemical reactions and cell damage. However, the mechanical properties of conductive polymers are not ideal, as they are quite brittle. Hydrogel polymers present a versatile coating option for electrodes as they can be chemically modified to provide a soft and conductive scaffold. However, the in vivo chronic inflammatory response of these conductive hydrogels remains unknown. A more recent approach proposes tissue engineering the electrode interface through the use of encapsulated neurons within hydrogel coatings. This approach may provide a method for activating tissue at the cellular scale, however, several technological challenges must be addressed to demonstrate feasibility of this innovative idea. The review focuses on the various organic coatings which have been investigated to improve neural interface electrodes

Stress analysis of a fixed implant-supported denture by the finite element method (FEM) when varying the number of teeth used as abutments

OBJECTIVES: In some clinical situations, dentists come across partially edentulous patients, and it might be necessary to connect teeth to implants. The aim of this study was to evaluate a metal-ceramic fixed tooth/implant-supported denture with a straight segment, located in the posterior region of the maxilla, when varying the number of teeth used as abutments. MATERIALS AND METHODS: A three-element fixed denture composed of one tooth and one implant (Model 1), and a four-element fixed denture composed of two teeth and one implant (Model 2) were modeled. A 100 N load was applied, distributed uniformly on the entire set, simulating functional mastication, for further analysis of the SEQV (Von Mises) principal stresses, which were compared with the flow limit of the materials. RESULTS: In a quantitative analysis, it may be observed that in the denture with one tooth, the maximum SEQV stress was 47.84 MPa, whereas for the denture with two teeth the maximum SEQV stress was 35.82 MPa, both located in the region between the pontic and the tooth. CONCLUSION: Lower stresses were observed in the denture with an additional tooth. Based on the flow limit of the materials, porcelain showed values below the limit of functional mastication