A Data Driven Approach To Optimize Re-Fracturing Operations In The Williston Basin

Because of the recent paradigm shift focusing heavily on cost minimization, many operators are now re-developing existing assets at much lower costs instead of developing newly drilled wells. Although it may seem that the hydraulic fracturing process on a well would be easier after initial stimulation, this is not usually the case and is often more difficult. Being able to identify high margin effects of treatment parameters will help engineers design hydraulic fracturing treatments to minimize average STP (STP) and minimize costs. This research develops a feature engineered multivariate regression model that identifies several high margin areas for STP reduction. These models also yield error around 2% when predicting average STP. Using the marginal effects estimated in this study, operators can start to consider minimizing STP as a design parameter that has implications for pump time, pump maintenance costs, fuel costs, and emissions

Floodplain Forest Regeneration Dynamics in the Lower Mississippi River Alluvial Valley

Floodplain forest species diversity is driven, in part, by variation in disturbance regime. Flood patterns create heterogeneity in microsite quality from small differences in elevation across a floodplain which, in turn, influence flood timing and duration. Differences in species’ regeneration niches in relation to hydrologic patterns can account for long-term coexistence of various species. In the past century floodplain forests have exhibited a wide range of changes in stand development and species composition as a result of altered hydrology in rivers and floodplains. I evaluated the role of regeneration in floodplain forest systems of the Lower Mississippi River Alluvial Valley to gain insight into the mechanisms behind compositional transitions. Specifically, I focused on how flood timing related to species-specific germination and first-year seedling survival patterns and processes. Through a controlled greenhouse experiment, I tested the effects of flood timing and duration on first-year seedlings of floodplain forest species. Results showed the effects of complete submergence on first-year seedling survival is affected by the age of the seedling at the time of flooding, and the duration of flooding. Moreover, species displayed specific responses to time of flood onset and flood duration that varied by their post-germination age. The onset of a spring flood event post-germination is therefore likely to have variable effects on woody seedling composition depending on its timing relative to germination. Through examining seedling dynamics at four floodplain locations in the Lower Mississippi River Alluvial Valley (LMAV), I found first-year seedling species composition was significantly influenced by floodplain hydrology through relationships between the timing of flooding and species-specific germination and first-year seedling survival processes. Species generally considered flood-tolerant at maturity tended to demonstrate later germination windows (May and beyond) while many (not all) species considered less-flood tolerant at maturity emerged early in the spring (March-May). Flood duration preceding a seed’s germination window inhibited germination when it fully overlapped with a species’ germination window. Flooding also benefited germination when it receded prior to the close of species’ germination windows, likely through improved soil moisture availability, but possibly through other mechanisms such as nutrient supplementation. Additionally, post-germination flood timing significantly influenced seedling composition through the event of a second flood which induced seedling mortality. Spatial and temporal variation in the timing of flood recession would diversify species’ opportunities to benefit from flooding in the LMAV because of the distinct emergence windows demonstrated by species in this study. This would ultimately lead to diversification in seedling species composition in both space and time. A temporally and spatially dynamic annual flood regime would likely promote greater diversity in seedling species composition through differentiation in species’ germination and seedling survival processes

Revisiting the Ecological Status of the Cheat Mountain Salamander (Plethodon nettingi) After 32 Years

The Cheat Mountain Salamander (Plethodon nettingi) is endemic to the high elevations of the Allegheny Mountains in West Virginia and is listed by the U.S. Fish and Wildlife Service as a threatened species. In 1978-79 and in 2011 the vertical distribution of P. nettingi was measured at four sites to determine their range of occupancy in relation to elevation. During both time periods, a transect was established at each site that ran from high to low elevation. Along each transect, quadrats were placed at regular, 12.2 m elevation intervals. Quadrats were searched twice for presence/absence (i.e., occupancy) and abundance of P. nettingi and competitor salamander species. To determine if salamander species distribution had changed over time, occupancy modeling was used to compare species occupancy between the two time periods. I found that Plethodon nettingi was positively associated with higher elevations, and competitor species were negatively associated with higher elevations. Plethodon nettingi occupancy probability declined the most at the middle to highest elevations. There was no relationship between the change in occupancy of P. nettingi and Desmognathus ochrophaeus, but at the highest elevations the changes in occupancy of P. nettingi and Plethodon cinereus was negatively correlated. I suggest competition between these species is most intense at higher elevations and P. nettingi is possibly being outcompeted by P. cinereus. Habitat properties were also measured at each site and comparisons between the two time periods revealed varying trends in temperature, relative humidity, and moisture, but additional research is needed to draw complete conclusions on site dynamics. Summaries of forest properties suggested slightly less diversity at sites in 2011 compared to 1978-79, but incomplete data prevented testing for significance

Structured eigenvectors, interlacing, and matrix completions

This dissertation presents results from three areas of applicable matrix analysis: structured eigenvectors, interlacing, and matrix completion problems. Although these are distinct topics, the structured eigenvector results provide connections.;It is a straightforward matrix calculation that if {dollar}\lambda{dollar} is an eigenvalue of A, x an associated structured eigenvector and {dollar}\alpha{dollar} the set of positions in which x has nonzero entries, then {dollar}\lambda{dollar} is also an eigenvalue of the submatrix of A that lies in the rows and columns indexed by {dollar}\alpha{dollar}. We present a converse to this statement and apply the results to interlacing and to matrix completion problems. Several corollaries are obtained that lead to results concerning the case of equality in the interlacing inequalities for Hermitian matrices, and to the problem of the relationship among eigenvalue multiplicities in various submatrices.;Classical interlacing for an Hermitian matrix A may be viewed as describing how many eigenvalues of A must be captured by intervals determined by eigenvalues of a principal submatrix of A. We generalize the classical interlacing theorems by using singular values of off-diagonal blocks of A to construct extended intervals that capture a larger number of eigenvalues. The union of pairs of intervals is also discussed, and applications are mentioned.;The matrix completion results that we present include: the positive semidefinite cycle completion problem for matrices with data from the complex numbers, distance matrix cycle completability conditions, the P-matrix completion problem, and the totally non-negative completion problem. We show that the positive semidefinite cycle completion problem for matrices with complex data is a special case of a larger real positive semidefinite completion problem. In addition, we characterize those graphs for which the cycle conditions on all minimal cycles imply that a partial distance matrix has a distance matrix completion. We also prove that every combinatorially symmetric partial P-matrix has a P-matrix completion and we characterize the class of graphs for which every partial totally nonnegative matrix has a totally nonnegative completion. The structured eigenvector results are used to give a new proof of the the maximum minimum eigenvalue problem for partial Hermitian matrices with a chordal graph

Farmers’ knowledge and perceptions of potato pests and their management in Uganda.

As we initiate entomological research on potato (Solanum tuberosum L.) in Uganda, there is need to understand farmers’ knowledge of existing insect pest problems and their management practices. Such information is important for designing a suitable intervention and successful integrated pest management (IPM) strategy. A farm household survey using a structured questionnaire was conducted among 204 potato farmers in six districts of Uganda (i.e., Kabale, Kisoro, Mbale, Kapchorwa, Mubende, and Kyegegwa) during August and September 2013. Diseases, insect pests, price fluctuations, and low market prices were the four highest ranked constraints in potato production, in order of decreasing importance. Cutworms (Agrotis spp.), aphids (Myzus persicae (Sulzer)), and potato tuber moth (Phthorimaea operculella (Zeller)) were the three most severe insect pests. Ants (Dorylis orantalis Westwood), whiteflies (Bemisia tabaci (Gennadius)), and leafminer flies (Liriomyza huidobrensis (Blanchard)) were pests of moderate importance. Major yield losses are predominantly due to late blight (Phytophthora infestans (Mont.) de Bary) and reached 100% without chemical control in the districts of Kabale, Kisoro, Mbale, and Kapchorwa. On average, farmers had little to moderate knowledge about pest characteristics. The predominant control methods were use of fungicides (72% of respondents) and insecticides (62% of respondents). On average, only 5% of the 204 farmers knew about insect pests and their natural enemies. This lack of knowledge calls for training of both farmers and extension workers in insect pest identification, their biology, and control. Empowering farmers with knowledge about insect pests is essential for the reduction of pesticide misuse and uptake of more environmentally friendly approaches like IPM. Field surveys would need follow-up in order to assess the actual field infestation rates and intensities of each insect pest and compare the results with the responses received from farmers

A cross-sectional study of pesticide use and knowledge of smallholder potato farmers in Uganda.

This study sought to promote proper and safe pesticide-handling practices by providing data needed to guide pesticide regulation policy and training for extension staff and farmers. A household survey was conducted in three major potato-growing agroecological zones of Uganda. Two hundred and four potato farmers were interviewed about the type and source of pesticides they use in potato cultivation, the frequency of applications, the use of protective clothing, and cases of pesticide poisoning

Pest Status of Acraea acerata Hew. and Cylas spp. in sweetpotato (Ipomoea batatas (L.) Lam.) and incidence of natural enemies in the Lake Albert Crescent agro-ecological zone of Uganda.

The present study presents the results of farmers’ field surveys of the sweetpotato butterfly, Acraea acerata Hew., and the two African sweetpotato weevils, Cylas puncticollis Boheman and C. brunneus F. infestation and damage. The objectives of this study were to determine (i) occurrence and distribution of A. acerata and Cylas spp. as well as infestation and losses in sweetpotato (Ipomoea batatas (L.) Lam.), and (ii) the occurrence and abundance of parasitoids of A. acerata in the Lake Albert Crescent (LAC) agro-ecological zone of Uganda. Field surveys were conducted in 240 sweetpotato fields in eight subcounties in Masindi and Buliisa districts at the end of each of the two cropping seasons of 2012 (March to May and September to November). A. acerata and Cylas spp. occurred in 17% and 90% of the fields, respectively. A. acerata did not occur in two subcounties of Buliisa district. A. acerata infestation was low, with up to two and four larvae per plant in the first and second cropping season, respectively, causing minor defoliation of up to 4.1% of the sweetpotato plant. Larvae of Cylas spp. caused root yield losses of up to 56.5% and 47.5% in the first and second cropping seasons, respectively. Parasitism rates of A. acerata larvae ranged from 0.0% to 15.1% in season 1 and 0.0% to 6.3% in season 2. Out of a total of 1020 larvae collected, 8.43% were found to be parasitized. Parasitoids occurred in 56% of fields infested by its host. Charops spp. was the main parasitoid. It was evident that Cylas spp. were more prevalent than A. acerata in the LAC agro-ecological zone of Uganda. Conservation of A. acerata natural enemies may contribute to better management of this pest. Urgent attention for management of Cylas spp. is required