Texas A&M University-Kingsville: AKM Digital Repository
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Deflection behavior of prestressed crumb rubber concrete beam reinforced with carbon fibers at elevated temperatures
No full textEngineers have always taken a different perception to the structural concepts of fire-resistant buildings in civil engineering. Concrete structural members are expected to satisfy appropriate fire safety requirements. To achieve fire safety various methods are used. One such method is to reduce the use of natural resources by suitable alternatives as aggregates at certain proportions to the concrete mixture. This can improve the strength of the concrete and life span of the structure. Numerous studies are focused on adding suitable proportion of crumb rubber particles, steel fibers and carbon fibers as an alternative to the rock particles. This has resulted in increasing the strength of concrete at normal temperatures. The corrosion of steel in concrete structure is a challenge that determines longevity of the structure. To overcome this limitation, fiber reinforced polymers (FRP) are used. They have high strength to weight ratio and an excellent resistance to corrosion. The use of carbon fiber reinforced polymer (CFRP) has shown some promise. To enhance the durability and serviceability of the structure, prestressing application is globally used. Prestressing CFRP tendons in structures has resulted in reducing crack formation. However, the behavior of a combination of prestressed CFRP with crumb rubber concrete at elevated temperature remains unknown. This study focusses on the deflection behavior of prestressed CFRP reinforced with crumb rubber concrete beam at elevated temperatures. In this study an analytical model to determine the deflection of CFRP prestressed crumb rubber concrete beam subjected to practical elevated temperature is developed. The results are validated with the finite element model developed using Ansys. In addition, the results obtained are compared with indirect references from literature to recognize the practical behavior of the material. To conclude, a practical application is provided
Strengthening the Mexican fruit fly, Anastrepha ludens (Loew) (Diptera: tephritidae), eradication program with the use of attract-and-kill devices
No full textThe Mexican fruit fly, Anastrepha ludens (Loew) (Diptera: Tephritidae), is a serious pest of numerous fruits in its native countries of Mexico and Central America. Anastrepha ludens is a pest of regulatory concern whose detections can lead to the establishment of a quarantine that negatively affects the economic viability of citrus production. Very low economic thresholds– including the detection of five wild adult flies within a three-mile radius circle, a wild mated female, or larva/egg found in fruit– trigger a quarantine requiring growers to follow costly and strict treatment protocols before fruits can be harvested. To ensure that the fly does not permanently establish itself in south Texas, a Preventative Release Program (PRP) comprised of releasing irradiated sterile adults has been ongoing for over 30 years. Sporadic detections of wild flies are made in the south Texas landscape in which unmanaged residential citrus or abandoned citrus groves are intermingled with managed commercial groves. To complement and strengthen the PRP program, an ‘Attract and Kill’ (AK) strategy incorporating lures for adult flies and an embedded insecticide as killing agent into a device has been developed and tested for its effectiveness as part of an integrated approach for A. ludens management
Oxidative potential and chemical characterization of ambient aerosols in a South Texas coastal city
No full textOxidative Potential (OP) is a valuable metric that, when quantified, better describes the cellular response to aerosol inhalation than size distribution and mass alone. Aerosol samples were collected at three different sites in Corpus Christi, TX, with varying levels of pollutant emissions. The dithiothreitol (DTT) assay was adapted to determine the OP of the samples collected. Stark variations in OP are expected between the three sampling sites. The multiple size ranges collected in this study (18-.18μm) are a unique aspect in that previous studies focus mainly on PM10 and PM2.5. Samples were extracted using sonication, and evaluated to find OP, chemical composition, and carbonic content. Plots were developed to evaluate trends between both OPmass and OPvol with ambient concentrations of carbon and metals. The Pearson correlation coefficient is reported to show any viable statically relationships between the different aspects of PM analyzed. As expected, higher traffic was found to be related with higher OP. Ambient carbon and metal concentrations were surprisingly found to have little predictable impact on OP. The most valuable information garnered stems from the carbon and metal fraction of the PM collected. These fractions consistently showed the highest correlation with the OP determined
Uncertainty estimation due to climate change fo improving water resources management in the Nueces River Basin, Texas
No full textEffective water management is needed in arid and semi-arid regions to ensure reliable water supply under competing demands for agriculture, municipal and domestic use and environmental flows. As uncertainties in climate system are common and cannot be eliminated, uncertainty analysis is critical to water resources planning and management. Thus, the goal of this study is to incorporate uncertainty arising from climate change into water management decisions for the Choke Canyon – Lake Corpus Christi (CC-LCC) Reservoir System, which is located in a semi-arid basin in Texas - the Nueces River Basin (NRB).
Despite recent studies on uncertainty analysis in climate change impact assessment and reservoir operations, very few studies have focused on semi-arid watersheds. In this study, the Variable Infiltration Capacity (VIC) model was calibrated to observed streamflow and subsequently implemented under multiple General Circulation Models historical climate change simulations. Multiple inflow scenarios at CC-LCC System were used to implement Water Rights Analysis Package (WRAP) water management model. The results indicate that increasing conservation pool at CCR by 1 foot can offset 10% increase in demands and reduce water shortages without increasing the flood risk. Such information will be valuable to water managers and policy makers
Finite element analysis of corroded steel beams
No full textThis research project analyzes the structural capacity of steel beams before and after corrosion using 3D steel beam models created with ABAQUS, a finite element modeling software. For analysis, ABAQUS-CAE (Computer-Aided Engineering) software shall be used. Corrosion losses at percentages of zero, five, seven, and nine of the cross-sectional area are modeled for three steel beam I-shaped geometries to determine the structural capacity before and after corrosion. A W14x82 was selected as one of the beam cross-sections in this study to provide a comparison with results obtained by Mr. Okafor in his master’s thesis [1]. Mr. Okafor considered non-corroded beam geometries only. The current work considers two additional cross-sections, W12x65 and W14x120. All beams models were 240 inches long and simply supported, which is consistent with previous research. The comparison of structural characteristics focused on nominal moment capacity, critical loads, and bending stresses before and after corrosion. Results for corroded and non-corroded models obtained from ABAQUS have been compared to capacity estimates using the 15th edition of the AISC Steel Construction Manual (or AISC manual) [2]. The AISC results were calculated assuming the decrease in plastic and elastic section modulus values, due to corrosion, applied throughout the length of the beams, whereas for analysis in ABAQUS corrosion was limited to the beam ends of each model. The results obtained had a maximum difference below nine% between the calculations from the code and finite element analysis results. The relationship between corroded and non-corroded beam models showed a decrease of moment and load capacity by 22% for nine % corrosion in the zero-corrosion models
Simulation and hardware validation of recurrent neural network current controller using TI microinverter for solar integration
No full textSingle-phase inverters are extensively used to integrate small-scale Distributed Generation (DG) renewable energy sources to the utility grid. A novel Recurrent Neural Network (RNN) current controller is introduced for a Texas Instruments (TI) solar micro inverter kit that contains a C2000 TI microcontroller. The RNN is trained through the Levenberg-Marquardt (LM) and Forward Accumulation Through Time (FATT) algorithm to obtain the weight configuration. A MATLAB Simulink model of the TI DC-AC inverter block control loop was designed, and its simulation results were compared with that of the RNN current controller. The simulation results proved that the proposed RNN current controller had a better tracking ability compared to that of the TI 3P3Z current controller at steady state condition. The novel RNN control algorithm was then loaded into the C2000 TI Digital Signal Processor (DSP) via the TI Code Composer Studio software and an inverter closed current loop test without grid connection was conducted in a laboratory setup to verify its functionality. The laboratory waveform results verified that the RNN current controller produced the best tracking of the measured inverter AC current to its reference value at a low sampling frequency of 5KHz. The proposed RNN current controller also proved to perform better to the 3P3Z current controller by producing lower values of Total Harmonic Distortion (THD) in both 5KHz and 50KHz sampling frequencies
Perceptions of EFL teachers and learners about implicit and explicit grammar instruction
No full textEnglish is one of the most spoken languages around the world. In Mexico and many other countries, this language has been officially categorized as a foreign language taught and learned in school settings. It has been solidified as an essential language not only for educational but also for international purposes (Kung, 2017). Many people in Mexico study English for different reasons and specific purposes. In Mexico, there is still a debate among educators and teachers concerning the teaching of grammar. Teachers' and mainly students' viewpoints about grammar instruction are scarcely considered. This is the reason why the researcher was interested in finding out about teachers' and learners' perceptions of grammar instruction. This quantitative survey study investigated the perceptions that English as a Foreign Language (EFL) teachers and adult learners had about explicit and implicit grammar instruction. Also, the impact the EFL language level course had on teachers and adult learners’ perceptions about such types of grammar instruction was studied. The research questions that this study considered were 1) what are the EFL teachers’ and adult learners’ perceptions about implicit and explicit grammar instruction? and 2) what impact does the EFL language level course have on teachers’ and adult EFL learners’ perceptions about implicit and explicit grammar instruction? A quantitative cross-sectional survey design formed part of this study. Participants of seven different language level courses at the beginning, intermediate and advanced EFL levels were considered in this study. Students and teachers were surveyed on their perceptions about explicit and implicit grammar instruction. A questionnaire, which is usually a paper-and-pencil instrument, is a type of survey used in survey research. In applied social studies, this type of research is one of the most important types of data measurement (Trochim, 2006). However, in this study, the researcher met with participants for them to complete self-administered questionnaires online in a computing room.
Keywords: teachers’ perceptions, learners’ perceptions, explicit grammar instruction, implicit grammar instruction, EFL language level clas
Season of burn effects on mortality, forage production and plant functional group omposition in gulf cordgrass vegetation communities
No full textGulf cordgrass (Spartina spartinae [Trin.] Merr. ex Hitchc.) is a productive, warm season, perennial bunchgrass. It can provide valuable forage for livestock when young, particularly when other forage may be scarce. However, a problem arises when Gulf cordgrass becomes mature: leaves and stems are very coarse and low in palatability and nutritive value for livestock and wildlife. Removing mature growth encourages production of tender, palatable shoots, and improves overall nutritive value. Fire is the most economical management tool to meet these objectives and is the natural process that kept these Gulf cordgrass communities in prime condition historically. In this study I applied prescribed burning at the pasture scale in grassland communities of coastal prairies and marshes dominated by either Gulf cordgrass or seacoast bluestem (Schizachyrium scoparium var. littorale [Nash] Bickn.). I burned two 200-ha pastures each winter and summer beginning in winter 2016 for a total of 8 burn and 2 control (no burn) pastures. My main objective was to determine the optimal season of burning by comparing winter and summer season burns in Gulf cordgrass communities of the Gulf Prairies and Marshes ecoregion of Texas. There was no difference in fire temperature between summer and winter burns. Gulf cordgrass plant mortality was higher in burn treatments compared to control treatments. However, there was no difference in Gulf cordgrass plant mortality between winter or summer burn treatments. There was a strong positive relationship between plant mortality and peak fire temperature, and between plant mortality and duration of heat over 65°C. Forage standing crop growth models were unique for each season; estimated regression coefficients were positive in each model in Gulf cordgrass vegetative groups, indicating that forage standing crop increased as days after burning progressed. Forage regrowth showed similar patterns following winter and summer burning for Gulf cordgrass, grasses other than Gulf cordgrass, or total forage standing crop. Forage production for approximately 90 days following burning did not differ between the four burns regardless of season, or between winter and summer burning. The removal of litter and excess growth of mature Gulf cordgrass by prescribed burning allowed native warm season forbs and native sub-shrubs to increase in their relative abundance of forage standing crop compared to control patches. A Non-metric multidimensional scaling ordination (NMDS) analyses showed there was more variation in functional group composition of burned Gulf cordgrass communities than non-burned communities when functional group composition was based on forage standing crop than when it was based on plant density. Burning Gulf cordgrass communities, regardless of season, enhanced production of palatable forage for livestock and created changes in functional group composition. This resulted in greater structural and species heterogeneity, additionally, creating more varied winter and summer habitat for a variety of wildlife species
Comparison of survey methods and development of habitat suitability models for wintering Wild Turkeys in North Texas
No full textRecent breeding bird surveys show that Wild Turkey populations in Texas are at a decline. As a consequence to their growing popularity by hunters, surveys must be taken in order to detect population trends. Identifying the optimal survey methodology in order to determine accurate Wild Turkey population densities as well as incorporating geospatial technologies and habitat suitability models can be beneficial for the development of management strategies for Wild Turkeys. The objectives of this project were to: 1) Compare estimates of wild turkey survey methods to estimate wild turkey density, 2) Develop habitat suitability models that will enable Texas Military Depmiment staff to determine which habitats are optimal for harboring turkeys, and 3) To incorporate concurrent survey methods to evaluate habitat suitability models in nearreal time. Eastern wild turkeys were surveyed at Camp Maxey Training Center near Paris, Texas while Rio Grande wild turkeys were surveyed at Fmi Wolters Training Center near Mineral Wells, Texas. My study tested the consistency and precision of point counts, road surveys, and roost surveys and determined that road surveys provided consistently higher detections than point count and roost surveys for both Fort Wolters (p=0. 0013) and Camp Maxey (p=0. 043). Surveys were then used to evaluate habitat suitability models developed using the gradient concept of landscape structure. Models were developed in regards to food, water, and cover for both study sites. Road surveys were used to evaluate food models and found that a majority of survey locations (89.7% at Fort Wolters and 93.1 % at Camp Maxey) were in areas classified as highly suitable. I then used roost surveys to evaluate my cover models and again found a majority of survey locations (93.8% at Fort Wolters and 100% at Camp Maxey) were in areas of high suitability
Courtship abnormalities in Drosophila melanogaster
No full textCourtship index (CI) is the percentage of time in which a male fly shows one of six stages in courtship. Normal CI values for wild-type Canton-S (CS) flies are typically around 80%. The aim of this thesis is to see if flies that have inhibitory insertions for various neural functions and abilities, will show abnormalities in CI compared to the results of normal naive CS flies. The inhibitory insertions in these flies means that each mutant stock expresses dsRNA (double stranded RNA) for RNAi of the certain gene that is targeted in the courtship circuit. Thus, the process of RNAi is suppressing the levels of those particular genes. In this experiment, par-6 and rut mutant flies exhibit a decreasing trend in courtship index levels compared to normal naive CS male flies. Gαs, dunce, and TBPH mutant flies show no difference in CI values compared to those of naive CS male flies. These results show that Gαs, dunce, and TBPH RNAi mutant flies demonstrated normal courtship circuit behavior. par-6 and rut RNAi mutant flies show a decreasing trend in CI that shows the courtship circuit is still functioning in its normal fashion