Texas A&M University-Kingsville: AKM Digital Repository
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Bucket loaders using adjustable linkages
No full textBucket loaders are machines that are commonly employed in construction, mining or landscaping projects for loading or moving debris, soil, sand, or rock. Wheeled bucket loaders are preferred in most situations because of their high speed, efficiency and flexibility, relatively low weight and operation and maintenance costs. Tracked bucket loaders are chosen due to their high surface traction, stability and maneuverability, better performance on uneven or rough terrain, and relatively less ground impact.
A payloader uses its front bucket to scoop materials that are stacked on the ground, and then either transport them to a different location or load them to a waiting transportation truck. The front bucket is pivoted to the end of the boom of the loader. The tilting motion of the bucket is generated by its corresponding hydraulic cylinder through a four-bar linkage. The boom link is connected to the chassis of the payloader using a revolute joint to lift or lower the bucket. The boom link has its driving hydraulic cylinder and its related driving linkage. The arm of a payloader consists of its bucket and boom, which moves the bucket to fulfill the payloader’s function. The position and orientation of the front bucket are determined by the joint efforts of the bucket and boom driving cylinders together with their driving linkages. The axes of the revolute joints of a payloader arm are parallel each other, which leads to a planar motion of the front bucket. The planar workspace of the front bucket is defined by the dimensions of the driving linkages and the driving strokes of the cylinders.
The existing payloaders usually have fixed workspace since their driving linkages are not adjustable and driving cylinders have fixed strokes. The fixed workspace of a payloader lacks operation flexibility and limits its applications. This research incorporates adjustable linkages into payloaders to enhance their operation flexibility. The motion performances of payloaders without and with adjustable linkages are analyzed, simulated, evaluated, and compared. The results from this research are tried to provide certain guidelines for improving operation flexibility of the existing bucket loaders
Long-term response of tanglehead (Heteropogon contortus) to prescibed burning and cattle grazing and a pilot study to estimate forage mass from unmanned aerial vehicles in a semi-arid rangeland
No full textTanglehead (Heteropogon contortus [L.] P. Beauv. ex Roem. & Shult.), an indigenous grass of South Texas has expressed invasive tendencies by creating monocultures of unpalatable vegetation, decreasing native vegetation species composition and changing structure on the landscape. Treating large patches of tanglehead with prescribed fire can remove coarse standing forage, allow lush green re-growth, change the vegetation structure, decrease tanglehead cover, and allow other species to establish. The objectives of this study were to determine the effects of prescribed fire and cattle grazing on (1) the composition of a plant community dominated by tanglehead; and (2) cattle use of tanglehead-dominated areas treated with prescribed fire. I documented the change of a tanglehead-dominated pasture that received two fire treatments (November 2016 and February 2019). Plant species richness, percent bare ground, and cattle utilization increased in the February 2019 burn plots compared to the November 2016 burn and control plots. Usable space for bobwhite quail increased with increased heterogeneity of the landscape and cattle productivity was acceptable for the parameters of the area.
The use of UAVs as a method to estimate forage mass in rangelands is a developing science and will be presented as a pilot site. The specific objectives of this research were to (1) evaluate the feasibility of quantifying forage mass in semi-arid rangelands using a double sampling technique with high-resolution imagery and (2) to compare the effect of UAV flight altitude on forage mass estimation. Orthoimagery and digital surface models (DSM) were
acquired with an UAV at different altitudes. Field forage mass data were regressed on volumes obtained from a DSM. My results show that volumes estimated with UAV data and forage mass as measured in the field have a significant relationship at all flight altitudes
The effect of citrus flush stage in the distribution of trunk injected oxytetracycline for HLB management
No full textHuanglongbing (HLB) or citrus greening, is one of the world’s most devastating and threatening citrus diseases. The causal agent is the phloem-limited bacteria ‘Candidatus Liberibacter asiaticus’ (CLas). Several studies have addressed the effect of oxytetracycline (OTC) applications on CLas titers under different conditions, from delivery methods to seasonal effects. However, there is limited information on how the vegetative growth cycle affects OTC distribution on the tree to target CLas populations. In this field study, OTC concentrations were measured in CLas positive grapefruit trees by LC/MS and CLas titers were assessed by qPCR in flushing and non-flushing branches after injecting 2.0 g of OTC in the trunk. Three trees injected with water were used as controls. Leaf samples were collected at 4 locations along flushing and non-flushing branches from the same trees after 0-, 4-, 8-, 16-, 32-, and 180-days post-treatment. Results indicate a significant difference in CLas titers between the OTC treated and control trees. We detected OTC residues in both flushing and non-flushing branches after 4 days post-injection. However, OTC was unevenly distributed overtime along the tree branches, and lower levels of residues were detected in flushing branches compared to non-flushing branches. Moreover, CLas titers were reduced at the same level in both, flushing and non-flushing branches, indicating that OTC worked regardless if the flushing stage if the branches or the tree. This study helps understand the translocation of therapeutic compounds within the tree for effective management against HLB
Examining the culturally responsive teaching self efficacy of inservice monolingual and bilingual teachers in rural Southeast Texas
No full textAs achievement gaps for emergent bilingual students (EBS) persist, teachers in rural Southeast Texas school districts face increasing demands to meet the needs of a culturally and linguistically diverse (CLD) student population. However, research suggests that teachers may need support developing the self-efficacy necessary to effectively implement culturally responsive teaching practices in the classroom. Cruz et al. (2019) found that “little research has examined the extent to which teachers feel competent specifically in their ability to implement culturally responsive teaching (CRT) practices” (p.3). Although existing research has explored teacher self-efficacy in other contexts, a dearth of research has examined whether in-service monolingual and bilingual teachers in dual language contexts possess the culturally responsive teaching self-efficacy necessary to meet the needs of EBS.
Using survey responses, this study examined the culturally responsive teaching self efficacy (CRTSE) of monolingual and bilingual teachers (N=55) in a one-way dual language immersion model. Guided by Bandura’s (1977) theory of self-efficacy and Gay’s (2002) culturally responsive teaching framework, this explanatory sequential mixed methods study utilizes quantitative survey data to examine monolingual and bilingual teachers’ CRTSE (as measured by Siwatu’s CRTSE scale), followed by qualitative semi-structured interviews to explore teacher perceptions and barriers towards the implementation of CRT in a one-way dual language model. This study addresses a gap by examining the culturally responsive teaching self efficacy (CRTSE) beliefs, perceptions, and barriers to CRT implementation of monolingual and bilingual teachers in a one-way dual language immersion model.
While the findings indicate a slight trend toward higher self-efficacy among bilingual teachers, the difference between monolingual (86.64) and bilingual teachers (89.36) was nominal. Moreover, the results show that the difference between the CRTSE scores was not statistically significant, suggesting that language background alone does not have an impact on CRTSE. Insights from the semi-structured interviews revealed that teachers perceive CRT as transformational, multidimensional, validating, and a means for promoting social justice in the classroom. The findings underscore the need for more in-depth examination of the culturally responsive teaching self-efficacy of in-service monolingual and bilingual teachers serving emergent bilingual students in rural communities. These findings offer valuable insight into how CRTSE shapes the instructional practices of monolingual and bilingual teachers within a dual language context, emphasizing the need for targeted teacher support to close achievement gaps among emergent bilingual students
Athletic directors' perceptions dealing with gender equity in Texas high school athletics
No full textThe struggle for equality between men and women has been an ongoing battle for centuries. From the seventeenth century to the present, women have made significant strides toward gender equity. Laws and regulations have continued to bridge the gap between men and women with the signing of Title IX (Title IX, 2015). Title IX is a federal law designed to close the gender gap in programs receiving federal funds, which includes education and sports programs. Even after enactment of Title IX, a problem continues to exist in high school athletic programs, a problem indicating the presence of gender inequality. Yet, the athletic directors and districts participating in the study understood the main perceptions of Title IX. There were five major themes that emerged from the study: responsibilities, budget, hiring of coaches, compliance and barriers in Title IX. The themes emerged consistently throughout the interviews, showing commonality between the districts involved. The study was important in identifying and offering strategies to enable a better understanding of the perceptions of athletic directors regarding issues related to Title IX as it pertains to athletic programs in the Region 2 educational service area of South Texas. Additionally, the perceptions of barriers which may prevent high schools from complying with Title IX were investigated
Evaluation of grassland restoration techniques and seed mix development for use on new solar developments in South Texas
No full textRenewable energy efforts across the country have grown significantly over the last decade. The objective of this project was to determine how to restore height-appropriate native grassland communities within utility-scale solar developments. The effects of planting date, planting technique, seed mix diversity, and sampling height on plant functional groups were evaluated during the active construction of a utility-scale solar development in Bee County, Texas. An 8-ha research area was used to test the planting of three seed mixes: low-diversity (4 species), mid-diversity (11 species), and high-diversity (19 species), planted using both drill and hydroseeding techniques during both pre- and post-installation of the solar development. I found that grassland restoration plantings influenced the percent cover of native plant species at the 5-cm sampling height (F 6, 121 = 2.58, P = 0.0021). The cover of seeded species was greatest at the low- and mid-diversity plantings when compared to the high-diversity, suggesting that additional diversity does not increase the percent cover of seeded species (F 6, 68.7 = 2.16, P = 0.0569). An inverse relationship was observed between sampling height and species cover. The same result was also observed in the analysis of species richness. This means that grassland restoration plantings can be used to effectively increase native vegetation cover on utility-scale solar developments in Bee County, Texas, by choosing seed mixes with 4-11 species that are quick to establish within one year. However, because my seed mixes with higher diversity also included species with a broader range of functional characteristics as well as some species that were less adapted to my study area, it cannot be determined whether the richness effects I recorded were attributable to effects of species richness, functional characteristics, or unequal species adaptability at the study site
Exploring bilingual elementary teachers' perceptions regarding STEM education teaching practices in the Mexican context
No full textIn the last decades, an interdisciplinary approach to teaching science, technology, engineering, and mathematics (STEM) that aims to engage K-12 students in a multidisciplinary manner has been implemented in different countries (Sias et al., 2017). Although research about elementary teachers' perceptions about STEM education and STEM teaching practices has been conducted in other countries, little research has been done in Northern Mexico to explore bilingual elementary teachers' perceptions about STEM education and STEM teaching practices in the private sector. Thus, this mixed-method study utilized an explanatory sequential design to investigate bilingual elementary teachers' perceptions about STEM education and STEM teaching practices. In phase one of the study, 83 bilingual teachers' quantitative data were gathered through an online survey. Six bilingual teachers were interviewed in phase two to collect qualitative data to explain in-depth quantitative results. In the qualitative phase one, it was found that the majority of participants perceived their preparation for STEM education as positive. Bivariate correlational analysis between participants' (a) years of teaching experience, (b) grade level taught, (c) highest level of education completed, and participants' perceptions on their preparation to teach STEM and their perceptions about STEM teaching practices effectiveness showed a little correlation between variables, that was not statistically significant. It was also found that the majority of participants positively perceived STEM teaching practices' effectiveness. In qualitative phase two, it was found that the majority of participants could identify teaching practices promoted by STEM education; however, only two participants could describe teaching practices clearly. Furthermore, qualitative data expanded on participants' quantitative responses about the type of preparation in STEM education they received and about participants' perceptions about STEM teaching practices' effectiveness. Implications and recommendations for future research about STEM education are presented
Dynamics and resiliency of networks with concurrent cascading failure and self-healing
No full textLocal attacks in networked systems can often propagate and trigger cascading failures. Designing effective healing mechanisms to counter cascading failures is critical to enhance system resiliency. A general modeling and simulation framework is developed in this work to quantitatively evaluate the resilience of networked systems under two types of failures: connectivity and load-based. Two newly designed dynamic healing mechanisms are demonstrated. The model considers concurrent cascading failure and healing processes on networks. A general discrete-time simulation (i.e., number of failed nodes at each time step) framework is developed to advance understanding of the dynamics of networks with concurrent cascading failure and self-healing. The resiliency is evaluated using various metrics, i.e., the recovery level, the average damage impact and the recovery time. Those metrics are used to evaluate and compare the healing performance. Based on several real-world networks models, the dependence of system trajectories and resilience metric on various model parameters is explored. If the triggering level (fraction of inactive nodes when healing starts) is too high, the system would either undergo a very slow recovery or never recover to a satisfactory level at all. However, this work provides a counter example to the intuition that the smaller the triggering level, the shorter the recovery time. While low budgets (number of nodes allowed to recover at each time step) lead to prolonged or unsuccessful recovery, it appears that the resilience metric converges to a limit when budget is raised to high enough. This may have practical implications, as node recovery requires resources and a budget too high or too low would be wasteful. It is also found that two parameters (reactivated node load parameter and node healing certainty level) span a phase plane for network dynamics where three regimes exist. To ensure full network recovery, the two parameters need to be moderate. Lastly, in this work, we study the possible linkage between robustness and resilience by finding the correlation between the two quantities. A resilient networked system is not necessarily robust, and vice versa. This works lays the foundation for subsequent studies on more complex mechanisms and processes on the networks, optimization of model parameters for maximum resilience, as well as applications to more real-world network models and scenarios
An improved scoring function for biological network alignment
No full textProtein-protein interactions (PPI) are important in biological processes. These interactions are mostly involved in biologic cell processes. Understanding PPIs is important in drug manufacturing as drugs can affect protein interactions. Protein-protein interactions occur when proteins bond together to perform their biological functions. System biology is heavily focused on the structure and nature of protein-protein interaction networks, the most well-known biological networks. There are so many diverse datasets of protein interactions that can be studied. In this thesis, I study algorithms for comparing PPI networks using network alignment. Network alignment (NA) is the process of aligning (or mapping) the nodes of one network with those of another network such that the edges and topological structures of the networks are also aligned. An algorithm typically maximizes the number of aligned edges by maximizing some scoring function. In addition to its application in comparing PPI networks, NA can also be used in aligning network regions (subnetworks) for the purpose of transferring biological information between species. There are some existing methods such as IsoRank, MI-GRAAL, GHOST, MAGNA, and MAGNA++ for network alignment.
In general, MAGNA is a better algorithm and provides better alignments in comparison with the other existing methods. MAGNA is a genetic algorithm that starts with a set of random alignments (initial population) and repeatedly executes many generations. In each generation, it tries to improve a given scoring function that evaluates an alignment. The original MAGNA algorithm used three different scoring functions: induced conserved structure (ICS), edge correctness (EC), and symmetric substructure score (S3). In this thesis, I design a new scoring function, named asymmetric substructure score (AS2), and performed rigorous experimentation with multiple PPI networks. In AS2, alignment quality is improved by increasing the penalty of the non-matching edges. This new scoring function is compared with the previous scoring functions. The experimental results show that AS2 provide better alignment for many PPI networks comparing to the other scoring functions. I also performed some other experiments on the effect of the number of generations and the size of the initial population on the quality of alignment. The results of these experiments can be useful in deciding the appropriate number of generations and size of initial population for a genetic algorithm
Isolation, identification, and monitoring of fungal plant pathogens in irrigation water from the Rio Grande River
No full textThe Lower Rio Grande Valley of South Texas is an important region for agriculture which depends on the Rio Grande River as a source of water for irrigation. The suitability of the river water for irrigation is dependent on the levels of total dissolved solids and other characteristics. However, water can be a main source of plant pathogen distribution, causing economic and yield loss in agricultural crops. The aim of this study was to isolate, identify, and monitor fungal plant pathogens present in irrigation water from the Rio Grande river. Monthly water sampling from the river was plated onto potato dextrose agar and individual fungal colonies were isolated in pure culture for identification by morphological characteristics and sequencing analysis. Results showed that total colony counts fluctuate during the year, with summer months having the largest amount of colony forming units. Fungal isolates were identified by DNA homology analysis of the ITS, TEF, and TUB genes using Blast n algorithm. A total of 31 genera and 42 species were identified and 19 of them are reported plant pathogens to a wide range of hosts. Eight fungal pathogens identified in this study were chosen for further characterization which belong to the following genera: Aspergillus, Cladosporium, Fusarium, Penicillium, Exserohilum, and Epicoccum. Monitoring of the selected fungal pathogens revealed a temporal fluctuation within species as well as abundance variation between species. Cladosporium spp. were the most abundant and were present in every sampling period except April. Tomato stem-inoculations with fungal plugs revealed that all of the isolates were able to colonize and were recovered from inoculated stems except for Cladosporium perangustum. This work shows that plant pathogenic fungi are present in irrigation water from the river which presents a potential risk for pathogen distribution and plant disease