Electronic Theses and Dissertations

The discovery of graphene and other two-dimensional (2-D) materials has opened the way for a huge opportunity in material development, manipulation, and their corresponding potential applications. 2-D materials including graphene have been shown to have unique properties such as high electrical conductivity, high mobility, and high surface area. These properties have made 2-dimensional materials amenable to small scale electronic applications, molecular sieves and for high strength composite applications. Despite the promise graphene holds, it has been difficult to completely harness its potential because it is difficult and expensive to produce single layer graphene sheets in substantial quantity. A unique class of 3-dimensional nanomaterials that can be produced in substantial quantity and cost effectively processed into 2-dimensional hybrid structures are the Metal Organic Frameworks (MOFs). MOFs, which are basically a composition of molecular complexes formed between metals and salts, organic and inorganic molecules, have been rationalized to be a coordination complex with a stereospecific structure. Transition Metal Cyanates are a unique class of 3-dimensional cyanometallate network. The most common are hexacyano transition metal complexes with divalent transition metal counter ions. We have prepared and exfoliated transition metal cyanates into 2-dimensional structures by exfoliation into separates sheets. Hybrid 2-D structures have also been produced and studied by intercalation with organic linkers.

Density Function Theory (DFT) studies have predicted an increase in the d spacing of potassium tetra-cyanonickelate, on substitution with di-metallic cation such as Fe2+, Mn2+, Cd2+ and Co2+, and additional processing with organic linkers. Dodecyl pyrrolidone (DDP) was used to intercalate the metal complexes and X-ray diffraction results showed significant peak shifts to the left on all metal complexes, corroborating the DFT predictions. The increased distance between layers allows for further separation into exfoliated sheets. In this report, we have demonstrated an approach for producing a long range defect-free 2-D sheets. We have grown di-metallic cation complexes of Fe2+, Mn2+, Ni2+ and Co2+ on Teflon supports. This was done by placing hydrophilic 1.0 micron Teflon as a barrier between a desired salt of the complex and potassium tetracyano nickelate. The desired metal complex was formed by diffusion of the opposing solution in the Teflon support. The membrane was dried and used as barrier for Na+ ion selectivity test. The test was carried with 1.0 M NaCl. The solution was pumped under vacuum through the membrane, and a pristine membrane was used as a control. Results showed that the Fe and Mn tetracyano nickelate selectively reject Na+ ion salts while control experiments proved otherwise.

These results hold promise for material applications in waste water remediation, separations, desalination, and purification. In this work, we also reported a simple process of synthesizing Nickel Ferrite-graphitic layers with inverted magnetic hysteresis.

Audio signal analysis has become prominent in biological domains for detecting endangered or threatened species like Houston toad and Crawfish frog. Researchers at Texas State University and Texas A&M University are working on a project to steward these species and understanding the causes of their decline. The researchers are currently using an Automated Recording Device (ARD), the Toadphone 1, which is an embedded solution. The hardware platform can perform detection tasks without human interruption and can provide near real-time notification. However, this device’s predictive model for the software solution has limited success to serve the primary purpose for which it was developed, which is to provide proper identification of Houston toad calls. Also, the current predictive model for Toadphone 1 was only designed for the Houston toad calls. There is another near-threatened chorusing amphibian, the Crawfish frog, which has become a concern of the researchers working to protect this species.

This thesis research experimented with a modified predictive model for the existing Toadphone 1 software solution, predicting a Houston toad call with decreased false-positive rates. The model can also perform the call recognition task for Crawfish frog calls. This work used the audio data for Houston toad and Crawfish frog collected by the Department of Biology to train the predictive model. Before training, the audio data spectrum was studied to find the frequency range of Houston toad and Crawfish frog call. Next, the audio data have been iteratively preprocessed using digital filters and then applying framing, the Hamming window function to each frame. Mel-frequency Cepstral Coefficients (MFCCs) with their first and second derivatives or Spectral Sub-band Centroids (SSCs) or Mel-spectrograms audio features have been extracted for each frame. These features were used to train the predictive or classification model for Houston toad or Crawfish frog call prediction. Advanced Recurrent Neural Network (RNN) algorithms such as Long Short-Term Memory unit (LSTM) or Gated Recurrent Unit (GRU) and Convolutional Neural Network (CNN) were utilized, which are sub-fields of deep learning network architectures. Several model architectures were experimented with using different combinations of classifiers and audio features with tuned hyperparameters to build the best predictive model. The voting mechanism of ensemble learning was developed to make the final prediction from the three-best models. Lastly, the predictive model was evaluated on a near real-time prediction system.

Ralph Vaughan Williams is recognized as being one of England’s most prolific and nationalistic composers of the early 20th century, incorporating such nationalistic elements as English folksong, imagery of English pastoralism, and Tudor music. Nevertheless, Vaughan Williams’s mature style familiar to both scholars and fans did not begin to take shape until the beginning of the 20th century. In 1899, Vaughan Williams completed a mass as his doctoral music composition, later known as A Cambridge Mass.1 The 1890s was a time of musical development, inspiration, and education for Vaughan Williams. This mass, written for double chorus, four vocal soloists, and orchestra, is an example of his musical development at the end of the nineteenth century along with some foreshadowing elements of his mature style. Predating A Sea Symphony (1909), his other massive choral work and possibly his most well known, A Cambridge Mass remained hidden in the Cambridge University Library for 111 years until scholar and conductor Alan Tongue discovered it in 2007.

This thesis will discuss Vaughan Williams’s educational background and influences during the 1890s by examining biographies, his autobiography, personal letters, documentaries, and other secondary literature in relation to A Cambridge Mass in order to fully understand which composers and teachers and what compositional techniques influenced Vaughan Williams. In the first chapter, drawing from articles, reviews, and interviews of Tongue and details surrounding the background of this piece, I will describe Tongue’s discovery, editing process, and performance history. Finally, I will investigate the similarities and differences between this early work and his later style, highlighting musical examples of his early influences in the second chapter and the hints of Vaughan Williams’s mature style in the mass along with the conclusion in the final chapter. Also, the third chapter will address the significance of this early work of Vaughan Williams while discussing which scholars and musicians have been studying and performing this work and others who have not been researching and performing such early Vaughan Williams compositions as A Cambridge Mass.