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d is for depression
No full textMorgan Jeanette McCullin is an MFA candidate in studio art at Louisiana Tech University where she earned her BFA in 2018. McCullin has interned as a portrait painter’s assistant and as a conservationist restoring paintings from a museum’s permanent collection. As an oil painter, McCullin’s personal work incorporates art history, politics, feminism, and humor to address life for young women in the American South.https://digitalcommons.latech.edu/quatrain-gallery-volume-4/1005/thumbnail.jp
Kisses on the Subject
No full textEvelyn Hinjosa is a junior studio art major at Louisiana Tech University who enjoys playing with color and abstraction. She grew up in a family of artists, so expression through art was something that she learned pretty early on in her childhood. Evelyn spends equal amounts of time researching concepts and painting or acting on instinct when it comes to her work.https://digitalcommons.latech.edu/quatrain-gallery-volume-4/1002/thumbnail.jp
A Different Perspective
No full texthttps://digitalcommons.latech.edu/quatrain-gallery-volume-4-cropped/1018/thumbnail.jp
Whale Spotted
No full texthttps://digitalcommons.latech.edu/quatrain-gallery-volume-4-cropped/1007/thumbnail.jp
From life 1
No full texthttps://digitalcommons.latech.edu/quatrain-gallery-volume-4-cropped/1000/thumbnail.jp
Understanding Oxidative Aging of Asphalt Binder and it\u27s Effects on Cracking Susceptibility of Asphalt Mix
Get PDFEvery year around 400 million tons of asphalt mix is being laid in the United States and a significant portion of it is required for pavement rehabilitation. Cracking is one of the most common pavement distresses that is still not fully understood by the researchers. Very few states mandate tests for cracking resistance during the mix design phase; in addition, the test methods vary a lot from state to state. In the presence of oxygen, the asphalt binder over time undergoes chemical changes and becomes stiff which is known as oxidative aging that makes asphalt pavement more susceptible to cracking. Therefore, proper characterization of asphalt aging is a prerequisite to study the cracking mechanism of asphalt mix. In this dissertation, efforts are given for characterization of oxidative aging, investigation of the effect of aged binder on cracking susceptibility, and development of an antioxidant to reduce the aging-induced cracking.
In this study, rheological characterization of laboratory aged binder and extracted binder from asphalt mix was performed using dynamic shear modulus of the binder to understand oxidative aging. Then the correlation between laboratory binder aging and binder aging in asphalt mix was established and a Rolling Thin Film Oven (RTFO) aging test protocol for warm mix asphalt (WMA) was developed. Another factor for cracking susceptibility of asphalt pavement is the excessive content of reclaimed asphalt pavement (RAP). RAP is added to the hot mix asphalt (HMA) for economic and environmental interest but the highly aged binder in RAP makes the mix stiffer and escalates the cracking. Because it is quick and simple, the viability of using a handheld Fourier Transformed Infrared (FT-IR) spectrometer was investigated to detect and quantify the aging of binder by measuring the absorbance intensity of carbonyl groups. An in-situ test method was developed to determine the reclaimed asphalt pavement (RAP) content in the plant mix using a handheld FT-IRS.
The use of rejuvenators is the most suitable strategy to accommodate a higher amount of RAP in HMA and bio-based rejuvenators are of high interest. In this study, four types of cracking tests were performed on asphalt mix made with two different categories of rejuvenators: petroleum-based and bio-based oil. It was concluded that petroleum-based aromatic oil performed better to restore the cracking potential of the mix with high RAP content. Sound understanding of the cracking mechanism is necessary to find the right cracking susceptibility test for asphalt mix and design a cracking resistant mix. A finite element model of semi-circular bend (SCB) test of asphalt mix incorporating the cohesive zone material (CZM) model was performed using ANSYS to simulate and predict the fracture potential of asphalt mix as conducted in the laboratory according to ASTM D 8044 test method. The CZM properties of fine aggregate mastic (FAM) needed for ANSYS model of SCB test was determined by a laboratory double cantilever beam test and corresponding finite element model of double cantilever beam test., It was concluded that critical energy release rate (Jc) of asphalt mixture predicted from ANSYS model of SCB test was precise when compared with the laboratory SCB test of asphalt mix.
Finally, locally sourced Lignin was used as an asphalt performance enhancer as well as an antioxidant. It was observed that lignin could improve the high-temperature performance grade of the binder and reduce the aging index. Mix made of lignin modified binder showed better cracking resistance by improving the flexibility index.
Through this study, understanding oxidative aging helped with developing a revised short-term aging protocol for warm mix asphalt. One of the immediately implementable outcomes of this research is the in-situ application of handheld FT-IR spectrometer for quality control during the mix production at the plant through determining the reclaimed asphalt pavement content. This research will contribute to choosing suitable rejuvenators by understanding the cracking mechanism of asphalt mix through different tests. The finite element cohesive zone material model developed in this study can precisely predict fracture resistance of the mix in semicircular bending test by performing a double cantilever beam test of fine aggregate mastic. Viability of using bio based rejuvenator for RAP mixes and also the suitability of utilizing locally sourced lignin as an oxidant in asphalt binder were addressed in this research and the findings will help implement these environmentally friendly alternatives in resolving cracking related problems in asphalt pavements
Quantum Corrections to the Electromagnetic Response of Conducting Nanostructures
Get PDFThe electromagnetic response of conducting nanostructures in the 1 to 10 nm size range is investigated using the quantum box model (QBM). The core purpose of this dissertation is to understand how quantum effects emerge in both the electric and magnetic response of nanostructures in this size range, and in particular, explore how these effects can improve the design of future technology in the fields of plasmonics, metamaterials, and nano-composite materials. One of the primary objectives is to study how quantum effects enhance magnetism in nanoconductors and determine whether quantum resonances give rise to negative permeability, a highly desirable property in the design of plasmonic and optical devices. This aspect is frequently overlooked since classical theory predicts that most materials are magnetically inert. With these goals in mind, this dissertation treats the quantum mechanical theory of the electromagnetic response of nanoconductors using perturbation theory. Theoretical expressions for bi-anisotropic susceptibility tensors are derived, and the gauge invariance of the tensors is then assessed. Verifying gauge invariance is of high importance since it is a fundamental property of nature, and it must hold true if the model is to be trusted. By formally including a gauge transformation in the perturbation theory, the susceptibility tensors are proven to be universally gauge-invariant. After treating the theoretical foundations of the QBM, the theory is then applied to study quantum size effects in the permittivity of metal nanoparticles. Convergence to classical Drude theory is observed for large systems (≳ 10 nm), but finite-size calculations are found to deviate from classical behavior in several ways. First of all, insulator-like, positive real permittivity is found at low frequencies in contrast to the large negative permittivity predicted classically. Secondly, when compared to classical calculations of absorption spectra, quantum calculations predict plasmon peak positions that are either red-shifted or blue-shifted, depending on the embedding material and size distribution of the particles. Finally, discrete quantum resonances emerge in the permittivity of systems sized smaller than 10 nm. Explicit upper and lower bounds are derived for these resonances, placing limits on the enhancement of the permittivity and relaxation rates due to quantum confinement effects. These bounds are verified numerically, and the size dependence and frequency dependence of the empirical Drude size parameter is extracted from the model. Comparisons with available experimental data suggest that the common practice of empirically modifying the Drude function can lead to inaccurate predictions for highly uniform distributions of nanoparticles with mean radius � \u3c 10 nm. Next, the QBM methodology is applied to study the magnetic response of conducting nanostructures. Calculations presented in this dissertation find that the magnetic susceptibility is enhanced in metal nanorods, thin slabs, and nanocubes. The calculations find both strong paramagnetism and diamagnetism orders of magnitude larger than semi-classical Landau diamagnetism. The degree of enhancement depends on the structure’s geometrical proportions and its orientation with respect to the magnetic field, but the calculations do not find negative permeability for the systems studied.
Because temperature plays an important role in magnetism, we also present a systematic study of temperature-dependent magnetic properties in nanosized rings and nanocubes using grand canonical statistics. Different domains of temperatures with distinct behavior of susceptibility are identified. In the case of nanocubes, calculations performed with size averaging collapse to the bulk Landau value in the thermodynamic limit, clearly demonstrating the transition from finite three-dimensional systems to semi- classical bulk Landau diamagnetism.
In the case of nanorings, we find that the magnetic susceptibility can exhibit multiple sign flips at intermediate and high temperatures depending on the number of electrons in the ring (�) and whether or not Zeeman splitting effects are included. When the temperature is increased from absolute zero, the susceptibility begins to flip sign above a characteristic temperature that scales inversely with the size of the ring according to �\u27( or �\u27(/*, depending on the presence of spin effects and the value of � mod 4. Analytical results are derived for the susceptibility in the low and high temperature limits, explicitly showing how spin affects the ring Curie constant. The studies of paramagnetic-diamagnetic transitions in thin conducting rings is then extended to the canonical ensemble and compared with the commonly used grand- canonical approximation. Exact calculations of the canonical partition function and magnetic susceptibility are evaluated numerically using a recursive method. Persistent differences between the canonical and grand-canonical calculations are found at both low and intermediate temperatures. Criteria for convergence between the ensembles is provided, establishing the temperature and system size requirements for reaching the thermodynamic limit in quantum rings