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Exploring the Impact of Catalyst Supports on Hydrogenolysis of Polyolefins over Cobalt-Based Catalyst
No full textThe persistent utilization of plastics and inadequate disposal methods post-consumption are responsible for causing numerous ecological challenges on a global scale. In recent years, hydrogenolysis has been studied as a promising route to chemically repurpose polypropylene and polyethylene, which are some of the most widely used plastics. In this study, polyethylene is subjected to hydrogenolysis, utilizing cobalt-based catalysts on three supports: Zinc Zirconium Oxide (ZnZrO), Cerium Oxide (CeO2), and Titania (TiO2). The reaction is conducted under batch conditions at 275��C and 30 bar H2 pressure, with reactions performed for periods ranging from 30 minutes to 32 hours. Our findings reveal that cobalt supported on ZnZrO exhibits a high yield of liquid phase alkanes (C5-C30) up to 67%. The evolution of products over time also aids us in understanding the influence of the support material on catalyst performance, we propose likely reaction routes followed for hydrogenolysis carried out in the case of Co/ZnZrO and Co/TiO2. A loading study is also carried out to assess the impact of active metal density on reaction product yield and selectivity. Further, the efficacy of Co/ZnZrO is examined by using it to carry out hydrogenolysis of a post-consumer LDPE bottle, yielding results largely consistent with those obtained from the model PE substrate employed in our investigation. These outcomes underscore the pivotal role of support materials in the hydrogenolysis reaction and contribute to the mitigation of challenges stemming from inefficient plastic disposal, providing a more feasible way of upcycling plastics
The Role of Auditors in Classification of Debt Securities: Evidence From Banks
No full textFirms that hold debt securities can exploit the discretion in security classification and classify securities as held-to-maturity when the classification provides a more favorable accounting treatment (hereby referred to as security classification shifting). In this study, I utilize the banking industry to examine whether auditors are associated with their clients��� security classification shifting strategies. I find a positive association between a bank-client���s security classification shifting and the classification shifting at other bank-clients audited by the same audit office. This finding is consistent with auditors influencing their clients��� security classification strategies. The effect of auditors is concentrated in banks engaging an audit office with a greater emphasis on bank-specific non-audit services and in smaller banks which suggests that auditors are more likely to influence their clients��� financial reporting strategies when the auditor has a greater proclivity to provide advice and when clients have a greater need for financial reporting expertise. Finally, I find evidence suggesting that industry-expert auditors limit security classification shifting in resource-constrained banks; however, non-expert auditors do not appear to have a similar effect
Improved Whitecap Quantification and Prediction Using Shipboard Remote Sensing and Machine Learning
No full textWhitecaps generated by wave breaking and air entrainment can be classified as active (stage A) or residual (stage B). Discrimination and measurement of each stage individually are essential for accurate parameterization of air-sea interaction processes, but conventional methods used for separation in visible images are subjective. This study provides a novel method to identify whitecap stages based on visible imagery using particle image velocimetry (PIV). A linear relationship was established between the lifetime of stage A and the timescale of averaged velocity. This novel method characterizes stage A whitecap lifetime using whitecap velocity and provides an objective approach to separate whitecap stages.
To estimate active whitecap fraction, we introduced a pipeline for active whitecap fraction measurement. In this pipeline, a new horizon detection method is developed to stabilize and rectify images and a deep learning model based on U-Net is trained and validated to identify and extract active whitecaps. The model is applied to 48 hours of video footage collected during a cruise in Gulf of Mexico. It is determined that, as a function of wind speed, active whitecap fraction has significant variability and disparity compared to previous research. This finding indicates that secondary factors should be considered for accurate whitecap parameterization. This is explored using principal component analyses and random forest, which indicate sea surface temperature, swell and wave age are important to active whitecap fraction. The precise impact of sea surface temperature is further explored using analyses of variance (ANOVA), which suggest it has a positive correlation with active whitecap fraction.
The decaying stage B foam with significant variability has been found to contribute 1.5 to 40 times more to total whitecap fraction than stage A foam. In this study, we present a novel model that describes the relationship between whitecap fraction and the evolution of whitecap area, providing a method to quantify the whitecap lifetime scale. The same data from a Gulf of Mexico cruise is processed using this method. The stage B lifetime scale shows weak positive correlation with active whitecap fraction and no correlation with sea surface temperature and wind speed
La Imagen del Recuerdo: Sagrada Memoria y Always from Somewhere Else de Marjorie Agos��n
No full textEl presente trabajo propone un an��lisis comparativo de Sagrada memoria (1994) y Always from somewhere else (1998) de la escritora chilena Marjorie Agos��n. Estas obras presentan los recuerdos de Frida y Mois��s Agos��n, los padres de la autora, pero constituyen un testimonio que va m��s all�� de sus vivencias personales. Estos testimonios trascienden el ��mbito familiar conformando memorias colectivas, siendo el retrato de la realidad heredada por los supervivientes del Holocausto que emigraron a Latinoam��rica. Los recuerdos, marcados por la imaginaci��n y subjetividad, son reflejo de experiencias discriminatorias antisemitas, pero tambi��n raciales y de g��nero. El presente estudio tiene como principal objetivo el an��lisis comparativo de dichas memorias en cuanto a conceptos como testimonio, memoria, postmemoria e imaginaci��n ic��nica, entre otros. Dicho an��lisis nos lleva a encontrar las siguientes tem��ticas comunes: el mandato jud��o de recordar, el trauma heredado, la imposibilidad de narrar el recuerdo, el antisemitismo, el exilio, la identidad del sujeto diasp��rico, la subjetividad, el imaginario o memoria social o colectiva y el reconocimiento. Estas tem��ticas permiten establecer nexos entre estas memorias y la concepci��n art��stica de la artista judeo-chilena Patricia Israel, cuya obra tambi��n conjuga la imagen y la palabra con el fin de abordar la memoria tanto privada como colectiva. La imaginaci��n ic��nica juega un papel importante en la elaboraci��n de im��genes verbales, lo que permite establecer relaciones entre la narraci��n y algunas de las obras del pintor jud��o Marc Chagall que propongo como un intertexto visual, as�� como entender el significado simb��lico que los tatuajes y los trenes adquirieron a partir del Holocausto. Adem��s, el contraste entre las memorias permite realizar una lectura de g��nero que manifiesta los estereotipos codificados en cuanto a la vida y funciones de la madre y del padre
A Comparative Analysis of Archaeological and Textual Evidence for Danubian Watercraft, First to Fourth Centuries CE
No full textThe Danube is one of the longest rivers in the world and has been a life source for peoples settled around it for millennia. Alongside local groups, Greeks and Romans used the river as a throughway. Though there are many accounts of the Danube in Roman history, few of them provide insight into what types of vessels were using along the river, despite many documented interactions with local groups. The archaeological record along the Lower Danube, that is the section from the Iron Gates to the Danube Delta, has begun to reveal more evidence of both Roman and local boats used along the ancient course of the Danube, but many of these are found in rescue excavations with limited recording available. In this thesis I combine these two fragmentary sources to examine if the literary accounts are reflective of the archaeological evidence regarding local boatbuilding traditions. Though brief, there are terms in literature which indicate construction methods (����������������), and hull shape (cavatis arborum alveis vs. truncis), which are reflected several times in the archaeological record. Other literary descriptions reveal little about the vessels themselves, but the contexts in which they are found are reflective of Roman perceptions of the users of the vessels. These sources both undermine the capability of the locals to boost military morale and also demonstrate their efficacy, as the Romans were intimidated by those who used the Danube for raiding and stealth attacks. Flat-bottomed barges fastened with closely spaced iron clamps also appear in the archaeological record several times along the Lower Danube and in the greater Danube Basin. Further archaeological research is needed to bolster this theory of a regional vessel type, and such work may continue to yield multiple ship types in the same contexts, increasing the number and variety of vessels from antiquity and perhaps revealing a regional tradition through time. Though there is still much to be excavated, this research has revealed the disparity between Roman descriptions of vessels in use along the Lower Danube and the reality of such boats by examining the archaeological evidence and contextualizing the Roman literature
A Study of Hard and Soft Materials Subjected to Ballistic and Hypervelocity Impact
No full textHypervelocity impacts (HVIs) (���2.0 km/s) can induce extremely high strain rates (>10��� s�����). Hence, developing materials to withstand HVIs is a key challenge in the effort to enhance protective infrastructure. Furthermore, computational software such as the Elastic Plastic Impact Computation (EPIC) code, can accelerate the development of these material systems.
Thermoplastics such as high-density polyethylene (HDPE) can be used to offer HVI damage resistance without compromising on weight and cost. This document reports a modeling effort to predict the HVI response of 6.35 mm HDPE plates when impacted by 10 mm Al spheres travelling 2.0���6.8 km/s. It was found that the simulation accurately predicted debris cloud velocity and shape, hole size, and mass loss for impact velocities <5.5 km/s.
Often, much denser high-performance concrete (HPC) mixtures like BBR9 are used as a HVI resistant building material. This work reports simulation and experimental efforts to predict the HVI response of BBR9 plates of varying thickness (25.4���127.0 mm) impacted by 10 mm S2 tool steel spheres travelling 1.8���3.1 km/s. Simulations reflected experimental fragmentation and energy absorption results well, and it was found that they even captured the transition region in which an increase in impact velocity resulted in a decrease in debris cloud velocity.
Layering materials to exploit their strengths can result in composites with increased kinetic energy dissipation and reduced target weight. The results reported in the HDPE and BBR9 investigations lead to their use in composite "sandwich" targets that can be optimized for key metrics. To test this principle, a multifaceted computational and experimental approach was used. By adjusting the volume fractions of the two materials in EPIC and subjecting the layered targets to a 2.0 km/s impact from a 10 mm S2 tool steel projectile, a mass-optimized, 50.8 mm thick composite target that dissipated maximum projectile kinetic energy was generated. Subsequently, the target was subjected to V������ ballistic limit testing with a 12.7 mm S2 tool steel spherical projectile, where it was found that the simulation-predicted and actual ballistic limits were within <1% of one another, justifying the idea that simulation-informed optimization is a useful tool in material design
Complex Fluids Formed from Surfactant-Based Dynamic Binary Complexes
No full textThis work attempts to study the rheological properties and corresponding morphologies associated with complex fluids formed by novel surfactant-based dynamic binary complexes. Dynamic binary complexes refer to non-covalent supramolecular assemblies of surfactants and an appropriate complexing agent, giving rise to the potential for stimuli-responsiveness. The fundamental mechanisms that constitute viscosity modifier systems are an important point of discussion as well. Such chemistries are capable of interesting nanoarchitectures in aqueous suspension, that can have wide-ranging implications in several multi-billion dollar industries such as pharmaceuticals, personal care and the energy sector.
We examined an aqueous system of zwitterionic surfactant stearyl betaine with diethylenetriamine as the complexing agent, which displayed pH-responsive rheological properties and morphological changes. The surfactant was synthesized via a straightforward condensation reaction and then mixed with diethylenetriamine in an aqueous suspension at 2wt% to formulate the system. Notably, acidic conditions exhibited substantial steady-shear viscosities (up to 160 Pa.s) and viscoelastic behavior, decreasing with rising pH. A temperature analysis using zero-shear viscosities and differential scanning calorimetry unveiled thermodynamic transitions. Morphological insights from AFM and SAXS revealed distinctive bilayer nanotubules at low pH, transforming into bilayer sheets and then vesicles with increasing pH.
We then studied a system comprising of ��-cyclodextrin (��-CD) with three sulfonic surfactants: sodium hexadecylsulfate, sodium dodecylbenzenesulfonate, and myristyl sulfobetaine. Optimal axial growth and high viscosities in the suspensions were achieved with a ��-CD:surfactant ratio of 2:1. The complexation processes exhibited nanostructural phase behaviors and rheological properties sensitive to the molecular structure of sulfonic surfactants. DIC microscopy provided visual insights into the microstructure regarding sulfonate molecular architecture. Additionally, surface tension measurements, along with FTIR and NMR spectroscopies, deepened the understanding of interactions leading to complexation and nanostructural features. The proposed mechanics aimed to correlate supramolecular morphologies with rheological properties
John Bickham field notebook: AK5001-AK5500.pdf
No full textBound book, each page corresponds to a karyotype slide data.Data pages for AK5501-AK6000 corresponding to unique identifiers of specimens/samples examined for biological research. Specimens are primarily housed at Texas A&M University; Biodiverstiy Research and Teaching Collection
NAC1 Restrains T Cell Memory Formation through Metabolism Regulation During Viral Infection
No full textOur recent studies uncovered the important roles of nucleus accumbens-associated protein 1 (NAC1), a transcriptional co-factor, in regulating the activity of regulatory T cells, and antitumor immunity. Little is known about how NAC1 interrupts T cell memory, despite its significance in the host's defensive response to invading pathogens. Many factors interrupt T cell memory formation, such as transcriptional factors, virus types, cell metabolism, and autophagic status.
In the current study, we analyzed T cells from wild-type (WT) and NAC1-deficient (-/-) mice and observed that NAC1 is essential for both CD8��� and CD4��� T cell metabolism including glycolysis and oxidative phosphorylation and supports T cell survival in vitro.
In vivo, compared with wild-type (WT) mice, NAC1-/- mice exhibit a slow decrease of viral antigen (Ag)-specific CD8��� T cells. Additionally, we observed that the NAC1-/- mice demonstrated a stronger memory formation of VACV-specific CD8��� T cells post-viral infection. Mechanically, we identified that compared with WT CD8��� T cells, the Interferon Regulatory Factor 4 (IRF4), a key transcription factor in T cell development, was highly expressed in NAC1-/- CD8��� T cells. For CD4��� T cells, we further demonstrated that deficiency of NAC1 downregulates glycolysis in CD4��� T cells through modulation of the AMPK-mTOR pathway. Moreover, loss of NAC1 reduces the expression of ROCK1, the phosphorylation and stabilization of BECLIN1. Furthermore, forced expression of ROCK1 in NAC1-/- CD4��� T cells results in the restoration of autophagy as well as the activity of the AMPK-mTOR pathway. In animal experiments, adoptively transferred NAC1-/- CD4��� T cells or NAC1-/- mice challenged with VACV show enhanced formation of the VACV-specific CD4��� memory T cells as compared with adoptively transferred WT CD4��� T cells or WT mice, but this enhancement of memory T cell formation can be abrogated by forced expression of ROCK1.
Overall, the results of this study reveal the novel role of NAC1 as a suppressor of T cell memory formation and imply that targeting NAC1 may be exploited as a new approach to promoting memory T cell development
The Effectiveness of a Newly Developed Fluoride-Releasing O-Ring for Prevention of White Spot Lesions: An In-Vitro Study
No full textPreventing white spot lesions (WSLs) in orthodontic patients remains a challenge. An effective method for incorporating calcium fluoride (Ca-F) into polycaprolactone (PCL), widely used for drug delivery, has been established. With this method, an elastomeric ligature (O-ring) is transformed into a Ca-F O-ring capable of consistently releasing therapeutic levels of fluoride ion over a span of seven weeks. The aim of this study is to assess the effectiveness of Ca-F O-ring in preventing WSL in vitro.
A Ca-F solution was combined with 10% PCL to create a mixture of 5% PCL with Ca-F. O-rings were briefly immersed in this mixture to generate the Ca-F O-rings. 60 premolars with sound enamel were bonded and randomly allocated into three groups for pH cycling: 1) ordinary O-ring with topical over-the-counter fluoridated toothpaste application (O-F); 2) ordinary O-ring (O-R); 3) Ca-F O-ring (O-CaF). Acid-resistant nail polish was applied to surrounding tooth surface, leaving a 4x2 mm2 treatment window of exposed enamel adjacent to cervical aspect of the bracket. All specimens underwent a 9-day pH cycling process. Lightness (L*) value within the treatment window of each sample was evaluated using spectrophotometer at baseline (T0) and after (T1) pH cycling. Mineral densities were determined after pH cycling for the treatment window, adjacent surface enamel layer, and deep enamel layer.
No significant differences in L* values were found between groups at T0 and T1. At T1, L* in group O-CaF was lower than other groups, but not significantly. Group O-CaF had significantly lower mineral densities in treatment window regions than the other groups at T1. For all groups, mineral density increased in the treatment window after pH cycling when compared to adjacent surface enamel control regions.
Use of Ca-F O-rings for prevention of WSLs in orthodontic patients is promising. When compared to controls with and without topical fluoride, the group O-CaF exhibited potentially more effective remineralization after pH cycling and less of a hypermineralized surface seen with WSLs. Future studies with SEM analysis and with increased pH cycling time are needed to confirm the ability of these Ca-F O-rings to effectively remineralize enamel after pH cycling