bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of transglutaminase enzymes in cerebrovascular amyloid deposition
Authors:   , Baradet Timothy C. , Balin Brian J
Published: July 2024

We investigated whether the [special characters omitted]-amyloid peptide, 1-40 sequence, (A[special characters omitted]) found in the Alzheimer brain could be covalently cross-linked by Factor XIIIa, plasma transglutaminase (E. C. 2.3.2.13, glutaminyl-peptide-gamma-glutamytransferase) to the common extracellular matrix proteins surrounding numerous blood vessels in the human brain. This mechanism of [special characters omitted]-amyloid accumulation, in addition to the aggregation of [special characters omitted]-pleated sheets, may help to explain the process by which cerebrovascular amyloid is deposited. Factor XIIIa and combinations of A[special characters omitted] and ECM proteins were incubated in vitro and analyzed by SDS-PAGE, Western blotting and electron microscopy. These experiments revealed that, in the presence of Factor XIIIa, A[special characters omitted] formed polymeric structures with itself as well as in association with collagen type IV, fibronectin and laminin. Western blotting revealed high molecular weight complexes of A[special characters omitted] and ECM proteins following transfer to PVDF membranes from denaturing polyacrylamide gels.
Spinning self-forging fragments and shaped charges
Authors:   , Weickert Chris Allen
Published: July 2024

This thesis is concerned with the application of fluted-liner technology to spinning self-forging fragments and shaped charges. Historically, shaped charge fluted liner research consisted of experimental parametric studies. The actual mechanism of spin compensation was not understood. Numerical results from the current research on the collapse of fluted shaped charge liners show that the explosive gases rotate in one direction but the jet and slug rotate opposite to each other with the net result being opposite to that of the explosive gases. Numerical calculations were used to predict the variation of angular momentum of the shaped-charge liner with the number of flutes and with the index angle. As the number of flutes is increased, the direction of rotation of the jet changes from clockwise to counter-clockwise. The reversals in spin direction from experiments are duplicated by the numerical results. Results from an experimental investigation of a spinning self-forging fragment have demonstrated for the first time that a spinning cohesive fragment could be formed with a backward-folding liner design at an SFF charge spin rate of 2500 RPM.
The regulation of Pho81p, a cyclin-dependent kinase inhibitor in Saccharomyces cerevisiae
Authors:   , Knight Janine Patricia , Bergman Lawrence W
Published: July 2024

Cyclins, cyclin-dependent kinases (CDK) and their inhibitors play a critical role in many biological processes, including Eukaryotic stress response and cell division. In humans, the ankyrin-repeat-containing CDK inhibitor p16 INK4 functions as a tumor suppressor in the regulation of the Rb protein. In yeast, repressible acid phosphatase, encoded by the PHO5 gene, is transcriptionally regulated by another ankyrin-repeat protein, Pho81p. PHO5 is repressed in high phosphate growth media and de-repressed in low phosphate. The Pho80p-Pho85p cyclin-cyclin dependent kinase complex acts as a negative regulator to block PHO5 expression when phosphate levels are high. The PHO81 gene encodes a 134 kD inhibitor of the Pho80p-PHO85p complex. In high phosphate, Pho81p is inactive, resulting in an active CDK complex and thus no expression of PHO5 . In low phosphate, Pho81p is an active inhibitor of the Pho80p-Pho85p complex, resulting in expression of PHO5. However, the mechanism of regulation of Pho81p activity is unclear. Recent studies in our laboratory have shown that Pho81p is phosphorylated by the Pho80p-Pho85p CDK complex in-vitro, and Pho81p contains 9 potential CDK phosphorylation sites. To determine the significance of phosphorylation, we used site-directed mutagenesis to alter these potential phosphorylation sites. The resulting mutants were introduced into a yeast strain containing a deletion of PHO81 and the effect of the mutation on PHO5 expression was assayed. Results suggest that phosphorylation of particular residues within Pho81p is crucial for its activity as an inhibitor. Studies using a GFP-Pho81p fusion and western analysis indicate that the localization and half-life of the mutant is similar to wild type. However, an in-vivo binding assay indicates that mutant Pho81p is deficient in binding to the Pho80p-Pho85p kinase complex. These findings support the observation that the mutant fails to inhibit kinase activity in low phosphate. These studies provide insight into the mechanism of regulation of cyclin-dependent kinase inhibitor activity.
Suppression of Interpretative Bias After Mood Induction in Socially Anxious Individuals
Authors:   , Rutigliano Peter J.
Published: July 2024

Cognitive biases have been the focus of study in experimental psychopathology for years. Individuals with increased fears, anxiety or depression have shown a bias for threat relevant information. Recently, however, three studies have found the opposite result when individuals high in fear or anxiety are further stressed. Increased anxiety in these subjects tends to reduce attentional bias. The purpose of the present study was to investigate if the suppression of cognitive bias is characteristic of clinical populations only, by testing a non-clinical socially anxious student sample. The second purpose of this study was to investigate whether interpretation biases would produce similar results to the attentional bias. A sample of students from a small urban university were randomly assigned to two conditions, socially anxious condition and a neutral condition. Subjects in the socially anxious condition were asked to give a speech to the class about their hometown, subjects in the neutral condition were asked to write a paragraph about their hometown. Subjects were then asked to complete a homograph task with both neutral and social threat interpretations. Homographs are words that are spelled the same but have more than one meaning. Subjects were asked to write the first word that came to mind upon reading each of the homographs. For example, the homograph "odd" could yield a social threat interpretation such a "weird" or a neutral interpretation such as "even". Subjects were grouped into high socially anxious and low socially anxious groups using a median split of scores on a social anxiety scale. Results revealed only a significant main effect for interpretation bias such that subjects high in social anxiety scores produced more threat interpretations. Exploratory follow-up analyses, however, found a significant interaction between condition and social anxiety such that individuals high in social anxiety upon mood induction produced a suppression of interpretation bias. Based on these results, it was suggested that there appears to be a suppression of interpretative bias in socially anxious individuals.
Strategy preferences in computer display navigation
Authors:   , Lipner Rebecca S. , Strong Gary W.
Published: July 2024

The increase in the complexity of computer systems and the number and diversity of people using them have made the study of individual differences in computer display navigation crucial to the development of robust human-computer interfaces. However, the study of individual differences among users has not been a major focus of applied research in human-computer interaction or of commercial computer interface designers. Accordingly, this study examined individual differences among computer users by studying the strategies users employed to navigate through a computer display network. The display network consisted of a 5 x 5 matrix of black and white objects of various shapes and densities. Subjects received either an outcome- or a method-based navigational task. An outcome-based task entailed navigating from the current object to a target object via any route in the shortest amount of time. A method-based task entailed navigating from the current object to a target object via the shortest route in the shortest amount of time. Additionally, subjects received one of two spatial navigational aids; a physical map or iconic road signs. Results showed that there were strategy differences among users that could not be readily explained as a function of users' navigational task and aid. Clusters of individuals, within the same task and aid condition, used different strategies to navigate the information space. In less complex conditions, different strategies did not lead to performance differences while in more complex conditions, different strategies did lead to significant performance differences. Differences in the way in which males and females navigated were also suggested but these gender differences were found only in the complex conditions. Males used constructive or global strategies whereas females used analytic or sequential strategies to navigate. In contrast to males, females deviated more from the direct path, were more disoriented and did not internalize the information space. Collectively, these findings demonstrate that strategy differences play an important role in determining users' spatial behavior in electronic information space. A better understanding of these individual differences should help design robust human-computer interfaces and minimize the gap between fast pacing technology and its users.
The Ecology of lguanid lizards at Las Baulas Park, Costa Rica
Authors:   , LaMarca Matthew Joseph , Spotila James Robert , Santidrián Tomillo Pilar
Published: July 2024

In Parque Marino Nacional Las Baulas Guanacaste, Costa Rica green iguanas (Iguana iguana) and ctenosaurs (Ctenosaura similis) were the largest lizards in the park. Until now little was known about the ecology of the iguanids in the park. I explored habitat use and behavior of these animals during the rainy (May to November) and dry season (December to April). I found the green iguanas to be elusive and quite rare in this area while the ctenosaurs were abundant and prominent in most of the park and surrounding area. Green iguanas were located in areas close to the estuary of the park. Ctenosaurs were in the secondary dry forest and in contrast locally developed areas. Juvenile ctenosaurs lived in a microhabitat ofjaragua grass (Hyparrhenia rufa), a non-native species of grass. Using radio telemetry I determined nesting sites and home ranges of both species. The beach ofPlaya Grande is the main nesting location for both species. Green iguanas started to nest at the end of January and continued into February and ctenosaurs nested at the end of February into March. Green iguanas had a much larger home range than ctenosaurs.
A model for nitrate mass in runoff during single storm events
Authors:   , Riley Karen Anne , Weggel John R
Published: July 2024

A model to predict the temporal distribution of nitrate mass in runoff during single storm events was developed using data measured at four Florida watersheds. The input influencing the mass of nitrate in rainfall was identified, and a model developed using these factors to predict the mass of nitrate in runoff. Validation showed successful results for 92% of the storms. The goal of this research was to develop a model to predict the temporal loads of a nonpoint source contaminant during single storm events. Nitrate was chosen as the contaminant because of the availability of data and the significant impact of high nitrate loads on receiving waters. The data was collected by the U.S. Geological Survey from four sites in Dade and Broward counties, Florida from 1974 to 1978. The sites were chosen because there were no point contaminant sources. For the four sites, there was a total of 77 storms. The drainage areas varied from 15 to 58 acres, and the impervious cover varied from 36% to 98%. Inspection of the measured data showed two patterns: as rainfall increases the mass of nitrate removed from the atmosphere increases, and during a storm with two occurrences of the same rainfall depth less nitrate is removed from the atmosphere for the later rainfall. To reflect the first pattern in the model, the mass of nitrate removed is directly related to the rainfall depth. To reflect the second pattern, the mass of nitrate is directly related to a factor representing the remaining atmospheric nitrate supply. The model can be used alone or with an hydrologic model. If additional nitrate sources are known, the nitrate from those sources can be added to the contribution predicted by this model. This model was both developed and validated using the Florida data, and without any watershed or meteorological limits. Its applicability to other sites should be determined.
Modal dependent fiber optic devices
Authors:   , Kieli Michael
Published: July 2024

The thesis discusses theory and the measurement of fiber optic devices employed in multimode network. In particular, an effectively nonreciprocal, multimode coupler has been studied. Development of such asymmetric coupler is required for implementation of passive linear bus, a very attractive topology of a fiber optic network. In the research presented in this work first the theoretical bases of effective nonreciprocal behaviour of fiber optic devices were developed. Next, a nonreciprocal coupler has been build and measured. Subsequently, a new measurement technique and, more significantly, component characterization method for fiber optic devices have been proposed. This method of characterizing multimode fiber optic components is of particular importance in modal dependent networks such as the one described. With many modal dependent devices in the same system, theoretical and experimental description of the performance of the network is missing. Each of the passive and active components of the system must be characterized in a way that would allow for network evaluation. The new modal dependent, nonreciprocal coupler was characterized this way, giving insights into details of its complex performance. Other fiber optic devices (sensors, modulators) have been proposed, built and measured. Finally, the multimode fiber optic system study has been suggested as the complete tool of describing the behaviour of complex fiber optic networks or systems.
Molecular basis for benzimidazole susceptibility and resistance in the opportunistic yeasts Cryptococcus neoformans and Candida albicans
Authors:   , Cruz Maria Cristina
Published: July 2024

The last twenty years have witnessed a dramatic increase in fungal infections, especially those affecting immunocompromised patients. Opportunistic pathogens such as Cryptococcus neoformans and Candida albicans have proven to be of great medical importance, not only because of their high incidence rate but also due to the life threatening diseases that they cause. Current antifungal therapies are characterized by high toxicity, failure, and resistance; thus there is a need for discovery of new antifungals with improved activity. This thesis examines the potential use of benzimidazoles to treat infections caused by the basidiomycete yeast C. neoformans. The research was focused on three areas: first, the determination of the in vitro anticryptococcal activity of benzimidazoles, followed by the characterization of C. neoformans [beta]-tubulin genes as targets for benzimidazole action, and finally the analysis of acquired resistance to these drugs. As an initial step in exploring the anticryptococcal potential of benzimidazoles we examined the in vitro activity of eleven derivatives against various C. neoformans clinical isolates. We found that their level of activity varied from non active to highly active; benzimidazoles were found to be not only highly inhibitory but also fungicidal. The cryptococcal [beta]-tubulin genes (TUB1 and TUB2) were then characterized to examine the hypothesis that [beta]-tubulin is the target for benzimidazole binding, through which these compounds disrupt microtubule polymerization. Comparison of these two genes with [beta]-tubulin sequences from benzimidazole-resistant and sensitive organisms, and identification of mutations in the TUB1 gene from independently isolated benzimidazole-resistant mutants, suggests that TUB1 is the basis for the benzimidazole susceptibility of C. neoformans. Resistance to benzimidazoles in C. neoformans seems to arise through different mechanisms, including modifications oF the drug's target and through a multidrug resistance (mdr) mechanism. Mdr was demonstrated to be not only more efficient in creating benzimidazole resistance in C. neoformans but it has previously been correlated in Candida albicans with resistance to the ergosterol synthesis inhibitor fluconazole. Candida albicans which is responsible for serious localized and invasive infections in immunocompromised individuals, is naturally resistant to benzimidazole derivatives. We have found an antagonistic effect between benzimidazoles (albendazole and benomyl) and fluconazole in C. albicans that was associated with the induction of a protein involved in a multidrug efflux mechanism. This observation has clinical implications in patients where both inhibitors, albendazole and fluconazole, are used together; e.g., in some AIDS patients.
Three essays on the empirical analyses of foreign exchange risk premiums
Authors:   , Yang Sheng-Yung , Chiang Thomas Chi-Nan
Published: July 2024

While there is a general consensus that forward rates have little if any power to forecast changes in spot rates, there is less consensus on the existence of time-varying premiums in forward rates. Progress has been made toward understanding foreign exchange risk premiums as empirical research continues, but the existence of forward foreign exchange premiums remains controversial. Unlike previous research, we have chosen to construct empirical asset pricing models that directly link the risk premiums to the state variables or risk factors that are thought to be the fundamental economic determinants of forward exchange pricing. We first link the foreign exchange risk premiums to real interest rate differentials, excess national equity market return differentials, and term structure slope differentials based on the various international parity conditions. We find that variations in risk premiums are closely linked to variations in risky asset return differentials. Accordingly, based on the modern asset pricing theory, we propose a time-varying risk premium model which links the risk premiums to macroeconomic and financial uncertainty. We find that volatilities from macroeconomic uncertainty and financial markets of the exchange countries can account for the variations in risk premiums and most of the state variables are priced. In particular, one common factor has been identified, namely the US real output shocks, which affect the pricing for all foreign currencies. The implication is that a shock in the US market might produce an uncertainty, transmitting into the national currency market. Finally, to distinguish the possibly short-lived risk premium and/or market inefficiency, we use high frequency data that relates the risk premiums to relative volatility perceived in the national equity markets. In general, the result is consistent with the risk premium hypothesis where a positive speculative profit is a reward for bearing a relatively higher risk. This dissertation contributes to existing literature by offering further evidence regarding the pricing of forward foreign exchange rates and time-varying risk premiums. Issues such as peso problems, learning, irrational speculative bubbles, as well as the effect of transaction costs will definitely play some roles in explaining forward rate determination and are left to future research.
An explicit time integration finite element method for metalrolling problems
Authors:   , Shivpuri Rajiv
Published: July 2024

This thesis presents a version of the explicit time integration finite-element method, DEFEL, for metalrolling problems. This method is capable of analyzing both the dynamic and static problems, and is effective in calculating the stress, deformation, and thermal behavior of metalrolling problems. DEFEL formulation utilizes the mass and capacitance lumping technique with explicit time integration to develop a code which does not require the formulation of global mass, stiffness and capacitance matrices. The equations of motion are decoupled and solved node by node. The computer storage requirements are small and the program can run on a microcomputer. The modification of DEFEL to simulate metalrolling problems and the implementation of heat transfer in the code are the main contributions of this thesis. Four sample problems in the area of plane strain rolling are analyzed by the modified code: crop loss in billet rolling, curling of strip in non-symmetrical rolling, roll force and torque calculations in steady state sheet rolling, and temperature distributions in non-isothermal cold and hot rolling. DEFEL results have been compared with existing experimental, analytical, and/or numerical results. It is concluded that this version of DEFEL calculates thermomechanical response of both the transient and steady state processes with reasonable accuracy. In addition, it is computer-resource efficient.
Alcohol and cocaine abuse comorbidity in schizophrenia
Authors:   , Kee Kimmy Seok-Lye
Published: July 2024

The prevalence of alcohol and cocaine abuse in schizophrenia has been established to be substantially higher than in the general population, but little is known about this increased vulnerability. The present research was designed to evaluate three hypotheses regarding the mechanisms by which the psychopathology of schizophrenia might lead to an increased vulnerability of alcohol and cocaine use disorders: (1) Schizophrenic individuals with a history of alcohol and cocaine use disorders will report significantly more use of alcohol and cocaine for social motives and will have higher levels of social drive (lower scores on social anhedonia); (2) Schizophrenic individuals with a history of alcohol and cocaine use disorders will report more coping motives for abusing alcohol and cocaine and will have higher levels of distress symptoms (i.e., depression and anxiety); and (3) Schizophrenic individuals with a history of alcohol and cocaine use disorders will report significantly more use of alcohol and cocaine for pleasure enhancement motives and will have higher capacity to experience pleasure (lower scores on physical anhedonia). Two groups of schizophrenic patients with different histories of substance use disorder were studied, one with a history of only alcohol and cocaine use disorders (n=19) and another with no lifetime history of alcohol or other drug use disorders (n=16). Results indicated that schizophrenic patients with a history of alcohol and cocaine use disorders were more likely to report having social, pleasure enhancement, and coping motives for using those substances, along with higher levels of distress symptoms such as depression and anxiety as compared to their non-abusing counterparts. However, findings for social and physical anhedonia revealed no significant differences between the two subject groups on these factors. Possible explanations were offered, along with indicated areas for future research.
The impact of telecommuting on the work outcomes of professionals
Authors:   , McCloskey Donna Weaver
Published: July 2024

Due to the numerous demands from a variety of different constituents and advances in technology which can make remote work a reality, it is not surprising that telecommuting is growing rapidly. Yet, despite this growth, the research in this area is surprisingly limited. Little empirical research has addressed research-based constructs, such as work-family conflict and job satisfaction. The literature that does exist is full of contradictions. Given the continued growth of telecommuting, there is a need to fully understand the outcomes of this work arrangement. This research addresses this need by exploring whether work outcomes differ for professionals who telecommute and those who do not telecommute. This research considers a network of relationships concerning the impact of the work arrangement on work characteristics and experiences and the eventual effect on work outcomes. This research also addresses the potential impact of the motivation for telecommuting and the level of telecommuting participation on work characteristics, experiences and outcomes. The responses from 89 telecommuters (40% response rate) and 71 non-telecommuters (49% response rate) from a large telecommunications firm were analyzed using hierarchical multiple regression. Telecommuting did not have a direct effect on any of the proposed work characteristics, experiences or outcomes. Additional analyses revealed there interactions between work arrangement and other study variables on autonomy, behavior based work-family conflict and role conflict. Level of telecommuting participation had a positive effect on autonomy. Motivation for telecommuting did not have a significant effect on any of the examined work characteristics, experiences and outcomes, including career advancement prospects. These findings contradict both the positive and negative conventional beliefs about telecommuting. Telecommuting does not appear to be the magical work arrangement that will allow employees to balance both work and family commitments while increasing autonomy and boosting job satisfaction. Likewise, telecommuting is not the oppressive work structure that will cause employees to work long hours, interfere with family relationships and lead to limited career advancement. Additional research is needed to test the generalizability of these results.
Test-retest reliability of Bricklin Perceptual Scales
Authors:   , Speth Eric B. , Seraydarian Louisa
Published: July 2024

Children in custody disputes are frequently assessed by mental health professionals in an attempt to determine which of two competent parents is best suited to be the child's primary caretaker. Intellectual and projective psychological tests are frequently administered as part of this process. While such tests may yield clinically useful information, they were not designed for use in custody evaluations, the goal of which is to determine which of two competing parents is best able to meet the unique need of a particular child. One test, the Bricklin Perceptual Scales, has been specifically developed for this purpose. The instrument consists of 64 questions that require the child to non-verbally rate parents with respect to various traits and how they might behave in certain hypothetical situations. Although the scale is currently in wide use, very little data have been reported concerning its reliability and validity. It is possible that the test measures transitory, situational phenomena and thus, the parent that "wins" in terms of the child's ratings, could quickly change. The present study addressed the issue of reliability. A test-retest design was used with 20 adolescent psychiatric inpatients with retesting occurring seven days after the initial administration. Pearson correlations were run to determine the stability of individual test items, overall scores and for summed scores for groups of questions which purportedly measure the same general parenting traits such as "Supportiveness" and "Follow-Up Consistency". The results generally support the hypothesis that the measure was reliable over a one week period. While certain items and one of the four categories of items did not reach significance, the reliability of the scores used by clinicians in formulating recommendations are significant at p <.001. In spite of this high degree of stability, a change in the parent chosen by the scale occurred in four of 20 cases. This study must be considered a pilot, given the very limited subject pool and the fact that random sampling was not possible. These results must be replicated by larger, better controlled studies before definitive conclusions can be drawn. However, the data do provide some useful preliminary information concerning the stability of this measure over time. These findings do not necessarily undermine the clinical utility of the measure. However, in situations where the parents are close, in terms of the number of items obtained, the results should be interpreted with caution and statements made based on the results should be qualified accordingly.
Innate and Adaptive Immune Responses in Herpes Simplex Virus Encephalitis
Authors:   , Kollias Christina Megan , Jennings Stephen R
Published: July 2024

Herpes simplex virus type 1 (HSV-1) is a ubiquitous, neurotropic human pathogen that causes diseases ranging from mild orofacial lesions to potentially fatal encephalitis. Cells present at the infection site express Toll-like receptors (TLRs) and intracellular nucleic acid sensors, which detect infection, produce antiviral cytokines, and limit viral invasion of the nervous system. This dissertation presents two studies examining mechanisms of resistance to HSV-1 encephalitis. In the main project, we showed TLR2-knockout (TIr2-/-) mice were highly susceptible to HSV-1-induced mortality. Their natural killer cells (NKs) responded normally, but the TIr2-/- mice exhibited impaired dendritic cell (DC) and CD8+ T cell activation. While virus replication was not different within the infected lip tissue, HSV-1 spread to the trigeminal ganglia more efficiently in the TIr2-/- group. Additionally, HSV-1 crossover to the central nervous system (CNS) was exacerbated in the deficient animals and viral loads there positively correlated with disease severity. This elevated CNS viral load precipitated the up-regulation of inducible nitric oxide synthase. Nitric oxide is neurotoxic at high concentrations and presumably its production contributed to the mortality of the TIr2 -/- group. We assessed the infiltration of leukocytes to the HSV-1-infected CNS and observed neutrophil migration to both TIr2-/- and WT brains. Lastly, we utilized an intracranial infection model to specifically assess the role of TLR2 within the CNS, but our virus proved too virulent to reveal a phenotype in the deficient mice. In the secondary project, we showed Venezuelan equine encephalitis virus replicon particles (VRPs) were effective as a prophylactic vaccine against a lethal HSV-1 challenge. Importantly, the VRP protection was non-specific, as the control GFPexpressing VRP protected as well as the HSV-1 gB-expressing VRP. Moreover, VRPs were effective for at least 4 weeks and were dependent on both NKs and DCs. Finally, we used TLR7-deficient mice to show for the first time that VRPs partially depend on this receptor for optimal protection. In summary, we utilized multiple approaches to investigate mechanisms of protection against serious HSV-1 disease. The design of efficacious anti-HSV therapies requires a full understanding of these mechanisms and this dissertation sheds light on some of these important concepts.
The role of monoacylglycerols in deep-fat frying studied by using a starch gel model food system
Authors:   , Thikkavarapu Hemaprakash Reddy
Published: July 2024

Deep-fat frying is a popular method of food preparation, especially in fast food restaurants. During deep-fat frying, the fat is exposed to high temperatures in the presence of moisture from food and air and a variety of reactions such as autoxidation, thermal polymerization, thermal oxidation, isomer cyclization, and hydrolysis can occur producing numerous decomposition products, both volatile and nonvolatile. Hydrolysis of frying fat results in the formation of diacylglycerols, monoacylglycerols and fatty acids. Monoacylglycerols (MG) are commonly used as emulsifiers in margarine and table spreads, and their addition to frying oils has been reported to decrease the interfacial tension (IFT) between frying oil and water. Reduction in IFT of frying oils was reported to highly correlate with increased fat absorption. The purpose of the present study is to understand the role of MG during frying using a model food system based on starch gel. A gas chromatographic method, using short-length packed columns, has been adapted to follow the increase in concentration of fatty acids, mono- and diacylglycerols during frying. A model food system based on corn starch gel has been developed and evaluated for its performance during frying. The model food system was noted to have features that mimic the characteristics of many foods undergoing deep-fat frying (moisture loss, fat absorption, crust formation etc.). High correlation has been determined between fat absorption and frying time (r = 0.96), and between concentration of MG and IFT of soybean oil with water. Use of the model food system to study the effect of MG concentration on fat absorption indicated a poor correlation between fat absorption and MG concentration at frying times of 3 and 5 minutes. However, a significant correlation between MG concentration and fat absorption was determined at a longer frying time of 8 minutes. These results suggest that reduction in IFT due to MG is not the sole reason for increased fat absorption of foods fried in degraded oils.
Evolution of microstructure and rheological behavior of alloys in the semisolid state
Authors:   , Tzimas Evangelos , Zavaliangos Antonios
Published: July 2024

Semisolid processing is a net-shape metal forming method that combines the advantages of forging and casting. In this work, emphasis is placed on a comparative evaluation of the major methods that produce near-equiaxed microstructures suitable for subsequent semisolid processing: magnetohydrodynamic (MHD) casting, strain-induced melt activation (SIMA), and spray casting. The microstructural, material and process parameters that affect the behavior of semisolid materials are identified in each method. The microstructural evolution of the solid phase within time intervals characteristic of semisolid processing is examined in wrought and cast aluminum alloys. This work shows the presence of abnormal grain growth in some spray cast materials as a result of the initial microstructure. A new model is proposed to describe the spherodization of dendrites in the semisolid state. Unconstrained compression and parallel plate 'viscometry' experiments were carried out in order to examine the rheological behavior of semisolid materials. The presence of strain localization and inhomogeneous deformation, especially at lower volume fractions of solid is observed. Deformation at low liquid contents creates significant internal damage imposing a low liquid content limit, of the order of 40v/o, for the applicability of the process. Strain rate 'jump' tests exhibit the reduction of the apparent strain rate sensitivity with the increase of the liquid content. Modulus measurements indicate that cohesion in semisolid materials is limited. The presence of liquid phase segregation during deformation is observed. Segregation is reduced by increasing triaxiality and strain rate and minimizing the total strain and grain size. A phenomenological model for a two-phase material is proposed, accompanied by a mathematical modeling framework, to describe the resistance to flow of semisolid materials. Semisolid materials exhibit non-uniform, pressure dependent, strain rate independent, granular flow during deformation at medium liquid contents and in the range of strain rates examined. Finally, a simple criterion for processability in the semisolid state is introduced, based on the sensitivity of the liquid content to temperature fluctuations. It is also proposed that processability is enhanced by using microsegregated raw materials, which decrease both the sensitivity of liquid content to temperature and the processing temperature.
Effects of pressure on hydrocarbon oxidation chemistry
Authors:   , Koert David Niel
Published: July 2024

A turbulent flow reactor has been constructed for chemical kinetic studies of hydrocarbon oxidation in the low to intermediate temperature regimes. The flow reactor enables the study of gas-phase kinetics from 2 to 20 atm. Experiments studying the effect of pressure on the oxidation chemistry during the transition from low to intermediate temperature have been conducted. Experimental conditions cover temperatures from 600 to 900 K, pressures from 5 to 15 atm and equivalence ratios from 0.4 to 2.8 using ethylene/air, ethane/air and propane/air mixtures. In these experiments, gas samples were extracted along the reactor centerline with a water-cooled probe. Species measurements were made using gas chromatography and reactivity mapping was conducted using CO measurements as an indicator of extent of reaction. Results for propane/air experiments indicate typical NTC behavior which manifests as a narrow temperature range (640 to 770 K) in which the rate of hydrocarbon oxidation peaks. The NTC region temperature range shifts to higher temperatures and broadens with increasing pressure. This behavior contrasts with Dryer's 1990 prediction suggesting that the NTC region narrows and disappears as pressure increases. Several changes in the major reaction products occur as temperature is varied indicating changes in the dominant branching agent. Below approximately 690 K, CO₂ is the major product. Above 690 K, CO is the major product. Above 740 K, propylene becomes the major product. The temperatures at which these transitions occur are observed to change with pressure. The pressure dependent shift in the NTC region temperature range is compared to Benson's 1981 analysis which is found to accurately predict the shift. Transition in the CO and propylene yields is explained by considering the fate of energetically unstable propylperoxy radicals in the coupled reaction mechanism of Slagle et al. (1985). The low temperature region in which CO₂ is the major product is explained by aldehyde and acylhydroperoxide branching.
Role of kinesin-5 in growth cone behavior
Authors:   , Nadar Vidya C. , Baas Peter W
Published: July 2024

The growth cone at the tip of the axon is essential for guiding the axon during development to its appropriate target. Growth cones can be divided into a microtubule-rich central (C-) domain, an actin-rich peripheral (P-) domain and the transition (T-) zone between them. Polarized rearrangement of cytoskeletal elements in the growth cone underlies its turning toward or away from environmental cues. Growth cone turning requires selective invasion of microtubules from the C-domain into the P-domain in the direction of the cue. Studies to date have attributed this invasion to the dynamic properties of the microtubules. I have tested another idea, specifically that molecular motors involved in organizing microtubules in the mitotic spindle play a critical role in regulating the polarized distribution of microtubules during growth cone turning. This idea builds on observations that the invasion of microtubules into the P-domain is determined by a tug-of-war between forces exerted by cytoplasmic dynein and myosin-II. I hypothesized that kinesin-5, a motor that counterbalances dynein-based forces during mitosis, tips the balance of forces in a polarized fashion within growth cones, to elicit the selective invasion of microtubules into the appropriate side of the growth cone during turning. I observed that depletion of kinesin-5 or pharmacologic inhibition of kinesin-5 inhibited growth cone turning in response to environmental cues. Kinesin-5 is enriched in the T-zone, where the phospho-kinesin-5 polarizes away from the direction of turning. Experiments with non-phosphorylatable kinesin-5 resulted in increased microtubule invasion and lack of growth cone turning, similar to depletion or inhibition of kinesin-5, indicating that phosphorylation regulates kinesin-5 function in the growth cone. This provides an attractive means by which signaling pathways relevant to growth cone turning could utilize kinesin-5 to polarize the microtubule array. As a test of the feasibility of this idea, I used micro-CALI to locally inactivate kinesin-5 in different domains of the growth cone, and found that local inactivation specifically in the T-zone results in increased invasion of microtubules into the P-domain. I conclude that kinesin-5 functions in the T-zone of growth cones to regulate growth cone turning and kinesin-5 function is regulated by phosphorylation.
The utilization of signal processing and pattern recognition for the advancement of ultrasonic nondestructive testing
Authors:   , Avioli Michael Joseph
Published: July 2024

Until recently, ultrasonic inspection has relied upon some very basic concepts, making use of, for example, a pulser unit, a piezoelectric transducer, and an oscilloscope display. These components were excellent for carrying out thickness measurements, and for determining defect locations. There exists today, however, a great need to do work in flaw classification, a topic that can only be covered by using computer technology, in particular utilizing aspect of signal processing and pattern recognition. Signal processing and pattern recognition have just been introduced to the ultrasonic inspection field and development has just entered a research and development phase. With this marriage, a large number of problems in both software and hardware and in demonstrated utility must still be solved. Current work in this area is presently being carried on in only a very few laboratories. Tools for carrying out this research have been embedded in other technologies for many years. The purpose of this thesis is to draw upon these different technologies that utilize signal processing and pattern recognition in an attempt to use these desciplines to advance the state of the art in flaw and material classification in ultrasonic inspection. The thesis consists of two major parts, the first describes the availability of suitable tools for analysis, and the second in describing two sample problems that can be handled with this integrated technology. The two problems are related to weld inspection, the first on welded plates, and the second for K-joint damage analysis in an offshore structure. This work culminates in the development of a system software package called GANPUI, an acronym for a Generalized Approach to New Problems in Ultrasonic Inspection.
The molecular mechanism of slow crack growth in polyethylene
Authors:   , Lustiger Arnold
Published: July 2024

Slow crack growth in polyethylene is characterized by a crack which propagates over a period of few minutes to many years after application of a load. The molecular mechanism of slow crack growth in polyethylene is posited to be interlamellar separation. The lamellae tend to separate as a response to the applied stress due to the slipping of tie molecule entanglements rather than reorganize into the fiber morphology typical of ductile creep-type deformation. Environmental stress cracking in polyethylene is an acceleration of this same process, since the environmental stress cracking agent acts as a plasticizer which accelerates the slipping of the tie molecule entanglements. Fracture surfaces of failed specimens display a short nonuniform fiber morphology due to craze formation at the crack tip. This suggests an interruption in the uniform fiber formation found in ductile creep occurring due to interlamellar separation. Cracks which are made to initiate on the surface of these specimens occur preferentially either on spherulite boundaries or radially down the center of spherulites, again suggesting interlamellar separation. Using transmission electron microscopy, interlamellar separation is directly observed. When applied strain is varied environmental stress cracking is not found in the regions of the specimens strained beyond yield (i.e. at the point beyond which lamellae have broke up and reorganized into fibers). On the basis of this understanding the slow crack resistance of polyethylene can be optimized by increasing the interlamellar strength. This can be done by increasing tie molecule concentration and enhancing the effectiveness of tie molecule entanglements. On the basis of a graphic model for failure it is proposed that this can be accomplished through increasing molecular weight, minimizing crystallinity, and lamellar thickness, maximizing comonomer content and using longer comonomer chains. Observed differences in slow crack growth resistance between seven lots of polyethylene piping materials tested can be rationalized by comparing these parameters among them.
Transport and mixing in gas-liquid and gas-liquid-solid flows in bubble columns
Authors:   , Mitra-Majumdar Debabrata
Published: July 2024

A research program to study the transport and mixing in slurry bubble columns (SBC) and a jet bubble column has been carried out. The main thrust of the research program was the development of computational fluid dynamic (CFD) models based on the fundamental governing equations of fluid motion for predicting the flow structures of cocurrent upward two-phase (air-water) and three-phase (air-water-glass beads) flows through slurry bubble and a jet bubble columns and mixing characteristics in a jet bubble column. The fundamental models developed were applied to predict the flow structure in air-water and air-water-glass bead flows through SBC for a wide range of flow conditions. The importance of various modes of interfacial momentum transfer in two-phase flows, under different flow conditions, was also examined. It was found that an accurate estimation of the interfacial forces must be made in order for the models to predict the flow structures well. In order to extend the use of these models to predict the flow structure in three-phase flows, the present study also proposed new correlations to modify the interfacial forces between the phases (gas-liquid and solid-liquid) to account for the effect of the bubbles on the motion of the solid particles and the effect of the solid particles on the bubble motion. Use of fundamental models to predict the flow structures in three-phase flows has not been reported in the literature. The model was also applied to study the flow structure and mixing characteristics in a jet bubble column. The phenomenon of bubble breakup in the jet bubble column was incorporated in the model. The model predicted the experimental data of axial variation of the gas volume fraction well. In the study of the mixing behavior of two phase air-water turbulent flow in a jet bubble, measured residence time distributions (RTD) of a liquid tracer within the cone agree well with the predicted values given by the model. Use of fundamental models to study the flow characteristics in a jet bubble column has also not been reported in the literature. The complimentary experimental program focused on the setup of an experimental facility and diagnostic tools for the measurement of phase holdups in a SBC (for both air-water and air-water-glass beads flows). Both the radial variation of the gas holdup and the axial variations of the solid and gas holdup were obtained for different flow conditions. The experimental data obtained were compared to existing correlations for the average phase volume fractions in the bubble columns. (Abstract shortened by UMI.).