Matching Items (240)
Description
Understanding charge transport in single molecules covalently bonded to electrodes is a fundamental goal in the field of molecular electronics. In the past decade, it has become possible to measure charge transport on the single-molecule level using the STM break junction method. Measurements on the single-molecule level shed light on charge transport phenomena which would otherwise be obfuscated by ensemble measurements of groups of molecules. This thesis will discuss three projects carried out using STM break junction. In the first project, the transition between two different charge transport mechanisms is reported in a set of molecular wires. The shortest wires show highly length dependent and temperature invariant conductance behavior, whereas the longer wires show weakly length dependent and temperature dependent behavior. This trend is consistent with a model whereby conduction occurs by coherent tunneling in the shortest wires and by incoherent hopping in the longer wires. Measurements are supported with calculations and the evolution of the molecular junction during the pulling process is investigated. The second project reports controlling the formation of single-molecule junctions by means of electrochemically reducing two axial-diazonium terminal groups on a molecule, thereby producing direct Au-C covalent bonds in-situ between the molecule and gold electrodes. Step length analysis shows that the molecular junction is significantly more stable, and can be pulled over a longer distance than a comparable junction created with amine anchoring bonds. The stability of the junction is explained by the calculated lower binding energy associated with the direct Au-C bond compared with the Au-N bond. Finally, the third project investigates the role that molecular conformation plays in the conductance of oligothiophene single-molecule junctions. Ethyl substituted oligothiophenes were measured and found to exhibit temperature dependent conductance and transition voltage for molecules with between two and six repeat units. While the molecule with only one repeat unit shows temperature invariant behavior. Density functional theory calculations show that at higher temperatures the oligomers with multiple repeat units assume a more planar conformation, which increases the conjugation length and decreases the effective energy barrier of the junction.
ContributorsHines, Thomas (Author) / Tao, Nongjian (Thesis advisor) / Li, Jian (Thesis advisor) / Mujica, Vladimiro (Committee member) / Allee, David (Committee member) / Arizona State University (Publisher)
Created2013
Description
ABSTRACT Vitamin C plays an important role in fatty acid metabolism because it is required for carnitine synthesis. Vitamin C has been shown to have an inverse relationship with weight and body fat percent in a number of studies. However, there has been limited research exploring the relationship between vitamin C status and fat oxidation. This cross-sectional study investigates the relationship between plasma vitamin C and fat oxidation in 69 participants and between plasma vitamin C and body fatness in 82 participants. Participants were measured for substrate utilization via indirect calorimetry while at rest and measured for body fatness via DEXA scan. Participants provided a single fasting blood draw for analysis of plasma vitamin C. Results did not show a significant association between vitamin C and fat oxidation while at rest, therefore the data do not support the hypothesis that vitamin C status affects fat oxidation in a resting state. However, a significant inverse association was found between vitamin C and both total body fat percent and visceral fat.
ContributorsObermeyer, Lindsay (Author) / Johnston, Carol (Thesis advisor) / Hall, Rick (Committee member) / Swan, Pamela (Committee member) / Arizona State University (Publisher)
Created2014
Description
Dietary counseling from a registered dietitian has been shown in previous studies to aid in weight loss for those receiving counseling. With the increasing use of smartphone diet/weight loss applications (app), this study sought to investigate if an iPhone diet app providing feedback from a registered dietitian improved weight loss and bio-markers of health. Twenty-four healthy adults who owned iPhones (BMI > 24 kg/m2) completed this trial. Participants were randomly assigned to one of three app groups: the MyDietitian app with daily feedback from a registered dietitian (n=7), the MyDietitian app without feedback (n=7), and the MyPlate feedback control app (n=10). Participants used their respective diet apps daily for 8-weeks while their weight loss, adherence to self-monitoring, blood bio-markers of health, and physical activity were monitored. All of the groups had a significant reduction in waist and hip circumference (p<0.001), a reduction in A1c (p=0.002), an increase in HDL cholesterol levels (p=0.012), and a reduction in calories consumed (p=0.022) over the duration of the trial. Adherence to diet monitoring via the apps did not differ between groups during the study. Body weight did not change during the study for any groups. However, when the participants were divided into low (<50% of days) or high adherence (>50% of days) groups, irrespective of study group, the high adherence group had a significant reduction in weight when compared to the low adherence group (p=0.046). These data suggest that diet apps may be useful tools for self-monitoring and even weight loss, but that the value appears to be the self-monitoring process and not the app specifically.
ContributorsThompson-Felty, Claudia (Author) / Johnston, Carol (Thesis advisor) / Wharton, Christopher (Christopher Mack), 1977- (Committee member) / Levinson, Simin (Committee member) / Arizona State University (Publisher)
Created2014
Description
The purpose of this study was to gather qualitative data on different and novel methods used to self-monitor diet and exercise during a weight loss study. Participants who used either a traditional paper and pencil method or a smart phone weight loss app for diet and exercise tracking were recruited for focus groups. Focus group discussions centered on the liked and disliked aspects of recording, perceived behavior changes, and suggestions for improved self-monitoring. Focus groups were organized based on the method of self-monitoring. The app group tracked calorie intake and expenditure via the "Lose It" app on their smart phones. The paper & pencil group recorded exercise and food intake in a journal and self-regulated diet based on recommended servings from each food group (or exchange lists). Focus group sessions were audio-recorded, transcribed and coded by the researcher and an independent coder. Results indicated that app participants liked the convenience, affordability, and user-friendly features, but wanted more nutrition advice. App participants liked self-managing their diet, not restricting certain foods or food groups and allowing for indulgences by balancing calories and exercise. Also, they desired an accurate estimation of energy expenditure from an app, based on individual characteristics (i.e., gender and age). Participants who recorded on paper liked the size for a visual layout of food entries, but desired a technology-enhanced method with an auto-calculation of calorie intake and expenditure. They also suggested increased accountability and opportunities for social support would enhance self-monitoring. Overall, an ideal technology-assisted self-monitoring app or program would be free and include an auto-calculation of calorie intake, a gender- and age- specific estimation of calories expended, easy entry of foods from a large database, the ability to enter whole recipes, nutrition information and recommendations, and be available via phone, tablet or computer (based on personal preference).
ContributorsSterner, Danielle (Author) / Wharton, Christopher (Christopher Mack), 1977- (Thesis advisor) / Johnston, Carol (Committee member) / Hall, Richard (Committee member) / Arizona State University (Publisher)
Created2012
Description
Birds have plasma glucose levels that are 1.5-2 times greater than mammals of similar body mass in addition to higher free fatty acid concentrations, both of which would typically impair endothelium-dependent vasodilation if observed in mammals. Endothelium-dependent vasodilation can be stimulated in mammals through the use of acetylcholine (ACh), which primarily acts through nitric oxide (NO) and cyclooxygenase (COX)-mediated pathways, with varying reliance on endothelial-derived hyperpolarizing factors (EDHFs). Very few studies have been conducted on small resistance systemic arteries from birds. The hypothesis was that because birds have naturally high glucose and free fatty acid concentrations, ACh-induced vasodilation of isolated arteries from mourning doves (Zenaida macroura) would be independent of endothelial-derived factors and resistant to high glucose-mediated vascular dysfunction. Small resistance mesenteric and cranial tibial (c. tibial) arteries were pre-constricted to 50% of resting inner diameter with phenyleprine then exposed to increasing doses of ACh (10-9 to 10-5 μM) or the NO donor, sodium nitroprusside (SNP; 10-12 to 10-3 μM). For both vessel beds, ACh-induced vasodilation occurred mainly through the activation of potassium channels, whereas vasodilation of mesenteric arteries additionally occurred through COX. Although arteries from both vessel beds fully dilated with exposure to sodium nitroprusside, ACh-mediated vasodilation was independent of NO. To examine the effect of high glucose on endothelium-dependent vasodilation, ACh dose response curves were conducted following exposure of isolated c. tibial arteries to either a control solution (20mM glucose) or high glucose (30mM). ACh-induced vasodilation was significantly impaired (p = 0.013) when exposed to high glucose, but normalized in subsequent vessels with pre-exposure to the superoxide dismutase mimetic tiron (10 mM). Superoxide concentrations were likewise significantly increased (p = 0.0072) following exposure to high glucose. These findings indicate that dove arteries do not appear to have endogenous mechanisms to counteract the deleterious effects of oxidative stress. Additional studies are required to assess whether endogenous mechanisms exist to protect avian vascular reactivity from systemic hyperglycemia.
ContributorsJarrett, Catherine Lee (Author) / Sweazea, Karen L (Thesis advisor) / Johnston, Carol (Committee member) / Gaesser, Glenn (Committee member) / Arizona State University (Publisher)
Created2012
Description
This work demonstrates the integration of a wearable particulate detector and a wireless chemical sensor into a single portable system. The detection philosophy of the chemical sensor is based on highly selective and sensitive microfabricated quartz tuning fork arrays and the particle detector detects the particulate level in real-time using a nephelometric (light scattering) approach. The device integration is realized by carefully evaluating the needs of flow rate, power and data collection. Validation test has been carried out in both laboratory and in field trials such as parking structures and highway exits with high and low traffic emissions. The integrated single portable detection system is capable of reducing the burden for a child to carry multiple devices, simplifying the task of researchers to synchronize and analyze data from different sensors, and minimizing the overall weight, size, and cost of the sensor. It also has a cell phone for data analysis, storage, and transmission as a user-friendly interface. As the chemical and particulate levels present important exposure risks that are of high interests to epidemiologists, the integrated device will provide an easier, wearable and cost effective way to monitor it.
ContributorsGao, Tianle (Author) / Tao, Nongjian (Thesis advisor) / Chae, Junseok (Committee member) / Tsow, Tsing (Committee member) / Arizona State University (Publisher)
Created2012
Description
Background: Obesity is considered one of the most serious public health issues worldwide. Small, feasible lifestyle changes are necessary to obtain and maintain weight loss. Clinical evidence is inconclusive about whether meal preloading is an example of a small change that could potentially increase the likelihood of weight loss and weight maintenance. Objective: The aim of this study is to determine if consuming 23 grams of peanuts, as a meal preload, before a carbohydrate-rich meal will lower post prandial glycemia and insulinemia and increase satiety in the 2 hour period after a carbohydrate-rich meal. Design: 15 healthy, non-diabetic adults without any known peanut or tree nut allergies were recruited from a campus community. A randomized, 3x3 block crossover design was used. The day prior to testing participants refrained from vigorous activity and consumed a standard dinner meal followed by a 10 hour fast. Participants reported to the test site in the fasted state to complete one of three treatment meals: control (CON), peanut (NUT), or grain bar (BAR) followed one hour later by a carbohydrate-rich meal. Satiety, glucose and insulin were measured at different time points throughout the visit. Each participant had a one-week washout period between visits. Results: Glucose curves varied between treatments (p=.023). Blood glucose was significantly higher one hour after ingestion of the grain bar compared to the peanut and control treatments (p<.001). At 30 minutes after the meal, the control glucose was significantly higher than for the peanut or grain bar (p=.048). Insulin did vary significantly between treatments (p<.001). The insulin change one hour after grain bar consumption was significantly higher than after the peanut or control at the same time point (p<.001). The change in insulin one hour after peanut consumption was significantly higher than for the control treatment (p=.002). Overall satiety, expressed as the 180 minute AUC, differed significantly between treatments (p=.001). One hour after preload consumption, peanut and bar consumption was associated with greater satiety than the water control (p<.001). At 30 minutes post-meal, the grain bar was associated with greater satiety versus the water control (p=.049). The bar was also associated with greater satiety versus peanut and control at 60 and 90 minutes post-meal (p=.003 and .034, respectively). At 120 minutes post-meal, the final satiety measurement, the bar was still associated with greater satiety than the peanut preload (p=.023). Total energy intake, including test meal, on treatment days did not differ significantly between treatment (p=.233). Conclusions: Overall satiety, blood glucose and blood insulin levels differed at different time points depending on treatment. Both meal preloads increased overall satiety. However, grain bar ingestion resulted in sustained satiety, greater than the peanut preload. Grain bar ingestion resulted in an immediate glycemic and insulinemic response. However, the response was not sustained after the test meal was ingested. The results of this study suggest that a low-energy, carbohydrate-rich meal preload may have a positive impact on weight maintenance and weight loss by initiating a sustained increase in overall satiety. More research is needed to confirm these findings.
ContributorsFleming, Katie R (Author) / Johnston, Carol (Thesis advisor) / Wharton, Christopher (Christopher Mack), 1977- (Committee member) / Shepard, Christina (Committee member) / Arizona State University (Publisher)
Created2012
Description
The popularization of energy drink use as a supplement to exercise is steadily increasing, especially among young adult males. However, the effects of energy drinks on muscular performance in young adults have yet to be clearly elucidated. Eight male subjects (mean age: 23.3 ± 4.3 yrs, height: 181.0 ± 5.3 cm, fat percent 17.8 ± 5.2%, and weight 85.3 ± 12.6 kg) completed this randomized double-blinded cross over study. The purpose of this study was to determine differences in acute muscular strength and endurance and Profile of Mood States (POMS) scores between three treatments (RockStar, sugar-free RockStar, and sugar-free caffeine-free Placebo). It was hypothesized that there would be no significant differences in acute peak torque and endurance of the knee extensors and flexors or on fatigue and vigor subscores from the POMS questionnaire. Each man was tested randomly at least 1 week apart. Diet and time of day were held constant across trials. Peak torque of knee extensors and flexors at 60, 180, 240 degress/second and fatigue index and total work were calculated by performing 50 repetitions at 240 degrees/second. There were no significant differences in peak torque, fatigue index, or total work measures or in subjective measures of fatigue or vigor from the POMS between the treatments. This study indicates that RockStar energy drinks have no acute ergogenic effects in young men performing isokinetic strength or endurance testing.
ContributorsHawley, Michelle (Author) / Swan, Pamela (Thesis advisor) / Campbell, Kathryn (Committee member) / Johnston, Carol (Committee member) / Arizona State University (Publisher)
Created2012
Description
Advances in miniaturized sensors and wireless technologies have enabled mobile health systems for efficient healthcare. A mobile health system assists the physician to monitor the patient's progress remotely and provide quick feedbacks and suggestions in case of emergencies, which reduces the cost of healthcare without the expense of hospitalization. This work involves development of an innovative mobile health system with adaptive biofeedback mechanism and demonstrates the importance of biofeedback in accurate measurements of physiological parameters to facilitate the diagnosis in mobile health systems. Resting Metabolic Rate (RMR) assessment, a key aspect in the treatment of diet related health problems is considered as a model to demonstrate the importance of adaptive biofeedback in mobile health. A breathing biofeedback mechanism has been implemented with digital signal processing techniques for real-time visual and musical guidance to accurately measure the RMR. The effects of adaptive biofeedback with musical and visual guidance were assessed on 22 healthy subjects (12 men, 10 women). Eight RMR measurements were taken for each subject on different days under same conditions. It was observed the subjects unconsciously followed breathing biofeedback, yielding consistent and accurate measurements for the diagnosis. The coefficient of variation of the measured metabolic parameters decreased significantly (p < 0.05) for 20 subjects out of 22 subjects.
ContributorsKrishnan, Ranganath (Author) / Tao, Nongjian (Thesis advisor) / Forzani, Erica (Committee member) / Yu, Hongyu (Committee member) / Arizona State University (Publisher)
Created2012
Description
In today's world there is a great need for sensing methods as tools to provide critical information to solve today's problems in security applications. Real time detection of trace chemicals, such as explosives, in a complex environment containing various interferents using a portable device that can be reliably deployed in a field has been a difficult challenge. A hybrid nanosensor based on the electrochemical reduction of trinitrotoluene (TNT) and the interaction of the reduction products with conducting polymer nanojunctions in an ionic liquid was fabricated. The sensor simultaneously measures the electrochemical current from the reduction of TNT and the conductance change of the polymer nanojunction caused from the reduction product. The hybrid detection mechanism, together with the unique selective preconcentration capability of the ionic liquid, provides a selective, fast, and sensitive detection of TNT. The sensor, in its current form, is capable of detecting parts per trillion level TNT in the presence of various interferents within a few minutes. A novel hybrid electrochemical-colorimetric (EC-C) sensing platform was also designed and fabricated to meet these challenges. The hybrid sensor is based on electrochemical reactions of trace explosives, colorimetric detection of the reaction products, and unique properties of the explosives in an ionic liquid (IL). This approach affords not only increased sensitivity but also selectivity as evident from the demonstrated null rate of false positives and low detection limits. Using an inexpensive webcam a detection limit of part per billion in volume (ppbV) has been achieved and demonstrated selective detection of explosives in the presence of common interferences (perfumes, mouth wash, cleaners, petroleum products, etc.). The works presented in this dissertation, were published in the Journal of the American Chemical Society (JACS, 2009) and Nano Letters (2010), won first place in the National Defense Research contest in (2009) and has been granted a patent (WO 2010/030874 A1). In addition, other work related to conductive polymer junctions and their sensing capabilities has been published in Applied Physics Letters (2005) and IEEE sensors journal (2008).
ContributorsDiaz Aguilar, Alvaro (Author) / Tao, Nongjian (Thesis advisor) / Tsui, Raymond (Committee member) / Barnaby, Hugh (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2012