No description available.

No description available.

Selective feeding in response to depletion of particular reserves was examined in the American cockroach, Periplaneta americana. Animals deprived of specific nutrients and subsequently provided with dietary choices, responded so as to restore their altered reserves. Since two foods of differing energy content were used, the fundamental hypothesis of optimality theory could be tested (i.e. do cockroaches behave so as to maximize energy intake?). Adult male cockroaches were placed in a computer-monitored artificial habitat containing routes to shelter, water, protein and carbohydrate. Measures of behaviour were compared over treatments. Treatments included control cockroaches (no starvation), cockroaches fed agar (originally fed protein and sugar), protein-starved cockroaches (originally fed sugar only) and starved cockroaches (no food in the pre-treatment). In all treatments, more time was spent feeding than drinking. In controls, feeding on carbohydrate took precedence over protein (for intake and duration). Protein-starved cockroaches showed increased intake (over controls) for protein, as expected, but also increased intake for both carbohydrate and water. Starved and agar-fed cockroaches displayed decreased carbohydrate and water intake while protein consumption increased. The compensatory responses showed large initial peaks that gradually approached control behaviour. The results indicate that feeding behaviour is strongly responsive to reserve state and reserves act as an integral part of a dynamic system which operates homeostatically. The fact that depletion of the protein reserve resulted in increased ingestion of both protein and carbohydrate strongly suggests that reserves are linked. Considerable variation in daily feeding was observed which may be related to overshoot/undershoot responses typical of homeostatic systems where time lags exist. The results are strongly at variance with the predictions of optimal foraging theory. Cockroaches appear to feed to homeostatic set points, largely regulated by reserves. Reserves are largely ignored in optimal foraging theory. Furthermore, the animals regulate intake of nitrogen (protein) and/or energy, and do not simply maximize energy intake. / Thesis / Master of Science (MS)

Exercise is important to employees’ health and well-being. Exercise has been found to increase resources, foster resource replenishment, and increase happiness, which may make it effective in supporting employees against the harmful effects of depletion that arise from emotion regulation. Surface acting is a demanding behavior in which employees must fake their emotions to follow organizational display rules, but we know little about how exercise breaks can prevent harmful effects extending from this common job demand in some organizational settings (e.g., customer service). Fifty participants (N = 50) completed a surface acting task in which they listened to audio-recorded negative restaurant reviews and were instructed to respond to the reviews without conveying negative emotions across a 90-minute in-lab experimental session. Participants were randomly assigned to one of four break conditions (no break, a passive break, an exercise break, or a flaw essay break) which occurred halfway through the experimental session. Participants then completed the surface acting task again for 20 minutes. The surface acting task was effective in inducing emotion regulation. Participants who received a break experienced a decrease in depletion after the break, while participants who did not receive a break experienced an increase in depletion. However, no evidence was obtained to suggest that exercise breaks led to a reduction in depletion relative to other experimental conditions, nor a difference in mastery or positive affect. This thesis contributes to research on emotion regulation and exercise break by creating a new surface acting task that can easily be given in experiments. Also, this thesis suggests that organizations should ensure that employees are receiving breaks during worktime to guarantee employees maintain high productivity. / M.S. / Work is stressful as individuals may need to enhance, change, fake or suppress emotions through a process known as emotion regulation. One type of emotion regulation is surface acting in which individuals fake emotions to better align with organizational display rules. Surface acting has been found to contribute to emotional exhaustion, work-to-family conflict, feelings of inauthenticity and insomnia. Surface acting is common in customer jobs in which employees need to address customer concerns. Research has demonstrated that breaks can be used to help restore resources and reduce depletion. Specifically, exercise has been found to be beneficial in helping employees combat the harmful effects of emotion regulation and the depletion that comes with it. In this study, fifty participants completed a surface acting task in which they listened to audio-recorded negative restaurant reviews and were instructed to respond to the reviews without conveying negative emotions across a 90-minute in-lab experimental session. Participants were randomly assigned to one of four break conditions (no break, a passive break, an exercise break, or a flaw essay break) which occurred halfway through the experimental session. Participants then completed the surface acting task again for 20 minutes. The surface acting task was found to induce emotion regulation. Participants who received a break experienced a decrease in depletion after the break, while participants who did not receive a break experienced an increase in depletion. There was no evidence to suggest that exercise breaks were better at reducing depletion than the other conditions. This thesis suggests that organizations should ensure that employees are receiving breaks during worktime to guarantee employees maintain high productivity.

No description available.

No description available.

Understanding and controlling the forces between colloidal particles in solution, along with the resulting stability of a dispersion of such particles, continues to be at topic of great interest. Although most laboratory studies focus on model systems in which the number of system species is kept to a minimum, real colloidal systems can be much more complex, consisting of multiple components that can vary greatly in size, charge, shape, etc. This dissertation focused on a topic that has received very little prior study, namely synergistic effects that can arise in mixed colloidal systems in which the resulting force and stability of the system cannot be predicted using results obtained in more idealized systems consisting of fewer components. Two specific systems were studied. The first was a ternary system of particles in which micron-sized particles were in a dispersion containing both nanoparticles and submicron particles. It was shown through both computation modeling and direct force measurements that the nanoparticles can create attractive forces between the micron and submicron particles such that a halo of submicron particles is formed. This halo results in long range forces between the microparticles that cannot be predicted from measurements in systems containing only nanoparticles or only submicron particles. In addition, the forces can be large enough to alter the stability of a dispersion of these microparticles. The second system consisted of microparticles in a solution containing nanoparticles and a polyelectrolyte, specifically poly(acrylic) acid. Again, through modeling and experimentation, it was found that complexation of the nanoparticles and polyelectrolyte molecules led to depletion and structural forces between the microparticles that were substantially greater than the sum of the forces measured in systems of only nanoparticles or only polyelectrolyte. It was also found that these greater forces could lead to destabilization of a dispersion of microparticles that was stable when only nanoparticles or only polyelectrolyte was present. While these results clearly demonstrate the difficulty associated with predicting forces and stability in mixed colloidal systems, they also indicate that such systems offer new and interesting opportunities for controlling stability that clearly warrant additional study. / Ph. D.

This study examines the effects of unit-level culture on abusive supervision. Utilizing Baumeister and colleagues' (2000) self-regulatory resource depletion model as an explanatory framework, I argue that aggressive unit-level culture will increase the incidence of abusive supervision, whereas people- and team-oriented unit-level cultures will decrease the incidence of abusive supervision. In line with these arguments, I then examine the degree to which those effects are mediated by ego depletion. In sum, I argue that aggressive unit-level culture will increase, while people- and team-oriented cultures will reduce, the amount of supervisor ego depletion, which then increases the incidence of abusive supervision. Using Hobfoll et al.'s (1990) Social Support Resource Theory, I further argue that the relationship between unit-level culture and ego depletion is moderated by supervisor home social support. I tested my model using a sample of 340 nurses and 52 nursing directors working in a large hospital system in the Southwestern United States. I was unable to demonstrate support for my model as hypothesized. However, I am able to contribute to the literature concerning antecedents to abusive supervision by showing that alternative conceptualization of culture impact abusive supervision. Further, I show that aggressive norms mediate the relationship between aggressive culture and abusive supervision. I also contribute to the literature examining resource depletion in the workplace by demonstrating the buffering role of supervisor home social support on ego depletion. Implications and future directions are discussed.

Mental fatigue decreases motivation. I tested whether applying electricity to a self-control region of the brain would replenish some of the motivation normally lost during mental fatigue. 224 people participated in this study. Each person received real or placebo brain stimulation while undergoing activities that increased mental fatigue. The dependent variable was a task where participants had to perform work by clicking a computer mouse repeatedly. Before performing this task, participants indicated how hard they were planning to work on this motivation task. Participants who received real brain stimulation were able to perform more work, but only if they also indicated they planned to work hard on the task.

This thesis comprises two parts, both concerned with the study of Escherichia coli bacterial suspensions. The first part investigates E. coli motility whilst the second part explores E. coli growth in the presence of the antimicrobial peptide pexiganan. In Part 1 I measure the three-dimensional diffusion of non-motile cells in an active suspension of E. coli, using Differential Dynamic Microscopy (DDM). It is found that tracer diffusivity is enhanced linearly as a function of the bath activity, defined as the product of the number density of active bacteria and their average speed. The absolute enhancement is measured to be 1:8 ± 0:1 times smaller that that published previously in the vicinity of a surface, in agreement with theoretical predictions of enhanced diffusion by far-field advection. The diffusivities of non-motile mutants with and without paralysed flagella are enhanced to the same extent, despite a difference in hydrodynamic radii. In addition, the protocol for growing, preparing and measuring motile E. coli is optimised using DDM. In Part 2 I investigate how E. coli density in liquid media supplemented with pexiganan influences the measurement of its Minimum Inhibitory Concentration (MIC). Growth curves, peptide bioassays and single cell microscopy are used. It is found that population density drops rapidly when pexiganan is introduced, but regrowth occurs within 24 hours at sub-MIC concentrations. The shape of the density curve is explained by peptide depletion linked to cell death and immediate recovery of cells exposed to the peptide. As expected from these findings, the system displays a substantial inoculum effect, quantified with a fitted power law. Substantial variation is seen between replicate MIC assays; an inherent property of the system which derives from the drop to small numbers of viable cells before regrowth. Finally, I show that DDM measurements of E. coli motility in antimicrobial peptides can provide an alternative, high-throughput density curve.