The sub-lethal effects of repeated cold exposure in insects

While insect cold tolerance has been well studied, the vast majority of work has focused on the effects of a single cold exposure. However, many abiotic environmental stresses, including temperature, fluctuate within an organism\u27s lifespan. In this thesis I address two major questions. First, does frequency of cold exposure impose additional stress on insects? Second, how does this stress translate to performance and fitness? I first summarize the literature on the effects of repeated cold exposure in insects, critically examining experimental designs. I then address my questions experimentally using four insect species with contrasting life histories and responses to cold exposure. I examine the fitness costs of repeated cold exposure in the chill-susceptible fly Drosophila melanogaster by recording survival, generation time, and number of offspring in flies that had received five 2 h, one 2 h, or one 10 h exposure to -0.5 ºC. I found that D. melanogaster trades off immediate survival and reproductive output in response to repeated cold exposure. In the freeze-tolerant caterpillar Pyrrharctia isabella, repeated freezing did not deplete energy reserves, but did damage hemocytes and Malpighian tubules, and led to decreased survival in repeatedly-frozen caterpillars. Similarly, I found in the freeze-avoiding caterpillar Choristoneura fumiferana that frequency of exposure, independent of period, intensity, or duration of cold exposures significantly decreased mortality, likely due to increased investment in cryoprotection at the expense of glycogen reserves. Finally, in the freeze-tolerant fly Eurosta solidaginis, the frequency of exposure, again independent of period, intensity, or duration of cold exposures led to a significant decline in egg production. Repeated cold exposure therefore imposes additional costs to insects, even when intensity and duration of cold are controlled for. This cost may either be a result of accrued damage, or may be energetic as individuals trade off investment in survival mechanisms for reproductive output. Given that many environments are not static, these effects indicate that investigating the effects of repeated stress exposure is important for understanding and predicting physiological responses in the wild

The Focal plane Detector Package on the TUNL Split-pole Spectrograph

A focal plane detector for the Enge Split-pole Spectrograph at Triangle Universities Nuclear Laboratory has been designed. The detector package consists of two position sensitive gas avalanche counters, a gas proportionality energy loss section, and a residual energy scintillator. This setup allows both particle identification and focal plane reconstruction. In this paper we will detail the construction of each section along with their accompanying electronics and data acquisition. Effects of energy loss throughout the detector, ray tracing procedures, and resolution as a function of fill pressure and bias voltage are also investigated. A measurement of the $^{27}\!$Al$(d,p)$ reaction is used to demonstrate detector performance and to illustrate a Bayesian method of energy calibration

Higgs vacuum decay and implications for the Standard Model

Ph. D. ThesisThe confirmed discovery of the Higgs boson in 2012 raises some intriguing cosmological questions about the fate of the false vacuum and what this means for the Standard Model. Quantum field theory allows for the existence of metastable fields where a potential develops a lower energy state, or true vacuum, at large field values where the energy is lower than its local minimum, or false vacuum, value. The most recent measurements of the Higgs and top masses suggest this is the case for the Higgs potential. A phase transition may occur through the process of quantum tunnelling, resulting in the nucleation of a rapidly expanding true vacuum bubble on a false vacuum background. Such a bubble may have devastating consequences for the universe if it expands to cover all of space. The fact that this has clearly not yet happened allows us to put constraints on our model for vacuum decay and provides insight into Beyond Standard Model physics. Using methods from Euclidean field theory, we find the tunnelling rates of toy model potentials as well as a close approximation to the Higgs in various spacetimes. We first investigate tunnelling in asymptotically at space before applying a similar method to false vacuum decay in de Sitter space, also incorporating the effects of back reaction. Two different potentials are considered to investigate vacuum decay in a Randall-Sundrum braneworld: a quartic potential with two well defined vacua, and a Higgs-like potential closely approximating the Higgs at high energies. Vacuum decay is studied for fields living on a 4-dimensional brane in RS2, and the presence of a fifth dimension is found to have little infuence on the decay rate. We further use these potentials to look at the case of vacuum decay seeded by the presence of a black hole in five dimensions. By comparing the tunnelling rate with the Hawking evaporation, it is found that small black holes at high energy scales can catalyse vacuum decay. The energy scales needed to form such black holes may potentially be reached in the most energetic of cosmic ray collisions. Finally, we look at the negative modes of O(4) and black hole instantons and find that instantons seeded by a black hole characteristically have a single negative mode. For O(4) instantons at energies close to the Planck scale, an infinite stack of negative modes arises, raising the question of how this is to be interpreted.Science and Technology Facilities Counci

Higgs vacuum decay in a braneworld

We examine the effect of large extra dimensions on vacuum decay in the Randall– Sundrum (RS) braneworld paradigm. We assume the scalar field is confined to the brane, and compute the probability for forming an “anti-de Sitter” (AdS) bubble inside a critical flat RS brane. We present the first full numerical solutions for the brane instanton considering two test potentials for the scalar field. We explore the geometrical impact of thin and thick bubble walls, and compute the instanton action in a range of cases. We conclude by commenting on a more physically realistic potential relevant for the Standard Model Higgs. For bubbles with large backreaction, the extra dimension has a dramatic effect on the tunnelling rate, however, for the weakly backreacting bubbles more relevant for realistic Standard Model potentials, the extra dimension has little impact