Development of the Trident 1 aerodynamic saike mechanism

The Aerospike drag reduction mechanism was designed and developed for use on the Trident I submarine launched ballistic missile. This mechanism encounters a unique combination of environments necessitating unique design solutions to ensure satisfactory operation over its design life. The development of the Aerospike is reviewed emphasizing the unique and interesting problems encountered and their solutions

Enumeration of RNA structures by Matrix Models

We enumerate the number of RNA contact structures according to their genus, i.e. the topological character of their pseudoknots. By using a recently proposed matrix model formulation for the RNA folding problem, we obtain exact results for the simple case of an RNA molecule with an infinitely flexible backbone, in which any arbitrary pair of bases is allowed. We analyze the distribution of the genus of pseudoknots as a function of the total number of nucleotides along the phosphate-sugar backbone.Comment: RevTeX, 4 pages, 2 figure

Integration of simulated and true herbivory with an emphasis on rapidly deployed anti-herbivore silicon defences

Plants and herbivorous insects have been locked in an evolutionary arms race for over 300 million years. As a result, plants have evolved a plethora of defences against herbivory, many of which are triggered by herbivore-associated stimuli, including mechanical stimulation (e.g., vibrations from herbivore movement), tissue damage (wounding), chemical elicitation, and transmission of microbes (including pathogens). Understanding how these stimuli affect plant defences is confounded by the fact that herbivores introduce uncontrolled bias stemming from variation in feeding patterns, intensity of damage, and the introduction of biotic and abiotic signals in a non-standardised way. Simulated herbivory is often incorporated into studies to uncouple the relative impacts of herbivore-associated stimuli, glean mechanistic details regarding plant defences, and for standardisation purposes. Some plants, namely grasses, have evolved the ability to uptake Si from the soil and accumulate it throughout their aboveground tissues. The role of Si in plant ecology is complex, as it has proven beneficial for plants in the context of growth, reproduction, and mitigation of diverse environmental stressors. But perhaps one of the most apparent advantages of Si accumulation is its strong anti-herbivory quality. In grasses specifically, it has been suggested that Si plays a critical role in their ability to combat herbivore attack. Although Si is well known to mitigate the negative impacts of herbivory, there are many knowledge gaps regarding the temporal scales of induced Si-based resistance and the mechanisms behind Si accumulation and deposition. Using both simulated and authentic herbivory techniques, this work identifies the extent that Si is integrated into wider plant defence machinery, how rapidly Si defences can be effectively deployed, and how quickly plants develop resistance to herbivores once Si is supplied. Collectively, this PhD research highlights the importance of herbivore-specific signals in shaping plant defence responses and integrates simulated and true herbivory to yield a robust mechanistic understanding of the temporal scale at which Si-based defences, which are critical for resistance to herbivory, are deployed in a model grass. These findings could have implications for the way Si is utilised in agricultural systems and provide novel insights regarding potential evolutionary strategies evolved in grasses to utilise Si as an inducible defence in an analogous way to inducible specialised metabolites. Collectively these works provide novel evidence for the specified role of Si as an anti-herbivore defence in grasses and systematically identify the role of simulated herbivory in ecological research

Using Emotional Framing to Manipulate Anchoring Effect: How Affect Influences Judgment and Perception

The anchoring effect is a well-established phenomenon in psychology. It is a cognitive bias that causes an individual to rely too heavily on one piece of information, the anchor, when making decisions and forming judgments. Regardless of how arbitrary that piece of information is, an individual forms a bias that effects all following related information. The current study will investigate whether the anchoring effect can be reduced or even eliminated by using a novel manipulation, such as a frame of emotion. Participants will be recruited through Psychology subject pool. They will be asked to answer a series of simple math questions, followed by the framing questionnaire. The framing involves choices with negative or positive influences to statements probing individual’s characteristics and also what others perceive of those characteristics. The anchoring effect will then be assessed by asking a question with either a low or high anchor (for example, 17 and 63, for the correct answer of 40) to see whether the participant’s perception of their experience of the simple math questions is affected by the exposure to an emotional frame. Although it has not been determined through prior experiments exactly in what manner the framing will affect judgment, results reflect no influence on the perception of the situation, due to either negative or positive framing. However, the judgment of the person’s perception of the situation was consistent (and consistently high) throughout all conditions, regardless of how well their perception of the situation actually was. This will help further determine how emotion interacts with judgment and perception, while considering both the substance of the information and the emotional state of the individual engaging in memory formation

Some remarks on Kuzmin's theorem for F-expansions

AbstractIn this paper a general Kuzmin theorem for a class of multidimensional F-expansions is given. This result gives the uniform rate at which a certain sequence of approximates converges to the density of the invariant measure associated with an F-expansion. Some metric theorems are also given. This work extends and corrects some earlier results. The Jacobi algorithm is included as an example

Similarity-Detection and Localization

The detection of similarities between long DNA and protein sequences is studied using concepts of statistical physics. It is shown that mutual similarities can be detected by sequence alignment methods only if their amount exceeds a threshold value. The onset of detection is a continuous phase transition which can be viewed as a localization-delocalization transition. The ``fidelity'' of the alignment is the order parameter of that transition; it leads to criteria for the selection of optimal alignment parameters.Comment: 4 pages including 4 figures (308kb post-script file

The Adaptive Function of Masturbation in a Promiscuous African Ground Squirrel

Background: Studies of animal mating systems increasingly emphasize female multiple mating and cryptic sexual selection, particularly sperm competition. Males under intense sperm competition may manipulate sperm quantity and quality through masturbation, which could waste sperm and decrease fertility. I examined the factors influencing masturbation by male Cape ground squirrels (Xerus inauris) in light of a number of functional hypotheses. Methodology: Observational data on a marked population of squirrels were collected in east-central Namibia using scan and all-occurrences sampling. Findings: Masturbation was far more frequent on days of female oestrus and mostly occurred after copulation. Masturbation rates were higher in dominant males, which copulate more, than in subordinates and increased with number of mates a female accepts. Conclusions: These results suggest that masturbation in this species was not a response to sperm competition nor a sexual outlet by subordinates that did not copulate. Instead masturbation could function as a form of genital grooming. Female Cape ground squirrels mate with up to 10 males in a 3-hr oestrus, and by masturbating after copulation males could reduce the chance of infection. Sexually transmitted infections (STIs) can profoundly affect fertility, and their consequences for mating strategies need to be examined more fully

Nature of the glassy phase of RNA secondary structure

We characterize the low temperature phase of a simple model for RNA secondary structures by determining the typical energy scale E(l) of excitations involving l bases. At zero temperature, we find a scaling law E(l) \sim l^\theta with \theta \approx 0.23, and this same scaling holds at low enough temperatures. Above a critical temperature, there is a different phase characterized by a relatively flat free energy landscape resembling that of a homopolymer with a scaling exponent \theta=1. These results strengthen the evidence in favour of the existence of a glass phase at low temperatures.Comment: 7 pages, 1 figur

Model for Folding and Aggregation in RNA Secondary Structures

We study the statistical mechanics of RNA secondary structures designed to have an attraction between two different types of structures as a model system for heteropolymer aggregation. The competition between the branching entropy of the secondary structure and the energy gained by pairing drives the RNA to undergo a `temperature independent' second order phase transition from a molten to an aggregated phase'. The aggregated phase thus obtained has a macroscopically large number of contacts between different RNAs. The partition function scaling exponent for this phase is \theta ~ 1/2 and the crossover exponent of the phase transition is \nu ~ 5/3. The relevance of these calculations to the aggregation of biological molecules is discussed.Comment: Revtex, 4 pages; 3 Figures; Final published versio