2,625 research outputs found
Ray-Singer Torsion, Topological field theories and the Riemann zeta function at s=3
Starting with topological field theories we investigate the Ray-Singer
analytic torsion in three dimensions. For the lens Spaces L(p;q) an explicit
analytic continuation of the appropriate zeta functions is contructed and
implemented. Among the results obtained are closed formulae for the individual
determinants involved, the large behaviour of the determinants and the
torsion, as well as an infinite set of distinct formulae for zeta(3): the
ordinary Riemann zeta function evaluated at s=3.
The torsion turns out to be trivial for the cases L(6,1), L((10,3) and
L(12,5) and is, in general, greater than unity for large p and less than unity
for a finite number of p and q.Comment: 10 page
BRST Quantisation and the Product Formula for the Ray-Singer Torsion
We give a quantum field theoretic derivation of the formula obeyed by the
Ray-Singer torsion on product manifolds. Such a derivation has proved elusive
up to now. We use a BRST formalism which introduces the idea of an infinite
dimensional Universal Gauge Fermion, and is of independent interest being
applicable to situations other than the ones considered here. We are led to a
new class of Fermionic topological field theories. Our methods are also
applicable to combinatorially defined manifolds and methods of discrete
approximation such as the use of a simplicial lattice or finite elements. The
topological field theories discussed provide a natural link between the
combinatorial and analytic torsion.Comment: 24 pages. TEX error of first version corrected: a \input is delete
An insight into the impact of arable farming on Irish biodiversity: A scarcity of studies hinders a rigorous assessment
peer-reviewedTo help understand and counteract future agronomic challenges to farmland biodiversity, it is essential to know how present farming practices have affected biodiversity on Irish farms. We present
an overview of existing research data and conclusions, describing the impact of crop cultivation on biodiversity on Irish arable farms. An extensive literature review clearly indicates that peer-reviewed
publications on research conducted in Ireland on this topic are quite scarce: just 21 papers investigating the effect of conventional crop cultivation on Irish biodiversity have been published
within the past 30 years. Principally, these studies have concluded that conventional crop cultivation has had an adverse impact on biodiversity on Irish farms, with 15 of the 21 studies demonstrating negative trends for the taxa investigated. Compared to other EU states, the relative dearth of baseline
data and absence of monitoring programmes designed to assess the specific impacts of crop cultivation on Irish biodiversity highlight the need to develop long-term research studies. With many new challenges facing Irish agriculture, a research programme must be initiated to measure
current levels of biodiversity on arable land and to assess the main farming âpressuresâ causing significant biodiversity loss or gains in these systems.This work was funded under the EPA ERTDI
Research Programme (Grant 2006-B-MS-46)
Processing, microstructure, and properties of engineered diboride structures
The mechanical properties and processing parameters of boride ceramics in foam and laminate architectures were evaluated. The ceramic reticulated foam was produced through a polymer substrate replication technique and the hardness and compressive strength were tested. The laminate structure was tested to evaluate the flexure strength and work of fracture as a function of temperature.
The foam architecture was produced using a TiB2 slurry coating on a polyurethane reticulated foam preform. Foams sintered to 2150â°C displayed an average grain size of 8.9 ± 7.3 ”m, and a hardness of 17.3 ± 2.4 GPa. Crush testing foams were sintered at 1975â°C, and displayed a specific strength of 208 ± 63 kPa with an overall porosity of 97%. For these specimens, it is likely that microcracking lowered the hardness, but the overall strength was controlled by the bulk density.
The laminate structures were fabricated using alternating layers of ZrB2 and C--10 vol% ZrB2. The structures were fabricated through the shaping of ceramic loaded thermoplastic polymers that underwent burnout and hot pressing cycles. These specimens had strong phase ZrB2 layers that were about 150 ”m thick alternating with weak phase layers that were about 20 ”m thick. Specimens exhibited a maximum flexure strength of 311 ± 10 MPa at 1600â°C, and an increased work of fracture compared to conventional ZrB2 ceramics. The maximum fraction of inelastic work of fracture occurred at room temperature, and decreased as temperature increased. This was reflected in the length of the crack path through the specimen. Deflected cracks travelled through the center of the C--ZrB2 layers in the material in Mode II fracture --Abstract, page iv
Predicting and optimising the postoperative outcomes of sagittal craniosynostosis correction
The neonate skull consists of several flat bones, connected by fibrous joints called sutures. Sutures regulate the bone formation along their adjoining edges, while providing mailability to assist with the early phases of rapid brain growth and passing through the birth canal with minimal restriction. By adolescents, these sutures fuse into solid bone, protecting the brain from impacts. The premature fusion of one or more of these sutures is a medical condition known as craniosynostosis, with its most common form being sagittal craniosynostosis (fusion of the midline suture). The condition results in compensatory overgrowth perpendicular to the fused suture, leading to calvarial deformation and possible neurofunctional defects. Surgeons have developed several surgical techniques to restore the normative shape. This has led to debates as to which surgical option provides the most beneficial long term outcome.
The overall aim of this thesis was to develop a computational approach using the finite element (FE) method capable of predicting and optimising the long term outcomes for treating sagittal craniosynostosis. A generic 3D pre-operative FE model was developed using patient specific CT data. The FE model was parameterised to predict the long term calvarial growth, the pattern of suture and bone formation, the pattern of bone healing across the replicated surgical techniques, and the changes in contact pressure levels across the modelled brain. All techniques underwent simulated growth up to the maximum age of 76 months. Morphological results were compared against the patient specific CT data at the same age. Where absent, technique specific follow up CT data were used instead.
Results highlighted a good morphological agreement between the predicted models and their comparative CT data. The FE model was highly sensitive to the choice of input parameters. Based on the findings of this thesis, the *** approach proved the most optimal across the predicted outcomes. The novel methodology and platform developed here has huge potential to better inform surgeons of the impact various techniques could have on long term outcomes and continue to improve the quality of care for patients undergoing corrective surgery
Electronic Bulletin Boards for Business, Education and Leisure
Electronic communication is one example of how technology is impacting and changing lifestyles. The result of this technology is one of benefiting the individual, especially since the cost of this technology is within the reach of most families
Dynamic Shape Synthesis in Posterior Inferotemporal Cortex
SummaryHow does the brain synthesize low-level neural signals for simple shape parts into coherent representations of complete objects? Here, we present evidence for a dynamic process of object part integration in macaque posterior inferotemporal cortex (IT). Immediately after stimulus onset, neural responses carried information about individual object parts (simple contour fragments) only. Subsequently, information about specific multipart configurations emerged, building gradually over the course of âŒ60 ms, producing a sparser and more explicit representation of object shape. We show that this gradual transformation can be explained by a recurrent network process that effectively compares parts signals across neurons to generate inferences about multipart shape configurations
STEM graduates in non STEM jobs (BIS Research Paper number 30)
"This report documents extensive new research, commissioned by the Department for
Business, Innovation & Skills (BIS) in 2009, into the early careers and career decisions of
STEM (Science, Technology, Engineering and Mathematics) students and graduates in order
to understand why many elect not to enter STEM occupations and/or STEM employment
sectors and what influences these career choices." - Page 13
A definitive merger-AGN connection at z~0 with CFIS: mergers have an excess of AGN and AGN hosts are more frequently disturbed
The question of whether galaxy mergers are linked to the triggering of active
galactic nuclei (AGN) continues to be a topic of considerable debate. The issue
can be broken down into two distinct questions: 1) Can galaxy mergers trigger
AGN? 2) Are galaxy mergers the dominant AGN triggering mechanism? A complete
picture of the AGN-merger connection requires that both of these questions are
addressed with the same dataset. In previous work, we have shown that galaxy
mergers selected from the Sloan Digital Sky Survey (SDSS) show an excess of
both optically-selected, and mid-IR colour-selected AGN, demonstrating that the
answer to the first of the above questions is affirmative. Here, we use the
same optical and mid-IR AGN selection to address the second question, by
quantifying the frequency of morphological disturbances in low surface
brightness r-band images from the Canada France Imaging Survey (CFIS). Only ~30
per cent of optical AGN host galaxies are morphologically disturbed, indicating
that recent interactions are not the dominant trigger. However, almost 60 per
cent of mid-IR AGN hosts show signs of visual disturbance, indicating that
interactions play a more significant role in nuclear feeding. Both mid-IR and
optically selected AGN have interacting fractions that are a factor of two
greater than a mass and redshift matched non-AGN control sample, an excess that
increases with both AGN luminosity and host galaxy stellar mass.Comment: Accepted for publication in MNRA
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