Aquatic Phycomycetes Collected from the Athens State Hospital Ponds

Author Institution: Department of Botany, Ohio University, Athens, Ohi

Cosmological Constant in LQG Vertex Amplitude

A new q-deformation of the Euclidean EPRL/FK vertex amplitude is proposed by using the evaluation of the Vassiliev invariant associated with a 4-simplex graph (related to two copies of quantum SU(2) group at different roots of unity) embedded in a 3-sphere. We show that the large-j asymptotics of the q-deformed vertex amplitude gives the Regge action with a cosmological constant. In the end we also discuss its relation with a Chern-Simons theory on the boundary of 4-simplex.Comment: 6 pages, 5 figures, result and presentation improve

Finite Number of States, de Sitter Space and Quantum Groups at Roots of Unity

This paper explores the use of a deformation by a root of unity as a tool to build models with a finite number of states for applications to quantum gravity. The initial motivation for this work was cosmological breaking of supersymmetry. We explain why the project was unsuccessful. What is left are some observations on supersymmetry for q-bosons, an analogy between black holes in de Sitter and properties of quantum groups, and an observation on a noncommutative quantum mechanics model with two degrees of freedom, depending on one parameter. When this parameter is positive, the spectrum has a finite number of states; when it is negative or zero, the spectrum has an infinite number of states. This exhibits a desirable feature of quantum physics in de Sitter space, albeit in a very simple, non-gravitational context.Comment: 25 pages, 5 figure

Must naive realists be relationalists?

Relationalism maintains that perceptual experience involves, as part of its nature, a distinctive kind of conscious perceptual relation between a subject of experience and an object of experience. Together with the claim that perceptual experience is presentational, relationalism is widely believed to be a core aspect of the naive realist outlook on perception. This is a mistake. I argue that naive realism about perception can be upheld without a commitment to relationalism

General practitioners' perceptions of population based bowel screening and their influence on practice: a qualitative study

© 2017 The Author(s). Background: Although largely preventable, Australia has one of the highest rates of bowel cancer in the world. General Practitioners (GPs) have an important role to play in prevention and early detection of bowel cancer, however in Australia this is yet to be optimised and participation remains low. This study sought to understand how GPs' perceptions of bowel screening influence their attitudes to, and promotion of the faecal occult blood test (FOBT), to identify opportunities to enhance their role. Methods: Interviews were conducted with 31 GPs from metropolitan and regional New South Wales (NSW), Australia. Discussions canvassed GPs' perceptions of their role in bowel screening and the national screening program; perceptions of screening tests; practices regarding discussing screening with patients; and views on opportunities to enhance their role. Transcripts were coded using Nvivo and thematically analysed. Results: The study revealed GPs' perceptions of screening did not always align with broader public health definitions of 'population screening'. While many GPs reportedly understood the purpose of population screening, notions of the role of asymptomatic screening for bowel cancer prevention were more limited. Descriptions of screening centred on two major uses: the use of a screening 'process' to identify individual patients at higher risk; and the use of screening 'tools', including the FOBT, to aid diagnosis. While the FOBT was perceived as useful for identifying patients requiring follow up, GPs expressed concerns about its reliability. Colonoscopy by comparison, was considered by many as the gold standard for both screening and diagnosis. This perception reflects a conceptualisation of the screening process and associated tools as an individualised method for risk assessment and diagnosis, rather than a public health strategy for prevention of bowel cancer. Conclusion: The results show that GPs' perceptions of screening do not always align with broader public health definitions of 'population screening'. Furthermore, the way GPs understood screening was shown to impact their clinical practice, influencing their preferences for, and use of 'screening' tools such as FOBT. The findings suggest emphasising the preventative opportunity of FOBT screening would be beneficial, as would formally engaging GPs in the promotion of bowel screening

Spacetime as a Feynman diagram: the connection formulation

Spin foam models are the path integral counterparts to loop quantized canonical theories. In the last few years several spin foam models of gravity have been proposed, most of which live on finite simplicial lattice spacetime. The lattice truncates the presumably infinite set of gravitational degrees of freedom down to a finite set. Models that can accomodate an infinite set of degrees of freedom and that are independent of any background simplicial structure, or indeed any a priori spacetime topology, can be obtained from the lattice models by summing them over all lattice spacetimes. Here we show that this sum can be realized as the sum over Feynman diagrams of a quantum field theory living on a suitable group manifold, with each Feynman diagram defining a particular lattice spacetime. We give an explicit formula for the action of the field theory corresponding to any given spin foam model in a wide class which includes several gravity models. Such a field theory was recently found for a particular gravity model [De Pietri et al, hep-th/9907154]. Our work generalizes this result as well as Boulatov's and Ooguri's models of three and four dimensional topological field theories, and ultimately the old matrix models of two dimensional systems with dynamical topology. A first version of our result has appeared in a companion paper [gr-qc\0002083]: here we present a new and more detailed derivation based on the connection formulation of the spin foam models.Comment: 32 pages, 2 figure

Kinematics of elliptical galaxies with a diffuse dust component

Observations show that early-type galaxies contain a considerable amount of interstellar dust, most of which is believed to exist as a diffusely distributed component. We construct a four-parameter elliptical galaxy model in order to investigate the effects of such a smooth absorbing component on the projection of kinematic quantities, such as the line profiles and their moments. We investigate the dependence on the optical depth and on the dust geometry. Our calculations show that both the amplitude and the morphology of these quantities can be significantly affected. Dust effects should therefore be taken in consideration when interpreting photometric and kinematic properties, and correlations that utilize these quantities.Comment: 12 pages, 9 figures, accepted for publication in MNRA

``Sum over Surfaces'' form of Loop Quantum Gravity

We derive a spacetime formulation of quantum general relativity from (hamiltonian) loop quantum gravity. In particular, we study the quantum propagator that evolves the 3-geometry in proper time. We show that the perturbation expansion of this operator is finite and computable order by order. By giving a graphical representation a' la Feynman of this expansion, we find that the theory can be expressed as a sum over topologically inequivalent (branched, colored) 2d surfaces in 4d. The contribution of one surface to the sum is given by the product of one factor per branching point of the surface. Therefore branching points play the role of elementary vertices of the theory. Their value is determined by the matrix elements of the hamiltonian constraint, which are known. The formulation we obtain can be viewed as a continuum version of Reisenberger's simplicial quantum gravity. Also, it has the same structure as the Ooguri-Crane-Yetter 4d topological field theory, with a few key differences that illuminate the relation between quantum gravity and TQFT. Finally, we suggests that certain new terms should be added to the hamiltonian constraint in order to implement a ``crossing'' symmetry related to 4d diffeomorphism invariance.Comment: Seriously revised version. LaTeX, with revtex and epsfi

The inner kiloparsec of the jet in 3C264

We present new multi-frequency EVN, MERLIN and VLA observations of the radio source 3C264, sensitive to linear scales ranging from the parsec to several kiloparsecs. The observations confirm the existence of regions with different properties in the first kiloparsec of the jet. The most remarkable feature is the transition between a well collimated narrow jet at distances from the core below 80 pc, to a conical-shaped wide jet, with an opening angle of 20 degrees. Another change of properties, consisting of an apparent deflection of the jet ridge line and a diminution of the surface brightness, occurs at a distance of 300 pc from the core, coincident with the radius of a ring observed at optical wavelengths. Our observations add new pieces of information on the spectrum of the radio-optical jet of 3C264, with results consistent with a synchrotron emission mechanism and a spectrum break frequency in the infrared. Brightness profiles taken perpendicularly to the jet of 3C264 are consistent with a spine brightened jet at distances below 100 pc from the core, and an edge-brightened jet beyond, which can be interpreted as evidence of a transverse jet velocity structure. Our observations do not allow us to distinguish between the presence of a face--on dust and gas disk at the center of the host galaxy of 3C264, or rather an evacuated bubble. However, the properties of the jet structure, the changes in the polarization angle, and the plausible jet orientation can be naturally brought into agreement in the bubble scenario.Comment: 10 pages, 9 figures, accepted in A&