1,730 research outputs found
The Logarithmic Triviality of Compact QED Coupled to a Four Fermi Interaction
This is the completion of an exploratory study of Compact lattice Quantum
Electrodynamics with a weak four-fermi interaction and four species of massless
fermions. In this formulation of Quantum Electrodynamics massless fermions can
be simulated directly and Finite Size Scaling analyses can be performed at the
theory's chiral symmetry breaking critical point. High statistics simulations
on lattices ranging from to yield the equation of state, critical
indices, scaling functions and cumulants. The measurements are well fit with
the orthodox hypothesis that the theory is logarithmically trivial and its
continuum limit suffers from Landau's zero charge problem.Comment: 27 pages, 15 figues and 10 table
Family memories in the home: contrasting physical and digital mementos
We carried out fieldwork to characterise and compare physical and digital mementos in the home. Physical mementos are highly valued, heterogeneous and support different types of recollection. Contrary to expectations, we found physical mementos are not purely representational, and can involve appropriating common objects and more idiosyncratic forms. In contrast, digital mementos were initially perceived as less valuable, although participants later reconsidered this. Digital mementos were somewhat limited in function and expression, largely involving representational photos and videos, and infrequently accessed. We explain these digital limitations and conclude with design guidelines for digital mementos, including better techniques for accessing and integrating these into everyday life, allowing them to acquire the symbolic associations and lasting value that characterise their physical counterparts
Quantitative analysis of the morphological changes of the pubic symphyseal face and the auricular surface and implications for age at death estimation
YesAge estimation methods are often based on the age-related morphological changes of the auricular surface and the pubic bone. In this study, a mathematical approach to quantify these changes has been tested analyzing the curvature variation on 3D models from CT and laser scans. The sample consisted of the 24 SucheyâBrooks (SB) pubic bone casts, 19 auricular surfaces from the Buckberry and Chamberlain (BC) ârecording kitâ and 98 pelvic bones from the Terry Collection (Smithsonian Institution). Strong and moderate correlations between phases and curvature were found in SB casts (Ï 0.60â0.93) and BC ârecording kitâ (Ï 0.47â0.75), moderate and weak correlations in the Terry Collection bones (pubic bones: Ï 0.29â0.51, auricular surfaces: Ï 0.33â0.50) but associated with large individual variability and overlap of curvature values between adjacent decades. The new procedure, requiring no expert judgment from the operator, achieved similar correlations that can be found in the classic methods
Nucleosynthesis of Nickel-56 from Gamma-Ray Burst Accretion Disks
We examine the prospects for producing Nickel-56 from black hole accretion
disks, by examining a range of steady state disk models. We focus on relatively
slowly accreting disks in the range of 0.05 - 1 solar masses per second, as are
thought to be appropriate for the central engines of long-duration gamma-ray
bursts. We find that significant amounts of Nickel-56 are produced over a wide
range of parameter space. We discuss the influence of entropy, outflow
timescale and initial disk position on mass fraction of Nickel-56 which is
produced. We keep careful track of the weak interactions to ensure reliable
calculations of the electron fraction, and discuss the role of the neutrinos.Comment: 10 pages, 9 figure
Uncertainties in Îœp-process nucleosynthesis from Monte Carlo variation of reaction rates
It has been suggested that a Îœp-process can occur when hot, dense, and proton-rich matter is expanding within a strong flux of antineutrinos. In such an environment, proton-rich nuclides can be produced in sequences of proton captures and (n, p) reactions, where the free neutrons are created in situ by Îœe + p â n + e+ reactions. The detailed hydrodynamic evolution determines where the nucleosynthesis path turns off from N = Z line and how far up the nuclear chart it runs. In this work, the uncertainties on the final isotopic abundances stemming from uncertainties in the nuclear reaction rates were investigated in a large-scale Monte Carlo approach, simultaneously varying more than 10 000 reactions. A large range of model conditions was investigated because a definitive astrophysical site for the Îœp-process has not yet been identified. The present parameter study provides, for each model, identification of the key nuclear reactions dominating the uncertainty for a given nuclide abundance. As all rates appearing in the Îœp-process involve unstable nuclei, and thus only theoretical rates are available, the final abundance uncertainties are larger than those for nucleosynthesis processes closer to stability. Nevertheless, most uncertainties remain below a factor of 3 in trajectories with robust nucleosynthesis. More extreme conditions allow production of heavier nuclides but show larger uncertainties because of the accumulation of the uncertainties in many rates and because the termination of nucleosynthesis is not at equilibrium conditions. It is also found that the solar ratio of the abundances of 92Mo and 94Mo could be reproduced within uncertainties
The involvement of type IV pili and the phytochrome CphA in gliding motility, lateral motility and photophobotaxis of the cyanobacterium Phormidium lacuna
Phormidium lacuna is a naturally competent, filamentous cyanobacterium that belongs to the order Oscillatoriales. The filaments are motile on agar and other surfaces and display rapid lateral movements in liquid culture. Furthermore, they exhibit a photophobotactic response, a phototactic response towards light that is projected vertically onto the area covered by the culture. However, the molecular mechanisms underlying these phenomena are unclear. We performed the first molecular studies on the motility of an Oscillatoriales member. We generated mutants in which a kanamycin resistance cassette (KanR) was integrated in the phytochrome gene cphA and in various genes of the type IV pilin apparatus. pilM, pilN, pilQ and pilT mutants were defective in gliding motility, lateral movements and photophobotaxis, indicating that type IV pili are involved in all three kinds of motility. pilB mutants were only partially blocked in terms of their responses. pilB is the proposed ATPase for expelling of the filament in type IV pili. The genome reveals proteins sharing weak pilB homology in the ATPase region, these might explain the incomplete phenotype. The cphA mutant revealed a significantly reduced photophobotactic response towards red light. Therefore, our results imply that CphA acts as one of several photophobotaxis photoreceptors or that it could modulate the photophobotaxis response
Dynamical q-deformation in quantum theory and the stochastic limit
A model of particle interacting with quantum field is considered. The model
includes as particular cases the polaron model and non-relativistic quantum
electrodynamics. We show that the field operators obey q-commutation relations
with q depending on time. After the stochastic (or van Hove) limit, due to the
nonlinearity, the atomic and field degrees of freedom become entangled in the
sense that the field and the atomic variables no longer commute but give rise
to a new algebra with new commutation relations replacing the Boson ones. This
new algebra allows to give a simple proof of the fact that the non crossing
half-planar diagrams give the dominating contribution in a weak coupling regime
and to calculate explicitly the correlations associated to the new algebra. The
above results depend crucially on the fact that we do not introduce any dipole
or multipole approximation.Comment: Latex, 11 page
Effect of side-chain asymmetry on the intermolecular structure and order-disorder transition in alkyl-substituted polyfluorenes
We study relations among the side-chain asymmetry, structure, and order-disorder transition (ODT) in hairy-rod-type poly(9,9-dihexylfluorene) (PF6) with two identical side chains and atactic poly(9-octyl-9-methylfluorene) (PF1-8) with two different side chains per repeat. PF6 and PF1-8 organize into alternating side-chain and backbone layers that transform into an isotropic phase at T-ODT(PF6) and T-bi(ODT)(PF1-8). We interpret polymers in terms of monodisperse and bidisperse brushes and predict scenarios T-ODT <T-bi(ODT) and T-ODT similar to T-bi(ODT) for high and low grafting densities (the side-chain length above or below the average grafting distance). Calorimetry and x-ray scattering indicate the condition T-ODT(PF6) similar to T-bi(ODT)(PF1-8) following the low grafting prediction. PF6 side chains coming from the alternating backbone layers appear as two separate layers with thickness H(PF6), whereas PF1-8 side chains appear as an indistinguishable bilayer with a half thickness H-bilayer(PF1-8)/2 approximate to H(PF6). The low grafting density region is structurally possible but not certain for PF6 and confirmed for PF1-8.Peer reviewe
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