818 research outputs found
Modelling the Response of Reef Rugosity and Fish Assemblages to Climate Change in the Caribbean
Sigma-model soliton intersections from exceptional calibrations
A first-order `BPS' equation is obtained for 1/8 supersymmetric intersections
of soliton-membranes (lumps) of supersymmetric (4+1)-dimensional massless sigma
models, and a special non-singular solution is found that preserves 1/4
supersymmetry. For 4-dimensional hyper-K\"ahler target spaces () the BPS
equation is shown to be the low-energy limit of the equation for a
Cayley-calibrated 4-surface in \bE^4\times HK_4. Similar first-order
equations are found for stationary intersections of Q-lump-membranes of the
massive sigma model, but now generic solutions preserve either 1/8
supersymmetry or no supersymmetry, depending on the time orientation.Comment: 21 pages. Version 3: Minor corrections and one further reference:
version published in JHE
Anti-field Formalism and Non-Abelian Duality
The act of implementing non-Abelian duality in two dimensional sigma models
results unavoidably in an additional reducible symmetry. The Batalin-Vilkovisky
formalism is employed to handle this new symmetry. Valuable lessons are learnt
here with respect to non-Abelian duality. We emphasise, in particular, the
effects of the ghost sector corresponding to this symmetry on non-Abelian
duality.Comment: 13 pages, LaTeX2
The shock compression of microorganism-loaded broths and emulsions: Experiments and simulations
By carefully selecting flyer plate thickness and the geometry of a target capsule for
bacterial broths and emulsions, we have successfully subjected the contents of the capsule to
simultaneous shock and dynamic compression when subjected to a flyer-plate impact
experiment. The capsules were designed to be recovered intact so that post experimental
analysis could be done on the contents. ANSYS® AUTODYN hydrocode simulations were
carried out to interrogate the deformation of the cover plate and the wave propagation in the
fluid. Accordingly, we have shown that microorganisms such as Escherichia coli,
Enterococcus faecalis and Zygosaccharomyces bailii are not affected by this type of loading
regime. However, by introducing a cavity behind the broth we were able to observe limited
kill in the yeast sample. Further, on using this latter technique with emulsions it was shown
that greater emulsification of an oil-based emulsion occurred due to the cavitation that was
introduced
Long range absorption in the scattering of 6He on 208Pb and 197Au at 27 MeV
Quasi-elastic scattering of 6He at E_lab=27 MeV from 197Au has been measured
in the angular range of 6-72 degrees in the laboratory system employing LEDA
and LAMP detection systems. These data, along with previously analysed data of
6He + 208Pb at the same energy, are analyzed using Optical Model calculations.
The role of Coulomb dipole polarizability has been investigated. Large
imaginary diffuseness parameters are required to fit the data. This result is
an evidence for long range absorption mechanisms in 6He induced reactions.Comment: 10 pages, 10 figures, minor corrections. To appear in Nucl. Phys.
Resummation of the Divergent Perturbation Series for a Hydrogen Atom in an Electric Field
We consider the resummation of the perturbation series describing the energy
displacement of a hydrogenic bound state in an electric field (known as the
Stark effect or the LoSurdo-Stark effect), which constitutes a divergent formal
power series in the electric field strength. The perturbation series exhibits a
rich singularity structure in the Borel plane. Resummation methods are
presented which appear to lead to consistent results even in problematic cases
where isolated singularities or branch cuts are present on the positive and
negative real axis in the Borel plane. Two resummation prescriptions are
compared: (i) a variant of the Borel-Pade resummation method, with an
additional improvement due to utilization of the leading renormalon poles (for
a comprehensive discussion of renormalons see [M. Beneke, Phys. Rep. vol. 317,
p. 1 (1999)]), and (ii) a contour-improved combination of the Borel method with
an analytic continuation by conformal mapping, and Pade approximations in the
conformal variable. The singularity structure in the case of the LoSurdo-Stark
effect in the complex Borel plane is shown to be similar to (divergent)
perturbative expansions in quantum chromodynamics.Comment: 14 pages, RevTeX, 3 tables, 1 figure; numerical accuracy of results
enhanced; one section and one appendix added and some minor changes and
additions; to appear in phys. rev.
Effects of impurities and vortices on the low-energy spin excitations in high-Tc materials
We review a theoretical scenario for the origin of the spin-glass phase of
underdoped cuprate materials. In particular it is shown how disorder in a
correlated d-wave superconductor generates a magnetic phase by inducing local
droplets of antiferromagnetic order which eventually merge and form a
quasi-long range ordered state. When correlations are sufficiently strong,
disorder is unimportant for the generation of static magnetism but plays an
additional role of pinning disordered stripe configurations. We calculate the
spin excitations in a disordered spin-density wave phase, and show how disorder
and/or applied magnetic fields lead to a slowing down of the dynamical spin
fluctuations in agreement with neutron scattering and muon spin rotation (muSR)
experiments.Comment: 4 pages, 3 figures, submitted for SNS2010 conference proceeding
BF models, Duality and Bosonization on higher genus surfaces
The generating functional of two dimensional field theories coupled to
fermionic fields and conserved currents is computed in the general case when
the base manifold is a genus g compact Riemann surface. The lagrangian density
is written in terms of a globally defined 1-form and a
multi-valued scalar field . Consistency conditions on the periods of
have to be imposed. It is shown that there exist a non-trivial dependence of
the generating functional on the topological restrictions imposed to . In
particular if the periods of the field are constrained to take values , with any integer, then the partition function is independent of the
chosen spin structure and may be written as a sum over all the spin structures
associated to the fermions even when one started with a fixed spin structure.
These results are then applied to the functional bosonization of fermionic
fields on higher genus surfaces. A bosonized form of the partition function
which takes care of the chosen spin structure is obtainedComment: 17 page
Three years with the World Register of marine Cave Species (WoRCS) initiative: current status and future perspectives
Characterization of a Mixed Methanotrophic Culture Capable of Chloroethylene Degradation
A consortium of methanotrophs cultured from the St. Joseph's aquifer in Schoolcraft, MI, was found to exhibit similar methane consumption rates as pure cultures of methanotrophs. The methanotrophic consortium resides within a portion of the aquifer contaminated with a mixed waste plume of perchloroethylene (PCE) and its reductive dechlorination products from natural attenuation, trichloroethylene (TCE), cis-dichloroethylene (c-DCE), and vinyl chloride (VC). Oxidation kinetics for TCE, c-DCE, and VC were measured for the mixed methanotroph consortium and compared to reported rate parameters for degradation of these chloroethylene compounds by pure methanotrophic cultures. The results demonstrate that the kinetics of chloroethylene oxidation by the Schoolcraft methanotroph population mimic the degradation rates of pure methanotrophic cultures that primarily express particulate methane monooxygenase (pMMO). Molecular and biochemical analyses confirmed that sMMO was not being expressed by these cells. Rather, using competitive reverse transcriptionpolymerase chain reaction, pmoA, a gene encoding one of the polypeptides of the pMMO was found at a level of (1.57 ± 0.10) × 10–17 mol pmoA mRNA/g wet soil in soil slurries and (2.65 ± 0.43) × 10–17 mol pmoA mRNA/μl in groundwater. No expression of mmoX, a gene encoding one of the polypeptides of the sMMO, was detected.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63398/1/ees.2005.22.177.pd
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