1,549 research outputs found
Presence of Legionellaceae in warm water supplies and typing of strains by polymerase chain reaction
Outbreaks of Legionnaire's disease present a public health challenge especially because fatal outcomes still remain frequent. The aim of this study was to describe the abundance and epidemiology of Legionellaceae in the human-made environment. Water was sampled from hot-water taps in private and public buildings across the area of Göttingen, Germany, including distant suburbs. Following isolation, we used polymerase chain reaction in order to generate strain specific banding profiles of legionella isolates. In total, 70 buildings were examined. Of these 18 (26%) had the bacterium in at least one water sample. Legionella pneumophila serogroups 1, 4, 5 and 6 could be identified in the water samples. Most of the buildings were colonized solely by one distinct strain, as proven by PCR. In three cases equal patterns were found in separate buildings. There were two buildings in this study where isolates with different serogroups were found at the same time
Interacting Crumpled Manifolds: Exact Results to all Orders of Perturbation Theory
In this letter, we report progress on the field theory of polymerized
tethered membranes. For the toy-model of a manifold repelled by a single point,
we are able to sum the perturbation expansion in the strength g of the
interaction exactly in the limit of internal dimension D -> 2. This exact
solution is the starting point for an expansion in 2-D, which aims at
connecting to the well studied case of polymers (D=1). We here give results to
order (2-D)^4, where again all orders in g are resummed. This is a first step
towards a more complete solution of the self-avoiding manifold problem, which
might also prove valuable for polymers.Comment: 8 page
Random RNA under tension
The Laessig-Wiese (LW) field theory for the freezing transition of random RNA
secondary structures is generalized to the situation of an external force. We
find a second-order phase transition at a critical applied force f = f_c. For f
f_c, the extension L as a function of
pulling force f scales as (f-f_c)^(1/gamma-1). The exponent gamma is calculated
in an epsilon-expansion: At 1-loop order gamma = epsilon/2 = 1/2, equivalent to
the disorder-free case. 2-loop results yielding gamma = 0.6 are briefly
mentioned. Using a locking argument, we speculate that this result extends to
the strong-disorder phase.Comment: 6 pages, 10 figures. v2: corrected typos, discussion on locking
argument improve
Systematic Low-Energy Effective Field Theory for Magnons and Holes in an Antiferromagnet on the Honeycomb Lattice
Based on a symmetry analysis of the microscopic Hubbard and t-J models, a
systematic low-energy effective field theory is constructed for hole-doped
antiferromagnets on the honeycomb lattice. In the antiferromagnetic phase,
doped holes are massive due to the spontaneous breakdown of the
symmetry, just as nucleons in QCD pick up their mass from spontaneous chiral
symmetry breaking. In the broken phase the effective action contains a
single-derivative term, similar to the Shraiman-Siggia term in the square
lattice case. Interestingly, an accidental continuous spatial rotation symmetry
arises at leading order. As an application of the effective field theory we
consider one-magnon exchange between two holes and the formation of two-hole
bound states. As an unambiguous prediction of the effective theory, the wave
function for the ground state of two holes bound by magnon exchange exhibits
-wave symmetry.Comment: 33 pages, 6 figure
Interacting crumpled manifolds
In this article we study the effect of a delta-interaction on a polymerized
membrane of arbitrary internal dimension D. Depending on the dimensionality of
membrane and embedding space, different physical scenarios are observed. We
emphasize on the difference of polymers from membranes. For the latter,
non-trivial contributions appear at the 2-loop level. We also exploit a
``massive scheme'' inspired by calculations in fixed dimensions for scalar
field theories. Despite the fact that these calculations are only amenable
numerically, we found that in the limit of D to 2 each diagram can be evaluated
analytically. This property extends in fact to any order in perturbation
theory, allowing for a summation of all orders. This is a novel and quite
surprising result. Finally, an attempt to go beyond D=2 is presented.
Applications to the case of self-avoiding membranes are mentioned
Microscopic Model versus Systematic Low-Energy Effective Field Theory for a Doped Quantum Ferromagnet
We consider a microscopic model for a doped quantum ferromagnet as a test
case for the systematic low-energy effective field theory for magnons and
holes, which is constructed in complete analogy to the case of quantum
antiferromagnets. In contrast to antiferromagnets, for which the effective
field theory approach can be tested only numerically, in the ferromagnetic case
both the microscopic and the effective theory can be solved analytically. In
this way the low-energy parameters of the effective theory are determined
exactly by matching to the underlying microscopic model. The low-energy
behavior at half-filling as well as in the single- and two-hole sectors is
described exactly by the systematic low-energy effective field theory. In
particular, for weakly bound two-hole states the effective field theory even
works beyond perturbation theory. This lends strong support to the quantitative
success of the systematic low-energy effective field theory method not only in
the ferromagnetic but also in the physically most interesting antiferromagnetic
case.Comment: 34 pages, 1 figur
Phase transitions of a tethered surface model with a deficit angle term
Nambu-Goto model is investigated by using the canonical Monte Carlo
simulations on fixed connectivity surfaces of spherical topology. Three
distinct phases are found: crumpled, tubular, and smooth. The crumpled and the
tubular phases are smoothly connected, and the tubular and the smooth phases
are connected by a discontinuous transition. The surface in the tubular phase
forms an oblong and one-dimensional object similar to a one-dimensional linear
subspace in the Euclidean three-dimensional space R^3. This indicates that the
rotational symmetry inherent in the model is spontaneously broken in the
tubular phase, and it is restored in the smooth and the crumpled phases.Comment: 6 pages with 6 figure
Systematic Low-Energy Effective Field Theory for Electron-Doped Antiferromagnets
In contrast to hole-doped systems which have hole pockets centered at , in lightly electron-doped antiferromagnets
the charged quasiparticles reside in momentum space pockets centered at
or . This has important consequences for
the corresponding low-energy effective field theory of magnons and electrons
which is constructed in this paper. In particular, in contrast to the
hole-doped case, the magnon-mediated forces between two electrons depend on the
total momentum of the pair. For the one-magnon exchange
potential between two electrons at distance is proportional to ,
while in the hole case it has a dependence. The effective theory
predicts that spiral phases are absent in electron-doped antiferromagnets.Comment: 25 pages, 7 figure
Field Theory of the RNA Freezing Transition
Folding of RNA is subject to a competition between entropy, relevant at high
temperatures, and the random, or random looking, sequence, determining the low-
temperature phase. It is known from numerical simulations that for random as
well as biological sequences, high- and low-temperature phases are different,
e.g. the exponent rho describing the pairing probability between two bases is
rho = 3/2 in the high-temperature phase, and approximatively 4/3 in the
low-temperature (glass) phase. Here, we present, for random sequences, a field
theory of the phase transition separating high- and low-temperature phases. We
establish the existence of the latter by showing that the underlying theory is
renormalizable to all orders in perturbation theory. We test this result via an
explicit 2-loop calculation, which yields rho approximatively 1.36 at the
transition, as well as diverse other critical exponents, including the response
to an applied external force (denaturation transition).Comment: 96 pages, 188 figures. v2: minor correction
First-order phase transition in the tethered surface model on a sphere
We show that the tethered surface model of Helfrich and Polyakov-Kleinert
undergoes a first-order phase transition separating the smooth phase from the
crumpled one. The model is investigated by the canonical Monte Carlo
simulations on spherical and fixed connectivity surfaces of size up to N=15212.
The first-order transition is observed when N>7000, which is larger than those
in previous numerical studies, and a continuous transition can also be observed
on small-sized surfaces. Our results are, therefore, consistent with those
obtained in previous studies on the phase structure of the model.Comment: 6 pages with 7 figure
- …