5,051 research outputs found
A keystone Methylobacterium strain in biofilm formation in drinking water
The structure of biofilms in drinking water systems is influenced by the interplay between
biological and physical processes. Bacterial aggregates in bulk fluid are important in seeding biofilm
formation on surfaces. In simple pure and co-cultures, certain bacteria, including Methylobacterium,
are implicated in the formation of aggregates. However, it is unclear whether they help to form
aggregates in complex mixed bacterial communities. Furthermore, different flow regimes could affect
the formation and destination of aggregates. In this study, real drinking water mixed microbial
communities were inoculated with the Methylobacterium strain DSM 18358. The propensity of
Methylobacterium to promote aggregation was monitored under both stagnant and flow conditions.
Under stagnant conditions, Methylobacterium enhanced bacterial aggregation even when it was
inoculated in drinking water at 1% relative abundance. Laminar and turbulent flows were developed
in a rotating annular reactor. Methylobacterium was found to promote a higher degree of aggregation
in turbulent than laminar flow. Finally, fluorescence in situ hybridisation images revealed that
Methylobacterium aggregates had distinct spatial structures under the different flow conditions.
Overall, Methylobacterium was found to be a key strain in the formation of aggregates in bulk water
and subsequently in the formation of biofilms on surfaces
Attitude determination of the spin-stabilized Project Scanner spacecraft
Attitude determination of spin-stabilized spacecraft using star mapping techniqu
Using Big Bang Nucleosynthesis to Extend CMB Probes of Neutrino Physics
We present calculations showing that upcoming Cosmic Microwave Background
(CMB) experiments will have the power to improve on current constraints on
neutrino masses and provide new limits on neutrino degeneracy parameters. The
latter could surpass those derived from Big Bang Nucleosynthesis (BBN) and the
observationally-inferred primordial helium abundance. These conclusions derive
from our Monte Carlo Markov Chain (MCMC) simulations which incorporate a full
BBN nuclear reaction network. This provides a self-consistent treatment of the
helium abundance, the baryon number, the three individual neutrino degeneracy
parameters and other cosmological parameters. Our analysis focuses on the
effects of gravitational lensing on CMB constraints on neutrino rest mass and
degeneracy parameter. We find for the PLANCK experiment that total (summed)
neutrino mass eV could be ruled out at or better.
Likewise neutrino degeneracy parameters and could be detected or ruled out at
confidence, or better. For POLARBEAR we find that the corresponding detectable
values are , , and , while for EPIC we obtain ,
, and . Our forcast for
EPIC demonstrates that CMB observations have the potential to set constraints
on neutrino degeneracy parameters which are better than BBN-derived limits and
an order of magnitude better than current WMAP-derived limits.Comment: 27 pages, 11 figures, matches published version in JCA
What is the probability that a random integral quadratic form in variables has an integral zero?
We show that the density of quadratic forms in variables over that are isotropic is a rational function of , where the rational
function is independent of , and we determine this rational function
explicitly. When real quadratic forms in variables are distributed
according to the Gaussian Orthogonal Ensemble (GOE) of random matrix theory, we
determine explicitly the probability that a random such real quadratic form is
isotropic (i.e., indefinite).
As a consequence, for each , we determine an exact expression for the
probability that a random integral quadratic form in variables is isotropic
(i.e., has a nontrivial zero over ), when these integral quadratic
forms are chosen according to the GOE distribution. In particular, we find an
exact expression for the probability that a random integral quaternary
quadratic form has an integral zero; numerically, this probability is
approximately .Comment: 17 pages. This article supercedes arXiv:1311.554
Revivification of confinement resonances in the photoionization of @C endohedral atoms far above thresholds
It is discovered theoretically that significant confinement resonances in an
photoionization of a \textit{multielectron} atom encaged in carbon
fullerenes, A@C, may re-appear and be strong at photon energies far
exceeding the ionization threshold, as a general phenomenon. The reasons
for this phenomenon are unraveled. The Ne photoionization of the
endohedral anion Ne@C in the photon energy region of about a
thousand eV above the threshold is chosen as case study.Comment: 3 pages, 1 figure, Revtex
On the resonance eigenstates of an open quantum baker map
We study the resonance eigenstates of a particular quantization of the open
baker map. For any admissible value of Planck's constant, the corresponding
quantum map is a subunitary matrix, and the nonzero component of its spectrum
is contained inside an annulus in the complex plane, . We consider semiclassical sequences of eigenstates, such that the
moduli of their eigenvalues converge to a fixed radius . We prove that, if
the moduli converge to , then the sequence of eigenstates
converges to a fixed phase space measure . The same holds for
sequences with eigenvalue moduli converging to , with a different
limit measure . Both these limiting measures are supported on
fractal sets, which are trapped sets of the classical dynamics. For a general
radius , we identify families of eigenstates with
precise self-similar properties.Comment: 32 pages, 2 figure
Renormalization of Quantum Anosov Maps: Reduction to Fixed Boundary Conditions
A renormalization scheme is introduced to study quantum Anosov maps (QAMs) on
a torus for general boundary conditions (BCs), whose number () is always
finite. It is shown that the quasienergy eigenvalue problem of a QAM for {\em
all} BCs is exactly equivalent to that of the renormalized QAM (with
Planck's constant ) at some {\em fixed} BCs that can
be of four types. The quantum cat maps are, up to time reversal, fixed points
of the renormalization transformation. Several results at fixed BCs, in
particular the existence of a complete basis of ``crystalline'' eigenstates in
a classical limit, can then be derived and understood in a simple and
transparent way in the general-BCs framework.Comment: REVTEX, 12 pages, 1 table. To appear in Physical Review Letter
Quantum graphs with singular two-particle interactions
We construct quantum models of two particles on a compact metric graph with
singular two-particle interactions. The Hamiltonians are self-adjoint
realisations of Laplacians acting on functions defined on pairs of edges in
such a way that the interaction is provided by boundary conditions. In order to
find such Hamiltonians closed and semi-bounded quadratic forms are constructed,
from which the associated self-adjoint operators are extracted. We provide a
general characterisation of such operators and, furthermore, produce certain
classes of examples. We then consider identical particles and project to the
bosonic and fermionic subspaces. Finally, we show that the operators possess
purely discrete spectra and that the eigenvalues are distributed following an
appropriate Weyl asymptotic law
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