5,053 research outputs found
Subfactors of index less than 5, part 1: the principal graph odometer
In this series of papers we show that there are exactly ten subfactors, other
than subfactors, of index between 4 and 5. Previously this
classification was known up to index . In the first paper we give
an analogue of Haagerup's initial classification of subfactors of index less
than , showing that any subfactor of index less than 5 must appear
in one of a large list of families. These families will be considered
separately in the three subsequent papers in this series.Comment: 36 pages (updated to reflect that the classification is now complete
How do field of view and resolution affect the information content of panoramic scenes for visual navigation? A computational investigation
The visual systems of animals have to provide information to guide behaviour and the informational requirements of an animal’s behavioural repertoire are often reflected in its sensory system. For insects, this is often evident in the optical array of the compound eye. One behaviour that insects share with many animals is the use of learnt visual information for navigation. As ants are expert visual navigators it may be that their vision is optimised for navigation. Here we take a computational approach in asking how the details of the optical array influence the informational content of scenes used in simple view matching strategies for orientation. We find that robust orientation is best achieved with low-resolution visual information and a large field of view, similar to the optical properties seen for many ant species. A lower resolution allows for a trade-off between specificity and generalisation for stored views. Additionally, our simulations show that orientation performance increases if different portions of the visual field are considered as discrete visual sensors, each giving an independent directional estimate. This suggests that ants might benefit by processing information from their two eyes independently
Cladding mode coupling in highly localized fiber Bragg gratings: modal properties and transmission spectra
The spectral characteristics of a fiber Bragg grating (FBG) with a
transversely inhomogeneous refractive index profile, differs con- siderably
from that of a transversely uniform one. Transmission spectra of inhomogeneous
and asymmetric FBGs that have been inscribed with focused ultrashort pulses
with the so-called point-by-point technique are investigated. The cladding mode
resonances of such FBGs can span a full octave in the spectrum and are very
pronounced (deeper than 20dB). Using a coupled-mode approach, we compute the
strength of resonant coupling and find that coupling into cladding modes of
higher azimuthal order is very sensitive to the position of the modification in
the core. Exploiting these properties allows precise control of such
reflections and may lead to many new sensing applications.Comment: Submission to OE, 16 pages, 6 figure
Boundary Limitation of Wavenumbers in Taylor-Vortex Flow
We report experimental results for a boundary-mediated wavenumber-adjustment
mechanism and for a boundary-limited wavenumber-band of Taylor-vortex flow
(TVF). The system consists of fluid contained between two concentric cylinders
with the inner one rotating at an angular frequency . As observed
previously, the Eckhaus instability (a bulk instability) is observed and limits
the stable wavenumber band when the system is terminated axially by two rigid,
non-rotating plates. The band width is then of order at small
() and agrees well with
calculations based on the equations of motion over a wide -range.
When the cylinder axis is vertical and the upper liquid surface is free (i.e.
an air-liquid interface), vortices can be generated or expelled at the free
surface because there the phase of the structure is only weakly pinned. The
band of wavenumbers over which Taylor-vortex flow exists is then more narrow
than the stable band limited by the Eckhaus instability. At small
the boundary-mediated band-width is linear in . These results are
qualitatively consistent with theoretical predictions, but to our knowledge a
quantitative calculation for TVF with a free surface does not exist.Comment: 8 pages incl. 9 eps figures bitmap version of Fig
Noncommutative Quantum Cosmology
We propose a model for noncommutative quantum cosmology by means of a
deformation of minisuperspace. For the Kantowski-Sachs metric we are able to
find the exact wave function. We construct wave packets and show that new
quantum states that ``compete'' to be the most probable state appear, in clear
contrast with the commutative case. A tunneling process could be possible among
these states.Comment: 5 pages, 5 figures, revtex4 file, major style changes, to be
published in PR
Influence of operating parameters on the biodegradation of steroid estrogens and nonylphenolic compounds during biological wastewater treatment processes
This document is the unedited author's version of a Submitted Work that was subsequently accepted for
publication in Environmental Science & Technology, copyright © American Chemical Society after peer
review. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/es901612v.This study investigated operational factors influencing the removal of steroid estrogens and nonylphenolic compounds in two sewage treatment works, one a nitrifying/denitrifying activated sludge plant and the other a nitrifying/denitrifying activated sludge plant with phosphorus removal. Removal efficiencies of >90% for steroid estrogens and for longer chain nonylphenol ethoxylates (NP4−12EO) were observed at both works, which had equal sludge ages of 13 days. However, the biological activity in terms of milligrams of estrogen removed per day per tonne of biomass was found to be 50−60% more efficient in the nitrifying/denitrifying activated sludge works compared to the works which additionally incorporated phosphorus removal. A temperature reduction of 6 °C had no impact on the removal of free estrogens, but removal of the conjugated estrone-3-sulfate was reduced by 20%. The apparent biomass sorption (LogKp) values were greater in the nitrifying/denitrifying works than those in the nitrifying/denitrifying works with phosphorus removal for both steroid estrogens and nonylphenolic compounds possibly indicating a different cell surface structure and therefore microbial population. The difference in biological activity (mg tonne−1 d−1) identified in this study, of up to seven times, suggests that there is the potential for enhancing the removal of estrogens and nonylphenols if more detailed knowledge of the factors responsible for these differences can be identified and maximized, thus potentially improving the quality of receiving waters.Public Utilities Board (Singapore), Anglian Water Ltd, Severn Trent Water Ltd, Thames Water Utilities Ltd, United Utilities 393 Plc and Yorkshire Water Services
Shining Light on Merging Galaxies I: The Ongoing Merger of a Quasar with a `Green Valley' Galaxy
Serendipitous observations of a pair z = 0.37 interacting galaxies (one
hosting a quasar) show a massive gaseous bridge of material connecting the two
objects. This bridge is photoionized by the quasar (QSO) revealing gas along
the entire projected 38 kpc sightline connecting the two galaxies. The emission
lines that result give an unprecedented opportunity to study the merger process
at this redshift. We determine the kinematics, ionization parameter (log U ~
-2.5 +- 0.03), column density (N_H ~ 10^{21} cm^{-2}), metallicity ([M/H] ~
-0.20 +- 0.15), and mass (~ 10^8 Msun) of the gaseous bridge. We simultaneously
constrain properties of the QSO-host (M_DM>8.8x 10^{11} Msun) and its companion
galaxy (M_DM>2.1 x 10^{11} Msun; M_star ~ 2 x 10^{10} Msun; stellar burst
age=300-800 Myr; SFR~6 Msun/yr; and metallicity 12+log (O/H)= 8.64 +- 0.2). The
general properties of this system match the standard paradigm of a
galaxy-galaxy merger caught between first and second passage while one of the
galaxies hosts an active quasar. The companion galaxy lies in the so-called
`green valley', with a stellar population consistent with a recent starburst
triggered during the first passage of the merger and has no detectable AGN
activity. In addition to providing case-studies of quasars associated with
galaxy mergers, quasar/galaxy pairs with QSO-photoionized tidal bridges such as
this one offer unique insights into the galaxy properties while also
distinguishing an important and inadequately understood phase of galaxy
evolution.Comment: 23 pages, 12 figures, 5 tables, Submitted to ApJ, revised to address
referee's comment
TLR7-mediated skin inflammation remotely triggers chemokine expression and leukocyte accumulation in the brain
Background:
The relationship between the brain and the immune system has become increasingly topical as, although it is immune-specialised, the CNS is not free from the influences of the immune system. Recent data indicate that peripheral immune stimulation can significantly affect the CNS. But the mechanisms underpinning this relationship remain unclear. The standard approach to understanding this relationship has relied on systemic immune activation using bacterial components, finding that immune mediators, such as cytokines, can have a significant effect on brain function and behaviour. More rarely have studies used disease models that are representative of human disorders.
Methods:
Here we use a well-characterised animal model of psoriasis-like skin inflammation—imiquimod—to investigate the effects of tissue-specific peripheral inflammation on the brain. We used full genome array, flow cytometry analysis of immune cell infiltration, doublecortin staining for neural precursor cells and a behavioural read-out exploiting natural burrowing behaviour.
Results:
We found that a number of genes are upregulated in the brain following treatment, amongst which is a subset of inflammatory chemokines (CCL3, CCL5, CCL9, CXCL10, CXCL13, CXCL16 and CCR5). Strikingly, this model induced the infiltration of a number of immune cell subsets into the brain parenchyma, including T cells, NK cells and myeloid cells, along with a reduction in neurogenesis and a suppression of burrowing activity.
Conclusions:
These findings demonstrate that cutaneous, peripheral immune stimulation is associated with significant leukocyte infiltration into the brain and suggest that chemokines may be amongst the key mediators driving this response
A nonlinear theory of the parallel firehose and gyrothermal instabilities in a weakly collisional plasma
Weakly collisional plasmas dynamically develop pressure anisotropies with
respect to the magnetic field. These anisotropies trigger plasma instabilities
at scales just above the ion Larmor radius \rho_i and much below the mean free
path \lambda_{mfp}. They have growth rates of a fraction of the ion cyclotron
frequency - much faster than either the global dynamics or local turbulence.
The instabilities dramatically modify the transport properties and, therefore,
the macroscopic dynamics of the plasma. Their nonlinear evolution drives
pressure anisotropies towards marginal stability, controlled by the plasma beta
\beta_i. Here this nonlinear evolution is worked out for the simplest
analytically tractable example - the parallel firehose instability. In the
nonlinear regime, both analytical theory and the numerical solution predict
secular growth of magnetic fluctuations. They develop a k^{-3} spectrum,
extending from scales somewhat larger than \rho_i to the maximum scale that
grows secularly with time (~t^{1/2}); the relative pressure anisotropy
(\pperp-\ppar)/\ppar tends to the marginal value -2/\beta_i. The marginal state
is achieved via changes in the magnetic field, not particle scattering. When a
parallel ion heat flux is present, the firehose mutates into the new
gyrothermal instability (GTI), which continues to exist up to firehose-stable
values of pressure anisotropy, which can be positive and are limited by the
heat flux. The nonlinear evolution of the GTI also features secular growth of
magnetic fluctuations, but the spectrum is eventually dominated by modes around
the scale ~\rho_i l_T/\lambda_{mfp}, where l_T is the scale of the parallel
temperature variation. Implications for momentum and heat transport are
speculated about. This study is motivated by the dynamics of galaxy cluster
plasmas.Comment: 34 pages, replaced with the version published in MNRA
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