17,878 research outputs found
Study of hot wire techniques in low density flows with high turbulence levels
Prediction of heat, mass, species, and momentum fluxes in a space vehicle and aerodynamic noise production by supersonic jet and rocket exhausts requires a predictability of the associated turbulence fields. The hot wire is a technique that will allow an experimental determination of turbulent properties
Desynchronization of pulse-coupled oscillators with delayed excitatory coupling
Collective behavior of pulse-coupled oscillators has been investigated
widely. As an example of pulse-coupled networks, fireflies display many kinds
of flashing patterns. Mirollo and Strogatz (1990) proposed a pulse-coupled
oscillator model to explain the synchronization of South East Asian fireflies
({\itshape Pteroptyx malaccae}). However, transmission delays were not
considered in their model. In fact, the presence of transmission delays can
lead to desychronization. In this paper, pulse-coupled oscillator networks with
delayed excitatory coupling are studied. Our main result is that under
reasonable assumptions, pulse-coupled oscillator networks with delayed
excitatory coupling can not achieve complete synchronization, which can explain
why another species of fireflies ({\itshape Photinus pyralis}) rarely
synchronizes flashing. Finally, two numerical simulations are given. In the
first simulation, we illustrate that even if all the initial phases are very
close to each other, there could still be big variations in the times to
process the pulses in the pipeline. It implies that asymptotical
synchronization typically also cannot be achieved. In the second simulation, we
exhibit a phenomenon of clustering synchronization
Invariant submanifold for series arrays of Josephson junctions
We study the nonlinear dynamics of series arrays of Josephson junctions in
the large-N limit, where N is the number of junctions in the array. The
junctions are assumed to be identical, overdamped, driven by a constant bias
current and globally coupled through a common load. Previous simulations of
such arrays revealed that their dynamics are remarkably simple, hinting at the
presence of some hidden symmetry or other structure. These observations were
later explained by the discovery of (N - 3) constants of motion, each choice of
which confines the resulting flow in phase space to a low-dimensional invariant
manifold. Here we show that the dimensionality can be reduced further by
restricting attention to a special family of states recently identified by Ott
and Antonsen. In geometric terms, the Ott-Antonsen ansatz corresponds to an
invariant submanifold of dimension one less than that found earlier. We derive
and analyze the flow on this submanifold for two special cases: an array with
purely resistive loading and another with resistive-inductive-capacitive
loading. Our results recover (and in some instances improve) earlier findings
based on linearization arguments.Comment: 10 pages, 6 figure
The Hillarys Transect (1): Seasonal and Coss-shelf Variability of Physical and Chemical Water Properties off Perth, Western Australia, 1996-98
A 27-month study of the water properties across the continental shelf off Perth, Western Australia (the Hillarys Transect ) has provided the first systematic inter-disciplinary climatology of the physical, chemical, optical and biological cycles across the shelf. This paper describes the main features of the seasonal and cross-shelf variability of the physical oceanography and chemistry, while companion papers discuss some of the links between the biology and physics of the regio
Spin dynamics in the optical cycle of single nitrogen-vacancy centres in diamond
We investigate spin-dependent decay and intersystem crossing in the optical
cycle of single negatively-charged nitrogen-vacancy (NV) centres in diamond. We
use spin control and pulsed optical excitation to extract both the
spin-resolved lifetimes of the excited states and the degree of
optically-induced spin polarization. By optically exciting the centre with a
series of picosecond pulses, we determine the spin-flip probabilities per
optical cycle, as well as the spin-dependent probability for intersystem
crossing. This information, together with the indepedently measured decay rate
of singlet population provides a full description of spin dynamics in the
optical cycle of NV centres. The temperature dependence of the singlet
population decay rate provides information on the number of singlet states
involved in the optical cycle.Comment: 11 pages, 5 figure
Biofilm formation is a risk factor for mortality in patients with Candida albicans bloodstream infection-Scotland, 2012-2013
Acknowledgements This work was supported by the Wellcome Trust Strategic Award for Medical Mycology and Fungal Immunology 097377/Z/11/Z. Data collection was supported by a grant from Pfizer. G. Ramage was also supported by a research fellowship grant from Gilead Sciences. We are grateful to microbiology colleagues throughout Scotland for submitting isolates.Peer reviewedPublisher PD
Evolution of an ancient protein function involved in organized multicellularity in animals.
To form and maintain organized tissues, multicellular organisms orient their mitotic spindles relative to neighboring cells. A molecular complex scaffolded by the GK protein-interaction domain (GKPID) mediates spindle orientation in diverse animal taxa by linking microtubule motor proteins to a marker protein on the cell cortex localized by external cues. Here we illuminate how this complex evolved and commandeered control of spindle orientation from a more ancient mechanism. The complex was assembled through a series of molecular exploitation events, one of which - the evolution of GKPID's capacity to bind the cortical marker protein - can be recapitulated by reintroducing a single historical substitution into the reconstructed ancestral GKPID. This change revealed and repurposed an ancient molecular surface that previously had a radically different function. We show how the physical simplicity of this binding interface enabled the evolution of a new protein function now essential to the biological complexity of many animals
Averaging approach to phase coherence of uncoupled limit-cycle oscillators receiving common random impulses
Populations of uncoupled limit-cycle oscillators receiving common random
impulses show various types of phase-coherent states, which are characterized
by the distribution of phase differences between pairs of oscillators. We
develop a theory to predict the stationary distribution of pairwise phase
difference from the phase response curve, which quantitatively encapsulates the
oscillator dynamics, via averaging of the Frobenius-Perron equation describing
the impulse-driven oscillators. The validity of our theory is confirmed by
direct numerical simulations using the FitzHugh-Nagumo neural oscillator
receiving common Poisson impulses as an example
Spatially Resolved Near-Infrared Spectroscopy of Seyfert 2 Galaxies Mk 1066, NGC 2110, NGC 4388, and Mk 3
We present near-infrared spectra with resolutions of lambda/dlambda~1200 in
the emission lines of Pa-beta, [FeII] (1.2567um), Br-gamma, and H2 v=1-0S(1) of
the nuclei and circumnuclear regions of the four Seyfert 2 galaxies Mk 1066,
NGC 2110, NGC 4388, and Mk 3. All of these galaxies show strong near-infrared
line emission that is detected at radii several times the spatial resolution,
corresponding to projected physical scales of 0.07 to 0.7 kpc. Velocity
gradients are detected in these nuclei, as are spatial variations in line
profiles and flux ratios. We compare the spatial and velocity distribution of
the line emission to previously observed optical line and radio emission. The
evidence indicates that the [FeII] emission is associated with the Seyfert
activity in the galaxies. Our data are consistent with X-ray heating being
responsible for most of the [FeII] emission, although differences in [FeII] and
Pa-beta line profiles associated with radio emission suggests that the [FeII]
emission is enhanced by fast shocks associated with radio outflows. The H2
emission is not as strongly associated with outflows or ionization cones as is
the emission in other lines, but rather appears to be primarily associated with
the disk of the galaxy.Comment: 35 pages, 24 figure
A Contour Integral Representation for the Dual Five-Point Function and a Symmetry of the Genus Four Surface in R6
The invention of the "dual resonance model" N-point functions BN motivated
the development of current string theory. The simplest of these models, the
four-point function B4, is the classical Euler Beta function. Many standard
methods of complex analysis in a single variable have been applied to elucidate
the properties of the Euler Beta function, leading, for example, to analytic
continuation formulas such as the contour-integral representation obtained by
Pochhammer in 1890. Here we explore the geometry underlying the dual five-point
function B5, the simplest generalization of the Euler Beta function. Analyzing
the B5 integrand leads to a polyhedral structure for the five-crosscap surface,
embedded in RP5, that has 12 pentagonal faces and a symmetry group of order 120
in PGL(6). We find a Pochhammer-like representation for B5 that is a contour
integral along a surface of genus five. The symmetric embedding of the
five-crosscap surface in RP5 is doubly covered by a symmetric embedding of the
surface of genus four in R6 that has a polyhedral structure with 24 pentagonal
faces and a symmetry group of order 240 in O(6). The methods appear
generalizable to all N, and the resulting structures seem to be related to
associahedra in arbitrary dimensions.Comment: 43 pages and 44 figure
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