7,021 research outputs found
Domain Coarsening in Systems Far from Equilibrium
The growth of domains of stripes evolving from random initial conditions is
studied in numerical simulations of models of systems far from equilibrium such
as Rayleigh-Benard convection. The scaling of the size of the domains deduced
from the inverse width of the Fourier spectrum is studied for both potential
and nonpotential models. The morphology of the domains and the defect
structures are however quite different in the two cases, and evidence is
presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende
Collective quantum jumps of Rydberg atoms
We study an open quantum system of atoms with long-range Rydberg interaction,
laser driving, and spontaneous emission. Over time, the system occasionally
jumps between a state of low Rydberg population and a state of high Rydberg
population. The jumps are inherently collective and in fact exist only for a
large number of atoms. We explain how entanglement and quantum measurement
enable the jumps, which are otherwise classically forbidden.Comment: 4 page
Orbital order-disorder transition in La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) and La(1-x-y)Nd(yx)Sr(y)MnO(3) (x = 0.1; y = 0.05,0.1)
The nature of orbital order-disorder transition has been studied in the
La(1-x)Nd(x)MnO(3) (x = 0.0-1.0) series which covers the entire range between
two end points - LaMnO(3) and NdMnO(3) - as well as in
La(0.85)Nd(0.1)Sr(0.05)MnO(3) and La(0.8)Nd(0.1)Sr(0.1)MnO(3). It has been
observed that the first-order nature of the transition gives way to higher
order with the increase in "x" in the case of pure manganites. The latent heat
(L) associated with the transition, first, drops with a steeper slope within x
= 0.0-0.3 and, then, gradually over a range 0.3<x<0.9. This drop could,
possibly, be due to evolution of finer orbital domain structure with "x". In
the case of Sr-doped samples, the transition appears to be of higher-order
nature even for a doping level 5 at%. In both cases, of course, the transition
temperature T(JT) rises systematically with the drop in average A-site radius
or rise in average Mn-O-Mn bond bending angle while no
apparent correlation could be observed with doping induced disorder sigma^2.
The cooperative nature of the orbital order, therefore, appears to be robust.Comment: 15 pages including 4 figures; pdf onl
The WFCAM Multi-wavelength Variable Star Catalog
Stellar variability in the near-infrared (NIR) remains largely unexplored.
The exploitation of public science archives with data-mining methods offers a
perspective for the time-domain exploration of the NIR sky. We perform a
comprehensive search for stellar variability using the optical-NIR multi-band
photometric data in the public Calibration Database of the WFCAM Science
Archive (WSA), with the aim of contributing to the general census of variable
stars, and to extend the current scarce inventory of accurate NIR light curves
for a number of variable star classes. We introduce new variability indices
designed for multi-band data with correlated sampling, and apply them for
pre-selecting variable star candidates, i.e., light curves that are dominated
by correlated variations, from noise-dominated ones. Pre-selection criteria are
established by robust numerical tests for evaluating the response of
variability indices to colored noise characteristic to the data. We find 275
periodic variable stars and an additional 44 objects with suspected variability
with uncertain periods or apparently aperiodic variation. Only 44 of these
objects had been previously known, including 11 RR~Lyrae stars in the outskirts
of the globular cluster M3 (NGC~5272). We provide a preliminary classification
of the new variable stars that have well-measured light curves, but the
variability types of a large number of objects remain ambiguous. We classify
most of the new variables as contact binary stars, but we also find several
pulsating stars, among which 34 are probably new field RR~Lyrae and 3 are
likely Cepheids. We also identify 32 highly reddened variable objects close to
previously known dark nebulae, suggesting that these are embedded young stellar
objects. We publish our results and all light-curve data as the WFCAM Variable
Star Catalog.Comment: 21 pages, 11 figure
On the usage of active learning for SHM
The key element of this work is to demonstrate a strategy for using pattern recognition algorithms to investigate
correlations between feature variables for Structural Health Monitoring (SHM). The task will take advantage
of data from a bridge. An informative chain of artificial intelligence tools will allow an active learning
interaction between the unfolded shapes of the manifold of online data by characterising the physical shape
between variables. In many data mining and machine learning applications, there is a significant supply
of unlabelled data but an important undersupply of labelled data. Semi-supervised active learning, which
combines both labelled and unlabelled data can offer serious access to useful information and may be the
crucial element in successful decision making, regarding the health of structures
Turing Instability in a Boundary-fed System
The formation of localized structures in the chlorine dioxide-idodine-malonic
acid (CDIMA) reaction-diffusion system is investigated numerically using a
realistic model of this system. We analyze the one-dimensional patterns formed
along the gradients imposed by boundary feeds, and study their linear stability
to symmetry-breaking perturbations (Turing instability) in the plane transverse
to these gradients. We establish that an often-invoked simple local linear
analysis which neglects longitudinal diffusion is inappropriate for predicting
the linear stability of these patterns. Using a fully nonuniform analysis, we
investigate the structure of the patterns formed along the gradients and their
stability to transverse Turing pattern formation as a function of the values of
two control parameters: the malonic acid feed concentration and the size of the
reactor in the dimension along the gradients. The results from this
investigation are compared with existing experiments.Comment: 41 pages, 18 figures, to be published in Physical Review
Phloem loading in the sucrose-export-defective (SXD-1) mutant maize is limited by callose deposition at plasmodesmata in bundle sheath-vascular parenchyma interface
Using Lucifer Yellow we have demonstrated that the phloem-loading pathway from the mesophyll to the bundle sheath-vascular parenchyma interface in Zea mays source leaves follows a symplasmic route in small and intermediate vascular bundles in control as well as in the green sections of mutant sucrose-export-defective (SXD-1) plants. In the anthocyanin-rich mutant leaf sections, Lucifer Yellow transport was prohibited along the same path, at the bundle sheath-vascular parenchyma interface in particular. Plasmodesmata at the latter interface in SXD-1 anthocyanin-rich leaf sections appear to be structurally altered through callose deposition at the plasmodesmal orifices. We suggest that a transport bottleneck at the bundle sheath-vascular parenchyma interface is thus orchestrated and regulated through callose formation, preventing symplasmic transport across this important loading interface
Direct observation of twist mode in electroconvection in I52
I report on the direct observation of a uniform twist mode of the director
field in electroconvection in I52. Recent theoretical work suggests that such a
uniform twist mode of the director field is responsible for a number of
secondary bifurcations in both electroconvection and thermal convection in
nematics. I show here evidence that the proposed mechanisms are consistent with
being the source of the previously reported SO2 state of electroconvection in
I52. The same mechanisms also contribute to a tertiary Hopf bifurcation that I
observe in electroconvection in I52. There are quantitative differences between
the experiment and calculations that only include the twist mode. These
differences suggest that a complete description must include effects described
by the weak-electrolyte model of electroconvection
Structure of surface vortex sheet between two rotating 3He superfluids
We study a two-phase sample of superfluid 3He where vorticity exists in one
phase (3He-A) but cannot penetrate across the interfacial boundary to a second
coherent phase (3He-B). We calculate the bending of the vorticity into a
surface vortex sheet on the interface and solve the internal structure of this
new type of vortex sheet. The compression of the vorticity from three to two
dimensions enforces a structure which is made up of half-quantum units,
independently of the structure of the source vorticity in the bulk. These
results are consistent with our NMR measurements.Comment: 4 pages, 4 figure
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