4,371 research outputs found
Superharmonic Perturbations of a Gaussian Measure, Equilibrium Measures and Orthogonal Polynomials
This work concerns superharmonic perturbations of a Gaussian measure given by
a special class of positive weights in the complex plane of the form , where is the logarithmic potential of
a compactly supported positive measure . The equilibrium measure of the
corresponding weighted energy problem is shown to be supported on subharmonic
generalized quadrature domains for a large class of perturbing potentials
. It is also shown that the matrix d-bar problem for
orthogonal polynomials with respect to such weights is well-defined and has a
unique solution given explicitly by Cauchy transforms. Numerical evidence is
presented supporting a conjectured relation between the asymptotic distribution
of the zeroes of the orthogonal polynomials in a semi-classical scaling limit
and the Schwarz function of the curve bounding the support of the equilibrium
measure, extending the previously studied case of harmonic polynomial
perturbations with weights supported on a compact domain.Comment: CRM preprint, 28 pages. To appear in: Complex Analysis and Operator
Theory (Special volume in honour of Bjorn Gustafsson). Two references added
(Oct. 2, 2008
Spread of \u3ci\u3eAcentria Ephemerella\u3c/i\u3e (Lepidoptera: Pyralidae) in Central North America
The aquatic moth, Acentria ephemerella, was first reported from North America in 1927. Recent records from widespread localities in central North America indicate that the range of this European introduction continues to expand. The moth is well established in the western Great Lakes region and is recorded west to the Missouri River valley in Iowa
Host Range Extension for \u3ci\u3eChlorochlamys Chloroleucaria\u3c/i\u3e (Geometrinae, Geometridae) to Include \u3ci\u3eEriogonum Alatum\u3c/i\u3e (Polygonaceae)
(excerpt)
Chlorochlamys chloroleucaria (Guenée) is a common moth of eastern North America, recorded from Nova Scotia south to Cuba and Mexico and as far west as Manitoba, the Black Hills of South Dakota, Wyoming and central Colorado (Boulder and El Paso counties) (Ferguson 1985)
Magnetic and Transport Properties of Fe-Ag granular multilayers
Results of magnetization, magnetotransport and Mossbauer spectroscopy
measurements of sequentially evaporated Fe-Ag granular composites are
presented. The strong magnetic scattering of the conduction electrons is
reflected in the sublinear temperature dependence of the resistance and in the
large negative magnetoresistance. The simultaneous analysis of the magnetic
properties and the transport behavior suggests a bimodal grain size
distribution. A detailed quantitative description of the unusual features
observed in the transport properties is given
Line Emission in the Brightest Cluster Galaxies of the NOAO Fundamental Plane and Sloan Digital Sky Surveys
We examine the optical emission line properties of Brightest Cluster Galaxies
(BCGs) selected from two large, homogeneous datasets. The first is the X-ray
selected National Optical Astronomy Observatory Fundamental Plane Survey
(NFPS), and the second is the C4 catalogue of optically selected clusters built
from the Sloan Digital Sky Survey Data Release ~3 (SDSS DR3). Our goal is to
better understand the optical line emission in BCGs with respect to properties
of the galaxy and the host cluster. Throughout the analysis we compare the line
emission of the BCGs to that of a control sample made of the other bright
galaxies near the cluster centre. Overall, both the NFPS and SDSS show a modest
fraction of BCGs with emission lines (~15%). No trend in the fraction of
emitting BCGs as a function of galaxy mass or cluster velocity dispersion is
found. However we find that, for those BCGs found in cooling flow clusters,
71^{+9}_{-14}% have optical emission. Furthermore, if we consider only BCGs
within 50kpc of the X-ray centre of a cooling flow cluster, the emission-line
fraction rises further to 100^{+0}_{-15}%. Excluding the cooling flow clusters,
only ~10% of BCGs are line emitting, comparable to the control sample of
galaxies. We show that the physical origin of the emission line activity
varies: in some cases it has LINER-like line ratios, whereas in others it is a
composite of star-formation and LINER-like activity. We conclude that the
presence of emission lines in BCGs is directly related to the cooling of X-ray
gas at the cluster centre.Comment: Accepted for publication in MNRAS. 13 pages mn2e style with 7 figures
and 2 table
The Routing of Complex Contagion in Kleinberg's Small-World Networks
In Kleinberg's small-world network model, strong ties are modeled as
deterministic edges in the underlying base grid and weak ties are modeled as
random edges connecting remote nodes. The probability of connecting a node
with node through a weak tie is proportional to , where
is the grid distance between and and is the
parameter of the model. Complex contagion refers to the propagation mechanism
in a network where each node is activated only after neighbors of the
node are activated.
In this paper, we propose the concept of routing of complex contagion (or
complex routing), where we can activate one node at one time step with the goal
of activating the targeted node in the end. We consider decentralized routing
scheme where only the weak ties from the activated nodes are revealed. We study
the routing time of complex contagion and compare the result with simple
routing and complex diffusion (the diffusion of complex contagion, where all
nodes that could be activated are activated immediately in the same step with
the goal of activating all nodes in the end).
We show that for decentralized complex routing, the routing time is lower
bounded by a polynomial in (the number of nodes in the network) for all
range of both in expectation and with high probability (in particular,
for and
for in expectation),
while the routing time of simple contagion has polylogarithmic upper bound when
. Our results indicate that complex routing is harder than complex
diffusion and the routing time of complex contagion differs exponentially
compared to simple contagion at sweetspot.Comment: Conference version will appear in COCOON 201
The Evolution of [OII] Emission from Cluster Galaxies
We investigate the evolution of the star formation rate in cluster galaxies.
We complement data from the CNOC1 cluster survey (0.15<z<0.6) with measurements
from galaxy clusters in the 2dF galaxy redshift survey (0.05<z<0.1) and
measurements from recently published work on higher redshift clusters, up to
almost z=1. We focus our attention on galaxies in the cluster core, ie.
galaxies with r<0.7h^{-1}_{70}Mpc. Averaging over clusters in redshift bins, we
find that the fraction of galaxies with strong [OII] emission is < 20% in
cluster cores, and the fraction evolves little with redshift. In contrast,
field galaxies from the survey show a very strong increase over the same
redshift range. It thus appears that the environment in the cores of rich
clusters is hostile to star formation at all the redshifts studied. We compare
this result with the evolution of the colours of galaxies in cluster cores,
first reported by Butcher & Oemler (1984). Using the same galaxies for our
analysis of the [OII] emission, we confirm that the fraction of blue galaxies,
which are defined as galaxies 0.2 mag bluer in the rest frame B-V than the red
sequence of each cluster, increases strongly with redshift. Since the colours
of galaxies retain a memory of their recent star formation history, while
emission from the [OII] line does not, we suggest that these two results can
best be reconciled if the rate at which the clusters are being assembled is
higher in the past, and the galaxies from which it is being assembled are
typically bluer.Comment: 8 pages, 7 figures, accepted for publication in MNRA
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