4,903 research outputs found
Push is Fast on Sparse Random Graphs
We consider the classical push broadcast process on a large class of sparse
random multigraphs that includes random power law graphs and multigraphs. Our
analysis shows that for every , whp rounds are
sufficient to inform all but an -fraction of the vertices.
It is not hard to see that, e.g. for random power law graphs, the push
process needs whp rounds to inform all vertices. Fountoulakis,
Panagiotou and Sauerwald proved that for random graphs that have power law
degree sequences with , the push-pull protocol needs
to inform all but vertices whp. Our result demonstrates that,
for such random graphs, the pull mechanism does not (asymptotically) improve
the running time. This is surprising as it is known that, on random power law
graphs with , push-pull is exponentially faster than pull
Smoothing -penalized estimators for high-dimensional time-course data
When a series of (related) linear models has to be estimated it is often
appropriate to combine the different data-sets to construct more efficient
estimators. We use -penalized estimators like the Lasso or the Adaptive
Lasso which can simultaneously do parameter estimation and model selection. We
show that for a time-course of high-dimensional linear models the convergence
rates of the Lasso and of the Adaptive Lasso can be improved by combining the
different time-points in a suitable way. Moreover, the Adaptive Lasso still
enjoys oracle properties and consistent variable selection. The finite sample
properties of the proposed methods are illustrated on simulated data and on a
real problem of motif finding in DNA sequences.Comment: Published in at http://dx.doi.org/10.1214/07-EJS103 the Electronic
Journal of Statistics (http://www.i-journals.org/ejs/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Discussion: One-step sparse estimates in nonconcave penalized likelihood models
Discussion of ``One-step sparse estimates in nonconcave penalized likelihood
models'' [arXiv:0808.1012]Comment: Published in at http://dx.doi.org/10.1214/07-AOS0316A the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Bridge trisections in rational surfaces
We study smooth isotopy classes of complex curves in complex surfaces from
the perspective of the theory of bridge trisections, with a special focus on
curves in and . We are
especially interested in bridge trisections and trisections that are as simple
as possible, which we call "efficient". We show that any curve in
or admits an efficient
bridge trisection. Because bridge trisections and trisections are nicely
related via branched covering operations, we are able to give many examples of
complex surfaces that admit efficient trisections. Among these are
hypersurfaces in , the elliptic surfaces , the Horikawa
surfaces , and complete intersections of hypersurfaces in
. As a corollary, we observe that, in many cases, manifolds that
are homeomorphic but not diffeomorphic have the same trisection genus, which is
consistent with the conjecture that trisection genus is additive under
connected sum. We give many trisection diagrams to illustrate our examples.Comment: 46 pages, 28 color figure
A New Method for Exposing Deposit Feeders to Contaminated Sediments for Food Chain Studies
(excerpt)
The ubiquity and refractory nature of certain organic compounds, such as chlorinated pesticides and polychlorinated biphenyls (PCB\u27s), results in their accumulation in aquatic sediments (Holdrinet et al. 1978, Peck et al. 1980, Wang et al. 1979). Their continuous release from this reservoir through physico-chemical and biogenic processes to the overlying water column results in the accumulation of xenobiotic compounds in the food chain
Intraspecific Variation in Taxonomic Characteristics of the Mayfly \u3ci\u3ePotamanthus Myops\u3c/i\u3e (Walsh)
Data collected from an ecological study of the mayfly Potamanthus rnyops (Walsh) in Michigan showed intraspecific variability in taxonomic characteristics that have been employed by previous investigators for species separation. Nymphal dorsal maculation patterns varied considerably within a single population. Also, the ratio of mandibular tusk length to head length increased with successive nymphal instars. Certain adult taxonomic characteristics, particularly relative male imago eye size and distance of separation, were either too poorly defined or too variable to be conclusive in species identification
Notes on the Life History of \u3ci\u3ePotamanthus Myops\u3c/i\u3e in Southeastern Michigan (Ephemeroptera: Potamanthidae)
Naiads of the mayfly Potamanthus myops were collected six times over a one year period from the Huron River to obtain some information on their natural history. Contrary to other Ephemeroidea, myops was never collected below the substrate surface, but was usually found on the underside of stones. The immature mayflies were measured and their length plotted for each collection period. The results support the hypothesis that the majority of myops requires two years to mature
A Modified Method for Reading Midges (Diptera: Chironomidae)
A small scale rearing chamber that provides a continuous source of different life stages of Glyptotendipes barbipes Staeger for bioassay studies was developed. A modified glass aquarium containing a substrate of shredded paper hand towels and artificial medium was employed. The amount of protein fed to the larvae can be used to trigger peak emergence, oviposition, and the rate of maturation. Fifty-three egg masses were sampled and 68% were fertile. Ninety-five percent of these hatched and 85% emerged as adults
Effects of Salmon Spawning Activity on Macroinvertebrates in a Small Michigan Stream
Density and composition of macroinvertebrate populations were examined prior to and during the migration and spawning of coho and chinook salmon in a small stream in Michigan. Data gathered from bottom samples indicated that disruption of substrate in the experimental area resulted in a significant decrease in the numbers and species of the macroinvertebrate community. This reduction of invertebrates can create a severe stress on native trout populations
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