1,356 research outputs found
Evanescent-wave coupled right angled buried waveguide: Applications in carbon nanotube mode-locking
In this paper we present a simple but powerful subgraph sampling primitive
that is applicable in a variety of computational models including dynamic graph
streams (where the input graph is defined by a sequence of edge/hyperedge
insertions and deletions) and distributed systems such as MapReduce. In the
case of dynamic graph streams, we use this primitive to prove the following
results:
-- Matching: First, there exists an space algorithm that
returns an exact maximum matching on the assumption the cardinality is at most
. The best previous algorithm used space where is the
number of vertices in the graph and we prove our result is optimal up to
logarithmic factors. Our algorithm has update time. Second,
there exists an space algorithm that returns an
-approximation for matchings of arbitrary size. (Assadi et al. (2015)
showed that this was optimal and independently and concurrently established the
same upper bound.) We generalize both results for weighted matching. Third,
there exists an space algorithm that returns a constant
approximation in graphs with bounded arboricity.
-- Vertex Cover and Hitting Set: There exists an space
algorithm that solves the minimum hitting set problem where is the
cardinality of the input sets and is an upper bound on the size of the
minimum hitting set. We prove this is optimal up to logarithmic factors. Our
algorithm has update time. The case corresponds to minimum
vertex cover.
Finally, we consider a larger family of parameterized problems (including
-matching, disjoint paths, vertex coloring among others) for which our
subgraph sampling primitive yields fast, small-space dynamic graph stream
algorithms. We then show lower bounds for natural problems outside this family
Exact Bayesian curve fitting and signal segmentation.
We consider regression models where the underlying functional relationship between the response and the explanatory variable is modeled as independent linear regressions on disjoint segments. We present an algorithm for perfect simulation from the posterior distribution of such a model, even allowing for an unknown number of segments and an unknown model order for the linear regressions within each segment. The algorithm is simple, can scale well to large data sets, and avoids the problem of diagnosing convergence that is present with Monte Carlo Markov Chain (MCMC) approaches to this problem. We demonstrate our algorithm on standard denoising problems, on a piecewise constant AR model, and on a speech segmentation problem
On the Security Cost of Using a Free and Open Source Component in a Proprietary Product
The work presented in this paper is motivated by the need to estimate the security effort of consuming Free and Open Source Software (FOSS) components within a proprietary software supply chain of a large European software vendor. To this extent we have identified three different cost models: centralized (the company checks each component and propagates changes to the different product groups), distributed (each product group is in charge of evaluating and fixing its consumed FOSS components), and hybrid (only the least used components are checked individually by each development team). We investigated publicly available factors (\eg, development activity such as commits, code size, or fraction of code size in different programming languages) to identify which one has the major impact on the security effort of using a FOSS component in a larger software product
‘O sibling, where art thou?’ – a review of avian sibling recognition with respect to the mammalian literature
Avian literature on sibling recognition is rare compared to that developed by mammalian researchers. We compare avian and mammalian research on sibling recognition to identify why avian work is rare, how approaches differ and what avian and mammalian researchers can learn from each other. Three factors: (1) biological differences between birds and mammals, (2) conceptual biases and (3) practical constraints, appear to influence our current understanding. Avian research focuses on colonial species because sibling recognition is considered adaptive where ‘mixing potential’ of dependent young is high; research on a wider range of species, breeding systems and ecological conditions is now needed. Studies of acoustic recognition cues dominate avian literature; other types of cues (e.g. visual, olfactory) deserve further attention. The effect of gender on avian sibling recognition has yet to be investigated; mammalian work shows that gender can have important influences. Most importantly, many researchers assume that birds recognise siblings through ‘direct familiarisation’ (commonly known as associative learning or familiarity); future experiments should also incorporate tests for ‘indirect familiarisation’ (commonly known as phenotype matching). If direct familiarisation proves crucial, avian research should investigate how periods of separation influence sibling discrimination. Mammalian researchers typically interpret sibling recognition in broad functional terms (nepotism, optimal outbreeding); some avian researchers more successfully identify specific and testable adaptive explanations, with greater relevance to natural contexts. We end by reporting exciting discoveries from recent studies of avian sibling recognition that inspire further interest in this topic
A search for resonant production of pairs in $4.8\ \rm{fb}^{-1}p\bar{p}\sqrt{s}=1.96\ \rm{TeV}$
We search for resonant production of tt pairs in 4.8 fb^{-1} integrated
luminosity of ppbar collision data at sqrt{s}=1.96 TeV in the lepton+jets decay
channel, where one top quark decays leptonically and the other hadronically. A
matrix element reconstruction technique is used; for each event a probability
density function (pdf) of the ttbar candidate invariant mass is sampled. These
pdfs are used to construct a likelihood function, whereby the cross section for
resonant ttbar production is estimated, given a hypothetical resonance mass and
width. The data indicate no evidence of resonant production of ttbar pairs. A
benchmark model of leptophobic Z \rightarrow ttbar is excluded with m_{Z'} <
900 GeV at 95% confidence level.Comment: accepted for publication in Physical Review D Sep 21, 201
Precision Top-Quark Mass Measurements at CDF
We present a precision measurement of the top-quark mass using the full
sample of Tevatron TeV proton-antiproton collisions collected
by the CDF II detector, corresponding to an integrated luminosity of 8.7
. Using a sample of candidate events decaying into the
lepton+jets channel, we obtain distributions of the top-quark masses and the
invariant mass of two jets from the boson decays from data. We then compare
these distributions to templates derived from signal and background samples to
extract the top-quark mass and the energy scale of the calorimeter jets with
{\it in situ} calibration. The likelihood fit of the templates from signal and
background events to the data yields the single most-precise measurement of the
top-quark mass, \mtop = 172.85 \pm\pmComment: submitted to Phys. Rev. Let
Inter-basin transfers as a supply option: the end of an era?
International audienceThis chapter discusses the evolving role of interbasin transfers (IBT) in urban water management. After providing an historical overview of IBT development, the chapter describes how IBTs are challenged by a change in the technological and socio-economic context. The emergence of alternative technologies, such as desalination, wastewater reclamation and reuse, or managed artificial groundwater recharge is reducing the attractiveness of IBTs. Water utilities are also becoming increasingly aware that water conservation programs can save volumes of water at a much cheaper cost than IBT. Various international examples are used to show that IBTs trigger increasing concerns from communities involved or affected, in particular related to the environmental impact on donor and receiving river basins, the economic impact on donor regions, the impact on local cultures and livelihoods, how costs and benefits are distributed (social justice), and issues related to public participation. The chapter concludes by looking ahead at new and more efficient uses of existing IBTs. As conjunctive use management approaches gain support, IBTs will be operated in conjunction with aquifer storage and recovery schemes. They will probably also support the development of emerging water markets, in particular during drought years
Evidence for t\bar{t}\gamma Production and Measurement of \sigma_t\bar{t}\gamma / \sigma_t\bar{t}
Using data corresponding to 6.0/fb of ppbar collisions at sqrt(s) = 1.96 TeV
collected by the CDF II detector, we present a cross section measurement of
top-quark pair production with an additional radiated photon. The events are
selected by looking for a lepton, a photon, significant transverse momentum
imbalance, large total transverse energy, and three or more jets, with at least
one identified as containing a b quark. The ttbar+photon sample requires the
photon to have 10 GeV or more of transverse energy, and to be in the central
region. Using an event selection optimized for the ttbar+photon candidate
sample we measure the production cross section of, and the ratio of cross
sections of the two samples. Control samples in the dilepton+photon and
lepton+photon+\met, channels are constructed to aid in decay product
identification and background measurements. We observe 30 ttbar+photon
candidate events compared to the standard model expectation of 26.9 +/- 3.4
events. We measure the ttbar+photon cross section to be 0.18+0.08 pb, and the
ratio of the cross section of ttbar+photon to ttbar to be 0.024 +/- 0.009.
Assuming no ttbar+photon production, we observe a probability of 0.0015 of the
background events alone producing 30 events or more, corresponding to 3.0
standard deviations.Comment: 9 pages, 3 figure
Graphene Photonics and Optoelectronics
The richness of optical and electronic properties of graphene attracts
enormous interest. Graphene has high mobility and optical transparency, in
addition to flexibility, robustness and environmental stability. So far, the
main focus has been on fundamental physics and electronic devices. However, we
believe its true potential to be in photonics and optoelectronics, where the
combination of its unique optical and electronic properties can be fully
exploited, even in the absence of a bandgap, and the linear dispersion of the
Dirac electrons enables ultra-wide-band tunability. The rise of graphene in
photonics and optoelectronics is shown by several recent results, ranging from
solar cells and light emitting devices, to touch screens, photodetectors and
ultrafast lasers. Here we review the state of the art in this emerging field.Comment: Review Nature Photonics, in pres
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