6,286 research outputs found
Sublinear Estimation of Weighted Matchings in Dynamic Data Streams
This paper presents an algorithm for estimating the weight of a maximum
weighted matching by augmenting any estimation routine for the size of an
unweighted matching. The algorithm is implementable in any streaming model
including dynamic graph streams. We also give the first constant estimation for
the maximum matching size in a dynamic graph stream for planar graphs (or any
graph with bounded arboricity) using space which also
extends to weighted matching. Using previous results by Kapralov, Khanna, and
Sudan (2014) we obtain a approximation for general graphs
using space in random order streams, respectively. In
addition, we give a space lower bound of for any
randomized algorithm estimating the size of a maximum matching up to a
factor for adversarial streams
A survey of the economics and management of gummy ewes
The purpose of this survey was to investigate the practice of running gummy ewes. Their management, production and costing factors were analysed. The information was gathered from fifty farmers in the Canterbury, Otago and Southland areas by a personal interview survey. The questionnaire covered the above aspects and aimed to gain farmer opinion on the practice of running these ewes.
It is evident from this survey that a decrease in wool weight can be expected; 47 percent of the farmers stated that they expected the drop to be approximately 1 kg compared with their mixed aged ewes. Furthermore, 67 percent of the farmers have found that slightly higher losses could be expected. These losses are significantly offset by a gain in lambing percentage of between 10 and 15 percent compared with mixed aged flocks on the same farms.
Gross margin analyses showed that a five year breeding own replacements system gave highest returns when the cull ewe and lamb prices were similar but as the difference between these two became larger, the two year flock system of buying gummy ewes was the more profitable. For the majority of the surveyed farms this latter policy has proven the most profitable over recent years
Submodular Maximization Meets Streaming: Matchings, Matroids, and More
We study the problem of finding a maximum matching in a graph given by an
input stream listing its edges in some arbitrary order, where the quantity to
be maximized is given by a monotone submodular function on subsets of edges.
This problem, which we call maximum submodular-function matching (MSM), is a
natural generalization of maximum weight matching (MWM), which is in turn a
generalization of maximum cardinality matching (MCM). We give two incomparable
algorithms for this problem with space usage falling in the semi-streaming
range---they store only edges, using working memory---that
achieve approximation ratios of in a single pass and in
passes respectively. The operations of these algorithms
mimic those of Zelke's and McGregor's respective algorithms for MWM; the
novelty lies in the analysis for the MSM setting. In fact we identify a general
framework for MWM algorithms that allows this kind of adaptation to the broader
setting of MSM.
In the sequel, we give generalizations of these results where the
maximization is over "independent sets" in a very general sense. This
generalization captures hypermatchings in hypergraphs as well as independence
in the intersection of multiple matroids.Comment: 18 page
Maximum Matching in Turnstile Streams
We consider the unweighted bipartite maximum matching problem in the one-pass
turnstile streaming model where the input stream consists of edge insertions
and deletions. In the insertion-only model, a one-pass -approximation
streaming algorithm can be easily obtained with space , where
denotes the number of vertices of the input graph. We show that no such result
is possible if edge deletions are allowed, even if space is
granted, for every . Specifically, for every , we show that in the one-pass turnstile streaming model, in order to compute
a -approximation, space is
required for constant error randomized algorithms, and, up to logarithmic
factors, space is sufficient. Our lower bound result is
proved in the simultaneous message model of communication and may be of
independent interest
Buyback Problem - Approximate matroid intersection with cancellation costs
In the buyback problem, an algorithm observes a sequence of bids and must
decide whether to accept each bid at the moment it arrives, subject to some
constraints on the set of accepted bids. Decisions to reject bids are
irrevocable, whereas decisions to accept bids may be canceled at a cost that is
a fixed fraction of the bid value. Previous to our work, deterministic and
randomized algorithms were known when the constraint is a matroid constraint.
We extend this and give a deterministic algorithm for the case when the
constraint is an intersection of matroid constraints. We further prove a
matching lower bound on the competitive ratio for this problem and extend our
results to arbitrary downward closed set systems. This problem has applications
to banner advertisement, semi-streaming, routing, load balancing and other
problems where preemption or cancellation of previous allocations is allowed
Susceptibility to apoptosis is differentially regulated by c-myc and mutated Ha-ras oncogenes and is associated with endonuclease availability.
Oncogenes and oncosuppressors can deregulate cell replication in tumours, and recently have been shown to influence the probability of apoptosis. The effects of human c-myc and mutated (T24) Ha-ras oncogenes on susceptibility to apoptosis were investigated by introducing them into immortalised rat fibroblasts. The resulting family of transfectants showed closely similar measures of proliferation, but widely divergent rates of apoptosis, differing by up to fifteen-fold, that correlated inversely with population expansion rates in vitro. T24-ras transfectants with moderate or high p21ras expression showed reduced apoptosis, and this was reversed by pharmacological inhibition of membrane localisation of p21ras by mevinolin. In contrast, c-myc stimulated apoptosis, and this was further enhanced by serum deprivation. Inducibility of effector proteins represents one possible mechanism of genetic control of the susceptibility to apoptosis, and its investigation showed that c-myc was associated with expression by viable cells of latent calcium/magnesium sensitive endonuclease activity characteristic of apoptosis. In contrast, endonuclease activity was not detected in viable cells of a T24-ras transfectant expressing high levels of p21ras. Thus, there appeared to be differential regulation of susceptibility to apoptosis, positively by c-myc and negatively by activated ras, and this was associated with availability of endonuclease activity. Genetic modulation of apoptosis in human neoplasms is likely to influence net growth rate, retention of cells acquiring new mutations and response to certain chemotherapeutic agents
A joint role for forced and internally-driven variability in the decadal modulation of global warming
Despite the observed monotonic increase in greenhouse-gas concentrations, global mean temperature displays important decadal fluctuations typically attributed to both external forcing and internal variability. Here, we provide a robust quantification of the relative contributions of anthropogenic, natural, and internally-driven decadal variability of global mean sea surface temperature (GMSST) by using a unique dataset consisting of 30-member large initial-condition ensembles with five Earth System Models (ESM-LE). We present evidence that a large fraction (~29–53%) of the simulated decadal-scale variance in individual timeseries of GMSST over 1950–2010 is externally forced and largely linked to the representation of volcanic aerosols. Comparison with the future (2010–2070) period suggests that external forcing provides a source of additional decadal-scale variability in the historical period. Given the unpredictable nature of future volcanic aerosol forcing, it is suggested that a large portion of decadal GMSST variability might not be predictable
The Black Hole Mass of NGC 4151. II. Stellar Dynamical Measurement from Near-Infrared Integral Field Spectroscopy
We present a revised measurement of the mass of the central black hole (Mbh)
in the Seyfert 1 galaxy NGC 4151. The new stellar dynamical mass measurement is
derived by applying an axisymmetric orbit-superposition code to near-infrared
integral field data obtained using adaptive optics with the Gemini NIFS
spectrograph. When our models attempt to fit both the NIFS kinematics and
additional low spatial resolution kinematics, our results depend sensitively on
how chi-squared is computed--probably a consequence of complex bar kinematics
that manifest immediately outside the nuclear region. The most robust results
are obtained when only the high spatial resolution kinematic constraints in the
nuclear region are included in the fit. Our best estimates for the BH mass and
H-band mass-to-light ratio are Mbh~(3.76+/-1.15)E7 Msun (1-sigma error) and
M/L(H-band)~0.34+/-0.03 Msun/Lsun (3-sigma error), respectively (the quoted
errors reflect the model uncertainties). Our BH mass measurement is consistent
with estimates from both reverberation mapping (3.57[+0.45/-0.37]E7 Msun) and
gas kinematics (3.0[+0.75/-2.2]E7 Msun; 1-sigma errors), and our best-fit
mass-to-light ratio is consistent with the photometric estimate of
M/L(H-band)=0.4+/-0.2 Msun/Lsun. The NIFS kinematics give a central bulge
velocity dispersion sigma_c=116+/-3 km/s, bringing this object slightly closer
to the M-sigma relation for quiescent galaxies. Although NGC 4151 is one of
only a few Seyfert 1 galaxies in which it is possible to obtain a direct
dynamical BH mass measurement--and thus, an independent calibration of the
reverberation mapping mass scale--the complex bar kinematics makes it less than
ideally suited for this purpose.Comment: 21 pages, 15 figures. Accepted for publication in Ap
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