5,958 research outputs found
Submodularity in Batch Active Learning and Survey Problems on Gaussian Random Fields
Many real-world datasets can be represented in the form of a graph whose edge
weights designate similarities between instances. A discrete Gaussian random
field (GRF) model is a finite-dimensional Gaussian process (GP) whose prior
covariance is the inverse of a graph Laplacian. Minimizing the trace of the
predictive covariance Sigma (V-optimality) on GRFs has proven successful in
batch active learning classification problems with budget constraints. However,
its worst-case bound has been missing. We show that the V-optimality on GRFs as
a function of the batch query set is submodular and hence its greedy selection
algorithm guarantees an (1-1/e) approximation ratio. Moreover, GRF models have
the absence-of-suppressor (AofS) condition. For active survey problems, we
propose a similar survey criterion which minimizes 1'(Sigma)1. In practice,
V-optimality criterion performs better than GPs with mutual information gain
criteria and allows nonuniform costs for different nodes
Portfolio optimisation using risky assets with options as derivative insurance
We introduce options on FTSE100 index in portfolio optimisation with shares in which conditional value at risk (CVaR) is minimised. The option considered here is the one that follows FTSE100 Index Option standards. Price of options are calculated under the risk neutral valuation. The efficient portfolio composed under this addition of options shows that put option will be selected as part of the investment for every level of targeted returns. Main finding shows that the use of options does indeed decrease downside risk, and leads to better in-sample portfolio performance. Out-of-sample and back-testing also shows better performance of CVaR efficient portfolios in which index options are included. All models are coded using AMPL and the results are analysed using Microsoft Excel. Data used in this study are obtained from Datastream. We conclude that adding a put index option in addition to stocks, in order to actively create a portfolio, can substantially reduce the risk at a relatively low cost. Further research work will consider the case when short positions are considered, including writing call options.This work was partially supported by the Department of Mathematics, Brunel University
Leverage Effect In Chinese And American Index Returns
A lot of changes have happened in the Chinese economy in the last three decades. To study whether these changes affect the symmetric or asymmetric behavior of the volatility in Chinese Stock Market, in this paper we analyze, first, the main stylized facts in similar Chinese and American index returns and, second, we compare the leverage effect of volatility in three different periods for these indexes.The estimated results with GJR-GARCH and TA-ARSV models have shown that the behaviour of Chinese index returns was different depending on whether China was part of the Trade World Trade Organization (WTO)
An updated catalog of M33 clusters and candidates: photometry, and some statistical results
We present photometry for 392 star clusters and candidates in the
field of M33, which are selected from the most recent star cluster catalog. In
this catalog, the authors listed star clusters' parameters such as cluster
positions, magnitudes and colors in the filters, and so on.
However, a large fraction of objects in this catalog do not have previously
published photometry. Photometry is performed using archival images from the
Local Group Galaxies Survey, which covers 0.8 deg along the major axis of
M33. Detailed comparisons show that, in general, our photometry is consistent
with previous measurements. Positions (right ascension and declination) for
some clusters are corrected here. Combined with previous literature, we
constitute a large sample of M33 star clusters. Based on this cluster sample,
we present some statistical results: none of the M33 youngest clusters ( yr) have masses approaching ; roughly half the star
clusters are consistent with the to mass models; the
continuous distribution of star clusters along the model line indicates that
M33 star clusters have been formed continuously from the epoch of the first
star cluster formation until recent times; there are star clusters
which being overlapped with the Galactic globular clusters on the color-color
diagram, and these clusters are old globular clusters candidates in M33.Comment: Accepted for Publication in AJ, 22 pages, 12 figures and 9 table
Quantum expander for gravitational-wave observatories
Quantum uncertainty of laser light limits the sensitivity of
gravitational-wave observatories. In the past 30 years, techniques for
squeezing the quantum uncertainty as well as for enhancing the
gravitational-wave signal with optical resonators were invented. Resonators,
however, have finite linewidths; and the high signal frequencies that are
produced during the scientifically highly interesting ring-down of
astrophysical compact-binary mergers cannot be resolved today. Here, we propose
an optical approach for expanding the detection bandwidth. It uses quantum
uncertainty squeezing inside one of the optical resonators, compensating for
finite resonators' linewidths while maintaining the low-frequency sensitivity
unchanged. Introducing the quantum expander for boosting the sensitivity of
future gravitational-wave detectors, we envision it to become a new tool in
other cavity-enhanced metrological experiments
Rankings In The Euro Zone Based On Macroeconomic Information
One consequence of the Great Recession that began in 2008 has been the sovereign debt crisis within the European Monetary Union (EMU) and the increasing risk premium associated with government debt of "peripheral" countries (primarily, Greece, Ireland, Portugal and Spain). Firstly, this paper analyses what macroeconomic variables are more related with the evolution of the risk premium, using panel data estimation. Secondly, we also try to sort the countries belonging to the monetary union in terms of their likelihood of experiencing an increase in the risk premium. To this purpose, we use discrete multicriteria decision aid methods
The M33 Globular Cluster System with PAndAS Data: The Last Outer Halo Cluster?
We use CFHT/MegaCam data to search for outer halo star clusters in M33 as
part of the Pan-Andromeda Archaeological Survey (PAndAS). This work extends
previous studies out to a projected radius of 50 kpc and covers over 40 square
degrees. We find only one new unambiguous star cluster in addition to the five
previously known in the M33 outer halo (10 kpc <= r <= 50 kpc). Although we
identify 2440 cluster candidates of various degrees of confidence from our
objective image search procedure, almost all of these are likely background
contaminants, mostly faint unresolved galaxies. We measure the luminosity,
color and structural parameters of the new cluster in addition to the five
previously-known outer halo clusters. At a projected radius of 22 kpc, the new
cluster is slightly smaller, fainter and redder than all but one of the other
outer halo clusters, and has g' ~ 19.9, (g'-i') ~ 0.6, concentration parameter
c ~ 1.0, a core radius r_c ~ 3.5 pc, and a half-light radius r_h ~ 5.5 pc. For
M33 to have so few outer halo clusters compared to M31 suggests either tidal
stripping of M33's outer halo clusters by M31, or a very different, much calmer
accretion history of M33.Comment: 37 pages, 9 figures. Accepted by the Astrophysical Journa
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