10,258 research outputs found
Assessing Malaysia’s Business Cycle indicators
An empirical assessment shows that Malaysia’s business cycle indicators can be improved. Turning point detection is not impressive, especially for troughs. Lead times are also variable. However, the relationship between the leading and coincident indicators over the entire cycle shows quite strong correlations from the late 1980s onwards, although lead times have shortened. Empirical evidence is very strong that the leading index Granger-causes the coincident index. Business and consumer confidence surveys also show much promise in improving prediction of the reference cycle. However, implications of the changing economic structure on the performance of the leading index needs to be fully taken into account, especially the emergence of new services sector activities.Business/growth cycle, Malaysian economy, growth cycle chronology, turning point analysis, Granger causality
Gamma-based clustering via ordered means with application to gene-expression analysis
Discrete mixture models provide a well-known basis for effective clustering
algorithms, although technical challenges have limited their scope. In the
context of gene-expression data analysis, a model is presented that mixes over
a finite catalog of structures, each one representing equality and inequality
constraints among latent expected values. Computations depend on the
probability that independent gamma-distributed variables attain each of their
possible orderings. Each ordering event is equivalent to an event in
independent negative-binomial random variables, and this finding guides a
dynamic-programming calculation. The structuring of mixture-model components
according to constraints among latent means leads to strict concavity of the
mixture log likelihood. In addition to its beneficial numerical properties, the
clustering method shows promising results in an empirical study.Comment: Published in at http://dx.doi.org/10.1214/10-AOS805 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Dynamical Friction and Galaxy Merging Timescales
The timescale for galaxies within merging dark matter halos to merge with
each other is an important ingredient in galaxy formation models. Accurate
estimates of merging timescales are required for predictions of astrophysical
quantities such as black hole binary merger rates, the build-up of stellar mass
in central galaxies, and the statistical properties of satellite galaxies
within dark matter halos. In this paper, we study the merging timescales of
extended dark matter halos using N-body simulations. We compare these results
to standard estimates based on the Chandrasekhar theory of dynamical friction.
We find that these standard predictions for merging timescales, which are often
used in semi-analytic galaxy formation models, are systematically shorter than
those found in simulations. The discrepancy is approximately a factor of 1.7
for and becomes larger for more disparate
satellite-to-host mass ratios, reaching a factor of for
. Based on our simulations, we propose a new, easily
implementable fitting formula that accurately predicts the timescale for an
extended satellite to sink from the virial radius of a host halo down to the
halo's center for a wide range of and orbits. Including a
central bulge in each galaxy changes the merging timescale by \la 10%. To
highlight one concrete application of our results, we show that merging
timescales often used in the literature overestimate the growth of stellar mass
by satellite accretion by , with the extra mass gained in low
mass ratio mergers.Comment: 10 pages, 7 figures; MNRAS, in press. Minor revisions, including
results from additional simulations with baryonic components; conclusions
unchange
Red Mergers and the Assembly of Massive Elliptical Galaxies: the Fundamental Plane and its Projections
Several recent observations suggest that gas-poor (dissipationless) mergers
of elliptical galaxies contribute significantly to the build-up of the massive
end of the red sequence. We perform a series of major merger simulations to
investigate the spatial and velocity structure of the remnants of such mergers.
Regardless of orbital energy or angular momentum, we find that the stellar
remnants lie on the fundamental plane defined by their progenitors, a result of
virial equilibrium with a small tilt due to an increasing central dark matter
fraction. However, the locations of merger remnants in the projections of the
fundamental plane -- the Faber-Jackson and R_e-M_* relations -- depend strongly
on the merger orbit, and the relations steepen significantly from the canonical
scalings (L sigma^4 and R_e M_*^0.6) for mergers on radial orbits. Our results
imply that the projections of the fundamental plane -- but not necessarily the
plane itself -- provide a powerful way of investigating the assembly history of
massive elliptical galaxies, including the brightest cluster galaxies at or
near the centers of galaxy clusters. We argue that most massive ellipticals are
formed by anisotropic merging and that their fundamental plane projections
should thus differ noticeably from those of lower mass ellipticals even though
they should lie on the same fundamental plane. Current observations are
consistent with this conclusion. The steepening in the L-sigma relation for
luminous ellipticals may also be reflected in a corresponding steepening in the
M_BH-sigma relation for massive black holes.Comment: 10 pages, 4 figures. Accepted for publication in MNRA
Economic Development in China and Its Implications for East Asia
Economic development in China, East Asia, trade adjustment
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