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 $M_sat/M_host \approx 0.1$ and becomes larger for more disparate satellite-to-host mass ratios, reaching a factor of $\sim 3.3$ for $M_sat/M_host\approx 0.01$. 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 $M_sat/M_host$ 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 $\approx 40$, 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