Theoretical Predictions for Surface Brightness Fluctuations and Implications for Stellar Populations of Elliptical Galaxies

(Abridged) We present new theoretical predictions for surface brightness fluctuations (SBFs) using models optimized for this purpose. Our predictions agree well with SBF data for globular clusters and elliptical galaxies. We provide refined theoretical calibrations and k-corrections needed to use SBFs as standard candles. We suggest that SBF distance measurements can be improved by using a filter around 1 micron and calibrating I-band SBFs with the integrated V-K galaxy color. We also show that current SBF data provide useful constraints on population synthesis models, and we suggest SBF-based tests for future models. The data favor specific choices of evolutionary tracks and spectra in the models among the several choices allowed by comparisons based on only integrated light. In addition, the tightness of the empirical I-band SBF calibration suggests that model uncertainties in post-main sequence lifetimes are less than +/-50% and that the IMF in ellipticals is not much steeper than that in the solar neighborhood. Finally, we analyze the potential of SBFs for probing unresolved stellar populations. We find that optical/near-IR SBFs are much more sensitive to metallicity than to age. Therefore, SBF magnitudes and colors are a valuable tool to break the age/metallicity degeneracy. Our initial results suggest that the most luminous stellar populations of bright cluster galaxies have roughly solar metallicities and about a factor of three spread in age.Comment: Astrophysical Journal, in press (uses Apr 20, 2000 version of emulateapj5.sty). Reposted version has a minor cosmetic change to Table

On the Survivability and Metamorphism of Tidally Disrupted Giant Planets: the Role of Dense Cores

A large population of planetary candidates in short-period orbits have been found through transit searches. Radial velocity surveys have also revealed several Jupiter-mass planets with highly eccentric orbits. Measurements of the Rossiter-McLaughlin effect indicate some misaligned planetary systems. This diversity could be induced by post-formation dynamical processes such as planet-planet scattering, the Kozai effect, or secular chaos which brings planets to the vicinity of their host stars. In this work, we propose a novel mechanism to form close-in super-Earths and Neptune-like planets through the tidal disruption of giant planets as a consequence of these dynamical processes. We model the core-envelope structure of giant planets with composite polytropes. Using three-dimensional hydrodynamical simulations of close encounters between planets and their host stars, we find that the presence of a core with a mass more than ten Earth masses can significantly increase the fraction of envelope which remains bound to it. After the encounter, planets with cores are more likely to be retained by their host stars in contrast with previous studies which suggested that coreless planets are often ejected. As a substantial fraction of their gaseous envelopes is preferentially lost while the dense incompressible cores retain most of their original mass, the resulting metallicity of the surviving planets is increased. Our results suggest that some gas giant planets can be effectively transformed into either super-Earths or Neptune-like planets after multiple close stellar passages. Finally, we analyze the orbits and structure of known planets and Kepler candidates and find that our model is capable producing some of the shortest-period objects.Comment: Accepted for publication in ApJ. 15 pages, 9 figures, 3 tables. Two movies at http://youtu.be/jHxPKAEgFic and http://youtu.be/QXqkS0vDi5

Quasi-local energy for cosmological models

First we briefly review our covariant Hamiltonian approach to quasi-local energy, noting that the Hamiltonian-boundary-term quasi-local energy expressions depend on the chosen boundary conditions and reference configuration. Then we present the quasi-local energy values resulting from the formalism applied to homogeneous Bianchi cosmologies. Finally we consider the quasi-local energies of the FRW cosmologies. Our results do not agree with certain widely accepted quasi-local criteria.Comment: Contributed to International Symposium on Cosmology and Particle Astrophysics (CosPA 2006), Taipei, Taiwan, 15-17 Nov 200

新兴非典型被动式“被 XX” 的句法与语义结构 (The syntax and semantics of the new non-canonical bei (被) XX construction.

提要 本文讨论新兴非典型“被 XX”结构的句法、语义特征及历史来源并进行跨 语言的比较研究。本文认为这种“新生”结构不是一个将不及物动词被动化的特殊 句法结构,而是一些隐含了使动、意动或施动成分的轻动词结构。受到被动化的动 词不是 XX 本身,而是其所隐含的无声轻动词。类似的隐含动词结构也大量见于古 汉语、英语等语言,不同的是,现代汉语的“被 XX”结构不能还原为主动形式。 本文将这一不同归因于综合性语言与分析性语言之间的不同,并以“派生时机参 数”为基础的参数理论对此提出解释。从语言演变角度来讲,“被 XX”结构在现 代汉语的出现反映了语言演变遵循“⋯ 综合 → 分析 → 综合 ⋯”的循环模式。Linguistic

Impulse distributions in dense granular flows: signatures of large-scale spatial structures

In this paper we report the results of simulations of a 2D gravity driven, dissipative granular flow through a hopper system. Measurements of impulse distributions P(I) on the simulated system show flow-velocity-invariant behavior of the distribution for impulses larger than the average impulse . For small impulses, however, P(I) decreases significantly with flow velocity, a phenomenon which can be attributed exclusively to collisions between grains undergoing frequent collisions. Visualizations of the system also show that these frequently colliding particles tend to form increasingly large linear clusters as the flow velocity decreases. A model is proposed for the form of P(I), given distributions of cluster size and velocity, which accurately predicts the observed form of the distribution. Thus the impulse distribution provides some insight into the formation and properties of these ``dynamic'' force chains.Comment: 4 pages, 4 figure

Quasi-local energy and the choice of reference

A quasi-local energy for Einstein's general relativity is defined by the value of the preferred boundary term in the covariant Hamiltonian formalism. The boundary term depends upon a choice of reference and a time-like displacement vector field (which can be associated with an observer) on the boundary of the region. Here we analyze the spherical symmetric cases. For the obvious analytic choice of reference based on the metric components, we find that this technique gives the same quasi-local energy values using several standard coordinate systems and yet can give different values in some other coordinate systems. For the homogeneous-isotropic cosmologies, the energy can be non-positive, and one case which is actually flat space has a negative energy. As an alternative, we introduce a way to determine the choice of both the reference and displacement by extremizing the energy. This procedure gives the same value for the energy in different coordinate systems for the Schwarzschild space, and a non-negative value for the cosmological models, with zero energy for the dynamic cosmology which is actually Minkowski space. The timelike displacement vector comes out to be the dual mean curvature vector of the two-boundary.Comment: 21 pages; revised version to appear in CQ