73 research outputs found
Probing Stellar Dynamics in Galactic Nuclei
Electromagnetic observations over the last 15 years have yielded a growing
appreciation for the importance of supermassive black holes (SMBH) to the
evolution of galaxies, and for the intricacies of dynamical interactions in our
own Galactic center. Here we show that future low-frequency gravitational wave
observations, alone or in combination with electromagnetic data, will open up
unique windows to these processes. In particular, gravitational wave detections
in the 10^{-5}-10^{-1} Hz range will yield SMBH masses and spins to
unprecedented precision and will provide clues to the properties of the
otherwise undetectable stellar remnants expected to populate the centers of
galaxies. Such observations are therefore keys to understanding the interplay
between SMBHs and their environments.Comment: 8 pages, Science white paper for the Astro2010 Decadal Surve
Decadal Survey White Paper: Probing Stellar Dynamics in Galactic Nuclei
Electromagnetic observations over the last 15 years have yielded a growing
appreciation for the importance of supermassive black holes (SMBH) to the
evolution of galaxies, and for the intricacies of dynamical interactions in our
own Galactic center. Here we show that future low-frequency gravitational wave
observations, alone or in combination with electromagnetic data, will open up
unique windows to these processes. In particular, gravitational wave detections
in the 10^{-5}-10^{-1} Hz range will yield SMBH masses and spins to
unprecedented precision and will provide clues to the properties of the
otherwise undetectable stellar remnants expected to populate the centers of
galaxies. Such observations are therefore keys to understanding the interplay
between SMBHs and their environments
Monte Carlo Simulations of Star Clusters - VII. The globular cluster 47 Tuc
We describe Monte Carlo models for the dynamical evolution of the massive
globular cluster 47 Tuc (NGC 104). The code includes treatments of two-body
relaxation, most kinds of three- and four-body interactions involving
primordial binaries and those formed dynamically, the Galactic tide, and the
internal evolution of both single and binary stars. We arrive at a set of
initial parameters for the cluster which, after 12Gyr of evolution, gives a
model with a fairly satisfactory match to surface brightness and density
profiles, the velocity dispersion profile, the luminosity function in two
fields, and the acceleration of pulsars. Our models appear to require a
relatively steep initial mass function for stars above about turnoff, with an
index of about 2.8 (where the Salpeter mass function has an index of 2.35), and
a relatively flat initial mass function (index about 0.4) for the lower main
sequence. According to the model, the current mass is estimated at 0.9 million
solar masses, of which about 34% consists of remnants. We find that primordial
binaries are gradually taking over from mass loss by stellar evolution as the
main dynamical driver of the core. Despite the high concentration of the
cluster, core collapse will take at least another 20Gyr.Comment: 16 pages, 16 figures, revised version submitted to MNRA
Production of Intermediate-Mass Black Holes in Globular Clusters
The discovery of numerous non-nuclear X-ray point sources with luminosities
L>10^39 erg/s in several starburst galaxies has stimulated speculation about
their nature and origin. The strong variability seen in several sources points
to massive black holes as the central engines. If the flux is isotropic, the
luminosities range up to roughly 10^41 erg/s, implying masses of M>10^3 Msun if
the luminosity is sub-Eddington. Here we explore a model for these sources. We
suggest that in some tens of percent of globular clusters a very massive black
hole, M>50 Msun, is formed. This black hole sinks in <10^6 yr to the center of
the cluster, where in the 10^10 yr lifetime of the cluster it accretes roughly
10^3 Msun, primarily in the form of lighter black holes. Unlike less massive
black holes in binaries, which are flung from clusters by recoil before they
can merge gravitationally, a >50 Msun black hole has enough inertia that it
remains bound to the cluster. We suggest that 10^3 Msun black holes may be
common in the centers of dense globular clusters, and may therefore exist in
some tens of percent of current globulars. If the cluster later merges with its
host galaxy, accretion from young star clusters in molecular clouds by the
black hole can generate luminosity consistent with that observed. We also
consider the detectability of massive black holes in globular clusters with
gravitational wave detectors such as LISA and LIGO, and speculate on future
observations that may test our predictions.Comment: 9 pages, submitted to MNRA
Limited Effect of Dietary Saturated Fat on Plasma Saturated Fat in the Context of a Low Carbohydrate Diet
We recently showed that a hypocaloric carbohydrate restricted diet (CRD) had two striking effects: (1) a reduction in plasma saturated fatty acids (SFA) despite higher intake than a low fat diet, and (2) a decrease in inflammation despite a significant increase in arachidonic acid (ARA). Here we extend these findings in 8 weight stable men who were fed two 6-week CRD (12%en carbohydrate) varying in quality of fat. One CRD emphasized SFA (CRD-SFA, 86 g/d SFA) and the other, unsaturated fat (CRD-UFA, 47 g SFA/d). All foods were provided to subjects. Both CRD decreased serum triacylglycerol (TAG) and insulin, and increased LDL-C particle size. The CRD-UFA significantly decreased plasma TAG SFA (27.48 ± 2.89 mol%) compared to baseline (31.06 ± 4.26 mol%). Plasma TAG SFA, however, remained unchanged in the CRD-SFA (33.14 ± 3.49 mol%) despite a doubling in SFA intake. Both CRD significantly reduced plasma palmitoleic acid (16:1n-7) indicating decreased de novo lipogenesis. CRD-SFA significantly increased plasma phospholipid ARA content, while CRD-UFA significantly increased EPA and DHA. Urine 8-iso PGF2α, a free radical-catalyzed product of ARA, was significantly lower than baseline following CRD-UFA (−32%). There was a significant inverse correlation between changes in urine 8-iso PGF2α and PL ARA on both CRD (r = −0.82 CRD-SFA; r = −0.62 CRD-UFA). These findings are consistent with the concept that dietary saturated fat is efficiently metabolized in the presence of low carbohydrate, and that a CRD results in better preservation of plasma ARA
Migration, Ethnicity and Economic Integration
This chapter deals with the economic and ethnic diversity caused by international labor migration, and their economic integration possibilities. It brings together three strands of literature dealing with the neoclassical economic assimilation, ethnic identities and attitudes towards immigrants and the natives, and provides an analysis in understanding their interactions. The issue of how immigrants fare in the host country especially in terms of their labor force participation and remuneration has been the core of research in the labor migration literature. If immigrants fare as well as the natives, then they are economically assimilated. While some immigrant groups do, most do not, especially in Europe. Of equal importance is how immigrants identify with the culture of their home and receiving countries, and if natives and immigrants have the right attitudes about each other. Ethnic identities and attitudes seem to be less affected by the economic environment but have implications for economic performance
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Intracrystalline diffusion in clinoptilolite: Implications for radionuclide isolation
Experiments have been performed to measure the rate of exchange diffusion in the zeolite clinoptilolite (CL) for elements important to radionuclide isolation at Yucca Mountain, NV. Clinoptilolite is one of the major sorptive minerals in the tuffs at Yucca Mountain, and occurs both as a major component in zeolitized units (Calico Hills), and in fractures in non-zeolitized tuffs (Topopah Spring). Field evidence and numerical modeling suggests that the movement of fluids through the tuff rocks adjacent to the potential repository may occur via episodic flow through fractures. Under conditions of rapid fracture flow the effective sorptive capacity of fracture-lining clinoptilolite may be controlled by exchange diffusion rather than exchange equilibrium
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