1,244 research outputs found
The Economic Impacts of the Regional Greenhouse Gas Initiative on Ten Northeast and Mid-Atlantic States
Assesses outcomes of the first U.S. market-based program to reduce emissions of carbon dioxide from power plants, including impact on electricity markets, power companies' costs, and consumer prices; use of auction proceeds; and states' economic benefits
How Dry Are Red Mergers?
The focus of current research in galaxy evolution has increasingly turned to
understanding the effect that mergers have on the evolution of systems on the
red sequence. For those interactions purported to occur dissipationlessly (so
called "dry mergers"), it would appear that the role of gas is minimal.
However, if these mergers are not completely dry, then even low levels of gas
may be detectable. The purpose of our study is to test whether early type
galaxies with HI in or around them, or "wet" ellipticals, would have been
selected as dry mergers by the criteria in van Dokkum (2005, AJ, 130, 2647). To
that end, we examine a sample of 20 early types from the HI Rogues Gallery with
neutral hydrogen in their immediate environs. Of these, the 15 brightest and
reddest galaxies match the optical dry merger criteria, but in each case, the
presence of HI means that they are not truly dry.Comment: 8 pages plus 1 table and 5 figures; accepted for publication in A
The Cold and Hot Gas Content of Fine-Structure E and S0 Galaxies
We investigate trends of the cold and hot gas content of early-type galaxies
with the presence of optical morphological peculiarities, as measured by the
fine-structure index (Sigma). HI mapping observations from the literature are
used to track the cold-gas content, and archival ROSAT PSPC data are used to
quantify the hot-gas content. We find that E and S0 galaxies with a high
incidence of optical peculiarities are exclusively X-ray underluminous and,
therefore, deficient in hot gas. In contrast, more relaxed galaxies with little
or no signs of optical peculiarities span a wide range of X-ray luminosities.
That is, the X-ray excess anticorrelates with Sigma. There appears to be no
similar trend of cold-gas content with either fine-structure index or X-ray
content. The fact that only apparently relaxed E and S0 galaxies are strong
X-ray emitters is consistent with the hypothesis that after strong disturbances
such as a merger hot-gas halos build up over a time scale of several gigayears.
This is consistent with the expected mass loss from stars.Comment: 12 pages, latex, 5 figures. Accepted for publication in A
AGI and the Knight-Darwin Law: why idealized AGI reproduction requires collaboration
Can an AGI create a more intelligent AGI? Under idealized assumptions, for a certain theoretical type of intelligence, our answer is: “Not without outside help”. This is a paper on the mathematical structure of AGI populations when parent AGIs create child AGIs. We argue that such populations satisfy a certain biological law. Motivated by observations of sexual reproduction in seemingly-asexual species, the Knight-Darwin Law states that it is impossible for one organism to asexually produce another, which asexually produces another, and so on forever: that any sequence of organisms (each one a child of the previous) must contain occasional multi-parent organisms, or must terminate. By proving that a certain measure (arguably an intelligence measure) decreases when an idealized parent AGI single-handedly creates a child AGI, we argue that a similar Law holds for AGIs
Star Clusters in the Tidal Tails of Interacting Galaxies: Cluster Populations Across a Variety of Tail Environments
We have searched for compact stellar structures within 17 tidal tails in 13
different interacting galaxies using F606W- and F814W- band images from the
Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST). The
sample of tidal tails includes a diverse population of optical properties,
merging galaxy mass ratios, HI content, and ages. Combining our tail sample
with Knierman et al. (2003), we find evidence of star clusters formed in situ
with Mv < -8.5 and V-I < 2.0 in 10 of 23 tidal tails; we are able to identify
cluster candidates to Mv = -6.5 in the closest tails. Three tails offer clear
examples of "beads on a string" star formation morphology in V-I color maps.
Two tails present both tidal dwarf galaxy (TDG) candidates and cluster
candidates. Statistical diagnostics indicate that clusters in tidal tails may
be drawn from the same power-law luminosity functions (with logarithmic slopes
~ -2 - -2.5) found in quiescent spiral galaxies and the interiors of
interacting systems. We find that the tail regions with the largest number of
observable clusters are relatively young (< 250 Myr old) and bright (V < 24 mag
arcsec^(-2)), probably attributed to the strong bursts of star formation in
interacting systems soon after periapse. Otherwise, we find no statistical
difference between cluster-rich and cluster-poor tails in terms of many
observable characteristics, though this analysis suffers from complex,
unresolved gas dynamics and projection effects.Comment: Accepted for publication in the Astrophysical Journal. 27 pages, 8
figure
Mesoscale Compositionally Modulated Nanocrystalline Ni-Fe Electrodeposits for Nanopatterning Applications
A considerable range of surface nanostructures can be fabricated by the selective dissolution of elements or phases from metallic alloys. Selectively etched electrodeposited multilayers may find useful application in optoelectronic and MEMS devices. One issue with electrodeposited multilayers is that the fine-scale multilayer structure can often exhibit significant waviness if the band layer spacing is on the same order of magnitude as the grain size. In the present study, the mean grain size was reduced to below 10 nm in a compositionally modulated Ni-Fe alloy. Preferential etching on the electroform cross-section resulted in highly uniform and directional surface channels. The evolution of this nanopatterned surface morphology was characterized by atomic force microscopy and directional roughness parameters were obtained
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