4,466 research outputs found
Condiciones para un aprendizaje de calidad en la enseñanza de las ciencias : reflexiones a partir del Proyecto Peel
In this summary of the topics presented in the closing lecture of the Congress, some of the key-ideas which from our view characterize the science quality learning are reviewed. These ideas have been developed in the framework of the PEEL, an investigation-action project in which teachers and researchers have collaborated
An FeLoBAL Binary Quasar
In an ongoing infrared imaging survey of quasars at Keck Observatory, we have
discovered that the z=1.285 quasar SDSS J233646.2-010732.6 comprises two point
sources with a separation of 1.67". Resolved spectra show that one component is
a standard quasar with a blue continuum and broad emission lines; the other is
a broad absorption line (BAL) quasar, specifically, a BAL QSO with prominent
absorption from MgII and metastable FeII, making it a member of the ``FeLoBAL''
class. The number of known FeLoBALs has recently grown dramatically from a
single example to more than a dozen, including a gravitationally lensed example
and the binary member presented here, suggesting that this formerly rare object
may be fairly common. Additionally, the presence of this BAL quasar in a
relatively small separation binary adds to the growing evidence that the BAL
phenomenon is not due to viewing a normal quasar at a specific orientation, but
rather that it is an evolutionary phase in the life of many, if not all,
quasars, and is particularly associated with conditions found in interacting
systems.Comment: AASTEX 13 pp., 4 figs; accepted by ApJ Letter
A massive warm baryonic halo in the Coma cluster
Several deep PSPC observations of the Coma cluster reveal a very large-scale
halo of soft X-ray emission, substantially in excess of the well known
radiation from the hot intra-cluster medium. The excess emission, previously
reported in the central region of the cluster using lower-sensitivity EUVE and
ROSAT data, is now evident out to a radius of 2.6 Mpc, demonstrating that the
soft excess radiation from clusters is a phenomenon of cosmological
significance. The X-ray spectrum at these large radii cannot be modeled
non-thermally, but is consistent with the original scenario of thermal emission
from warm gas at ~ 10^6 K. The mass of the warm gas is on par with that of the
hot X-ray emitting plasma, and significantly more massive if the warm gas
resides in low-density filamentary structures. Thus the data lend vital support
to current theories of cosmic evolution, which predict that at low redshift
\~30-40 % of the baryons reside in warm filaments converging at clusters of
galaxies.Comment: Astrophysical Journal, in pres
Cosmic microwave background snapshots: pre-WMAP and post-WMAP
Abbreviated: We highlight the remarkable evolution in the CMB power spectrum
over the past few years, and in the cosmological parameters for minimal
inflation models derived from it. Grand unified spectra (GUS) show pre-WMAP
optimal bandpowers are in good agreement with each other and with the one-year
WMAP results, which now dominate the L < 600 bands. GUS are used to determine
calibrations, peak/dip locations and heights, and damping parameters. These CMB
experiments significantly increased the case for accelerated expansion in the
early universe (the inflationary paradigm) and at the current epoch (dark
energy dominance) when they were combined with `prior' probabilities on the
parameters. A minimal inflation parameter set is applied in the same way to the
evolving data. Grid-based and and Monte Carlo Markov Chain methods are shown to
give similar values, highly stable over time and for different prior choices,
with the increasing precision best characterized by decreasing errors on
uncorrelated parameter eigenmodes. After marginalizing over the other cosmic
and experimental variables for a weak+LSS prior, the pre-WMAP data of Jan03 cf.
the post-WMAP data of Mar03 give Omega_{tot} =1.03^{+0.05}_{-0.04} cf.
1.02^{+0.04}_{-0.03}. Adding the flat prior, n_s =0.95^{+0.07}_{-0.04} cf.
0.97^{+0.02}_{-0.02}, with < 2\sigma evidence for a log variation of n_s. The
densities have concordance values. The dark energy pressure-to-density ratio is
not well constrained by our weak+LSS prior, but adding SN1 gives w_Q < -0.7. We
find \sigma_8 = 0.89^{+0.06}_{-0.07} cf. 0.86^{+0.04}_{-0.04}, implying a
sizable SZ effect; the high L power suggest \sigma_8 \sim 0.94^{+0.08}_{-0.16}
is needed to be SZ-compatible.Comment: 36 pages, 5 figures, 5 tables, Jan 2003 Roy Soc Discussion Meeting on
`The search for dark matter and dark energy in the Universe', published PDF
(Oct 15 2003) is http://www.cita.utoronto.ca/~bond/roysoc03/03TA2435.pd
The Human Occupation Along the Steel Creek Floodplain: Results of an Intensive Archeological Survey for the L Area Reactivation Project, Savannah River Plant, Barnwell County, South Carolina
https://scholarcommons.sc.edu/archanth_books/1164/thumbnail.jp
Control theory for principled heap sizing
We propose a new, principled approach to adaptive heap sizing based on control theory. We review current state-of-the-art heap sizing mechanisms, as deployed in Jikes RVM and HotSpot. We then formulate heap sizing as a control problem, apply and tune a standard controller algorithm, and evaluate its performance on a set of well-known benchmarks. We find our controller adapts the heap size more responsively than existing mechanisms. This responsiveness allows tighter virtual machine memory footprints while preserving target application throughput, which is ideal for both embedded and utility computing domains. In short, we argue that formal, systematic approaches to memory management should be replacing ad-hoc heuristics as the discipline matures. Control-theoretic heap sizing is one such systematic approach
Discovery of a Radio-Selected z ~ 6 Quasar
We present the discovery of only the second radio-selected, z ~ 6 quasar. We
identified SDSS J222843.54+011032.2 (z=5.95) by matching the optical detections
of the deep Sloan Digital Sky Survey (SDSS) Stripe 82 with their radio
counterparts in the Stripe82 VLA Survey. We also matched the
Canadian-France-Hawaiian Telescope Legacy Survey Wide (CFHTLS Wide) with the
Faint Images of the Radio Sky at Twenty-cm (FIRST) survey but have yet to find
any z ~ 6 quasars in this survey area. The discovered quasar is
optically-faint, z = 22.3 and M_{1450} ~ -24.5, but radio-bright, with a flux
density of f = 0.31mJy and a radio-loudness of R ~ 1100 (where
R = f_{5GHz}/f_{2500}). The i-z color of the discovered quasar places it
outside the color selection criteria for existing optical surveys. We conclude
by discussing the need for deeper wide-area radio surveys in the context of
high-redshift quasars.Comment: 20 pages, 6 figures, and ApJ accepte
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