828 research outputs found
Computing with Beowulf
Parallel computers built out of mass-market parts are cost-effectively performing data processing and simulation tasks. The Supercomputing (now known as "SC") series of conferences celebrated its 10th anniversary last November. While vendors have come and gone, the dominant paradigm for tackling big problems still is a shared-resource, commercial supercomputer. Growing numbers of users needing a cheaper or dedicated-access alternative are building their own supercomputers out of mass-market parts. Such machines are generally called Beowulf-class systems after the 11th century epic. This modern-day Beowulf story began in 1994 at NASA's Goddard Space Flight Center. A laboratory for the Earth and space sciences, computing managers there threw down a gauntlet to develop a $50,000 gigaFLOPS workstation for processing satellite data sets. Soon, Thomas Sterling and Don Becker were working on the Beowulf concept at the University Space Research Association (USRA)-run Center of Excellence in Space Data and Information Sciences (CESDIS). Beowulf clusters mix three primary ingredients: commodity personal computers or workstations, low-cost Ethernet networks, and the open-source Linux operating system. One of the larger Beowulfs is Goddard's Highly-parallel Integrated Virtual Environment, or HIVE for short
Making the MUVE to virtual education
Second Life, a 3D multi-user virtual environment (MUVE), is becoming an increasingly popular topic at educational technology conferences and in the media these days. What’s all the fuss about
Caltech Faint Field Galaxy Redshift Survey IX: Source detection and photometry in the Hubble Deep Field Region
Detection and photometry of sources in the U_n, G, R, and K_s bands in a 9x9
arcmin^2 region of the sky, centered on the Hubble Deep Field, are described.
The data permit construction of complete photometric catalogs to roughly
U_n=25, G=26, R=25.5 and K_s=20 mag, and significant photometric measurements
somewhat fainter. The galaxy number density is 1.3x10^5 deg^{-2} to R=25.0 mag.
Galaxy number counts have slopes dlog N/dm=0.42, 0.33, 0.27 and 0.31 in the
U_n, G, R and K_s bands, consistent with previous studies and the trend that
fainter galaxies are, on average, bluer. Galaxy catalogs selected in the R and
K_s bands are presented, containing 3607 and 488 sources, in field areas of
74.8 and 59.4 arcmin^2, to R=25.5 and and K_s=20 mag.Comment: Accepted for publication in ApJS; some tables and slightly nicer
figures available at http://www.sns.ias.edu/~hogg/deep
ACME Stellar Spectra. I. Absolutely Calibrated, Mostly Empirical Flux Densities of 55 Cancri and its Transiting Planet 55 Cancri e
The ACME Spectra project provides absolutely calibrated, mostly empirical
spectra of exoplanet host stars for use in analysis of the stars and their
planets. Spectra are obtained from ground-based telescopes and are tied
directly to calibrated ground- and space-based photometry. The spectra remain
only "mostly" empirical because of telluric absorption, but interpolation of
stellar models over the gaps in wavelength coverage provides continuous stellar
spectra. Among other uses, the spectra are suitable for precisely converting
observed secondary eclipses (occultations) into absolute flux units with
minimal recourse to models. In this letter I introduce ACME's methods and
present a calibrated spectrum of the nearby, super-Earth hosting star 55 Cancri
that spans the range from 0.81-5.05 micron. This spectrum is well-suited for
interpreting near- and thermal-infrared eclipse observations. With this
spectrum I show that the brightness temperature of the small, low-mass
transiting planet 55 Cnc e is 1950 +260/-190 K at 4.5 micron (cooler than
previously reported), which corresponds to a planetary flux of 0.44 +0.12/-0.08
mJy. This result suggests the planet has some combination of a nonzero albedo,
a moderately efficient redistribution of absorbed stellar irradiation, and/or
an optically thick atmosphere, but more precise eclipse measurements are
required to distinguish between these scenarii.Comment: Accepted to A&A. 6 pages, 1 figure, 1 electronic table. See
http://irtfweb.ifa.hawaii.edu/~spex/IRTF_Spectral_Library/ for an alternative
spectru
Galaxy luminosity evolution: how much is due to a model choice?
The cluster and field luminosity functions (LFs) determined on large
homogeneous samples (N>2200 galaxies each) are almost indistinguishable, down
to M^*+4 in the r and i filters, hence suggesting that the effect of the
cluster environment on the galaxy properties does not affect the galaxy
luminosity function in red bands. The similarity of the red band LFs in
different environments suggests that the galaxy mass function is preserved
during the galaxy infall in the cluster. By analyzing a large sample of
galaxies in clusters, ideal from many points of view (multicolor data, large
size, many clusters, metric magnitudes) we found that luminosity evolution is
required by the data but the latter do not unambiguously derive its flavour if
a differential luminosity evolution between bright and faint galaxies is
allowed. We show that the LF parameters (slope, characteristic magnitude and
their evolution) and errors depend on assumptions in a way seldom recognized in
literature. We also point out logical inconsistencies between hypothesis
assumed in deriving literature LF and presented results, suggesting caution in
interpreting similar published results.Comment: A&A, in pres
J.S. Bell's Concept of Local Causality
John Stewart Bell's famous 1964 theorem is widely regarded as one of the most
important developments in the foundations of physics. It has even been
described as "the most profound discovery of science." Yet even as we approach
the 50th anniversary of Bell's discovery, its meaning and implications remain
controversial. Many textbooks and commentators report that Bell's theorem
refutes the possibility (suggested especially by Einstein, Podolsky, and Rosen
in 1935) of supplementing ordinary quantum theory with additional ("hidden")
variables that might restore determinism and/or some notion of an
observer-independent reality. On this view, Bell's theorem supports the
orthodox Copenhagen interpretation. Bell's own view of his theorem, however,
was quite different. He instead took the theorem as establishing an "essential
conflict" between the now well-tested empirical predictions of quantum theory
and relativistic \emph{local causality}. The goal of the present paper is, in
general, to make Bell's own views more widely known and, in particular, to
explain in detail Bell's little-known mathematical formulation of the concept
of relativistic local causality on which his theorem rests. We thus collect and
organize many of Bell's crucial statements on these topics, which are scattered
throughout his writings, into a self-contained, pedagogical discussion
including elaborations of the concepts "beable", "completeness", and
"causality" which figure in the formulation. We also show how local causality
(as formulated by Bell) can be used to derive an empirically testable Bell-type
inequality, and how it can be used to recapitulate the EPR argument.Comment: 19 pages, 4 figure
Caltech Faint Galaxy Redshift Survey. IX. Source Detection and Photometry in the Hubble Deep Field Region
Detection and photometry of sources in the U_n, G, ℛ, and K_s bands in a 9 × 9 arcmin^2 region of the sky, centered on the Hubble Deep Field, are described. The data permit construction of complete photometric catalogs to roughly U_n = 25, G = 26, ℛ = 25.5, K_s = 20 mag and significant photometric measurements somewhat fainter. The galaxy number density is 1.3 × 10^5 deg^(-2) to ℛ = 25.0 mag. Galaxy number counts have slopes d log N/dm = 0.42, 0.33, 0.27, and 0.31 in the U_n, G, ℛ, and K_s bands, consistent with previous studies and the trend that fainter galaxies are, on average, bluer. Galaxy catalogs selected in the ℛ and K_s bands are presented, containing 3607 and 488 sources in field areas of 74.8 and 59.4 arcmin^2, to ℛ = 25.5 and K_s = 20 mag
For whom does it work? Moderators of outcome on the effect of a transdiagnostic internet-based maintenance treatment after inpatient psychotherapy: Randomized controlled trial
Background: Recent studies provide evidence for the effectiveness of Internet-based maintenance treatments for mental disorders. However, it is still unclear which participants might or might not profit from this particular kind of treatment delivery. Objective: The study aimed to identify moderators of treatment outcome in a transdiagnostic Internet-based maintenance treatment (TIMT) offered to patients after inpatient psychotherapy for mental disorders in routine care. Methods: Using data from a randomized controlled trial (N=400) designed to test the effectiveness of TIMT, we performed secondary analyses to identify factors moderating the effects of TIMT (intervention) when compared with those of a treatment-as-usual control condition. TIMT involved an online self-management module, asynchronous patient-therapist communication, a peer support group, and online-based progress monitoring. Participants in the control condition had unstructured access to outpatient psychotherapy, standardized outpatient face-to-face continuation treatment, and psychotropic management. Self-reports of psychopathological symptoms and potential moderators were assessed at the start of inpatient treatment (T1), at discharge from inpatient treatment/start of TIMT (T2), and at 3-month (T3) and 12-month follow-up (T4). Results: Education level, positive outcome expectations, and diagnoses significantly moderated intervention versus control differences regarding changes in outcomes between T2 and T3. Only education level moderated change differences between T2 and T4. The effectiveness of the intervention (vs control) was more pronounced among participants with a low (vs high) education level (T2-T3: B=-0.32, SE 0.16, P=.049; T2-T4: B=-0.42, SE 0.21, P=.049), participants with high (vs low) positive outcome expectations (T2-T3: B=-0.12, SE 0.05, P=.02) and participants with anxiety disorder (vs mood disorder) (T2-T3: B=-0.43, SE 0.21, P=.04). Simple slope analyses revealed that despite some subgroups benefiting less from the intervention than others, all subgroups still benefited significantly. Conclusions: This transdiagnostic Internet-based maintenance treatment might be suitable for a wide range of participants differing in various clinical, motivational, and demographic characteristics. The treatment is especially effective for participants with low education levels. These findings may generalize to other Internet-based maintenance treatments. Trial Registration: International Standard Randomized Controlled Trial Number (ISRCTN): 28632626; http://www.controlled-trials.com/isrctn/pf/ 28632626 (Archived by WebCite at http://www.webcitation.org/6IqZjTLrx). © David Daniel Ebert, Mario Gollwitzer, Heleen Riper, Pim Cuijpers, Harald Baumeister, Matthias Berking
Star Clusters in M31: I. A Catalog and a Study of the Young Clusters
We present an updated catalog of 1300 objects in the field of M31, including
670 likely star clusters of various types. Archival images were inspected to
confirm cluster classifications where possible, but most of the classifications
were based on spectra taken of ~1000 objects with the Hectospec fiber
positioner and spectrograph on the 6.5m MMT. The spectra and images of young
clusters are analyzed in detail in this paper. Ages, reddenings and masses of
140 young clusters are derived by comparing the observed spectra and photometry
with model spectra. We find these to have masses as great as 10^5 with a median
of 10^4 M_sun, and a median age of 0.25 Gyr. Thus these clusters are similar in
mass to the LMC young massive clusters, and are in between Milky Way open
clusters and the globulars of M31 and the Milky Way. Most of the M31 young
clusters have the low concentration typical of Milky Way open clusters, and we
expect that most of these will be disrupted in the next Gyr, but a few have
high concentrations and will likely survive longer. The spatial distribution of
the young clusters is well correlated with the star-forming regions as mapped
out by mid-IR emission. A kinematic analysis likewise confirms the spatial
association of the young clusters with the young disk in M31.Comment: 18 pages of text and figures, 23 of tables, to appear in AJ.
http://www.cfa.harvard.edu/oir/eg/m31clusters/M31_Hectospec.html is a new M31
web site containing tables and postage stamp images of the entire catalo
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