2,659 research outputs found
A Meta-Analysis of Procedures to Change Implicit Measures
Using a novel technique known as network meta-analysis, we synthesized evidence from 492 studies (87,418 participants) to investigate the effectiveness of procedures in changing implicit measures, which we define as response biases on implicit tasks. We also evaluated these proceduresâ effects on explicit and behavioral measures. We found that implicit measures can be changed, but effects are often relatively weak (|ds| \u3c .30). Most studies focused on producing short-term changes with brief, single-session manipulations. Procedures that associate sets of concepts, invoke goals or motivations, or tax mental resources changed implicit measures the most, whereas procedures that induced threat, affirmation, or specific moods/emotions changed implicit measures the least. Bias tests suggested that implicit effects could be inflated relative to their true population values. Procedures changed explicit measures less consistently and to a smaller degree than implicit measures and generally produced trivial changes in behavior. Finally, changes in implicit measures did not mediate changes in explicit measures or behavior. Our findings suggest that changes in implicit measures are possible, but those changes do not necessarily translate into changes in explicit measures or behavior
Practical Strategic Reasoning with Applications in Market Games.
Strategic reasoning is part of our everyday lives: we negotiate prices, bid in auctions, write contracts, and play games. We choose actions in these scenarios based on our preferences, and our beliefs about preferences of the other participants. Game theory provides a rich mathematical framework through which we can reason about the influence of these preferences. Clever abstractions allow us to predict the outcome of complex agent interactions, however, as the scenarios we model increase in complexity, the abstractions we use to enable classical game-theoretic analysis lose fidelity. In empirical game-theoretic analysis, we construct game models using empirical sources of knowledgeâsuch as high-fidelity simulation. However, utilizing empirical knowledge introduces a host of different computational and statistical problems.
I investigate five main research problems that focus on efficient selection, estimation, and analysis of empirical game models. I introduce a flexible modeling approach, where we may construct multiple game-theoretic models from the same set of observations. I propose a principled methodology for comparing empirical game models and a family of algorithms that select a model from a set of candidates.
I develop algorithms for normal-form games that efficiently identify formationsâsets of strategies that are closed under a (correlated) best-response correspondence. This aids in problems, such as finding Nash equilibria, that are key to analysis but hard to solve. I investigate policies for sequentially determining profiles to simulate, when constrained by a budget for simulation. Efficient policies allow modelers to analyze complex scenarios by evaluating a subset of the profiles. The policies I introduce outperform the existing policies in experiments.
I establish a principled methodology for evaluating strategies given an empirical game model. I employ this methodology in two case studies of market scenarios: first, a case study in supply chain management from the perspective of a strategy designer; then, a case study in Internet ad auctions from the perspective of a mechanism designer. As part of the latter analysis, I develop an ad-auctions scenario that captures several key strategic issues in this domain for the first time.Ph.D.Computer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75848/1/prjordan_1.pd
The Relative Ages of the Globular Cluster Subpopulations in M87
Relative ages for the globular cluster (GC) subpopulations in the Virgo giant
elliptical galaxy M87 (NGC 4486) have been determined from Stroemgren
photometry obtained with WFPC2 on board HST. Using a variety of population
synthesis models, and assuming the GC mass at the turnover of the luminosity
function is the same for both subpopulations, differential ages have been
determined from the observed magnitudes at the turnover of the globular cluster
luminosity function and from the mean color of each subpopulation. We measure
an age difference between the two subpopulations of 0.2 +/- 1.5 (systematic)
+/- 2 (random) Gyr, in the sense that the blue GCs are formally older. Thus, to
within our measurement errors, the two subpopulations are found to be coeval.
Combined with previous spectroscopic age determinations for M87 GCs, our
results favor a picture in which the GCs associated with this galaxy are formed
at high redshift, and within a period of a few Gyr.Comment: 5 pages, 2 postscript figures. Accepted for publication in ApJ
Letter
Intergalactic Globular Clusters
We confirm and extend our previous detection of a population of intergalactic
globular clusters in Abell 1185, and report the first discovery of an
intergalactic globular cluster in the nearby Virgo cluster of galaxies. The
numbers, colors and luminosities of these objects can place constraints on
their origin, which in turn may yield new insights to the evolution of galaxies
in dense environments.Comment: 2 pages, no figures. Talk presented at JD6, IAU General Assembly XXV,
Sydney, Australia, July 2003, to appear in Highlights of Astronomy, Vol. 1
The Next Generation Virgo Cluster Survey. IX. Estimating the Efficiency of Galaxy Formation on the Lowest-Mass Scales
The Next Generation Virgo Cluster Survey has recently determined the
luminosity function of galaxies in the core of the Virgo cluster down to
unprecedented magnitude and surface brightness limits. Comparing simulations of
cluster formation to the derived central stellar mass function, we attempt to
estimate the stellar-to-halo-mass ratio (SHMR) for dwarf galaxies, as it would
have been before they fell into the cluster. This approach ignores several
details and complications, e.g., the contribution of ongoing star formation to
the present-day stellar mass of cluster members, and the effects of adiabatic
contraction and/or violent feedback on the subhalo and cluster potentials. The
final results are startlingly simple, however; we find that the trends in the
SHMR determined previously for bright galaxies appear to extend down in a
scale-invariant way to the faintest objects detected in the survey. These
results extend measurements of the formation efficiency of field galaxies by
two decades in halo mass, or five decades in stellar mass, down to some of the
least massive dwarf galaxies known, with stellar masses of .Comment: 18 pages, 12 figures; published in ApJ July 1st 201
The Next Generation Virgo cluster Survey. V. modelling the dynamics of M87 with the Made-to-Measure method
We study the dynamics of the giant elliptical galaxy M87 from the central to
the outermost regions with the made-to-measure (M2M) method. We use a new
catalogue of 922 globular cluster line-of- sight velocities extending to a
projected radius of 180 kpc (equivalent to 25 M87 effective radii), and SAURON
integral field unit data within the central 2.4 kpc. 263 globular clusters,
mainly located beyond 40 kpc, are newly observed by the Next Generation Virgo
Survey (NGVS). For the M2M modelling, the gravitational potential is taken as a
combination of a luminous matter potential with a constant stellar
mass-to-light ratio and a dark matter potential modelled as a logarithmic
potential. Our best dynamical model returns a stellar mass-to-light ratio in
the I band of M/LI = 6.0(+ -0.3) M_sun/L_sun with a dark matter potential scale
velocity of 591(+ -50) km/s and scale radius of 42(+ -10) kpc. We determine the
total mass of M87 within 180 kpc to be (1.5 + - 0.2) 10^13 M_sun. The mass
within 40 kpc is smaller than previous estimates determined using globular
cluster kinematics that did not extend beyond 45 kpc. With our new globular
cluster velocities at much larger radii, we see that globular clusters around
40 kpc show an anomalously large velocity dispersion which affected previous
results. The mass we derived is in good agreement with that inferred from ROSAT
X-ray observation out to 180 kpc. Within 30 kpc our mass is also consistent
with that inferred from Chandra and XMM-Newton X-ray observations, while within
120 kpc it is about 20% smaller. The model velocity dispersion anisotropy beta
parameter for the globular clusters in M87 is small, varying from -0.2 at the
centre to 0.2 at 40 kpc, and gradually decreasing to zero at 120 kpc.Comment: 20 pages, 16 figures, Accepted by Ap
The Next Generation Virgo Cluster Survey. X. Properties of Ultra-Compact Dwarfs in the M87, M49 and M60 Regions
We use imaging from the Next Generation Virgo cluster Survey (NGVS) to
present a comparative study of ultra-compact dwarf (UCD) galaxies associated
with three prominent Virgo sub-clusters: those centered on the massive,
red-sequence galaxies M87, M49 and M60. We show how UCDs can be selected with
high completeness using a combination of half-light radius and location in
color-color diagrams ( or ). Although the central galaxies in
each of these sub-clusters have nearly identical luminosities and stellar
masses, we find large differences in the sizes of their UCD populations, with
M87 containing ~3.5 and 7.8 times more UCDs than M49 and M60, respectively. The
relative abundance of UCDs in the three regions scales in proportion to
sub-cluster mass, as traced by X-ray gas mass, total gravitating mass, number
of globular clusters, and number of nearby galaxies. We find that the UCDs are
predominantly blue in color, with ~85% of the UCDs having colors similar to
blue GCs and stellar nuclei of dwarf galaxies. We present evidence that UCDs
surrounding M87 and M49 may follow a morphological sequence ordered by the
prominence of their outer, low surface brightness envelope, ultimately merging
with the sequence of nucleated low-mass galaxies, and that envelope prominence
correlates with distance from either galaxy. Our analysis provides evidence
that tidal stripping of nucleated galaxies is an important process in the
formation of UCDs.Comment: 37 pages, 40 figures. To appear in The Astrophysical Journa
The Next Generation Virgo Cluster Survey. VIII. The Spatial Distribution of Globular Clusters in the Virgo Cluster
We report on a large-scale study of the distribution of globular clusters
(GCs) throughout the Virgo cluster, based on photometry from the Next
Generation Virgo Cluster Survey, a large imaging survey covering Virgo's
primary subclusters to their virial radii. Using the g', (g'-i')
color-magnitude diagram of unresolved and marginally-resolved sources, we
constructed 2-D maps of the GC distribution. We present the clearest evidence
to date showing the difference in concentration between red and blue GCs over
the extent of the cluster, where the red (metal-rich) GCs are largely located
around the massive early-type galaxies, whilst the blue (metal-poor) GCs have a
more extended spatial distribution, with significant populations present beyond
83' (215 kpc) along the major axes of M49 and M87. The GC distribution around
M87 and M49 shows remarkable agreement with the shape, ellipticity and boxiness
of the diffuse light surrounding both galaxies. We find evidence for spatial
enhancements of GCs surrounding M87 that may be indicative of recent
interactions or an ongoing merger history. We compare the GC map to the
locations of Virgo galaxies and the intracluster X-ray gas, and find good
agreement between these baryonic structures. The Virgo cluster contains a total
population of 6730014400 GCs, of which 35% are located in M87 and M49
alone. We compute a cluster-wide specific frequency S_N,CL=,
including Virgo's diffuse light. The GC-to-baryonic mass fraction is
e_b=and the GC-to-total cluster mass formation
efficiency is e_t=, values slightly lower than, but
consistent with, those derived for individual galactic halos. Our results show
that the production of the complex structures in the unrelaxed Virgo cluster
core (including the diffuse intracluster light) is an ongoing
process.(abridged)Comment: 23 pages, 17 figures. Accepted for publication in the Astrophysical
Journal. Figure 1 has reduced resolution. Revised version with updated
references, corrected typos -- no changes to result
The ACS Virgo Cluster Survey. XIV. Analysis of Color-Magnitude Relations in Globular Cluster Systems
We examine the correlation between globular cluster (GC) color and magnitude
using HST/ACS imaging for a sample of 79 early-type galaxies (-21.7<M_B<-15.2
mag) with accurate SBF distances from the ACS Virgo Cluster Survey. Using the
KMM mixture modeling algorithm, we find a highly significant correlation,
d(g-z)/dz = -0.037 +- 0.004, between color and magnitude for the subpopulation
of blue GCs in the co-added GC color-magnitude diagram of the three brightest
Virgo galaxies (M49, M87 and M60): brighter GCs are redder than their fainter
counterparts. For the single GC systems of M87 and M60, we find similar
correlations; M49 does not appear to show a significant trend. There is no
correlation between (g-z) and M_z for GCs of the red subpopulation. The
correlation d(g-z)/dg for the blue subpopulation is much weaker than d(g-z)/dz.
Using Monte Carlo simulations, we attribute this to the fact that the blue
subpopulation in M_g extends to higher luminosities than the red subpopulation,
which biases the KMM fits. The correlation between color and M_z thus is a real
effect. This conclusion is supported by biweight fits to the same color
distributions. We identify two environmental dependencies of the
color-magnitude relation: (1) the slope decreases in significance with
decreasing galaxy luminosity; and (2) the slope is stronger for GCs at smaller
galactocentric distances. We examine several mechanisms that might give rise to
the observed color-magnitude relation: (1) presence of contaminators; (2)
accretion of GCs from low-mass galaxies; (3) stochastic effects; (4) capture of
field stars by individual GCs; and (5) GC self-enrichment. We conclude that
self-enrichment and field-star capture, or a combination of these processes,
offer the most promising means of explaining our observations.Comment: 15 pages, 12 figures, accepted for publication in the Astrophysical
Journal. Uses emulateapj.cl
Fish Colonization of a Newly Deployed Vessel-reef off Southeast Florida: Preliminary Results
Fish colonization on the Ebenezer II, a 25.5m merchant marine vessel, was studied from May 2002 - July 2003. The ship was scuttled in May 2002 off Broward County, Florida at a depth of 21m and was censused 10 times during the study period using a modified Bohnsack and Bannerot visual census method. Adjacent natural reefs and the Mcallister, a nearby, 30m tugboat deployed in June 1998, were censused during the same period.
Distinct changes in the fish assemblage on the Ebenezer II were observed throughout the sample period. A pioneer assemblage was observed during the first three months, characterized by the settlement of juvenile fishes «5 cm). Subsequently, numbers of juveniles decreased either through emigration, predation or growth. Resident species made up 52.5% of the total abundance but transient fish species made up 78% of the total fish biomass during the study period.
Surprisingly, attraction of adult fish from both natural reefs and the Mcallister was not a major factor in assemblage fonnation. The primary adult fishes attracted to the Ebenezer II were herbivores. These fishes steadily increased in abundance throughout the study period, presumably due to increased food availability as benthic algal communities developed. A similar trend of increasing herbivores with increasing soak time was observed on the Spiegel Grove, a 153m vessel-reef sunk off Key Largo in May 2002.
The fish assemblages on the artificial reefs were more similar to each other than to natural reefs. Vessel-reefs had sixty species in common, while the Ebenezer II only had thirty-nine species in common with natural reefs. Several species common to vessel-reefs were absent or rare on nearby natural reefs. This may indicate that vessel-reefs are providing early juvenile and adult habitat that is not available on natural reefs
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