115 research outputs found
Middle-earth\u27s War on Terror: a Post-9/11 Reception Study on the Works of J.R.R. Tolkien
This thesis investigates how Americans can and do interpret Tolkien\u27s works in light of 9/11 and its proximity to Peter Jackson\u27s film adaptations hitting theaters
Semantic Photo Manipulation with a Generative Image Prior
Despite the recent success of GANs in synthesizing images conditioned on
inputs such as a user sketch, text, or semantic labels, manipulating the
high-level attributes of an existing natural photograph with GANs is
challenging for two reasons. First, it is hard for GANs to precisely reproduce
an input image. Second, after manipulation, the newly synthesized pixels often
do not fit the original image. In this paper, we address these issues by
adapting the image prior learned by GANs to image statistics of an individual
image. Our method can accurately reconstruct the input image and synthesize new
content, consistent with the appearance of the input image. We demonstrate our
interactive system on several semantic image editing tasks, including
synthesizing new objects consistent with background, removing unwanted objects,
and changing the appearance of an object. Quantitative and qualitative
comparisons against several existing methods demonstrate the effectiveness of
our method.Comment: SIGGRAPH 201
The pre-inflationary vacuum in the cosmic microwave background
We consider the effects on the primordial power spectrum of a period of
radiation-dominated expansion prior to the inflationary era. If inflation lasts
a total of only 60 e-folds or so, the boundary condition for quantum modes
cannot be taken in the short-wavelength limit as in the standard perturbation
calculation. Instead, the boundary condition is set by the vacuum state of the
prior radiation-dominated epoch, which only corresponds to the inflationary
vacuum state in the ultraviolet limit. This altered vacuum state results in a
modulation of the inflationary power spectrum. We calculate the modification to
a best-fit model from the WMAP3 data set, and find that power is suppressed at
large scales. The modified power spectrum is favored only very weakly by the
data.Comment: 4 pages, 2 figures, references added. Version submitted to PRL. (v3:
9 pages, 4 figures, detailed justification of Eq. 11 of v2. Version accepted
for publication by PRD.
The galaxy counts-in-cells distribution from the SDSS
We determine the galaxy counts-in-cells distribution from the Sloan Digital
Sky Survey (SDSS) for 3D spherical cells in redshift space as well as for 2D
projected cells. We find that cosmic variance in the SDSS causes the
counts-in-cells distributions in different quadrants to differ from each other
by up to 20%. We also find that within this cosmic variance, the overall galaxy
counts-in-cells distribution agrees with both the gravitational
quasi-equilibrium distribution and the negative binomial distribution. We also
find that brighter galaxies are more strongly clustered than if they were
randomly selected from a larger complete sample that includes galaxies of all
luminosities. The results suggest that bright galaxies could be in dark matter
haloes separated by less than ~10 Mpc/h.Comment: Accepted for publication in the Astrophysical Journal. Revised
version with referee suggestions and corrected typo
Seeing What a GAN Cannot Generate
Despite the success of Generative Adversarial Networks (GANs), mode collapse
remains a serious issue during GAN training. To date, little work has focused
on understanding and quantifying which modes have been dropped by a model. In
this work, we visualize mode collapse at both the distribution level and the
instance level. First, we deploy a semantic segmentation network to compare the
distribution of segmented objects in the generated images with the target
distribution in the training set. Differences in statistics reveal object
classes that are omitted by a GAN. Second, given the identified omitted object
classes, we visualize the GAN's omissions directly. In particular, we compare
specific differences between individual photos and their approximate inversions
by a GAN. To this end, we relax the problem of inversion and solve the
tractable problem of inverting a GAN layer instead of the entire generator.
Finally, we use this framework to analyze several recent GANs trained on
multiple datasets and identify their typical failure cases.Comment: ICCV 2019 oral; http://ganseeing.csail.mit.edu
Controlling Chaos through Compactification in Cosmological Models with a Collapsing Phase
We consider the effect of compactification of extra dimensions on the onset
of classical chaotic "Mixmaster" behavior during cosmic contraction. Assuming a
universe that is well-approximated as a four-dimensional
Friedmann-Robertson--Walker model (with negligible Kaluza-Klein excitations)
when the contraction phase begins, we identify compactifications that allow a
smooth contraction and delay the onset of chaos until arbitrarily close the big
crunch. These compactifications are defined by the de Rham cohomology (Betti
numbers) and Killing vectors of the compactification manifold. We find
compactifications that control chaos in vacuum Einstein gravity, as well as in
string theories with N = 1 supersymmetry and M-theory. In models where chaos is
controlled in this way, the universe can remain homogeneous and flat until it
enters the quantum gravity regime. At this point, the classical equations
leading to chaotic behavior can no longer be trusted, and quantum effects may
allow a smooth approach to the big crunch and transition into a subsequent
expanding phase. Our results may be useful for constructing cosmological models
with contracting phases, such as the ekpyrotic/cyclic and pre-big bang models.Comment: 1 figure. v2/v3: minor typos correcte
X-ray emission from the Sombrero galaxy: discrete sources
We present a study of discrete X-ray sources in and around the
bulge-dominated, massive Sa galaxy, Sombrero (M104), based on new and archival
Chandra observations with a total exposure of ~200 ks. With a detection limit
of L_X = 1E37 erg/s and a field of view covering a galactocentric radius of ~30
kpc (11.5 arcminute), 383 sources are detected. Cross-correlation with Spitler
et al.'s catalogue of Sombrero globular clusters (GCs) identified from HST/ACS
observations reveals 41 X-rays sources in GCs, presumably low-mass X-ray
binaries (LMXBs). We quantify the differential luminosity functions (LFs) for
both the detected GC and field LMXBs, whose power-low indices (~1.1 for the
GC-LF and ~1.6 for field-LF) are consistent with previous studies for
elliptical galaxies. With precise sky positions of the GCs without a detected
X-ray source, we further quantify, through a fluctuation analysis, the GC LF at
fainter luminosities down to 1E35 erg/s. The derived index rules out a
faint-end slope flatter than 1.1 at a 2 sigma significance, contrary to recent
findings in several elliptical galaxies and the bulge of M31. On the other
hand, the 2-6 keV unresolved emission places a tight constraint on the field
LF, implying a flattened index of ~1.0 below 1E37 erg/s. We also detect 101
sources in the halo of Sombrero. The presence of these sources cannot be
interpreted as galactic LMXBs whose spatial distribution empirically follows
the starlight. Their number is also higher than the expected number of cosmic
AGNs (52+/-11 [1 sigma]) whose surface density is constrained by deep X-ray
surveys. We suggest that either the cosmic X-ray background is unusually high
in the direction of Sombrero, or a distinct population of X-ray sources is
present in the halo of Sombrero.Comment: 11 figures, 5 tables, ApJ in pres
The Ages, Metallicities and Alpha Element Enhancements of Globular Clusters in the Elliptical NGC 5128: A Homogeneous Spectroscopic Study with Gemini/GMOS
We present new integrated light spectroscopy of globular clusters (GCs) in
NGC 5128 in order to measure radial velocities and derive ages, metallicities,
and alpha-element abundance ratios. Using Gemini-S 8-m/GMOS, we obtained
spectroscopy in the range of ~3400-5700 AA for 72 GCs with S/N > 30 /AA and we
have also discovered 35 new GCs within NGC 5128 from our radial velocity
measurements. We measured and compared the Lick indices from HdeltaA through
Fe5406 with the single stellar population (SSP) models of Thomas et
al.(2003,2004). We also measure Lick indices for 41 Milky Way GCs from Puzia et
al. (2002) and Schiavon et al. (2005) with the same methodology for direct
comparison. Our results show that 68% of the NGC 5128 GCs have old ages (> 8
Gyr), 14% have intermediate ages (5-8 Gyr), and 18% have young ages (< 5 Gyr).
However, when we look at the metallicity of the GCs as a function of age, we
find 92% of metal-poor GCs and 56% of metal-rich GCs in NGC 5128 have ages > 8
Gyr, indicating that the majority of both metallicity subpopulations of GCs
formed early, with a significant population of young and metal-rich GCs forming
later. Our metallicity distribution function generated directly from
spectroscopic Lick indices is clearly bimodal, as is the color distribution of
the same set of GCs. Thus the metallicity bimodality is real and not an
artifact of the color to metallicity conversion. The [alpha/Fe] values are
supersolar with a mean value of 0.14pm0.04, indicating a fast formation
timescale. However, the GCs in NGC 5128 are not as [alpha/Fe] enhanced as the
Milky Way GCs also examined in this study. Our results support a rapid, early
formation of the GC system in NGC 5128, with subsequent major accretion and/or
GC and star forming events in more recent times (abridged).Comment: Accepted to The Astrophysical Journal, 36 pages, 14 figures, 7 table
Cosmology with a long range repulsive force
We consider a class of cosmological models in which the universe is filled
with a (non-electric) charge density that repels itself by means of a force
carried by a vector boson with a tiny mass. When the vector's mass depends upon
other fields, the repulsive interaction gives rise to an electromagnetic
barrier which prevents these fields from driving the mass to zero. This can
modify the cosmology dramatically. We present a very simple realization of this
idea in which the vector's mass arises from a scalar field. The electromagnetic
barrier prevents this field from rolling down its potential and thereby leads
to accelerated expansion.Comment: 15 pages, 8 figures, LaTeX (version accepted for publication in PRD).
3 new figures, extended discussion of observational consequence
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