1,855 research outputs found
DriftRec: Adapting diffusion models to blind JPEG restoration
In this work, we utilize the high-fidelity generation abilities of diffusion
models to solve blind JPEG restoration at high compression levels. We propose
an elegant modification of the forward stochastic differential equation of
diffusion models to adapt them to this restoration task and name our method
DriftRec. Comparing DriftRec against an regression baseline with the same
network architecture and two state-of-the-art techniques for JPEG restoration,
we show that our approach can escape the tendency of other methods to generate
blurry images, and recovers the distribution of clean images significantly more
faithfully. For this, only a dataset of clean/corrupted image pairs and no
knowledge about the corruption operation is required, enabling wider
applicability to other restoration tasks. In contrast to other conditional and
unconditional diffusion models, we utilize the idea that the distributions of
clean and corrupted images are much closer to each other than each is to the
usual Gaussian prior of the reverse process in diffusion models. Our approach
therefore requires only low levels of added noise, and needs comparatively few
sampling steps even without further optimizations. We show that DriftRec
naturally generalizes to realistic and difficult scenarios such as unaligned
double JPEG compression and blind restoration of JPEGs found online, without
having encountered such examples during training.Comment: This work has been submitted to the IEEE for possible publication.
Copyright may be transferred without notice, after which this version may no
longer be accessibl
Changes in Length of Grandparenthood in Finland 1790-1959
The importance of grandparents for their grandchildren is well-studied in several disciplines, and studies are now also addressing the potential effects of grandchildren on grandparental wellbeing. Any such effects are limited by the time grandparents share with their grandchildren. Changing child mortality rates, grandparental longevity, and childbearing patterns may have profoundly altered the length of grandparenthood across the demographic transition, but this has received little scientific attention. Using a genealogical dataset from Finland, we investigate changes in this shared time, from the late 18th to mid-20th century. We found the number of shared years between grandparents and grandchildren was low until roughly the onset of industrialisation in Finland, after which point shared time increased rapidly, from both the grandchild and grandparent perspectives. Understanding changing patterns in the opportunity for intergenerational transfers between grandparents and grandchildren has implications for several fields of study, including biology, demography, sociology, health studies, and economics
Dynamics in the satellite system of Triangulum: Is AndXXII a dwarf satellite of M33?
We present results from a spectroscopic survey of the dwarf spheroidal And
XXII and the two extended clusters EC1 and EC2. These three objects are
candidate satellites of the Triangulum galaxy, M33, which itself is likely a
satellite of M31. We use the DEep Imaging Multi-Object Spectrograph mounted on
the Keck-II telescope to derive radial velocities for candidate member stars of
these objects and thereby identify the stars that are most likely actual
members. Eleven most probable stellar members (of 13 candidates) are found for
AndXXII. We obtain an upper limit of sigma_v < 6.0 km s-1 for the velocity
dispersion of AndXXII, [Fe/H] ~ -1.6 for its metallicity, and 255pc for the
Plummer radius of its projected density profile. We construct a colour
magnitude diagram for AndXXII and identify both the red giant branch and the
horizontal branch. The position of the latter is used to derive a heliocentric
distance to And XXII of 853 pm 26 kpc. The combination of the radial velocity,
distance, and angular position of AndXXII indicates that it is a strong
candidate for being the first known satellite of M33 and one of the very few
examples of a galactic satellite of a satellite. N-body simulations imply that
this conclusion is unchanged even if M31 and M33 had a strong encounter in the
past few Gyr. We test the hypothesis that the extended clusters highlight
tidally stripped galaxies by searching for an excess cloud of halo-like stars
in their vicinity. We find such a cloud for the case of EC1 but not EC2. The
three objects imply a dynamical mass for M33 that is consistent with previous
estimates.Comment: 14 pages, 14 figures, revised for MNRAS publicatio
The kinematic footprints of five stellar streams in Andromeda's halo
(abridged) We present a spectroscopic analysis of five stellar streams (`A',
`B', `Cr', `Cp' and `D') as well as the extended star cluster, EC4, which lies
within streamC, all discovered in the halo of M31 from our CFHT/MegaCam survey.
These spectroscopic results were initially serendipitous, making use of our
existing observations from the DEep Imaging Multi-Object Spectrograph mounted
on the Keck II telescope, and thereby emphasizing the ubiquity of tidal streams
that account for ~70% of the M31 halo stars in the targeted fields. Subsequent
spectroscopy was then procured in streamCr/p and streamD to trace the velocity
gradient along the streams. For the cluster EC4, candidate member stars with
average [Fe/H]~-1.4 (Fe/H_spec=-1.6), are found at v_{hel}=-285 km/s suggesting
it could be related to streamCp. No similarly obvious cold kinematic candidate
is found for streamD, although candidates are proposed in both of two
spectroscopic pointings along the stream (both at -400 km/s). Spectroscopy near
the edge of streamB suggests a likely kinematic detection, while a candidate
kinematic detection of streamA is found (plausibly associated to M33 rather
than M31). The low dispersion of the streams in kinematics, physical thickness,
and metallicity makes it hard to reconcile with a scenario whereby these stream
structures as an ensemble are related to the giant southern stream. We conclude
that the M31 stellar halo is largely made up of multiple kinematically cold
streams.Comment: 19 pages, 12 figures, accepted in MNRAS. High resolution version,
with fig10 here: http://www.ast.cam.ac.uk/~schapman/streams.pd
A Keck/DEIMOS spectroscopic survey of the faint M31 satellites And IX, And XI, And XII, and And XIII
We present the first spectroscopic analysis of the faint M31 satellite
galaxies, AndXI and AndXIII, and a reanalysis of existing spectroscopic data
for two further faint companions, And IX and AndXII. By combining data obtained
using the DEIMOS spectrograph mounted on the Keck II telescope with deep
photometry from the Suprime-Cam instrument on Subaru, we have calculated global
properties for the dwarfs, such as systemic velocities, metallicites and
half-light radii.We find each dwarf to be very metal poor ([Fe/H] -2 both
photometrically and spectroscopically, from their stacked spectrum), and as
such, they continue to follow the luminosity-metallicity relationship
established with brighter dwarfs. We are unable to resolve a dispersion for And
XI due to small sample size and low S/N, but we set a one sigma upper limit of
sigma-v <5 km/s. For And IX, And XII and And XIII we resolve velocity
dispersions of v=4.5 (+3.4,-3.2), 2.6(+5.1,-2.6) and 9.7(+8.9,-4.5) km/s, and
derive masses within the half light radii of 6.2(+5.3,-5.1)x10^6 Msun, 2.4
(+6.5,-2.4)x10^6 Msun and 1.1(+1.4,-0.7)x10^7 Msun respectively. We discuss
each satellite in the context of the Mateo relations for dwarf spheroidal
galaxies, and the Universal halo profiles established for Milky Way dwarfs
(Walker et al. 2009). For both galaxies, this sees them fall below the
Universal halo profiles of Walker et al. (2009). When combined with the
findings of McConnachie & Irwin (2006a), which reveal that the M31 satellites
are twice as extended (in terms of both half-light and tidal radii) as their
Milky Way counterparts, these results suggest that the satellite population of
the Andromeda system could inhabit halos that are significantly different from
those of the Milky Way in terms of their central densities (abridged).Comment: 26 pages, 18 figures, MNRAS submitte
Will granny save me? Birth status, survival, and the role of grandmothers in historical Finland
Grandmothers play a crucial role in families enhancing grandchild
wellbeing and survival but their effects can be context-dependent, and
the children born in poor conditions are most likely to benefit from the
investments made by helping grandmothers. In this study, we examined,
for the first time, whether grandmothers' presence modified associations
between adverse birth status and survival up to 5 years of age. In
detail, we verified, whether (i) firstborns, (ii) twins, (iii) children born within 24 months after their sibling, and (iv)
children followed by short interval (i.e. their younger sibling was
born within 24 months) survived better when either their maternal,
paternal, or both grandmothers were present. Moreover, we evaluated
whether illegitimate children survived better when the maternal
grandmother was present. We used an extensive and largely pre-industrial
demographic dataset collected from parish population registers kept by
the Lutheran Church of Finland from years 1730–1895. We show that
although grandmother presence cannot mitigate adverse effects of many
poorer birth conditions, grandchildren whose next sibling was born after
a short interval survived better when the maternal grandmother was
present. Taken together, these findings highlight an important role of
grandmothers in compensating the mother's investment in the new baby,
thus enabling overall faster successful reproductive rate of mothers.
Whilst the opportunity for grandmothers to mitigate the risks of adverse
birth statuses is limited, this study does show - through the
beneficial effect on survival for those with a short subsequent birth
interval - that grandmothers can increase their daughters' and their own
reproductive success.</p
Offspring fertility and grandchild survival enhanced by maternal grandmothers in a pre-industrial human society
Help is directed towards kin in many cooperative species, but its nature and intensity can vary by context. Humans are one of few species in which grandmothers invest in grandchildren, and this may have served as an important driver of our unusual life history. But helping behaviour is hardly uniform, and insight into the importance of grandmothering in human evolution depends on understanding the contextual expression of helping benefits. Here, we use an eighteenth-nineteenth century pre-industrial genealogical dataset from Finland to investigate whether maternal or paternal grandmother presence (lineage relative to focal individuals) differentially affects two key fitness outcomes of descendants: fertility and survival. We found grandmother presence shortened spacing between births, particularly at younger mother ages and earlier birth orders. Maternal grandmother presence increased the likelihood of focal grandchild survival, regardless of whether grandmothers had grandchildren only through daughters, sons, or both. In contrast, paternal grandmother presence was not associated with descendants’ fertility or survival. We discuss these results in terms of current hypotheses for lineage differences in helping outcomes.</p
The kinematic identification of a thick stellar disc in M31
We present the first characterization of a thick disc component in the
Andromeda galaxy (M31) using kinematic data from the DEIMOS multi-object
spectrograph instrument on Keck II. Using 21 fields in the South West of the
galaxy, we measure the lag of this component with respect to the thin disc, as
well as the dispersion, metallicity and scale length of the component. We find
an average lag between the two components of =46.0+/-3.9km/s. The velocity
dispersion of the thick disc is sigma_{thick}=50.8+/-1.9km/s, greater than the
value of dispersion we determine for the thin disc,
sigma_{thin}=35.7+/-1.0km/s. The thick disc is more metal poor than the thin
disc, with [Fe/H]_{spec}=-1.0+/-0.1 compared to [Fe/H]_{spec}=-0.7+/-0.05 for
the thin disc. We measure a radial scale length of the thin and thick discs of
h_r=7.3+/-1.0 kpc and h_r=8.0+/-1.2 kpc. From this, we infer scale heights for
both discs of 1.1+/-0.2 kpc and 2.8+/-0.6 kpc, both of which are ~2--3 times
larger than those observed in the Milky Way. We estimate a mass range for the
thick disc component of 2.4x10^{10}Msun< M_{*,thick} <4.1x10^{10}Msun. This
value provides a useful constraint on possible formation mechanisms, as any
proposed method for forming a thick disc must be able to heat (or deposit) at
least this amount of material.Comment: 22 pages, 17 figures. Minor revisions made to text following referee
report. Accepted for publication in MNRA
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