1,267 research outputs found
Uncovering Unique Concept Vectors through Latent Space Decomposition
Interpreting the inner workings of deep learning models is crucial for
establishing trust and ensuring model safety. Concept-based explanations have
emerged as a superior approach that is more interpretable than feature
attribution estimates such as pixel saliency. However, defining the concepts
for the interpretability analysis biases the explanations by the user's
expectations on the concepts. To address this, we propose a novel post-hoc
unsupervised method that automatically uncovers the concepts learned by deep
models during training. By decomposing the latent space of a layer in singular
vectors and refining them by unsupervised clustering, we uncover concept
vectors aligned with directions of high variance that are relevant to the model
prediction, and that point to semantically distinct concepts. Our extensive
experiments reveal that the majority of our concepts are readily understandable
to humans, exhibit coherency, and bear relevance to the task at hand. Moreover,
we showcase the practical utility of our method in dataset exploration, where
our concept vectors successfully identify outlier training samples affected by
various confounding factors. This novel exploration technique has remarkable
versatility to data types and model architectures and it will facilitate the
identification of biases and the discovery of sources of error within training
data
Genetic associations with childhood brain growth, defined in two longitudinal cohorts
Genome-wide association studies (GWASs) are unraveling the genetics of adult brain neuroanatomy as measured by cross-sectional anatomic magnetic resonance imaging (aMRI). However, the genetic mechanisms that shape childhood brain development are, as yet, largely unexplored. In this study we identify common genetic variants associated with childhood brain development as defined by longitudinal aMRI. Genome-wide single nucleotide polymorphism (SNP) data were determined in two cohorts: one enriched for attention-deficit/hyperactivity disorder (ADHD) (LONG cohort: 458 participants; 119 with ADHD) and the other from a population-based cohort (Generation R: 257 participants). The growth of the brain's major regions (cerebral cortex, white matter, basal ganglia, and cerebellum) and one region of interest (the right lateral prefrontal cortex) were defined on all individuals from two aMRIs, and a GWAS and a pathway analysis were performed. In addition, association between polygenic risk for ADHD and brain growth was determined for the LONG cohort. For white matter growth, GWAS meta-analysis identified a genome-wide significant intergenic SNP (rs12386571, P = 9.09 × 10-9 ), near AKR1B10. This gene is part of the aldo-keto reductase superfamily and shows neural expression. No enrichment of neural pathways was detected and polygenic risk for ADHD was not associated with the brain growth phenotypes in the LONG cohort that was enriched for the diagnosis of ADHD. The study illustrates the use of a novel brain growth phenotype defined in vivo for further study
Rapid planetesimal formation in turbulent circumstellar discs
The initial stages of planet formation in circumstellar gas discs proceed via
dust grains that collide and build up larger and larger bodies (Safronov 1969).
How this process continues from metre-sized boulders to kilometre-scale
planetesimals is a major unsolved problem (Dominik et al. 2007): boulders stick
together poorly (Benz 2000), and spiral into the protostar in a few hundred
orbits due to a head wind from the slower rotating gas (Weidenschilling 1977).
Gravitational collapse of the solid component has been suggested to overcome
this barrier (Safronov 1969, Goldreich & Ward 1973, Youdin & Shu 2002). Even
low levels of turbulence, however, inhibit sedimentation of solids to a
sufficiently dense midplane layer (Weidenschilling & Cuzzi 1993, Dominik et al.
2007), but turbulence must be present to explain observed gas accretion in
protostellar discs (Hartmann 1998). Here we report the discovery of efficient
gravitational collapse of boulders in locally overdense regions in the
midplane. The boulders concentrate initially in transient high pressures in the
turbulent gas (Johansen, Klahr, & Henning 2006), and these concentrations are
augmented a further order of magnitude by a streaming instability (Youdin &
Goodman 2005, Johansen, Henning, & Klahr 2006, Johansen & Youdin 2007) driven
by the relative flow of gas and solids. We find that gravitationally bound
clusters form with masses comparable to dwarf planets and containing a
distribution of boulder sizes. Gravitational collapse happens much faster than
radial drift, offering a possible path to planetesimal formation in accreting
circumstellar discs.Comment: To appear in Nature (30 August 2007 issue). 18 pages (in referee
mode), 3 figures. Supplementary Information can be found at 0708.389
Recommended from our members
Scanning Kelvin Probe Microscopy Investigation of the Role of Minority Carriers on the Switching Characteristics of Organic Field-Effect Transistors
We have developed a Scanning Kelvin Probe Microscopy (SKPM) based method to probe the effects of low-mobility minority carriers on the switching characteristics of organic field effect transistors (OFETs). By measuring and modeling the transient potential changes in the OFET channel after an applied gate bias pulse, we can extract the low mobility of the minority carriers and understand how these carriers play a key role in the device operation, in particular, in the screening of the gate potential in the OFF state of the transistor and in the recombination of majority carriers trapped in the channel after an ON state stress.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) Centre for Innovative Manufacturing in Large-Area Electronics(EP/K03099X/1). Y. Hu thanks the Cambridge Overseas Trust and Chinese Scholarship Council for a postgraduate award. We thank Robin Lamboll and Dr. Abhishek Kumar for helpful discussions about the modeling work
Muon-spin rotation studies of SmFeAsO_0.85 and NdFeAsO_0.85 superconductors
Measurements of the in-plane magnetic field penetration depth \lambda_{ab} in
Fe-based superconductors with the nominal composition SmFeAsO_0.85
(T_c\simeq52K) and NdFeAsO_0.85 (T_c\simeq51K) were carried out by means of
muon-spin-rotation. The absolute values of \lambda_{ab} at T=0 were found to be
189(5)nm and 195(5)nm for Sm and Nd substituted samples, respectively. The
analysis of the magnetic penetration depth data within the Uemura
classification scheme, which considers the correlation between the
superconducting transition temperature T_c and the effective Fermi temperature
T_F, reveal that both families of Fe-based superconductors (with and without
fluorine) falls to the same class of unconventional superconductors.Comment: 5 pages, 4 figure
Far-infrared transmission studies of c-axis oriented superconducting MgB2 thin film
We reported far-infrared transmission measurements on a c-axis oriented
superconducting MgB thin film in the frequency range of 30 250
cm. We found that these measurements were sensitive to values of
scattering rate and superconducting gap . By fitting the
experimental transmission spectra at 40 K and below, we obtained
(700 1000) cm and 42 cm. These two
quantities suggested that MgB belong to the dirty limit.Comment: submitted at May
Brown dwarfs and very low mass stars in the Praesepe open cluster: a dynamically unevolved mass function?
[Abridged] In this paper, we present the results of a photometric survey to
identify low mass and brown dwarf members of the old open cluster Praesepe (age
of 590[+150][-120]Myr and distance of 190[+6.0][-5.8]pc) and use this to infer
its mass function which we compare with that of other clusters. We have
performed an optical (Ic-band) and near-infrared (J and Ks-band) photometric
survey of Praesepe with a spatial coverage of 3.1deg^2. With 5sigma detection
limits of Ic=23.4 and J=20.0, our survey is sensitive to objects with masses
from about 0.6 to 0.05Msol. The mass function of Praesepe rises from 0.6Msol
down to 0.1Msol and then turns-over at ~0.1Msol. The rise observed is in
agreement with the mass function derived by previous studies, including a
survey based on proper motion and photometry. Comparing our mass function with
that for another open cluster with a similar age, the Hyades (age ~ 600Myr), we
see a significant difference. Possible reasons are that dynamical evaporation
has not influenced the Hyades and Praesepe in the same way, or that the
clusters did not have the same initial mass function, or that dynamical
interactions have modified the evolution of one or both clusters. Although a
difference in the binary fractions of the clusters could cause the observed
(i.e. system) mass functions to differ, measurements in the literature give no
evidence for a significant difference in the binary fractions of the two
clusters. Of our cluster candidates, six have masses predicted to be equal to
or below the stellar/substellar boundary at 0.072Msol.Comment: 11 pages, 11 figures, accepted for publication in A&A. Higher
resolution of Figures 2-3-4-5 in A&A published version. Revised version
corrected for Englis
Dark sectors 2016 Workshop: community report
This report, based on the Dark Sectors workshop at SLAC in April 2016,
summarizes the scientific importance of searches for dark sector dark matter
and forces at masses beneath the weak-scale, the status of this broad
international field, the important milestones motivating future exploration,
and promising experimental opportunities to reach these milestones over the
next 5-10 years
Biosignals reflect pair-dynamics in collaborative work : EDA and ECG study of pair-programming in a classroom environment
Collaboration is a complex phenomenon, where intersubjective dynamics can greatly affect the productive outcome. Evaluation of collaboration is thus of great interest, and can potentially help achieve better outcomes and performance. However, quantitative measurement of collaboration is difficult, because much of the interaction occurs in the intersubjective space between collaborators. Manual observation and/or self-reports are subjective, laborious, and have a poor temporal resolution. The problem is compounded in natural settings where task-activity and response-compliance cannot be controlled. Physiological signals provide an objective mean to quantify intersubjective rapport (as synchrony), but require novel methods to support broad deployment outside the lab. We studied 28 student dyads during a self-directed classroom pair-programming exercise. Sympathetic and parasympathetic nervous system activation was measured during task performance using electrodermal activity and electrocardiography. Results suggest that (a) we can isolate cognitive processes (mental workload) from confounding environmental effects, and (b) electrodermal signals show role-specific but correlated affective response profiles. We demonstrate the potential for social physiological compliance to quantify pair-work in natural settings, with no experimental manipulation of participants required. Our objective approach has a high temporal resolution, is scalable, non-intrusive, and robust.Peer reviewe
EDEN Survey: Small Transiting Planet Detection Limits and Constraints on the Occurrence Rates for Late M Dwarfs within 15 pc
Earth-sized exoplanets that transit nearby, late spectral type red dwarfs
will be prime targets for atmospheric characterization in the coming decade.
Such systems, however, are difficult to find via wide-field transit surveys
like Kepler or TESS. Consequently, the presence of such transiting planets is
unexplored and the occurrence rates of short-period Earth-sized planets around
late M dwarfs remain poorly constrained. Here, we present the deepest
photometric monitoring campaign of 22 nearby late M dwarf stars, using data
from over 500 nights on seven 1-2 meter class telescopes. Our survey includes
all known single quiescent northern late M dwarfs within 15 pc. We use
transit-injection-and-recovery tests to quantify the completeness of our
survey, successfully identify most () transiting short-period (0.5-1 d)
super-Earths (), and are sensitive () to transiting
Earth-sized planets (). Our high sensitivity to transits with
a near-zero false positive rate demonstrates an efficient survey strategy. Our
survey does not yield a transiting planet detection, yet it provides the most
sensitive upper limits on transiting planets orbiting our target stars.
Finally, we explore multiple hypotheses about the occurrence rates of
short-period planets (from Earth-sized planets to giant planets) around late M
dwarfs. We show, for example, that giant planets at short periods ( day)
are uncommon around our target stars. Our dataset provides some insight into
occurrence rates of short-period planets around TRAPPIST-1-like stars, and our
results can help test planetary formation and system evolution models, as well
as guide future observations of nearby late M dwarfs.Comment: 27 pages, 11 figure
- …