3,306 research outputs found
How galactic environment regulates star formation
In a new simple model I reconcile two contradictory views on the factors that determine the rate at which molecular clouds form stars-internal structure versus external, environmental influences-providing a unified picture for the regulation of star formation in galaxies. In the presence of external pressure, the pressure gradient set up within a self-gravitating turbulent (isothermal) cloud leads to a non-uniform density distribution. Thus the local environment of a cloud influences its internal structure. In the simple equilibrium model, the fraction of gas at high density in the cloud interior is determined simply by the cloud surface density, which is itself inherited from the pressure in the immediate surroundings. This idea is tested using measurements of the properties of local clouds, which are found to show remarkable agreement with the simple equilibrium model. The model also naturally predicts the star formation relation observed on cloud scales and at the same time provides a mapping between this relation and the closer-to-linear molecular star formation relation measured on larger scales in galaxies. The key is that pressure regulates not only the molecular content of the ISM but also the cloud surface density. I provide a straightforward prescription for the pressure regulation of star formation that can be directly implemented in numerical models. Predictions for the dense gas fraction and star formation efficiency measured on large-scales within galaxies are also presented, establishing the basis for a new picture of star formation regulated by galactic environment
Optical Music Recognition with Convolutional Sequence-to-Sequence Models
Optical Music Recognition (OMR) is an important technology within Music
Information Retrieval. Deep learning models show promising results on OMR
tasks, but symbol-level annotated data sets of sufficient size to train such
models are not available and difficult to develop. We present a deep learning
architecture called a Convolutional Sequence-to-Sequence model to both move
towards an end-to-end trainable OMR pipeline, and apply a learning process that
trains on full sentences of sheet music instead of individually labeled
symbols. The model is trained and evaluated on a human generated data set, with
various image augmentations based on real-world scenarios. This data set is the
first publicly available set in OMR research with sufficient size to train and
evaluate deep learning models. With the introduced augmentations a pitch
recognition accuracy of 81% and a duration accuracy of 94% is achieved,
resulting in a note level accuracy of 80%. Finally, the model is compared to
commercially available methods, showing a large improvements over these
applications.Comment: ISMIR 201
Automated tracking of colloidal clusters with sub-pixel accuracy and precision
Quantitative tracking of features from video images is a basic technique
employed in many areas of science. Here, we present a method for the tracking
of features that partially overlap, in order to be able to track so-called
colloidal molecules. Our approach implements two improvements into existing
particle tracking algorithms. Firstly, we use the history of previously
identified feature locations to successfully find their positions in
consecutive frames. Secondly, we present a framework for non-linear
least-squares fitting to summed radial model functions and analyze the accuracy
(bias) and precision (random error) of the method on artificial data. We find
that our tracking algorithm correctly identifies overlapping features with an
accuracy below 0.2% of the feature radius and a precision of 0.1 to 0.01 pixels
for a typical image of a colloidal cluster. Finally, we use our method to
extract the three-dimensional diffusion tensor from the Brownian motion of
colloidal dimers.Comment: 20 pages, 8 figures. Non-revised preprint version, please refer to
http://dx.doi.org/10.1088/1361-648X/29/4/04400
Riskfree Rate Dynamics: Information, Trading and State Space Modeling
Lucas, A. [Promotor]Koopman, S.J. [Promotor]Menkveld, A.J. [Copromotor
Domain swapping and amyloid fibril conformation
For several different proteins an apparent correlation has been observed between the propensity for dimerization by domain-swapping and the ability to aggregate into amyloid-like fibrils. Examples include the disease-related proteins beta2-microglobulin and transthyretin. This has led to proposals that the amyloid-formation pathway may feature extensive domain swapping. One possible consequence of such an aggregation pathway is that the resulting fibrils would incorporate structural elements that resemble the domain-swapped forms of the protein and, thus, reflect certain native-like structures or domain-interactions. In magic angle spinning solid-state NMR-based and other structural studies of such amyloid fibrils, it appears that many of these proteins form fibrils that are not native-like. Several fibrils instead have an in-register, parallel conformation, which is a common amyloid structural motif and is seen, for instance, in various prion fibrils. Such a lack of native structure in the fibrils suggests that the apparent connection between domain-swapping ability and amyloid-formation may be more subtle or complex than may be presumed at first glance. © 2012 Landes Bioscience
Rapportage leerlijn verbrede NME gezonde en duurzame voeding
Vanuit de Proeftuin Amsterdam zijn diverse projecten gestart om duurzaam en gezond eten onder de aandacht te brengen van kinderen uit het basisonderwijs. Er zijn mogelijkheden voor het ontwikkelen van een verbrede leerlijn Natuur en Milieueducatie (NME) voor gezonde en duurzame voeding. Gekeken wordt in dit rapport naar aansluiting bij zaken die docenten belangrijk vinden en naar aansluiting bij bestaande initiatieven, zoals boerderijeducatie, schooltuinen, SchoolGruiten en smaaklessen. Tot slot wordt een uitgewerkte leerlijn weergegeven met als hoofdthema's: Wat eet je en waarom? Wat doet eten met jou? Hoe functioneert de boerderij? Weet jij wat je koopt
Strategies of Climate Change Denial: The case of Thierry Baudet
This paper discusses different strategies of climate change denial and focusses on the specific case of Dutch politician Thierry Baudet. Much of the literature concerning climate change denial focusses on Anglo-American cases, therefore more research non-English speaking countries is necessary. The theoretical framework describes the state of the art concerning climate change denialism and its links to occurring phenomena in Western societies and politics such as post-truth and populism. Afterwards, by conducting a deductive analysis of Thierry Baudet’s climate denialism in the Netherlands, a more thorough understanding of the different strategies proposed by Stefan Rahmstorf and Engels et al. is reached. Although all four categories are detected in Baudet’s denialism, consensus denial seems to be the most prevalent. The analysis of his usage of the notion of a climate apocalypse, combined with the analysis of his specific focus on consensus denial, broadens the understanding of how climate change denial can relate to populism. 
Dihedral Angle Measurements for Structure Determination by Biomolecular Solid-State NMR Spectroscopy
In structural studies of immobilized, aggregated and self-assembled biomolecules, solid-state NMR (ssNMR) spectroscopy can provide valuable high-resolution structural information. Among the structural restraints provided by magic angle spinning (MAS) ssNMR the canonical focus is on inter-atomic distance measurements. In the current review, we examine the utility of ssNMR measurements of angular constraints, as a complement to distance-based structure determination. The focus is on direct measurements of angular restraints via the judicious recoupling of multiple anisotropic ssNMR parameters, such as dipolar couplings and chemical shift anisotropies. Recent applications are highlighted, with a focus on studies of nanocrystalline polypeptides, aggregated peptides and proteins, receptor-substrate interactions, and small molecule interactions with amyloid protein fibrils. The review also examines considerations of when and where ssNMR torsion angle experiments are (most) effective, and discusses challenges and opportunities for future applications
A mass-dependent slope of the galaxy size-mass relation out to z~3: further evidence for a direct relation between median galaxy size and median halo mass
We reassess the galaxy size-mass relation out to z~3 using a new definition
of size and a sample of >29,000 galaxies from the 3D-HST, CANDELS, and
COSMOS-DASH surveys. Instead of the half-light radius r_50 we use r_80, the
radius containing 80% of the stellar light. We find that the r_80 -- M_star
relation has the form of a broken power law, with a clear change of slope at a
pivot mass M_p. Below the pivot mass the relation is shallow (r_80 \propto
M_star^0.15) and above it it is steep (r_80\propto M_star^0.6). The pivot mass
increases with redshift, from log(M_p/M_sun)~ 10.2 at z=0.4 to log(M_p/M_sun)~
10.9 at z=1.7-3. We compare these r_80-M_star relations to the M_halo-M_star
relations derived from galaxy-galaxy lensing, clustering analyses, and
abundance matching techniques. Remarkably, the pivot stellar masses of both
relations are consistent with each other at all redshifts, and the slopes are
very similar both above and below the pivot when assuming M_halo \propto
r_80^3. The implied scaling factor to relate galaxy size to halo size is r_80 /
R_vir = 0.047, independent of stellar mass and redshift.From redshift 0 to 1.5,
the pivot mass also coincides with the mass where the fraction of star-forming
galaxies is 50%, suggesting that the pivot mass reflects a transition from
dissipational to dissipationless galaxy growth. Finally, our results imply that
the scatter in the stellar-to-halo mass ratio is relatively small for massive
halos (~0.2 dex for M_halo>10^12.5 M_sun).Comment: Accepted in ApJL. Please also see complementary paper Miller et al.
201
Confirmation of the compactness of a z=1.91 quiescent galaxy with Hubble Space Telescope's Wide Field Camera 3
We present very deep Wide Field Camera 3 (WFC3) photometry of a massive,
compact galaxy located in the Hubble Ultra Deep Field. This quiescent galaxy
has a spectroscopic redshift z=1.91 and has been identified as an extremely
compact galaxy by Daddi et al. 2005. We use new H-F160W imaging data obtained
with Hubble Space Telescope/WFC3 to measure the deconvolved surface brightness
profile to H = 28 mag arcsec**-2. We find that the surface brightness profile
is well approximated by an n=3.7 Sersic profile. Our deconvolved profile is
constructed by a new technique which corrects the best-fit Sersic profile with
the residual of the fit to the observed image. This allows for galaxy profiles
which deviate from a Sersic profile. We determine the effective radius of this
galaxy: r_e=0.42 +- 0.14 kpc in the observed H-F160W-band. We show that this
result is robust to deviations from the Sersic model used in the fit. We test
the sensitivity of our analysis to faint "wings" in the profile using simulated
galaxy images consisting of a bright compact component and a faint extended
component. We find that due to the combination of the WFC3 imaging depth and
our method's sensitivity to extended faint emission we can accurately trace the
intrinsic surface brightness profile, and that we can therefore confidently
rule out the existence of a faint extended envelope around the observed galaxy
down to our surface brightness limit. These results confirm that the galaxy
lies a factor of 10 off from the local mass-size relation.Comment: 6 pages, 4 figures. Accepted for publication in ApJ Letters
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