4,219 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
The Effect of Psychiatric Rehabilitation on the Activity and Participation Level of Clients with Long-Term Psychiatric Disabilities
During the last decades of the 20th century, many psychiatric hospitals changed the living environments of their clients with long-term psychiatric disabilities.
We investigated the effect of this environmental psychiatric rehabilitation and normalization process on the activity and participation level of such clients residing in one Dutch psychiatric hospital. The seven years of panel research demonstrated that more normal living environments have a positive effect on clientsâ activity and participation level. This is controlled for the fact that younger clients, and clients with a relative high activity and participation level were selected for these normal living environments.
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
Propfan noise propagation
The unconventional supersonic tip speed of advanced propellers has led to uncertainties about Propfan's noise acceptability and compliance with Federal Aviation Noise Regulation (FAR 36). Overhead flight testing of the Propfan with an SR-7L blade during 1989's Propfan Test Assessment (PTA) Program have shown unexpectedly high far-field sound pressure levels. This study here attempts to provide insights into the acoustics of a single-rotating propeller (SRP) with supersonic tip speed. At the same time, the role of the atmosphere in shaping the far-field noise characteristics is investigated
Customer flow, intermediaries, and the discovery of the equilibrium riskfree rate
Macro announcements change the equilibrium riskfree rate. We find that treasury prices reflect part of the impact instantaneously, but intermediaries rely on their customer order flow in the 15 minutes after the announcement to discover the full impact. We show that this customer flow informativeness is strongest at times when analyst forecasts of macro variables are highly dispersed. We study 30 year treasury futures to identify the customer flow. We further show that intermediaries appear to benefit from privately recognizing informed customer flow, as, in the cross-section, their own-account trade profitability correlates with access to customer orders, controlling for volatility, competition, and the announcement surprise. These results suggest that intermediaries learn about equilibrium riskfree rates through customer orders
Microparticle assembly pathways on lipid membranes
Understanding interactions between microparticles and lipid membranes is of
increasing importance, especially for unraveling the influence of microplastics
on our health and environment. Here, we study how a short-ranged adhesive force
between microparticles and model lipid membranes causes membrane-mediated
particle assembly. Using confocal microscopy, we observe the initial particle
attachment to the membrane, then particle wrapping, and in rare cases
spontaneous membrane tubulation. In the attached state, we measure that the
particle mobility decreases by 26%. If multiple particles adhere to the same
vesicle, their initial single-particle state determines their interactions and
subsequent assembly pathways: 1) attached particles only aggregate when small
adhesive vesicles are present in solution, 2) wrapped particles reversibly
attract one another by membrane deformation, and 3) a combination of wrapped
and attached particles form membrane-mediated dimers, which further assemble
into a variety of complex structures. The experimental observation of distinct
assembly pathways induced only by a short ranged membrane-particle adhesion,
shows that a cellular cytoskeleton or other active components are not required
for microparticle aggregation. We suggest that this membrane-mediated
microparticle aggregation is a reason behind reported long retention times of
polymer microparticles in organisms.Comment: 20 pages, 11 figures (including supporting material
The Relation between Galaxy Structure and Spectral Type: Implications for the Buildup of the Quiescent Galaxy Population at 0.5<z<2.0
We present the relation between galaxy structure and spectral type, using a
K-selected galaxy sample at 0.5<z<2.0. Based on similarities between the
UV-to-NIR spectral energy distributions, we classify galaxies into 32 spectral
types. The different types span a wide range in evolutionary phases, and thus
-- in combination with available CANDELS/F160W imaging -- are ideal to study
the structural evolution of galaxies. Effective radii (R_e) and Sersic
parameters (n) have been measured for 572 individual galaxies, and for each
type, we determine R_e at fixed stellar mass by correcting for the mass-size
relation. We use the rest-frame U-V vs. V-J diagram to investigate evolutionary
trends. When moving into the direction perpendicular to the star-forming
sequence, in which we see the Halpha equivalent width and the specific star
formation rate (sSFR) decrease, we find a decrease in R_e and an increase in n.
On the quiescent sequence we find an opposite trend, with older redder galaxies
being larger. When splitting the sample into redshift bins, we find that young
post-starburst galaxies are most prevalent at z>1.5 and significantly smaller
than all other galaxy types at the same redshift. This result suggests that the
suppression of star formation may be associated with significant structural
evolution at z>1.5. At z<1, galaxy types with intermediate sSFRs
(10^{-11.5}-10^{-10.5} yr^-1) do not have post-starburst SED shapes. These
galaxies have similar sizes as older quiescent galaxies, implying that they can
passively evolve onto the quiescent sequence, without increasing the average
size of the quiescent galaxy population.Comment: 7 pages, 5 figures; Accepted for publication in ApJ
A constant limiting mass scale for flat early-type galaxies from z=1 to z=0: density evolves but shapes do not
We measure the evolution in the intrinsic shape distribution of early-type
galaxies from z~1 to z~0 by analyzing their projected axis-ratio distributions.
We extract a low-redshift sample (0.04 < z < 0.08) of early-type galaxies with
very low star-formation rates from the SDSS, based on a color-color selection
scheme and verified through the absence of emission lines in the spectra. The
inferred intrinsic shape distribution of these early-type galaxies is strongly
mass dependent: the typical short-to-long intrinsic axis-ratio of high-mass
early-type galaxies (>1e11 M_sun) is 2:3, where as at masses below 1e11 M_sun
this ratio narrows to 1:3, or more flattened galaxies. In an entirely analogous
manner we select a high-redshift sample (0.6 < z < 0.8) from two deep-field
surveys: GEMS and COSMOS. We find a seemingly universal mass of ~1e11 M_sun for
highly flatted early-type systems at all redshifts. This implies that the
process that grows an early-type galaxy above this ceiling mass involves
forming round systems. Using both parametric and non-parametric tests, we find
no evolution in the projected axis-ratio distribution for galaxies with masses
>3e10 M_sun with redshift. At the same time, our samples imply an increase of
2-3x in co-moving number density for early-type galaxies at masses >3e10 M_sun,
in agreement with previous studies. Given the direct connection between the
axis-ratio distribution and the underlying bulge-to-disk ratio distribution,
our findings imply that the number density evolution of early-type galaxies is
not exclusively driven by the emergence of either bulge- or disk-dominated
galaxies, but rather by a balanced mix that depends only on the stellar mass of
the galaxy. The challenge for galaxy formation models is to reproduce this
overall non-evolving ratio of flattened to round early-type galaxies in the
context of a continually growing population.Comment: 14 pages in emulate ApJ format, 8 color figures, submitted to ApJ,
comments welcome, fixed missing reference
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