499 research outputs found
Local Surface Density of the Galactic Disk from a 3-D Stellar Velocity Sample
We have re-estimated the surface density of the Galactic disk in the solar
neighborhood within 0.4 kpc of the Sun using parallaxes and proper
motions of a kinematically and spatially unbiased sample of 1476 old bright red
giant stars from the Hipparcos catalog with measured radial velocities from
Barbier-Brossat & Figon (2000). We determine the vertical distribution of the
red giants as well as the vertical velocity dispersion of the sample, (14.4
0.26 km/sec), and combine these to derive the surface density of
gravitating matter in the Galactic disk as a function of the galactic
coordinate . The surface density of the disk increases from 10.5 0.5
/ pc within 50 pc to 42 6 / pc
within 350 pc. The estimated volume density of the galactic disk within
50 pc is about 0.1 / pc which is close to the volume
density estimates of the observed baryonic matter in the solar neighborhood.Comment: 24 pages, 15 figures, AJ in pres
Digital Film Listings (DIGIFIL):Final Report
Final report of the Digifil project (CLARIAH, 2018) that aimed at automatically extracting, digitizing and publishing film screening data from the weekly films listings published in historical newspapers
Can yield gap analysis be used to inform R & D prioritisation?
The phrase “biggest bang for a buck” is associated with the policy making question that governments and development agencies face: “Where and which crops should receive highest priority for improving local and global food supply?”. A first step of prioritisation is to identify region x crop combinations for which high impact can be anticipated. We developed a new method for this prioritisation exercise and applied it to data from the Global Yield Gap and Water Productivity Atlas (GYGA). Our prioritisation distinguishes between two policy objectives (humanitarian and economic) and builds upon the relative yield gap and climate risk. Results of the prioritisation are presented and visualised in Google Earth
Proper Motions in the Galactic Bulge: Plaut's Window
A proper motion study of a field of 20' x 20' inside Plaut's low extinction
window (l,b)=(0 deg,-8 deg), has been completed. Relative proper motions and
photographic BV photometry have been derived for ~21,000 stars reaching to
V~20.5 mag, based on the astrometric reduction of 43 photographic plates,
spanning over 21 years of epoch difference. Proper motion errors are typically
1 mas/yr and field dependent systematics are below 0.2 mas/yr.
Cross-referencing with the 2MASS catalog yielded a sample of ~8,700 stars, from
which predominantly disk and bulge subsamples were selected photometrically
from the JH color-magnitude diagram. The two samples exhibited different
proper-motion distributions, with the disk displaying the expected reflex solar
motion as a function of magnitude. Galactic rotation was also detected for
stars between ~2 and ~3 kpc from us. The bulge sample, represented by red
giants, has an intrinsic proper motion dispersion of (sigma_l,sigma_b)=(3.39,
2.91)+/-(0.11,0.09) mas/yr, which is in good agreement with previous results,
and indicates a velocity anisotropy consistent with either rotational
broadening or tri-axiality. A mean distance of 6.37^{+0.87}_{-0.77} kpc has
been estimated for the bulge sample, based on the observed K magnitude of the
horizontal branch red clump. The metallicity [M/H] distribution was also
obtained for a subsample of 60 bulge giants stars, based on calibrated
photometric indices. The observed [M/H] shows a peak value at [M/H]~-0.1 with
an extended metal poor tail and around 30% of the stars with supersolar
metallicity. No change in proper motion dispersion was observed as a function
of [M/H]. We are currently in the process of obtaining CCD UBVRI photometry for
the entire proper-motion sample of ~21,000 stars.Comment: Submitted to AJ April 17th 2007. Accepted June 8th 2007. 45 pages, 14
figure
Assisting Human Balance in Standing With a Robotic Exoskeleton
This letter presents an experimental study on balance recovery control with a lower limb exoskeleton robot. Four participants were subjected to a perturbation during standing, a forward force impulse applied to their pelvis that forced them to step forward with the right leg for balance recovery. Trials with and without exoskeleton assistance to move the stepping legs thigh were conducted to investigate the influence of the exoskeletons control assistance on balancing performance and a potential adaptation. Analysis of the body kinematics and muscle activation demonstrates that robotic assistance: first, was easy to use and did not require learning, nor inhibited the healthy stepping behavior; second, it modified the stepping leg trajectories by increasing hip and knee movement; third, increased reaction speed and decreased the step duration; and finally, generally increased biceps femoris and rectus femoris muscle activity
THE BEHAVE APPLICATION: AN EVIDENCE-BASED TOOL TO MANAGE SOCIAL EMOTIONAL BEHAVIOURAL DIFFICULTIES
Social Emotional and Behavioural Difficulties (SEBD) are a persistent and multiple manifestation of maladaptive behaviours which interfere with the students’ learning, social functioning and development and/or that of their peers. They may become apparent through withdrawn, passive, aggressive or self-injurious tendencies. The prevalence of these disorders is 2-16% of the general population. Children with SEBD, diagnosed or not, are likely to live in social isolation, to receive a poor education, and they risk becoming deviant teenagers, or unemployed adults. A way to approach SEBD with consistent level of educational success is to equip teachers with proper training on practical and proven classroom management strategies, but also with evidence-based tools that can help them to effectively control difficult behaviours with confidence and competence. This contribution presents the web-based BEHAVE application aimed to ease the way for teachers to apply behavioural evidence-based interventions at school. The paper describes the main features of the BEHAVE application: the definition of the behaviour to be observed, the creation and selection of appropriate measures, the collection of behavioural data, and the statistical analysis to evaluate the direction and the power of the effect of the carried-out intervention
Structure, mass and stability of galactic disks
In this review I concentrate on three areas related to structure of disks in
spiral galaxies. First I will review the work on structure, kinematics and
dynamics of stellar disks. Next I will review the progress in the area of
flaring of HI layers. These subjects are relevant for the presence of dark
matter and lead to the conclusion that disk are in general not `maximal', have
lower M/L ratios than previously suspected and are locally stable w.r.t.
Toomre's Q criterion for local stability. I will end with a few words on
`truncations' in stellar disks.Comment: Invited review at "Galaxies and their Masks" for Ken Freeman's 70-th
birthday, Sossusvlei, Namibia, April 2010. A version with high-res. figures
is available at
http://www.astro.rug.nl/~vdkruit/jea3/homepage/Namibiachapter.pd
Shape parameters of Galactic open clusters
(abridged) In this paper we derive observed and modelled shape parameters
(apparent ellipticity and orientation of the ellipse) of 650 Galactic open
clusters identified in the ASCC-2.5 catalogue. We provide the observed shape
parameters of Galactic open clusters, computed with the help of a
multi-component analysis. For the vast majority of clusters these parameters
are determined for the first time. High resolution ("star by star") N-body
simulations are carried out with the specially developed GRAPE code
providing models of clusters of different initial masses, Galactocentric
distances and rotation velocities. The comparison of models and observations of
about 150 clusters reveals ellipticities of observed clusters which are too low
(0.2 vs. 0.3), and offers the basis to find the main reason for this
discrepancy. The models predict that after Myr clusters reach an
oblate shape with an axes ratio of , and with the major axis
tilted by an angle of with respect to the
Galactocentric radius due to differential rotation of the Galaxy. Unbiased
estimates of cluster shape parameters require reliable membership determination
in large cluster areas up to 2-3 tidal radii where the density of cluster stars
is considerably lower than the background. Although dynamically bound stars
outside the tidal radius contribute insignificantly to the cluster mass, their
distribution is essential for a correct determination of cluster shape
parameters. In contrast, a restricted mass range of cluster stars does not play
such a dramatic role, though deep surveys allow to identify more cluster
members and, therefore, to increase the accuracy of the observed shape
parameters.Comment: 13 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
Deep Westerbork 1.4 GHz Imaging of the Bootes Field
We present the results from our deep (16x12 hour) Westerbork Synthesis Radio
Telescope (WSRT) observations of the approximately 7 square degree Bootes Deep
Field, centered at 14h32m05.75s, 34d16'47.5" (J2000). Our survey consists of 42
discrete pointings, with enough overlap to ensure a uniform sensitivity across
the entire field, with a limiting sensitivity of 28 microJy (1 sigma rms). The
catalog contains 3172 distinct sources, of which 316 are resolved by the
13"x27" beam. The Bootes field is part of the optical/near-infrared imaging and
spectroscopy survey effort conducted at various institutions. The combination
of these data sets, and the deep nature of the radio observations will allow
unique studies of a large range of topics including the redshift evolution of
the luminosity function of radio sources, the K-z relation and the clustering
environment of radio galaxies, the radio / far-infrared correlation for distant
starbursts, and the nature of obscured radio loud AGN.Comment: Accepted for publication in AJ, 23 pages, 17 figures. Additional
information can be obtained through anonymous ftp to
ftp://ftp.nfra.nl/pub/Boote
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