4,452 research outputs found
The efficiency of production systems in developing countries : a case study in Peruvian metalworking industry
The dynamical distance and intrinsic structure of the globular cluster omega Centauri
We determine the dynamical distance D, inclination i, mass-to-light ratio M/L
and the intrinsic orbital structure of the globular cluster omega Cen, by
fitting axisymmetric dynamical models to the ground-based proper motions of van
Leeuwen et al. and line-of-sight velocities from four independent data-sets. We
correct the observed velocities for perspective rotation caused by the space
motion of the cluster, and show that the residual solid-body rotation component
in the proper motions can be taken out without any modelling other than
assuming axisymmetry. This also provides a tight constraint on D tan i.
Application of our axisymmetric implementation of Schwarzschild's orbit
superposition method to omega Cen reveals no dynamical evidence for a
significant radial dependence of M/L. The best-fit dynamical model has a
stellar V-band mass-to-light ratio M/L_V = 2.5 +/- 0.1 M_sun/L_sun and an
inclination i = 50 +/- 4 degrees, which corresponds to an average intrinsic
axial ratio of 0.78 +/- 0.03. The best-fit dynamical distance D = 4.8 +/- 0.3
kpc (distance modulus 13.75 +/- 0.13 mag) is significantly larger than obtained
by means of simple spherical or constant-anisotropy axisymmetric dynamical
models, and is consistent with the canonical value 5.0 +/- 0.2 kpc obtained by
photometric methods. The total mass of the cluster is (2.5 +/- 0.3) x 10^6
M_sun. The best-fit model is close to isotropic inside a radius of about 10
arcmin and becomes increasingly tangentially anisotropic in the outer region,
which displays significant mean rotation. This phase-space structure may well
be caused by the effects of the tidal field of the Milky Way. The cluster
contains a separate disk-like component in the radial range between 1 and 3
arcmin, contributing about 4% to the total mass.Comment: 37 pages (23 figures), accepted for publication in A&A, abstract
abridged, for PS and PDF file with full resolution figures, see
http://www.strw.leidenuniv.nl/~vdven/oc
Three flow regimes of viscous jet falling onto a moving surface
A stationary viscous jet falling from an oriented nozzle onto a moving
surface is studied, both theoretically and experimentally. We distinguish three
flow regimes and classify them by the convexity of the jet shape (concave,
vertical and convex). The fluid is modeled as a Newtonian fluid, and the model
for the flow includes viscous effects, inertia and gravity. By studying the
characteristics of the conservation of momentum for a dynamic jet, the boundary
conditions for each flow regime are derived, and the flow regimes are
characterized in terms of the process and material parameters. The model is
solved by a transformation into an algebraic equation. We make a comparison
between the model and experiments, and obtain qualitative agreement
Falling of a viscous jet onto a moving surface
We analyze the stationary flow of a jet of Newtonian fluid that is drawn by
gravity onto a moving surface. The situation is modeled by a third-order ODE on
a domain of unknown length and with an additional integral condition; by
solving part of the equation explicitly we can reformulate the problem as a
first-order ODE, again with an integral constraint. We show that there are two
flow regimes, and characterize the associated regions in the three-dimensional
parameter space in terms of an easily calculable quantity. In a qualitative
sense the results from the model are found to correspond with experimental
observations.Comment: 16 pages, 11 figure
Schwarzschild models of the Sculptor dSph galaxy
We have developed a spherically symmetric dynamical model of a dwarf
spheroidal galaxy using the Schwarzschild method. This type of modelling yields
constraints both on the total mass distribution (e.g. enclosed mass and scale
radius) as well as on the orbital structure of the system modelled (e.g.
velocity anisotropy). Therefore not only can we derive the dark matter content
of these systems, but also explore possible formation scenarios. Here we
present preliminary results for the Sculptor dSph. We find that the mass of
Sculptor within 1kpc is 8.5\times10^(7\pm0.05) M\odot, its anisotropy profile
is tangentially biased and slightly more isotropic near the center. For an NFW
profile, the preferred concentration (~15) is compatible with cosmological
models. Very cuspy density profiles (steeper than NFW) are strongly disfavoured
for Sculptor.Comment: 2 pages, 4 figures, to appear in the proceedings of "Assembling the
Puzzle of the Milky Way", Le Grand Bornand (Apr. 17-22, 2011
A resonant feature near the Perseus arm revealed by red clump stars
We investigate the extinction together with the radial velocity dispersion
and distribution of red clump stars in the anti-center direction using spectra
obtained with Hectospec on the MMT. We find that extinction peaks at
Galactocentric radii of about 9.5 and 12.5 kpc, right in front of the locations
of the Perseus and Outer arms and in line with the relative position of dust
and stars in external spiral galaxies. The radial velocity dispersion peaks
around 10kpc, which coincides with the location of the Perseus arm, yields an
estimated arm-interarm density contrast of 1.3-1.5 and is in agreement with
previous studies. Finally, we discover that the radial velocity distribution
bifurcates around 10-11 kpc into two peaks at +27 km/s and -4 km/s. This seems
to be naturally explained by the presence of the outer Lindblad resonance of
the Galactic bar, but further observations will be needed to understand if the
corotation resonance of the spirals arms also plays a role.Comment: 8 pages, 2 figures, accepted for publication in ApJ
Automatisering broedeilogistiek
Bij een wegrolsysteem wordt het ei, nadat het gelegd is, gelijktijdig door aanraking van het dier naar een transportband verwerkt. Dit proces geeft minder temperatuurschommelingen ten aanzien van het ei en minder kans tot besmetting door micro-organismen. Ook de bevuiling van het broedei is bij een wegrolsysteem beduidend minder
An easy method for the preparation of anion exchange membranes: Graft-polymerization of ionic liquids in porous supports
A novel way for anion exchange membrane (AEM) preparation has been investigated, avoiding the use of expensive and toxic chemicals. This new synthetic approach to prepare AEMs was based on the use of a porous polybenzylimidazole membrane as support in which functionalized ILs were introduced and subsequently grafted on the polymer backbone. These new AEMs were prepared and their chemical structures and properties including morphology, thermal stability, and ionic conductivity were characterized. The hydroxyl ionic conductivity of the synthesized membranes can reach values upto 6.62 × 10−3 S cm−1 at 20°C. Although the ionic conductivity is not very high yet, the work shows the strength of the concept. Membrane properties can be easily tailored toward specific applications by choosing the proper chemistry, i.e., porous polymer support, ionic liquid, and method of initiation and polymerizatio
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