1,399 research outputs found
Breaking the degeneracy between anisotropy and mass: The dark halo of the E0 galaxy NGC 6703
(abridged) We have measured line-of-sight velocity profiles (VPs) in the E0
galaxy NGC 6703 out to 2.6 R_e. From these data we constrain the mass
distribution and the anisotropy of the stellar orbits in this galaxy.
We have developed a non-parametric technique to determine the DF f(E,L^2)
directly from the kinematic data. From Monte Carlo tests using the spatial
extent, sampling, and error bars of the NGC 6703 data we find that smooth
underlying DFs can be recovered to an rms accuracy of 12%, and the anisotropy
parameter beta(r) to an accuracy of 0.1, in a given potential. An
asymptotically constant halo circular velocity v_0 can be determined with an
accuracy of +- \lta 50km/s.
For NGC 6703 we determine the true circular velocity at 2.6 R_e to be 250 +-
40km/s at 95% c.l., corresponding to a total mass in NGC 6703 inside 78'' (13.5
h_50^-1 kpc), of 1.6-2.6 x 10^11 h_50^-1 Msun. No model without dark matter
will fit the data; however, a maximum stellar mass model in which the luminous
component provides nearly all the mass in the centre does. In such a model, the
total luminous mass inside 78'' is 9 x 10^10 Msun and the integrated
M/L_B=5.3-10, corresponding to a rise from the center by at least a factor of
1.6.
The anisotropy of the stellar distribution function in NGC 6703 changes from
near-isotropic at the centre to slightly radially anisotropic (beta=0.3-0.4 at
30'', beta=0.2-0.4 at 60'') and is not well-constrained at the outer edge of
the data.
Our results suggest that also elliptical galaxies begin to be dominated by
dark matter at radii of \sim 10kpc.Comment: 19 pages LaTex, 18 figures. MNRAS, in press. Also available at
http://www.astro.unibas.ch/~gerhard/papers/dm6703.ps.g
Collective waves in dense and confined microfluidic droplet arrays
Excitation mechanisms for collective waves in confined dense one-dimensional
microfluidic droplet arrays are investigated by experiments and computer
simulations. We demonstrate that distinct modes can be excited by creating
specific `defect' patterns in flowing droplet trains. Excited longitudinal
modes exhibit a short-lived cascade of pairs of laterally displacing droplets.
Transversely excited modes obey the dispersion relation of microfluidic phonons
and induce a coupling between longitudinal and transverse modes, whose origin
is the hydrodynamic interaction of the droplets with the confining walls.
Moreover, we investigate the long-time behaviour of the oscillations and
discuss possible mechanisms for the onset of instabilities. Our findings
demonstrate that the collective dynamics of microfluidic droplet ensembles can
be studied particularly well in dense and confined systems. Experimentally, the
ability to control microfluidic droplets may allow to modulate the refractive
index of optofluidic crystals which is a promising approach for the production
of dynamically programmable metamaterials.Comment: 13 pages, 17 figure
Efficient creation and incremental maintenance of the hopi index for complex xml document collections
The HOPI index, a connection index for XML documents based on the concept of a 2–hop cover, provides space – and time–efficient reachability tests along the ancestor, descendant, and link axes to support path expressions with wildcards in XML search engines. This paper presents enhanced algorithms for building HOPI, shows how to augment the index with distance information, and discusses incremental index maintenance. Our experiments show substantial improvements over the existing divide-and-conquer algorithm for index creation, low space overhead for including distance information in the index, and efficient updates
Certification of Mass Fractions of Aflatoxin B1, B2, G1 and G2 in Peanut Butter, BCR-385R and BCR-401R
This report describes the preparation of peanut butter (BCR-385R and BCR-401R) matrix reference materials and the certification of their content (mass fraction) of aflatoxin B1, B2, G1 and G2.
The preparation of the materials, the homogeneity and stability studies and the characterisation are described and the results are discussed. Uncertainties were calculated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM), including uncertainties due to possible heterogeneity and instability.JRC.D.2-Reference material
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