18,777 research outputs found
Molecular biology on a microfluidic chip
We have developed microfluidic chips for automating molecular biology processes such as gene ligation and gene transformation from nanolitre sample volumes with parallel architecture. Unlike conventional tube methods with cumbersome pipetting procedures, all processes, including metering of samples, ligation and transformation, were carried out in the microfluidic chips through pneumatic control of the nanofluid. The microfluidic devices presented here offer an illustration of some of the basic physics that arises when trying to miniaturize and automate biological techniques
VLT/VIMOS Observations of an Occulting Galaxy Pair: Redshifts and Effective Extinction Curve
We present VLT/VIMOS IFU observations of an occulting galaxy pair previously
discovered in HST observations. The foreground galaxy is a low-inclination
spiral disk, which causes clear attenuation features seen against the bright
bulge and disk of the background galaxy. We find redshifts of and z=0.065 for the foreground and background galaxy respectively.
This relatively small difference does not rule out gravitational interaction
between the two galaxies. Emission line ratios point to a star-forming, not
AGN-dominated foreground galaxy.
We fit the Cardelli, Clayton & Mathis (CCM) extinction law to the spectra of
individual fibres to derive slope () and normalization (). The
normalization agrees with the HST attenuation map and the slope is lower than
the Milky Way relation (), which is likely linked to the spatial
sampling of the disk. We speculate that the values of point to either
coherent ISM structures in the disk larger than usual ( kpc) or higher
starting values of , indicative of recent processing of the dust.
The foreground galaxy is a low stellar mass spiral () with a high dust content (). The dust disk geometry visible in the HST image would explain the
observed SED properties of smaller galaxies: a lower mean dust temperature, a
high dust-to-stellar mass ratio but relatively little optical attenuation.
Ongoing efforts to find occulting pairs with a small foreground galaxies will
show how common this geometry is.Comment: 16 pages, 3 tables, 13 figures, accepted for publication in MNRA
Evaluation of spoken document retrieval for historic speech collections
The re-use of spoken word audio collections maintained by audiovisual archives is severely hindered by their generally limited access. The CHoral project, which is part of the CATCH program funded by the Dutch Research Council, aims to provide users of speech archives with online, instead of on-location, access to relevant fragments, instead of full documents. To meet this goal, a spoken document retrieval framework is being developed. In this paper the evaluation efforts undertaken so far to assess and improve various aspects of the framework are presented. These efforts include (i) evaluation of the automatically generated textual representations of the spoken word documents that enable word-based search, (ii) the development of measures to estimate the quality of the textual representations for use in information retrieval, and (iii) studies to establish the potential user groups of the to-be-developed technology, and the first versions of the user interface supporting online access to spoken word collections
Dark and Baryonic Matter in Bright Spiral Galaxies: I.Near-infrared and Optical Broadband Surface Photometry of 30 Galaxies
We present photometrically calibrated images and surface photometry in the B,
V, R, J, H, and K-bands of 25, and in the g, r, and K-bands of 5 nearby bright
(Bo_T<12.5 mag) spiral galaxies with inclinations between 30-65 degrees
spanning the Hubble Sequence from Sa to Scd. Data are from The Ohio State
University Bright Spiral Galaxy Survey, the Two Micron All Sky Survey, and the
Sloan Digital Sky Survey Second Data Release. Radial surface brightness
profiles are extracted, and integrated magnitudes are measured from the
profiles. Axis ratios, position angles, and scale lengths are measured from the
near-infrared images. A 1-dimensional bulge/disk decomposition is performed on
the near-infrared images of galaxies with a non-negligible bulge component, and
an exponential disk is fit to the radial surface brightness profiles of the
remaining galaxies.Comment: 28 page
Galaxies with Spiral Structure up to z = 0.87 --Limits on M/L and the Stellar Velocity Dispersion
We consider seven distant galaxies with clearly evident spiral structure from
HST images. Three of these were chosen from Vogt et al. (1996) (VFP) and have
measured rotational velocities. Five were chosen from the Medium Deep Survey
and are studied in Sarajedini et al. 1996 (SGGR), and one galaxy is found in
both papers. We place upper limits on their mass-to-light ratios (M/L) by
computing M/L_B for a maximal disk. We find that these galaxies have maximal
disk mass-to-light ratios M/L_B = 1.5 - 3.5 M_sol/L_Bsol at the low end, but
within the range seen in nearby galaxies. The mass-to-light ratios are low
enough to suggest that the galaxies contain a young, rapidly formed stellar
population.
By using a Toomre stability criterion for formation of spiral structure, we
place constraints on the ratio of M/L to the stellar velocity dispersion. If
these galaxies have maximal disks they would have to be nearly unstable so as
to have small enough velocity dispersions that their disks are not
unrealistically thick. This suggests that there is a substantial amount of dark
matter present in the luminous regions of the galaxy.Comment: AAS Latex + PS Figure, accepted for publication in A
An investigation into the prominence of spiral galaxy bulges: The Data
The best-fitting B, R, I and K-band (Sersic R^(1/n) bulge + exponential disk)
model parameters for the de Jong & van der Kruit (1994) sample of 86 spiral
galaxies are made electronically available. This sample covers all spiral
galaxy types and provides the largest homogeneous set of structural parameters
for spiral galaxies modeled with an R^(1/n) bulge.Comment: An Addendum to appear in AJ. Readers are welcome to request ascii
tables and/or diagrams of the fitted profiles from the Autho
Evolution in the Dust Lane Fraction of Edge-on L* Spiral Galaxies since z=0.8
The presence of a well-defined and narrow dust lane in an edge-on spiral
galaxy is the observational signature of a thin and dense molecular disk, in
which gravitational collapse has overcome turbulence. Using a sample of
galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction
of massive disks that display a dust lane. Our goal is to explore the evolution
in the stability of the molecular ISM disks in spiral galaxies over a cosmic
timescale. We check the reliability of our morphological classifications
against changes in restframe wavelength, resolution, and cosmic dimming with
(artificially redshifted) images of local galaxies from SDSS. We find that the
fraction of L* disks with dust lanes in COSMOS is consistent with the local
fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly
lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively
supports the notion that a high specific star formation rate can efficiently
destroy or inhibit a dense molecular disk. A small subsample of higher redshift
COSMOS galaxies display low internal reddening (E[B-V]), as well as a low
incidence of dust lanes. These may be disks in which the growth of the dusty
ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most
massive galaxies display a lower dust lane fraction than lower mass galaxies. A
small contribution of recent mergers or starbursts to this most massive
population may be responsible. The fact that the fraction of galaxies with dust
lanes in COSMOS is consistent with little or no evolution implies that models
to explain the Spectral Energy Distribution or the host galaxy dust extinction
of supernovae based on local galaxies are still applicable to higher redshift
spirals. It also suggests that dust lanes are long lived phenomena or can be
reformed over very short time-scales.Comment: 14 pages, 9 figures, 2 tables, accepted for publication by Ap
A Morphological-type dependence in the mu_0-log(h) plane of Spiral galaxy disks
We present observational evidence for a galaxy `Type' dependence to the
location of a spiral galaxy's disk parameters in the mu_0-log(h) (central disk
surface-brightness - disk scale-length) plane. With a sample of ~40 Low Surface
Brightness galaxies (both bulge- and disk-dominated) and ~80 High Surface
Brightness galaxies, the early-type disk galaxies (<=Sc) tend to define a
bright envelope in the mu_0-log(h) plane, while the late-type (>=Scd) spiral
galaxies have, in general, smaller and fainter disks. Below the defining
surface brightness threshold for a Low Surface Brightness galaxy (i.e. more
than 1 mag fainter than the 21.65 B-mag arcsec^(-2) Freeman value), the
early-type spiral galaxies have scale-lengths greater than 8-9 kpc, while the
late-type spiral galaxies have smaller scale-lengths. All galaxies have been
modelled with a seeing-convolved Sersic r^(1/n) bulge and exponential disk
model. We show that the trend of decreasing bulge shape parameter (n) with
increasing Hubble type and decreasing bulge-to-disk luminosity ratio, which has
been observed amongst the High Surface Brightness galaxies, extends to the Low
Surface Brightness galaxies, revealing a continuous range of structural
parameters.Comment: To be published in ApJ. Inc. three two-part figure
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