508 research outputs found
The analysis of lipophilic marine toxins : development of an alternative method
Lipophilic marine toxins are produced by certain algae species and can accumulate in filter feeding shellfish such as mussels, scallops and oysters. Consumption of contaminated shellfish can lead to severe intoxications such as diarrhea, abdominal cramps and vomiting. Methods described in European Union (EU) legislation to test for the presence of these toxins are based on a mouse or rat bioassay. These assays are unethical and have a poor sensitivity and selectivity. The aim of this thesis is to develop an alternative method based on liquid chromatography - tandem mass spectrometry (LC-MS/MS) for the quantitative analysis of lipophilic marine toxins. LC-MS/MS methods described in literature for the determination of lipophilic marine toxins used an acidic chromatographic system. Under acidic conditions peak shape and separation of a number of toxins preferably analyzed in electrospray ionization negative (ESI–) and positive (ESI+) were poor. A LC-MS/MS method with alkaline chromatographic conditions in which we were able to analyze 28 different toxins in a single analysis in separated retention time windows operating in either ESI– or ESI+ was developed. Furthermore, a clean up procedure based on solid phase extraction (SPE) was developed to reduce the amount of matrix effects (ion suppression and enhancement). A combination of SPE clean up and alkaline chromatographic conditions resulted in reduced matrix effects for all matrices tested (mussel, scallop and oyster). The developed SPE & LC-MS/MS method was in-house validated at regulatory limits based on EU Commission Decision 2002/657/EC. With respect to accuracy, repeatability, reproducibility, decision limit, specificity and ruggedness the method performed well. The method also performed excellently in view of possible new limits that are four- to five-fold lower than current limits for some toxins. Finally a screening method based on LC orbitrap MS was developed for 85 marine toxins of which most are not stated in EU legislation. The screening used in-house developed software which made it possible to reduce the complex data files and screen for a large number of toxins within seconds. This thesis will contribute to the replacement of the animal assays that are still prescribed in EU legislation for the determination of lipophilic marine toxins in shellfish. </p
Disc heating in NGC 2985
Various processes have been proposed to explain how galaxy discs acquire
their thickness. A simple diagnostic for ascertaining this ``heating''
mechanism is provided by the ratio of the vertical to radial velocity
dispersion components. In a previous paper we have developed a technique for
measuring this ratio, and demonstrated its viability on the Sb system NGC 488.
Here we present follow-up observations of the morphologically similar Sab
galaxy NGC 2985, still only the second galaxy for which this ratio has been
determined outside of the solar neighbourhood. The result is consistent with
simple disc heating models which predict ratios of less
than oneComment: 5 pages, 4 figures. Accepted for publication in MNRA
Kinematic detection of the double nucleus in M31
Using a spectrum obtained under moderate (of order 1 arcsecond) seeing, we
show that the double nucleus in M31 produces a strong kinematic signature even
though the individual components are not spatially resolved. The signature
consists of a significant asymmetric wing in the stellar velocity distribution
close to the center of the system. The properties of the second nucleus derived
from this analysis agree closely with those measured from high-spatial
resolution Hubble Space Telescope images. Even Space Telescope only has
sufficient resolution to study the structure of very nearby galactic nuclei
photometrically; this spectroscopic approach offers a tool for detecting
structure such as multiple nuclei in a wider sample of galaxy cores.Comment: 4 pages of uuencoded compressed postscript, figures included.
Accepted for publication in MNRA
Nieuwe giftest spaart proefdieren
Oesters en mosselen kunnen van nature een gif bevatten dat door algen in zee ontstaat. Mensen kunnen diarree krijgen als ze zulke schelpdieren eten. Tot nog toe werden er ratten of muizen gebruikt om schelpdieren op de aanwezigheid van dat gif te testen. Arjen Gerssen, onderzoeker bij RIKILT, ontwikkelde een slimmere methode om de aanwezigheid van het gif aan te tonen
Dynamics of the Disks of Nearby Galaxies
I describe how the dynamics of galactic disks can be inferred by imaging and
spectroscopy. Next I demonstrate that the decomposition of the rotation curves
of spiral galaxies into the contributions by the various components of the
galaxies is highly degenerate. Constraints on the decomposition can be found by
considering implications for the dynamics of the galactic disks. An important
diagnostic is the Toomre Q stability parameter which controls the stability of
a galactic disk against local Jeans collapse. I also show how the density wave
theory of galactic spiral arms can be employed to constrain the mass of a
galactic disk. Applying both diagnostics to the example of NGC 2985 and
discussing also the implied mass-to-light ratio I demonstrate that the inner
parts of the galaxy, where the optical disk resides, are dominated by baryons.
When I apply this method to the disks of low surface brightness galaxies, I
find unexpectedly high mass-to light ratios. These could be explained by
population synthesis models which assume a bottom heavy initial mass function
similar to the recently proposed `integrated galactic initial mass function'.Comment: 6 pages, 12 figures, invited contribution to `Galactic and Stellar
Dynamics in the era of high resolution surveys', Strasbourg, March 16 -20,
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The effect of dust on Tremaine-Weinberg measurements
We investigate the effect of dust on the observed rotation rate of a stellar
bar. The only direct way to measure this quantity relies on the Tremaine &
Weinberg method which requires that the tracer satisfies the continuity
equation. Thus it has been applied largely to early-type barred galaxies. We
show using numerical simulations of barred galaxies that dust attenuation
factors typically found in these systems change the observed bar pattern speed
by 20-40 percent. We also address the effect of star formation on the TW method
and find that it does not change the results significantly. The results
presented here suggest that applications of the TW method can be extended to
include barred galaxies covering the full range of Hubble type.Comment: 10 pages, 7 figures. Accepted for publication in MNRA
p3d: a general data-reduction tool for fiber-fed integral-field spectrographs
The reduction of integral-field spectrograph (IFS) data is demanding work.
Many repetitive operations are required in order to convert raw data into,
typically a large number of, spectra. This effort can be markedly simplified
through the use of a tool or pipeline, which is designed to complete many of
the repetitive operations without human interaction. Here we present our
semi-automatic data-reduction tool p3d that is designed to be used with
fiber-fed IFSs. Important components of p3d include a novel algorithm for
automatic finding and tracing of spectra on the detector, and two methods of
optimal spectrum extraction in addition to standard aperture extraction. p3d
also provides tools to combine several images, perform wavelength calibration
and flat field data. p3d is at the moment configured for four IFSs. In order to
evaluate its performance we have tested the different components of the tool.
For these tests we used both simulated and observational data. We demonstrate
that for three of the IFSs a correction for so-called cross-talk due to
overlapping spectra on the detector is required. Without such a correction
spectra will be inaccurate, in particular if there is a significant intensity
gradient across the object. Our tests showed that p3d is able to produce
accurate results. p3d is a highly general and freely available tool. It is
easily extended to include improved algorithms, new visualization tools and
support for additional instruments. The program code can be downloaded from the
p3d-project web site http://p3d.sourceforge.netComment: 18 pages, 15 figures, 3 tables, accepted for publication in A&
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