576 research outputs found
Bewaarproeven op voorverpakte verse haring (<i>Clupea harengus</i> L.) onder gesimuleerde verkoopsomstandigheden
Prepackaged herring was stored under simulated selling conditions for up to 5 days: by day (from 9 to 21 h) at 0°, 4° and 8°C and by night at 0°C. Samples withdrawn every day were analysed by sensory, chemical and bacteriological quality determination methods. Gram-negative bacteria were indentified according to the Shewan scheme. The results indicated that the herring had a shelf life of > 5 days at 0°C, 5 days at 4°-2°C and 4 days at 8°C- 0°C. The results indicated that the herring had a total-shelf life of > 5 days revealed by the counts of total aerobic bacteria and by the Enterobacteriaceae. At the end of the storage period the Pseudomonas and the Acinetobacter group represented {approx} 80% of total flora. Furthermore the results showed that Pseudomonas spoilers have a more psychrophilic character than the Acinetobacter group
Reionization history constraints from neural network based predictions of high-redshift quasar continua
Observations of the early Universe suggest that reionization was complete by
, however, the exact history of this process is still unknown. One
method for measuring the evolution of the neutral fraction throughout this
epoch is via observing the Ly damping wings of high-redshift quasars.
In order to constrain the neutral fraction from quasar observations, one needs
an accurate model of the quasar spectrum around Ly, after the spectrum
has been processed by its host galaxy but before it is altered by absorption
and damping in the intervening IGM. In this paper, we present a novel machine
learning approach, using artificial neural networks, to reconstruct quasar
continua around Ly. Our QSANNdRA algorithm improves the error in this
reconstruction compared to the state-of-the-art PCA-based model in the
literature by 14.2% on average, and provides an improvement of 6.1% on average
when compared to an extension thereof. In comparison with the extended PCA
model, QSANNdRA further achieves an improvement of 22.1% and 16.8% when
evaluated on low-redshift quasars most similar to the two high-redshift quasars
under consideration, ULAS J1120+0641 at and ULAS J1342+0928 at
, respectively. Using our more accurate reconstructions of these two
quasars, we estimate the neutral fraction of the IGM using a homogeneous
reionization model and find at
and at . Our
results are consistent with the literature and favour a rapid end to
reionization
Catalogues of voids as antihaloes in the local Universe
A recently proposed algorithm identifies voids in simulations as the regions associated with haloes when the initial overdensity field is negated. We apply this method to the real Universe by running a suite of constrained simulations of the 2M++ volume with initial conditions inferred by the BORG algorithm, along with the corresponding inverted set. Our 101 inverted and uninverted simulations, spanning the BORG posterior, each identify âŒ150â000 âvoids as antihaloesâ with mass exceeding 4.38 Ă 1011âMâ (100 particles) at z = 0 in a full-sky sphere of radius 155 Mpcâhâ1 around the Milky Way. We calculate the size function, volume filling fraction, ellipticity, central density, specific angular momentum, clustering, and stacked density profile of the voids, and cross-correlate them with those produced by VIDE on the same simulations. We make our antihalo and VIDE catalogues publicly available
Accretion, feedback and galaxy bimodality: a comparison of the GalICS semi-analytic model and cosmological SPH simulations
We compare the galaxy population of an SPH simulation to those predicted by
the GalICS semi-analytic model and a stripped down version without supernova
and AGN feedback. The SPH simulation and the no-feedback GalICS model make
similar predictions for the baryonic mass functions of galaxies and for the
dependence of these mass functions on environment and redshift. The two methods
also make similar predictions for the galaxy content of dark matter haloes as a
function of halo mass and for the gas accretion history of galaxies. Both the
SPH and no-feedback GalICS models predict a bimodal galaxy population at z=0.
The "red'' sequence of gas poor, old galaxies is populated mainly by satellite
systems while, contrary to observations, the central galaxies of massive haloes
lie on the "blue'' star-forming sequence as a result of continuing hot gas
accretion at late times. Furthermore, both models overpredict the observed
baryonic mass function, especially at the high mass end. In the full GalICS
model, supernova-driven outflows reduce the masses of low and intermediate mass
galaxies by about a factor of two. AGN feedback suppresses gas cooling in large
haloes, producing a sharp cut-off in the baryonic mass function and moving the
central galaxies of these massive haloes to the red sequence. Our results imply
that the observational failings of the SPH simulation and the no-feedback
GalICS model are a consequence of missing input physics rather than
computational inaccuracies, that truncating gas accretion by satellite galaxies
automatically produces a bimodal galaxy distribution with a red sequence, but
that explaining the red colours of the most massive galaxies requires a
mechanism like AGN feedback that suppresses the accretion onto central galaxies
in large haloes.Comment: 17 pages, 11 figures, submitted to MNRA
On Measuring the Infrared Luminosity of Distant Galaxies with the Space Infrared Telescope Facility
The Space Infrared Telescope Facility (SIRTF) will revolutionize the study of
dust-obscured star formation in distant galaxies. Although deep images from the
Multiband Imaging Photometer for SIRTF (MIPS) will provide coverage at 24, 70,
and 160 micron, the bulk of MIPS-detected objects may only have accurate
photometry in the shorter wavelength bands due to the confusion noise.
Therefore, we have explored the potential for constraining the total infrared
(IR) fluxes of distant galaxies with solely the 24 micron flux density, and for
the combination of 24 micron and 70 micron data. We also discuss the inherent
systematic uncertainties in making these transitions. Under the assumption that
distant star-forming galaxies have IR spectral energy distributions (SEDs) that
are represented somewhere in the local Universe, the 24 micron data (plus
optical and X-ray data to allow redshift estimation and AGN rejection)
constrains the total IR luminosity to within a factor of 2.5 for galaxies with
0.4 < z < 1.6. Incorporating the 70 micron data substantially improves this
constraint by a factor < 6. Lastly, we argue that if the shape of the IR SED is
known (or well constrained; e.g., because of high IR luminosity, or low
ultraviolet/IR flux ratio), then the IR luminosity can be estimated with more
certainty.Comment: 4 pages, 3 figures (2 in color). Accepted for Publication in the
Astrophysical Journal Letters, 2002 Nov
De bewaarkapaciteit van voorverpakte schol = L'aptitude à la conservation de la plie préemballée
The present study was undertaken to determine changes in storage life, spoilage pattern and bacterial flora of prepackaged plaice (Pleuronectes platessa L.) as a consequence of changes in temperature of the refrigerated display cabinet. Prepacked fillets and whole fish were stored for up to 4 days under simulated selling conditions and at 3 different temperatures: by day (from 9 to 18 h) at 1, 4 or 8° C and by night at 1°C. Every day the bacterial decay of the plaice was determined by sensory, chemical and bacteriological methods. The results indicated that a retail shelf-life of 4 days can be guaranteed for prepackaged whole plaice and fillets at temperatures not exceeding 4°C. The storage at 8°C not only limited the keeping time but also could not satisfactorily prevent the proliferation of coliforms. Prepacked plaice picked up a considerable load of these bacteria, especially during the sequence of filleting under existing commercial conditions
Simulations of Dust in Interacting Galaxies I: Dust Attenuation
A new Monte-Carlo radiative-transfer code, Sunrise, is used in conjunction
with hydrodynamic simulations of major galaxy mergers to calculate the effects
of dust in such systems. The simulations are in good agreement with
observations of dust absorption in starburst galaxies, and the dust has a
profound effect on their appearance. The dust attenuation increases with
luminosity such that at peak luminosities ~90% of the bolometric luminosity is
absorbed by dust. In general, the detailed appearance of the merging event
depends on the stage of the merger and the geometry of the encounter. The
fraction of bolometric energy absorbed by the dust, however, is a robust
quantity that can be predicted from the intrinsic properties bolometric
luminosity, baryonic mass, star-formation rate, and metallicity of the system.
This paper presents fitting formulae, valid over a wide range of masses and
metallicities, from which the absorbed fraction of luminosity (and consequently
also the infrared dust luminosity) can be predicted. The attenuation of the
luminosity at specific wavelengths can also be predicted, albeit with a larger
scatter due to the variation with viewing angle. These formulae for dust
attenuation appear to be valid for both isolated and interacting galaxies, are
consistent with earlier studies, and would be suitable for inclusion in
theoretical models, e.g. semi-analytic models of galaxy formation.Comment: 12 pages, 10 figures, submitted to Ap
Unveiling a Population of X-ray Non-Detected AGN
We define a sample of 27 radio-excess AGN in the Chandra Deep Field North by
selecting galaxies that do not obey the radio/infrared correlation for
radio-quiet AGN and star-forming galaxies. Approximately 60% of these
radio-excess AGN are X-ray undetected in the 2 Ms Chandra catalog, even at
exposures of > 1 Ms; 25% lack even 2-sigma X-ray detections. The absorbing
columns to the faint X-ray-detected objects are 10^22 cm^-2 < N_H < 10^24
cm^-2, i.e., they are obscured but unlikely to be Compton thick. Using a local
sample of radio-selected AGN, we show that a low ratio of X-ray to radio
emission, as seen in the X-ray weakly- and non-detected samples, is correlated
with the viewing angle of the central engine, and therefore with obscuration.
Our technique can explore the proportion of obscured AGN in the distant
Universe; the results reported here for radio-excess objects are consistent
with but at the low end of the overall theoretical predictions for
Compton-thick objects.Comment: Accepted for publication in the Astrophysical Journal, 15 pages, 10
figures, 4 table
Evolution of the IBDM Structural Latch Development into a Generic Simplified Design
This paper presents the evolution in the development of the structural latch for the International Berthing Docking Mechanism (IBDM, see Figure 1). It reports on the lessons learned since completion of the test program on the engineering development unit of the first generation latching system in 2007. The initial latch design has been through a second generation concept in 2008, and now evolved into a third generation of this mechanism. Functional and structural testing on the latest latch hardware has recently been completed with good results. The IBDM latching system will provide the structural connection between two mated space vehicles after berthing or docking. The mechanism guarantees that the interface seals become compressed to form a leak-tight pressure system that creates a passageway for the astronauts
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