1,098 research outputs found
Meerjarige wortelonkruiden : onderzoeksplan
Er zijn op akkerbouwbedrijven, vooral op biologisch, problemen met de bestrijding van meerjarige wortelonkruiden. Het probleem wordt ook steeds groter. Door middel van biologische grond ontsmetting (BGO) wordt het aantal meerjarige wortelonkruiden verminderd, maar hoeveel en hoe sterk dat is, is niet bekend. Het effect van BGO werd voornamelijk onderzocht op het onkruid akkermelkdistel. Dit onderzoek werd uitgevoerd door PPO-AGV te Lelystad geholpen door leerlingen van de CAH Dronten. Het onderzoek is een echte proef van PPO en geeft studenten de kans om te leren hoe het in de praktijk gaat met uitvoering en verwerking van gegevens in het onderzoek
The mass and energy budget of Cassiopeia A
Further analysis of X-ray spectroscopy results recently obtained from the MOS
CCD cameras on-board XMM-Newton provides a detailed description of the hot and
cool X-ray emitting plasma in Cas A. Measurement of the Doppler broadening of
the X-ray lines is consistent with the expected ion velocities, ~1500 km/s
along the line of sight, in the post shock plasma. Assuming a constant total
pressure throughout the remnant we estimate the total remnant mass as 10 Msun
and the total thermal energy as 7E43 J. We derive the differential mass
distribution as a function of ionisation age for both X-ray emitting
components. This distribution is consistent with a hot component dominated by
swept up mass heated by the primary shock and a cool component which are
ablated clumpy ejecta material which were and are still being heated by
interaction with the preheated swept up material. We calculate a balanced mass
and energy budget for the supernova explosion giving 1E44 J in ejected mass;
approximately 0.4 Msun of the ejecta were diffuse with an initial rms velocity
of 15000 km/s while the remaining ~1.8 Msun were clumpy with an initial rms
velocity of ~2400 km/s. Using the Doppler velocity measurements of the X-ray
spectral lines we can project the mass into spherical coordinates about the
remnant. This provides quantitative evidence for mass and energy beaming in the
supernova explosion. The mass and energy occupy less than 4.5 sr (<40 % of the
available solid angle) around the remnant and 64 % of the mass occurs in two
jets within 45 degrees of a jet axis. We calculate a swept up mass of 7.9 Msun
in the emitting plasma and estimate that the total mass lost from the
progenitor prior to the explosion could be as high as ~20 Msun.Comment: 8 pages, 7 figures, submitted to Astronomy & Astrophysic
The short-chain fatty acid uptake fluxes by mice on a guar gum supplemented diet associate with amelioration of major biomarkers of the metabolic syndrome
Studies with dietary supplementation of various types of fibers have shown beneficial effects on symptoms of the metabolic syndrome. Short-chain fatty acids (SCFAs), the main products of intestinal bacterial fermentation of dietary fiber, have been suggested to play a key role. Whether the concentration of SCFAs or their metabolism drives these beneficial effects is not yet clear. In this study we investigated the SCFA concentrations and in vivo host uptake fluxes in the absence or presence of the dietary fiber guar gum. C57Bl/6J mice were fed a high-fat diet supplemented with 0%, 5%, 7.5% or 10% of the fiber guar gum. To determine the effect on SCFA metabolism, C-13-labeled acetate, propionate or butyrate were infused into the cecum of mice for 6 h and the isotopic enrichment of cecal SCFAs was measured. The in vivo production, uptake and bacterial interconversion of acetate, propionate and butyrate were calculated by combining the data from the three infusion experiments in a single steady-state isotope model. Guar gum treatment decreased markers of the metabolic syndrome (body weight, adipose weight, triglycerides, glucose and insulin levels and HOMA-IR) in a dose-dependent manner. In addition, hepatic mRNA expression of genes involved in gluconeogenesis and fatty acid synthesis decreased dose-dependently by guar gum treatment. Cecal SCFA concentrations were increased compared to the control group, but no differences were observed between the different guar gum doses. Thus, no significant correlation was found between cecal SCFA concentrations and metabolic markers. In contrast, in vivo SCFA uptake fluxes by the host correlated linearly with metabolic markers. We argue that in vivo SCFA fluxes, and not concentrations, govern the protection from the metabolic syndrome by dietary fibers
Synoptic study of the SMC SNRs using XMM-Newton
We present a detailed X-ray spectral analysis of 13 supernova remnants (SNR)
in the Small Magellanic Cloud (SMC). We apply both single-temperature
non-equilibrium ionisation models and models based on the Sedov similarity
solution, where applicable. We also present detailed X-ray images of individual
SNRs, which reveal a range of different morphological features. Eight remnants,
viz DEM S 32, IKT 2, HFPK 419, IKT 6, IKT 16, IKT 18 and IKT 23, are consistent
with being in their Sedov evolutionary phase. IKT 6 and IKT 23 both have a
clear shell like morphology with oxygen-rich X-ray emitting material in the
centre. We draw attention to similarities between these two remnants and the
well studied, oxygen-rich remnant IKT 22 (SNR 0102-72.3) and propose that they
are more evolved versions of IKT 22. IKT 4, IKT 5, DEM S 128 and IKT 5 are
evolved remnants which are in, or in the process of entering, the radiative
cooling stage. We argue that the X-ray emission from these four remnants is
most likely from the ejecta remains of type Ia SNe. Our modeling allow us to
derive estimates for physical parameters, such as densities, ages, masses and
initial explosion energies. Our results indicate that the average SMC hydrogen
density is a factor of ~6 lower as compared to the Large Magellanic Cloud. This
has obvious implications for the evolution and luminosities of the SMC SNRs. We
also estimate the average SMC gas phase abundances for the elements O, Ne, Mg,
Si and Fe.Comment: submitted to A&
Measuring the cosmic ray acceleration efficiency of a supernova remnant
Cosmic rays are the most energetic particles arriving at earth. Although most
of them are thought to be accelerated by supernova remnants, the details of the
acceleration process and its efficiency are not well determined. Here we show
that the pressure induced by cosmic rays exceeds the thermal pressure behind
the northeast shock of the supernova remnant RCW 86, where the X-ray emission
is dominated by synchrotron radiation from ultra-relativistic electrons. We
determined the cosmic-ray content from the thermal Doppler broadening measured
with optical spectroscopy, combined with a proper-motion study in X- rays. The
measured post-shock proton temperature in combination with the shock velocity
does not agree with standard shock heating, implying that >50% of the
post-shock pressure is produced by cosmic rays.Comment: Published in Science express, 10 pages, 5 figures and 2 table
X-ray spectral imaging and Doppler mapping of Cassiopeia A
A detailed X-ray spectral analysis of Cas A using a deep exposure from the
EPIC-MOS cameras on-board XMM-Newton is presented. Spectral fitting was
performed on a 15x15 grid of 20"x20" pixels using a two component
non-equilibrium ionisation model (NEI) giving maps of ionisation age,
temperature, interstellar column density, abundances and Doppler velocities.
The abundances of Si, S, Ar and Ca are strongly correlated. The abundance
ratios are consistent with the nucleosynthesis yield from the collapse of a 12
Msun progenitor. The abundance ratios Ne/Si, Mg/Si, Fe/Si and Ni/Si are very
variable and distinctly different from S/Si, Ar/Si and Ca/Si, in line with the
current explosive nucleosynthesis models. The ionisation age and temperature of
both NEI components varies considerably over the remnant. Accurate
determination of these parameters yield reliable Doppler velocities for both
components. The data are consistent with a plasma velocity of 2600 km/s at the
shock radius of 153" implying a primary shock velocity of 4000+/-500 km/s. The
Si-K and S-K line emission from the cool component is confined to a relatively
narrow shell with radius 100-150". This component is almost certainly ejecta
material which has been heated by a combination of the reverse shock and
heating of ejecta clumps as they plough through the medium which has been
pre-heated by the primary shock. The Fe-K line emission is expanding faster and
spans a radius range 110-170". The bulk of the Fe emission is confined to two
large clumps and it is likely that these too are the result of ablation from
ejecta bullets rather swept up circumstellar medium.Comment: 10 pages, 11 figures, submitted to Astronomy and Astrophysic
A revision of the akysid catfish genus Acrochordonichthys Bleeker
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75446/1/j.1095-8649.2001.tb02260.x.pd
The Radial Structure of the Cygnus Loop Supernova Remnant --- Possible evidence of a cavity explosion ---
We observed the North-East (NE) Limb toward the center region of the Cygnus
Loop with the ASCA Observatory. We found a radial variation of electron
temperature (kTe) and ionization timescale (log(\tau)) whereas no variation
could be found for the abundances of heavy elements. In this paper, we
re-analyzed the same data set and new observations with the latest calibration
files. Then we constructed the precise spatial variations of kTe, log(\tau),
and abundances of O, Ne, Mg, Si, and Fe over the field of view (FOV). We found
a spatial variation not only in kTe and in log(\tau) but also in most of heavy
elements. As described in Miyata et al. (1994), values of kTe increase and
those of log(\tau) decrease toward the inner region. We found that the
abundance of heavy elements increases toward the inner region. The radial
profiles of O, Ne, and Fe show clear jump structures at a radius of 0.9 Rs,
where Rs is the shock radius. Outside of 0.9 Rs, abundances of all elements are
constant. On the contrary, inside of 0.9 Rs, abundances of these elements are
20--30 % larger than those obtained outside of 0.9 Rs. The radial profile of
kTe also shows the jump structure at 0.9 Rs. This means that the hot and metal
rich plasma fills the volume inside of 0.9 Rs. We concluded that this jump
structure was the possible evidence for the pre-existing cavity produced by the
precursor. If the ejecta fills inside of 0.9 Rs, the total mass of the ejecta
was roughly 4\Msun. We then estimated the main-sequence mass to be roughly
15\Msun, which supports the massive star in origin of the Cygnus Loop supernova
remnant and the existence of a pre-existing cavity.Comment: 37 pages, 14 figures. Accepted for publication of Ap
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