236 research outputs found
Mindful with your baby for mothers of infants with (parental) stress in a non-clinical setting: A wait-list controlled pilot trial.
Dynamiek en robuustheid van multifunctionele landbouw : rapport onderzoeksfase 2: empirisch onderzoek onder 120 multifunctionele landbouwbedrijven
In deze rapportage de uitkomsten van de kwantitatieve en kwalitatieve analyse van het verzamelde praktijkmateriaal op de volgende niveaus; De multifunctionele activiteit (zorg, educatie, toerisme etc.), het multifunctionele landbouwbedrijf en de multifunctionele regio
An interferometric study of the low-mass protostar IRAS 16293-2422: small scale organic chemistry
Aims: To investigate the chemical relations between complex organics based on
their spatial distributions and excitation conditions in the low-mass young
stellar objects IRAS 16293-2422 A and B. Methods: Interferometric observations
with the Submillimeter Array have been performed at 5''x3'' resolution
revealing emission lines of HNCO, CH3CN, CH2CO, CH3CHO and C2H5OH. Rotational
temperatures are determined from rotational diagrams when a sufficient number
of lines are detected. Results: Compact emission is detected for all species
studied here. For HNCO and CH3CN it mostly arises from source A, CH2CO and
C2H5OH have comparable strength for both sources and CH3CHO arises exclusively
from source B. HNCO, CH3CN and CH3CHO have rotational temperatures >200 K. The
(u,v)-visibility data reveal that HNCO also has extended cold emission.
Conclusions: The abundances of the molecules studied here are very similar
within factors of a few to those found in high-mass YSOs. Thus the chemistry
between high- and low-mass objects appears to be independent of luminosity and
cloud mass. Bigger abundance differences are seen between the A and B source.
The HNCO abundance relative to CH3OH is ~4 times higher toward A, which may be
due to a higher initial OCN- ice abundances in source A compared to B.
Furthermore, not all oxygen-bearing species are co-existent. The different
spatial behavior of CH2CO and C2H5OH compared with CH3CHO suggests that
hydrogenation reactions on grain-surfaces are not sufficient to explain the
observed gas phase abundances. Selective destruction of CH3CHO may result in
the anti-coincidence of these species in source A. These results illustrate the
power of interferometric compared with single dish data in terms of testing
chemical models.Comment: 11 pages, 15 figures, accepeted by A&
Cold gas as an ice diagnostic toward low mass protostars
Up to 90% of the chemical reactions during star formation occurs on ice
surfaces, probably including the formation of complex organics. Only the most
abundant ice species are however observed directly by infrared spectroscopy.
This study aims to develop an indirect observational method of ices based on
non-thermal ice desorption in the colder part of protostellar envelopes. For
that purpose the IRAM 30m telescope was employed to observe two molecules that
can be detected both in the gas and the ice, CH3 OH and HNCO, toward 4 low mass
embedded protostars. Their respective gas-phase column densities are determined
using rotational diagrams. The relationship between ice and gas phase
abundances is subsequently determined. The observed gas and ice abundances span
several orders of magnitude. Most of the CH3OH and HNCO gas along the lines of
sight is inferred to be quiescent from the measured line widths and the derived
excitation temperatures, and hence not affected by thermal desorption close to
the protostar or in outflow shocks. The measured gas to ice ratio of ~10-4
agrees well with model predictions for non-thermal desorption under cold
envelope conditions and there is a tentative correlation between ice and gas
phase abundances. This indicates that non-thermal desorption products can serve
as a signature of the ice composition. A larger sample is however necessary to
provide a conclusive proof of concept.Comment: accepted by A&A letters, 10 pages including 5 figure
Ieder zijn eigen Saïdjah en Adinda? De narratieve betrokkenheid van vwo-scholieren bij verschillende bewerkingen van Multatuli’s Max Havelaar (1860)
Contains fulltext :
250247.pdf (Publisher’s version ) (Open Access)18 p
Infrared spectroscopy of solid CO-CO2 mixtures and layers
The spectra of pure, mixed and layered CO and CO2 ices have been studied
systematically under laboratory conditions using infrared spectroscopy. This
work provides improved resolution spectra (0.5 cm-1) of the CO2 bending and
asymmetric stretching mode, as well as the CO stretching mode, extending the
existing Leiden database of laboratory spectra to match the spectral resolution
reached by modern telescopes and to support the interpretation of the most
recent data from Spitzer. It is shown that mixed and layered CO and CO2 ices
exhibit very different spectral characteristics, which depend critically on
thermal annealing and can be used to distinguish between mixed, layered and
thermally annealed CO-CO2 ices. CO only affects the CO2 bending mode spectra in
mixed ices below 50K under the current experimental conditions, where it
exhibits a single asymmetric band profile in intimate mixtures. In all other
ice morphologies the CO2 bending mode shows a double peaked profile, similar to
that observed for pure solid CO2. Conversely, CO2 induces a blue-shift in the
peak-position of the CO stretching vibration, to a maximum of 2142 cm-1 in
mixed ices, and 2140-2146 cm-1 in layered ices. As such, the CO2 bending mode
puts clear constraints on the ice morphology below 50K, whereas beyond this
temperature the CO2 stretching vibration can distinguish between initially
mixed and layered ices. This is illustrated for the low-mass YSO HH46, where
the laboratory spectra are used to analyse the observed CO and CO2 band
profiles and try to constrain the formation scenarios of CO2.Comment: Accepted in A&
The effect of unfiltered coffee on potential biomarkers for colonic cancer risk in healthy volunteers: a randomized trial
Background: Epidemiologic studies suggest that coffee use might protect against colorectal cancer. Inconsistencies as to the effect of coffee use and colorectal cancer between epidemiologic studies might be related to the type of coffee brew. Objective: We studied the effect of unfiltered coffee consumption on putative biomarkers for colonic cancer risk. Design: A total of 64 healthy volunteers (31 men and 33 women), with a mean age of 43 ± 11 years were randomly assigned to two groups in a crossover design, with two intervention periods of 2 weeks separated by a washout period of 8 weeks. Treatments were 1 L of cafetiere (French press) coffee daily or no coffee. At the end of each intervention period, fasting blood samples, colorectal biopsies and 48 h faeces were collected. Results: No effect of coffee on colorectal cell proliferation, assayed by estimating the Proliferating Cell Nuclear Antigen labelling index, was seen. Additionally, no effects were seen on the concentrations of faecal soluble bile acids and colorectal mucosal glutathione S-transferase activity. However, unfiltered coffee significantly increased the glutathione content in the colorectal mucosa by 8% and in plasma by 15%. Other aminothiols in plasma also increased on coffee. Conclusion: Unfiltered coffee does not influence the colorectal mucosal proliferation rate, but might increase the detoxification capacity and anti-mutagenic properties in the colorectal mucosa through an increase in glutathione concentration. Whether this effect indeed contributes to a lower colon cancer risk remains to be established
Quantification of segregation dynamics in ice mixtures
(Abridged) The observed presence of pure CO2 ice in protostellar envelopes is
attributed to thermally induced ice segregation, but a lack of quantitative
experimental data has prevented its use as a temperature probe. Quantitative
segregation studies are also needed to characterize diffusion in ices, which
underpins all ice dynamics and ice chemistry. This study aims to quantify the
segregation mechanism and barriers in different H2O:CO2 and H2O:CO ice mixtures
covering a range of astrophysically relevant ice thicknesses and mixture
ratios. The ices are deposited at 16-50 K under (ultra-)high vacuum conditions.
Segregation is then monitored at 23-70 K as a function of time, through
infrared spectroscopy. Thin (8-37 ML) H2O:CO2/CO ice mixtures segregate
sequentially through surface processes, followed by an order of magnitude
slower bulk diffusion. Thicker ices (>100 ML) segregate through a fast bulk
process. The thick ices must therefore be either more porous or segregate
through a different mechanism, e.g. a phase transition. The segregation
dynamics of thin ices are reproduced qualitatively in Monte Carlo simulations
of surface hopping and pair swapping. The experimentally determined
surface-segregation rates for all mixture ratios follow the Ahrrenius law with
a barrier of 1080[190] K for H2O:CO2 and 300[100] K for H2O:CO mixtures. During
low-mass star formation H2O:CO2 segregation will be important already at 30[5]
K. Both surface and bulk segregation is proposed to be a general feature of ice
mixtures when the average bond strengths of the mixture constituents in pure
ice exceeds the average bond strength in the ice mixture.Comment: Accepted for publication in A&A. 25 pages, including 13 figure
Influence of UV radiation from a massive YSO on the chemistry of its envelope
We have studied the influence of far ultraviolet (UV) radiation from a
massive young stellar object (YSO) on the chemistry of its own envelope by
extending the models of Doty et al. (2002) to include a central source of UV
radiation. The models are applied to the massive star-forming region AFGL 2591
for different inner UV field strengths. Depth-dependent abundance profiles for
several molecules are presented and discussed. We predict enhanced column
densities for more than 30 species, especially radicals and ions. Comparison
between observations and models is improved with a moderate UV field incident
on the inner envelope, corresponding to an enhancement factor G0~10-100 at 200
AU from the star with an optical depth tau~15-17. Subtle differences are found
compared with traditional models of Photon Dominated Regions (PDRs) because of
the higher temperatures and higher gas-phase H2O abundance caused by
evaporation of ices in the inner region. In particular, the CN/HCN ratio is not
a sensitive tracer of the inner UV field, in contrast with the situation for
normal PDRs: for low UV fields, the extra CN reacts with H2 in the inner dense
and warm region and produces more HCN. It is found that the CH+ abundance is
strongly enhanced and grows steadily with increasing UV field. High-J lines of
molecules like CN and HCN are most sensitive to the inner dense region where UV
radiation plays a role. Thus, even though the total column density affected by
UV photons is small, comparison of high-J and low-J lines can selectively trace
and distinguish the inner UV field from the outer one. In addition, future
Herschel-HIFI observations of hydrides can sensitively probe the inner UV
field.Comment: Accepted for publication in A&A. 13 pages, 10 figure
Endothelial surface layer degradation by chronic hyaluronidase infusion induces proteinuria in apolipoprotein e-deficient mice
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