1,893 research outputs found
Biologische producten natuurlijk verpakt
Hoe milieuvriendelijk zijn hernieuwbare en biologisch afbreekbare kunststofverpakkingen eigenlijk? Voor het verpakkend bedrijfsleven is het lastig om daarachter te komen en dus weloverwogen keuzes te maken. In het onderzoek ‘Natuurlijk verpakt’ – uitgevoerd door Wageningen UR Food & Biobased Research – is zoveel mogelijk informatie verzameld en samengevat
The Determination of the `Diffusion Coefficients' and the Stellar Wind Velocities for X-Ray Binaries
The distribution of neutron stars (NS's) is determined by stationary solution
of the Fokker-Planck equation. In this work using the observed period changes
for four systems: Vela X-1, GX 301-2, Her X-1 and Cen X-3 we determined D, the
'diffusion coefficient',-parameter from the Fokker-Planck equation. Using
strong dependence of D on the velocity for Vela X-1 and GX 301-2, systems
accreting from a stellar wind, we determined the stellar wind velocity. For
different assumptions for a turbulent velocity we obtained . It is in good agreement with the stellar wind velocity determined by
other methods. We also determined the specific characteristic time scales for
the 'diffusion processes' in X-ray pulsars. It is of order of 200 sec for
wind-fed pulsars and 1000-10000 sec for the disk accreting systems.Comment: 8 pages, Latex, no figures, accepted for publication to Astronomical
and Astrophysical Transactions (1995). Admin note 20Feb2000: original
(broken) version now paper.tex.orig in source; fixed version with two bad
equations set in verbatim used for PS, paper.tex in sourc
Chemokine-induced secretion of gelatinase B in primary human monocytes
Chemokines help control normal leukocyte trafficking as well as their infiltration into tissues during acute and chronic inflammation. Matrix metalloproteinases (MMPs) help support the extravasation and infiltration of leukocytes through limited proteolysis of basement membranes and matrix material. The effect of the chemokines RANTES/CCL5, MCP-1/CCL and SDF-1 /CXCL12 on secretion of the matrix metalloproteinase B and its endogenous inhibitor TIMP-1 was studied. RANTES/CCL5 and SDF-1/CXCL12 were found to induce MMP-9 secretion in primary human monocytes while TIMP-1 secretion was not affected. RANTES/CCL5 effects were mediated through CCR1 because the CCR1 antagonist BX471 was found to effectively block RANTES/CCL5-induced MMP-9 secretion
Resolving the Fe xxv Triplet with Chandra in Cen X-3
We present the results of a 45 ks Chandra observation of the high-mass X-ray
binary Cen X--3 at orbital phases between 0.13 and 0.40 (in the eclipse
post-egress phases). Here we concentrate on the study of discrete features in
the energy spectrum at energies between 6 and 7 keV, i.e. on the iron
K line region, using the High Energy Transmission Grating Spectrometer
on board the Chandra satellite. We clearly see a K neutral iron line
at keV and were able to distinguish the three lines of the
\ion{Fe}{25} triplet at 6.61 keV, 6.67 keV, and 6.72 keV, with an equivalent
width of 6 eV, 9 eV, and 5 eV, respectively. The equivalent width of the
K neutral iron line is 13 eV, an order of magnitude lower than
previous measures. We discuss the possibility that the small equivalent width
is due to a decrease of the solid angle subtended by the reflector.Comment: 11 pages, 2 figures, To appear in the Astrophysical Journal Letter
Discovery of a 6.4 keV Emission Line in a Burst from SGR 1900+14
We present evidence of a 6.4 keV emission line during a burst from the soft
gamma-ray repeater SGR 1900+14. The Rossi X-ray Timing Explorer (RXTE)
monitored this source extensively during its outburst in the summer of 1998. A
strong burst observed on August 29, 1998 revealed a number of unique
properties. The burst exhibits a precursor and is followed by a long (~ 1000 s)
tail modulated at the 5.16 s stellar rotation period. The precursor has a
duration of 0.85 s and shows both significant spectral evolution as well as an
emission feature centered near 6.4 keV during the first 0.3 s of the event,
when the X-ray spectrum was hardest. The continuum during the burst is well fit
with an optically thin thermal bremsstrahlung (OTTB) spectrum with the
temperature ranging from about 40 to 10 keV. The line is strong, with an
equivalent width of 400 eV, and is consistent with Fe K-alpha fluorescence from
relatively cool material. If the rest-frame energy is indeed 6.4 keV, then the
lack of an observed redshift indicates that the source is at least 80 km above
the neutron star surface. We discuss the implications of the line detection in
the context of models for SGRs.Comment: AASTex preprint, 14 pages, 3 embedded figures. Accepted for
Publication in Astrophysical Journal Letter
The X-ray Luminosity Function of "The Antennae" Galaxies (NGC4038/39) and the Nature of Ultra-Luminous X-ray Sources
We derive the X-ray luminosity function (XLF) of the X-ray source population
detected in the Chandra observation of NGC4038/39 (the Antennae).
We explicitly include photon counting and spectral parameter uncertainties in
our calculations. The cumulative XLF is well represented by a flat power law
(), similar to those describing the XLFs of other star-forming
systems (e.g. M82, the disk of M81), but different from those of early type
galaxies. This result associates the X-ray source population in the Antennae
with young High Mass X-ray Binaries. In comparison with less actively
star-forming galaxies, the XLF of the Antennae has a highly significant excess
of sources with luminosities above 10^{39} erg\s (Ultra Luminous Sources;
ULXs). We discuss the nature of these sources, based on the XLF and on their
general spectral properties, as well as their optical counterparts discussed in
Paper III. We conclude that the majority of the ULXs cannot be intermediate
mass black-holes (M > 10-1000 \msun) binaries, unless they are linked to the
remnants of massive Population III stars (the Madau & Rees model). Instead,
their spatial and multiwavelength properties can be well explained by beamed
emission as a consequence of supercritical accretion.
Binaries with a neutron star or moderate mass black-hole (up to 20\msun), and
B2 to A type star companions would be consistent with our data. In the beaming
scenario, the XLF should exibit caracteristic breaks that will be visible in
future deeper observations of the Antennae.Comment: 15 pages, submitted to Ap
Neutron Star Masses and Radii as Inferred from kilo-Hertz QPOs
Kilo-Hertz (kHz) Quasi-periodic oscillations (QPOs) have been discovered in
the X-ray fluxes of 8 low-mass X-ray binaries (LMXBs) with the Rossi X-ray
Timing Explorer (RXTE). The characteristics of these QPOs are remarkably
similar from one source to another. In particular, the highest observed QPO
frequencies for 6 of the 8 sources fall in a very narrow range: 1,066 to 1,171
Hz. This is the more remarkable when one considers that these sources are
thought to have very different luminosities and magnetic fields, and produce
very different count rates in the RXTE detectors. Therefore it is highly
unlikely that this near constancy of the highest observed frequencies is due to
some unknown selection effect or instrumental bias. In this letter we propose
that the highest observed QPO frequency can be taken as the orbital frequency
of the marginally stable orbit. This leads to the conclusions that the neutron
stars in these LMXBs are inside their marginally stable orbits and have masses
in the vicinity of 2.0 solar masses. This mass is consistent with the
hypothesis that these neutron stars were born with about 1.4 solar masses and
have been accreting matter at a fraction of the Eddington limit for 100 million
years.Comment: 7 pages, uses aas2pp4.sty, Accepted by ApJ
Role of the Netrin-like Domain of Procollagen C-Proteinase Enhancer-1 in the Control of Metalloproteinase Activity
The netrin-like (NTR) domain is a feature of several extracellular proteins, most notably the N-terminal domain of tissue inhibitors of metalloproteinases (TIMPs), where it functions as a strong inhibitor of matrix metalloproteinases and some other members of the metzincin superfamily. The presence of a C-terminal NTR domain in procollagen C-proteinase enhancers (PCPEs), proteins that stimulate the activity of astacin-like tolloid proteinases, raises the possibility that this might also have inhibitory activity. Here we show that both long and short forms of the PCPE-1 NTR domain, the latter beginning at the N-terminal cysteine known to be critical for TIMP activity, show no inhibition, at micromolar concentrations, of several members of the metzincin superfamily, including matrix metalloproteinase-2, bone morphogenetic protein-1 (a tolloid proteinase), and different ADAMTS (a disintegrin and a metalloproteinase with thrombospondin motifs) proteinases from the adamalysin family. In contrast, we report that the NTR domain within PCPE-1 leads to superstimulation of bone morphogenetic protein-1 activity in the presence of heparin and heparan sulfate. These observations point to a new mechanism whereby binding to cell surface-associated or extracellular heparin-like sulfated glycosaminoglycans might provide a means to accelerate procollagen processing in specific cellular and extracellular microenvironments
Timing, glitches and braking index of PSR B0540-69
We report a pulse-time history of PSR B054069 based on the analysis of an
extended Data set including ASCA, BeppoSAX and RXTE observations spanning a
time interval of about 8 years. This interval includes also the epoch of the
glitch episode reported by Zhang et al. (2001). Our analysis shows the presence
of a relevant timing noise and does not give a clear evidence of the glitch
occurrence. We performed an accurate evaluation of the main timing parameters,
, and and derived a mean braking index of
quite different from the lower value found by Zhang et al.
(2001), but in rather good agreement with other several values reported in the
literature.Comment: 9 pages 5 figures, accepted by A&A, main journa
X-ray and optical periodicities in X-ray binaries. I.A0535+26
A homogeneous set of UBV photometry (354 data points obtained between 1983
and 1998) for the Be/X-ray binary A0535+26 = V725Tau is analysed, aiming to
look for possible periodic component(s). After subtraction of the long-term
variation it was found that only a 103-day periodic component remains in the
power spectra in both the V and B colour bands. The probability of chance
occurrence of such a peak is less than 0.1%. There are no signs of optical
variability at the X-ray period (111 d). We discuss possible reasons for a
103-day modulation and suggest that it corresponds to a beat frequency of the
orbital period of the neutron star and the precession period (~1400 d) either
of an accretion disc around the neutron star or a warped decretion disc around
the Be star.Comment: LaTeX, 6 pages, 5 figures, uses psfig.st
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