330 research outputs found
Stereospecific hydroxylation of long chain compounds by a species of Torulopsis.
Abstract A species of yeast of the genus Torulopsis hydroxylates long chain C18 compounds and then converts them to glycosides of 17-l-hydroxy C18 fatty acids. Incubation of methyl [17-18O]hydroxyoleate with whole cells and of methyl oleate in the presence of 18O2 or H218O showed that the oxygen atom, introduced on hydroxylation, is not lost on glycoside formation and that it is derived from molecular oxygen and not from water. Esters of [18-2H3], [16,18-2H5], [17-2H2], [17-d-2H], and [17-l-2H]octadecanoates have been synthesized. On incubation of these compounds no deuterium atoms at C-16 and C-18 are removed but the 17-l-deuterium atom is lost. Unsaturated intermediates are, therefore, most probably not involved and 17-l-hydroxy acid is produced by displacement of an l-hydrogen atom (retention of configuration). The rate of formation of glycoside from l-deuterostearate was less than half of that from d-deuterostearate or from unlabeled stearate, suggesting the operation of a primary isotope effect
The MeV spectral tail in Cyg X-1 and optically-thin emission of jets
We study the average X-ray and soft gamma-ray spectrum of Cyg X-1 in the hard
spectral state, using data from INTEGRAL. We compare these results with those
from CGRO, and find a good agreement. Confirming previous studies, we find the
presence of a high-energy MeV tail beyond a thermal-Comptonization spectrum;
however, the tail is much softer and weaker than that recently published by
Laurent et al. In spite of this difference, the observed high-energy tail could
still be due to the synchrotron emission of the jet of Cyg X-1, as claimed by
Laurent et al.
To test this possibility, we study optically-thin synchrotron and
self-Compton emission from partially self-absorbed jets. We develop formalisms
for calculating both emission of the jet base (which we define here as the
region where the jet starts its emission) and emission of the entire jet. We
require the emission to match that observed at the turnover energy. The
optically thin emission is dominated by that from the jet base, and it has to
become self-absorbed within it at the turnover frequency. We find this implies
the magnetic field strength at the jet base of B_0 prop. to z_0^4, where z_0 is
the distance of the base from the black-hole centre. The value of B_0 is then
constrained from below by the condition that the self-Compton emission is below
an upper limit in the GeV range, and from above by the condition that the
Poynting flux does not exceed the jet kinetic power. This yields B_0 of the
order of ~10^4 G and the location of the jet base at ~10^3 gravitational radii.
Using our formalism, we find the MeV tail can be due to jet synchrotron
emission, but this requires the electron acceleration at a rather hard
power-law index, p~1.3-1.6. For acceleration indices of p> 2, the amplitude of
the synchrotron component is much below that of MeV tail, and its origin is
likely to be due to hybrid Comptonization in the accretion flow.Comment: MNRAS, in press, 13 page
A broadband leptonic model for gamma-ray emitting microquasars
Observational and theoretical studies point to microquasars (MQs) as possible
counterparts of a significant fraction of the unidentified gamma-ray sources
detected so far. At present, a proper scenario to explain the emission beyond
soft X-rays from these objects is not known, nor what the precise connection is
between the radio and the high-energy radiation. We develop a new model where
the MQ jet is dynamically dominated by cold protons and radiatively dominated
by relativistic leptons. The matter content and power of the jet are both
related with the accretion process. The magnetic field is assumed to be close
to equipartition, although it is attached to and dominated by the jet matter.
For the relativistic particles in the jet, their maximum energy depends on both
the acceleration efficiency and the energy losses. The model takes into account
the interaction of the relativistic jet particles with the magnetic field and
all the photon and matter fields. Such interaction produces significant amounts
of radiation from radio to very high energies through synchrotron, relativistic
Bremsstrahlung, and inverse Compton (IC) processes. Variability of the emission
produced by changes in the accretion process (e.g. via orbital eccentricity) is
also expected. The effects of the gamma-ray absorption by the external photon
fields on the gamma-ray spectrum have been taken into account, revealing clear
spectral features that might be observed. This model is consistent to the
accretion scenario, energy conservation laws, and current observational
knowledge, and can provide deeper physical information of the source when
tested against multiwavelength data.Comment: 15 pages, 12 figures, A&A, in press (text and plots improved after
minor corrections in calculations, text improved also by referee comments
Theoretical overview on high-energy emission in microquasars
Microquasar (MQ) jets are sites of particle acceleration and synchrotron
emission. Such synchrotron radiation has been detected coming from jet regions
of different spatial scales, which for the instruments at work nowadays appear
as compact radio cores, slightly resolved radio jets, or (very) extended
structures. Because of the presence of relativistic particles and dense photon,
magnetic and matter fields, these outflows are also the best candidates to
generate the very high-energy (VHE) gamma-rays detected coming from two of
these objects, LS 5039 and LS I +61 303, and may be contributing significantly
to the X-rays emitted from the MQ core. In addition, beside electromagnetic
radiation, jets at different scales are producing some amount of leptonic and
hadronic cosmic rays (CR), and evidences of neutrino production in these
objects may be eventually found. In this work, we review on the different
physical processes that may be at work in or related to MQ jets. The jet
regions capable to produce significant amounts of emission at different
wavelengths have been reduced to the jet base, the jet at scales of the order
of the size of the system orbital semi-major axis, the jet middle scales (the
resolved radio jets), and the jet termination point. The surroundings of the
jet could be sites of multiwavelegnth emission as well, deserving also an
insight. We focus on those scenarios, either hadronic or leptonic, in which it
seems more plausible to generate both photons from radio to VHE and high-energy
neutrinos. We briefly comment as well on the relevance of MQ as possible
contributors to the galactic CR in the GeV-PeV range.Comment: Astrophysics & Space Science, in press (invited talk in the
conference: The multimessenger approach to the high-energy gamma-ray
sources", Barcelona/Catalonia, in July 4-7); 10 pages, 6 figures, 2 tables
(one reference corrected
Long term variability of Cygnus X-1, III. Radio-X-ray correlations
Long time scale radio-X-ray correlations in black holes during the hard state
have been found in many sources and there seems to emerge a universal
underlying relationship which quantitatively describes this behavior. Although
it would appear only natural to detect short term emission patterns in the
X-ray and - with a certain time lag - in the radio, there has been little
evidence for this up to now. The most prominent source for radio-X-ray
correlations on short time scales (minutes) so far remains GRS 1915+105 where a
single mass ejection could be detected successively in the X-ray, IR, and radio
wavebands. We analyze a database of more than 4 years of simultaneous
radio-X-ray data for Cygnus X-1 from the Ryle Telescope and RXTE PCA/HEXTE. We
confirm the existence of a radio-X-ray correlation on long time scales,
especially at hard energies. We show that apparent correlations on short time
scales in the lightcurves of Cygnus X-1 are most likely the coincidental
outcome of white noise statistics. Interpreting this result as a breakdown of
radio-X-ray correlations on shorter time scales, this sets a limit to the speed
of the jet.Comment: 8 pages, 7 figures, accepted for publication in A&
A decade of radio imaging the relativistic outflow in the peculiar X-ray binary Circinus X-1
We present observations of the neutron star X-ray binary and relativistic jet
source Circinus X-1 made at 4.8 and 8.6 GHz with the Australia Telescope
Compact Array during a time interval of almost 10 years. The system shows
significant variations in the morphology and brightness of the radio features
on all timescales from days to years. Using the time delay between the
successive brightening of the different components of the radio emission we
were able to provide further evidence for the relativistic nature of the arcsec
scale outflow, with an apparent velocity beta_app >= 12. No compelling evidence
for an evolution of the orientation of the jet axis was found. We also place an
upper limit on the proper motion of the system which is consistent with
previous optical studies. Besides the previously reported radio flares close to
the orbital phase 0.0 (interpreted as enhanced accretion at periastron
passage), we also identified outbursts with similar properties near the orbital
phase 0.5. The global spectral index revealed a preferentially steep spectrum
over the entire period of monitoring with a mean value and standard deviation
alpha=-0.9 +/- 0.6 (F_nu ~ nu^{alpha}), which became significantly flatter
during the outbursts. Polarization was detected in one third of the epochs and
in one case Faraday rotation close to the core of the system was measured.Comment: Accepted for publication in MNRA
Overview of the perceived risk of transboundary pig diseases in South Africa
Pig production is one of the most important animal agricultural activities in South Africa,
and plays a definite role in providing food security for certain population groups in the
country. As with all animal production systems, it is subject to the risk of outbreak of
transboundary diseases. In the present overview, evaluations of the perceived risk of selected
transboundary animal diseases of pigs, as collated from the willing participants from the
provincial veterinary services of South Africa, are presented. A scenario tree revealed that
infected but undetected pigs were the greatest perceived threat. The provincial veterinary
services, according to participants in the study, face certain difficulties, including the
reporting of disease and the flow of disease information amongst farmers. Perceived strengths
in surveillance and disease monitoring include the swiftness of sample despatch to the
national testing laboratory, as well as the ease of flow of information between the provincial
and national agricultural authorities. The four factors were identified that were perceived to
most influence animal health-service delivery: transport, access, livestock policy and
resources. African swine fever was perceived to be the most important pig disease in South
Africa. Because the decentralisation of veterinary services in South Africa was identified as a
potential weakness, it is recommended that national and provincial veterinary services need
to work together and interdependently to achieve centrally controlled surveillance systems.
Regionally-coordinated surveillance activities for certain transboundary diseases were
identified as needing priority for the southern African region. It is proposed that an emergency
preparedness document be made available and regularly revised according to the potential
risks identified on a continuous basis for South Africa.http://www.jsava.co.zaam201
Overview of the perceived risk of transboundary pig diseases in South Africa
Pig production is one of the most important animal agricultural activities in South Africa,
and plays a definite role in providing food security for certain population groups in the
country. As with all animal production systems, it is subject to the risk of outbreak of
transboundary diseases. In the present overview, evaluations of the perceived risk of selected
transboundary animal diseases of pigs, as collated from the willing participants from the
provincial veterinary services of South Africa, are presented. A scenario tree revealed that
infected but undetected pigs were the greatest perceived threat. The provincial veterinary
services, according to participants in the study, face certain difficulties, including the
reporting of disease and the flow of disease information amongst farmers. Perceived strengths
in surveillance and disease monitoring include the swiftness of sample despatch to the
national testing laboratory, as well as the ease of flow of information between the provincial
and national agricultural authorities. The four factors were identified that were perceived to
most influence animal health-service delivery: transport, access, livestock policy and
resources. African swine fever was perceived to be the most important pig disease in South
Africa. Because the decentralisation of veterinary services in South Africa was identified as a
potential weakness, it is recommended that national and provincial veterinary services need
to work together and interdependently to achieve centrally controlled surveillance systems.
Regionally-coordinated surveillance activities for certain transboundary diseases were
identified as needing priority for the southern African region. It is proposed that an emergency
preparedness document be made available and regularly revised according to the potential
risks identified on a continuous basis for South Africa.http://www.jsava.co.zaam201
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Pelargonidin-3-O-glucoside and its metabolites have modest anti-inflammatory effects in human whole blood cultures
This study hypothesized that the predominant strawberry anthocyanin, pelargonidin-3-O-glucoside (Pg-3-glc), and three of its plasma metabolites (4-hydroxybenzoic acid, protocatechuic acid and phloroglucinaldehyde [PGA]) would affect phagocytosis, oxidative burst and the production of selected pro- and anti-inflammatory cytokines in a whole blood culture model. For the assessment of phagocytosis and oxidative burst activity of monocytes and neutrophils, whole blood was pre-incubated in the presence or absence of the test compounds at concentrations up to 5 μM, followed by analysis of phagocytic and oxidative burst activity using commercially available test kits. For the cytokine analysis, diluted whole blood was stimulated with lipopolysaccharide in the presence or absence of the test compounds at concentrations up to 5 μM. Concentrations of selected cytokines (tumor necrosis factor-α [TNF-α], interleukin [IL]-1β, IL-6, IL-8 and IL-10) were determined using a cytometric bead array kit. There were no effects of any of the test compounds on phagocytosis of opsonized or non-opsonized E. coli or on oxidative burst activity. Pg-3-glc and PGA at 0.08 μM increased the concentration of IL-10 (P<0.01 and P<0.001, respectively), but there was no effect on TNF-α, IL-1β, IL-6 and IL-8 and there were no effects of the other compounds. In conclusion, this study demonstrated a lack of effect of these compounds on the opsonization, engulfment and subsequent destruction of bacteria. Pg-3-glc and PGA, at physiologically relevant concentrations, had anti-inflammatory properties; however, effects were modest, only observed at the lowest dose tested and limited to IL-10
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