1,918 research outputs found
Chiral two-loop pion-pion scattering parameters from crossing-symmetric constraints
Constraints on the parameters in the one- and two-loop pion-pion scattering
amplitudes of standard chiral perturbation theory are obtained from explicitly
crossing-symmetric sum rules. These constraints are based on a matching of the
chiral amplitudes and the physical amplitudes at the symmetry point of the
Mandelstam plane. The integrals over absorptive parts appearing in the sum
rules are decomposed into crossing-symmetric low- and high-energy components
and the chiral parameters are finally related to high-energy absorptive parts.
A first application uses a simple model of these absorptive parts. The
sensitivity of the results to the choice of the energy separating high and low
energies is examined with care. Weak dependence on this energy is obtained as
long as it stays below ~560 MeV. Reliable predictions are obtained for three
two-loop parameters.Comment: 23 pages, 4 figures in .eps files, Latex (RevTex), our version of
RevTex runs under Latex2.09, submitted to Phys. Rev. D,minor typographical
corrections including the number at the end of the abstract, two sentences
added at the end of Section 5 in answer to a referee's remar
Characterization of the human omega-oxidation pathway for omega-hydroxy-very-long-chain fatty acids
Very-long-chain fatty acids (VLCFAs) have long been known to be degraded exclusively in peroxisomes via beta-oxidation. A defect in peroxisomal beta-oxidation results in elevated levels of VLCFAs and is associated with the most frequent inherited disorder of the central nervous system white matter, X-linked adrenoleukodystrophy. Recently, we demonstrated that VLCFAs can also undergo omega-oxidation, which may provide an alternative route for the breakdown of VLCFAs. The omega-oxidation of VLCFA is initiated by CYP4F2 and CYP4F3B, which produce omega-hydroxy-VLCFAs. In this article, we characterized the enzymes involved in the formation of very-long-chain dicarboxylic acids from omega-hydroxy-VLCFAs. We demonstrate that very-long-chain dicarboxylic acids are produced via two independent pathways. The first is mediated by an as yet unidentified, microsomal NAD(+)-dependent alcohol dehydrogenase and fatty aldehyde dehydrogenase, which is encoded by the ALDH3A2 gene and is deficient in patients with Sjogren-Larsson syndrome. The second pathway involves the NADPH-dependent hydroxylation of omega-hydroxy-VLCFAs by CYP4F2, CYP4F3B, or CYP4F3A. Enzyme kinetic studies show that oxidation of omega-hydroxy-VLCFAs occurs predominantly via the NAD(+)-dependent route. Overall, our data demonstrate that in humans all enzymes are present for the complete conversion of VLCFAs to their corresponding very-long-chain dicarboxylic acids
BeppoSAX observations of the Seyfert 1 Galaxy NGC 3516
We present the results of two observations of the bright Seyfert 1 galaxy NGC
3516, obtained with BeppoSAX in 1996 November and 1997 March. Useful signal is
detected between 0.2 and 60 keV, allowing for the first time the simultaneous
observation of all main spectral features. The source was brighter by a factor
2 at the second epoch of observation. Both spectra present a strong Fe Kalpha
line, and a reflection hump at high energy. An absorption edge at 0.8 keV is
visible in the later spectrum, but not in the earlier one, indicating that this
feature is strongly variable.Comment: to appear in : The Active X-ray Sky: Results from BeppoSAX and
Rossi-XTE, Nuclear Physics B Proceedings Supplements, L. Scarsi, H. Bradt, P.
Giommi and F. Fiore (eds.), Elsevier Science B.V. 4 pages LateX and 6 ps
figures, using espcrc2 and epsfi
A general introduction to the biochemistry of mitochondrial fatty acid β-oxidation
Over the years, the mitochondrial fatty acid β-oxidation (FAO) pathway has been characterised at the biochemical level as well as the molecular biological level. FAO plays a pivotal role in energy homoeostasis, but it competes with glucose as the primary oxidative substrate. The mechanisms behind this so-called glucose–fatty acid cycle operate at the hormonal, transcriptional and biochemical levels. Inherited defects for most of the FAO enzymes have been identified and characterised and are currently included in neonatal screening programmes. Symptoms range from hypoketotic hypoglycaemia to skeletal and cardiac myopathies. The pathophysiology of these diseases is still not completely understood, hampering optimal treatment. Studies of patients and mouse models will contribute to our understanding of the pathogenesis and will ultimately lead to better treatment
Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency
A new case of 3-hydroxyacyl-CoA dehydrogenase deficiency is described with a relatively benign course
Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
We present improved black hole masses for 35 active galactic nuclei (AGNs)
based on a complete and consistent reanalysis of broad emission-line
reverberation-mapping data. From objects with multiple line measurements, we
find that the highest precision measure of the virial product is obtained by
using the cross-correlation function centroid (as opposed to the
cross-correlation function peak) for the time delay and the line dispersion (as
opposed to full width half maximum) for the line width and by measuring the
line width in the variable part of the spectrum. Accurate line-width
measurement depends critically on avoiding contaminating features, in
particular the narrow components of the emission lines. We find that the
precision (or random component of the error) of reverberation-based black hole
mass measurements is typically around 30%, comparable to the precision attained
in measurement of black hole masses in quiescent galaxies by gas or stellar
dynamical methods. Based on results presented in a companion paper by Onken et
al., we provide a zero-point calibration for the reverberation-based black hole
mass scale by using the relationship between black hole mass and host-galaxy
bulge velocity dispersion. The scatter around this relationship implies that
the typical systematic uncertainties in reverberation-based black hole masses
are smaller than a factor of three. We present a preliminary version of a
mass-luminosity relationship that is much better defined than any previous
attempt. Scatter about the mass-luminosity relationship for these AGNs appears
to be real and could be correlated with either Eddington ratio or object
inclination.Comment: 61 pages, including 8 Tables and 16 Figures. Accepted for publication
in The Astrophysical Journa
Magnetic Confinement, MHD Waves, and Smooth Line Profiles in AGN
In this paper, we show that if the broad line region clouds are in
approximate energy equipartition between the magnetic field and gravity, as
hypothesized by Rees, there will be a significant effect on the shape and
smoothness of broad emission line profiles in active galactic nuclei. Line
widths of contributing clouds or flow elements are much wider than their
thermal widths, due to the presence of non-dissipative MHD waves, and their
collective contribution produce emission line profiles broader and smoother
than would be expected if a magnetic field were not present. As an
illustration, a simple model of isotropically emitting clouds, normally
distributed in velocity, is used to show that smoothness can be achieved for
less than 80,000 clouds and may even be as low as a few hundred. We conclude
that magnetic confinement has far reaching consequences for observing and
modeling active galactic nuclei.Comment: to appear in MNRA
Determination of SU(2) Chiral Perturbation Theory low energy constants from a precise description of pion-pion scattering threshold parameters
We determine the values of the one- and two-loop low energy constants
appearing in the SU(2) Chiral Perturbation Theory calculation of pion-pion
scattering. For this we use a recent and precise sum rule determination of some
scattering lengths and slopes that appear in the effective range expansion. In
addition we provide sum rules for these coefficients up to third order in the
expansion. Our results when using only the scattering lengths and slopes of the
S, P, D and F waves are consistent with previous determinations, but seem to
require higher order contributions if they are to accommodate the third order
coefficients of the effective range expansion.Comment: 16 pages. Version published in Phys. Rev. D. Enlarged discussions in
several sections, appendices and many references added. Results and
conclusions unchange
Feasibility and potential effectiveness of an intensive trauma-focused treatment programme for families with PTSD and mild intellectual disability
Background: Persons with mild intellectual disabilities or borderline intellectual functioning (MID-BIF; IQ 50–85) have a higher risk of being exposed to traumatic events and developing posttraumatic stress disorder (PTSD). EMDR therapy has shown to be applicable, safe and
potentially effective for the treatment of PTSD in individuals with MID-BIF. However, in traumatized multi-problem families with MID-BIF and (impending) out of home placement of children, standard PTSD treatment in an outpatient setting may not be appropriate.
Objective: To evaluate the feasibility and potential effectiveness of KINGS-ID, a six-week clinical trauma-focused treatment programme consisting of intensive EMDR therapy with parents and children, and parental skills training followed by two weeks of parent support at home.
Method: Six families (nine parents of whom six had MID-BIF) and 10 children (all having MID-BIF) participated in the KINGS-ID programme. Seven parents and seven children had PTSD. Data were collected within a single case study design. For each family member data were collected during baseline (three measurements), treatment (seven weekly measurements), posttreatment (three measurements) and at follow-up (three measurements).
Results: None of the family members dropped out. Within the first two treatment weeks all but one child and one parent no longer met PTSD symptom criteria. In both children and parents, trauma-related symptoms and daily life impairment significantly decreased following treatment and in parents a significant decrease in symptoms of general psychopathology and parental stress was found. Results were maintained at six-month follow-up.
Conclusions: The findings of the current study are promising given that the treatment
programme seems to offer new perspectives for traumatized multi-problem families with
MID-BIF
A Cutoff in the X-ray Fluctuation Power Density Spectrum of the Seyfert 1 Galaxy NGC 3516
During 1997 March-July, XTE observed the bright, strongly variable Seyfert 1
galaxy NGC 3516 once every ~12.8 hr for 4.5 months and nearly continuously
(with interruptions due to SAA passage but not Earth occultation) for a 4.2 day
period in the middle. These were followed by ongoing monitoring once every ~4.3
days. These data are used to construct the first well-determined X-ray
fluctuation power density spectrum (PDS) of an active galaxy to span more than
4 decades of usable temporal frequency. The PDS shows no signs of any strict or
quasi-periodicity, but does show a progressive flattening of the power-law
slope from -1.74 at short time scales to -0.73 at longer time scales. This is
the clearest observation to date of the long-predicted cutoff in the PDS. The
characteristic variability time scale corresponding to this cutoff temporal
frequency is 1 month. Although it is unclear how this time scale may be
interpreted in terms of a physical size or process, there are several promising
candidate models. The PDS appears similar to those seen for Galactic black hole
candidates such as Cyg X-1, suggesting that these two classes of objects with
very different luminosities and putative black hole masses (differing by more
than a factor of 10^5) may have similar X-ray generation processes and
structures.Comment: 21 pages, incl. 5 figures, AASTe
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