36 research outputs found
The black-hole masses of Seyfert galaxies and quasars
The central black-hole masses of a sample of 30 luminous quasars are
estimated using H-beta FWHM measurements from a combination of new and
previously-published nuclear spectra. The quasar black-hole mass estimates are
combined with reverberation-mapping measurements for a sample of Seyfert
galaxies (Wandel 1999) in order to study AGN black-hole masses over a wide
range in nuclear luminosity. It is found that black-hole mass and bulge
luminosity are well correlated and follow a relation consistent with that
expected if black-hole and bulge mass are directly proportional. Contrary to
the results of Wandel (1999) no evidence is found that Seyfert galaxies follow
a different Mblack-Mbulge relation to quasars. However, the black-hole mass
distributions of the radio-loud and radio-quiet quasar sub-samples are found to
be significantly different, with the median black-hole mass of the radio-loud
quasars a factor of three larger than their radio-quiet counterparts. Finally,
utilizing the elliptical galaxy fundamental plane to provide stellar velocity
dispersion estimates, a comparison is performed between the virial H-beta
black-hole mass estimates and those of the Mblack-sigma correlations of
Gebhardt et al. (2000a) and Merritt & Ferrarese (2000). With the disc-like
geometry of the broad-line region adopted in this paper, the virial H-beta
black-hole masses indicate that the correct normalization of the black-hole vs.
bulge mass relation is Mblack=0.0025Mbulge, while the standard assumption of
purely random broad-line velocities leads to Mblack=0.0008Mbulge. The
normalization of Mblack=0.0025Mbulge provided by the disc model is in
remarkably good agreement with that inferred for our quasar sample using the
(completely independent) Mblack-sigma correlations.Comment: 10 pages, 6 figures, accepted for publication in MNRA
Magnetic field-dependent interplay between incoherent and Fermi liquid transport mechanisms in low-dimensional tau phase organic conductors
We present an electrical transport study of the 2-dimensional (2D) organic
conductor tau-(P-(S,S)-DMEDT-TTF)_2(AuBr)_2(AuBr_2)_y (y = 0.75) at low
temperatures and high magnetic fields. The inter-plane resistivity rho_zz
increases with decreasing temperature, with the exception of a slight anomaly
at 12 K. Under a magnetic field B, both rho_zz and the in-plane resistivity
plane rho_xx show a pronounced negative and hysteretic magnetoresistance with
Shubnikov de Haas (SdH)oscillations being observed in some (high
quality)samples above 15 T. Contrary to the predicted single, star-shaped,
closed orbit Fermi surface from band structure calculations (with an expected
approximate area of 12.5% of A_FBZ), two fundamental frequencies F_l and F_h
are detected in the SdH signal. These orbits correspond to 2.4% and 6.8% of the
area of the first Brillouin zone(A_FBZ), with effective masses F_l = 4.0 +/-
0.5 and F_h = 7.3 +/- 0.1. The angular dependence, in tilted magnetic fields of
F_l and F_h, reveals the 2D character of the FS and Angular dependent
magnetoresistance (AMRO) further suggests a FS which is strictly 2-D where the
inter-plane hopping t_c is virtually absent or incoherent. The Hall constant
R_xy is field independent, and the Hall mobility increases by a factor of 3
under moderate magnetic fields. Our observations suggest a unique physical
situation where a stable 2D Fermi liquid state in the molecular layers are
incoherently coupled along the least conducting direction. The magnetic field
not only reduces the inelastic scattering between the 2D metallic layers, but
it also reveals the incoherent nature of interplane transport in the AMRO
spectrum. The apparent ferromagnetism of the hysteretic magnetoresistance
remains an unsolved problem.Comment: 33 pages, 11 figure
The lifecycle of powerful AGN outflows
During the course of this conference, much evidence was presented that points
to an intimate connection between the energetic outflows driven by AGN and the
energy budget and quite possibly also the evolution of their gaseous
environments. However, it is still not clear if and how the AGN activity is
triggered by the cooling gas, how long the activity lasts for and how these
effects give rise to the observed distribution of morphologies of the outflows.
In this contribution we concentrate on the high radio luminosity end of the AGN
population. While most of the heating of the environmental gas may be due to
less luminous and energetic outflows, these more powerful objects have a very
profound influence on their surroundings. We will describe a simple model for
powerful radio galaxies and radio-loud quasars that explains the dichotomy of
their large-scale radio morphologies as well as their radio luminosity
function.Comment: 6 pages, contribution to 'Heating vs. coooling in galaxies and galaxy
clusters', Garching 2006, proceedings to be published by Springer (ESO
Astrophysics Symposia), eds. H. Boehringer, P. Schuecker, G.W. Pratt & A.
Finogueno
Étude comparative des vibrations de basses fréquences de la β-hydroquinone par infrarouge et par diffusion inélastique des neutrons
Neutron scattering by β quinol gives a strong peak at 102 cm-1 with no I. R. counter-part, one peak at 65 cm-1 corresponding to an I.R. absorption band and a low frequency background which may be related to impurity induced absorption observed at 57 and 75 cm-1. The frequency of the 102 cm-1 strongest peak is increased by 10 % when D 2S is introduced into all cages.La diffusion des neutrons lents par l'hydroquinone β pure donne un pic intense à 102 cm-1 sans corrélation avec le spectre infrarouge, un pic à 65 cm-1 qui correspond à une raie infrarouge et un fond continu de basse fréquence correspondant à l'absorption induite à 57 et 75 cm-1 lorsqu'on introduit diverses molécules dans les cages. La fréquence du pic à 102 cm-1 augmente de 10 % lorsqu'on remplit les cages du clathrate avec des molécules D2S
A Multicellular Approach Forms a Significant Amount of Tissue-Engineered Small Intestine in the Mouse
Tissue-engineered small intestine (TESI) has successfully been used to rescue Lewis rats after massive small bowel resection. In this study, we transitioned the technique to a mouse model, allowing investigation of the processes involved during TESI formation through the transgenic tools available in this species. This is a necessary step toward applying the technique to human therapy. Multicellular organoid units were derived from small intestines of transgenic mice and transplanted within the abdomen on biodegradable polymers. Immunofluorescence staining was used to characterize the cellular processes during TESI formation. We demonstrate the preservation of Lgr5- and DcamKl1-positive cells, two putative intestinal stem cell populations, in proximity to their niche mesenchymal cells, the intestinal subepithelial myofibroblasts (ISEMFs), at the time of implantation. Maintenance of the relationship between ISEMF and crypt epithelium is observed during the growth of TESI. The engineered small intestine has an epithelium containing a differentiated epithelium next to an innervated muscularis. Lineage tracing demonstrates that all the essential components, including epithelium, muscularis, nerves, and some of the blood vessels, are of donor origin. This multicellular approach provides the necessary cell population to regenerate large amounts of intestinal tissue that could be used to treat short bowel syndrome