156 research outputs found
The LBDS Hercules sample of mJy radio sources at 1.4 GHz - II. Redshift distribution, radio luminosity function, and the high-redshift cut-off
{Abridged} A combination of spectroscopy and broadband photometric redshifts
has been used to find the complete redshift distribution of the Hercules sample
of millijansky radio sources. These data have been used to examine the
evolution of the radio luminosity function (RLF) and its high-redshift cut-off.
New redshifts have been measured for eleven sources, and a further ten upper
limits are given. The total number of sources with known redshifts in the
sample is now 47 (65%). We calculated broadband photometric redshifts for the
remaining one-third of the sample.
For the luminosity range probed by the present study (P_1.4 > 10^24.5
W/Hz/sr), we use the V/V_max test to show conclusively that there is a deficit
of high-redshift (z > 2-2.5) objects. Comparison with the model RLFs of Dunlop
& Peacock (1990) shows that our data can now exclude pure luminosity evolution.
Two of the models of DP90, and the RLF deduced by direct binning of the data,
both favour a luminosity dependence for the high-redshift cut-off, with
lower-luminosity sources (P_1.4 \simeq 10^24 W/Hz/sr) in decline by z \simeq
1-1.5 while higher-luminosity sources (P_1.4 \simeq 10^{25-26} W/Hz/sr) decline
in comoving number density beyond z \simeq 2-2.5.Comment: Revised version submitted to MNRAS. 16 pages, 12 figure
A guanosine 5′-triphosphate-dependent protein kinase is localized in the outer envelope membrane of pea chloroplasts
A guanosine 5-triphosphate (GTP)-dependent protein kinase was detected in preparations of outer chloroplast envelope membranes of pea (Pisum sativum L.) chloroplasts. The protein-kinase activity was capable of phosphorylating several envelope-membrane proteins. The major phosphorylated products were 23- and 32.5-kilo-dalton proteins of the outer envelope membrane. Several other envelope proteins were labeled to a lesser extent. Following acid hydrolysis of the labeled proteins, most of the label was detected as phosphoserine with only minor amounts detected as phosphothreonine. Several criteria were used to distinguish the GTP-dependent protein kinase from an ATP-dependent kinase also present in the outer envelope membrane. The ATP-dependent kinase phosphorylated a very different set of envelope-membrane proteins. Heparin inhibited the GTP-dependent kinase but had little effect upon the ATP-dependent enzyme. The GTP-dependent enzyme accepted phosvitin as an external protein substrate whereas the ATP-dependent enzyme did not. The outer membrane of the chloroplast envelope also contained a phosphotransferase capable of transferring labeled phosphate from [-32P]GTP to ADP to yield (-32P]ATP. Consequently, addition of ADP to a GTP-dependent protein-kinase assay resulted in a switch in the pattern of labeled products from that seen with GTP to that typically seen with ATP
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
Fermi acceleration in astrophysical jets
We consider the acceleration of energetic particles by Fermi processes (i.e.,
diffusive shock acceleration, second order Fermi acceleration, and gradual
shear acceleration) in relativistic astrophysical jets, with particular
attention given to recent progress in the field of viscous shear acceleration.
We analyze the associated acceleration timescales and the resulting particle
distributions, and discuss the relevance of these processes for the
acceleration of charged particles in the jets of AGNs, GRBs and microquasars,
showing that multi-component powerlaw-type particle distributions are likely to
occur.Comment: 6 pages, one figure; based on talk at "The multimessenger approach to
unidentified gamma-ray sources", Barcelona/Spain, July 2006; accepted for
publication in Astrophysics and Space Scienc
Enhanced Secretion of Amylase from Exocrine Pancreas of Connexin32-deficient Mice
To determine whether junctional communication between pancreatic acinar cells contributes to their secretory function in vivo, we have compared wild-type mice, which express the gap junctional proteins connexin32 (Cx32) and connexin26, to mice deficient for the Cx32 gene. Pancreatic acinar cells from Cx32 (−/−) mice failed to express Cx32 as evidenced by reverse transcription–PCR and immunolabeling and showed a marked reduction (4.8- and 25-fold, respectively) in the number and size of gap junctions. Dye transfer studies showed that the extent of intercellular communication was inhibited in Cx32 (−/−) acini. However, electrical coupling was detected by dual patch clamp recording in Cx32 (−/−) acinar cell pairs. Although wild-type and Cx32 (−/−) acini were similarly stimulated to release amylase by carbamylcholine, Cx32 (−/−) acini showed a twofold increase of their basal secretion. This effect was caused by an increase in the proportion of secreting acini, as detected with a reverse hemolytic plaque assay. Blood measurements further revealed that Cx32 (−/−) mice had elevated basal levels of circulating amylase. The results, which demonstrate an inverse relationship between the extent of acinar cell coupling and basal amylase secretion in vivo, support the view that the physiological recruitment of secretory acinar cells is regulated by gap junction mediated intercellular communication
Magnetic Field Amplification in Galaxy Clusters and its Simulation
We review the present theoretical and numerical understanding of magnetic
field amplification in cosmic large-scale structure, on length scales of galaxy
clusters and beyond. Structure formation drives compression and turbulence,
which amplify tiny magnetic seed fields to the microGauss values that are
observed in the intracluster medium. This process is intimately connected to
the properties of turbulence and the microphysics of the intra-cluster medium.
Additional roles are played by merger induced shocks that sweep through the
intra-cluster medium and motions induced by sloshing cool cores. The accurate
simulation of magnetic field amplification in clusters still poses a serious
challenge for simulations of cosmological structure formation. We review the
current literature on cosmological simulations that include magnetic fields and
outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure
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