591 research outputs found
Jet-Induced Emission-Line Nebulosity and Star Formation in the High-Redshift Radio Galaxy 4C41.17
The high redshift radio galaxy 4C41.17 consists of a powerful radio source in
which previous work has shown that there is strong evidence for jet-induced
star formation along the radio axis. We argue that nuclear photoionization is
not responsible for the excitation of the emission line clouds and we construct
a jet-cloud interaction model to explain the major features revealed by the
data. The interaction of a high-powered jet with a dense cloud in the halo of
4C41.17 produces shock-excited emission-line nebulosity through ~1000 km/s
shocks and induces star formation. The CIII to CIV line ratio and the CIV
luminosity emanating from the shock, imply that the pre-shock density in the
line-emitting cloud is high enough (~1-10 cm^-3) that shock initiated star
formation could proceed on a timescale of order a few x 10^6 yrs, well within
the estimated dynamical age of the radio source. Broad (FWHM ~ 100 - 1400 km/s)
emission lines are attributed to the disturbance of the gas cloud by a partial
bow--shock and narrow emission lines (FWHM ~ 500 - 650 km/s) (in particular
CIV) arise in precursor emission in relatively low metallicity gas. The implied
baryonic mass ~ 8 \times 10^{10} solar masses of the cloud is high and implies
that Milky Way size condensations existed in the environments of forming radio
galaxies at a redshift of 3.8. Our interpretation of the data provides a
physical basis for the alignment of the radio, emission-line and UV continuum
images in some of the highest redshift radio galaxies and the analysis
presented here may form a basis for the calculation of densities and cloud
masses in other high redshift radio galaxies.Comment: 18 pages, 5 figures; uses astrobib.sty and aaspp4.sty. Better
versions of figures available via anonymous from
ftp://mso.anu.edu.au:pub/pub/geoff/4C41.1
Towards a New Standard Theory for Astrophysical Disk Accretion
We briefly review recent developments in black hole accretion disk theory,
placing new emphasis on the vital role played by magnetohydrodynamic (MHD)
stresses in transporting angular momentum. The apparent universality of
accretion-related outflow phenomena is a strong indicator that vertical
transport of angular momentum by large-scale MHD torques is important and may
even dominate radial transport by small-scale MHD turbulence. This leads to an
enhanced overall rate of angular momentum transport and allows accretion of
matter to proceed at an interesting rate. Furthermore, we argue that when
vertical transport is important, the radial structure of the accretion disk is
modified and this affects the disk emission spectrum. We present a simple model
demonstrating that energetic, magnetically-driven outflows give rise to a disk
spectrum that is dimmer and redder than a standard accretion disk accreting at
the same rate. We briefly discuss the implications of this key result for
accreting black holes in different astrophysical systems.Comment: Accepted for publication as brief review in Mod. Phys. Let.
Equation of state and transport processes in self--similar spheres
We study the effect of transport processes (diffusion and free--streaming) on
a collapsing spherically symmetric distribution of matter in a self--similar
space--time. A very simple solution shows interesting features when it is
matched with the Vaidya exterior solution. In the mixed case (diffusion and
free--streaming), we find a barotropic equation of state in the stationary
regime. In the diffusion approximation the gravitational potential at the
surface is always constant; if we perturb the stationary state, the system is
very stable, recovering the barotropic equation of state as time progresses. In
the free--streaming case the self--similar evolution is stationary but with a
non--barotropic equation of state.Comment: 9 pages, 2 figure
Guidelines for Energy Efficient Schools
Operational experience of several schools
designed with energy efficiency as a design
criteria is discussed in this paper. Actual
monthly energy usage and cost are provided. Annual
energy cost performance ($/ft^2-yr) and energy
performance (BTU/FT^2-yr) of these example case
study schools with flexible mechanical and
electrical systems are compared to published design
performance guidelines and similar schools
constructed without energy efficiency as a design
criteria. The authors have conducted energy
studies of more than 400 schools which serve as a
comparative data base range of performance.
Of the schools compared, those with the
lowest operating cost and energy usage employed
flexible HVAC systems which inherently provided for
control of electrical demand. The resulting
electrical demand profile of most of theme case
study schools were relatively constant throughout
the year which is uncommon to most schools. The
design approach employed to achieve lowar operating
costs and inherent demand control is a hybrid HVAC
system with a designed mixture or balance between
electric and natural gas energy sources.
The summary of this paper will compare
operating cost performance, energy performance,
HVAC system type of the case study schools, eight
schools with water source heat pumps, and other
data base schools with various other types of HVAC
systems. Design guidelines for energy efficient
schools are presented
T helper cell subsets specific for pseudomonas aeruginosa in healthy individuals and patients with cystic fibrosis
Background: We set out to determine the magnitude of antigen-specific memory T helper cell responses to Pseudomonas aeruginosa in healthy humans and patients with cystic fibrosis.
Methods: Peripheral blood human memory CD4+ T cells were co-cultured with dendritic cells that had been infected with different strains of Pseudomonas aeruginosa. The T helper response was determined by measuring proliferation, immunoassay of cytokine output, and immunostaining of intracellular cytokines.
Results: Healthy individuals and patients with cystic fibrosis had robust antigen-specific memory CD4+ T cell responses to Pseudomonas aeruginosa that not only contained a Th1 and Th17 component but also Th22 cells. In contrast to previous descriptions of human Th22 cells, these Pseudomonal-specific Th22 cells lacked the skin homing markers CCR4 or CCR10, although were CCR6+. Healthy individuals and patients with cystic fibrosis had similar levels of Th22 cells, but the patient group had significantly fewer Th17 cells in peripheral blood.
Conclusions: Th22 cells specific to Pseudomonas aeruginosa are induced in both healthy individuals and patients with cystic fibrosis. Along with Th17 cells, they may play an important role in the pulmonary response to this microbe in patients with cystic fibrosis and other conditions
The unfriendly ISM in the radio galaxy 4C12.50 (PKS 1345+12)
The radio source 4C12.50 has often been suggested to be a prime candidate for
the link between ultraluminous infrared galaxies and young radio galaxies. A
VLBI study of the neutral hydrogen in the nuclear regions of this object shows
that most of the gas detected close to the systemic velocity is associated with
an off-nuclear cloud (~50 to 100 pc from the radio core) with a column density
of ~10^22 T_spin/100 K) cm^(-2) and an HI mass of a few times 10^5 to 10^6
M_sun. We consider a number of possibilities to explain the results. In
particular, we discus the possibility that this cloud indicates the presence of
a rich and clumpy interstellar medium in the centre, likely left over from the
merger that triggered the activity and that this medium influences the growth
of the radio source. The location of the cloud -- at the edge of the northern
radio jet/lobe -- suggests that the radio jet might be interacting with a gas
cloud. This interaction could be responsible for bending the young radio jet.
The velocity profile of the gas is relatively broad (~150$ km/s) and we
interpret this as kinematical evidence for interaction of the radio plasma with
the cloud. We also consider the model where the cloud is part of a broader
circumnuclear structure. Only a limited region of this structure would have
sufficient background radio brightness and large enough column depth in neutral
gas to obtain detectable HI absorption against the counterjet. The VLBI study
of the neutral hydrogen in 4C12.50 suggests that HI detected near the systemic
velocity (as it is often the case in radio galaxies) may not necessarily be
connected with a circumnuclear disk or torus (as is very often assumed) but
instead could be a tracer of the large-scale medium that surrounds the active
nucleus and that may influence the growth of the young radio source.Comment: 7 pages, 2 figures. Accepted for publication in A&
Metric gravity theories and cosmology:II. Stability of a ground state in f(R) theories
A fundamental criterion of viability of any gravity theory is existence of a
stable ground-state solution being either Minkowski, dS or AdS space. Stability
of the ground state is independent of which frame is physical. In general, a
given theory has multiple ground states and splits into independent physical
sectors. All metric gravity theories with the Lagrangian being a function of
Ricci tensor are dynamically equivalent to Einstein gravity with a source and
this allows us to study the stability problem using methods developed in GR. We
apply these methods to f(R) theories. As is shown in 13 cases of Lagrangians
the stability criterion works simply and effectively whenever the curvature of
the ground state is determined. An infinite number of gravity theories have a
stable ground state and further viability criteria are necessary.Comment: A modified and expanded version of a second part of the paper which
previously appeared as gr-qc/0702097v1. The first, modified part is now
published as gr-qc/0702097v2 and as a separate paper in Class. Qu. Grav. The
present paper matches the published versio
Deficiency in origin licensing proteins impairs cilia formation: implications for the aetiology of meier-gorlin syndrome
Mutations in ORC1, ORC4, ORC6, CDT1, and CDC6, which encode proteins required for DNA replication origin licensing, cause Meier-Gorlin syndrome (MGS), a disorder conferring microcephaly, primordial dwarfism, underdeveloped ears, and skeletal abnormalities. Mutations in ATR, which also functions during replication, can cause Seckel syndrome, a clinically related disorder. These findings suggest that impaired DNA replication could underlie the developmental defects characteristic of these disorders. Here, we show that although origin licensing capacity is impaired in all patient cells with mutations in origin licensing component proteins, this does not correlate with the rate of progression through S phase. Thus, the replicative capacity in MGS patient cells does not correlate with clinical manifestation. However, ORC1-deficient cells from MGS patients and siRNA-mediated depletion of origin licensing proteins also have impaired centrosome and centriole copy number. As a novel and unexpected finding, we show that they also display a striking defect in the rate of formation of primary cilia. We demonstrate that this impacts sonic hedgehog signalling in ORC1-deficient primary fibroblasts. Additionally, reduced growth factor-dependent signaling via primary cilia affects the kinetics of cell cycle progression following cell cycle exit and re-entry, highlighting an unexpected mechanism whereby origin licensing components can influence cell cycle progression. Finally, using a cell-based model, we show that defects in cilia function impair chondroinduction. Our findings raise the possibility that a reduced efficiency in forming cilia could contribute to the clinical features of MGS, particularly the bone development abnormalities, and could provide a new dimension for considering developmental impacts of licensing deficiency
RhoJ interacts with the GIT-PIX complex and regulates focal adhesion disassembly
RhoJ is a Rho GTPase expressed in endothelial cells and tumour cells, which regulates cell motility, invasion, endothelial tube formation and focal adhesion numbers. This study aimed to further delineate the molecular function of RhoJ. Using timelapse microscopy RhoJ was found to regulate focal adhesion disassembly; small interfering RNA (siRNA)-mediated knockdown of RhoJ increased focal adhesion disassembly time, whereas expression of an active mutant (daRhoJ) decreased it. Furthermore, daRhoJ co-precipitated with the GIT–PIX complex, a regulator of focal adhesion disassembly. An interaction between daRhoJ and GIT1 was confirmed using yeast two-hybrid experiments, and this depended on the Spa homology domain of GIT1. GIT1, GIT2, β-PIX (also known as ARHGEF7) and RhoJ all colocalised in focal adhesions and depended on each other for their recruitment to focal adhesions. Functionally, the GIT–PIX complex regulated endothelial tube formation, with knockdown of both GIT1 and GIT2, or β-PIX phenocopying RhoJ knockdown. RhoJ-knockout mice showed reduced tumour growth and diminished tumour vessel density, identifying a role for RhoJ in mediating tumour angiogenesis. These studies give new insight into the molecular function of RhoJ in regulating cell motility and tumour vessel formation
Evolution of the Bianchi I, the Bianchi III and the Kantowski-Sachs Universe: Isotropization and Inflation
We study the Einstein-Klein-Gordon equations for a convex positive potential
in a Bianchi I, a Bianchi III and a Kantowski-Sachs universe. After analysing
the inherent properties of the system of differential equations, the study of
the asymptotic behaviors of the solutions and their stability is done for an
exponential potential. The results are compared with those of Burd and Barrow.
In contrast with their results, we show that for the BI case isotropy can be
reached without inflation and we find new critical points which lead to new
exact solutions. On the other hand we recover the result of Burd and Barrow
that if inflation occurs then isotropy is always reached. The numerical
integration is also done and all the asymptotical behaviors are confirmed.Comment: 22 pages, 12 figures, Self-consistent Latex2e File. To be published
in Phys. Rev.
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