687 research outputs found
Obscuring Material around Seyfert Nuclei with Starbursts
The structure of obscuring matter in the environment of active galactic
nuclei with associated nuclear starbursts is investigated using 3-D
hydrodynamical simulations. Simple analytical estimates suggest that the
obscuring matter with energy feedback from supernovae has a torus-like
structure with a radius of several tens of parsecs and a scale height of about
10 pc. These estimates are confirmed by the fully non-linear numerical
simulations, in which the multi-phase inhomogeneous interstellar matter and its
interaction with the supernovae are consistently followed. The globally stable,
torus-like structure is highly inhomogeneous and turbulent. To achieve the high
column densities (> 10^{24} cm^{-2}) as suggested by observations of some
Seyfert 2 galaxies with nuclear starbursts, the viewing angle should be larger
than about 70 degree from the pole-on for a 10^8 solar mass massive black hole.
Due to the inhomogeneous internal structure of the torus, the observed column
density is sensitive to the line-of-sight, and it fluctuates by a factor of
order 100. The covering fraction for N > 10^{23} cm^{-2} is about 0.4. The
average accretion rate toward R < 1 pc is 0.4 solar mass/yr, which is boosted
to twice that in the model without the energy feedback.Comment: ApJL in press (4 pages, 3 figures) A gziped ps file with high
resolution figures is available at http://th.nao.ac.jp/~wada/AGN
The Global Structure and Evolution of a Self-Gravitating Multi-phase Interstellar Medium in a Galactic Disk
Using high resolution, two-dimensional hydrodynamical simulations, we
investigate the evolution of a self-gravitating multi-phase interstellar medium
in the central kiloparsec region of a galactic disk. We find that a
gravitationally and thermally unstable disk evolves, in a self-stabilizing
manner, into a globally quasi-stable disk that consists of cold (T < 100 K),
dense clumps and filaments surrounded by hot (T > 10^4 K), diffuse medium. The
quasi-stationary, filamentary structure of the cold gas is remarkable. The hot
gas, characterized by low-density holes and voids, is produced by shock
heating. The shocks derive their energy from differential rotation and
gravitational perturbations due to the formation of cold dense clumps. In the
quasi-stable phase where cold and dense clouds are formed, the effective
stability parameter, Q, has a value in the range 2-5. The dynamic range of our
multi-phase calculations is 10^6 - 10^7 in both density and temperature. Phase
diagrams for this turbulent medium are analyzed and discussed.Comment: 10 pages, 3 figures, ApJ Letters in press (vol. 516
MEN 2A: Update on the Northern Ireland and Australian Family
The Northern Ireland/Australian family with multiple endocrine neoplasia type 2A (MEN 2A) originally described in 1987 is presented with a revised and enlarged pedigree. Four members of the first generation studied have died. A seventh member of the second generation studied has developed medullary thyroid carcinoma and has progressed to surgery. None of the third generation members studied has shown any conclusive abnormality in metabolic screening tests. Each member of the third and fourth generations has had genetic counseling and (if appropriate) DNA analysis with gene probes close to the MEN 2A gene locus on chromosome 10. All members of this highly penetrant family have remained asymptomatic for their disease
Targeting metastatic colorectal cancer with immune oncological therapies
Metastatic colorectal cancer carries poor prognosis, and current therapeutic regimes convey limited improvements in survival and high rates of detrimental side effects in patients that may not stand to benefit. Immunotherapy has revolutionised cancer treatment by restoring antitumoural mechanisms. However, the efficacy in metastatic colorectal cancer, is limited. A literature search was performed using Pubmed (Medline), Web of Knowledge, and Embase. Search terms included combinations of immunotherapy and metastatic colorectal cancer, primarily focusing on clinical trials in humans. Analysis of these studies included status of MMR/MSS, presence of combination strategies, and disease control rate and median overall survival. Evidence shows that immune checkpoint inhibitors, such as anti-PD1 and anti-PD-L1, show efficacy in less than 10% of patients with microsatellite stable, MMR proficient colorectal cancer. In the small subset of patients with microsatellite unstable, MMR deficient cancers, response rates were 40â50%. Combination strategies with immunotherapy are under investigation but have not yet restored antitumoural mechanisms to permit durable disease regression. Immunotherapy provides the potential to offer additional strategies to established chemotherapeutic regimes in metastatic colorectal cancer. Further research needs to establish which adjuncts to immune checkpoint inhibition can unpick resistance, and better predict which patients are likely to respond to individualised therapies to not just improve response rates but to temper unwarranted side effects
Progressing the care, husbandry and management of ageing mice used in scientific studies
Driven by the longer lifespans of humans, particularly in Westernised societies, and the need to know more about âhealthy ageingâ, ageing mice are being used increasingly in scientific research. Many departments and institutes involved with ageing research have developed their own systems to determine intervention points for potential refinements and to identify humane end points. Several good systems are in use, but variations between them could contribute to poor reproducibility of the science achieved. Working with scientific and regulatory communities in the UK, we have reviewed the clinical signs observed in ageing mice and developed recommendations for enhanced monitoring, behaviour assessment, husbandry and veterinary interventions. We advocate that the default time point for enhanced monitoring should be 15 months of age, unless prior information is available. Importantly, the enhanced monitoring should cause no additional harms to the animals. Where a mouse strain is well characterised, the onset of age-related enhanced monitoring may be modified based on knowledge of the onset of an expected age-related clinical sign. In progeroid models where ageing is accelerated, enhanced monitoring may need to be brought forward. Information on the background strain must be considered, as it influences the onset of age-related clinical signs. The range of ageing models currently used means that there will be no âone-size fits allâ solution. Increased awareness of the issues will lead to more refined and consistent husbandry of ageing mice, and application of humane end points will help to reduce the numbers of animals maintained for longer than is scientifically justified
The Evolution of Cuspy Triaxial Galaxies Harboring Central Black Holes
We use numerical simulations to study the evolution of triaxial elliptical
galaxies with central black holes. In contrast to earlier numerical studies
which used galaxy models with central density ``cores,'' our galaxies have
steep central cusps, like those observed in real ellipticals. As a black hole
grows in these cuspy triaxial galaxies, the inner regions become rounder owing
to chaos induced in the orbit families which populate the model. At larger
radii, however, the models maintain their triaxiality, and orbital analyses
show that centrophilic orbits there resist stochasticity over many dynamical
times. While black hole induced evolution is strong in the inner regions of
these galaxies, and reaches out beyond the nominal ``sphere of influence'' of a
black hole, our simulations do not show evidence for a rapid {\it global}
transformation of the host. The triaxiality of observed elliptical galaxies is
therefore not inconsistent with the presence of supermassive black holes at
their centers.Comment: 15 pages, 7 figures (1 color). Accepted for publication in Ap
Detection of the Entropy of the Intergalactic Medium: Accretion Shocks in Clusters, Adiabatic Cores in Groups
The thermodynamics of the diffuse, X-ray emitting gas in clusters of galaxies
is linked to the entropy level of the intra cluster medium. In particular,
models that successfully reproduce the properties of local X-ray clusters and
groups require the presence of a minimum value for the entropy in the center of
X-ray halos. Such a minimum entropy is most likely generated by
non-gravitational processes, in order to produce the observed break in
self-similarity of the scaling relations of X-ray halos. At present there is no
consensus on the level, the source or the time evolution of this excess
entropy. In this paper we describe a strategy to investigate the physics of the
heating processes acting in groups and clusters. We show that the best way to
extract information from the local data is the observation of the entropy
profile at large radii in nearby X-ray halos (z~0.1), both at the upper and
lower extremes of the cluster mass scale. The spatially and spectrally resolved
observation of such X-ray halos provides information on the mechanism of the
heating. We demonstrate how measurements of the size of constant entropy
(adiabatic) cores in clusters and groups can directly constrain heating models,
and the minimum entropy value. We also consider two specific experiments: the
detection of the shock fronts expected at the virial boundary of rich clusters,
and the detection of the isentropic, low surface-brightness emission extending
to radii larger than the virial ones in low mass clusters and groups. Such
observations will be a crucial probe of both the physics of clusters and the
relationship of non-gravitational processes to the thermodynamics of the
intergalactic medium.Comment: ApJ accepted, 31 pages including 8 figures. Important material added;
references update
Sequential Electrostatic Assembly of a Polymer Surfactant Corona Increases Activity of the Phosphotriesterase arPTE
We present a new methodology for the generation of discrete molecularly dispersed enzymeâpolymerâsurfactant bioconjugates. Significantly, we demonstrate that >3-fold increase in the catalytic efficiency of the diffusion-limited phosphotriesterase arPTE can be achieved through sequential electrostatic addition of cationic and anionic polymer surfactants, respectively. Here, the polymer surfactants assemble on the surface of the enzyme via ion exchange to yield a compact corona. The observed rate enhancement is consistent with a mechanism whereby the polymerâsurfactant corona gives rise to a decrease in the dielectric constant in the vicinity of the active site of the enzyme, accelerating the rate-determining product diffusion step. The facile methodology has significant potential for increasing the efficiency of enzymes and could therefore have a substantially positive impact for industrial enzymology
Evolution of the Lyman-alpha Halos around High-Redshift Radio Galaxies
We have obtained the first constraints on extended Ly-alpha emission at z ~ 1
in a sample of five radio galaxies. We detect Ly-alpha emission from four of
the five galaxies. The Ly-alpha luminosities range from 0.1 - 4 times 10^43
erg/s and are much smaller than those observed for halos around higher redshift
radio galaxies. If the z ~ 1 radio galaxies are the descendents the z >~ 2
radio galaxies, then their Ly-alpha luminosities evolve strongly with redshift
as ~(1+z)^5. There do not appear to be strong correlations between other
parameters, such as radio power, suggesting that this observed evolution is
real and not an observational artifact or secondary correlation. We speculate
that this evolution of luminous halos may be due to gas depletion (as gas
cools, settles, and forms stars) accompanied by an overall rise in the mean gas
temperature and a decrease in specific star-formation rate in and around these
massive galaxies.Comment: 5 pages, 4 figures, published in ApJ Letters, 694, L31-35 March 20
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