656 research outputs found
OH main line masers in the M82 starburst
A study of the distribution of OH gas in the central region of the nearby
active starburst galaxy M82 has confirmed two previously known bright masers
and revealed several new main line masers. Three of these are seen only at 1665
MHz, one is detected only at 1667 MHz, while the rest are detected in both
lines. Observations covering both the 1665 and 1667 MHz lines, conducted with
both the Very Large Array (VLA) and the Multi-Element Radio Linked
Interferometer Network (MERLIN), have been used to accurately measure the
positions and velocities of these features. This has allowed a comparison with
catalogued continuum features in the starburst such as HII regions and
supernova remnants, as well as known water and satellite line OH masers. Most
of the main line masers appear to be associated with known HII regions although
the two detected only at 1665 MHz are seen along the same line of sight as
known supernova remnants.Comment: MNRAS accepted. 16 pages, 13 figure
Multi-epoch VLBA observations of 3C 66A
We present the results of six-epoch Very Long Baseline Array (VLBA)
observations of 3C~66A. The high-resolution Very Long Baseline Interferometer
(VLBI) maps obtained at multi-frequency (2.3, 8.4, and 22.2 GHz) simultaneously
enabled us to identify the brightest compact component with the core. We find
that the spectrum of the core can be reasonably fitted by the synchrotron
self-absorption model. Our VLBA maps show that the jet of 3C~66A has two
bendings at about 1.2 and 4 mas from the core. We also give possible
identifications of our jet components with the components in previous VLBA
observations by analysing their proper motions. We find consistent differences
of the position from the core in one component between different frequencies at
six epochs.Comment: 10 pages, 5 figures, received 30 January 2007, accepted 22 March 200
Strongly Correlated Cerium Systems: Non-Kondo Mechanism for Moment Collapse
We present an ab initio based method which gives clear insight into the
interplay between the hybridization, the coulomb exchange, and the
crystal-field interactions, as the degree of 4f localization is varied across a
series of strongly correlated cerium systems. The results for the ordered
magnetic moments, magnetic structure, and ordering temperatures are in
excellent agreement with experiment, including the occurence of a moment
collapse of non-Kondo origin. In contrast, standard ab initio density
functional calculations fail to predict, even qualitatively, the trend of the
unusual magentic properties.Comment: A shorter version of this has been submitted to PR
The dependence of the EIT wave velocity on the magnetic field strength
"EIT waves" are a wavelike phenomenon propagating in the corona, which were
initially observed in the extreme ultraviolet (EUV) wavelength by the EUV
Imaging Telescope (EIT). Their nature is still elusive, with the debate between
fast-mode wave model and non-wave model. In order to distinguish between these
models, we investigate the relation between the EIT wave velocity and the local
magnetic field in the corona. It is found that the two parameters show
significant negative correlation in most of the EIT wave fronts, {\it i.e.},
EIT wave propagates more slowly in the regions of stronger magnetic field. Such
a result poses a big challenge to the fast-mode wave model, which would predict
a strong positive correlation between the two parameters. However, it is
demonstrated that such a result can be explained by the fieldline stretching
model, \emph{i.e.,} that "EIT waves" are apparently-propagating brightenings,
which are generated by successive stretching of closed magnetic field lines
pushed by the erupting flux rope during coronal mass ejections (CMEs).Comment: 11 pages, 8 figures, accepted for publication in Solar Phy
Could the Compact Radio Sources in M82 be Cluster Wind Driven Bubbles?
The compact non-thermal sources in M82 and other starburst galaxies are generally thought to be supernova remnants (SNRs). We consider an alternative hypothesis that most are wind driven bubbles (WDBs) associated with very young super star clusters (SSCs). In this scenario, the synchrotron emitting particles are produced at the site of the shock transition between the cluster wind and the hot bubble gas. The particles radiate in the strong magnetic field produced in the expanding shell of shocked ambient interstellar gas. One of the motivations for this hypothesis is the lack of observed time variability in most of the sources, implying ages greater than expected for SNRs, but comfortably within the range for WDBs. In addition, as SNRs, these sources are not effective in driving the starburst mass outflow associated with the nuclear region of M82, thus requiring a separate mechanism for coupling SN energy to this outflow. The WDB hypothesis is found to be feasible for underlying clusters in the mass range ~2x10^(4+/-1)Msun, and ambient gas densities in the range ~3x10^(3+/-1)cm^-3. The ages of the bubbles are between several x10^3 and several x10^4 years. Since the SNR picture cannont be ruled out, we provide suggestions for specific observational tests which could confirm or rule out the WDB hypothesis. Finally, we discuss the WDB hypothesis in the context of broader phenomena in M82, such as the rate of star formation and starburst outflows, and the possible interpretation of supershells in M82 as the products of multiple supernovae in young SSCs
Impacts of COVID-19 on the Energy System
This Briefing Paper explores the impact the COVID-19 pandemic had on the UK’s energy sector over the course of the first government-mandated national lockdown that began on 23 March 2020. Research from several aspects of the Integrated Development of Low-carbon Energy Systems (IDLES) programme at Imperial College London is presented in one overarching paper. The main aim is to determine what lessons can be learnt from that lockdown period, given the unique set of challenges it presented in our daily lives and the changes it brought about in energy demand, supply, and use. Valuable insights are gained into how working-from-home policies, electric vehicles, and low-carbon grids can be implemented, incentivised, and managed effectively
Cytotoxic polyfunctionality maturation of cytomegalovirus-pp65-specific CD4 + and CD8 + T-cell responses in older adults positively correlates with response size
Cytomegalovirus (CMV) infection is one of the most common persistent viral infections in humans worldwide and is epidemiologically associated with many adverse health consequences during aging. Previous studies yielded conflicting results regarding whether large, CMV-specific T-cell expansions maintain their function during human aging. In the current study, we examined the in vitro CMV-pp65-reactive T-cell response by comprehensively studying five effector functions (i.e., interleukin-2, tumor necrosis factor-α, interferon-γ, perforin, and CD107a expression) in 76 seropositive individuals aged 70 years or older. Two data-driven, polyfunctionality panels (IL-2-associated and cytotoxicity-associated) derived from effector function co-expression patterns were used to analyze the results. We found that, CMV-pp65-reactive CD8 + and CD4 + T cells contained similar polyfunctional subsets, and the level of polyfunctionality was related to the size of antigen-specific response. In both CD8 + and CD4 + cells, polyfunctional cells with high cytotoxic potential accounted for a larger proportion of the total response as the total response size increased. Notably, a higher serum CMV-IgG level was positively associated with a larger T-cell response size and a higher level of cytotoxic polyfunctionality. These findings indicate that CMV-pp65-specific CD4 + and CD8 + T cell undergo simultaneous cytotoxic polyfunctionality maturation during aging
The nanoscale phase separation in hole-doped manganites
A macroscopic phase separation, in which ferromagnetic clusters are observed
in an insulating matrix, is sometimes observed, and believed to be essential to
the colossal magnetoresistive (CMR) properties of manganese oxides. The
application of a magnetic field may indeed trigger large magnetoresistance
effects due to the percolation between clusters allowing the movement of the
charge carriers. However, this macroscopic phase separation is mainly related
to extrinsic defects or impurities, which hinder the long-ranged charge-orbital
order of the system. We show in the present article that rather than the
macroscopic phase separation, an homogeneous short-ranged charge-orbital order
accompanied by a spin glass state occurs, as an intrinsic result of the
uniformity of the random potential perturbation induced by the solid solution
of the cations on the -sites of the structure of these materials. Hence the
phase separation does occur, but in a more subtle and interesting nanoscopic
form, here referred as ``homogeneous''. Remarkably, this ``nanoscale phase
separation'' alone is able to bring forth the colossal magnetoresistance in the
perovskite manganites, and is potentially relevant to a wide variety of other
magnetic and/or electrical properties of manganites, as well as many other
transition metal oxides, in bulk or thin film form as we exemplify throughout
the article.Comment: jpsj2 TeX style (J. Phys. Soc. Jpn); 18 pages, 7 figure
Initiation and propagation of coronal mass ejections
This paper reviews recent progress in the research on the initiation and
propagation of CMEs. In the initiation part, several trigger mechanisms are
discussed; In the propagation part, the observations and modelings of EIT
waves/dimmings, as the EUV counterparts of CMEs, are described.Comment: 8 pages, 1 figure, an invited review, to appear in J. Astrophys.
Astro
Modelling spectral and timing properties of accreting black holes: the hybrid hot flow paradigm
The general picture that emerged by the end of 1990s from a large set of
optical and X-ray, spectral and timing data was that the X-rays are produced in
the innermost hot part of the accretion flow, while the optical/infrared (OIR)
emission is mainly produced by the irradiated outer thin accretion disc. Recent
multiwavelength observations of Galactic black hole transients show that the
situation is not so simple. Fast variability in the OIR band, OIR excesses
above the thermal emission and a complicated interplay between the X-ray and
the OIR light curves imply that the OIR emitting region is much more compact.
One of the popular hypotheses is that the jet contributes to the OIR emission
and even is responsible for the bulk of the X-rays. However, this scenario is
largely ad hoc and is in contradiction with many previously established facts.
Alternatively, the hot accretion flow, known to be consistent with the X-ray
spectral and timing data, is also a viable candidate to produce the OIR
radiation. The hot-flow scenario naturally explains the power-law like OIR
spectra, fast OIR variability and its complex relation to the X-rays if the hot
flow contains non-thermal electrons (even in energetically negligible
quantities), which are required by the presence of the MeV tail in Cyg X-1. The
presence of non-thermal electrons also lowers the equilibrium electron
temperature in the hot flow model to <100 keV, making it more consistent with
observations. Here we argue that any viable model should simultaneously explain
a large set of spectral and timing data and show that the hybrid
(thermal/non-thermal) hot flow model satisfies most of the constraints.Comment: 26 pages, 13 figures. To be published in the Space Science Reviews
and as hard cover in the Space Sciences Series of ISSI - The Physics of
Accretion on to Black Holes (Springer Publisher
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