2,537 research outputs found
Asymmetry of jets, lobe size and spectral index in radio galaxies and quasars
We investigate the correlations between spectral index, jet side and extent
of the radio lobes for a sample of nearby FRII radio galaxies. In
Dennett-Thorpe et al. (1997) we studied a sample of quasars and found that the
high surface brightness regions had flatter spectra on the jet side (explicable
as a result of Doppler beaming) whilst the extended regions had spectral
asymmetries dependent on lobe length. Unified schemes predict that asymmetries
due to beaming will be much smaller in narrow-line radio galaxies than in
quasars: we therefore investigate in a similar manner, a sample of radio
galaxies with detected jets. We find that spectral asymmetries in these objects
are uncorrelated with jet sidedness at all brightness levels, but depend on
relative lobe volume. Our results are not in conflict with unified schemes, but
suggest that the differences between the two samples are due primarily to power
or redshift, rather than to orientation. We also show directly that hotspot
spectra steepen as a function of radio power or redshift. Whilst a shift in
observed frequency due to the redshift may account for some of the steepening,
it cannot account for all of it, and a dependence on radio power is required.Comment: accepted for publication in MNRAS, 10 pages; typos/minor correctio
Lithographically fabricated optical cavities for refractive index sensing
Since the development of distributed Bragg gratings, high resolution lithography and etching have been applied towards the concentration of light. The most important application of lithographically fabricated microcavities has been for the spectral control over laser emission. Here we describe the opportunities that arise from further miniaturization of laser cavities by using high index contrast photonic crystal mirrors and annular Bragg reflectors. We have used these optical cavities, with mode volumes as small as 10^–17 l, to perform spectroscopic analysis and compare the mode volumes and sensitivities of these geometries
In situ evidence for renitrification in the Arctic lower stratosphere during the polar aura validation experiment (PAVE)
In-situ measurements of nitric acid (HNO3), ozone (O3), and nitrous oxide (N2O) were made from the NASA DC-8 during the Polar Aura Validation Experiment in January/February 2005. In the lower stratosphere (9–12.5 km, potential temperature 300–350 K) characteristic compact relationships were observed between all three gases. The ratio HNO3/O3 averaged 3.5 (±0.7) ppt/ppb. Samples with enhanced HNO3/O3 (\u3e4.0) were most abundant under the edge of the Arctic Polar vortex in airmasses with enhanced mixing ratios of both gases (\u3e400 ppb O3 and \u3e2000 ppt HNO3) and reduced mixing ratios of N2O (\u3c305 ppb), indicating air from higher levels in the stratosphere. Relationships to N2O in the anomalous samples under the vortex edge indicate that increases in HNO3/O3 reflect renitrification at DC-8 flight levels, with no indication of significant O3 loss. Renitrified air was only observed at potential temperatures above 340 K, and was most abundant on the PAVE flights on 27 and 29 January
Radiative Efficiencies of Continuously Powered Blast Waves
We use general arguments to show that a continuously powered radiative blast
wave can behave self similarly if the energy injection and radiation mechanisms
are self similar. In that case, the power-law indices of the blast wave
evolution are set by only one of the two constituent physical mechanisms. If
the luminosity of the energy source drops fast enough, the radiation mechanisms
set the power-law indices, otherwise, they are set by the behavior of the
energy source itself. We obtain self similar solutions for the Newtonian and
the ultra-relativistic limits. Both limits behave self similarly if we assume
that the central source supplies energy in the form of a hot wind, and that the
radiative mechanism is the semi-radiative mechanism of Cohen, Piran & Sari
(1998). We calculate the instantaneous radiative efficiencies for both limits
and find that a relativistic blast wave has a higher efficiency than a
Newtonian one. The instantaneous radiative efficiency depends strongly on the
hydrodynamics and cannot be approximated by an estimate of local microscopic
radiative efficiencies, since a fraction of the injected energy is deposited in
shocked matter. These solutions can be used to calculate Gamma Ray Bursts
afterglows, for cases in which the energy is not supplied instantaneously.Comment: 28 LaTeX pages, including 9 figures and 3 table
Interactions of a Light Hypersonic Jet with a Non-Uniform Interstellar Medium
We present three dimensional simulations of the interaction of a light
hypersonic jet with an inhomogeneous thermal and turbulently supported disk in
an elliptical galaxy. We model the jet as a light, supersonic non-relativistic
flow with parameters selected to be consistent with a relativistic jet with
kinetic power just above the FR1/FR2 break.
We identify four generic phases in the evolution of such a jet with the
inhomogeneous interstellar medium: 1) an initial ``flood and channel'' phase,
where progress is characterized by high pressure gas finding changing weak
points in the ISM, flowing through channels that form and re-form over time, 2)
a spherical, energy-driven bubble phase, were the bubble is larger than the
disk scale, but the jet remains fully disrupted close to the nucleus, 3) a
rapid, jet break--out phase the where jet breaks free of the last dense clouds,
becomes collimated and pierces the spherical bubble, and 4) a classical phase,
the jet propagates in a momentum-dominated fashion leading to the classical jet
+ cocoon + bow-shock structure.
Mass transport in the simulations is investigated, and we propose a model for
the morphology and component proper motions in the well-studied Compact
Symmetric Object 4C31.04.Comment: 66 pages, 22 figures, PDFLaTeX, aastex macros, graphicx and amssymb
packages, Accepted, to be published 2007 ApJ
Synchrotron Emission from Hot Accretion Flows and the Cosmic Microwave Background Anisotropy
Current estimates of number counts of radio sources in the frequency range
where the most sensitive Cosmic Microwave Background (CMB) experiments are
carried out significantly under-represent sources with strongly inverted
spectra. Hot accretion flows around supermassive black holes in the nuclei of
nearby galaxies are expected to produce inverted radio spectra by thermal
synchrotron emission. We calculate the temperature fluctuations and power
spectra of these sources in the Planck Surveyor 30 GHz energy channel, where
their emission is expected to peak. We find that their potential contribution
is generally comparable to the instrumental noise, and approaches the CMB
anisotropy level at small angular scales. Forthcoming CMB missions, which will
provide a large statistical sample of inverted-spectra sources, will be crucial
for determining the distribution of hot accretion flows in nearby quiescent
galactic nuclei. Detection of these sources in different frequency channels
will help constrain their spectral characteristics, hence their physical
properties.Comment: 10 pages, 4 figures, accepted for publication in Ap
Assessment of lithographic process variation effects in InGaAsP annular Bragg resonator lasers
Optical microresonators based on an annular geometry of radial Bragg reflectors have been designed and fabricated by electron-beam lithography, reactive ion etching, and an epitaxial transfer process. Unlike conventional ring resonators that are based on total internal reflection of light, the annular structure described here is designed to support optical modes with very small azimuthal propagation coefficient and correspondingly large free spectral range. The effect of lithographic process variation upon device performance is studied. Laser emission wavelength and threshold optical pump power are found to vary between similar devices given different electron doses during electron-beam lithography. As the resonance wavelength and quality factor of these resonators are very sensitive to environmental changes, these resonators make ideal active light sources that can be integrated into large arrays for gas and liquid sensing applications and are easily interrogated
Stable and chaotic solutions of the complex Ginzburg-Landau equation with periodic boundary conditions
We study, analytically and numerically, the dynamical behavior of the
solutions of the complex Ginzburg-Landau equation with diffraction but without
diffusion, which governs the spatial evolution of the field in an active
nonlinear laser cavity. Accordingly, the solutions are subject to periodic
boundary conditions. The analysis reveals regions of stable stationary
solutions in the model’s parameter space, and a wide range of oscillatory
and chaotic behaviors. Close to the first bifurcation destabilizing the
spatially uniform solution, a stationary single-humped solution is found in an
asymptotic analytical form, which turns out to be in very good agreement with
the numerical results. Simulations reveal a series of stable stationary
multi-humped solutionsComment: 9 pages, 15 figure
The Moral Responsibility of the Corporate Lawyer
Lawyers traditionally claim that they are not morally accountable for the goals or activities of their clients that are within the bounds of the law. This essay explores this concept of non-accountability in the context of corporate transactional representation. We argue that corporate lawyers, whose practice is forward looking, undertaken on behalf of corporate clients who have legally impaired ability to engage in independent moral reasoning, and who function in a world of relatively minimal legal oversight (i.e. whose work is furthest from the model of the adversary system) cannot persuasively claim that they are not morally responsible for the work on behalf of their corporate clients. This conclusion is, in fact, heartening if it encourages corporate transactional attorneys to focus more deeply on the value of their work to society
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