3,366 research outputs found
Neutrino spin rotation in dense matter and electromagnetic field
Exact solutions of the Dirac--Pauli equation for massive neutrino with
anomalous magnetic moment interacting with dense matter and strong
electromagnetic field are found. The complete system of neutrino wavefunctions,
which show spin rotation properties are obtained and their possible
applications are discussed.Comment: 11 pages, latex, misprints are correcte
NB SPUTTER COATING ON QWR IN ANU
ABSTRACT Nb sputtered QWRs are to be used for the future extension of the Linac. The magnetron sputtering system and its operational performance are described. A magnetron discharge in argon is used for sputtering niobium and in helium for cleaning of the resonator. The cathode comprises two cylindrical and one ring element. The I-V characteristics of the sputtering in argon are given. The superconducting film is deposited with a uniform film thickness and coverage of the resonator. The distribution of the deposition rate f r o m different cathode-resonator geometry and film thickness profiles are discussed. The switching of the cylindrical sputtering cathode from external to internal regions of the cathode, is described. A sputtering procedure, t e s t depositions on ceramic samples and sputtering on the QWR for Time-Energy Lens, will be outlined. The composition of impurities stemming from t h e sputtering process, will be discussed. . I n t r o d u c t i o n The ANU accelerator system, comprising the 14UD and Linac, continues t o evolve toward a competent integrated research facility. The Linac successfully passed important milestones in 1996, including the f i r s t nuclear physics experiment performed on 5 June, and its o f f i c i a l inauguration on 11 July. Good progress has been made in the conditioning of the Pb plated, split loop resonators. Combinations of pulsed RF power conditioning and helium conditioning have enabled all resonators to operate near and above 2 MV/m
VSOP observation of the quasar PKS 2215+020: a new laboratory for core-jet physics at z=3.572
We report results of a VSOP (VLBI Space Observatory Programme) observation of
a high redshift quasar PKS 2215+020 (z=3.572). The ~1 milliarcsecond resolution
image of the quasar reveals a prominent `core-jet' structure on linear scales
from 5/h to 300/h pc ($H_0=100*h km/(s*Mpc). The brightness temperatures and
sizes of bright features identified in the jet are consistent with emission
from relativistic shocks dominated by adiabatic energy losses. The jet is
powered by the central black hole with estimated mass of ~4*10^9 solar masses.
Comparisons with VLA and ROSAT observations indicate a possible presence of an
extended radio/X-ray halo surrounding 2215+020.Comment: 15 pages, 6 figures, aastex macros; accepted for publication in The
Astrophysical Journal, V.546, N.2 *(January 10 2001
Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine Scale Structure
We have used VLBA fringe visibility data obtained at 15 GHz to examine the
compact structure in 250 extragalactic radio sources. For 171 sources in our
sample, more than half of the total flux density seen by the VLBA remains
unresolved on the longest baselines. There are 163 sources in our list with a
median correlated flux density at 15 GHz in excess of 0.5 Jy on the longest
baselines. For about 60% of the sources, we have at least one observation in
which the core component appears unresolved (generally smaller than 0.05 mas)
in one direction, usually transverse to the direction into which the jet
extends. BL Lacs are on average more compact than quasars, while active
galaxies are on average less compact. Also, in an active galaxy the
sub-milliarcsecond core component tends to be less dominant. IDV sources
typically have a more compact, more core-dominated structure on
sub-milliarcsecond scales than non-IDV sources, and sources with a greater
amplitude of intra-day variations tend to have a greater unresolved VLBA flux
density. The objects known to be GeV gamma-ray loud appear to have a more
compact VLBA structure than the other sources in our sample. This suggests that
the mechanisms for the production of gamma-ray emission and for the generation
of compact radio synchrotron emitting features are related. The brightness
temperature estimates and lower limits for the cores in our sample typically
range between 10^11 and 10^13 K, but they extend up to 5x10^13 K, apparently in
excess of the equipartition brightness temperature, or the inverse Compton
limit for stationary synchrotron sources. The largest component speeds are
observed in radio sources with high observed brightness temperatures, as would
be expected from relativistic beaming (abridged).Comment: 31 pages, 13 figures, 4 tables, accepted for publication in the
Astronomical Journal; minor changes to the text are mad
Essential spectra of difference operators on \sZ^n-periodic graphs
Let (\cX, \rho) be a discrete metric space. We suppose that the group
\sZ^n acts freely on and that the number of orbits of with respect to
this action is finite. Then we call a \sZ^n-periodic discrete metric
space. We examine the Fredholm property and essential spectra of band-dominated
operators on where is a \sZ^n-periodic discrete metric space.
Our approach is based on the theory of band-dominated operators on \sZ^n and
their limit operators.
In case is the set of vertices of a combinatorial graph, the graph
structure defines a Schr\"{o}dinger operator on in a natural way. We
illustrate our approach by determining the essential spectra of Schr\"{o}dinger
operators with slowly oscillating potential both on zig-zag and on hexagonal
graphs, the latter being related to nano-structures
Large orders in strong-field QED
We address the issue of large-order expansions in strong-field QED. Our
approach is based on the one-loop effective action encoded in the associated
photon polarisation tensor. We concentrate on the simple case of crossed fields
aiming at possible applications of high-power lasers to measure vacuum
birefringence. A simple next-to-leading order derivative expansion reveals that
the indices of refraction increase with frequency. This signals normal
dispersion in the small-frequency regime where the derivative expansion makes
sense. To gain information beyond that regime we determine the factorial growth
of the derivative expansion coefficients evaluating the first 80 orders by
means of computer algebra. From this we can infer a nonperturbative imaginary
part for the indices of refraction indicating absorption (pair production) as
soon as energy and intensity become (super)critical. These results compare
favourably with an analytic evaluation of the polarisation tensor asymptotics.
Kramers-Kronig relations finally allow for a nonperturbative definition of the
real parts as well and show that absorption goes hand in hand with anomalous
dispersion for sufficiently large frequencies and fields.Comment: 26 pages, 6 figure
Active Galactic Nuclei at the Crossroads of Astrophysics
Over the last five decades, AGN studies have produced a number of spectacular
examples of synergies and multifaceted approaches in astrophysics. The field of
AGN research now spans the entire spectral range and covers more than twelve
orders of magnitude in the spatial and temporal domains. The next generation of
astrophysical facilities will open up new possibilities for AGN studies,
especially in the areas of high-resolution and high-fidelity imaging and
spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These
studies will address in detail a number of critical issues in AGN research such
as processes in the immediate vicinity of supermassive black holes, physical
conditions of broad-line and narrow-line regions, formation and evolution of
accretion disks and relativistic outflows, and the connection between nuclear
activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic
Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical
Symposia Serie
On-chip coherent detection with quantum limited sensitivity
While single photon detectors provide superior intensity sensitivity, spectral resolution is usually lost after the detection event. Yet for applications in low signal infrared spectroscopy recovering information about the photonâs frequency contributions is essential. Here we use highly efficient waveguide integrated superconducting single-photon detectors for on-chip coherent detection. In a single nanophotonic device, we demonstrate both single-photon counting with up to 86% on-chip detection efficiency, as well as heterodyne coherent detection with spectral resolution f/âf exceeding 1011. By mixing a local oscillator with the single photon signal field, we observe frequency modulation at the intermediate frequency with ultra-low local oscillator power in the femto-Watt range. By optimizing the nanowire geometry and the working parameters of the detection scheme, we reach quantum-limited sensitivity. Our approach enables to realize matrix integrated heterodyne nanophotonic devices in the C-band wavelength range, for classical and quantum optics applications where single-photon counting as well as high spectral resolution are required simultaneously
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