8,122 research outputs found
Testing Lorentz invariance by use of vacuum and matter filled cavity resonators
We consider tests of Lorentz invariance for the photon and fermion sector
that use vacuum and matter-filled cavities. Assumptions on the wave-function of
the electrons in crystals are eliminated from the underlying theory and
accurate sensitivity coefficients (including some exceptionally large ones) are
calculated for various materials. We derive the Lorentz-violating shift in the
index of refraction n, which leads to additional sensitivity for matter-filled
cavities ; and to birefringence in initially isotropic media. Using published
experimental data, we obtain improved bounds on Lorentz violation for photons
and electrons at levels of 10^-15 and below. We discuss implications for future
experiments and propose a new Michelson-Morley type experiment based on
birefringence in matter.Comment: 15 pages, 8 table
Towards Einstein-Podolsky-Rosen quantum channel multiplexing
A single broadband squeezed field constitutes a quantum communication
resource that is sufficient for the realization of a large number N of quantum
channels based on distributed Einstein-Podolsky-Rosen (EPR) entangled states.
Each channel can serve as a resource for, e.g. independent quantum key
distribution or teleportation protocols. N-fold channel multiplexing can be
realized by accessing 2N squeezed modes at different Fourier frequencies. We
report on the experimental implementation of the N=1 case through the
interference of two squeezed states, extracted from a single broadband squeezed
field, and demonstrate all techniques required for multiplexing (N>1). Quantum
channel frequency multiplexing can be used to optimize the exploitation of a
broadband squeezed field in a quantum information task. For instance, it is
useful if the bandwidth of the squeezed field is larger than the bandwidth of
the homodyne detectors. This is currently a typical situation in many
experiments with squeezed and two-mode squeezed entangled light.Comment: 4 pages, 4 figures. In the new version we cite recent experimental
work bei Mehmet et al., arxiv0909.5386, in order to clarify the motivation of
our work and its possible applicatio
Summary of Shoreline Situation Reports for Virginia\u27s Tidewater Localities
This summary report marks the completion of the Shoreline Situation Report project. For over six years project team members with the Department of Geological Oceanography at the Virginia Institute of Marine Science have inventoried over 5,000 miles of shoreline in Tidewater Virginia. The methodology was developed and evaluated with funding through the Chesapeake Research Consortium, Inc. from the Research Applied to National Needs (RANN) program of the National Science Foundation. After preliminary evaluation as to its worth, the project became part of Virginia\u27s Coastal Resources Management Program, supported by the Office of Conmerce and Resources with funds provided by the Office of Coastal Zone Management, National Oceanographic and Atmospheric Administration, U.S. Department of Commerce
Timing measurements and proper motions of 74 pulsars using the Nanshan radio telescope
We have measured the positions of 74 pulsars from regular timing observations
using the Nanshan radio telescope at Urumqi Observatory between 2000 January
and 2004 August (MJD 51500 -- 53240). Proper motions were determined for these
pulsars by comparing their current positions with positions given in pulsar
catalogues. We compare our results to earlier measurements in the literature
and show that, in general, the values agree. New or improved proper motions are
obtained for 16 pulsars. The effect of period fluctuations and other timing
noise on the determination of pulsar positions is investigated. For our sample,
the mean and rms transverse velocities are 443 and 224 km/s respectively,
agreeing with previous work even though we determine distances using the new
NE2001 electron density model.Comment: 9 pages, 7 figures and 3 tables. Accepted by MNRA
30 Glitches in slow pulsars
We have analyzed 5.5 years of timing observations of 7 'slowly' rotating
radio pulsars, made with the Westerbork Synthesis Radio Telescope. We present
improved timing solutions and 30, mostly small, new glitches. Particularly
interesting are our results on PSR J1814-1744, which is one of the pulsars with
similar rotation parameters and magnetic field strength to the Anomalous X-ray
Pulsars (AXPs). Although the high-B radio pulsars do not show X-ray emission,
and no radio emission is detected for AXPs, the roughly similar glitch
parameters provide us with another tool to compare these classes of neutron
stars. Furthermore, we were able to detect glitches one to two orders of
magnitude smaller than before, for example in our well-sampled observations of
PSR B0355+54. We double the total number of known glitches in PSR B1737-30, and
improve statistics on glitch sizes for this pulsar individually and pulsars in
general. We detect no significant variations in dispersion measure for PSRs
B1951+32 and B2224+65, two pulsars located in high-density surroundings. We
discuss the effect of small glitches on timing noise, and show it is possible
to resolve timing-noise looking structures in the residuals of PSR B1951+32 by
using a set of small glitches.Comment: 9 pages, 6 figures, accepted by A&
Gravitational wave astronomy with the SKA
On a time scale of years to decades, gravitational wave (GW) astronomy will
become a reality. Low frequency (nanoHz) GWs are detectable through long-term
timing observations of the most stable pulsars. Radio observatories worldwide
are currently carrying out observing programmes to detect GWs, with data sets
being shared through the International Pulsar Timing Array project. One of the
most likely sources of low frequency GWs are supermassive black hole binaries
(SMBHBs), detectable as a background due to a large number of binaries, or as
continuous or burst emission from individual sources. No GW signal has yet been
detected, but stringent constraints are already being placed on galaxy
evolution models. The SKA will bring this research to fruition.
In this chapter, we describe how timing observations using SKA1 will
contribute to detecting GWs, or can confirm a detection if a first signal
already has been identified when SKA1 commences observations. We describe how
SKA observations will identify the source(s) of a GW signal, search for
anisotropies in the background, improve models of galaxy evolution, test
theories of gravity, and characterise the early inspiral phase of a SMBHB
system.
We describe the impact of the large number of millisecond pulsars to be
discovered by the SKA; and the observing cadence, observation durations, and
instrumentation required to reach the necessary sensitivity. We describe the
noise processes that will influence the achievable precision with the SKA. We
assume a long-term timing programme using the SKA1-MID array and consider the
implications of modifications to the current design. We describe the possible
benefits from observations using SKA1-LOW. Finally, we describe GW detection
prospects with SKA1 and SKA2, and end with a description of the expectations of
GW astronomy.Comment: 19 pages, 3 figures, to be published in: "Advancing Astrophysics with
the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)03
Interaction of quasilocal harmonic modes and boson peak in glasses
The direct proportionality relation between the boson peak maximum in
glasses, , and the Ioffe-Regel crossover frequency for phonons,
, is established. For several investigated materials . At the frequency the mean free path of the
phonons becomes equal to their wavelength because of strong resonant
scattering on quasilocal harmonic oscillators. Above this frequency phonons
cease to exist. We prove that the established correlation between
and holds in the general case and is a direct consequence of
bilinear coupling of quasilocal oscillators with the strain field.Comment: RevTex, 4 pages, 1 figur
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