2,655 research outputs found
Two-way satellite time transfer using low power CW tones
In the search for an economical means of precise time transfer, the NRC Time Laboratory decided to adapt the techniques used by radio astronomers in an experiment to compare the phases of the local oscillators at widely separated VLBI stations. The objective is to design a system which would use commercial satellites, and which would be of reasonable cost for the ground stations and for operations. Two satellite ground stations were installed at NRC about 100 m from the Time Laboratory. For the preliminary experiment, a channel on the Anik Al 6/4 GHz satellite was made available by TELESAT Canada. Two tones were transmitted + or - MHz from the suppressed carrier. The difference frequency of 32 MHz was recorded using narrow band receivers. A low level 1 MHz phase modulation was added to identify the 32 MHz cycle, giving 1 microsec ambiguity in the time transfer. With less than 1/4 W in each tone, the EIRP is 43 dB below that of a normal TV Earth station, and no frequency dispersion is required. The measurements taken each second for the 32 MHz have an rms scatter of 1 ns
Alien Registration- Boulanger, Joseph H. (Lewiston, Androscoggin County)
https://digitalmaine.com/alien_docs/30677/thumbnail.jp
Compactifications of conformal gravity
We study conformal theories of gravity, i.e. those whose action is invariant
under the local transformation g_{\mu\nu} -> \omega^2 (x) g_{\mu\nu}. As is
well known, in order to obtain Einstein gravity in 4D it is necessary to
introduce a scalar compensator with a VEV that spontaneously breaks the
conformal invariance and generates the Planck mass. We show that the
compactification of extra dimensions in a higher dimensional conformal theory
of gravity also yields Einstein gravity in lower dimensions, without the need
to introduce the scalar compensator. It is the field associated with the size
of the extra dimensions (the radion) who takes the role of the scalar
compensator in 4D. The radion has in this case no physical excitations since
they are gauged away in the Einstein frame for the metric. In these models the
stabilization of the size of the extra dimensions is therefore automatic.Comment: 13 page
Windows in the Milky Way
The objectives were twofold: (1) to study the IRAS emission levels in the vicinity of Baade's Window and in other optically transparent regions near the Galactic Center; and (2) to study the IRAS emission levels along sightlines in the Milky Way that exhibit very little CO emission. Tests were attempted to see whether the optically transparent 'windows' near the Galactic center can be identified (as FIR-weak regions) in the IRAS data base; and if so, whether the CO weak regions found elsewhere in the Milky Way represent similarly FIR weak and thus optically transparent sightlines through the Galaxy. The CO weak regions were also targeted in an effort to study the diffuse intercloud dust and its warming by the interstellar radiation field
First Order Actions and Duality
We consider some aspects of classical S-duality transformations in first
order actions taken into account the general covariance of the Dirac algorithm
and the transformation properties of the Dirac bracket. By classical S-Duality
transformations we mean a field redefinition that interchanges the equations of
motion and its associated Bianchi identities. By working from a first order
variational principle and performing the corresponding Dirac analysis we find
that the standard electro-magnetic duality can be reformulated as a canonical
local transformation. The reduction from this phase space to the original phase
space variables coincides with the well known result about duality as a
canonical non local transformation. We have also applied our ideas to the
bosonic string. These Dualities are not canonical transformations for the Dirac
bracket and relate actions with different kinetic terms in the reduced space.Comment: accepted for publication in IJMP
Two-way time transfers between NRC/NBS and NRC/USNO via the Hermes (CTS) satellite
At each station the differences were measured between the local UTC seconds pulse and the remote UTC pulse received by satellite. The difference between the readings, if station delays are assumed to be symmetrical, is two times the difference between the clocks at the two ground station sites. Over a 20-minute period, the precision over the satellite is better than 1 ns. The time transfer from NRC to the CRC satellite terminal near Ottawa and from NBS to the Denver HEW terminal was examined
Gauge fields and infinite chains of dualities
We show that the particle states of Maxwell's theory, in dimensions, can
be represented in an infinite number of ways by using different gauge fields.
Using this result we formulate the dynamics in terms of an infinite set of
duality relations which are first order in space-time derivatives. We derive a
similar result for the three form in eleven dimensions where such a possibility
was first observed in the context of E11. We also give an action formulation
for some of the gauge fields. In this paper we give a pedagogical account of
the Lorentz and gauge covariant formulation of the irreducible representations
of the Poincar\'e group, used previously in higher spin theories, as this plays
a key role in our constructions. It is clear that our results can be
generalised to any particle.Comment: 37 page
Calibrated Dynamic Response Analysis of Stafford Dam
Stafford Dam, an approximately 79-ft high compacted earthfill founded on stream alluvium approximately 40 feet thick, was shaken by the 1989 Lorna Prieta Earthquake. Records of the earthquake motions were obtained from seismographs located at the dam crest and at the right abutment on rock. Two-dimensional dynamic finite element analyses were performed to calibrate a model of the dam using the recorded motions. Excellent agreement between the recorded and calculated response was obtained by appropriate adjustments to material parameters based on shear wave velocity measurements. Various deconvolution methods for obtaining input bedrock motions to calculate the dam response are discussed
Infrared dust emission in the outer disk of M51
We examine faint infrared emission features detected in Spitzer Space
Telescope images of M51, which are associated with atomic hydrogen in the outer
disk and tidal tail at R greater than R_25 (4.9', ~14 kpc at d=9.6 Mpc). The
infrared colors of these features are consistent with the colors of dust
associated with star formation in the bright disk. However, the star formation
efficiency (as a ratio of star formation rate to neutral gas mass) implied in
the outer disk is lower than that in the bright disk of M51 by an order of
magnitude, assuming a similar relationship between infrared emission and star
formation rate in the inner and outer disks.Comment: 13 pages in manuscript form, 2 figures; download PDF of manuscript
with original-resolution Figure 1 at
http://www.eg.bucknell.edu/physics/thornley/thornleym51.pd
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