21,892 research outputs found
Notes on drift theory
It is shown that there is a simpler way to derive the average guiding center drift of a distribution of particles than via the so-called single particle analysis. Based on this derivation it is shown that the entire drift formalism can be considerably simplified, and that results for low order anisotropies are more generally valid than is usually appreciated. This drift analysis leads to a natural alternative derivation of the drift velocity along a neutral sheet
Solutions to the tethered galaxy problem in an expanding universe and the observation of receding blueshifted objects
We use the dynamics of a galaxy, set up initially at a constant proper
distance from an observer, to derive and illustrate two counter-intuitive
general relativistic results. Although the galaxy does gradually join the
expansion of the universe (Hubble flow), it does not necessarily recede from
us. In particular, in the currently favored cosmological model, which includes
a cosmological constant, the galaxy recedes from the observer as it joins the
Hubble flow, but in the previously favored cold dark matter model, the galaxy
approaches, passes through the observer, and joins the Hubble flow on the
opposite side of the sky. We show that this behavior is consistent with the
general relativistic idea that space is expanding and is determined by the
acceleration of the expansion of the universe -- not a force or drag associated
with the expansion itself. We also show that objects at a constant proper
distance will have a nonzero redshift; receding galaxies can be blueshifted and
approaching galaxies can be redshifted.Comment: 8 pages including 6 figures, to appear in Am. J. Phys., 2003.
Reference added in postscrip
Study of V/STOL aircraft implementation. Volume 2: Appendices
An analysis of V/STOL aircraft implementation and utilization is presented. The subjects discussed are: (1) short haul air transportation requirements, (2) available aircraft technology, (3) aircraft production requirements, (4) airport requirements, (5) roles and responsibilities, and (6) cost and funding
Supersolid Helium at High Pressure
We have measured the pressure dependence of the supersolid fraction by a
torsional oscillator technique. Superflow is found from 25.6 bar up to 136.9
bar. The supersolid fraction in the low temperature limit increases from 0.6 %
at 25.6 bar near the melting boundary up to a maximum of 1.5% near 55 bar
before showing a monotonic decrease with pressure extrapolating to zero near
170 bar.Comment: 4 pages, 4 figure
Multiplexed communication over a high-speed quantum channel
In quantum information systems it is of particular interest to consider the
best way in which to use the non-classical resources consumed by that system.
Quantum communication protocols are integral to quantum information systems and
are amongst the most promising near-term applications of quantum information
science. Here we show that a multiplexed, digital quantum communications system
supported by comb of vacuum squeezing has a greater channel capacity per photon
than a source of broadband squeezing with the same analogue bandwidth. We
report on the time-resolved, simultaneous observation of the first dozen teeth
in a 2.4 GHz comb of vacuum squeezing produced by a sub-threshold OPO, as
required for such a quantum communications channel. We also demonstrate
multiplexed communication on that channel
The UNSW Extrasolar Planet Search: Methods and First Results from a Field Centred on NGC 6633
We report on the current status of the University of New South Wales
Extrasolar Planet Search project, giving details of the methods we use to
obtain millimagnitude precision photometry using the 0.5m Automated Patrol
Telescope. We use a novel observing technique to optimally broaden the PSF and
thus largely eliminate photometric noise due to intra-pixel sensitivity
variations on the CCD. We have observed 8 crowded Galactic fields using this
technique during 2003 and 2004. Our analysis of the first of these fields
(centred on the open cluster NGC 6633) has yielded 49 variable stars and 4
shallow transit candidates. Follow-up observations of these candidates have
identified them as eclipsing binary systems. We use a detailed simulation of
our observations to estimate our sensitivity to short-period planets, and to
select a new observing strategy to maximise the number of planets detected.Comment: 16 pages, 9 figures, version published in MNRAS Updated figures,
references, and additional discussion in section
Temperature dependent asymmetry of the nonlocal spin-injection resistance: evidence for spin non-conserving interface scattering
We report nonlocal spin injection and detection experiments on mesoscopic
Co-Al2O3-Cu spin valves. We have observed a temperature dependent asymmetry in
the nonlocal resistance between parallel and antiparallel configurations of the
magnetic injector and detector. This strongly supports the existence of a
nonequilibrium resistance that depends on the relative orientation of the
detector magnetization and the nonequilibrium magnetization in the normal metal
providing evidence for increasing interface spin scattering with temperature.Comment: 5 pages, 4 figures, accepted for publication in PRL, minor
corrections (affiliation, acknowledgements, typo
Aharonov-Bohm interference in the presence of metallic mesoscopic cylinders
This work studies the interference of electrons in the presence of a line of
magnetic flux surrounded by a normal-conducting mesoscopic cylinder at low
temperature. It is found that, while there is a supplementary phase
contribution from each electron of the mesoscopic cylinder, the sum of these
individual supplementary phases is equal to zero, so that the presence of a
normal-conducting mesoscopic ring at low temperature does not change the
Aharonov-Bohm interference pattern of the incident electron. It is shown that
it is not possible to ascertain by experimental observation that the shielding
electrons have responded to the field of an incident electron, and at the same
time to preserve the interference pattern of the incident electron. It is also
shown that the measuring of the transient magnetic field in the region between
the two paths of an electron interference experiment with an accuracy at least
equal to the magnetic field of the incident electron generates a phase
uncertainty which destroys the interference pattern.Comment: 15 pages, 5 Postscript figure
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