52,119 research outputs found
Radio Images of 3C 58: Expansion and Motion of its Wisp
New 1.4 GHz VLA observations of the pulsar-powered supernova remnant 3C 58
have resulted in the highest-quality radio images of this object to date. The
images show filamentary structure over the body of the nebula. The present
observations were combined with earlier ones from 1984 and 1991 to investigate
the variability of the radio emission on a variety of time-scales. No
significant changes are seen over a 110 day interval. In particular, the upper
limit on the apparent projected velocity of the wisp is 0.05c. The expansion
rate of the radio nebula was determined between 1984 and 2004, and is
0.014+/-0.003%/year, corresponding to a velocity of 630+/-70 km/s along the
major axis. If 3C 58 is the remnant of SN 1181, it must have been strongly
decelerated, which is unlikely given the absence of emission from the supernova
shell. Alternatively, the low expansion speed and a number of other arguments
suggest that 3C 58 may be several thousand years old and not be the remnant of
SN 1181.Comment: 12 pages; accepted for publication in the Astrophysical Journa
Charge shelving and bias spectroscopy for the readout of a charge-qubit on the basis of superposition states
Charge-based qubits have been proposed as fundamental elements for quantum
computers. One commonly proposed readout device is the single-electron
transistor (SET). SETs can distinguish between localized charge states, but
lack the sensitivity to directly distinguish superposition states, which have
greatly enhanced coherence times compared with position states. We propose
introducing a third dot, and exploiting energy dependent tunnelling from the
qubit into this dot (bias spectroscopy) for pseudo-spin to charge conversion
and superposition basis readout. We introduce an adiabatic fast passage-style
charge pumping technique which enables efficient and robust readout via charge
shelving, avoiding problems due to finite SET measurement time.Comment: 4 pages, 3 figures, note slightly changed title, replaced with
journal versio
What is novel in quantum transport for mesoscopics?
The understanding of mesoscopic transport has now attained an ultimate
simplicity. Indeed, orthodox quantum kinetics would seem to say little about
mesoscopics that has not been revealed - nearly effortlessly - by more popular
means. Such is far from the case, however. The fact that kinetic theory remains
very much in charge is best appreciated through the physics of a quantum point
contact. While discretization of its conductance is viewed as the exclusive
result of coherent, single-electron-wave transmission, this does not begin to
address the paramount feature of all metallic conduction: dissipation. A
perfect quantum point contact still has finite resistance, so its ballistic
carriers must dissipate the energy gained from the applied field. How do they
manage that? The key is in standard many-body quantum theory, and its
conservation principles.Comment: 10 pp, 3 figs. Invited talk at 50th Golden Jubilee DAE Symposium,
BARC, Mumbai, 200
Ballistic transport is dissipative: the why and how
In the ballistic limit, the Landauer conductance steps of a mesoscopic
quantum wire have been explained by coherent and dissipationless transmission
of individual electrons across a one-dimensional barrier. This leaves untouched
the central issue of conduction: a quantum wire, albeit ballistic, has finite
resistance and so must dissipate energy. Exactly HOW does the quantum wire shed
its excess electrical energy? We show that the answer is provided, uniquely, by
many-body quantum kinetics. Not only does this inevitably lead to universal
quantization of the conductance, in spite of dissipation; it fully resolves a
baffling experimental result in quantum-point-contact noise. The underlying
physics rests crucially upon the action of the conservation laws in these open
metallic systems.Comment: Invited Viewpoint articl
Time-fixed rendezvous by impulse factoring with an intermediate timing constraint
A method is presented for factoring a two-impulse orbital transfer into a three- or four-impulse transfer which solves the rendezvous problem and satisfies an intermediate timing constraint. Both the time of rendezvous and the intermediate time of a alinement are formulated as any element of a finite sequence of times. These times are integer multiples of a constant plus an additive constant. The rendezvous condition is an equality constraint, whereas the intermediate alinement is an inequality constraint. The two timing constraints are satisfied by factoring the impulses into collinear parts that vectorially sum to the original impulse and by varying the resultant period differences and the number of revolutions in each orbit. Five different types of solutions arise by considering factoring either or both of the two impulses into two or three parts with a limit for four total impulses. The impulse-factoring technique may be applied to any two-impulse transfer which has distinct orbital periods
Many-body theory for positronium-atom interactions
A many-body-theory approach has been developed to study positronium-atom
interactions. As first applications, we calculate the elastic scattering and
momentum-transfer cross sections and the pickoff annihilation rate
for Ps collisions with He and Ne. The cross section for He is
in agreement with previous coupled-state calculations, and the
momentum-transfer cross section for Ne agrees with available experimental data.
is found to be 0.13 and 0.26 for He and Ne, respectively, in
excellent agreement with the measured values.Comment: Accepted by Phys. Rev. Lett. (V2 contains update to text and Figs. 3
and 5. V3 contains further discussion on the calculation of pickoff
annihilation rates.
Space-time symplectic extension
It is conjectured that in the origin of space-time there lies a symplectic
rather than metric structure. The complex symplectic symmetry Sp(2l,C), l\ge1
instead of the pseudo-orthogonal one SO(1,d-1), d\ge4 is proposed as the
space-time local structure group. A discrete sequence of the metric space-times
of the fixed dimensionalities d=(2l)^2 and signatures, with l(2l-1) time-like
and l(2l+1) space-like directions, defined over the set of the Hermitian
second-rank spin-tensors is considered as an alternative to the
pseudo-Euclidean extra dimensional space-times. The basic concepts of the
symplectic framework are developed in general, and the ordinary and
next-to-ordinary space-time cases with l=1,2, respectively, are elaborated in
more detail. In particular, the scheme provides the rationale for the
four-dimensionality and 1+3 signature of the ordinary space-time.Comment: 15 pp, LaTe
PATENT LICENSING BY MEANS OF AN AUCTION: INTERNAL VS. EXTERNAL PATENTEE
An independent research laboratory owns a patented process innovation that can be licensed by means of an auction to two Cournot duopolists producing differentiated goods. For large innovations and close enough substitute goods the patentee auctions o¤ only one license, preventing the full diffusion of the innovation. For this range of parameters, however, if the laboratory merged with one of the firms in the industry, full technology diffusion would be implemented as the merged entity would always license the innovation to the rival firm. This explains that, in this context, a vertical merger is both profitable and welfare improving.Patent licensing, two-part tariff contracts, vertical mergers
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