3,965 research outputs found
The effects of water impinging on thermally controlled surfaces under space conditions
Analysis of monochromatic reflectance changes due to impinging water spray from sharp-edge nozzles on thermally-controlled paints under space condition
Estimating the Welfare Effects of Digital Infrastructure
While much economic policy presumes that more information infrastructure yields higher economic returns, little empirical work measures the magnitudes of these returns. We examine investment by local exchange telephone companies in fiber optic cable, ISDN lines and signal seven software, infrastructure which plays an essential role in bringing digital technology to local telephone networks. We estimate the elasticity of the derived demand for infrastructure investment faced by local exchange companies, controlling for factors such as local economic activity and the political disposition of state regulators. Our model postulates a regulated profit maximizing local exchange firm and a regulatory agency with predetermined political leanings in favor of consumer prices or firm profits. The model accounts for variation in state regulation and local economic conditions. In all our estimates we find that consumer demand is sensitive to investment in modern infrastructure, particularly as represented by fiber optic cable. Our estimates imply that infrastructure investment is responsible for a substantial fraction of the recent growth in consumer surplus and business revenue in local telecommunication services.
The quantum-classical crossover of a field mode
We explore the quantum-classical crossover in the behaviour of a quantum
field mode. The quantum behaviour of a two-state system - a qubit - coupled to
the field is used as a probe. Collapse and revival of the qubit inversion form
the signature for quantum behaviour of the field and continuous Rabi
oscillations form the signature for classical behaviour of the field. We
demonstrate both limits in a single model for the full coupled system, for
states with the same average field strength, and so for qubits with the same
Rabi frequency.Comment: 6 pages, 3 figures (in this version the figures, text and references
have all been expanded
Signatures of the collapse and revival of a spin Schr\"{o}dinger cat state in a continuously monitored field mode
We study the effects of continuous measurement of the field mode during the
collapse and revival of spin Schr\"{o}dinger cat states in the Tavis-Cummings
model of N qubits (two-level quantum systems) coupled to a field mode. We show
that a compromise between relatively weak and relatively strong continuous
measurement will not completely destroy the collapse and revival dynamics while
still providing enough signal-to-noise resolution to identify the signatures of
the process in the measurement record. This type of measurement would in
principle allow the verification of the occurrence of the collapse and revival
of a spin Schr\"{o}dinger cat state.Comment: 5 pages, 2 figure
Cool for Cats
The iconic Schr\"odinger's cat state describes a system that may be in a
superposition of two macroscopically distinct states, for example two clearly
separated oscillator coherent states. Quite apart from their role in
understanding the quantum classical boundary, such states have been suggested
as offering a quantum advantage for quantum metrology, quantum communication
and quantum computation. As is well known these applications have to face the
difficulty that the irreversible interaction with an environment causes the
superposition to rapidly evolve to a mixture of the component states in the
case that the environment is not monitored. Here we show that by engineering
the interaction with the environment there exists a large class of systems that
can evolve irreversibly to a cat state. To be precise we show that it is
possible to engineer an irreversible process so that the steady state is close
to a pure Schr\"odinger's cat state by using double well systems and an
environment comprising two-photon (or phonon) absorbers. We also show that it
should be possible to prolong the lifetime of a Schr\"odinger's cat state
exposed to the destructive effects of a conventional single-photon decohering
environment. Our protocol should make it easier to prepare and maintain
Schr\"odinger cat states which would be useful in applications of quantum
metrology and information processing as well as being of interest to those
probing the quantum to classical transition.Comment: 10 pages, 7 figures. Significantly updated version with supplementary
informatio
Mental imagery in synaesthesia
The current thesis addressed the question of whether an internally generated mental image can elicit a concurrent in grapheme colour synaesthesia; although there is experimental and anecdotal evidence that this is the case, to date this had not been systematically explored. As there are purportedly distinct object-based and spatial-based imagery processes it was necessary to explore the role different imagery processes may play. In Experiment 1 synaesthetes and matched control groups completed a grapheme-based object-imagery task against congruently and incongruently coloured backgrounds. Four synaesthetes, but none of the control groups, showed an effect of colour on task performance. In Experiment 2 and 3 synaesthetes (and matched controls for Experiment 2) completed a grapheme-based spatial-imagery task, with either the stimuli or background colour manipulated as before. In each experiment colour was found to interact with grapheme presentation format for two different synaesthetes. Experiments 1-3 therefore provided support for the idea that an internally generated mental image can elicit a concurrent. Importantly, the results suggested a difference in the way the concurrent generated from object or spatial imagery processes influenced task performance. Consequently Experiments 4 and 5 used a battery of comparable imagery tasks that had either an object or spatial rate-limiting imagery process. Manipulation of the task background colour again showed the variety of effects the concurrent generated with these different imagery processes can have on task performance. Overall the results of these experiments suggest that a concurrent can be elicited from both object and spatial imagery processes; important individual differences were found, and individual performance varied between tasks, suggesting the possible role of strategy effects. Models of synaesthesia need to be able to explain these differences and further studies are needed to address this issue of task approach
Freezing distributed entanglement in spin chains
We show how to freeze distributed entanglement that has been created from the
natural dynamics of spin chain systems. The technique that we propose simply
requires single-qubit operations and isolates the entanglement in specific
qubits at the ends of branches. Such frozen entanglement provides a useful
resource, for example for teleportation or distributed quantum processing. The
scheme can be applied to a wide range of systems -- including actual spin
systems and alternative qubit embodiments in strings of quantum dots, molecules
or atoms.Comment: 5 pages, to appear in Phys. Rev. A (Rapid Communication
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