21,175 research outputs found
Bearing and gimbal lock mechanism and spiral flex lead module Patent
Low friction bearing and lock mechanism for two-axis gimbal carrying satellite payloa
Symmetry-enhanced supertransfer of delocalized quantum states
Coherent hopping of excitation rely on quantum coherence over physically
extended states. In this work, we consider simple models to examine the effect
of symmetries of delocalized multi-excitation states on the dynamical
timescales, including hopping rates, radiative decay, and environmental
interactions. While the decoherence (pure dephasing) rate of an extended state
over N sites is comparable to that of a non-extended state, superradiance leads
to a factor of N enhancement in decay and absorption rates. In addition to
superradiance, we illustrate how the multi-excitonic states exhibit
`supertransfer' in the far-field regime: hopping from a symmetrized state over
N sites to a symmetrized state over M sites at a rate proportional to MN. We
argue that such symmetries could play an operational role in physical systems
based on the competition between symmetry-enhanced interactions and localized
inhomogeneities and environmental interactions that destroy symmetry. As an
example, we propose that supertransfer and coherent hopping play a role in
recent observations of anomolously long diffusion lengths in nano-engineered
assembly of light-harvesting complexes.Comment: 6 page
Piecewise smooth chebfuns
Algorithms are described that make it possible to manipulate piecewise-smooth functions on real intervals numerically with close to machine precision. Breakpoints are introduced in some such calculations at points determined by numerical rootfinding, and in others by recursive subdivision or automatic edge detection. Functions are represented on each smooth subinterval by Chebyshev series or interpolants. The algorithms are implemented in object-oriented MATLAB in an extension of the chebfun system, which was previously limited to smooth functions on [-1, 1]
Quantum operations that cannot be implemented using a small mixed environment
To implement any quantum operation (a.k.a. ``superoperator'' or ``CP map'')
on a d-dimensional quantum system, it is enough to apply a suitable overall
unitary transformation to the system and a d^2-dimensional environment which is
initialized in a fixed pure state. It has been suggested that a d-dimensional
environment might be enough if we could initialize the environment in a mixed
state of our choosing. In this note we show with elementary means that certain
explicit quantum operations cannot be realized in this way. Our counterexamples
map some pure states to pure states, giving strong and easily manageable
conditions on the overall unitary transformation. Everything works in the more
general setting of quantum operations from d-dimensional to d'-dimensional
spaces, so we place our counterexamples within this more general framework.Comment: LATEX, 8 page
VALUING LOSSES FROM DEPOPULATING MICHIGAN DAIRY HERDS
Depopulating dairy herds in the effort to eradicate disease would have significant economic effects. This paper evaluates farm-level effects that might occur and puts forth a method for quantifying losses. The reader is directed elsewhere for industry or state-level effects of disease eradication or depopulation.Livestock Production/Industries,
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