40,578 research outputs found
Finite size scaling of the bayesian perceptron
We study numerically the properties of the bayesian perceptron through a
gradient descent on the optimal cost function. The theoretical distribution of
stabilities is deduced. It predicts that the optimal generalizer lies close to
the boundary of the space of (error-free) solutions. The numerical simulations
are in good agreement with the theoretical distribution. The extrapolation of
the generalization error to infinite input space size agrees with the
theoretical results. Finite size corrections are negative and exhibit two
different scaling regimes, depending on the training set size. The variance of
the generalization error vanishes for confirming the
property of self-averaging.Comment: RevTeX, 7 pages, 7 figures, submitted to Phys. Rev.
Cosmology With A Dark Refraction Index
We review Gordon's optical metric and the transport equations for the
amplitude and polarization of a geometrical optics wave traveling in a gravity
field. We apply the theory to the FLRW cosmologies by associating a refraction
index with the cosmic fluid. We then derive an expression for the accumulated
effect of a refraction index on the distance redshift relations and fit the
Hubble curve of current supernova observations with a non-accelerating
cosmological model. We also show that some observational effects caused by
inhomogeneities, e.g. the Sachs-Wolfe effect, can be interpreted as being
caused by an effective index of refraction, and hence this theory could extend
to other speed of light communications such as gravitational radiation and
neutrino fluxes.Comment: 21 pages, 3 figure
Spectroscopic characterization and detection of Ethyl Mercaptan in Orion
New laboratory data of ethyl mercaptan, CHCHSH, in the millimeter
and submillimeter-wave domains (up to 880 GHz) provided very precise values of
the spectroscopic constants that allowed the detection of
-CHCHSH towards Orion KL. 77 unblended or slightly blended
lines plus no missing transitions in the range 80-280 GHz support this
identification. A detection of methyl mercaptan, CHSH, in the spectral
survey of Orion KL is reported as well. Our column density results indicate
that methyl mercaptan is 5 times more abundant than ethyl mercaptan in
the hot core of Orion KL.Comment: Accepted for publication in ApJL (30 January 2014)/ submitted (8
January 2014
Contact resistance and shot noise in graphene transistors
Potential steps naturally develop in graphene near metallic contacts. We
investigate the influence of these steps on the transport in graphene Field
Effect Transistors. We give simple expressions to estimate the
voltage-dependent contribution of the contacts to the total resistance and
noise in the diffusive and ballistic regimes.Comment: 6 pages, 4 figures; Figs 3 and 4 completed and appendix adde
Dynamical control of quantum state transfer within hybrid open systems
We analyze quantum state-transfer optimization within hybrid open systems,
from a "noisy" (write-in) qubit to its "quiet" counterpart (storage qubit).
Intriguing interplay is revealed between our ability to avoid bath-induced
errors that profoundly depend on the bath-memory time and the limitations
imposed by leakage out of the operational subspace. Counterintuitively, under
no circumstances is the fastest transfer optimal (for a given transfer energy)
Possible High-Redshift, Low-Luminosity AGN Activity in the Hubble Deep Field
In the Hubble Deep Field (HDF), twelve candidate sources of high-redshift (z
> 3.5) AGN activity have been identified. The color selection criteria were
established by passing spectra of selected quasars and Seyfert galaxies
(appropriately redshifted and modified for "Lyman forest" absorption), as well
as stars, observed normal and starburst galaxies, and galaxy models for various
redshifts through the filters used for the HDF observations. The actual
identification of AGN candidates also involved convolving a
Laplacian-of-Gaussian filter with the HDF images, thereby removing relatively
flat galactic backgrounds and leaving only the point-like components in the
centers. Along with positions and colors, estimated redshifts and absolute
magnitudes are reported, with the candidates falling toward the faint end of
the AGN luminosity function. One candidate has been previously observed
spectroscopically, with a measured redshift of 4.02. The number of sources
reported here is consistent with a simple extrapolation of the observed quasar
luminosity function to magnitude 30 in B_Johnson. Implications for ionization
of the intergalactic medium and for gravitational lensing are discussed.Comment: 10 pages LaTex plus 2 separate files (Table 1 which is a two-page
landscape LaTex file; and Figure 6 which is a large (0.7 MB) non-encapsulated
postscript file). Accepted for publication in the Astronomical Journa
Hubbard ring: currents induced by change of magnetic flux
We investigate currents in a quantum ring threaded by a magnetic flux which
can be varied in an arbitrary way from an initial value at time
to a final value at time . Dynamics of electrons in the ring is
described by the Hubbard and the extended Hubbard models. We demonstrate that
time dependence of the induced current bears information on electron
correlations. In the case of the Hubbard model with infinite on--site repulsion
we prove that the current for is independent of the flux variation
before . Additionally, this current is fully determined by a solution of
the initial equilibrium problem and the value of . Apart from
mesoscopic rings our results pose important implications for designing of
quantum motors built out as the ring--shaped optical lattice
Distillation protocols: Output entanglement and local mutual information
A complementary behavior between local mutual information and average output
entanglement is derived for arbitrary bipartite ensembles. This leads to bounds
on the yield of entanglement in distillation protocols that involve
disinguishing. This bound is saturated in the hashing protocol for
distillation, for Bell-diagonal states.Comment: 4 pages, RevTeX, no figures; v2: presentation improved, results
unchanged; v3: published versio
Circuit analysis of quantum measurement
We develop a circuit theory that enables us to analyze quantum measurements
on a two-level system and on a continuous-variable system on an equal footing.
As a measurement scheme applicable to both systems, we discuss a swapping state
measurement which exchanges quantum states between the system and the measuring
apparatus before the apparatus meter is read out. This swapping state
measurement has an advantage in gravitational-wave detection over contractive
state measurement in that the postmeasurement state of the system can be set to
a prescribed one, regardless of the outcome of the measurement.Comment: 11pages, 7figure
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