9,037 research outputs found
Diagonal Based Feature Extraction for Handwritten Alphabets Recognition System using Neural Network
An off-line handwritten alphabetical character recognition system using
multilayer feed forward neural network is described in the paper. A new method,
called, diagonal based feature extraction is introduced for extracting the
features of the handwritten alphabets. Fifty data sets, each containing 26
alphabets written by various people, are used for training the neural network
and 570 different handwritten alphabetical characters are used for testing. The
proposed recognition system performs quite well yielding higher levels of
recognition accuracy compared to the systems employing the conventional
horizontal and vertical methods of feature extraction. This system will be
suitable for converting handwritten documents into structural text form and
recognizing handwritten names
Rayleigh scattering, mode coupling, and optical loss in silicon microdisks
High refractive index contrast optical microdisk resonators fabricated from
silicon-on-insulator wafers are studied using an external silica fiber taper
waveguide as a wafer-scale optical probe. Measurements performed in the 1500 nm
wavelength band show that these silicon microdisks can support
whispering-gallery modes with quality factors as high as 5.2 x 10^5, limited by
Rayleigh scattering from fabrication induced surface roughness. Microdisks with
radii as small as 2.5 microns are studied, with measured quality factors as
high as 4.7 x 10^5 for an optical mode volume of 5.3 cubic wavelengths in the
material.Comment: 4 pages, 2 figures; contains minor correction to doublet splitting
theor
Estimation of properties of low-lying excited states of Hubbard models : a multi-configurational symmetrized projector quantum Monte Carlo approach
We present in detail the recently developed multi-configurational symmetrized
projector quantum Monte Carlo (MSPQMC) method for excited states of the Hubbard
model. We describe the implementation of the Monte Carlo method for a
multi-configurational trial wavefunction. We give a detailed discussion of
issues related to the symmetry of the projection procedure which validates our
Monte Carlo procedure for excited states and leads naturally to the idea of
symmetrized sampling for correlation functions, developed earlier in the
context of ground state simulations. It also leads to three possible averaging
schemes. We have analyzed the errors incurred in these various averaging
procedures and discuss and detail the preferred averaging procedure for
correlations that do not have the full symmetry of the Hamiltonian. We study
the energies and correlation functions of the low-lying excited states of the
half-filled Hubbard model in 1-D. We have used this technique to study the
pair-binding energies of two holes in and systems, which compare
well the Bethe ansatz data of Fye, Martins and Scalettar. We have also studied
small clusters amenable to exact diagonalization studies in 2-D and have
reproduced their energies and correlation functions by the MSPQMC method. We
identify two ways in which a multiconfigurational trial wavefunction can lead
to a negative sign problem. We observe that this effect is not severe in 1-D
and tends to vanish with increasing system size. We also note that this does
not enhance the severity of the sign problem in two dimensions.Comment: 29 pages, 2 figures available on request, submitted to Phys. Rev.
Linear and nonlinear optical spectroscopy of a strongly-coupled microdisk-quantum dot system
A fiber taper waveguide is used to perform direct optical spectroscopy of a
microdisk-quantum-dot system, exciting the system through the photonic (light)
channel rather than the excitonic (matter) channel. Strong coupling, the regime
of coherent quantum interactions, is demonstrated through observation of vacuum
Rabi splitting in the transmitted and reflected signals from the cavity. The
fiber coupling method also allows the examination of the system's steady-state
nonlinear properties, where saturation of the cavity-QD response is observed
for less than one intracavity photon.Comment: adjusted references, added minor clarification
Dispersive Photon Blockade in a Superconducting Circuit
Mediated photon-photon interactions are realized in a superconducting
coplanar waveguide cavity coupled to a superconducting charge qubit. These
non-resonant interactions blockade the transmission of photons through the
cavity. This so-called dispersive photon blockade is characterized by measuring
the total transmitted power while varying the energy spectrum of the photons
incident on the cavity. A staircase with four distinct steps is observed and
can be understood in an analogy with electron transport and the Coulomb
blockade in quantum dots. This work differs from previous efforts in that the
cavity-qubit excitations retain a photonic nature rather than a hybridization
of qubit and photon and provides the needed tolerance to disorder for future
condensed matter experiments.Comment: 4 pages, 3 figure
High contrast imaging and thickness determination of graphene with in-column secondary electron microscopy
We report a new method for quantitative estimation of graphene layer
thicknesses using high contrast imaging of graphene films on insulating
substrates with a scanning electron microscope. By detecting the attenuation of
secondary electrons emitted from the substrate with an in-column low-energy
electron detector, we have achieved very high thickness-dependent contrast that
allows quantitative estimation of thickness up to several graphene layers. The
nanometer scale spatial resolution of the electron micrographs also allows a
simple structural characterization scheme for graphene, which has been applied
to identify faults, wrinkles, voids, and patches of multilayer growth in
large-area chemical vapor deposited graphene. We have discussed the factors,
such as differential surface charging and electron beam induced current, that
affect the contrast of graphene images in detail.Comment: 5 pages, 4 figure
A Formal, Resource Consumption-Preserving Translation of Actors to Haskell
We present a formal translation of an actor-based language with cooperative
scheduling to the functional language Haskell. The translation is proven
correct with respect to a formal semantics of the source language and a
high-level operational semantics of the target, i.e. a subset of Haskell. The
main correctness theorem is expressed in terms of a simulation relation between
the operational semantics of actor programs and their translation. This allows
us to then prove that the resource consumption is preserved over this
translation, as we establish an equivalence of the cost of the original and
Haskell-translated execution traces.Comment: Pre-proceedings paper presented at the 26th International Symposium
on Logic-Based Program Synthesis and Transformation (LOPSTR 2016), Edinburgh,
Scotland UK, 6-8 September 2016 (arXiv:1608.02534
Flux Expulsion - Field Evolution in Neutron Stars
Models for the evolution of magnetic fields of neutron stars are constructed,
assuming the field is embedded in the proton superconducting core of the star.
The rate of expulsion of the magnetic flux out of the core, or equivalently the
velocity of outward motion of flux-carrying proton-vortices is determined from
a solution of the Magnus equation of motion for these vortices. A force due to
the pinning interaction between the proton-vortices and the neutron-superfluid
vortices is also taken into account in addition to the other more conventional
forces acting on the proton-vortices. Alternative models for the field
evolution are considered based on the different possibilities discussed for the
effective values of the various forces. The coupled spin and magnetic evolution
of single pulsars as well as those processed in low-mass binary systems are
computed, for each of the models. The predicted lifetimes of active pulsars,
field strengths of the very old neutron stars, and distribution of the magnetic
fields versus orbital periods in low-mass binary pulsars are used to test the
adopted field decay models. Contrary to the earlier claims, the buoyancy is
argued to be the dominant driving cause of the flux expulsion, for the single
as well as the binary neutron stars. However, the pinning is also found to play
a crucial role which is necessary to account for the observed low field binary
and millisecond pulsars.Comment: 23 pages, + 7 figures, accepted for publication in Ap
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