50,847 research outputs found
Symmetric ideals in group rings and simplicial homotopy
In this paper homotopical methods for the description of subgroups determined
by ideals in group rings are introduced. It is shown that in certain cases the
subgroups determined by symmetric product of ideals in group rings can be
described with the help of homotopy groups of spheres.Comment: 10 pages, to appear in J. Pure Appl. Algebr
2-D Compass Codes
The compass model on a square lattice provides a natural template for
building subsystem stabilizer codes. The surface code and the Bacon-Shor code
represent two extremes of possible codes depending on how many gauge qubits are
fixed. We explore threshold behavior in this broad class of local codes by
trading locality for asymmetry and gauge degrees of freedom for stabilizer
syndrome information. We analyze these codes with asymmetric and spatially
inhomogeneous Pauli noise in the code capacity and phenomenological models. In
these idealized settings, we observe considerably higher thresholds against
asymmetric noise. At the circuit level, these codes inherit the bare-ancilla
fault-tolerance of the Bacon-Shor code.Comment: 10 pages, 7 figures, added discussion on fault-toleranc
Vector Meson Propagator and Baryon Current Conservation
If baryons couple only with -mesons, one found the baryon spectral
function may be negative. We show this unacceptable result is caused by the
-terms in the -meson propagator. Their contribution may
not vanish in approximate calculations which violate the baryon current
conserves. A rule is suggested, by which the calculated baryon spectral
function is well behaved.Comment: 9 pages (LaTeX file), 3 figures (PostScript file
Painting Analysis Using Wavelets and Probabilistic Topic Models
In this paper, computer-based techniques for stylistic analysis of paintings
are applied to the five panels of the 14th century Peruzzi Altarpiece by Giotto
di Bondone. Features are extracted by combining a dual-tree complex wavelet
transform with a hidden Markov tree (HMT) model. Hierarchical clustering is
used to identify stylistic keywords in image patches, and keyword frequencies
are calculated for sub-images that each contains many patches. A generative
hierarchical Bayesian model learns stylistic patterns of keywords; these
patterns are then used to characterize the styles of the sub-images; this in
turn, permits to discriminate between paintings. Results suggest that such
unsupervised probabilistic topic models can be useful to distill characteristic
elements of style.Comment: 5 pages, 4 figures, ICIP 201
A multi-photon magneto-optical trap
We demonstrate a Magneto-Optical Trap (MOT) configuration which employs
optical forces due to light scattering between electronically excited states of
the atom. With the standard MOT laser beams propagating along the {\it x}- and
{\it y}- directions, the laser beams along the {\it z}-direction are at a
different wavelength that couples two sets of {\it excited} states. We
demonstrate efficient cooling and trapping of cesium atoms in a vapor cell and
sub-Doppler cooling on both the red and blue sides of the two-photon resonance.
The technique demonstrated in this work may have applications in
background-free detection of trapped atoms, and in assisting laser-cooling and
trapping of certain atomic species that require cooling lasers at inconvenient
wavelengths.Comment: 10 pages, 5 figure
Coupled Dyson-Schwinger Equations and Effects of Self-Consistency
Using the model as an effective tool, the effects of
self-consistency are studied in some detail. A coupled set of Dyson-Schwinger
equations for the renormalized baryon and meson propagators in the model is solved self-consistently according to the dressed
Hartree-Fock scheme, where the hadron propagators in both the baryon and meson
self-energies are required to also satisfy this coupled set of equations. It is
found that the self-consistency affects the baryon spectral function
noticeably, if only the interaction with mesons is considered.
However, there is a cancellation between the effects due to the and
mesons and the additional contribution of mesons makes the
above effect insignificant. In both the and cases the
effects of self-consistency on meson spectral function are perceptible, but
they can nevertheless be taken account of without a self-consistent
calculation. Our study indicates that to include the meson propagators in the
self-consistency requirement is unnecessary and one can stop at an early step
of an iteration procedure to obtain a good approximation to the fully
self-consistent results of all the hadron propagators in the model, if an
appropriate initial input is chosen. Vertex corrections and their effects on
ghost poles are also studied.Comment: 20 pages (include 5 tables), 17 figures (PostScript file
ArrayBridge: Interweaving declarative array processing with high-performance computing
Scientists are increasingly turning to datacenter-scale computers to produce
and analyze massive arrays. Despite decades of database research that extols
the virtues of declarative query processing, scientists still write, debug and
parallelize imperative HPC kernels even for the most mundane queries. This
impedance mismatch has been partly attributed to the cumbersome data loading
process; in response, the database community has proposed in situ mechanisms to
access data in scientific file formats. Scientists, however, desire more than a
passive access method that reads arrays from files.
This paper describes ArrayBridge, a bi-directional array view mechanism for
scientific file formats, that aims to make declarative array manipulations
interoperable with imperative file-centric analyses. Our prototype
implementation of ArrayBridge uses HDF5 as the underlying array storage library
and seamlessly integrates into the SciDB open-source array database system. In
addition to fast querying over external array objects, ArrayBridge produces
arrays in the HDF5 file format just as easily as it can read from it.
ArrayBridge also supports time travel queries from imperative kernels through
the unmodified HDF5 API, and automatically deduplicates between array versions
for space efficiency. Our extensive performance evaluation in NERSC, a
large-scale scientific computing facility, shows that ArrayBridge exhibits
statistically indistinguishable performance and I/O scalability to the native
SciDB storage engine.Comment: 12 pages, 13 figure
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