29,868 research outputs found
Performance of silicon solar cell assemblies
Solar cell assembly current-voltage characteristics, thermal-optical properties, and power performance were determined. Solar cell cover glass thermal radiation, optical properties, confidence limits, and temperature intensity effects on maximum power were discussed
Preliminary investigations of ion thruster cathodes
Mercury vapor fed hollow cathodes for electron bombardment ion thruster
A scheme for demonstration of fractional statistics of anyons in an exactly solvable model
We propose a scheme to demonstrate fractional statistics of anyons in an
exactly solvable lattice model proposed by Kitaev that involves four-body
interactions. The required many-body ground state, as well as the anyon
excitations and their braiding operations, can be conveniently realized through
\textit{dynamic}laser manipulation of cold atoms in an optical lattice. Due to
the perfect localization of anyons in this model, we show that a quantum
circuit with only six qubits is enough for demonstration of the basic braiding
statistics of anyons. This opens up the immediate possibility of
proof-of-principle experiments with trapped ions, photons, or nuclear magnetic
resonance systems.Comment: 4 pages, 3 figure
Irrational charge from topological order
Topological or deconfined phases of matter exhibit emergent gauge fields and
quasiparticles that carry a corresponding gauge charge. In systems with an
intrinsic conserved U(1) charge, such as all electronic systems where the
Coulombic charge plays this role, these quasiparticles are also characterized
by their intrinsic charge. We show that one can take advantage of the
topological order fairly generally to produce periodic Hamiltonians which endow
the quasiparticles with continuously variable, generically irrational,
intrinsic charges. Examples include various topologically ordered lattice
models, the three dimensional RVB liquid on bipartite lattices as well as water
and spin ice. By contrast, the gauge charges of the quasiparticles retain their
quantized values.Comment: 4 pages, 1 figure with two panel
Classification of Gapped Symmetric Phases in 1D Spin Systems
Quantum many-body systems divide into a variety of phases with very different
physical properties. The question of what kind of phases exist and how to
identify them seems hard especially for strongly interacting systems. Here we
make an attempt to answer this question for gapped interacting quantum spin
systems whose ground states are short-range correlated. Based on the local
unitary equivalence relation between short-range correlated states in the same
phase, we classify possible quantum phases for 1D matrix product states, which
represent well the class of 1D gapped ground states. We find that in the
absence of any symmetry all states are equivalent to trivial product states,
which means that there is no topological order in 1D. However, if certain
symmetry is required, many phases exist with different symmetry protected
topological orders. The symmetric local unitary equivalence relation also
allows us to obtain some simple results for quantum phases in higher dimensions
when some symmetries are present.Comment: 21 pages, 7 figures. Version 2, classification for parity and
translation symmetry update
Detecting extreme mass ratio inspirals with LISA using time-frequency methods II: search characterization
The inspirals of stellar-mass compact objects into supermassive black holes
constitute some of the most important sources for LISA. Detection of these
sources using fully coherent matched filtering is computationally intractable,
so alternative approaches are required. In a previous paper (Wen and Gair 2005,
gr-qc/0502100), we outlined a detection method based on looking for excess
power in a time-frequency spectrogram of the LISA data. The performance of the
algorithm was assessed using a single `typical' trial waveform and
approximations to the noise statistics. In this paper we present results of
Monte Carlo simulations of the search noise statistics and examine its
performance in detecting a wider range of trial waveforms. We show that typical
extreme mass ratio inspirals (EMRIs) can be detected at distances of up to 1--3
Gpc, depending on the source parameters. We also discuss some remaining issues
with the technique and possible ways in which the algorithm can be improved.Comment: 15 pages, 9 figures, to appear in proceedings of GWDAW 9, Annecy,
France, December 200
Mosaic spin models with topological order
We study a class of two-dimensional spin models with the Kitaev-type
couplings in mosaic structure lattices to implement topological orders. We show
that they are exactly solvable by reducing them to some free Majorana fermion
models with gauge symmetries. The typical case with a 4-8-8 close packing is
investigated in detail to display the quantum phases with Abelian and
non-Abelian anyons. Its topological properties characterized by Chern numbers
are revealed through the edge modes of its spectrum.Comment: 4 pages, 3 figures. Final version to appear in Phys. Rev. B as a
Rapid Communicatio
Bosonic model with fractionalization
Bosonic model with unfrustrated hopping and short-range repulsive interaction
is constructed that realizes fractionalized insulator phase in two
dimensions and in zero magnetic field. Such phase is characterized as having
gapped charged excitations that carry fractional electrical charge 1/3 and also
gapped vortices above the topologically ordered ground state.Comment: 7 pages, 3 figure
Detecting extreme mass ratio inspiral events in LISA data using the Hierarchical Algorithm for Clusters and Ridges (HACR)
One of the most exciting prospects for the Laser Interferometer Space Antenna
(LISA) is the detection of gravitational waves from the inspirals of
stellar-mass compact objects into supermassive black holes. Detection of these
sources is an extremely challenging computational problem due to the large
parameter space and low amplitude of the signals. However, recent work has
suggested that the nearest extreme mass ratio inspiral (EMRI) events will be
sufficiently loud that they might be detected using computationally cheap,
template-free techniques, such as a time-frequency analysis. In this paper, we
examine a particular time-frequency algorithm, the Hierarchical Algorithm for
Clusters and Ridges (HACR). This algorithm searches for clusters in a power map
and uses the properties of those clusters to identify signals in the data. We
find that HACR applied to the raw spectrogram performs poorly, but when the
data is binned during the construction of the spectrogram, the algorithm can
detect typical EMRI events at distances of up to Gpc. This is a little
further than the simple Excess Power method that has been considered
previously. We discuss the HACR algorithm, including tuning for single and
multiple sources, and illustrate its performance for detection of typical EMRI
events, and other likely LISA sources, such as white dwarf binaries and
supermassive black hole mergers. We also discuss how HACR cluster properties
could be used for parameter extraction.Comment: 21 pages, 11 figures, submitted to Class. Quantum Gravity. Modified
and shortened in light of referee's comments. Updated results consider tuning
over all three HACR thresholds, and show 10-15% improvement in detection rat
The Origin of \lya Absorption Systems at ---Implications from the Hubble Deep Field
The Hubble Deep Field images have provided us with a unique chance to relate
statistical properties of high-redshift galaxies to statistical properties of
\lya absorption systems. Combining an {\em empirical} measure of the galaxy
surface density versus redshift with an {\em empirical} measure of the gaseous
extent of galaxies, we predict the number density of \lya absorption systems
that originate in extended gaseous envelopes of galaxies versus redshift. We
show that at least 50% and as much as 100% of observed \lya absorption systems
of W\apg0.32 \AA can be explained by extended gaseous envelops of galaxies.
Therefore, we conclude that known galaxies of known gaseous extent must produce
a significant fraction and perhaps all of \lya absorption systems over a large
redshift range.Comment: 12 pages, 3 figures, accepted for publication in the Astrophysical
Journal, April 10, 2000 issu
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