9,332 research outputs found
Wavefunctions for the Luttinger liquid
Standard bosonization techniques lead to phonon-like excitations in a
Luttinger liquid (LL), reflecting the absence of Landau quasiparticles in these
systems. Yet in addition to the above excitations some LL are known to possess
solitonic states carrying fractional quantum numbers (e.g. the spin 1/2
Heisenberg chain). We have reconsidered the zero modes in the low-energy
spectrum of the gaussian boson LL hamiltonian both for fermionic and bosonic
LL: in the spinless case we find that two elementary excitations carrying
fractional quantum numbers allow to generate all the charge and current excited
states of the LL. We explicitly compute the wavefunctions of these two objects
and show that one of them can be identified with the 1D version of the Laughlin
quasiparticle introduced in the context of the Fractional Quantum Hall effect.
For bosons, the other quasiparticle corresponds to a spinon excitation. The
eigenfunctions of Wen's chiral LL hamiltonian are also derived: they are quite
simply the one dimensional restrictions of the 2D bulk Laughlin wavefunctions.Comment: 5 pages; accepted for publication in EPR B, Rapid Note
Fractional excitations in the Luttinger liquid
We reconsider the spectrum of the Luttinger liquid (LL) usually understood in
terms of phonons (density fluctuations), and within the context of bosonization
we give an alternative representation in terms of fractional states. This
allows to make contact with Bethe Ansatz which predicts similar fractional
states. As an example we study the spinon operator in the absence of spin
rotational invariance and derive it from first principles: we find that it is
not a semion in general; a trial Jastrow wavefunction is also given for that
spinon state. Our construction of the new spectroscopy based on fractional
states leads to several new physical insights: in the low-energy limit, we find
that the continuum of gapless spin chains is due to pairs of
fractional quasiparticle-quasihole states which are the 1D counterpart of the
Laughlin FQHE quasiparticles. The holon operator for the Luttinger liquid with
spin is also derived. In the presence of a magnetic field, spin-charge
separation is not realized any longer in a LL: the holon and the spinon are
then replaced by new fractional states which we are able to describe.Comment: Revised version to appear in Physical Review B. 27 pages, 5 figures.
Expands cond-mat/9905020 (Eur.Phys.Journ.B 9, 573 (1999)
K Means Segmentation of Alzheimers Disease in PET scan datasets: An implementation
The Positron Emission Tomography (PET) scan image requires expertise in the
segmentation where clustering algorithm plays an important role in the
automation process. The algorithm optimization is concluded based on the
performance, quality and number of clusters extracted. This paper is proposed
to study the commonly used K Means clustering algorithm and to discuss a brief
list of toolboxes for reproducing and extending works presented in medical
image analysis. This work is compiled using AForge .NET framework in windows
environment and MATrix LABoratory (MATLAB 7.0.1)Comment: International Joint Conference on Advances in Signal Processing and
Information Technology, SPIT201
Coherence of Nitrogen-Vacancy Electronic Spin Ensembles in Diamond
We present an experimental and theoretical study of electronic spin
decoherence in ensembles of nitrogen-vacancy (NV) color centers in bulk
high-purity diamond at room temperature. Under appropriate conditions, we find
ensemble NV spin coherence times (T_2) comparable to that of single NVs, with
T_2 > 600 microseconds for a sample with natural abundance of 13C and
paramagnetic impurity density ~10^15 cm^(-3). We also observe a sharp decrease
of the coherence time with misalignment of the static magnetic field relative
to the NV electronic spin axis, consistent with theoretical modeling of NV
coupling to a 13C nuclear spin bath. The long coherence times and increased
signal-to-noise provided by room-temperature NV ensembles will aid many
applications of NV centers in precision magnetometry and quantum information.Comment: 5 pages, 3 figures; v2 minor correction
Ultrahigh sensitivity of slow-light gyroscope
Slow light generated by Electromagnetically Induced Transparency is extremely
susceptible with respect to Doppler detuning. Consequently, slow-light
gyroscopes should have ultrahigh sensitivity
Specimens at the Center: An Informatics Workflow and Toolkit for Specimen-level analysis of Public DNA database data
Major public DNA databases — NCBI GenBank, the DNA DataBank of Japan (DDBJ), and the European Molecular Biology
Laboratory (EMBL) — are invaluable biodiversity libraries. Systematists and other biodiversity scientists commonly mine these databases for
sequence data to use in phylogenetic studies, but such studies generally use only the taxonomic identity of the sequenced tissue, not the
specimen identity. Thus studies that use DNA supermatrices to construct phylogenetic trees with species at the tips typically do not take
advantage of the fact that for many individuals in the public DNA databases, several DNA regions have been sampled; and for many species,
two or more individuals have been sampled. Thus these studies typically do not make full use of the multigene datasets in public DNA
databases to test species coherence and select optimal sequences to represent a species. In this study, we introduce a set of tools developed
in the R programming language to construct individual-based trees from NCBI GenBank data and present a set of trees for the genus Carex
(Cyperaceae) constructed using these methods. For the more than 770 species for which we found sequence data, our approach recovered an
average of 1.85 gene regions per specimen, up to seven for some specimens, and more than 450 species represented by two or more specimens.
Depending on the subset of genes analyzed, we found up to 42% of species monophyletic. We introduce a simple tree statistic—the
Taxonomic Disparity Index (TDI)—to assist in curating specimen-level datasets and provide code for selecting maximally informative (or,
conversely, minimally misleading) sequences as species exemplars. While tailored to the Carex dataset, the approach and code presented in
this paper can readily be generalized to constructing individual-level trees from large amounts of data for any species group
Role of Light Vector Mesons in the Heavy Particle Chiral Lagrangian
We give the general framework for adding "light" vector particles to the
heavy hadron effective chiral Lagrangian. This has strong motivations both from
the phenomenological and aesthetic standpoints. An application to the already
observed D \rightarrow \overbar{K^*} weak transition amplitude is discussed.Comment: 19 pages, LaTeX documen
ATP level variations in heterotrophic bacteria during attachment on hydrophilic and hydrophobic surfaces
A survey of the extracellular ATP levels of 86 heterotrophic bacteria showed that gram-negative bacteria of the genera Sulfitobacter, Staleya, and Marinobacter secreted elevated amounts of extracellular ATP, ranging from 6.0 to 9.8 pM ATP/colony forming unit (cfu), and that gram-positive bacteria of the genera Kocuria and Planococcus secreted up to 4.1 pM ATP/cfu. Variations in the levels of extracellular and intracellular ATP-dependent luminescence were monitored in living cells of Sulfitobacter mediterraneus ATCC 700856T and Planococcus maritimus F 90 during 48 h of attachment on hydrophobic (poly[tert-butyl methacrylate], PtBMA) and hydrophilic (mica) surfaces. The bacteria responded to different polymeric surfaces by producing either intracellular or extracellular ATP. The level of intracellular ATP in S. mediterraneus ATCC 700856T attached to either surface was as high as 50–55 pM ATP/cfu, while in P. maritimus F 90 it was 120 and 250 pM ATP/cfu on PtBMA and mica, respectively. S. mediterraneus ATCC 700856T generated about 20 and 50 pM of extracellular ATP/cfu on PtBMA and mica, respectively, while the amount generated by P. maritimus F 90 was about the same for both surfaces, 6 pM ATP/cfu. The levels of extracellular ATP generated by S. mediterraneus during attachment on PtBMA and mica were two to five times higher than those detected during the initial screening. High-resolution atomic force microscopy imaging revealed a potentially interesting correlation between the porous cell-surface of certain (α- and γ-proteobacteria and their ability to secrete high amounts of ATP. [Int Microbiol 2006; 9(1):37-46
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