2,347 research outputs found
An MLSA-based online scheme for the rapid identification of Stenotrophomonas isolates
An online scheme to assign Stenotrophomonas isolates to genomic groups was developed using the multilocus sequence analysis (MLSA), which is based on the DNA sequencing of selected fragments of the housekeeping genes ATP synthase alpha subunit (atpA), the recombination repair protein (recA), the RNA polymerase alpha subunit (rpoA) and the excision repair beta subunit (uvrB). This MLSA-based scheme was validated using eight of the 10 Stenotrophomonas species that have been previously described. The environmental and nosocomial Stenotrophomonas strains were characterised using MLSA, 16S rRNA sequencing and DNA-DNA hybridisation (DDH) analyses. Strains of the same species were found to have greater than 95% concatenated sequence similarity and specific strains formed cohesive readily recognisable phylogenetic groups. Therefore, MLSA appeared to be an effective alternative methodology to amplified fragment length polymorphism fingerprint and DDH techniques. Strains of Stenotrophomonas can be readily assigned through the open database resource that was developed in the current study (www.steno.lncc.br/)
Calculation of the average Green's function of electrons in a stochastic medium via higher-dimensional bosonization
The disorder averaged single-particle Green's function of electrons subject
to a time-dependent random potential with long-range spatial correlations is
calculated by means of bosonization in arbitrary dimensions. For static
disorder our method is equivalent with conventional perturbation theory based
on the lowest order Born approximation. For dynamic disorder, however, we
obtain a new non-perturbative expression for the average Green's function.
Bosonization also provides a solid microscopic basis for the description of the
quantum dynamics of an interacting many-body system via an effective stochastic
model with Gaussian probability distribution.Comment: RevTex, no figure
Fermi edge singularities in X-ray spectra of strongly correlated fermions
We discuss the problem of the X-ray absorption in a system of interacting
fermions and, in particular, those features in the X-ray spectra that can be
used to discriminate between conventional Fermi-liquids and novel "strange
metals". Focusing on the case of purely forward scattering off the core-hole
potential, we account for the relevant interactions in the conduction band by
means of the bosonization technique. We find that the X-ray Fermi edge
singularities can still be present, although modified, even if the density of
states vanishes at the Fermi energy, and that, in general, the relationship
between the two appears to be quite subtle.Comment: Latex, 16 pages, Princeton preprin
Bosonization and the eikonal expansion: similarities and differences
We compare two non-perturbative techniques for calculating the
single-particle Green's function of interacting Fermi systems with dominant
forward scattering: our recently developed functional integral approach to
bosonization in arbitrary dimensions, and the eikonal expansion. In both
methods the Green's function is first calculated for a fixed configuration of a
background field, and then averaged with respect to a suitably defined
effective action. We show that, after linearization of the energy dispersion at
the Fermi surface, both methods yield for Fermi liquids exactly the same
non-perturbative expression for the quasi-particle residue. However, in the
case of non-Fermi liquid behavior the low-energy behavior of the Green's
function predicted by the eikonal method can be erroneous. In particular, for
the Tomonaga-Luttinger model the eikonal method neither reproduces the correct
scaling behavior of the spectral function, nor predicts the correct location of
its singularities.Comment: Revtex, one figur
Correlation functions of higher-dimensional Luttinger liquids
Using higher-dimensional bosonization, we study correlation functions of
fermions with singular forward scattering. Following Bares and Wen [Phys. Rev.
B 48, 8636 (1993)], we consider density-density interactions in d dimensions
that diverge for small momentum transfers as q^{- eta} with eta = 2 (d-1). In
this case the single-particle Green's function shows Luttinger liquid behavior.
We discuss the momentum distribution and the density of states and show that,
in contrast to d=1, in higher dimensions the scaling behavior cannot be
characterized by a single anomalous exponent. We also calculate the irreducible
polarization for q close to 2 k_F and show that the leading singularities
cancel. We discuss consequences for the effect of disorder on
higher-dimensional Luttinger liquids.Comment: 7 RevTex pages, 2 figures, minor modifications, to appear in Phys.
Rev. B (Feb. 1999
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The Massive Progenitor of the Type II-Linear Supernova 2009kr
We present early-time photometric and spectroscopic observations of supernova (SN) 2009kr in NGC 1832. We find that its properties to date support its classification as Type II-linear (SN II-L), a relatively rare subclass of core-collapse supernovae (SNe). We have also identified a candidate for the SN progenitor star through comparison of pre-explosion, archival images taken with WFPC2 on board the Hubble Space Telescope with SN images obtained using adaptive optics plus NIRC2 on the 10 m Keck-II telescope. Although the host galaxy's substantial distance (similar to 26 Mpc) results in large uncertainties in the relative astrometry, we find that if this candidate is indeed the progenitor, it is a highly luminous (M(V)(0) = -7.8 mag) yellow supergiant with initial mass similar to 18-24 M(circle dot). This would be the first time that an SN II-L progenitor has been directly identified. Its mass may be a bridge between the upper initial mass limit for the more common Type II-plateau SNe and the inferred initial mass estimate for one Type II-narrow SN.Hungarian OTKA K76816NSF AST-0707769, AST-0908886Sylvia & Jim Katzman FoundationTABASGO FoundationNASA through STScI AR-11248, GO-10877Harvard UniversityUC BerkeleyUniversity of VirginiaNASA/Swift NNX09AQ66GDOEAstronom
Medical diagnosis using NIR and THz tissue imaging and machine learning methods
The problem of extracting useful information for medical diagnosis from 2D and 3D optical imaging experimental data is of great importance. We are discussing challenges and perspectives of medical diagnosis using machine learning analysis of NIR and THz tissue imaging. The peculiarities of tissue optical clearing for tissue imaging in NIR and THz spectral ranges aiming the improvement of content data analysis, methods of extracting of informative features from experimental data and creating of prognostic models for medical diagnosis using machine learning methods are discussed
Dynamics of fermions coupling to a U(1) gauge field in the limit
We study in this paper the properties of a gas of fermions coupling to a U(1)
gauge field at wavevectors at dimensions larger than one,
where is a high momentum cutoff and is the fermi wave
vector. In particular, we shall consider the limit where charge
and current fluctuations at wave vectors are forbidden. Within a
bosonization approximation, effective actions describing the low energy physics
of the system are constructed, where we show that the system can be described
as a fermion liquid formed by chargeless quasi-particles which has vanishing
wavefunction overlap with the bare fermions in the system.Comment: 25 page
Landau level bosonization of a 2D electron gas
In this work we introduce a bosonization scheme for the low energy
excitations of a 2D interacting electron gas in the presence of an uniform
magnetic field under conditions where a large integral number of Landau levels
are filled. We give an explicit construction for the electron operator in terms
of the bosons. We show that the elementary neutral excitations, known as the
magnetic excitons or magnetoplasma modes, can be described within a bosonic
language and that it provides a quadratic bosonic Hamiltonian for the
interacting electron system which can be easily diagonalized.Comment: 4 pages, revte
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