684 research outputs found
A General Precipitation-Limited L_X-T-R Relation Among Early-Type Galaxies
The relation between X-ray luminosity (L_X) and ambient gas temperature (T)
among massive galactic systems is an important cornerstone of both
observational cosmology and galaxy-evolution modeling. In the most massive
galaxy clusters, the relation is determined primarily by cosmological structure
formation. In less massive systems, it primarily reflects the feedback response
to radiative cooling of circumgalactic gas. Here we present a simple but
powerful model for the L_X-T relation as a function of physical aperture R
within which those measurements are made. The model is based on the
precipitation framework for AGN feedback and assumes that the circumgalactic
medium is precipitation-regulated at small radii and limited by cosmological
structure formation at large radii. We compare this model with many different
data sets and show that it successfully reproduces the slope and upper envelope
of the L_X-T-R relation over the temperature range from ~0.2 keV through >10
keV. Our findings strongly suggest that the feedback mechanisms responsible for
regulating star formation in individual massive galaxies have much in common
with the precipitation-triggered feedback that appears to regulate
galaxy-cluster cores.Comment: Submitted to ApJ, 9 pages, 3 figures (v2 fixes a few small typos
Magnetoconductance oscillations in quasiballistic multimode nanowires
We calculate the conductance of quasi-one-dimensional nanowires with
electronic states confined to a surface charge layer, in the presence of a
uniform magnetic field. Two-terminal magnetoconductance (MC) between two leads
deposited on the nanowire via tunnel barriers is dominated by density-of-states
(DOS) singularities, when the leads are well apart. There is also a mesoscopic
correction due to a higher-order coherent tunneling between the leads for small
lead separation. The corresponding MC structure depends on the interference
between electron propagation via different channels connecting the leads, which
in the simplest case, for the magnetic field along the wire axis, can be
crudely characterized by relative winding numbers of paths enclosing the
magnetic flux. In general, the MC oscillations are aperiodic, due to the Zeeman
splitting, field misalignment with the wire axis, and a finite extent of
electron distribution across the wire cross section, and are affected by
spin-orbit coupling. The quantum-interference MC traces contain a wealth of
information about the electronic structure of multichannel wires, which would
be complimentary to the DOS measurements. We propose a four-terminal
configuration to enhance the relative contribution of the higher-order
tunneling processes and apply our results to realistic InAs nanowires carrying
several quantum channels in the surface charge-accumulation layer.Comment: 11 pages, 8 figure
Spectral sum rules for the Tomonaga-Luttinger model
In connection with recent publications we discuss spectral sum rules for the
Tomonaga-Luttinger model without using the explicit result for the one-electron
Green's function. They are usefull in the interpretation of recent high
resolution photoemission spectra of quasi-one-dimensional conductors. It is
shown that the limit of infinite frequency and band cut\-off do not commute.
Our result for arbitrary shape of the interaction potential generalizes an
earlier discussion by Suzumura. A general analytical expression for the
spectral function for wave vectors far from the Fermi wave vector is
presented. Numerical spectra are shown to illustrate the sum rules.Comment: 9 pages, REVTEX 3.0, 2 figures added as postscript file
A Deoxyribonucleic Acid Decoy Trapping DUX4 for the Treatment of Facioscapulohumeral Muscular Dystrophy
Facioscapulohumeral dystrophy (FSHD) is characterized by a loss of repressive epigenetic marks leading to the aberrant expression of the DUX4 transcription factor. In muscle, DUX4 acts as a poison protein though the induction of multiple downstream genes. So far, there is no therapeutic solution for FSHD. Because DUX4 is a transcription factor, we developed an original therapeutic approach, based on a DNA decoy trapping the DUX4 protein, preventing its binding to genomic DNA and thereby blocking the aberrant activation of DUX4’s transcriptional network. In vitro, transfection of a DUX4 decoy into FSHD myotubes reduced the expression of the DUX4 network genes. In vivo, both double-stand DNA DUX4 decoys and adeno-associated viruses (AAVs) carrying DUX4 binding sites reduced transcriptional activation of genes downstream of DUX4 in a DUX4-expressing mouse model. Our study demonstrates, both in vitro and in vivo, the feasibility of the decoy strategy and opens new avenues of research
Quasi-Particles in Two-Dimensional Hubbard Model: Splitting of Spectral Weight
It is shown that the energy and momentum dependences of
the electron self-energy function are, where is some
constant, being the band energy,
and the critical exponent , which depends on the curvature of the
Fermi surface at , satisfies, . This leads to a
new type of electron liquid, which is the Fermi liquid in the limit of but for has a split
one-particle spectra as in the Tomonaga-Luttinger liquid.Comment: 8 pages (LaTeX) 4 figures available upon request will be sent by air
mail. KomabaCM-preprint-O
SET based experiments for HTSC materials: II
The cuprates seem to exhibit statistics, dimensionality and phase transitions
in novel ways. The nature of excitations
[i.e. quasiparticle or collective], spin-charge separation, stripes [static
and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn,
Ni] and any other phenomenon in these materials must be consistently
understood. In this note we further discuss our original suggestion of using
Single Electron Tunneling Transistor
[SET] based experiments to understand the role of charge dynamics in these
systems. Assuming that SET operates as an efficient charge detection system we
can expect to understand the underlying physics of charge transport and charge
fluctuations in these materials for a range of doping. Experiments such as
these can be classed in a general sense as mesoscopic and nano characterization
of cuprates and related materials. In principle such experiments can show if
electron is fractionalized in cuprates as indicated by ARPES data. In contrast
to flux trapping experiments SET based experiments are more direct in providing
evidence about spin-charge separation. In addition a detailed picture of nano
charge dynamics in cuprates may be obtained.Comment: 10 pages revtex plus four figures; ICMAT 2001 Conference Symposium P:
P10-0
Unconventional magnetoresistance in long InSb nanowires
Magnetoresistance in long correlated nanowires of degenerate semiconductor
InSb in asbestos matrix (wire diameter of around 5 nm, length 0.1 - 1 mm) is
studied over temperature range 2.3 - 300 K. At zero magnetic field the electric
conduction and the current-voltage characteristics of such wires obey the
power laws , , expected for
one-dimensional electron systems. The effect of magnetic field corresponds to a
20% growth of the exponents , at H=10 T. The observed
magnetoresistance is caused by the magnetic-field-induced breaking of the
spin-charge separation and represents a novel mechanism of magnetoresistance.Comment: To be published in JETP Letters, vol. 77 (2003
Friedel oscillations in a gas of interacting one-dimensional fermionic atoms confined in a harmonic trap
Using an asymptotic phase representation of the particle density operator
in the one-dimensional harmonic trap, the part which describes the Friedel oscillations is extracted. The
expectation value with respect to the interacting
ground state requires the calculation of the mean square average of a properly
defined phase operator. This calculation is performed analytically for the
Tomonaga-Luttinger model with harmonic confinement. It is found that the
envelope of the Friedel oscillations at zero temperature decays with the
boundary exponent away from the classical boundaries. This
value differs from that known for open boundary conditions or strong pinning
impurities. The soft boundary in the present case thus modifies the decay of
Friedel oscillations. The case of two components is also discussed.Comment: Revised version to appear in Journal of Physics B: Atomic, Molecular
and Optical Physic
Correlation functions for a two-dimensional electron system with bosonic interactions and a square Fermi surface
We calculate zero-temperature correlation functions for a model of 2D
interacting electrons with short-range interactions and a square Fermi surface.
The model was arrived at by mapping electronic states near a square Fermi
surface with Hubbard-like interactions onto one-dimensional quantum chains,
retaining terms which can be written in terms of bosonic density operators.
Interactions between orthogonal chains, corresponding to orthogonal faces of
the square Fermi surface, are neglected. The correlation functions become sums
of Luttinger-type correlation functions due to the bosonic model. However, the
correlation function exponents differ in form from those of the Luttinger
model. As a consequence, the simple scaling relations found to exist between
the Luttinger model exponents, do not carry over to the leading exponents of
our model. We find that for repulsive effective interactions, charge-density
wave/spin-density wave instabilities are dominant. We do not consider d-wave
instabilities here.Comment: 12 pages, no figures; to be published in Physical Review
Nonuniversal spectral properties of the Luttinger model
The one electron spectral functions for the Luttinger model are discussed for
large but finite systems. The methods presented allow a simple interpretation
of the results. For finite range interactions interesting nonunivesal spectral
features emerge for momenta which differ from the Fermi points by the order of
the inverse interaction range or more. For a simplified model with interactions
only within the branches of right and left moving electrons analytical
expressions for the spectral function are presented which allows to perform the
thermodynamic limit. As in the general spinless model and the model including
spin for which we present mainly numerical results the spectral functions do
not approach the noninteracting limit for large momenta. The implication of our
results for recent high resolution photoemission measurements on quasi
one-dimensional conductors are discussed.Comment: 19 pages, Revtex 2.0, 5 ps-figures, to be mailed on reques
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