15,140 research outputs found
Spiral phases and two-particle bound states from a systematic low-energy effective theory for magnons, electrons, and holes in an antiferromagnet
We have constructed a systematic low-energy effective theory for hole- and
electron-doped antiferromagnets, where holes reside in momentum space pockets
centered at and where electrons live in
pockets centered at or . The effective
theory is used to investigate the magnon-mediated binding between two holes or
two electrons in an otherwise undoped system. We derive the one-magnon exchange
potential from the effective theory and then solve the corresponding
two-quasiparticle Schr\"odinger equation. As a result, we find bound state wave
functions that resemble -like or -like symmetry. We also
study possible ground states of lightly doped antiferromagnets.Comment: 2 Pages; Proc. of SCES'07, Housto
Visualization of leukocyte transendothelial and interstitial migration using reflected light oblique transillumination in intravital video microscopy
Dynamic visualization of the intravascular events leading to the extravasation of leukocytes into tissues by intravital microscopy has significantly expanded our understanding of the underlying molecular processes. In contrast, the detailed observation of leukocyte transendothelial and interstitial migration in vivo has been hampered by the poor image contrast of cells within turbid media that is obtainable by conventional brightfield microscopy. Here we present a microscopic method, termed reflected light oblique transillumination microscopy, that makes use of the optical interference phenomena generated by oblique transillumination to visualize subtle gradients of refractive indices within tissues for enhanced image contrast. Using the mouse cremaster muscle, we demonstrate that this technique makes possible the reliable quantification of extravasated leukocytes as well as the characterization of morphological phenomena of leukocyte transendothelial and interstitial migration
From spin-Peierls to superconductivity: (TMTTF)_2PF_6 under high pressure
The nature of the attractive electron-electron interaction, leading to the
formation of Cooper-pairs in unconventional superconductors has still to be
fully understood and is subject to intensive research. Here we show that the
sequence spin-Peierls, antiferromagnetism, superconductivity observed in
(TMTTF)_2PF_6 under pressure makes the (TM)_2X phase diagram universal. We
argue that the suppression of the spin-Peierls transition under pressure, the
close vicinity of antiferromagnetic and superconducting phases at high pressure
as well as the existence of critical antiferromagnetic fluctuations above T_c
strongly support the intriguing possibility that the interchain exchange of
antiferromagnetic fluctuations provides the pairing mechanism required for
bound charge carriers.Comment: 4 pages, revtex, 4 figures (jpeg,eps,png
Single spike solutions for strings on S2 and S3
We study solutions for rigidly rotating strings on a two sphere. Among them
we find two limiting cases that have a particular interest, one is the already
known giant magnon and the other we call the single spike solution. The
limiting behavior of this last solution is a string infinitely wrapped around
the equator. It differs from that solution by the existence of a single spike
of height theta that points toward the north pole.
We study its properties and compute its energy E and angular momentum J as a
function of theta. We further generalize the solution by adding one angular
momentum to obtain a solution on S3. We find a spin chain interpretations of
these results in terms of free fermions and the Hubbard model but the exact
relation with the same models derived from the field theory is not clear.Comment: LaTeX, 20 pages, 3 figures. v2: Refs adde
Spin chain from membrane and the Neumann-Rosochatius integrable system
We find membrane configurations in AdS_4 x S^7, which correspond to the
continuous limit of the SU(2) integrable spin chain, considered as a limit of
the SU(3) spin chain, arising in N=4 SYM in four dimensions, dual to strings in
AdS_5 x S^5. We also discuss the relationship with the Neumann-Rosochatius
integrable system at the level of Lagrangians, comparing the string and
membrane cases.Comment: LaTeX, 16 pages, no figures; v2: 17 pages, title changed,
explanations and references added; v3: more explanations added; v4: typos
fixed, to appear in Phys. Rev.
Phase decorrelation, streamwise vortices and acoustic radiation in mixing layers
Several direct numerical simulations were performed and analyzed to study various aspects of the early development of mixing layers. Included are the phase jitter of the large-scale eddies, which was studied using a 2-D spatially-evolving mixing layer simulation; the response of a time developing mixing layer to various spanwise disturbances; and the sound radiation from a 2-D compressible time developing mixing layer
Temporal order processing of syllables in the left parietal lobe
Speech processing requires the temporal parsing of syllable order. Individuals suffering from posterior left hemisphere brain injury often exhibit temporal processing deficits as well as language deficits. Although the right posterior inferior parietal lobe has been implicated in temporal order judgments (TOJs) of visual information, there is limited evidence to support the role of the left inferior parietal lobe (IPL) in processing syllable order. The purpose of this study was to examine whether the left inferior parietal lobe is recruited during temporal order judgments of speech stimuli. Functional magnetic resonance imaging data were collected on 14 normal participants while they completed the following forced-choice tasks: (1) syllable order of multisyllabic pseudowords, (2) syllable identification of single syllables, and (3) gender identification of both multisyllabic and monosyllabic speech stimuli. Results revealed increased neural recruitment in the left inferior parietal lobe when participants made judgments about syllable order compared with both syllable identification and gender identification. These findings suggest that the left inferior parietal lobe plays an important role in processing syllable order and support the hypothesized role of this region as an interface between auditory speech and the articulatory code. Furthermore, a breakdown in this interface may explain some components of the speech deficits observed after posterior damage to the left hemisphere
Constructive counterexamples to additivity of minimum output R\'enyi entropy of quantum channels for all p>2
We present a constructive example of violation of additivity of minimum
output R\'enyi entropy for each p>2. The example is provided by antisymmetric
subspace of a suitable dimension. We discuss possibility of extension of the
result to go beyond p>2 and obtain additivity for p=0 for a class of
entanglement breaking channels.Comment: 4 pages; a reference adde
Probing the electron-phonon coupling in ozone-doped graphene by Raman spectroscopy
We have investigated the effects of ozone treatment on graphene by Raman
scattering. Sequential ozone short-exposure cycles resulted in increasing the
doping levels as inferred from the blue shift of the 2 and peak
frequencies, without introducing significant disorder. The two-phonon 2 and
2 Raman peak intensities show a significant decrease, while, on the
contrary, the one-phonon G Raman peak intensity remains constant for the whole
exposure process. The former reflects the dynamics of the photoexcited
electrons (holes) and, specifically, the increase of the electron-electron
scattering rate with doping. From the ratio of 2 to 2 intensities, which
remains constant with doping, we could extract the ratio of electron-phonon
coupling parameters. This ratio is found independent on the number of layers up
to ten layers. Moreover, the rate of decrease of 2 and 2 intensities
with doping was found to slowdown inversely proportional to the number of
graphene layers, revealing the increase of the electron-electron collision
probability
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