374 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
Emotions while awaiting lung transplantation : a comprehensive qualitative analysis
Patients awaiting lung transplantation are at risk of negative emotional and physical experiences. How do they talk about emotions? Semi-structured interviews were performed (15 patients). Categorical analysis focusing on emotion-related descriptions was organized into positive–negative–neutral descriptions: for primary and secondary emotions, evaluation processes, coping strategies, personal characteristics, emotion descriptions associated with physical states, (and) contexts were listed. Patients develop different strategies to maintain positive identity and attitude, while preserving significant others from extra emotional load. Results are discussed within various theoretical and research backgrounds, in emphasizing their importance in the definition of emotional support starting from the patient’s perspective
Magnon-mediated binding between holes in an antiferromagnet
Abstract.: The long-range forces between holes in an antiferromagnet are due to magnon exchange. The one-magnon exchange potential between two holes is proportional to cos(2 ϕ)/r 2 where r is the distance vector of the holes and ϕ is the angle between r and an axis of the square crystal lattice. One-magnon exchange leads to bound states of holes with antiparallel spins resembling d-wave symmetr
Systematic Low-Energy Effective Field Theory for Electron-Doped Antiferromagnets
In contrast to hole-doped systems which have hole pockets centered at , in lightly electron-doped antiferromagnets
the charged quasiparticles reside in momentum space pockets centered at
or . This has important consequences for
the corresponding low-energy effective field theory of magnons and electrons
which is constructed in this paper. In particular, in contrast to the
hole-doped case, the magnon-mediated forces between two electrons depend on the
total momentum of the pair. For the one-magnon exchange
potential between two electrons at distance is proportional to ,
while in the hole case it has a dependence. The effective theory
predicts that spiral phases are absent in electron-doped antiferromagnets.Comment: 25 pages, 7 figure
Homogeneous versus Spiral Phases of Hole-doped Antiferromagnets: A Systematic Effective Field Theory Investigation
Using the low-energy effective field theory for magnons and holes -- the
condensed matter analog of baryon chiral perturbation theory for pions and
nucleons in QCD -- we study different phases of doped antiferromagnets. We
systematically investigate configurations of the staggered magnetization that
provide a constant background field for doped holes. The most general
configuration of this type is either constant itself or it represents a spiral
in the staggered magnetization. Depending on the values of the low-energy
parameters, a homogeneous phase, a spiral phase, or an inhomogeneous phase is
energetically favored. The reduction of the staggered magnetization upon doping
is also investigated.Comment: 35 pages, 5 figure
Two-Hole Bound States from a Systematic Low-Energy Effective Field Theory for Magnons and Holes in an Antiferromagnet
Identifying the correct low-energy effective theory for magnons and holes in
an antiferromagnet has remained an open problem for a long time. In analogy to
the effective theory for pions and nucleons in QCD, based on a symmetry
analysis of Hubbard and t-J-type models, we construct a systematic low-energy
effective field theory for magnons and holes located inside pockets centered at
lattice momenta (\pm pi/2a,\pm pi/2a). The effective theory is based on a
nonlinear realization of the spontaneously broken spin symmetry and makes
model-independent universal predictions for the entire class of lightly doped
antiferromagnetic precursors of high-temperature superconductors. The
predictions of the effective theory are exact, order by order in a systematic
low-energy expansion. We derive the one-magnon exchange potentials between two
holes in an otherwise undoped system. Remarkably, in some cases the
corresponding two-hole Schr\"odinger equations can even be solved analytically.
The resulting bound states have d-wave characteristics. The ground state wave
function of two holes residing in different hole pockets has a d_{x^2-y^2}-like
symmetry, while for two holes in the same pocket the symmetry resembles d_{xy}.Comment: 35 pages, 11 figure
A convergent interaction engine: vocal communication among marmoset monkeys
To understand the primate origins of the human interaction engine, it is worthwhile to focus not only on great apes but also on callitrichid monkeys (marmosets and tamarins). Like humans, but unlike great apes, callitrichids are cooperative breeders, and thus habitually engage in coordinated joint actions, for instance when an infant is handed over from one group member to another. We first explore the hypothesis that these habitual cooperative interactions, the marmoset interactional ethology, are supported by the same key elements as found in the human interaction engine: mutual gaze (during joint action), turn-taking, volubility, as well as group-wide prosociality and trust. Marmosets show clear evidence of these features. We next examine the prediction that, if such an interaction engine can indeed give rise to more flexible communication, callitrichids may also possess elaborate communicative skills. A review of marmoset vocal communication confirms unusual abilities in these small primates: high volubility and large vocal repertoires, vocal learning and babbling in immatures, and voluntary usage and control. We end by discussing how the adoption of cooperative breeding during human evolution may have catalysed language evolution by adding these convergent consequences to the great ape-like cognitive system of our hominin ancestors.
This article is part of the theme issue ‘Revisiting the human ‘interaction engine’: comparative approaches to social action coordination’
The Human Upper Respiratory Tract Epithelium Is Susceptible to Flaviviruses
Flaviviruses replicate in a wide variety of species and have a broad cellular tropism. They are isolated from various body fluids, and Zika virus (ZIKV), Japanese encephalitis virus (JEV), and West Nile virus (WNV) RNAs have been detected in nasopharyngeal swabs. Consequently, we evaluated the cellular tropism and host responses upon ZIKV, JEV, WNV, and Usutu virus (USUV) infection using a relevant model of the human upper respiratory tract epithelium based on primary human nasal epithelial cells (NECs) cultured at the air-liquid interface. NECs were susceptible to all the viruses tested, and confocal analysis showed evidence of infection of ciliated and non-ciliated cells. Each flavivirus productively infected NECs, leading to apical and basolateral live virus shedding with particularly high basal release for JEV and WNV. As demonstrated by a paracellular permeability assay, the integrity of the epithelium was not affected by flavivirus infection, suggesting an active release of live virus through the basolateral surface. Also, we detected a significant secretion of interferon type III and the pro-inflammatory cytokine IP-10/CXCL10 upon infection with JEV. Taken together, our data suggest that the human upper respiratory tract epithelium is a target for flaviviruses and could potentially play a role in the spread of infection to other body compartments through basolateral virus release. Undoubtedly, further work is required to evaluate the risks and define the adapted measures to protect individuals exposed to flavivirus-contaminated body fluids
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