25,165 research outputs found
The Electronic States of Two Oppositely doped Mott Insulators Bilayers
We study the effect of Coulomb interaction between two oppositely doped
low-dimensional tJ model systems. We exactly show that, in the one-dimensional
case, an arbitrarily weak interaction leads to the formation of charge neutral
electron-hole pairs. We then use two different mean-field theories to address
the two-dimensional case, where inter-layer excitons also form and condense. We
propose that this results in new features which have no analog in single
layers, such as the emergence of an insulating spin liquid phase. Our simple
bilayer model might have relevance to the physics of doped Mott insulator
interfaces and of the new four layer Ba2CaCu4O8 compound.Comment: 4 pages, 1 figur
Fast gates for ion traps by splitting laser pulses
We present a fast phase gate scheme that is experimentally achievable and has an operation time more than two orders of magnitude faster than current experimental schemes for low numbers of pulses. The gate time improves with the number of pulses following an inverse power law. Unlike
implemented schemes which excite precise motional sidebands, thus limiting
the gate timescale, our scheme excites multiple motional states using discrete
ultra-fast pulses.We use beam-splitters to divide pulses into smaller components
to overcome limitations due to the finite laser pulse repetition rate. This provides
gate times faster than proposed theoretical schemes when we optimize a practical
setup
Anopheline salivary protein genes and gene families: an evolutionary overview after the whole genome sequence of sixteen Anopheles species
Background: Mosquito saliva is a complex cocktail whose pharmacological properties play an essential role in
blood feeding by counteracting host physiological response to tissue injury. Moreover, vector borne pathogens are
transmitted to vertebrates and exposed to their immune system in the context of mosquito saliva which, in virtue
of its immunomodulatory properties, can modify the local environment at the feeding site and eventually affect
pathogen transmission. In addition, the host antibody response to salivary proteins may be used to assess human
exposure to mosquito vectors. Even though the role of quite a few mosquito salivary proteins has been clarified in
the last decade, we still completely ignore the physiological role of many of them as well as the extent of their
involvement in the complex interactions taking place between the mosquito vectors, the pathogens they transmit
and the vertebrate host. The recent release of the genomes of 16 Anopheles species offered the opportunity to get
insights into function and evolution of salivary protein families in anopheline mosquitoes.
Results: Orthologues of fifty three Anopheles gambiae salivary proteins were retrieved and annotated from 18
additional anopheline species belonging to the three subgenera Cellia, Anopheles, and Nyssorhynchus. Our analysis
included 824 full-length salivary proteins from 24 different families and allowed the identification of 79 novel
salivary genes and re-annotation of 379 wrong predictions. The comparative, structural and phylogenetic analyses
yielded an unprecedented view of the anopheline salivary repertoires and of their evolution over 100 million years
of anopheline radiation shedding light on mechanisms and evolutionary forces that contributed shaping the
anopheline sialomes.
Conclusions: We provide here a comprehensive description, classification and evolutionary overview of the main
anopheline salivary protein families and identify two novel candidate markers of human exposure to malaria vectors
worldwide. This anopheline sialome catalogue, which is easily accessible as hyperlinked spreadsheet, is expected to
be useful to the vector biology community and to improve the capacity to gain a deeper understanding of
mosquito salivary proteins facilitating their possible exploitation for epidemiological and/or pathogen-vector-host
interaction studies
Generalized Chaplygin gas with and the cosmological model
The generalized Chaplygin gas model is characterized by the equation of state
. It is generally stated that the case is equivalent to a model with cosmological constant and dust (). In this work we show that, if this is true for the background equations,
this is not true for the perturbation equations. Hence, the mass spectrum
predicted for both models may differ.Comment: Latex file, 4 pages, 2 figures in eps forma
Electromagnetic response of high-Tc superconductors -- the slave-boson and doped-carrier theories
We evaluate the doping dependence of the quasiparticle current and low
temperature superfluid density in two slave-particle theories of the tt't''J
model -- the slave-boson theory and doped-carrier theory. In the slave-boson
theory, the nodal quasiparticle current renormalization factor
vanishes proportionally to the zero temperature superfluid density ;
however, we find that away from the limit displays a
much weaker doping dependence than . A similar conclusion applies to
the doped-carrier theory, which differentiates the nodal and antinodal regions
of momentum space. Due to its momentum space anisotropy, the doped-carrier
theory enhances the value of in the hole doped regime, bringing it to
quantitative agreement with experiments, and reproduces the asymmetry between
hole and electron doped cuprate superconductors. Finally, we use the
doped-carrier theory to predict a specific experimental signature of local
staggered spin correlations in doped Mott insulator superconductors which, we
propose, should be observed in STM measurements of underdoped high-Tc
compounds. This experimental signature distinguishes the doped-carrier theory
from other candidate mean-field theories of high-Tc superconductors, like the
slave-boson theory and the conventional BCS theory.Comment: 12 pages, RevTeX4, homepage http://dao.mit.edu/~we
Doped carrier formulation and mean-field theory of the tt't''J model
In the generalized-tJ model the effect of the large local Coulomb repulsion
is accounted for by restricting the Hilbert space to states with at most one
electron per site. In this case the electronic system can be viewed in terms of
holes hopping in a lattice of correlated spins, where holes are the carriers
doped into the half-filled Mott insulator. To explicitly capture the interplay
between the hole dynamics and local spin correlations we derive a new
formulation of the generalized-tJ model where doped carrier operators are used
instead of the original electron operators. This ``doped carrier'' formulation
provides a new starting point to address doped spin systems and we use it to
develop a new, fully fermionic, mean-field description of doped Mott insulators
This mean-field approach reveals a new mechanism for superconductivity, namely
spinon-dopon mixing, and we apply it to the tt't''J model as of interest to
high-temperature superconductors. In particular, we use model parameters
borrowed from band calculations and from fitting ARPES data to obtain a
mean-field phase diagram that reproduces semi-quantitatively that of hole and
electron doped cuprates. The mean-field approach hereby presented accounts for
the local antiferromagnetic and d-wave superconducting correlations which, we
show, provide a rational for the role of t' and t'' in strengthening
superconductivity as expected by experiments and other theoretical approaches.
As we discuss how t, t' and t'' affect the phase diagram, we also comment on
possible scenarios to understand the differences between as-grown and oxygen
reduced electron doped samples.Comment: 17 pages, 2 figures. Homepage http://dao.mit.edu/~wen
A curious cause of pseudo-haematuria: a neglected vaginal pessary
info:eu-repo/semantics/publishedVersio
- …