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Learning Effects on Pain Generalize to Perceptually and Conceptually Similar Cues and Modify Pain Perception
Prior learning about pain can drive a placebo or nocebo effect in later settings and influence pain more broadly. This up- or down-modulation of pain is influenced by expectations and learning during conditioning. After conditioning, it has been shown that the association between the original conditioned stimulus (CS) and the unconditioned stimulus (UCS) can generalize to novel, but similar stimuli. This is known as generalization, which is seen across humans and non-human animals. The present studies tested the hypothesis that conditioning effects on pain will generalize to similar, but novel stimuli; meaning that pain will be modulated in new situations based on perceptual or conceptual similarity to previous conditioned stimuli. Two studies were conducted with healthy participants (study 1, n=40; study 2 n=36) to test the generalization of pain learning to novel, but perceptually and conceptually similar stimuli, respectively. The results of both studies show that learned conditioned pain modulation generalizes to perceptually and conceptually similar stimuli, and that explicit awareness of the cue-pain relationship was necessary for this effect. These findings provide evidence that pain perception can be modulated by generalization stimuli, which could also play a role in clinical placebo effects
Matrix Element and Strong Electron Correlation Effects in ARPES from Cuprates
We discuss selected results from our recent work concerning the ARPES
(angle-resolved photoemission) spectra from the cuprates. Our focus is on
developing an understanding of the effects of the ARPES matrix element and
those of strong electron correlations in analyzing photointensities. With
simulations on BiSrCaCuO (Bi2212), we show that the
ARPES matrix element possesses remarkable selectivity properties, such that by
tuning the photon energy and polarization, emission from the bonding or the
antibonding states can be enhanced. Moreover, at low photon energies (below 25
eV), the Fermi surface (FS) emission is dominated by transitions from just the
O-atoms in the CuO planes. In connection with strong correlation effects,
we consider the evolution with doping of the FS of
NdCeCuO (NCCO) in terms of the -- Hubbard
model Hamiltonian. We thus delineate how the FS evolves on electron doping from
the insulating state in NCCO. The Mott pseudogap is found to collapse around
optimal doping suggesting the existence of an associated quantum critical
point.Comment: 5 pages, 4 figures, accepted to be published in Journal of Physics
and Chemistry of Solid
Precision microwave dielectric and magnetic susceptibility measurements of correlated electronic materials using superconducting cavities
We analyze microwave cavity perturbation methods, and show that the technique
is an excellent, precision method to study the dynamic magnetic and dielectric
response in the frequency range. Using superconducting cavities, we
obtain exceptionally high precision and sensitivity for measurements of
relative changes. A dynamic electromagnetic susceptibility
is introduced, which
is obtained from the measured parameters: the shift of cavity resonant
frequency and quality factor . We focus on the case of a
spherical sample placed at the center of a cylindrical cavity resonant in the
mode. Depending on the sample characteristics, the magnetic
permeability , the dielectric permittivity and
the complex conductivity can be extracted from
. A full spherical wave analysis of the cavity perturbation
is given. This analysis has led to the observation of new phenomena in novel
low dimensional materials.Comment: 16 pages, 5 figure
Quantum communication networks with optical vortices
Quantum communications bring a paradigm change in internet security by using
quantum resources to establish secure keys between parties. Present-day quantum
communications networks are mainly point-to-point and use trusted nodes and key
management systems to relay the keys. Future quantum networks, including the
quantum internet, will have complex topologies in which groups of users are
connected and communicate with each-other. Here we investigate several
architectures for quantum communication networks. We show that photonic orbital
angular momentum (OAM) can be used to route quantum information between
different nodes. Starting from a simple, point-to-point network, we will
gradually develop more complex architectures: point-to-multipoint,
fully-connected and entanglement-distribution networks. As a particularly
important result, we show that an -node, fully-connected network can be
constructed with a single OAM sorter and OAM values. Our results pave the
way to construct complex quantum communication networks with minimal resources.Comment: 10 pages, 9 figure
Fate of Quasiparticle at Mott Transition and Interplay with Lifshitz Transition Studied by Correlator Projection Method
Filling-control metal-insulator transition on the two-dimensional Hubbard
model is investigated by using the correlator projection method, which takes
into account momentum dependence of the free energy beyond the dynamical
mean-field theory. The phase diagram of metals and Mott insulators is analyzed.
Lifshitz transitions occur simultaneously with metal-insulator transitions at
large Coulomb repulsion. On the other hand, they are separated each other for
lower Coulomb repulsion, where the phase sandwiched by the Lifshitz and
metal-insulator transitions appears to show violation of the Luttinger sum
rule. Through the metal-insulator transition, quasiparticles retain nonzero
renormalization factor and finite quasi-particle weight in the both sides of
the transition. This supports that the metal-insulator transition is caused not
by the vanishing renormalization factor but by the relative shift of the Fermi
level into the Mott gap away from the quasiparticle band, in sharp contrast
with the original dynamical mean-field theory. Charge compressibility diverges
at the critical end point of the first-order Lifshitz transition at finite
temperatures. The origin of the divergence is ascribed to singular momentum
dependence of the quasiparticle dispersion.Comment: 24 pages including 10 figure
Characteristic features of the temperature dependence of the surface impedance in polycrystalline MgB samples
The real and imaginary parts of the surface impedance
in polycrystalline MgB samples of different density
with the critical temperature K are measured at the frequency
of 9.4 GHz and in the temperature range K. The normal skin-effect
condition at holds only for the samples of the
highest density with roughness sizes not more than 0.1 m. For such samples
extrapolation of the linear at temperature dependences
and results in values of the London
penetration depth \AA and residual surface resistance
m. In the entire temperature range the dependences
and are well described by the modified two-fluid model.Comment: 7 pages, 3 figures. Europhysics Letters, accepted for publicatio
Influence of spin structures and nesting on Fermi surface and a pseudogap anisotropy in t-t'-U Hubbard model
Influence of two type of spin structures on the form of the Fermi surface
(FS) and a photoemission intensity map is studied for t-t'-U Hubbard model.
Mean field calculations are done for the stripe phase and for the spiral spin
structure. It is shown, that unlike a case of electron doping, the hole-doped
models are unstable with respect to formation of such structures. The pseudogap
anisotropies are different for h- and e- doping. In accordance with ARPES data
for La2SrxCuO4 the stripe phase is characterized by quasi-one-dimensional
segments of FS at k=(\pi,0) and by suppression of spectral weight in diagonal
direction. It is shown that spiral structures display the polarisation
anisotropy: different segments of FS correspond to electros with different spin
polarisations.Comment: 12 pages, 4 figure
Remnant Fermi Surfaces in Photoemission
Recent experiments have introduced a new concept for analyzing the
photoemission spectra of correlated electrons -- the remnant Fermi surface
(rFs), which can be measured even in systems which lack a conventional Fermi
surface. Here, we analyze the rFs in a number of interacting electron models,
and find that the results fall into two classes. For systems with pairing
instabilities, the rFs is an accurate replica of the true Fermi surface. In the
presence of nesting instabilities, the rFs is a map of the resulting
superlattice Brillouin zone. The results suggest that the gap in Ca_2CuO_2Cl_2
is of nesting origin.Comment: 4 pages LaTex, 3 ps figure
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