1,018 research outputs found
The Temperature Evolution of the Spectral Peak in High Temperature Superconductors
Recent photoemission data in the high temperature cuprate superconductor
Bi2212 have been interpreted in terms of a sharp spectral peak with a
temperature independent lifetime, whose weight strongly decreases upon heating.
By a detailed analysis of the data, we are able to extract the temperature
dependence of the electron self-energy, and demonstrate that this intepretation
is misleading. Rather, the spectral peak loses its integrity above Tc due to a
large reduction in the electron lifetime.Comment: 5 pages, revtex, 4 encapsulated postscript figure
Dispersion of the odd magnetic resonant mode in near-optimally doped Bi2Sr2CaCu2O8+d
We report a neutron scattering study of the spin excitation spectrum in the
superconducting state of slightly overdoped Bi2Sr2CaCu2O8+d system (Tc=87 K).
We focus on the dispersion of the resonance peak in the superconducting state
that is due to a S=1 collective mode. The measured spin excitation spectrum
bears a strong similarity to the spectrum of the YBa2Cu3O6+x system for a
similar doping level i.e. x= 0.95-1), which consists of intersecting upward-
and downward-dispersing branches. A close comparison of the threshold of the
electron-hole spin flip continuum, deduced from angle resolved photo-emission
measurements in the same system, indicates that the magnetic response in the
superconducting state is confined, in both energy and momentum, below the
gapped Stoner continuum. In contrast to YBa2Cu3O6+x, the spin excitation
spectrum is broader than the experimental resolution. In the framework of an
itinerant-electron model, we quantitatively relate this intrinsic energy width
to the superconducting gap distribution observed in scanning tunnelling
microscopy experiments. Our study further suggests a significant in-plane
anisotropy of the magnetic response.Comment: 10 figure
Reliability and validity of brief psychosocial measures related to dietary behaviors
<p>Abstract</p> <p>Background</p> <p>Measures of psychosocial constructs are required to assess dietary interventions. This study evaluated brief psychosocial scales related to 4 dietary behaviors (consumption of fat, fiber/whole grains, fruits, and vegetables).</p> <p>Methods</p> <p>Two studies were conducted. Study 1 assessed two-week reliability of the psychosocial measures with a sample of 49 college students. Study 2 assessed convergent and discriminant validity of the psychosocial measures with dietary nutrient estimates from a Food Frequency Questionnaire on 441 men and 401 women enrolled in an Internet-based weight loss intervention study.</p> <p>Results</p> <p>Study 1 test-retest reliability ICCs were strong and ranged from .63 to .79. In study 2, dietary fat cons, fiber/whole grain cons and self-efficacy, fruit and vegetable cons and self-efficacy, and healthy eating social support, environmental factors, enjoyment, and change strategies demonstrated adequate correlations with the corresponding dietary nutrient estimates.</p> <p>Conclusions</p> <p>Brief psychosocial measures related to dietary behaviors demonstrated adequate reliability and in most cases validity. The strongest and most consistent scales related to dietary behaviors were healthy eating change strategies and enjoyment. Consistent convergent validity was also found for the cons of change scales. These measures can be used in intervention studies to evaluate psychosocial mediators of dietary change in overweight and obese individuals.</p
Coherent quasiparticle weight and its connection to high-T_c superconductivity from angle-resolved photoemission
In conventional superconductors, the pairing energy gap (\Delta) and
superconducting phase coherence go hand-in-hand. As the temperature is lowered,
both the energy gap and phase coherence appear at the transition temperature
T_c. In contrast, in underdoped high-T_c superconductors (HTSCs), a pseudogap
appears at a much higher temperature T^*, smoothly evolving into the
superconducting gap at T_c. Phase coherence on the other hand is only
established at T_c, signaled by the appearance of a sharp quasiparticle (QP)
peak in the excitation spectrum. Another important difference between the two
types of superconductors is in the ratio of 2\Delta / T_c=R. In BCS theory,
R~3.5, is constant. In the HTSCs this ratio varies widely, continuing to
increase in the underdoped region, where the gap increases while T_c decreases.
Here we report that in HTSCs it is the ratio z_A\Delta_m/T_c which is
approximately constant, where \Delta_m is the maximum value of the d-wave gap,
and z_A is the weight of the coherent excitations in the spectral function.
This is highly unusual, since in nearly all phase transitions, T_c is
determined by an energy scale alone. We further show that in the
low-temperature limit, z_{\it A} increases monotonically with increasing doping
x. The growth is linear, i.e. z_A(x)\propto x, in the underdoped to optimally
doped regimes, and slows down in overdoped samples. The reduction of z_A with
increasing temperature resembles that of the c-axis superfluid density.Comment: 11 pages, 5 figures, revised versio
The Underestimation Of Egocentric Distance: Evidence From Frontal Matching Tasks
There is controversy over the existence, nature, and cause of error in egocentric distance judgments. One proposal is that the systematic biases often found in explicit judgments of egocentric distance along the ground may be related to recently observed biases in the perceived declination of gaze (Durgin & Li, Attention, Perception, & Psychophysics, in press), To measure perceived egocentric distance nonverbally, observers in a field were asked to position themselves so that their distance from one of two experimenters was equal to the frontal distance between the experimenters. Observers placed themselves too far away, consistent with egocentric distance underestimation. A similar experiment was conducted with vertical frontal extents. Both experiments were replicated in panoramic virtual reality. Perceived egocentric distance was quantitatively consistent with angular bias in perceived gaze declination (1.5 gain). Finally, an exocentric distance-matching task was contrasted with a variant of the egocentric matching task. The egocentric matching data approximate a constant compression of perceived egocentric distance with a power function exponent of nearly 1; exocentric matches had an exponent of about 0.67. The divergent pattern between egocentric and exocentric matches suggests that they depend on different visual cues
Fermi liquid interactions and the superfluid density in d-wave superconductors
We construct a phenomenological superfluid Fermi liquid theory for a
two-dimensional d-wave superconductor on a square lattice, and study the effect
of quasiparticle interactions on the superfluid density. Using simple models
for the dispersion and the Landau interaction function, we illustrate the
deviation of these results from those for the isotropic superfluid. This allows
us to reconcile the value and doping dependence of the superfluid density slope
at low temperature obtained from penetration depth measurements, with
photoemission data on nodal quasiparticles.Comment: 5 latex pages, 1 eps-figure. submitted to PR
Nature of the Electronic Excitations near the Brillouin Zone Boundary of BiSrCaCuO
Based on angle resolved photoemission spectra measured on different systems
at different dopings, momenta and photon energies, we show that the anomalously
large spectral linewidth in the region of optimal doped and
underdoped BiSrCaCuO has significant contributions
from the bilayer splitting, and that the scattering rate in this region is
considerably smaller than previously estimated. This new picture of the
electronic excitation near puts additional experimental constraints
on various microscopic theories and data analysis.Comment: 5 pages, 4 figure
Perception and manipulation of game control
Humans have humorous conversations and interactions. Nowadays our real life existence is integrated with our life in social media, videogames, mixed reality and physical environments that sense our activities and that can adapt appearance and properties due to our activities. There are other inhabitants in these environments, not only human, but also virtual agents and social robots with which we interact and who decide about their participation in activities. In this paper we look at designing humor and humor opportunities in such environments, providing them with a sense of humor, and able to recognize opportunities to generate humorous interactions or events on the fly. Opportunities, made possible by introducing incongruities, can be exploited by the environment itself, or they can be communicated to its inhabitants
Phase fluctuations, dissipation and superfluid stiffness in d-wave superconductors
We study the effect of dissipation on quantum phase fluctuations in d-wave
superconductors. Dissipation, arising from a nonzero low frequency optical
conductivity which has been measured in experiments below , has two
effects: (1) a reduction of zero point phase fluctuations, and (2) a reduction
of the temperature at which one crosses over to classical thermal fluctuations.
For parameter values relevant to the cuprates, we show that the crossover
temperature is still too large for classical phase fluctuations to play a
significant role at low temperature. Quasiparticles are thus crucial in
determining the linear temperature dependence of the in-plane superfluid
stiffness. Thermal phase fluctuations become important at higher temperatures
and play a role near .Comment: Presentation improved, new references added (10 latex pages, 3 eps
figures). submitted to PR
Low energy collective modes, Ginzburg-Landau theory, and pseudogap behavior in superconductors with long-range pairing interactions
We study the superconducting instability in systems with long but finite
ranged, attractive, pairing interactions. We show that such long-ranged
superconductors exhibit a new class of fluctuations in which the internal
structure of the Cooper pair wave function is soft, and thus lead to
"pseudogap" behavior in which the actual transition temperature is greatly
depressed from its mean field value. These fluctuations are {\it not} phase
fluctuations of the standard superconducting order parameter, and lead to a
highly unusual Ginzburg-Landau description. We suggest that the crossover
between the BCS limit of a short-ranged attraction and our problem is of
interest in the context of superconductivity in the underdoped cuprates.Comment: 20 pages with one embedded ps figure. Minor revisions to the text and
references. Final version to appear in PRB on Nov. 1st, 200
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