1,167 research outputs found
Does the motor system need intermittent control?
Explanation of motor control is dominated by continuous neurophysiological pathways (e.g. trans-cortical, spinal) and the continuous control paradigm. Using new theoretical development, methodology and evidence, we propose intermittent control, which incorporates a serial ballistic process within the main feedback loop, provides a more general and more accurate paradigm necessary to explain attributes highly advantageous for competitive survival and performance
Gauge approach to the specific heat in the normal state of cuprates
Many experimental features of the electronic specific heat and entropy of
high Tc cuprates in the normal state, including the nontrivial temperature
dependence of the specific heat coefficient and negative intercept of the
extrapolated entropy to T=0 for underdoped cuprates, are reproduced using the
spin-charge gauge approach to the t-J model. The entropy turns out to be
basically due to fermionic excitations, but with a temperature dependence of
the specific heat coefficient controlled by fluctuations of a gauge field
coupling them to gapful bosonic excitations. In particular the negative
intercept of the extrapolated entropy at T=0 in the pseudogap ``phase'' is
attributed to the scalar component of the gauge field, which implements the
local no-double occupancy constraint.Comment: 5 pages, 5 figure
A study of low temperature magnetic anomalies in dilute alloys by specific heat measurements
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Disorder effect in low dimensional superconductors
The quasiparticle density of states (DOS), the energy gap, the superfluid
density , and the localization effect in the s- and d-wave
superconductors with non-magnetic impurity in two dimensions (2D) are studied
numerically. For strong (unitary) scatters, we find that it is the range of the
scattering potential rather than the symmetry of the superconducting pairing
which is more important in explaining the impurity dependences of the specific
heat and the superconducting transition temperature in Zn doped YBCO. The
localization length is longer in the d-wave superconducting state than in the
normal state, even in the vicinity of the Fermi energy.Comment: 2 pages, uuencoded compressed postscript file, IRC-940610
What can we learn from comparison between cuprates and He films ? : phase separation and fluctuating superfluidity
In the underdoped, overdoped, Zn-doped or stripe-forming regions of
high- cuprate superconductors (HTSC), the superfluid density
at shows universal correlations with . Similar
strong correlations exist between 2-dimensional superfluid density and
superfluid transition temperature in thin films of He in non-porous or
porous media, and He/He film adsorbed on porous media. Based on
analogy between HTSC and He film systems, we propose a model for cuprates
where: (1) the overdoped region is characterized by a phase separation similar
to He/He; and (2) pair (boson) formation and fluctuating
superconductivity occur at separate temperatures above in the
underdoped region.Comment: 8 pages, 5 figures. Invited paper presented at the third
international conference on stripes and high-Tc superconductivity
(STRIPE-2000), Sept. 25-30th, 2000, Rome, Italy. To be published in the
International Journal of Modern Physics
Condensation Energy and High Tc Superconductivity
From an analysis of the specific heat of one of the cuprate superconductors
it is shown, that even if a large part of the experimental specific heat
associated with the superconducting phase transition is due to fluctuations,
this part must be counted when one tries to extract the condensation energy
from the data. Previous work by Chakravarty, Kee and Abrahams, where the
fluctuation part was subtracted, has resulted in an incorrect estimation of the
condensation energy.Comment: 4 pages, 5 encapsulated Postscript figures, uses ReVTeX.st
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