45,108 research outputs found
A competing order scenario of two-gap behavior in hole doped cuprates
Angle-dependent studies of the gap function provide evidence for the
coexistence of two distinct gaps in hole doped cuprates, where the gap near the
nodal direction scales with the superconducting transition temperature ,
while that in the antinodal direction scales with the pseudogap temperature. We
present model calculations which show that most of the characteristic features
observed in the recent angle-resolved photoemission spectroscopy (ARPES) as
well as scanning tunneling microscopy (STM) two-gap studies are consistent with
a scenario in which the pseudogap has a non-superconducting origin in a
competing phase. Our analysis indicates that, near optimal doping,
superconductivity can quench the competing order at low temperatures, and that
some of the key differences observed between the STM and ARPES results can give
insight into the superlattice symmetry of the competing order.Comment: 9 pages, 7 fig
Electroweak Theory Without Higgs Bosons
A perturbative SU(2)_L X U(1)_Y electroweak theory containing W, Z, photon,
ghost, lepton and quark fields, but no Higgs or other fields, gives masses to
W, Z and the non-neutrino fermions by means of an unconventional choice for the
unperturbed Lagrangian and a novel method of renormalisation. The
renormalisation extends to all orders. The masses emerge on renormalisation to
one loop. To one loop the neutrinos are massless, the A -> Z transition drops
out of the theory, the d quark is unstable and S-matrix elements are
independent of the gauge parameter xi.Comment: 27 pages, LaTex, no figures; revised for publication; accepted by
Int. J. Mod. Phys. A; includes biographical note on A. F. Nicholso
Evaluation of large area crop estimation techniques using LANDSAT and ground-derived data
The results of the Domestic Crops and Land Cover Classification and Clustering study on large area crop estimation using LANDSAT and ground truth data are reported. The current crop area estimation approach of the Economics and Statistics Service of the U.S. Department of Agriculture was evaluated in terms of the factors that are likely to influence the bias and variance of the estimator. Also, alternative procedures involving replacements for the clustering algorithm, the classifier, or the regression model used in the original U.S. Department of Agriculture procedures were investigated
Unified theory of phase separation and charge ordering in doped manganite perovskites
A unified theory is developed to explain various types of electronic
collective behaviors in doped manganites RXMnO (R = La, Pr,Nd
etc. and X = Ca, Sr, Ba etc.). Starting from a realistic electronic model, we
derive an effective Hamiltonianis by ultilizing the projection perturbation
techniques and develop a spin-charge-orbital coherent state theory, in which
the Jahn-Teller effect and the orbital degeneracy of e electrons in Mn ions
are taken into account. Physically, the experimentally observed charge ordering
state and electronic phase separation are two macroscopic quantum phenomena
with opposite physical mechanisms, and their physical origins are elucidated in
this theory. Interplay of the Jahn-Teller effect, the lattice distortion as
well as the double exchange mechanism leads to different magnetic structures
and to different charge ordering patterns and phase separation.Comment: 10 ReVTEX pages with 4 figures attache
Possible dibaryons in the quark cluster model
In the framework of RGM, the binding energy of one channel
() and are studied in the
chiral SU(3) quark cluster model. It is shown that the binding energies of the
systems are a few tens of MeV. The behavior of the chiral field is also
investigated by comparing the results with those in the SU(2) and the extended
SU(2) chiral quark models. It is found that the symmetry property of the
system makes the contribution of the relative kinetic energy
operator between two clusters attractive. This is very beneficial for forming
the bound dibaryon. Meanwhile the chiral-quark field coupling also plays a very
important role on binding. The S-wave phase shifts and the corresponding
scattering lengths of the systems are also given.Comment: LeTex with 2 ps figure
On resonant scatterers as a factor limiting carrier mobility in graphene
We show that graphene deposited on a substrate has a non-negligible density
of atomic scale defects. This is evidenced by a previously unnoticed D peak in
the Raman spectra with intensity of about 1% with respect to the G peak. We
evaluated the effect of such impurities on electron transport by mimicking them
with hydrogen adsorbates and measuring the induced changes in both mobility and
Raman intensity. If the intervalley scatterers responsible for the D peak are
monovalent, their concentration is sufficient to account for the limited
mobilities achievable in graphene on a substrate.Comment: version 2: several comments are taken into account and refs adde
Polarization-squeezed light formation in a medium with electronic Kerr nonlinearity
We analyze the formation of polarization-squeezed light in a medium with
electronic Kerr nonlinearity. Quantum Stokes parameters are considered and the
spectra of their quantum fluctuations are investigated. It is established that
the frequency at which the suppression of quantum fluctuations is the greatest
can be controlled by adjusting the linear phase difference between pulses. We
shown that by varying the intensity or the nonlinear phase shift per photon for
one pulse, one can effectively control the suppression of quantum fluctuations
of the quantum Stokes parameters.Comment: final version, RevTeX, 10 pages, 5 eps figure
Motility of small nematodes in disordered wet granular media
The motility of the worm nematode \textit{Caenorhabditis elegans} is
investigated in shallow, wet granular media as a function of particle size
dispersity and area density (). Surprisingly, we find that the nematode's
propulsion speed is enhanced by the presence of particles in a fluid and is
nearly independent of area density. The undulation speed, often used to
differentiate locomotion gaits, is significantly affected by the bulk material
properties of wet mono- and polydisperse granular media for .
This difference is characterized by a change in the nematode's waveform from
swimming to crawling in dense polydisperse media \textit{only}. This change
highlights the organism's adaptability to subtle differences in local structure
and response between monodisperse and polydisperse media
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