2,956 research outputs found
Conditions for magnetically induced singlet d-wave superconductivity on the square lattice
It is expected that at weak to intermediate coupling, d-wave
superconductivity can be induced by antiferromagnetic fluctuations. However,
one needs to clarify the role of Fermi surface topology, density of states,
pseudogap, and wave vector of the magnetic fluctuations on the nature and
strength of the induced d-wave state. To this end, we study the generalized
phase diagram of the two-dimensional half-filled Hubbard model as a function of
interaction strength , frustration induced by second-order hopping
, and temperature . In experiment, and
can be controlled by pressure. We use the two-particle self-consistent approach
(TPSC), valid from weak to intermediate coupling. We first calculate as a
function of and the temperature and wave vector at which
the spin response function begins to grow exponentially.D-wave
superconductivity in a half-filled band can be induced by such magnetic
fluctuations at weak to intermediate coupling, but only if they are near
commensurate wave vectors and not too close to perfect nesting conditions where
the pseudogap becomes detrimental to superconductivity. For given there
is thus an optimal value of frustration where the
superconducting is maximum. The non-interacting density of states plays
little role. The symmetry d vs d of the superconducting
order parameter depends on the wave vector of the underlying magnetic
fluctuations in a way that can be understood qualitatively from simple
arguments
Characteristics of oxygen isotope substitutions in the quasiparticle spectrum of BiSrCaCuO
There is an ongoing debate about the nature of the bosonic excitations
responsible for the quasiparticle self energy in high temperature
superconductors -- are they phonons or spin fluctuations? We present a careful
analysis of the bosonic excitations as revealed by the `kink' feature at 70 meV
in angle resolved photoemission data using Eliashberg theory for a d-wave
superconductor. Starting from the assumption that nodal quasiparticles are not
coupled to the magnetic resonance, the sharp structure at meV
can be assigned to phonons. We find that not only can we account for the shifts
of the kink energy seen on oxygen isotope substitution but also get a
quantitative estimate of the fraction of the area under the electron-boson
spectral density which is due to phonons. We conclude that for optimally doped
BiSrCaCuO phonons contribute % and
non-phononic excitations %.Comment: 6 pages, 3 figure
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Effect of Adjusting Pseudo-Guessing Parameter Estimates on Test Scaling When Item Parameter Drift Is Present
In item response theory test scaling/equating with the three-parameter model, the scaling coefficients A and B have no impact on the c-parameter estimates of the test items since the c-parameter estimates are not adjusted in the scaling/equating procedure. The main research question in this study concerned how serious the consequences would be if c-parameter estimates are not adjusted in the test equating procedure when item-parameter drift (IPD) is present. This drift is commonly observed in equating studies and hence, has been the source of considerable research. The results from a series of Monte-Carlo simulation studies conducted under 32 different combinations of conditions showed that some calibration strategies in the study, where the c-parameters were adjusted to be identical across two test forms, resulted in more robust equating performance in the presence of IPD. This paper discusses the practical effectiveness and the theoretical importance of appropriately adjusting c-parameter estimates in equating. Accessed 3,754 times on https://pareonline.net from July 04, 2015 to December 31, 2019. For downloads from January 1, 2020 forward, please click on the PlumX Metrics link to the right
Using Hierarchical Data Mining to Characterize Performance of Wireless System Configurations
This paper presents a statistical framework for assessing wireless systems
performance using hierarchical data mining techniques. We consider WCDMA
(wideband code division multiple access) systems with two-branch STTD (space
time transmit diversity) and 1/2 rate convolutional coding (forward error
correction codes). Monte Carlo simulation estimates the bit error probability
(BEP) of the system across a wide range of signal-to-noise ratios (SNRs). A
performance database of simulation runs is collected over a targeted space of
system configurations. This database is then mined to obtain regions of the
configuration space that exhibit acceptable average performance. The shape of
the mined regions illustrates the joint influence of configuration parameters
on system performance. The role of data mining in this application is to
provide explainable and statistically valid design conclusions. The research
issue is to define statistically meaningful aggregation of data in a manner
that permits efficient and effective data mining algorithms. We achieve a good
compromise between these goals and help establish the applicability of data
mining for characterizing wireless systems performance
BSML: A Binding Schema Markup Language for Data Interchange in Problem Solving Environments (PSEs)
We describe a binding schema markup language (BSML) for describing data
interchange between scientific codes. Such a facility is an important
constituent of scientific problem solving environments (PSEs). BSML is designed
to integrate with a PSE or application composition system that views model
specification and execution as a problem of managing semistructured data. The
data interchange problem is addressed by three techniques for processing
semistructured data: validation, binding, and conversion. We present BSML and
describe its application to a PSE for wireless communications system design
Higgs Structures of Dyonic Instantons
We study Higgs field configurations of dyonic instantons in spontaneously
broken (4+1)-dimensional Yang-Mills theory. The adjoint scalar field solutions
to the covariant Laplace equation in the ADHM instanton background are
constructed in general noncanonical basis, and they are used to study
explicitly the Higgs field configurations of dyonic instantons when the gauge
fields are taken by Jackiw-Nohl-Rebbi instanton solutions. For these solutions
corresponding to small instanton number we then consider in some detail the
zero locus of the Higgs field, which describes the cross section of supertubes
connecting parallel D4-branes in string theory. Also the information on the
Higgs zeroes is used to discuss the residual gauge freedom concerning the
Jackiw-Nohl-Rebbi solutions.Comment: 1+27 pages, 6 figure
Superconductivity and Pseudogap in Quasi-Two-Dimensional Metals around the Antiferromagnetic Quantum Critical Point
Spin fluctuations (SF) and SF-mediated superconductivity (SC) in
quasi-two-dimensional metals around the antiferrromagnetic (AF) quantum
critical point (QCP) are investigated by using the self-consistent
renormalization theory for SF and the strong coupling theory for SC. We
introduce a parameter y0 as a measure for the distance from the AFQCP which is
approximately proportional to (x-xc), x being the electron (e) or hole (h)
doping concentration to the half-filled band and xc being the value at the
AFQCP. We present phase diagrams in the T-y0 plane including contour maps of
the AF correlation length and AF and SC transition temperatures TN and Tc,
respectively. The Tc curve is dome-shaped with a maximum at around the AFQCP.
The calculated one-electron spectral density shows a pseudogap in the
high-density-of-states region near (pi,0) below around a certain temperature T*
and gives a contour map at the Fermi energy reminiscent of the Fermi arc. These
results are discussed in comparison with e- and h-doped high-Tc cuprates.Comment: 5 pages, 3 figure
Variational Monte Carlo Study of Electron Differentiation around Mott Transition
We study ground-state properties of the two-dimensional Hubbard model at half
filling by improving variational Monte Carlo method and by implementing
quantum-number projection and multi-variable optimization. The improved
variational wave function enables a highly accurate description of the Mott
transition and strong fluctuations in metals. We clarify how anomalous metals
appear near the first-order Mott transition. The double occupancy stays nearly
constant as a function of the on-site Coulomb interaction in the metallic phase
near the Mott transition in agreement with the previous unbiased results. This
unconventional metal at half filling is stabilized by a formation of
``electron-like pockets'' coexisting with an arc structure, which leads to a
prominent differentiation of electrons in momentum space. An abrupt collapse of
the ``pocket'' and ``arc'' drives the first-order Mott transition.Comment: 4 pages, 3 figure
Trolling in asynchronous computer-mediated communication: From user discussions to academic definitions
Whilst computer-mediated communication (CMC) can benefit users by providing quick and easy communication between those separated by time and space, it can also provide varying degrees of anonymity that may encourage a sense of impunity and freedom from being held accountable for
inappropriate online behaviour. As such, CMC is a fertile ground for studying impoliteness, whether it occurs in response to perceived threat (flaming), or as an end in its own right (trolling). Currently, first and secondorder
definitions of terms such as im/politeness (Brown and Levinson 1987; Bousfield 2008; Culpeper 2008; Terkourafi 2008), in-civility (Lakoff 2005), rudeness (Beebe 1995, Kienpointner 1997, 2008), and etiquette (Coulmas 1992), are subject to much discussion and debate, yet the CMC
phenomenon of trolling is not adequately captured by any of these terms. Following Bousfield (in press), Culpeper (2010) and others, this paper suggests that a definition of trolling should be informed first and foremost
by user discussions. Taking examples from a 172-million-word, asynchronous CMC corpus, four interrelated conditions of aggression, deception, disruption, and success are discussed. Finally, a working definition of trolling
is presented
512 THE PROPER REHABILITATION EXERCISE IN PATIENITS WITH DEGENERATIVE ARTHRITIS OF THE TOTAL KNEE ARTHROPLASTY
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