922 research outputs found
Magnetic field effects on the density of states of orthorhombic superconductors
The quasiparticle density of states in a two-dimensional d-wave
superconductor depends on the orientation of the in-plane external magnetic
field H. This is because. in the region of the gap nodes, the Doppler shift due
to the circulating supercurrents around a vortex depend on the direction of H.
For a tetragonal system the induced pattern is four-fold symmetric and, at zero
energy, the density of states exhibits minima along the node directions. But
YBa_2C_3O_{6.95} is orthorhombic because of the chains and the pattern becomes
two-fold symmetric with the position of the minima occuring when H is oriented
along the Fermi velocity at a node on the Fermi surface. The effect of impurity
scattering in the Born and unitary limit is discussed.Comment: 24 pages, 11 Figure
Local density of states induced by anisotropic impurity scattering in a d-wave superconductor
We study a single impurity effect on the local density of states in a d-wave
superconductor accounting for the momentum-dependent impurity potential. We
show that the anisotropy of the scattering potential can alter significantly
the spatial dependence of the quasiparticle density of states in the vicinity
of the impurity.Comment: 8 pages, revtex4, 14 figure
Orthorhombicity mixing of s- and d- gap components in without involving the chains
Momentum decoupling develops when forward scattering dominates the pairing
interaction and implies tendency for decorrelation between the physical
behavior in the various regions of the Fermi surface. In this regime it is
possible to obtain anisotropic s- or d-wave superconductivity even with
isotropic pairing scattering. We show that in the momentum decoupling regime
the distortion of the planes is enough to explain the experimental
reports for s- mixing in the dominantly d-wave gap of . In the
case of spin fluctuations mediated pairing instead, a large part of the
condensate must be located in the chains in order to understand the
experiments.Comment: LATEX file and 3 Postscript figure
Impact of thixotropy on flow patterns induced in a stirred tank : numerical and experimental studies
Agitation of a thixotropic shear-thinning fluid exhibiting a yield stress is investigated both experimentally and via simulations. Steady-state experiments are conducted at three impeller rotation rates (1, 2 and 8 s−1) for a tank stirred with an axial-impeller and flow-field measurements are made using particle image velocimetry (PIV) measurements. Threedimensional numerical simulations are also performed using the commercial CFD code ANSYS CFX10.0. The viscosity of the suspension is determined experimentally and is modelled using two shear-dependant laws, one of which takes into account the flow instabilities of such fluids at low shear rates. At the highest impeller speed, the flow exhibits the familiar outward pumping action associated with axial-flow impellers. However, as the impeller speed decreases, a cavern is formed around the impeller, the flow generated in the vicinity of the agitator reorganizes and its pumping capacity vanishes. An unusual flow pattern, where the radial velocity dominates, is observed experimentally at the lowest stirring speed. It is found to result from wall slip effects. Using blades with rough surfaces prevents this peculiar behaviour and mainly resolves the discrepancies between the experimental and computational results
Fermi-Liquid Interactions in d-Wave Superconductor
This article develops a quantitative quasiparticle model of the
low-temperature properties of d-wave superconductors which incorporates both
Fermi-liquid effects and band-structure effects. The Fermi-liquid interaction
effects are found to be classifiable into strong and negligible renormalizaton
effects, for symmetric and antisymmetric combinations of the energies of
and quasiparticles, respectively. A particularly
important conclusion is that the leading clean-limit temperature-dependent
correction to the superfluid density is not renormalized by Fermi-liquid
interactions, but is subject to a Fermi velocity (or mass) renormalization
effect. This leads to difficulties in accounting for the penetration depth
measurements with physically acceptable parameters, and hence reopens the
question of the quantitative validity of the quasiparticle picture.Comment: 4 page
Effect of pseudogap formation on the penetration depth of underdoped high cuprates
The penetration depth is calculated over the entire doping range of the
cuprate phase diagram with emphasis on the underdoped regime. Pseudogap
formation on approaching the Mott transition, for doping below a quantum
critical point, is described within a model based on the resonating valence
bond spin liquid which provides an ansatz for the coherent piece of the Green's
function. Fermi surface reconstruction, which is an essential element of the
model, has a strong effect on the superfluid density at T=0 producing a sharp
drop in magnitude, but does not change the slope of the linear low temperature
variation. Comparison with recent data on Bi-based cuprates provides validation
of the theory and shows that the effects of correlations, captured by
Gutzwiller factors, are essential for a qualitative understanding of the data.
We find that the Ferrell-Glover-Tinkham sum rule still holds and we compare our
results with those for the Fermi arc and the nodal liquid models.Comment: 14 pages, 9 figures, submitted to PR
Evaluating automatic LFG f-structure annotation for the Penn-II treebank
Lexical-Functional Grammar (LFG: Kaplan and Bresnan, 1982; Bresnan, 2001; Dalrymple, 2001) f-structures represent abstract syntactic information approximating to basic predicate-argument-modifier (dependency) structure or simple logical form (van Genabith and Crouch, 1996; Cahill et al., 2003a) . A number of methods have been developed (van Genabith et al., 1999a,b, 2001; Frank, 2000; Sadler et al., 2000; Frank et al., 2003) for automatically annotating treebank resources with LFG f-structure information. Until recently, however, most of this work on automatic f-structure annotation has been applied only to limited data sets, so while it may have shown lsquoproof of conceptrsquo, it has not yet demonstrated that the techniques developed scale up to much larger data sets. More recent work (Cahill et al., 2002a,b) has presented efforts in evolving and scaling techniques established in these previous papers to the full Penn-II Treebank (Marcus et al., 1994). In this paper, we present a number of quantitative and qualitative evaluation experiments which provide insights into the effectiveness of the techniques developed to automatically derive a set of f-structures for the more than 1,000,000 words and 49,000 sentences of Penn-II. Currently we obtain 94.85% Precision, 95.4% Recall and 95.09% F-Score for preds-only f-structures against a manually encoded gold standard
Enabling Hyper-Personalisation: Automated Ad Creative Generation and Ranking for Fashion e-Commerce
Homepage is the first touch point in the customer's journey and is one of the
prominent channels of revenue for many e-commerce companies. A user's attention
is mostly captured by homepage banner images (also called Ads/Creatives). The
set of banners shown and their design, influence the customer's interest and
plays a key role in optimizing the click through rates of the banners.
Presently, massive and repetitive effort is put in, to manually create
aesthetically pleasing banner images. Due to the large amount of time and
effort involved in this process, only a small set of banners are made live at
any point. This reduces the number of banners created as well as the degree of
personalization that can be achieved. This paper thus presents a method to
generate creatives automatically on a large scale in a short duration. The
availability of diverse banners generated helps in improving personalization as
they can cater to the taste of larger audience. The focus of our paper is on
generating wide variety of homepage banners that can be made as an input for
user level personalization engine. Following are the main contributions of this
paper: 1) We introduce and explain the need for large scale banner generation
for e-commerce 2) We present on how we utilize existing deep learning based
detectors which can automatically annotate the required objects/tags from the
image. 3) We also propose a Genetic Algorithm based method to generate an
optimal banner layout for the given image content, input components and other
design constraints. 4) Further, to aid the process of picking the right set of
banners, we designed a ranking method and evaluated multiple models. All our
experiments have been performed on data from Myntra (http://www.myntra.com),
one of the top fashion e-commerce players in India.Comment: Workshop on Recommender Systems in Fashion, 13th ACM Conference on
Recommender Systems, 201
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