12,789 research outputs found
Nonequilibrium quantum phase transition in itinerant electron systems
We study the effect of the voltage bias on the ferromagnetic phase transition
in a one-dimensional itinerant electron system. The applied voltage drives the
system into a nonequilibrium steady state with a non-zero electric current. The
bias changes the universality class of the second order ferromagnetic
transition. While the equilibrium transition belongs to the universality class
of the uniaxial ferroelectric, we find the mean-field behavior near the
nonequilibrium critical point.Comment: Final version as accepted to Phys. Rev. Let
Projective measurement in nuclear magnetic resonance
It is demonstrated that nuclear magnetic resonance experiments using
pseudopure spin states can give possible outcomes of projective quantum
measurement and probabilities of such outcomes. The physical system is a
cluster of six dipolar-coupled nuclear spins of benzene in a liquid-crystalline
matrix. For this system with the maximum total spin S=3, the results of
measuring are presented for the cases when the state of the system is one
of the eigenstates of .Comment: 9 pages incluing 3 figure
Phyllosilicate Transitions in Ferromagnesian Soils: Short-Range Order Materials and Smectites Dominate Secondary Phases
Analyses of X-ray diffraction (XRD) patterns taken by the CheMin instrument on the Curiosity Rover in Gale crater have documented the presence of clay minerals interpreted as smectites and a suite of amorphous to short-range order materials termed X-ray amorphous materials. These X-ray amorphous materials are commonly ironrich and aluminum poor and likely some of them are weathering products rather than primary glasses due to the presence of volatiles. Outstanding questions remain regarding the chemical composition and mineral structure of these X-ray amorphous materials and the smectites present at Gale crater and what they indicate about environmental conditions during their formation. To gain a better understanding of the mineral transitions that occur within ferromagnesian parent materials, we have investigated the development of secondary clay minerals and shortrange order materials in two soil chronosequences with varying climates developing on ultramafic bedrock. Field Sites: We investigated soil weathering within two field locations, the Klamath Mountains of Northern California, and the Tablelands of Newfoundland, Canada. Both sites possess age dated or correlated recently deglaciated soils and undated but substantially older soils. In the Klamath mountains the Trinity Ultramafic Body was deglaciated roughly 15,000 years bp while in the Tablelands a moraine was dated to about 17,600 years bp. The Klamath Mountains feature a seasonally wet and dry climate while the Tablelands are wet year-round with saturated soil conditions observed during sampling and standing water observed within 3 of 4 soil pit sampling locations
On Some Positivity Properties of the Interquark Potential in QCD
We prove that the Fourier transform of the exponential e^{-\b V(R)} of the
{\bf static} interquark potential in QCD is positive. It has been shown by
Eliott Lieb some time ago that this property allows in the same limit of static
spin independent potential proving certain mass relation between baryons with
different quark flavors.Comment: 6 pages, latex with one postscript figur
Exact Diagonalisation of The XY-Hamiltonian of Open Linear Chains with Periodic Coupling Constants and Its Application to Dynamics of One-Dimensional Spin Systems
A new method of diagonalisation of the XY-Hamiltonian of inhomogeneous open
linear chains with periodic (in space) changing Larmor frequencies and coupling
constants is developed. As an example of application, multiple quantum dynamics
of an inhomogeneous chain consisting of 1001 spins is investigated. Intensities
of multiple quantum coherences are calculated for arbitrary inhomogeneous
chains in the approximation of the next nearest interactions.
{\it Key words:} linear spin chain, nearest--neighbour approximation,
three--diagonal matrices, diagonalisation, fermions, multiple--quantum NMR,
multiple--quantum coherence, intensities of multiple--quantum coherences.
{\it PACS numbers:} 05.30.-d; 76.20.+qComment: 21 pages + 1 figure (to download separately via ps-format
Rectification in one--dimensional electronic systems
Asymmetric current--voltage () curves, known as the diode or
rectification effect, in one--dimensional electronic conductors can have their
origin from scattering off a single asymmetric impurity in the system. We
investigate this effect in the framework of the Tomonaga--Luttinger model for
electrons with spin. We show that electron interactions strongly enhance the
diode effect and lead to a pronounced current rectification even if the
impurity potential is weak. For strongly interacting electrons and not too
small voltages, the rectification current, , measuring
the asymmetry in the current--voltage curve, has a power--law dependence on the
voltage with a negative exponent, , leading to a bump in the
current--voltage curve.Comment: 9 pages; 3 figure
Dynamical Mass Generation of Composite Dirac Fermions and Fractional Quantum Hall Effects near Charge Neutrality in Graphene
We develop a composite Dirac fermion theory for the fractional quantum Hall
effects (QHE) near charge neutrality in graphene. We show that the interactions
between the composite Dirac fermions lead to dynamical mass generation through
exciton condensation. The four-fold spin-valley degeneracy is fully lifted due
to the mass generation and the exchange effects such that the odd-denominator
fractional QHE observed in the vicinity of charge neutrality can be understood
in terms of the integer QHE of the composite Dirac fermions. At the filling
factor , we show that the massive composite Dirac fermion liquid is
unstable against chiral p-wave pairing for weak Coulomb interactions and the
ground state is a paired nonabelian state described by the Moore-Read Pfaffian
in the long wavelength limit.Comment: Extended, published version, 9 pages, 3 figure
Statistical Arbitrage Mining for Display Advertising
We study and formulate arbitrage in display advertising. Real-Time Bidding
(RTB) mimics stock spot exchanges and utilises computers to algorithmically buy
display ads per impression via a real-time auction. Despite the new automation,
the ad markets are still informationally inefficient due to the heavily
fragmented marketplaces. Two display impressions with similar or identical
effectiveness (e.g., measured by conversion or click-through rates for a
targeted audience) may sell for quite different prices at different market
segments or pricing schemes. In this paper, we propose a novel data mining
paradigm called Statistical Arbitrage Mining (SAM) focusing on mining and
exploiting price discrepancies between two pricing schemes. In essence, our
SAMer is a meta-bidder that hedges advertisers' risk between CPA (cost per
action)-based campaigns and CPM (cost per mille impressions)-based ad
inventories; it statistically assesses the potential profit and cost for an
incoming CPM bid request against a portfolio of CPA campaigns based on the
estimated conversion rate, bid landscape and other statistics learned from
historical data. In SAM, (i) functional optimisation is utilised to seek for
optimal bidding to maximise the expected arbitrage net profit, and (ii) a
portfolio-based risk management solution is leveraged to reallocate bid volume
and budget across the set of campaigns to make a risk and return trade-off. We
propose to jointly optimise both components in an EM fashion with high
efficiency to help the meta-bidder successfully catch the transient statistical
arbitrage opportunities in RTB. Both the offline experiments on a real-world
large-scale dataset and online A/B tests on a commercial platform demonstrate
the effectiveness of our proposed solution in exploiting arbitrage in various
model settings and market environments.Comment: In the proceedings of the 21st ACM SIGKDD international conference on
Knowledge discovery and data mining (KDD 2015
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