383 research outputs found
Direct determinations of the nucleon and pion terms at nearly physical quark masses
We present a high statistics study of the pion and nucleon light and strange
quark sigma terms using dynamical non-perturbatively improved clover
fermions with a range of pion masses down to MeV and several
volumes, up to , and lattice spacings, fm,
enabling a study of finite volume and discretisation effects for MeV. Systematics are found to be reasonably under control. For the nucleon
we obtain MeV and MeV, or equivalently
in terms of the quark fractions, , and
, where the errors include estimates of both the systematic
and statistical uncertainties. These values, together with perturbative
matching in the heavy quark limit, lead to ,
and . In addition, through the use of the
(inverse) Feynman-Hellmann theorem our results for are shown
to be consistent with the nucleon masses determined in the analysis. For the
pion we implement a method which greatly reduces excited state contamination to
the scalar matrix elements from states travelling across the temporal boundary.
This enables us to demonstrate the Gell-Mann-Oakes-Renner expectation
over our range of pion masses.Comment: 31 pages, 18 figures, v2, small changes to text and figure
Color-Coulomb Force Calculated from Lattice Coulomb Hamiltonian
The static color-Coulomb potential is calculated as the solution of a
non-linear integral equation. This equation has been derived recently as a
self-consistency condition which arises in the Coulomb Hamiltonian formulation
of lattice gauge theory when the restriction to the interior of the Gribov
horizon is implemented. The potential obtained is in qualitative agreement with
expectations, being Coulombic with logarithmic corrections at short range and
confining at long range. The values obtained for the string tension and
are in semi-quantitative agreement with lattice Monte
Carlo and phenomenological determinations.Comment: 4 pages (including 1 figure); (latex using espcrc2.sty). Talk
presented at LATTICE96(poster
Wiki SaGa: an Interactive Timeline to Visualize Historical Documents
Searching for information inside a repository of digitised historical
documents is a very common task. A timeline interface that represents the historical
content which can perform the same search function will reveal better results
to researchers. This paper presents the integration of SIMILE Timeline within a
wiki, named Wiki SaGa, containing digitised version of Sarawak Gazette. The
proposed approach allows display of events and relevant information search compared
to traditional list of documents
Scale setting and the light baryon spectrum in QCD with Wilson fermions
We determine the light baryon spectrum on ensembles generated by the
Coordinated Lattice Simulations (CLS) effort, employing flavours of
non-perturbatively improved Wilson fermions. The hadron masses are interpolated
and extrapolated within the quark mass plane, utilizing three distinct
trajectories, two of which intersect close to the physical quark mass point and
the third one approaching the SU(3) chiral limit. The results are extrapolated
to the continuum limit, utilizing six different lattice spacings ranging from
fm down to below fm. The light pion mass varies from
MeV down to MeV. In general, the spatial extent is
kept larger than four times the inverse pion mass and larger than fm,
with additional small and large volume ensembles to investigate finite size
effects. We determine the Wilson flow scales fm and from the octet
cascade ( baryon). Determining the light baryon spectrum in the continuum
limit, we find the nucleon mass MeV and the other
stable baryon masses to agree with their experimental values within sub-percent
level uncertainties. Moreover, we determine SU(3) and SU(2) chiral perturbation
theory low energy constants, including the octet and the baryon
sigma~terms MeV,
MeV,
MeV,
MeV and
MeV, as well as various parameters,
renormalization factors and improvement coefficients that are relevant for
simulations with our lattice action.Comment: 128 pages, many figure
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The value premium and time-varying volatility
Numerous studies have documented the failure of the static and conditional capital asset pricing models to explain the difference in returns between value and growth stocks. This paper examines the post-1963 value premium by employing a model that captures the time-varying total risk of the value-minus-growth portfolios. Our results show that the time-series of value premia is strongly and positively correlated with its volatility. This conclusion is robust to the criterion used to sort stocks into value and growth portfolios and to the country under review (the US and the UK). Our paper is consistent with evidence on the possible role of idiosyncratic risk in explaining equity returns, and also with a separate strand of literature concerning the relative lack of reversibility of value firms' investment decisions
Tailoring the Surface Chemistry of PEDOT:PSS to Promote Supported Lipid Bilayer Formation
This communication reports on a versatile and substrate-agnostic method to tune the surface chemistry of conducting polymers with the aim of bridging the chemical mismatch between bioelectronic devices and biological systems. As a proof of concept, the surface of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is grafted with a short-chain oligoethylene glycol monolayer to favor the formation of cell-derived supported lipid bilayers (SLBs). This method is tuned to optimize the affinity between the supported lipid bilayer and the conducting polymer, leading to significant improvements in bilayer quality and therefore electronic readouts. To validate the impact of surface functionalization on the system's ability to transduce biological phenomena into quantifiable electronic signals, the activity of a virus commonly used as a surrogate for SARS-CoV-2 (mouse hepatitis virus) is monitored with and without surface treatment. The functionalized devices exhibit significant improvements in electronic output, stemming from the improved SLB quality, therefore strengthening the case for the use of such an approach in membrane-on-a-chip systems
Extraction of Spin-Dependent Parton Densities and Their Uncertainties
We discuss techniques and results for the extraction of the nucleon's
spin-dependent parton distributions and their uncertainties from data for
polarized deep-inelastic lepton-nucleon and proton-proton scattering by means
of a global QCD analysis. Computational methods are described that
significantly increase the speed of the required calculations to a level that
allows to perform the full analysis consistently at next-to-leading order
accuracy. We examine how the various data sets help to constrain different
aspects of the quark, anti-quark, and gluon helicity distributions. Uncertainty
estimates are performed using both the Lagrange multiplier and the Hessian
approaches. We use the extracted parton distribution functions and their
estimated uncertainties to predict spin asymmetries for high-transverse
momentum pion and jet production in polarized proton-proton collisions at 500
GeV center-of-mass system energy at BNL-RHIC, as well as for W boson
production.Comment: 25 pages, 15 eps figures, v2: minor changes, final version to appear
in Phys. Rev.
Gribov Problem for Gauge Theories: a Pedagogical Introduction
The functional-integral quantization of non-Abelian gauge theories is
affected by the Gribov problem at non-perturbative level: the requirement of
preserving the supplementary conditions under gauge transformations leads to a
non-linear differential equation, and the various solutions of such a
non-linear equation represent different gauge configurations known as Gribov
copies. Their occurrence (lack of global cross-sections from the point of view
of differential geometry) is called Gribov ambiguity, and is here presented
within the framework of a global approach to quantum field theory. We first
give a simple (standard) example for the SU(2) group and spherically symmetric
potentials, then we discuss this phenomenon in general relativity, and recent
developments, including lattice calculations.Comment: 24 pages, Revtex 4. In the revised version, a statement has been
amended on page 11, and References 14, 16 and 27 have been improve
Water advance model and sensor system can reduce tail runoff in irrigated alfalfa fields
Surface irrigation, such as flood or furrow, is the predominant form of irrigation
in California for agronomic crops. Compared to other irrigation methods, however,
it is inefficient in terms of water use; large quantities of water, instead of being
used for crop production, are lost to excess deep percolation and tail runoff. In
surface-irrigated fields, irrigators commonly cut off the inflow of water when the
water advance reaches a familiar or convenient location downfield, but this experience-based
strategy has not been very successful in reducing the tail runoff water. Our study
compared conventional cutoff practices to a retroactively applied model-based cutoff
method in four commercially producing alfalfa fields in Northern California, and evaluated
the model using a simple sensor system for practical application in typical alfalfa
fields. These field tests illustrated that the model can be used to reduce tail runoff
in typical surface-irrigated fields, and using it with a wireless sensor system saves
time and labor as well as water
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