278,146 research outputs found
Off-forward parton distributions and impact parameter dependence of parton structure
The connection between parton distributions as a function of the impact
parameter and off-forward parton distributions is discussed in the limit of
vanishing skewedness parameter , i.e. when the off-forwardness is purely
transverse. For the moment it is also illustrated how to relate
data to data, which is important for experimental
measurements of these observables.Comment: invited talk presented at `Light-Cone Meeting on Non-Perturbative QCD
and Hadron Phenomenology', Heidelberg, June 2000, 10 pages, elsart.st
Generalized Parton Distributions and the Spin Structure of the Nucleon
Generalized parton distributions are a new type of hadronic observables which
has recently stimulated great interest among theorists and experimentalists
alike. Introduced to delineate the spin structure of the nucleon, the orbital
angular momentum of quarks in particular, the new distributions contain vast
information about the internal structure of the nucleon, with the usual
electromagnetic form factors and Feynman parton distributions as their special
limits. While new perturbative QCD processes, such as deeply virtual Compton
scattering and exclusive meson production, have been found to measure the
distributions directly in experiments, lattice QCD offers a great promise to
provide the first-principle calculations of these interesting observables.Comment: 9 pages, plenary talk given at Lattice 2002, Cambridge, MA, US
Form factor decomposition of generalized parton distributions at leading twist
We extend the counting of generalized form factors presented in PRD63(2000)
by Ji and Lebed to the axial vector and the tensor operator at twist-2 level.
Following this, a parameterization of all higher moments in x of the tensor
(helicity flip) operator is given in terms of generalized form factors.Comment: 9 page
On scale dependence of QCD string operators
We have obtained a general solution of evolution equations for QCD twist-2
string operators in form of expansion over complete set of orthogonal
eigenfunctions of evolution kernels in coordinate-space representation. In the
leading logarithmic approximation the eigenfunctions can be determined using
constraints imposed by conformal symmetry. Explicit formulae for the LO
scale-dependence of quark and gluon twist-2 string operators are given
A Provable Smoothing Approach for High Dimensional Generalized Regression with Applications in Genomics
In many applications, linear models fit the data poorly. This article studies
an appealing alternative, the generalized regression model. This model only
assumes that there exists an unknown monotonically increasing link function
connecting the response to a single index of explanatory
variables . The generalized regression model is flexible and
covers many widely used statistical models. It fits the data generating
mechanisms well in many real problems, which makes it useful in a variety of
applications where regression models are regularly employed. In low dimensions,
rank-based M-estimators are recommended to deal with the generalized regression
model, giving root- consistent estimators of . Applications of
these estimators to high dimensional data, however, are questionable. This
article studies, both theoretically and practically, a simple yet powerful
smoothing approach to handle the high dimensional generalized regression model.
Theoretically, a family of smoothing functions is provided, and the amount of
smoothing necessary for efficient inference is carefully calculated.
Practically, our study is motivated by an important and challenging scientific
problem: decoding gene regulation by predicting transcription factors that bind
to cis-regulatory elements. Applying our proposed method to this problem shows
substantial improvement over the state-of-the-art alternative in real data.Comment: 53 page
Development of a high strength Al-Mg2Si-Mg-Zn based alloy for high pressure die casting
A high strength Al-Mg2Si-Mg-Zn based alloy has been developed for the application in high pressure die casting to provide improved mechanical properties. The effect of various alloying elements on the microstructure and mechanical properties including yield strength, ultimate tensile strength and elongation of the alloy was investigated under the as-cast and heat-treated conditions. The typical composition of the high strength alloy has been optimised to be Al-8.0wt%Mg2Si-6.0wt%Mg-3.5wt%Zn-0.6wt%Mn (Al-11.0wt%Mg-2.9wt%Si-3.5wt%Zn-0.6wt%Mn) with unavoidable trace impurities. The mechanical properties of the alloy were enhanced by a quick solution treatment followed by ageing treatment. The improved tensile properties were at a level of yield strength over 300MPa, the ultimate tensile strength over 420MPa and the elongation over 3% assessed using international standard tensile samples made by high pressure die casting. The microstructure of the die-cast alloy consisted of the primary α-Al phase, Al-Mg2Si eutectics, AlMgZn intermetallics and α-AlFeMnSi intermetallics under the as-cast condition. The AlMgZn intermetallic compound was dissolved into the Al-matrix during solution treatment and subsequently precipitated during ageing treatment for providing the effective improvement of the mechanical properties.The financial support is gratefully acknowledged for the Engineering and Physical Sciences Research Council (EPSRC) (Project number: EP/I038616/1), Technology Strategy Board (TSB) (Project number: 101172) and Jaguar Land Rover (JLR), United Kingdom
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