272,765 research outputs found
Spin Structure of the Nucleon - Status and Recent Results
After the initial discovery of the so-called "spin crisis in the parton
model" in the 1980's, a large set of polarization data in deep inelastic
lepton-nucleon scattering was collected at labs like SLAC, DESY and CERN. More
recently, new high precision data at large x and in the resonance region have
come from experiments at Jefferson Lab. These data, in combination with the
earlier ones, allow us to study in detail the polarized parton densities, the
Q^2 dependence of various moments of spin structure functions, the duality
between deep inelastic and resonance data, and the nucleon structure in the
valence quark region. Together with complementary data from HERMES, RHIC and
COMPASS, we can put new limits on the flavor decomposition and the gluon
contribution to the nucleon spin. In this report, we provide an overview of our
present knowledge of the nucleon spin structure and give an outlook on future
experiments. We focus in particular on the spin structure functions g_1 and g_2
of the nucleon and their moments.Comment: 69 pages, 46 figures. Report to be published in "Progress in Particle
and Nuclear Physics". v2 with added references and minor edit
Pair Correlation Function of Wilson Loops
We give a path integral prescription for the pair correlation function of
Wilson loops lying in the worldvolume of Dbranes in the bosonic open and closed
string theory. The results can be applied both in ordinary flat spacetime in
the critical dimension d or in the presence of a generic background for the
Liouville field. We compute the potential between heavy nonrelativistic sources
in an abelian gauge theory in relative collinear motion with velocity v =
tanh(u), probing length scales down to r_min^2 = 2 \pi \alpha' u. We predict a
universal -(d-2)/r static interaction at short distances. We show that the
velocity dependent corrections to the short distance potential in the bosonic
string take the form of an infinite power series in the dimensionless variables
z = r_min^2/r^2, uz/\pi, and u^2.Comment: 16 pages, 1 figure, Revtex. Corrected factor of two in potential.
Some changes in discussio
The Market Fraction Hypothesis under different GP algorithms
In a previous work, inspired by observations made in many agent-based financial models, we formulated and presented the Market Fraction Hypothesis, which basically predicts a short duration for any dominant type of agents, but then a uniform distribution over all types in the long run. We then proposed a two-step approach, a rule-inference step and a rule-clustering step, to testing this hypothesis. We employed genetic programming as the rule inference engine, and applied self-organizing maps to cluster the inferred rules. We then ran tests for 10 international markets and provided a general examination of the plausibility of the hypothesis. However, because of the fact that the tests took place under a GP system, it could be argued that these results are dependent on the nature of the GP algorithm. This chapter thus serves as an extension to our previous work. We test the Market Fraction Hypothesis under two new different GP algorithms, in order to prove that the previous results are rigorous and are not sensitive to the choice of GP. We thus test again the hypothesis under the same 10 empirical datasets that were used in our previous experiments. Our work shows that certain parts of the hypothesis are indeed sensitive on the algorithm. Nevertheless, this sensitivity does not apply to all aspects of our tests. This therefore allows us to conclude that our previously derived results are rigorous and can thus be generalized
Ground resonance analysis using a substructure modeling approach
A convenient and versatile procedure for modeling and analyzing ground resonance phenomena is described and illustrated. A computer program is used which dynamically couples differential equations with nonlinear and time dependent coefficients. Each set of differential equations may represent a component such as a rotor, fuselage, landing gear, or a failed damper. Arbitrary combinations of such components may be formulated into a model of a system. When the coupled equations are formed, a procedure is executed which uses a Floquet analysis to determine the stability of the system. Illustrations of the use of the procedures along with the numerical examples are presented
Strongly Coupled Inflaton
We continue to investigate properties of the strongly coupled inflaton in a
setup introduced in arXiv:0807.3191 through the AdS/CFT correspondence. These
properties are qualitatively different from those in conventional inflationary
models. For example, in slow-roll inflation, the inflaton velocity is not
determined by the shape of potential; the fine-tuning problem concerns the dual
infrared geometry instead of the potential; the non-Gaussianities such as the
local form can naturally become large.Comment: 12 pages; v3, minor revision, comments and reference added, JCAP
versio
Lyapunov functions and the exact differential equation
Liapunov functions and exact differential equatio
Lyapunov functions for a class of Nth order nonlinear differential equations
Sequential development of quadratic polynomial into Liapunov function for nonlinear differential equation
Application of NASTRAN to TFTR toroidal field coil structures
The primary applied loads on the TF coils were electromagnetic and thermal. The complex structure and the tremendous applied loads necessitated computer type of solutions for the design problems. In the early stage of the TF coil design, many simplified finite element models were developed for the purpose of investigating the effects of material properties, supporting schemes, and coil case material on the stress levels in the case and in the copper coil. In the more sophisticated models that followed the parametric and scoping studies, the isoparametric elements, such as QUAD4, HEX8, and HEXA, were used. The analysis results from using these finite element models and the NASTRAN system were considered accurate enough to provide timely design information
Lyapunov functions from auxiliary exact differential equations
Use of auxiliary differential equations derived from nonlinear differential equations to find Lyapunov functio
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