3,395 research outputs found
Regge Asymptotics of Scattering with Flavour Exchange in QCD
The contribution to the perturbative Regge asymptotics of the exchange of two
reggeized fermions with opposite helicity is investigated. The methods of
conformal symmetry known for the case of gluon exchange are extended to this
case where double-logarithmic contributions dominate the asymptotics. The Regge
trajectories at large momentum transfer are calculated.Comment: 18 pages LATEX, 3 figures using package FEYNMAN, N3-9
Orthogonal and symplectic Yangians and Yang-Baxter R-operators
Yang-Baxter R operators symmetric with respect to the orthogonal and
symplectic algebras are considered in an uniform way. Explicit forms for the
spinorial and metaplectic R operators are obtained. L operators, obeying the
RLL relation with the orthogonal or symplectic fundamental R matrix, are
considered in the interesting cases, where their expansion in inverse powers of
the spectral parameter is truncated. Unlike the case of special linear algebra
symmetry the truncation results in additional conditions on the Lie algebra
generators of which the L operators is built and which can be fulfilled in
distinguished representations only. Further, generalised L operators, obeying
the modified RLL relation with the fundamental R matrix replaced by the
spinorial or metaplectic one, are considered in the particular case of linear
dependence on the spectral parameter. It is shown how by fusion with respect to
the spinorial or metaplectic representation these first order spinorial L
operators reproduce the ordinary L operators with second order truncation.Comment: 24 page
A rocket ozonesonde for geophysical research and satellite intercomparison
The in-situ rocketsonde for ozone profile measurements developed and flown for geophysical research and satellite comparison is reviewed. The measurement principle involves the chemiluminescence caused by ambient ozone striking a detector and passive pumping as a means of sampling the atmosphere as the sonde descends through the atmosphere on a parachute. The sonde is flown on a meteorological sounding rocket, and flight data are telemetered via the standard meteorological GMD ground receiving system. The payload operation, sensor performance, and calibration procedures simulating flight conditions are described. An error analysis indicated an absolute accuracy of about 12 percent and a precision of about 8 percent. These are combined to give a measurement error of 14 percent
Angular-dependence of magnetization switching for a multi-domain dot: experiment and simulation
We have measured the in-plane angular variation of nucleation and
annihilation fields of a multi-domain magnetic single dot with a microsquid.
The dots are Fe/Mo(110) self-assembled in UHV, with sub-micron size and a
hexagonal shape. The angular variations were quantitatively reproduced by
micromagnetic simulations. Discontinuities in the variations are observed, and
shown to result from bifurcations related to the interplay of the non-uniform
magnetization state with the shape of the dot.Comment: 4 pages, 4 figures, for submission as a regular articl
Parton interactions in the Bjorken limit of QCD
We consider the Bjorken limit in the framework of the effective action
approach and discuss its similarities to the Regge limit. The proposed
effective action allows for a rather simple calculation of the known evolution
kernels. We represent the result in terms of two-parton interaction operators
involving gluon and quark operators depending on light-ray position and
helicity and analyze their symmetry properties.Comment: 32 pages LaTex, 4 eps-figures, comments added, minor correction
Formative peer assessment in a CSCL environment
In this case study our aim was to gain more insight in the possibilities of qualitative formative peer assessment in a computer supported collaborative learning (CSCL) environment. An approach was chosen in which peer assessment was operationalised in assessment assignments and assessment tools that were embedded in the course material. The course concerned a higher education case-based virtual seminar, in which students were asked to conduct research and write a report in small multidisciplinary teams. The assessment assignments contained the discussion of assessment criteria, the assessment of a group report of a fellow group, and writing an assessment report. A list of feedback rules was one of the assessment tools. A qualitative oriented study was conducted, focussing on the attitude of students towards peer assessment and practical use of peer assessment assignments and tools. Results showed that studentsâ attitude towards peer assessment was positive and that assessment assignments had added value. However, not all students fulfilled all assessment assignments. Recommendations for implementation of peer assessment in CSCL environments as well as suggestions for future research are discussed
Factorization of R-matrix and Baxter's Q-operator
The general rational solution of the Yang-Baxter equation with the symmetry
algebra sl(2) can be represented as the product of the simpler building blocks
denoted as R-operators. The R-operators are constructed explicitly and have
simple structure. Using the R-operators we construct the two-parametric
Baxter's Q-operator for the generic inhomogeneous periodic XXX spin chain. In
the case of homogeneous XXX spin chain it is possible to reduce the general
Q-operator to the much simpler one-parametric operator.Comment: 17 page
Next-to-leading Order Evolution of Transversity Distributions and Soffer's Inequality
We present a calculation of the two-loop splitting functions for the
evolution of the twist-2 `transversity' parton densities of transversely
polarized nucleons. We study the implications of our results for Soffer's
inequality for the case of valence quark densities.Comment: 23 Pages, LaTeX, 2 figures as eps files, final, slightly modified
version, to appear in Phys. Rev.
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