The Use of PIT Apertures as Windows To Measure Microfibril Angle in Chemical Pulp Fibers

A technique for measuring microfibril angle in chemical pulp fibers using polarized light is described. Pit apertures are used as windows so that measurements can be made on single cell walls behind the pit in the absence of pit membranes. Typical data are presented using two neutral sulphite anthraquinone pulps as examples. Problems in data analysis are discussed with respect to sample size and heterogeneity of the pulp. The technique can be used on unrefined softwood chemical pulp fibers

Stability and Hermitian-Einstein metrics for vector bundles on framed manifolds

We adapt the notions of stability of holomorphic vector bundles in the sense of Mumford-Takemoto and Hermitian-Einstein metrics in holomorphic vector bundles for canonically polarized framed manifolds, i.e. compact complex manifolds X together with a smooth divisor D such that K_X \otimes [D] is ample. It turns out that the degree of a torsion-free coherent sheaf on X with respect to the polarization K_X \otimes [D] coincides with the degree with respect to the complete K\"ahler-Einstein metric g_{X \setminus D} on X \setminus D. For stable holomorphic vector bundles, we prove the existence of a Hermitian-Einstein metric with respect to g_{X \setminus D} and also the uniqueness in an adapted sense.Comment: 21 pages, International Journal of Mathematics (to appear

Retaining women students in science involves more than course selection.

Difficulties in retaining women students in undergraduate science courses are well known, but reasons for the attrition are less well understood. Data from a survey of first-year chemistry students suggests that gender differences with regard to pre-entry attributes and the transition to the university, the on- campus experience, perceived competencies in academic skills and science literacy, and undergraduate transitions to work may contribute to decisions to leave science, but not necessarily to leave the university. In one university, short-term intervention strategies such as curricula changes, the addition of female faculty role models, the introduction of promotional activities, and the formation of peer support groups are increasing retention. Follow-up data from Phase Two of this study should provide other indicators, but differences in course selection between young women and men enrolled in university appear to be influenced by their values, thus contributing to differing career choices.Les difficultés à garder des étudiantes dans les cours de sciences sont bien connues mais les raisons pour le décrochage sont moins comprises. Les données d'une étude sur des étudiants dans un cours de première année de chimie suggère que les différences de genre en ce qui concerne leurs qualités avant l'inscription et la transition à l'université, l'expérience d'apprentissage postsecondaire, les capacités perçues dans les habiletés académiques, l'alphabétisme scientifique, et la transition de l'école secondaire à l'université pourraient contribuer à la décision de laisser tomber les sciences, mais pas nécessairement l'université. Dans une université, les stratégies d'intervention à court terme telles que la commission de pilotage pour les étudiants en première année, qui fait des changements au programme d'études, les modèles de rôles des femmes de la faculté, les activités promotionnelles et le soutien des groupes de pairs, semble augmenter l'inscription. Les données issues du suivi de la deuxième phase de l'étude devrait fournir d'autres indices, Mais les différences dans le choix des cours entre les jeunes femmes et les jeunes hommes qui s'inscrivent à l'université semblent influencées par les valeurs, lesquelles contribuent à différencier les choix de carrière.&nbsp

The ADHM Construction of Instantons on Noncommutative Spaces

We present an account of the ADHM construction of instantons on Euclidean space-time $\mathbb{R}^4$ from the point of view of noncommutative geometry. We recall the main ingredients of the classical construction in a coordinate algebra format, which we then deform using a cocycle twisting procedure to obtain a method for constructing families of instantons on noncommutative space-time, parameterised by solutions to an appropriate set of ADHM equations. We illustrate the noncommutative construction in two special cases: the Moyal-Groenewold plane $\mathbb{R}^4_\hbar$ and the Connes-Landi plane $\mathbb{R}^4_\theta$.Comment: Latex, 40 page

A cusp electron gun for millimeter wave gyrodevices

The experimental results of a thermionic cusp electron gun, to drive millimeter and submillimeter wave harmonic gyrodevices, are reported in this paper. Using a "smooth" magnetic field reversal formed by two coils this gun generated an annular-shaped, axis-encircling electron beam with 1.5 A current, and an adjustable velocity ratio alpha of up to 1.56 at a beam voltage of 40 kV. The beam cross-sectional shape and transported beam current were measured by a witness plate technique and Faraday cup, respectively. These measured results were found to be in excellent agreement with the simulated results using the three-dimensional code MAGIC

Brst Cohomology and Invariants of 4D Gravity in Ashtekar Variables

We discuss the BRST cohomologies of the invariants associated with the description of classical and quantum gravity in four dimensions, using the Ashtekar variables. These invariants are constructed from several BRST cohomology sequences. They provide a systematic and clear characterization of non-local observables in general relativity with unbroken diffeomorphism invariance, and could yield further differential invariants for four-manifolds. The theory includes fluctuations of the vierbein fields, but there exits a non-trivial phase which can be expressed in terms of Witten's topological quantum field theory. In this phase, the descent sequences are degenerate, and the corresponding classical solutions can be identified with the conformally self-dual sector of Einstein manifolds. The full theory includes fluctuations which bring the system out of this sector while preserving diffeomorphism invariance.Comment: 15 page

Nonsingular solutions of Hitchin's equations for noncompact gauge groups

We consider a general ansatz for solving the 2-dimensional Hitchin's equations, which arise as dimensional reduction of the 4-dimensional self-dual Yang-Mills equations, with remarkable integrability properties. We focus on the case when the gauge group G is given by a real form of SL(2,C). For G=SO(2,1), the resulting field equations are shown to reduce to either the Liouville, elliptic sinh-Gordon or elliptic sine-Gordon equations. As opposed to the compact case, given by G=SU(2), the field equations associated with the noncompact group SO(2,1) are shown to have smooth real solutions with nonsingular action densities, which are furthermore localized in some sense. We conclude by discussing some particular solutions, defined on R^2, S^2 and T^2, that come out of this ansatz.Comment: 12 pages, 3 figures. To appear in Nonlinearit

Topological field theory and physics

Topological Yang-Mills theory with the Belavin-Polyakov-Schwarz-Tyupkin $SU(2)$ instanton is solved completely, revealing an underlying multi-link intersection theory. Link invariants are also shown to survive the coupling to a certain kind of matter (hyperinstantons). The physical relevance of topological field theory and its invariants is discovered. By embedding topological Yang-Mills theory into pure Yang-Mills theory, it is shown that the topological version TQFT of a quantum field theory QFT allows us to formulate consistently the perturbative expansion of QFT in the topologically nontrivial sectors. In particular, TQFT classifies the set of good measures over the instanton moduli space and solves the inconsistency problems of the previous approaches. The qualitatively new physical implications are pointed out. Link numbers in QCD are related to a non abelian analogoue of the Aharonov-Bohm effect.Comment: 23 pages, 1 figure. Revision: additional explanation

N=2 Topological Yang-Mills Theory on Compact K\"{a}hler Surfaces

We study a topological Yang-Mills theory with $N=2$ fermionic symmetry. Our formalism is a field theoretical interpretation of the Donaldson polynomial invariants on compact K\"{a}hler surfaces. We also study an analogous theory on compact oriented Riemann surfaces and briefly discuss a possible application of the Witten's non-Abelian localization formula to the problems in the case of compact K\"{a}hler surfaces.Comment: ESENAT-93-01 & YUMS-93-10, 34pages: [Final Version] to appear in Comm. Math. Phy