A "poor man's approach" to modelling of micro-structured optical fibres

Based on the scalar Helmholtz equation and the finite-difference approximation, we formulate a matrix eigenvalue problem for the calculation of propagation constants, beta(omega), in micro-structured optical fibres. The method is applied to index-guiding fibres as well as air-core photonic bandgap fibres, and in both cases qualitatively correct results are found. The strength of this approach lies in its very simple numerical implementation and its ability to find eigenmodes at a specific eigenvalue, which is of great interest, when modelling defect modes in photonic bandgap fibres.Comment: 9 pages including 5 figures. Accepted for Journal of Optics A: Pure and Applied Optic

Are we making progress in mechanical weed control research?

This study investigates whether researchers’ perceptions of good research are in agreement with current research practice as reflected in Weed Research. A high degree of agreement is assumed to indicate progress. The instrument used to survey researchers perceptions was a questionnaire consisting of 28 items related to (1) research methodologies, (2) research priorities, (3) quality of publications, (4) future developments in technology and agriculture and (5) general attitudes to alternative and conventional agriculture. Questions about gender and personal research engagement were also laid down in the questionnaire. The questionnaire was sent out by e-mail to about 140 researchers on the mailing list of the EWRS – Physical and Cultural Weed Control Group and 60 questionnaires were completed and returned. An analysis of all Weed Research publications in the period 1998-2003 investigated current research practices. The questionnaire showed that researchers in the working group are not specialized. Of the respondents, only 4 researchers (7%) used 50% or more of their research hours on mechanical weed control but a total of 44 researchers (73%) were active within this area. Views on research and agriculture varied significantly within the group and two counter paradigms were identified often refereed to as alternative and dominant. The alternative paradigm was connected with organic farming and the dominant paradigm was connected with conventional agriculture. Alternative paradigmatic positions prevailed among the respondents although strong dominant positions were also represented. Females (N=15) held more alternative positions than males (P < 0.01) and researchers engaged in herbicide technology (N=13) held more dominant positions than the rest (P < 0.05). By using an alternative-dominant scale, it was evident that respondents’ perceptions of good research was linked to basic values and beliefs that determine the overall understanding of how agriculture works and should be developed. Alternative perceptions of good research, however, seemed to be inconsistent with the current research practice as reflected in Weed Research. Consistency between ideals and reality should result in (1) more multidisciplinary studies to facilitate broader perspectives on weed control, (2) more studies carried out on working farms, (3) more system approaches that include whole agro-ecosystems with farmers and other stakeholders, (4) value inquiries, (5) participative research and (6) reflective approaches. Papers published in Weed Research clearly demonstrate, that alternative research in the ideal is different from research in reality. The main difference between alternative and dominant research is in what gets studied, not in how it is studied. In conclusion, research in physical and cultural weed control may be evaluated successful in a dominant paradigmatic perspective but progress is very limited in an alternative paradigmatic perspective. There seems to exist a mismatch between ideals and reality in weed research, which challenges ideals as well as practice

The classification of p-compact groups and homotopical group theory

We survey some recent advances in the homotopy theory of classifying spaces, and homotopical group theory. We focus on the classification of p-compact groups in terms of root data over the p-adic integers, and discuss some of its consequences e.g. for finite loop spaces and polynomial cohomology rings.Comment: To appear in Proceedings of the ICM 2010

Bacillus based biocontrol on Brassica

Many bacterial strains have been shown to mediate protection to biotic stress and promote growth of plants. Different bacteria can mediate protection in different ways e.g. by inhibition, competition or increasing plant resistance. Examples of bacteria that mediate protection to plants include different Pseudomonas, Serratia and Bacillus strains. Bacillus strains have one major advantage toward other biocontrol strains and that is the ability to form spores that are resilient against chemicals and mechanical damage. I have studied the effect of four closely related Bacillus strains on plants in two different projects, one concerned with oilseed rape (Brassica napus) and the other using Arabidopsis thaliana to allow mechanistic studies of the interaction. The bacterial strains are all classified as Bacillus amyloliquefaciens. These bacterial strains have been tested for phenological effects on plants and for plant protection towards pathogens like Alternaria brassicae, Botrytis cinerea, Leptosphaeria maculans, and Verticillium longisporum. Production of antifungal compounds by the strains and the effects on the different pathogens were investigated. Two potential candidates for biocontrol were identified. Both Bacillus strains were found to provide significant protection of oilseed rape against the four pathogens. The effects of Bacillus treatment on the B. napus transcriptome were studied using the cDNA-AFLP technique. Bacillus priming had strong systemic effects on leaf transcripts but small effects on roots. This far 65 differentially expressed plant genes have been identified due to Bacillus treatment, of which many seem related to metabolism. The effect of Bacillus seed treatment has also been studied on Arabidopsis. Significant protection was achieved also here using the same two strains toward Alternaria and Leptosphaeria as well as Pseudomonas syringae as pathogens. Arabidopsis signalling mutant studies showed that functional jasmonic acid (JA) and ethylene (Et) signalling as well as Npr1 were needed for Bacillus biocontrol. Expression levels of marker genes depending on these signalling pathways showed no increase upon Bacillus treatment, while an increase of the JA dependent marker occurred after Bacillus treated plants were infected by P. syringae. Altogether, Bacillus primed biocontrol seems to be based on induced systemic resistance (ISR)

SICStus MT - A Multithreaded Execution Environment for SICStus Prolog

The development of intelligent software agents and other complex applications which continuously interact with their environments has been one of the reasons why explicit concurrency has become a necessity in a modern Prolog system today. Such applications need to perform several tasks which may be very different with respect to how they are implemented in Prolog. Performing these tasks simultaneously is very tedious without language support. This paper describes the design, implementation and evaluation of a prototype multithreaded execution environment for SICStus Prolog. The threads are dynamically managed using a small and compact set of Prolog primitives implemented in a portable way, requiring almost no support from the underlying operating system

Finite Volume Chiral Partition Functions and the Replica Method

In the framework of chiral perturbation theory we demonstrate the equivalence of the supersymmetric and the replica methods in the symmetry breaking classes of Dyson indices \beta=1 and \beta=4. Schwinger-Dyson equations are used to derive a universal differential equation for the finite volume partition function in sectors of fixed topological charge, \nu. All dependence on the symmetry breaking class enters through the Dyson index \beta. We utilize this differential equation to obtain Virasoro constraints in the small mass expansion for all \beta and in the large mass expansion for \beta=2 with arbitrary \nu. Using quenched chiral perturbation theory we calculate the first finite volume correction to the chiral condensate demonstrating how, for all \betathere exists a region in which the two expansion schemes of quenched finite volume chiral perturbation theory overlap.Comment: RevTeX, 18 pages. Some typos corrected and a note added in the introduction to section III. To appear in Phys. Rev.