Solving String Field Equations: New Uses for Old Tools

It is argued that the (NS-sector) superstring field equations are integrable, i.e. their solutions are obtainable from linear equations. We adapt the 25-year-old solution-generating "dressing" method and reduce the construction of nonperturbative superstring configurations to a specific cohomology problem. The application to vacuum superstring field theory is outlined.Comment: Talk presented by O.L. at the 35th International Symposium Ahrenshoop on the Theory of Elementary Particles, Berlin, Germany, 26-30 Aug 2002; v2: minor corrections, textheight adjuste

Two-Dimensional Wess-Zumino Models at Intermediate Couplings

We consider the two-dimensional N=(2,2) Wess-Zumino model with a cubic superpotential at weak and intermediate couplings. Refined algorithms allow for the extraction of reliable masses in a region where perturbation theory no longer applies. We scrutinize the Nicolai improvement program which is supposed to guarantee lattice supersymmetry and compare the results for ordinary and non-standard Wilson fermions with those for SLAC derivatives. It turns out that this improvement completely fails to enhance simulations for Wilson fermions and only leads to better results for SLAC fermions. Furthermore, even without improvement terms the models with all three fermion species reproduce the correct values for the fermion masses in the continuum limit.Comment: 15 pages, 18 figure

Modified sorting technique to mitigate the collateral mortality of trawled school prawns (Metapenaeus macleayi)

The potential for changes to onboard handling practices in order to improve the fate of juvenile school prawns (Metapenaeus macleayi) discarded during trawling were investigated in two Australian rivers (Clarence and Hunter) by comparing a purpose-built, water-filled sorting tray against a conventional dry tray across various conditions, including the range of typical delays before the start of sorting the catch (2 min vs. 15 min). Juvenile school prawns (n= 5760), caught during 32 and 16 deployments in each river, were caged and sacrificed at four times: immediately (T0), and at 24 (T24), 72 (T72), and 120 (T12 0) hours after having been discarded. In both rivers, most mortalities occurred between T0 and T24 and, after adjusting for control deaths (<12%), were greatest for the 15-min conventional treatment (up to 41% at T120). Mixed-effects logistic models revealed that in addition to the sampling time, method of sorting, and delay in sorting, the weight of the catch, salinity, and percentage cloud cover were significant predictors of mortality. Although trawling caused some mortalities and comparable stress (measured as L -lactate) in all school prawns, use of the water tray lessened the negative impacts of some of the above factors across both the 2-min and 15-min delays in sorting so that the overall discard mortality was reduced by more than a third. When used in conjunction with selective trawls, widespread application of the water tray should help to improve the sustainability of trawling for school prawns

Digital image analysis of flatfish bleeding injury

To improve accuracy of post-release mortality predictions and facilitate the routine collection of information about physical condition of catches after commercial fishing capture, traditional visual assessment by potentially subjective human observers or raters may be automated by digital image analysis. The purpose of this study was to develop a method and device that can eliminate subjectivity in scoring external injury of commercially beam-trawled flatfish by taking standardized, high resolution images to allow for automated calculation of the % surface area of visible bleeding injury relative to the whole fish based on digital image analysis. A reference library was compiled by photographing ventral sides of 67 fish of six flatfish species of different sizes and freshness (fresh vs defrosted). All fish were sourced from the R/V Simon Stevin while beam-trawling in the Belgian coastal zone of the Southern North Sea. All images that were neither over- nor under-exposed were compiled (n = 51) and scored for the extent (%) of multifocal cutaneous petechial ('point bleeding'), and suffusion or haemorrhaging ('bruising') of the ventral head and body region, respectively, by three experienced raters using a continuous scale (between 0 and 100 %). Then, several state-of-the-art computer vision algorithms were tested on the dataset to develop a protocol that can 1) align each image; 2) identify fin, body and head regions; and 3) quantify the surface area of bleeding injury of each region by using appropriate thresholding techniques. For validation of the computer-derived % surface coverage estimates of bleeding injury, these were compared to the average rater's score. For bruising injury, a significant difference between human- vs computer-derived scores persisted. For point bleeding of the head region, computer-based estimates of % coverage were not different from those of the human raters. Overall, species, size and their freshness did not have a significant effect. By consistently recording the coverage of externally visible bleeding injury, this image analysis protocol may find its application in measuring the effect of different capture techniques on whole fish quality, and in improving vitality assessments as part of the transition towards a more sustainable fishery and the implementation of the European Landing Obligation

High Speed Cutting of Carbon Fibre Reinforced Plastics

The effects of high speed cutting (HSC) on metallic workpiece materials have been widely studied and the benefits are commonly employed in the machining industry. However, in the machining of composite materials, these effects have not yet been a focus of significant research work and core questions such as what impact HSC cutting parameters have on tool wear, process forces and workpiece quality remain open. As such, the work described in this paper shall focus on the use of HSC cutting parameters with spindle speeds up to 60000 rpm for the machining of carbon fibre reinforced composites. Workpiece quality and tool wear are quantified in dependence of cutting speed and feed rate and the known phenomena of reduced cutting forces at high cutting speeds are examined in the case of CFRP machining