3,065 research outputs found
Rapid tooling application for the evaluation of a greensand casting defect
Abstract: The ability to produce production quality tooling, directly from CAD data, through additive manufacturing (AM) processes has obvious advantages with regards to the reduced lead time and labour costs. This, together with the ability to simulate the metal casting process, opens new doors for researchers in the field of metal casting. This paper reviews the suitability of tooling produced in PA 2200 polyamide material, for use in a research environment, where the failure of greensand, a mixture of silica sand, bentonite (clay) and water, is to be replicated as it would occur in an industrial setting
Measurement of neutron capture on Ca at thermal and thermonuclear energies
At the Karlsruhe pulsed 3.75\,MV Van de Graaff accelerator the thermonuclear
Ca(n,)Ca(8.72\,min) cross section was measured by the
fast cyclic activation technique via the 3084.5\,keV -ray line of the
Ca-decay. Samples of CaCO enriched in Ca by 77.87\,\% were
irradiated between two gold foils which served as capture standards. The
capture cross-section was measured at the neutron energies 25, 151, 176, and
218\,keV, respectively. Additionally, the thermal capture cross-section was
measured at the reactor BR1 in Mol, Belgium, via the prompt and decay
-ray lines using the same target material. The
Ca(n,)Ca cross-section in the thermonuclear and thermal
energy range has been calculated using the direct-capture model combined with
folding potentials. The potential strengths are adjusted to the scattering
length and the binding energies of the final states in Ca. The small
coherent elastic cross section of Ca+n is explained through the nuclear
Ramsauer effect. Spectroscopic factors of Ca have been extracted from
the thermal capture cross-section with better accuracy than from a recent (d,p)
experiment. Within the uncertainties both results are in agreement. The
non-resonant thermal and thermonuclear experimental data for this reaction can
be reproduced using the direct-capture model. A possible interference with a
resonant contribution is discussed. The neutron spectroscopic factors of
Ca determined from shell-model calculations are compared with the values
extracted from the experimental cross sections for Ca(d,p)Ca and
Ca(n,)Ca.Comment: 15 pages (uses Revtex), 7 postscript figures (uses psfig), accepted
for publication in PRC, uuencoded tex-files and postscript-files also
available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Ca.u
Exotic Invasive Elm Bark Beetle, \u3cem\u3eScolytus kirschii\u3c/em\u3e, Detected in South Africa
In February 2005, the exotic bark beetle, Scolytus kirschii (Curculionidae: Scolytinae), was detected infesting English elms (Ulmus procera) in Stellenbosch, South Africa. This appears to be the first report of an infestation of Scolytus species in this country. The presence of this beetle is of concern for several reasons. Scolytus kirschii is a serious pest of elms, capable of killing healthy trees, resulting in considerable economic impact. There also exists the possibility that the beetle may undergo a host switch to indigenous trees, with potentially serious ecological consequences. Furthermore, the beetle is capable of being the vector of the pathogens responsible for Dutch elm disease (DED), Ophiostoma ulmi and Ophiostoma novo-ulmi. None of the trees that we inspected in Stellenbosch exhibited symptoms or signs of DED. Isolations from infested host material likewise failed to detect these pathogens. Nonetheless, the damage to the trees by the beetles alone was sufficient to cause tree death. Future directions for research and management of the beetle in its new environment are discussed
Characterisation of Pinotage Wine During Maturation on Different Oak Products
The effect of oak contact on the phenolic composition, total antioxidant capacity (TAC) and colour of Pinotage wineswas investigated during maturation. Oak maturation included traditional treatments, such as new, second-fill andthird-fill barrels, as well as alternative treatments (oak chips, staves, extract and dust) applied in old barrels over aperiod of 28 weeks. Oak maturation using traditional and alternative treatments improved the objective colour ofPinotage wine by decreasing the L* value. Losses in TAC caused by decreased concentrations of monomeric phenoliccompounds (most anthocyanins, flavan-3-ols, flavonols and hydroxycinnamic acids) during oak maturation werenegated by increased concentrations of gallic acid and the formation of new oligomeric and polymeric pigments.Wine maturation in stainless steel containers also resulted in a decrease in anthocyanin content. The decreasein phenolic acid content for wines matured in stainless steel was less pronounced, while their flavan-3-ol contentremained stable. The new-barrel treatment had the most pronounced effect on all parameters. Oak maturation canbe used for the production of Pinotage wine when the retention of TAC is a high priority
Ophiostoma denticiliatum sp. nov. and other Ophiostoma species associated with the birch bark beetle in southern Norway
Ophiostomatoid fungi were isolated from Scolytus ratzeburgi infesting Betula pendula and B. pubescens in Norway. Fungi were identified based on morphology, DNA sequence comparison for two gene regions and phylogenetic analyses. The most abundant fungus was Ophiostoma karelicum, suggesting a specific relationship between the fungus, the vector insect and the host tree. Our results suggest that O. karelicum occurs across the geographic range of S. ratzeburgi and its close relatedness to the Dutch elm disease fungi suggests that it could be important if introduced into other parts of the world. Other fungi, only occasionally isolated from S. ratzeburgi, were identified as O. quercus and a novel taxon, described here as O. denticiliatum sp. nov
Hydrodynamic dispersion within porous biofilms
Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher's equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels' network; (2) the solute's diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport
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