440 research outputs found
Rapid Prototyping Using 3-D Welding
Rapid prototyping systems are based, almost exclusively on polymer, or paper materials.
The dimensions of the parts produced are limited by the volume of the processing area within
the machine, and parts tend to warp or distort due to shrinkage and lack of support. Also the
mechanical properties of the part are restricted to those of the processable materials and thus,
in many cases, required 'engineering properties' cannot be obtainedMechanical Engineerin
A method for the in vivo measurement of zebrafish tissue neutrophil lifespan.
Neutrophil function is thought to be regulated, in large part, by limitation of lifespan by apoptosis. A number of studies suggest that circulating neutrophils have a half-life of approximately 6 hours, although contradictory evidence exists. Measuring tissue neutrophil lifespan, however, is more problematic. It is thought that tissue neutrophils survive longer, perhaps with a half-life in the order of 3-5 days, but this has never been directly measured. Zebrafish are an emerging model organism, with several advantages for the study of vertebrate immunity. In zebrafish, neutrophils constitutively assume tissue locations allowing their direct study in vivo. Using a transgenic approach, neutrophils were labelled with a photoconvertible pigment, Kaede. Photoconversion parameters were optimised and the stability of the Kaede confirmed. Individual neutrophils were photoconverted by scanning a confocal 405ânm laser specifically over each cell and their survival monitored for 48 hours, revealing an in vivo half-life for zebrafish tissue neutrophils of around 120 hours (117.7âhrs, 95% CI 95.67-157.8). Laser energy did not extend neutrophil lifespan, and we conclude that this represents a lower bound for the lifespan of a resting tissue neutrophil in the developing zebrafish larva. This is the first direct measurement of the lifespan of an in vivo tissue neutrophil
Universal moduli-dependent thresholds in Z(2)xZ(2) orbifolds
In the context of a recently proposed method for computing exactly string
loop corrections regularized in the infra-red, we determine and calculate the
universal moduli-dependent part of the threshold corrections to the gauge
couplings for the symmetric orbifold model. We show that these
corrections decrease the unification scale of the underlying effective field
theory. We also comment on the relation between this infra-red regularization
scheme and other proposed methods.Comment: 12 pages, Latex, contains two figures, final version, typos correcte
Biogeochemical processes in the active layer and permafrost of a high Arctic fjord valley
Warming of ground is causing microbial decomposition of previously frozen sedimentary organic carbon in Arctic permafrost. However, the heterogeneity of the permafrost landscape and its hydrological processes result in different biogeochemical processes across relatively small scales, with implications for predicting the timing and magnitude of permafrost carbon emissions. The biogeochemical processes of iron- and sulfate-reduction produce carbon dioxide and suppress methanogenesis. Hence, in this study, the biogeochemical processes occurring in the active layer and permafrost of a high Arctic fjord valley in Svalbard are identified from the geochemical and stable isotope analysis of aqueous and particulate fractions in sediment cores collected from ice-wedge polygons with contrasting water content. In the drier polygons, only a small concentration of organic carbon (<5.40 dry weight%) has accumulated. Sediment cores from these drier polygons have aqueous and solid phase chemistries that imply sulfide oxidation coupled to carbonate and silicate dissolution, leading to high concentrations of aqueous iron and sulfate in the pore water profiles. These results are corroborated by ÎŽ34S and ÎŽ18O values of sulfate in active layer pore waters, which indicate the oxidative weathering of sedimentary pyrite utilising either oxygen or ferric iron as oxidising agents. Conversely, in the sediments of the consistently water-saturated polygons, which contain a high content of organic carbon (up to 45 dry weight%), the formation of pyrite and siderite occurred via the reduction of iron and sulfate. ÎŽ34S and ÎŽ18O values of sulfate in active layer pore waters from these water-saturated polygons display a strong positive correlation (R2 = 0.98), supporting the importance of sulfate reduction in removing sulfate from the pore water. The significant contrast in the dominant biogeochemical processes between the water-saturated and drier polygons indicates that small-scale hydrological variability between polygons induces large differences in the concentration of organic carbon and in the cycling of iron and sulfur, with ramifications for the decomposition pathway of organic carbon in permafrost environments
Dimensions of Diastemata and Associated Periodontal Food Pockets in Donkey Cheek Teeth
Equine cheek teeth (CT) diastemata often cause deep periodontal food pocketing and are therefore regarded as a painful dental disorder of equidae. However, there appears to be no information available on the size or shape of these diastemata. This post mortem study examined 16 donkey skulls (mean age = 32-years) containing 45 CT diastemata to define the anatomical shape and dimensions of these diastemata, and of the associated periodontal food pockets that occur with this disorder. Diastemata were found to more commonly involve mandibular (56.0 %) compared with maxillary CT (44.0 %), and 71.0 % of these diastemata had adjacent intercurrent dental disorders that may have predisposed donkeys to the diastemata. The median widths of all diastemata were 2.0-mm at the occlusal surface and 3.1-mm at the gingival margin, with no differences in widths between the lateral or medial aspects of diastemata. Diastemata were defined as open (60.0 %) or valve (40.0 %) based on their gross appearance. This classification was confirmed to be accurate by measurements that showed valve diastemata to have an occlusal to gingival width ratio of 0.4, in contrast to open diastemata where this ratio was 1.07. Food was impacted in 89.0 % of diastemata, but all diastemata had adjacent periodontal disease. Periodontal food pocketing was present adjacent to 76.0 % of diastemata, more commonly on the lateral aspect (73.0 % prevalence; mean pocket depth = 4.1-mm) than the medial aspect (47.0 % prevalence; mean pocket depth = 2.4-mm). The depth of periodontal pockets of diastemata was not associated with the height of the erupted crowns of adjacent CT. </jats:p
Solving the Decompactification Problem in String Theory
We investigate heterotic ground states in four dimensions in which N=4
supersymmetry is spontaneously broken to N=2. N=4 supersymmetry is restored at
a decompactification limit corresponding to . We calculate the
full moduli dependent threshold corrections and confirm that they are supressed
in the decompactification limit as expected from the restoration
of N=4 supersymmetry. This should be contrasted with the behavior of the
standard N=2 groundstates where the coupling blow up linearly with the volume
of the decompactifying manifold. This mechanism provides a solution to the
decompactification problem for the gauge coupling constants.
We also discuss how the mechanism can be implemented in ground states with
lower supersymmetry.Comment: 14pp, LaTeX some typos correcte
Assessment of weeds of cassava and farmers management practices in Nigeria
Open Access JournalLa concurrence des mauvaises herbes est un obstacle Ă la rentabilitĂ© de la production du manioc. La connaissance des espĂšces de mauvaises herbes qui affectent nĂ©gativement la productivitĂ© du manioc est essentielle pour une gestion efficace. Une Ă©tude a Ă©tĂ© conduite entre mai et juin 2014 et 2015 pour Ă©valuer les mauvaises herbes dans 200 exploitations agricoles de manioc, dans trois zones agroĂ©cologiques au Nigeria. LâAnalyse des Correspondances DĂ©tendancĂ©es (ACD) a permis dâidentifier quatre groupes distincts illustrant la variation des espĂšces de mauvaises herbes parmi les zones agroĂ©cologiques. Le pH du sol et la teneur en limon, la durĂ©e des jachĂšres, la mĂ©thode de culture et la mĂ©thode de gestion des mauvaises herbes ont contribuĂ© Ă la variation de la composition des espĂšces. LâĂ©valuation par les agriculteurs et sur le terrain ont identifiĂ© Euphorbia heterophylla, Imperata cylindrica, Aspilia africana, Panicum maximum, Chromolaena odorata, Commelina benghalensis, Digitaria horizontalis, et Rottboellia cochinchinensis comme principales mauvaises herbes du manioc. La gestion de ces mauvaises herbes par les paysans varie Ă travers les zones, suggĂ©rant ainsi que les stratĂ©gies de gestion de ces mauvaises herbes devraient ĂȘtre axĂ©es sur les zones Ă©cologiques. Dans la zone forestiĂšre humide, le dĂ©sherbage Ă la houe (51,2%) et Ă la machette (43,0%) Ă©taient les principales mĂ©thodes de contrĂŽle. Lâutilisation dâherbicides Ă©tait Ă©levĂ©e dans le sud de la savane guinĂ©enne et modĂ©rĂ©e dans la savane dĂ©rivĂ©e. LâĂ©ducation afin dâaccroitre la connaissance des agriculteurs sur la problĂ©matique des mauvaises herbes et lâamĂ©lioration de leur choix Ă la fois sur les herbicides appropriĂ©s et leur utilisation sans risque est essentielle pour une gestion efficace des mauvaises herbes dans la culture du manioc.
Competition from weeds is an obstacle to profitable cassava production. Knowledge of weed species negatively affecting productivity is essential for effective management. A field evaluation of weeds and management practices was conducted between May and June in 2014 and 2015 in 200 cassava farms in three agroecologies in Nigeria. Detrended Correspondence Analysis identified four distinct clusters depicting variation in weed species composition among the agroecologies. Soil pH and silt content, fallow length, cultivation method, and weed management method contributed to the variation in species composition. Farmers and field evaluations identified Euphorbia heterophylla, Imperata cylindrica, Aspilia africana, Panicum maximum, Chromolaena odorata, Commelina benghalensis, Digitaria horizontalis, and Rottboellia cochinchinensis as major problem weeds in cassava. Farmersâ management of these weeds varied across zones, suggesting that weed management strategies in cassava should be focused on ecological zones. In the Humid forest, hoe-weeding (51.2%) and slashing (43.0%) with machetes were the predominant methods of control. Herbicide use was high in the Southern Guinea Savanna and medium to high in the Derived Savanna (26.3-42.2%). Education to increase farmersâ knowledge of the problematic of weeds and to improve both their choice of appropriate herbicides and their safe use is critical to effective and efficient weed management in cassava
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