Global ETD Search

1	Heliconius in a New Light: The Effects of Light Environments on Mimetic Coloration, Behavior, and Visual Systems January 2016 (has links) abstract: Although mimetic animal coloration has been studied since Darwin's time, many questions on the efficacy, evolution, and function of mimicry remain unanswered. Müller (1879) hypothesized that unpalatable individuals converge on the same conspicuous coloration to reduce predation. However, there are many cases where closely related, unpalatable species have diverged from a shared conspicuous pattern. What selection pressures have led to divergence in warning colors? Environmental factors such as ambient light have been hypothesized to affect signal transmission and efficacy in animals. Using two mimetic pairs of Heliconius butterflies, Postman and Blue-white, I tested the hypothesis that animals with divergent mimetic colors segregate by light environment to maximize conspicuousness of the aposematic warning signal under their particular environmental conditions. Each mimetic pair was found in a light environment that differed in brightness and spectral composition, which affected visual conspicuousness differently depending on mimetic color patch. I then used plasticine models in the field to test the hypothesis that mimics had higher survival in the habitat where they occurred. Although predation rates differed between the two habitats, there was no interactive effect of species by habitat type. Through choice experiments, I demonstrated that mimetic individuals preferred to spend time in the light environment where they were most often found and that their absolute visual sensitivity corresponds to the ambient lighting of their respective environment. Eye morphology was then studied to determine if differences in total corneal surface area and/or facet diameters explained the differences in visual sensitivities, but the differences found in Heliconius eye morphology did not match predictions based upon visual sensitivity. To further understand how eye morphology varies with light environments, I studied many tropical butterflies from open and closed habitats to reveal that forest understory butterflies have larger facets compared to butterflies occupying open habitats. Lastly, I tested avian perception of mimicry in a putative Heliconius mimetic assemblage and show that the perceived mimetic resemblance depends upon visual system. This dissertation reveals the importance of light environments on mimicry, coloration, behavior and visual systems of tropical butterflies. / Dissertation/Thesis / Doctoral Dissertation Biology 2016 Biology Zoology Ecology Butterflies Electroretinography Irradiance Plasticine Models Visual Models Visual Sensitivity
2	Material Flow Behavior in Friction Stir Welding Liechty, Brian C. 04 June 2008 (has links) (PDF) Material flow in friction stir welding is largely uncharacterized due to the difficulty in material flow measurement and visualization in metals. This study investigates plasticine for use as an analog for modeling material flow in friction stir welding (FSW) of metals. Qualitative comparisons between welded plasticine and metal sections exhibit many similarities. The transient temperature response of the plasticine also shows the same qualitative behavior as welds conducted in metal. To quantify its similarity to metal, the plasticine is further analyzed through compression tests to characterize its strain, strain-rate, and temperature sensitivities. A detailed analysis is presented which defines the criteria for rigorous mechanical and thermal similarity between metals and analog materials. The mechanical response of the plasticine is quantitatively similar to many aluminum and steel alloys. In addition to the mechanical properties of the plasticine, thermal properties are measured and thermal similarity is investigated. Generally, complete thermal similarity cannot be achieved in FSW. However, given the similarities between other critical parameters, and observed qualitatively similarity, it is possible to satisfy similarity approximately, such that information can be obtained from the physical model and extrapolated to metals. Using plasticine, material flow behavior in FSW is investigated under various operating conditions. The physical model permits visualization and characterization of material flow around a suspended welding tool. Depending on operating conditions, several material flow regimes are observed, including simple extrusion with substantial tool/material slip, defect formation, a region of rotating material adjacent to the tool, and vertical deformation. Material flow and frictional heating in FSW are also investigated using a three-dimensional numerical model. Two mechanical boundary conditions are investigated, including 1) a sticking constant velocity, and 2) a slipping variable shear stress model. The constant velocity model generally over-predicts the extent of material flow in the weld region. The variable shear model predicts simple extrusion of material around the tool, and substantial tool/material slip. Additionally, the variable shear model exhibits a region of diminishing shear stress, velocity, and pressure at the back advancing side of the pin, suggesting formation of an internal void. The limited deformation, low velocities, and indication of void formation agree well with flow visualization studies using plasticine under identical operating parameters. friction stir welding plasticine material flow plasticity viscoplasticity FEA/FEM Mechanical Engineering
3	Diagnostiese waarde van klei as projeksiemedium Breytenbach, Frieda 11 1900 (has links) Text in Afrikaans / he goal of this research study is to determine whether clay has any diagnostic value to the Educational Psychologist. The phenomenon of claywork with children has been examined by literature to determine whether this subject has been researched before. The developmental phases in claywork and the development of clayfigures are discussed, as well as the clay techniques which are applied by children. A comparison between clay as a three-dimensional medium and drawings as two-dimensional medium is made. The ways of application of clay are discussed by means of case studies. The general value of clay for the Educational Psychologist is also mentioned. On the grounds of certain short-comings in the literature study, "The Clay-feelingstory technique" is initiated and applied. For the empirical study eighty learners in the foundation phase, aged between five and nine years, were involved. Random sampling was used. This research study uses the combined method design in order to better understand the phenomenon of clay projections. Although the study is mainly qualitative in nature, some data is quantified. The research results prove that clay projections have diagnostic value, concerning the child's verbal and non-verbal messages, the way he applies clay techniques, by decoding his symbolic messages, emotions come to the fore, actions are portrayed and described, relations are revealed, themes come to the fore and needs are expressed. It also seems that clay projections can be taken in group context as an identification medium to help the child in need. It also seems that clay projections can be applied as a supplementary projection medium and that hypothesis can be verified with other exploratory media. Guidelines are given for the application and interpretation of clay as projection medium. / Educational Studies / D.Ed. (Sielkundige Opvoedkunde) Clayprojection Diagnostic value Observation Emotions Metaphor Claytherapy Playdoh Plasticine 615.85156 Clay -- Therapeutic use Occupational therapy Modeling -- Therapuetic use
4	Diagnostiese waarde van klei as projeksiemedium Breytenbach, Frieda 11 1900 (has links) Text in Afrikaans / he goal of this research study is to determine whether clay has any diagnostic value to the Educational Psychologist. The phenomenon of claywork with children has been examined by literature to determine whether this subject has been researched before. The developmental phases in claywork and the development of clayfigures are discussed, as well as the clay techniques which are applied by children. A comparison between clay as a three-dimensional medium and drawings as two-dimensional medium is made. The ways of application of clay are discussed by means of case studies. The general value of clay for the Educational Psychologist is also mentioned. On the grounds of certain short-comings in the literature study, "The Clay-feelingstory technique" is initiated and applied. For the empirical study eighty learners in the foundation phase, aged between five and nine years, were involved. Random sampling was used. This research study uses the combined method design in order to better understand the phenomenon of clay projections. Although the study is mainly qualitative in nature, some data is quantified. The research results prove that clay projections have diagnostic value, concerning the child's verbal and non-verbal messages, the way he applies clay techniques, by decoding his symbolic messages, emotions come to the fore, actions are portrayed and described, relations are revealed, themes come to the fore and needs are expressed. It also seems that clay projections can be taken in group context as an identification medium to help the child in need. It also seems that clay projections can be applied as a supplementary projection medium and that hypothesis can be verified with other exploratory media. Guidelines are given for the application and interpretation of clay as projection medium. / Educational Studies / D.Ed. (Sielkundige Opvoedkunde) Clayprojection Diagnostic value Observation Emotions Metaphor Claytherapy Playdoh Plasticine 615.85156 Clay -- Therapeutic use Occupational therapy Modeling -- Therapuetic use
5	Studies on the Effect of Process Aspects on Material Mixing and Defect Formation in Friction Stir Welding Malik, Vinayak January 2017 (has links) (PDF) Friction Stir Welding (FSW) is a rapidly growing solid state welding process and has been a proven method for welding high strength aluminium alloys which were formerly not recommended for joining by conventional fusion welding methods. Based on the information acquired from previous studies, to obtain a defect free Friction Stir (FS) weld with suitable strength, three basic requirements need to be fulfilled (i) Filling of the cavity created behind the tool pin during its traverse and ensuring satisfactory contact of filled material with newly generated surface (on advancing side trailing edge of the pin) (ii) Disrupting and distributing the oxide layer at the initial weld interface (iii) Adequate level of mixing of both side material (Adjacent and Retreating side) in similar welding. In the case of dissimilar welding mixing is desired in controlled amount (to prevent or curtail formation of intermetallics) depending on material combination. Failure to achieve the first precondition results in void. Second and third precondition are interconnected for similar FSW as adequate mixing in weld helps in disruption and distribution of oxide layer at initial weld interface. Failure to achieve this, results in Joint Line Remnant (JLR). Metal to metal contact cannot be established due to the presence of JLR (aligned oxide particles) and subsequently initial interface is left unwelded which deteriorate the static and dynamic strength of friction stir welds. The problem aggravates while friction stir welding materials with tenacious contaminant layer. Therefore, appropriate stirring (which entails large deformation and mixing) of initial weld interface is essential for successful FS welds. Hence, process aspects assisting mixing of adjacent (Advancing and Retreating side) materials need to identified and studied, which are missing in former studies. Experiments are conducted with classical FS tool (possessing frustum shaped/tapered circular pin) to analyse the effect of welding parameters (tool rotation speed, traverse speed, plunge depth, tool tilt and tool position w.r.t initial interface) and tool runout by changing these parameters over a range. Tool rotation speed, traverse speed, plunge depth and tool position with initial interface are changed continuously and tool tilt and tool runout are changed in discrete steps. Tool geometry is considered to be a prime parameter controlling the magnitude of mixing, as interaction of rotating tool with initial abutting base metal interface makes the process mechanism complex, unlike other solid state welding process, namely forge welding, diffusion welding, friction welding, explosive welding, ultrasonic welding and roll bonding. Furthermore, due to asymmetric nature of material flow in FSW process, the material located in different locations with respect to the tool is subjected to different levels of deformation. For this purpose experiments have been carried out to analyse the effect of different tool geometrical aspects on level of mixing and material flow. On the other hand, visualizing flow and mixing in metals is debatable as insertion of marker material in the weld line can alter the nature of material flow in the weld due to different material flow characteristics of the base and marker materials and introduction of additional interfaces. Further, using dissimilar materials for flow studies cannot be considered for comparison with similar friction stir welds as their flow properties are different. Therefore, an alternate experimental strategy is devised in these studies using physical modelling approach which is effective and helps in identifying and quantifying mixing observed under different tooling and process conditions. In the present investigation, plasticine of primary colours is adopted and the hue attribute of colour is used to study and quantify intermixing. Yellow and Blue plasticine are placed on advancing and retreating sides respectively. The degree of mixing is indicated by the intensity of generated green. Digital images of the cross section in weld nugget region are taken. To obtain hue component of these digital images the RGB color-maps are converted to HSV color-maps. Overall, these studies help in formulating the guidelines which are useful during tool design, and administering the process to obtain a defect free well mixed welds. Based on the experimental results following conclusions are derived. 1. Following process aspects: tool geometry, interface offset, tool rotation and tool runout demonstrate a significant impact on material mixing and breaking and dispersion of initial interface in weld nugget. Tool tilt, plunge depth, tool traverse exhibit negligible effect on degree of mixing. 2. Increase in tool rotation speed (with other parameters fixed) improves mixing substantially but can be increased to a certain limit after which voids emerge due to loss of weld nugget material in the form of flash. 3. Reducing the weld pitch (i.e. increasing tool rotation speed for a given tool traverse speed) reduces the size of the weld nugget and vice versa. Tool traverse speed largely affects advancing side material and rotation speed affects retreating side material. Therefore, for higher weld pitch advancing side material (yellow plasticine) dominates the weld nugget, whereas for lower weld pitch retreating side material (blue plasticine) dominates the weld nugget. 4. The extended macro-structural feature commonly observed in FS welds occurs under influence of plunge depth. Consequently, this macro-structural feature serves as the demarcation point between shoulder affected and pin induced material flow in FS weld. 5. The degree of mixing and subsequent elimination of JLR, improves, when original interface is offset on the advancing side w.r.t tool axis for all the tools investigated in the present study. Triangular and square pin generate larger pin induced mixing which intensifies further with interface on advancing side, indicating tools with such profiles to possess larger safe zone with better mixing characteristics 6. At zero interface offset with all the process parameters fixed, tapered triangular and square pin profile tools produce welds with maximum mixing. For pins with faces, material is transported in lumps around the pin. The size of lump increases with lesser number of faces on pin. Material in the vicinity of the pin experiences spinning/whirling movement. The volume of material experiencing spinning in a single tool revolution depends on (a) weld-pitch (lesser volume of material for smaller weld pitch and vice versa) and (b) number of faces on the pin (lesser volume of material for greater number of faces and vice versa). Therefore, circular pin which can be considered to be made of infinite faces, spinning of material occurs at micro level for relatively smaller weld pitch. 7. For classical FS tool (tapered circular/frustum shape), there exists an optimum ratio (shoulder diameter/pin diameter) situated between 2.7 to 3.6 to produce void free well mixed welds. Tools with ratio of 2.7 and below possess a tendency to produce welds with void but with better mixing in weld region. Tools with ratio of 3.6 and above possess a tendency to produce void free welds but with poor mixing in weld region. Voids appear and grow under following circumstances (a) with increase in pin diameter (for a fixed shoulder diameter), (b) with decrease in shoulder diameter (for a fixed pin diameter), (c) with decrease in pin taper (for a fixed shoulder diameter and top diameter of pin). Pin length has no effect on void formation. However, it is obvious, length of root defect increases with decrease in pin length. The tooling guidelines established in this study through plasticine work can be extended to metallic friction stir welds of various thickness plates by proportionately increasing or decreasing the tool dimensions as long as they fall in the recommended range. 8. Smaller pin diameter tools exhibit higher optimum weld pitch (but with lower degree of mixing) when compared to larger pins (but with higher degree of mixing). Optimum weld pitch represents weld pitch resulting in void free welds. Consequently, tools with higher optimum weld pitch help in welding at a better rate. 9. Tool runout is replicated through tools with eccentric pins. It is interesting to note that, all the tools with pin eccentricities do not assist in mixing but tools with only certain eccentricities (0.3 and 0.6mm assisted in mixing in the present investigation). It implies that tool runout of certain values facilitate mixing in weld. On the other hand density of void increases with eccentricity of pin/tool runout. 10. In dissimilar FSW investigated with plasticine A, B, C and D possessing different flow stresses (flow stresses ascending in the order of A, B, C and D) and strain rate sensitivity of 0.24, 0.22, 0.19 and 0.18 respectively, following inferences are drawn (i) For combination A and B, weldability improves when plasticine B is on Advancing Side (AS) and A is on Retreating Side (RS). The level of mixing also improves when interface is on AS (w.r.t tool axis) for this handedness. On the contrary, severe discontinuities emerge when plasticine B is on RS and A is on AS, especially when interface is closer to the tool pin axis. (ii) For combination A and C, weldability improves when C is on AS and A is on RS. The level of mixing also enhances when interface is on AS (w.r.t tool axis) for this handedness. (iii) For combination A and D, joining is poor for both the handedness. However, nature of defect is different in both the combinations. Cracks are observed when A is located on AS and voids emerge when D is located on AS. On the other hand, placing A on AS results in weld thinning. (iv) For combination B and C, there is no appreciable change in terms of weldability and level of mixing. Both the handedness in this combination yielded fairly similar results. (v) For combination B and D, though discontinuities do not emerge with change in handedness, mixing in weld improves when B is on AS unlike to its location on RS. (vi) For combination C and D, there is no appreciable change in terms of defect formation and level of mixing with change in handedness. Both the handedness in this combination yield fairly similar results. Friction Stir Welding (FSW) Joint Line Remnant (JLR) Finite Element Thermo Mechanically Affected Zone Inter Metallic Compounds Solid State Welding Process Plasticine Mechanical Engineering
6	Birds, bats and arthropods in tropical agroforestry landscapes: Functional diversity, multitrophic interactions and crop yield Maas, Bea 20 November 2013 (has links) No description available. 630 birds bats arthropods multitrophic interactions agroforestry tropical landscape forest margin landscape functional diversity crop yield exclosure experiments experimental exclusion arthropod suppression avian predation ecosystem services mist netting point counts artificial plasticine caterpillar dummy experiment biological control monitoring mapping Lemon-bellied White-eye Grosbeak Starling Zosterops chloris Scissiostrum dubium Theobroma cacao cacao agroforestry cacao diseases cacao harvest cacao pests flying vertebrates aerial insectivores volant vertebrates logging breeding colony flower herbivory mesopredator release predatory insects ants spiders aphids Lepidoptera Coleoptera Lepidopteran larvae sustainable agriculture sustainable agroforestry management implications management recommendations applied managament extensive land use management landscape management conservation biodiversity-friendly dbh distance to forest forest proximity habitat conversion herbivory Indonesia insectivorous bats insectivorous birds invertebrates Central Sulawesi Napu valley leaf gleaning leaf herbivory pests insects phytophagous insects plant productivity remnant forest trees shade tree managament South-east Asia Paleotropics tropical landscape tree height landscape gradient local shade management Cacao Pod Borer Cherelle Wilt fruit abortion Helopeltis sulawesi deforestation habitat fragmentation land use intensification forest margin species critical decline predation experiment species-specific functions Southeast Asia biodiversity conservation mesopredators food security human welfare human well-being poverty alleviation poverty reduction smallholder cacao smallholder plantation cacao farmers sustainable cacao management landscape perspective landscape scale large scale field experiment long term field experiment human wellbeing economic importance economic value valuation ecosystem services landscape matrix yield quality yield quantity fruit productivity species identity species diversity species richness ecosystem functioning pesticide use chemical compounds complex food web tritrophic interactions wildlife-friendly rural livelihoods endangered bird species endangered bat species endemic endemic birds endemic bats beneficial impact IUCN Lore Lindu National Park bioindicator indicator species forest margin agricultural habitat agroforestry systems population density predation activity species activity cacao flower cacao pod Orthoptera linear mixed effect models Tukey Post Hoc Test AICc model selection generalized least squares restricted maximum likelihood model simplification species richness estimator species accumulation linear mixed-effects models Likelihood Ratio Test Maximum Likelihood nocturnal insects diurnal arthropods nocturnal arthropods diurnal insects landscape context Land- und Forstwirtschaft (PPN621302791)

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