Factors driving urban biodiversity remain poorly documented in the rapidly growing tropical cities. We investigated the drivers of bird diversity in Dhaka city, located in Bangladesh, South Asia. Using existing sources, we compiled a bird checklist of the city. Next, we conducted point-count surveys of birds across its urban areas. Using field survey data, we investigated urban land cover and socioeconomic effects on resident bird species richness and abundance by applying linear regression modeling. Additionally, we performed path analyses for an in-depth understanding of direct and indirect relationships between selected urban land covers and socioeconomic variables and bird diversity. Our linear regression model assessment indicated that land cover is significantly shaping resident bird richness, whereas bird abundance is influenced by the combined effect of land cover and socioeconomic factors. Specifically, an increasing proportion of imperviousness was causing low bird richness, whereas bird abundance increased in areas with high habitat heterogeneity and proximity to parks but decreased with rising poverty (one of the major socioeconomic issues in Dhaka). Causal path analysis revealed that socioeconomic status, directly as well as indirectly mediated by urban land cover factors, affects bird diversity. Most importantly, it confirmed the greater significance of the direct negative effect of imperviousness on bird richness and of poverty on bird abundance in urban areas. This, in turn, suggests that bird diversity is favored by heterogeneous habitats and in wealthier neighborhoods. Nevertheless, overall bird diversity in Dhaka city was largely made up of generalist species of low conservation concern; species of the omnivore feeding guild and with ubiquitous habitat preferences were the most abundant. Our results represent the first step toward understanding drivers of biodiversity patterns across urban areas of tropical megacities within South Asia and contribute to a solid basis for urban biodiversity planning in the region.
Roll-drawing of full sections is an alternate process for wire drawing through a closed die, as it conserves less hard tool materials. It therefore enhances the resource efficiency of thin wire production. As the tools are rotating, the relative velocity is lower and friction is reduced. Apart from this, there is only little knowledge about the process mechanics inside the deformation region. According to the relative motion mentioned above, a neutral point should exist within the deformation region, but this hypothesis is unconfirmed until today. In the present work, a combination of an improved empirical model for the lateral spread in roll-drawing and a mechanical model for roll drawing based on the slab method is proposed. The mechanical model deviates from the well-known rolling theory by the fact that a zero deformation torque should exist on the rolls, it predicts the neutral angle, the forward-slip, the external drawing force and the roll separating force. The hypothesis of existence of a neutral point in the deformation region is supported by experimental measurements of the nonzero forward slip in the roll-drawing process. Measurement is done on copper wire, where 200 passes with initial round section sizes ranging from 2 mm to 1.3 mm with an increment of 0.1 mm are evaluated.
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