Embedded Ribbons of Graphene Allotropes: An Extended Defect Perspective

Four fundamental dimer manipulations can be used to produce a variety of localized and extended defect structures in graphene. Two-dimensional templates result in graphene allotropes, here viewed as extended defects, which can exhibit either metallic or semiconducting electrical character. \emph{Embedded allotropic ribbons}--i.e. thin swaths of the new allotropes--can also be created within graphene. We examine these ribbons and find that they maintain the electrical character of their parent allotrope even when only a few atoms in width. Such extended defects may facilitate the construction of monolithic electronic circuitry.Comment: 24 pages, 21 figure

A Two-Dimensional Carbon Semiconductor

We show that patterned defects can be used to disrupt the sub-lattice symmetry of graphene so as to open up a band gap. This way of modifying graphene's electronic structure does not rely on external agencies, the addition of new elements or special boundaries. The method is used to predict a planar, low energy, graphene allotrope with a band gap of 1.2 eV. This defect engineering also allows semiconducting ribbons of carbon to be fabricated within graphene. Linear arrangements of defects lead to naturally embedded ribbons of the semiconducting material in graphene, offering the prospect of two-dimensional circuit logic composed entirely of carbon.Comment: 4 pages, 5 figure

Benthic interactions in a high CO2-world

The Baltic Sea is a physically diverse habitat with a generally low species diversity. The blue mussel Mytilus edulis is widely distributed in the benthic macrozoobenthos of the Western Baltic, the main predators of which are the common sea star Asterias rubens and the shore crab Carcinus maenas. Any environmental stress influencing the predator-prey interactions between these species has the potential to shape the entire ecosystem. The current increase in atmospheric pCO2 causes a concurrent increase in the acidification of seawater and can thus pose such an environmental stress. In coastal habitats and specifically the Baltic Sea, the decrease of seawater pH can be much more pronounced than in the open ocean. In order to estimate possible interaction shifts in the macrozoobenthos under conditions of seawater acidification, this work investigates the effect of an increase in water pCO2 on the predators A. rubens and C. maenas and their consumption of M. edulis. The results of three different own studies show an impact of increased seawater pCO2 around 3500 μatm on growth and mussel consumption in adult sea stars and a seawater pCO2 of around 1200 μatm to impact growth, mussel consumption, scope for growth and righting response of juvenile A. rubens. Mussel sizes consumed, metabolism, NH4+-excretion and calcification were, however, not impacted by an increase in seawater acidification and coelomic pH not regulated by means of active bicarbonate accumulation. Crabs were impacted in metabolism, NH4+-excretion, O:N-ratio and metabolic energy loss at a seawater pCO2 of about 3500 μatm. Mussel consumption was only impacted at a pCO2 of 3500 μatm, over intermediate time spans (10 weeks), but not over a longer (six month) time span. Hemolyph pH was regulated to remain at control levels by active bicarbonate accumulation at intermediate (10 week) time spans over all levels of seawater acidification, while hemolymph pH followed the non-bicarbonate buffer line at the intermediate (around 1200 μatm) level and was only regulated at the high (around 3500 μatm) treatment level over the long (six month) time span. Moulting intervals, growth, mussel sizes consumed, carapace thickness, stability, dry weight and calcification were not influenced by seawater acidification These results indicate a change in feeding pressure on the blue mussel M. edulis under future high levels of seawater acidification. Further, A. rubens appears stronger impacted by seawater acidification than C. maenas and juvenile A. rubens even stronger than adult specimen. I conclude that seawater acidification has the potential to reshape the benthic ecosystem of the Western Baltic. This work therefore helps to understand ecosystem responses to environmental stress and contributes to making predictions on future species distributions in the Baltic Sea

Humidity effects on wire insulation breakdown strength.

Methods for the testing of the dielectric breakdown strength of insulation on metal wires under variable humidity conditions were developed. Two methods, an ASTM method and the twisted pair method, were compared to determine if the twisted pair method could be used for determination of breakdown strength under variable humidity conditions. It was concluded that, although there were small differences in outcomes between the two testing methods, the non-standard method (twisted pair) would be appropriate to use for further testing of the effects of humidity on breakdown performance. The dielectric breakdown strength of 34G copper wire insulated with double layer Poly-Thermaleze/Polyamide-imide insulation was measured using the twisted pair method under a variety of relative humidity (RH) conditions and exposure times. Humidity at 50% RH and below was not found to affect the dielectric breakdown strength. At 80% RH the dielectric breakdown strength was significantly diminished. No effect for exposure time up to 140 hours was observed at 50 or 80%RH

Urban Planning and Everyday Urbanisation: A Case Study on Bahir Dar, Ethiopia

Urbanisation in Bahir Dar, Ethiopia, poses challenges to urban living conditions. Despite large scale housing programmes from the side of the government, construction and settling processes have largely remained incremental. The author focuses on the relation between statutory planning and practices of everyday urbanisation. The findings from Bahir Dar suggest that some mundane regimes of building the city are patronised, while others are considered undesired by policy makers. Based on this insight, the author argues that urban development in Bahir Dar needs to be locally grounded, differentiated and inclusive to avoid further tendencies of segregation

Urban Planning and Everyday Urbanisation

Urbanisation in Bahir Dar, Ethiopia, poses challenges to urban living conditions. Despite large scale housing programmes from the side of the government, construction and settling processes have largely remained incremental. Nadine Appelhans focuses on the relation between statutory planning and practices of everyday urbanisation. The findings from Bahir Dar suggest that some mundane regimes of building the city are patronised, while others are considered undesired by policy makers. Based on this insight, the author argues that urban development in Bahir Dar needs to be locally grounded, differentiated and inclusive to avoid further tendencies of segregation

Synthesis of 1,2,3-triazole functionalized hyperbranched poly(ethyleneimine) and its use as multifunctional anionic macroinitiator for diglycidyl ether of bisphenol A curing

Hyperbranched poly(ethyleneimine) (PEI) has been modified by the addition of propargyl acrylate following a Michael addition reaction. On this polymer (PEI-yne) a copper (I)-catalyzed azide alkyne cycloaddition (CuAAC) has been performed to obtain a multifunctional triazole initiator (PEI-TA). After structural and thermal characterization, this polymer has been used in different proportions as anionic multifunctional macroinitiator in diglycidyl ether of bisphenol A (DGEBA) homopolymerization. The curing process has been studied by calorimetry and the thermosets obtained have been thermally characterized and compared with thermosets prepared by using 1-methylimidazole (1-MI) as standard initiator. The electron microscopy inspection of the fracture surfaces of the new materials prepared shows the formation of submicrometer particles that should enhance toughness characteristics, changing smooth fracture surfaces in 1-MI initiated materials to multi-planar surface with tortuous and thicker cracks.Postprint (author's final draft

Chapter 5 Adaptability, decarbonisation and accessibility

This chapter focuses on the status quo of transport for people in relation to integrated planning attempts in the city of Dar es Salaam. With the population increase and urban expansion, the need for transport infrastructure and mobility within Dar es Salaam is continuously growing. To manage transport development under these conditions of rapid urban growth, the Dar es Salaam Master Plan of 1979 was the last official master plan authorised by the Ministry of Lands, Housing and Human Settlements Development and has not been replaced Daladalas, small buses and the even smaller microbuses called vipanya are by far the most common way to travel in Dar es Salaam. The World Bank notes that Dar es Salaam’s four primary roads and arterial roads are dominated by public transit and walking. However, walking has not yet been sufficiently considered in transport policies in Dar es Salaam, which – unlike Nairobi – does not have a Non-Motorised Transport Policy to date

Cure behavior and thermo-mechanical properties of dual-cure thermoset resins containing functionalized fillers

Thermoset polymers are of interest for many structural applications due to their mechanical, thermal, and chemical resiliency in comparison to thermoplastic polymers. Dual-cure resins are comprised of multiple thermoset polymers that are cured using different stimuli or variations of the same stimuli (i.e. temperatures, wavelengths, etc.). Sequential curing of the resin, via UV exposure followed by thermal exposure, creates interpenetrating polymer networks which enhance the overall mechanical properties compared to either parent material. The addition of inorganic fillers alters the rheology and printability of the resin in addition to improving mechanical properties. When these fillers are functionalized with epoxy and/or acrylate groups, we hypothesize that they will not only further improve the mechanical properties, but also aid in each individual network formation. This research describes the influence of different filler materials and filler surface functionalization on the cure behavior and thermomechanical properties of a UV/thermal acrylate-epoxy dual-cure system for use in direct ink write additive manufacturing. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA000352