Gel-spun polyethylene fibres. Part 2. Influence of polymer concentration and molecular weight distribution on morphology and properties

In addition to spinning temperature, spinline stretching and spinning speed, the properties of gel-spun polyethylene fibres hot-drawn to the maximum draw ratio also depend on the polymer concentration, molecular weight and molecular weight distribution. Reducing the polymer concentration reduces the number of entanglements, and fibres with better properties are obtained. However, a minimum number of entanglements is necessary to ensure sufficient coherence of the entanglement network and avoid premature breakage of the spinline. Therefore, an optimal concentration exists which is shown to shift to a lower value for polyethylene with a smaller molecular weight distribution. Fibres with a tensile strength exceeding 6 GPa and a modulus of about 160 GPa can be prepared as long as spinline stretching is avoided. A smaller molecular weight distribution enhances the deteriorating effect of spinline stretching. The difference in morphologies for as-spun fibres prepared from different gel compositions and under different spinning conditions also strongly affects the cold-drawing behaviour of the extracted as-spun fibres

Effects of the Invasive Freshwater Mussel Limnoperna fortunei on Sediment Properties and Accumulation Rates

Since its introduction into South America around 1990, the freshwater bivalve Limnoperna fortunei (the golden mussel) has spread rapidly and is now a dominant component of the benthic and periphytic fauna in many rivers, lakes, and reservoirs. Sizable impacts of this nonindigenous species on nutrient recycling, plankton abundance and composition, and trophic relationships with fishes have been reported, but its effects on the sediments have received little attention. In this work, we use eighteen 20-L flow-through experimental units with and without mussels where changes in the mass and characteristics of the sediments accumulated throughout a yearly cycle in monthly, biannual, and annual intervals are analyzed. Experimental units with mussels yielded almost 2 times more sediments than units without mussels and contained significantly higher loads of organic matter and total N. Total P was not affected by the presence of mussels. Sediments accumulated in the biannual and annual experimental units agreed well with the yields of the monthly units, but the vertical stratification of organic matter, N, and P was unpatterned. Seasonal changes in the volume of total sediments, biodeposits, and their organic matter and N contents were positively associated with ambient water temperature and with intermediate (~150–250 NTU, nephelometric turbidity units) turbidity. Our results suggest that ecosystem-wide modifications in the living conditions of the benthic epifaunal and infaunal organisms in waterbodies invaded by the mussel are likely significant, although variable locally, regionally, and across taxa.Fil: Tokumon, Romina Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin

Leadership, Teacher Learning, and Assessment: A Strategic Approach to Improving Writing Achievement

In an era with increasing accountability and pressures to increase student achievement across all levels, school-based leaders need support in bringing about such changes. The problem of practice addressed in the organizational improvement plan is stated as: A document known as Saskatchewan Reads for Administrators exists to support leadership for best practice in reading in elementary school. No such document exists for writing. The problem of practice under investigation is the need for a strategic approach to support school leaders in improving student achievement levels in writing. Attempting to address this gap in a comprehensive fashion and using a strategic approach means lending credence to the myriad of factors that makes change successful and sustainable. Facets of school structure, leadership approaches and practices focusing on instructional, distributed and teacher leadership, staff development and teacher learning through collaborative inquiry, and improved assessment techniques need to be given due attention. Improving writing achievement has long been a goal, and a struggle in Saskatchewan. Throughout the struggle, advancement in writing has not occurred, and specific areas need to be attended to in order to make it happen. To attain the lofty goals set by the province, schools need to make these areas a priority

Empower the Workforce, Empower the Company? Citizen Development Adoption

IT departments today face a substantial backlog of business innovation-related activities and struggle with a shortage of software developers. Low-code development platforms can help solve these issues by using technology to empower end-users without programming background to participate in the software development process. This trend is referred to as “citizen development.” Through six case studies, this study advances our understanding of the factors that influence organizational citizen development adoption decisions. We use an extended technology–organization–environment (TOE) framework, which enhances the explanatory power of the base TOE framework. Our results show that multiple risk perceptions, active top management support, project-based business-IT alignment, centralized IT governance, and business network systems influence organizational citizen development adoption decisions. Based on the results, we discuss academic and practical implications and suggestions for future research

DSC experiments on gel-spun polyethylene fibers

The tensile strength of gel-spun polyethylene fibers obtained after hot-drawing depends on spinning conditions such as spinning speed, spinning temperature, spinline stretching, polymer concentration, and molecular weight/molecular weight distribution. High deformation rates in the spinline result in shish-kebab structures which after hot-drawing lead to fibers with poor properties. This is in contrast to hot-drawn fibers obtained from gel-spun fibers with a lamellar structure. Lamellar or shish-kebab structures in the gel-spun fibers can be distinguished by means of DSC experiments on strained fibers. On the basis of these experiments a qualitative prediction of the final tensile properties can be made. DSC experiments on (un)strained hot-drawn fibers show that in the case of shish-kebab structures an incomplete transformation into a fibrillar structure takes place which partly explains the low tensile strength. Chain slippage which becomes possible after the orthorhombic-hexagonal phase transition is involved in the fracture mechanism. The shift of the orthorhombic-hexagonal phase transition to higher temperatures with increasing tensile strength indicates that the increase in strength corresponds to an increase in length of the crystal blocks. Consequently, creep failure also occurs at higher stresses. The melting behavior of cold-drawn and hot-drawn fibers is qualitatively similar, but the transformation into a fibrillar structure is more complete in the latter case

Fair and Efficient Congestion Management for Low Voltage Distribution Networks

The widespread increase of photovoltaic panels in the distribution grid often leads to overvoltage. Traditional voltage regulation techniques are unfair for prosumers at the sensitive part of the grid due to larger power curtailment. Consequently, there has been considerable research on implementing fair curtailment strategies for congestion management. However, existing fairness-incorporated curtailment approaches yield varying results based on changes in the grid topology and integration of renewable energy sources. Therefore, this paper introduces proportional voltage fairness that is independent of the above-mentioned network properties and inherently distinguishes regions for fair curtailment. Additionally, there is a need to consider the underutilisation of the grid while adhering to a fair curtailment scheme. Thus this paper proposes a control algorithm incorporating proportional voltage fairness and gives the opportunity to specify the trade-off between fairness and the total power curtailed. Further, a comparative analysis with respect to state-of-the-art notions of fairness is performed

On the Scalability of Decentralized Energy Management using Profile Steering

Optimizing the use of flexibility, provided by e.g. batteries and electric vehicles, provides opportunities for various stakeholders. Examples are aggregators acting on energy markets, or energy cooperations willing to maximize their self-consumption. However, with large numbers of devices that need to be scheduled, the underlying optimization problem becomes difficult. This paper investigates the scalability of a smart grid optimization approach called Profile Steering. This approach uses a hierarchical structure to perform distributed optimization. In this paper, the approach is extended with methods to accept multiple profiles at once and the possibility to prune children with little flexibility. Simulation studies with almost 20,000 households are carried out to evaluate the scalability of Profile Steering. The results show that, with the presented improvements, the required optimization time of Profile Steering scales linearly with the number of children and a speedup factor of 56 is achieved with 1000 households. Furthermore, the approach scales well across multiple computing processes.</p