391 research outputs found
Cement treated recycled crushed concrete and masonry aggregates for pavements
No full textThis research is focusing on the characterization of the mechanical and deformation properties of cement treated mixtures made of recycled concrete and masonry aggregates (CTMiGr) in relation to their mixture variables. An extensive laboratory investigation was carried out, in which the mechanical properties of CTMiGr and the deformation characteristics relevant to shrinkage crack susceptibility were evaluated. The main aim of this research is to develop models which allow the structural properties of CTMiGr to be estimated from its mixture composition. These models are then used to develop a mixture optimization tool for CTMiGr taking into account the requirements that have to be set to the material in structural pavement designs. To realize the research objective, firstly a series of tests were conducted on CTMiGr mixtures which varied in composition. The test program comprised of measuring compression, indirect tension and deformation properties of CTMiGr mixtures. The recycled construction and demolition materials used in this study were recycled masonry aggregate (RMA) and recycled concrete aggregate (RCA) which are used for unbound granular bases/sub-bases in the Netherlands. For a good understanding of the influence of the mixture variables on the properties of CTMiGr, four important mixture variables (ratio of amount of RMA to RCA by mass, cement content, degree of compaction and curing time) were selected to be taken into account in an elaborate experimental program. The experimental results gave insight into the influences of the different mixture variables on the structural properties of CTMiGr. They showed that the mechanical properties and deformation behavior of CTMiGr depend on the mixture proportioning of CTMiGr. It was possible to develop accurate models to estimate the structural properties of CTMiGr from the mixture variables. It is noteworthy that the RMA content in CTMiGr strongly determines its mechanical and deformation properties. Due to the presence of the low-strength RMA, failure of CTMiGr originates either through the RMA particles or in cracks and discontinuities in the internal structure (the matrix) or in the bonding layer between aggregates and matrix. This will depend on the mixture variables. Numerical work using a lattice model further demonstrated that if the tensile strength of RMA is higher than 1.0 MPa, its contribution to the strength of CTMiGr becomes less important. Finally, by implementing a comprehensive analysis of the structural properties of CTMiGr, some guidelines have been given for its mixture optimization. In this way the mixture design of CTMiGr can be optimally related to the characteristics of the designed pavement structure. If in a pavement the vertical compressive stresses at the top of the CTMiGr layer are low, crushing that might occur at the top of the CTMiGr layer is not an issue. In that case it is preferred to design the CTMiGr mixture by lowering the cement content, enhancing the degree of compaction and increasing the RMA content. On the other hand, when the vertical compressive stresses at the top of the CTMiGr layer are high, it is recommended to decrease the RMA content as well as to adjust the cement content and the degree of compaction. In all cases increasing the degree of compaction is beneficial.Structural EngineeringCivil Engineering and Geoscience
Fast Pareto Optimization for Subset Selection with Dynamic Cost Constraints
No full textSubset selection with cost constraints is a fundamental problem with various applications such as influence maximization and sensor placement. The goal is to select a subset from a ground set to maximize a monotone objective function such that a monotone cost function is upper bounded by a budget. Previous algorithms with bounded approximation guarantees include the generalized greedy algorithm, POMC and EAMC, all of which can achieve the best known approximation guarantee. In real-world scenarios, the resources often vary, i.e., the budget often changes over time, requiring the algorithms to adapt the solutions quickly. However, when the budget changes dynamically, all these three algorithms either achieve arbitrarily bad approximation guarantees, or require a long running time. In this paper, we propose a new algorithm FPOMC by combining the merits of the generalized greedy algorithm and POMC. That is, FPOMC introduces a greedy selection strategy into POMC. We prove that FPOMC can maintain the best known approximation guarantee efficiently.Chao Bian, Chao Qian, Frank Neumann, and Yang Y
O(p6) extension of the large-NC partial wave dispersion relations
No full textAbstractContinuing our previous work [Z.H. Guo, J.J. Sanz-Cillero, H.Q. Zheng, JHEP 0706 (2007) 030], large-NC techniques and partial wave dispersion relations are used to discuss ππ scattering amplitudes. We get a set of predictions for O(p6) low-energy chiral perturbation theory couplings. They are provided in terms of the masses and decay widths of scalar and vector mesons
Some Aspects of Low Content Mono- and Hybrid-Fibre Reinforced Cementitious Composites
No full textCivil Engineering and Geoscience
Seeding Moral Responsibility in Ownership: How to Deal with Uncertain Risks of GMOs
No full textEthics & Philosophy of Technolog
Solvability conditions for mixed sylvester equations in rings
No full textThis paper has been motivated byWang and He [Q.W.Wang and Z.H. He,
Solvability conditions and general solution for mixed Sylvester equations.
Automatica, 49 (2013) 2713-2719] in which the authors consider some
solvability conditions for mixed Sylvester matrix equations. The paper also
considers the same problem in the setting of a regular ring. Using the
purely algebraic technique, we present some necessary and sufficient
conditions for the solvability to mixed Sylvester equations in rings.</jats:p
Generation of design knowledge from the development of a theoretically idealized wind turbine
No full textWind turbines have significantly evolved in the last three decades, though they still need significant improvements to become more competitive in the energy market. These improvements depend to a great extent on the development of wind turbine technology. In this respect, the design of an idealized wind turbine may provide a potential quantitative insight into further improvement in the design of these systems. Therefore, the objective of this work is to generate design knowledge for wind turbine technology through the development of a theoretically idealized wind turbine. To do so, the concept and the design process of this idealized wind turbine are defined based on the general design theory. Moreover, a design case study is implemented as a demonstration of how the proposed design process is applied. The blade was selected for the case study because it is the most representative component of wind turbines and represents several challenges for the development of the future wind turbine industry. The results of this case study give insight into potential design knowledge generated from the proposed design process. Finally, some recommendations about how the designer can use this knowledge for the improvement of wind turbine design are given.Aerospace EngineeringSustainable Energy Technolog
Gone with the Wind: Conceiving of Moral Responsibility in the Case of GMO Contamination
Get PDFGenetically modified organisms are a technology now used with increasing frequency in agriculture. Genetically modified seeds have the special characteristic of being living artefacts that can reproduce and spread; thus it is difficult to control where they end up. In addition, genetically modified seeds may also bring about uncertainties for environmental and human health. Where they will go and what effect they will have is therefore very hard to predict: this creates a puzzle for regulators. In this paper, I use the problem of contamination to complicate my ascription of forward-looking moral responsibility to owners of genetically modified organisms. Indeed, how can owners act responsibly if they cannot know that contamination has occurred? Also, because contamination creates new and unintended ownership, it challenges the ascription of forward-looking moral responsibility based on ownership. From a broader perspective, the question this paper aims to answer is as follows: how can we ascribe forward-looking moral responsibility when the effects of the technologies in question are difficult to know or unknown? To solve this problem, I look at the epistemic conditions for moral responsibility and connect them to the normative notion of the social experiment. Indeed, examining conditions for morally responsible experimentation helps to define a range of actions and to establish the related epistemic virtues that owners should develop in order to act responsibly where genetically modified organisms are concerned.Values Technology and InnovationTechnology, Policy and Managemen
Fatigue failure of welded connections at orthotropic bridges
Get PDFOrthotropic decks were applied to the long span bridges after World War II due to several advantages, such as light weight, high strength, few deck joints, durability, rapid construction, life-cycle economy. The fatigue problem of orthotropic decks was realized twenty years ago since fatigue failure was found. In the past two decades large amount of studies and investigations were carried out and fruitful achievements were obtained. It was found that most of the fatigue cracks were occurred at the welded connection details, such as rib-to-deck plate, rib-to-diaphragm, and rib-to-diaphragm-to-deck plate (RDDP). These connections are sensitive to fatigue cracking due to high concentrated stress and residual stress at welded connections. In this paper practical fatigue failure cases at the welded connections, ease to occur fatigue cracking, are presented, and analyzed through a numerical modeling of orthotropic deck via FE (finite element) software. Furthermore, the improvement technologies of fatigue are also discussed. The results of the analysis can be contributed to the evaluation of the fatigue design for the orthotropic deck
Transferring Moral Responsibility for Technological Hazards: The Case of GMOs in Agriculture
No full textThe use of genetically modified organisms in agriculture makes great promises of better seeds, but also raises many controversies about ownership of seeds and about potential hazards. I suggest that owners of these seeds bear the responsibility to do no harm in using these seeds. After defining the nature of this responsibility, this paper asks, if ownership entails moral responsibility, and ownership can be transferred, then how is moral responsibility transferred? Building on the literature on use plans, I suggest five conditions for a good transfer of moral responsibility for genetically modified seeds. I also look at the Monsanto Technology Use Guide and Technology/Stewardship Agreement, as an examplar of a use plan, to explore the extent to which these conditions are present. I conclude that use plans can play a role in the distribution and transfer of moral responsibility for technologies with high benefits and potential harmful uncertainties.</p
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