| 128801. |
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| 128802. |
- Jowkar Deriss, Mehrnoush, et al.
(författare)
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High Solids Waterborne Hybrid Systems: Effect of Surfactant Concentration and pH on Droplet Size and Morphology
- 2004
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Ingår i: Aqueous Polymer Dispersions (Progress in Colloid and Polymer Science). - 0340-255X. - 9783540005780 ; 124, s. 149-153
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Konferensbidrag (refereegranskat)abstract
- Hybrid systems have been made by taking an acrylic latex dispersion and slowly dropping an alkyd resin into the dispersion while stirring to achieve a solid content of 75–80%. The particle size distributions of alkyd droplets were studied with a laser diffraction instrument and the structure of the hybrid system in the liquid state has been studied by light microscopy. The hybrid system was defined as a suspoemulsion, which are mixtures of suspensions and emulsions. In the present hybrid system the alkyd is present as an oil-in-water (O/W) emulsion and the suspension is represented by the acrylic latex. When the way of adding surfactant and the added amount of surfactant were changed, it was found that addition of surfactant to the system decreases alkyd droplet size more effectively if the surfactant is present in the acrylic latex. If the surfactant was added to the latex prior to the addition of alkyd it resulted in the formation of O/W emulsions. On the other hand, in the case of addition of surfactant to the alkyd before dropping it into the latex, water-in-oil-in-water (W/O/W) double emulsions in respect of the alkyd were observed, and in order to obtain the same decrease in alkyd droplet size as in the experiments where surfactant was added to the latex, a higher surfactant concentration was needed.
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| 128803. |
- Joy, Jesline, et al.
(författare)
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Draft tube guide vane system to mitigate pressure pulsations
- 2022
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Ingår i: 31st IAHR Symposium on Hydraulic Machinery and Systems 26/06/2022 - 01/07/2022 Trondheim, Norway. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- The present study introduces the concept of mitigating pressure pulsations in a hydro-turbine draft tube. The concept refers to using an adjustable guide vane system in the draft tube. The adjustability relates to its ability to rotate around an axis. The test rig for the experimental study is a high-head Francis model turbine. Three sets of guide vanes are distributed evenly circumferentially in the draft tube. Each guide vanes consists of two hydrofoils. The upper hydrofoil can move around an axis. The lower hydrofoil is fixed. The turbine operating head for the experiments was 12 m. The operating condition considered is at part load, for Q/QBEP = 0.71. The results indicate that using the guide vanes in the draft tube, the plunging mode of the rotating vortex rope becomes insignificant for nearly all upper hydrofoil configurations considered. The reduction in the rotating mode of the vortex rope is between 50% and 80%. The vortex rope frequency shifts from 0.307·f0 and varies between 0.33·f0 to 0.617·f0, which is a function of upper hydrofoil angles.
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| 128804. |
- Joy, Jesline, et al.
(författare)
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Numerical Study of Reduced Francis-99 Turbine Model During Part Load Operation
- 2019
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Konferensbidrag (refereegranskat)abstract
- Numerical investigation was performed on a reduced model of a high head Francis turbine model at part load (PL) operating condition. Studies performed in the past on nearly complete Francis-99 turbine model (inclusive of spiral casing, stay vanes, guide vanes, runner and draft tube) reportedly consisted of large number of mesh elements, which increase the computational time and power significantly. In the present paper, numerical study was performed on a standalone model of the Francis-99 elbow draft tube so as to imitate the flow behaviour inside the draft tube during PL condition. The inlet profiles of the axial, radial and tangential velocity were considered from the study performed on a semi- Francis-99 model (1 stay vane, 2 guide vanes, 1 runner passage and draft tube) considered from NVKS Francis-99 second workshop. Additionally, turbulent kinetic energy (k) and turbulent eddy dissipation (ε) variables were also considered for better flow prediction inside the draft tube. Two approaches were implemented in the present study. In the first approach, the entire planar profile between the runner and draft tube interface was considered and in the second approach, flow variables along a radial profile at the runner exit was considered together with an axisymmetric flow assumption. The numerical results obtained from the present study were validated against the experimental results and were found to be in good agreement, both qualitatively and quantitatively, thus, ensuring the fidelity of the numerical methodology. The present study could be considered useful for mitigation of rotating vortex rope (RVR) studies.
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| 128805. |
- Joy, Jesline, et al.
(författare)
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Study of Flow Characteristics inside Francis Turbine Draft Tube with Adjustable Guide Vanes
- 2021
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Ingår i: 30th IAHR Symposium on Hydraulic Machinery and Systems (IAHR 2020) 21-26 March 2021, Lausanne, Switzerland. - : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- Numerical investigation was performed on a semi-model (one stay vane, two guide vanes, one runner passage inclusive of one main and one splitter blade, and the draft tube) of a high-head Francis turbine model with adjustable guide vanes in the draft tube. The motive of the present study is to investigate the possibility to mitigate the rotating vortex rope (RVR) formed at part load operating condition. Each guide vane in the draft tube consists of two hydrofoils. The upper hydrofoil is adjustable according to the flow angles leaving the runner. The lower hydrofoil is stationary and corresponds to the flow angle at best efficiency point (BEP).The factors considered while designing these guide vanes were a) number of guide vanes, b) chord length, c) span and d) position in the draft tube. The preliminary results indicate that the RVR pressure amplitude was suppressed by 97% compared to the reference model with no guide vanes at part load (PL) operating condition. An 8.7% increment in the draft tube pressure recovery was obtained which indicates that implementation of the guide vanes in the draft tube could positively impact the turbine efficiency beside the mitigation of the pressure pulsations at PL operation.
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| 128806. |
- Joy, Mike, et al.
(författare)
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Student perspectives on plagiarism on computing
- 2012
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Ingår i: Conference proceeding of the 5th International Plagiarism Conference.
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Konferensbidrag (refereegranskat)abstract
- Prevention and detection of plagiarism have formed the basis for many research projects, but student perceptions on plagiarism are arguably not well understood, and this is particularly true in the computing disciplines. This paper considers two aspects of the student experience, (i) the types of plagiaristic activity that students engage in, and (ii) the specific understanding of what plagiarism means for students who write computer programs. In a recent study we classified types of plagiarism in computing, collecting data from two sources: published material (books, published papers, web sites), and on-line formative quizzes and questionnaires used by universities to test student knowledge of what constitutes plagiarism. Facet analysis was used to categorise the data into four initial categories (sources, actions, material, extrinsic). Further analysis suggested a refinement to six categories and 23 sub-categories which directly relate to the computing disciplines. In a further study we analysed data collected from 18 UK institutions via an online questionnaire, in which over 700 computing students were invited to scrutinise fifteen scenarios which may (or may not) contain plagiarism, and to identify which they thought did contain plagiarism. The results of this study suggest that there are certain types of plagiaristic activity which are poorly understood, and demographic factors which correlate with student understanding. This paper summarises and compares the results of these two studies and reflects on the implications for educating computing students about how they should avoid plagiarism.
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| 128807. |
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| 128808. |
- Jr., Andrew J. Meade, et al.
(författare)
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Adaptive solution of differential equations for the regularization of artificial neural networks
- 1998
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Ingår i: Intelligent systems for humans in a cyberworld. - Piscataway, NJ : IEEE Communications Society. - 0780347781 ; , s. 3130-3135
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Konferensbidrag (refereegranskat)abstract
- The authors propose using artificial neural networks to model the solution of the two-dimensional Euler equation which models inviscid and compressible fluid flow. The code thus created should not only have the same accuracy as a more conventional computer code, but should still retain the ability of an ANN to modify itself when exposed to experimental data, thus yielding software that could be specialized with experimental results. To accomplish these objectives, the method of optimal incremental function approximation has been developed for the adaptive solution of differential equations using ANN architecture. Two major attractive features of this approach are that: (1) the developed method is flexible enough to use any of the popular transfer functions and (2) the developed method requires minimal user interaction. The latter is especially advantageous when dealing with complicated physical or computational domains. Numerical results are presented and compared to conventional methods. The accuracy is considered satisfactory
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| 128809. |
- Ju, Fengkui, et al.
(författare)
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A logic for temporal conditionals and a solution to the Sea Battle Puzzle
- 2018
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Ingår i: Advances in Modal Logic. - London : College Publications. - 9781848902558 ; , s. 379-398
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Konferensbidrag (refereegranskat)abstract
- Temporal reasoning with conditionals is more complex than both classical temporal reasoning and reasoning with timeless conditionals, and can lead to some rather counter-intuitive conclusions. For instance, Aristotle’s famous “Sea Battle Tomorrow” puzzle leads to a fatalistic conclusion: whether there will be a sea battle tomorrow or not, but that is necessarily the case now. We propose a branching-time logic LTC to formalise reasoning about temporal conditionals and provide that logic with adequate formal semantics. The logic LTC extends the Nexttime fragment of CTL∗ , with operators for model updates, restricting the domain to only future moments where antecedent is still possible to satisfy. We provide formal semantics for these operators that implements the restrictor interpretation of antecedents of temporalized conditionals, by suitably restricting the domain of discourse. As a motivating example, we demonstrate that a naturally formalised in our logic version of the ‘Sea Battle’ argument renders it unsound, thereby providing a solution to the problem with fatalist conclusion that it entails, because its underlying reasoning per cases argument no longer applies when these cases are treated not as material implications but as temporal conditionals. On the technical side, we analyze the semantics of LTC and provide a series of reductions of LTC-formulae, first recursively eliminating the dynamic update operators and then the path quantifiers in such formulae. Using these reductions we obtain a sound and complete axiomatization for LTC, and reduce its decision problem to that of the modal logic KD.
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| 128810. |
- Ju, Fengkui, et al.
(författare)
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Normative properties of sequential actions
- 2023
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Ingår i: Deontic Logic and Normative Systems. - London : College Publications. - 9781848904385 ; , s. 139-157
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Konferensbidrag (refereegranskat)abstract
- This paper develops a deontic logic based on dynamic logic for reasoning about permission and prohibition of sequential actions. Our approach is characterized by two main features. First, permission and prohibition of sequential actions are not necessarily reduced to permission and prohibition of the actions' constituent parts. Second, we incorporate the idea that actions may be permitted or prohibited conditional on another action being performed first. The logic interprets actions in terms of sequences of states, and the deontic component of the logic is introduced by relating sequences of states to their legal and illegal future continuations. We consider various different logics obtained by imposing natural constraints on models, and formulate complete axiom systems for several of these logics.
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