74,725 research outputs found
A Note on the Ky Fan Inequality
No full textThe Ky Fan inequality is essentially the assertion that t/(1−t) is log-concave. We study its weighted form in the context of signed weights
Using performance assessment in secondary school mathematics: an empirical study in a Singapore classroom
No full textThis article reports an exploratory study on using performance assessment in mathematics instruction in a high-performing secondary school in Singapore. An intact mathematics class participated in the study, and received chapter-based performance tasks as intervention during regular mathematics lessons for about one and a half school years. The performance tasks used included authentic and/or open-ended tasks. The students’ academic achievements and attitudes in mathematics were compared with a comparison class that did not receive the intervention. Both quantitative and qualitative data were collected, mainly through questionnaire surveys, performance task tests, conventional school exams, and interviews with students and teachers. The results suggest that the students receiving the intervention performed significantly better than their counterparts in solving conventional exam problems, and in general they also showed more positive changes in attitudes towards mathematics and mathematics learning. The students from the experimental class also expressed positive views about the benefits of using performance tasks in promoting their ability in higher order thinking, though no statistically significant difference was detected between the two classes of students in solving unconventional tasks before and after intervention. Overall, the results appear to support teachers’ using contextualised problems in real life situations and open-ended investigations in students’ learning of mathematic
Design of a low speed vaneaxial fan
Full text linkThe ventilation of industrial areas and tunnels is a safety requirement and
characterizes the quality of a working environment. Low speed fans are used to
achieve the required ventilation level. An attempt to design a low speed
vaneaxial fan, meeting the specifications of a given fan that is already in the
market takes place in this Thesis. The project was conducted with the support of
the Fläkt-Woods Company and the main target is to design a ventilation fan,
meeting the requirements for pressure rise, volume flow and size, of an existing
model. The efficiency improvement is driven in part by the new national and
international legislation concerning the operation of electrical equipment.
Companies require higher efficiencies without compromising safety features of
the fan and the fan capability to operate at high temperatures.
A low speed fan design procedure is established based on the available
literature and design tools. The free vortex approach is employed, which provides
acceptable efficiency and relatively simpler design. The design procedure can be
used to design a fan given a set of customer requirements. Many software tools
are used to design the fan. A Matlab code for the blade design is developed and
other codes are used to establish the final fan design. The effectiveness of the
design procedure is verified with CFD simulations carried out as part of this
project. Three new designs that are developed with the established design
procedure are presented in this Thesis. The new designs differ in the hub to tip
ratio, the rotational speed and the number of the blades and the vanes. The
experience acquired from the analysis of the performance of the first new design
is used to improve the performance of the following designs in order to achieve
the best efficiency possible. The effect of tip clearance is investigated thoroughly
in the new designs because the tip clearance has a major impact on the fan
performance and safe operation of the fan at high temperatures. The mechanical
integrity of the fan is examined last to verify that the fan can operate in high
temperature.
The target of improved efficiency (higher than 79%) is achieved in one of
the fan designs attempted and it was calculated 82%. The off design
performance of the new fan is satisfactory as well. This new design can be
further optimized, since the modification of minor design features is in itself a
methodology that can incrementally improve the efficiency of a low speed fan.
The new fan can operate at high temperatures (400°C), however the safety factor
at this temperature is 1.25 for combined steady mechanical and thermal loading
and it can be further improved either through the use of materials with better
resistance in thermal loading or with an increased tip clearance
Richardson, Barbauld, and the construction of an early modern fan club
No full textMPhilMuch has been written about the life and long works of the eighteenth century epistolary novelist, Samuel Richardson, but the prospect of his position as the first celebrity novelist – responsible for courting his own fame as well as initiating his own fan club – has largely been ignored. The body of manuscripts housed at the National Art Library in the Victoria and Albert Museum in London provides the modern scholar with evidence of the skeletal beginnings of an early fan club. This thesis aims to show how these manuscripts were turned into a saleable commodity by the publisher and entrepreneur Richard Phillips, while under the guiding hand of another, slightly later, literary celebrity, Anna Laetitia Barbauld. In order to restore Richardson’s reputation amongst a new nineteenth century audience, Barbauld was required to construct her own idea of him as an eighteenth century celebrity author, and in doing so the insecurities of a self-professed, apparently diffident man, are revealed. Barbauld’s capacious, but heavily edited selection of letters is analyzed in this thesis, providing ample evidence that Richardson’s correspondents were more than just eager letter writers. By using Barbauld’s biography of Richardson this thesis aims to show how she manipulates the genre of life writing in her construction of him.
This thesis offers an alternative reading of how the Richardson manuscripts are viewed, redefining them as not simply a collection of letters, but as a collective entity, deliberately selected and archived as evidence of an early modern fan club, and its celebrity managing director
Experimental study of blade thickness effects on the global and local performances of a Controlled Vortex Designed axial-flow fan
Full text linkThe purpose of this work is to study the effects of blade thickness on the performances of an axial-flow fan. Two fans that differ only in the thickness of their blades were studied. The first fan was designed to be part of the cooling system of an automotive vehicle power unit and has very thin blades. The second fan has much thicker blades compatible with the rotomoulding conception process. The global performances of the fans were measured in a test bench designed according to the ISO-5801 standard. The curve of aerodynamics characteristics (pressure head versus ow-rate) is slightly steeper for the fan with thick blades, and the nominal point is shifted towards lower flow-rates. The efficiency of the thick blades fan is lower than the efficiency of the fan with thin blades but remains high on a wider flow-rate range. The mean velocity field downstream of the rotors are very similar at nominal points with less centrifugation for the thick blades fan. The thick blades fan moreover maintains an axial exit-flow on a wider range of flow-rates. The main dierences concern local properties of the flow: Phase-averaged velocities and wall pressure fluctuations strongly differ at the nominal flow-rates. The total level of fluctuations is lower for the thick blades fan that for the thin blades fan and the spectral decomposition of the wall fluctuations and velocity signals reveal more harmonics for the thick blades fan, with less correlation between the different signals. For this kind of turbomachinery, the use of thick blades could lead to a good compromise between aerodynamic and acoustic performances, on a wider operating range
Development of a Method for Enhanced Fan Representation in Gas Turbine Modeling
Full text linkA challenge in civil aviation future propulsion systems is expected to be the integration with the airframe, coming as a result of increasing bypass ratio or above wing installations for noise mitigation. The resulting highly distorted inlet flows to the engine, make a clear demand for advanced gas turbine performance prediction models. Since the dawn of jet engine several models have been proposed and the present work comes to add a model that combines two well established compressor performance methods in order to create a quasi three dimensional representation of the fan of a modern turbofan. A streamline curvature model is coupled to a parallel compressor method, covering radial and circumferential directions respectively. Model testing has shown a close agreement to experimental data, making it a good candidate for assessing the loss of surge margin on a high bypass ratio turbofan, semi-embedded on the upper surface of a broad wing airframe
Use of fan rig data for the understanding and prediction of fan broadband noise and noise changes due to a variable area nozzle
No full textThis thesis presents the results of the research component of this EngD, entitledUse of fan rig data for the understanding and prediction of fan broadband noise and noisechanges due to a variable area nozzleAs suggested by the title, fan rig noise measurements form an integral part of this thesis. Theanalysis of a database of rig noise measurements forms the first section of this thesis, in twoparts. The first part describes the analysis of a set of fan rig noise measurements, including thevariation of fan broadband and tone noise in forward and rearward arcs. The second partexamines a large database of fan rig noise measurements, and attempts to derive correlationsof fan broadband noise and fan performance parameters. Cluster Analysis, PrincipleComponent Analysis, and Regression Analysis are used to understand and describe theunderlying physics of broadband noise generation and the relationships between thesepredictors.The second section of this thesis uses a cascade broadband noise model to investigate rotorstatorbroadband noise. Predictions of the broadband noise from this noise model arecompared to rig measurements, showing good accuracy. The underlying physics of rotorstatorbroadband noise generation is investigated by performing two parametric studies usingthe broadband noise model. The first parametric study investigates the effect on broadbandnoise of simple flow and geometric parameters, namely number of vanes, vane chord, vanestagger angle, and rotor wake turbulence intensity, turbulent length scale, and flow Machnumber onto the cascade. These results are used to derive scaling power laws for theprediction of changes in broadband noise due to changes in these parameters. The secondparametric study expands upon this by investigating the effect on broadband noise of the fandesign parameters shaft speed, pressure ratio, and efficiency, at approach, cutback and cruiseconditions. The variation in broadband noise due to these design parameters is explained byconsidering the underlying flow and geometric parameters such as number of vanes and Machnumber, and the scaling power laws based on these simple parameters are used to predict thechange in broadband noise between different performance points.The final section of this thesis investigates the effect of varying exhaust nozzle area on totalengine noise. A new method is presented that allows the transfer of changes in fan rig noise toEugene P. Deane EngD Thesis September 2009 2engine noise predictions, to estimate the change in fan noise due to the pressure ratio changesbrought about by a variable area nozzle. Changes in engine noise are investigated forapproach, cutback, and sideline conditions, and the application of the new method assessed.As the research displayed in this thesis is closely linked to industry, the foundation of workpresented in several chapters is dependent on data or figures that are commercially sensitive.It has therefore been necessary to create a confidential appendix (Appendix X) to includethese commercially sensitive items. These additional results and figures in Appendix X aresupplementary in nature, and sufficient results are presented in the public thesis to illustratethe results of the various chapters. Where supplementary information and results are available,this is clearly indicated at the pertinent point in the published thesis, along with the section ofAppendix X where the information can be found
Phenotype of <i>fan</i> mutants.
No full text<p>(A–C′) Live images of developmentally staged wild type (A–C) and <i>fan</i> mutant (A′–C′) zebrafish. Arrow in A′ indicates necrotic cells in the presumptive eye region. Bracket in B′ shows necrosis in neural and pharyngeal arch tissues. Arrow in C′ points to the distinct hydrocephaly in <i>fan</i> mutant hind brain ventricles, arrowhead indicates incomplete choroid fissure closure and craniofacial defects. (D–D′) Alcian blue stained pharyngeal arch cartilages in 4dpf wild type (D) and <i>fan</i> mutant (D′). (E–K′) Whole mount ISH images of wild type (E–K) and <i>fan</i> mutants (E′–K′) for neural crest markers at indicated developmental stage. Arrows in (E′–G′) and asterisks in (I′–K′) indicate reduced gene expression in <i>fan</i> mutant embryos. Interestingly, <i>fan</i> mutant embryos exhibit similar <i>crestin</i> expression in the trunk NCCs (asterisks in H, H′) but reduced expression in cranial NCCs. (L–L′) <i>Tg(fli1a:EGFP)/fan</i> mutants (L′) exhibit reduced GFP expression in the pharyngeal arch region as compared to wild type embryos (L).</p
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