107,484 research outputs found
A Novel Airframe Design Methodology For Silent Aircraft
No full textThe impact of noise on civil aviation is not just a localised airport problem, but a global concern, due
to the ever-increasing demands for passenger travel. The challenge of designing a ‘Silent Aircraft’
lies within the development, integration, and optimisation of efficient airframe-engine technologies.
This research study investigates the design of novel airframes with the aim of producing a
methodology that incorporates airframe noise. Studies investigating the design of Broad Deltas (BD),
Blended Wing Bodies (BWB), and Joined Wing airframe configurations are integrated with
innovative propulsion systems designs to identify key parameters in order to design a Silent Aircraft.
The airframe configuration plays an important role in the total aircraft noise, where the novel
airframes that are analysed, are compared to a datum ‘baseline’ aircraft. All novel configurations
show significant improvements in airframe noise reduction, enhanced by the addition of ultra-efficient
propulsion systems, for which integration studies are discussed. The research into novel airframes
uses a developed design methodology which integrates design considerations such as aerodynamics,
performance, and cost models to complement the noise analysis and identify the most silent airframe
configuration.
The research goal was to identify a silent airframe solution for a future viable short-medium range
airliner, where the final solutions described suggest proposals for the future development of aviation.
The proposals suggested describe a short-term solution to the noise challenge, with a longer-term
solution to aid the development of technologies, maturity in technology release levels (TRLs), and
development of a future 2050 medium capacity civil airliner
Representations of migrant and nation in selected works of Rohinton Mistry and Salman Rushdie
No full textThis thesis explores the representations of, and the relationship between. the migrant and the nation in selected works of the Bombay-born novelists Rohinton Mistry and Salman Rushdie. I explore each writer's engagement with contemporary debates surrounding the material, political, social and imaginative consequences of the crisis in secularism in India during the 1970s, 1980s and 1990s, and consider how this engagement is informed by their
migrant positions beyond India's borders. A primary concern is the way in which Mistry's and Rushdie's representations of the nation, and of migrant and diasporic subjects, intersects with the representation of Bombay in their work.
This thesis is divided into five chapters. The first two chapters concentrate on Mistry's fiction, the remaining three on Rushdie's work. Published between 1988 and 2002, the central novels examined are situated within debates regarding the founding principles of the Indian nation, and notions of Indianness, the rise of communalism in general and Hindu nationalism in particular, and the renaming of Bombay as Mumbai. My readings foreground the necessity of a
close understanding of the historical and political transformations taking place within Bombay and India during the 1970s, 1980s and 1990s, but also during the 1950s and 1960s. I argue that Mistry's and Rushdie's work is informed by a deepening anxiety over these socio-political transformations, and over how reconfigurations of Indianness increasingly position minority communities, and migrant and diasporic subjects, outside of definitions of national identity.
This anxiety extends into the negotiation of their own migrant positions. My reading of the differing representations of the migrant in Mistry's and Rushdie's work engages with ideas of accountability, political responsibility, and with notions of cosmopolitanism. In doing so, I question familiar assumptions regarding the migrant condition as one of predominantly empowering political agency. I argue that, while both authors emphasise the importance of the migrant sustaining a critical engagement with India's politics, they also foreground the anxious difficulties of doing so. This difficulty informs Mistry's and Rushdie's divergent negotiation of their own position as migrant writers, and I examine how their fiction is marked by an anxiety over the adequacy of writing as a mode of political engagement with the crisis in secularism and the parochialisation of Bombay, and as a means of negotiating the politics of migrancy
Generalized Least Energy of Separation for Desalination and Other Chemical Separation Processes
No full textIncreasing global demand for fresh water is driving the development and implementation of a wide variety of seawater desalination technologies driven by different combinations of heat, work, and chemical energy. This paper develops a consistent basis for comparing the energy consumption of such technologies using Second Law efficiency. The Second Law efficiency for a chemical separation process is defined in terms of the useful exergy output, which is the minimum least work of separation required to extract a unit of product from a feed stream of a given composition. For a desalination process, this is the minimum least work of separation for producing one kilogram of product water from feed of a given salinity. While definitions in terms of work and heat input have been proposed before, this work generalizes the Second Law efficiency to allow for systems that operate on a combination of energy inputs, including fuel. The generalized equation is then evaluated through a parametric study considering work input, heat inputs at various temperatures, and various chemical fuel inputs. Further, since most modern, large-scale desalination plants operate in cogeneration schemes, a methodology for correctly evaluating Second Law efficiency for the desalination plant based on primary energy inputs is demonstrated. It is shown that, from a strictly energetic point of view and based on currently available technology, cogeneration using electricity to power a reverse osmosis system is energetically superior to thermal systems such as multiple effect distillation and multistage flash distillation, despite the very low grade heat input normally applied in those systems.Center for Clean Water and Clean Energy at MIT and KFUPM (Project R13-CW-10
An Economics-Based Second Law Efficiency
No full textSecond Law efficiency is a useful parameter for characterizing the energy requirements of a system in relation to the limits of performance prescribed by the Laws of Thermodynamics. However, since energy costs typically represent less than 50% of the overall cost of product for many large-scale plants (and, in particular, for desalination plants), it is useful to have a parameter that can characterize both energetic and economic effects. In this paper, an economics-based Second Law efficiency is defined by analogy to the exergetic Second Law efficiency and is applied to several desalination systems. It is defined as the ratio of the minimum cost of producing a product divided by the actual cost of production. The minimum cost of producing the product is equal to the cost of the primary source of energy times the minimum amount of energy required, as governed by the Second Law. The analogy is used to show that thermodynamic irreversibilities can be assigned costs and compared directly to non-energetic costs, such as capital expenses, labor and other operating costs. The economics-based Second Law efficiency identifies costly sources of irreversibility and places these irreversibilities in context with the overall system costs. These principles are illustrated through three case studies. First, a simple analysis of multistage flash and multiple effect distillation systems is performed using available data. Second, a complete energetic and economic model of a reverse osmosis plant is developed to show how economic costs are influenced by energetics. Third, a complete energetic and economic model of a solar powered direct contact membrane distillation system is developed to illustrate the true costs associated with so-called free energy sources.Center for Clean Water and Clean Energy at MIT and KFUPM (Project R13-CW-10
Population-weighted degree-days: The global shift between heating and cooling
No full textAnthropogenic greenhouse gas emissions are driving global increases in temperature. This rise will likely lead to an increase in demand for cooling in the coming years. However, increasing temperatures are not the main explanatory factor for why the world is moving towards more cooling. This paper compares population and area-weighted cooling and heating degree-days derived using ERA5-Land reanalysis temperature, to show that population growth in warmer parts of the world drives cooling demand globally. The analysis shows that mean global area-weighted heating degree-days have fallen 8.46 degrees C days/year, whereas population-weighted heating degree-days have fallen by 12.5 degrees C days/year. At the same time, mean global area-weighted cooling degree-days have risen by 3.0 degrees C days/year, while populationweighted cooling degree-days have risen at 6.0 degrees C days/year. By using sub-country analysis, this paper shows that population-weighted degree-days can substantially differ from area-weighted degree-days. Finally, the findings highlight that the choice of heating and cooling degree-day base temperature is the most important parameter in the variability of degree-days and will need to be understood better in order to accurately account for future heating and cooling energy demand. (c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Effect of nonideal solution behavior on desalination of a sodium chloride (NaCl) solution and comparison to seawater
No full textProper evaluation of the Gibbs free energy and other properties
of seawater and other aqueous solutions is essential in
the analysis of desalination systems. Standard seawater has
been studied extensively and property data are readily accessible.
However, many aqueous solutions requiring desalination have
significantly different composition from seawater and seawater
data is generally not accurate for these solutions. Experimental
data for a given aqueous solution may be unavailable under the
conditions of interest. Therefore, there is a need to model relevant
physical properties from chemical thermodynamic principles. In
particular, for solutions that are not ideal, the activity and fugacity
coefficients must be considered. In this paper, the effect of
nonidealities in sodium chloride (NaCl) solutions is considered
through a parametric study of the least work of separation for a
desalination system. This study is used to determine the conditions
under which the ideal solution approximation is valid and
also to determine when an NaCl solution is a good approximation
to standard seawater. It is found that the ideal solution approximation
is reasonable within ranges of salinities and recovery
ratios typical of those found in the seawater desalination industry
because many of the nonidealities cancel out, but not because
the solution behaves ideally. Additionally, it is found that NaCl
solutions closely approximate natural seawater only at salinities
typically found in seawater and not for salinities found in typical
brackish waters.Massachusetts Institute of Technology. Center for Clean Water and Clean EnergyKing Fahd University of Petroleum and Minerals (project number R13-CW-10
The effects of driving with different levels of unreliable automation on self-reported workload and secondary task performance
No full textUntil automated cars function perfectly, drivers will have to take over control when automation fails or reaches its functional limits. Two simulator experiments (N = 24 and 27) were conducted, each testing four automation levels ranging from manual control (MC) to highly automated driving. In both experiments, participants about once every 3 min experienced an event that required intervention. Participants performed a secondary divided attention task while driving. Automation generally resulted in improved secondary task performance and reduced self-reported physical demand and effort as compared to MC. However, automated speed control was experienced as more frustrating than MC. Participants responded quickly to the events when the stimulus was salient (i.e., stop sign, crossing pedestrian, and braking lead car), but often failed to react to an automation failure when their vehicle was driving slowly. In conclusion, driving with imperfect automation can be frustrating, even though mental and physical demands are reduced
The spatial and temporal expression of calretinin in developing rat teeth (Rattus Norvegicus)
No full textAppropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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