To see the other types of publications on this topic, follow the link: Receptivity.
Dissertations / Theses on the topic 'Receptivity'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Receptivity.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Giannetti, Flavio. "Boundary layer receptivity." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620646.
Full text
2
de, Rosa Donato. "Receptivity in transition prediction." Doctoral thesis, Universita degli studi di Salerno, 2014. http://hdl.handle.net/10556/1859.
Full textAbstract:
2011 - 2012The laminar-turbulent transition is a complex phenomenon involved in several multidisciplinary design issues, such as skin friction drag reduction, anti-icing and de-icing system performance prediction and heat transfer rates assessment. An accurate prediction of the boundary layer state is needed in order to control its thickness by active or passive systems. The state of the boundary layer is of high importance since skin friction drag and heat transfer rates in a turbulent boundary layer can be several times higher than those expected in laminar one. Furthermore, predicting the state of the boundary layer in wind tunnels and ensuring the same state during the real flight, by taking disturbances resulting from the experimental set up into account, leads to the design of transition triggering devices.[edited by author]
XI n.s.
3
Antil, Laurence R. "Teacher receptivity to peer tutoring /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/7927.
Full text
4
Fleming, Miri. "Teachers' receptivity to teaching models." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185807.
Full textAbstract:
The focus of this study is teachers' receptivity to new teaching models. Traditionally, research has been conducted to assess teachers' implementation of innovations. The stage prior to learning and implementing the model generally has been generally ignored. In this study, the researcher assumed that the level of teachers' receptivity could influence upon whether and to what extent the new teaching model is implemented. This study was designed to identify personal characteristics and environmental variables that affect the degree of teacher receptivity to a teaching model. Four teacher-participants were selected according to their level of receptivity to one of the models included in the study, Madeline Hunter's Essential Elements of Instruction or Hilda Taba's Teaching Strategies. The data collected through interviews were analyzed in two directions. First, participants' beliefs, experiences, and workplace conditions were identified using qualitative case study methodology. Second, participants' perceptions of the teaching models were analyzed using Rogers' (1962) framework for determining characteristics of an innovation. Several themes related to participants' receptivity to new teaching models, and their beliefs, experiences, and workplace conditions were revealed. These comprise differences in teachers' pedagogical orientations and in their perceptions of teaching models' characteristics, including the way the model was introduced, changes in levels receptivity, teaching models in relation to the student population served, satisfaction with workplace conditions, level of familiarity with the new teaching model, teachers' independence, and behavioral changes required by the teaching model. The study may be of particular interest to staff developers and educators of students teachers because of the importance of considering teachers' individual needs and characteristics when introducing new teaching models.
5
Tempelmann, David. "Receptivity of crossflow-dominated boundary layers." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-48467.
Full textAbstract:
This thesis deals with receptivity mechanisms of three-dimensional, crossflow-dominated boundary layers. The receptivity of two model problems, a swept-flat-plate and a swept-wing boundary layer, is investigated by solving the parabolised stability equations (PSE) as well as by performing direct numerical simulations (DNS).Both flow cases are known to exhibit strong inflectional instabilities, the crossflow disturbances, whose excitation by external disturbances such as surface roughness or free-stream vorticity is studied. One focus is on worst-case scenarios. This involves the determination of optimal conditions, i.e. those disturbance environments yielding the largest possible response inside the boundary layer. A new method on the basis of the PSE is presented which allows to study optimal disturbances of swept-flat-plate boundary layers. These take the form of tilted streamwise vortices. While convected downstream they develop into streamwise streaks experiencing strong non-modal growth. Eventually, they turn into crossflow disturbances and undergo exponential growth. Non-modal growth is thus found to optimally excite crossflow disturbances and can be related to a receptivity mechanism of three-dimensional boundary layers. Evaluating effects of compressibility reveals that the potential for both non-modal and modal growth increases for higher Mach numbers. It is shown that wall cooling has diverse effects on disturbances of non-modal and modal nature. While destabilising the former it attenuates the growth of modal disturbances. Concave curvature on the other hand is found to be equally destabilising for both types of disturbances. The adjoint of the linearised Navier-Stokes equations is solved for a swept-wing boundary layer by means of DNS. The adjoint solution of a steady crossflow disturbance is computed in the boundary layer as well as in the free-stream upstream of the leading edge. This allows to determine receptivity to incoming free-stream disturbances and surface roughness as well as the corresponding worst-case scenarios. Upstream of a swept wing the optimal initial free-stream disturbance is found to be of streak-type which convects downstream towards the leading edge. It entrains the boundary layer a short distance downstream of the stagnation line. While minor streamwise vorticity is present the streak component is dominant all the way into the boundary layer where the optimal disturbance turns into a crossflow mode. Futher, the worst-case surface roughness is determined. It takes a wavy shape and is distributed in the chordwise direction. It is shown that, under such optimal conditions, the swept-wing boundary layer is more receptive to surface roughness than to free-stream disturbances. Another focus of this work has been the development and evaluation of tools for receptivity prediction. Both DNS and direct and adjoint solutions of the PSE are used to predict the receptivity of a swept-wing boundary layer to localised surface roughness. The configuration conforms to wind tunnel experiments performed by Saric and coworkers at the Arizona State University. Both the DNS and the PSE are found to predict receptivity amplitudes which are in excellent agreement with each other. Though the predicted disturbance amplitudes are slightly lower than experimental measurements the overall agreement with experimental results is very satisfactory. Finally, a DNS of the stabilisation of a transitional swept-wing boundary layer by means of discrete roughness elements is presented. This control approach is found to completely suppress transition to turbulence within the domain studied and confirms experimental results by Saric & coworkers.QC 20111124
6
Horne, Andrew Wemyss. "The MUC1 mucin and endometrial receptivity." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404938.
Full text
7
Chiquete, Carlos. "Stability and Receptivity of Idealized Detonations." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/145419.
Full textAbstract:
The linear receptivity and stability of plane idealized detonation with one-step Arrhenius type reaction kinetics is explored in the case of three-dimensional perturbations to a Zel'dovich-von Neumann-Doering base flow. This is explored in both overdriven and explicitly Chapman-Jouguet detonation. Additionally, the use of a multi-domain spectral collocation method for solving the conventional stability problem is explored within the context of normal-mode detonation. An extension of the stability analysis to confined detonations in a slightly porous walled tube is also carried out. Finally, an asymptotic analysis of a detonation with two-step reaction kinetics in the limit of large activation energy and for general overdrive and reaction order is performed yielding a nonlinear evolution equation for perturbations that produce stable limit cycle solutions.
8
Hirekhan, Manjusha. "Organisational receptivity for change : a multilevel theory." Thesis, Aston University, 2017. http://publications.aston.ac.uk/37489/.
Full textAbstract:
The main theoretical contribution of this thesis is in the development and advancing of the organisational receptivity for change (ORC) theory adopting a multilevel perspective. Organisational change is a multilevel, multifaceted and complex phenomena which require cohesiveness of all levels for effective change implementation (Pettigrew et al., 1987; Butler, 2003). The ORC theory has been around for a decade, still, there is not much development on the original model (Bennett and Ferlie 1994; Butler 2003). Butler and Allen (2008) argue that receptivity factors are ‘higher order capabilities’ that organisations use to achieve intended strategic agendas. According to them higher the receptivity to change, the more flexible the organisation is to adapt to the environmental pressures. Emerging economies and high pace changing industrial sector provide best opportunities for advancing the theory and research on organisational change (Meyer and Gelbuda, 2006). Therefore, the research context of this thesis is the renewable energy sector in India. This study adopts a cross-sectional multilevel research design, and quantitative methods of analysis for the survey based primary data, to assess how organisational receptivity for change affects performance outcomes at different levels within an organisation. The three key findings of this thesis are: (1) ORC factors as higher order dynamic capability interact across the levels and have potential to affect performance outcomes at individual perception and behavior towards change (e.g., resistance to change), project and organisational level. (2) ORC as higher order dynamic capability acts as an antecedent, influences, and foster ambidexterity by enabling a firm to alter its capability based by negotiating the fit between existing and new organisational practices. (3) the key moderators/factors (HR power and competence, social climate and daily work context) act as a process, practices, activities and/or mechanism at various unit levels within an organisation that works effectively along with ORC factors to impact performance outcome variables (including employees response to change).
9
Schrader, Lars-Uve. "Receptivity of Boundary Layers under Pressure Gradient." Licentiate thesis, Stockholm : Mekanik, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9379.
Full text
10
Biswas, Minoti. "University students' receptivity to peers with disabilities." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2007. https://ro.ecu.edu.au/theses/247.
Full textAbstract:
This research investigates university students' receptivity to peers with disabilities at two universities in Perth, Western Australia (Edith Cowan University and the University of Notre Dame in Fremantle), and two universities in India (The University of Kolkata (previously Calcutta) and the University of Jadavpur). Data were collected by three methods: (1) a 60 item questionnaire (N=996) based on six aspects supporting receptivity to peers with disabilities-Academic, Interactive, Social, Personal, Professional and Supportive; (2) written open-ended data (N= 201); and (3) four focus groups, two in Perth (N=1O) and two in Kolkata (N=10). The final questionnaire was composed of 30 stem-items each answered in two perspectives: (1) an ideal self-view (What I think I should do) and (2) their self-reported behaviour (what I actually do), making a total of 60 items.
11
Tempelmann, David. "Stability and Receptivity of Three-Dimensional Boundary Layers." Licentiate thesis, KTH, Mechanics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11579.
Full textAbstract:
The stability and the receptivity of three-dimensional flat plate boundary layers is studied employing parabolised stability equations. These allow for computationally efficient parametric studies. Two different sets of equations are used. The stability of modal disturbances in the form of crossflow vortices is studied by means of the well-known classical parabolised stability equations (PSE). A new method is developed which is applicable to more general vortical-type disturbances. It is based on a modified version of the classical PSE and describes both modal and non-modal growth in three-dimensional boundary layers. This modified PSE approach is used in conjunction with a Lagrange multiplier technique to compute spatial optimal disturbances in three-dimensional boundary layers. These take the form of streamwise oriented tilted vortices initially and develop into streaks further downstream. When entering the domain where modal disturbances become unstable optimal disturbances smoothly evolve into crossflow modes. It is found that non-modal growth is of significant magnitude in three-dimensional boundary layers. Both the lift-up and the Orr mechanism are identified as the physical mechanisms behind non-modal growth. Furthermore, the modified PSE are used to determine the response of three-dimensional boundary layers to vortical free-stream disturbances. By comparing to results from direct numerical simulations it is shown that the response, including initial transient behaviour, is described very accurately. Extensive parametric studies are performed where effects of free-stream turbulence are modelled by filtering with an energy spectrum characteristic for homogeneous isotropic turbulence. It is found that a quantitative prediction of the boundary layer response to free-stream turbulence requires detailed information about the incoming turbulent flow field. Finally, the adjoint of the classical PSE is used to determine the receptivity of modal disturbances with respect to localised surface roughness. It is shown that the adjoint approach yields perfect agreement with results from Finite-Reynold-Number Theory (FRNT) if the boundary layer is assumed to be locally parallel. Receptivity is attenuated if nonlocal and non-parallel effects are accounted for. Comparisons to direct numerical simulations and extended parametric studies are presented.
12
Marions, Lena. "Endometrial receptivity and development of new contraceptive methods /." Stockholm, 2001. http://diss.kib.ki.se/2001/91-628-4836-4/.
Full text
13
Cullen, Lachlan Michael. "Acoustic receptivity in boundary layers with surface roughness." Thesis, Queen Mary, University of London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327024.
Full text
14
Huang, Jui-Che. "Boundary layer receptivity of flow over compliant surfaces." Thesis, University of Liverpool, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428289.
Full text
15
Shahriari, Nima. "On stability and receptivity of boundary-layer flows." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-196878.
Full textAbstract:
This work is concerned with stability and receptivity analysis as well as studies on control of the laminar-turbulent transition in boundary-layer flows through direct numerical simulations. Various flow configurations are considered to address flow around straight and swept wings. The aim of this study is to contribute to a better understanding of stability characteristics and different means of transition control of such flows which are of great interest in aeronautical applications. Acoustic receptivity of flow over a finite-thickness flat plate with elliptic leading edge is considered. The objective is to compute receptivity coefficient defined as the relative amplitude of acoustic disturbances and TS wave. The existing results in the literature for this flow case plot a scattered image and are inconclusive. We have approached this problem in both compressible and incompressible frameworks and used high-order numerical methods. Our results have shown that the generally-accepted level of acoustic receptivity coefficient for this flow case is one order of magnitude too high. The continuous increase of computational power has enabled us to perform global stability analysis of three-dimensional boundary layers. A swept flat plate of FSC type boundary layer with surface roughness is considered. The aim is to determine the critical roughness height for which the flow becomes turbulent. Global stability characteristics of this flow have been addressed and sensitivity of such analysis to domain size and numerical parameters have been discussed. The last flow configuration studied here is infinite swept-wing flow. Two numerical set ups are considered which conform to wind-tunnel experiments where passive control of crossflow instabilities is investigated. Robustness of distributed roughness elements in the presence of acoustic waves have been studied. Moreover, ring-type plasma actuators are employed as virtual roughness elements to delay laminar-turbulent transition.QC 20161124
16
Kondoh, Eiji. "Stress Affects Uterine Receptivity through Ovarian-Independent Pathway." Kyoto University, 2009. http://hdl.handle.net/2433/124308.
Full text
17
Bessell, Sarah Linnell. "Early warning receptivity in the UN and US." Connect to Electronic Thesis (CONTENTdm), 2008. http://worldcat.org/oclc/441831864/viewonline.
Full text
18
Durfey, Rebecca K. "Receptivity to women missionaries' ministry experiences among Muslims." Theological Research Exchange Network (TREN), 1999. http://www.tren.com.
Full text
19
Addison, Patricia A. "Receptivity to a proposed change in accounting education." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 1995. https://ro.ecu.edu.au/theses/1196.
Full textAbstract:
This cross-sectional correlation study is concerned with accounting practitioners' receptivity to a propose change in accounting education; specifically, that the existing three year degree course be extended to four years. This change is proposed by the Accounting Profession in Australia. A model of accounting practitioners' receptivity towards the proposed change, at the adoption stage, was revised and adapted from a general model of teacher receptivity to any system-wide change. The revised model has one dependent variable, receptivity, which is measured in three aspects; overall feelings, attitudes, and general behaviour intentions towards the proposed change in accounting education. It has eight Independent variables, and a number of situation variables. These independent variables are; attitudes towards the structure and content of the proposed change, general beliefs about the change based on the expanding scope of accounting practice, overall feelings about the strengths and weaknesses of accounting graduates, overall feelings about alleviating fears and uncertainties of the proposed change, overall feelings about the practicality of the proposed change in the lecture room and tutorial room in two aspects, general behaviour intentions about expectations and achievements for the proposed change, and general behaviour intentions to support instructors and the accounting profession. The relationships between the dependent variables and the independent variables are examined in the context of a number of situation variables.
20
Kim, Jung Il. "Distance-learning receptivity differences between American and Korean graduate students." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/2223.
Full textAbstract:
The purposes of this study were to determine if differences exist in distance-learning receptivity and perceived technology usefulness between American and Korean graduate students as well as Individualists and Collectivists. Results indicated that the two groups differed in distance-learning receptivity and perceived technology usefulness. However, cultural value tendency did not influence either receptivity or usefulness. Recommendations based on this study: 1. Researchers who are interested in cross-cultural field of distance learning should find what potential factors influence the differences in the receptivity and perceived usefulness between American and Korean group. 2. Administrators and decision makers who want to implement or adopt distance learning for their employees or students need to understand that cultural value, at least individualism and collectivism, is not a significant factor in distance learning. Instead, they should understand the importance of prior experience because people feel that distance is better than they??ve ever thought possible once they experience. 3. In implementing distance learning, practitioners should consider interactive media more than non-interactive media. Distance learning is mostly dependent upon technology. Practitioners should consider that distance-learning technology should be developed in terms of perceived usefulness to users. 4. In respect to usefulness, advanced and contemporary technologies were perceived more useful than traditional technologies in distance learning. Therefore, practitioners should also consider advanced technology rather than traditional technology in distance learning. Recommendations for future research: 1. It is suggested that Hofstede??s other cultural value dimensions should be included in future studies. 2. Future researchers should consider other factors such as personal background, learning style, skill level, and motivation. 3. Future research is needed to extend the current findings and test their generalizability to other types of users, for example, undergraduate students or organization employees. 4. This study used American and Korean samples only. Other national cultures should be tested with various cultural dimensions in a future study.
21
Teitelbaum, Dina. "The Jewish ossuary phenomenon: Cultural receptivity in Roman Palestine." Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/29265.
Full textAbstract:
The discovery of Jewish ossuaries in the nineteenth century raised a host of questions, paramount among them the questions of the origin and purpose of the ossuaries. It was also realized that ossuaries were a short lived phenomenon, appearing and disappearing relatively suddenly. A number of theories were proposed: The ossuaries were thought to have to do either with transport or space-saving, protection, martyrdom, resurrection, atonement, individuation, or Roman convention. All of these theories focused on Judea as the origin of the phenomenon. However, no one theory was satisfactory in itself. The dissertation presents a fresh examination of all available evidence in the light of ancient Jewish burial customs from the First Temple period to the Hellenistic and Roman times, using the approaches of archaeology, anthropology, and socio-rhetorical analysis. It concludes that foreign influence triggered the adoption of the ossuary in Judea during the Herodian period and that Judeans adopted the Greco-Roman ash chest as a model, modifying an aniconic version for use with bones alone. A comparison of the Jewish ossuary with the Greco-Roman ash urn reveals parallels and striking similarities in terms of ritual, material culture, terminology, manufacture and time lines. In particular, the temporal distribution of ossuaries and ash chests points to a general diffusion of the concept throughout the Empire over a long period of time, with ossuaries appearing relatively late in Judea. Using the innovation-diffusion theory of Roberts, the dissertation argues that, once implanted, the idea of ossuaries, in conjunction with ossilegium, spread rapidly throughout Judea, each special interest group or individual adopting it for their own unique reasons. Ultimately it became a fashionable secondary burial instrument. The disappearance of the Judean ossuary can be explained in terms of the adoption of the subsequent fashion in the Roman Empire to bury the dead in coffins or sarcophagi. In conclusion, it has been shown in the dissertation that Jews of the Second Temple Period were attracted to, adopted, re-invented and reconfigured a foreign convention in such a way that it became consistent with their Torah laws and their beliefs.
22
Fischer, Joel. "Understanding receptivity to interruptions in mobile human-computer interaction." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12499/.
Full textAbstract:
Interruptions have a profound impact on our attentional orientation in everyday life. Recent advances in mobile information technology increase the number of potentially disruptive notifications on mobile devices by an increasing availability of services. Understanding the contextual intricacies that make us receptive to these interruptions is paramount to devising technology that supports interruption management. This thesis makes a number of contributions to the methodology of studying mobile experiences in situ, understanding receptivity to interruptions, and designing context-sensitive systems. This thesis presents a series of real-world studies that investigate opportune moments for interruptions in mobile settings. In order to facilitate the study of the multi-faceted ways opportune moments surface from participants' involvement in the world this thesis develops: - a model of the contextual factors that interact to guide receptivity to interruptions, and - an adaptation of the Experience-Sampling Method (ESM) to capture behavioural response to interruptions in situ. In two naturalistic experiments, participants' experiences of being interrupted on a mobile phone are sampled as they go about their everyday lives. In a field study, participants' experiences are observed and recorded as they use a notification-driven mobile application to create photo-stories in a theme park. Experiment 1 explores the effects of content and time of delivery of the interruption. The results show that receptivity to text messages is significantly affected by message content, while scheduling one's own interruption times in advance does not improve receptivity over randomly timed interruptions. Experiment 2 investigates the hypothesis that opportune moments to deliver notifications are located at the endings of episodes of mobile interaction such as texting and calling. This notification strategy is supported by significant effects in behavioural measures of receptivity, while self-reports and interviews reveal complexities in the subjective experience of the interruption. By employing a mixed methods approach of interviews, observations and an analysis of system logs in the field study, it is shown that participants appreciated location-based notifications as prompts to foreground the application during relative 'downtimes' from other activities. However, an unexpected quantity of redundant notifications meant that visitors soon habituated to and eventually ignored them, which suggests careful, sparing use of notifications in interactive experiences. Overall, the studies showed that contextual mediation of the timing of interruptions (e.g. by phone activity in Experiment 2 and opportune places in the field study) is more likely to lead to interruptions at opportune moments than when participants schedule their own interruptions. However, momentary receptivity and responsiveness to an interruption is determined by the complex and situated interactions of local and relational contextual factors. These contextual factors are captured in a model of receptivity that underlies the interruption process. The studies highlight implications for the design of systems that seek to manage interruptions by adapting the timing of interruptions to the user's situation. In particular, applications to manage interruptions in personal communication and pervasive experiences are considered.
23
Sherwin, James Robert Alexander. "The role of leukaemia inhibitory factor in endometrial receptivity." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619897.
Full text
24
Choudhari, Meelan. "Boundary layer receptivity mechanisms relevant to laminar flow control." Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/184964.
Full textAbstract:
Receptivity processes by which free-stream acoustic waves generate instability waves in boundary layers are investigated. Concentration is placed on mechanisms associated with local regions of short scale variation in wall suction or admittance distribution. These mechanisms are relevant to laminar flow control technology, in which suction is utilized to control the growth of boundary layer instabilities. The receptivity process requires a transfer of energy from the long wavelength of the free-stream disturbance to the short wavelength of the instability wave. In the case of wall suction, this occurs through the unsteady modulation, by the acoustic wave, of the short scale mean flow variation due to the steady wall suction. In the wall admittance mechanism, the boundary condition for the unsteady motion contains a short scale variation which directly scatters energy from the acoustic wave into the instability wave. The latter mechanism does not require a short scale adjustment in the mean boundary layer. Time harmonic, two and three-dimensional interactions are analyzed using the asymptotic, high Reynolds number, triple deck structure. The influence of subsonic compressibility is examined for the case of two-dimensional interactions, and a similarity transform is found which reduces the problem to an equivalent incompressible flow. For three-dimensional interactions, a similarity transform is possible only in the Fourier transform wavenumber space, and in the equivalent two-dimensional problem the frequency is complex. However, in many cases of practical interest, the imaginary component of this frequency is quite small and can be neglected. The acoustic wave orientation and the geometry of the wall suction or admittance distribution are found to significantly influence the amplitude of the generated instability wave. For an isolated, three-dimensional region of wall suction or admittance, instability wave growth is confined to a downstream, wedge shaped region. The saddle point method is utilized to calculate the characteristics of this instability wave pattern. In some ranges of parameter space, two saddle points are found to make comparable contributions. The instability wave pattern in these directions exhibits a beat phenomenon, due to constructive and destructive interference of the contributions from the two saddle points.
25
Wang, Xiaowen. "Numerical simulations of hypersonic boundary-layer stability and receptivity." Diss., Restricted to subscribing institutions, 2007. http://proquest.umi.com/pqdweb?did=1464122601&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Full text
26
Schrader, Lars-Uve. "Receptivity of Boundary-Layer Flows over Flat and Curved Walls." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25439.
Full textAbstract:
Direct numerical simulations of the receptivity and instability of boundary layers on flat and curved surfaces are herein reported. Various flow models are considered with the aim to capture aspects of flows over straight and swept wings such as wall curvature, pressure variations, leading-edge effects, streamline curvature and crossflow. The first model problem presented, the flow over a swept flat plate, features a crossflow inside the boundary layer. The layer is unstable to steady and traveling crossflow vortices which are nearly aligned with the free stream. Wall roughness and free-stream vortical modes efficiently excite these crossflow modes, and the associated receptivity mechanisms are linear in an environment of low-amplitude perturbations. Receptivity coefficients for roughness elements with various length scales and for free-stream vortical modes with different wavenumbers and frequencies are reported. Key to the receptivity to free-stream vorticity is the upstream excitation of streamwise streaks evolving into crossflow modes. This mechanism is also active in the presence of free-stream turbulence. The second flow model is that of a Görtler boundary layer. This flow type forms on surfaces with concave curvature, e.g. the lower side of a turbine blade. The dominant instability, driven by a vertically varying centrifugal force, appears as pairs of steady, streamwise counter-rotating vortical rolls and streamwise streaks. The Görtler boundary layer is in particular receptive to free-stream vortical modes with zero and low frequencies. The associated mechanism builds on the excitation of upstream disturbance streaks from which the Görtler modes emerge, similar to the mechanism in swept-plate flows. The receptivity to free-stream vorticity can both be linear and nonlinear. In the presence of free-stream turbulence, nonlinear receptivity is more likely to trigger steady Görtler vortices than linear receptivity unless the frequencies of the free-stream fluctuations are very low. The third set of simulations considers the boundary layer on a flat plate with an elliptic leading edge. This study aims to identify the effect of the leading edge on the boundary-layer receptivity to impinging free-stream vortical modes. Three types of modes with streamwise, vertical and spanwise vorticity are considered. The two former types trigger streamwise disturbance streaks while the latter type excites Tollmien-Schlichting wave packets in the shear layer. Simulations with two leading edges of different bluntness demonstrate that the leading-edge shape hardly influences the receptivity to streamwise vortices, whereas it significantly enhances the receptivity to vertical and spanwise vortices. It is shown that the receptivity mechanism to vertical free-stream vorticity involves vortex stretching and tilting - physical processes which are clearly enhanced by blunt leading edges. The last flow configuration studied models an infinite wing at 45 degrees sweep. This model is the least idealized with respect to applications in aerospace engineering. The set-up mimics the wind-tunnel experiments carried out by Saric and coworkers at the Arizona State University in the 1990s. The numerical method is verified by simulating the excitation of steady crossflow vortices through micron-sized roughness as realized in the experiments. Moreover, the receptivity to free-stream vortical disturbances is investigated and it is shown that the boundary layer is most receptive, if the free-stream modes are closely aligned with the most unstable crossflow modeQC 20101025
27
Turner, M. R. "Numerical and asymptotic approaches to boundary-layer receptivity and transition." Thesis, University of East Anglia, 2005. http://eprints.brighton.ac.uk/5351/.
Full textAbstract:
We consider the interaction of a uniformly pulsating free-stream with the leading edge of a body, and consider its effect on transition. The free-stream is assumed to be incompressible, high Reynolds number flow parallel to the chord of the body, with a small, unsteady, perturbation of a single harmonic frequency. We present a method which calculates Tollmien-Schlichting (T-S) wave amplitudes downstream of the leading edge, by a combination of an asymptotic receptivity approach in the leading edge region and a numerical method which marches through the Orr-Sommerfeld region. The asymptotic receptivity analysis produces a three deck eigenmode which, in its far downstream limiting form, produces an upstream initial condition for our numerical Parabolized Stability Equation (PSE). Downstream T-S wave amplitudes are calculated for the flat plate, and good comparisons are found with the Orr-Sommerfeld asymptotics available in this region. The importance of the O(Re^{−1/2} ) term of the asymptotics is discussed, and, due to the complexity in calculating this term, we show the importance of numerical methods in the Orr-Sommerfeld region to give accurate results. We also discuss the initial transients present for certain parameter ranges, and show that their presence appears to be due to the existence of higher T-S modes in the initial upstream boundary condition. Extensions of the receptivity/PSE method to the parabola and the Rankine body are considered, and a drop in T-S wave amplitudes at lower branch is observed for both bodies, as the nose radius increases. The only exception to this trend occurs for the Rankine body at very large Reynolds numbers, which are not accessible in experiments, where a double maximum of the T-S wave amplitude at lower branch is observed. The extension of the receptivity/PSE method to experimentally realistic bodies is also considered, by using slender body theory to model the inviscid flow around a modified super ellipse to compare with numerical studies.
28
Roland, Hannah. "Instability and receptivity of subsonic flow in the boundary layer." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/64819.
Full textAbstract:
In this thesis, the main focus is on the interaction of an incoming Tollmien–Schlichting wave with an isolated, stationary wall roughness in subsonic flow. In Part I, this problem is analysed by means of the Triple Deck theory. The linearised sublayer equations are solved under the assumption that the horizontal extent of the roughness is of O(L Re^(−3/8)) and that its height h is small, and an expression for the pressure perturbation is found. The transmission coefficient T_I , defined as the amplitude of the T–S wave downstream of the roughness divided by its initial amplitude, is then calculated, where |T_I | > 1 means that the wave is amplified and |T_I | < 1 represents an attenuation of the T–S wave. The transmission coefficient is dependent on the frequency ω, the height h of the roughness and on the Fourier transform of the roughness shape evaluated at zero value of the wavenumber. The same setup is investigated in Part II through numerical calculations: a DNS solver provides the base flows for 25 different gaps of varying width and height, which are then run through a PSE analysis to examine the stability of the flow. From the results of both methods it can be concluded that a surface indentation amplifies an incoming T–S wave, and that the amplification increases with the width and depth of the roughness. An additional geometry is studied in Part I by again employing the Triple Deck theory to investigate the effect small elastic vibrations of a semi-infinite plate attached to a stationary plate have on the boundary layer, and the receptivity coefficient is calculated for varying ω.
29
Choudhari, Meelan 1963. "Boundary layer receptivity at a suction surface-hard wall junction." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277030.
Full textAbstract:
Receptivity refers to the generation of boundary layer instability waves by external disturbances. Recent work by M. E. Goldstein has set the general framework for the different types of boundary layer receptivity mechanisms. Therefore, it is now understood that receptivity occurs near the leading edge or at locations downstream where the boundary layer undergoes a rapid streamwise adjustment. The present work analyzes the receptivity due to a free-stream acoustic wave interacting with a suction surface--hard wall junction. In this case, receptivity occurs because of the rapid changes in wall suction distribution. Analytical expressions for the amplitude of the generated instability wave have been derived and numerical estimates provided for parameter values typical of hybrid laminar flow control applications. The importance of the junction receptivity as compared to other receptivity mechanisms has been assessed.
30
Doan, Huyen Van. "ROLES OF HAND2 TRANSCRIPTION FACTOR IN UTERINE RECEPTIVITY AND DECIDUALIZATION." OpenSIUC, 2013. https://opensiuc.lib.siu.edu/dissertations/670.
Full textAbstract:
Blastocyst implantation is the process in which a competent blastocyst acquires the ability to tether into the mother endometrium. At the same time, the endometrial tissue undergoes the process of decidualization to support the anchoring of the blastocyst and provides the blastocyst with nutrition until the fully functional placenta is formed. Although the process of implantation and decidualization are under control of progesterone and estrogen, the precise mechanisms involved in this regulation are not fully understood. Here, we report the expression and function of a transcription factor, HAND2, in sensitizing mouse uterus for implantation and decidualization. In mouse, HAND2 expression was localized mainly in the endometrial stromal cells even before the blastocyst implantation. The expression of HAND2 increased after blastocyst implantation and correlated with the increase in decidual compartment. The expression of HAND2 depended on progesterone but not estrogen. Further investigation using conditional knockout mouse revealed that HAND2 was important for both implantation and decidualization. Hand2d/d mice were infertile and had defects in decidualization. It seemed that HAND2 was an important factor that mediates the anti-estrogenic effect of progesterone on luminal epithelial proliferation. The abnormal in expression of Mucin 1, Calcitonin and E-Cadherin in Hand KO uterus may be responsible for defects in the uterine receptivity. The expression of HAND2 was also critical in decidualization in vitro. Silencing and over-expression HAND2 disclosed the roles of HAND2 in regulating the expression of FOXO1A, IGFBP1, BMP2 as well as WNT4. It seemed that HAND2 promoter worked in tissue specific manner and although both HOXA10 and cAMP binding sites were found in proposed HAND2 promoters, its activity was stimulated by cAMP and steroid hormones rather than the expression of HOXA10.
31
Jacobson, Willow Serene Ingraham Patricia W. "Receptivity to change in the public sector: two federal case studies." Related Electronic Resource: Current Research at SU : database of SU dissertations, recent titles available full text, 2003. http://wwwlib.umi.com/cr/syr/main.
Full text
32
Polanski, Lukasz T. "Markers of endometrial receptivity : a study of ultrasonographic and molecular factors." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/31634/.
Full textAbstract:
The evidence suggests that alteration of the endometrial environment in women with previous failed in vitro fertilization (IVF) or intra-cytoplasmic sperm injection (ICSI) by inflicting endometrial injury improves the outcome of the subsequent treatment cycle. The selected population assessed in the studies supporting this statement prevents from generalizing this to all women undergoing IVF or ICSI treatment. The mechanisms responsible for alteration of the endometrial environment following biopsy remain still unclear. If proven effective, endometrial injury could serve as a beneficial adjunct for all couples undergoing assisted reproductive treatment (ART). The hypothesis forming the basis of the work reported in this thesis was that endometrial injury in the cycle directly preceding an embryo transfer cycle, be it fresh or frozen, improves the outcome of that treatment irrespective of previous reproductive history. In order to support or refute this hypothesis, a clinical trial of endometrial biopsy prior to IVF or ICSI treatment has been designed. Additional objectives that allow examining the mechanisms responsible for the beneficial effects of the biopsy on the endometrium included utilization of two-dimensional, three- dimensional and Spatio-Temporal Image Correlation (STIC) ultrasound and assessment of the predictive value of any sonographic indices on ART outcome. Same sonographic modalities were used to determine the effect of endometrial injury on endometrial and subendometrial blood flow. Similarly, an examination of the value of uterine natural killer (uNK) cell numbers and expression of selected molecular markers of endometrial function as a predictors of ART outcome was explored. In this work it was not possible to clearly demonstrate a benefit of routine endometrial biopsy in all women undergoing ART on treatment outcomes, though clues, as to which population might benefit from the procedure, were identified. Extensive sonographic analysis of endometrial factors did not produce results allowing for unequivocal non- invasive identification of a receptive endometrial milieu. Triple layer endometrial pattern at oocyte collection was correlated with positive outcome and endometrial biopsy. Spatio-Temporal Image Correlation did not fulfil expectations as a non-invasive marker of endometrial receptivity and was not able to identify women that would go on to have a successful ART outcome. In a small number of patients, STIC indices were able to predict first trimester miscarriage with relatively high sensitivity and specificity. uNK cell numbers were not associated nor predictive of ART outcome, and as such not useful as a routine diagnostic tests prior to ART. An observed significant decrease in uNK cell levels following endometrial biopsy indicates a possible mechanism of action of this intervention. Limited (3) molecular cues were not able to differentiate between a receptive and non-receptive endometrium. This work, however extensive, indicates that the endometrium is a complex microenvironment requiring further investigation in order to understand and influence the mechanisms related to pregnancy establishment and development.
33
Turmel, Andrée. "The influence of culture and lifestyles on receptivity to direct mail." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0008/MQ39092.pdf.
Full text
34
Ali, Reza. "Receptivity & transition in boundary layers over rigid and compliant surfaces." Thesis, University of Warwick, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397560.
Full text
35
Manners, Carole V. "Endometrial proteins and uterine receptivity during human and mouse embryo implantation." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386172.
Full text
36
Heinrich, Roland Adolf Eberhard. "Flat-plate leading edge receptivity to various free-stream disturbance structures." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184860.
Full textAbstract:
The receptivity process by which two-dimensional, time-harmonic freestream disturbances generate instability waves in the incompressible Blasius boundary layer is investigated analytically. The importance of the leading edge region and the linear nature of the receptivity process are discussed, and Goldstein's (1983a, 1983b) theoretical framework for the leading edge receptivity problem is reviewed. His approach utilizes asymptotic matching of a region close to the leading edge, which is governed by the linearized unsteady boundary layer equation, with a region further downstream, which is described by an Orr-Sommerfeld type equation. The linearized unsteady boundary layer equation is solved numerically, using the slip velocity and pressure gradient obtained from the inviscid interaction of the freestream disturbance with the semi-infinite plate. A new method is developed to extract the receptivity coefficient from this numerical solution. The receptivity coefficient determines the amplitude of the instability wave--a quantity not available from classical stability theory. The freestream disturbances investigated are oblique plane acoustic waves, vortical gusts of various orientations convected downstream with freestream speed U(∞), and a Karman vortex street passing above the plate surface with speed U(p). In addition, the case of a semi-infinite plate in a channel of finite width subject to an upstream traveling acoustic wave on the upper plate surface is considered. For oblique acoustic waves, the dominant receptivity mechanism is related to scattering of the waves by the leading edge. In contrast, for vortical gusts the receptivity produced by leading edge scattering is very small. The boundary layer receptivity to a Karman vortex street is found to be a strong function of the speed ratio U(p)/U(∞). A pronounced influence of channel walls, which is related to the alternate cut-on of higher modes in the upstream and downstream channel halves, is found. A comparison of the present results with available experiments shows good qualitative and quantitative agreement.
37
Christie, M. Lee Kennedy Larry DeWitt. "Teacher receptivity and commitment to critical teaching in bachelor's degree nursing programs." Normal, Ill. Illinois State University, 1992. http://wwwlib.umi.com/cr/ilstu/fullcit?p9227163.
Full textAbstract:
Thesis (Ed. D.)--Illinois State University, 1992.Title from title page screen, viewed January 10, 2006. Dissertation Committee: Larry D. Kennedy (chair), Eugene R. Irving, John R. McCarthy, Kenneth H. Strand. Includes bibliographical references (leaves 150-158) and abstract. Also available in print.
38
Akbaripour, Sheijnai Solmaz. "Numerical studies on receptivity and control of a three-dimensional boundary layer." Thesis, KTH, Mekanik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-87117.
Full textAbstract:
Receptivity in three-dimensional boundary layer ow to localized roughness elements over a at plate is studied by means of direct numerical simulations (DNS). The surface roughness is modeled by applying nonhomogeneous boundary conditions along the wall as well as considering as a surface deformation by inserting the bump shape into the numerical mesh. Under the assumption of the small amplitudes of the roughness, although dierent disturbances amplitudes are observed in the vicinity of the bump for the meshed and modeled case, the boundary layer response downstream of the roughness is independent if the way of the bump implementation. Dierent roughness heights are considered in order to compare the boundary layer response of two approaches. Also, the boundary layer is excited by random distributed surface roughness and the receptivity results are studied. Moreover, a simple model for natural roughness excites steady multi wavenumber crossow instabilities. A localised surface roughness i.e. control roughness is applied to stabilise the latter. The control mode which is subcritical with respect to transition aects the most steady unstable mode. Suppression of the most dangerous mode is observed through nonlinear interactions with the control mode.
39
Hambley, Laura Anne. "The receptivity of career counsellors toward career development services on the Internet." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0020/MQ48006.pdf.
Full text
40
Chan, Kin-wa, and 陳建華. "Transcriptomic approach to study the effect of polypectomy on human endometrial receptivity." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206559.
Full textAbstract:
Background: Endometrial polyps are common in women at reproductive ages, and found in more than 11% of infertile women. Hysteroscopic polypectomy is recommended to alleviating symptoms in patients with abnormal uterine bleeding. While the relationship between an endometrial polyp and subfertility is not clearly established, there is some evidence that hysteroscopic polypectomy may improve fertility outcome in IVF patients. Accumulating evidence suggested that elevated levels of activated mast cells as well as elevated matrix MMPs and cytokines levels in the patients who suffer from endometrial polyps. Moreover, significant increases in glycodelin levels were found in patients’ plasma and uterine. And there was a significant negative relationship between plasma glycodelin and progesterone levels in patients with endometrial polyps. To further understand whether hysteroscopic polypectomy affects endometrial microenvironment that is conductive to embryo implantation, we recruited 9 IVF patients and use microarray to compare their endometrial gene expressions before and after polypectomy. Methods: We investigated the change of endometrial gene expression patterns before and after polypectomy. Three out of 9 samples were subjected to microarray study. Quantitative-PCR (qPCR) was used to confirm the expression in all 9 samples, and compared with endometrial samples taken from patients underwent natural (LH+7 days, n = 8) and stimulated (hCG+7 days, n = 8) IVF cycles but without polyps. The outcome of subsequent IVF cycle was obtained to correlate the change of gene expression patterns. Results: Microarray analysis demonstrated that no genes are commonly differentially expressed in all 3 samples. One of the samples has shown very heterogeneous result. Sixteen genes (hERα, hERβ, OLFM1, OLFM2, IL15, CXCL14, GPX3, CCL4, UPKIB, PAEP, MMP26, SLC1A1, MUC15, MUC16, TM4SF4 and TFPI2) that are differentially expressed in any 2 of the samples and genes related to endometrial receptivity (OLFM1, IL15, CXCL14, GPX3, PAEP, MMP26, SLC1A1, MUC16) were selected for further analysis. We found that 3 samples have a gene expression pattern similar to natural cycle (LH+7 days) after polypectomy; while the other samples have a gene expression similar to the stimulated cycle (hCG+7 days). Clinical findings of the treated patients did not have strong correlation with pregnancy outcome. One out of two patients who had gene expression patterns similar to natural cycle got pregnant; while one out of seven patients who has gene expression patterns similar to stimulated cycle get pregnant after polypectomy. Conclusion: Polypectomy modulates endometrial gene expression patterns in some patients similar to those in natural cycles. However, our data did not support endometrial polypectomy significantly improved pregnancy outcome in the limited number of patient subjects (n=9) in this study.published_or_final_version
Obstetrics and Gynaecology
Master
Master of Medical Sciences
41
Nichols, Dawn Elizabeth. "Boundary layer receptivity of a flat plate with a rounded leading edge." Thesis, University of East Anglia, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395146.
Full text
42
Bernots, Tomass. "Receptivity of the boundary layer in transonic flow past an aircraft wing." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/21181.
Full textAbstract:
This thesis presents a theoretical analysis of the generation of Tollmien- Schlichting waves in a boundary layer on the wing surface due to external acoustic disturbances and elastic vibrations of the wing itself. An asymptotic approach based on the assumption that the Reynolds number, Re, is large is adopted here. In addition, it is assumed that in the spectrum of these disturbances there are harmonics, which come in resonance with the Tollmien-Schlichting wave on the lower branch of the stability curve. This work is restricted to the cases when the Stokes layer interacts with an isolated roughness, and the flow near the roughness is described by the triple-deck theory. The solution of the triple-deck problem is found in an analytic form and the main concern is with the flow behaviour downstream of the roughness. Further, it is found that there are Tollmien-Schlichting waves forming in the boundary layer behind the roughness, and their amplitudes have been expressed in terms of the receptivity coefficients, which represent the efficiency of the Tollmien-Schlichting wave generation process. The analysis of the boundary layer receptivity to the acoustic disturbances is conducted with an assumption that the flow in the free-stream is in the transonic regime. It is shown that in this situation there are two plane acoustic waves with distinctively different characteristics. One wave always travels downstream in the streamwise direction and has O(1) phase velocity. The second wave phase velocity is an order Re−1/9 quantity and it changes the direction of propagation depending on the Mach number. The analysis has shown that the receptivity coefficient depends on the initial frequency of the perturbations and on the free-stream Mach number. It has been shown that the absolute value of the receptivity coefficient is achieved when the Mach number is one. For the negative values of the parameter, the subsonic behaviour of the receptivity coefficient is recovered. The study of the “slow” moving wave shows that the receptivity coefficient now depends on the shape of the roughness itself as well as acoustic wave parameters and the free-stream Mach number. The third problem considered is a receptivity of the boundary layer on the wing surface due to an elastic vibration of the wing itself. It is found that, when the frequency of the wing surface vibrations is high, the perturbations produced by wing surface vibrations can be described in the framework of “piston” theory. In the flow considered there are two physical mechanisms through which an oscillatory motion of the fluid in the Stokes layer is ex- cited. The first one is the same as for the acoustic problem where the pressure gradient forces the fluid to oscillate in the direction along the wing surface. The second mechanism can only be observed in compressible flows. It was found that there are two Tollmien-Schlichting waves forming in the boundary layer behind the roughness. The first receptivity process is similar to the one studied earlier with the difference that now the flow is considered to be in the subsonic regime. The second receptivity process does not have an analogue in the literature, and it was found that it is large as compared with the first receptivity. This suggests that the receptivity to the wing surface vibrations has to play a major role in the laminar-turbulent transition in the boundary layer.
43
Melford, Sarah Emily. "An exploration into the role of the endocannabinoid system in endometrial receptivity." Thesis, University of Leicester, 2017. http://hdl.handle.net/2381/39713.
Full textAbstract:
While it is clear that the control of implantation is multifactorial, one emerging component that appears to be important in the success or failure of embryo implantation is the endocannabinoid system. The primary ligand of the endocannabinoid system (ECS) is anandamide (AEA) which is synthesised by a N-acylphosphatidylethanolamine-specific phospholipase D (NAPE-PLD) and degraded by fatty acid amide hydrolase (FAAH). A careful balance in the activities of NAPE-PLD and FAAH is required to ensure the appropriate levels of AEA are available during implantation. The purpose of this thesis was to explore further the role of the ECS, specifically its role in uterine receptivity using both in-vivo and in-vitro models. In-vivo models were used to study the expression of the ECS by measuring plasma concentrations of AEA, along with OEA and PEA (two other ligands of the ECS). A statistically significant change in plasma PEA concentrations was noted when comparing urine pregnancy test results. No significant differences in either AEA or OEA plasma concentrations were demonstrated. In-vitro models were used to investigate the interactions between galectin 3, integrin β3 and the ECS. The results show that while galectin 3 did not have any effect on the ECS, up-regulation of the expression of integrin β3 in receptive endometrial cells both increased the expression of FAAH and decreased the expression on NAPE-PLD in a dose-dependent manner. However, no effect was demonstrated in non-receptive endometrial cells, suggesting that integrin β3 expression, in collaboration with the ECS, plays an important role in endometrial receptivity. Overall, this work gives us further insight into the immensely complex processes involved in ensuring the endometrium is receptive to an embryo. Most importantly, it has suggested a link between the expression of integrin β3 and the enzymes of the ECS that is absent in the non-receptive endometrium.
44
De, Tullio Nicola. "Receptivity and transition to turbulence of supersonic boundary layers with surface roughness." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/348815/.
Full textAbstract:
A deeper understanding of the different factors that influence the laminar-turbulent transition in supersonic boundary layers will help the design of efficient high-speed vehicles. In this work we study the effects of surface roughness on the stability and transition to turbulence of supersonic boundary layers. The investigation is carried out by direct numerical simulations (DNS) of the compressible Navier-Stokes equations and focuses on the modifications introduced in the transition process by localised roughness elements, for Mach numbers M∞ = 6.0 and M∞ = 2.5, and distributed slender pores at M∞ = 6.0. The first part of the investigation into the effects of localised roughness deals with the receptivity and initial exponential amplification of disturbances in boundary layers subjected to small external perturbations. Different transition scenarios are investigated by considering different free-stream disturbances and roughness elements with different heights. The results show that, for roughness heights approaching the local displacement thickness, transition is dominated by the growth of a number of instability modes in the roughness wake. These modes are damped by wall cooling and their receptivity is found to be more efficient in the case of free-stream disturbances dominated by sound. At M∞ = 6 the growth of Mack modes in the boundary layer is found to play a crucial role in the excitation of the most unstable wake modes. An investigation into the nonlinear stages of transition shows that the breakdown to turbulence starts with nonlinear interactions of the wake instability modes. This leads to the formation of a turbulent wedge behind the roughness element, which spreads laterally following mechanisms similar to those observed for the evolution of compressible turbulent spots. An oblique shock impinging on the transitional boundary layer significantly accelerates the breakdown process and leads to a wider turbulent wedge. The study ends with an analysis of porous walls as a passive method for transition control, which is carried out using a temporal DNS approach. The results show damping of both the primary, of second or Mack mode type, and secondary instabilities and indicate that, despite the high Mack number, first mode waves regain importance in this modified transition scenario.
45
Taha, Azni. "Organisational receptivity for change : combining context and capability to explain competitive advantage." Thesis, Aston University, 2014. http://publications.aston.ac.uk/21408/.
Full textAbstract:
This thesis explores efforts to conjoin organisational contexts and capabilities in explaining sustainable competitive advantage. Oliver (1997) argued organisations need to balance the need to conform to industry's requirements to attain legitimization (e.g. DiMaggio & Powell, 1983), and the need for resource optimization (e.g. Barney, 1991). The author hypothesized that such balance can be viewed as movements along the homogeneity-heterogeneity continuum. An organisation in a homogenous industry possesses similar characteristics as its competitors, as opposed to a heterogeneous industry in which organisations within are differentiated and competitively positioned (Oliver, 1997). The movement is influenced by the dynamic environmental conditions that an organisation is experiencing. The author extended Oliver's (1997) propositions of combining RBV's focus on capabilities with institutional theory's focus on organisational context, as well as redefining organisational receptivity towards change (ORC) factors from Butler and Allen's (2008) findings. The authors contributed to the theoretical development of ORC theory to explain the attainment of sustainable competitive advantage. ORC adopts the assumptions from both institutional and RBV theories, where the receptivity factors include both organisational contexts and capabilities. The thesis employed a mixed method approach in which sequential qualitativequantitative studies were deployed to establish a robust, reliable, and valid ORC scale. The adoption of Hinkin's (1995) three-phase scale development process was updated, thus items generated from interviews and literature reviews went through numerous exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) to achieve convergent, discriminant, and nomological validities. Samples in the first phase (semi structured interviews) were hotel owners and managers. In the second phase, samples were MBA students, and employees of private and public sectors. In the third phase, samples were hotel managers. The final ORC scale is a parsimonious second higher-order latent construct. The first-order constructs comprises four latent receptivity factors which are ideological vision (4 items), leading change (4 items), implementation capacity (4 items), and change orientation (7 items). Hypotheses testing revealed that high levels of perceived environmental uncertainty leads to high levels of receptivity factor. Furthermore, the study found a strong positive correlation between receptivity factors and competitive advantage, and between receptivity factors and organisation performance. Mediation analyses revealed that receptivity factors partially mediate the relationship between perceived environmental uncertainty, competitive advantage and organisation performance.
46
Zhao, Difei. "Instability and receptivity of boundary layers on concave surfaces and swept wings." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/9118.
Full textAbstract:
This thesis studies the instability and receptivity of boundary layers over a concave wall and a swept Joukowski airfoil. The main interest is in excitation of relevant instability waves by free-stream vortical disturbances and in their subsequent linear development. We first consider excitation of Gortler vortices in a Blasius boundary layer over a concave wall. Attention is focused on disturbances with long streamwise wavelengths, to which the boundary layer is most receptive. The appropriate initial-boundary-value problem describing both the receptivity process and the subsequent development of the induced perturbation is formulated for the generic case where the Gortler number GΛ (based on the spanwise wavelength Λ of the disturbance) is of order one. The impact of free-stream disturbances on the boundary layer is accounted for by the far-field boundary condition and the initial condition near the leading edge, both of which turn out to be the same as those given by Leib, Wundrow and Goldstein (J. Fluid Mech. vol. 380, 1999, p.169) for the flatplate boundary layer. Numerical solutions of the initial-value problem show that for a sufficiently small GΛ, the induced perturbation exhibits essentially the same characteristics as streaks occuring in the flat plate case: the streamwise velocity undergoes considerable amplification and then decays. However, when GΛ exceeds a critical value, the induced perturbation exhibits (quasi-)exponential growth. Comparison with local parallel and non-parallel instability theories reveal that the perturbation acquires the modal shape of Gortler vortices rather quickly, but its growth rate differs appreciably from that predicted by local instability theories before the convergence at large downstream distances. Nevertheless, the overall agreement is close enough to indicate that Gortler vortices have been excited by free-stream disturbances. The amplitude of excited Gortler vortices is found to decrease with the frequency. Steady vortices, generated by steady components of free-stream disturbances, tend to be dominant. Detailed quantitative comparisons with experiments were performed. It is found that the eigenvalue approach predicts the modal shape adequately, but only the initial-value approach can accurately predict the evolution of the amplitude as well as the modal shape. An asymptotic analysis is performed on the assumption of GΛ >>1 to map out distinct regimes through which a disturbance of a fixed spanwise wavelength evolves. The centrifugal force enters the play to influence the generation of the pressure when x* ~ΛRΛG−2/3 Λ , where RΛ denotes the Reynolds number based on Λ. The induced pressure leads to full coupling of the momentum equations when x* ~ ΛRΛG−2/5 Λ . This is the crucial regime linking the pre-modal and modal phases of the perturbation because the governing equations admit a countable set of growing asymptotic eigensolutions, which develop into fully fledged Gortler vortices of inviscid nature when x* ~ ΛRΛ. From this position onwards, local eigenvalue formulations are mathematically justified. The generated Gortler vortices continue to amplify and enter the so-called most unstable regime when x* ~ ΛRΛGΛ, and ultimately approach the right-branch regime when x* ~ ΛRΛG2 Λ. We then extend our study to the receptivity of a three-dimensional boundary layer over a swept wing to free-stream vortical disturbances. The base flow is taken to be the boundary layer over a swept Joukowski airfoil. In contrast to the two-dimensional boundary layer, external disturbances with comparable streamwise and spanwise wavelengths are relevant to receptivity. The appropriate initial-boundary-value problem consists of linearised boundary-layer equations supplemented by the initial condition at the leading edge and the boundary condition in the far field, which are derived by applying the rapid distortion theory, and matching the resultant inviscid solution with the boundary-layer solution. It is found that the linearised boundary-layer equations support spatially growing eigenmodes despite the absence of a pressure gradient. The modes may be first excited by free-stream disturbances, and eventually evolve into fully fledged crossflow vortices.
47
Baker, John C. "The relationship between teacher efficacy, cultural receptivity, and the decision to refer." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0006700.
Full text
48
Hacker, Wayne. "An asymptotic theory for distributed receptivity of flow fields with pressure gradients." Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280035.
Full textAbstract:
A systematic asymptotic analysis is used to devise a model for distributed boundary-layer receptivity for flow fields with pressure gradients. The model predicts the generation of a Tollmien-Schlichting (TS) wave due to the interaction of a time-harmonic free-stream disturbance with distributed wall waviness and the subsequent evolution of this TS wave under the influence of wall waviness. The model is restricted to two dimensions and the Reynolds number is assumed to be large. Unlike previous models, the present model allows a nonzero pressure gradient in the base flow, and accounts for nonparallel-flow effects. A Green's-function approach was employed. The interaction between the free-stream disturbance and a point source at the wall was first examined in a local region near the point source. Only the component corresponding to the largest-growing instability wave was determined. The downstream evolution of this wave was then investigated over a region that extended for many TS wavelengths. For this reason it was necessary to account for the nonparallel-flow effects. By solving for the dispersion relation in this downstream region, the evolution of the eigenmode was determined. A match between the local-region and the downstream solution led to a uniform approximation for the TS wave emerging from the point source. Summing over a region of point-source solutions and approximating the resulting integral using the method of steepest descents yielded the instability wave for the wavy wall. The principal results of the present work included a solution to the dispersion relation for a general base flow with a nonzero pressure gradient beyond leading order. A region of maximal growth for TS waves that were generated from point sources located in a region of width O (Re-3/16) surrounding the lower branch neutral stability point (LBNSP) was identified. Here Re is the global Reynolds number. For adverse pressure gradients, it was also determined that, when the wall waviness and the TS wave are in exact resonance, the wave produced from distributed receptivity is significantly smaller than the wave generated by a point source at the LBNSP. For the case of a strong favorable pressure gradient the reverse is true. Finally, an investigation of the effect of pressure gradient on detuning was carried out. It showed that complete detuning occurs when the relative difference between the wavenumber of the TS wave at the LBNSP and the wavenumber of the sinusoidal wall is O (Re-3/16). It also revealed that the response to detuning varies with pressure gradient. For situations with a strong favorable pressure gradient, growth rates are highly sensitive to an exact match between the wavenumbers of the wall and the TS wave. On the other hand, as the pressure gradient grows less favorable, sensitivity to detuning decreases.
49
Grote, Dustin Michael. "Enhancing the Community College Transfer Pathway: Exploring Aspects of Transfer Receptivity at 4-Year Institutions in Engineering." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/99298.
Full textAbstract:
Community college transfer pathways may play a critical role in realizing broadened participation in engineering; Community colleges serve as an important access-oriented pathway through the postsecondary system in the United States, and also depend on 4-year institutions to streamline vertical transfer. The extent to which 4-year institutions are receptive to community college transfer as a viable pathway to engineering degrees may play a significant role in its efficacy. This dissertation explores a few aspects of transfer receptivity at 4-year institutions to understand how they relate to the efficacy of vertical transfer pathways in engineering disciplines. The first manuscript is a case study of an articulation agreement partnership between one 4-year institution and two public community college partners. The second manuscript examines how transfer policies and institutional characteristics of 4-year institutions in the U.S. relate to the enrollment, graduation and reporting of transfer students in engineering. I use a combination of quantitative and qualitative methodologies across both manuscripts. The results of these studies revealed that: 1) specific challenges for transfer in engineering suggest that adequate examinations of transfer receptivity need be discipline-specific, 2) institutions encounter dissonance when simultaneously managing aims to increase access and prestige, 3) there is a need for shifts in policy and ranking systems that incentivize increases and improvements in vertical transfer, 4) there is a need for more transparency of transfer-related policies and transfer student data, and 5) our understanding of transfer matriculation remains well ahead of graduation outcomes.Doctor of Philosophy
Community college transfer pathways may be critical to increasing the number of women and underrepresented minority engineers. Community colleges serve as an affordable way for students and families to begin their postsecondary education in the United States, but depend on universities to support community college transfer to complete bachelor's degrees. How well universities partner with community colleges in transfer may determine how well it works for students and families. This dissertation explores a few ways that universities encourage or discourage community college transfer as a way to earn a bachelor's degree in engineering. The first study looks closely at a transfer partnership between one university and two community colleges. The second study looks at how transfer policies and characteristics of universities relate to the enrollment, graduation and reporting of engineering transfer students. The results of these studies revealed several important themes. First, there are specific challenges to transfer in engineering. Next, institutions have a hard time increasing access to their institutions for community college students while also increasing their academic ranking and prestige. With this in mind, there is a need to shift policies and ranking systems that encourage institutions to focus more on increasing community college transfer. Next, universities need to be more transparent about their policies and data that influence transfer students. Finally, we know a lot more about how often transfer students successfully transfer to universities than we do about how many students end up graduating from the university and how long it takes them to do so.
50
Ahearn, Gavin. "Friendship and Anonymity in Collective Free Music Improvisation." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20923.
Full textAbstract:
Researchers interested in the musical practice of free improvisation have historically prioritised studies of improvisatory process at both the individual or group level. In the realm of jazz studies, discussions of group interactivity have long pointed to the role friendship plays in facilitating these processes (Berliner, 1994; Monson, 1997; Jackson, 2012) and recent qualitative studies of group decision making and interaction in jazz have demonstrated that the shared understanding embedded within relationships can help facilitate open environments ideal for free improvisation (Canonne and Aucouturier, 2015; Wilson and Macdonald, 2017). Yet parallel research into group creativity outside the jazz context has put forth an intriguing alternate idea – the notion that anonymity amongst group participants may also lead to openness during the collaborative process (Bryan-Kinns, Healey and Leach, 2007). This thesis unpacks the experiences of four Australian free music practitioners in terms of friendship and anonymity in an attempt to flesh out a spectrum of optimal conditions that might underpin successful free music exchanges. In doing so, it lays open potential areas of future research in terms of delineating how a range of different sorts of relationships might impact improvised group creativity.