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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Rigid, Melting, and Flowing Fluid

Carlson, Mark Thomas 29 October 2004 (has links)
This work focuses on the simulation of fluids as they transition between a solid and a liquid state, and as they interact with rigid bodies in a realistic fashion. There is an underlying theme to my work that I did not recognize until I examined my body of research as a whole. The equations of motion that are generally considered appropriate only for liquids or gas can also be used to model solids. Without adding extra constraints, one can model a solid simply as a fluid with a high viscosity. Admittedly, this representation will only get you so far, but this simple representation can create some very nice animations of objects that start as solids, and then melt into liquid over time. Another way to represent solids with the fluid equations is to add extra constraints to the equations. I use this representation in the parts of this work that focus on the two-way coupling of liquids with rigid bodies. The coupling affects both how the liquid moves the rigid bodies, and how the rigid bodies in turn affect the motion of the fluid. There are three components that are needed to allow solids and fluids to interact: a rigid body solver, a fluid solver, and a mechanism for the coupling of the two solvers. The fluid solver used in this work was presented in [8]. This Melting and Flowing solver is a fast and stable system for animating materials that melt, flow, and solidify. Examples of realworld materials that exhibit these phenomena include melting candles, lava flow, the hardening of cement, icicle formation, and limestone deposition. Key to this fluid solver is the idea that we can plausibly simulate such phenomena by simply varying the viscosity inside a standard fluid solver, treating solid and nearly-solid materials as very high viscosity fluids. The computational method modifies the Marker-And-Cell algorithm [99] in order to rapidly simulate fluids with variable and arbitrarily high viscosity. The modifications allow the viscosity of the material to change in space and time according to variation in temperature, water content, or any other spatial variable. This in turn allows different locations in the same continuous material to exhibit states ranging from the absolute rigidity or slight bending of hardened wax to the splashing and sloshing of water. The coupling that ties together the rigid body and fluid solvers was presented in [7], and is known as the Rigid Fluid method. It is a technique for animating the interplay between rigid bodies and viscous incompressible fluid with free surfaces. Distributed Lagrange multipliers are used to ensure two-way coupling that generates realistic motion for both the solid objects and the fluid as they interact with one another. The rigid fluid method is so named because the simulator treats the rigid objects as if they were made of fluid. The rigidity of such an object is maintained by identifying the region of the velocity field that is inside the object and constraining those velocities to be rigid body motion. The rigid fluid method is straightforward to implement, incurs very little computational overhead, and can be added as a bridge between current fluid simulators and rigid body solvers. Many solid objects of different densities (e.g., wood or lead) can be combined in the same animation. The rigid body solver used in this work is the impulse based solver, with shock propagation introduced by Guendelman et al. in [36]. The rigid body solver allows for collisions ranging from completely elastic, where an object can bounce around forever without loss of energy, to completely inelastic where all energy is spent in the collision. Static and dynamic frictional forces are also incorporated. The details of this rigid body solver will not be discussed, but the small changes needed to couple this solver to interact with fluid will be. When simulating fluids, the fluid-air interface (free surface) is an important part of the simulation. In [8], the free surface is modelled by a set of marker particles, and after running a simulation we create detailed polygonal models of the fluid by splatting particles into a volumetric grid and then render these models using ray tracing with sub-surface scattering. In [7], I model the free surface with a particle level set technique [14]. The surface is then rendered by first extracting a triangulated surface from the level set and then ray tracing that surface with the Persistence of Vision Raytracer (http://povray.org).
42

A Classification of the Weed Vegetation in Mituo County, Kaohsiung

Lin, Chun-yi 07 February 2010 (has links)
This study surveyed floristic composition and distribution of weed vegetation in Mituo County. 206 relevés were surveyed according to relevé method. A total of 140 species belonging to 32 families of the vascular plants were recorded. The weed communities were classified with nonmetric multidimentional scaling, two-way indicator species analysis, tabular comparison method, fidelity and synoptic table analysis. Discriminate analysis was used to evaluate the distinctness of classification unitsal vegetation classification system was made using Braun-Blanquet approach of floristic-sociological classification in lower levels and physiognomic-sociological classification in higher levels. In floristic-sociological classification, assication is the basic unit, and it should be grouped into higher units (alliance) by floristic composition. The results showed 1 formation class, 2 formations in phsiogonomic units, and 4 alliances, 6 associations in floristic units: I. Lower montane-lowland weed vegetation formation A. Echinochloa colona alliance a. Echinochloa colona association b. Trianthemum portulacastrum association c. Panicum maximum association B. Dichanthium aristatum alliance d. Dichanthium aristatum association C. Eriochloa procera alliance e. Eriochloa procera association II. Sand dune vegetation formation D. Ipomoea pescaprae subsp. brasiliensis alliance f. Ipomoea pescaprae subsp. brasiliensis association
43

EM-Based Joint Detection and Estimation for Two-Way Relay Network

Yen, Kai-wei 01 August 2012 (has links)
In this paper, the channel estimation problem for a two-way relay network (TWRN) based on two different wireless channel assumptions is considered. Previous works have proposed a training-based channel estimation method to obtain the channel state information (CSI). But in practice the channel change from one data block to another, which may cause the performance degradation due to the outdated CSI. To enhance the performance, the system has to insert more training signal. In order to improve the bandwidth efficiency, we propose a joint channel estimation and data detection method based on expectation-maximization (EM) algorithm. From the simulation results, the proposed method can combat the effect of fading channel and still the MSE results are very close to Cramer-Rao Lower Bound (CRLB) at the high signal-to-noise ratio (SNR) region. Additionally, as compare with the previous work, the proposed scheme also has a better detection performance for both time-varying and time-invariant channels.
44

An investigation of passing operations on a rural, two-lane, two-way highway with centerline rumble strips

Miles, Jeffrey David 17 February 2005 (has links)
The research in this thesis was conducted to investigate the initial stage of passing maneuvers on a rural, two-lane, two-way (RTLTW) highway with centerline rumble strips (CRSs). Four measures of effectiveness were used: (1) number and type of erratic movements by a passing vehicle, (2) number of and time between centerline encroachments of a passing vehicle, (3) gap distance of a passing vehicle, and (4) centerline crossing time. Data were collected for a before-and-after analysis at one site, in Comanche County, Texas. The test section was on US 67 from Comanche, Texas to the county line south of Dublin, Texas. The posted speed limit for this RTLTW highway was 70 mph during the day. CRSs were installed along approximately 15 miles of US 67. Only one test design for CRSs was installed. The design specification was for a CRS to be milled to a 0.5-inch depth, 7-inch length, and 16-inch width. This specification was developed from current state practices throughout the United States. CRSs were installed continuously through passing and no-passing zones, and they were spaced at 24 inches on-centers. Pavement markings were striped over the CRSs. Data were collected using an innovative data collection system developed by the author through the Texas Transportation Institute (TTI). This system was mounted to a four-door sedan, and it consisted of four concealed cameras that recorded the entire passing maneuver around the data collection vehicle. Data were collected at three different speeds during the daytime. The speeds were 55, 60, and 65 mph (15, 10, and 5 mph, respectively, under the posted speed limit). Based on the assessment of the four MOEs, the overall finding of this thesis was that driver performance during the initial phase of passing maneuvers was not negatively impacted after the installation of CRSs on US 67. The caveat is that differences in the weather conditions may have influenced the results. The weather was dry with clear skies at the study site during data collection prior to the installation of CRSs; however, the weather consisted of intermittent rain during the data collection after the installation of CRSs.
45

Strengthening of two-way reinforced concrete slabs with Textile Reinforced Mortars (TRM)

Papanicolaou, Catherine, Triantafillou, Thanasis, Papantoniou, Ioannis, Balioukos, Christos 03 June 2009 (has links) (PDF)
An innovative strengthening technique is applied for the first time in this study to provide flexural strengthening in two-way reinforced concrete (RC) slabs supported on edge beams. The technique comprises external bonding of textiles on the tension face of RC slabs through the use of polymer-modified cement- based mortars. The textiles used in the experimental campaign comprised fabric meshes made of long stitch-bonded fibre rovings in two orthogonal directions. The specimens measured 2 x 2 m in plan and were supported on hinges at the corners. Three RC slabs strengthened by textile reinforced mortar (TRM) overlays and one control specimen were tested to failure. One specimen received one layer of carbon fibre textile, another one received two, whereas the third specimen was strengthened with three layers of glass fibre textile having the same axial rigidity (in both directions) with the single-layered carbon fibre textile. All specimens failed due to flexural punching. The load-carrying capacity of the strengthened slabs was increased by 26%, 53%, and 20% over that of the control specimen for slabs with one (carbon), two (carbon) and three (glass) textile layers, respectively. The strengthened slabs showed an increase in stiffness and energy absorption. The experimental results are compared with theoretical predictions based on existing models specifically developed for two-way slabs and the performance of the latter is evaluated. Based on the findings of this work the authors conclude that TRM overlays comprise a very promising solution for the strengthening of two-way RC slabs.
46

Trust, risk and vulnerability : towards a philosophy of risk communication

Hayenhjelm, Madeleine January 2006 (has links)
<p>This thesis is a philosophical contribution to the theories on risk communication. The topic of risk communication is approached from several different angles, but with a normative focus on equality and vulnerability.</p><p>Essay I is a comment on risk perception theory and the psychometric model in particular. In risk perception research individual risk taking is described as either a result of valuing the benefits from risk taking or a failure of comprehending the severity or probability of risks. The essay argues that sometimes individuals take risks simply because they are in a vulnerable position and have no other choice. Four factors are identified as crucial in risks from vulnerability: poor outset conditions, lack of reasonable options, hope and liability to disinformation.</p><p>Essay II addresses the democratic approach to risk communication and the ideal of risk communication as a dialogue between more or less equal stakeholders. The Essay argues that even the more innovative and dialogue oriented approaches to risk communication are unequal. This is often blurred by the confusion between the described ideal and the description of these newer approaches. This inequality is analysed in a three-fold way: influence over the communication process; influence over and access to information; and influence over risk decisions. The Essay develops a typology of different risk communication practices and influence distributions and concludes that the form of risk communication most commonly referred in the literature is the most imbalanced kind where all three types of influence falls to the same party.</p><p>Essay III explores the concept of trust, an often-mentioned objective for risk communication. The concept of trust is analyzed from previous philosophical approaches, and the idea of trust as comfortable defocusing is introduced. It is argued that not only the gains for the trustee but also the gains and risks for the truster, generally and in the case from risk communication, can be explained by this notion. It is concluded that public trust for institutions or organizations need not be framed on an individual level. Instead, the vulnerability of trusting can be counter-acted by a delegation of different stances, including both control and trust, among different individuals and institutions in society.</p>
47

Modelling of turbulent gas-particle flow

Strömgren, Tobias January 2008 (has links)
<p>An Eulerian-Eulerian model for dilute gas-particle turbulent flows is</p><p>developed for engineering applications. The aim is to understand the effect of particles on turbulent flows. The model is implemented in a finite element code which is used to perform numerical simulations. The feedback from the particles on the turbulence and the mean flow of the gas in a vertical channel flow is studied. In particular, the influence of the particle response time and particle volume fraction on the preferential concentration of the particles near the walls, caused by the turbophoretic effect is explored. The study shows that the particle feedback decreases the accumulation of particles on the walls. It is also found that even a low particle volume fraction can have a significant impact on the turbulence and the mean flow of the gas. A model for the particle fluctuating velocity in turbulent gas-particle flow is derived using a set of stochastic differential</p><p>equations. Particle-particle collisions were taken into account. The model shows that the particle fluctuating velocity increases with increasing particle-particle collisions and that increasing particle response times decrease the fluctuating velocity.</p>
48

Hygiene and Sanitation Promotion towards Cholera Prevention on District Level in Mozambique : A Communication Analysis

Booij, Dorrit, Al-Ayoubi, Daniel January 2015 (has links)
Cholera remains a threat to public health in many developing countries, including Mozambique. Although the disease is easily preventable by practices of hygiene and sanitation, cases are reported in the country every year, as for example in the Lago district in 2015. This qualitative research project set out to explore in what ways the promotion of hygiene and sanitation practices on district level in Mozambique is carried out. Therefore, actors, messages and channels involved in these communication processes were explored via a field study in Lago and a review of relevant literature. Subsequently, the results of the field study and literature review were analysed by applying the concepts of one-way and two-way communication which are part of public relations theory. This analytical framework allowed the researchers to fill a gap identified in the existing literature about hygiene and sanitation promotion, which did not seem to include communication theories linked to public relation practices when it came to hygiene and sanitation promotion in developing countries as a method to prevent cholera. It has been found that the one-way communication approach towards the public was successful in handling the recent cholera outbreak of 2015, however, the approach is not substantial and should be improved into a two-way communication approach, which would allow the local population to express their needs in hygiene and sanitation, as well as their capabilities to implement change in these matters. Simultaneously, a lack of resources within the district authorities involved in hygiene and sanitation promotion seems to encourage one-way communication towards the public from their side, as two-way communication would demand further resources for research into the above mentioned needs and capabilities of communities.
49

Relay-aided communications with partial channel state information

Yazdan Panah, Ali 21 October 2011 (has links)
Modern wireless communication systems strive to enable communications at high data rates, over wide geographical areas, and to multiple users. Unfortunately, this can be a daunting task in practice, as natural laws governing the wireless medium may hinder point-to-point transmissions. Communications over large distances (path loss), and physical obstructions in line-of-sight signals (shadowing) are prime examples of such impediments. One promising solution is to deploy intermediary terminals to help reestablish such broken point-to-point communication links. Such terminals are called relay nodes, and the corresponding systems are referred to as being relay-aided. As in the case of point-to-point communication, design of efficient transmission and reception techniques in relay-aided systems depends on the availability of propagational channel state information. In practice, such information is only accurate to a certain degree which is governed by overhead constraints, feedback delay, and channel fluctuations due to mobility. Understanding the impacts of such partial channel state information, and devising transmission and reception methods based on such understandings, is the main topic of this dissertation. The transmission protocol classifies relays as either one-way, where the relay receives signals from one terminal, or two-way, where the relay receives signals from more than one terminal. Designs and solutions for both one- and two-way relaying systems are presented in this dissertation. Emphasis is placed on two-way relaying systems given their superior efficiency in utilizing channel resources. For one-way relaying this dissertation presents power loading strategies for multiuser-multicast systems derived based on the availability of full or partial channel state information at the terminals. In the case of two-way relaying, both single and multi-user systems are analyzed. For single-user two-way relaying, this dissertation presents optimal methods of acquiring partial channel state information via pilot-aided channel estimation methods. This includes an analysis of the effects of channel estimation upon the system sum-rate. Also, the design of channel equalizers exhibiting robustness to partial channel state information is proposed. For multi-user two-way relaying, this dissertation presents several precoding strategies at the relay terminal(s) to combat the effects co-channel interference in light of the existence of self-interference inherent to two-way relaying operations. / text
50

Improvement of the one-way and two-way shape memory effects in ti-ni shape memory alloys by thermomechanical treatments

Urbina Pons, Cristina 11 July 2011 (has links)
Ti-Ni phase transformation behaviour is very sensitive to the thermal and mechanical history of the alloy. Thermomechanical cycling through the full transformation range may degrade the Ti-Ni functional properties (functional fatigue). These repeated transformation cycles cause changes in the SMA phase transformation behaviour due to the formation and accumulation of defects in the alloy microstructure. The main objective of this thesis is to establish the relationships between the changes in Ti-Ni phase transformation behaviour caused by thermomechanical processes, especially in the R-phase range, and the functional properties of the Ti-Ni shape memory alloys (SMAs). Establishing these relationships should allow us to find appropriate thermomechanical processes to substantially improve the Ti-Ni one-way and two-way shape memory effects. To achieve this objective, several experimental techniques are used including measuring variations of the electrical resistivity with temperature, X-ray diffraction, isothermal tension testing, thermal cycling under constant stress, and thermal cycling under zero stress. This study of the phase transformation changes caused by thermomechanical processes has led to a new way of interpreting resistivity curves for calculating the transformation temperatures. Moreover, we have determined how the R-phase influences the functional properties of SMA and, finally, we have substantially improved the properties of one-way and two-way shape memory effects by using thermal processes that avoid permanent deformation of the alloy. / Las transformaciones de fase en aleaciones de NiTi son altamente dependientes de la composición de la aleación, así como de la historia térmica y mecánica previa al uso de la SMA. El objetivo principal de esta tesis es establecer los vínculos existentes entre los cambios producidos en las transformaciones de fase por procesos termomecánicos y las propiedades funcionales en aleaciones con memoria de forma de Ti-Ni, tal que nos permita hallar los procesos termomecánicos más adecuados que proporcionen una mejora substancial en las propiedades funcionales de estas aleaciones. La determinación de estas relaciones, prestando especial atención a la fase-R, nos debe proporcionar las claves para incrementar las propiedades de memoria de forma y doble memoria de forma. Para la consecución de este objetivo se han usado diferentes técnicas de caracterización experimental: variación de la resistividad eléctrica con la temperatura (ER), difractometría de rayos X (DRX), ensayos de tracción isotérmicos, ciclados térmicos a tensión constante y ciclados térmicos a tensión nula. A través del estudio exhaustivo de las transformaciones de fase, se ha aportado una nueva interpretación de las curvas de resistividad para el cálculo de las temperaturas de transformación, se ha determinado la influencia de la fase-R en las propiedades funcionales de las SMA y se han mejorado substancialmente las propiedades de memoria simple y doble memoria de forma mediante procesos térmicos que evitan deformaciones permanentes antes del uso de la aleación. / Les transformacions de fase en aliatges de NiTi són altament dependents de la composició de l'aliatge, així com de la història tèrmica i mecànica prèvia a l'ús de la SMA. L'objectiu principal d'aquesta tesi és establir els vincles existents entre els canvis produïts en les transformacions de fase per processos termomecànics i les propietats funcionals en aliatges amb memòria de forma de Ti-Ni, tal que ens permeti trobar els processos termomecànics més adequats que proporcionin una millora substancial en les propietats funcionals d'aquests aliatges. La determinació d'aquestes relacions, prestant especial atenció a la fase-R, ens ha de proporcionar les claus per incrementar les propietats de memòria de forma i doble memòria de forma. Per a la consecució d'aquest objectiu s'han usat diferents tècniques de caracterització experimental: variació de la resistivitat elèctrica amb la temperatura (ER), difractometria de raigs X (DRX), assaigs de tracció isotèrmics, ciclats tèrmics a tensió constant i ciclats tèrmics a tensió nula. A través de l'estudi exhaustiu de les transformacions de fase, s'ha aportat una nova interpretació de les corbes de resistivitat per al càlcul de les temperatures de transformació, s'ha determinat la influència de la fase-R en les propietats funcionals de les SMA i s'han millorat substancialment les propietats de memòria simple i doble memòria de forma mitjançant processos tèrmics que eviten deformacions permanents abans de l'ús de l'aliatge.

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