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1
Hetting, Oscar, Joakim Hellman, and Maryam Tarighi. "Capitalizing on seasonalities in the Singapore Straits Times Index." Thesis, Internationella Handelshögskolan, Högskolan i Jönköping, IHH, Företagsekonomi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-18167.
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Purpose: The purpose of this thesis is to study the possible existence of day-of-the-week effects and month-of-the-year effects in the Singapore stock market over the period January 1st 1993 to December 31st 2011. The findings are analysed with the intention of developing investment strategies and to investigate if behavioural finance can help to explain the existence of seasonal anomalies. Background: A number of previous studies have found evidence of seasonal anomalies in global stock markets, and by challenging the core assumptions of market efficiency, such anomalies may make it possible to predict the movement of stock prices at certain periods during the year. Consequently, there may be substantial profit-making opportunities that clever investors can benefit from, raising two important questions: (1) can such anomalies be strategically used to outperform the market and (2) why do such cyclical return patterns exist? Method: Daily closing prices from the Singapore Straits Times Index (STI) are used to compute average daily and monthly returns, which are further analysed through the use of statistical significance analysis and hypothesis testing to identify the possible existence of day-of-the-week effects and month-of-the-year effects in the Singapore stock market. The results of the statistical investigation are used to develop investment strategies that are designed to take advantage of both positive and negative effects, and the theories of behavioural finance are applied to help explain why seasonalities occur at certain points in time. Conclusions: This study finds evidence of several seasonal anomalies in the Singapore stock market. Both day-of-the-week effects and month-of-the-year effects are present in the STI over the full sample period. Many of these effects can be explained by behavioural finance, and used to develop investment strategies that outperform the market.
2
Tan, Lay Siong, and n/a. "The Straits Times' reporting of Singapore's communication news, 1992-1995." University of Canberra. Communication, Media & Tourism, 1996. http://erl.canberra.edu.au./public/adt-AUC20061113.101002.
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The purpose of this study is to analyse how the Straits Times reported
Singapore's communication news between May 1992 and October 1995,
with a focus on Singapore's communication regionalisation. This study is
a modest attempt to depart from some of the approaches taken by recent
communication related studies of the Singapore experience. They tend to
focus on the domestic side of state-press relationship and the issue of
Singaporean press freedom, without sustained consideration of external
forces, such as globalisation.
This analysis provides a synthesis of secondary sources and a qualitative
content analysis of communication news in the Straits Times. The results
suggest there has been a convergence between the stories in the Straits
Times and official views about two themes - business regionalisation and
'Asian' media standards. Results suggest the government has an
extensive influence over Singapore's communication, especially with
regard to media content. Also, the analysis shows Singapore's
identification with Asia, despite bilateral and regional tensions in business
and culture, and suggests an uneasy relationship between Singapore and
the West, in particular, with the US. That is, while Singapore's business
relations with the US are good, its cultural relations are not, especially
when Singapore's practice of media standards does not accept the
American interpretation, but one based on its national interests.
This study provides a glimpse of global communication forces which
are influencing Singapore's communication development, as interpreted
in the stories from the Straits Times. Although there remains
uncertainties about Singapore's communication future, this study may
provide an insight as to whether Singapore has taken the right direction
in becoming a leading country in advocating an 'Asian voice'.
3
Suhonen, Lari-Valtteri. "Speak Good English Movement in Singapore : Reactions in Social and Traditional Media." Thesis, Högskolan Dalarna, Engelska, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:du-6283.
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The first Speak Good English Movement, SGEM, took place in 2000, and has been organized annually ever since. Speaking a “standard” form of English is considered to bring increased personal power. However, the SGEM wants the Singaporeans to use “standard” English in their private life as well. A decade after the beginning of the campaign, a Speak Good Singlish Movement was started. Based on studies of language and identity, it is understandable why some Singaporeans might feel the SGEM threatens their identity. However, the reactions towards the campaign are mainly positive. For the purposes of this analysis, Twitter messages, Facebook pages, and newspaper articles from The Straits Times were collected. The SGEM has hailed both direct and indirect praise and criticism in both social and traditional media: Five newspaper articles praise the campaign while five criticize it; the results are nine and seven respectively for social media. This thesis looks at reactions towards the SGEM in both social and traditional media, analyzes how these reactions might relate to the ideas of the power of language, its variety and the relation of language and identity.
4
Garcia, Azuero Alejandro. "Dynamic reservoir characterization from overburden time-lapse strains." Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2525.
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Accurate reservoir depletion or pressure change patterns are of great value when planning infill drilling programs for field development, as well as when monitoring injection wells and swept/unswept areas. In addition, a precise dynamic geomechanical description of the reservoir and overburden stress state could prevent costly undesired effects on the production infrastructure such as sea floor subsidence, casing shear and well failure. Dynamic characterization of reservoirs, until recently, had only well data to rely on, which apart from the inherent uncertainties (e.g. due to formation damage), provides no direct information on what is taking place between the wells. The advent of time-lapse seismic at the end of the 1990s meant that this gap could be bridged, providing measurements of the changes taking place in the subsurface. In its origins, time-lapse seismic was conceived as a tool to image intra-reservoir fluid movements via the dependency of reflection amplitudes on acoustic impedance, which is affected by fluid saturation changes in the porous reservoir rocks. However, depletion induced velocity changes are also non negligible. Furthermore, the reflectors may undergo deformation and displacement where compaction and subsidence are involved. As a consequence, analysis of amplitude changes is not straightforward, since in most cases, amplitudes have been shifted by a non negligible time difference or time-shift, presenting not only challenges, but also new possibilities. It is in the possibilities of these time-shifts that the present study is based. This research presents a novel method which numerically solves the static field problem in a multilayered heterogeneous media, relating overburden strain to reservoir depletion. It builds up on previous works based on Geertsma type solutions requiring a homogeneous half-space. This technique makes it possible to estimate the reservoir’s stress state, strain and pressure changes from measured overburden strain by considering the earth as a linear filter with reservoir compaction and overburden strain as parameters. However, some a priori knowledge is needed in the form of a rough subsurface model and a preliminary geomechanics simulation in order to approximate the transfer functions as Wiener filters. In this thesis, the Wiener filter concept has been applied to three real North Sea fields. First, to the Elgin field, an HP/HT shallow marine Upper Jurassic sandstone reservoir located in the UK sector of the North Sea. Then, to the Ekofisk and South Arne fields, both compacting chalk reservoirs in the Norwegian and Danish sector of the North Sea respectively. Additionally, by using a synthetic example the method has been validated and compared with a linear inversion approach using a Geertsma type Green’s function achieving higher accuracy. The project involved not only the development and application of the method itself, but the calculation of time-strains from the measured seismic and the construction and implementation of full field geomechanical models.
5
Thomas, Daniel D. "High resolution optical time domain methods for measuring strain." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03242009-040449/.
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Bergström, Jörgen S. (Jörgen Stefan) 1969. "Large strain time-dependent behavior of elastomeric materials." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9794.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.Includes bibliographical references (p. 248-254).
The mechanical behavior of elastomeric materials is known to be rate-dependent and to exhibit hysteresis upon cyclic loading. Although these features of the rubbery constitutive response are well-recognized and important to its function, few models attempt to quantify these aspects of response. Based on a detailed experimental investigation a new constitutive model for the time-dependence of unfilled elastomers has been developed. The foundation of the model is that the mechanical behavior can be decomposed into two parts: an equilibrium network corresponding to the state that is approached in long time stress relaxation tests; and a second network capturing the non-linear rate-dependent deviation from the equilibrium state. The time-dependence of the second network is further assumed to be governed by the reputational motion of molecules having the ability to significantly change conformation and thereby relaxing the overall stress state. To model the behavior of particle filled elastomers the newly developed constitutive framework is then extended to include filler interactions by amplification of the first strain invariant. In an effort to examine some of the assumptions that are common in the constitutive modeling of particle filled elastomers, a detailed series of micromechanical models were constructed using two- and three-dimensional finite elP.ment simulations. The results indicate that the effect of filler particles can be accurately predicted using stochastic three-dimensional simulations suggesting that successful modeling mainly requires a rigorous treatment of the composite nature of the microstructure and not molecular level concepts such as alteration of mobility or effective crosslinking density in the elastomeric phase of the material. A direct comparison between the new model and experimental data for a number of different elastomers the observed behavior.
by Jörgen S. Bergström.
Ph.D.
7
Olson, Ted. "Old Time and Bluegrass: Two Main Strains of Music Along The Crooked Road." Digital Commons @ East Tennessee State University, 2016. https://dc.etsu.edu/etsu-works/1206.
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Cook, Frederick Philip. "Characterization of UHMWPE Laminates for High Strain Rate Applications." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/30849.
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The research presented in this thesis represents an effort to characterize the properties of ultra-high molecular weight polyethylene (UHMWPE). As a composite of polymers, the properties of UHMWPE are time-dependent. It is desired by research sponsors to know the properties of the material at high strain rates, in order to simulate the use of these materials in computer models. Properties believed to be significant which are investigated in this research are the tensile properties of lamina and laminates, and the interlaminar shear properties of laminates. The efficacy of using time-temperature superposition to shift tensile properties of the composite is investigated, and a novel apparent shear strength test is proposed and demonstrated. The effects of processing the material at various temperatures and pressures are also investigated.Master of Science
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Lee, Z. S. "Towards real-time imaging of strain in soft tissue." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/20003/.
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Jacobson, Carl P. "Temperature corrected strain measurements using optical time domain reflectometry." Thesis, Virginia Tech, 1990. http://hdl.handle.net/10919/41906.
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A method of using optical fiber to measure strain and
correct for the effects of temperature is proposed. A means
of measuring apparent strain is given, pure temperature is
measured using Fresnel-backscatter based Optical Time Domain
Reflectametry, and a method for combining the two measurements
to obtain a measurement of mechanically-induced strain alone
is developed. The background, theory and experimental results
that demonstrate the feasibility of such a system are
presented and the results are compared with the performance
of existing fiber-based means of measuring temperature.
Experiments on several OTDR-addressed, intensity-based optical
temperature sensors are performed and a method for
manufacturing small air gap splices for use in measuring
strain at several places along an optical fiber are presented.
Master of Science
11
Adendorff, Christo Johan. "The time-dependent cracking behaviour of strain hardening cement-based composite." Thesis, Stellenbosch: University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/2847.
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Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2009.ENGLISH ABSTRACT: Strain Hardening Cement-based Composite (SHCC) is part of the High Performance Fibre Reinforced Cement-based Composite (HPFRCC) family and is a relative new concrete composite. This Fibre Reinforced Cement-based Composite (FRCC) contains randomly distributed short fibres and when subjected to a uni-axial tensile load multiple cracking occurs. The multiple cracking generates fine cracks which are normally smaller than 100 μm and achieve a strain capacity of more than 5 %. There are limited publications regarding the research of sustained tensile tests on SHCC and especially the cracking behaviour of SHCC under quasi-static uni-axial as well as sustained tensile loads. The cracking behaviour is described as the average crack width, number of cracks and descriptive statistical properties which could be used to represent the distribution of the multiple fine cracks under uni-axial tension. There are two types of tests that were under consideration to determine the cracking behaviour of SHCC. The first is quasi-static uniaxial tensile tests and the second is sustained tensile tests. The latter was dependant on the uni-axial tensile tests in terms of the sustained load applied. The sustained loads ranged from 40 % to 80 % of the ultimate tensile resistance recorded from the uni-axial tensile tests that correspond with a strain rate of 0.001 /s. Different strain rates were used for the uni-axial tensile tests to determine the effect on the cracking behaviour. The cracking behaviour was determined with the aid of a non-contact optical 3D digital deformation measuring device called ARAMIS. The content of this thesis gives a background study of the cracking behaviour and relevant research performed on SHCC under certain loads as well as some literature about the timedependant effects of a cement-based composite. The functioning of the device called ARAMIS is explained as well as the resulting effects of this device on the preparation of the test specimens. The experimental framework for the uni-axial and sustained tensile tests is discussed. Thereafter, the experimental results of the tests are depicted and discussed. The results shed some light on the basic material properties such as the average ultimate stress and average ultimate strain, Young’s modulus, etc. for the quasi-static tensile tests as well as shrinkage and creep of SHCC. The cracking behaviour such as the average crack width, number of cracks, the variance and skewness of the distribution of the crack widths in the test specimens for the quasi-static uni-axial and sustained tensile tests are depicted and discussed. The cracking behaviour when subjected to uni-axial tensile tests with different strain rates is significantly governed by the formation of new cracks and the average crack width remains small with increase in strain. There is no significant difference for the cracking behaviour found when subjected to different strain rates. However, when SHCC is subjected to a sustained load then the average crack width is dependant on the number of cracks that form over time as well as the load level. The formation of fewer and wider cracks was observed for specimens loaded at average 40 % of the ultimate tensile resistance stress, however at loading percentages of higher than 65 % more cracks developed which resulted in a smaller average crack width.
AFRIKAANSE OPSOMMING: Vervorming Verharding Sement gebaseerde samestelling “Strain Hardening Cement-based Composite” (SHCC) is deel van die familie van “High Performance Fibre Reinforced Cement-based Composite” (HPFRCC) en is ʼn relatiewe nuwe beton samestelling. Hierdie vesel versterkte sement gebaseerde beton bevat willekeurig verspreide kort vesels en veelvoudige klein krake vorm onder monotoniese trekkragte. Hierdie veelvoudige klein krake is minder as 100 μm wyd en lei tot ʼn vervorming van meer as 5 %. Daar is ʼn tekort aan navorsing oor die kruip van SHCC sowel as die kraak gedrag van hierdie sement gebaseerde samestelling onderhewig aan trek. Die kraak gedrag word beskryf as die gemiddelde kraakwydte, aantal krake en ʼn paar beskrywende statistiese parameters. Hierdie kraak gedrag parameters kan gebruik word om ʼn verdeling te kan weergee van die veelvoudige klein krake onder ʼn trek belasting. Twee tipes toetse was uitgevoer om die kraak gedrag te beskryf. Die eerste tipe toets was monotoniese trek toetse en die tweede tipe was kruip toetse. Die tweede toets was afhanklik van die monotoniese trek toetse in terme van die belasting wat gebruik was vir die kruip toetse. Die belasting was gevarieer vanaf 40 % tot 80 % van die breekbelasting wat bepaal is met die monotoniese trektoetse wat ooreenstem met ʼn vervorming tempo van 0.001 /s. Verskillende vervorming tempo’s vir die monotoniese trektoetse was uitgevoer om te bepaal wat die effek is op die kraak gedrag. Die kraak gedrag was bepaal met behulp van ʼn geen-kontak optiese 3D digitale deformasie meet instrument genoem ARAMIS. Die inhoud van die tesis bevat ʼn kort opsoming oor ʼn agtergrond studie van die kraak gedrag en relevante navorsing oor vesel versterkte sement gebaseerde beton, sowel as literatuur oor die tydafhanklike effekte van ʼn sement gebaseerde samestelling. Die beheer en gebruik van die meet instrument ARAMIS word verduidelik, sowel as die effek van hierdie masjien op die voorbereiding vir die eksperimente. Die eksperimentele uiteensetting vir die monotoniese en kruip toetse word beskryf. Daarvolgens is die resultate van die eksperimentele toetse getoon en verduidelik. Die resultate verduidelik die basiese materiaal eienskappe, byvoorbeeld die gemiddelde breekspanning met die ooreenkomstige breekvervorming, Young’s modulus en so voorts vir die monotoniese trektoetse, sowel as eienskappe met betrekking tot krimp en kruip van SHCC. Die kraak gedrag naamlik die gemiddelde kraakwydte, aantal krake per meter, variansie en die skuinsheid van die ontwikkelde krake met die toets proefstukke vir die monotoniese en kruip trek toetse word weergegee en verduidelik. Die kraak gedrag van SHCC wanneer getoets word met verskillende monotoniese trektoets tempo’s word beheer deur die ontwikkeling van nuwe krake en die gemiddelde kraakwydte is beduidend laag met toenemende vervorming. Daar is geen beduidende verskil in die kraak gedrag ten opsigte van die verskillende monotoniese trek tempo’s nie. In teendeel, wanneer SHCC belas word met ʼn konstante las oor tyd word die gemiddelde kraakwydte beheer deur die ontwikkeling van nuwe krake sowel as die belasting wat aangewend is. Onder ʼn belasting van so laag as 40 % van die breekbelasting vorm daar minder krake, maar met ʼn groter gemiddelde kraakwydte. Wanneer belas word met meer as 65 % van die breekbelasting vorm meer krake wat lei tot ʼn kleiner gemiddelde kraakwydte.
12
Miyazono, Toshiya. "Constitutive models of a time dependent material at finite strain levels /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/7134.
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Nowak, Stephanie Beth. "Understanding Time-Variant Stress-Strain in Turkey: A Numerical Modeling Approach." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/26072.
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Over the past century, a series of large (> 6.5) magnitude earthquakes have struck along the North Anatolian Fault Zone (NAFZ) in Turkey in a roughly East to West progression. The progression of this earthquake sequence began in 1939 with the Ms 8.0 earthquake near the town of Erzincan and continued westward, with two of the most recent ruptures occurring near the Sea of Marmara in 1999. The sequential nature of ruptures along this fault zone implies that there is a connection between the location of the previous rupture and that of the future rupture zones. This study focuses on understanding how previous rupture events and tectonic influences affect the stress regime of the NAFZ and how these stress changes affect the probability of future rupture along any unbroken segments of the fault zone using a two dimensional finite element modeling program.
In this study, stress changes due to an earthquake are estimated using the slip history of the event, estimations of rock and fault properties along the fault zone (elastic parameters), and the far-field tectonic influence due to plate motions. Stress changes are not measured directly. The stress regime is then used to calculate the probability of rupture along another segment of the fault zone.
This study found that when improper estimates of rock properties are utilized, the stress changes may be under- or over- estimated by as much as 350% or more. Because these calculated stress changes are used in probability calculations, the estimates of probability can be off by as much as 20%. A two dimensional model was built to reflect the interpreted geophysical and geological variations in elastic parameters and the 1939 through 1999 rupture sequence was modeled. The far-field tectonic influence due to plate motions contributed between 1 and 4 bars of stress to the unbroken segments of the fault zone while earthquake events transferred up to 50 bars of stress to the adjacent portions of the fault zone.
The 1999 rupture events near Izmit and Düzce have increased the probability of rupture during the next ten years along faults in the Marmara Sea to 38% while decreasing the probability of rupture along the faults near the city of Bursa by ~6%. Large amounts of strain accumulation are interpreted along faults in the Marmara Sea, further compounding the case for a large rupture event occurring in that area in the future.Ph. D.
14
Quinton, Cheryl Denise. "Growth rate and spawning time in diallel crosses of three strains of rainbow trout, Oncorhynchus mykiss." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ58370.pdf.
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French, Kimberly A. "Episodic Work-Family Conflict and Strain: A Dynamic Perspective." Scholar Commons, 2017. https://scholarcommons.usf.edu/etd/7399.
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Given rising work and family demands in our society for both men and women, the experience of work-family conflict is commonplace. Work-family conflict occurs when the demands of work or family make it difficult to meet the demands of the alternate domain. A sizeable body of research has established work-family conflict and its nomological network. Despite decades of research, we have yet to form a precise understanding of when work-family conflicts occur and what happens when a conflict arises. The current research addresses these questions using an experience sampling, episodic approach. Two primary research questions are addressed. First, I used border and boundary theory to identify when work-family conflict episodes are likely to occur. Second, I used stressor-strain and allostatic load theories to examine what happens with regard to psychological, physiological, and behavioral strain following an episodic work-family conflict over time. The results suggest work-family conflict occurs when individuals transition in between work and family domains. Further, family-to-work conflict tends to occur in the morning, while work-to-family conflict tends to occur in the afternoon. Fatigue showed significant reactivity at the time of a family-to-work conflict and recovered in the following time point. Unhealthy eating also showed a sleeper pattern, such that unhealthy eating increased at the end of the day, following a work-to-family conflict. Unexpectedly, fatigue decreased at the time of a family-to-work conflict, indicating family-to-work conflict may be a restorative, rather than taxing. Post-hoc analyses showed some evidence that work-to-family conflict accumulation is associated with increased strain over the course of three days. Again, results suggest family-to-work conflict accumulation may reduce, rather than increase, strain. Implications for the theoretical relationship between work-family conflict and strain, as well as border/boundary theory are discussed. In addition, practical implications for flexible work initiatives and episodic research design are considered.
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O'Brien, Edwin William. "Cold expansion of large holes in thick 7010 light alloy aircraft material : strains in the time domain." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248826.
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Pereira, Pedro André Marques. "Measuring the strain of metallic surfaces in real time through vision systems." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/16447.
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Mestrado em Engenharia MecânicaVision systems have already proven to be a useful tool in various elds. The ease of their implementation, allied to their low cost mean that their growth potential is immense. In this dissertation it is proposed a approach to measure strains in metallic surfaces, using stereo vision. This approach is based on the 3D DIC. This method measures the strain of the surface by dividing this surface in small sections, called subsets, and iteratively nding the equation that describes its shape variation through time. However, calculating the transformation of this subset is very timeconsuming. The proposed approach tries to optimize this calculation by rst determine the displacement eld, and then the strain eld by derivation. The dissertation also presents some experimental data and practical considerations relatively to the camera setup and image equalization algorithms in order to obtain better disparity maps. The results were veri ed experimentally and compared with the results obtained from other softwares.
Os sistemas de vis~ao j a provaram ser uma ferramenta util em v arios campos. A facilidade da sua implementa c~ao, aliada ao seu baixo custo signi cam que o seu potencial de crescimento e enorme. Nesta disserta c~ao e proposta uma abordagem para medir deforma c~oes em superf cies met alicas usando vis~ao stereo. Esta abordagem e baseada na t ecnica 3D DIC. Este m etodo mede as deforma c~oes da superf cie dividindo-a em pequenas se c~oes, designadas por sub- sets, tentando iterativamente encontrar a equa c~ao que de ne as varia c~oes das suas formas ao longo do tempo. No entanto, o c alculo das transforma c~oes destes subsets e demorado. A abordagem proposta pretende pretende otimizar este c alculo determinando primeiro o campo de deslocamentos e depois o campo das deforma c~oes atrav es da deriva c~ao. A disserta c~ao apresenta tamb em dados experimentais e considera c~oes pr aticas relativamente a con gura c~ao (setup) das c^amaras e algoritmos de equaliza c~ao de imagens de forma a se obterem melhores mapas de disparidade. Os resultados foram veri cados experimentalmente e comparados com os resultados obtidos por outros softwares.
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Oatway, Wayne Brian. "Time resolved study of the deformation of polyethylene at high strain rates using X-ray diffraction and stress-strain techniques." Thesis, Keele University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263196.
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Albahttiti, Mohammed T. "Freeze-thaw performance of prestressed concrete railroad ties." Diss., Kansas State University, 2015. http://hdl.handle.net/2097/20376.
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Doctor of PhilosophyCivil Engineering
Kyle Riding
Air voids are purposefully entrained in concrete to provide freeze-thaw durability of prestressed concrete railroad ties. Durability assurance requires consistent provision of an air void system comprised of small, well-distributed bubbles in sufficient quantity for durability and a quality control method for testing tie freeze-thaw durability. Manufacturing processes at three concrete manufacturing plants were investigated in order to determine the effects of process variability on resulting concrete air void system variability. Variation in the concrete air void system and other rheological properties occurred as results of the manufacturing process and vibration. Freezing and thawing durability testing of prestressed concrete ties is currently performed by applying ASTM C666 on 3 x 4 x 11 to 16 in. specimens cut from the shoulders of concrete ties. However, excising these specimens from prestressed concrete could lead to stress changes in the sample and cracking, potentially causing false interpretations of results. Therefore, testing was undertaken to understand the effects of prestressing and sample extraction on freeze-thaw durability measured by ASTM C666. In order to assess the effects of sampling and testing procedures on freeze-thaw quality control testing results of prestressed concrete railroad ties, full ties, half ties, and 3 x 4 x 11 in. excised samples were tested. Freeze-thaw testing included determination of the optimal method to measure freeze-thaw deterioration in large sections, the effects of saw-cutting, and the presence of reinforcement. Results indicated that the Ultrasonic Pulse Velocity accurately represented deterioration in large sections. The presence of reinforcement in excised samples led to faster deterioration compared to cast ASTM C666 samples, while saw-cutting without reinforcement did not significantly affect freeze-thaw durability.
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Riche, Olivier. "Time-dependent inverse box-model for the estuarine circulation and primary productivity in the Strait of Georgia." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37738.
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During 2002–2006, a comprehensive set of observations covering physical, biological, radiative and atmospheric parameters was obtained from the southern Strait of Georgia (SoG), Western Canada by the STRATOGEM program. Monthly time series of estuarine layer transports over 2002–2005 were estimated using a time-dependent 2-box model in a formal inverse approach. These transports are then consistent with the temperature and salinity fields, as well as riverine freshwater inflow (R) and atmospheric heat fluxes. Uncertainty was analyzed by resampling observations using bootstrap methods. The transport time series were then combined with observations of nutrient concentrations to construct monthly time series of nutrient uptake for nitrate, phosphate, and silicic acid.
Analysis of these time series suggests that the SoG estuarine circulation is not very sensitive to the seasonal changes of R. Comparison of the surface layer transport (U₁) and R yields the first observational relationship between the SoG estuarine circulation and R. This relationship (U₁=2.68 m²s⁻²/³× 10³ R¹/³) is consistent with estuarine theories. Although the flows change slightly with the freshet, a 5-fold change in R results only in a 40% change in U₁. Based on the calculated sink of near-surface nutrients, net primary productivity is estimated to be 212 gC m⁻²yr⁻¹, which is similar to values obtained differently in similar estuaries. Comparison of the nitrate and phosphate uptake rates suggests that the primary productivity (PP) is mainly new PP during spring and summer. Thus, PP is mainly controlled by the upwelling supply of nutrients through deep inflow and entrainment. The uptake of silicic acid (Si) is almost two times larger than the uptake of nitrate during diatom spring blooms, while it is similar during the summer blooms. Such a high Si uptake suggests that spring diatoms form heavier frustules or that heterotrophic silicoflagellates compete with diatoms for Si. Speculative considerations based on comparison of the estimated production rate of near-surface oxygen and new PP also suggest that the regenerated PP is small. In addition, the summer heterotrophic respiration might be in excess by as much as
2 gO m⁻² d⁻¹ relative to the net PP.
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Chen, Yu-Szu. "Testing and modeling tensile stress-strain curve for prestressing wires in railroad ties." Thesis, Kansas State University, 2016. http://hdl.handle.net/2097/32582.
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Master of ScienceDepartment of Civil Engineering
Robert J. Peterman
Prestressed concrete is commonly used for bridges, pavement and railroad ties because of economic advantages in cost, sustainability service life, and environmental friendliness. In general concrete design standard, the ultimate moment strength in flexure design is computed by finding the equilibrium of the internal force in the section (the compressive force in concrete and tension force in the steel and reinforcement). To predict tension force in steel one generally applies the 7-wire low-relaxation prestressing strand equation from the PCI manual even though the design employed prestressing wires instead of strand. The other method is to use equations from the ACI Code which is over conservative. Considering both approaches are lack accuracy, this research will provide an accurate estimation of the stress in prestressing wires through an experimental program and analytical modeling. The real stress-strain curves are collected through experimental testing in 13 types of prestressing wire. Experimental results are then used for modeling existing equations. As a result a more precise estimation is achieved. Additionally, this research simplifies the procedure for utilizing the equations which offers convenience in practical application.
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Khurelbaatar, Tsolmonbaatar. "Quantitative Imaging and Computational Modelling to Estimate the Relationship between Mechanical Strain and Changes within the Distal Tibia in First-Time Marathon Trainees." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-theses/1323.
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Background Running is a popular form of exercise that more than 55 million Americans actively participate. Endurance running like marathon and half- marathon is getting increasingly popular among active runners. Although the effect of running is considered beneficial to bone health, the direct relationship between strains and strain gradients occurred during long distance running and bone changes is still not clear. Especially, given a high rate of injury associated with the first-time marathon, understanding the direct effect of strain stimuli on bone health is an important issue. Based on the previous studies, we hypothesized that the higher values of strain will induce bone adaptation more effectively and will lead to higher bone osteogenic changes. Since osteocytes sense shear stress caused by the interstitial fluid flow, which is created by the deformations, and regulate activities of osteoblasts and osteoclast that govern bone adaptation, we also hypothesized that the local strain gradient will create pressure differences within the interstitial fluid network and will increase fluid flow. Furthermore, due to that increased fluid flow, the regions with the higher strain gradient will experience a higher amount of bone adaptation. Thus, in this study, our purpose was to define the effect of the strains and strain gradients on bone changes within distal tibia, which is the most prone anatomical site to low risk stress fracture, during training for first-time marathon. Methods High-resolution and low-resolution computed tomographic (CT) images of the distal tibia were obtained before and after a self-selected training from runners who were actively training to participate in their first-time marathon in the next calendar year. The low resolution scan covered a 69.864 mm length of the distal end of the tibia while the high resolution CT scan covered a 9.02 mm region of the distal tibia. Using low resolution CT image based subject specific finite element (FE) models, the strains and strain gradients of the distal tibia at the instance of the peak ground reaction force (GRF) were calculated. The baseline and follow-up high resolution CT scans were used in high resolution peripheral quantitative CT (HRpQCT) analysis and the estimation of bone changes over the training period. Finally, the effect of strains and strain gradients on the distal tibia bone changes was estimated based on the FE model driven strain values and HRpQCT analysis driven bone changes. We used a linear mixed model to define the relationship between strain values and bone changes in the distal tibia. Results The strain values that occurred during marathon training had significant effects on bone changes in the distal tibia. Particularly, the strain gradients showed a higher effect than the strains. In the cortical compartment, the strain gradients, which were calculated as a strain difference of a node from the surrounding nodes (Strain Gradient-1), affected the bone mineral density (BMD) negatively, and per 1000 µε increase resulted in 2.123% decrease in the cortical BMD. The strain gradients, which were calculated as a strain difference of a node from the surrounding nodes normalized to distance to surrounding nodes (Strain Gradient-2), presented a positive effect on the cortical bone volume with a slope of 4.335% / 1000 µε. In the trabecular compartment, the strain gradient-1 showed negative effects on the percent change in BMD and bone mineral density (BMC), whereas the strain gradient-2 showed positive effects on the percent change in BMD and BMC. Conclusion The linear mixed model analysis revealed a statistically significant (p < 0.05) relationship between strain gradients that occurred during running and distal tibia bone changes. The strains, biometrics, and initial parameters of bone did not show any significant effect on the bone changes. The connection between local strain environment and bone changes in the distal tibia investigated in this study is an important step to understand the mechanism of mechanically induced bone adaptation.
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Fung, Wing Wah. "Lightly cemented rubber tire chips as highway pavement sub-base and the use of fiber Bragg's grating (FBG) as instrumentation sensors /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202004%20FUNG.
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Dunford, Kristin Marie. "Effect of Postmortem Time and Preservation Fluid on the Tensile Material Properties of Bovine Liver Parenchyma." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/90179.
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The liver is one of the most frequently injured abdominal organs in motor vehicle collisions. Although previous studies have quantified the tensile failure properties of human liver parenchyma at 48hrs postmortem, it is currently unknown how the material properties change between time of death and 48hrs postmortem. Therefore, the purpose of this study was to quantify the effects of postmortem degradation on the tensile material properties of bovine liver parenchyma when stored in DMEM or saline. Fourteen fresh bovine livers were obtained from a local slaughter house and stored in either DMEM or saline as large blocks, small blocks, or slices of tissue. Multiple parenchyma dog-bone samples from each liver were tested once to failure at three time points: ~6hrs, ~24hrs, and ~48hrs postmortem. The data were then analyzed to determine if there were significant changes in the material properties with respect to postmortem time. The results showed that the failure strain decreased significantly between 6hrs and 48hrs after death when stored as large blocks in saline. Conversely, neither the failure stress nor failure strain changed significantly with respect to postmortem time when stored as large blocks in DMEM. The modulus did not significantly change for tissue stored as large blocks in either fluid. Preliminary results indicated that reducing the tissue storage size had a negative effect on the material properties and cellular architecture. Overall, this study illustrated that the effects of postmortem liver degradation varied with respect to the preservation fluid, storage time, and storage block size.MS
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Rydén, Alex, and Mattias Langsér. "Data-driven Strain Sensor Modelling in Mining Applications : Artificial strain sensors for material fatigue estimation." Thesis, Linköpings universitet, Fordonssystem, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-176682.
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When boring machines are used, large loads are exerted on their structure. The load cycles cause material fatigue on the boring machine structure. If the material fatigue can be estimated in real-time, maintenance can be planned more efficiently and the effect of different types of usage can be evaluated. Because of the many advantages of knowing the material fatigue, the goal of this thesis is to develop a model to predict the strain of a boring machine structure and then derive an estimate of the material fatigue caused by the strain. To do this several approaches using machine learning techniques are evaluated. The input signals were selected using both coherence analysis and mutual information. It was found that linear models outperform the tested non-linear model structures, and that non-linear mechanical connections cause difficulties. The signals to be modelled contained high frequency components that were not present in the available input signals. The results show that given favorable sensor positions, an estimate of the material fatigue can be made with sufficient accuracy when using a noise model and noise realization to cover the non-existent high frequency components.
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Dharanguttikar, Abhaysinh Arvind. "Biosorption of Cobalt by Using Pseudomonas Aerguinosa Bacterial Strain." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7280.
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A study of biosorption of cobalt metal by Pseudomonas Aerguinosa gram-negative bacterial strain is presented. The present study is carried out to determine the optimum conditions of cobalt biosorption at ultra-low concentration (ppb range) in aqueous solutions. The receptiveness of cobalt metal on the extracellular surface of bacterial strain was examined by varying the pH, Initial concentration of metal and treatment time. Experimental data showed that effect of pH and treatment time is prevalent in biosorption of cobalt and by increasing both these parameters resulted in the efficient sorption of cobalt on the extracellular surface of Pseudomonas Aerguinosa. In some cases, higher initial concentration of cobalt resulted in higher metal removal. However, there is no clear relationship is obtained between efficiency of biosorption and initial concentration of cobalt.
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Shah, Niksha Chimanlal Meghji. "Construction and development of bioluminescent Pseudomonas aeruginosa strains : application in biosensors for preservative efficacy testing." Thesis, University of Hertfordshire, 2014. http://hdl.handle.net/2299/15592.
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Whole cell biosensors have been extensively used for monitoring toxicity and contamination of compounds in environmental biology and microbial ecology. However, their application in the pharmaceutical and cosmetics industries for preservative efficacy testing (PET) has been limited. According to several pharmacopoeias, preservatives should be tested for microbial activity using traditional viable count techniques; the use of whole cell microbial biosensors potentially provides an alternative, fast, and efficient method. The aim of the study was to construct and develop whole cell microbial biosensors with Pseudomonas aeruginosa ATCC 9027. Constitutive promoters: PlysS, Pspc, Ptat, Plpp and PldcC and the lux-cassette were inserted into plasmid pME4510 and transformed into P. aeruginosa ATCC 9027 cells to produce bioluminescent strains. Plasmids were found to be maintained stably (~50 copies per cell) throughout the growth and death cycle. The novel bioluminescent strains were validated in accordance with the pharmacopoeia using bioluminescence detection and quantification followed by comparison with the traditional plate counting method. The bioluminescent method was found to be accurate, precise and equivalent at a range of 103 – 107 CFU/mL, as compared with plate counting. Recovery of bacterial cells was quantified using bioluminescence; this method proved to be accurate with percentage recoveries between 70-130% for all bioluminescent strains. The method was also more precise (relative standard deviation less than 15%) than the traditional plate counting method or the ATP bioluminescent method. Therefore, the bioluminescent constructs passed/exceeded pharmacopoeial specified criteria for range, limit of detection, accuracy, precision and equivalence. Physiology of the validated bioluminescent strains was studied by assessing the growth and death patterns using constitutive gene expression linked with bacterial replication. Promoter strengths were evaluated at various stages of the growth and death pattern and related to promoter sequences. PlysS, Ptat and Plpp were relatively strong promoters whilst PldcC and Pspc were relatively weak promoters. Relative promoter strength decreased in the order of Plpp>Ptat>PlysS>PldcC>Pspc during the exponential phase whilst Ptat was stronger than Plpp during the stationary phase of growth. Plpp had its highest level of expression during the exponential phase, while Ptat had relatively stable lux expression during the stationary phase. Correlations between relative bioluminescence and CFU at 24 hours were greater than 0.9 indicating a strong relationship for all bioluminescent strains. Reduction in correlation coefficients to approximately 0.6 between relative bioluminescence and CFU and between relative fluorescence and CFU beyond 24 hours indicated that a certain proportion of cells were viable but non-culturable. Tat-pME-lux showed steady bioluminescence compared to CFU count (R>0.9) throughout 28 days of growth. Equivalence analysis showed no significant difference between the bioluminescence and plate count method throughout 28 days of growth for all five bioluminescent strains. Applicability of these novel bioluminescent strains was evaluated for preservative efficacy tests (PET) using bacterial replication and bioluminescence as a measure of constitutive gene expression. PET using benzalkonium chloride and benzyl alcohol showed no significant difference between the bioluminescent method and the plate count method. Good correlations between bioluminescence, CFU count and fluorescence were obtained for benzalkonium chloride (BKC) concentrations (R>0.9) between 0.0003% and 0.0025% against strains lysR25, lppR4 and tatH5. Similarly, good correlations (R>0.9) between the three parameters were obtained for benzyl alcohol (BA) concentrations between 0.125% and 2% against strains lysR25, lppR4 and tatH5. The bioluminescent method and traditional plate counting method were equivalent for concentrations of BKC (0.0003 - 0.02%) and BA (0.25 - 2%) during preservative efficacy tests. These bioluminescent constructs therefore are good candidates for selection for preservative efficacy testing. The bioluminescent method and traditional plate counting method were also found to be equivalent for construct tatH5 at a concentration of 0.125% BA. PET testing with BKC and BA showed that tatH5-pMElux (R>0.9) had consistently high correlation coefficients between CFU and relative bioluminescence. Together with the results from growth and death kinetics, where tatH5 showed the greatest constitutive expression, it can be concluded that P. aeruginosa ATCC 9027 tatH5-pMElux is the best construct for testing various antimicrobial agents. This study has shown that according to the pharmacopoeial requirements, the bioluminescent method is more accurate, precise and equivalent to the traditional plate counting method and therefore can be utilised instead of the traditional plate counting method for the purpose of preservative efficacy testing.
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Slocum, Lee Ann. "General strain theory and stability in offending and substance use over time a dynamic approach /." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7353.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Criminology and Criminal Justice. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Fettro, Marshal Neal. "Spousal Problems and Family-To-Work Conflict; Mediating Effects of Time, Relationship, and Financial Strain." Bowling Green State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1404317088.
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Song, Fei. "Modelling time-dependent plastic behaviour of geomaterials." Doctoral thesis, Universitat Politècnica de Catalunya, 2021. http://hdl.handle.net/10803/672273.
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Representing the time-dependent plastic behaviour of geomaterials is a critical issue in the correct application of tunnelling design techniques such as the convergence-confinement method or numerical modelling. Furthermore, during underground excavations below the water table, the effect of seepage flow cannot be ignored, and the behaviour of the tunnel must be analysed in a coupled hydro-mechanical framework.
The main objective of this thesis is to analyse the response of tunnels excavated in saturated time-dependent plastic rock masses. For this purpose, a time-dependent plastic constitutive model has been developed and implemented in the software CODE_BRIGHT to simulate the time-dependent, strain-softening and creep-induced failure behaviour of geomaterials. Moreover, a coupled hydro-mechanical model is utilised to simulate the interaction between solid deformations and fluid flows. The obtained results provide relevant insights into the response of tunnels excavated in saturated time-dependent plastic rock masses. However, numerical difficulties might occur when modelling multi-stage excavations problems, when considering multi-physics coupled processes or non-linear mechanical material models, especially if the layers or pieces of excavated material are relatively coarse. In order to mitigate these numerical difficulties, a smoothed excavation (SE) method has been proposed and implemented in the software CODE_BRIGHT, which can improve numerical efficiency and mitigate non-convergence issues.
Subsequently, to analyse the stability of tunnels with a combined support system, numerical solutions have been developed for tunnels excavated in strain-softening rock masses, considering the whole process of tunnel advancement, and the sequential installation of primary and secondary support systems. For this purpose, the actual compatibility conditions at both the rock-support interface and the support-support interface are considered. This method provides a convenient alternative method for the preliminary design of supported tunnels.La adecuada representación del comportamiento plástico y dependiente del tiempo de los geomateriales es una cuestión crítica en la correcta aplicación de técnicas de diseño de túneles como el método de convergencia-confinamiento o el modelado numérico. Por otro lado, durante las excavaciones subterráneas por debajo del nivel freático no se puede ignorar el efecto del flujo de filtración y, por tanto, el comportamiento del túnel debe analizarse en un marco hidromecánico acoplado. El principal objetivo de esta tesis es analizar la respuesta de túneles excavados en macizos rocosos plásticos saturados y dependientes del tiempo. Para este propósito, se ha desarrollado e implementado un modelo constitutivo plástico dependiente del tiempo en el software CODE_BRIGHT, que permite simular el comportamiento dependiente del tiempo, el de reblandecimiento por deformación y el inducido por fluencia de los geomateriales. Además, se ha utilizado un modelo hidromecánico acoplado para simular la interacción entre la deformación del sólidas y el flujo de fluido. Los resultados obtenidos proporcionan información relevante sobre la respuesta de los túneles excavados en macizos rocosos plásticos, saturados y dependientes del tiempo. Sin embargo, pueden surgir dificultades numéricas al modelar problemas de excavaciones en varias etapas, al considerar procesos multifísicos acoplados o modelos de materiales mecánicos no lineales, especialmente si las capas o piezas de material excavado son relativamente gruesas. Para mitigar estas dificultades numéricas, se ha propuesto e implementado un método de excavación suavizada (SE) en el software CODE_BRIGHT, que puede mejorar la eficiencia numérica y mitigar los problemas de no convergencia. Posteriormente, para analizar la estabilidad de túneles con sistemas de sostenimiento combinado, se han desarrollado soluciones numéricas para túneles excavados en macizos con reblandecimiento por deformación, considerando todo el proceso de avance del túnel y la instalación secuencial de los sistemas de sostenimiento primario y secundario. Con este propósito, se han considerado las condiciones reales de compatibilidad tanto en la interfaz roca- sostenimiento como en la interfaz sostenimiento-sostenimiento. Este método proporciona un método alternativo conveniente para el diseño preliminar de túneles con sostenimiento.
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Luna, Erich Daniel. "Fukuyama, Francis. The Origins of Political Order. From Prehuman Times to the French Revolution. Nueva York: Farrar, Strauss and Giroux, 2011, 585 pp." Economía, 2014. http://repositorio.pucp.edu.pe/index/handle/123456789/118221.
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Umberger, Pierce David. "Modeling the High Strain Rate Tensile Response and Shear Failure of Thermoplastic Composites." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23846.
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The high strain rate fiber direction tensile response of Ultra High Molecular Weight Polyethylene (UHMWPE) composites is of interest in applications where impact damage may occur. This response varies substantially with strain rate. However, physical testing of these composites is difficult at strain rates above 10^-1/s. A Monte Carlo simulation of composite tensile strength is constructed to estimate the tensile behavior of these composites. Load redistribution in the vicinity of fiber breaks varies according to fiber and matrix properties, which are in turn strain rate dependent. The distribution of fiber strengths is obtained from single fiber tests at strain rates ranging from 10^-4/s to 10^-1/s and shifted using the time-Temperature Superposition Principle (tTSP) to strain rates of 10^-4/s to 10^6/s. Other fiber properties are obtained from the same tests, but are assumed to be deterministic. Matrix properties are also assumed to be deterministic and are obtained from mechanical testing of neat matrix material samples. Simulation results are compared to experimental data for unidirectional lamina at strain rates up to 10^-1/s.
Above 10^-1/s, simulation results are compared to experimental data shifted using tTSP. Similarly, through-thickness shear response of UHMWPE composites is of interest to support computational modeling of impact damage. In this study, punch shear testing of UHMWPE composites is conducted to determine shear properties. Two test fixtures, one allowing, and one preventing backplane curvature are used in conjunction with finite element modeling to investigate the stress state under punch shear loading and the resulting shear strength of the composite.Ph. D.
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Nanjappa, Jagdish. "Web-based dynamic material modeling." Ohio University / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1174918633.
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Hamilton, Bryan. "DNA Analysis of Surfactant Associated Bacteria in the Sea Surface Microlayer in Application to Satellite Remote Sensing Techniques: Case Studies in the Straits of Florida and the Gulf of Mexico." NSUWorks, 2015. http://nsuworks.nova.edu/occ_stuetd/39.
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Several genera of bacteria residing in the sea surface microlayer and in the near-surface layer of the ocean have been found to be involved in the production and decay of surfactants. Under low wind speed conditions, surfactants can suppress short gravity capillary waves at the sea surface and form natural sea slicks. These features can be observed with both airborne and satellite-based synthetic aperture radar (SAR). Using a new microlayer sampling method, a series of experiments have been conducted in the Straits of Florida and the Gulf of Mexico in 2013 to establish a connection between the presence of surfactant-associated bacteria in the upper layer of the ocean and sea slicks. In a number of cases, sampling coincided with TerraSAR-X and RADARSAT-2 satellite overpasses to obtain SAR images of each study site. Samples collected from slick and non slick conditions have been analyzed using real time PCR techniques to determine Bacillus relative abundance in each area sampled. Previous work has shown that the sea surface microlayer plays a role in air-sea gas exchange, sea surface temperature, climate-active aerosol production, biochemical cycling, as well as the dampening of ocean capillary waves. Determining the effect of surfactant-associated bacteria on the state of the sea surface may help provide a more complete global picture of biophysical processes at the air-sea interface and uptake of greenhouse gases by the ocean.
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Silberstein, Meredith N. "Mechanics of proton exchange membranes : time, temperature, and hydration dependence of the stress-strain behavior of persulfonated polytetrafluorethylene." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43125.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaves 169-170).
Fuel cells are an important part of the future strategy for reducing dependence on fossil fuels as the world's supplies become more limited and greenhouse gasses become more of a concern. Proton Exchange Membrane Fuel Cells (PEMFC), in which protons from hydrogen gas are passed across a membrane to react with oxygen gas producing electricity, with water as the only waste product, are a cleaner and potentially more efficient chemical energy conversion method. However, the current usefulness of PEMFC is limited by the lifespan and high cost of the fuel cell unit, and more specifically the membrane electrode assembly (MEA). At the center of most contemporary MEA is a thin membrane (- 25 - 100pm thick) of persulfonated polytetrafluoroethylene manufactured by Dupont and known commercially as Nafion. Nafion has the unique quality of being microphase separated into hydrophobic and hydrophilic domains composed of backbone rich and sulfonic acid side chain rich regions respectively. This polymer electrolyte membrane is responsible for rapidly conducting the protons from the hydrogen side to the oxygen side while preventing electrons, hydrogen, and oxygen from passing through. Because of this selective permeability requirement it is important that the membrane possess good mechanical durability so that it does not form pinholes during operation (something which it has been shown to do experimentally). The goal of this thesis was to develop an understanding of the mechanical properties of Nafion as well as a comprehensive material model that captures all the features that are important to how a membrane deforms in an operational fuel cell, including the time, temperature, and hydration dependence of the elastic regime, yield, strain hardening, and stress relaxation at low to moderate strains.
(cont) In order to accomplish this understanding a comprehensive experimental study was undertaken in which Nafion was characterized in uniaxial tension under monotonic, cyclic, and stress relaxation loading profiles at strain rates from 0.001/s to 0.1/s, temperatures from 250C to 1000C, and from dry to fully hydrated conditions. The evolution of the microstructure with applied deformation was then investigated with diffraction techniques. Wide and small angle x-ray scattering data was collected during uniaxial tensile monotonic extension, cyclic, and stress relaxation loading profiles. The SAXS peaks and two WAXS peaks were seen to be isotropic in the initial state. Their evolution with strain was interpreted to indicate that the ionic clusters deform to an elliptical shape with major axis parallel to the tensile direction with an applied strain, whereas the backbone segments align themselves parallel to the tensile direction with an applied strain. Combining these results with those in literature we revise an existing conceptual model for how each of the micromechanical features evolves with strain and how that contributes to the stress response. From mechanical and microstructural data, a constitutive model was developed which is able to capture the key features of the mechanical behavior of Nafion as functions of time, temperature, and hydration. The model is then applied to a simulated fuel cell. The results from the fuel cell simulations indicate that the hypothesis that cyclic stress states and permanent membrane deformation result from hygro-thermal cycling and can lead to pinhole formation.
by Meredith Natania Silberstein.
S.M.
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Bu, Lei. "Computational and experimental studies of strain sensitive carbon nanotube films." Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-156473.
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The excellent electrical and mechanical properties of carbon nanotubes (CNTs) provide interesting opportunities to realize new types of strain gauges. However, there are still challenges for the further development of CNT film strain gauges, for instance the lack of design rules, the homogeneity, stability and reproducibility of CNT films. This thesis aims to address these issues from two sides: simulation and experiment. Monte Carlo simulations show that both the sheet resistance and gauge factor of CNT films are determined essentially by the two-dimensional exclude area of CNTs. It was shown, for the first time, that the variation of the CNT film gauge factor follows the percolation scaling law. The sheet resistance and gauge factor both have a power-law divergence when approaching the percolation threshold. The standard deviation of film resistances, however, also increases correspondingly. These findings of simulations provide a general guide to the tailoring of material property of CNT films in strain sensing applications: a compromise should be made between the reproducibility, conductivity and sensitivity of CNT films depending on application purposes. From the experimental side, the processing parameters for the preparation of CNT dispersions were first investigated and optimized. The reproducibility of the film resistance is significantly improved by selecting a suitable sonication time. In strain measurements it was found that for most CNT films the film resistance responses nonlinearly to the applied strain. The dependence of the film resistance on the strain can be roughly divided into two regions with nearly linear behavior respectively. The gauge factor varies with the quality of CNTs and the depositing method. A gauge factor up to 8 was achieved in the high strain region. The nonlinear response behavior was found in simulations when the CNT waviness is properly taken into account. To achieve a high gauge factor and simultaneously retain the high conductivity and reproducibility, good-quality MWCNTs were integrated in polyethylene oxide (PEO). A high gauge factor up to 10 was achieved for the composite film with CNT weight fraction of 2.5%. The resistance and gauge factor can be tuned by changing the MWCNT weight fraction with respect to PEO. A careful comparison of simulation and experiment results show that a good qualitative agreement can be achieved between them in many respects.
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vechalapu, uday bhaskar. "Real-Time 2D Digital Image Correlation to Measure Surface Deformation on Graphics Processing Unit using CUDA C." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1522108261138081.
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Bennington, J. Bret. "Community persistence and the pattern of community variability over time : a test using fossil assemblages from four marine transgressions in the Breathitt Formation (Middle Pennsylvanian) of Eastern Kentucky /." Diss., This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-10052007-143840/.
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Molony, Anna. "The application of fibre Bragg grating networks as strain sensors and as phased array antenna true time delay elements." Thesis, Aston University, 1996. http://publications.aston.ac.uk/15355/.
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The fabrication of in-fibre Bragg gratings, and the application of arrays of such gratings as strain sensors and as true time delay elements for the control of phased array antennas is reported. Chirped period Bragg gratings were produced using the fibre deformation fabrication technique, with chirps of between 2.9nm and 17.3nm achieved. Arrays of 5mm and 2mm long uniform period Bragg gratings were fabricated using the inscription method, for use as true time delay elements,dissimilar wavefronts and their spectral characteristics recorded. The uniform period grating arrays were used to create minimum time delays of 9.09ps, 19.02ps and 31ps; making them suitable for controlling phased array antennas operating at RF frequencies of up to 3GHz, with 10° phase resolution. Four 4mm long chirped gratings were produced using the dissimilar wavefronts fabrication method, having chirps of 7nm, 12nm, 20nm and 30nm, and were used to create time delays of between 0.3ps and 59ps. Hence they are suitable for controlling phased array antennas at RF frequencies of up to 48GHz. The application of in fibre Bragg gratings as strain sensors within smart structure materials was investigated, with their sensitivity to applied strain and compression measured for both embedded and surface mounted uniform period and fibre Fabry-Perot filter gratings. A fibre Bragg grating sensor demultiplexing scheme based on a liquid crystal filled Fabry-Perot etalon tuneable transmission filter was proposed, successfully constructed and fully characterised. Three characteristics of the LCFP etalon were found to pose operational limitations to its application in a Bragg grating sensor system; most significantly, the resonance peak wavelength was highly (-2,77nm/°C) temperature dependent. Several methods for minimising this temperature sensitivity were investigated, but enjoyed only limited success. It was therefore concluded that this type (E7 filled) of LCFP etalon is unsuitable for use as a Bragg grating sensor demultiplexing element.
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Vance, Elizabeth Anne Middleton. "Effects of time specific F-strain Mycoplasma gallisepticum inoculation overlays on pre-lay ts-11-strain Mycoplasma gallisepticum inoculation on performance, egg, blood, and visceral characteristics of commercial egg laying hens." Master's thesis, Mississippi State : Mississippi State University, 2007. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11022007-152112.
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Edgemon, Glenn Leon. "The time-temperature-sensitization behavior of alloy 800 as determined by the electrochemical potentiokinetic reactivation test and the modified strauss test." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/20034.
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Boardman, Paul Craig. "University research centers and the composition of academic work." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-11172006-161054/.
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Thesis (Ph. D.)--Public Policy, Georgia Institute of Technology, 2007.Barry Bozeman, Committee Member ; Juan Rogers, Committee Chair ; Diana Hicks, Committee Member ; Gordon Kingsley, Committee Member ; Phil Shapira, Committee Member.
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Wernike, Kerstin. "Establishment of a multiplex real-time PCR assay for the detection and differentiation of wild-type and glycoprotein E-deleted vaccine strains of bovine herpesvirus type 1." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-140605.
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Strauss, Roelf du Toit. "Modelling of cosmic ray modulation in the heliosphere by stochastic processes / Roelf du Toit Strauss." Thesis, North-West University, 2013. http://hdl.handle.net/10394/10217.
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The transport of cosmic rays in the heliosphere is studied by making use of a newly developed
modulation model. This model employes stochastic differential equations to numerically solve
the relevant transport equation, making use of this approach’s numerical advantages as well
as the opportunity to extract additional information regarding cosmic ray transport and the
processes responsible for it. The propagation times and energy losses of galactic electrons
and protons are calculated for different drift cycles. It is confirmed that protons and electrons
lose the same amount of rigidity when they experience the same transport processes. These
particles spend more time in the heliosphere, and also lose more energy, in the drift cycle
where they drift towards Earth mainly along the heliospheric current sheet. The propagation
times of galactic protons from the heliopause to Earth are calculated for increasing heliospheric
tilt angles and it is found that current sheet drift becomes less effective with increasing solar
activity. Comparing calculated propagation times of Jovian electrons with observations, the
transport parameters are constrained to find that 50% of 6 MeV electrons measured at Earth
are of Jovian origin. Charge-sign dependent modulation is modelled by simulating the proton
to anti-proton ratio at Earth and comparing the results to recent PAMELA observations.
A hybrid cosmic ray modulation model is constructed by coupling the numerical modulation
model to the heliospheric environment as simulated by a magneto-hydrodynamic model. Using
this model, it is shown that cosmic ray modulation persists beyond the heliopause. The
level of modulation in this region is found to exhibit solar cycle related changes and, more
importantly, is independent of the magnitude of the individual diffusion coefficients, but is
rather determined by the ratio of parallel to perpendicular diffusion.PhD (Space Physics), North-West University, Potchefstroom Campus, 2013
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Hamid, Waleed Khalid. "Behavior of Bridge with Internally Cured Concrete Deck under Environmental and TruckLoading." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1603311306491899.
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Mohamed, Zin Muhammad Rawi. "Time resolved x-ray diffraction studies of strain-induced crystallisation in poly(lactic acid) using synchrotron radiation under industrial processing conditions." Thesis, Keele University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.528364.
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Zhang, Jiaxiang. "Single- and entangled-photon emission from strain tunable quantum dots devices." Doctoral thesis, Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-177579.
Full textAbstract:
On demand single-photon and entangled-photon sources are key building-blocks for many proposed photonic quantum technologies. For practical device applications, epitaxially grown quantum dots (QDs) are of increasing importance due to their bright photon emission with sharp line width. Particularly, they are solid-state systems and can be easily embedded within a light-emitting diode (LED) to achieve electrically driven sources. Therefore, one would expect a full-fledged optoelectronic quantum network that is running on macroscopically separated, QD-based single- and entangled-photon devices.
An all-electrically operated wavelength-tunable on demand single-photon source (SPS) is demonstrated first. The device consists of a LED in the form of self-assembled InGaAs QDs containing nanomembrane integrated onto a piezoelectric crystal. Triggered single photons are generated via injection of ultra-short electrical pulses into the diode, while their energy can be precisely tuned over a broad range of about 4.8 meV by varying the voltage applied to the piezoelectric crystal. High speed operation of this single-photon emitting diode up to 0.8 GHz is demonstrated.
In the second part of this thesis, a fast strain-tunable entangled-light-emitting diode (ELED) is demonstrated. It has been shown that the fine structure splitting of the exciton can be effectively overcome by employing a specific anisotropic strain field. By injecting ultra-fast electrical pulses to the diode, electrically triggered entangled-photon emission with high degree of entanglement is successfully realized. A statistical investigation reveals that more than 30% of the QDs in the strain-tunable quantum LED emit polarization-entangled photon-pairs with entanglement-fidelities up to f+ = 0.83(5). Driven at the highest operation speed ever reported so far (400 MHz), the strain-tunable quantum LED emerges as unique devices for high-data rate entangled-photon applications.
In the end of this thesis, on demand and wavelength-tunable LH single-photon emission from strain engineered GaAs QDs is demonstrated. Fourier-transform spectroscopy is performed, from which the coherence time of the LH single-photon emission is studied. It is envisioned that this new type of LH exciton-based SPS can be applied to realize an all-semiconductor based quantum interface in the foreseeable distributed quantum networks.
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Janz, Alexander [Verfasser], and P. [Akademischer Betreuer] Betsch. "Structure-preserving space-time discretization in a mixed framework for multi-field problems in large strain elasticity / Alexander Janz ; Betreuer: P. Betsch." Karlsruhe : KIT Scientific Publishing, 2019. http://d-nb.info/1190285630/34.
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Mphuthi, Malekoba Batseba Nthabisheng. "Development of a real-time PCR assay to detect the fusion gene of the D26 strain of a commercial avian avulavirus 1." Diss., University of Pretoria, 2009. http://hdl.handle.net/2263/67823.
Full textAbstract:
Newcastle disease (ND), caused by avian avulavirus 1 (AA1), an enveloped, negative sense, single stranded RNA virus belonging to the Paramyxoviridae family. ND is found world-wide and leads to severe economic losses from mortality and condemnation of carcasses. Virulent ND causes clinical signs such as respiratory distress, central nervous signs, drop in egg production, weakness, gastro-intestinal symptoms and death. The disease is listed by the World Organisation for Animal Health (OIE) and outbreaks require reporting to the OIE. The OIE requires a definitive diagnosis of virulent AA1 to enable effective control of an outbreak by strict control measures and trade restrictions.
Currently the real-time reverse transcription polymerase chain reaction (RRT-PCR) assay used to diagnose ND does not differentiate between field and vaccine strain. The aim of this study was to develop and optimise a real time RT-PCR assay that detects chickens vaccinated with Vectormune® HVT NDV vaccine based on the F gene of the D26 strain. NDV F gene sequences were downloaded from Genbank® and aligned. A region unique to the D26 strain, between nucleotides 69 to 131 (using accession number M24692 for numbering) was identified and a TaqMan® MGB™ assay was developed. Primer and probe concentrations were optimised at 200 nM.
Nucleic acid was purified using a MagMax™ Pathogen RNA/DNA extraction kit and a MagMax™ Express Magnetic Particle Processor (ThermoFisher Scientific). TaqMan Fast Advanced Master Mix PCR reagents were used to amplify the AA1 F gene with one StepOnePlus Real-time PCR system.
The PCR efficiency was calculated to be 81.8% with 0.9942 coefficient correlation (R2). The 95% limit of detection was 10-1.31 plaque forming units per reaction. The assay was specific and did not detect any other AA1 isolates tested.
Twenty-four spleen impression smear field samples from chickens (12 Vectormune® HVT NDV vaccine samples and 12 vaccinated with ND virus conventional vaccine) preserved on Whatman® FTA cards, were collected between day 21 and 28 post vaccination. The assay detected only the D26 vaccine strain and was negative when tested on other field samples.
The developed real time PCR was sensitive, reliable and repeatable and will also be able to produce results rapidly as compared to other conventional methods.Dissertation (MSc)--University of Pretoria, 2018.
Veterinary Tropical Diseases
MSc
Unrestricted
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Phung, Kent, and Charles Chu. "Adhesives for Load-Bearing Timber-Glass Elements : Elastic, plastic and time dependent properties." Thesis, Linnéuniversitetet, Institutionen för bygg- och energiteknik (BE), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-27386.
Full textAbstract:
This thesis work is part of an on-going project regarding load-bearing timber glass composites within the EU program WoodWisdom-Net. One major scope of that project is the adhesive material between the glass and timber parts. The underlying importance of the bonding material is related to the transfer of stress between the two materials – the influence of the adhesive stiffness and ductility on the possibility of obtaining uniform stress distributions. In this study the mechanical properties of two different adhesives are investigated, an epoxy (3M DP490) and an acrylate (SikaFast 5215). The differences of the adhesives lay in dissimilar stiffness, strength and viscous behaviour. In long term load caring design is important to understand the materials behavior under a constant load and a permanent displacement within the structure can cause major consequences. Therefore the main aim in this project is to identify the adhesives strength, deformation capacity and possible viscous (time dependent) effects. Because of the limitation of equipment and time this study is restricted to only three different experiments. Three different types of tensile tests have been conducted: monotonic, cyclic relaxation tests.The results of the experiments show that 3M DP490 has a higher strength and a smaller deformation capacity as compared to the SikaFast 5215. Thus, the SikaFast 5215 is more ductile. The 3M DP490 exhibits a lower loss of strength under constant strain (at relaxation). SikaFast 5215 showed also a large dependency of strain level on the stress loss in relaxation.