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1
Long, Douglas Colfer. "Aging Effects of Incarceration." Thesis, University of California, San Francisco, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10690081.
Testo completoAbstract (sommario):
<p> Whether incarceration confers excessive risk for accelerated aging or premature mortality remains an open question. Earlier studies suggested excess risk for aging and premature mortality but the data were either anecdotal or using population comparisons. One of the major risk factors for persons incarcerated is a history of substance abuse which alone is associated with adverse outcomes. Thus, we chose to examine the question of incarceration and adverse outcomes among a sample restricted to drug users, to determine if there was an independent risk related to incarceration. In terms of drug use, it is well documented that the risk of mortality is highest within the first couple of weeks after release. We framed the question, does a history of incarceration have a latency for a long term effect on accelerated aging and premature mortality after accounting for drug use. To examine this question, we used data from the AIDS Linked to the IntraVenous Experience (ALIVE) cohort, which consisted of injection drug users (IDU) presenting to a community clinic in Baltimore and followed semiannually for up to 30 years. Data were collected from 2005–2013 and history of incarceration was based on self-report for when the participant was entered into the cohort study anytime between 1988–2005. Outcome data were frailty using Fried’s criteria (For frailty, operationalized according to Fried, we used a three-level scale of non-frail, prefrail, and frail) that was collected from 2005 onward, and all-cause mortality collected from NDI-Plus. For statistical analysis, ALIVE participants were divided into two cohorts, those recruited before the introduction of highly active antiretroviral therapy (HAART) when HIV infection was a significant cause of premature mortality, and those recruited after the advent of HAART when the risk of death from HIV dropped significantly. We started the investigation with a literature review that included scholarly studies published from 1990 until 2017 on the association between incarceration and prevalence of chronic disease. In the cross-sectional study, the independent variable was a history of incarceration, operationalized as the total number of reported incarcerations in the six months prior to baseline. We examined two dependent variables: Frailty and mortality. No statistically significant effect of incarceration on frailty was found even after controlling for age, gender, race, educational attainment, HIV status, or current injection drug use. For mortality by a history of incarceration a survival analysis showed no significant difference even after controlling for age, gender, and HIV status. The adjusted relative hazard (95% CI) of mortality for those with a history of incarceration was 1.14 (0.81, 1.60) among those enrolled in the Pre-HAART era cohort and 1.19 (0.68, 2.10) for those enrolled in the HAART era cohort. Although earlier studies observed excess mortality soon after release, our data suggests that the role of past incarceration may have modest if any impact on the long term occurrence of frailty or mortality.</p><p>
2
Andrade, González Neivi Rocío. "Aging effects in 319-type alloys." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102477.
Testo completoAbstract (sommario):
The present work was performed on primary A319.2 alloy to investigate the effect of magnesium and strontium additions on the heat treatment behaviour and mechanical properties of the alloy. Samples were cast in permanent mould, then cut in order to obtain coupons which were solution heat treated at 495°C for 4 and 24 hours, followed by quenching in hot water. Two different artificial aging temperatures were applied at 180°C and 220°C for times from 0.5 h up to 24 hours. The investigation consisted of a systematic measurement of macrohardness and matrix microhardness of samples under different heat treatment conditions. Tensile properties were also measured and electron microscopy study of critical samples was done.<br>It is seen that the alloy does not exhibit the common peak-overaged aging conditions due to the presence of several coexisting phases. It was found that multiple aging peaks are present in the age-hardening curves of Al-Si-Cu-Mg alloys. From the scanning electron microscopy studies, it is seen that addition of magnesium (~0.40 wt%) leads to the precipitation of coarse A1 5Mg8Si6Cu2 particles. Strontium modification of the high magnesium alloys leads to segregation of Cu-intermetallics in areas away from the growing Al-Si eutectic regions. It was found that strontium modification retards the precipitation of the silicon out of the matrix.<br>The effect of aging time and temperature on the structure of the age-hardening precipitates was studied with TEM. TEM observations reveal that the age-hardening behavior is related to the precipitation sequence of the alloy. For the Al-Si-Cu-Mg alloy, the first aging peak is the result from the high-density GP zones, while the subsequent are from metastable phases. The transition from GP zones to metastable phases may be the main reason for the formation of multiple aging peaks.
3
Ledur, Mônica Corrêa. "Genetic effects of aging in laying hens." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq24414.pdf.
Testo completo
4
Akin, Faith W. "Effects of Aging on the Vestibular System." Digital Commons @ East Tennessee State University, 2010. https://dc.etsu.edu/etsu-works/2443.
Testo completo
5
Fulton, Susan E. "The Effects of Aging on Temporal Masking." Scholar Commons, 2010. https://scholarcommons.usf.edu/etd/1636.
Testo completoAbstract (sommario):
The ability to resolve rapid intensity and frequency fluctuations in sound is important for understanding speech, especially in real-world environments that include background noise and reverberation. Older listeners often complain of difficulties understanding speech in such real-world environments. One factor thought to influence speech understanding in noisy and reverberant environments is temporal resolution, the ability to follow rapid acoustic changes over time. Temporal resolution is thought to help listeners resolve rapid acoustic changes in speech as well as use small glimpses of speech available in the dips or gaps in the background sounds. Temporal resolution is an ability that is known to deteriorate with age and hearing loss, negatively affecting the ability to understand speech in noisy real-world environments.
Measures of temporal resolution, including temporal masking, gap detection, and speech in interrupted noise, use a silent gap as the cue of interest. Temporal masking and speech in interrupted noise tasks measure how well a listener resolves a stimulus before, after, or between sounds (i.e., within a silent gap), while gap detection tasks measure how well the listener resolves the timing of a silent gap itself. A listener needs to resolve information within the gap and the timing of the gap when listening to speech in background sounds. This study examined the role of aging and hearing loss on three measures of temporal resolution: temporal masking, gap detection, and speech understanding in interrupted noise. For all three measures, participants were young listeners with normal hearing (n = 8, mean age = 25.4 years) and older listeners with hearing loss (n = 9, mean age = 72.1 years).
Results showed significant differences between listener groups for all three temporal measures. Specifically, older listeners with hearing loss had higher temporal masked thresholds, larger gap detection thresholds, and required a higher signal-to-noise ratio for speech understanding in interrupted noise. Relations between temporal tasks were observed. Temporal masked thresholds and gap detection thresholds accounted for a significant amount of the variance in speech-in-noise scores. Findings suggest that deficits in temporal resolution abilities may contribute to the speech-in-noise difficulties reported by older listeners.
6
Huang, Jing [Verfasser]. "Differential Aging effects on visuomotor control : evidence for an adaptive aging brain / Jing Huang." Gießen : Universitätsbibliothek, 2019. http://d-nb.info/1174938846/34.
Testo completo
7
Gilkes, Daniele. "Copper seed aging effects on post electroplating defects." [Gainesville, Fla.]: University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE0000536.
Testo completo
8
Willemien, Meijer. "Cognitive aging: effects of education and task demands." Maastricht : Maastricht : Neuropsych Publishers ; University Library, Universiteit Maastricht [host], 2006. http://arno.unimaas.nl/show.cgi?fid=5955.
Testo completo
9
Roy, Marc Andre. "Cognitive aging effects in schizophrenia: a quantitative review /." Burnaby B.C. : Simon Fraser University, 2005. http://ir.lib.sfu.ca/handle/1892/2406.
Testo completoAbstract (sommario):
Thesis (M.A.) - Simon Fraser University, 2005.<br>Theses (Dept. of Psychology) / Simon Fraser University. Includes bibliographical references :leaves 31-58. Also issued in digital format and available on the World Wide Web.
10
Ünlü, Ercan Selçuk Koç Ahmet. "Effects of Deleting Mitochondrial Antioxidant Genes on Aging/." [s.l.]: [s.n.], 2007. http://library.iyte.edu.tr/tezler/master/biyoloji/T000644.pdf.
Testo completo
11
Alves, Renato Manuel Pereira. "Aging effects on the skeletal muscle mitochondrial proteome." Master's thesis, Universidade de Aveiro, 2008. http://hdl.handle.net/10773/3012.
Testo completoAbstract (sommario):
Mestrado em Métodos Biomoleculares<br>Este trabalho teve como objectivo determinar de que forma o envelhecimento
afecta o proteoma mitocondrial do músculo-esquelético. Para tal, foram
analisadas (i) alterações na composição (ii) variações da actividade dos
complexos da cadeia respiratória, (iii) a oxidação de proteínas mitocondriais e
(iv) os locais específicos de oxidação dos Complexo I da Cadeia de Transporte
de Electrões (ETC). Simultaneamente, verificou-se de que forma o estilo de
vida sedentário vs. não-sedentário pode condicionar cada um dos parâmetros
observados. Para atingir estes objectivos ratinhos C57BL/6 machos foram
sujeitos a um protocolo para simular o envelhecimento sedentário e
não-sedentário. Os animais foram depois sacrificados e isoladas as
mitocôndrias dos músculos dos membros traseiros. As proteínas mitocondriais
foram depois separadas por 2D-PAGE e identificadas por espectrometria de
massa. Após a comparação dos perfis de 2D-PAGE pode-se observar que a
maioria das proteínas analisadas se encontra sobre-representadas no
proteoma mitocondrial de ratinhos sedentários. Para avaliar se estas
diferenças se correlacionavam com eventuais alterações na actividade dos
complexos da cadeira respiratória, estes foram separados por BN-PAGE e
corados com soluções específicas para determinar a sua actividade.
Verificou-se uma diminuição na actividade dos complexos IV e V da cadeia
respiratória que parece indicar que o aumento da quantidade de proteínas dos
complexos da ETC no proteoma mitocondrial surge como um mecanismo de
compensação para suprimir a diminuição da actividade da cadeia respiratória.
Como parâmetro de oxidação proteica foi determinado o conteúdo em grupos
carbonilos das amostras por slot blot. Verificou-se que há uma diminuição
significativa do conteúdo em grupos carbonilos nas proteínas dos ratinhos que
foram sujeitos a um estilo de vida não-sedentário. Para determinar os locais de
oxidação do Complexo I da ETC, as sete subunidades deste complexo,
identificadas previamente, foram sujeitas a espectrometria de massa tandem.
Foram detectadas modificações em vários péptidos, sendo os resíduos de
triptofano mais afectados pela oxidação. Contrariamente ao esperado, as
subunidades membranares apresentaram-se mais modificadas que as
subunidades mais próximas do centro catalítico. Os resultados permitem
sugerir que as subunidades membranares são mais tolerantes aos efeitos da
oxidação e que as subunidades do Complexo I podem ser substituídas
individualmente quando são danificadas pelos efeitos da oxidação.
Globalmente podemos concluir que a realização de actividade física moderada
previne os efeitos do envelhecimento, nomeadamente a nível de danos
oxidativos nas proteínas mitocondriais.
ABSTRACT: This work aimed to assess how aging influences the skeletal muscle
mitochondrial proteome. To achieve this, we have analyzed (i) alterations on its
composition, (ii) variations on the activity of the respiratory chain complexes,
(iii) the oxidation of mitochondrial proteins and (iv) the specific sites for
oxidative modification on Complex I from the Electron Transport Chain (ETC).
Simultaneously, we assessed how these parameters may be conditioned by a
sedentary vs. a non-sedentary lifestyle. C57BL/6 male mice were subjected to
a protocol to simulate sedentary and non-sedentary aging. The animals were
then sacrificed and mitochondria from the hind limbs muscles were isolated.
Mitochondrial proteins were resolved by 2D-PAGE and identified by mass
spectrometry. Following a comparison of the 2DE profiles, we have observed
that most of the analyzed proteins were up-regulated in sedentary mice
mitochondrial proteome. To assess if these alterations were related to any
functional variations, the respiratory chain complexes were resolved by
BN-PAGE and differentially stained to determine the in-gel activity. We
observed a reduction of the activity of Complexes IV and V in sedentary mice,
which may suggest that the up-regulation of the respiratory chain complexes in
sedentary mice may be a mechanism to overcome the loss of functionality. To
assess the level of oxidative stress, we have determined the carbonyl content
by slot blot and observed a significant decrease in the carbonyl content of
non-sedentary mice. To locate the precise sites for oxidative damage in
Complex I of the ETC, the seven subunits of this complex, previously isolated
by 2D-PAGE, were subjected to tandem mass spectrometry. We have detected
several modified peptides, with tryptophan being the most affected residue.
Unexpectedly the membrane subunits presented more modification sites than
the peripheral arm subunits. These results may suggest that membrane
subunits are more tolerant to oxidative damage and Complex I subunits may be
replaced by newly synthesized ones when oxidative damage becomes
unbearable. In conclusion, we may assume that moderate physical activity
attenuates the effects of aging, namely the oxidative damage of mitochondrial
proteins.
12
Hogg, Ellen Louise. "Effects of environment and aging on synaptic plasticity." Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683563.
Testo completoAbstract (sommario):
Alzheimer's Disease (AD) is a neurodegenerative disease that causes a severe and global loss of cognitive function. The amyloid cascade hypothesis states that it is the deposition of amyloid Beta ABeta in AD that triggers neuronal dysfunction and cell death in the brain. Traditionally the neurotoxic effects of A [Beta] have been attributed to the buildup of extracellular A [Beta] that causes aberrant synaptic plasticity. However more recently it has been established that A [Beta] accumulates intraneuronaly before the formation of extracellular plaques when mild cognitive impairment can be detected. Therefore exposure to intracellular A[Beta]could be a key step in the early stages of AD pathology.
13
Corbin, Stacey Michelle Pest, and Stacey Michelle Pest Corbin. "The Effects of Healthy Aging On Memory Reconsolidation." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625609.
Testo completoAbstract (sommario):
Reconsolidation theory states that stabilized memories can be reactivated and altered in some way; the memory must then be made stable once again by a process known as reconsolidation. A substantial number of studies have aimed to examine this process and the conditions under which it can occur in animal models and young adults. However, few studies have examined the impact of aging on memory reconsolidation. It has been established that aging affects episodic memories, as a result of several different changes in aging. Further, associative, source, and context memories have been found to be affected by aging. Additionally, consolidation, the process that occurs prior to reconsolidation, has been linked to age-related memory deficits. Given these changes with age, it is possible that memory reconsolidation could also be affected. This dissertation sought to examine the effects of aging on reconsolidation in an established set-learning paradigm typically utilized in young adults to demonstrate reconsolidation-mediated memory updating.
In Experiment 1, older adult participants were taught sets of objects on two different days, with one group receiving a reminder intended to reactivate the first day's memory. On a third day, a recognition memory task was given. We found that reconsolidation processes seem relatively intact in our population of older adults. Further, source confusion was implicated in addition to memory updating as the cause of memory errors in the group that received the reminder. Other measures, such as spatial awareness and sleep, were utilized to help explain the outcome of the experiment.
In Experiment 2, young adults performed the same procedure as in Experiment 1 to determine the role of some of the aspects of the procedure in this paradigm. Specifically, we wanted to establish whether an added task, spread across the two days of learning, influenced the outcome of this paradigm. It was concluded that this task likely had an influence, such that even the group that did not receive the reminder showed evidence of memory updating. We also wanted to determine a baseline for the spatial awareness task used in the previous experiment. However, results were inconclusive.
In Experiment 3, we investigated the time line of errors made by older adults by testing their memory for the first set of objects shortly after they learned the second set, as opposed to on a third day. However, free recall was used as the memory task, unlike the previous two experiments. Unexpectedly, errors were immediately apparent for the group that did not receive the reminder but not for the group that did. The conclusion of this experiment was that the task used to test memory may play a major role in the outcome of this paradigm when performed by older adults. Further testing will need to be performed to fully understand this result.
Overall, memory reconsolidation appears to be intact in older adults, though perhaps not in the form seen in young adults. Reconsolidation seen in older adults could be affected by different modes of reactivation, sleep, and methods of memory testing. However, several of the present results could be open to multiple interpretations, which require future research to untangle.
14
Colledge, Alexander. "Hypertension, Infection and Inflammation and their Effects on Memory and Visuospatial Skills in Ageing." Thesis, Umeå universitet, Institutionen för psykologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-122132.
Testo completoAbstract (sommario):
Blood pressure has previously been associated with decline in memory over time, though the exact mechanism behind this effect is uncertain. Infections, which can lead to systemic inflammation have also been linked to some cardiovascular damage to the brain, known as microbleeds, which have themselves been linked to greater declines in cognition in old age. The present study investigates whether blood pressure, a self-reported history of infection, and an indirect measure of inflammation known as the erythrocyte sedimentation rate have any association with on episodic and semantic memory and visuospatial skills in the Betula study, a Swedish longitudinal population study. The effect of elevated blood pressure (over 140 mm Hg systolic and/or 90 mm Hg diastolic), high blood sedimentation (top 33% against bottom 33% of participants), and self-reported infection were all found to not have any significant effect on episodic memory, semantic memory or visuospatial skills. Some of the possible explanations are elaborated in the discussion.<br>Högt blodtryck har associerats med minnesnedsättning men den exakta mekanismen hur ett samband kan förstås är dock oklar. Infektioner har visat sig ge systematiska inflammationer och har också satts i samband med vissa kardiovaskulära förändringar i hjärnan, så kallade mikroblödningar, vilka i sig har associerats med ökad risk för kognitive nedsättning i hög ålder. Denna uppsats syftar till att undersöka om blodtryck och infektion (självrapporterad infektion samt infektion indirekt mätt genom sänkereaktion) kan relateras till episodiskt och semantisk minne samt visuospatial förmåga i Betula studien, som är en svensk longitudinell populationsbaserad studie. Resultatet visade att varken högt blodtryck (över 140 mm Hg systoliskt eller 90 mm Hg diastoliskt), hög sänkereaktion (de 33 % med högst värde jämfört med de 33 % med lägst värde) eller självrapporterad infektion hade någon signifikant effekt för episodiskt minne, semantiskt minne eller visuospatial förmåga. Några möjliga förklaringar till detta resultat utvecklas i diskussionen.<br>The Betula Study
15
Wang, Jason Lee. "Effects of aging and remodeling on bone microdamage formation." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37114.
Testo completoAbstract (sommario):
Skeletal fragility is characterized by low bone mass, negative changes in bone microarchitecture, and compromised tissue matrix properties, including accumulation of microdamage. Microdamage accumulates in vivo from daily physiological loading and is targeted for repair through a normal remodeling process, thus preventing microcrack growth and potential fracture. However, impaired remodeling is associated with aging and osteoporosis, resulting in an increased accumulation of microdamage which contributes to reduced bone mechanical properties. The current clinical method for assessing increased risk of fracture involves measuring bone mineral density (BMD) of the hip and spine, locations of trabecular bone where high rates of remodeling occur. The bisphosphonate alendronate (ALN) reduces clinical risk for fracture by significantly increasing BMD, but studies have shown a concomitant reduction in intrinsic properties that may be the underlying cause for recent reports of spontaneous fractures with long-term alendronate use. Another anti-resorptive agent called raloxifene (RAL) is a selective estrogen receptor modulator (SERM) and has been shown to modestly improve BMD while decreasing fracture risk to a similar degree as alendronate. The combination of RAL and ALN as a treatment for osteoporosis may provide the benefits of each drug without the negative effects of ALN.
Therefore, the overall goal of this thesis was to address the effects of aging and anti-resorptive agents on the properties of bone through the formation of microdamage. Assessment of age-related effects on bone was conducted through quantification of microdamage progression. It was found that old bone results in greater incidences of microdamage progression, reflecting a compromised tissue matrix with reduced resistance to crack growth. Effects of combination treatment with RAL and ALN were evaluated through biomechanical testing, micro-CT imaging, and microdamage quantification. Results showed improved trabecular bone volume and ultimate load with positive effects on trabecular architecture. Combination treatment reduced the proportion of microdamage that may lead to catastrophic fracture, indicating an improvement in the local tissue matrix properties.
16
Fox, Geoffrey Arthur. "Effects of aging on functions of the prefrontal cortex." Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20050112.155754/index.html.
Testo completo
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Choi, Heesun 1954. "EFFECTS OF AGING ON NUTRIENTS DIGESTIBILITY IN NONHUMAN PRIMATES." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/277103.
Testo completo
18
Abutalebi, Jubin. "The neuro-protective effects of bilingualism in aging populations." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/211128.
Testo completoAbstract (sommario):
Culture, education and of other forms of acquired capacities act on individual differences in skill to shape how individuals perform cognitive tasks such as attentional and executive control. Of interest, the use of more than one language (bilingualism) also appears to be a factor that shapes individual performance on tests of cognitive functioning. Indeed, researchers have shown that a bilingual can have better attention and executive control capacities than monolingual speakers and this is argued to be due the ability to inhibit one language while using another. Beyond behavioral differences, bilingualism seems to affect brain structure as well. Recent evidence also shows bilinguals develop more gray matter in crucial brain areas responsible for executive control, hence, providing a neurological basis for why bilinguals outperform monolinguals on many attentional control tasks. It has been postulated that this cognitive advantage offers protection to bilinguals against cognitive decline in aging. Bilingualism affords a cognitive reserve in the form of a set of skills that allows some people to cope with cognitive decline such as mild cognitive decline or Alzheimer's disease better than others.
The primary aim of the studies here performed was to investigate if and how the bilingual brain becomes more resistant to cognitive decline. Three combined comparative behavioral and structural neuroimaging studies were carried out in bilingual and monolingual seniors. The overall results show a rather interesting pattern of findings that may be summarized as follows: if well matched for demographic and behavioral variables such as age, socio-economic status, education, and global cognitive functioning, bilinguals have generally increased gray matter densities as compared to monolinguals in those brain areas that are known to be more affected by physiological aging such as the orbitofrontal cortex, the temporal poles and parietal lobules, and in areas involved in cognitive control such as the prefrontal cortex and the anterior cingulate cortex. Increased gray matter in these latter areas also correlates with the superior performance of bilinguals on executive control tasks. Interestingly, in order to keep such a neural benefit (i.e. increased gray matter density) the degree of proficiency of the second language has to be relatively high and bilinguals have to be constantly exposed to their second language. Finally, specifically for the aging population, age of second language acquisition has no major role in determining putative neural differences. Any putative neural differences between bilingual speakers are determined by factors such as the degree of proficiency and exposure to a second language.
In conclusion, as thoroughly investigated here, bilingualism represents a neural reserve for healthy aging. However, the benefits are most prominent when second language proficiency and exposure are kept high.<br>published_or_final_version<br>Education<br>Doctoral<br>Doctor of Philosophy
19
Barger, John D. "Effects of aging on bond between FRP and concrete." Morgantown, W. Va. : [West Virginia University Libraries], 2000. http://etd.wvu.edu/templates/showETD.cfm?recnum=1288.
Testo completoAbstract (sommario):
Thesis (M.S.)--West Virginia University, 2000.<br>Title from document title page. Document formatted into pages; contains xi, 102 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 86-87).
20
Tampas, J., C. Clinard, Faith W. Akin, and Owen D. Murnane. ""The Effects of Aging on Tonic EMG and VEMP"." Digital Commons @ East Tennessee State University, 2006. https://dc.etsu.edu/etsu-works/1899.
Testo completo
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Chong, Hsu Phern. "The effects of aging on myometrial function and transcriptome." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708157.
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Chau, Nguyen Lan. "Aging Effects on the Mechanical Properties of Waste Landfills." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/179380.
Testo completo
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Narynbek, Ulu Kubat. "Fatigue of HNBR - Effects of formulation and thermal aging." Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0006/document.
Testo completoAbstract (sommario):
Cette thèse de doctorat s’intéresse à la fatigue des élastomères, et plus particulièrement des caoutchoucs nitrile hydrogénés (sigle HNBR en anglais). Les HNBR sont des élastomères de haute performance,classiquement utilisés pour des applications industrielles à haute température où une bonne résistance chimique aux hydrocarbures est également requise.La thèse est divisée en trois parties principales.En premier lieu, des améliorations majeures pour les expériences de durée de vie en fatigue des élastomères sont proposées. Une approche expérimentale originale permettant le pilotage des essais en contrainte vraie est détaillée.Grâce à cette méthode, la première « vraie »courbe de Wöhler (contrainte vraie en fonction du nombre de cycles) pour des élastomères est tracée. Ensuite, des outils statistiques, issus de la recherche médicale, permettent une analyse probabiliste des résultats présentant une grande dispersion et des durées de vie censurées.Dans un second temps, ces nouveaux outils sont utilisés pour étudier l'effet de la formulation chimique – les taux d’acrylonitrile et d'hydrogénation notamment - sur la résistance en fatigue du HNBR à 120 oC. Ces résultats sont complétés par des expériences de propagation de fissure de fatigue et par une analyse de l'endommagement. Finalement, l'influence du vieillissement thermique sur la résistance en fatigue du HNBR est étudiée ; deux nouveaux essais sont développés : des essais simultanés de vieillissement et de fatigue, et des expériences de fatigue sur des échantillons préalablement vieillis.De plus, la cristallisation sous tension dans le HNBR est pour la première fois étudiée de manière quantitative<br>The present PhD thesis is devoted to investigation of fatigue in elastomers, andmore particularly of carbon black-filled hydrogenated nitrile butadiene rubber (HNBR).HNBR is a high performance elastomer classically used for high temperature industrial applications, where high resistance to industrial solvents is also required.The thesis is divided into three main parts.First, major improvements of testing procedures utilized in fatigue life testing ofelastomers are proposed. An original method to prescribe the true stress throughout fatigue experiments is developed; it permits to plot the first “true” Wöhler curve, i.e. true stress vs.number of cycles, for elastomers. Then,statistical tools, widely applied in medical research, are adopted for a comprehensive probabilistic analysis of fatigue life results that exhibit high scatter and censored lifetimes.Second, these novel tools are used to investigate the effect of chemical formulation -acrylonitrile content, percent hydrogenation,and of a composite blend - on fatigue resistance of HNBR at the service temperature of 120 oC. In addition to these fatigue life tests,fatigue crack propagation experiments and microscopic fatigue damage analysis are carried out. Third, the influence of thermal aging on fatigue performances of HNBR is investigated.To this end, two additional fatigue life tests are carried out: simultaneous aging and fatigue experiments, and fatigue experiments on preaged samples.Additionally, strain-induced crystallization in HNBR is studied; for the first time, quantitative relationships between crystallization, strain,and stress are established for unfilled HNBR blends
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Slusher, Aaron L. "COUNTERREGULATORY EFFECTS OF PTX3 ON INFLAMMATION AND CELLULAR AGING." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5287.
Testo completoAbstract (sommario):
Pentraxin 3 (PTX3) is a vital regulator of innate immune function that has been shown to counterregulate pro-inflammatory signaling and protect against the development of cardiovascular disease (CVD). Less is known about how PTX3 may mitigate against CVD risk by regulating the pro-inflammatory response at the cellular level. Therefore, this dissertation details four manuscripts which aimed to examine the capacity of PTX3 to regulate the innate immune response of peripheral blood mononuclear cells (PBMCs) isolated from healthy adults. Manuscript 1 examined the capacity of PTX3 to alter the inflammatory milieu following in vitro stimulation of isolated PBMCs with the pro-inflammatory lipid palmitate. In addition, Manuscript 2 sought to examine how participation in acute exercise, a powerful anti-inflammatory behavior that reduces CVD risk, alters the inflammatory phenotype and response of mononuclear cells following ex vivo stimulation with lipopolysaccharide (LPS). Manuscript 3 aimed to further elucidate the potential impact of cardiorespiratory fitness on the capacity of PTX3 to stimulate an innate immune response prior to and immediately following acute exercise in aerobically trained and untrained individuals. Finally, Manuscript 4 investigated the impact of healthy aging on plasma PTX3 concentrations and its relationship with telomere length in middle-aged compared to young adults. The capacity of isolated PBMCs to express a key cellular mechanism involved in maintaining longer telomere lengths, human telomerase reverse transcriptase (hTERT), following cellular stimulation with LPS, PTX3, and PTX3+LPS was also examined to address a mechanism that might explain how persistent exposure of circulating immune cells to the age-related pro-inflammatory milieu contributes to the shortening of telomere lengths.
25
Chaswal, Vibhor. "Thermal Aging Effects on IN718 Plus Nickel-base Superalloy." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1299854439.
Testo completo
26
Cady, Paul Stevens. "THE EFFECTS OF AGING ON COLOR DISCRIMINATION OF CAPSULES (DIABETES, MEDICATION, VISION)." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/291334.
Testo completo
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Lass, Jordan W., Patrick J. Bennett, Mary A. Peterson, and Allison B. Sekuler. "Effects of aging on figure-ground perception: Convexity context effects and competition resolution." ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2017. http://hdl.handle.net/10150/623274.
Testo completoAbstract (sommario):
We examined age-related differences in figure-ground perception by exploring the effect of age on Convexity Context Effects (CCE; Peterson & Salvagio, 2008). Experiment 1, using Peterson and Salvagio's procedure and black and white stimuli consisting of 2 to 8 alternating concave and convex regions, established that older adults exhibited reduced CCEs compared to younger adults. Experiments 2 and 3 demonstrated that this age difference was found at various stimulus durations and sizes. Experiment 4 compared CCEs obtained with achromatic stimuli, in which the alternating convex and concave regions were each all black or all white, and chromatic stimuli in which the concave regions were homogeneous in color but the convex regions varied in color. We found that the difference between CCEs measured with achromatic and colored stimuli was larger in older than in younger adults. Our results are consistent with the hypothesis that the senescent visual system is less able to resolve the competition among various perceptual interpretations of the figure-ground relations among stimulus regions.
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Bouvier, Frederic. "Effects of ageing and training on the human heart /." Stockholm, 1998. http://diss.kib.ki.se/search/diss.se.cfm?19981023bouv.
Testo completo
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Strauss, Eva von. "Being old in our society : health, functional status, and effects of research /." Stockholm, 2000. http://diss.kib.ki.se/2000/91-628-4189-0/.
Testo completo
30
Khanna, Sumee. "Aging effects of environmental factors on rolled erosion control products." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4862.
Testo completoAbstract (sommario):
This thesis presents a study made on erosion control blankets with respect to their
aging and longevity. Erosion control blankets have been relied upon increasingly in
recent times replacing the old and traditional methods for protecting areas from erosion
by storm water and other factors. But what can be an estimated duration for which a
given set of blankets can be functional in channel erosion control. This research is done
with the ultimate aim of understanding whether these erosion control blankets can stay in
place and be conducive to some vegetation growth, which is said to be the most reliable
measure for long-lasting erosion control.
Seven erosion control blankets, consisting of natural, synthetic and composite
types, were put to actual use for erosion control for 3 years in a field. After 3 years these
used materials were cut from the field for conducting the tests. Unused blankets of the
same brands were obtained. Index tests were conducted on both used and unused
material specimens to measure the erosion control properties. All materials experienced
a significant amount of strength loss after use. The natural materials show 80% strength
loss, while the composite and synthetic materials were tested to have around 50%
strength losses after being put to use for 3 years. Thus it can be observed that the
composite and synthetic materials have a decent amount of life where erosion control is
concerned. Other tests also proved that composite materials can be relied upon for
erosion control to a reasonable extent, and the research goal was achieved.
31
Strain, Laura. "Aging and the Effects of Prior Expectancies in Contingency Judgment." TopSCHOLAR®, 2004. http://digitalcommons.wku.edu/theses/519.
Testo completoAbstract (sommario):
This study examined how prior expectancies affect young and older adults' contingency judgments. Participants completed contingency problems representing all combinations of expectancy (positive, negative, unrelated, and unknown) and contingency (positive, negative, and zero). I originally predicted that the largest age differences would emerge when both the expectancy and the contingency were strong and incongruent, regardless of the nature of the expectancy. However, age differences in the effect of expectancy were strongest when the expectancy was positive and the contingency was Incongruent, and older adults' judgments were more biased by this expectancy. Likewise, I predicted that there would be no age differences when the expectancy and the contingency were congruent, but young adults showed a greater confirmation effect than older adults when the expectancy was negative. The results may not have matched the predictions because they were based on the assumption that all types of expectancies would affect judgments in the same way. The findings of the current study suggest that this is not the case. Future research is needed to explain why certain types of expectancies affect young and older adults' contingency judgment differently.
32
Lynk, Lisa. "Aging effects of binocular summation on contrast sensitivity and hyperacuity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0009/MQ34976.pdf.
Testo completo
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LeBlanc, Amanda Jo. "Effects of aging and gender on vasoreactivity of coronary arterioles." Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5805.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--West Virginia University, 2008.<br>Title from document title page. Document formatted into pages; contains xi, 87 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 71-79).
34
Vennelaganti, Swetha. "AGING AND SLEEP STAGE EFFECTS ON ENTROPY OF ELECTROENCEPHALOGRAM SIGNALS." UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_theses/553.
Testo completoAbstract (sommario):
The aging brain is characterized by alteration in synaptic contacts, which leads to decline of motor and cognitive functions. These changes are reflected in the age related shifts in power spectrum of electroencephalogram (EEG) signals in both wakefulness and sleep. Various non-linear measures have been used to obtain more insights from EEG analysis compared to the conventional spectral analysis. In our study we used Sample Entropy to quantify regularity of the EEG signal. Because elderly subjects arouse from sleep more often than younger subjects, we hypothesized that Entropy of EEG signals from elderly subjects would be higher than that from middle aged subjects, within a sleep stage. We also hypothesized that the entropy increases during and following an arousal and does not return to background levels immediately after an arousal. Our results show that Sample Entropy varies systematically with sleep state in healthy middle-aged and elderly female subjects, reflecting the changing regularity in the EEG. Sample Entropy is significantly higher in elderly in sleep Stage 2 and REM, suggesting that in these two sleep stages the cortical state is closer to wake than in middle-aged women. Sample Entropy is higher in post-arousal compared to the pre-arousal and stays high for a 30 sec period.
35
Flach, Johanna [Verfasser]. "The effects of aging on hematopoietic stem cells / Johanna Flach." Ulm : Universität Ulm. Medizinische Fakultät, 2015. http://d-nb.info/1078674248/34.
Testo completo
36
Artale, Lisa M. "The effects of physical activity on aging : a longitudinal analysis." Virtual Press, 1998. http://liblink.bsu.edu/uhtbin/catkey/1115727.
Testo completoAbstract (sommario):
The purpose of this study was to examine the participants of the Ball State University Retirees Fitness (BSURF) program in order to determine the role that habitual participation in an exercise program plays on the aging process. The participants of the BSURF program were divided into two groups: those that have been exercising for seven or more years (LT; n=14), and those that have been exercising for six years or less (ST; n=10). Subjects underwent testing on the following variables: BMI, body composition, resting heart rate and blood pressure, blood lipid profile, biceps muscular strength, trunk flexibility, and the Rockport Walk Test. Group differences were determined using an independent t-test. Despite a significant difference in age and duration of participation time between the LT and ST groups, no statistically significant differences in cardiovascular measurements, anthropometric measurements, and body size were seen between the two study groups. The only exception to the positive effects of this exercise program on the aging process is demonstrated by the trunk flexibility data. The ST group was significantly more flexible (27.6 ± 1.51 cm) than the LT group (17.7 ± 2.67 cm). The results of this study suggest that continued participation in the BSURF program enabled the LT group to maintain their physiological functioning. Further, the length of participation by the members of the BSURF program clearly demonstrates significant adherence, and suggests that a program of moderate intensity in combination with a large social aspect may play a role in the exercise adherence of older adults.<br>School of Physical Education
37
Adoutte, Danielle. "Sexually dimorphic effects of aging on the rat somatotrophic axis /." [S.l.] : [s.n.], 1992. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
Testo completo
38
DiBlasi, Anita F. "Evaluating the Effects of Aging on American Sign Language Users." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1310670070.
Testo completo
39
Yamakawa, Isao. "Effects of aging on Leachate characteristics of Alkaline Stabilized Biosolids /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu148819244742797.
Testo completo
40
Santiago, de Snyder Soami. "Aging effects on distortion product otoacoustic emissions and speech perception /." The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487847761306525.
Testo completo
41
Balog, Nicole Lynn Balog. "Older Adults and Successful Aging: The Effects of Lifelong Learning." Youngstown State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1527019677357409.
Testo completo
42
Mohney, Jack D. "Age and vigilance: The effects of event rate and task pacing." CSUSB ScholarWorks, 1986. https://scholarworks.lib.csusb.edu/etd-project/329.
Testo completo
43
Yu, Fushun. "Adaptability of skeletal muscle to hormone treatment in relation to gender and aging /." Stockholm, 1999. http://diss.kib.ki.se/1999/91-628-3585-8/.
Testo completo
44
吳勝前 and Shengqian Wu. "Study of atrial natriuretic peptide and endothelin in streptozotocin-diabetic rats and in the aging rats." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31237885.
Testo completo
45
O'Neal, Jessica. "The effects of aging and remodeling on bone quality and microdamage." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/44724.
Testo completoAbstract (sommario):
One indication of increasing fragility of bone is the accumulation of microscopic cracks, or microdamage, within the bone matrix. Microdamage accumulates in bone of the elderly, when changes in bone material properties and matrix architecture coupled with a decrease in bone repair mechanisms compromise bone integrity. To preserve bone mass and reduce fracture risk, therapeutics such as alendronate are prescribed which increase bone volume fraction by decreasing the rate of bone turnover. However, concerns over adverse effects of prolonged turnover suppression have been reinforced by findings of increased microdamage density with alendronate use. Microdamage formation is not always pathologic, but extensive accumulation of damage can be an indicator of reduced bone quality. The work in this thesis explores the hypothesis that microdamage in bone of lower quality will form more easily and progress more extensively than in bone of higher quality. Microdamage initiation stresses and strains were obtained for trabecular bone from older females, older males, and younger females to determine whether thresholds for damage initiation were lower in older females. Results suggest that the stress threshold for damage initiation in older females may indeed be lower compared with younger females, and that normalized strain thresholds for severe damage formation in older males may be decreased compared with older females. Damage propagation was evaluated as a function of age and sex to determine whether damage in older women progressed more extensively than in younger women or men. Results suggest that bone from older individuals had decreased resistance to crack propagation evidenced by an increased number of severely damaged trabeculae which expanded in area under cyclic loading; however no sex differences were uncovered. Finally, the stress/strain thresholds for damage initiation were investigated in alendronate-treated bone, and results indicate that a decreased stress threshold was needed to initiate damage formation of a linear and severe morphology after one year of treatment. After three years of treatment, however, micromechanical properties recovered, perhaps due to increased matrix mineralization which increased tissue level stiffness.
46
Bérard, Jessica. "Visuomotor control of locomotion and the effects of aging and stroke." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104655.
Testo completoAbstract (sommario):
Vision is arguably the most important sensory cue for the control of goal-directed locomotion. Optic flow, broadly defined as the pattern of light at the eye of a person moving through the environment, provides strong cues on the direction of locomotion, also known as heading. To date, most studies have only investigated the use of optic flow for heading in healthy young subjects. However, the capacity for visual processing can decline with advancing age or a neurological insult, such as stroke. These changes could impact on the control of heading and locomotion. The purpose of this thesis was to explore the role of optic flow in the control of locomotion in older adults and in stroke patients. In the first study, 2 groups of subjects (young: n=9, age 21.56 ± 3.20; old: n=9, age 66.11 ± 3.95) were instructed to walk straight in a virtual environment. As they progressed forward, the location from which the scene was expanding from, also know as the focus of expansion (FOE), was offset with a translation of 20° or 40° either to the left or right of the midline of the virtual scene. Young adults responded by displacing their centre of mass (CoM) mediolaterally in the direction opposite to the FOE shift, thus correcting their virtual trajectory so that they perceived walking straight in the virtual environment. In contrast, older adults showed very little trajectory corrections to the optic flow, resulting in large heading errors. In the second study, 10 young (age 23.49 ± 4.72) and 10 older adults (age 76.22 ± 3.11) were instructed to walk straight in a virtual environment where the FOE was gradually rotated until reaching 40° to the right or left at the end of the walking trial. Young adults displayed very small net heading errors in the virtual environment and responded by physically reorienting their heading and head in the direction opposite to the FOE rotation. Older adults showed similar responses, though they had smaller head rotations and slightly larger errors. Taken together, these 2 studies indicate that the effects of aging on the control of heading from optic flow are dependent on the type of flow presented and that the utilization of rotational flows while walking are less susceptible to aging than translational flows. In the third study, the same groups of healthy young and older adults (n=10 each) were tested on their ability to re-weight sensory information and maintain a straight heading in the physical environment while being exposed to rotational flows, as they walked at normal and fast walking speeds. Older participants made significantly larger heading errors than younger adults at normal walking speeds. Fast walking speed was found to improve the heading performance of young subjects but led to even larger heading errors in the older adults. This study suggests an increased reliance on visual cues for locomotor control in older adults who are less adept in visual reweighting. In the final study, a single-subject design was used to investigate the effects of stroke on the ability to use rotational optic flow cues while walking. Nine stroke patients were instructed to walk straight in a virtual environment with the FOE rotating 40° either towards the ipsilesional or contra-lesional side. Patterns of heading responses varied, with individuals having a history of neglect consistently showing heading larger errors than those without. The presence of persistent visuomotor deficits, particularly in far space, in stroke patients with a history of visuospatial neglect, is a novel finding of this thesis. In conclusion, central nervous system changes due to aging and stroke can impact the ability to use optic flow for the control of goal-directed locomotion. The underlying changes may pertain to the processing and/or integration of visual motion information.<br>La vision est sans doute l'information sensorielle la plus importante dans le contrôle de la marche. Le flux optique, qui peut être défini comme le patron de lumière dirigé sur la rétine quand une personne avance dans l'environnement, donne de puissantes indications quant à la trajectoire ou la direction de la marche. Le vieillissement et la présence de lésions neurologiques peuvent altérer la capacité à traiter les informations visuelles. Le but de cette thèse était d'explorer le rôle du flux optique dans le contrôle de la trajectoire de la marche chez les personnes âgées et les patients ayant subi un accident vasculaire cérébral (AVC). Dans la première étude, deux groupes de sujets (jeunes : n=9, 21.56 ± 3.20 ans; Âgés: n=9, 66.11 ± 3.95 ans) ont reçu pour instruction de marcher en ligne droite dans un environnement virtuel. Alors qu'ils avançaient, l'endroit à partir duquel la scène prenait de l'expansion, connu également comme le focus d'expansion (FE), a été déplacé latéralement pour atteindre une translation de 20° ou de 40° vers la gauche ou la droite par rapport à la ligne centrale de l'environnement virtuel. Les jeunes adultes ont répondu en déplaçant leur centre de masse médiolatéralement dans la direction opposée au déplacement du FE, corrigeant ainsi leur trajectoire de sorte qu'ils marchent en ligne droite dans l'environnement virtuel. Au contraire, les adultes plus âgés ont montré très peu de corrections en réponse au flux optique, résultant en de grandes erreurs de trajectoire. Dans la seconde étude, 10 jeunes adultes (âge 23.49 ± 4.72 ans) et 10 adultes âgés (âge 76.22 ± 3.11 ans) ont reçu pour instruction de marcher droit dans un environnement virtuel alors que le FE a été graduellement déplacé en rotation, jusqu'à l'obtention d'un angle de 40° vers la droite ou la gauche à la fin de l'essai de marche. Les sujets jeunes ont démontré des erreurs nettes de trajectoire très petites dans l'environnement virtuel et ont répondu en tournant et redirigeant la tête et le corps dans la direction opposée à la rotation du FE. Les adultes plus âgés ont répondu de la même façon, bien qu'ils aient eu moins de rotation de la tête et des erreurs légèrement plus grandes. Les résultats combinés de ces deux études indiquent que les effets du vieillissement sur le contrôle de la trajectoire à l'aide du flux optique sont dépendants du type de flux optique présenté et que l'utilisation du flux en rotation pendant la marche est moins sensible au vieillissement que celle du flux en translation. Dans la troisième étude, les sujets jeunes et âgés ont été testés quant à leur habileté à re-pondérer les informations sensorielles et maintenir une trajectoire rectiligne dans l'environnement réel alors qu'ils étaient exposés à des flux optiques en rotation, lors de la marche à vitesse confortable et rapide. Les sujets âgés ont fait de plus grandes erreurs de trajectoire à vitesse confortable que les sujets plus jeunes. Une vitesse de marche plus rapide a amélioré la performance des sujets jeunes mais a entraîné des erreurs de trajectoire plus grandes chez les adultes plus âgés. Dans la dernière étude neuf patients avec un AVC ont reçu comme instruction de marcher droit dans un environnement virtuel avec un FE se déplaçant à 40 ° de rotation vers le côté lésionnel ou contra-lésionnel. Les patrons de réponse se sont révélés variables, alors que les sujets ayant une histoire d'héminégligence ont constamment montré de plus grandes erreurs de trajectoire. La présence de déficits visuomoteurs persistants chez les sujets avec une historique d'heminégligence est une nouvelle découverte de cette thèse. En conclusion, les changements au système nerveux central causés par le vieillissement et la présence d'un AVC peuvent influencer la capacité à utiliser le flux optique pour contrôler la marche. Les changements sous-jacents pourraient être liés au traitement et/ou à l'intégration des informations de mouvement visuel.
47
Conde, Jessica Renee. "Effects of aging on microglial activation in response to neuronal injury." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0010110.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--University of Florida, 2005.<br>Typescript. Title from title page of source document. Document formatted into pages; contains 142 pages. Includes Vita. Includes bibliographical references.
48
Sifrit, Kathy J. Chaparro Alex. "The effects of aging and cognitive decrements on simulated driving performance." Diss., Click here for available full-text of this thesis, 2006. http://library.wichita.edu/digitallibrary/etd/2005/d008.pdf.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Psychology.<br>"December 2005." Title from PDF title page (viewed on February 8, 2007). Thesis adviser: Alex Chaparro. Includes bibliographic references (leaves 81-90).
49
Farrimond, Samantha, and n/a. "The effects of aging on remembering intentions : the virtual street task." University of Otago. Department of Psychology, 2006. http://adt.otago.ac.nz./public/adt-NZDU20070322.142811.
Testo completoAbstract (sommario):
In everyday life memory is commonly used in the completion of future intentions, such as remembering to attend a meeting or remembering to make a purchase at a particular time or place. The ability to remember to complete future intentions plays an important role in older adults maintaining independent living within the community (Cherry & LeCompte, 1999). The studies presented in this thesis evolved out of the lack of current understanding about which component processes involved in remembering future intentions are most susceptible to the effects of aging. In order to investigate these processes, a computer-based analogue of a real-life task was developed (the Virtual Street) that enabled participants to complete a series of intentions (shopping errands) during a simulated visit to a shopping centre.
There were two main objectives of this thesis. The first objective was to examine whether the Virtual Street shopping task was appropriate for assessing older and younger adults ability to remember to complete delayed intentions and whether the task had better ecological and face validity than current assessment measures. The second objective was to identify the cognitive processes involved in the task that were vulnerable to the effects of aging, and whether the process of recognising the cues or the memory search of the intention content would be affected. In order to examine these cognitive processes, various factors were manipulated in ways designed to be analogous to real-world situations, which were hypothesized to be sensitive to the effects of aging. These factors include: a change in the location where an intention can be realised (Study 1), the opportunity to learn the intentions (Study 2), the familiarity of the shopping environment (Study 3), and the presence of distractions (Study 4).
Overall, the results from the four studies demonstrated that older adults have difficulty remembering delayed intentions, even when the test uses naturalistic stimuli, the tasks are familiar, and they are able to move at their own pace. Furthermore, the results from Study 2 demonstrated that the memory search component but not cue detection was affected in older persons when they were given fewer trials to learn the shopping errands, possibly due to the accessibility of the cue-intention associations may be impaired in older adults. There was no age specific effect on cue detection or memory search in either an unfamiliar street environment (Study 3) or one with increased levels of irrelevant auditory and visual noise (distraction condition, Study 4). In the interruption condition of Study 4, however, cue detection but not memory search was disproportionately affected in older adults after filled interruptions, suggesting that the capacity for self-initiated reinstatement of working memory is reduced in old age.
In general, the Virtual Street task was to be a practical means of examining younger and older adults ability to remember to complete delayed intentions. The Virtual Street task also provided an opportunity for behavioural observation of real-life skills and cognitive abilities, within a controlled context. It is hoped that the Virtual Street shopping task will continue to be developed into an ecologically valid measure of assessing older adults memory functioning.
50
Cornejo, Orlando A. "Aging effects on microstructure and creep in Sn-3.8Ag-0.7Cu solder." Thesis, Monterey, Calif. : Naval Postgraduate School, 2007. http://bosun.nps.edu/uhtbin/hyperion-image.exe/07Sep%5FCornejo.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, September 2007.<br>Thesis Advisor(s): Dutta, Indranath. "September 2007." Description based on title screen as viewed on October 22, 2007. Includes bibliographical references (p. 75-78). Also available in print.