71 |
Predicting Length of Stay and Non-Home Discharge: A Novel Approach to Reduce Wasted Resources after Cardiac SurgeryPattakos, Gregory January 2011 (has links)
No description available.
|
72 |
Factors Predictive of Adverse Postoperative Events Following TonsillectomySubramanyam, Rajeev January 2013 (has links)
No description available.
|
73 |
A Biomechanical Comparison of Locking Compression Plate Constructs with Plugs/Screws in Osteoporotic Bone ModelDesai, Krishna P. 22 April 2010 (has links)
No description available.
|
74 |
Model prediction of the effects of ameliorating cosmetics on the performance of airport surveillance radar and air traffic control radar beacon systemsFofie, Francis Obeng January 2003 (has links)
No description available.
|
75 |
Bond of nanoinclusions reinforced concrete with old concrete: strength, reinforcing mechanisms and prediction modelWang, X., Dong, S., Ashour, Ashraf, Han, B. 16 February 2021 (has links)
Yes / This paper investigated the bond strength of eight nanoinclusions reinforced concrete with old concrete through a splitting tensile test. The reinforcing mechanisms of bond due to nanoinclusion was also explored by means of scanning electron microscope and energy dispersive spectrometer. A prediction model for the bond strength between nanoinclusion reinforced concrete with old concrete substrate was developed and calibrated against the experimental results obtained. The experimental results indicated that bond strength between nanoinclusions reinforced concrete and old concrete can reach 2.85 MPa, which is 0.8 MPa/39.0% higher than that between new concrete without nanoinclusions and old concrete. The reinforcing mechanisms can be attributed to the enrichment of nanoinclusions in the new-to-old concrete interface, compacting the interfacial microstructures and connecting hydration products in micropores of old concrete with that in bulk new concrete. In addition, the prediction model proposed on the basis of reinforcing mechanisms can accurately describe the relationship of the nanoinclusion content and the bond strength of nanoinclusions reinforced concrete with old concrete.
|
76 |
Analysis and Modeling of the Mechanical Durability of Proton Exchange Membranes Using Pressure-Loaded Blister TestsGrohs, Jacob R. 29 May 2009 (has links)
Environmental fluctuations in operating fuel cells impose significant biaxial stresses in the constrained proton exchange membranes (PEM). The PEM's ability to withstand cyclic environment-induced stresses plays an important role in membrane integrity and consequently, fuel cell durability. In this thesis, pressure loaded blister tests are used to study the mechanical durability of Gore-Select® series 57 over a range of times, temperatures, and loading histories. Ramped pressure tests are used with a linear viscoelastic analog to Hencky's classical solution for a pressurized circular membrane to estimate biaxial burst strength values. Biaxial strength master curves are constructed using traditional time-temperature superposition principle techniques and the associated temperature shift factors show good agreement when compared with shifts obtained from other modes of testing on the material. Investigating a more rigorous blister stress analysis becomes nontrivial due to the substantial deflections and thinning of the membrane. To further improve the analysis, the digital image correlation (DIC) technique is used to measure full-field displacements under ramped and constant pressure loading. The measured displacements are then used to validate the constitutive model and methods of the finite element analysis (FEA). With confidence in the FEA, stress histories of constant pressure tests are used to develop linear damage accumulation and residual strength based lifetime prediction models. Robust models, validated by successfully predicting fatigue failures, suggest the ability to predict failures under any given stress history whether mechanically or environmentally induced - a critical step in the effort to predict fuel cell failures caused by membrane mechanical failure. / Master of Science
|
77 |
Statistical Methods for Variability Management in High-Performance ComputingXu, Li 15 July 2021 (has links)
High-performance computing (HPC) variability management is an important topic in computer science. Research topics include experimental designs for efficient data collection, surrogate models for predicting the performance variability, and system configuration optimization. Due to the complex architecture of HPC systems, a comprehensive study of HPC variability needs large-scale datasets, and experimental design techniques are useful for improved data collection. Surrogate models are essential to understand the variability as a function of system parameters, which can be obtained by mathematical and statistical models. After predicting the variability, optimization tools are needed for future system designs.
This dissertation focuses on HPC input/output (I/O) variability through three main chapters. After the general introduction in Chapter 1, Chapter 2 focuses on the prediction models for the scalar description of I/O variability. A comprehensive comparison study is conducted, and major surrogate models for computer experiments are investigated. In addition, a tool is developed for system configuration optimization based on the chosen surrogate model.
Chapter 3 conducts a detailed study for the multimodal phenomena in I/O throughput distribution and proposes an uncertainty estimation method for the optimal number of runs for future experiments. Mixture models are used to identify the number of modes for throughput distributions at different configurations. This chapter also addresses the uncertainty in parameter estimation and derives a formula for sample size calculation. The developed method is then applied to HPC variability data.
Chapter 4 focuses on the prediction of functional outcomes with both qualitative and quantitative factors. Instead of a scalar description of I/O variability, the distribution of I/O throughput provides a comprehensive description of I/O variability. We develop a modified Gaussian process for functional prediction and apply the developed method to the large-scale HPC I/O variability data.
Chapter 5 contains some general conclusions and areas for future work. / Doctor of Philosophy / This dissertation focuses on three projects that are all related to statistical methods in performance variability management in high-performance computing (HPC). HPC systems are computer systems that create high performance by aggregating a large number of computing units. The performance of HPC is measured by the throughput of a benchmark called the IOZone Filesystem Benchmark. The performance variability is the variation among throughputs when the system configuration is fixed. Variability management involves studying the relationship between performance variability and the system configuration. In Chapter 2, we use several existing prediction models to predict the standard deviation of throughputs given different system configurations and compare the accuracy of predictions. We also conduct HPC system optimization using the chosen prediction model as the objective function. In Chapter 3, we use the mixture model to determine the number of modes in the distribution of throughput under different system configurations. In addition, we develop a model to determine the number of additional runs for future benchmark experiments. In Chapter 4, we develop a statistical model that can predict the throughout distributions given the system configurations. We also compare the prediction of summary statistics of the throughput distributions with existing prediction models.
|
78 |
BRIDGE END SETTLEMENT EVALUATION AND PREDICTIONZhang, Jiwen 01 January 2016 (has links)
A bridge approach is usually built to provide a smooth and safe transition for vehicles from the roadway pavement to the bridge structure. However, differential settlement between the roadway pavement resting on embankment fill and the bridge abutment built on more rigid foundation often creates a bump in the roadway. Previous work examined this issue at a microscopic level and presented new methods for eliminating or minimizing the effects at specific locations.
This research studies the problem at a macroscopic level by determining methods to predict settlement severity to assist designers in developing remediation plans during project development to minimize the lifecycle costs of bridge bump repairs. The study is based on historic data from a wide range of Kentucky roads and bridges relating to bridge approach inspection and maintenance history. A macro method considering a combination of maintenance times, maintenance measures, and observed settlement was used to classify the differential settlement scale as minimal, moderate, and severe, corresponding to the approach performance status good, fair, and poor. A series of project characteristics influencing differential settlement were identified and used as parameters to develop a model to accurately predict settlement severity during preliminary design. Eighty-seven bridges with different settlement severities were collected as the first sample by conducting a survey of local bridge engineers in 12 transportation districts. Sample two was created by randomly selecting 600 bridges in the inspection history of bridges in Kentucky. Ordinal and/or multinomial logistic regression analyses were implemented to identify the relationships between the levels of differential settlement and the input variables. Two predictive models were developed. Prediction of bridge approach settlement can play an important role in selecting proper design, construction, and maintenance techniques and measures. The users can select one or two models to predict the approach settlement level for a new bridge or an existing bridge with different purposes.
The significance of this study lies in its identification of parameters that had the most influence on the settlement severity at bridge ends, and how those parameters interacted in developing of a prediction model. The important parameters include geographic regions, approach age, average daily traffic (ADT), the use of approach slabs, and the foundation soil depth. The regression results indicate that the use of approach slabs can improve the performance of approaches on mitigating the problem caused by differential settlement. In addition, current practices regarding differential settlement prediction and mitigation were summarized by surveying the bridge engineers in 5 transportation districts.
|
79 |
Sistema de gerência de pavimentos urbanos: avaliação de campo, modelo de desempenho e análise econômica / Urban pavement management system: field evaluation, prediction model and economic analysesZanchetta, Fábio 04 August 2017 (has links)
As vias pavimentadas se deterioram com o passar do tempo, por ação das cargas do tráfego e das intempéries. Por isso necessitam de intervenções (atividades de Manutenção e Reabilitação - M&R). No Brasil é mais comum que sejam realizadas apenas operações tapa-buracos e recapeamentos. São soluções sem eficiência técnica ou econômica. Uma alternativa mais racional e já em uso em países desenvolvidos é um Sistema de Gerência de Pavimentos Urbanos - SGPU. Os objetivos desta tese são apresentar uma propostas para avaliação da condição de vias urbanas com base na identificação dos defeitos da superfície do revestimento, um modelo de previsão de desempenho de vias urbanas com base em séries históricas obtidas no Município de São Carlos e uma análise econômica com a simulação de diferentes cenários para diferentes opções de M&R. Ainda como objetivos desta tese estão a apresentação das vantagens de utilizar um Sistema de Informações Geográficas - SIG, em uso no SGPU do Distrito Federal. Com base nos resultados encontrados, pode-se inferir que a avaliação de campo pode ser mais eficiente se forem considerados menos defeitos e os critérios de severidade e extensão forem fixados, com menos critérios subjetivos do avaliador. Considerando-se as estratégias de M&R adotadas pela Prefeitura Municipal de São Carlos e, ainda, de acordo com as avaliações de campo, pôde-se verificar que os pavimentos necessitam de Reforço Estrutural após 6 anos da sua construção. Os custos de manutenção, ao longo do tempo, são influenciados pela escolha da M&R a ser aplicada na preservação das vias e, também, pela época em que são realizadas, sendo as manutenções preventivas menos onerosas. Nos Estados Unidos, por exemplo, particularmente na cidade de San Antonio, Texas, são realizadas manutenções preventivas e, nas corretivas, há rigoroso controle de qualidade, o que não se verifica nas cidades brasileiras. Um SGPU possui critérios de análise de dados que, aliados ao Sistema de Informações Geográficas - SIG, garantem clareza na apresentação dos resultados, tanto em mapas temáticos quanto em gráficos e planilhas. Os relatórios no padrão SGPU possibilitam solicitar recursos federais e internacionais para manutenção viária, como o Programa Asfalto Novo do DF, que obteve, no ano de 2013, R$565 milhões para a pavimentação urbana. Em simulação de diferentes cenários de M&R, pôde-se concluir que a opção por tapa-buracos e recapeamentos é mais de duas vezes mais onerosa e mantém o pavimento em condição inferior ao que é possível com base nas técnicas de SGPU. Portanto, um SGPU proporciona benefícios socioeconômicos para toda a sociedade, com vantagens no médio e longo prazo e, ainda, mantém as vias em melhor condição. / The paved roads deteriorate over time, due to traffic loads and bad weather. Therefore, they need interventions (Maintenance and Rehabilitation activities - M & R). In Brazil, it is more common to carry out only hole-hole operations and resurfacing. They are solutions without technical or economic efficiency. A more rational alternative already in use in developed countries is an Urban Pavement Management System - UPMS. In this thesis proposals are presented for the evaluation of urban road conditions based on defects of the surface of the coating, a performance prediction model and an economic analysis with the simulation of different scenarios for different M & R options. Data were analyzed from the Municipality of São Carlos, in the State of São Paulo and the Distrito Federal - DF. Based on the results, it can be inferred that the field evaluation can be more efficient if less defects are considered and the criteria of severity and extension are fixed, with less subjectivity on the part of the evaluator. Considering the M & R strategies adopted by the municipal government of São Carlos and also, according to the field evaluations, it was possible to verify that the pavements have a useful life of 6 years. The maintenance costs, over time, are strongly influenced by the choice of M & R to be applied in the preservation of roads and also by the time in which they are carried out. In the United States, for example, preventive maintenance is carried out and, in the correctives, there is strict quality control, which is not the case in Brazilian cities. An UPMS has data analysis criteria that, together with the Geographic Information System - GIS, guarantee clarity in the presentation of results, both in thematic maps and in charts and spreadsheets. The reports in the UPMS standard make it possible to request federal and international resources for road maintenance, such as the DF Asphalt New Program, which obtained R$ 565 million for urban paving. In the simulation of different M & R scenarios, it was concluded that the option to cover holes and resurfacing is more than twice as expensive and keeps the pavement in a lower condition than is possible based on SGPU techniques. Therefore, an SGPU confers socio-economic benefits for the whole society, with advantages in the medium and long term, and also keeps the roads in better condition.
|
80 |
[en] RADIOMETEOROLOGICAL STUDY IN THE AMAZON REGION / [pt] ESTUDO RADIOMETEOROLÓGICO DA REGIÃO AMAZÔNICAJORGE LUIS RODRIGUES P DE CERQUEIRA 29 August 2006 (has links)
[pt] A região amazônica é uma extensa área de grande
importância política e
estratégica para o futuro do Brasil. Por suas
características, tais como, a distâncias
entre cidades e vilarejos, a impenetrabilidade da
floresta, a dificuldade de
construção de rodovias, etc. é imediato constatar a
importância primordial de ser
atendida por sistemas de telecomunicações sem fio,
particularmente de redes via
satélite, eficientes e confiáveis. Qualquer operação
militar ou civil na região,
como o próprio sistema SIPAM (Sistema de Proteção da
Amazônia) ou qualquer
sistema de comando e controle necessita, para o seu êxito,
do planejamento
correto dos sistemas de comunicações via satélite
fundamentais para a defesa e a
manutenção da soberania e da integridade territorial da
região, diretamente
relacionado ao conceito de segurança nacional. O problema
é que, devido à
necessidade de descongestionar o uso do espectro, tais
sistemas passaram a
utilizar freqüências acima de 10 GHz de forma mais
intensa. Esta situação tornou
primordial a avaliação dos efeitos da precipitação sobre a
propagação dos sinais
radioelétricos. O planejamento dos atuais sistemas de
comunicações por satélite
que operam nas bandas Ka e Ku
está, nos dias de
hoje, fortemente dependente da atenuação produzida pela
chuva, que delimita, na
maioria dos casos, até mesmo a sua disponibilidade. Neste
contexto, o presente
trabalho procura contribuir através de um estudo
radiometeorológico da região
Amazônica. O levantamento e a análise de informações sobre
a chuva permite a
obtenção de parâmetros a serem utilizados no aprimoramento
e no
desenvolvimento de modelos que visam à otimização dos
projetos de novos
sistemas de comunicações e/ou a expansão de sistemas
existentes. Tendo em vista
que, no processo de avaliação do efeito da chuva sobre o
sinal, a distribuição
estatística da taxa de precipitação de um determinado
local é um parâmetro
meteorológico essencial, foram realizadas medidas em nove
localidades da Amazônia, por uma rede de pluviógrafos do
tipo caçamba basculante, instalada na
região com este objetivo específico. As distribuições
estatísticas cumulativas da
taxa de precipitação, anual e para o pior mês, foram
levantadas e processadas,
assim como confrontadas com os modelos de predição atuais
de forma a avaliá-los
quanto à aplicabilidade na região. O modelo atualmente
adotado pela
Recomendação do UIT-R1 P.837-4, foi cuidadosamente
investigado, sendo
proposta a atualização de alguns de seus parâmetros,
objetivando aprimorar o
desempenho na região. O comportamento dinâmico da
precipitação e o
conseqüente efeito sobre a propagação dos sinais foram
discutidos e comentados
os aspectos onde este conhecimento é fundamental para a
implementação de
técnicas de melhoria para aumentar a confiabilidade dos
sistemas. Foi também
realizado, com base em dados provenientes dos radares
meteorológicos do SIPAM
(Sistema de Proteção da Amazônia), um estudo da estrutura
espacial da
precipitação, de grande utilidade no aprimoramento de
modelos físicos de
predição da atenuação por chuva. Neste particular, foi
possível tratar nesta tese
questões como a relação Z-R (refletividade-precipitação)
para os radares e a
determinação das dimensões horizontais e vertical da
célula de chuva. Por fim, foi
desenvolvido um modelo matemático para representar o
comportamento
estatístico de duas células de chuva, separadas por uma
dada distância, com a
finalidade de fornecer subsídios para a interpretação
física do funcionamento da
técnica de diversidade de sítio em um sistema de
comunicações por satélite. / [en] The Brazilian Amazon is a very large equatorial region,
covered by a
dense jungle and located in the North of Brazil. Its
political and strategic
importance is nationally recognized. Consequently,
wireless communications
play a fundamental role under the point of view of its
development, support to
its inhabitants and state security. In this context, the
main motivation for the
work described in this dissertation was the possibility of
contributing to the
progress of the Amazon region. Nowadays, the use of
frequencies above 10
GHz is growing fast, not only as a solution to overcome
the problem of
spectrum congestion, but also to increase the capacity of
telecommunications
systems. Unfortunately, these frequencies are strongly
affected by precipitation.
Once the equatorial climate is characterized by heavy
rain, a
radiometeorological study in the Amazon region seems to be
essential for
acquiring the information needed to improve the project
criteria and the
performance analysis of communication systems in this
area. The first step in
the investigation reported here was a study about the
climate of the Amazon
region. Köppen classification was adopted because its
structure depends on
temperature, precipitation and vegetation, factors that
can be related to the
statistical distribution of rain in a given area.
According to this classification,
the climate in the Amazon region is a tropical rainy (A),
where 3 subtypes can
be identified: Rainy equatorial (Af); Monsoon tropical
(Am); Wet-and-dry
tropical (Aw). The rainfall characteristics analysis was
carried out with data
from a pluviograph network covering the region of interest
and consisting of 9
(nine) rain gauges. Tipping bucket rain gauges were used,
in which, each tip
corresponds to 0.1mm rainfall, the integration time being
one minute and
measuring a maximum precipitation rate of 240 mm/h.
Complementary radar
data from the SIPAM (Amazon system protection) network
were also taken into
account in this research. Radars operate in the frequency
of 2.8 GHz (S-band), with 4.3m parabolic antennas and a
maximum coverage of 400km. Based on
precipitation measurements carried out for a period of one
year (June 2004 to
May 2005), a detailed study of rainfall rate distribution
was developed. Both
annual and monthly cumulative distributions were derived.
Three mathematical
models available in the literature for predicting the
cumulative distribution of
rainfall rate were compared and tested against the
experimental data available.
The Salonen-Baptista (S-B) was taken as reference in this
dissertation. The
reason for choosing this model was its global coverage and
its dependence on
meteorological parameters available in the region under
study, allowing to be
continuously extended over a large area. Additionally,
this model is the basis of
ITU-R Recommendation P.837-4. On the other hand, as radar
measurements are
of paramount importance in the analysis of the spatial
structure of rain, based on
the classical relation Z(mm6/m3) = a[R(mm/h)]b the
conversion between radar
reflectivity (Z) and rainfall rate (R) were carefully
investigated. The
experimental data from rain gauge and radar networks have
allowed the
examination of different questions: a) Dynamic behaviour
of the rainfall rate; b)
Horizontal and vertical distribution of rain; c)
Correlation of rainfall rate
measured in two points separated by a given distance. In
each case, the use of
the final results to the analysis of problems related to
telecommunication
systems was pointed out. Due to its relevance in the
Amazon region, the
application to satellite communications was emphasized.
|
Page generated in 0.1373 seconds