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Title: Evolution and distribution of phenotypic diversity in the venom of Mojave Rattlesnakes (Crotalus scutulatus).
Creator: Strickland, Jason, Savage, Anna, Parkinson, Christopher, Hoffman, Eric, Rokyta, Darin, University of Central Florida
Abstract / Description: Intraspecific phenotype diversity allows for local adaption and the ability for species to respond to changing environmental conditions, enhancing survivability. Phenotypic variation could be stochastic, genetically based, and/or the result of different environmental conditions. Mojave Rattlesnakes, Crotalus scutulatus, are known to have high intraspecific venom variation, but the geographic extent of the variation and factors influencing venom evolution are poorly understood. Three primary...
Show moreIntraspecific phenotype diversity allows for local adaption and the ability for species to respond to changing environmental conditions, enhancing survivability. Phenotypic variation could be stochastic, genetically based, and/or the result of different environmental conditions. Mojave Rattlesnakes, Crotalus scutulatus, are known to have high intraspecific venom variation, but the geographic extent of the variation and factors influencing venom evolution are poorly understood. Three primary venom types have been described in this species based on the presence (Type A) or absence (Type B) of a neurotoxic phospholipase A2 called Mojave toxin and an inverse relationship with the presence of snake venom metalloproteinases (SVMPs). Individuals that contain both Mojave toxin and SVMPs, although rare, are the third, and designated Type A + B. I sought to describe the proteomic and transcriptomic venom diversity of C. scutulatus across its range and test whether diversity was correlated with genetic or environmental differences. This study includes the highest geographic sampling of Mojave Rattlesnakes and includes the most venom-gland transcriptomes known for one species. Of the four mitochondrial lineages known, only one was monophyletic for venom type. Environmental variables poorly correlated with the phenotypes. Variability in toxin and toxin family composition of venom transcriptomes was largely due to differences in transcript expression. Four of 19 toxin families identified in C. scutulatus account for the majority of differences in toxin number and expression variation. I was able to determine that the toxins primarily responsible for venom types are inherited in a Mendelian fashion and that toxin expression is additive when comparing heterozygotes and homozygotes. Using the genetics to define venom type is more informative and the Type A + B phenotype is not unique, but rather heterozygous for the PLA2 and/or SVMP alleles. Intraspecific venom variation in C. scutulatus highlights the need for fine scale ecological and natural history information to understand how phenotypic diversity is generated and maintained geographically through time.
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Date Issued: 2018
Identifier: CFE0007252, ucf:52198
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007252

Title: A Methodology on Weapon Combat Effectiveness Analytics using Big Data and Live, Virtual, or/and Constructive Simulations.
Creator: Jung, Won Il, Lee, Gene, Rabelo, Luis, Elshennawy, Ahmad, Ahmad, Ali, University of Central Florida
Abstract / Description: The Weapon Combat Effectiveness (WCE) analytics is very expensive, time-consuming, and dangerous in the real world because we have to create data from the real operations with a lot of people and weapons in the actual environment. The Modeling and Simulation (M(&)S) of many techniques is used for overcoming these limitations. Although the era of big data has emerged and achieved a great deal of success in a variety of fields, most WCE research using the Defense Modeling and Simulation (DM(&)S...
Show moreThe Weapon Combat Effectiveness (WCE) analytics is very expensive, time-consuming, and dangerous in the real world because we have to create data from the real operations with a lot of people and weapons in the actual environment. The Modeling and Simulation (M(&)S) of many techniques is used for overcoming these limitations. Although the era of big data has emerged and achieved a great deal of success in a variety of fields, most WCE research using the Defense Modeling and Simulation (DM(&)S) techniques were studied without the help of big data technologies and techniques. The existing research has not considered various factors affecting WCE. This is because current research has been restricted by only using constructive simulation, a single weapon system, and limited scenarios. Therefore, the WCE analytics using existing methodologies have also incorporated the same limitations, and therefore, cannot help but get biased results.To solve the above problem, this dissertation is to initially review and compose the basic knowledge for the new WCE analytics methodology using big data and DM(&)S to further serve as the stepping-stone of the future research for the interested researchers. Also, this dissertation presents the new methodology on WCE analytics using big data generated by Live, Virtual, or/and Constructive (LVC) simulations. This methodology can increase the fidelity of WCE analytics results by considering various factors. It can give opportunities for application of weapon acquisition, operations analytics and plan, and objective level development on each training factor for the weapon operators according to the selection of Measures of Effectiveness (MOEs) and Measures of Performance (MOPs), or impact factors, based on the analytics goal.
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Date Issued: 2018
Identifier: CFE0007025, ucf:52870
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007025

Title: An Agile Roadmap for Live, Virtual and Constructive-Integrating Training Architecture (LVC-ITA): A Case Study Using a Component based Integrated Simulation Engine.
Creator: Park, Tae Woong, Lee, Gene, Rabelo, Luis, Elshennawy, Ahmad, Kincaid, John, University of Central Florida
Abstract / Description: Conducting seamless Live Virtual Constructive (LVC) simulation remains the most challenging issue of Modeling and Simulation (M(&)S). There is a lack of interoperability, limited reuse and loose integration between the Live, Virtual and/or Constructive assets across multiple Standard Simulation Architectures (SSAs). There have been various theoretical research endeavors about solving these problems but their solutions resulted in complex and inflexible integration, long user-usage time and...
Show moreConducting seamless Live Virtual Constructive (LVC) simulation remains the most challenging issue of Modeling and Simulation (M(&)S). There is a lack of interoperability, limited reuse and loose integration between the Live, Virtual and/or Constructive assets across multiple Standard Simulation Architectures (SSAs). There have been various theoretical research endeavors about solving these problems but their solutions resulted in complex and inflexible integration, long user-usage time and high cost for LVC simulation. The goal of this research is to provide an Agile Roadmap for the Live Virtual Constructive-Integrating Training Architecture (LVC-ITA) that will address the above problems and introduce interoperable LVC simulation. Therefore, this research describes how the newest M(&)S technologies can be utilized for LVC simulation interoperability and integration. Then, we will examine the optimal procedure to develop an agile roadmap for the LVC-ITA.In addition, this research illustrated a case study using an Adaptive distributed parallel Simulation environment for Interoperable and reusable Model (AddSIM) that is a component based integrated simulation engine. The agile roadmap of the LVC-ITA that reflects the lessons learned from the case study will contribute to guide M(&)S communities to an efficient path to increase interaction of M(&)S simulation across systems.
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Date Issued: 2015
Identifier: CFE0005682, ucf:52867
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005682

Title: Integrating Spray Aeration and Granular Activated Carbon for Disinfection By-Product Control in a Potable Water System.
Creator: Rodriguez, Angela, Duranceau, Steven, Lee, Woo Hyoung, Sadmani, A H M Anwar, University of Central Florida
Abstract / Description: Public water systems add disinfectants in water treatment to inactivate microbial pathogens. Chlorine, when used as a disinfectant, reacts with natural organic matter in the water to form trihalomethane (THM) and haloacetic acid (HAA5) disinfection by-products (DBPs), which are suspected carcinogens. The Safe Drinking Water Act's Disinfectant and Disinfection By-Product (D/DBP) Rules were promulgated by the U.S. Environmental Protection Agency to regulate the amount of DBPs in water systems....
Show morePublic water systems add disinfectants in water treatment to inactivate microbial pathogens. Chlorine, when used as a disinfectant, reacts with natural organic matter in the water to form trihalomethane (THM) and haloacetic acid (HAA5) disinfection by-products (DBPs), which are suspected carcinogens. The Safe Drinking Water Act's Disinfectant and Disinfection By-Product (D/DBP) Rules were promulgated by the U.S. Environmental Protection Agency to regulate the amount of DBPs in water systems. Regulatory compliance is based on maximum contaminant levels (MCL), measured as a locational running annual average (LRAA), for total THM (TTHM) and HAA5 of 80 (&)#181;g/L and 60 (&)#181;g/L, respectively. Regulated DBPs, if consumed in excess of EPA's MCL standard over many years, may increase chronic health risks. In order to comply with the D/DBP Rules, the County of Maui Department of Water Supply (DWS) adopted two DBP control technologies. A GridBee(&)#174; spray-aeration process was place into DWS's Lower Kula water system's Brooks ground storage tank in February of 2013. In March of 2015 the second DBP control technology, granular activated carbon (GAC), was integrated into DWS's Pi'iholo surface water treatment plant. To investigate the integration effectiveness of GAC and spray-aeration into a water system for DBP control, DBP data was gathered from the system between August of 2011 and August 2016, and analyzed relative to cost and performance.Prior to the spray aeration and GAC integration, it was found that TTHM levels at the LRAA compliance site ranged between 58.5 (&)#181;g/L and 125 (&)#181;g/L (at times exceeding the MCL). Additionally, HAA5 levels at the LRAA compliance site ranged between 21.2 and 52.0 (&)#181;g/L. The concerted efforts of the GAC and GridBee(&)#174; system was found to reduce LRAA TTHM and HAA5 concentrations to 38.5 (&)#181;g/L and 20.5 (&)#181;g/L, respectively, in the Lower Kula system. Hypothesis testing utilizing t-Tests confirmed that TTHMs levels were controlled by the spray aeration system and the GAC was responsible for controlling HAA5 formation. Although TTHM levels were reduced by 58 percent, and HAA5 levels by 48 percent, the estimated cumulative annual operation and maintenance (O(&)M) cost of the two systems was $1,036,000. In light of the cost analysis, total organic carbon (TOC)-based models for predicting LRAA TTHM and HAA5 levels were developed as equation (i) and (ii), respectively:(i) TTHM (&)#181;g/L = (32.5 x (TOC ppm)) + 5.59, (ii) HAA5 (&)#181;g/L = (8.37 x (TOC ppm)) + 12.4.The TTHM model yielded an R2 of 0.93, and the HAA5 model had an R2 of 0.52. F-Tests comparing predicted LRAA TTHM and HAA5 levels to actual LRAA TTHM and HAA5 levels determined no statistically-significant difference. With the knowledge of how the GAC and spray aerator controlled DBPs in the water system, a cost-effective and practical treatment operating parameter was developed. The parameter, Pi'iholo water plant filter effluent TOC content, can serve as an indicator that operators would use to alter DBP treatment process flow set points to achieve cost-effective treatment. Furthermore, the significant annual cost contribution by the GAC, coupled with HAA5 levels below DWS's MCLG, led to the recommendation of variable frequency drive (VFD) pumps for the GAC system. The addition of VFD pumps should reduce the frequency of carbon change outs while preserving adequate HAA5 control in the system.
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Date Issued: 2016
Identifier: CFE0006841, ucf:52881
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006841

Title: Shock Tube Investigations of Novel Combustion Environments Towards a Carbon-Neutral Future.
Creator: Barak, Samuel, Vasu Sumathi, Subith, Kapat, Jayanta, Ahmed, Kareem, University of Central Florida
Abstract / Description: Supercritical carbon dioxide (sCO2) cycles are being investigated for the future of power generation. These cycles will contribute to a carbon-neutral future to combat the effects of climate change. These direct-fired closed cycles will produce power without adding significant pollutants to the atmosphere. For these cycles to be efficient, they will need to operate at significantly higher pressures (e.g., 300 atm for Allam Cycle) than existing systems (typically less than 40 atm). There is...
Show moreSupercritical carbon dioxide (sCO2) cycles are being investigated for the future of power generation. These cycles will contribute to a carbon-neutral future to combat the effects of climate change. These direct-fired closed cycles will produce power without adding significant pollutants to the atmosphere. For these cycles to be efficient, they will need to operate at significantly higher pressures (e.g., 300 atm for Allam Cycle) than existing systems (typically less than 40 atm). There is limited knowledge on combustion at these pressures or at the high dilution of carbon dioxide. Nominal fuel choices for gas turbines include natural gas and syngas (mixture of CO and H2). Shock tubes study these problems in order to understand the fundamentals and solve various challenges. Shock tube experiments have been studied by the author in the sCO2 regime for various fuels including natural gas, methane and syngas. Using the shock tube to take measurements, pressure and light emissions time-histories measurements were taken at a 2-cm axial location away from the end wall. Experiments for syngas at lower pressure utilized high-speed imaging through the end wall to investigate the effects of bifurcation. It was found that carbon dioxide created unique interactions with the shock tube compared to tradition bath gasses such as argon. The experimental results were compared to predictions from leading chemical kinetic mechanisms. In general, mechanisms can predict the experimental data for methane and other hydrocarbon fuels; however, the models overpredict for syngas mixtures. Reaction pathway analysis was evaluated to determine where the models need improvements. A new shock tube has been designed and built to operate up to 1000 atm pressures for future high-pressure experiments. Details of this new facility are included in this work. The experiments in this work are necessary for mechanism development to design an efficient combustor operate these cycles.
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Date Issued: 2019
Identifier: CFE0007781, ucf:52359
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007781

Title: ORGANIZATIONAL SUPPORT, ORGANIZATIONAL CITIZENSHIP BEHAVIOR, AND PERCEIVED PERFORMANCE: ANALYSIS OF CRIME SCENE INVESTIGATION UNITS OF TURKISH NATIONAL POLICE.
Creator: Tongur, Aykut, Kapucu, Naim, University of Central Florida
Abstract / Description: Policing is more difficult than ever before in today's world since types of crime and criminal profiles change as a result of technological development and globalization. Police organizations should review their organizational and operational strategies to improve the fight against contemporary crimes and criminals. Behaviors and performance of police officers are very important in fighting crime. In this struggle, especially today, officers should exhibit organizational citizenship behaviors...
Show morePolicing is more difficult than ever before in today's world since types of crime and criminal profiles change as a result of technological development and globalization. Police organizations should review their organizational and operational strategies to improve the fight against contemporary crimes and criminals. Behaviors and performance of police officers are very important in fighting crime. In this struggle, especially today, officers should exhibit organizational citizenship behaviors and perform better. One of the most important factors affecting these two concepts in organizations is organizational support. The literature stresses the social exchange cycle and reciprocity rules in the relationships of organizations and their members. In this cycle, if the organization cares about its members and if members perceive that the organization is supportive, they feel obliged to behave positively, perform better, and help the organization to reach its goals and objectives. If they don't perceive organizational support, they won't care about the organization, either. Hypotheses were developed based on these assumptions in the literature. This study tested these assumptions in Crime Scene Investigation units of the Turkish National Police (TNP). Structural Equation Modeling (SEM) was used to analyze the relationships among variables of Perceived Organizational Support (POS), Organizational Citizenship Behavior (OCB), and Perceived Performance (PP). Measurement models for these three latent constructs were developed by deriving the indicators from the literature. Most earlier studies tried to figure out reasons of the OCB. This study has a different perspective that investigates both reasons and results of OCB. A survey was developed to measure the latent variables of the study, and 405 of approximately 3,000 Crime Scene Investigators in the Turkish National Police responded to the iv survey. Results of the study showed that the relationship between POS and OCB is positive and significant. This is consistent with the literature. The relationship between OCB and PP is also positive and significant, and this is also consistent with the literature. However, the relationship between POS and PP is negative and insignificant. This result contradicts the results of previous studies in the literature and can be attributed to the subjective nature of measuring individuals' perceptions. According to the literature, perceptions are subjective rather than objective; therefore, data coming from reports of individual perceptions may not reflect the actual situation. Demographic information of the participants served as the control variables of the study. Information about the education level, rank, age, gender, size of the unit, and tenure of the respondents was collected by way of the conducted survey, and the effects of these variables were analyzed on the endogenous variable of the study, Perceived Performance. This study found no significant relationships between these control variables and Perceived Performance. Therefore, all these control variables were removed from the Structural Equation Model of the study. This study revealed that the TNP needs to be more supportive toward its members in order to have officers show organizational citizenship behavior and perform better. The TNP should revise its policies, especially regarding rotations from one province to another, working hours, rewards, and overtime pay. These are all indicators of organizational support and will result in a higher performance level among officers.
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Date Issued: 2011
Identifier: CFE0004058, ucf:49124
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004058

Title: Multi-Level Safety Performance Functions for High Speed Facilities.
Creator: Ahmed, Mohamed, Abdel-Aty, Mohamed, Radwan, Ahmed, Al-Deek, Haitham, Mackie, Kevin, Pande, Anurag, Uddin, Nizam, University of Central Florida
Abstract / Description: High speed facilities are considered the backbone of any successful transportation system; Interstates, freeways, and expressways carry the majority of daily trips on the transportation network. Although these types of roads are relatively considered the safest among other types of roads, they still experience many crashes, many of which are severe, which not only affect human lives but also can have tremendous economical and social impacts. These facts signify the necessity of enhancing the...
Show moreHigh speed facilities are considered the backbone of any successful transportation system; Interstates, freeways, and expressways carry the majority of daily trips on the transportation network. Although these types of roads are relatively considered the safest among other types of roads, they still experience many crashes, many of which are severe, which not only affect human lives but also can have tremendous economical and social impacts. These facts signify the necessity of enhancing the safety of these high speed facilities to ensure better and efficient operation. Safety problems could be assessed through several approaches that can help in mitigating the crash risk on long and short term basis. Therefore, the main focus of the research in this dissertation is to provide a framework of risk assessment to promote safety and enhance mobility on freeways and expressways. Multi-level Safety Performance Functions (SPFs) were developed at the aggregate level using historical crash data and the corresponding exposure and risk factors to identify and rank sites with promise (hot-spots). Additionally, SPFs were developed at the disaggregate level utilizing real-time weather data collected from meteorological stations located at the freeway section as well as traffic flow parameters collected from different detection systems such as Automatic Vehicle Identification (AVI) and Remote Traffic Microwave Sensors (RTMS). These disaggregate SPFs can identify real-time risks due to turbulent traffic conditions and their interactions with other risk factors.In this study, two main datasets were obtained from two different regions. Those datasets comprise historical crash data, roadway geometrical characteristics, aggregate weather and traffic parameters as well as real-time weather and traffic data.At the aggregate level, Bayesian hierarchical models with spatial and random effects were compared to Poisson models to examine the safety effects of roadway geometrics on crash occurrence along freeway sections that feature mountainous terrain and adverse weather. At the disaggregate level; a main framework of a proactive safety management system using traffic data collected from AVI and RTMS, real-time weather and geometrical characteristics was provided. Different statistical techniques were implemented. These techniques ranged from classical frequentist classification approaches to explain the relationship between an event (crash) occurring at a given time and a set of risk factors in real time to other more advanced models. Bayesian statistics with updating approach to update beliefs about the behavior of the parameter with prior knowledge in order to achieve more reliable estimation was implemented. Also a relatively recent and promising Machine Learning technique (Stochastic Gradient Boosting) was utilized to calibrate several models utilizing different datasets collected from mixed detection systems as well as real-time meteorological stations. The results from this study suggest that both levels of analyses are important, the aggregate level helps in providing good understanding of different safety problems, and developing policies and countermeasures to reduce the number of crashes in total. At the disaggregate level, real-time safety functions help toward more proactive traffic management system that will not only enhance the performance of the high speed facilities and the whole traffic network but also provide safer mobility for people and goods. In general, the proposed multi-level analyses are useful in providing roadway authorities with detailed information on where countermeasures must be implemented and when resources should be devoted. The study also proves that traffic data collected from different detection systems could be a useful asset that should be utilized appropriately not only to alleviate traffic congestion but also to mitigate increased safety risks. The overall proposed framework can maximize the benefit of the existing archived data for freeway authorities as well as for road users.
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Date Issued: 2012
Identifier: CFE0004508, ucf:49274
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004508

Title: The Collector as Arbiter of Art: A Phenomenological Investigation of Collectors' Critical Judgment Development and Their Understanding of Art Toward a Theoretical Model for Appreciation and Criticism in Art Education.
Creator: Grey, Anne, Brewer, Thomas, Sivo, Stephen, Kaplan, Jeffrey, Price, Mark, Roberts, Sherron, University of Central Florida
Abstract / Description: The purpose of this study was to investigate art collectors' specific method of developing and making critical judgments in the context of their understanding of art. Phenomenological research methods were employed to obtain data through interviews with collectors of Contemporary African American art, Latin American art, and Minimalist and Conceptual art. Based on the findings, collectors' approaches to critical judgment can be categorized into three areas. First, critical skills are both...
Show moreThe purpose of this study was to investigate art collectors' specific method of developing and making critical judgments in the context of their understanding of art. Phenomenological research methods were employed to obtain data through interviews with collectors of Contemporary African American art, Latin American art, and Minimalist and Conceptual art. Based on the findings, collectors' approaches to critical judgment can be categorized into three areas. First, critical skills are both intuitive and developed over time, through a holistic and aesthetic process set in the art world. Collectors' edification requires commitment, and intense looking enabling them to see how works of art communicate. Second, key events that marked collectors' methodological approaches were connections with artists and art, notable purchases, and exhibitions of their collection. These events resulted from an integration of the collectors' identification with the art work, manifested over time in various forms. Finally, those objects that best reflected collectors' specific development of critical judgment and understanding of art were noted either by specific artists in their collection or the collection as a whole, functioning as vital aspects of the collectors' life and at the same time contributing to culture and society in its capacity to cause conversations. There is an opportunity to apply the information from collectors' processes as an educational model for teaching and learning about appreciation and criticism in art education by thinking about art collections more broadly, as another way to look at life and the art in life.
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Date Issued: 2011
Identifier: CFE0004115, ucf:49103
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004115

Title: Estimation for the Cox Model with Various Types of Censored Data.
Creator: Riddlesworth, Tonya, Ren, Joan, Mohapatra, Ram, Richardson, Gary, Ni, Liqiang, Schott, James, University of Central Florida
Abstract / Description: In survival analysis, the Cox model is one of the most widely used tools. However, up to now there has not been any published work on the Cox model with complicated types of censored data, such as doubly censored data, partly-interval censored data, etc., while these types of censored data have been encountered in important medical studies, such as cancer, heart disease, diabetes, etc. In this dissertation, we first derive the bivariate nonparametric maximum likelihood estimator (BNPMLE) Fn(t...
Show moreIn survival analysis, the Cox model is one of the most widely used tools. However, up to now there has not been any published work on the Cox model with complicated types of censored data, such as doubly censored data, partly-interval censored data, etc., while these types of censored data have been encountered in important medical studies, such as cancer, heart disease, diabetes, etc. In this dissertation, we first derive the bivariate nonparametric maximum likelihood estimator (BNPMLE) Fn(t,z) for joint distribution function Fo(t,z) of survival time T and covariate Z, where T is subject to right censoring, noting that such BNPMLE Fn has not been studied in statistical literature. Then, based on this BNPMLE Fn we derive empirical likelihood-based (Owen, 1988) confidence interval for the conditional survival probabilities, which is an important and difficult problem in statistical analysis, and also has not been studied in literature. Finally, with this BNPMLE Fn as a starting point, we extend the weighted empirical likelihood method (Ren, 2001 and 2008a) to the multivariate case, and obtain a weighted empirical likelihood-based estimation method for the Cox model. Such estimation method is given in a unified form, and is applicable to various types of censored data aforementioned.
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Date Issued: 2011
Identifier: CFE0004158, ucf:49051
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004158

Title: The Response of American Police Agencies to Digital Evidence.
Creator: Yesilyurt, Hamdi, Wan, Thomas, Potter, Roberto, Applegate, Brandon, Lang, Sheau-Dong, University of Central Florida
Abstract / Description: Little is known about the variation in digital forensics practice in the United States as adopted by large local police agencies. This study investigated how environmental constraints, contextual factors, organizational complexity, and organizational control relate to the adoption of digital forensics practice. This study integrated 3 theoretical perspectives in organizational studies to guide the analysis of the relations: institutional theory, contingency theory, and adoption-of-innovation...
Show moreLittle is known about the variation in digital forensics practice in the United States as adopted by large local police agencies. This study investigated how environmental constraints, contextual factors, organizational complexity, and organizational control relate to the adoption of digital forensics practice. This study integrated 3 theoretical perspectives in organizational studies to guide the analysis of the relations: institutional theory, contingency theory, and adoption-of-innovation theory. Institutional theory was used to analyze the impact of environmental constraints on the adoption of innovation, and contingency theory was used to examine the impacts of organizational control on the adoption of innovation. Adoption of innovation theory was employed to describe the degree to which digital forensics practice has been adopted by large municipal police agencies having 100 or more sworn police officers.The data set was assembled primarily by using Law Enforcement Management and Administrative Statistics (LEMAS) 2003 and 1999. Dr. Edward Maguire`s survey was used to obtain 1 variable. The joining up of the data set to construct the sample resulted in 345 large local police agencies. The descriptive results on the degree of adoption of digital forensics practice indicate that 37.7% of large local police agencies have dedicated personnel to address digital evidence, 32.8% of police agencies address digital evidence but do not have dedicated personnel, and only 24.3% of police agencies have a specialized unit with full-time personnel to address digital evidence. About 5% of local police agencies do nothing to address digital evidence in any circumstance. These descriptive statistics indicate that digital evidence is a matter of concern for most large local police agencies and that they respond to varying degrees to digital evidence at the organizational level. Agencies that have not adopted digital forensics practice are in the minority. The structural equation model was used to test the hypothesized relations, easing the rigorous analysis of relations between latent constructs and several indicator variables. Environmental constraints have the largest impact on the adoption of innovation, exerting a positive influence. No statistically significant relation was found between organizational control and adoption of digital forensic practice. Contextual factors (task scope and personnel size) positively influence the adoption of digital forensics. Structural control factors, including administrative weight and formalization, have no significant influence on the adoption of innovation. The conclusions of the study are as follows. Police agencies adopt digital forensics practice primarily by relying on environmental constraints. Police agencies exposed to higher environmental constraints are more frequently expected to adopt digital forensics practice. Because organizational control of police agencies is not significantly related to digital forensics practice adoption, police agencies do not take their organizational control extensively into consideration when they consider adopting digital forensics practice. The positive influence of task scope and size on digital forensics practice adoption was expected. The extent of task scope and the number of personnel indicate a higher capacity for police agencies to adopt digital forensics practice. Administrative weight and formalization do not influence the adoption of digital forensics practice. Therefore, structural control and coordination are not important for large local police agencies to adopt digital forensics practice.The results of the study indicate that the adoption of digital forensics practice is based primarily on environmental constraints. Therefore, more drastic impacts on digital forensics practice should be expected from local police agencies' environments than from internal organizational factors. Researchers investigating the influence of various factors on the adoption of digital forensics practice should further examine environmental variables. The unexpected results concerning the impact of administrative weight and formalization should be researched with broader considerations.
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Date Issued: 2011
Identifier: CFE0004181, ucf:49081
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004181

Title: PERCEIVED SERVICE QUALITY'S IMPACT ON BEHAVIORAL INTENTIONS IN THE TIMESHARE INDUSTRY.
Creator: Pollard, Leonard, Malone, Linda, University of Central Florida
Abstract / Description: This study created a model using factor analysis and structural equation modeling to investigate the relationship of service quality, word-of-mouth recommendation and price sensitivity of individuals who experienced a timeshare mini vacation at a branded timeshare resort. The constructs of service quality were developed by creating a survey tool. A total of 4,797 surveys were electronically sent resulting in a total of 1,275 of the individuals surveyed who met the criteria of staying at a...
Show moreThis study created a model using factor analysis and structural equation modeling to investigate the relationship of service quality, word-of-mouth recommendation and price sensitivity of individuals who experienced a timeshare mini vacation at a branded timeshare resort. The constructs of service quality were developed by creating a survey tool. A total of 4,797 surveys were electronically sent resulting in a total of 1,275 of the individuals surveyed who met the criteria of staying at a branded hotel or resort during their mini vacation. Six different variables were created from the ordinal level questions on the survey: Resort Accommodations, Sales Gallery, Sales Presentation, Resort Activities, Resort Staff and Brand Value. These were then used in an exploratory factor analysis to identify latent factors after which structural equation modeling was used to define the relationship between the factors and the independent variables. A total of 44 models were explored and evaluated based on goodness-of-fit metrics. The model that had the best level of fit was a first-order two-factor model. This model was created with an 80% subset and confirmed with a 20% subset of the sample. The factors found represent the Vacation Experience Promise (VEP) and the Vacation Experience Delivery (VED). There was a positive correlation for both VEP and VED with word-of-mouth recommendation and price sensitivity. The research also posited 24 hypotheses of the relationship between the service quality constructs, word-of-mouth recommendation and price sensitivity with the demographic characteristics of guest type, gender, stay type, age, marital status, gross income, timeshare ownership and the number of presentations attended. There was not enough information to support a relationship between the service quality constructs, word-of-mouth recommendation and price sensitivity with regards to gender, gross income and marital status. There was a difference in the scores for the service quality constructs and the varying categories within the age, stay type, and timeshare ownership demographic variables. There was a difference only in the VED scores and the varying categories within the guest type and presentations attended demographic variables. There was also a difference in the scores for the word-of-mouth recommendation construct and the varying categories within the age, guest type, timeshare ownership and number of presentations attended demographic variables. Lastly, there was also a difference in the scores for the price sensitivity construct and the varying categories within the guest type, timeshare ownership and presentation attended demographic variables. The research discusses the business implications associated with these findings and proposes next steps for future research.
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Date Issued: 2010
Identifier: CFE0003475, ucf:48942
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003475

Title: CMOS RF CITUITS VARIABILITY AND RELIABILITY RESILIENT DESIGN, MODELING, AND SIMULATION.
Creator: Liu, Yidong, Yuan, Jiann-Shiun, University of Central Florida
Abstract / Description: The work presents a novel voltage biasing design that helps the CMOS RF circuits resilient to variability and reliability. The biasing scheme provides resilience through the threshold voltage (VT) adjustment, and at the mean time it does not degrade the PA performance. Analytical equations are established for sensitivity of the resilient biasing under various scenarios. Power Amplifier (PA) and Low Noise Amplifier (LNA) are investigated case by case through modeling and experiment. PTM 65nm...
Show moreThe work presents a novel voltage biasing design that helps the CMOS RF circuits resilient to variability and reliability. The biasing scheme provides resilience through the threshold voltage (VT) adjustment, and at the mean time it does not degrade the PA performance. Analytical equations are established for sensitivity of the resilient biasing under various scenarios. Power Amplifier (PA) and Low Noise Amplifier (LNA) are investigated case by case through modeling and experiment. PTM 65nm technology is adopted in modeling the transistors within these RF blocks. A traditional class-AB PA with resilient design is compared the same PA without such design in PTM 65nm technology. Analytical equations are established for sensitivity of the resilient biasing under various scenarios. A traditional class-AB PA with resilient design is compared the same PA without such design in PTM 65nm technology. The results show that the biasing design helps improve the robustness of the PA in terms of linear gain, P1dB, Psat, and power added efficiency (PAE). Except for post-fabrication calibration capability, the design reduces the majority performance sensitivity of PA by 50% when subjected to threshold voltage (VT) shift and 25% to electron mobility (¼n) degradation. The impact of degradation mismatches is also investigated. It is observed that the accelerated aging of MOS transistor in the biasing circuit will further reduce the sensitivity of PA. In the study of LNA, a 24 GHz narrow band cascade LNA with adaptive biasing scheme under various aging rate is compared to LNA without such biasing scheme. The modeling and simulation results show that the adaptive substrate biasing reduces the sensitivity of noise figure and minimum noise figure subject to process variation and device aging such as threshold voltage shift and electron mobility degradation. Simulation of different aging rate also shows that the sensitivity of LNA is further reduced with the accelerated aging of the biasing circuit. Thus, for majority RF transceiver circuits, the adaptive body biasing scheme provides overall performance resilience to the device reliability induced degradation. Also the tuning ability designed in RF PA and LNA provides the circuit post-process calibration capability.
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Date Issued: 2011
Identifier: CFE0003595, ucf:48861
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003595

Title: Analysis of Behaviors in Crowd Videos.
Creator: Mehran, Ramin, Shah, Mubarak, Sukthankar, Gita, Behal, Aman, Tappen, Marshall, Moore, Brian, University of Central Florida
Abstract / Description: In this dissertation, we address the problem of discovery and representation of group activity of humans and objects in a variety of scenarios, commonly encountered in vision applications. The overarching goal is to devise a discriminative representation of human motion in social settings, which captures a wide variety of human activities observable in video sequences. Such motion emerges from the collective behavior of individuals and their interactions and is a significant source of...
Show moreIn this dissertation, we address the problem of discovery and representation of group activity of humans and objects in a variety of scenarios, commonly encountered in vision applications. The overarching goal is to devise a discriminative representation of human motion in social settings, which captures a wide variety of human activities observable in video sequences. Such motion emerges from the collective behavior of individuals and their interactions and is a significant source of information typically employed for applications such as event detection, behavior recognition, and activity recognition. We present new representations of human group motion for static cameras, and propose algorithms for their application to variety of problems.We first propose a method to model and learn the scene activity of a crowd using Social Force Model for the first time in the computer vision community. We present a method to densely estimate the interaction forces between people in a crowd, observed by a static camera. Latent Dirichlet Allocation (LDA) is used to learn the model of the normal activities over extended periods of time. Randomly selected spatio-temporal volumes of interaction forces are used to learn the model of normal behavior of the scene. The model encodes the latent topics of social interaction forces in the scene for normal behaviors. We classify a short video sequence of $n$ frames as normal or abnormal by using the learnt model. Once a sequence of frames is classified as an abnormal, the regions of anomalies in the abnormal frames are localized using the magnitude of interaction forces.The representation and estimation framework proposed above, however, has a few limitations. This algorithm proposes to use a global estimation of the interaction forces within the crowd. It, therefore, is incapable of identifying different groups of objects based on motion or behavior in the scene. Although the algorithm is capable of learning the normal behavior and detects the abnormality, but it is incapable of capturing the dynamics of different behaviors.To overcome these limitations, we then propose a method based on the Lagrangian framework for fluid dynamics, by introducing a streakline representation of flow. Streaklines are traced in a fluid flow by injecting color material, such as smoke or dye, which is transported with the flow and used for visualization. In the context of computer vision, streaklines may be used in a similar way to transport information about a scene, and they are obtained by repeatedly initializing a fixed grid of particles at each frame, then moving both current and past particles using optical flow. Streaklines are the locus of points that connect particles which originated from the same initial position.This approach is advantageous over the previous representations in two aspects: first, its rich representation captures the dynamics of the crowd and changes in space and time in the scene where the optical flow representation is not enough, and second, this model is capable of discovering groups of similar behavior within a crowd scene by performing motion segmentation. We propose a method to distinguish different group behaviors such as divergent/convergent motion and lanes using this framework. Finally, we introduce flow potentials as a discriminative feature to recognize crowd behaviors in a scene. Results of extensive experiments are presented for multiple real life crowd sequences involving pedestrian and vehicular traffic.The proposed method exploits optical flow as the low level feature and performs integration and clustering to obtain coherent group motion patterns. However, we observe that in crowd video sequences, as well as a variety of other vision applications, the co-occurrence and inter-relation of motion patterns are the main characteristics of group behaviors. In other words, the group behavior of objects is a mixture of individual actions or behaviors in specific geometrical layout and temporal order.We, therefore, propose a new representation for group behaviors of humans using the inter-relation of motion patterns in a scene. The representation is based on bag of visual phrases of spatio-temporal visual words. We present a method to match the high-order spatial layout of visual words that preserve the geometry of the visual words under similarity transformations. To perform the experiments we collected a dataset of group choreography performances from the YouTube website. The dataset currently contains four categories of group dances.
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Date Issued: 2011
Identifier: CFE0004482, ucf:49317
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004482

Title: Chemometric Applications to a Complex Classification Problem: Forensic Fire Debris Analysis.
Creator: Waddell, Erin, Sigman, Michael, Belfield, Kevin, Campiglia, Andres, Yestrebsky, Cherie, Ni, Liqiang, University of Central Florida
Abstract / Description: Fire debris analysis currently relies on visual pattern recognition of the total ion chromatograms, extracted ion profiles, and target compound chromatograms to identify the presence of an ignitable liquid according to the ASTM International E1618-10 standard method. For large data sets, this methodology can be time consuming and is a subjective method, the accuracy of which is dependent upon the skill and experience of the analyst. This research aimed to develop an automated classification...
Show moreFire debris analysis currently relies on visual pattern recognition of the total ion chromatograms, extracted ion profiles, and target compound chromatograms to identify the presence of an ignitable liquid according to the ASTM International E1618-10 standard method. For large data sets, this methodology can be time consuming and is a subjective method, the accuracy of which is dependent upon the skill and experience of the analyst. This research aimed to develop an automated classification method for large data sets and investigated the use of the total ion spectrum (TIS). The TIS is calculated by taking an average mass spectrum across the entire chromatographic range and has been shown to contain sufficient information content for the identification of ignitable liquids. The TIS of ignitable liquids and substrates, defined as common building materials and household furnishings, were compiled into model data sets. Cross-validation (CV) and fire debris samples, obtained from laboratory-scale and large-scale burns, were used to test the models. An automated classification method was developed using computational software, written in-house, that considers a multi-step classification scheme to detect ignitable liquid residues in fire debris samples and assign these to the classes defined in ASTM E1618-10. Classifications were made using linear discriminant analysis, quadratic discriminant analysis (QDA), and soft independent modeling of class analogy (SIMCA). Overall, the highest correct classification rates were achieved using QDA for the first step of the scheme and SIMCA for the remaining steps. In the first step of the classification scheme, correct classification rates of 95.3% and 89.2% were obtained for the CV test set and fire debris samples, respectively. Correct classifications rates of 100% were achieved for both data sets in the majority of the remaining steps which used SIMCA for classification. In this research, the first statistically valid error rates for fire debris analysis have been developed through cross-validation of large data sets. The error rates reduce the subjectivity associated with the current methods and provide a level of confidence in sample classification that does not currently exist in forensic fire debris analysis.
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Date Issued: 2013
Identifier: CFE0004954, ucf:49586
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004954

Title: AN EXAMINATION OF CENTRAL ASIAN GEOPOLITICS THROUGH THE EXPECTED UTILITY MODEL: THE NEW GREAT GAME.
Creator: Stutte, Corey, Wan, Thomas, University of Central Florida
Abstract / Description: The New Great Game is a geopolitical competition between regional stakeholders over energy resources in Central Asia. The author seeks to use the expected utility voting model based on Black's median voter theorem for forecasting the New Great Game in Central Asia. To judge the external validity of the voting model, the author uses data from the Correlates of War project data set, to formulate three distinct models based only on the numbers in 1992 and 1993. Capabilities and alliance data...
Show moreThe New Great Game is a geopolitical competition between regional stakeholders over energy resources in Central Asia. The author seeks to use the expected utility voting model based on Black's median voter theorem for forecasting the New Great Game in Central Asia. To judge the external validity of the voting model, the author uses data from the Correlates of War project data set, to formulate three distinct models based only on the numbers in 1992 and 1993. Capabilities and alliance data were used to develop balance of power positions and compare the outcome of 100 simulations to the actual outcome in 2000 based on Correlates of War project data. This allows us to judge whether the emergence of Russia's weak advantage as well as the continuation of the competition in the New Great Game as of 2000 could have been predicted based on what was known in 1992 and 1993. By using only one year's data to forecast the New Great Game, we are able to eliminate historical and researcher bias and judge the applicability of the model in global policy and strategic analysis.
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Date Issued: 2009
Identifier: CFE0002861, ucf:48088
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002861

Title: Social Disorganization and Florida Public High School Academic Performance.
Creator: Kanaan, David, Wan, Thomas, Wolf, Ross, Stevenson, Robyne, Mitchell, David, University of Central Florida
Abstract / Description: Failing public high schools are a perpetual limitation to community sustainability. Conversely, economically disadvantaged communities more often produce schools with reduced academic performance. Unfortunately, comprehensive community-based remedies are generally outside the scope of a school district's control. Social disorganization theory attributes variations in crime and delinquency to a breakdown in communal structure and relationships. Applied in a similar manner, social...
Show moreFailing public high schools are a perpetual limitation to community sustainability. Conversely, economically disadvantaged communities more often produce schools with reduced academic performance. Unfortunately, comprehensive community-based remedies are generally outside the scope of a school district's control. Social disorganization theory attributes variations in crime and delinquency to a breakdown in communal structure and relationships. Applied in a similar manner, social disorganization has also been associated with lower student achievement.This research examined how social disorganization is associated with Florida public high school academic performance in a two phase analysis at the community and school district levels. In addition, the research tested a potential moderating effect of receiving the Five Star School Award, recognizing family and community involvement, and Florida public high school academic performance with social disorganization factors simultaneously considered. In the first phase, the study used a cross-sectional, non-experimental design analyzing secondary data by structural equation modeling (SEM) at the community-level. For the second phase, the study used a cross-sectional, non-experimental design analyzing aggregated secondary data in multiple linear regressions assessing statistically significant associations between social disorganization predictors and school academic performance variables at the school district-level. SEM analysis found a statistically significant and large negative association between the social disorganization factors residential mobility, single-parent households, socio-economic status and percentage of divorced or separated persons, and Florida public high school academic performance at the community-level. Also at the community-level, results showed that receiving the Five Star School award for satisfying family and community involvement criteria had a statistically significant but small positive association with Florida public high school performance when social disorganization factors were simultaneously considered. At the district or county level, multiple regression analyses found relevant negative associations between social disorganization predictors low median income and ethnic heterogeneity and school district average FCAT scores and Adequate Yearly Progress (AYP) percentages. The study results reinforce existing neighborhood deprivation and social disorganization literature and articulate the need for a community-based approach to improve high school academic performance. Finally, the research suggests prominent education policy reforms may exacerbate social disorganization in communities and proposes alternative policy implementations.
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Date Issued: 2016
Identifier: CFE0006335, ucf:51548
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006335

Title: A multi-scale approach to study Solid Oxide Fuel Cells: from Mechanical Properties and Crystal Structure of the Cell's Materials to the Development of an Interactive and Interconnected Educational Tool.
Creator: Aman, Amjad, Orlovskaya, Nina, Xu, Yunjun, Das, Tuhin, University of Central Florida
Abstract / Description: Solid Oxide Fuel Cells are energy conversion devices that convert chemical energy of a fuel directly into electrical energy. They are known for being fuel-flexible, have minimal harmful emissions, ideal for combined heat and power applications, highly energy-efficient when combined with gas or steam turbines. The current challenges facing the widespread adoption these fuel cells include cost reduction, long-term testing of fully integrated systems, improving the fuel cell stack and system...
Show moreSolid Oxide Fuel Cells are energy conversion devices that convert chemical energy of a fuel directly into electrical energy. They are known for being fuel-flexible, have minimal harmful emissions, ideal for combined heat and power applications, highly energy-efficient when combined with gas or steam turbines. The current challenges facing the widespread adoption these fuel cells include cost reduction, long-term testing of fully integrated systems, improving the fuel cell stack and system performance, and studies related to reliability, robustness and durability. The goal of this dissertation is to further the understanding of the mechanical properties and crystal structure of materials used in the cathode and electrolyte of solid oxide fuel cells, as well as to report on the development of a supplementary educational tool that could be used in course related to fuel cells. The first part of the dissertation relates to the study of LaCoO3 based perovskites that are used as cathode material in solid oxide fuel cells and in other energy-related applications. In-situ neutron diffraction of LaCoO3 perovskite during uniaxial compression was carried out to study crystal structure evolution and texture development. In this study, LaCoO3 was subjected to two cycles of uniaxial loading and unloading with the maximum stress value being 700-900 MPa. The in-situ neutron diffraction revealed the dynamic crystallographic changes occurring which is responsible for the non-linear ferroelastic deformation and the appearance of hysteresis in LaCoO3. At the end of the first cycle, irreversible strain was observed even after the load was removed, which is caused by non-recoverable domain reorientation and texture development. At the end of the second cycle, however, no irreversible strain was observed as domain reorientation seemed fully recovered. Elastic constants were calculated and Young's modulus was estimated for LaCoO3 single crystals oriented along different crystallographic directions. The high temperature mechanical behavior study of LaCoO3 based perovskites is also of prime importance as solid oxide fuel cells operate at high temperatures. Incidentally, it was observed that as opposed to the behavior of most materials, LaCoO3 exhibits stiffening between 700 oC to 900 oC, with the Young's modulus going from a value of ~76 GPa at room temperature to ~120 GPa at 900 oC. In-situ neutron diffraction, XRD and Raman spectroscopy were used to study structural changes occurring in the material as it was heated. The results from these experiments will be discussed.The next portion of the dissertation will focus on electrolytes. Numerical simulation was carried out in order to predict the non-linear load-stress relationship and estimation of biaxial flexure strength in layered electrolytes, during ring-on-ring mechanical testing.Finally, the development of an interactive and inter-connected educational software is presented that could serve as a supplementary tool to teach fuel cell related topics.
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Date Issued: 2016
Identifier: CFE0006436, ucf:51467
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006436

Title: Jail Mental Health Innovations: Factors Influencing Mental Health Services Innovations for Jails.
Creator: Clayton, Orville, Wan, Thomas, Anderson, Kim, Winton, Mark, Zhang, Ning, University of Central Florida
Abstract / Description: ABSTRACTThe U.S. is recognized for uniquely high incarceration rates. Over recent decades, there has been a concurrent dramatic increase of jail detainees with mental disorders. Provision of adequate mental health services for jail inmates is constitutionally mandated, and has legal, ethical, quality of care, and fiscal implications for jails, families, communities, and detainees. Significant variation exists in the provision of mental health services across jails, and increased understanding...
Show moreABSTRACTThe U.S. is recognized for uniquely high incarceration rates. Over recent decades, there has been a concurrent dramatic increase of jail detainees with mental disorders. Provision of adequate mental health services for jail inmates is constitutionally mandated, and has legal, ethical, quality of care, and fiscal implications for jails, families, communities, and detainees. Significant variation exists in the provision of mental health services across jails, and increased understanding of the factors that influence the adoption of such services may help guide jails to implement beneficial services, and ensure that such services reflect, reflect quality standards. This study used a mixed methods strategy to examine the influence of theoretically determined variables on the adoption of jail mental health services, and the quality assessment of such services. Data was gathered by survey instrumentation, secondary data review, and in-depth interviews with jail leaders. The study found that isomorphism has a significant effect on the structural adequacy of jail mental health services, innovation characteristics have a negligible relationship to structural adequacy and process integrity, structural adequacy mediates the effects of isomorphism on process integrity, and jail size has a significant effect on structural adequacy. This study advances the knowledge base in its specification of the roles of internal, external, and demographic factors in the adoption of jail mental health services, and in the testing and application of Donabedian's healthcare model to assess the quality of such services.
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Date Issued: 2017
Identifier: CFE0006866, ucf:51755
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006866

Title: Habitat selection in transformed landscapes and the role of novel ecosystems for native species persistence.
Creator: Sanchez Clavijo, Lina, Quintana-Ascencio, Pedro, Noss, Reed, Weishampel, John, Rodewald, Amanda, University of Central Florida
Abstract / Description: To understand native species persistence in transformed landscapes we must evaluate how individual behaviors interact with landscape structure through ecological processes such as habitat selection. Rapid, widespread landscape transformation may lead to a mismatch between habitat preference and quality, a phenomenon known as ecological traps that can have negative outcomes for populations. I applied this framework to the study of birds inhabiting landscapes dominated by forest remnants and...
Show moreTo understand native species persistence in transformed landscapes we must evaluate how individual behaviors interact with landscape structure through ecological processes such as habitat selection. Rapid, widespread landscape transformation may lead to a mismatch between habitat preference and quality, a phenomenon known as ecological traps that can have negative outcomes for populations. I applied this framework to the study of birds inhabiting landscapes dominated by forest remnants and shade coffee plantations, a tropical agroforestry system that retains important portions of native biodiversity. I used two different approaches to answer the question: What is the role of habitat selection in the adaptation of native species to transformed landscapes? First, I present the results of a simulation model used to evaluate the effects of landscape structure on population dynamics of a hypothetical species under two mechanisms of habitat selection. Then I present the analyses of seven years of capture-mark-recapture and resight data collected to compare habitat preference and quality between shade coffee and forest for twelve resident bird species in the Sierra Nevada de Santa Marta (Colombia). I provide evidence for the importance of including the landscape context in the evaluation of ecological traps and for using long-term demographic data when evaluating the potential of novel ecosystems and intermediately-modified habitats for biodiversity conservation. Beyond suggestions to improve bird conservation in shade coffee, my findings contribute to theory about ecological traps and can be applied to understand population processes in a wide variety of heterogeneous landscapes.
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Date Issued: 2016
Identifier: CFE0006494, ucf:51392
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006494

Title: A Study On The Plasticity And Fracture Behaviors Of Inconel 718 Under Multiaxial Stress And Extremely Low Cycle Fatigue Loadings.
Creator: Algarni, Mohammed, Bai, Yuanli, Gordon, Ali, Gou, Jihua, University of Central Florida
Abstract / Description: Engineering materials and structures are usually subjected to multiaxial stress states loading due to geometrical effects, residual stresses, or multi-directional loading. Ductile fracture and Extremely Low Cycle Fatigue (ELCF), less than 100 cycles to fail, are two common and co-exist failure modes in many engineering structures. However, the linkage between these two failure modes under multi-axial loading conditions has never been systematically studied. This research summarizes an...
Show moreEngineering materials and structures are usually subjected to multiaxial stress states loading due to geometrical effects, residual stresses, or multi-directional loading. Ductile fracture and Extremely Low Cycle Fatigue (ELCF), less than 100 cycles to fail, are two common and co-exist failure modes in many engineering structures. However, the linkage between these two failure modes under multi-axial loading conditions has never been systematically studied. This research summarizes an extensive work of experimental and numerical studies of ductile fracture and ELCF under different stress states for nickel-base superalloy material (")IN718(") under room temperature. Specially designed specimens and tests were used to achieve desired multi-axial loading conditions. Four types of specimens with four different shapes, total of 16 specimens, were tested until complete fracture. Two groups of tests were conducted: (a) round bar specimens with different notches; (b) plane strain specimens. Experimental data of force-displacement curves and strain-life graph were plotted for analysis. The first part of this research focuses on a numerical study of monotonic tensile loading with different stress states. This part of the investigation deeply studies the dependency of the hydrostatic stress (related to stress triaxiality) and the normalized third invariant of the deviatoric stress (related to Lode angle parameter) in plastic behavior and ductile fracture. Constitutive plasticity model proposed by Bai (&) Wierzbicki and the modified Mohr-Coulomb (MMC) ductile fracture model were adapted with several extensions. The plasticity model and ductile fracture criterion were implemented into ABAQUS through a user-defined material subroutine (VUMAT). Extensive experimental results are used to calibrate the models. After setting up the parameter optimization during model calibration, the experimental results and numerical simulations were well correlated in both plasticity deformation and fracture initiation. A 3D fracture locus of Inconel 718 was constructed by knowing the strain at fracture, stress triaxiality, and normalized Lode angle of the tested samples. By introducing a suitable element post-failure behavior, not only the fracture initiation but also the fracture propagation modes are successfully predicted in finite element simulations for monotonic loading.The second part extensively investigates ELCF on IN718. The IN718 cyclic plasticity behavior and the Bauschinger effect are studied and simulated using the well-known nonlinear kinematic hardening law by J. L. Chaboche and his co-workers under different strain amplitudes and different stress states. Moreover, the Voc(&)#233; isotropic hardening law was applied in combination with the Bai-Wierzbicki plasticity model. The Bai-Wierzbicki plasticity model was used to capture the effect of different stress states on ELCF based on the stress triaxiality and Lode angle parameters. On the other hand, the modified Mohr(-)Coulomb (MMC) ductile fracture model for monotonic loading was extended by a new damage evolution rule to cover the ELCF regime. A new parameter was introduced to represent the effect of the cyclic loading at ELCF. The new parameter is responsible for capturing the change of non-proportional loading direction between the current stress and the backstress tensors. The model explores the underlying damage and fracture mechanisms through the equivalent plastic strain evolution under cycling loading. Finally, the mechanism linkage between these two failure modes was studied. A comparison between the experimental data and the finite element simulation results (by Abaqus/Explicit) shows very good correlations. In addition, fractographic examinations, analysis, and finite element simulations are presented.
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Date Issued: 2017
Identifier: CFE0006553, ucf:51338
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006553

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