Browsing by Subject "Risk assessment"
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Item Avian-locust interactions in eastern Australia and the exposure of birds to locust control pesticides(Texas Tech University, 2005-12) Szabo, Judit K.; Astheimer, Lee; Hooper, Michael J.; Buttemer, William A.; McMurry, Scott T.There is growing worldwide pressure to develop new and effective chemicals against agricultural pests. Unfortunately, many pesticides have unanticipated and undesired effects on the environment. In eastern Australia, the Australian Plague Locust Commission (APLC) has responsibility for locust control, currently using three pesticides (fenitrothion, fipronil and the fungal agent, Metarhizium) to limit locust populations during outbreaks. In an effort to evaluate the potential impact of these practices on Australian native fauna, this dissertation aims to assess the probability of pesticide exposure in 285 avian species, due primarily to their co-occurrence with locusts in areas where pesticide treatments are most likely to occur. Due to the unpredictable nature of rainfall, locust outbreaks and control events, I have taken a landscape approach to this question, with the area of interest coincident with the area of responsibility of the APLC. Rainfall, vegetation and soil characteristics strongly influence locust and avian distributions. I have examined spatial and temporal patterns in these factors, as well as the relationships between them with a final aim of evaluating their impact on the spatio-temporal distribution of three locust species, locust control events and avian distributions. Avian species distributions were obtained by applying generalized linear models to presence/absence data for the areas of interest for the years 1998–2002. Probabilities of a bird species present at times and locations of locust control applications were calculated. Field observations of avian species’ occurrence and behavior during locust outbreaks were used to evaluate the model. In the last step, the risk of exposure to fipronil was evaluated considering fipronil levels in three avian food items, seed, vegetation and locust samples. Small granivorous birds consuming high amounts of food daily relative to their body weight are predicted to be at greatest risk from exposure.Item Avian-locust interactions in eastern Australia and the exposure of birds to locust control pesticides(2005-12) Szabo, Judit K.; Astheimer, Lee; Hooper, Michael J.; Buttemer, William A.; McMurry, Scott T.There is growing worldwide pressure to develop new and effective chemicals against agricultural pests. Unfortunately, many pesticides have unanticipated and undesired effects on the environment. In eastern Australia, the Australian Plague Locust Commission (APLC) has responsibility for locust control, currently using three pesticides (fenitrothion, fipronil and the fungal agent, Metarhizium) to limit locust populations during outbreaks. In an effort to evaluate the potential impact of these practices on Australian native fauna, this dissertation aims to assess the probability of pesticide exposure in 285 avian species, due primarily to their co-occurrence with locusts in areas where pesticide treatments are most likely to occur. Due to the unpredictable nature of rainfall, locust outbreaks and control events, I have taken a landscape approach to this question, with the area of interest coincident with the area of responsibility of the APLC. Rainfall, vegetation and soil characteristics strongly influence locust and avian distributions. I have examined spatial and temporal patterns in these factors, as well as the relationships between them with a final aim of evaluating their impact on the spatio-temporal distribution of three locust species, locust control events and avian distributions. Avian species distributions were obtained by applying generalized linear models to presence/absence data for the areas of interest for the years 1998–2002. Probabilities of a bird species present at times and locations of locust control applications were calculated. Field observations of avian species’ occurrence and behavior during locust outbreaks were used to evaluate the model. In the last step, the risk of exposure to fipronil was evaluated considering fipronil levels in three avian food items, seed, vegetation and locust samples. Small granivorous birds consuming high amounts of food daily relative to their body weight are predicted to be at greatest risk from exposure.Item Can strategic reasoning prompts improve auditors' sensitivity to fraud risk?(2008-08) Bowlin, Kendall Owen; Kachelmeier, Steven J. (Steven John), 1958-The basic premise of risk-based auditing is that more (fewer) audit resources should be allocated to accounts that are more (less) likely to be misstated. However, financial reporting managers can exploit such allocations by intentionally misstating balances that are less likely to draw auditor attention. If auditors do not recognize this strategic implication of risk-based auditing, undetected misstatements among ostensibly low-risk accounts could be much more common than traditional risk assessment procedures suggest. The purpose of this study is to examine whether prompting auditors to form beliefs about managers’ expectations of, and responses to, audit strategies can enhance auditors’ sensitivity to the strategic risk of fraud among accounts typically considered low-risk. Using a multi-account audit game, I find that auditors do not naturally attune to strategic risks but instead tend to focus resources on “highrisk” accounts. However, when auditors are prompted to reason strategically, they utilize more resources and devote that increase almost entirely to “low-risk” accounts. I also find that, although increasing available resources does result in an overall increase in the amount of utilized resources, the relative effect of the strategic prompt is robust to the level of available audit resources.Item Fuzzy representations of statistical uncertainty for risk assessment(Texas Tech University, 1997-05) Saad, Ihab WilliamWhen insufficient data is available, the use of probability theory for risk assessment may be both difficult and highly inaccurate. In such cases, subjective expert experience may be a viable alternative. Experts can give their degree of belief that a parameter's value would fall within a given range. These parameters are interpreted as fuzzy variables. Hazardous material transportation is one topic in which the constraints and consequences of possible actions/events are not known precisely, with no means to acquire enough statistical data. This motivates our investigation using fuzzy set theory. We use a fuzzy fault tree to assess the risk of failure associated with transportation of hazardous material. The fault tree describes the sequence/combination of events that may lead to a failure. Such events may be due to human errors, severe weather conditions, intelligence leaks, etc. The top event of the tree is a catastrophic failure, such as environmental contamination or cross of material. Each event in the fault tree has its own membership function in which the fuzzy variable is the probability that this even may occur. The membership grade is the degree of belief that this probability may take on a certain value. Our work is inspired by PHASER (Probabilistic Hybrid Analytical System Evaluation Routine), implemented at Sandia National Laboratories by R.J. Roginski and J.A. Cooper. PHASER calculates the top event probability of failure for a fault.Item International project risk assessment(2005) Walewski, John; Gibson, G. Edward (George Edward), 1958-International construction projects are managed most effectively by planning for and addressing the risks that occur to all participants across the project’s entire life cycle. The first step in this process is the identification and assessment of such risks; however, there are few tools that provide such assistance. This research was undertaken to produce a user-friendly, systematic management tool to identify and assess the risks specific to international construction with the ultimate goal of improving project performance. This dissertation presents the development of the International Project Risk Assessment (IPRA) management tool including the methodology to create it, an analysis of its effectiveness in determining the relative importance of the identified risks, and the steps necessary to document, track, and mitigate international project-specific risks. The IPRA tool consists of 82 risk elements that are assessed by likelihood of occurrence and relative impact to identify those elements having the greatest potential impact on the project. Baseline Relative Impact values were developed for each of the 82 based on input from industry experts reporting on recently completed projects. The IPRA tool was tested on projects to verify its completeness and to assess the relationship of test and workshop relative impact values. Project performance data on test projects was collected to identify the relationship between risk and performance. A standardized case-study format was developed to identify which IPRA elements had the most impact on project performance. These results show that the IPRA tool is a sound method to identify and assess the relative impact of international risk issues. Nonetheless, this research also reveals that there is no single blueprint that adequately captures all the risks associated with every international project. Therefore, use of the IPRA tool must be tailored to adjust for country, user, and business sector concerns. Finally, although this research was limited by the paucity of empirical data on risk in international construction projects, the IPRA may provide a framework for the future collection and organization of such data.Item Loss ratios and the market position of casualty insurers(Texas Tech University, 1964-05) Louden, CharlesNot availableItem Modeling Endemic Bark Beetle Populations in Southwestern Ponderosa Pine Forests(2015-02-20) Garza, ChristopherBark beetle populations phase between epidemic, outbreak levels, and low population density, endemic levels. The majority of scientific research is focused on outbreak populations because of the associated economic, ecological, and social impacts. Endemic populations are rarely studied but could provide information about the triggers that cause outbreaks. The goal of this thesis was to gain a better understanding of how endemic populations persist in a landscape through time by looking at the spatial distribution and susceptibility of host trees in southwestern US forested landscapes. To do this, I (1) analyzed 21 years of field data to examine the population dynamics of bark beetles and the factors that affect them, (2) created a statistical model for predicting the absolute risk of individual trees to bark beetle-cause mortality using tree, stand, and beetle pressure variables, and (3) simulated a forest landscape to develop a framework for applying tree-level risk assessments. In 1995, forty-five sites were established throughout the southwestern US to measure bark beetle activity and associated tree and stand characteristics. The plots were periodically revisited through 2012 resulting in over twenty years of bark beetle data with highly variable population densities over time and space. Site maximum dbh and the number of ponderosa pines per acre were significant (P <.029) for predicting the probability a rise in the population density of bark beetles. Tree, stand, and beetle pressure were significant (P < .001) in predicting the probability of beetle caused tree mortality per year. Using GIS, remote sensing, and ground truth data, a ponderosa pine forest was simulated with information about the size and configuration of trees in the landscape. This simulated landscape was used to develop a framework for tree-level risk assessments. The results are discussed further in the context of bark beetle management and further research opportunities. In 1995, forty-five sites were established throughout the southwestern US to measure bark beetle activity and associated tree and stand characteristics. The plots were periodically revisited through 2012 resulting in over twenty years of bark beetle data with highly variable population densities over time and space. Site maximum dbh and the number of ponderosa pines per acre were significant (P <.029) for predicting the probability a rise in the population density of bark beetles. Tree, stand, and beetle pressure were significant (P < .001) in predicting the probability of beetle caused tree mortality per year. Using GIS, remote sensing, and ground truth data, a ponderosa pine forest was simulated with information about the size and configuration of trees in the landscape. This simulated landscape was used to develop a framework for tree-level risk assessments. The results are discussed further in the context of bark beetle management and further research opportunities.Item Modeling the post shear failure behavior of reinforced concrete columns(2012-05) LeBorgne, Matthew Ronald; Ghannoum, Wassim M.; Wood, Sharon L.; Aggarwal, J K.; Bayrak, Oguzhan; Jirsa, James O.Numerous reinforced concrete buildings vulnerable to earthquake induced collapse have been constructed in seismic zones prior to the 1970s. A major contributor to building collapse is the loss of axial load carrying capacity in non-seismically detailed columns. Experimental investigations have shown that non-seismically detailed columns will only experience axial failure after shear failure and subsequent lateral shear strength degradation have occurred. Therefore, column shear failure and degrading behavior must be modeled accurately before axial collapse algorithms can be properly implemented. Furthermore, accurate modeling of the degrading lateral-load behavior of columns is needed if lateral load sharing between structural elements is to be assessed with reasonable accuracy during seismic analyses. A calibrated analytical model was developed that is capable of estimating the lateral strength degrading behavior of RC columns prone to shear failure. Existing analytical models poorly approximate nonlinear column behavior and require several nonphysical damage parameters to be defined. In contrast, the proposed calibrated model provides the engineering community with a valuable tool that only requires the input of column material and geometric properties to simulate column behavior up to loss of lateral strength. In developing the model, a database of RC columns was compiled. Parameters extracted from database column-tests were scrutinized for trends and regression models relating damage parameters to column physical properties and boundary conditions were produced. The regression models were implemented in the degrading analytical framework that was developed in this project. Two reinforced concrete columns exhibiting significant inelastic deformations prior to failing in shear were tested in support of the analytical work. A newly developed Vision System was used to track a grid of targets on the column face with a resolution of three-thousands of an inch. Surface column deformations were measured to further the understanding of the fundamental changes in column behavior that accompany shear and axial failure and validate the proposed analytical model. This research provides the engineering community with an analytical tool that can be used to perform nonlinear dynamic analysis of buildings that are at risk of collapse and help engineers improve retrofit techniques. Further insight into shear behavior attained through this project is an important step toward the development of better shear and axial degradation models for reinforced concrete columns.Item Quantitative Microbial Risk Assessment for Listeria Monocytogenes on Fresh Baby Spinach Leaves(2014-01-06) Omac, BasriThe increase in foodborne illness outbreaks associated with leafy green vegetables can be attributed to the minimal processing required of this group of fresh produce. Neglecting effective microbial elimination steps result in leafy green vegetables that naturally contain microorganisms such as pathogens microorganisms. This quantitative microbial risk assessment describe the change of L. monocytogenes concentration in fresh baby spinach from farm to table. This model also consists of several scenarios to evaluate decontamination treatments, cross-contamination, and temperature abuse. Cross-contamination was the biggest issue when ensuring safety of leafy green vegetables. Temperature abuse also increased the risk of listeriosis. On the other hand, irradiation treatment with Modified Atmosphere Packaging reduced the number of annual cases of listeriosis by 99.99%. In addition, the validation of L. innocua used as a surrogate for L. monocytogenes in fresh baby spinach was evaluated based on reductions by washing (water and chlorine) treatments and growth at temperatures between 5 and 36oC. According to the results of the washing treatments, the concentration of L. innocua was reduced by almost 0.5 log CFU/g. This is more than that of L. monocytogenes. Furthermore, the effect of natural background microflora on the growth of L. monocytogenes and L. innocua in fresh baby spinach was determined. The results showed that the growth of L. innocua was affected more than that of L. monocytogenes at temperatures 10> T >30^(o)C. Although L. innocua and L. monoctogenes are genetically similar, their behavior changes under stress conditions. Ultimately, the dynamic growth models for L. monocytogenes in fresh baby spinach was presented. These models can be used to estimate the growth of L. monocytogenes in fresh baby spinach during distribution, storage or market, and potential growth at a consumer level.Item Risk assessment model for wind-induced fatigue failure of cantilever traffic signal structures(Texas Tech University, 2007-08) Cruzado, Hector J.; Letchford, Christopher W.; Ewing, Bradley T.; Mehta, Kishor C.; Peterson, Richard E.The wind-induced vibrations of the mast arm of cantilever traffic signal structures can lead to the fatigue failure of these structures. Both full-scale and wind tunnel tests were conducted to study the behavior of the structures. Results of these experiments indicated that when the signals have backplates, vortex shedding can cause large-amplitude vibrations that may lead to fatigue failure. These results contradict what has been generally accepted by other researchers: that galloping is the main cause for the fatigue inducing vibrations and that vortex shedding is of no relevance in this type of structure. A methodology to estimate the fatigue life of these structures was developed. Using the climatology of the region, the methodology was applied as a risk assessment model to traffic signal structures of the city of Lubbock. Guidance is given on how life-cycle cost analysis can be applied to the structures.Item Some nonparametric methods in estimating the hazard rate function(Texas Tech University, 1989-12) Chen, DafengThe hazard rate function h{x) = f{x)/[1-F{x)], corresponding to a distribution function F with density function / , is one of the most important parameters in reliability and other fields, since h{x)dx can be interpreted as the probability that an object fails in the time interval [x,x + dx] given that the object has survived to time x. A problem of considerable interest, especially to reusability engineers, is the estimation of h from a sample of n independent and identically distributed nonnegative lifetimes X1 , X2,…,Xn , with or without censoring. By censoring we mean that the occurrence of the random event of interest (called a failure) is prevented by the previous occurrence of another event (called a censoring event). If the censoring event is also a random variable, we have the randomly censored model. If there are several randomly censoring events, we have the multiple competing risks model. This paper discusses three nonparametric estimators of the hazard rate function h: the Fourier integral estimator, the nearest neighbor estimator in the multiple competing risks model, and the discrete maximum penalized-likelihood estimator in the randomly censored model. The asymptotic behavior of these estimators will be studied and conditions for strong consistency will be given.Item The Association between Structured Professional Judgment Measure Total Scores and Summary Risk Ratings: Implications for Predictive Validity(2017-06-22) Chevalier, Caroline S.; Boccaccini, MarcusStructured professional judgment (SPJ) instruments are used by mental health professionals to assess risk for future violence and assess treatment needs. Current literature tends to examine SPJ instruments in a way that is not congruent with how the instruments are designated to be used in the field. Specifically, studies often leave out analyses of the structured professional judgment piece of the instrument (summary risk rating, SRR) and, when the analysis is included, authors rarely compare the SRR to the actuarially derived total score. This study sought to provide practitioners with a comparison of the SPJ measure total scores and SRRs. I conducted a review of the literature to find studies that measured the predictive validity of SPJ measure total scores and SRRs. I requested additional data from corresponding authors in order to compare the two scores using varying statistical methods. In total I included 69 samples (n = 10,871). I performed several meta-analyses to determine if a) the predictive validity of the total score and SRR were similar, and b) if the SRR adds any additional predictive power to the total score. Findings suggest that the total score and SRR have similar predictive abilities. The small difference between the mean weighted SRR (AUC = .701) and total score (AUC = .698) effect sizes was not significant. I also calculated a z-score to test the difference between the SRR and total score effect size in each sample, and found a statistically significant difference in only 8 of the 69 samples. However, a meta-analysis of odds ratio values from logistic regression models including effects for both total scores and SRRS revealed a consistent incremental validity effect for SRRs (OR = 1.96, p < .001) over total scores. Overall, this review provides evidence to suggest that the total score and SRR provide similar predictive effects, but also reveals that using the SRR is worthwhile for practicing clinicians. Implications for both research and practice are discussed.Item Using high performance computing and visualization to enhance risk assessment methodology: case study with perchlorate(Texas Tech University, 2004-05) Albers, Eric PeterSite-specific risk assessments commonly result in large amounts of information that needs to be processed for a wide, often non-scientific, audience consisting of risk managers, regulators, and other decision makers. For this work we combined a series of models into a large virtual representation of the study system. By using a location-based approach, we were able to arrive at a more accurate determination of risk compared to just a maximum-dose approach. Caddo Lake at Longhom Army Ammunition Plant was used to study the impacts of perchlorate (C104') on thyroid hormone secretion in the channel catfish (Ictalurus punctatus). Two hypothetical contaminant plumes were modeled accounting for groundwater upwelling into the lake and effluent discharge near the surface. Results were compared between environmental systems and the three dosing techniques; maximum dose, time-lapsed maximum dose, and location-based dose. Perchlorate tissue concentrations for liver, kidney, gill, skin, muscle, GI tract, and thyroid, as well as thyroid hormone levels and secretion rates were simulated. We have shown that a standard maximum dose approach vastly overestimates exposure for individuals and populations. By simulating large numbers of individuals we are able to achieve low probability extreme events, thereby limiting the need for uncertainty factors. Through the use of commercially available graphics software Maya®, we were able to generate 3- dimensional visualizations of our study site, PBTK model, thyroid hormone secretion, catfish movement, and contaminant plumes, further aiding in data comprehension. This is the first study to generate a 3-dimensional PBTK with commercially available software, as well as use grid computing and 3-d visualization for risk assessment.