Browsing by Subject "Risk assessment"

Now showing 1 - 18 of 18

Open Access
Application of the RIMARC algorithm to a large data set of action potentials and clinical parameters for risk prediction of atrial fibrillation
(Springer, 2015) Ravens, U.; Katircioglu-Öztürk, D.; Wettwer, E.; Christ, T.; Dobrev, D.; Voigt, N.; Poulet, C.; Loose, S.; Simon, J.; Stein, A.; Matschke, K.; Knaut, M.; Oto, E.; Oto, A.; Güvenir, H. A.
Ex vivo recorded action potentials (APs) in human right atrial tissue from patients in sinus rhythm (SR) or atrial fibrillation (AF) display a characteristic spike-and-dome or triangular shape, respectively, but variability is huge within each rhythm group. The aim of our study was to apply the machine-learning algorithm ranking instances by maximizing the area under the ROC curve (RIMARC) to a large data set of 480 APs combined with retrospectively collected general clinical parameters and to test whether the rules learned by the RIMARC algorithm can be used for accurately classifying the preoperative rhythm status. APs were included from 221 SR and 158 AF patients. During a learning phase, the RIMARC algorithm established a ranking order of 62 features by predictive value for SR or AF. The model was then challenged with an additional test set of features from 28 patients in whom rhythm status was blinded. The accuracy of the risk prediction for AF by the model was very good (0.93) when all features were used. Without the seven AP features, accuracy still reached 0.71. In conclusion, we have shown that training the machine-learning algorithm RIMARC with an experimental and clinical data set allows predicting a classification in a test data set with high accuracy. In a clinical setting, this approach may prove useful for finding hypothesis-generating associations between different parameters.
Open Access
Assessment of hazardous material risks for rail yard safety
(Elsevier, 2007) Glickman, T. S.; Erkut, E.
This paper illustrates the application of quantitative risk assessment in a rail yard where tank cars of hazardous materials are received and stored. The assessment was conducted in response to community concerns about the safety of a proposed yard expansion. Six different chemicals are involved. For each one, the average monthly volume and the hazard of most concern are specified. We use an event tree populated with empirical data to compute the probability of a major spill in each case and we estimate the corresponding critical impact distances using available modeling tools. We find that for some of the chemicals, the relative increases in risk are appreciable, but that in all cases, the absolute levels of risk remain low. Then we identify some ways in which such an analysis can be extended and discuss the potential difficulties associated with these extensions.
Open Access
Automatic detection of geospatial objects using multiple hierarchical segmentations
(Institute of Electrical and Electronics Engineers, 2008-07) Akçay, H. G.; Aksoy, S.
The object-based analysis of remotely sensed imagery provides valuable spatial and structural information that is complementary to pixel-based spectral information in classification. In this paper, we present novel methods for automatic object detection in high-resolution images by combining spectral information with structural information exploited by using image segmentation. The proposed segmentation algorithm uses morphological operations applied to individual spectral bands using structuring elements in increasing sizes. These operations produce a set of connected components forming a hierarchy of segments for each band. A generic algorithm is designed to select meaningful segments that maximize a measure consisting of spectral homogeneity and neighborhood connectivity. Given the observation that different structures appear more clearly at different scales in different spectral bands, we describe a new algorithm for unsupervised grouping of candidate segments belonging to multiple hierarchical segmentations to find coherent sets of segments that correspond to actual objects. The segments are modeled by using their spectral and textural content, and the grouping problem is solved by using the probabilistic latent semantic analysis algorithm that builds object models by learning the object-conditional probability distributions. The automatic labeling of a segment is done by computing the similarity of its feature distribution to the distribution of the learned object models using the Kullback-Leibler divergence. The performances of the unsupervised segmentation and object detection algorithms are evaluated qualitatively and quantitatively using three different data sets with comparative experiments, and the results show that the proposed methods are able to automatically detect, group, and label segments belonging to the same object classes. © 2008 IEEE.
Open Access
Aviation risk perception: a comparison between experts and novices
(Wiley-Blackwell Publishing, 2004) Thomson, M. E.; Önkal D.; Avcioǧlu, A.; Goodwin, P.
This article describes an exploratory investigation of the risk perceptions of experts and novices in relation to helicopter operations, under conditions where the participants are matched on various characteristics previously found to affect perceptions, such as demographic, gender, and background factors. The study reports considerable evidence of perceptual differences between the two participant groups (i.e., expert pilots and candidate pilots). We find that the experts' perceptions of relative risks are more veridical, in terms of their higher correlation with the true relative frequencies. A significant positive correlation between the flight hours and the contextual risk-taking tendency is also shown, leading the experienced pilots' choices toward risky alternatives in scenarios - a potential result of their overconfidence based on superior task performance. Possible explanations are offered for the findings and potential avenues for future research are identified.
Open Access
Cognitive and emotional representations of terror attacks: a cross-cultural exploration
(Wiley-Blackwell Publishing, 2007) Shiloh, S.; Güvenç, G.; Önkal D.
A questionnaire measuring cognitive and affective representations of terror risk was developed and tested in Turkey and Israel. Participants in the study were university students from the two countries (n = 351). Four equivalent factors explained terror risk cognitions in each sample: costs, vulnerability, trust, and control. A single negative emotionality factor explained the affective component of terror risk representations in both samples. All factors except control could be measured reliably. Results supported the validity of the questionnaire by showing expected associations between cognitions and emotions, as well as indicating gender differences and cultural variations. Current findings are discussed in relation to previous results, theoretical approaches, and practical implications.
Open Access
Coordination of staffing and pricing decisions in a service firm
(John Wiley & Sons, 2008) Serel, D. A.; Erel, E.
Customer demand is sensitive to the price paid for the service in many service environments. Using queueing theory framework, we develop profit maximization models for jointly determining the price and the staffing level in a service company. The models include constraints on the average waiting time and the blocking probability. We show convexity of the single-variable subproblem under certain plausible assumptions on the demand and staffing cost functions. Using numerical examples, we investigate the sensitivity of the price and the staffing level to changes in the marginal service cost and the user-specified constraint on the congestion measure.
Open Access
Designing a road network for hazardous materials shipments
(Elsevier, 2007) Erkut, E.; Alp, O.
We consider the problem of designating hazardous materials routes in and through a major population center. Initially, we restrict our attention to a minimally connected network (a tree) where we can predict accurately the flows on the network. We formulate the tree design problem as an integer programming problem with an objective of minimizing the total transport risk. Such design problems of moderate size can be solved using commercial solvers. We then develop a simple construction heuristic to expand the solution of the tree design problem by adding road segments. Such additions provide carriers with routing choices, which usually increase risks but reduce costs. The heuristic adds paths incrementally, which allows local authorities to trade off risk and cost. We use the road network of the city of Ravenna, Italy, to demonstrate the solution of our integer programming model and our path-addition heuristic.
Open Access
Designing emergency response networks for hazardous materials transportation
(2007) Berman O.; Verter V.; Kara, B.Y.
Undesirable consequences of dangerous goods incidents can be mitigated by quick arrival of specialized response teams at the accident site. We present a novel methodology to determine the optimal design of a specialized team network so as to maximize its ability to respond to such incidents in a region. We show that this problem can be represented via a maximal arc-covering model. We discuss two formulations for the maximal arc-covering problem, a known one and a new one. Through computational experiments, we establish that the known formulation has excessive computational requirements for large-scale problems, whereas the alternative model constitutes a basis for an efficient heuristic. The methodology is applied to assess the emergency response capability to transport incidents, that involve gasoline, in Quebec and Ontario. We point out the possibility of a significant improvement via relocation of the existing specialized teams, which are currently stationed at the shipment origins. © 2005 Elsevier Ltd. All rights reserved.
Open Access
Dynamic financial planning: certainty equivalents, stochastic constraints and functional conjugate duality
(Taylor & Francis, 2005) Jefferson, T. R.; Scott, C. H.
This paper studies portfolios under risk and stochastic constraints. Certainty equivalents combine risk aversion and exponential utility to form the objective. Budget and stochastic constraints on the account balance are used to ensure a positive net worth over time. These portfolio models are analyzed by functional conjugate duality for general distributions and by conjugate duality for the normal distribution. All the programs are convex. The duals provide insight into this approach and relate it to other stochastic and financial concepts.
Open Access
Dynamic risk spillovers between gold, oil prices and conventional, sustainability and Islamic equity aggregates and sectors with portfolio implications
(Elsevier B.V., 2017) Mensi, W.; Hammoudeh, S.; Al-Jarrah, I. M. W.; Sensoy A.; Kang, S. H.
This paper investigates the time-varying equicorrelations and risk spillovers between crude oil, gold and the Dow Jones conventional, sustainability and Islamic stock index aggregates and 10 associated disaggregated Islamic sector stock indexes (basic materials, consumer services, consumer goods, energy, financials, health care, technology, industrials, telecommunications and utilities), using the multivariate DECO-FIAPARCH model and the spillover index of Diebold and Yilmaz (2012). We also conduct a risk management analysis at the sector level for commodity-Islamic stock sector index portfolios, using different risk exposure measures. For comparison purposes, we add the aggregate conventional Dow Jones global index and the Dow Jones sustainability world index. The results show evidence of time-varying risk spillovers between these markets. Moreover, there are increases in the correlations among the markets in the aftermath of the 2008–2009 GFC. Further, the oil, gold, energy, financial, technology and telecommunications sectors are net receivers of risk spillovers, while the sustainability and conventional aggregate DJIM indexes as well as the remaining Islamic stock sectors are net contributors of risk spillovers. Finally, we provide evidence that gold offers better portfolio diversification benefits and downside risk reductions than oil. © 2017 Elsevier B.V.
Open Access
The effects of different inflation risk premiums on interest rate spreads
(Elsevier BV, 2004) Berument, Hakan; Kilinc, Z.; Ozlale, U.
This paper analyzes how the different types of inflation uncertainty affect a set of interest rate spreads for the UK. Three types of inflation uncertainty - structural uncertainty, impulse uncertainty, and steady-state inflation uncertainty - are defined and derived by using a time-varying parameter model with a GARCH specification. It is found that both the structural and steady-state inflation uncertainties increase interest rate spreads, while the empirical evidence for the impulse uncertainty is not conclusive. © 2003 Elsevier B.V. All rights reserved.
Open Access
Functional mobility, depressive symptoms, level of independence, and quality of life of the elderly living at home and in the nursing home
(Elsevier Inc., 2009) Karakaya, M. G.; Bilgin, S. C.; Ekici, G.; Köse, N.; Otman, A. S.
Objectives: To compare functional mobility, depressive symptoms, level of independence, and quality of life of the elderly living at home and in the nursing home. Design: A prospectively designed, comparative study. Setting: A nursing home and a university hospital department. Participants: In this study, 33 elderly living in a nursing home and 25 elderly living at home, who fulfilled the inclusion criteria and volunteered to participate, were included. Measurements: Sociodemographic characteristics were recorded. Functional mobility (Timed Up & Go Test), depressive symptoms (Geriatric Depression Scale), level of independence (Kahoku Aging Longitudinal Study Scale), and quality of life (Visual Analogue Scale) scores were compared between the groups. Results: Functional mobility and independence level of the nursing home residents were higher than the home-dwelling elderly (95% CI: -4.88, -0.29 and 0.41, 6.30, respectively), but they had more depressive symptoms (95% CI: 0.30, 5.45), and their level of QoL was lower (95% CI: -15.55, -2.93). Conclusion: These findings are thought to be important and of benefit for health care professionals and caregivers as indicating the areas that need to be supported for the elderly living at home (functional mobility and independence) and in the nursing home (depressive symptoms and quality of life). © 2009 American Medical Directors Association.
Open Access
Gain-loss pricing under ambiguity of measure
(E D P Sciences, 2010) Pınar, M. Ç.
Motivated by the observation that the gain-loss criterion, while offering economically meaningful prices of contingent claims, is sensitive to the reference measure governing the underlying stock price process (a situation referred to as ambiguity of measure), we propose a gain-loss pricing model robust to shifts in the reference measure. Using a dual representation property of polyhedral risk measures we obtain a one-step, gain-loss criterion based theorem of asset pricing under ambiguity of measure, and illustrate its use.
Open Access
Insights into autism spectrum disorder genomic architecture and biology from 71 risk loci
(Cell Press, 2015) Sanders, S. J.; He, X.; Willsey, A. J.; Ercan-Sencicek, A. G.; Samocha, K. E.; Cicek, A. E.; Murtha, M. T.; Bal, V. H.; Bishop, S. L.; Dong, S.; Goldberg, A. P.; Jinlu, C.; Keaney, J. F.; Keaney III, J. F.; Mandell, J. D.; Moreno-De-Luca, D.; Poultney, C. S.; Robinson, E. B.; Smith L.; Solli-Nowlan, T.; Su, M. Y.; Teran, N. A.; Walker, M. F.; Werling, D. M.; Beaudet, A. L.; Cantor, R. M.; Fombonne, E.; Geschwind, D. H.; Grice, D. E.; Lord, C.; Lowe, J. K.; Mane, S. M.; Martin, D.M.; Morrow, E. M.; Talkowski, M. E.; Sutcliffe, J. S.; Walsh, C. A.; Yu, T. W.; Ledbetter, D. H.; Martin, C. L.; Cook, E. H.; Buxbaum, J. D.; Daly, M. J.; Devlin, B.; Roeder, K.; State, M. W.
Analysis of de novo CNVs (dnCNVs) from the full Simons Simplex Collection (SSC) (N = 2,591 families) replicates prior findings of strong association with autism spectrum disorders (ASDs) and confirms six risk loci (1q21.1, 3q29, 7q11.23, 16p11.2, 15q11.2-13, and 22q11.2). The addition of published CNV data from the Autism Genome Project (AGP) and exome sequencing data from the SSC and the Autism Sequencing Consortium (ASC) shows that genes within small de novo deletions, but not within large dnCNVs, significantly overlap the high-effect risk genes identified by sequencing. Alternatively, large dnCNVs are found likely to contain multiple modest-effect risk genes. Overall, we find strong evidence that de novo mutations are associated with ASD apart from the risk for intellectual disability. Extending the transmission and de novo association test (TADA) to include small de novo deletions reveals 71 ASD risk loci, including 6 CNV regions (noted above) and 65 risk genes (FDR ≤ 0.1). Through analysis of de novo mutations in autism spectrum disorder (ASD), Sanders et al. find that small deletions, but not large deletions/duplications, contain one critical gene. Combining CNV and sequencing data, they identify 6 loci and 65 genes associated with ASD.
Open Access
p53 codon 72 polymorphism in bladder cancer-No evidence of association with increased risk or invasiveness
(Springer, 2001) Törüner, G. A.; Uçar, A.; Tez, M.; Çetinkaya, M.; Özen, H.; Özçelik, T.
We studied the effect of the p53 gene Arg72Pro polymorphism on bladder cancer susceptibility in a case control study of 121 bladder cancer patients and 114 age-sex matched controls to determine whether this polymorphism is a biomarker for the risk and how aggressive the disease is. Genomic DNA was obtained from venous blood samples for genotype determination by PCR and restriction digestion. The genotype frequencies in the patient group were Arg/Arg: 0.3553, Arg/Pro: 0.4711, Pro/Pro: 0.1736, and in the control group Arg/Arg: 0.3684, Arg/Pro: 0.4825, Pro/Pro: 0.1491. The distribution of genotypes between the two groups was not statistically different (χ2 = 0.260, df: 2, P = 0.878). The patient group was subdivided into two groups as superficial bladder cancer (n = 88) and invasive bladder cancer (n = 33), according to the presence of muscle invasion. The distribution of genotypes in the superficial group was Arg/Arg: 0.3409, Arg/Pro: 0.5114, Pro/Pro: 0.1477 and in the invasive group Arg/Arg: 0.3940, Arg/Pro: 0.3636, Pro/Pro: 0.2424. No association was observed with the invasiveness of the tumor (χ2 = 2.542, df: 2, P = 0.281). Stratification of the data by tobacco exposure did not result in a significant difference in genotype frequencies. These data do not support an association between the p53 Arg72Pro polymorphism and bladder cancer.
Open Access
Risk and career choice: evidence from Turkey
(Pergamon Press, 2010) Caner, A.; Okten, C.
In this paper, we examine the college major choice decision in a risk and return framework using university entrance exam data from Turkey. Specifically we focus on the choice between majors with low income risk such as education and health and others with riskier income streams. We use a unique dataset that allows us to control for the choice set of students and parental attitudes towards risk. Our results show that father's income, self-employment status and social security status are important factors influencing an individual in choosing a riskier career such as business over a less risky one such as education or health. © 2010 Elsevier Ltd.
Open Access
Risk-averse control of undiscounted transient Markov models
(Society for Industrial and Applied Mathematics, 2014) Çavuş, Ö.; Ruszczyński, A.
We use Markov risk measures to formulate a risk-averse version of the undiscounted total cost problem for a transient controlled Markov process. Using the new concept of a multikernel, we derive conditions for a system to be risk transient, that is, to have finite risk over an infinite time horizon. We derive risk-averse dynamic programming equations satisfied by the optimal policy and we describe methods for solving these equations. We illustrate the results on an optimal stopping problem and an organ transplantation problem.
Open Access
Safety of nanomaterials
(John Wiley & Sons, 2016-03-11) Gündüz, Nuray; Arslan, Elif; Güler, Mustafa O.; Tekinay, Ayşe B.; Güler, Mustafa O.; Tekinay, Ayşe B.
This chapter overviews the attempts in understanding the biocompatibility of nanomaterials and provides an account of how these views changed in light of recent findings, with emphasis on the methodology used in nanotoxicology studies. The excretion and clearance of engineered nanomaterials (ENMs) is discussed in the chapter, but it should be noted that cells themselves respond to ENMs by activating their exocytosis mechanisms, thus extruding or degrading ENMs at the subcellular level. Although the in vitro tests previously outlined in the chapter provide means of predicting the behavior of nanomaterials, it is nonetheless possible that unforeseen in vivo effects may occur. As with any material intended for human use, their safety must first and foremost be investigated to sufficient detail, through both in vitro experiments and animal studies, before they can be administered to human patients.