Cox-type model validation with recurrent event data

Recurrent event data occurs in many disciplines such as actuarial science, biomedical studies, sociology, and environment to name a few. It is therefore important to develop models that describe the dynamic evolution of the event occurrences. One major problem of interest to researchers with these types of data is models for the distribution function of the time between events occurrences, especially in the presence of covariates that play a major role in having a better understanding of time to events. This work pertains to statistical inference of the regression parameter and the baseline hazard function in a Cox-type model for recurrent events that accounts for the effective age and time varying covariates. Estimators of the regression parameters as well as baseline hazard function are obtained using the counting processes and martingales machinery techniques. Asymptotic properties of the proposed estimators and how they can be used to construct confidence intervals are investigated. The results of the simulation studies assessing the performance of the estimators and an application to a biomedical dataset illustrating the models are presented. The impact of unit effective age is also assessed. To check the validity of the models used, many decision rules are developed for checking the validity of the various components of Cox-type model. Specifically, using martingales residuals, we proposed test statistics for checking the link function and the covariates functional form. Asymptotic properties of test statistics and simulation studies are presented as well --Abstract, page iii

Enhanced oil recovery by surfactant alternate carbonated water injection

Surfactant alternate carbonated water (SACW) injection is a novel mode for enhanced oil recovery (EOR), a method to produce residual oil. This process may overcome the shortcomings that seriously associate carbon dioxide (CO2) injection such as high CO2 mobility, viscous fingering and gravity override. Combinations of sodium dodecyl sulfate (SDS) surfactant and carbonated water (CW) system were not used for EOR yet. So, SDS and CW were selected for evaluating wettability, interfacial tension (IFT), and displacement stability. In addition, the oil recovery factor (RF) was evaluated at different reservoir conditions, carbonation levels and SACW injection cycles scenarios. The sessile drop method was used to measure the contact angle in presence of CW, SDS solution and a mixture of CW and SDS at different quartz sandstone reservoir conditions. A sandpack model was utilised for CW, SDS, water flood (WF) and CO2 flood to measure the displacement instability number (Isc). The obtained results revealed that combinations of SDS and CW system reduce the IFT and contact angle. The IFT values for SDS solution with and without carbonation were 0.2 and 2 mN/m, respectively. The respective contact angles for SDS solution with and without carbonation were 32° and 21.7° at 50°C and 1500 psi. The Isc for CW and WF were 11.6 and 10, respectively, which are considered stable at 60°C and 2750 psi. On the other hand, SDS and CO2 flood processes revealed unstable displacement. Moreover, low pH of CW system depicted a significant change in the SDS adsorption on the glass beads as compared to non-CW system. The 100% CO2 content, reservoir temperature of 60°C and pressure of 2750 psi increased RF up to 83.05, 84.42 and 85.22%, respectively. The highest RF was 86.58% which procured from the largest SDS slug scenario. In conclusion, SACW may have a positive impact on the recoverable oil and it can display a technical knowledge to study other techniques for EOR

Face Detection Using Single Cascade of Customized Features Discriminators

Face detection has become an important and helpful tool for camera and video processing. Useful human-computer interaction (HCI) applications such as drivers assistant system that prevents accidents and saves pedestrian lives when drivers attention is absent, needs a head pose estimator. A head pose estimator cannot function without face detector. There has been a considerable amount of literature to address the problem. The most significant results obtained on uptight frontal face detection which is a sub-problem of a larger problem of face detection. There are other types of sub-problems that has been studied with least significant advancements that the upright frontal face detection had accomplished. The problem of multi-pose detection is still under study and it remains hard. A solution to this large scale of the problem (multi-pose face detection) is critical in head pose accuracy. This thesis suggests a multi-pose face detection algorithm for uncontrolled environments. The detector is designed to be used in building head pose estimator for a human-computer interaction application. The observed design of the detector has to implement a cascade of classifiers. Each classifier has to address at least one certain area of the problem. The design have to maintain speed and an acceptable detection rate. These requirements can be satisfied by constructing the cascade to implement fast and simple classifiers at first stages of the cascade. A novel use of the integral image as a fast filter was invented to be placed at the start of the detection process. Included in the cascade, classifiers that are trained on special designed features aimed to solve part of the problem. One special unique classifier is a data mining based classifier that uses a modified version of the Maximal Frequent Itemset Algorithm (MAFIA) [2] for feature extraction. Special features classifiers use the extracted facial features information extracted from a new knowledge-based classifier/filter that was created with the capacity to locate to an acceptable ac- curacy the location of eyes, mouth and nose using a suite of approaches including discreet local minima and geometric measures. The extracted facial features were used to estimate head pose and extract classifier features accordingly to enhance detection rates. A cascade of classifiers based on fast and simple contrast features was used to refine and speed up the detection process. To further improve speed some components were parallelized. As an attempt to overcome some of the fundamental challenges of face detection, lighting correction and noise reduction were implemented based on the information extracted from images. Results are reported on the FDDB [12] benchmark showed 5.22% detection rate with 2000 false positives while OpenCV implementation of Viola-Jones [19] face detector showed 65.92 detection rate with 2010 false positives. This comparison is flawed; because Viola-Jones is an upright face detector and even though FDDB [12] includes a number on non-frontal faces and profiles the majority of the faces are frontal. The two solutions address two different problems that reflect large differences in difficulty. A standard benchmark testset and evaluation system as FDDB [12] benchmark and com- parable results from the same class of the problem at the time of writing this document was not available. The key points to building good face detector in general are; (1) resolving speed issues using fast techniques (e.g. integral image) at the start of the cascade and a powerful design, (2) using a huge number of different strong and weak features, and (3) eliminating variations (i.e. pose , noise and lighting variations). The algorithm was also tested on MIT+CMU upfront faces testset and reported 43.56% detection rate with 504 false positives

Factors moderating the risk of PTSD, emotional and behavioral problems amongst children in war zones and refugees escaping from warfare

Children who grow up in war zones are typically exposed to multiple stressors including physical harm, intimidation or other forms of psychological trauma. This can also lead to Post Traumatic Stress Disorder. On the other hand, resilient children show no psychiatric distress even when they are exposed to severe traumatic stress. Additionally, the number of refugee children due to warfare reasons is increasing. Past empirical studies have recognized that the process of migration and living life as a refugee is detrimental to the psychological health of young refugees. In this symposium we will examine the prevalence and determinants of resiliency among refugee children and children living in conditions of war and violence. The first study investigated the psychological, social and somatic effects of chronic traumatic experience on Palestinian children over six years (2000-2006). The sample consisted of 1,137 children who completed: Checklist of Traumatic Experiences, Symptoms of PTSD Scale, Network of Psycho-Social Support and Personality Assessment Questionnaire. It was found that 41% of the participants suffered from PTSD. From these 25% suffered from cognitive symptoms; 22% suffered from emotional symptoms; 22% suffered from social behavioral problems; 17% suffered from academic and 14% suffered from somatic symptoms. The support of family, friends, relatives and teachers, and positive personality traits were found to be strong protective factors aiding recovery from trauma and PTSD. The second study evaluated the relation of exposure to war traumas, and violence in the family, community, and school, to PTSD symptoms, emotional and behavioral problems amongst 330 Palestinian children. Results highlight the additive effects of exposure to war traumas and violence in different settings. In addition, it was found that psychosocial support reduced the effects of environmental factors in developing PTSD and behavioral problems. The third study included data from two refugee charity organizations in the UK. There were 200 refugee children coming from war zones and 210 control children (non-refugees). The study aimed to look at a range of factors to assess the differences between the above groups with regards to their well-being and peer and sibling relationships. Results showed that refugee children were significantly more likely to be in the clinical range for total difficulties and to have higher health and physical problems, negative friendship quality and low self esteem compared to the control group. Refugees who were bullied at home and at school were also more likely to develop PTSD symptoms. Protective factors are also discussed in this study. The above studies emphasize the fact that interventionists should consider the full range of sources of environmental risk for PTSD and emotional and behavioral problems and should strengthen the psychosocial support for children in or coming from war zones

Disaster management in industrial areas: Perspectives, challenges and future research

Purpose: In most countries, development, growth, and sustenance of industrial facilities are given utmost importance due to the influence in the socio-economic development of the country. Therefore, special economic zones, or industrial areas or industrial cities are developed in order to provide the required services for the sustained operation of such facilities. Such facilities not only provide a prolonged economic support to the country but it also helps in the societal aspects as well by providing livelihood to thousands of people. Therefore, any disaster in any of the facilities in the industrial area will have a significant impact on the population, facilities, the economy, and threatens the sustainability of the operations. This paper provides review of such literature that focus on theory and practice of disaster management in industrial cities. Design/methodology/approach: In the paper, content analysis method is used in order to elicit the insights of the literature available. The methodology uses search methods, literature segregation and developing the current knowledge on different phases of industrial disaster management. Findings: It is found that the research is done in all phases of disaster management, namely, preventive phase, reactive phase and corrective phase. The research in each of these areas are focused on four main aspects, which are facilities, resources, support systems and modeling. Nevertheless, the research in the industrial cities is insignificant. Moreover, the modeling part does not explicitly consider the nature of industrial cities, where many of the chemical and chemical processing can be highly flammable thus creating a very large disaster impact. Some research is focused at an individual plant and scaled up to the industrial cities. The modeling part is weak in terms of comprehensively analyzing and assisting disaster management in the industrial cities. Originality/value: The comprehensive review using content analysis on disaster management is presented here. The review helps the researchers to understand the gap in the literature in order to extend further research for disaster management in large scale industrial cities.Scopu

The Mediating Role of Bullying and Victimisation on the Relationship Between Problematic Internet Use and Substance Abuse Among Adolescents in the UK: The Parent–Child Relationship as a Moderator

Over the last decade, research into the negative effects of problematic internet use has greatly increased. The current study adopted a mediation-moderation model in exploring the relationship between problematic internet use and substance abuse (drinking, drug use, and smoking tobacco cigarettes) among 1,613 adolescents (aged 10–16) in the UK. The findings of the study revealed a significant positive correlation between problematic internet use and substance abuse, which is mediated by traditional and cyber bullying and victimisation. Furthermore, the parent–child relationship was found to be a protective factor that moderated the correlation between problematic internet use and substance abuse and the correlation between problematic internet use and traditional bullying. The study emphasises the critical need to reduce problematic internet use among adolescents as a risk factor for involvement in bullying as perpetrators and victims, in addition to substance abuse. Furthermore, the findings of the study highlight the importance of a good parent–child relationship as a protective factor among adolescents. In light of the findings of the study, interventions for reducing problematic internet use taking into account bullying and the parent–child relationship are needed among adolescents