Sharareh Taghipour - Academia.edu (original) (raw)

Papers by Sharareh Taghipour

Http Dx Doi Org 10 1080 0740817x 2011 618176, Aug 23, 2012

ABSTRACT This paper proposes a model to find an optimal periodic inspection interval over a finit... more ABSTRACT This paper proposes a model to find an optimal periodic inspection interval over a finite time horizon for a multi-component system. The system components are subject to either hard or soft failures. Hard failures are detected and fixed instantaneously. Soft failures are unrevealed and can only be detected at inspections. Soft failures do not stop the system operation even if they may reduce its designed performance. The system is inspected periodically to detect soft failures; however, a hard failure instance also provides opportunity called “opportunistic inspection” to inspect and fix soft failures. Two models are discussed in the paper. The first model assumes that components with soft and hard failures are minimally repaired. The second model assumes possibility of either minimal repair or replacement of a component with soft failure, with some age dependent probabilities. Recursive procedures are developed to calculate expected number of minimal repairs and replacements, and expected downtimes of components with soft failure. Examples of the calculation of the optimal inspection intervals are given. The data used in the examples is adapted from a hospital's maintenance data for general infusion pump.

Medical decision making : an international journal of the Society for Medical Decision Making, Feb 27, 2016

Modeling breast cancer progression and the effect of various risk is helpful in deciding when a w... more Modeling breast cancer progression and the effect of various risk is helpful in deciding when a woman should start and end screening, and how often the screening should be undertaken. We modeled the natural progression of breast cancer using a hidden Markov process, and incorporated the effects of covariates. Patients are women aged 50-59 (older) and 40-49 (younger) years from the Canadian National Breast Screening Studies. We included prevalent cancers, estimated the screening sensitivities and rates of over-diagnosis, and validated the models using simulation. We found that older women have a higher rate of transition from a healthy to preclinical state and other causes of death but a lower rate of transition from preclinical to clinical state. Reciprocally, younger women have a lower rate of transition from a healthy to preclinical state and other causes of death but a higher rate of transition from a preclinical to clinical state. Different risk factors were significant for the ...

Reliability Engineering & System Safety, 2014

2015 Annual Reliability and Maintainability Symposium (RAMS), 2015

In this paper, we propose a replacement decision model for a truck, which takes into account both... more In this paper, we propose a replacement decision model for a truck, which takes into account both economic aspects of the vehicle and the amount of emission released during its use phase. From an economic perspective, we consider the truck's acquisition, fuel and maintenance costs, and the resale value. For the emission consideration, we calculate the amount of CO 2 produced based on the estimated vehicle's miles traveled, emission factor, and fuel use. The latter is a function of the fuel economy, which depends on the truck's model year and its current age.

IEEE Transactions on Reliability, 2015

In this paper, we consider a k-out-of-n load-sharing system with identical components sharing a c... more In this paper, we consider a k-out-of-n load-sharing system with identical components sharing a certain amount of load. Each time a component fails, its load is distributed to the remaining components; we assume an increase in load increases the hazard rates of the remaining components. The system is periodically inspected to detect failed components. Two cases may occur in an inspection interval: if the number of failed components is less than , then the failed components are only rectified at periodic inspections; if the number of failures reaches , then the system fails, and at this time, all the failed components are inspected and rectified. A failed component is replaced or minimally repaired according to a probability which depends on its age at the failure time. The components' failures follow a Non-Homogenous Poisson Process (NHPP), and their intensity functions depend on their ages and the loads to which they are exposed at any moment. In this paper, we develop a model to find the optimal inspection interval for such a system, which minimizes the total expected cost incurred over the system lifecycle. We derive the analytical solution for the special case of a 1-out-of-2 system, and discuss its computational difficulties. We then present a simulation algorithm to find the required expected values in the objective function. Several numerical examples are presented to illustrate the proposed model.

British journal of cancer, Jan 19, 2013

The aim of screening is to detect a cancer in the preclinical state. However, a false-positive or... more The aim of screening is to detect a cancer in the preclinical state. However, a false-positive or a false-negative test result is a real possibility. We describe invasive breast cancer progression in the Canadian National Breast Screening Study and construct progression models with and without covariates. The effect of risk factors on transition intensities and false-negative probability is investigated. We estimate the transition rates, the sojourn time and sensitivity of diagnostic tests for women aged 40-49 and 50-59. Although younger women have a slower transition rate from healthy state to preclinical, their screen-detected tumour becomes evident sooner. Women aged 50-59 have a higher mortality rate compared with younger women. The mean sojourn times for women aged 40-49 and 50-59 are 2.5 years (95% CI: 1.7, 3.8) and 3.0 years (95% CI: 2.1, 4.3), respectively. Sensitivity of diagnostic procedures for older women is estimated to be 0.75 (95% CI: 0.55, 0.88), while women aged 40-...

2013 Proceedings Annual Reliability and Maintainability Symposium (RAMS), 2013

ABSTRACT In this paper we use a five-state model to describe the progression of invasive breast c... more ABSTRACT In this paper we use a five-state model to describe the progression of invasive breast cancer. The states of the model are: 1. Healthy or non-detectable cancer, 2. Preclinical (screening detectable cancer), 3. Clinical (symptoms are evident), 4. Death due to breast cancer, and 5. Death due to causes other than breast cancer. We model the natural progression of breast cancer from healthy state to clinical cancer using a partially observable Markov model. We model the survival time from cancer diagnosis to breast cancer mortality using a Weibull Proportional Hazards Model (PHM). The effect of covariates in both models are also studied. We then combine the two models and develop a simulation model to evaluate the effect of different screening intervals in reducing breast cancer mortality. We use the data from the Canadian National Breast Screening Study (CNBSS), which consists of two randomized screening trials designed to evaluate the effect of mammography on women aged 40-59. The results reveal that screening can be effective in detecting breast cancer at earlier stages, so reducing breast cancer mortality. We estimated a higher reduction for older women.

Lecture Notes in Statistics, 2013

ABSTRACT We present a brief overview of the methods which are commonly used for statistical analy... more ABSTRACT We present a brief overview of the methods which are commonly used for statistical analysis of data in competing risks settings. Moreover, we review 37 recent published clinical papers on breast cancer which consider an event of interest, such as breast cancer incident, while they also take into account the competing events, such as death due to other causes. The papers are selected based on the number of citations and publication year.

2008 3rd International Conference on Information and Communication Technologies: From Theory to Applications, 2008

The Global Positioning System is the most popular choice for positioning in car navigation system... more The Global Positioning System is the most popular choice for positioning in car navigation systems. But in real life, the various noise sources affecting the signals and the instrumentation used by the positioning system, along with the map inaccuracies, result in the estimated position not necessarily being overlaid onto the road network. The process of mapping the output from the positioning system on to the road network is called map matching. In a recent study, a map matching algorithms that work based on weight factor has been verified then a new map matching algorithm based on is proposed. The proposed algorithm is a modified version of one of the topological map matching algorithms called Quddus's algorithm In order to show the effectiveness of the proposed algorithm, it is tested on the city map Arak and then the result is compared with the result obtained for Quddus's algorithm. In this paper, Correct mapping the output from GPS on the road network parameters is our purpose. The input to the system comes from Gps receiver (Gpsmap 76CS) and Arak map database. In this paper, the results show that the proposed algorithms can be effectively used to map matching

Canadian journal of public health = Revue canadienne de santé publique

While controversies regarding optimal breast cancer screening modalities, screening start and end... more While controversies regarding optimal breast cancer screening modalities, screening start and end ages, and screening frequencies continue to exist, additional population-based randomized trials are unlikely to be initiated to examine these concerns. Simulation models have been used to evaluate the efficacy and effectiveness of various breast cancer screening strategies, however these models were all developed using US data. Currently, there is a need to examine the optimal screening and treatment policies in the Canadian context. In this commentary, we discuss the current controversies pertaining to breast cancer screening, and describe the fundamental components of a simulation model, which can be used to inform breast cancer screening and treatment policies.

Condition Monitoring of Machinery in Non-Stationary Operations, 2012

ABSTRACT This paper gives a brief background to the optimization of condition based maintenance (... more ABSTRACT This paper gives a brief background to the optimization of condition based maintenance (CBM) decisions, through proportional hazards modeling. It then shows how risk factors for breast cancer and its competing mortalities can be similar to condition monitoring variables and be used as predictors in a risk model.

2014 Reliability and Maintainability Symposium, 2014

ABSTRACT In this paper, we will present a model for joint optimization of periodic inspection and... more ABSTRACT In this paper, we will present a model for joint optimization of periodic inspection and inventory levels for a k-out-of-n system. The component failures follow a Non-Homogeneous Poisson Process and failed components can only be revealed at inspection times. We have two types of inspections; planned periodic inspections and non-planned opportunistic inspections. Opportunistic inspections are performed when the system fails, which occurs when n-k+1 components are down at the same time. Failed components are either minimally repaired or replaced with spare parts from the inventory. The inventory policy needs to support the inspection policy so that spare parts are available when needed. The inventory is replenished to level S at periodic inspections, after a random lead-time. However, when the system fails within an inspection interval, the inventory is replenished to level s, with no lead-time (because it is an emergency order). We assume that placing an emergency order is more expensive, and that it depends on the number of spares which is ordered. A simulation model is developed to find the expected total cost for given inspection interval τ and inventory levels S and s. In order to find the combination of τ, s and S, that minimizes the total cost over the system life cycle, we use a genetic algorithm. It is necessary to use a search heuristic method because the size of the search space makes it not feasible to find the optimal solution by trying all combinations of τ, s and S.

2011 Proceedings - Annual Reliability and Maintainability Symposium, 2011

In this paper we assume that the failures of a system follow a non-homogenous Poisson process (NH... more In this paper we assume that the failures of a system follow a non-homogenous Poisson process (NHPP) with a power law intensity function. NHPP is a model commonly used to describe a system with minimal repairs. In many situations, such as hidden failures, failure times of a system are subject to censoring. Current trend analysis methods in the literature for NHPP consider only right censoring and do not address recurrent failure data with left or interval censoring and periodic or non-periodic inspections. We use the likelihood ratio test to check for trend in the failure data. We use the EM algorithm and a recursive method to calculate the likelihood for estimating the parameters of the power law process in the case of null and alternative hypotheses (no trend and trend assumptions). As an example, the proposed method is applied to the failures of a medical infusion pump. It was found that the likelihood ratio test and the proposed recursive method can be applied successfully to censored data, although the method may be computationally intensive for larger datasets. We also compared the likelihood method to an adhoc method using the mid points of censoring intervals instead of unknown failure times. The comparison showed that using the midpoints is not reliable and may result in incorrect conclusion about the trend. The proposed method can be applied to other repairable systems used in industry.

Reliability Engineering & System Safety, 2011

ABSTRACT Trend analysis is a common statistical method used to investigate the operation and chan... more ABSTRACT Trend analysis is a common statistical method used to investigate the operation and changes of a repairable system over time. This method takes historical failure data of a system or a group of similar systems and determines whether the recurrent failures exhibit an increasing or decreasing trend. Most trend analysis methods proposed in the literature assume that the failure times are known, so the failure data is statistically complete; however, in many situations, such as hidden failures, failure times are subject to censoring. In this paper we assume that the failure process of a group of similar independent repairable units follows a non-homogenous Poisson process with a power law intensity function. Moreover, the failure data are subject to left, interval and right censoring. The paper proposes using the likelihood ratio test to check for trends in the failure data. It uses the Expectation–Maximization (EM) algorithm to find the parameters, which maximize the data likelihood in the case of null and alternative hypotheses. A recursive procedure is used to solve the main technical problem of calculating the expected values in the Expectation step. The proposed method is applied to a hospital's maintenance data for trend analysis of the components of a general infusion pump.

Reliability Engineering & System Safety, 2010

... deterioration. Minor and major defects are identified and repaired, respectively, at routine ... more ... deterioration. Minor and major defects are identified and repaired, respectively, at routine and major inspections. In many real-world situations where safety and reliability of devices is vital, devices must be inspected periodically. For ...

Quality and Reliability Engineering International, 2011

This paper proposes a method to analyze statistically maintenance data for complex medical device... more This paper proposes a method to analyze statistically maintenance data for complex medical devices with censoring and missing information. It presents a classification of different types of failures and establishes policies for analyzing data at system and component levels taking into account the failure types. The results of this analysis can be used as basic assumptions in development of a maintenance/inspection optimization model. As a case study, we present the reliability analysis of a general infusion pump from a hospital.

Journal of the Operational Research Society, 2011

Clinical engineering departments in hospitals are responsible for establishing and regulating a M... more Clinical engineering departments in hospitals are responsible for establishing and regulating a Medical Equipment Management Program to ensure that medical devices are safe and reliable. In order to mitigate functional failures, significant and critical devices should be identified and prioritized. In this paper, we present a multi-criteria decision-making model to prioritize medical devices according to their criticality. Devices with lower criticality scores can be assigned a lower priority in a maintenance management program. However, those with higher scores should be investigated in detail to find the reasons for their higher criticality, and appropriate actions, such as 'preventive maintenance', 'user training', 'redesigning the device', etc, should be taken. In this paper,we also describe how individual score values obtained for each criterion can be used to establish guidelines for appropriate maintenance strategies for different classes of devices. The information of 26 different medical devices is extracted from a hospital's maintenance management system to illustrate an application of the proposed model.