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Discrete event simulation

Amy Trentham-Dietz, Mehmet Ali Ergun, Oguzhan Alagoz, Natasha K Stout, Ronald E Gangnon, John M Hampton, Kim Dittus, Ted A James, Pamela M Vacek, Sally D Herschorn, Elizabeth S Burnside, Anna N A Tosteson, Donald L Weaver, Brian L Sprague
PURPOSE: Due to limitations in the ability to identify non-progressive disease, ductal carcinoma in situ (DCIS) is usually managed similarly to localized invasive breast cancer. We used simulation modeling to evaluate the potential impact of a hypothetical test that identifies non-progressive DCIS. METHODS: A discrete-event model simulated a cohort of U.S. women undergoing digital screening mammography. All women diagnosed with DCIS underwent the hypothetical DCIS prognostic test...
November 28, 2017: Breast Cancer Research and Treatment
Anna Irene Vedel Sørensen, Nils Toft, Anette Boklund, Carmen Espinosa-Gongora, Kaare Græsbøll, Jesper Larsen, Tariq Halasa
Before an efficient control strategy for livestock-associated methicillin resistant Staphylococcus aureus (LA-MRSA) in pigs can be decided upon, it is necessary to obtain a better understanding of how LA-MRSA spreads and persists within a pig herd, once it is introduced. We here present a mechanistic stochastic discrete-event simulation model for spread of LA-MRSA within a farrow-to-finish sow herd to aid in this. The model was individual-based and included three different disease compartments: susceptible, intermittent or persistent shedder of MRSA...
2017: PloS One
Abidemi K Adeniji, Jesse Y Hsu, Abdus S Wahed
The product limit or Kaplan-Meier (KM) estimator is commonly used to estimate the survival function in the presence of incomplete time to event. Application of this method assumes inherently that the occurrence of an event is known with certainty. However, the clinical diagnosis of an event is often subject to misclassification due to assay error or adjudication error, by which the event is assessed with some uncertainty. In the presence of such errors, the true distribution of the time to first event would not be estimated accurately using the KM method...
November 26, 2017: Pharmaceutical Statistics
Pelham Barton, James P Sheppard, Cristina M Penaloza-Ramos, Sue Jowett, Gary A Ford, Daniel Lasserson, Jonathan Mant, Ruth M Mellor, Tom Quinn, Peter M Rothwell, David Sandler, Don Sims, Richard J McManus
OBJECTIVES: The aim of this study was to examine the impact of transient ischaemic attack (TIA) service modification in two hospitals on costs and clinical outcomes. DESIGN: Discrete event simulation model using data from routine electronic health records from 2011. PARTICIPANTS: Patients with suspected TIA were followed from symptom onset to presentation, referral to specialist clinics, treatment and subsequent stroke. INTERVENTIONS: Included existing versus previous (less same day clinics) and hypothetical service reconfiguration (7-day service with less availability of clinics per day)...
November 25, 2017: BMJ Open
Mehdi Najafzadeh, Jorge A Garces, Alejandra Maciel
BACKGROUND: The response to therapeutics varies widely in patients with depression and anxiety, making selection of an optimal treatment choice challenging. IDgenetix(®), a novel pharmacogenomic test, has been shown to improve outcomes by predicting the likelihood of response to different psychotherapeutic medications. OBJECTIVE: The objective of this study was to estimate the cost effectiveness of implementing a novel pharmacogenomic test (IDgenetix(®)) to guide treatment choices in patients with depression and/or anxiety compared with treatment as usual from the US societal perspective...
November 6, 2017: PharmacoEconomics
Magali Alexander López Chavira, Ricardo Marcelín-Jiménez
The study of complex networks has become an important subject over the last decades. It has been shown that these structures have special features, such as their diameter, or their average path length, which in turn are the explanation of some functional properties in a system such as its fault tolerance, its fragility before attacks, or the ability to support routing procedures. In the present work, we study some of the forces that help a network to evolve to the point where structural properties are settled...
2017: PloS One
Vladimir Klinshov, Vladimir Nekorkin
Pulse-mediated interactions are common in networks of different nature. Here we develop a general framework for simulation of networks with pulse delayed coupling. We introduce the discrete map governing the dynamics of such networks and describe the computation algorithm for its numerical simulation.
October 2017: Chaos
Jonathon R Campbell, James C Johnston, Mohsen Sadatsafavi, Victoria J Cook, R Kevin Elwood, Fawziah Marra
BACKGROUND: The majority of tuberculosis in migrants to Canada occurs due to reactivation of latent TB infection. Risk of tuberculosis in those with latent tuberculosis infection can be significantly reduced with treatment. Presently, only 2.4% of new migrants are flagged for post-landing surveillance, which may include latent tuberculosis infection screening; no other migrants receive routine latent tuberculosis infection screening. To aid in reducing the tuberculosis burden in new migrants to Canada, we determined the cost-effectiveness of using different latent tuberculosis infection interventions in migrants under post-arrival surveillance and in all new migrants...
2017: PloS One
Michael Beckmann, Emma Paterson, Ashleigh Smith
BACKGROUND: An 'in-hours' birth represents a desired outcome following induction of labour (IOL) in terms of safety, efficiency and satisfaction. Women booked for IOL are often not commenced at their allocated times, and these sometimes complex births happen after-hours. AIMS: To measure the effect of an 11:00 hours commencement time for IOL. MATERIALS AND METHODS: A discrete-event-simulation patient-flow model was constructed. Multiple staffing and scheduling combinations were tested, before a brief pilot and subsequent introduction of a second IOL commencement time...
October 25, 2017: Australian & New Zealand Journal of Obstetrics & Gynaecology
Kristin Fitzgerald, Lori Pelletier, Martin A Reznek
Emergency departments (EDs) are seeking ways to utilize existing resources more efficiently as they face rising numbers of patient visits. This study explored the impact on patient wait times and nursing resource demand from the addition of a fast track, or separate unit for low-acuity patients, in the ED using a queue-based Monte Carlo simulation in MATLAB. The model integrated principles of queueing theory and expanded the discrete event simulation to account for time-based arrival rates. Additionally, the ED occupancy and nursing resource demand were modeled and analyzed using the Emergency Severity Index (ESI) levels of patients, rather than the number of beds in the department...
2017: Journal of Healthcare Engineering
Beate Jahn, Ursula Rochau, Christina Kurzthaler, Michael Hubalek, Rebecca Miksad, Gaby Sroczynski, Mike Paulden, Marvin Bundo, David Stenehjem, Diana Brixner, Murray Krahn, Uwe Siebert
BACKGROUND: Due to high survival rates and the relatively small benefit of adjuvant therapy, the application of personalized medicine (PM) through risk stratification is particularly beneficial in early breast cancer (BC) to avoid unnecessary harms from treatment. The new 21-gene assay (OncotypeDX, ODX) is a promising prognostic score for risk stratification that can be applied in conjunction with Adjuvant!Online (AO) to guide personalized chemotherapy decisions for early BC patients...
October 16, 2017: BMC Cancer
Chung Chan, John Onofrey, Yiqiang Jian, Mary Germino, Xenophon Papademetris, Richard E Carson, Chi Liu
Respiratory motion during PET/CT imaging can cause significant image blurring and underestimation of tracer concentration for both static and dynamic studies. In this study, with the aim to eliminate both intra-cycle and inter-cycle motions, and apply to dynamic imaging, we developed a non-rigid event-byevent (NR-EBE) respiratory motion compensated list-mode reconstruction algorithm. The proposed method consists of 2 components, the first component estimates a continuous non-rigid motion field of the internal organs using the internal-external motion correlation (NR-INTEX)...
October 10, 2017: IEEE Transactions on Medical Imaging
Robin M Famiglietti, Emily C Norboge, Valentine Boving, James R Langabeer, Thomas A Buchholz, Osama Mikhail
BACKGROUND: To meet demand for radiation oncology services and ensure patient-centered safe care, management in an academic radiation oncology department initiated quality improvement efforts using discrete-event simulation (DES). Although the long-term goal was testing and deploying solutions, the primary aim at the outset was characterizing and validating a computer simulation model of existing operations to identify targets for improvement. METHODS: The adoption and validation of a DES model of processes and procedures affecting patient flow and satisfaction, employee experience, and efficiency were undertaken in 2012-2013...
October 2017: Quality Management in Health Care
John D Rice, Robert L Strawderman, Brent A Johnson
Assessment of the regularity of a sequence of events over time is important for clinical decision-making as well as informing public health policy. Our motivating example involves determining the effect of an intervention on the regularity of HIV self-testing behavior among high-risk individuals when exact self-testing times are not recorded. Assuming that these unobserved testing times follow a renewal process, the goals of this work are to develop suitable methods for estimating its distributional parameters when only the presence or absence of at least one event per subject in each of several observation windows is recorded...
October 9, 2017: Biometrics
Ewan Gray, Anna Donten, Nico Karssemeijer, Carla van Gils, D Gareth Evans, Sue Astley, Katherine Payne
OBJECTIVES: To identify the incremental costs and consequences of stratified national breast screening programs (stratified NBSPs) and drivers of relative cost-effectiveness. METHODS: A decision-analytic model (discrete event simulation) was conceptualized to represent four stratified NBSPs (risk 1, risk 2, masking [supplemental screening for women with higher breast density], and masking and risk 1) compared with the current UK NBSP and no screening. The model assumed a lifetime horizon, the health service perspective to identify costs (£, 2015), and measured consequences in quality-adjusted life-years (QALYs)...
September 2017: Value in Health: the Journal of the International Society for Pharmacoeconomics and Outcomes Research
Mohammad Nazrul Ishlam Patoary, Carl Tropper, Robert A McDougal, Lin Zhongwei, William W Lytton
The intra-cellular calcium signaling pathways of a neuron depends on both biochemical reactions and diffusions. Some quasi-isolated compartments (e.g. spines) are so small and calcium concentrations are so low that one extra molecule diffusing in by chance can make a nontrivial difference in its concentration (percentage-wise). These rare events can affect dynamics discretely in such way that they cannot be evaluated by a deterministic simulation. Stochastic models of such a system provide a more detailed understanding of these systems than existing deterministic models because they capture their behavior at a molecular level...
September 26, 2017: IEEE/ACM Transactions on Computational Biology and Bioinformatics
Cesar Pichardo-Almarza, Vanessa Diaz-Zuccarini
Background and Objective: Statins are one of the most prescribed drugs to treat atherosclerosis. They inhibit the hepatic HMG-CoA reductase, causing a reduction of circulating cholesterol and LDL levels. Statins have had undeniable success; however, the benefits of statin therapy crystallize only if patients adhere to the prescribed treatment, which is far away from reality since adherence decreases with time with around half of patients discontinue statin therapy within the first year. The objective of this work is to; firstly, demonstrate a formal in-silico methodology based on a hybrid, multiscale mathematical model used to study the effect of statin treatment on atherosclerosis under different patient scenarios, including cases where the influence of medication adherence is examined and secondly, to propose a flexible simulation framework that allows extensions or simplifications, allowing the possibility to design other complex simulation strategies, both interesting features for software development...
2017: Frontiers in Pharmacology
A Sengar, J A M Kuipers, Rutger A van Santen, J T Padding
Connecting the macroscopic world of continuous fields to the microscopic world of discrete molecular events is important for understanding several phenomena occurring at physical boundaries of systems. An important example is heterogeneous catalysis, where reactions take place at active surfaces, but the effective reaction rates are determined by transport limitations in the bulk fluid and reaction limitations on the catalyst surface. In this work we study the macro-micro connection in a model heterogeneous catalytic reactor by means of stochastic rotation dynamics...
August 2017: Physical Review. E
Adriaan M Dokter, E Emiel van Loon, Wimke Fokkema, Thomas K Lameris, Bart A Nolet, Henk P van der Jeugd
A common problem with observational datasets is that not all events of interest may be detected. For example, observing animals in the wild can difficult when animals move, hide, or cannot be closely approached. We consider time series of events recorded in conditions where events are occasionally missed by observers or observational devices. These time series are not restricted to behavioral protocols, but can be any cyclic or recurring process where discrete outcomes are observed. Undetected events cause biased inferences on the process of interest, and statistical analyses are needed that can identify and correct the compromised detection processes...
September 2017: Ecology and Evolution
Zhongwei Lin, Carl Tropper, Robert A Mcdougal, Mohammand Nazrul Ishlam Patoary, William W Lytton, Yiping Yao, Michael L Hines
Cells exhibit stochastic behavior when the number of molecules is small. Hence a stochastic reaction-diffusion simulator capable of working at scale can provide a more accurate view of molecular dynamics within the cell. This paper describes a parallel discrete event simulator, Neuron Time Warp-Multi Thread (NTW-MT), developed for the simulation of reaction diffusion models of neurons. To the best of our knowledge, this is the first parallel discrete event simulator oriented towards stochastic simulation of chemical reactions in a neuron...
July 2017: ACM Transactions on Modeling and Computer Simulation: a Publication of the Association for Computing Machinery
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