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Discrete event simulation

W S Hambright, Jie Deng, James M Tiedje, Ingrid Brettar, Jorge L M Rodrigues
In bacterial populations, subtle expressional differences may promote ecological specialization through the formation of distinct ecotypes. In a barrier-free habitat, this process most likely precedes population divergence and may predict speciation events. To examine this, we used four sequenced strains of the bacterium Shewanella baltica, OS155, OS185, OS195, and OS223, as models to assess transcriptional variation and ecotype formation within a prokaryotic population. All strains were isolated from different depths throughout a water column of the Baltic Sea, occupying different ecological niches characterized by various abiotic parameters...
September 2016: MSphere
Ahmed Almashrafi, Laura Vanderbloemen
BACKGROUND: Postoperative adverse events are known to increase length of stay and cost. However, research on how adverse events affect patient flow and operational performance has been relatively limited to date. Moreover, there is paucity of studies on the use of simulation in understanding the effect of complications on care processes and resources. In hospitals with scarcity of resources, postoperative complications can exert a substantial influence on hospital throughputs. METHODS: This paper describes an evaluation method for assessing the effect of complications on patient flow within a cardiac surgical department...
October 21, 2016: BMC Medical Informatics and Decision Making
Ruben Perez-Carrasco, Pilar Guerrero, James Briscoe, Karen M Page
During tissue development, patterns of gene expression determine the spatial arrangement of cell types. In many cases, gradients of secreted signalling molecules-morphogens-guide this process by controlling downstream transcriptional networks. A mechanism commonly used in these networks to convert the continuous information provided by the gradient into discrete transitions between adjacent cell types is the genetic toggle switch, composed of cross-repressing transcriptional determinants. Previous analyses have emphasised the steady state output of these mechanisms...
October 2016: PLoS Computational Biology
Youfang Cao, Anna Terebus, Jie Liang
The discrete chemical master equation (dCME) provides a fundamental framework for studying stochasticity in mesoscopic networks. Because of the multi-scale nature of many networks where reaction rates have large disparity, directly solving dCMEs is intractable due to the exploding size of the state space. It is important to truncate the state space effectively with quantified errors, so accurate solutions can be computed. It is also important to know if all major probabilistic peaks have been computed. Here we introduce the Accurate CME (ACME) algorithm for obtaining direct solutions to dCMEs...
2016: Multiscale Modeling & Simulation: a SIAM Interdisciplinary Journal
Michel Debacker, Filip Van Utterbeeck, Christophe Ullrich, Erwin Dhondt, Ives Hubloue
It is recognized that the study of the disaster medical response (DMR) is a relatively new field. To date, there is no evidence-based literature that clearly defines the best medical response principles, concepts, structures and processes in a disaster setting. Much of what is known about the DMR results from descriptive studies and expert opinion. No experimental studies regarding the effects of DMR interventions on the health outcomes of disaster survivors have been carried out. Traditional analytic methods cannot fully capture the flow of disaster victims through a complex disaster medical response system (DMRS)...
December 2016: Journal of Medical Systems
P M Derlet, R Maaß
The statistics and origin of the first discrete plastic event in a one-dimensional dislocation dynamics simulation are studied. This is done via a linear stability analysis of the evolving dislocation configuration up to the onset of irreversible plasticity. It is found that, via a fold catastrophe, the dislocation configuration prior to loading directly determines the stress at which the plastic event occurs and that between one and two trigger dislocations are involved. The resulting irreversible plastic strain arising from the instability is found to be highly correlated with these triggering dislocations...
September 2016: Physical Review. E
Daniel A Asamoah, Ramesh Sharda, Howard N Rude, Derek Doran
Long queues and wait times often occur at hospitals and affect smooth delivery of health services. To improve hospital operations, prior studies have developed scheduling techniques to minimize patient wait times. However, these studies lack in demonstrating how such techniques respond to real-time information needs of hospitals and efficiently manage wait times. This article presents a multi-method study on the positive impact of providing real-time scheduling information to patients using the RFID technology...
October 12, 2016: Health Care Management Science
Mercè Comas, Joan Mendivil, Montserrat Andreu, Cristina Hernández, Xavier Castells
OBJECTIVE: To estimate the long-term need for colonoscopies after a positive fecal immunochemical test (FIT) and post-polypectomy surveillance in the context of a population-based colorectal cancer (CRC) screening program. METHODS: A discrete-event simulation model was built to reproduce the process of CRC screening and post-polypectomy surveillance following European guidelines in a population of 100,000 men and women aged 50-69 years over a 20-year period. Screening consisted of biennial FIT and colonoscopy in participants with positive results...
2016: PloS One
Ying Zheng, Feng Pan, Sonja Sorensen
As the number of interventions available in a therapeutic area increases, the relevant decision questions in health technology assessment (HTA) expand to compare treatment sequences instead of discrete treatments and identify optimal sequences or position for a particular treatment in a sequence. The objective of this work was to review approaches used to model treatment sequences and provide practical guidance on conceptualizing whether and how to model sequences in health economic models. Economic models including treatment sequencing assessed by the National Institute for Health and Care Excellence were reviewed, as these assessments generally provide both policy relevance and comprehensive model detail...
October 8, 2016: PharmacoEconomics
Wang Jin, Catherine J Penington, Scott W McCue, Matthew J Simpson
Two-dimensional collective cell migration assays are used to study cancer and tissue repair. These assays involve combined cell migration and cell proliferation processes, both of which are modulated by cell-to-cell crowding. Previous discrete models of collective cell migration assays involve a nearest-neighbour proliferation mechanism where crowding effects are incorporated by aborting potential proliferation events if the randomly chosen target site is occupied. There are two limitations of this traditional approach: (i) it seems unreasonable to abort a potential proliferation event based on the occupancy of a single, randomly chosen target site; and, (ii) the continuum limit description of this mechanism leads to the standard logistic growth function, but some experimental evidence suggests that cells do not always proliferate logistically...
October 7, 2016: Physical Biology
Virginia Ahalt, Nilay Tanık Argon, Serhan Ziya, Jeff Strickler, Abhi Mehrotra
According to American College of Emergency Physicians, emergency department (ED) crowding occurs when the identified need for emergency services exceeds available resources for patient care in the ED, hospital, or both. ED crowding is a widely reported problem and several crowding scores are proposed to quantify crowding using hospital and patient data as inputs for assisting healthcare professionals in anticipating imminent crowding problems. Using data from a large academic hospital in North Carolina, we evaluate three crowding scores, namely, EDWIN, NEDOCS, and READI by assessing strengths and weaknesses of each score, particularly their predictive power...
October 4, 2016: Health Care Management Science
Kirk Dombrowski, Bilal Khan, Patrick Habecker, Holly Hagan, Samuel R Friedman, Mohamed Saad
This article explores how social network dynamics may have reduced the spread of HIV-1 infection among people who inject drugs during the early years of the epidemic. Stochastic, discrete event, agent-based simulations are used to test whether a "firewall effect" can arise out of self-organizing processes at the actor level, and whether such an effect can account for stable HIV prevalence rates below population saturation. Repeated simulation experiments show that, in the presence of recurring, acute, and highly infectious outbreaks, micro-network structures combine with the HIV virus's natural history to reduce the spread of the disease...
October 3, 2016: AIDS and Behavior
Thomas Monks, David Worthington, Michael Allen, Martin Pitt, Ken Stein, Martin A James
BACKGROUND: Mathematical capacity planning methods that can take account of variations in patient complexity, admission rates and delayed discharges have long been available, but their implementation in complex pathways such as stroke care remains limited. Instead simple average based estimates are commonplace. These methods often substantially underestimate capacity requirements. We analyse the capacity requirements for acute and community stroke services in a pathway with over 630 admissions per year...
September 29, 2016: BMC Health Services Research
Leslie Anne Campbell, John T Blake, George Kephart, Eva Grunfeld, Donald MacIntosh
BACKGROUND: Median wait times for gastroenterology services in Canada exceed consensus-recommended targets and have worsened substantially over the past decade. Meanwhile, efforts to control colorectal cancer have shifted their focus to screening asymptomatic, average-risk individuals. Along with increasing prevalence of colorectal cancer due to an aging population, screening programs are expected to add substantially to the existing burden on colonoscopy services, and create competition for limited services among individuals of varying risk...
September 28, 2016: Medical Decision Making: An International Journal of the Society for Medical Decision Making
Giuseppe D'Onofrio, Enrica Pirozzi
We consider a stochastic differential equation in a strip, with coefficients suitably chosen to describe the acto-myosin interaction subject to time-varying forces. By simulating trajectories of the stochastic dynamics via an Euler discretization-based algorithm, we fit experimental data and determine the values of involved parameters. The steps of the myosin are represented by the exit events from the strip. Motivated by these results, we propose a specific stochastic model based on the corresponding time-inhomogeneous Gauss-Markov and diffusion process evolving between two absorbing boundaries...
September 26, 2016: Journal of Mathematical Biology
Vincent Bürger, Heiko Briesen
For colloidal particles interacting in suspensions, clusters, or gels, contact models should attempt to include all physical phenomena experimentally observed. One critical point when formulating a contact model is to ensure that the interaction parameters can be easily obtained from experiments. Experimental determinations of contact parameters for particles either are based on bulk measurements for simulations on the macroscopic scale or require elaborate setups for obtaining tangential parameters such as using atomic force microscopy...
October 5, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Ahmad Khosravi, Mohammad Ali Mansournia, Mahmood Mahmoodi, Ali Akbar Pouyan, Kourosh Holakouie-Naieni
BACKGROUND: Cigarette smoking is one of the most important health-related risk factors in terms of morbidity and mortality. In this study, we introduced a new method for deriving the transitional probabilities of smoking stages from a cross-sectional study and simulated a long-term smoking behavior for adolescents. METHODS: In this study in 2010, a total of 4853 high school students were randomly selected and were completed a self-administered questionnaire about cigarette smoking...
2016: International Journal of Preventive Medicine
Noemi Picco, Robert A Gatenby, Alexander R A Anderson
OBJECTIVE: Cancer stem cells (CSCs) have been hypothesized to initiate and drive tumor growth and recurrence due to their self-renewal ability. If correct, this hypothesis implies that successful therapy must focus primarily on eradication of this CSC fraction. However, recent evidence suggests stemness is niche dependent and may represent one of many phenotypic states that can be accessed by many cancer genotypes when presented with specific environmental cues. A better understanding of the relationship of stemness to niche-related phenotypic plasticity could lead to alternative treatment strategies...
September 8, 2016: IEEE Transactions on Bio-medical Engineering
Laura Paparelli, Nikky Corthout, Benjamin Pavie, Devin L Wakefield, Ragna Sannerud, Tijana Jovanovic-Talisman, Wim Annaert, Sebastian Munck
Cell surface protein and lipid molecules are organized in various patterns: randomly, along gradients, or clustered when segregated into discrete micro- and nano-domains. Their distribution is tightly coupled to events such as polarization, endocytosis, and intracellular signaling, but challenging to quantify using traditional techniques. Here we present a novel approach to quantify the distribution of plasma membrane proteins and lipids. This approach describes spatial patterns in degrees of inhomogeneity and incorporates an intensity-based correction to analyze images with a wide range of resolutions; we have termed it Quantitative Analysis of the Spatial distributions in Images using Mosaic segmentation and Dual parameter Optimization in Histograms (QuASIMoDOH)...
September 2016: PLoS Computational Biology
C DeRienzo, J A Kohler, E Lada, P Meanor, D Tanaka
OBJECTIVE: Health-care leaders place significant focus on reducing the average length of stay (ALOS). We examined the relationships among ALOS, cost and clinical outcomes using a neonatal intensive care unit (NICU) simulation model. STUDY DESIGN: A discrete-event NICU simulation model based on the Duke NICU was created. To identify the relationships among ALOS, cost and clinical outcomes, we replaced the standard probability distributions with composite distributions representing the best and worst outcomes published by the National Institutes of Health Neonatal Research Network...
September 1, 2016: Journal of Perinatology: Official Journal of the California Perinatal Association
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