Browsing by Subject "Simulation"

Sort by: Order: Results:

Now showing items 1-14 of 14
  • Tovia, F. (2007)
    International Journal of Logistics Research and Applications
  • Tokariev, Anton; Vanhatalo, Sampsa; Palva, J. Matias (ELSEVIER IRELAND LTD, 2016)
    Objective: To assess how the recording montage in the neonatal EEG influences the detection of cortical source signals and their phase interactions. Methods: Scalp EEG was simulated by forward modeling 20-200 simultaneously active sources covering the cortical surface of a realistic neonatal head model. We assessed systematically how the number of scalp electrodes (11-85), analysis montage, or the size of cortical sources affect the detection of cortical phase synchrony. Statistical metrics were developed for quantifying the resolution and reliability of the montages. Results: The findings converge to show that an increase in the number of recording electrodes leads to a systematic improvement in the detection of true cortical phase synchrony. While there is always a ceiling effect with respect to discernible cortical details, we show that the average and Laplacian montages exhibit superior specificity and sensitivity as compared to other conventional montages. Conclusions: Reliability in assessing true neonatal cortical synchrony is directly related to the choice of EEG recording and analysis configurations. Because of the high conductivity of the neonatal skull, the conventional neonatal EEG recordings are spatially far too sparse for pertinent studies, and this loss of information cannot be recovered by re-montaging during analysis. Significance: Future neonatal EEG studies will need prospective planning of recording configuration to allow analysis of spatial details required by each study question. Our findings also advice about the level of details in brain synchrony that can be studied with existing datasets or by using conventional EEG recordings. (C) 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
  • Tokariev, Anton; Vanhatalo, Sampsa; Palva, J. Matias (2016)
    Objective: To assess how the recording montage in the neonatal EEG influences the detection of cortical source signals and their phase interactions. Methods: Scalp EEG was simulated by forward modeling 20-200 simultaneously active sources covering the cortical surface of a realistic neonatal head model. We assessed systematically how the number of scalp electrodes (11-85), analysis montage, or the size of cortical sources affect the detection of cortical phase synchrony. Statistical metrics were developed for quantifying the resolution and reliability of the montages. Results: The findings converge to show that an increase in the number of recording electrodes leads to a systematic improvement in the detection of true cortical phase synchrony. While there is always a ceiling effect with respect to discernible cortical details, we show that the average and Laplacian montages exhibit superior specificity and sensitivity as compared to other conventional montages. Conclusions: Reliability in assessing true neonatal cortical synchrony is directly related to the choice of EEG recording and analysis configurations. Because of the high conductivity of the neonatal skull, the conventional neonatal EEG recordings are spatially far too sparse for pertinent studies, and this loss of information cannot be recovered by re-montaging during analysis. Significance: Future neonatal EEG studies will need prospective planning of recording configuration to allow analysis of spatial details required by each study question. Our findings also advice about the level of details in brain synchrony that can be studied with existing datasets or by using conventional EEG recordings. (C) 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
  • Sipola, Aleksi (Helsingin yliopisto, 2020)
    Most of the standard statistical inference methods rely on the evaluating so called likelihood functions. But in some cases the phenomenon of interest is too complex or the relevant data inapplicable and as a result the likelihood function cannot be evaluated. Such a situation blocks frequentist methods based on e.g. maximum likelihood estimation and Bayesian inference based on estimating posterior probabilities. Often still, the phenomenon of interest can be modeled with a generative model that describes supposed underlying processes and variables of interest. In such scenarios, likelihood-free inference, such as Approximate Bayesian Computation (ABC), can provide an option for overcoming the roadblock. Creating a simulator that implements such a generative model provides a way to explore the parameter space and approximate the likelihood function based on similarity between real world data and the data simulated with various parameter values. ABC provides well defined and studied framework for carrying out such simulation-based inference with Bayesian approach. ABC has been found useful for example in ecology, finance and astronomy, in situations where likelihood function is not practically computable but models and simulators for generating simulated data are available. One such problem is the estimation of recombination rates of bacterial populations from genetic data, which often is unsuitable for typical statistical methods due to infeasibly massive modeling and computation requirements. Overcoming these hindrances should provide valuable insight into evolution of bacteria and possibly aid in tackling significant challenges such as antimicrobial resistance. Still, ABC inference is not without its limitations either. Often considerable effort in defining distance functions, summary statistics and threshold for similarity is required to make the comparison mechanism successful. High computational costs can also be a hindrance in ABC inference; As increasingly complex phenomena and thus models are studied, the computations that are needed for sufficient exploration of parameter space with the simulation-comparison cycles can get too time- and resource-consuming. Thus efforts have been made to improve the efficiency of ABC inference. One improvement here has been the Bayesian Optimization for Likelihood-Free Inference algorithm (BOLFI), which provides efficient method to optimize the exploration of parameter space, reducing the amount of needed simulation-comparison cycles by up to several magnitudes. This thesis aims to describe some of the theoretical and applied aspects of the complete likelihood-free inference pipelines using both Rejection ABC and BOLFI methods. The thesis presents also use case where the neutral evolution recombination rate in Streptococcus pneumoniae population is inferred from well-studied real world genome data set. This inference task is used to provide context and concrete examples for the theoretical aspects, and demonstrations for numerous applied aspects. The implementations, experiments and acquired results are also discussed in some detail.
  • Vu, T. H. Y.; Dufour, C.; Khomenkov, V.; Leino, A. A.; Djurabekova, F.; Nordlund, K.; Coulon, P. -E.; Rizza, G.; Hayoun, M. (2019)
    The elongation process under swift heavy ion irradiation (74 MeV Kr ions) of gold NPs, with a diameter in the range 10-30 nm, and embedded in a silica matrix has been investigated by combining experiment and simulation techniques: three-dimensional thermal spike (3DTS), molecular dynamics (MD) and a phenomenological simulation code specially developed for this study. 3DTS simulations evidence the formation of a track in the host matrix and the melting of the NP after the passage of the impinging ion. MD simulations demonstrate that melted NPs have enough time to expand after each ion impact. Our phenomenological simulation relies on the expansion of the melted NP, which flows in the track in silica with modified (lower) density, followed by its recrystallization upon cooling. Finally, the elongation of the spherical NP into a cylindrical one, with a length proportional to its initial size and a width close to the diameter of the track, is the result of the superposition of the independent effects of each expansion/recrystallization process occurring for each ion impact. In agreement with experiment, the simulation shows the gradual elongation of spherical NPs in the ion-beam direction until their widths saturate in the steady state and reach a value close to the track diameter. Moreover, the simulations indicate that the expansion of the gold NP is incomplete at each ion impact.
  • Özpolat, Koray; Rilling, Juanita; Altay, Nezih; Chavez, Eric (2015)
    Journal of Humanitarian Logistics and Supply Chain Management
  • Lejonqvist, Gun-Britt; Eriksson, Katie; Meretoja, Riitta (2016)
    Making the transition from theory to practise easier in nursing education through simulation is widely implemented all over the world, and there is research evidence of the positive effects of simulation. The pre understanding for this study is based on a definition of clinical competence as encountering, knowing, performing, Maturing and developing, and the hypothesis is that these categories should appear in simulated situations. The aim of the study was to explore the forms and expressions of clinical competence in simulated situations and furthermore to explore if and how clinical competence could be developed by simulation. An observational hermeneutic study with a hypothetic-deductive approach was used in 18 simulated situations with 39 bachelor degree nursing students. In the situations, the scenarios, the actors and the plots were described. The story told was "the way from suffering to health" in which three main plots emerged. The first was, doing as performing and knowing, which took the shape of knowing what to do, acting responsibly, using evidence and equipment, appearing confident and feeling comfortable, and sharing work and information with others. The second was, being as encountering the patient, which took the shape of being there for him/her and confirming by listening and answering. The third plot was becoming as maturing and developing which took the shape of learning in co-operation with other students. All the deductive categories, shapes and expressions appeared as dialectic patterns having their negative counterparts. The study showed that clinical competence can be made evident and developed by simulation and that the challenge is in encountering the patient and his/her suffering. (C) 2015 Elsevier Ltd. All rights reserved.
  • European Neurosurg Simulation Stud; Perin, Alessandro; Galbiati, Tommaso Francesco; Gambatesa, Enrico; Ayadi, Roberta; Orena, Eleonora Francesca; Cuomo, Valentina; Riker, Nicole Irene; Falsitta, Lydia Viviana; Schembari, Silvia; Rizzo, Stefano; Luciano, Cristian; Cappabianca, Paolo; Meling, Torstein Ragnar; Schaller, Karl; DiMeco, Francesco; Laakso, Aki (2018)
    Currently available simulators are supposed to allow young neurosurgeons to hone their technical skills in a safe environment, without causing any unnecessary harm to their patients caused by their inexperience. For this training method to be largely accepted in neurosurgery, it is necessary to prove simulation efficacy by means of large-scale clinical validation studies. We correlated and analysed the performance at a simulator and the actual operative skills of different neurosurgeons (construct validity). We conducted a study involving 92 residents and attending neurosurgeons from different European Centres; each participant had to perform a virtual task, namely the placement of an external ventricular drain (EVD) at a neurosurgical simulator (ImmersiveTouch). The number of attempts needed to reach the ventricles and the accuracy in positioning the catheter were assessed. Data suggests a positive correlation between subjects who placed more EVDs in the previous year and those who get better scores at the simulator (p = .008) (fewer attempts and better surgical accuracy). The number of attempts to reach the ventricle was also analysed; senior residents needed fewer attempts (mean = 2.26; SD = 1.11) than junior residents (mean = 3.12; SD = 1.05) (p = .007) and staff neurosurgeons (mean = 2.89, SD = 1.23). Scoring results were compared by using the Fisher's test, for the analysis of the variances, and the Student's T test. Surprisingly, having a wider surgical experience overall does not correlate with the best performance at the simulator. The performance of an EVD placement on a simulator correlates with the density of the neurosurgical experience for that specific task performed in the OR, suggesting that simulators are able to differentiate neurosurgeons according to their surgical ability. Namely this suggests that the simulation performance reflects the surgeons' consistency in placing EVDs in the last year.
  • Vauhkonen, Jari; Mutanen, Antti; Packalen, Tuula; Asikainen, Antti (2021)
    Background The current EU LULUCF regulation calls for member state-specific Forest Reference Levels (FRLs) for benchmark in the accounting of greenhouse gas emissions and removals of managed forest land during the compliance period (2021-2030). According to the technical guidance on developing and reporting the FRLs, it could be actualized by projecting a ratio of harvested to total available biomass. We tested how the initial age distribution may affect the aforementioned ratio by simulating the continuation of forest management based on several descriptive shapes of forest age class distribution. Results Our simulations suggest that when the FRLs are prepared by employing the harvest ratio and forest management is assumed strictly age dynamics driven, the shape of the initial forest age class distribution gives rise to computational sinks or sources of carbon in managed forest land. Harvests projected according to the ratio corresponded those resulting from the age dynamics only in the case of uniform age distribution. Conclusions The result calls for a better consideration of variation in initial states between countries when determining the future LULUCF regulation. Our exercise demonstrates how generic simulations in a standardized modeling framework could help in ex-ante impact assessment of proposed changes to the LULUCF regulation.
  • Beamon, Benita; Kotleba, Stephen (2006)
    The International Journal of Logistics Management
  • Airaksinen, Timo (2020)
    Irony and sarcasm are common linguistic tropes. They are both based on falsehoods that the speaker pretends to be true. I briefly characterize their differences. A third trope exists that works when the relevant propositions are true – yet its rhetorical effect resembles irony and sarcasm, I call it mocking. It is mimetic evil: an agent copies another so that the result ridicules him. The image is, in a limited way, true of him and it hurts; we all are vulnerable. I provide a systematic framework for understanding this phenomenon, mocking, in terms of emulation and simulation. Finally, I introduce an idea of universal mimesis and discuss René Gir-ard’s theory of desire. He argues that desires are copies of a model. This may not be possible, and I suggest a modification to his theory. I pay attention to his idea of mimetic desire as a source of hatred, which is elated to what I call here mimetic mocking.
  • Kuva, J.; Voutilainen, M.; Mattila, K. (2019)
    The time domain-random walk method was developed further for simulating mass transfer in fracture flows together with matrix diffusion in surrounding porous media. Specifically, a time domain-random walk scheme was developed for numerically approximating solutions of the advection-diffusion equation when the diffusion coefficient exhibits significant spatial variation or even discontinuities. The proposed scheme relies on second-order accurate, central-difference approximations of the advective and diffusive fluxes. The scheme was verified by comparing simulated results against analytical solutions in flow configurations involving a rectangular channel connected on one side with a porous matrix. Simulations with several flow rates, diffusion coefficients, and matrix porosities indicate good agreement between the numerical approximations and analytical solutions.
  • Karttunen, Kalle; Ahtikoski, Anssi; Kujala, Susanna; Törmä, Hannu; Kinnunen, Jouko; Salminen, Hannu; Huuskonen, Saija; Kojola, Soili; Lehtonen, Mika; Hynynen, Jari; Ranta, Tapio (2018)
    The demand for and supply of forest biomass have both been increasing in recent years, which will set new requirements for forest management. Thus, new studies on regionally suitable forest management regimes to fulfill the needs of potential new investments and the impacts on wood supply potential on regional socioeconomic welfare are called for. The aim of this study was to examine the impacts of intensive forest management due to increased demand for wood biomass, from the regional economy point of view. In particular, the impact of intensive forest management on 1) regional gross domestic product (GDP), 2) private consumption, and 3) employment were assessed. The study was carried out by using computable general equilibrium (CGE) modelling combined with the requisite statistics and simulation of regional forest potential in the future. The results showed that total regional forest biomass supply with more intensive forest management could be increased annually on average by 26% (1.7Mm(3)) by 2030 compared to the business as usual (BAU) scenario. In this study, regional demand was increased by a hypothetical saw mill (0.5Mm(3)) and biorefinery (0.7Mm(3)). Total regional socio-economic benefits could be 2.8% ((sic)150 M) for GDP, 1.5% ((sic) 49 M) for private consumption and 1.6% (780 person-years) for employment, larger by 2030 than in the BAU scenario including multiplier effects. The study demonstrated how much regional socio-economic welfare would increase if regional wood demand with new investments combined with more intensive forest management and wood supply had more attention paid to it.
  • Aho, Pekka; Vikatmaa, Leena; Niemi-Murola, Leila; Venermo, Maarit (2019)
    Objective: Difficulties in distributing endovascular experience among all operating room (OR) personnel prevented full-scale use of endovascular aneurysm repair (EVAR) in emergencies. To streamline the procedure of EVAR for ruptured aneurysm (rEVAR) and to provide this method even to unstable patients, we initiated regular simulation training sessions. Methods: This is an observational study of 29 simulation sessions performed between January 2015 and December 2017. We analyzed the development of time from OR door to aortic balloon occlusion during simulations and OR door to needle times in real-life rEVARs as well as the outcome of the 185 ruptured abdominal aortic aneurysm (rAAA) patients who arrived at the university hospital between January 2013 and December 2017. A questionnaire was sent for simulation attendants before and after the simulation session. Results: In the first simulations, the door to occlusion time was 20 to 35 minutes. After adding a hemodynamic collapse to the simulation protocol, the time decreased to 10 to 13 minutes in the 10 recent simulations, including a 5-minute cardiopulmonary resuscitation (P = .01). The electronic questionnaire performed for attendees before and after the simulation session showed significant improvement in both confidence and knowledge of the OR staff regarding rEVAR procedure. In the real-life rEVARs, 75 of the 185 patients with rAAAs underwent EVAR. Among rEVAR patients, the median OR door to needle time was 65 minutes before and 16 minutes after the onset of simulations (P = .000). The overall 30-day mortality among all rAAA patients was 44.8% and 30.6% accordingly (P = .046). When patients who were turned down from the emergency surgery were excluded, the 30-day operative mortality was 39.2% and 25.1% during the periods, respectively (P = .051). The 30-day mortality was 16.2% after rEVAR and 40.6% after open surgery (P = .001). Conclusions: Simulation training for rEVAR significantly improves the treatment process in real-life patients and may enhance the outcome of rAAA patients.