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  • 1.
    Albing, Malin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Contributions to process capability indices and plots2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents contributions within the field of process capability analysis. Process capability analysis deals with how to assess the capability of processes. Based on process capability analysis one can determine how the process performs relative to its product requirements or specifications. An important part within process capability analysis is the use of process capability indices. This thesis focuses on process capability indices and process capability plots. The thesis consists of six papers and a summary. The summary gives a background to the research area, a short overview of the six papers, and some suggestions for future research. The thesis summary also consists of some new results, not presented in any of the appended papers. In paper I, the frequency and use of process capability analysis, together with statistical process control and design of experiments, within Swedish companies hiring alumni students are investigated. We also investigate what motivates organisations to implement or not implement these statistical methods, and what is needed to increase the use. In papers II-III we generalize the ideas with process capability plots and propose two graphical methods, for deeming a process capable at a given significance level, when the studied quality characteristic is assumed to be normally distributed. In paper II we derive estimated process capability plots for the case when the specification interval is one-sided. In paper III we derive elliptical safety region plots for the process capability index Cpk and its one-sided correspondences. The proposed graphical methods are helpful to determine if it is the variability, the deviation from target, or both that need to be reduced to improve the capability. In papers IV-VI we propose a new class of process capability indices designed for the situation with an upper specification limit, a target value zero, and where the studied quality characteristic has a skewed, zero- bound distribution with a long tail towards large values. The proposed class of indices is simple and possesses properties desirable for process capability indices. The results in papers IV-VI are also valid for the situation with a target value, not equal to zero but equal to a natural lower limit of the quality characteristic. Three estimators of the proposed class of indices are studied and the asymptotic distributions of these estimators are derived. We also consider decision procedures, based on the estimated indices, suitable for deeming the process capability at a given significance level. The new results in the summary combines the ideas from paper II with the results in papers IV-VI and a graphical method for the class of indices proposed in IV-VI are derived.

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  • 2.
    Albing, Malin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Process capability analysis with focus on indices for one-sided specification limits2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis some aspects of process capability analysis are considered. Process capability analysis deals with how to assess the capability of manufacturing processes. Based on the process capability analysis one can determine how the process performs relative to its product requirements or specifications. An important part within process capability analysis is the use of process capability indices. This thesis focuses on process capability indices in the situation when the specification limits are one- sided. The thesis consists of a summary and three papers, of which one is already published in an international journal. The summary gives a background to the research area, a short overview of the three papers, and some suggestions for future research. In Paper I, the frequency and use of process capability analysis together with statistical process control and design of experiments, within Swedish companies hiring alumni students are investigated. We also investigate what motivates organisations to implement or not implement these statistical methods, if there are differences in use that can be related to organisational types and what will be needed to increase the use. One conclusion drawn from the results is that the students employed in the Swedish industrial sector witness a modest use of these statistical methods and use in other sectors hiring the alumni is uncommon. In Paper II we present a graphical method useful when doing capability analysis having one-sided specification limits. This is an extension of the process capability plots previously developed for two-sided specification intervals. Under the assumption of normality we suggest estimated process capability plots to be used to assess process capability at a given significance level. The presented graphical approach is helpful to determine if it is the variability, the deviation from target, or both that need to be reduced to improve the capability. In Paper III the situation with non-negative process data having a skew distribution with a long tail towards large values are considered, when an upper specification limit only exists and the target value is 0. No proper indices exist for this specific situation, which is common in practice. We contribute to this area by proposing a new class of indices designed for skew, zero-bound distributions when an upper specification only exists and the target value is 0. This new class of indices is simple and possesses properties desirable for process capability indices. Two estimators of the proposed index are studied and the asymptotic distributions of these estimators are derived. Furthermore, we consider decision procedures, based on the estimated indices, suitable for deeming the process capability or not.

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  • 3.
    Albing, Malin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Process capability indices for Weibull distributions and upper specification limits2008Report (Other academic)
  • 4.
    Albing, Malin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Process capability indices for Weibull distributions and upper specification limits2009In: Quality and Reliability Engineering International, ISSN 0748-8017, E-ISSN 1099-1638, Vol. 25, no 3, p. 317-334Article in journal (Refereed)
    Abstract [en]

    We consider a previously proposed class of capability indices that are useful when the quality characteristic of interest has a skewed, zero-bound distribution with a long tail towards large values and there is an upper specification with a pre-specified target value, T = 0. We investigate this class of process capability indices when the underlying distribution is a Weibull distribution and focus on the situation when the Weibull distribution is highly skewed. We propose an estimator of the index in the studied class, based on the maximum likelihood estimators of the parameters in the Weibull distribution, and derive the asymptotic distribution for this estimator. Furthermore, we suggest a decision rule based on the estimated index and its asymptotic distribution, and presents a power comparison between the proposed estimator and a previously studied estimator. A simulation study is also performed to investigate the true significance level when the sample size is small or moderate. An example from a Swedish industry is presented.

  • 5. Albing, Malin
    et al.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Elliptical safety region plots for Cpk2011In: Journal of Applied Statistics, ISSN 0266-4763, E-ISSN 1360-0532, Vol. 38, no 6, p. 1169-1187Article in journal (Refereed)
    Abstract [en]

    The process capability index Cpk is widely used when measuring the capability of a manufacturing process. A process is defined to be capable if the capability index exceeds a stated threshold value, e.g. Cpk4/3. This inequality can be expressed graphically using a process capability plot, which is a plot in the plane defined by the process mean and the process standard deviation, showing the region for a capable process. In the process capability plot, a safety region can be plotted to obtain a simple graphical decision rule to assess process capability at a given significance level. We consider safety regions to be used for the index Cpk. Under the assumption of normality, we derive elliptical safety regions so that, using a random sample, conclusions about the process capability can be drawn at a given significance level. This simple graphical tool is helpful when trying to understand whether it is the variability, the deviation from target, or both that need to be reduced to improve the capability. Furthermore, using safety regions, several characteristics with different specification limits and different sample sizes can be monitored in the same plot. The proposed graphical decision rule is also investigated with respect to power

  • 6. Albing, Malin
    et al.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Elliptical Safety Region Plots for Cpk, Cpu and Cpl2008Report (Other academic)
  • 7. Albing, Malin
    et al.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Process capability indices for one-sided specifications and skew zero-bound distributions2006Report (Other academic)
  • 8. Albing, Malin
    et al.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Skewed zero-bound distributions and process capability indices for upper specifications2009In: Journal of Applied Statistics, ISSN 0266-4763, E-ISSN 1360-0532, Vol. 36, no 2, p. 205-221Article in journal (Refereed)
    Abstract [en]

    A common practical situation in process capability analysis, which is not well developed theoretically, is when the quality characteristic of interest has a skewed distribution with a long tail towards relatively large values and an upper specification limit only exists. In such situations it is not uncommon that the smallest possible value of the characteristic is 0 and this also is the best value to obtain. Hence a target value 0 is assumed to exist. We investigate a new class of process capability indices for this situation. Two estimators of the proposed index are studied and the asymptotic distributions of these estimators are derived. Furthermore we suggest a decision procedure useful when drawing conclusions about the capability at a given significance level, based on the estimated indices and their asymptotic distributions. A simulation study is also performed, assuming that the quality characteristic is Weibull distributed, to investigate the true significance level when the sample size is finite.

  • 9.
    Al-Chalabi, Hussan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Lundberg, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Ahmadi, Alireza
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Jonsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Case Study: Model for Economic Lifetime of Drilling Machines in the Swedish Mining Industry2015In: The Engineering Economist, ISSN 0013-791X, E-ISSN 1547-2701, Vol. 60, no 2, p. 138-154Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to develop a practical economic replacement decision model to identify the economic lifetime of a mining drilling machine. A data driven optimisation model was developed for operating and maintenance costs, purchase price and machine resale value. Equivalent present value of these costs by using discount rate was considered. The proposed model shows that the absolute optimal replacement time (ORT) of a drilling machine used in one underground mine in Sweden is 115 months. Sensitivity and regression analysis show that the maintenance cost has the largest impact on the ORT of this machine. The proposed decision making model is applicable and useful and can be implemented within the mining industry.

  • 10.
    Antoch, Jaromír
    et al.
    Charles University, Prague, Czech Republic.
    Ekblom, Håkan
    Luleå University of Technology.
    Recursive robust regression computational aspects and comparison1995In: Computational Statistics & Data Analysis, ISSN 0167-9473, E-ISSN 1872-7352, Vol. 19, no 2, p. 115-128Article in journal (Refereed)
    Abstract [en]

    The main objective of this paper is to show how algorithms for classical robust regression can be modified for recursive evaluation. It is shown that such a modification can be utilized to increase the algorithmic efficiency for convex object functions. However, for the non-convex ones it is demonstrated that recursion gives little help to find the optimal solution.

  • 11.
    Bakhtiari, Hamed
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Zhong, Jin
    University of Hong Kong, Hong Kong.
    Alvarez, Manuel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Uncertainty modeling methods for risk-averse planning and operation of stand-alone renewable energy-based microgrids2022In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 199, p. 866-880Article in journal (Refereed)
    Abstract [en]

    The accuracy of models to capture the uncertainty of renewables significantly affects the planning and operation of renewable energy-based stand-alone (REB-SA) microgrids. This paper aims to first study different stochastic and deterministic models for renewables, then evaluate the performance of an REB-SA microgrid planning problem and provide qualitative and quantitative comparisons. A modified Metropolis-coupled Markov chain Monte Carlo simulation is considered for the first time in the planning of an REB-SA microgrid to predict the behavior of renewables with minimum iterations. The modified model is benchmarked against two prevalent models including the retrospective model with worst-case scenarios and the Monte Carlo simulation. The operations of three designed microgrids (by these three methods) are evaluated using the last three-year historical data of a city in northern Sweden including solar radiation, wind speed, the water flow of a river, and load consumption. The impacts of the considered methods on using PV panels and hydrogen systems are investigated. The results verify that the modified model decreases the risk of planning and operation of an REB-SA microgrid from the energy and power shortage viewpoints. Moreover, the designed microgrid with the modified model can cope with all possible scenarios from economic, technical, and environmental viewpoints.

  • 12.
    Bergquist, Bjarne
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Business Administration and Industrial Engineering.
    Albing, Malin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Statistical methods - does anyone really use them?2006In: Total Quality Management and Business Excellence, ISSN 1478-3363, E-ISSN 1478-3371, Vol. 17, no 8, p. 961-972Article in journal (Refereed)
    Abstract [en]

    Students taking courses in quality management at Luleå University of Technology receive extensive education in statistical methods. To improve the education and to understand what kind of competence students need when they graduate, a survey was preformed examining how and to what extent the methods Statistical Process Control, Capability Analysis and Design of Experiments are used by organisations hiring the alumni. The result shows that the students employed in the Swedish industrial sector witness a modest use of statistical methods, while use of statistical methods in other sectors hiring the alumni is uncommon. Lack of competence and resources within the organizations are stated as hindrances to expanded use. Conclusions from the study are that implementation techniques must be emphasized in the curriculum and that different types of courses should be given - practical, hands-on courses for engineers, managers and others working in organizations. Furthermore, courses offered at universities must have a strong focus on practical problems such as difficulties randomizing experiments and that graphical methods should be favoured.

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  • 13.
    Bota, András
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Gardner, Lauren
    Department of Civil and Systems Engineering, Johns Hopkins University, Baltimore, MD 21218, USA.
    A Generalized Framework for the Estimation of Edge Infection Probabilities2023In: Algorithms, E-ISSN 1999-4893, Vol. 16, no 8, article id 390Article in journal (Refereed)
    Abstract [en]

    Modeling the spread of infections in networks is a well-studied and important field of research. Most infection and diffusion models require a real value or probability at the edges of the network as an input, but this is rarely available in real-life applications. The Generalized Inverse Infection Model (GIIM) has previously been used in real-world applications to solve this problem. However, these applications were limited to the specifics of the corresponding case studies, and the theoretical properties, as well as the wider applicability of the model, are yet to be investigated. Here, we show that the general model works with the most widely used infection models and is able to handle an arbitrary number of observations on such processes. We evaluate the accuracy and speed of the GIIM on a large variety of realistic infection scenarios.

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  • 14. Castagliola, Philippe
    et al.
    Maravelakis, P.
    Psarakis, S.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Monitoring capability indices using run rules2007In: Proceedings of International Conference on Industrial Engineering and Systems Management, ISEM 07, ISEM 07 , 2007Conference paper (Refereed)
  • 15. Castagliola, Philippe
    et al.
    Maravelakis, P.
    University of the Aegean, Samos.
    Psarakis, S.
    Athens University of Economics and Business.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Monitoring capability indices using run rules2009In: Journal of Quality in Maintenance Engineering, ISSN 1355-2511, E-ISSN 1758-7832, Vol. 15, no 4, p. 358-370Article in journal (Refereed)
    Abstract [en]

    PurposeThe purpose of this paper is propose a methodology for monitoring industrial processes that cannot be stabilized, but are nevertheless capable. Design/methodology/approach The proposed procedure uses the C P (u,v) family of capability indices proposed by Vännman (including the indices C PK , C PM , C PMK ) combined with one-sided two-out-of-three and three-out-of-four run rules strategies. FindingsThis paper introduces a new strategy, where capability indices are monitored in place of the classical sample statistics like the mean, median, standard deviation or range. Practical implicationsWhen doing a capability analysis it is recommended to first check that the process is stable, e.g. by using control charts. However, there are occasions when a process cannot be stabilized, but is nevertheless capable. Then the classical control charts fail to efficiently monitor the process position and variability. The approach suggested in this paper overcomes this problem. Originality/valueThe experimental results presented in this paper demonstrate how the new proposed approach efficiently monitors capable processes by detecting decreases or increases of capability level.

  • 16. Castagliola, Philippe
    et al.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Average run length when monitoring capability indices using EWMA2008In: Quality and Reliability Engineering International, ISSN 0748-8017, E-ISSN 1099-1638, Vol. 24, no 8, p. 941-955Article in journal (Refereed)
    Abstract [en]

    In order to monitor unstable but capable processes Castagliola and Vännman have recently suggested a procedure based on an EWMA approach, called EWMA capability chart, for monitoring Vännman's Cp(u,v)-family of capability indices and showed how their proposed approach efficiently monitors capable processes by detecting a decrease or increase in the capability level. The goal of this paper is to investigate the efficiency of this capability chart in terms of ARL. The procedure used for computing this ARL is presented and simple guidelines for obtaining approximations to the optimal EWMA parameters are proposed.

  • 17.
    Castagliola, Philippe
    et al.
    Université de Nantes and IRCCyN.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Monitoring capability indices using an EWMA approach2007In: Quality and Reliability Engineering International, ISSN 0748-8017, E-ISSN 1099-1638, Vol. 23, no 7, p. 769-790Article in journal (Refereed)
    Abstract [en]

    When performing a capability analysis it is recommended to first check that the process is stable, for example, by using control charts. However, there are occasions when a process cannot be stabilized, but it is nevertheless capable. Then the classical control charts fail to efficiently monitor the process position and variability. In this paper we propose a new strategy to solve this problem, where capability indices are monitored in place of the classical sample statistics such as the mean, median, standard deviation, or range. The proposed procedure uses the Cp(u,v) family of capability indices proposed by Vännman combined with a logarithmic transformation and an EWMA approach. One important property of the procedure presented here is that the control limits used for the monitoring of capability indices only depend on the capability level assumed for the process. The experimental results presented in this paper demonstrates how this new approach efficiently monitors capable processes by detecting changes in the capability level.

  • 18.
    Castagliola, Philippe
    et al.
    Université de Nantes.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Monitoring capability indices using EWMA2006Report (Other academic)
  • 19.
    Castagliola, Philippe
    et al.
    Université de Nantes and IRCCyN.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    The efficiency of the EWMA capability chart2007In: IEEE International Conference on Industrial Engineering and Engineering Management, 2007: IEEM 2007 ; 2 - 4 Dec. 2007, Singapore / [ed] Martin Helander, Piscataway, NJ: IEEE Communications Society, 2007, p. 1389-1393Conference paper (Refereed)
    Abstract [en]

    In order to monitor unstable but capable processes Castagliola & Vännman have recently suggested a procedure based on an EWMA approach, called EWMA capability chart, for monitoring Vännman's Cp(u, v)-family of capability indices and showed how their proposed approach efficiently monitors capable processes by detecting a decrease or increase of the capability level. The goal of this paper is to investigate the efficiency of this capability chart by computing optimal EWMA parameters yielding the smallest possible ARL's. The method for computing the ARL is explained and a table summarizing optimal values for the EWMA parameters (λ*,K*) is given for the Cpk chart.

  • 20.
    Cederwall, Krister
    et al.
    Luleå University of Technology.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Composite beams from a statistical point of view1982Report (Other academic)
  • 21.
    Cheng, Haibo
    et al.
    Shenyang Institute of Automation, Chinese Academy of Sciences, State Key Laboratory of Robotics, Shenyang, China; Chinese Academy of Sciences, Key Laboratory of Networked Control Systems, Shenyang, China; Institutes for Robotics and Intelligent Manufacturing, Chinese Academy of Sciences, Shenyang, China.
    He, Yunpeng
    Shenyang Institute of Automation, Chinese Academy of Sciences, State Key Laboratory of Robotics, Shenyang, China; Chinese Academy of Sciences, Key Laboratory of Networked Control Systems, Shenyang, China; Institutes for Robotics and Intelligent Manufacturing, Chinese Academy of Sciences, Shenyang, China; University of Chinese Academy of Sciences, Beijing, China.
    Zeng, Peng
    Shenyang Institute of Automation, Chinese Academy of Sciences, State Key Laboratory of Robotics, Shenyang, China; Chinese Academy of Sciences, Key Laboratory of Networked Control Systems, Shenyang, China; Institutes for Robotics and Intelligent Manufacturing, Chinese Academy of Sciences, Shenyang, China.
    Li, Shichao
    Shenyang Institute of Automation, Chinese Academy of Sciences, State Key Laboratory of Robotics, Shenyang, China; Chinese Academy of Sciences, Key Laboratory of Networked Control Systems, Shenyang, China; Institutes for Robotics and Intelligent Manufacturing, Chinese Academy of Sciences, Shenyang, China.
    Vyatkin, Valeriy
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science. Aalto University, Department of Electrical Engineering and Automation, Helsinki, Finland.
    Deep Learning-Based Prediction of Subsurface Oil Reservoir Pressure Using Spatio-Temporal Data2023In: IECON 2023 - 49th Annual Conference of the IEEE Industrial Electronics Society, Institute of Electrical and Electronics Engineers (IEEE), 2023Conference paper (Refereed)
    Abstract [en]

    Prediction of subsurface oil reservoir pressure are critical to hydrocarbon production. However, the accurate pressure estimation faces great challenges due to the complexity and uncertainty of reservoir. The underground seepage flow and petrophysical parameters (permeability and porosity) are important but difficult to measure in oilfield. Deep learning methods have been successfully used in reservoir engineering and oil & gas production process. In this study, the effective but inaccessible subsurface seepage fields are not used, only the spatial coordinates and temporal information are selected as model input to predict reservoir pressure. A stacked GRU-based deep learning model is proposed to map the relationship between spatio-temporal data and reservoir pressure. The proposed deep learning method is verified by using a three-dimensional reservoir model, and compared with commonly-used methods. The results show that the stacked GRU model has a better performance and higher accuracy than other deep learning or machine learning methods in pressure prediction.

  • 22.
    Deleryd, Mats
    et al.
    Adtranz Nordic.
    Lundqvist, Robert
    Control charts and capability studies revisited: a model for better decision-making1999In: Productivity & quality management frontiers, VIII: refereed papers presented at the 8th International Conference on Productivity & Quality Research, June 14-16, 1999, Vaasa, Finland / [ed] William Werther, Jr; Josu Takala; David J. Sumanth., MCB University Press , 1999Conference paper (Refereed)
    Abstract [en]

    Two fundamental aspects of decision-making concern stability and capability: is the process stable and predictable and does it meet the requirements? These aspects are often studied by use of control charts and of capability studies. The former comprises techniques based on plotting the longitudinal outcome of some process measure and estimation of what could be called the “natural variation” for the process. Capability studies are based on comparisons between the variation and tolerance limits.If these aspects are addressed explicitly at all, then they often seem to be dealt with incompletely or even inappropriately. Control charts are often described as techniques for determining when the process should be adjusted. This is evidently one possible use for control charts, but it is far too restricted. We claim that control charts have their most important use as tools for discerning what kinds of actions which might be appropriate in improvement efforts, hence an instrument to be used in fairly high level decision making. As for capability studies, these are often made without considerations to the process stability. This can result in making the final capability indices more or less useless.The intention in this paper is to advocate an alternative and more general perspective on these two aspects. The basic argument is that the tools should first of all be used on the level of manager's decision-making. A simple model for the use of the tools is proposed. The model could hopefully provide support to decision-making as it results in better facts.

  • 23.
    Deleryd, Mats
    et al.
    Luleå University of Technology.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Process capability plots—a quality improvement tool1999In: Quality and Reliability Engineering International, ISSN 0748-8017, E-ISSN 1099-1638, Vol. 15, no 3, p. 213-227Article in journal (Refereed)
    Abstract [en]

    We introduce the concept of process capability plots, which are powerful tools to monitor and improve the capability of industrial processes. An advantage of using a process capability plot, compared with using a traditional process capability index alone, when deciding whether a process can be considered capable or not, is that we will instantly get information about the location and spread of the studied characteristic. When the process is non-capable, the plots are helpful when trying to understand if it is the variability, the deviation from target or both that need to be reduced to improve the capability. In this way the proposed graphical methods give a clear direction of quality improvement. We evaluate two different process capability plots, the (δ*, γ*)-plot and the confidence rectangle plot, from a theoretical as well as a practical point of view. When studying them from a theoretical point of view, among other things, a simulation study is conducted to investigate the ability of each of the two methods to identify that a process is capable when it actually is. The comparison from a practical point of view is made by discussing the advantages and disadvantages of the two methods in different practical situations. Based on the above-mentioned comparisons, the recommendation is that the practitioner should use the (δ*, γ*)-plot.

  • 24.
    Deleryd, Mats
    et al.
    Luleå University of Technology.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Process capability studies for short production runs1998In: International Journal of Reliability, Quality and Safety Engineering (IJRQSE), ISSN 0218-5393, Vol. 5, no 4, p. 383-401Article in journal (Refereed)
    Abstract [en]

    The current trend in modern production is directed towards shorter and shorter production runs. The two major reasons causing this trend are the rapid spread of the just in time (JIT) philosophy and the constantly increasing multiplicity of customer demands. The short runs of modern production not only constitute a challenge for production management, but they also cause some problems when applying traditional statistical methods, designed to be used for large sets of data. One of these methods is process capability studies. Since theories on how to use process capability studies in short production environments are incomplete, the aim of this paper is to present some ideas which will partly fill this gap. The theories of process capability studies for short runs presented are based on ideas of focusing on the process, not on the products, and on using data transformation. By using the transformation presented, it is possible to conduct process capability studies in a traditional straightforward manner. A simulation study shows that the suggested transformation technique works satisfactorily in real situations. Finally, the ....-plot is introduced as a method of interpreting and analyzing the capability of a short run production process. By using the .... -plot, additional information is obtained concerning the capability of a process, compared to using traditional process capability indices only.

  • 25.
    Ekblom, Håkan
    Luleå University of Technology.
    A new algorithm for the huber estimator in linear models1988In: BIT Numerical Mathematics, ISSN 0006-3835, E-ISSN 1572-9125, Vol. 28, no 1, p. 123-132Article in journal (Refereed)
    Abstract [en]

    This paper considers algorithms for solving the linear robust regression problem by minimizing the Huber function. In the computational methods for this problem used so far, the scale estimate is adjusted separately. The new algorithm, based on Newton's method, treats both the scale and the location parameters as independent variables. The special form of the Hessian allows for an efficient updating scheme.

  • 26.
    Ekblom, Håkan
    Luleå University of Technology.
    Generation of test problems for Lp - and Huber regression1990In: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, Vol. 19, no 2, p. 481-489Article in journal (Refereed)
    Abstract [en]

    Numerical methods for obtaining (X|y), related to the linear model y = X + e, are presented. The user is allowed to specify the Lp or Huber solution vector B* and is also free to choose the conditioning and the structure of X.

  • 27. Ekblom, Håkan
    The L1 -estimate as limiting case of an Lp - or Huber-estimate1987In: Statistical data analysis based on the L1-norm and related methods: papers presented at the 1. international conference held in Neuchatel 1987 / [ed] Yadolah Dodge, Amsterdam: Elsevier, 1987, p. 109-116Conference paper (Refereed)
  • 28. Ekblom, Håkan
    What can numerical analysis do for statistics?1994In: COMPSTAT [1994] : proceedings in computational statistics ; 11th symposium held in Vienna, Austria, 1994, Physica-Verlag Rudolf Liebig GmbH , 1994, p. 31-45Conference paper (Refereed)
    Abstract [en]

    Basic numerical concepts, like cancellation, instability and condition number, are described and discussed. The implication on statistical computation is exemplified on computing variances and regression coefficients

  • 29.
    Ekblom, Håkan
    et al.
    Luleå University of Technology.
    Madsen, Kaj
    Institute of Numerical Analysis DTH, Lyngby, Denmark.
    Algorithms for non linear huber estimation1989In: BIT Numerical Mathematics, ISSN 0006-3835, E-ISSN 1572-9125, Vol. 29, no 1, p. 60-76Article in journal (Refereed)
    Abstract [en]

    The Huber criterion for data fitting is a combination of thel 1 and thel 2 criteria which is robust in the sense that the influence of wild data points can be reduced. We present a trust region and a Marquardt algorithm for Huber estimation in the case where the functions used in the fit are non-linear. It is demonstrated that the algorithms converge under the usual conditions.

  • 30. Ekblom, Håkan
    et al.
    Nielsen, Hans Bruun
    Technical University of Denmark.
    Computing M-Estimates1996In: COMPSTAT [1996]: proceedings in computational statistics ; 12th symposium held in Barcelona, Spain, 1996 / [ed] Albert Prat, Heidelberg: Physica-Verlag Rudolf Liebig GmbH , 1996, p. 247-252Conference paper (Refereed)
  • 31.
    Fabricius, John
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Manjate, Salvador
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science. Department of Mathematics and Informatics, Eduardo Mondlane University, Av. Julius Nyerere, 3453 Maputo, Mozambique.
    Wall, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Error estimates for pressure-driven Hele-Shaw flow2022In: Quarterly of Applied Mathematics, ISSN 0033-569X, E-ISSN 1552-4485, Vol. 80, no 3, p. 575-595Article in journal (Refereed)
    Abstract [en]

    We consider Stokes flow past cylindrical obstacles in a generalized Hele-Shaw cell, i.e. a thin three-dimensional domain confined between two surfaces. The flow is assumed to be driven by an external pressure gradient, which is modeled as a normal stress condition on the lateral boundary of the cell. On the remaining part of the boundary we assume that the velocity is zero. We derive a divergence-free (volume preserving) approximation of the flow by studying its asymptotic behavior as the thickness of the domain tends to zero. The approximation is verified by error estimates for both the velocity and pressure in H1- and L2-norms, respectively.

  • 32.
    Ghorbani, Mohammad
    Department of Mathematical Sciences, Aalborg University, Aalborg, Denmark.
    Cauchy cluster process2013In: Metrika (Heidelberg), ISSN 0026-1335, E-ISSN 1435-926X, Vol. 76, no 5, p. 697-706Article in journal (Refereed)
    Abstract [en]

    In this paper we introduce an instance of the well-know Neyman–Scott cluster process model with clusters having a long tail behaviour. In our model the offspring points are distributed around the parent points according to a circular Cauchy distribution. Using a modified Cramér-von Misses test statistic and the simulated pointwise envelopes it is shown that this model fits better than the Thomas process to the frequently analyzed long-leaf pine data-set.

  • 33. Ghorbani, Mohammad
    Maximum Entropy-Based Fuzzy Clustering by Using L_1-norm Space2005In: Turkish Journal of Mathematics, ISSN 1300-0098, E-ISSN 1303-6149, Vol. 29, no 4, article id 9Article in journal (Refereed)
  • 34.
    Ghorbani, Mohammad
    Department of Mathematical Sciences, Aalborg University, Aalborg, Denmark.
    Testing the weak stationarity of a spatio-temporal point process2013In: Stochastic environmental research and risk assessment (Print), ISSN 1436-3240, E-ISSN 1436-3259, Vol. 27, no 2, p. 517-524Article in journal (Refereed)
    Abstract [en]

    A common assumption in analyzing spatial and spatio-temporal point processes is stationarity, while in many real applications because of the environmental effects the stationarity condition is not often met. We propose two types of test statistics to test stationarity for spatio-temporal point processes, by adapting, Palahi, Pukkala & Mateu (2009) and by considering the square difference between observed and expected (under stationarity) intensities. We study the efficiency of the new statistics by simulated data, and we apply them to test the stationarity of real data.

  • 35.
    Ghorbani, Mohammad
    et al.
    Department of mathematics and mathematical statistics, Umeå University, Sweden.
    Mateu, Jorge
    Department of Mathematics, Jaume I University, Castellón, Spain.
    A new class of spatial covariance functions generated by higher-order kernelsManuscript (preprint) (Other academic)
  • 36.
    Ghorbani, Mohammad
    et al.
    Department of Mathematics and Mathematical Statistics, Umeå University, Sweden.
    Vafaei, Nafiseh
    Department of Computer and Statistics Sciences, Faculty of Sciences, Mohaghegh Ardabili University, Ardabil, Iran.
    Dvořák, Jiří
    Department of Probability and Mathematical Statistics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic.
    Myllymäki, Mari
    Natural Resources Institute Finland (Luke), Helsinki, Finland.
    Testing the first-order separability hypothesis for spatio-temporal point patterns2021In: Computational Statistics & Data Analysis, ISSN 0167-9473, E-ISSN 1872-7352, Vol. 161, article id 107245Article in journal (Refereed)
    Abstract [en]

    First-order separability of a spatio-temporal point process plays a fundamental role in the analysis of spatio-temporal point pattern data. While it is often a convenient assumption that simplifies the analysis greatly, existing non-separable structures should be accounted for in the model construction. Three different tests are proposed to investigate this hypothesis as a step of preliminary data analysis. The first two tests are exact or asymptotically exact for Poisson processes. The first test based on permutations and global envelopes allows one to detect at which spatial and temporal locations or lags the data deviate from the null hypothesis. The second test is a simple and computationally cheap X2-test. The third test is based on stochastic reconstruction method and can be generally applied for non-Poisson processes. The performance of the first two tests is studied in a simulation study for Poisson and non-Poisson models. The third test is applied to the real data of the UK 2001 epidemic foot and mouth disease.

  • 37.
    Grip, Niklas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Sabourova, Natalia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Simple non-iterative calibration for triaxial accelerometers2011Report (Other academic)
  • 38.
    Gustafsson, Silje
    et al.
    Luleå University of Technology, Department of Health Sciences, Nursing Care.
    Martinsson, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Välivaara, Britt-Marie
    Luleå University of Technology, Department of Health Sciences, Nursing Care.
    Vikman, Irene
    Luleå University of Technology, Department of Health Sciences, Health and Rehabilitation.
    Sävenstedt, Stefan
    Luleå University of Technology, Department of Health Sciences, Nursing Care.
    Influence of self-care advice on patient satisfaction and healthcare utilization2016In: Journal of Advanced Nursing, ISSN 0309-2402, E-ISSN 1365-2648, Vol. 72, no 8, p. 1789-1799Article in journal (Refereed)
    Abstract [en]

    AimThe aim of this study is to explore the influence of nurse-led self-care advice on healthcare utilization and patients' satisfaction with telephone nursing.BackgroundMany consultations in high-cost settings are for conditions that are manageable through self-care and callers with greater satisfaction with the nurse interaction are nearly four times more likely to engage in self-care.DesignCross-sectional study.MethodsQuestionnaires were sent out to 500 randomly selected callers to the Swedish Healthcare Direct in Northern Sweden during March 2014. Callers were asked about their satisfaction with the consultation, their intended actions prior to consultation, the recommendation given by the nurse and the action undertaken after the call.ResultsYoung callers and persons recommended watchful waiting or recurrence if no improvements were significantly less satisfied with their care. When calling on their own behalf, both men and women rated the severity of their symptoms equally and were advised to self-care to the same extent. Self-care advice had a constricting influence on self-reported healthcare utilization, with 66·1% of cases resulting in a lower level of care than first intended. Feeling reassured after the call was the aspect of nursing care that influenced satisfaction the most.ConclusionReceiving self-care advice rather than referral to a general practitioner influences patient satisfaction negatively. Feeling reassured after consultation is strongly related to satisfaction, which in turn has been found to increase the likelihood of engaging in self-care behaviour.

  • 39.
    Gustafsson, Silje
    et al.
    Luleå University of Technology, Department of Health Sciences, Nursing Care.
    Sävenstedt, Stefan
    Luleå University of Technology, Department of Health Sciences, Nursing Care.
    Martinsson, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Välivaara, Britt-Marie
    Luleå University of Technology, Department of Health Sciences, Nursing Care.
    Need for reassurance in self-care of minor illnesses2018In: Journal of Clinical Nursing, ISSN 0962-1067, E-ISSN 1365-2702, Vol. 27, no 5-6, p. 1183-1191Article in journal (Refereed)
    Abstract [en]

    AIMS AND OBJECTIVES:

    This study describes people's need for reassurance in self-care of minor illnesses.

    BACKGROUND:

    Self-care and active surveillance are advocated as important strategies to manage minor illnesses. Reassurance influences patient satisfaction and confidence in the practicing of self-care.

    DESIGN:

    This study is a descriptive and interpretive qualitative study.

    METHODS:

    Twelve persons with experience in self-care and receiving self-care advice were recruited, and data were collected using semi-structured interviews between September and December 2014. Data were analyzed using qualitative content analyses.

    RESULTS:

    Having previous experience and the ability to actively manage symptoms using self-care interventions was described as reassuring. Participants became stressed and concerned when the symptoms persisted and interventions lacked the desired effect, which often resulted in a decision to consult. Participants wanted to feel that the nurse was an actual person, who was sympathetic, present and understanding, when they received self-care advice. The nurse's assessment and reasoning of the symptoms facilitated care-seekers' assessments of risk, and clear and concrete advice on how to manage the symptoms exerted a calming effect. Patients needed to trust that the nurse understood their situation to embrace the advice, and being invited to return created a feeling that the nurse had listened and taken them seriously.

    CONCLUSION:

    Reassurance has the potential to allay doubts and fears to build confidence, which influences self-care and consultation behavior. Personal presence in the encounter, receiving an assessment and an explanation of the symptoms and precise advice are reassuring. This article is protected by copyright. All rights reserved.

  • 40.
    Gustafsson, Silje
    et al.
    Luleå University of Technology, Department of Health Sciences, Nursing Care.
    Vikman, Irene
    Luleå University of Technology, Department of Health Sciences, Health and Rehab.
    Sävenstedt, Stefan
    Luleå University of Technology, Department of Health Sciences, Nursing Care.
    Martinsson, Jesper
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Perceptions of needs related to the practice of self-care for minor illness2015In: Journal of Clinical Nursing, ISSN 0962-1067, E-ISSN 1365-2702, Vol. 24, no 21-22, p. 3255-3265Article in journal (Refereed)
    Abstract [en]

    Aims and objectivesThe aim of this study was to describe people's perceptions of needs to feel confident in self-care for minor illnesses as well as their perceptions about supporting and obstructing factors in the practice of self-care.BackgroundMinor illness constitutes a large part of primary care, and patients' attendance to doctors' appointments for minor illness has been seen to increase future attendance for the same condition. Almost half of the consultations with telenurses result in the provision of self-care advice.DesignA cross-sectional survey.MethodPrimary data were collected using a questionnaire, and the study participants (n = 315) were randomly selected from the national Swedish address register.ResultsHaving knowledge and receiving health care advice and reliable information were perceived to be needs in order for participants to feel confident in self-care. Having family or friends to consult with was perceived to be a positive factor influencing confidence in self-care, especially for persons under the age of 35. Health care services were perceived to support self-care practice by offering easy access to care, giving information about self-care, and offering increased follow-up after consultations. Lack of knowledge, along with difficulties being away from work, were obstructing factors in the practice of self-care.ConclusionsYoung age was the factor influencing people's perceptions of needs and supporting factors the most. Young age and low knowledge scores about minor illnesses were the two factors that had the most influence on perceived obstructing factors.Relevance to clinical practiceNurses play a major role in the promotion of self-care and in the dissemination of self-care advice. If health care services fail to meet the needs of care-seekers with minor illnesses, patients might turn to out-of-hours clinics and emergency departments for help.

  • 41.
    Hamodi, Hussan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Lundberg, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Jonsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Economic lifetime of a drilling machine: a case study on mining industry2015In: International Journal of Strategic Engineering Asset Management (IJSEAM), ISSN 1759-9733, E-ISSN 1759-9741, Vol. 2, no 2, p. 177-189Article in journal (Refereed)
    Abstract [en]

    Underground mines use many different types of machinery duringthe drift mining processes of drilling, charging, blasting, loading, scaling andbolting. Drilling machines play a critical role in the mineral extraction processand thus are important economically. However, as the machines age, theirefficiency and effectiveness decrease, negatively affecting productivity andprofitability and increasing total cost. Hence, the economic replacementlifetime of the machine is a key performance indicator. This paper introducesan optimisation model that gives the optimal lifetime for a drilling machine. Acase study has been done at an underground Swedish mine to identify theeconomic replacement time of a drilling machine. It considers the purchaseprice, maintenance and operation costs, and the machine’s second-hand value.Findings show that the economic replacement lifetime of a drilling machine inthis mine is 96 months. The proposed model can be used for other undergroundmining machines.

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  • 42.
    Hamodi, Hussan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics. Mechanical engineering Department, College of Engineering University of Mosul, Mosul, Iraq.
    Lundberg, Jan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Jonsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Economic lifetime of a drilling machine: a case study on mining industry2013In: MPMM 2013 (Maintenance Performance Measurement and Management) / [ed] sari Monto; Miia Pirttilä; Timo Kärri, Lappeenranta, Finland: MPMM 2013 , 2013, p. 138-147Conference paper (Refereed)
    Abstract [en]

    Underground mines use many different types of machinery during the drift mining processesof drilling, charging, blasting, loading, scaling and bolting. Drilling machines play a criticalrole in the mineral extraction process and thus are important economically. However, as themachines age, their efficiency and effectiveness decrease, negatively affecting productivityand profitability and increasing total cost. Hence, the economic replacement lifetime of themachine is a key performance indicator. This paper introduces an optimisation model thatgives the optimal lifetime for a drilling machine. A case study has been done at anunderground Swedish mine to identify the economic replacement time of a drilling machine.It considers the purchase price, maintenance and operation costs, and the machine’s secondhandvalue. Findings show that the economic replacement lifetime of a drilling machine inthis mine is 96 months. The proposed model can be used for other underground miningmachines.

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  • 43.
    Hubele, Norma Faris
    et al.
    Arizona State University.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    The effect of pooled and un-pooled variance estimators on Cpm when using subsamples2004In: Journal of QualityTechnology, ISSN 0022-4065, Vol. 36, no 2, p. 207-222Article in journal (Refereed)
    Abstract [en]

    The vast majority of research on capability indices has assumed that the data consists of one large, representative sample. In practice, and in much of the quality control literature, process data are collected over time in subsamples representing rational subgroups. In this paper we examine the statistical behavior of two Cpm estimators based on this more realistic data structure. The estimators correspond to pooled and un-pooled variance estimators. The theoretical findings are applied to hypothesis testing and power calculations.The power functions of the tests based on the two estimators are used to determine the minimum number of subsamples needed to meet a threshold requirement that power exceeds 0.80. Extensive tables of the recommended number of subsamples are provided with comments on their usage

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  • 44.
    Ingri, Johan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Vännman, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Vattenmonitoringteknik1997Other (Other (popular science, discussion, etc.))
  • 45.
    Jagers, Sverker
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences. Department of Political Science, University of Gothenburg.
    Martinsson, Johan
    Department of Political Science, University of Gothenburg, Gothenburg.
    Matti, Simon
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences. Centre for Collective Action Research (CeCAR), University of Gothenburg.
    The impact of compensatory measures on public support for carbon taxation: an experimental study in Sweden2019In: Climate Policy, ISSN 1469-3062, E-ISSN 1752-7457, Vol. 19, no 2, p. 147-160Article in journal (Refereed)
    Abstract [en]

    This study aims at better understanding how, and to what extent, perceptions of a policy instrument’s distributional effects impact on policy support, focusing on the case of CO2 taxes on petrol in Sweden. Through a large-scale (N = 5000) randomized survey experiment with a 2 × 3 factorial design, the extent to which perceptions of fairness determine attitudes to a suggested increase of the Swedish CO2 tax is explored. Furthermore, the study considers whether these effects change with the level of the suggested tax increase, as well as whether negative sentiments can be alleviated by combining it with a compensatory measure in the shape of a simultaneous income tax cut financed by the revenues from the tax increase. The results show that a higher tax increase is both viewed as more unfair and enjoys weaker support. Furthermore, compensatory measures can be a powerful policy design tool to increase perceptions of the policy as fair, but the effect of compensation on policy support is conditioned by the individual’s left–right ideological position. Whereas people self-identifying to the right react favourably to compensatory measures, people self-identifying to the left become less supportive of a tax increase when combined with a simultaneous cut in income taxes.

  • 46.
    Jamei, Mehdi
    et al.
    Engineering Faculty, Shohadaye Hoveizeh Campus of Technology, Shahid Chamran University of Ahvaz, Dashte Azadegan, Iran.
    Bailek, Nadjem
    Energies and Materials Research Laboratory, Department of Matter Sciences, Faculty of Sciences and Technology, University of Tamanghasset, Tamanghasset, Algeria.
    Bouchouicha, Kada
    Unité de Recherche en Energies Renouvelables en Milieu Saharien (URERMS),Centre de Développement des Energies Renouvelables (CDER), 01000, Adrar, Algeria.
    Hassan, Muhammed A.
    Mechanical Power Engineering Department, Faculty of Engineering, Cairo University, Giza, 12613, Giza, Egypt.
    Elbeltagi, Ahmed
    Agricultural Engineering Department, Faculty of Agriculture, Mansoura University, Mansoura, 35516, Egypt.
    Kuriqi, Alban
    CERIS, Instituto Superior Técnico,Universidade de Lisboa, Lisbon, Portugal.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Almorox, Javier
    Universidad Politécnica de Madrid,UPM, Avd., Puerta de Hierro, 28040, Madrid, Spain.
    El-kenawy, El-Sayed M.
    Department of Communications and Electronics, Delta Higher Institute of Engineering and Technology, Mansoura, 35111, Egypt; Faculty of Artificial Intelligence, Delta University for Science and Technology, Mansoura, 35712, Egypt.
    Data-Driven Models for Predicting Solar Radiation in Semi-Arid Regions2023In: Computers, Materials and Continua, ISSN 1546-2218, E-ISSN 1546-2226, Vol. 74, no 1, p. 1625-1640Article in journal (Refereed)
    Abstract [en]

    Solar energy represents one of the most important renewable energy sources contributing to the energy transition process. Considering that the observation of daily global solar radiation (GSR) is not affordable in some parts of the globe, there is an imperative need to develop alternative ways to predict it. Therefore, the main objective of this study is to evaluate the performance of different hybrid data-driven techniques in predicting daily GSR in semi-arid regions, such as the majority of Spanish territory. Here, four ensemble-based hybrid models were developed by hybridizing Additive Regression (AR) with Random Forest (RF), Locally Weighted Linear Regression (LWLR), Random Subspace (RS), and M5P. The base algorithms of the developed models are scarcely applied in previous studies to predict solar radiation. The testing phase outcomes demonstrated that the AR-RF models outperform all other hybrid models. The provided models were validated by statistical metrics, such as the correlation coefficient (R) and root mean square error (RMSE). The results proved that Scenario #6, utilizing extraterrestrial solar radiation, relative humidity, wind speed, and mean, maximum, and minimum ambient air temperatures as the model inputs, leads to the most accurate predictions among all scenarios (R = 0.968–0.988 and RMSE = 1.274–1.403 MJ/m2⋅d). Also, Scenario #3 stood in the next rank of accuracy for predicting the solar radiation in both validating stations. The AD-RF model was the best predictive, followed by AD-RS and AD-LWLR. Hence, this study recommends new effective methods to predict GSR in semi-arid regions.

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  • 47.
    Jonsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    An axiomatic approach to Markov decision processes2023In: Mathematical Methods of Operations Research, ISSN 1432-2994, E-ISSN 1432-5217, Vol. 97, no 1, p. 117-133Article in journal (Refereed)
    Abstract [en]

    This paper presents an axiomatic approach to finite Markov decision processes where the discount rate is zero. One of the principal difficulties in the no discounting case is that, even if attention is restricted to stationary policies, a strong overtaking optimal policy need not exists. We provide preference foundations for two criteria that do admit optimal policies: 0-discount optimality and average overtaking optimality. As a corollary of our results, we obtain conditions on a decision maker's preferences which ensure that an optimal policy exists. These results have implications for disciplines where dynamic programming problems arise, including automatic control, dynamic games, and economic development. 

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  • 48.
    Jonsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Infinite utility: counterparts and ultimate locationsManuscript (preprint) (Other academic)
    Abstract [en]

    The locations problem in infinite ethics concerns the relative moral status of different categories of potential bearers of value, the primary examples of which are people and points in time. The challenge is to determine which category of value bearers are of ultimate moral significance: the ultimate locations, for short. This paper defends the view that the ultimate locations are people at times. A person at a time is not a specific person, but the person born at a specific point in time (de dicto). The main conclusion of the paper is that the unsettling implications of the time- and person-centered approaches to infinite ethics can be avoided by taking people at times as the ultimate locations. Most notably, a broad class of worlds that are incomparable using the person-centered approach can be strictly ranked. 

  • 49.
    Jonsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Invariant sets for QMF functions2018In: Rocky Mountain Journal of Mathematics, ISSN 0035-7596, E-ISSN 1945-3795, Vol. 48, no 8, p. 2559-2571Article in journal (Refereed)
    Abstract [en]

    A quadrature mirror filter (QMF) function can be considered as the transition function for a Markov process on the unit interval. The QMF functions that generate scaling functions for multiresolution analyses are then distinguished by properties of their invariant sets. By characterizing these sets, we answer in the affirmative a question raised by Gundy.

  • 50.
    Jonsson, Adam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    On g-functions for countable state subshifts2017In: Archiv der Mathematik, ISSN 0003-889X, E-ISSN 1420-8938, Vol. 109, no 4, p. 373-381Article in journal (Refereed)
    Abstract [en]

    This note revisits the problem of finding necessary and sufficient conditions for a subshift to admit a continuous g-function. Results obtained by Krieger (in: IMS lecture notes monograph series, vol 48, pp 306-316, 2006) on finite alphabet subshifts are generalized to countable state subshifts.

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