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  • 1.
    Helgesson, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. Nucl Res & Consultancy Grp NRG, Petten, Netherlands.
    Sjöstrand, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Arjan, J. Koning
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. Nucl Res & Consultancy Grp NRG, Petten, Netherlands.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Rochman, Dimitri
    PSI, Villigen, Switzerland.
    Alhassan, Erwin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Pomp, Stephan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Combining Total Monte Carlo and Unified Monte Carlo: Bayesian nuclear data uncertainty quantification from auto-generated experimental covariances2017In: Progress in nuclear energy (New series), ISSN 0149-1970, E-ISSN 1878-4224, Vol. 96, p. 76-96Article in journal (Refereed)
    Abstract [en]

    The Total Monte Carlo methodology (TMC) for nuclear data (ND) uncertainty propagation has been subject to some critique because the nuclear reaction parameters are sampled from distributions which have not been rigorously determined from experimental data. In this study, it is thoroughly explained how TMC and Unified Monte Carlo-B (UMC-B) are combined to include experimental data in TMC. Random ND files are weighted with likelihood function values computed by comparing the ND files to experimental data, using experimental covariance matrices generated from information in the experimental database EXFOR and a set of simple rules. A proof that such weights give a consistent implementation of Bayes' theorem is provided. The impact of the weights is mainly studied for a set of integral systems/applications, e.g., a set of shielding fuel assemblies which shall prevent aging of the pressure vessels of the Swedish nuclear reactors Ringhals 3 and 4.

    In this implementation, the impact from the weighting is small for many of the applications. In some cases, this can be explained by the fact that the distributions used as priors are too narrow to be valid as such. Another possible explanation is that the integral systems are highly sensitive to resonance parameters, which effectively are not treated in this work. In other cases, only a very small number of files get significantly large weights, i.e., the region of interest is poorly resolved. This convergence issue can be due to the parameter distributions used as priors or model defects, for example.

    Further, some parameters used in the rules for the EXFOR interpretation have been varied. The observed impact from varying one parameter at a time is not very strong. This can partially be due to the general insensitivity to the weights seen for many applications, and there can be strong interaction effects. The automatic treatment of outliers has a quite large impact, however.

    To approach more justified ND uncertainties, the rules for the EXFOR interpretation shall be further discussed and developed, in particular the rules for rejecting outliers, and random ND files that are intended to describe prior distributions shall be generated. Further, model defects need to be treated.

  • 2.
    Helgesson, Petter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Sjöstrand, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    J. Koning, Arjan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. IAEA.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Rochman, Dimitri
    Paul Scherrer Institute PSI, Villigen, Switzerland.
    Alhassan, Erwin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Pomp, Stephan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Sampling of systematic errors to estimate likelihood weights in nuclear data uncertainty propagation2016In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 807, p. 137-149Article in journal (Refereed)
    Abstract [en]

    In methodologies for nuclear data (ND) uncertainty assessment and propagation based on random sampling, likelihood weights can be used to infer experimental information into the distributions for the ND. As the included number of correlated experimental points grows large, the computational time for the matrix inversion involved in obtaining the likelihood can become a practical problem. There are also other problems related to the conventional computation of the likelihood, e.g., the assumption that all experimental uncertainties are Gaussian. In this study, a way to estimate the likelihood which avoids matrix inversion is investigated; instead, the experimental correlations are included by sampling of systematic errors. It is shown that the model underlying the sampling methodology (using univariate normal distributions for random and systematic errors) implies a multivariate Gaussian for the experimental points (i.e., the conventional model). It is also shown that the likelihood estimates obtained through sampling of systematic errors approach the likelihood obtained with matrix inversion as the sample size for the systematic errors grows large. In studied practical cases, it is seen that the estimates for the likelihood weights converge impractically slowly with the sample size, compared to matrix inversion. The computational time is estimated to be greater than for matrix inversion in cases with more experimental points, too. Hence, the sampling of systematic errors has little potential to compete with matrix inversion in cases where the latter is applicable. Nevertheless, the underlying model and the likelihood estimates can be easier to intuitively interpret than the conventional model and the likelihood function involving the inverted covariance matrix. Therefore, this work can both have pedagogical value and be used to help motivating the conventional assumption of a multivariate Gaussian for experimental data. The sampling of systematic errors could also be used in cases where the experimental uncertainties are not Gaussian, and for other purposes than to compute the likelihood, e.g., to produce random experimental data sets for a more direct use in ND evaluation.

  • 3. Jonsson, Fredrik
    et al.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Statistical studies of the Beta Gumbel distribution: estimation of extreme levels of precipitation2017In: Statistica Applicata, Vol. 29, p. 5-27Article in journal (Refereed)
  • 4. Lindgren, Georg
    et al.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Transfer-function approximations of the rainflow filter2002In: Mechanical Systems and Signal Processing, Vol. 16, p. 979-989Article in journal (Refereed)
    Abstract [en]

    The rainflow filter is a non-linear filter which can be used to eliminate small-amplitude oscillations in a signal. In this paper, two approaches for investigation of the filter by means of an approximating transfer function are presented. The estimates are obtained from rainflow-filtered spectral simulations. One method is based on clipped Gaussian processes, the other uses a spline interpolation in the filtered time series. Examples are given for processes with different types of spectral densities. A certain reduction of small-amplitude cycles is obtained by use of the transfer function, but the threshold effect, characteristic for the rainflow filter, is missed.

  • 5.
    Munkhammar, Joakim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mattsson, Lars
    Nordita, Stockholms University.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Polynomial probability distribution estimation using the method of moments2017In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 4, p. 1-14, article id e0174573Article in journal (Refereed)
    Abstract [en]

    We suggest a procedure for estimating Nth degree polynomial approximations to unknown (or known) probability density functions (PDFs) based on N statistical moments from each distribution. The procedure is based on the method of moments and is setup algorithmically to aid applicability and to ensure rigor in use. In order to show applicability, polynomial PDF approximations are obtained for the distribution families Normal, Log-Normal, Weibull as well as for a bimodal Weibull distribution and a data set of anonymized household electricity use. The results are compared with results for traditional PDF series expansion methods of Gram–Charlier type. It is concluded that this procedure is a comparatively simple procedure that could be used when traditional distribution families are not applicable or when polynomial expansions of probability distributions might be considered useful approximations. In particular this approach is practical for calculating convolutions of distributions, since such operations become integrals of polynomial expressions. Finally, in order to show an advanced applicability of the method, it is shown to be useful for approximating solutions to the Smoluchowski equation.

  • 6.
    Munkhammar, Joakim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Widen, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Characterizing probability density distributions for household electricity load profiles from high-resolution electricity use data2014In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 135, p. 382-390Article in journal (Refereed)
    Abstract [en]

    This paper presents a high-resolution bottom-up model of electricity use in an average household based on fit to probability distributions of a comprehensive high-resolution household electricity use data set for detached houses in Sweden. The distributions used in this paper are the Weibull distribution and the Log-Normal distribution. These fitted distributions are analyzed in terms of relative variation estimates of electricity use and standard deviation. It is concluded that the distributions have a reasonable overall goodness of fit both in terms of electricity use and standard deviation. A Kolmogorov-Smirnov test of goodness of fit is also provided. In addition to this, the model is extended to multiple households via convolution of individual electricity use profiles. With the use of the central limit theorem this is analytically extended to the general case of a large number of households. Finally a brief comparison with other models of probability distributions is made along with a discussion regarding the model and its applicability.

  • 7.
    Munkhammar, Joakim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lingfors, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Simulating dispersed photovoltaic power generation using a bimodal mixture model of the clear-sky index2015Conference paper (Refereed)
    Abstract [en]

    Improved probability distribution models for power generation are useful e.g. forprobabilistic power flow simulations. This paper presents a distribution modelfor photovoltaic (PV) power generation based on the clear-sky index.With the use of minute-resolution data on globalhorizontal irradiation (GHI) we fit unimodal normal,bimodal normal and trimodal normal mixture distributionfamilies to the clear-sky index. Based on Kolmogorov-Smirnov (K-S) teststhe best fit distribution family consisting of a bimodal normal distribution isthen used for estimating an aggregate clear-sky index for multipledispersed locations that are assumed to be uncorrelated in terms of sky clearness.For five or more locations the aggregate clear-sky indexfollows a normal distribution due to the central limit theorem.Models for solar radiation on tilted planes and PV power generation areapplied to the clear-sky index to generate probability distributions for anarbitrary PV system.

  • 8.
    Munkhammar, Joakim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Grahn, Pia
    KTH.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    A Bernoulli Distribution Model for Plug-in Electric Vehicle Charging based on Time-use Data for Driving Patterns2014In: Proceedings of IEEE International Electric Vehicle Conference (IEVC), 2014Conference paper (Refereed)
    Abstract [en]

    This paper presents a Bernoulli distribution model for plug-in electric vehicle (PEV)charging based on high resolution activity data for Swedish drivingpatterns. Based on the activity ``driving vehicle" from a time diary studya Monte Carlo simulation is made of PEV state of chargewhich is then condensed down to Bernoulli distributions representingcharging for each hour during weekday and weekend day. Thesedistributions are then used as a basis for simulations of PEVcharging patterns. Results regarding charging patterns for a numberof different PEV parameters are shown along with a comparison with resultsfrom a different stochastic model for PEV charging. A convergence test forMonte Carlo simulations of the distributions is also provided.In addition to this we show that multiple PEV charging patterns are representedby Binomial distributions via convolution ofBernoulli distributions. Also the distribution for aggregatecharging of many PEVs is shown to be normally distributed. Finally a fewremarks regarding the applicability of the model are given along witha discussion on potential extensions.

  • 9.
    Munkhammar, Joakim
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Widén, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    On a probability distribution model combining household power consumption, electric vehicle home-charging and photovoltaic power production2015In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 142, p. 135-143Article in journal (Refereed)
    Abstract [en]

    In this paper we develop a probability distribution model combining household power consumption, electric vehicle (EV) home-charging and photovoltaic (PV) power production. The model is set up using a convolution approach to merge three separate existing probability distribution models for household electricity use, EV home-charging and PV power production. This model is investigated on two system levels: household level and aggregate level of multiple households. Results for the household level show the power consumption/production mismatch as probability distributions for different time bins. This is further investigated with different levels of PV power production. The resulting yearly distribution of the aggregate scenario of multiple uncorrelated households with EV charging and PV power production is shown to not be normally distributed due to the mismatch of PV power production and household power consumption on a diurnal and annual basis.

  • 10.
    Nedelcu, Robert
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Oral and Maxillofacial Surgery.
    Olsson, Pontus
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Nyström, Ingela
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction. Uppsala Univ, Dept Informat Technol, Ctr Image Anal, Box 337, S-75105 Uppsala, Sweden..
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Thor, Andreas
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Oral and Maxillofacial Surgery.
    Accuracy and precision of 3 intraoral scanners and accuracy of conventional impressions: A novel in vivo analysis method2018In: Journal of Dentistry, ISSN 0300-5712, E-ISSN 1879-176X, Vol. 69, p. 110-118Article in journal (Refereed)
    Abstract [en]

    Objective: To evaluate a novel methodology using industrial scanners as a reference, and assess in vivo accuracy of 3 intraoral scanners (IOS) and conventional impressions. Further, to evaluate IOS precision in vivo.

    Methods: Four reference-bodies were bonded to the buccal surfaces of upper premolars and incisors in five subjects. After three reference-scans, ATOS Core 80 (ATOS), subjects were scanned three times with three IOS systems: 3M True Definition (3M), CEREC Omnicam (OMNI) and Trios 3 (TRIOS). One conventional impression (IMPR) was taken, 3M Impregum Penta Soft, and poured models were digitized with laboratory scanner 3shape D1000 (D1000). Best-fit alignment of reference-bodies and 3D Compare Analysis was performed. Precision of ATOS and D1000 was assessed for quantitative evaluation and comparison. Accuracy of IOS and IMPR were analyzed using ATOS as reference. Precision of IOS was evaluated through intra-system comparison.

    Results: Precision of ATOS reference scanner (mean 0.6 mu m) and D1000 (mean 0.5 mu m) was high. Pairwise multiple comparisons of reference-bodies located in different tooth positions displayed a statistically significant difference of accuracy between two scanner-groups: 3M and TRIOS, over OMNI (p value range 0.0001 to 0.0006). IMPR did not show any statistically significant difference to IOS. However, deviations of IOS and IMPR were within a similar magnitude. No statistical difference was found for IOS precision.

    Conclusion: The methodology can be used for assessing accuracy of IOS and IMPR in vivo in up to five units bilaterally from midline. 3M and TRIOS had a higher accuracy than OMNI. IMPR overlapped both groups. Clinical significance: Intraoral scanners can be used as a replacement for conventional impressions when restoring up to ten units without extended edentulous spans.

  • 11.
    Olauson, Jon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bergkvist, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Simulating intra-hourly wind power fluctuations on a power system level2017In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 20, no 6, p. 973-985Article in journal (Refereed)
    Abstract [en]

    In wind integration studies, sub-hourly, load synchronous wind data are often preferable. These datasets can be generatedby a hybrid approach, combining hourly measurements or output from meteorological models with a stochastic simulationof the high-frequency fluctuations. This paper presents a method for simulating aggregated intra-hourly wind power fluc-tuations for a power system, taking into account the time-varying volatility seen in measurements. Some key elements inthe modelling were transformations to stationarity, the use of frequency domain techniques including a search for appropri-ate phase angles and an adjustment of the resulting time series in order to get correct hourly means. Generation data fromDenmark and Germany with 5 and 15 min temporal resolution were used for training models. It is shown that the distribu-tion and non-stationarity of simulated deviations from hourly means closely follow those of measurements. Power spectraldensities and step change distributions agree well. Of particular importance is that the results are good also when the train-ing and objective power systems are not the same. The computational cost is low in comparison with other approaches forgenerating high-frequency data.

  • 12.
    Olauson, Jon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Edström, Per
    Sweco.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Wind turbine performance decline in Sweden2017In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 20, no 12, p. 2049-2053Article in journal (Refereed)
    Abstract [en]

    We show that Swedish wind turbines constructed before 2007 lose 0.15 capacity factor percentage points per year, corresponding to a lifetime energy loss of 6%. A gradual increase of downtime accounts for around one third of the deterioration and worsened efficiency for the remaining. Although the performance loss in Sweden is considerably smaller than previously reported in the UK, it is statistically significant and calls for a revision of the industry practice for wind energy calculations. The study is based on two partly overlapping datasets, comprising 1,100 monthly and 1,300 hourly time series spanning 5–25 years each.

  • 13.
    Persson, Klara
    et al.
    Skandia.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Mathematical Statistics.
    Exponentiated Gumbel distribution for estimation of return levels of significant wave height2010In: Journal of Environmental Statistics, ISSN 1945-1296, Vol. 1, no 3, p. 1-12Article in journal (Refereed)
    Abstract [en]

    The exponentiated Gumbel (EG) distribution has been proposed as a generalization of the classical Gumbel distribution. In this paper we discuss estimation of T-year return values for significant wave height in a case study and compare point estimates and their uncertainties to the results given by alternative approaches using Gumbel or Generalized Extreme Value distributions. A jackknife approach is made to investigate the sensitivity of the parameter estimates and various model selection criteria are employed to compare the models. When examining Anderson–Darling distances between samples and extreme value distributions, the EG distribution turns out to give the closest fit. However, general recommendations whether to use Gumbel or EG distribution cannot be given.

  • 14. Rychlik, Igor
    et al.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Probability and Risk Analysis: An Introduction for Engineers2006Book (Other academic)
  • 15. Rychlik, Igor
    et al.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Mathematical Statistics.
    Anderson, Clive W.
    Estimation of return values for significant wave height from satellite data2011In: Extremes, ISSN 1386-1999, E-ISSN 1572-915X, Vol. 14, no 2, p. 167-186Article in journal (Refereed)
    Abstract [en]

    Estimation of extreme wave height across the oceans is important for marine safety and design, but is hampered by lack of data. Buoy and platform data are geographically limited, and though satellite observations offer global coverage, they suffer from temporal sparsity and intermittency, making application of standard methods of extreme value estimation problematical. A possible strategy in the face of such difficulty is to use extra model assumptions to compensate for lack of data. In this spirit we report initial exploration of an approach to estimation of extreme wave heights using crossings methods based on a log-Gaussian model. The suggested procedure can utilize either intermittent satellite data or regular time series data such as obtained from a buoy, and it is adapted to seasonal variation in the wave height climate. The paper outlines derivation of the method and illustrates its application to data from the Atlantic and Pacific oceans. A numerical comparison is made with the results of an annual maximum analysis for sites at which both satellite and buoy data are available. The paper concludes with a discussion of the applicability of the new approach, its relationship to other extreme value methods and desirable directions for further development.

  • 16.
    Ryden, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    A Statistical Analysis of Trends for Warm and Cold Spells in Uppsala by Means of Counts2015In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 97, no 3, p. 431-436Article in journal (Refereed)
    Abstract [en]

    Statistical studies of extremes are of interest in the climatic sciences, in particular trends of periods of unusually warm or cold weather, which could be labelled warm and cold spells, respectively. We study the yearly number of spells in Uppsala, Sweden which from a data-analytic point of view truly are counts, and employ theory and methods from the field of regression models for counts. A possible trend for the period 1840-2012 was investigated. The trend for warm spells is positive and demonstrated to be larger in magnitude compared with the one for cold spells, and is found to be statistically significant. The methodology could be extended to analyse other climate indicators.

  • 17.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    A note on asymptotic approximations of distributions for maxima of wave crests2006In: Stochastic Environmental Research and Risk Assessment, Vol. 20, no 4, p. 238-242Article in journal (Refereed)
    Abstract [en]

    The distribution of maxima during a given time interval is of interest in many applications in risk analysis. Within the framework of stationary Gaussian processes, several theoretical results considering asymptotics from different aspects have been derived for this distribution. In this note, we review results from the theory and study the accuracy of these approximations by exemplifying with a model for wave heights from oceanography. It turns out that for high values and the time periods normally encountered for buoy measurements, care should be taken in use of approximation based on the Gumbel distribution.

  • 18.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Aspects on estimation of return values for extreme wind speeds2006In: Proceedings of the 16th International Offshore and Polar Engineering Conference, San Francisco, 2006Conference paper (Refereed)
  • 19.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Estimation of return values of wave height: consequences of missing observations2008In: International journal of mathematical education in science and technology, ISSN 0020-739X, Vol. 39, no 3, p. 357-363Article in journal (Refereed)
    Abstract [en]

    Extreme-value statistics is often used to estimate so-called return values (actually related to quantiles) for environmental quantities like wind speed or wave height. A basic method for estimation is the method of block maxima which consists in partitioning observations in blocks, where maxima from each block could be considered independent. Typically a block could be chosen as one year. Large portions of missing data could result in problems for estimation and seems to be an issue not highlighted in detail in the literature. The method of block maxima is here applied to real data and a related simulation study was performed, pointing out that substantially low values tend to increase the estimated return values. A plausible explanation is given by studying the redistribution of probability mass and the implications of this for the behaviours of the tails of distributions.

  • 20.
    Rydén, Jesper
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Mathematics. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Mathematics, Mathematical Statistics.
    Exploring possibly increasing trend of hurricane activity by a SiZer approach2006Report (Other (popular scientific, debate etc.))
  • 21.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Mathematical Statistics.
    Exploring possibly increasing trend of hurricane activity by a SiZer approach2010In: Environmental and Ecological Statistics, ISSN 1352-8505, E-ISSN 1573-3009, Vol. 17, no 1, p. 125-132Article in journal (Refereed)
    Abstract [en]

    Statistical studies of hurricane activity in the North Atlantic basin are of current interest, not the least after the year of 2005 when many records were broken. An exploratory analysis of possibly increasing trend of the yearly number of hurricanes can be carried out by employing a graphic device, the SiZer map. Use of this method provides a useful complement to other statistical techniques for detection of trends or shifts in time series.

  • 22.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Extreme-value modelling: A preliminary analysis of monthly precipitation at Havana.2006In: Ingeniería Energética, ISSN 0253-5645, Vol. 27, no 1, p. 20-23Article in journal (Other academic)
  • 23.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Is a White Christmas becoming rarer in southern parts of Sweden?2015In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 121, no 1-2, p. 53-59Article in journal (Refereed)
    Abstract [en]

    The notion of White Christmas, for instance snow conditions at Christmas Day, is occasionally discussed among people in certain countries in the northern hemisphere. In this paper, the state of snow occurrence at Christmas Day at locations in Sweden are primarily considered binary events and methodology for statistical analysis of time series with binary responses is employed to investigate trend over time. None of the six locations studied showed a significant change over time.

  • 24.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Statistical analysis of golden-ratio forms in piano sonatas by Mozart and Haydn2007In: The Mathematical Scientist, ISSN 0312-3685, E-ISSN 1475-6080, Vol. 32, no 1, p. 1-5Article in journal (Refereed)
    Abstract [en]

    The golden ratio is occasionally referred to when describing issues of form in various arts. Among musicians, Mozart (1756–1791) is often considered a master of form. Introducing a regression model, we carry out a statistical analysis of possible golden-ratio forms in the musical works of Mozart. The model allows for statistical hypothesis testing and comparison with similar compositions by another master composer, Haydn (1732–1809), of the same epoch.

  • 25.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Mathematical Statistics.
    Statistical analysis of temperature extremes in long-time series from Uppsala2011In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 105, no 1-2, p. 193-197Article in journal (Refereed)
    Abstract [en]

    Temperature records in Uppsala, Sweden, during the period 1840-2001, are analysed. More precisely, yearly maxima and minima are studied in order to investigate possible trends. Extreme-value distributions are fitted, and a nonstationary model is introduced by allowing for a time-dependent location parameter. Comparisons are made with an estimated trend for mean temperature. In addition, a Mann-Kendall test is performed in order to investigate a present trend. The results obtained from the statistical models agree with those found earlier by descriptive statistics, in particular an increasing trend for the coldest days of the year.

  • 26.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Applied Mathematics and Statistics.
    Statistical modelling of warm-spell duration series using hurdle models2017In: SORT - Statistics and Operations Research Transactions, ISSN 1696-2281, Vol. 41, no 1, p. 177-188Article in journal (Refereed)
    Abstract [en]

    Regression models for counts could be applied to the earth sciences, for instance when studying trends of extremes of climatological quantities. Hurdle models are modified count models which can be regarded as mixtures of distributions. In this paper, hurdle models are applied to model the sums of lengths of periods of high temperatures. A modification to the common versions presented in the literature is presented, as left truncation as well as a particular treatment of zeros is needed for the problem. The outcome of the model is compared to those of simpler count models.

  • 27.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Mathematical Statistics.
    Statistical techniques for exploring possibly increasing trend of hurricane activity2011In: Recent Hurricane Research - Climate, Dynamics, and Societal Impacts / [ed] A. Lupo, InTech , 2011, p. 119-128Chapter in book (Other academic)
  • 28.
    Rydén, Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Stokastik för ingenjörer2015 (ed. 2)Book (Other academic)
  • 29.
    Rydén, Jesper
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Mathematical Statistics.
    Alm, Sven Erick
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Mathematical Statistics.
    The effect of interaction and rounding error in two-way ANOVA: example of impact on testing for normality2010In: Journal of Applied Statistics, ISSN 0266-4763, E-ISSN 1360-0532, Vol. 37, no 10, p. 1695-1701Article in journal (Refereed)
    Abstract [en]

    A key issue in various applications of analysis of variance (ANOVA) is testing for the interaction and the interpretation of resulting ANOVA tables. In this note it is demonstrated that for a two-way ANOVA, whether interactions are incorporated or not may have a dramatic influence when considering the usual statistical tests for normality of residuals. The effect of numerical rounding is also discussed.

  • 30.
    Rydén, Jesper
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Lindgren, Georg
    Frequency properties of the rainflow filter - some examples in oceanography2002In: Proceedings of the 4th International Symposium on Ocean Wave Measurement and Analysis, WAVES 2001, 2002Conference paper (Refereed)
  • 31.
    Rydén, Jesper
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Rychlik, Igor
    A note on estimation of intensitites of fire ignitions with incomplete data2006In: Fire Safety Journal, Vol. 41, no 5, p. 399-405Article in journal (Refereed)
    Abstract [en]

    Occurrences of fire ignitions in a given region during a specified period of time are modelled as outcomes of a Poisson point process. The ignition frequency is considered a function of the total floor area of the building. Parameter estimates and their uncertainties are computed. Different criteria for model selection are used. The proposed methodology is specifically useful in the case with small data sets or lack of information about the population at risk.

  • 32.
    Rydén, Jesper
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    van Iseghem, Sylvie
    Olagnon, Michel
    Rychlik, Igor
    Evaluating height–length joint distributions for the crests of ocean waves2002In: Applied Ocean Research, Vol. 24, p. 189-201Article in journal (Refereed)
    Abstract [en]

    The wavelength is an important quantity in a number of ocean-engineering applications, e.g. for design of structures that have dimensions of the same order of magnitude as the wavelength. Most often however, the description of the wave climate is given by a spectrum. We present a methodology based on a representation of a sea state in the frequency domain which returns the joint distribution of crest amplitudes and wavelengths. The method is validated with experimental empirical data, obtained by application of a technique based on Fourier transformation combined with use of the dispersion relation. The algorithm allows for investigation of the influence of spectral shape and directionality on the joint distribution; examples are given in the paper.

  • 33.
    Rydén, Jesper
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    van Iseghem, Sylvie
    Olagnon, Michel
    Rychlik, Igor
    Height-length joint distributions for computation of static wave loading on floating bodies2002In: Proceedings of the 12th International Offshore and Polar Engineering Conference, Kitakyushu, 2002Conference paper (Refereed)
1 - 33 of 33
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