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Publications (10 of 33) Show all publications
Nedelcu, R., Olsson, P., Nyström, I., Rydén, J. & Thor, A. (2018). Accuracy and precision of 3 intraoral scanners and accuracy of conventional impressions: A novel in vivo analysis method. Journal of Dentistry, 69, 110-118
Open this publication in new window or tab >>Accuracy and precision of 3 intraoral scanners and accuracy of conventional impressions: A novel in vivo analysis method
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2018 (English)In: Journal of Dentistry, ISSN 0300-5712, E-ISSN 1879-176X, Vol. 69, p. 110-118Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
ELSEVIER SCI LTD, 2018
Keywords
Digital impression, Intraoral scanner, Polyether impression, Accuracy, Precision, In vivo
National Category
Dentistry
Identifiers
urn:nbn:se:uu:diva-349829 (URN)10.1016/j.jdent.2017.12.006 (DOI)000425888000014 ()29246490 (PubMedID)
Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2018-05-07Bibliographically approved
Helgesson, P., Sjöstrand, H., Arjan, J. K., Rydén, J., Rochman, D., Alhassan, E. & Pomp, S. (2017). Combining Total Monte Carlo and Unified Monte Carlo: Bayesian nuclear data uncertainty quantification from auto-generated experimental covariances. Progress in nuclear energy (New series), 96, 76-96
Open this publication in new window or tab >>Combining Total Monte Carlo and Unified Monte Carlo: Bayesian nuclear data uncertainty quantification from auto-generated experimental covariances
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2017 (English)In: Progress in nuclear energy (New series), ISSN 0149-1970, E-ISSN 1878-4224, Vol. 96, p. 76-96Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Nuclear data, Uncertainty propagation, Total Monte Carlo, Experimental correlations, Unified Monte Carlo
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-313644 (URN)10.1016/j.pnucene.2016.11.006 (DOI)000392676800007 ()
Available from: 2017-01-23 Created: 2017-01-23 Last updated: 2018-04-16Bibliographically approved
Munkhammar, J., Mattsson, L. & Rydén, J. (2017). Polynomial probability distribution estimation using the method of moments. PLoS ONE, 12(4), 1-14, Article ID e0174573.
Open this publication in new window or tab >>Polynomial probability distribution estimation using the method of moments
2017 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 4, p. 1-14, article id e0174573Article in journal (Refereed) Published
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.

National Category
Probability Theory and Statistics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-319998 (URN)10.1371/journal.pone.0174573 (DOI)000399954800004 ()28394949 (PubMedID)
Funder
Swedish Energy AgencySwedish Research Council, 2015-04505
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-11-29Bibliographically approved
Olauson, J., Bergkvist, M. & Rydén, J. (2017). Simulating intra-hourly wind power fluctuations on a power system level. Wind Energy, 20(6), 973-985
Open this publication in new window or tab >>Simulating intra-hourly wind power fluctuations on a power system level
2017 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 20, no 6, p. 973-985Article in journal (Refereed) Published
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.

Keywords
Wind power, Sub-hourly fluctuations, Simulation, FFT, Power system studies
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-302826 (URN)10.1002/we.2074 (DOI)000400860700003 ()
Funder
Swedish Civil Contingencies Agency, 2010-2787
Available from: 2016-09-10 Created: 2016-09-10 Last updated: 2017-07-07Bibliographically approved
Rydén, J. (2017). Statistical modelling of warm-spell duration series using hurdle models. SORT - Statistics and Operations Research Transactions, 41(1), 177-188
Open this publication in new window or tab >>Statistical modelling of warm-spell duration series using hurdle models
2017 (English)In: SORT - Statistics and Operations Research Transactions, ISSN 1696-2281, Vol. 41, no 1, p. 177-188Article in journal (Refereed) Published
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.

National Category
Probability Theory and Statistics
Research subject
Statistics
Identifiers
urn:nbn:se:uu:diva-326703 (URN)10.2436/20.8080.02.57 (DOI)000407307600009 ()
Available from: 2017-07-25 Created: 2017-07-25 Last updated: 2017-11-16Bibliographically approved
Jonsson, F. & Rydén, J. (2017). Statistical studies of the Beta Gumbel distribution: estimation of extreme levels of precipitation. Statistica Applicata, 29, 5-27
Open this publication in new window or tab >>Statistical studies of the Beta Gumbel distribution: estimation of extreme levels of precipitation
2017 (English)In: Statistica Applicata, Vol. 29, p. 5-27Article in journal (Refereed) Published
National Category
Probability Theory and Statistics
Research subject
Mathematical Statistics
Identifiers
urn:nbn:se:uu:diva-326702 (URN)
Available from: 2017-07-25 Created: 2017-07-25 Last updated: 2017-07-31Bibliographically approved
Olauson, J., Edström, P. & Rydén, J. (2017). Wind turbine performance decline in Sweden. Wind Energy, 20(12), 2049-2053
Open this publication in new window or tab >>Wind turbine performance decline in Sweden
2017 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 20, no 12, p. 2049-2053Article in journal (Refereed) Published
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.

National Category
Energy Systems
Identifiers
urn:nbn:se:uu:diva-327406 (URN)10.1002/we.2132 (DOI)000417631900011 ()
Available from: 2017-08-10 Created: 2017-08-10 Last updated: 2018-03-07Bibliographically approved
Helgesson, P., Sjöstrand, H., J. Koning, A., Rydén, J., Rochman, D., Alhassan, E. & Pomp, S. (2016). Sampling of systematic errors to estimate likelihood weights in nuclear data uncertainty propagation. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 807, 137-149
Open this publication in new window or tab >>Sampling of systematic errors to estimate likelihood weights in nuclear data uncertainty propagation
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2016 (English)In: 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) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Nuclear data, Uncertainty propagation, Experimental correlations, Systematic uncertainty, Total Monte Carlo
National Category
Physical Sciences
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-265321 (URN)10.1016/j.nima.2015.10.024 (DOI)000365596200019 ()
Available from: 2015-10-27 Created: 2015-10-27 Last updated: 2018-04-16
Ryden, J. (2015). A Statistical Analysis of Trends for Warm and Cold Spells in Uppsala by Means of Counts. Geografiska Annaler. Series A, Physical Geography, 97(3), 431-436
Open this publication in new window or tab >>A Statistical Analysis of Trends for Warm and Cold Spells in Uppsala by Means of Counts
2015 (English)In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 97, no 3, p. 431-436Article in journal (Refereed) Published
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.

Keywords
warm spell, cold spell, trend, Poisson regression
National Category
Mathematics
Identifiers
urn:nbn:se:uu:diva-264064 (URN)10.1111/geoa.12083 (DOI)000361234200001 ()
Available from: 2015-10-05 Created: 2015-10-05 Last updated: 2017-12-01Bibliographically approved
Rydén, J. (2015). Is a White Christmas becoming rarer in southern parts of Sweden?. Journal of Theoretical and Applied Climatology, 121(1-2), 53-59
Open this publication in new window or tab >>Is a White Christmas becoming rarer in southern parts of Sweden?
2015 (English)In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 121, no 1-2, p. 53-59Article in journal (Refereed) Published
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.

National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-258758 (URN)10.1007/s00704-014-1220-1 (DOI)000356539300005 ()
Available from: 2015-07-20 Created: 2015-07-20 Last updated: 2017-12-04Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5451-4563

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