| 1. |
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| 2. |
- Larsson, Andreas, 1968-, et al.
(författare)
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On the Parameter Identifiability and Test Data Informativeness in Finite Element Model Error Localization
- 2000
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Ingår i: Proceedings of IMAC XVIII. - San Antonio, TX. ; , s. 1520-1527, s. 1520-1527
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Konferensbidrag (refereegranskat)abstract
- Two fundamental questions that arise in finite ele- ment model updating and error localization prob- lems are addressed. These are whether available test data are informative enough with respect to the quantification of possible model errors and whether sufficient identifiability of such errors is at hand for a given test data set. We advocate the use of informativeness and identifiability based indices in a preparatory process to increase the likelihood of a successful error localization. Based on model properties, such informativeness and identifiability indices may be used in the pre-test planning for the determination of frequency, time and spatial resolution to be used in a vibratory test. First, the test data informativeness with respect to model parameters which might be in error is quan- tified. Here a dual assumption is made such that if model parameter perturbations could be detected by data from the planned test, then the test data could be used to detect such perturbations, i.e. the test is informative. A Data Information Richness (DIR) index has been developed to assess the level od Data Informativeness with respect to model parameters. Secondly, the identifiability of the model parame- ters are studied. The dynamic properties of a struc- ture, as recorded by a measurement system, may under certain conditions change similarly by changing one parameter or a set of other parameters. Should that be the case, there is no identifi- ability and before a meaningful error localization may take place, either complementary test data have to be added or a re-parameterization of the model has to be made. To assess the identifiability, identifiability based criteria are further developed, based on earlier work by the authors. A newly developed orthogonality/co-linearity index ocI assist in the re-parameterization of systems with low identifiability. The methods of preparatory error localisation are applied to a six-degree-of-freedom system in a numerical example in which the analytical results of a finite element analysis are taken as substitute for measured data.
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| 3. |
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| 4. |
- Abrahamsson, Thomas, 1968-
(författare)
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Can Lactobacillus Reuteri Prevent Allergic Disease in Early Childhood?
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: An altered microbial exposure may be partly responsible for the increase of allergic diseases in populations with a western lifestyle. Activation of the immune system by microbes early in life is probably required for an accurate maturation of the immune system. Probiotics, live bacteria which are considered to confer health when ingested, have been suggested to prevent eczema and sensitisation infants.Aim: The general aim of this thesis was to assess the effect of oral supplementation with the probiotic bacterium Lactobacillus reuteri (L. reuteri) in infancy on the development of allergic disease and sensitisation during the first 2 years of life and to examine mechanisms possibly underlying eventual effects on allergic manifestations.Subjects: The thesis is based on results obtained from a prospective double-blind placebo-controlled multicenter trial, comprising 232 families with allergic disease, of whom 188 completed the study.Methods: The families were recruited at the antenatal clinic, and the mothers received L. reuteri ATCC 55730 (1 x 108 colony forming units) or placebo daily from gestational week 36 until delivery. Their babies then continued with the same study product from birth until 12 months of age and were followed up for another year. The primary outcomes were allergic disease, with or without positive skin prick test or circulating IgE to food allergens. Bacterial counts and prevalence were assessed in maternal breast milk and faeces and infant faeces, employing conventional cultivation methods. Cytokines and IgA antibodies were analysed in colostrum and mature milk from the mothers with ELISA, and Na/K- ratio in breast milk with ion selective electrodes. Circulating Th1/Th2-associated chemokines were analysed in cord and peripheral blood in the infants with Luminex or ELISA technique.Results: The incidence of eczema was similar, 36% in the treated versus 34% in the placebo group. The L. reuteri group had a lower cumulative incidence of IgE-associated allergic disease, 20% versus 35% (p=0.04), and less IgE-associated eczema during the second year, 8% versus 20% (p=0.02). The prevalence of L. reuteri was higher during the first year of life in stool samples from infants, as well as in colostrum, in the active as compared to the placebo treated group. Colostrum from L. reuteri supplemented mothers had lower levels of TGF-β2, and low levels of this cytokine were associated with less sensitisation. Low Th1- and high Th2-associated chemokine levels preceded allergic disease. The presence of L. reuteri in stool was associated with lower levels of the Th2-associated chemokines CCL17 and CCL22 and higher levels of the Th1-associated CXCL11.Conclusion: Although a preventive effect of probiotics on infant eczema was not confirmed, the L. reuteri treated infants had lower incidence of IgE-associated allergic disease at two years of age, and therefore possibly run a reduced risk to develop later respiratory allergic disease. The mechanisms underlying this effect require further elucidation.
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| 5. |
- Abrahamsson, Thomas R, 1968-, et al.
(författare)
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Probiotics in prevention of IgE-associated eczema : a double-blind, randomized, placebo-controlled trial
- 2007
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Ingår i: Journal of Allergy and Clinical Immunology. - : Elsevier BV. - 0091-6749 .- 1097-6825. ; 119:5, s. 1174-1180
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: An altered microbial exposure may underlie the increase of allergic diseases in affluent societies. Probiotics may alleviate and even prevent eczema in infants. OBJECTIVE: To prevent eczema and sensitization in infants with a family history of allergic disease by oral supplementation with the probiotic Lactobacillus reuteri. METHODS: Double-blind, randomized, placebo-controlled trial, which comprised 232 families with allergic disease, of whom 188 completed the study. The mothers received L reuteri ATCC 55730 (1 x 10(8) colony forming units) daily from gestational week 36 until delivery. Their babies then continued with the same product from birth until 12 months of age and were followed up for another year. Primary outcome was allergic disease, with or without positive skin prick test or circulating IgE to food allergens. RESULTS: The cumulative incidence of eczema was similar, 36% in the treated versus 34% in the placebo group. The L reuteri group had less IgE-associated eczema during the second year, 8% versus 20% (P = .02), however. Skin prick test reactivity was also less common in the treated than in the placebo group, significantly so for infants with mothers with allergies, 14% versus 31% (P = .02). Wheeze and other potentially allergic diseases were not affected. CONCLUSION: Although a preventive effect of probiotics on infant eczema was not confirmed, the treated infants had less IgE-associated eczema at 2 years of age and therefore possibly run a reduced risk to develop later respiratory allergic disease. CLINICAL IMPLICATION: Probiotics may reduce the incidence of IgE-associated eczema in infancy.
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| 6. |
- Ashwear, Nasseradeen, 1968-
(författare)
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Vibration-based Assessment of Tensegrity Structures
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Vibration structural health monitoring (VHM) uses the vibration properties to evaluate many civil structures during the design steps, building steps and service life.The whole function, expressed by stiffness and frequencies of tensegrity structures are primarily related to the level of pre-stress. The present work investigates the possibilities to use this relation in designing, constructing and evaluating the tensegrity structures.One of the aims of the thesis was to improve the current models for resonance frequency simulation of tensegrities. This has been achieved by introducing the bending behaviour of all components, and by a one-way coupling between the axial force and the stiffness.The environmental temperature effects on vibration properties of tensegrity structures have been also investigated. Changes in dynamic characteristics due to temperature variations were compared with the changes due to decreasing pre-tension in one of the cables. In general, it is shown that the change in structural frequencies coming from temperature changes could of several magnitude as those from damage.Coinciding natural frequencies and low stiffness are known issues of tensegrity structures. The former can be an obstacle in VHM, while the later normally limits their uses in real engineering applications. It has been shown that the optimum self-stress vector of tensegrity structures can be chosen such that their lowest natural frequency is high, and separated from others.The environmental temperature effects on vibration properties of tensegrity structures were revisited to find a solution such that the natural frequencies of the tensegrity structures are not strongly affected by the changes in the environmental temperature. An asymmetric self-stress vector can be chosen so that the criterion is fulfilled as well as possible. The level of pre-stress can also be regulated to achieve the solution. The last part of this thesis, services as a summary of the work.
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| 7. |
- Chen, Yousheng, 1985-, et al.
(författare)
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A Pretest Planning Method for Model Calibration for Nonlinear Systems
- 2016
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Ingår i: Model Validation and Uncertainty Quantification, Volume 3. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319297538 - 9783319297545 ; , s. 371-379
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With increasing demands on more flexible and lighter engineering structures, it has been more common to take nonlinearity into account. Model calibration is an important procedure for nonlinear analysis in structural dynamics with many industrial applications. Pretest planning plays a key role in the previously proposed calibration method for nonlinear systems, which is based on multi-harmonic excitation and an effective optimization routine. This paper aims to improve the pretest planning strategy for the proposed calibration method. In this study, the Fisher information matrix (FIM), which is calculated from the gradients with respect to the chosen parameters with unknown values, is used for determining the locations, frequency range, and the amplitudes of the excitations as well as the sensor placements. This pretest planning based model calibration method is validated by a structure with clearance nonlinearity. Synthetic test data is used to simulate the test procedure. Model calibration and K-fold cross validation are conducted for the optimum configurations selected from the pretest planning as well as three other configurations. The calibration and cross validation results show that a more accurate estimation of parameters can be obtained by using test data from the optimum configuration.
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| 8. |
- Chen, Yousheng, 1985-, et al.
(författare)
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An Efficient Simulation Method for Large-Scale Systems with Local Nonlinearities
- 2016
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Ingår i: Special topics in structural dynamics, 34th IMAC. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319299105 - 9783319299099
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In practice, most mechanical systems show nonlinear characteristics within the operational envelope. However, the nonlinearities are often caused by local phenomena and many mechanical systems can be well represented by a linear model enriched with local nonlinearities. Conventional nonlinear response simulations are often computationally intensive; the problem which becomes more severe when large-scale nonlinear systems are concerned. Thus, there is a need to further develop efficient simulation techniques. In this work, an efficient simulation method for large-scale systems with local nonlinearities is proposed. The method is formulated in a state-space form and the simulations are done in the Matlab environment. The nonlinear system is divided into a linearized system and a nonlinear part represented as external nonlinear forces acting on the linear system; thus taking advantage in the computationally superiority in the locally nonlinear system description compared to a generally nonlinear counterpart. The triangular-order hold exponential integrator is used to obtain a discrete state-space form. To shorten the simulation time additionally, auxiliary matrices, similarity transformation and compiled C-codes (mex) to be used for the time integration are studied. Comparisons of the efficiency and accuracy of the proposed method in relation to simulations using the ODE45 solver in Matlab and MSC Nastran are demonstrated on numerical examples of different model sizes.
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| 9. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Experimental Validation of a Nonlinear Model Calibration Method Based on Multiharmonic Frequency Responses
- 2017
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Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME Press. - 1555-1415 .- 1555-1423. ; 12:4
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Tidskriftsartikel (refereegranskat)abstract
- Correlation and calibration using test data are natural ingredients in the process of validating computational models. Model calibration for the important subclass of nonlinear systems which consists of structures dominated by linear behavior with the presence of local nonlinear effects is studied in this work. The experimental validation of a nonlinear model calibration method is conducted using a replica of the École Centrale de Lyon (ECL) nonlinear benchmark test setup. The calibration method is based on the selection of uncertain model parameters and the data that form the calibration metric together with an efficient optimization routine. The parameterization is chosen so that the expected covariances of the parameter estimates are made small. To obtain informative data, the excitation force is designed to be multisinusoidal and the resulting steady-state multiharmonic frequency response data are measured. To shorten the optimization time, plausible starting seed candidates are selected using the Latin hypercube sampling method. The candidate parameter set giving the smallest deviation to the test data is used as a starting point for an iterative search for a calibration solution. The model calibration is conducted by minimizing the deviations between the measured steady-state multiharmonic frequency response data and the analytical counterparts that are calculated using the multiharmonic balance method. The resulting calibrated model's output corresponds well with the measured responses.
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| 10. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Frequency Response Calculations of a Nonlinear Structure a Comparison of Numerical Methods
- 2014
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Ingår i: Nonlinear Dynamics, Volume 2. - Cham : Springer. - 9783319045221 - 9783319045221 ; 2, s. 35-44
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Konferensbidrag (refereegranskat)abstract
- Mechanical systems having presence of nonlinearities are often represented by nonlinear ordinary differential 5 equations. For most of such equations, exact analytic solutions are not found; thus numerical techniques have to be used. 6 In many applications, among which model calibration can be one, steady-state frequency response functions are the desired 7 quantities to calculate. 8 The objective of this paper is to compare the performance of computations of nonlinear frequency response functions 9 (FRFs) calculated directly within the frequency domain, using the Multi-Harmonic Balance method, with the time-domain 10 methods Runge–Kutta, Newmark and Pseudo Force in State Space (PFSS). The PFSS method is a recently developed state- 11 space based force feedback method that is shown to give efficient solutions. 12 The accuracy and efficiency of the methods are studied and compared using a model of a cantilever beam connected to a 13 non-linear spring at its free end.
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| 11. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Informative Data for Model Calibration of Locally Nonlinear Structures Based on Multi-Harmonic Frequency Responses
- 2016
-
Ingår i: Journal of Computational and Nonlinear Dynamics. - : ASME Press. - 1555-1415 .- 1555-1423. ; 11:5
-
Tidskriftsartikel (refereegranskat)abstract
- In industry, linear FE-models commonly serve as baseline models to represent the global structural dynamics behavior. However, available test data may show evidence of significant nonlinear dynamic characteristics. In such a case, the baseline linear model may be insufficient to represent the dynamics of the structure. The causes of the nonlinear characteristics may be local in nature and the remaining parts of the structure may be satisfactorily represented by linear descriptions. Although the baseline model can then serve as a good foundation, the physical phenomena needed to substantially increase the model's capability of representing the real structure are most likely not modelled in it. Therefore, a set of candidate nonlinear property parameters to control the nonlinear effects have to be added and subjected to calibration to form a credible model. The selection of the calibration parameters and the choice of data for a calibration metric form a coupled problem. An over-parameterized model for calibration may result in parameter value estimates that do not survive a validation test. The parameterization is coupled to the test data and should be chosen so that the expected co-variances of the chosen parameter's estimates are made small. Accurate test data, suitable for calibration, is often obtained from sinusoidal testing. Because a pure mono-sinusoidal excitation is difficult to achieve during a test of a nonlinear structure, the excitation is here designed to contain sub and super harmonics besides the fundamental harmonic. The steady-state responses at the side frequencies are shown to contain valuable information for the calibration process that can improve the accuracy of the parameter estimates. The nonlinear steady-state solutions can be found efficiently using the multi-harmonic balance method. In this paper, synthetic test data from a model of a nonlinear benchmark structure are used for illustration. The model calibration and an associated K-fold cross-validation are based on the Levenberg-Marquardt and the undamped Gauss-Newton algorithm, respectively. Starting seed candidates for calibration are found by the Latin hypercube sampling method. The realization that gives the smallest deviation to test data is selected as a starting point for the iterative search for a calibration solution. The calibration result shows good agreement with the true parameter setting, and the K-fold cross validation result shows that the variance of the estimated parameters shrinks when adding sub and super harmonics to the nonlinear frequency response functions.
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| 12. |
- Chen, Yousheng, 1985-, et al.
(författare)
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Model calibration of locally nonlinear structures using information from sub and super harmonic responses
- 2012
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Ingår i: International Conference on Noise and Vibration Engineering 2012 (ISMA 2012). - Leuven : Katholieke Universiteit Leuven, Department of Mechanical Engineering. - 9781622768257 ; , s. 2451-2464
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Large linear finite element models are commonly used in industry to represent global structural behavior and such models are often validated by use of data from vibrational tests. The validated models serve to predict the structural responses due to dynamic loads. Hence, it is important to have models that are able to represent the structural dynamics within the given operating envelope. When test data show proof of non linear behavior, a linear model may not be able to represent the dynamics well enough and thus a modification of the model is required. The main part of the structure may have a linear characteristic whereas localized physical processes can be sources of the observed nonlinearities. Model calibration of such locally nonlinear structures is studied in this paper. Specifically, the calibration process including the selection of appropriate data to be used for calibration of the model parameters chosen is treated. Here, synthetic test data stemming from a model of the Ecole Centrale de Lyon (ECL) nonlinear benchmark are used.
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| 13. |
- Chen, Yousheng, et al.
(författare)
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Validation of a model calibration method through vibrational testing of a mechanical system with local clearance
- 2016
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Ingår i: Proceedings of ISMA2016 International conference on noise and vibration engineering and USD2016 International conference on uncertainty in structural dynamics. - Leuven, Belgium : Katholieke University Leuven. - 9789073802940 ; , s. 2581-2595
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Konferensbidrag (refereegranskat)abstract
- Nonlinear finite element models are often validated using experimental data. A previously proposed calibration method, which concerns pre-test planning, multi-sinusoidal excitation and an effective optimization routine, is improved with an extended version of the pre-test planning. The improved method is validated using a test structure with a clearance type nonlinearity. From the pretest planning, an optimal configuration for the data acquisition is determined. The multi-harmonic nonlinear frequency response functions (FRFs) of the structure under test are then generated by a multi-sinusoidal excitation. Model calibration is conducted by minimizing the difference between the experimental multi-harmonic nonlinear FRFs and their analytical counterparts. The uncertainties of the estimated parameters are assessed by a k-fold cross validation, which confirm that the uncertainties of the estimated parameters are small when the optimal configuration is applied.
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| 14. |
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| 15. |
- Dzidic, Majda, et al.
(författare)
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Allergy development is associated with consumption of breastmilk with a reduced microbial richness in the first month of life
- 2020
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Ingår i: Pediatric Allergy and Immunology. - : WILEY. - 0905-6157 .- 1399-3038. ; 31, s. 250-257
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Tidskriftsartikel (refereegranskat)abstract
- Background Early colonization with a diverse microbiota seems to play a crucial role for appropriate immune maturation during childhood. Breastmilk microbiota is one important source of microbes for the infant, transferred together with maternal IgA antibodies. We previously observed that allergy development during childhood was associated with aberrant IgA responses to the gut microbiota already at 1 month of age, when the IgA antibodies are predominantly maternally derived in breastfed infants. Objective To determine the microbial composition and IgA-coated bacteria in breastmilk in relation to allergy development in children participating in an intervention trial with pre- and post-natal Lactobacillus reuteri supplementation. Methods A combination of flow cytometric cell sorting and 16S rRNA gene sequencing was used to characterize the bacterial recognition patterns by IgA in breastmilk samples collected one month post-partum from 40 mothers whose children did or did not develop allergic and asthmatic symptoms during the first 7 years of age. Results The milk fed to children developing allergic manifestations had significantly lower bacterial richness, when compared to the milk given to children that remained healthy. Probiotic treatment influenced the breastmilk microbiota composition. However, the proportions of IgA-coated bacteria, the total bacterial load and the patterns of IgA-coating were similar in breastmilk between mothers of healthy children and those developing allergies. Conclusion Consumption of breastmilk with a reduced microbial richness in the first month of life may play an important role in allergy development during childhood.
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| 16. |
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| 17. |
- Forsberg, Anna, 1985-
(författare)
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Immunomodulatory effects of probiotic supplementation during pregnancy and infancy in allergy prevention studies
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The incidence of allergic diseases is increasing, possibly due to a reduced intensity and diversity of microbial stimulation. More knowledge is needed on the immunological mechanisms underlying the eczema preventive effect of pre- and postnatal probiotic supplementation. The pregnancy period seems to be of essential importance, since both epidemiological and experimental animal studies show the importance of microbial exposure during gestation on allergy prevention.We have performed a study where the probiotic lactic acid producing bacteria Lactobacillus reuteri was supplemented to pregnant women, at risk of having an allergic infant. The pregnant mothers received the study product from gestational week 36 until delivery, and the infants then continued with the same product until one year of age. The probiotic, as compared with placebo, supplemented infants had less IgE-associated eczema at two years of age.In order to investigate how the supplementation affected the immune system peripheral blood was collected and immune cells were stimulated with common allergens and TLR ligands. The probiotic treated group responded with a more regulated response to allergens and TLR2 ligands in comparison to the placebo supplemented group. We also investigated how the probiotic supplementation affected the epigenetic methylation pattern in circulating T helper cells during infancy, observing the most pronounced effects at birth.In a follow up study, supplementation was started earlier to possibly gain a stronger allergy preventive effect via changes in maternal immune regulation. Supplementation with Lactobacillus reuteri and ω-3 fatty acids started at gestational week 20 and throughout pregnancy. After 20 weeks of supplementation, some immunomodulatory effects among circulating activated regulatory T cells and a subpopulation of monocytes were noted. Several systemic immune modifying effects of pregnancy were observed.In summary, probiotics show several immunomodulatory effects in infants and pregnant women. However, more research is needed to better understand the effects of the probiotic supplementation to aid future identification of more efficacious allergy preventive strategies.
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| 18. |
- Generó, Magalí Martí, 1983-, et al.
(författare)
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A protocol for characterization of extremely preterm infant gut microbiota in double-blind clinical trials
- 2021
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Ingår i: STAR Protocols. - Cambridge, MA, United States : Cell press. - 2666-1667. ; 2:3
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Tidskriftsartikel (refereegranskat)abstract
- 16S rRNA gene sequencing enables microbial community profiling, but recovering fecal DNA from extremely premature infants is challenging. Here, we describe an optimized protocol for fecal DNA isolation, library preparation for 16S rRNA gene sequencing, taxonomy assignation, and statistical analyses. The protocol is complemented with a quantitative PCR for probiotic L. reuteri identification. This protocol describes how to characterize preterm infant gut microbiota and relate it to probiotic supplementation and clinical outcomes. It is customizable for other clinical trials. For complete details on the use and execution of this protocol, please refer to Martí et al. (2021) and Spreckels et al. (2021).
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| 19. |
- Jacobsson, Bo, et al.
(författare)
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Förtidsbörd största perinatala problemet [Preterm delivery an overview on epidemiology, pathophysiology and consequences for the individual and the society]
- 2019
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Ingår i: Läkartidningen. - : Läkartidningen Förlag AB. - 0023-7205 .- 1652-7518. ; 116
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Forskningsöversikt (refereegranskat)abstract
- Preterm delivery in Sweden constitutes 5.7 % of all deliveries, which is among the lowest rates in the world. There has not been any increase in the proportion of iatrogenic preterm deliveries during the last decades.The main hypothesis concerning the causality of preterm delivery is still that of the ascending infection from the vagina to the uterus and inflammation resulting in contractions, rupture of membranes and delivery. The mechanisms behind parturition at term are still elusive and this is also true for preterm delivery. The genetic contribution to preterm delivery is about 25-30 %. The first genes that are associated with preterm delivery and gestational duration have recently been published. Huge progress has been made in care of preterm born infants. Sweden has among the lowest rates of mortality and morbidity in the world, especially in the lowest gestational weeks. New modes of care, family-centered care and hospital-assisted home care, have empowered the parents and reduced the cost for care.
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| 20. |
- Johansson, Anders, 1982, et al.
(författare)
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Model calibration and uncertainty of A600 wind turbine blades
- 2014
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Ingår i: Model Validation and Uncertainty Quantification, Volume 3. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319045511 ; , s. 215-227
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Konferensbidrag (refereegranskat)abstract
- Recently, a lot of work has been made on modeling, testing and calibrating Ampair 600W wind turbine blades, owing to the use of that turbine as a test bed structure for the Dynamic Substructuring Focus Group within the Society of Experimental Mechanics. In Sweden alone, more than 20 blades have been tested for dynamical properties, geometrical differences and material properties as was presented in several papers at IMAC XXXI. The quantity of blades, originating from different manufacturing batches, makes them ideal for investigations of component variability.In this paper, measurement variability predominantly stemming from the difference between individual blades is propagated backwards to model parameters, using model calibration techniques, in an effort to quantify their uncertainties. The coupling between spread in structural properties such as mass, center of gravity together with blade twist angles and spread in the resulting blade dynamics is shown.
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| 21. |
- Kindgren, Erik, 1977-
(författare)
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Early Life Environmental Risk Factors and Gut Microbiota in Juvenile Idiopathic Arthritis : - More than a gut feeling
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: The autoimmune disease juvenile idiopathic arthritis (JIA) is the most common rheumatic disease in children, but the cause is not fully established. Only a small percentage (13–18%) of the risk of contracting the disease can be attributed to genetic factors, but environmental factors are believed to be behind most of the risk. An unfavourable composition of gut bacteria has also been suggested as a factor that may increase the risk of developing JIA. Aims: The main aim of this thesis was to study risk factors during fetal life and in the early childhood environment for future onset of JIA. A further aim was to study the composition and importance of the gut microbiota before the onset of JIA. Methods: In the ABIS study, a population-based prospective birth cohort of 17,055 children, data were collected on environmental factors during pregnancy and childhood. We identified 111 individuals with a JIA diagnosis. Environmental factors were mainly analysed using multivariable logistic regression, with adjustment for confounding factors. The microbiome at one year of age was analysed from stool samples by 16S rRNA PCR. Results: Significant associations could be noted between mode of birth, duration of breastfeeding, birth order and exposure to antibiotics or fish early in life with future onset of JIA. These risk factors were found to pose an even higher cumulative risk if several of the factors were present. Carrying a risk allele in combination with being exposed to a specific environmental factor further increased the risk. In addition, several taxa were identified in the gut microbiota at one year that were associated with future onset of JIA. Many of these taxa were associated with one or more of the identified early childhood environmental risk factors. Conclusion: In these studies, it has been demonstrated that children with JIA have, very early in life, already been exposed to negative environmental factors (caesarean section, short-term breastfeeding, being firstborn and being exposed to antibiotics or fish during the first year of life). The effect from these risk factors appears to be to some extent mediated via a changed composition of the gut microbiota. An environmentally induced dysregulation of the microbiome can trigger or accelerate the development of JIA in genetically predisposed children.
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| 22. |
- Larsson, Andreas, 1968-, et al.
(författare)
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A Comparison of Finite Element Model Error Localization Methods
- 1999
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Ingår i: 1999 IMAC XVII - 17th International Modal Analysis Conference. - Orlando, Florida. ; , s. 929-935
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Konferensbidrag (refereegranskat)abstract
- The aim of this study is to compare a new and some existing finite element model error localization methods. The methods are applied to two problems. First, fundamental properties of the error localization methods are studied on a simple sprung mass system. In the second problem a three-bay frame structure is studied. Here the analytical results of a finite element analysis is taken as substitute for measured data. The model differences between this model and a perturbed model are then found by use of error localization methods.When data from a known finite element model take place as substitute for test data, the cause of the differences between the data sets are known. A so-called consistent para- meterization, i.e. a parameterization of the quantities known to be in error, is then possible. The error localization method are compared for both consistent and inconsistent parameterization.A pre-error localization is made. It is based on the finite element model’s properties. Candidate model parameters, possibly in error, for which the experimental data are not informative, are rejected. Non-identifiable parameters are also rejected. Quantification of data information richness and identifiability with newly developed index numbers support the pre-error localization.Four error localization methods are compared. Two of these are developed by Lallement and Piranda. These are the so- called Balancing of Eigenvalue Equation and Best Subspace Methods. The third is developed by Link and Santiago and is the Substructure Energy Function Method. A new localization method, using gradient and Hessian information of the error criterion function, constitute the fourth method.
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| 23. |
- Ley, David, et al.
(författare)
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Extremt förtidig födelse – svåra utmaningar trots stora framsteg [Extremely preterm birth in Sweden - clear progress but remaining challenges]. : Överlevnaden till 1 års ålder är hög, men allvarlig neonatal sjuklighet är en utmaning
- 2019
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Ingår i: Läkartidningen. - : Läkartidningen förlag AB. - 0023-7205 .- 1652-7518. ; 116
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Forskningsöversikt (refereegranskat)abstract
- The recently documented high survival of extremely preterm infants in Sweden is related to a high degree of centralization of pre- and postnatal care and to recently issued national consensus guidelines providing recommendations for perinatal care at 22-24 gestational weeks. The prevalence of major neonatal morbidity remains high and exceeded 60 % in a recent study of extremely preterm infants born at < 27 gestational weeks delivered in Sweden in 2014-2016 and surviving to 1 year of age. Damage to immature organ systems inflicted during the neonatal period causes varying degrees of functional impairment with lasting effects in the growing child. There is an urgent need for evidence-based novel interventions aiming to prevent neonatal morbidity with a subsequent improvement of long-term outcome.
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| 24. |
- Linderholt, Andreas, 1968-, et al.
(författare)
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A Comparison of Finite Element Model ErrorLocalization Methods
- 1999
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Ingår i: International Modal Analysis Conference (IMAC) XVII, Orlando, Florida, 1999.. ; , s. 929-935
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study is to compare a new and some existing finite elementmodel error localization methods. The methods are applied to two problems. First,fundamental properties of the error localization methodsare studied on asimple sprung mass system. Inthe second problem a three-bay frame structure is studied.Here the analytical results of a finite element analysisis taken as substitute for measured data. The model differences between thismodel and a perturbed model are then found by use of error localization methods. When data from a known finite element model take place as substitute for test data, the cause of the differences between the data sets are known. A so-calledconsistent para meterization, i.e. a parameterization of the quantities known to be in error, is then possible. The error localization methods are compared for both consistent and inconsistent parameterization. A pre-error localization is made. It is based on the finiteelement model's properties. Candidatemodel parameters, possibly in error, for which the experimental data are not informative, are rejected. Non-identifiable parameters are also rejected. Quantification of data information richness and identifiability with newly developed index numbers support the pre-error localization.Four error localization methods are compared. Two of these are developed by Lallement and Piranda. These are the so called Balancing of Eigenvalue Equation and Best Subspace Methods. The third is developed by Link and Santiago and is the Substructure Energy Function Method. A new localization method, using gradient and Hessian information of the error criterion function, constitute the fourth method.
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| 25. |
- Linderholt, Andreas, 1968-, et al.
(författare)
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A Comparison of the Dynamic Behavior of Three Sets of the Ampair 600 Wind Turbine
- 2015
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Ingår i: Dynamics of Coupled Structures. - Cham : Springer. - 2191-5644 .- 2191-5652. - 9783319152080 ; , s. 99-110
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Ampair 600 wind turbine assembly has been modified to suit as a benchmark structure in the pursuit of finding best practices for experimental substructure coupling of structural dynamic systems. Seven such systems have been assembled in test laboratories in Europe and in the USA. We scrutinize the dynamic behavior of the total assembly of three of those by vibration testing and compare the test outcome from seemingly identical assemblies. The aim is to support future component synthesis activities with high fidelity data and support future model validation. Comparisons are made by evaluating deviations of measured frequency response functions, the differences of identified structural eigenfrequencies and the correlation between eigenvector estimates. The testing is made in two parts. First, a partly assembled system, not including the hub and blades, is tested. This constitutes one possible and logical subsystem splitting that is likely to appear in future substructure synthesis efforts. In the second part, the full system assembly is tested. The test procedure, the test setup, the obtained test data and test data statistics are presented.
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