| 1. |
|
|
| 2. |
|
|
| 3. |
- Malmborg, J., et al.
(författare)
-
Effects of modeling strategies for a slab track on predicted ground vibrations
- 2020
-
Ingår i: Soil Dynamics and Earthquake Engineering. - : Elsevier BV. - 0267-7261. ; 136
-
Tidskriftsartikel (refereegranskat)abstract
- In the paper, the effect of modeling strategies regarding the dynamic behavior of a railway slab track on a layered half-space is studied. The track is modeled with various degrees of accuracy through the use of either beam theory, shell finite elements or solid finite elements. The underlying soil response is included through a dynamic stiffness, obtained via the Green's function for a horizontally layered visco-elastic half-space in the frequency–wavenumber domain. The effect of different assumptions regarding the track cross-section behavior and the track–soil interface conditions on the resulting free-field vibrations are studied for a harmonic load moving along the track. First, only the out-of-plane displacements of the slab–soil interface are coupled, i.e. only the vertical contact pressure is accounted for. Secondly, the effect of coupling the slab–soil in-plane displacements on the free-field vibrations is studied. It is found that the in-plane slab–soil coupling significantly affects the vertical vibration in the free-field. It is also found that a beam model of the track yields accurate response levels compared to a solid continuum model in the case of a thick slab, whereas considerable differences are obtained for a thin slab.
|
|
| 4. |
- Malmborg, J., et al.
(författare)
-
Numerical investigation of railway subgrade stiffening : Critical speed and free-field vibrations
- 2022
-
Ingår i: Transportation Geotechnics. - : Elsevier BV. - 2214-3912. ; 34
-
Tidskriftsartikel (refereegranskat)abstract
- For a train speed close to the speed of elastic waves in the soil, often referred to as “critical speed”, largely elevated vibration responses occur. This can be a practical problem for soft soil sites, where the phenomenon may cause excessive vibrations in the track and also at distances far from the track. To ensure the running safety of the train, the long-term quality of the track and to reduce the vibrations in the surroundings, such effects must be avoided. An effective counter-measure is to increase the stiffness of the soil underneath the track, thereby increasing the critical velocity. In this paper, a 2.5D finite element model is used for studying the critical velocity phenomenon and its mitigation through soil stiffening, for a ballasted track on a layered half-space with very soft soil. Soil improvement under the track, in the shape of a solid block or as various number of panels, with varying depth and stiffness is considered. The effect of the soil improvement is evaluated both in terms of the maximum rail and free-field displacements. It is shown that a shallow soil stiffening increases the critical velocity and reduces the rail and free-field response for load speeds near the shear wave velocity of the soft top soil layer. It is also demonstrated that a deep soil stiffening, by use of panels along the track direction, increases the critical velocity further, and may also be efficient in reducing the response for load speeds near the shear wave speed of the underlying half-space.
|
|
| 5. |
- Malmborg, J., et al.
(författare)
-
Numerical study on train-induced vibrations : A comparison of timber and concrete buildings
- 2024
-
Ingår i: Structures. - 2352-0124. ; 62
-
Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the prediction of train-induced building vibrations by using a numerical framework. The framework is based on a sub-structure approach, where a sequence of different models are used. The free-field ground vibrations and the track receptance are calculated using 2.5D technique where the railway track is represented by finite elements that couple to a dynamic stiffness of the underlying soil, which in turn is obtained from the Green's function of a horizontally layered half-space using a layer transfer matrix approach. A planar multi-body model of the train, coupled to the track receptance, is used for calculating the train–track interaction forces as the train runs over an uneven rail. Finally, the building response to the incident wavefield is calculated using a 3D finite element model, accounting for the soil dynamic stiffness. The framework is used to evaluate the vibrations in two buildings with identical layout, one lightweight wooden building and one heavyweight concrete building, due to a passenger train passing by at two different speeds. It was found that the difference in response between the two buildings were small. Compared to the incident wavefield, an amplification of the response inside the building was found in frequency bands around the fundamental natural frequencies of the slabs; however for higher frequencies and in terms of the 1 s running RMS velocity the building response was reduced. Further, it was found that accounting for soil-structure-interaction, as opposed to simply enforcing the free-field displacements at the building foundations, significantly reduced the building response in terms of 1 s RMS velocity.
|
|
| 6. |
- Malmquist, Marianne, 1961, et al.
(författare)
-
Frequent Occurrence of Perianal Disease and Granuloma Formation in Patients with Crohn's Disease and Coexistent Orofacial Granulomatosis
- 2023
-
Ingår i: Digestive Diseases and Sciences. - : Springer Science and Business Media LLC. - 0163-2116 .- 1573-2568. ; 68:7, s. 3129-3138
-
Tidskriftsartikel (refereegranskat)abstract
- BackgroundOrofacial granulomatosis (OFG) is an inflammatory disorder of the perioral region and oral cavity. Crohn's disease (CD) in conjunction with OFG (CD-OFG), has been suggested to constitute a phenotype of CD with distinct features at diagnosis.AimsThe aim of this project was to investigate whether the distinct phenotypic features of CD-OFG persist in the years following the initial diagnosis of CD.MethodsClinical data were extracted from medical records covering the first 5 years post-diagnosis for a cohort of patients with CD-OFG, and were compared to those of references with CD without OFG.ResultsThe clinical characteristics of our cohort of patients with CD-OFG (N = 25) were evaluated in comparison to references with CD without OFG (ratio 1:2). Five years post-diagnosis, more patients with CD-OFG had a phenotype with perianal disease (cumulative incidence: 16/25, 64% vs 13/50, 26%, P = 0.002) and intestinal granulomas (cumulative incidence: 22/25, 88% vs 24/50, 48%, P = 0.0009) than patients in the CD reference group. The patients with CD-OFG were also more likely to have undergone perianal surgery (12/25, 48% vs 4/50, 8%, P = 0.0002). At the end of the observation period, more of the patients with CD-OFG were receiving combination therapy, i.e., immunomodulators and tumor necrosis factor antagonists, than those in the CD reference group (9/25, 36% vs 5/50, 10%, P = 0.01).ConclusionThe results support the notion that CD in conjunction with OFG represents a specific phenotype of CD that is characterized by frequent perianal disease, pronounced intestinal granuloma formation and a need for extensive therapy.
|
|
| 7. |
- Mouratidou, N., et al.
(författare)
-
Identification of Childhood-Onset Inflammatory Bowel Disease in Swedish Healthcare Registers: A Validation Study
- 2022
-
Ingår i: CLINICAL EPIDEMIOLOGY. - 1179-1349. ; 14, s. 591-600
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: The Swedish National Patient Register (NPR) is often used in observational studies of childhood-onset inflammatory bowel disease (IBD) (<18 years of age) and its subtypes, but the validity of previously used register-based algorithms for capturing childhood-onset IBD has never been examined. Methods: We identified a random sample of 233 individuals with at least two first ever diagnostic listings of IBD in the NPR between 2002 and 2014. We calculated the test characteristics for different register-based definitions of IBD and its subtypes using the Copenhagen criteria and the revised Porto criteria as gold standard, both based on medical chart review. We made assumptions of the occurrence of undiagnosed IBD in the general child population based on available literature. Results: Out of 233 individuals with at least two diagnostic listings of IBD, 216 had true IBD, resulting in a positive predictive value (PPV) = 93% (95% confidence interval (CI) 89-96), sensitivity = 88% (95% CI 83-92), specificity = 100% (95% CI 100-100), and negative predictive value (NPV) = 100% (95% CI 100-100). The PPV for the NPR-based definitions of IBD subtypes at time of first IBD diagnosis and at end of follow-up were 78% (95% CI 69-86) and 88% (95% CI 80-94), respectively, for Crohn's disease and 74% (95% CI 63-83) and 71% (95% CI 60-80), respectively, for ulcerative colitis. Conclusion: The validity of register-based definitions of childhood-onset IBD in the Swedish NPR is high and can be used to identify patients in observational research.
|
|
| 8. |
|
|
| 9. |
- Tjernberg, A. R., et al.
(författare)
-
Coronavirus disease 2019 and gastrointestinal disorders in children
- 2023
-
Ingår i: Therapeutic Advances in Gastroenterology. - 1756-283X. ; 16
-
Tidskriftsartikel (refereegranskat)abstract
- During the past 3 years, the coronavirus disease 2019 (COVID-19) pandemic has had a great impact on people all over the world. However, it has become evident that disease manifestations and severity differ across age groups. Most children have a milder disease course than adults but possibly more pronounced gastrointestinal (GI) symptoms. Given the child's developing immune system, the impact of COVID-19 on disease development may differ compared to adults. This study reviews the potential bi-directional relationship between COVID-19 and GI diseases in children, focusing on common pediatric conditions such as functional GI disorders (FGID), celiac disease (CeD), and inflammatory bowel disease (IBD). Children with GI diseases, in general, and CeD and IBD, in particular, do not seem to have an increased risk of severe COVID-19, including risks of hospitalization, critical care need, and death. While infections are considered candidate environmental factors in both CeD and IBD pathogenesis, and specific infectious agents are known triggers for FGID, there is still not sufficient evidence to implicate COVID-19 in the development of either of these diseases. However, given the scarcity of data and the possible latency period between environmental triggers and disease development, future investigations in this field are warranted.
|
|
