| 1. |
- Lassmann-Klee, P. G., et al.
(author)
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Parallel gradients in F-ENO and in the prevalences of asthma and atopy in adult general populations of Sweden, Finland and Estonia - A Nordic EpiLung study
- 2020
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In: Respiratory Medicine. - : Elsevier BV. - 0954-6111 .- 1532-3064. ; 173
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Journal article (peer-reviewed)abstract
- The prevalence of asthma is higher in Sweden and Finland than in neighbouring eastern countries including Estonia. Corresponding difference in bronchial eosinophilic inflammation could be studied by FENO measurements. We aimed to compare FENO in adult general populations of Sweden, Finland, and Estonia, to test the plausibility of the west-east disparity hypothesis of allergic diseases. We conducted clinical interviews (N = 2658) with participants randomly selected from the general populations in Sweden (Stockholm and dOrebro), Finland (Helsinki), and Estonia (Narva and Saaremaa), and performed FENO (n = 1498) and skin prick tests (SPT) in 1997-2003. The median (interquartile range) of FENO (ppb) was 15.5 (9.3) in Sweden, 15.4 (13.6) in Finland and 12.5 (9.6) in Estonia. We found the lowest median FENO values in the Estonian centres Saaremaa 13.1 (9.5) and Narva 11.8 (8.6). In the pooled population, asthma was associated with FENO >= 25 ppb, odds ratio (OR) 3.91 (95% confidence intervals: 2.29-6.32) after adjusting for SPT result, smoking, gender and study centre. A positive SPT test increased the likelihood of asthma OR 3.19 (2.02-5.11). Compared to Saaremaa, the likelihood of having asthma was higher in Helsinki OR 2.40 (1.04-6.02), Narva OR 2.45 (1.05-6.19), dOrebro OR 3.38 (1.59-8.09), and Stockholm OR 5.54 (2.18-14.79). There was a higher prevalence of asthma and allergic airway inflammation in adult general populations of Sweden and Finland compared to those of Estonia. Atopy and elevated FEND level were independently associated with an increased risk of asthma. In conclusion, the findings support the earlier west-east disparity hypothesis of allergic diseases.
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| 2. |
- Jalasto, J., et al.
(author)
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Self-Reported Physician Diagnosed Asthma with COPD is Associated with Higher Mortality than Self-Reported Asthma or COPD Alone - A Prospective 24-Year Study in the Population of Helsinki, Finland
- 2022
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In: Copd-Journal of Chronic Obstructive Pulmonary Disease. - : Informa UK Limited. - 1541-2555 .- 1541-2563. ; 19:1, s. 226-235
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Journal article (peer-reviewed)abstract
- Asthma and COPD are common chronic obstructive respiratory diseases. COPD is associated with increased mortality, but for asthma the results are varying. Their combination has been less investigated, and the results are contradictory. The aim of this prospective study was to observe the overall mortality in obstructive pulmonary diseases and how mortality was related to specific causes using postal questionnaire data. This study included data from 6,062 participants in the FinEsS Helsinki Study (1996) linked to mortality data during a 24-year follow-up. According to self-reported physician diagnosed asthma, COPD, or smoking status, the population was divided into five categories: combined asthma and COPD, COPD alone and asthma alone, ever-smokers without asthma or COPD and never-smokers without asthma or COPD (reference group). For the specific causes of death both the underlying and contributing causes of death were used. Participants with asthma and COPD had the highest hazard of mortality 2.4 (95% CI 1.7-3.5). Ever-smokers without asthma or COPD had a 9.5 (3.7-24.2) subhazard ratio (sHR) related to lower respiratory tract disease specific causes. For asthma, COPD and combined, the corresponding figures were 10.8 (3.4-34.1), 25.0 (8.1-77.4), and 56.1 (19.6-160), respectively. Ever-smokers without asthma or COPD sHR 1.7 (95% CI 1.3-2.5), and participants with combined asthma and COPD 3.5 (1.9-6.3) also featured mortality in association with coronary artery disease. Subjects with combined diseases had the highest hazard of overall mortality and combined diseases also showed the highest hazard of mortality associated with lower respiratory tract causes or coronary artery causes.
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| 3. |
- Kou, Shao Quan, et al.
(author)
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Numerical investigation of particle breakage as applied to mechanical crushing—Part II: Interparticle breakage
- 2001
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In: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 38:8, s. 1163-1172
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Journal article (peer-reviewed)abstract
- A numerical approach to interparticle breakage is applied using the rock failure process analysis code, RFPA2D. A 2D particle assembly in a container is first numerically simulated to obtain the fringe patterns of stress fields that resemble the photoelastic test. Then, in addition, the interparticle breakage of the particle assembly in a chamber is conducted. The chamber consists of a steel container and a steel platen for transferring the load, and contains 15 particles of arbitrary sizes and irregular shapes. A plane strain condition is assumed. The particle bed is loaded under form conditions, in which the size reduction and the applied force are a function of the displacement. The numerical results indicate that, during the crushing process, three principal regimes appear: (i) the elastic deformation regime, where each particle deforms elastically; (ii) the fragmentation regime, where the particle assembly is crushed in a particle-by-particle fashion; and (iii) the assembly hardening regime, where the densified assembly recovers a significant stiffness. The dominant mode of failure is at first splitting, which is more or less parallel to the loading direction, and then progressive crushing, which mainly depends on the confinement from the chamber walls. The analysis of the load–displacement curves of the assembly obtained from the simulations reveals a high undulating load plateau, which suggests a macro-ductile behaviour.
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| 4. |
- Kou, Shao Quan, et al.
(author)
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Numerical simulation of the cutting of inhomogeneous rocks
- 1999
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In: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 36:5, s. 711-717
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Journal article (peer-reviewed)abstract
- In this study, the possible modes of crack initiation and propagation leading to chip formation in rock cutting are studied numerically by using a rock failure process analysis code referred to as RFPA. By using this approach, additional information is obtained on the tool-rock interaction and the failure mechanisms of rock under mechanical tools.
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| 5. |
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| 6. |
- Kou, Shaoquan, et al.
(author)
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Rock fragmentation mechanisms induced by a drill bit
- 2004
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In: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 41:Suppl. 1, s. 527-532
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Journal article (peer-reviewed)abstract
- In most of the mechanical excavation methods the fundamental process is indentation of the rock by a bit. The present paper focuses on discussing how the rock is fragmented under the action of a drill bit. The discussions are mainly based on numerical modelling using the rock and tool interaction code (R-T2D) and taking rock heterogeneity into consideration. The simulated results concerning rock penetrations with one, two and multiple indenters are, however, compared with experiments available from the literature. The emphasis is put on discussion of the formation of side-cracks and crushed zones that constitute the major rock removal fractures. The agreement between numerical simulation and experimental observations are reasonably good. This reveals the mechanisms of crack initiation, propagation and coalescence induced by the action of button bits to form the rock fragmentation in a drilling process. The investigation can contribute not only to improving percussive drilling but also to understanding other rock fragmentation and comminution methods and equipment since indentation is also the fundamental process for them.
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| 7. |
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| 8. |
- Liu, Hongyuan, et al.
(author)
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Numerical simulation of shear fracture (mode II) in heterogeneous brittle rock
- 2004
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In: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 41:Suppl. 1, s. 14-19
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Journal article (peer-reviewed)abstract
- The fracture process of a heterogeneous brittle rock in the shear-box test is numerically investigated by means of the rock and tool interaction code (R-T2D). On the basis of the simulated results, the mode II fracture toughness is calculated, which is KIIC =7.72MPa root m, and the influence of heterogeneity and confinement on the formation and characteristics of shear fracture is discussed. It is found that with the confinement increasing, the fracture mechanisms in the shear-box test of heterogeneous brittle rock change from mixed tensile and shear failure but are dominated with tensile failure to dominant shear failure. It is concluded that the shear-box test under a confined condition is favourable for creating a condition for mode II fracture and a suitable method for measuring the mode II fracture toughness.
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| 9. |
- Liu, Hongyuan, et al.
(author)
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Numerical simulation of the rock fragmentation process induced by indenters
- 2002
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In: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 39:4, s. 491-505
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Journal article (peer-reviewed)abstract
- Rock fragmentation processes induced by single and double indenters were examined by a numerical method. The simulated results reproduce the progressive process of rock fragmentation in indentation. Rock deforms elastically at the initial loading stage. Then tensile cracks are initiated around the two corners of the truncated indenter and propagate in the well-known conical Hertzian manner. The rocks immediately under the indenter are in a highly tri-axial stress state, and some of them fail in the ductile cataclastic mode with the stress satisfying the ductile failure surface of the double elliptic strength criterion. With the tensile cone cracks and ductile cataclastic failure releasing the confining pressure, the rocks under the indenter are compressed into failure and the crushed zone gradually comes into being. With increasing loading displacement, the re-compaction behaviour of the crushed zone occurs. Side cracks initiated from the crushed zone or bifurcated from cone cracks are driven by tensile stress associated with the crushed zone to propagate in a curvilinear path and finally intersect with the free surface to form chips. It is pointed out that the curvilinear path is caused by heterogeneity. The simulated force-penetration curve is in fact the indication of the propagation of cracks, the crushing of microstructural grains and the formation of chips. It is found that the confining pressure has an important influence on the indentation results. With decreasing confining pressure, there is a decrease in the indentation strength and a change in the rock failure process from the formation of rock chips to a vertically axially splitting failure. The simulated fragmentation process in the double indenter test reproduces the side cracks, which are induced by two indenters, propagate, interact and finally coalesce, chipping the rock between the indenters. The line spacing is an important factor that affects the fragmentation efficiency in multiple indenter tests. It is pointed out that simultaneous loading with multiple indenters with an appropriate line spacing seems to provide a possibility of forming larger rock chips, controlling the direction of subsurface cracks and consuming a minimum total specific energy. According to the simulated results, it is believed that the numerical simulation method will contribute to an improved knowledge of rock fragmentation in indentation, which will in turn help to enhance mining and drilling efficiency through the improved design of mining tools and equipment.
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| 10. |
- Liu, H. Y., et al.
(author)
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Numerical modelling of the heterogeneous rock fracture process using various test techniques
- 2007
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In: Rock Mechanics and Rock Engineering. - : Springer Science and Business Media LLC. - 0723-2632 .- 1434-453X. ; 40:2, s. 107-144
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Journal article (peer-reviewed)abstract
- A series of numerical tests including both rock mechanics and fracture mechanics tests are conducted by the rock and tool (R-T2D) interaction code coupled with a heterogeneous masterial model to obtain the physical-mechanical properties and fracture toughness, as well as to simulate the crack initiation and propagation, and the fracture progressive process. The simulated results not only predict relatively accurate physical-mechanical parameters and fracture toughness, but also visually reproduce the fracture progressive process compared with the experimental and theoretical results. The detailed stress distribution and redistribution, crack nucleation and initiation, stable and unstable crack propagation, interaction and coalescence, and corresponding load-displacement curves can be proposed as benchmarks for experimental study and theoretical research on crack propagation. It is concluded that the heterogeneous material model is reasonable and the R-T2D code is stable, repeatable and a valuable numerical tool for research on the rock fracture process.
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