| 1. |
- Karlsson, Christofer M. G., et al.
(författare)
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Metatranscriptomic analysis uncovers divergent responses of Baltic Sea bacteria to forest and agriculture river loadings
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Climate change is predicted to induce substantial changes in precipitation patterns across the globe. In Northern Europe, precipitation is expected to increase more than the global average (particularly in northern Scandinavia), causing increased river runoff. The Baltic Sea is one of the largest brackish environments on earth with a catchment area that spans 14 countries, encompassing primarily forested areas and agricultural landscapes. Despite the acknowledged role of marine bacteria in nutrient cycling, there is a lack of knowledge in their metabolic responses to inorganic and organic nutrient loading from riverine runoff. We investigated the bacterial growth and gene expression responses in a mesocosm experiment in which river water from boreal forest- (enriched in humic substances) or agriculture- influenced catchment areas were added to Baltic Sea Proper water. The riverine nutrient input triggered extensive phytoplankton blooms and bacterial growth, most notably in the agriculture river treatment. Interestingly, bacterial gene expression analysis (metatranscriptomics) showed similar responses to agriculture and humic river inputs at the start of the experiment (before the phytoplankton bloom), but expression patterns diverged significantly upon bloom senescence.Notably, transcripts associated with phosphate metabolism were significantly enriched , whereas transcripts related to nitrogen metabolism were significantly lower in the agriculture river treatment compared to the boreal forest river treatment. The opposite pattern was observed in the boreal forest river water treatment. Overall, our results showed that interactions between river nutrient loading and phytoplankton organic matter are important in regulating bacterial activities and responses at the molecular level. This suggests that bacterial transformations of organic matter and nutrient cycling in coastal waters and estuarine environments are sensitive to changes in precipitation patterns in a catchment area-dependent manner.
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| 2. |
- Osbeck, Christofer M. G., et al.
(författare)
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Divergent transcriptional responses of Baltic Sea bacteria to forest and agriculture river loadings
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Climate change is projected to induce substantial changes in precipitation patterns across the globe. In Northern Europe, precipitation is expected to increase more than the global average (particularly in northern Scandinavia), causing increased river runoff. The Baltic Sea is one of the largest brackish environments on earth with a catchment area that spans 14 countries, encompassing primarily forested areas and agricultural landscapes. Despite the acknowledged role of marine bacteria in nutrient cycling, there is a lack of knowledge in their metabolic responses to inorganic and organic nutrient loading from riverine runoff. We investigated the bacterial growth and gene expression responses in a mesocosm experiment in which river water from boreal forest- (enriched in humic substances) or agriculture-influenced catchment areas (enriched in nitrogen) were added to Baltic Proper water. The riverine nutrient input triggered extensive phytoplankton blooms and bacterial growth, most notably in the agriculture river treatment. Interestingly, bacterial gene expression analysis (metatranscriptomics) showed similar responses to agriculture and humic river inputs at the start of the experiment during phytoplankton development, but expression patterns diverged upon bloom senescence. This indicated that interactions between river nutrient loading and phytoplankton organic matter are important in regulating bacterial activities and responses at the molecular level. Notably, transcripts associated with phosphate metabolism were significantly enriched in the agriculture river treatment compared to the boreal forest river treatment, whereas transcripts related to nitrogen metabolism were significantly lower. The opposite pattern was observed in the boreal forest river water treatment. This suggests that bacterial transformations of organic matter and nutrient processing in coastal environments are sensitive to alterations in the precipitation-induced riverine runoff in a catchment area-dependent manner, which has implications for interpreting the ecosystem effects of globally changing precipitation patterns.
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| 3. |
- Tonpheng, Bounphanh, 1959-, et al.
(författare)
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Tensile strength and young's modulus of polyisoprene/single-wall carbon nanotube composites increased by high pressure cross-linking
- 2010
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Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 43:18, s. 7680-7688
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Tidskriftsartikel (refereegranskat)abstract
- High-viscosity liquid cis-1,4 polyisoprene (PI), with up to 20 wt % single-wall carbon nanotubes (SWCNTs), has been cross-linked by high pressure and high temperature (HP&HT) treatment at 513 K and pressures in the range 0.5 to 1.5 GPa to yield densified network polymer composites. A composite with 5 wt % SWCNTs showed 2.2 times higher tensile strength σUTS (σUTS = 17 MPa), 2.3 times higher Young’s modulus E (E = 220 MPa) and longer extension at break than pure PI. The improvement is attributed to SWCNT reinforcement and improved SWCNT−PI interfacial contact as a result of the HP&HT cross-linking process, and reduced brittleness despite a higher measured cross-link density than that of pure PI. The latter may originate from an effect similar to crazing, i.e., bridging of microcracks by polymer fibrils. We surmise that the higher cross-link densities of the composites are due mainly to physical cross-links/constraints caused by the SWCNT−PI interaction, which also reflects the improved interfacial contact, and that the CNTs promote material flow by disrupting an otherwise chemically cross-linked network. We also deduce that the PI density increase at HP&HT cross-linking is augmented by the presence of CNTs.
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| 4. |
- Andersson, Britt M., et al.
(författare)
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Defects and the thermal conductivity of YBa2Cu3O7-d and YBa2Cu4O8
- 1993
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Ingår i: Journal of Alloys and Compounds, volume 195. - : Elsevier Sequoia S.A.. - 0 444 81529 5 ; , s. 655-658
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Konferensbidrag (refereegranskat)abstract
- We present below the first measured data for the thermal diffusivity and the thermal conductivity, λ, of dense, sintered ceramic YBa2Cu4O8 (1-2-4) as a function of temperature T between 40 and 310 K. At 300 K, λ is 6.3 Wm−1K−1, increasing with decreasing T to about 9.5 Wm−1K−1 near Tc. This T dependence is much stronger than in YBa2Cu3O7−δ (1-2-3). Only a very small enhancement is observed in λ below Tc. As in 1-2-3, λ is mainly limited by phonon scattering by defects.
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| 5. |
- Andersson, Britt M., et al.
(författare)
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Electrical resistivity and critical temperature of Bi-based high-Tc superconductors to 1 GPa
- 1990
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Ingår i: High Pressure Research, volumes 3 to 5. - London : Gordon and Breach. - 2881247466 ; 3:1-6, s. 120-122
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Konferensbidrag (refereegranskat)abstract
- We have measured the electrical resistance R of a sintered, two-phase, high-TC superconductor with the nominal composition BiSrCaCu2Ox, as a function of T and p. We find d(lnR)/dp ≃ -0.06 GPa-1 at 295 K, while dTC/dp is 2.5 K/GPa for the phase with Tc ≃ 76 and 2 K/GPa for that with TC ≃ 106 K.
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| 6. |
- Andersson, Britt M., et al.
(författare)
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Electrical transport in dense, bulk YBa2Cu4O8 produced by hot isostatic pressing
- 1990
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Ingår i: Physica B Volumes 165 & 166, Part 2. - : Elsevier B.V.. ; , s. 1699-1700
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Konferensbidrag (refereegranskat)abstract
- Dense (98.5%) bulk sintered specimens of YBa2Cu4O8 have been produced by hot isostatic pressing. Data for the electrical resistivity π versus temperature T and pressure p in the range 70–300 K and 0–0.7 GPa are reported and discussed. The critical current density of the material studied exceeds 100 Acm−2 below 60 K.
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| 7. |
- Andersson, Britt M., et al.
(författare)
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Electrical transport properties of dense bulk YBa2Cu4O8 produced by hot isostatic pressing
- 1990
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Ingår i: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 170:5-6, s. 521-531
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Tidskriftsartikel (refereegranskat)abstract
- Highly dense sintered YBa2Cu4O8 has been produced by hot isostatic pressing (HIP). The electrical resistivity varrho of this material has been measured as a function of temperature T and pressure varrho in the range 40–650 K and 0–0.7 GPa. Both the temperature dependence and the pressure dependence of varrho are found to be well described by a model based on the standard Bloch-Grüneisen theory. It is pointed out that varrho is liner in T only under isobaric conditions, while varrho is strongly nonlinear in all high-Tc superconductors under isochoric (constant volume) conditions. The critical current density of the material is 900 A/cm2 at 4 K, while the resistivity is 630 μΩ cm at 294 K.
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| 8. |
- Andersson, Britt M., et al.
(författare)
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High-pressure properties of high-Tc superconductor samples produced by hot isostatic pressing
- 1990
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Ingår i: High Pressure Research, volumes 3 to 5. - London : Gordon and Breach. - 2881247466 ; 3:1-6, s. 123-125
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Konferensbidrag (refereegranskat)abstract
- The electrical resistance of dense YBa2Cu3Ox and YBa2Cu4Oy produced by hot isostatic pressing has been measured vs. T and p. At 295 K we find d (ln R)/dp ≃ -0.12 and -0.09 GPa-1, respectively, with no systematic dependence on initial density. For 1-2-4, dTC/dp ≃ 5.1 K/GPa, which is ten times that of 1-2-3.
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| 9. |
- Andersson, Britt M., et al.
(författare)
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Thermal conductivity and thermal diffusivity of dense, bulk YBa2Cu4O8
- 1994
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Ingår i: High Temperatures - High Pressures volume 26, issue 1. - London : Pion Press. ; , s. 53-57
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Konferensbidrag (refereegranskat)abstract
- We have measured the thermal conductivity, lambda, and the thermal diffusivity, a, of dense bulk ceramic YBa2Cu4O8 (1-2-4) between 30 and 300 K. For this material lambda is about 10 W/Km near 100 K, comparable with the in-plane thermal conductivity for single crystals of the more common high-Tc material YBa2Cu3O7 (1-2-3). Also, lambda has a much stronger T dependence in 1-2-4 than in 1-2-3. We find that, for 1-2-4, lambda can be very well described by a semiclassical phonon theory, which includes phonon, electron, and boundary scattering. The difference between the present results and those for 1-2-3 can be explained mainly in terms of a smaller amount of point-defect scattering in 1-2-4 because of the stable oxygen stoichiometry of this material.
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| 10. |
- Andersson, Britt M., et al.
(författare)
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Thermal conductivity of polycrystalline YBa2Cu4O8
- 1994
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 49:6, s. 4189-4198
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the thermal conductivity κ and the thermal diffusivity a of a dense bulk ceramic polycrystalline sample of YBa2Cu4O8 (1:2:4) in the temperature range 30–300 K. We find κ≊10 W m-1 K-1 at 100 K, significantly higher than in ceramic YBa2Cu3O7-δ (1:2:3) and approaching the in-plane value for single-crystal 1:2:3, and decreasing to 7.6 W m-1 K-1 at 300 K. The data for this sample can be described by standard theories for phonon thermal conductivity of crystalline materials with boundary, phonon, and electron scattering. The higher κ in 1:2:4 as compared to 1:2:3 is, in this model, due to the smaller point defect scattering in the former. The fitted parameters for the three scattering mechanisms all agree with independent estimates based on simple models; inserting data for electric resistivity, grain size, carrier density, and lattice properties we can predict κ and its T dependence to within about 20%. We also discuss models for the phonon and electron thermal conductivities in some detail, including some second-order effects such as inelastic electron scattering and a T-dependent carrier density.
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| 11. |
- Andersson, Britt M., et al.
(författare)
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Thermal conductivity of YBa2Cu4O8 dominated by phonon-phonon interactions
- 1993
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 48:5, s. 3575-3578
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity κ of dense sintered ceramic YBa2Cu4O8 in the range 30–310 K has been measured. At 100 K, κ is 10 W m-1 K-1, approaching the in-plane κ of single crystals of other high-Tc materials. κ decreases rapidly with increasing T to 7.4 W m-1 K-1 at 300 K. Fitting standard models for κ(T) to the data we find that κ is limited mainly by phonon-phonon interactions. Depending on the model used, the best fit is found for effective values of FTHETADebye between 155 and 185 K, characteristic for the acoustic phonon branches, indicating that such phonons carry most of the heat. Finally, we suggest a possible way to test the electron-phonon model for the electrical and thermal conductivities in high-Tc materials.
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| 12. |
- Andersson, Britt M., et al.
(författare)
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Thermal conductivity of YBa2Cu4O8 under high pressure
- 1993
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Ingår i: Physica. C, Superconductivity. - : Elsevier B.V.. - 0921-4534 .- 1873-2143. ; 216:1-2, s. 187-194
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Tidskriftsartikel (refereegranskat)abstract
- The thermal diffusivity a of YBa2Cu4O8 (1-2-4) has been measured as a function of pressure p and temperature T over the range 85
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| 13. |
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| 14. |
- Eklund, Anders, et al.
(författare)
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Evaluation of applanation resonator sensors for intra-ocular pressure measurement : results from clinical and in vitro studies.
- 2003
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 41:2, s. 190-197
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Tidskriftsartikel (refereegranskat)abstract
- Glaucoma is an eye disease that, in its most common form, is characterised by high intra-ocular pressure (IOP), reduced visual field and optic nerve damage. For diagnostic purposes and for follow-up after treatment, it is important to have simple and reliable methods for measuring IOP. Recently, an applanation resonator sensor (ARS) for measuring IOP was introduced and evaluated using an in vitro pig-eye model. In the present study, the first clinical evaluation of the same probe has been carried out, with experiments in vivo on human eyes. There was a low but significant correlation between IOP(ARS) and the IOP measured with a Goldmann applanation tonometer (r = 0.40, p = 0.001, n = 72). However, off-centre positioning of the sensor against the cornea caused a non-negligible source of error. The sensor probe was redesigned to have a spherical, instead of flat, contact surface against the eye and was evaluated in the in vitro model. The new probe showed reduced sensitivity to off-centre positioning, with a decrease in relative deviation from 89% to 11% (1 mm radius). For normalised data, linear regression between IOP(ARS) and direct IOP measurement in the vitreous chamber showed a correlation of r = 0.97 (p < 0.001, n = 108) and a standard deviation for the residuals of SD < or = 2.18 mm Hg (n = 108). It was concluded that a spherical contact surface should be preferred and that further development towards a clinical instrument should focus on probe design and signal analysis.
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| 15. |
- Ekstrand-Hammarström, Barbro, et al.
(författare)
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Oxidative stress and cytokine expression in respiratory epithelial cells exposed to well-characterized aerosols from Kabul, Afghanistan
- 2013
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Ingår i: Toxicology in Vitro. - : Elsevier BV. - 0887-2333 .- 1879-3177. ; 27:2, s. 825-833
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Tidskriftsartikel (refereegranskat)abstract
- In this study aerosol samples collected in an Asian mega-city (Kabul, Afghanistan) were compared to PM samples collected in a European location with traffic (Umea, Sweden) and a reference urban dust material (SRM 1649b). The toxicity of each sample towards normal human bronchial epithelial (NHBE) cells and a human bronchial epithelial cell line (BEAS-2B) was tested along with their ability to induce reactive oxygen species (ROS) formation and inflammatory responses. The extracts' morphology and elemental composition was studied by SEM-EDXRF, and filter samples were analyzed for metals and organic compounds. The PM from Kabul contained a larger fraction of fine particles, 19 times more polyaromatic hydrocarbons (PAH) and 37 times more oxygenated PAH (oxy-PAH) compared to samples from timed. The PM-samples from Kabul and the reference material (SRM 1649b) induced significantly stronger oxidative stress responses than the samples from Umea. Furthermore, samples collected in Kabul induced significantly higher secretion of the cytokines IL-6, IL-8 and GM-CSF while SRM1649b induced a cytokine pattern more similar to samples collected in Umea. Several properties of the particles could potentially explain these differences, including differences in their size distribution and contents of PAH and oxy-PAH, possibly in combination with their relative transition metal contents.
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| 16. |
- Geschwindner, Stefan, et al.
(författare)
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Characterisation of de novo mutations in the C-terminal domain of proprotein convertase subtilisin/kexin type 9.
- 2015
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Ingår i: Protein Engineering Design & Selection. - : Oxford University Press (OUP). - 1741-0126 .- 1741-0134.
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Tidskriftsartikel (refereegranskat)abstract
- Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes the degradation of the hepatic low-density lipoprotein receptor (LDL-R) and is therefore a prominent therapeutic target for reducing LDL-cholesterol. The C-terminal domain of PCSK9 is unlikely to be involved in a direct extracellular interaction with the LDL-R. We probed the importance of the C-terminus for the degradation of the LDL-R by designing seven de novo mutants of PCSK9 that fill potential druggable cavities. The mutants were tested for their ability to diminish LDL uptake in human HepG2 cells and for affinity towards a calcium independent mutant of the EGF(A) domain of the human LDL-R. The later was done by a newly developed surface plasmon resonance-based assay format. We identified three mutant proteins (G517R, V610R and V644R) with decreased ability to block LDL uptake into HepG2 cells. These mutations define areas outside the direct interaction area between PCSK9 and the LDL-R that could be targeted to inhibit the PCSK9 triggered degradation of the LDL-R. We also describe the mechanistic rationalisation of the affinity changes seen with the natural occurring human D374Y (gain of function) mutation causing severe hypercholesterolaemia. The action of this mutant is due to a significantly decreased dissociation rate constant, whereas the mutation does not affect the association rate constant.
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Jalkanen, Ville, 1978-, et al.
(författare)
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Explanatory models for a tactile resonance sensor system-elastic and density-related variations of prostate tissue in vitro
- 2008
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Ingår i: Physiological Measurement. - Bristol : IOP Publ. Ltd. - 0967-3334 .- 1361-6579. ; 29:7, s. 729-745
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Tidskriftsartikel (refereegranskat)abstract
- Tactile sensors based on piezoelectric resonance have been adopted for medical applications. The sensor consists of an oscillating piezoelectric sensor–circuit system, and a change in resonance frequency is observed when the sensor tip contacts a measured object such as tissue. The frequency change at a constant applied force or mass load is used as a stiffness-sensitive parameter in many applications. Differential relations between force and frequency have also been used for monitoring intraocular pressure and stiffness variations in prostate tissue in vitro. The aim of this study was to relate the frequency change (Δf), measured force (F) and the material properties, density and elasticity to an explanatory model for the resonance sensor measurement principle and thereby to give explanatory models for the stiffness parameters used previously. Simulations of theoretical equations were performed to investigate the relation between frequency change and contact impedance. Measurements with a resonance sensor system on prostate tissue in vitro were used for experimental validation of the theory. Tissue content was quantified with a microscopic-based morphometrical method. Simulation results showed that the frequency change was dependent upon density (ρ) and contact area (S) according to Δf ∝ ρS3/2. The experiments followed the simulated theory at small impression depths. The measured contact force followed a theoretical model with the dependence of the elastic modulus (E) and contact area, F ∝ ES3/2. Measured density variations related to histological variations were statistically weak or non-significant. Elastic variations were statistically significant with contributions from stroma and cancer relative to normal glandular tissue. The theoretical models of frequency change and force were related through the contact area, and a material-dependent explanatory model was found as Δf ∝ ρE−1F. It explains the measurement principle and the previously established stiffness parameters from the material properties point of view.
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| 21. |
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| 22. |
- Jalkanen, Ville, 1978-, et al.
(författare)
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Prostate tissue stiffness as measured with a resonance sensor system : a study on silicone and human prostate tissue in vitro.
- 2006
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Ingår i: Medical and Biological Engineering and Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 44:7, s. 593-603
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Tidskriftsartikel (refereegranskat)abstract
- Prostate cancer is the most common form of cancer in men in Europe and in the USA. Some prostate tumours are stiffer than the surrounding normal tissue, and it could therefore be of interest to measure prostate tissue stiffness. Resonance sensor technology based on piezoelectric resonance detects variations in tissue stiffness due to a change in the resonance frequency. An impression-controlled resonance sensor system was used to detect stiffness in silicone rubber and in human prostate tissue in vitro using two parameters, both combinations of frequency change and force. Variations in silicone rubber stiffness due to the mixing ratio of the two components could be detected (p<0.05) using both parameters. Measurements on prostate tissue showed that there existed a statistically significant (MANOVA test, p<0.001) reproducible difference between tumour tissue (n=13) and normal healthy tissue (n=98) when studying a multivariate parameter set. Both the tumour tissue and normal tissue groups had variations within them, which were assumed to be related to differences in tissue composition. Other sources of error could be uneven surfaces and different levels of dehydration for the prostates. Our results indicated that the resonance sensor could be used to detect stiffness variations in silicone and in human prostate tissue in vitro. This is promising for the development of a future diagnostic tool for prostate cancer.
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| 23. |
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| 24. |
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| 25. |
- Jalkanen, Ville, 1978-, et al.
(författare)
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Resonance sensor measurements of stiffness variations in prostate tissue in vitro : a weighted tissue proportion model
- 2006
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Ingår i: Physiological Measurement. - : IOP Publishing. - 0967-3334 .- 1361-6579. ; 27:12, s. 1373-86
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Tidskriftsartikel (refereegranskat)abstract
- Prostate cancer is the most common type of cancer in men in Europe and the US. The methods to detect prostate cancer are still precarious and new techniques are needed. A piezoelectric transducer element in a feedback system is set to vibrate with its resonance frequency. When the sensor element contacts an object a change in the resonance frequency is observed, and this feature has been utilized in sensor systems to describe physical properties of different objects. For medical applications it has been used to measure stiffness variations due to various patho-physiological conditions. In this study the sensor's ability to measure the stiffness of prostate tissue, from two excised prostatectomy specimens in vitro, was analysed. The specimens were also subjected to morphometric measurements, and the sensor parameter was compared with the morphology of the tissue with linear regression. In the probe impression interval 0.5-1.7 mm, the maximum R(2) > or = 0.60 (p < 0.05, n = 75). An increase in the proportion of prostate stones (corpora amylacea), stroma, or cancer in relation to healthy glandular tissue increased the measured stiffness. Cancer and stroma had the greatest effect on the measured stiffness. The deeper the sensor was pressed, the greater, i.e., deeper, volume it sensed. Tissue sections deeper in the tissue were assigned a lower mathematical weighting than sections closer to the sensor probe. It is concluded that cancer increases the measured stiffness as compared with healthy glandular tissue, but areas with predominantly stroma or many stones could be more difficult to differ from cancer.
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| 26. |
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| 27. |
- Jalkanen, Ville, 1978-, et al.
(författare)
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Spatial variations in prostate tissue histology as measured by a tactile resonance sensor
- 2007
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Ingår i: Physiological Measurement. - : IOP Publishing. - 0967-3334 .- 1361-6579. ; 28:10, s. 1267-81
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, tactile sensors based on piezoelectric resonance sensor technology have been used for medical diagnosis where the sensor's stiffness-measuring properties can reflect tissue pathology. The change in the frequency of the resonating system and the change in force when contact is made with tissue are used as a stiffness parameter. Earlier stiffness measurements of prostate tissue in vitro demonstrate variations related to tissue composition. In this study, measured stiffness from two human prostate specimens was compared to histological composition of prostate tissue below and around the measurement points. Tissue stiffness was measured with the resonance sensor system. Tissue composition was measured at four different depths in the tissue specimen using a microscopic-image-based morphometrical method. With this method, the proportion of tissue types was determined at the points of intersections in a circular grid on the images representing each measurement point. Numerical values were used for weighting the tissue proportions at different depths in the tissue specimen. For an impression depth of 1.0 mm, the sensing depth in this study was estimated to be 3.5-5.5 mm. Stiffness variations due to horizontal tissue variations were investigated by studying the dependence of the size of the circular grid area relative to the contact area of the sensor tip. The sensing area (grid radius) was estimated to be larger than the contact area (contact radius) between the sensor tip and the tissue. Thus, the sensor tip registers spatial variations in prostate tissue histology, both directly below and lateral to the tip itself. These findings indicate that tumours around the sensor tip could be detected, which in turn supports the idea of a future resonance-sensor-based clinical device for detecting tumours and for guiding biopsies.
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| 28. |
- Jalkanen, V., et al.
(författare)
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Stiffness of a small tissue phantom measured by a tactile resonance sensor
- 2010
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Ingår i: XIIth Mediterranean Conference on Medical and Biological Engineering and Computing 2010. - Berlin : Springer Science+Business Media B.V.. - 9783642130380 - 9783642130397 ; , s. 395-398
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Konferensbidrag (refereegranskat)abstract
- Many pathological conditions, for instance cancer, alter the elastic stiffness of tissues. Therefore, it is of interest to objectively quantify the stiffness of tissue samples. Tactile resonance sensor technology has been proven to measure the stiffness of tissues in a variety of medical applications. The technique is based on a vibrating piezoelectric sensor element that changes its resonance frequency when it is put in contact with a soft object to be measured. The frequency change is related to the mechanical properties of the soft object. This principle is implemented in an indentation setup where also the impression force and impression depth can be measured. The aim of this study was to investigate how the measured parameters of a tactile resonance sensor system depend on the limited size of a small gelatin tissue phantom sample. Indentation measurements were conducted on different locations on a small gelatin sample. Results showed that the force and frequency change were dependent of the measurement location and thus the sample geometry. The estimated stiffness was independent of the measurement location. Further studies must be conducted to determine the full value of the method for measuring the stiffness of small tissue samples.
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| 29. |
- Jonsson, Ulf G., 1950-, et al.
(författare)
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A FEM-Based Method Using Harmonic Overtones to Determine the Effective Elastic, Dielectric, and Piezoelectric Parameters of Freely Vibrating Thick Piezoelectric Disks
- 2013
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - New York : IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society. - 0885-3010 .- 1525-8955. ; 60:1, s. 243-255
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Tidskriftsartikel (refereegranskat)abstract
- To gain an understanding of the electroelasticproperties of tactile piezoelectric sensors used in the characterizationof soft tissue, the frequency-dependent electric impedanceresponse of thick piezoelectric disks has been calculatedusing finite element modeling. To fit the calculated to the measuredresponse, a new method was developed using harmonicovertones for tuning of the calculated effective elastic, piezoelectric,and dielectric parameters. To validate the results, theimpedance responses of 10 piezoelectric disks with diameterto-thickness ratios of 20, 6, and 2 have been measured from10 kHz to 5 MHz. A two-dimensional, general purpose finiteelement partial differential equation solver with adaptive meshingcapability run in the frequency-stepped mode, was used.The equations and boundary conditions used by the solver arepresented. Calculated and measured impedance responses arepresented, and resonance frequencies have been compared indetail. The comparison shows excellent agreement, with averagerelative differences in frequency of 0.27%, 0.19%, and0.54% for the samples with diameter-to-thickness ratios of 20,6, and 2, respectively. The method of tuning the effective elastic,piezoelectric, and dielectric parameters is an importantstep toward a finite element model that describes the propertiesof tactile sensors in detail.
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| 30. |
- Jonsson, Ulf G, et al.
(författare)
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Modeling the high-frequency complex modulus of a silicone rubber using standing lamb waves and an inverse finite element method
- 2014
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - : IEEE Press. - 0885-3010 .- 1525-8955. ; 61:12, s. 2106-2120
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Tidskriftsartikel (refereegranskat)abstract
- To gain an understanding of the high-frequency elastic properties of silicone rubber, a finite element model of a cylindrical piezoelectric element, in contact with a silicone rubber disk, was constructed. The frequency dependent elastic modulus of the silicone rubber was modeled by a four parameter fractional derivative viscoelastic model in the 100 kHz to 250 kHz frequency range. The calculations were carried out in the range of the first radial resonance frequency of the sensor. At the resonance, the hyperelastic effect of the silicone rubber was modeled by a hyperelastic compensating function. The calculated response was matched to the measured response by using the transitional peaks in the impedance spectrum that originates from the switching of standing Lamb wave modes in the silicone rubber. To validate the results, the impedance responses of three 5 mm thick silicone rubber disks, with different radial lengths, were measured. The calculated and measured transitional frequencies have been compared in detail. The comparison showed very good agreement, with average relative differences of 0.7 %, 0.6 %, and 0.7 % for the silicone rubber samples with radial lengths of 38.0 mm, 21.4 mm, and 11.0 mm, respectively. The average, complex, elastic modulus of the samples were: (0.97 + 0.009i) GPa at 100 kHz and (0.97 + 0.005i) GPa at 250 kHz.
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| 31. |
- Jonsson, Ulf G., et al.
(författare)
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Using a look-up table technique and finite element calculations for quick detection of stiff inclusions in silicone rubber
- 2020
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Ingår i: Engineering computations. - : Emerald Group Publishing Limited. - 0264-4401 .- 1758-7077. ; 37:6, s. 2137-2153
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The aim of the study was to show that a new method, using a look-up table technique, can be used to detect the presence and position of an inclusion embedded in a tissue-like material. Due to the time-consuming nature of the finite element (FE) method or FEM, real-time applications involving FEM as part of a control loop, are traditionally limited to slowly varying systems. By using a simplified two-dimensional FE model and a look-up table, we show by simulations and experiments that it is possible to achieve reasonable computational times in a tactile resonance sensor application.Design/methodology/approach: A piezoelectric disk was placed in the center of a silicone rubber disk (SRD) with viscoelastic properties, where it acted as both sensor and actuator and dissipated radial acoustic waves into the silicone. The look-up table was constructed by calculating the radial Lamb wave transition frequencies in the impedance frequency response of the sensor while varying the position of an inclusion. A position-matching algorithm was developed that matched measured and calculated Lamb wave transitions and thereby identified the presence and position of an inclusion.Findings: In an experiment, the position of a hard inclusion was determined by measuring the Lamb transition frequencies of the first radial resonance in two SRDs. The result of the matching algorithm for Disk 1 was that the matched position was less than 3% from the expected value. For Disk 2, the matching algorithm erroneously reported two false positions before reporting a position that was less than 5% from the expected value. An explanation for this discrepancy is presented. In a verifying experiment, the algorithm identified the condition with no inclusion present.Originality/value: The approach outlined in this work, adds to the prospect of developing time-sensitive diagnostic instruments. This approach has the potential to provide a powerful technique to quickly present spatial information on detected tumors.
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| 32. |
- Jonsson, Ulf G, et al.
(författare)
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Using Standing Lamb waves and the Finite Element Method to Detect Hard Inclusions in Silicone Rubber Disks
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The presence of an inclusion in a cylindrical silicone rubber disk is determined using FEM, standing Lamb waves, and an algorithm using multiple frequency footprints. Radial elastic waves are emitted into the disk by a cylindrical piezoelectric sensor placed in the center of the disk. The visco-elastic properties of the silicone rubber disk is modeled by a fractional derivative model and the hyperelastic effect at the radial resonance frequency was compensated for. Using the finite element model, the Lamb wave transition frequencies in the impedance frequency response of the sensor was calculated for a specified position of the inclusion. The set of frequencies was named the footprint for that position. The position of the inclusion was varied between 0.05 to 0.95, with a step of 0.01, of the radial length of the silicone rubber disk. For each position, a footprint was calculated. The footprints,s, with corresponding positions, were stored in a database. A positioning algorithm was developed that could match an unknown footprint to a footprint in the database. A self-test of the algorithm showed that the correct position was found for 94% of the tested positions. The results of the positioning algorithm was that the presence of the inclusions were detected, and that the positions of the inclusions at 0.38 and 0.63 were estimated by the positioning algorithm as: 0.45 and 0.74, with relative errors +18% and +17% respectively. The positions are given as the ratio of the radius of the inclusion to the silicone rubber disk radius.
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| 33. |
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| 34. |
- Kumar Wagri, Naresh, 1988-
(författare)
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Assessment of bio-based fuel ash effects on magnesia refractory materials in quicklime production kilns
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Limestone is calcined into quicklime in lime kilns at temperatures above 1000°C. Heat is supplied through combustion inside the kilns, which are insulated with a lining of refractory bricks to mitigate heat loss and to protect the kiln from the hot, chemically aggressive, and mechanically abrasive environment. While magnesia bricks have proven to be effective lining materials, they are still susceptible to extensive wear in lime kilns, especially in the burn zone. Refractory corrosion, in particular, can occur when melted fuel ash infiltrates the refractory materials through pores and small cracks. This resultant wear can lead to high maintenance and operational costs, often due to unplanned kiln shutdowns.To reduce the release of fossil-based carbon dioxide into the atmosphere from lime production kilns, there is a growing interest in introducing bio-based fuels with only relatively minor modifications to the process. Biomass fuels can be sourced from bio-based waste streams from industries or be specifically cultivated for combustion. However, the ash content and properties of bio-based fuels tend to be problematic from an ash chemistry perspective. Therefore, before introducing a new fuel source, it is essential to investigate its potential effects on the kiln lining material. In this thesis work, the interactions between melted olive pomace ash and coal ash with commercially available magnesia refractory materials, primarily composed of periclase (MgO) with minor amounts of spinel (MgAl2O4), were studied. A procedure for quantifying the intrusion depths was described. Refractory samples were exposed to the fuel ashes under a simulated lime kiln atmosphere with high CO2 levels at 1200 and 1400°C for 15 and 60 minutes. Cold crushing strength tests were conducted on refractory samples exposed to coal and olive pomace ash, along with CaO powder, at 1400°C for 96 hours. Additionally, postmortem analyses of spent MgO-based refractory bricks were carried out to investigate their chemical characterization and resistance to slag attack after serving as part of the lining in a quick lime rotary kiln for six months.The morphology and elemental compositions of the exposed samples were examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Crystalline phases were investigated with powder X-ray diffraction. Thermodynamic equilibrium calculations were performed to further investigate the ash’s melting behavior in contact with the refractories.The results indicated that the potassium-rich olive pomace ash exhibited a greater tendency to infiltrate compared to the silicon-rich coal ash, while the latter formed a glassy melt layer on top of the refractory samples. The ash slags primarily infiltrated through the porous matrix and grain boundaries of the refractory materials. Also, refractory phases were observed in both types of ashes, indicating migration of refractory constituents. K2MgSiO4 phase was found in the olive pomace ash residues on top of the samples, both for the 1200°C and 1400°C exposures. Similarly, Al6Si2O13 phase was dominant in the residual coal ash, in both the 1200°C and 1400°C exposed samples. None of these phases were present in the original ashes.The results of the postmortem analysis revealed that there was no potassium (K) from the fuel ash present on the hot side of the refractory bricks. However, some K was detected in the middle and back parts of the bricks. On the other hand, some phases, possibly connected to degradation, could be found on the hot side of the bricks, where most of the wear was observed.The crushing strengths increased after exposure for all samples, except for those exposed exclusively to coal ash. One possible explanation for this is that the refractory materials exhibited a sintered structure, as a result of their interaction with the ashes and CaO. However, in the samples exposed to coal ash, forsterite (Mg2SiO4) was identified, which can be considered a corrosion product.
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| 35. |
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| 36. |
- Kumar Wagri, Naresh, et al.
(författare)
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High temperature interactions between coal ash and MgO-based refractories in lime kiln conditions
- 2023
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Ingår i: Fuel. - : Elsevier. - 0016-2361 .- 1873-7153. ; 342
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Tidskriftsartikel (refereegranskat)abstract
- Magnesium oxide (MgO)-based refractories are commonly used in quicklime and cement rotary kilns. At the high temperatures in the kiln burn zone, the infiltration of molten fuel ash into the refractory can occur. Subsequent chemical interactions can cause refractory wear that inflicts high maintenance costs and loss of production. To improve refractory reliability, it is necessary to increase the understanding of the interactions between fuel ash slag and refractory liner materials. Three commercially available MgO-based refractory materials were exposed to coal ash at 1200 °C and 1400 °C for between 15 and 60 min under a CO2-rich gaseous environment. Hot slag from the coal ash infiltrated the refractories and the infiltration depths were estimated with scanning electron microscope with energy dispersive X-ray spectroscopy. Based on detailed elemental and microstructure analyses, the interactions between ash and refractory were examined. Molten silicates infiltrated the refractory through grain boundaries and pores into depths of up to 2.8 mm. Powder X-ray diffraction of the exposed refractory samples indicated that MgO grains reacted with SiO2-containing phases to form Mg2SiO4. This was identified as a corrosion product whose formation was supported by thermochemical equilibrium calculations. Elevated Mg content was found in the ash residue on top of the samples, indicating the dissolution or dislocation of refractory components. In addition, phases such as MgO were identified in the ash residue.
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| 37. |
- Kumar Wagri, Naresh, et al.
(författare)
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High temperature interactions between K-rich biomass ash and MgO-based refractories
- 2023
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Ingår i: Journal of the European Ceramic Society. - : Elsevier. - 0955-2219 .- 1873-619X. ; 43:8, s. 3770-3777
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Tidskriftsartikel (refereegranskat)abstract
- MgO-based refractories are used in lime kilns to withstand the high temperature and chemical environment. Efforts to reduce CO2 emissions have led to an increased interest to use bio-based fuels as alternatives to traditional fossil sources. The potential for refractory corrosion from a potassium-rich biomass ash was investigated by studying the infiltration of olive pomace ash into magnesia/spinel refractories. Refractory samples were exposed to the ash at up to 1400 °C for 15–60 min in a CO2–rich atmosphere. Molten ash infiltrated the refractories through pores and grain boundaries to a depth of up to 9.6 mm, which was quantified with a new systematic procedure. The phase KAlO2 was identified inside the refractories after exposure, indicating an attack of spinel components by potassium. Phases found in the ash residues also indicated the migration of refractory constituents. Thermochemical equilibrium calculations were also used to investigate the ash/refractory chemistry.
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| 38. |
- Kumar Wagri, Naresh, et al.
(författare)
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Interaction of olive pomace ash and coal ash with magnesium oxide based refractories
- 2022
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Ingår i: Proceedings of the 28th International Conference on the Impact of Fuel Quality on Power Production and the Environment. - : Department of Applied Physics and Electronics, Umeå University.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In quicklime production, limestone is calcined at temperatures above 1000°C, depending on the desired product quality. Heat is supplied to the process from combustion inside the kilns that are insulated to reduce heat loss. The kilns are lined with insulating refractory bricks to withstand the hot, chemically aggressive, and mechanically abrasive environment. Magnesia bricks have emerged as well-performinglining materials, but they are still prone to extensive wear in kilns that are operated at higher temperatures. In particular, refractory corrosion can be caused by fuel ash infiltration that results inmaterial wear, which can incur high maintenance and operational costs through unplanned shutdowns of the kilns. At the same time, to reduce the release of fossil-based carbon to the atmosphere, it is of interest to introduce bio-based fuels into the kilns with only relatively small modifications to the process. Biobased waste streams from existing industries are preferable rather than biomass grown with the sole purpose of combustion. The ash content and properties of these types of waste residues do, however, tend to be problematic from a fuel ash chemistry point of view. Therefore, before introducing a new fuel, their potential effects on kiln lining material should be investigated. In this study, the infiltration of olivepomace ash and coal ash into commercially available refractory materials composed of mainly periclase(MgO) with minor amounts of spinel (MgAl2O4) were compared. They were exposed to the fuel ashes under a simulated lime kiln high CO2 atmosphere at 1200 and 1400°C for 15 and 60 minutes. The morphology and elemental composition of the exposed samples were investigated with scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. Ash-forming elements infiltrated the porous parts of the materials. The analytical results are complemented with thermodynamic equilibrium calculations to investigate the ash melting behavior. Crystalline phases in the residual ashes were investigated with X-ray diffraction. Refractory phases could be found in both ashes, indicating migration of refractory constituents. Olive pomace ash formed new crystalline compounds together with the refractory components whereas this was not observed for the coal ash, indicating that the former is more of a risk for material failure.
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| 39. |
- Lindahl, Olof A, et al.
(författare)
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Biomedical engineering research improves the health care industry
- 2014
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Ingår i: XIII Mediterranean Conference on Medical and Biological Engineering and Computing 2013. - Cham : Springer. - 9783319008455 - 9783319008462 ; , s. 1124-1126
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Konferensbidrag (refereegranskat)abstract
- The health care industry is dependent on new innovations for its survival and expansion. Health care innovations are also important for improving patient care. Through activities at the centre for biomedical engineering and physics (CMTF) we have generated growth both in academia at the universities and in the industry in northern Sweden. Fruitful cooperation was generated between 26 research projects and about 15 established companies in the field of biomedical engineering. The established researcher-owned company for business development of the research results from the CMTF, CMTF Business Development Co Ltd, has so far launched three spin-off companies and has 10 new business leads to develop. The activities have also increased the interest for commercialization and entrepreneurship among the scientists in the centre. So far a total of nine spin-off companies have resulted from the CMTF-research since the year 2000 that has improved the health care market in northern Sweden. © Springer International Publishing Switzerland 2014.
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| 40. |
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| 41. |
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| 42. |
- Lindberg, Peter L, et al.
(författare)
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An image analysis method for prostate tissue classification : preliminary validation with resonance sensor data
- 2009
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Ingår i: Journal of Medical Engineering & Technology. - : Informa healthcare. - 0309-1902 .- 1464-522X. ; 33:1, s. 18-24
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Tidskriftsartikel (refereegranskat)abstract
- Resonance sensor systems have been shown to be able to distinguish between cancerous and normal prostate tissue, in vitro. The aim of this study was to improve the accuracy of the tissue determination, to simplify the tissue classification process with computerized morphometrical analysis, to decrease the risk of human errors, and to reduce the processing time. In this article we present our newly developed computerized classification method based on image analysis. In relation to earlier resonance sensor studies we increased the number of normal prostate tissue classes into stroma, epithelial tissue, lumen and stones. The linearity between the impression depth and tissue classes was calculated using multiple linear regression (R(2) = 0.68, n = 109, p < 0.001) and partial least squares (R(2) = 0.55, n = 109, p < 0.001). Thus it can be concluded that there existed a linear relationship between the impression depth and the tissue classes. The new image analysis method was easy to handle and decreased the classification time by 80%.
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| 43. |
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| 44. |
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| 45. |
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| 46. |
- Mejtoft, Thomas, Universitetslektor, 1976-, et al.
(författare)
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Medtech innovation guide : an empiric model to support medical technology innovation
- 2022
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Ingår i: Health and Technology. - : Springer. - 2190-7188 .- 2190-7196. ; 12:5, s. 911-922
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Tidskriftsartikel (refereegranskat)abstract
- Innovation has become increasingly important for most industries to cope with rapid technological changes as well as changing societal needs. Even though there are many sectors with specific needs when it comes to supporting innovation, the medical technology sector is facing several unique challenges that both increases the lead-time from idea to finished product and decreases the number of innovations that are developed. This paper presents a proposed innovation guide that has been developed and evaluated as a support for the innovation process within medical technology research. The guide takes the unique characteristics of the medical technology sector into account and serves as a usable guide for the innovator. The complete guide contains both a structure for the process and a usable web application to support the journey from idea to finished products and services. The paper also includes a new readiness level, Sect. 4.2 to provide support both when developing and determining the readiness for clinical implementation of a medical technology innovation.
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| 47. |
- Niska, John, et al.
(författare)
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Formation of the 124 phase superconductor (YBa2Cu4O8) by retaining oxygen in a reaction HIP sintering process
- 1990
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Ingår i: Journal of materials science letters. - 0261-8028 .- 1573-4811. ; 9:7, s. 770-771
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Tidskriftsartikel (refereegranskat)abstract
- The ceramic superconductor YBa2Cu4O8 has been produced by high temperature sintering of a mixture of CuO and YBa2Cu3O7 in a glass capsule under high hydrostatic argon pressure. The resulting highly dense material is investigated by X-ray diffraction, optical and electron microscopy, resistance measurements and hardness measurements, and shown to be a homogeneous High transition temperature superconductor.
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| 48. |
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