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| 2. |
- Blom, Hans, et al.
(författare)
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Nearest neighbor analysis of dopamine D1 receptors and Na plus -K plus -ATPases in dendritic spines dissected by STED microscopy
- 2012
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Ingår i: Microscopy research and technique (Print). - : Wiley. - 1059-910X .- 1097-0029. ; 75:2, s. 220-228
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Tidskriftsartikel (refereegranskat)abstract
- Protein localization in dendritic spines is the focus of intense investigations within neuroscience. Applications of super-resolution microscopy to dissect nanoscale protein distributions, as shown in this work with dual-color STED, generate spatial correlation coefficients having quite small values. This means that colocalization analysis to some extent looses part of its correlative impact. In this study we thus introduced nearest neighbor analysis to quantify the spatial relations between two important proteins in neurons, the dopamine D1 receptor and Na+,K+-ATPase. The analysis gave new information on how dense the D1 receptor and Na+,K+-ATPase constituting nanoclusters are located both with respect to the homogenous (self to same) and the heterogeneous (same to other) topology. The STED dissected nanoscale topologies provide evidence for both a joint as well as a separated confinement of the D1 receptor and the Na+,K+-ATPase in the postsynaptic areas of dendritic spines. This confined topology may have implications for generation of local sodium gradients and for structural and functional interactions modulating slow synaptic transmission processes. Microsc. Res. Tech., 2011.
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| 3. |
- Ferraz, Natalia, 1976-, et al.
(författare)
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Time sequence of blood activation by nanoporous alumina : Studies on platelets and complement system
- 2010
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Ingår i: Microscopy research and technique (Print). - : Wiley-Liss Inc.. - 1059-910X .- 1097-0029. ; 73:12, s. 1101-1109
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Tidskriftsartikel (refereegranskat)abstract
- In the present work the time sequence of blood activation by alumina membranes with different porosities (20 and 200 nm in diameter) was studied. The membranes were incubated with whole blood from 2 min to 4 h. Platelet adhesion and activation in addition to complement activation were monitored at different time points. Evaluation of platelet adhesion and activation was done by determining the change in platelet number and the levels of thrombospondin-1 in the fluid phase. Scanning electron microscopy studies were done to further evaluate platelet adhesion and morphology. Immunocytochemical staining was used to evaluate the presence of CD41 and CD62P antigens on the material surface. Complement activation was monitored by measuring C3a and sC5b-9 in plasma samples by means of enzyme immunoassays. Both alumina membranes displayed similar complement activation time profiles, with levels of C3a and sC5b-9 increasing with incubation time. A statistically significant difference between the membranes was found after 60 min of incubation. Platelet activation characteristics and time profile were different between the two membranes. Platelet adhesion increased over time for the 20 nm surface, while the clusters of microparticles on the 200 nm surface did not appreciably change during the course of the experiment. The release of thrombospondin-1 increased with time for both membranes, however much later for the 200 nm alumina (240 min) as compared to the 20 nm membrane (60 min). The surface topography of the alumina most probably influence protein transition rate, which in turn affects material-platelet activation kinetics.
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| 4. |
- Rieppo, Lassi, et al.
(författare)
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Quantitative analysis of spatial proteoglycan content in articular cartilage with Fourier transform infrared imaging spectroscopy : Critical evaluation of analysis methods and specificity of the parameters.
- 2010
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Ingår i: Microscopy research and technique (Print). - : John Wiley & Sons. - 1059-910X .- 1097-0029. ; 73:5, s. 503-512
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To evaluate the specificity of the current Fourier transform infrared imaging spectroscopy (FT-IRIS) methods for the determination of depthwise proteoglycan (PG) content in articular cartilage (AC). In addition, curve fitting was applied to study whether the specificity of FT-IRIS parameters for PG determination could be improved.METHODS: Two sample groups from the steer AC were prepared for the study (n = 8 samples/group). In the first group, chondroitinase ABC enzyme was used to degrade the PGs from the superficial cartilage, while the samples in the second group served as the controls. Samples were examined with FT-IRIS and analyzed using previously reported direct absorption spectrum techniques and multivariate methods and, in comparison, by curve fitting. Safranin O-stained sections were measured with digital densitometry to obtain a reference for depthwise PG distribution.RESULTS: Carbohydrate region-based absorption spectrum methods showed a statistically weaker correlation with the PG reference distributions than the results of the curve fitting (subpeak located approximately at 1,060 cm(-1)). Furthermore, the shape of the depthwise profiles obtained using the curve fitting was more similar to the reference profiles than with the direct absorption spectrum analysis.CONCLUSIONS: Results suggest that the current FT-IRIS methods for PG analysis lack the specificity for quantitative measurement of PGs in AC. The curve fitting approach demonstrated that it is possible to improve the specificity of the PG analysis. However, the findings of the present study suggest that further development of the FT-IRIS analysis techniques is still needed.
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| 5. |
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| 6. |
- Ask, Anna, et al.
(författare)
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Inverse-motion-based form finding for quasi-incompressible finite electroelasticity
- 2013
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 1097-0207 .- 0029-5981. ; 94:6, s. 554-572
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Tidskriftsartikel (refereegranskat)abstract
- This work deals with inverse-motion-based form finding for electroelasticity. The inverse motion problem is formulated for the electroelastic case, and the resulting equations are implemented within a finite element framework. A four-field variational approach is adopted, taking into consideration the typically incompressible behavior of the elastomer materials commonly used in electromechanical applications. By means of numerical simulations, the inverse-motion-based form finding makes it possible to design the referential configuration so that a given set of loads and boundary conditions results in a prespecified deformed configuration. The computational finite element framework established in this work allows for such numerical simulations and testing and thereby the possibility to improve the design and accuracy in electroelastic applications such as grippers, sensors, and seals.
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| 7. |
- Becker, R., et al.
(författare)
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A hierarchical NXFEM for fictitious domain simulations
- 2011
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 86:4-5, s. 549-559
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Tidskriftsartikel (refereegranskat)abstract
- We suggest a fictitious domain method, based on the Nitsche XFEM method of (Comput. Meth. Appl. Mech. Engrg 2002; 191: 5537-5552), that employs a band of elements adjacent to the boundary. In contrast, the classical fictitious domain method uses Lagrange multipliers on a line (surface) where the boundary condition is to be enforced. The idea can be seen as an extension of the Chimera method of (ESAIM: Math. Model Numer. Anal. 2003; 37: 495-514), but with a hierarchical representation of the discontinuous solution field. The hierarchical formulation is better suited for moving fictitious boundaries since the stiffness matrix of the underlying structured mesh can be retained during the computations. Our technique allows for optimal convergence properties irrespective of the order of the underlying finite element method.
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| 8. |
- Bengzon, Fredrik, 1978-, et al.
(författare)
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Adaptive finite element approximation of multiphysics problems : a fluid structure interaction model problem
- 2010
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 84:12, s. 1451-1465
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Tidskriftsartikel (refereegranskat)abstract
- We consider computation of the displacement of an elastic object immersed into a viscous incompressible flow. For simplicity, we assume that the mechanics of the solid is governed by linear elasticity and the motion of the fluid by the Stokes equation. We derive an a posteriori error estimate for this one way coupled problem using duality techniques. Based on these estimates we develop an adaptive algorithm that automatically constructs a suitable adapted mesh for the fluid and solid domains given goal quantities specified on the solid problem.
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| 9. |
- Compere, Gaetan, et al.
(författare)
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A mesh adaptation framework for dealing with large deforming meshes
- 2010
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley. - 0029-5981 .- 1097-0207. ; 82:7, s. 843-867
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Tidskriftsartikel (refereegranskat)abstract
- In this paper. we identify and propose solutions for several issues encountered when designing a mesh adaptation package, such as mesh-to-mesh projections and mesh database design, and we describe an algorithm to integrate a mesh adaptation procedure in a physics solver. The open-source MAdLib package is presented as an example of such a mesh adaptation library. A new technique combining global node repositioning and mesh optimization in order to perform arbitrarily large deformations is also proposed. We then present several test cases to evaluate the performances of the proposed techniques and to show their applicability to fluid-structure interaction problems with arbitrarily large deformations. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 10. |
- Dazel, Olivier, et al.
(författare)
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A normal modes technique to reduce the order of poroelastic models : application to 2D and coupled 3D models
- 2013
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Ingår i: International Journal for Numerical Methods in Engineering. - : Wiley-Blackwell. - 0029-5981 .- 1097-0207. ; 96:2, s. 110-128
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Tidskriftsartikel (refereegranskat)abstract
- A reduced-order model for structures involving poroelastic materials is proposed in this paper. The approach is based on a separation of the solid and fluid phases of the porous material into separate substructures. For each individual substructure, a decoupled normal mode basis is considered, from which a set of vectors for the decomposition is selected. The preserved modes are completed by an additional family to correct for the influence of the static response of the non-preserved. It is shown that the only neglected phenomenons in the model are the inertia of the non-preserved modes and part of their intercoupling. The following three features render the proposed scheme computationally attractive: (i) real valued matrices are involved in the transformations; (ii) the assembly of complex, frequency dependent matrices is only performed at the stage of solving for a particular frequency; and (iii) the number of normal modes required are selected using a novel method.The computational efficacy is demonstrated, on a simple but realistic 3D case, through numerical results obtained using a reduced number of DOFs, showing a significant reduction of computational cost compared with traditional methods.
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