| 1. |
- Forslind, Bo, et al.
(författare)
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Aspects on the physiology of human skin : studies using particle probe analysis
- 1997
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Ingår i: Microscopy research and technique (Print). - 1059-910X .- 1097-0029. ; 38:4, s. 373-386
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Tidskriftsartikel (refereegranskat)abstract
- The cellular part of the skin, the epidermis, is a very thin structure, approximately 120 microns thick, a fact which has hindered the exploration of the physiology of the epidermis in normal and pathological conditions. An additional complication is the fact that the epidermis contains layers of cells at different stages of differentiation. Therefore, conventional physiological capillary probes cannot, with any satisfactory precision, be located within a specified cell of a specified layer of the skin in vivo. Hence, alternative ways for the exploration of skin physiology have been sought for. In the past, analysis of the elemental content of skin was done was done as bulk measurements, and surprisingly wide ranges of elemental content were recorded. The width of these ranges was most certainly due to the sampling methods used rather than the sensitivity of the chosen method of analysis. Also, these older measurements did not discriminate between the different strata, and therefore the information provided little if any substance for a functional analysis of processes involved in normal and pathological differentiation of the epidermis. Particle probes, however, have been able to overcome such methodological problems. Over a period of 15 years we have studied normal human skin, normal-looking, paralesional skin from psoriatics, and skin from persons suffering from atopic dermatitis using PIXE analysis. In recent years, trace elements have been shown to work as secondary messengers or regulatory substances. As an example, calcium (Ca2+) has proven to be a very important signalling substance in a great variety of cellular systems. Studies with the transmission electron microscope (TEM) as well as histochemical methods have allowed an understanding of the role of Ca2+ in the differentiation process of the epidermis. Ca2+ has also been shown to play an important role in apoptosis (programmed cell death), which is currently a hot subject for the obvious reason that the final differentiation step between the stratum granulosum level and the stratum corneum represents a particular aspect of programmed cell death. The importance of the balance between calcium and zinc in apoptosis has been clearly demonstrated in a number of cellular systems, but we have still to clarify the validity of topical treatment with Zn ointments in different skin conditions. Substantial iron (Fe) losses via psoriatic lesions were demonstrated more than two decades ago, and these data were given new meaning when we found that a more discrete loss occurs in clinically normal-looking psoriatic skin. Obviously, such findings stress the importance of understanding the relation between the elemental content and normal and abnormal physiology. The ultimate goal of particle probe studies is to provide an understanding of the formation of a mature stratum corneum with a functional barrier reflected in physiological/biochemical mechanisms behind the properties of changed skin in patients afflicted with skin disorders of genetic or constitutional origin. This paper aims to give an overview of the state of the art in skin physiology made possible through the use of particle probes.
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| 2. |
- Wei, Liu-Ying, et al.
(författare)
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Ultramicrotomy of powder material for TEM/STEM study
- 1997
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Ingår i: Microscopy research and technique (Print). - 1059-910X .- 1097-0029. ; 36:5, s. 380-381
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Tidskriftsartikel (refereegranskat)abstract
- This paper summarizes methods conventionally used to prepare thin foil samples of powder materials for transmission electron microscopy (TEM) and introduces another variant, ultramicrotomy, for the preparation of TEM samples of industrial dust powder. The choice of ultramicrotoming in the present work was based on two features of this technique: (1) it can produce thin-sectioned specimens with a uniform thickness; (2) it can retain the original elemental distribution in phases of the sample during sectioning. Dust powder preparation and the sectioning procedure are described in this paper. The results of the method are illustrated by examples of TEM/STEM micrographs of industrial dust.
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| 3. |
- Westman, Anna-Karin, et al.
(författare)
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Preparation for TEM of layered samples with fragile microstructure and weak layer interface
- 1999
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Ingår i: Microscopy research and technique (Print). - 1059-910X .- 1097-0029. ; 45:3, s. 198-202
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this work was to prepare for transmission electron microscopy (TEM) a layered structure of materials with fragile microstructure. The samples consisted of two layers of different materials, silicon nitride and borosilicate glass, loosely bonded together. The low strength of the sample resulted in fragmentation during more conventional preparation. However, it was possible to prepare the fragments by mounting them in a titanium specimen carrier with aluminium strips as support. After grinding and polishing, a technique of low-angle ion milling was used to obtain electron beam transparent areas at the nitride/glass interface.
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| 4. |
- Siegel, G, et al.
(författare)
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Tumor cell locomotion and metastatic spread
- 1998
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Ingår i: Microscopy research and technique (Print). - 1059-910X .- 1097-0029. ; 43, s. 276-282
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Tidskriftsartikel (refereegranskat)abstract
- The cytoskeletal filament proteins cu-actinin, filamin, desmin, and filamin-desmin aggregates were adsorbed to a hydrophobic silica surface. The adsorbed amount as measured by ellipsometric methods after rinsing and equilibration was 2.7 mg/m(2) for alpha-actinin and 0.4 mg/m(2) for filamin plus desmin, respectively. Adsorbed layer thicknesses in physiological salt solution were about 107 nm, 89 nm, 108 nm and 93 nm for alpha-actinin, filamin, desmin, and cross-linked filamin-desmin, respectively. Ca2+ ions in a concentration of 10(-4), 10(-3), and 2.52 mmol/l had no effect on the adsorbed amount, refractive index, and adsorbed layer thickness of the individual intermediate filament proteins. Cross-linked filamin-desmin, however, reacted markedly upon the addition of these Ca2+ concentrations with a change in refractive index and adsorbed layer thickness. The layer formed by the filamin- desmin complex contracted by 2-3, 6-7, and 6-7 nm, respectively. The maximum shortening occurred at 1 mu mol/l Ca2+. The Ca2+-dependent adsorbed layer changes of cross-linked filamin-desmin supports the contractile mechanisms in muscular tissues and forms the basis for migration and motility in nonmuscular cells. These motional events are crucially involved in peripheral organ perfusion, inflammation, and tumor invasion and metastasis.
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| 5. |
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| 6. |
- Christensen, P. W., et al.
(författare)
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Formulation and comparison of algorithms for frictional contact problems
- 1998
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Ingår i: International Journal for Numerical Methods in Engineering. - : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 42:1, s. 145-173
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents two algorithms for solving the discrete, quasi-static, small-displacement, linear elastic, contact problem with Coulomb friction. The algorithms are adoptions of a Newton method for solving B-differentiable equations and an interior point method for solving smooth, constrained equations. For the application of the former method, the contact problem is formulated as a system of B-differentiable equations involving the projection operator onto sets with simple structure; for the application of the latter method, the contact problem is formulated as a system of smooth equations involving complementarity conditions and with the non-negativity of variables treated as constraints. The two algorithms are numerically tested for two-dimensional problems containing up to 100 contact nodes and up to 100 time increments. Results show that at the present stage of development, the Newton method is superior both in robustness and speed. Additional comparison is made with a commercial finite element code.
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| 7. |
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| 8. |
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| 9. |
- Kjellmert, Bo
(författare)
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A Chebyshev collocation multidomain method to solve the Reissner-Mindlin equations for the transient response of an anisotropic plate subjected to impact
- 1997
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Ingår i: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 40:20, s. 3689-3702
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Tidskriftsartikel (refereegranskat)abstract
- The transient response of an anisotropic rectangular plate subjected to impact is described through a Chebyshev collocation multidomain discretization of the Reissner-Mindlin plate equations. The trapezoidal rule is used for time-integration. The spatial collocation derivative operators are represented by matrices, and the subdomains are patched by natural and essential conditions. At each time level the resulting governing matrix equation is reduced by two consecutive block Gaussian eliminations, so that an equation for the variables at the subdomain corners has to be solved. Back-substitution gives the variables at all other collocation points. The time history as represented by computed contour plots has been compared with analytical results and with photos produced by holographic interferometry. The agreements are satisfactory.
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| 10. |
- Kjellmert, Bo
(författare)
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A spectral method to solve the equations of linear elasticity for the transient response of a tube subjected to impact
- 1999
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Ingår i: International Journal for Numerical Methods in Engineering. - 0029-5981 .- 1097-0207. ; 45:8, s. 1115-1133
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Tidskriftsartikel (refereegranskat)abstract
- The transient response of a tube subjected to impact is described through Fourier-Galerkin and Chebyshev collocation multidomain discretizations of the equations of linear elasticity. The trapezoidal rule is used for time integration. For each Fourier mode the spatial collocation derivative operators are represented by matrices, and the subdomains are patched by natural and essential conditions. At each time level the resulting governing matrix equation is reduced by two consecutive block Gaussian eliminations, so that an equation for the complex Fourier coefficients at die subdomain corners has to be solved. Back-substitution gives the coefficients at all other collocation points. An inverse discrete Fourier transform generates, at optional time levels, the three components of the displacement field. Through this method the long-term evolution of the field may be calculated, provided the impact time is long enough. The time history as represented by computed contour plots has been compared with photos produced by holographic interferometry. The agreements are satisfactory.
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