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  • 1
    Digitale Medien
    Digitale Medien
    α-Tocopherol modulates lipoprotein cytotoxicity in obstructive nephropathy (2000)
    Springer
    Pediatric nephrology 14 (2000), S. 740-746 
    Details
    ISSN: 1432-198X
    Schlagwort(e): Key words Unilateral ureteral obstruction ; Oxidized low-density lipoprotein ; α-Tocopherol ; Malondialdehyde ; Transforming growth factor β1
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Oxidative stress in unilateral ureteral obstruction (UUO) contributes to the development of glomerular and tubulointerstitial lesions. The present study investigated whether oxidized low-density lipoprotein (oLDL) contributes to the pathogenesis of kidney injury in UUO, and whether α-tocopherol modulates such cytotoxicity and promotes repair. Male Sprague-Dawley rats weighing 100–125 g were assigned to three groups of 6 animals each: (1) sham, regular chow; (2) UUO, regular chow; and (3) UUO, α-tocopherol supplementation. We found a significant increase in the level of oxidative stress in the UUO group as measured by malondialdehyde (MDA) content in both plasma and kidneys. The LDL isolated from this group was cytotoxic to rat mesangial cells. The level of oxidation and cytotoxicity was significantly reduced when animals were treated with α-tocopherol. Plasma cholesterol concentration, kidney MDA, and transforming growth factor β1 mRNA expression were all significantly increased in the UUO animals, and partially reduced in α-tocopherol-treated animals. Our data suggest that oxidative modification of LDL is associated with the renal injury in UUO. Taken together, our data support the concept that α-tocopherol can modulate LDL oxidation and its cytotoxic effects on rat mesangial cells in vitro.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/PL00013428
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  • 2
    Digitale Medien
    Digitale Medien
    Influence of α-tocopherol over the time course of experimental IgA nephropathy (1999)
    Springer
    Pediatric nephrology 13 (1999), S. 108-112 
    Details
    ISSN: 1432-198X
    Schlagwort(e): Key words Experimental IgA nephropathy ; Rats ; Malondialdehyde ; Transforming growth factor β1 mRNA
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  The present study investigated the pathogenesis and the time course of kidney injury in experimental IgA nephropathy. In order to determine an appropriate period in the course of experimental IgA nephropathy to study renal injury and repair, we examined proteinuria and IgA deposition in the renal mesangium after 4, 8, and 16 weeks of mucosal challenge by bovine gamma globulins (BGG) provided in the drinking water. The hallmark of IgA deposition in the mesangium was present after 4 weeks and 8 weeks of BGG inoculation, but by 16 weeks, the mesangial IgA deposition had resolved. In addition, we confirmed our previous report on the beneficial effects of α-tocopherol in reducing proteinuria in IgA nephropathy at 8 weeks, and extended this observation to investigate the effects of dietary supplementation of α-tocopherol at both 4 weeks and 16 weeks. Proteinuria resolved spontaneously at 16 weeks. There is oxidative stress, as suggested by the elevation in plasma and renal malondialdehyde content, and increased fibrogenic cytokine message, as suggested by elevated transforming growth factor β1 mRNA. These increases were clearly blunted by α-tocopherol at both 4 weeks and 8 weeks. Treatment with α-tocopherol was associated with a significant reduction in the severity of proteinuria. Thus, our data suggest that the period between 4 and 8 weeks of BGG vaccination could be relevant in designing an appropriate model to study the molecular biology of the pathogenesis of renal injury and the effects of treatment. The 16-week model may be useful in exploring gene expression involved with spontaneous resolution.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004670050573
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  • 3
    Digitale Medien
    Digitale Medien
    Vitamin E suppresses oxidative stress and glomerulosclerosis in rat remnant kidney (1999)
    Springer
    Pediatric nephrology 13 (1999), S. 195-198 
    Details
    ISSN: 1432-198X
    Schlagwort(e): Key words Vitamin E ; 5/6 Nephrectomy rats ; Oxidative stress ; Malondialdehyde ; Transforming growth factor β ; Glomerulosclerotic index ; Remnant kidney
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract  Previous studies have shown that reduction of renal mass in the rat remnant kidney model induces overproduction of transforming growth factor β1 (TGFβ1). We investigated whether an antioxidant, vitamin E, administered before the renal mass reduction, could prevent oxidative stress, reduce the overproduction of TGFβ1, and mitigate against the subsequent glomerulosclerosis. Our results revealed that the oxidative stress, as measured by the change in plasma malondialdehyde, is significantly reduced by prior vitamin E dietary supplementation. Finally, our data show that dietary vitamin E supplementation ameliorates the rise in TGFβ1 secondary to renal mass reduction and inhibits the glomerular sclerosis of the remnant kidney over the time course of this experiment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s004670050591
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  • 4
    Digitale Medien
    Digitale Medien
    An acoustically matched high pressure chamber for control of cavitation in shock wave lithotripsy: Mechanisms of shock wave damage in vitro (1998)
    Springer
    Methods in cell science 19 (1998), S. 303-310 
    Details
    ISSN: 1573-0603
    Schlagwort(e): Cavitation ; Cell injury ; Shock wave lithotripsy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Increased ambient pressure (excess hydrostatic pressure) was used to regulate cavitation in the aqueous media surrounding isolated red blood cells and aluminum foils used as targets in studies of the mechanisms of shock wave (SW) damage in shock wave lithotripsy (SWL). Foils or cells were placed in a cylindrical chamber (bronze-aluminum alloy) connected to a regulator and nitrogen source. The ends of the cylinder were capped with planar, plastic plates 12.7 mm thick. Tests performed with a PVDF membrane hydrophone showed that SW's passed through the plastic without significant loss of amplitude or change in waveform. Pitting of foils, a form of damage that can only be due to cavitation, was eliminated by very high (∼70 atm) added pressure. It took substantially greater added pressure to reduce damage to foils than has been reported to reduce damage to cells, suggesting differences in how cavitation is regulated in bulk fluid versus a solid surface. This report describes the design of the pressure chamber used in these studies and explains how SW exposures of isolated cells and foil targets were performed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009799222889
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  • 5
    Digitale Medien
    Digitale Medien
    An apporach to automatic three-dimensional finite element mesh generation (1985)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 21 (1985), S. 329-347 
    Details
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Recently developed solid modelling systems for the design of complex physical solids using interactive computer graphics offer the exciting possibility of an integrated design/analysis system. Called geometric modellers, these systems build complex solids from primitive solids (cubes, cylinders, spheres, solid patches, etc.) and macro solids (combination of primitives)3, 4, 8, 16, 18, 25, 38. To provide an effective structural analysis capability for these systems, methods must be devised to ease the burden of discretizing the solid geometry into a user controlled (usually locally graded) finite element mesh. The purpose of this paper is to describe an interactive solid mesh generation system capable of generating valid meshes of well-proportional tetrahedral finite elements for the decomposition of multiply connected solid structures. The system uses a semi-automatic node insertion procedure to locate element node points within and on the surface of a structure. An independent automatic three-dimensional triangulator then accepts these nodes as input and connects them to form a valid finite element mesh oftetrahedral elements. Although this report makes use of a modeller based on a constructive solid geometry representation (a so-called CSG modeller), the mesh generation strategy elaborated herein is completely general and makes no particular use of the CSG representation.
    Zusätzliches Material: 20 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/nme.1620210210
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  • 6
    Digitale Medien
    Digitale Medien
    Punch stretching of sheet metal and differential equations on manifolds (1988)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 25 (1988), S. 269-282 
    Details
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: The goal of mathematical modelling of sheet metal forming processes is to provide predictive tools for use in the design of stamping processes and the selection of sheet materials. Most current approaches to finite element modelling of large deformation, elastic-plastic sheet metal forming problems use a rate form of the virtual work (equilibrium) equations, and a single-field finite element representation of the displacement components. Called the incremental method, this approach does not produce approximations which satisfy the discrete equilibrium equations at all times, and consequently it demands small time steps to insure stability and numerical accuracy. This paper describes a variant of the mixed method in which displacements, stresses, effective strain and pressures are all given separate finite element representations. The equilibrium equations in non-rate form are discretized to produce a system of algebraic equations which are coupled with the constitutive equations and then integrated using state-of-the-art numerical software. When used to model rate sensitive sheet materials in hydrostatic bulging, plane strain punch stretching and hemispherical punch stretching, the new approach proved to be between 6 and 26 times as fast as the old incremental method.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/nme.1620250120
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  • 7
    Digitale Medien
    Digitale Medien
    Substructured macro elements based on locally blended interpolation (1977)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 11 (1977), S. 1405-1421 
    Details
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: In this paper we describe a new class of locally refined macro finite elements which are especially amenable to the use of substructuring techniques for the efficient solution of the resulting idealization. The tools and guidelines illustrated by the examples of modelling crack tips, point load singularities and singularities at re-entrant corners should enable an analyst to construct other such blended macro elements specifically tailored to his particular class of problems. The use of such substructured macro elements in finite element calculations permits substantial reduction in the manual effort of data preparation and the computational cost of numerical solution.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/nme.1620110906
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  • 8
    Digitale Medien
    Digitale Medien
    Blended infinite elements for paraboblic boundary value problems (1978)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 12 (1978), S. 1841-1851 
    Details
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A common method for numerically approximating two-point parabolic boundary value problems of the form ut = L[u]+f(u) defined of the semi-infinite strip S = [0, 1]×[0, ∞] is to first discretize the spatial operator in the differential equation and then solve for the time evolution. Such an approach typically involves solving a system of algebriaic equations at a sequence of time steps. In this paper we take a different approach and subdivide S into a collection of semi-infinite substrips Si = [xi, xi+1]×[0, ∞], and use blending function techniques to derive finite parameter functions ei(x, t) defined on Si. Spectral matching methods are used in deriving ei to ensure that (u - ei) can be made small on Si. Galerkin's method, with associated integration sover the entire space-time domain S, is then used to generate approximations to u(x, t) based upon the so defined infinite element (ei, Si). Approximations are hence found for all (x, t) in S by solving one well structed system of algebraic equations. We apply the method to several linear and non-linear problms.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/nme.1620121206
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  • 9
    Digitale Medien
    Digitale Medien
    A new class of transitional blended finite elements for the analysis of solid structuresPresented at the SIAM 30th Anniversary Meeting, Stanford University, 19-23 July 1982. (1984)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 20 (1984), S. 241-253 
    Details
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Recently developed computer aided design systems for the design and modification of complex physical solids using interactive computer graphics offer the exciting possibility of an integrated design/analysis system. Called geometric modellers, these systems build complex solids from primitive solids (cubes, cylinders, spheres, etc.) and macro solids (combinations of primitives). To provide an effective finite element analysis capability for these systems, methods must be devised to ease the burden of discretizing the solid geometry into a user controlled finite element mesh. In this paper we describe a new class of transitional blended finite elements which make substantially simpler the task of finite element mesh generation and local mesh refinement. Computational experience indicates that numerical accuracy is not compromised by use of these flexible elements.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/nme.1620200205
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  • 10
    Digitale Medien
    Digitale Medien
    DEM: A new computational approach to sheet metal forming problems (1986)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 23 (1986), S. 847-862 
    Details
    ISSN: 0029-5981
    Schlagwort(e): Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Many current approaches to finite element modelling of large deformation elastic - plastic forming problems use a rate form of the virtual work (equilibrium) equations, and a finite element representation of the displacement components. Called the incremental method, this approach produces a three-field formulation in which displacements, stresses and effective strain are dependent variables. Next, the formulation is converted to a one-field displacement formulation by an algebraic time discretization which uses a low order explicit time-stepping procedure to integrate the equations. This approach does not produce approximations which satisfy the discrete equilibrium equations at all times and, moreover, the advantage of the single-field algebraic formulation is realized at the expense of very small time steps needed to produce stability and accuracy in the numerical calculations.This paper describes a variant of the mixed method in which all three field variables (displacements, stresses and effective strain) are given finite element representations. The discrete equilibrium equations then generate a nonlinear system of algebraic equations whose solutions represent a manifold, while the constitutive equations form a system of ordinary differential equations. A commercially available, variable time step/variable order code is then used to integrate this differential/algebraic system. When applied to the problem of hydrostatic bulging of a membrane, the new approach requires far less computer time than the incremental method.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/nme.1620230507
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