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  • 1
    ISSN: 1433-2965
    Keywords: Key words:High-resolution computed tomography – Histomorphometry – Human cancellous bone – Mechanical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract: The aim of the present study on human vertebral cancellous bone was to validate structural parameters measured with high-resolution (150 μm) computed tomography (HRCT) by referring to histomorphometry and to try to predict mechanical properties of bone using HRCT. Two adjacent vertical cores were removed from the central part of human L2 vertebral body taken after necropsy in 22 subjects aged 47–95 years (10 women, 12 men; mean age 79 ± 14 years). The right core was used for structural analysis performed by both HRCT and histomorphometry. Two cancellous bone specimens were extracted from the left core: a cube for HRCT and a compression test, and a cylinder for a shear test. Significant correlations were found between HRCT and histomorphometric measurements (BV/TV, trabecular thickness, separation and number, and node-strut analysis), but with higher values for most of the tomographic parameters (BV/TV and trabecular thickness determined by HRCT were overestimated by a factor 3.5 and 2.5 respectively, as compared with histomorphometry). The maximum compressive strength and Young’s modulus were highly correlated (ρ= 0.99, p〈0.0005). Significant correlation was obtained between bone mineral density (determined using dual-energy X-ray absorptiometry) and the maximum compressive strength (ρ= 0.64, p= 0.002). In addition the maximum compressive strength and architectural parameters determined by HRCT or histomorphometry showed significant correlations (e.g., for HRCT, BV/TV: ρ = 0.88, p〈0.0005, N.Nd/TV: ρ= 0.73, p〈0.001). The shear strength was significantly correlated with BV/TV (ρ= 0.62, p= 0.002), Tb.Sp (ρ=−0.58, p= 0.004) and TSL (ρ= 0.55, p= 0.006) measured by HRCT. In conclusion, an HRCT system with 150 μm resolution is not sufficient to predict the true values of the structural parameters measured by histomorphometry, although high correlations were found between the two methods. However, we showed that a resolution of 150 μm allowed us to predict the mechanical properties of human cancellous bone. In vivo peripheral systems with such a resolution should be of interest and would deliver an acceptable radiation dose to the patient.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    International journal of earth sciences 84 (1995), S. 626-635 
    ISSN: 1437-3262
    Keywords: Cape orogeny ; Karoo Basin ; Gondwanaland ; Paroxysm ; Sedimentation rates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Careful consideration of the effects of the Cape orogeny on sedimentation in the Carboniferous-Jurassic Karoo Basin provides an indirect tool for accurately dating these rocks. Fossil and radiometric data, especially when combined with sedimentological and structural information, yield partly overlapping age brackets which can be used to correlate the successive tectonic pulses with specific depositional events. Application of these principles to associated basins in Gondwanaland can provide a firm foundation for more dependable stratigraphic correlation on a global scale. The exercise also suggests that a number of widely held opinions on the age of certain stratigraphic units in the Karoo Supergroup may be incorrect.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 48 (1987), S. 977-990 
    ISSN: 1572-9613
    Keywords: Nonlinear dynamics ; chaos ; crisis ; Belousov-Zhabotinskii reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An abrupt transition that has the character of aninterior crisis was observed in an experiment on the Belousov-Zhabotinskii reaction as a control parameter was varied (a crisis is a qualitative change in the dynamics of a system observed when an attractor collides with the stable manifold of a fixed point). The interpretation of the observed behavior as a crisis is corroborated by a numerical analysis of a seven-variable model of the reaction. The waveforms, attractors, and maps obtained in the simulation are remarkably similar to those obtained in the laboratory experiment. The simulation indicates that the crisis is a consequence of a multivalued first return map.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0584
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0827
    Keywords: Key words: Fractal analysis—Os calcis—Radiographs—Histomorphometry—Microarchitecture.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Microarchitecture of trabecular bone is an important determinant of bone fragility; to date, its evaluation requires bone biopsy with histomorphometry analysis. Methods of noninvasive characterization of trabecular bone microarchitecture are in development and we have developed and validated a bone texture analysis applied to bone radiographs and based on fractal geometry. The aim of our study was to compare this fractal analysis of trabecular bone texture on radiographs to the trabecular microarchitecture analyzed by bone histomorphometry on os calcis biopsies. Thirty eight ossa calcis from 19 human cadavers were studied. Fractal analysis of the trabecular bone of os calcis radiographs was performed by the maximum likelihood estimator following the fractional brownian motion model. The ossa calcis were dissected, then transcortical biopsy cores focused on the fractal analysis region of interest were obtained. Structural and connectivity parameters were measured with both automatic and semiautomatic analyzers. We have found a significant relationship between the fractal Hmean parameter and structural histomorphometric indices; the best correlation was found with trabecular separation (r =−0.55; P= 0.0004). Based on a stepwise regression analysis, trabecular spacing and trabeculae number together would explain 38% of the variance of the fractal parameter. Although the relationship with connectivity indices was poor, our fractal analysis of os calcis trabecular bone texture on radiographs seemed to partially reflect the trabecular bone microarchitecture.
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  • 6
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Polynesians have lower heterozygosities at minisatellite VNTR (Variable Number of Tandem Repeat) loci than have Melanesians; this has been taken as evidence of population-size bottlenecks during the colonisation of Polynesia. We have analysed the allelic distribution of several minisatellite loci in the population of Rapa, a Polynesian island that is known to have undergone a demographic reduction of approximately 95% since first contact with European explorers 200 years ago, leaving a surviving population of 120. We found that the minisatellite diversity of this population does not differ significantly from that of other Polynesian populations, and appears consistent with the neutral expectation of diversity assuming the infinite alleles model. This suggests that the demographic crisis that Rapa underwent did not perturb the allele distribution to the extent that the tests used here could detect. Thus we cannot say that a demographic change of this magnitude constitutes a genetic bottleneck detectable at these loci. The reduced diversity seen in Polynesia must therefore be explained either by more severe bottlenecks as might be expected during colonisation, or else by other causes.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Radiation and environmental biophysics 13 (1976), S. 177-186 
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Summary The survival curves obtained when cellular recovery follows various first radiation dose deliveriesDI seem, when semi-logarithmically plotted, to be translated from the part of the curve corresponding to an unfractionated irradiation beyond a doseDR. A possible assumption consistent with such experimental observations is proposed which allows the generalization of any survival modelS = f(D). The derived equationS = f(DR + D - DI)f(DI)/f(DR) is convenient for the whole family of experimental survival curves involving cellular damage repairs when the first radiation doses vary. All the parameters of the family equation can be simultaneously fitted so that their reliability is increased. The generalized equations are given for the four following models: two-hits targets, Chadwick and Leenhouts, Green and Burki, Wideröe. As an example, the Chadwick and Leenhouts generalized model parameters are fitted to a family of experimental survival curves concerningChlorella cells exposed to fractionated and continuous gamma irradiation. The fittings are presented with their confidence limits and are briefly discussed.
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  • 8
    ISSN: 1432-1084
    Keywords: Key words: Penis ; Fracture ; Injuries ; Urethra ; Corpus cavernosum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. We report a case of traumatic urethral tear associated with a rupture of the corpus cavernosum, demonstrated on MRI. We discuss the potential role of a non-invasive preoperative assessment by MRI.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 61 (1977), S. 279-298 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Sub-potassic nephelines in the system NaAlSiO4(Ne)-KAlSiO4(Ks) were synthesized under a variety of conditions and studied at room temperature and up to 1000 °C using an X-ray powder diffractometer. At low temperatures they do not have the hexagonal structure determined by Hahn and Buerger (1955) for natural nepheline. Samples with ∼0.7 to 2.5 mole % Ks have an orthorhombic supercell with parameters equivalent to a, √3a, 3c where a and c are Hahn and Buerger structure cell parameters. Nephelines with 0 to ∼0.7% Ks consist of two phases with different c axes; one of these phases has the orthorhombic supercell. Pure-Na nephelines (NaAlSiO4) invert to a hexagonal phase with the Hahn and Buerger structure at 190 °±10 °C; this inversion temperature decreases with increasing Ks and a sample with 0.5% Ks inverts at 170 °±5 °C. The inversion is reversible and is displacive. Another reversible inversion begins at 875 °±10 °C in pure-Na nepheline; this inversion increases in temperature with increasing Ks and a sample with 1.8% Ks begins to invert at 960 °±10 °C. Superstructures with “anomalous” low-temperature cell parameters in sub-potassic nephelines are attributed to reversible collapse of the framework about the larger cation sites which must be occupied by small Na in subpotassic nephelines. Superstructures in natural nephelines are also related to framework collapse at a displacive inversion.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 346 (1993), S. 69-74 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The initial stages of oxidation of clean (110), (100), and (111) oriented β-NiAl single crystals, with and without Pt doping (50 nm), were followed at 973 K using LEED and AES. Upon oxidation, Al2O3 is selectively formed. On NiAl (110) a complex surface structure is observed which according to Jäger et al. [13] is a duplex oxide structure similar to α- or γ-Al2O3. On the (100) face, submicroscopic facetting occurs during oxidation. For the (111) oriented sample the hexagonal structure remains and only an increased background intensity for the LEED pattern is observed for the oxidized surface. After Pt doping, the phenomena observed for the Pt-free sample are not significantly changed. However the following differences exist: 1. the formation of the Al2O3 oxide is more difficult for the (110) and (111) samples but Pt doping facilitates facetting and oxide formation on the (100) oriented sample; 2. sputtering of the oxide layers on Pt-doped samples is retarded in all cases, a very stable and dense oxide seems to be formed which adheres well; 3. Pt seems to hinder the Al diffusion to the unoxidized surface of the samples.
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