Experimental Validation of Finite Element Analysis of Human Vertebral Collapse Under Large Compressive Strains

Osteoporosis-related vertebral fractures represent a major health problem in elderly populations. Such fractures can often only be diagnosed after a substantial deformation history of the vertebral body. Therefore, it remains a challenge for clinicians to distinguish between stable and progressive potentially harmful fractures. Accordingly, novel criteria for selection of the appropriate conservative or surgical treatment are urgently needed. Computer tomography-based finite element analysis is an increasingly accepted method to predict the quasi-static vertebral strength and to follow up this small strain property longitudinally in time. A recent development in constitutive modeling allows us to simulate strain localization and densification in trabecular bone under large compressive strains without mesh dependence. The aim of this work was to validate this recently developed constitutive model of trabecular bone for the prediction of strain localization and densification in the human vertebral body subjected to large compressive deformation. A custom-made stepwise loading device mounted in a high resolution peripheral computer tomography system was used to describe the progressive collapse of 13 human vertebrae under axial compression. Continuum finite element analyses of the 13 compression tests were realized and the zones of high volumetric strain were compared with the experiments. A fair qualitative correspondence of the strain localization zone between the experiment and finite element analysis was achieved in 9 out of 13 tests and significant correlations of the volumetric strains were obtained throughout the range of applied axial compression. Interestingly, the stepwise propagating localization zones in trabecular bone converged to the buckling locations in the cortical shell. While the adopted continuum finite element approach still suffers from several limitations, these encouraging preliminary results towardsthe prediction of extended vertebral collapse may help in assessing fracture stability in future work.

Use of nitinol self-expandable stents in 26 dogs with tracheal collapse

A study was designed to describe a novel approach to the treatment of tracheal collapse (TC) in dogs using self-expandable nitinol stents. Medical records were reviewed retrospectively for 26 client owned dogs in which nitinol stents were deployed. The entire length of trachea was supported independently of the extent of TC. Two overlapping stents were used instead of one in cases where one stent was not spanning the entire trachea adequately. The diameter of the cranial radiolucent portion of trachea, just behind the cricoid cartilage, was measured as a specific landmark to select the appropriate size of the stent. Two self-expandable nitinol stents were inserted in 9 of 26 dogs; the trachea in the rest of the cases was supported with only one stent. A follow up tracheoscopy was performed in 10 of 26 cases with recurrent clinical signs. Secondary tracheal stenosis in these cases was caused by stent fracture, granuloma or excessive stent shortening. Additional stents were placed successfully to expand the stenotic lumen. A support of the entire trachea may decrease risk of nitinol fracture at the end of the implant. Long term clinical improvement (25 of 26 dogs, 96 %) is comparable with the results of other studies.

Alveolar derecruitment and collapse induration as crucial mechanisms in lung injury and fibrosis.

Idiopathic pulmonary fibrosis (IPF) and bleomycin-induced pulmonary fibrosis are associated with surfactant system dysfunction, alveolar collapse (derecruitment), and collapse induration (irreversible collapse). These events play undefined roles in the loss of lung function. The purpose of this study was to quantify how surfactant inactivation, alveolar collapse, and collapse induration lead to degradation of lung function. Design-based stereology and invasive pulmonary function tests were performed 1, 3, 7, and 14 days after intratracheal bleomycin-instillation in rats. The number and size of open alveoli was correlated to mechanical properties. Active surfactant subtypes declined by Day 1, associated with a progressive alveolar derecruitment and a decrease in compliance. Alveolar epithelial damage was more pronounced in closed alveoli compared with ventilated alveoli. Collapse induration occurred on Day 7 and Day 14 as indicated by collapsed alveoli overgrown by a hyperplastic alveolar epithelium. This pathophysiology was also observed for the first time in human IPF lung explants. Before the onset of collapse induration, distal airspaces were easily recruited, and lung elastance could be kept low after recruitment by positive end-expiratory pressure (PEEP). At later time points, the recruitable fraction of the lung was reduced by collapse induration, causing elastance to be elevated at high levels of PEEP. Surfactant inactivation leading to alveolar collapse and subsequent collapse induration might be the primary pathway for the loss of alveoli in this animal model. Loss of alveoli is highly correlated with the degradation of lung function. Our ultrastructural observations suggest that collapse induration is important in human IPF.

Local formation of varved sediments in a karstic collapse depression of Lake Banyoles (NE Spain)

Banyoles is the largest and deepest lake of karstic-tectonic origin in the Iberian Peninsula. The lake comprises several circular sub-basins characteri- zed by different oxygenation conditions at their hypolimnions. The multiproxy analysis of a > 5 m long sediment core combined with high resolution seis- mic stratigraphy (3.5 kHz pinger and multi-frequency Chirp surveys), allow a precise reconstruction of the evolution of a karstic depression (named B3) until present times. Local meromictic conditions in this sub-basin have been conducive to deposition and preservation of ca. 85 cm of varved sediments since the late 19th century. The onset of these conditions is likely related to lake waters eutrophication caused by increasing farming activities in the wa- tershed. Increasing clastic input and organic productivity during the second half of the 20th century have also been recorded within the laminated sedi- ments, revealing an intensification of human impact and warmer water tem- peratures.

Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse

Pits have been observed on many cometary nuclei mapped by spacecraft(1-4). It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments(5,6) andmodels(7,8) cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts(8,9). Alternative mechanisms like explosive activity(10) have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply that large heterogeneities exist in the physical, structural or compositional properties of the first few hundred metres below the current nucleus surface.

Na 1 Nachlass Max Horkheimer, 694 - "German Economy, Politics and Culture, 1900-1933", "The Collapse of German Democracy and the Expansion of National Socialism" (p. IX 168e - IX 169a)

"German Economy, Politics and Culture, 1900-1933. A Research Project of the International Institute of Social Research" (1940):; 1. Umriß des Forschungsprojekts: e)-g) Fassung vom 25.5.1940: e) Typoskript, 63 Blatt, f) Typoskript mit handschriftlichen Korrekturen, 61 Blatt, g) Typoskript, 61 Blatt, h)-k) "Introduction": h) Typoskript, 21 Blatt, i) Typoskript, 15 Blatt, k) D.V. Glass: Entwurf, Manuskript, 17 Blatt; 2. Kostenschätzung zum Forschungsprojekt. 1 Blatt; "The Collapse of German Democracy and the Expansion of National Socialism" (1940):; 1. Darstellung des Forschungsprojekts (15.9.1940), a) als Typoskript vervielfältigt, 70 Blatt;

Na 1 Nachlass Max Horkheimer, 695 - "The Collapse of German Democracy and the Expansion of National Socialism", "Cultural Aspects of National Socialism" u.a. (p. IX 169.1a - IX 170.1-4)

"The Collapse of German Democracy and the Expansion of National Socialism" (1940):; 1. Darstellung des Forschungsprojekts (15.9.1940), b. Typoskript mit handschriftlichen Korrekturen, 78 Blatt; 2. "Research work on recent trends in the history of ideas (parts of the Research project on the Collapse of German Democracy would be included)". Als Memorandum zur Eröffnung zur Eröffnung einer Zweigstelle des Instituts in Los Angeles (12.12.1940): a) Typoskript, 2 Blatt, b) Teilstück, Typoskript mit handschriftlichen Korrekturen, 1 Blatt, c) Teilstück, Typoskript mit handschriftlichen Korrekturen, 1 Blatt, d) Teilstück, Typoskript, 1 Blatt, e) Teilstück, Typoskript, 1 Blatt, f) Entwurf, Typoskript mit handschriftlichen Korrekturen und Manuskript, 3 Blatt; 3. University of California, Los Angeles: 2 Briefe (Abschrift) von Max Horkheimer, o.O., 1940, 2 Briefe (Abschrift) an Max Horkheimer, 1940, 2 Blatt; A.R.L. Gurland: "Survey of Structural Changes in the German Economy, 1933 to 1939. Technological Bases and Organizational Forms of the National Socialist Economic System". Typoskript mit handschriftlichen Korrekturen unter anderem von Theodor W. Adorno, 48 Blatt (formal nicht identisch mit "Technological Trends and Economic Structure under National Socialism", Studies in Philosophy and Social Science, Bd. IX, 1941, S. 226ff.); "Cultural Aspects of National Socialism. A Research Project" (1941):; 1. Institute of Social Research: Mitteilung über das Forschungsprojekt und das 'Supplementary Statement', Typoskript, englisch, 4 Blatt; 2. Supplementary Statement to the Research Project, a) Typoskript, 14.4.1941, 63 Blatt, b) Typoskript, 12.4.1941, mit handschriftlichen Korrekturen, 35 Blatt; 3. "Cultural Aspects of National Socialism. A Research Project" (24.2.1941), a) als Typoskript vervielfältigt, 54 Blatt, b) Typoskript mit handschriftlichen Korrekturen, 34 Blatt, c) Fassung Januar 1941, Typoskript mit handschriftlichen Korrekturen, 40 Blatt; 4. Inhaltsverzeichnisse, mit handschriftlichen Korrekturen, 3 Blatt;

Geological patterns in the collapse of certain rock sanctuaries of Spain

Descripción de ciertos rasgos geológicos que amenazan el patrimonio religioso rupestre español. Rock sanctuaries are a historical heritage not as well-known as other religious constructions, due to their usual recondite location and abandoned condition. Spain has a large number of examples, mostly excavated during the Early Middle Age or even before. Fortunately, some of them are used on present worship, but the majority of these ancient shrines have suffered of severe damage through time, mostly due to common geological patterns. Some others threaten to collapse soon unless urgent remedial improvement is applied. Some examples at different locations are shown, reviewing their problems, which involve weathering, major rock cracks, soft rock pillars and others related to the defective site where they were located.

Semaphorin 3A growth cone collapse requires a sequence homologous to tarantula hanatoxin

Axonal guidance is key to the formation of neuronal circuitry. Semaphorin 3A (Sema 3A; previously known as semaphorin III, semaphorin D, and collapsin-1), a secreted subtype of the semaphorin family, is an important axonal guidance molecule in vitro and in vivo. The molecular mechanisms of the repellent activity of semaphorins are, however, poorly understood. We have now found that the secreted semaphorins contain a short sequence of high homology to hanatoxin, a tarantula K+ and Ca2+ ion channel blocker. Point mutations in the hanatoxin-like sequence of Sema 3A reduce its capacity to repel embryonic dorsal root ganglion axons. Sema 3A growth cone collapse activity is inhibited by hanatoxin, general Ca2+ channel blockers, a reduction in extracellular or intracellular Ca2+, and a calmodulin inhibitor, but not by K+ channel blockers. Our data support an important role for Ca2+ in mediating the Sema 3A response and suggest that Sema 3A may produce its effects by causing the opening of Ca2+ channels.

Direct observation of fast protein folding: the initial collapse of apomyoglobin.

The rapid refolding dynamics of apomyoglobin are followed by a new temperature-jump fluorescence technique on a 15-ns to 0.5-ms time scale in vitro. The apparatus measures the protein-folding history in a single sweep in standard aqueous buffers. The earliest steps during folding to a compact state are observed and are complete in under 20 micros. Experiments on mutants and consideration of steady-state CD and fluorescence spectra indicate that the observed microsecond phase monitors assembly of an A x (H x G) helix subunit. Measurements at different viscosities indicate diffusive behavior even at low viscosities, in agreement with motions of a solvent-exposed protein during the initial collapse.

Why fisheries collapse and what to do about it.

With the collapse of fisheries in many parts of the world causing widespread economic harm, attention is focused on a possible cause and remedy of fishery collapse. Economic theory for managing a renewable resource, such as a fishery, leads to an ecologically unstable equilibrium as difficult to maintain as balancing a marble on top of a dome. A fishery should be managed for ecological stability instead--in the analogy, as easy to maintain as keeping a marble near the base of a bowl. The goal of ecological stability is achieved if the target stock is above that producing maximum sustainable yield and harvested at less than the maximum sustainable yield. The cost of managing for ecological stability, termed "natural insurance," is low if the fishery is sufficiently productive. This cost is shown to pay for itself over the long term in a variable and uncertain environment. An ecologically stable target stock may be attained either with annually variable quotas following current practice or, preferably, through a market mechanism whereby fish are taxed at dockside if caught when the stock was below target and are untaxed otherwise. In this regulatory environment, the goal of maximizing short-term revenue coincides with the goal of ecological stability, thereby also maximizing long-term revenue. This new approach to fishery management is illustrated with the recently collapsed Newfoundland fishing industry. The Newfoundland cod fishery is expected to rebuild to an ecologically stable level in about 9 years and thereafter support an annual harvest of about 75% of the 1981-1990 average.

The terminal Paleozoic fungal event: evidence of terrestrial ecosystem destabilization and collapse.

Because of its prominent role in global biomass storage, land vegetation is the most obvious biota to be investigated for records of dramatic ecologic crisis in Earth history. There is accumulating evidence that, throughout the world, sedimentary organic matter preserved in latest Permian deposits is characterized by unparalleled abundances of fungal remains, irrespective of depositional environment (marine, lacustrine, fluviatile), floral provinciality, and climatic zonation. This fungal event can be considered to reflect excessive dieback of arboreous vegetation, effecting destabilization and subsequent collapse of terrestrial ecosystems with concomitant loss of standing biomass. Such a scenario is in harmony with predictions that the Permian-Triassic ecologic crisis was triggered by the effects of severe changes in atmospheric chemistry arising from the rapid eruption of the Siberian Traps flood basalts.

Partial collapse of a ventilated stone façade: Diagnosis and analysis of the anchorage system

The mechanical behaviour of transventilated façades performed by natural stone is necessarily based on the correct execution of both anchoring elements on the stone cladding as in the ones corresponding to the enclosure support, either with brick masonry walls or reinforced concrete walls. In the case studied in the present work, the origin of the damages suffered on the façade of a building located in Alcoy has been analyzed, where the detachment of part of the outer enclosure occurred. This enclosure is a transventilated façade formed by Bateig Blue stone tiles. To this end, “in situ” tests of the anchoring systems employed have been performed, as well as laboratory tests of mechanical characterization of the material and of different types of anchor, comparing these results with those obtained in both the simplified analytical models of continuum mechanics as developed by the Finite Element Method (FEM).