Direct Visualization of the Initiation and Progression of Vertebral Fractures

2010 ◽  
Author(s):  
Amira I. Hussein ◽  
Elise F. Morgan
Keyword(s):  
Vertebral Fractures ◽  
Failure Mechanisms ◽  
Image Data ◽  
Quantitative Information ◽  
Digital Volume Correlation ◽  
Direct Visualization ◽  
Finite Element Analyses ◽  
Micro Computed Tomography ◽  
Failure Patterns ◽  
Large Size

Vertebral fractures are the hallmark of osteoporosis, yet the failure mechanisms involved in these fractures are not well understood. Failure patterns within whole vertebrae are typically estimated from finite element analyses or from images acquired after fracture has occurred. Experimental measurement of deformations sustained by vertebrae during injurious loading would enable direct visualization of vertebral failure mechanisms as well as the possibility of validating the results of numerical simulations of vertebral fracture. Time-lapsed micro-computed tomography (μCT) has been used previously to visualize failure processes in excised specimens of trabecular bone [1,2], and methods of digital volume correlation (DVC) can be applied to these types of image series to obtain quantitative information on the deformations that the bone undergoes [3]. However, application of DVC to whole bones has not been reported and involves additional challenges such as the irregular geometry of the volume and the large size of the sets of image data. The overall goal of this study was to develop a DVC-based method for quantifying deformations throughout entire vertebrae as these vertebrae are loaded to failure.

Comparison of Techniques for EELS Mapping in Biology

1996 ◽  
Vol 54 ◽  
pp. 300-301
Author(s):  
R.D. Leapman ◽  
S.B. Andrews
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Image Data ◽  
Beam Current ◽  
Quantitative Information ◽  
Acquisition Time ◽  
Uniform Thickness ◽  
Electron Dose ◽  
Array Detectors ◽  
Transmission Electron

Elemental mapping of biological specimens by electron energy loss spectroscopy (EELS) can be carried out both in the scanning transmission electron microscope (STEM), and in the energy-filtering transmission electron microscope (EFTEM). Choosing between these two approaches is complicated by the variety of specimens that are encountered (e.g., cells or macromolecules; cryosections, plastic sections or thin films) and by the range of elemental concentrations that occur (from a few percent down to a few parts per million). Our aim here is to consider the strengths of each technique for determining elemental distributions in these different types of specimen.On one hand, it is desirable to collect a parallel EELS spectrum at each point in the specimen using the ‘spectrum-imaging’ technique in the STEM. This minimizes the electron dose and retains as much quantitative information as possible about the inelastic scattering processes in the specimen. On the other hand, collection times in the STEM are often limited by the detector read-out and by available probe current. For example, a 256 x 256 pixel image in the STEM takes at least 30 minutes to acquire with read-out time of 25 ms. The EFTEM is able to collect parallel image data using slow-scan CCD array detectors from as many as 1024 x 1024 pixels with integration times of a few seconds. Furthermore, the EFTEM has an available beam current in the µA range compared with just a few nA in the STEM. Indeed, for some applications this can result in a factor of ~100 shorter acquisition time for the EFTEM relative to the STEM. However, the EFTEM provides much less spectral information, so that the technique of choice ultimately depends on requirements for processing the spectrum at each pixel (viz., isolated edges vs. overlapping edges, uniform thickness vs. non-uniform thickness, molar vs. millimolar concentrations).

Numerical Study of the Combined Loading Envelope of a Skirted Spudcan Foundation

2014 ◽  
Author(s):  
Ning Cheng ◽  
Mark J. Cassidy ◽  
Yinghui Tian
Keyword(s):  
Clay Soil ◽  
Numerical Study ◽  
Failure Mechanisms ◽  
Small Strain ◽  
Offshore Structures ◽  
Combined Loading ◽  
Finite Element Analyses ◽  
Failure Envelope ◽  
Foundation Type ◽  
Jack Up

Foundations for offshore structures, such as mobile jack-up units, are subjected to large horizontal (H) and moment (M) loads in addition to changing vertical (V) loads. The use of a combined vertical, horizontal and moment (V-H-M) loading envelope to define foundation capacities has become increasingly applied in recent years. However, there is no study on the skirted spudcan, a new alternative foundation type to the conventional spudcan footing for jack-ups. In this study, the combined V-H-M yield envelope of a skirted spudcan foundation in clay soil is investigated with small strain finite element analyses using 3D modeling. The footing’s uniaxial bearing capacities and failure mechanisms are described. The failure envelope for the combined V-H-M loadings is presented. A comparison of the bearing capacities between the spudcan and skirted spudcan of various dimensions is also presented.

scholarly journals Pull-Out Capacity and Failure Mechanisms of Strip Anchors in Clay

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3853
Author(s):  
Fernando Cañizal ◽  
Jorge Castro ◽  
Jorge Cañizal ◽  
César Sagaseta
Keyword(s):  
Failure Mechanisms ◽  
Cohesive Soils ◽  
Finite Element Analyses ◽  
Bottom Part ◽  
Pull Out ◽  
Shallow Failure ◽  
Plate Anchors ◽  
Floating Platforms ◽  
First Time ◽  
Analytical Limit

Plate anchors are a well-established solution for supporting the efforts of floating platforms for wind and marine renewable energies. The behavior of ultrathin rigid plate anchors buried in purely cohesive soils under undrained and plane-strain conditions is analyzed. As already known, a dimensional analysis shows that the pull-out capacity of the anchor may be expressed using a weightless break-out factor (Nc0) that only depends on the ratio between the depth and the anchor width (H/B). Using finite element analyses, tabulated values of the weightless break-out factor are provided in this paper and three different failure mechanisms are identified, namely very shallow (quasi-vertical), shallow or intermediate (semi-vertical), and deep (rotational). For very shallow failure mechanisms, the studied problem is completely equivalent to the trapdoor problem because immediate breakaway at the bottom part of the anchor is considered (vented conditions). The existing analytical solutions for the very shallow (Nc0 = 1.956 H/B) and deep cases (Nc = 3π + 2) using the slip-line method are reviewed and an analytical limit is proposed for the first time for the very shallow mechanism (H/B = 1.314). For shallow (intermediate) cases, the failure mechanism is identified and the angle of the main slip lines is numerically evaluated.

Effect of Superstructure Stiffness on Liquefaction-Induced Failure Mechanisms

2010 ◽  
Vol 1 (1) ◽  
pp. 70-87 ◽  
Author(s):  
S.P.G. Madabhushi ◽  
S.K. Haigh
Keyword(s):  
Failure Mechanisms ◽  
Soil Liquefaction ◽  
Field Observations ◽  
Finite Element Analyses ◽  
Bhuj Earthquake ◽  
Engineering Structures ◽  
Strong Earthquakes ◽  
Mode Of Failure ◽  
Dynamic Centrifuge Test ◽  
Recent Earthquakes

Soil liquefaction following strong earthquakes causes extensive damage to civil engineering structures. Foundations of buildings, bridges etc can suffer excessive rotation/settlement due to liquefaction. Many of the recent earthquakes bear testimony for such damage. In this article a hypothesis that “Superstructure stiffness can determine the type of liquefaction-induced failure mechanism suffered by the foundations” is proposed. As a rider to this hypothesis, it will be argued that liquefaction will cause failure of a foundation system in a mode of failure that offers least resistance. Evidence will be offered in terms of field observations during the 921 Ji-Ji earthquake in 1999 in Taiwan and Bhuj earthquake of 2001 in India. Dynamic centrifuge test data and finite element analyses results are presented to illustrate the traditional failure mechanisms.

scholarly journals Stereological assessment of mouse lung parenchyma via nondestructive, multiscale micro-CT imaging validated by light microscopic histology

2013 ◽  
Vol 114 (6) ◽  
pp. 716-724 ◽  
Author(s):  
Dragoş M. Vasilescu ◽  
Christine Klinge ◽  
Lars Knudsen ◽  
Leilei Yin ◽  
Ge Wang ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Lung Parenchyma ◽  
Quantitative Information ◽  
Mouse Lung ◽  
Imaging Method ◽  
Micro Computed Tomography ◽  
Lung Structure ◽  
Internal Structures ◽  
Multiple Resolutions ◽  
Conventional Histology

Quantitative assessment of the lung microstructure using standard stereological methods such as volume fractions of tissue, alveolar surface area, or number of alveoli, are essential for understanding the state of normal and diseased lung. These measures are traditionally obtained from histological sections of the lung tissue, a process that ultimately destroys the three-dimensional (3-D) anatomy of the tissue. In comparison, a novel X-ray-based imaging method that allows nondestructive sectioning and imaging of fixed lungs at multiple resolutions can overcome this limitation. Scanning of the whole lung at high resolution and subsequent regional sampling at ultrahigh resolution without physically dissecting the organ allows the application of design-based stereology for assessment of the whole lung structure. Here we validate multiple stereological estimates performed on micro–computed tomography (μCT) images by comparing them with those obtained via conventional histology on the same mouse lungs. We explore and discuss the potentials and limitations of the two approaches. Histological examination offers higher resolution and the qualitative differentiation of tissues by staining, but ultimately loses 3-D tissue relationships, whereas μCT allows for the integration of morphometric data with the spatial complexity of lung structure. However, μCT has limited resolution satisfactory for the sterological estimates presented in this study but not for differentiation of tissues. We conclude that introducing stereological methods in μCT studies adds value by providing quantitative information on internal structures while not curtailing more complex approaches to the study of lung architecture in the context of physiological or pathological studies.

Failure Mechanisms of Pipelines Subjected to Loss of Support Under Deep Burial Conditions

2004 ◽  
Author(s):  
Yuri D. Costa ◽  
Jorge G. Zornberg ◽  
Benedito S. Bueno ◽  
Carina L. Costa
Keyword(s):  
Vertical Section ◽  
Failure Mechanisms ◽  
Soil Mass ◽  
Experimental Program ◽  
Rigid Base ◽  
Failure Patterns ◽  
Slip Surfaces ◽  
Deep Burial ◽  
Flexible Pipes ◽  
Adjacent Soil

This paper investigates the failure mechanisms of pipelines subjected to a localized loss of support. An experimental program was conducted, which consisted of a series of four centrifuge model tests containing an aluminum tube embedded in a pure dry sand backfill that was placed over an underlying rectangular rigid base moving downwards during the test. All models were built taking advantage of the longitudinal symmetry of the problem. The prototype pipe had a diameter (D) of 1.1 m and a soil cover height of about 5 D, characterizing deep burial conditions. Failure patterns were observed within a vertical section comprising the central axis of the pipe and also in four distinct vertical transverse sections along the length of the pipe in the region of ground loss. The influence of pipe stiffness and backfill density on the behavior of the system was assessed. The transverse sections showed fully developed slip surfaces starting in the vicinity of the edge of the void towards the adjacent soil mass. The mode of failure of the flexible pipes took the form of a severe deformation at the region of the shoulder and a reversal of curvature at the invert due to over-deflection. This situation was more critical in the central section. The damage experienced by the flexible pipes was noticeably more pronounced when using the looser backfill, whereas only negligible deflections were observed when using the denser backfill. The experimental results were compared with analytical predictions, which showed to be highly unconservative for the case loose backfill.

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