Gross morphology and topography of the digestive apparatus in rheas (Rhea americana americana)

Rodrigues M.N., Oliveira G.B., Silva R.S.S, Tivane C.T., Albuquerque J.F.G., Miglino M.A. & Oliveira M.F. 2012. [Gross morphology and topography of the digestive apparatus in rheas (Rhea americana americana).] Macroscopia e topografia do aparelho digestorio de emas (Rhea americana americana). Pesquisa Veterinaria Brasileira 32(7):681-686. Departamento de Cirurgia, Faculdade de Medicina Veterinaria e Zootecnia, Universidade de Sao Paulo, Cidade Universitaria, Av. Prof. Dr. Orlando Marques de Paiva 87, Sao Paulo, SP 05508270, Brazil. E-mail: marcio_medvet@hotmail.com Rheas are birds belonging to the ratites group and, among ostriches and emus, are the largest birds currently alive. In this work we studied the macroscopic aspects of rheas' digestive tract in order to provide important information to a better understanding of these birds' eating habits as well their anatomy. Twenty young animals aging between two and six months from the Centre for Wild Animals Multiplication (Cemas, scientific breeding license form Ibama no.1478912) were used. After dissection it was observed that their tongue was small and presented a rhomboid form, being disposed on the oral cavity floor, and inserted in its base by a frenulum. The esophagus was a rectilinear tube with elastic aspect and longitudinal elastic fibers, without dilation, which gives it an absence of crop. The proventriculus presented a fusiform form and the gastric ventricle showed and slightly oval form when filled, and was internally coated with a thick gastric cuticle. The small intestine was composed of three distinct regions: duodenum, jejunum and ileum. The duodenum had a light gray color and showed a "U" curved shaped. The jejunum was dark green, long and composed of several short loops arranged above each other. The ileum had a gray color and was connected with the jejunum. In ventral line to the rectum and cloaca, the ileum extended cranially, dorsally to the ascending duodenum. The large intestine was composed of two caeca, one right and one left, and colon-rectum and ileum were continuous with the cloaca. The structures of the rhea digestive tract resemble those described in the literature regarding to its shape and topography, even though rhea's caeca are well developed and relatively long.

Human eosinophil adhesion and degranulation stimulated with eotaxin and RANTES in vitro: Lack of interaction with nitric oxide

Abstract Background Airway eosinophilia is considered a central event in the pathogenesis of asthma. The toxic components of eosinophils are thought to be important in inducing bronchial mucosal injury and dysfunction. Previous studies have suggested an interaction between nitric oxide (NO) and chemokines in modulating eosinophil functions, but this is still conflicting. In the present study, we have carried out functional assays (adhesion and degranulation) and flow cytometry analysis of adhesion molecules (VLA-4 and Mac-1 expression) to evaluate the interactions between NO and CC-chemokines (eotaxin and RANTES) in human eosinophils. Methods Eosinophils were purified using a percoll gradient followed by immunomagnetic cell separator. Cell adhesion and degranulation were evaluated by measuring eosinophil peroxidase (EPO) activity, whereas expression of Mac-1 and VLA-4 was detected using flow cytometry. Results At 4 h incubation, both eotaxin (100 ng/ml) and RANTES (1000 ng/ml) increased by 133% and 131% eosinophil adhesion, respectively. L-NAME alone (but not D-NAME) also increased the eosinophil adhesion, but the co-incubation of L-NAME with eotaxin or RANTES did not further affect the increased adhesion seen with chemokines alone. In addition, L-NAME alone (but not D-NAME) caused a significant cell degranulation, but it did not affect the CC-chemokine-induced cell degranulation. Incubation of eosinophils with eotaxin or RANTES, in absence or presence of L-NAME, did not affect the expression of VLA-4 and Mac-1 on eosinophil surface. Eotaxin and RANTES (100 ng/ml each) also failed to elevate the cyclic GMP levels above baseline in human eosinophils. Conclusion Eotaxin and RANTES increase the eosinophil adhesion to fibronectin-coated plates and promote cell degranulation by NO-independent mechanisms. The failure of CC-chemokines to affect VLA-4 and Mac-1 expression suggests that changes in integrin function (avidity or affinity) are rather involved in the enhanced adhesion.

Recurring extensional and strike-slip tectonics after the Neoproterozoic collisional events in the southern Mantiqueira province

In Eastern South America, a series of fault-bounded sedimentary basins that crop out from Southern Uruguay to Southeastern Brazil were formed after the main collisional deformation of the Brasiliano Orogeny and record the tectonic events that affected the region from the Middle Ediacaran onwards. We address the problem of discerning the basin-forming tectonics from the later deformational events through paleostress analysis of more than 600 fault-slip data, mainly from the Camaquã Basin (Southern Brazil), sorted by stratigraphic level and cross-cutting relationships of superposed striations, and integrated with available stratigraphic and geochronological data. Our results show that the Camaquã Basin was formed by at least two distinct extensional events, and that rapid paleostress changes took place in the region a few tens of million years after the major collision (c.a. 630 Ma), probably due to the interplay between local active extensional tectonics and the distal effects of the continued amalgamation of plates and terranes at the margins of the still-forming Gondwana Plate. Preliminary paleostress data from the Castro Basin and published data from the Itajaí Basin suggest that these events had a regional nature.

Open bite: diagnosis, treatment and stability

Open bite has fascinated Orthodontics due to the difficulties regarding its treatment and maintenance of results. This anomaly has distinct characteristics that, in addition to the complexity of multiple etiological factors, have aesthetic and functional consequences. Within this etiological context, several types of mechanics have been used in open bite treatment, such as palatal crib, orthopedic forces, occlusal adjustment, orthodontic camouflage with or without extraction, orthodontic intervention using mini-implants or mini-plates, and even orthognathic surgery. An accurate diagnosis and etiological determination are always the best guides to establish the objectives and the ideal treatment plan for such a malocclusion. This report describes two cases of open bite. At the end of the treatment, both patients had their canines and molars in Class I occlusion, normal overjet and overbite, and stability during the posttreatment period.

Monitoring and determination of fungi and mycotoxins in stored Brazil nuts

Brazil nut (Bertholletia excelsa) is an important commodity from the Brazilian Amazon, and approximately 37,000 tons (3.36 × 10⁷ kg) of Brazil nuts are harvested each year. However, substantial nut contamination by Aspergillus section Flavi occurs, with subsequent production of mycotoxins. In this context, the objective of the present investigation was to evaluate the presence of fungi and mycotoxins (aflatoxins and cyclopiazonic acid) in 110 stored samples of cultivated Brazil nut (55 samples of nuts and 55 samples of shells) collected monthly for 11 months in Itacoatiara, State of Amazonas, Brazil. The samples were inoculated in duplicate onto Aspergillus flavus and Aspergillus parasiticus agar and potato dextrose agar for the detection of fungi, and the presence of mycotoxins was determined by high-performance liquid chromatography. The most prevalent fungi in nuts and shells were Aspergillus spp., Fusarium spp., and Penicillium spp. A polyphasic approach was used for identification of Aspergillus species. Aflatoxins and cyclopiazonic acid were not detected in any of the samples analyzed. The low water activity of the substrate was a determinant factor for the presence of fungi and the absence of aflatoxin in Brazil nut samples. The high frequency of isolation of aflatoxigenic Aspergillus section Flavi strains, mainly A. flavus, and their persistence during storage increase the chances of aflatoxin production on these substrates and indicates the need for good management practices to prevent mycotoxin contamination in Brazil nuts.

A new insight in stress recovery tecniques and hessian reconstruction methods

Stress recovery techniques have been an active research topic in the last few years since, in 1987, Zienkiewicz and Zhu proposed a procedure called Superconvergent Patch Recovery (SPR). This procedure is a last-squares fit of stresses at super-convergent points over patches of elements and it leads to enhanced stress fields that can be used for evaluating finite element discretization errors. In subsequent years, numerous improved forms of this procedure have been proposed attempting to add equilibrium constraints to improve its performances. Later, another superconvergent technique, called Recovery by Equilibrium in Patches (REP), has been proposed. In this case the idea is to impose equilibrium in a weak form over patches and solve the resultant equations by a last-square scheme. In recent years another procedure, based on minimization of complementary energy, called Recovery by Compatibility in Patches (RCP) has been proposed in. This procedure, in many ways, can be seen as the dual form of REP as it substantially imposes compatibility in a weak form among a set of self-equilibrated stress fields. In this thesis a new insight in RCP is presented and the procedure is improved aiming at obtaining convergent second order derivatives of the stress resultants. In order to achieve this result, two different strategies and their combination have been tested. The first one is to consider larger patches in the spirit of what proposed in [4] and the second one is to perform a second recovery on the recovered stresses. Some numerical tests in plane stress conditions are presented, showing the effectiveness of these procedures. Afterwards, a new recovery technique called Last Square Displacements (LSD) is introduced. This new procedure is based on last square interpolation of nodal displacements resulting from the finite element solution. In fact, it has been observed that the major part of the error affecting stress resultants is introduced when shape functions are derived in order to obtain strains components from displacements. This procedure shows to be ultraconvergent and is extremely cost effective, as it needs in input only nodal displacements directly coming from finite element solution, avoiding any other post-processing in order to obtain stress resultants using the traditional method. Numerical tests in plane stress conditions are than presented showing that the procedure is ultraconvergent and leads to convergent first and second order derivatives of stress resultants. In the end, transverse stress profiles reconstruction using First-order Shear Deformation Theory for laminated plates and three dimensional equilibrium equations is presented. It can be seen that accuracy of this reconstruction depends on accuracy of first and second derivatives of stress resultants, which is not guaranteed by most of available low order plate finite elements. RCP and LSD procedures are than used to compute convergent first and second order derivatives of stress resultants ensuring convergence of reconstructed transverse shear and normal stress profiles respectively. Numerical tests are presented and discussed showing the effectiveness of both procedures.

Experimental investigation into the effect of stress on dissolution and growth of very soluble brittle salts in aqueous solution

Das Studium der Auflösungs- und Wachstumsprozesse an Feststoff-Flüssigkeits-Grenzflächen unter nicht-hydrostatischen Beanspruchungen ist wesentlich für das Verständnis von Defor-mationsprozessen, die in der Erde ablaufen. Unter diesen genannten Prozessen gehört die Drucklösung zu den wichtigsten duktilen Deformationsprozessen, von der Diagenese bishin zur niedrig- bis mittelgradigen metamorphen Bedingungen. Bisher ist allerdings wenig darüber bekannt, welche mechanischen, physikalischen oder chemischen Potentialenergie-Gradienten die Drucklösung steuern. I.a. wird angenommen, daß die Drucklösung durch Un-terschiede kristallplastischer Verformungsenergien oder aber durch Unterschiede der Normal-beanspruchung an Korngrenzen gesteuert wird. Unterschiede der elastischen Verformungs-energien werden dabei allerdings als zu gering erachtet, um einen signifikanten Beitrag zu leisten. Aus diesem Grund werden sie als mögliche treibende Kräfte für die Drucklösung vernachlässigt. Andererseits haben neue experimentelle und theoretische Untersuchungen gezeigt, daß die elastische Verformung in der Tat einen starken Einfluß auf Lösungs- und Wachstumsmechanismen von Kristallen in einer Lösung haben kann. Da die in der Erdkruste vorherrschenden Deformationsmechanismen überwiegend im elastischen Verformungsbereich der Gesteine ablaufen, ist es sehr wichtig, das Verständnis für die Effekte, die die elastische Verformung verursacht, zu erweitern, und ihre Rolle während der Deformation durch Drucklösung zu definieren. Die vorliegende Arbeit beschäftigt sich mit Experimenten, bei denen der Effekt der mechanisch kompressiven Beanspruchung auf Lösungs- und Wachstumsprozesse von Einzelkristallen unterschiedlicher, sehr gut löslicher, elastisch/spröder Salze untersucht wurde. Diese Salze wurden als Analoga gesteinsbildender Minerale wie Quarz und Calcit ausgewählt. Der Einfluß von Stress auf die Ausbildung der Oberflächenmikrostrukturen in einer untersättigten Lösung wurde an Kaliumalaun untersucht.Lösungsrillen (20 – 40 µm breit, 10 – 40 µm tief und 20 – 80 µm Abstand) entwickelten sich in den Bereichen, in denen die Beanspruchung im Kristall am größten war. Sie verschwanden wieder, sobald der Kristall entlastet wurde. Diese Rillen entwickelten sich parallel zu niedrig indizierten kristallographischen Richtungen und sub-perpendikular zu den Trajektorien, die der maximalen, lokalen kompressiven Beanspruchung entsprachen. Die Größe der Lösungsrillen hing von der lokalen Oberflächenbeanspruchung, der Oberflächenenergie und dem Untersättigungsgrad der wässrigen Lösung ab. Die mikrostrukturelle Entwicklung der Kristalloberflächen stimmte gut mit den theoretischen Vorhersagen überein, die auf den Modellen von Heidug & Leroy (1994) und Leroy & Heidug (1994) basieren. Der Einfluß der Beanspruchung auf die Auflösungsrate wurde an Natriumchlorat-Einzelkristallen untersucht. Dabei wurde herausgefunden, daß sich gestresste Kristalle schneller lösen als Kristalle, auf die keine Beanspruchung einwirkt. Der experimentell beobachtete Anstieg der Auflösungsrate der gestressten Kristalle war ein bis zwei Größenordnungen höher als theoretisch erwartet. Die Auflösungsrate stieg linear mit dem Stress an, und der Anstieg war um so größer, je stärker die Lösung untersättigt war. Außerdem wurde der Effekt der Bean-spruchung auf das Kristallwachstum an Kaliumalaun- und Kaliumdihydrogenphosphat-Ein-zelkristallen untersucht. Die Wachstumsrate der Flächen {100} und {110} von Kalium-alaun war bei Beanspruchung stark reduziert. Für all diese Ergebnisse spielte die Oberflächenrauhigkeit der Kristalle eine Schlüsselrolle, indem sie eine nicht-homogene Stressverteilung auf der Kristalloberfläche verursachte. Die Resultate zeigen, daß die elastische Verformung eine signifikante Rolle während der Drucklösung spielen kann, und eine signifikante Deformation in der oberen Kruste verursachen kann, bei Beanspruchungen, die geringer sind, als gemeinhin angenommen wird. Somit folgt, daß die elastische Bean-spruchung berücksichtigt werden muß, wenn mikrophysikalische Deformationsmodelle entwickelt werden sollen.

Modelling and analysis of internally BFRP reinforced beams at elevated temperatures

The aim of the work is to conduct a finite element model analysis on a small – size concrete beam and on a full size concrete beam internally reinforced with BFRP exposed at elevated temperatures. Experimental tests performed at Kingston University have been used to compare the results from the numerical analysis for the small – size concrete beam. Once the behavior of the small – size beam at room temperature is investigated and switching to the heating phase reinforced beams are tested at 100°C, 200°C and 300°C in loaded condition. The aim of the finite element analysis is to reflect the three – point bending test adopted into the oven during the exposure of the beam at room temperature and at elevated temperatures. Performance and deformability of reinforced beams are straightly correlated to the material properties and a wide analysis on elastic modulus and coefficient of thermal expansion is given in this work. Develop a good correlation between the numerical model and the experimental test is the main objective of the analysis on the small – size concrete beam, for both modelling the aim is also to estimate which is the deterioration of the material properties due to the heating process and the influence of different parameters on the final result. The focus of the full – size modelling which involved the last part of this work is to evaluate the effect of elevated temperatures, the material deterioration and the deflection trend on a reinforced beam characterized by a different size. A comparison between the results from different modelling has been developed.

Hypersonic elastic excitations in soft mesoscopic structures

This dissertation is devoted to the experimental exploration of the propagation of elastic waves in soft mesoscopic structures with submicrometer dimensions. A strong motivation of this work is the large technological relevance and the fundamental importance of the subject. Elastic waves are accompanied by time-dependent fluctuations of local stress and strain fields in the medium. As such, the propagation phase velocities are intimately related to the elastic moduli. Knowledge of the elastic wave propagation directly provides information about the mechanical properties of the probed mesoscopic structures, which are not readily accessible experimentally. On the other hand, elastic waves, when propagating in an inhomogeneous medium with spatial inhomogeneities comparable to their wavelength, exhibit rather rich behavior, including the appearance of novel physical phenomena, such as phononic bandgap formation. So far, the experimental work has been restricted to macroscopic structures, which limit wave propagation below the KHz range. It was anticipated that an experimental approach capable of probing the interplay of the wave propagation with the controlled mesoscopic structures would contribute to deeper insights into the fundamental problem of elastic wave propagation in inhomogeneous systems. The mesoscopic nature of the structures to be studied precludes the use of traditional methods, such as sound transmission, for the study of elastic wave propagation. In this work, an optical method utilizing the inelastic scattering of photons by GHz frequency thermally excited elastic waves, known as Brillouin light scattering spectroscopy (BLS), was employed. Two important classes of soft structures were investigated: thin films and colloidal crystals. For the former, the main interest was the effect of the one-dimensional (1D) confinement on the wave propagation due to the presence of the free-surface or interface of the layer and the utilization of these waves to extract relevant material parameters. For the second system, the primary interest was the interaction of the elastic wave and the strong scattering medium with local resonance units in a three-dimensional (3D) periodic arrangement.

Mapping the elastic response of epithelial apical cell membranes suspended across porous array

As the elastic response of cell membranes to mechanical stimuli plays a key role in various cellular processes, novel biophysical strategies to quantify the elasticity of native membranes under physiological conditions at a nanometer scale are gaining interest. In order to investigate the elastic response of apical membranes, elasticity maps of native membrane sheets, isolated from MDCK II (Madine Darby Canine kidney strain II) epithelial cells, were recorded by local indentation with an Atomic Force Microscope (AFM). To exclude the underlying substrate effect on membrane indentation, a highly ordered gold coated porous array with a pore diameter of 1.2 μm was used to support apical membranes. Overlays of fluorescence and AFM images show that intact apical membrane sheets are attached to poly-D-lysine coated porous substrate. Force indentation measurements reveal an extremely soft elastic membrane response if it is indented at the center of the pore in comparison to a hard repulsion on the adjacent rim used to define the exact contact point. A linear dependency of force versus indentation (-dF/dh) up to 100 nm penetration depth enabled us to define an apparent membrane spring constant (kapp) as the slope of a linear fit with a stiffness value of for native apical membrane in PBS. A correlation between fluorescence intensity and kapp is also reported. Time dependent hysteresis observed with native membranes is explained by a viscoelastic solid model of a spring connected to a Kelvin-Voight solid with a time constant of 0.04 s. No hysteresis was reported with chemically fixated membranes. A combined linear and non linear elastic response is suggested to relate the experimental data of force indentation curves to the elastic modulus and the membrane thickness. Membrane bending is the dominant contributor to linear elastic indentation at low loads, whereas stretching is the dominant contributor for non linear elastic response at higher loads. The membrane elastic response was controlled either by stiffening with chemical fixatives or by softening with F-actin disrupters. Overall, the presented setup is ideally suitable to study the interactions of the apical membrane with the underlying cytoskeleton by means of force indentation elasticity maps combined with fluorescence imaging.

Study of the Compressive Strength of Aluminum Curved Elements

Currently, the Specification for Aluminum Structures (Aluminum Association, 2010) shows thin-walled aluminum plate sections with radii greater than eight inches have a lower compressive strength capacity than a flat plate with the same width and thickness. This inconsistency with intuition, which suggests any degree of folding a plate should increase its elastic buckling strength, inspired this study. A wide range of curvatures are studied—from a nearly flat plate to semi-circular. To quantify the curvature, a single non-dimensional parameter is used to represent all combinations of width, thickness and radius. Using the finite strip method (CU-FSM), elastic local buckling stresses are investigated. Using the ratio of stress values of curved plates compared to flat plates of the same size, equivalent plate-buckling coefficients are calculated. Using this data, nonlinear regression analyses are performed to develop closed form equations for five different edge support conditions. These equations can be used to calculate the elastic critical buckling stress for any curved aluminum section when the geometric properties (width, thickness, and radius) and the material properties (elastic modulus and Poisson’s ratio) are known. This procedure is illustrated in examples, each showing the applicability of the derived equations to geometries other than those investigated in this study and also providing comparisons with theoretically exact numerical analysis results.

Adaptation to hard-object feeding in sea otters and hominins

The large, bunodont postcanine teeth in living sea otters (Enhydra lutris) have been likened to those of certain fossil hominins, particularly the ’robust’ australopiths (genus Paranthropus). We examine this evolutionary convergence by conducting fracture experiments on extracted molar teeth of sea otters and modern humans (Homo sapiens) to determine how load-bearing capacity relates to tooth morphology and enamel material properties. In situ optical microscopy and x-ray imaging during simulated occlusal loading reveal the nature of the fracture patterns. Explicit fracture relations are used to analyze the data and to extrapolate the results from humans to earlier hominins. It is shown that the molar teeth of sea otters have considerably thinner enamel than those of humans, making sea otter molars more susceptible to certain kinds of fractures. At the same time, the base diameter of sea otter first molars is larger, diminishing the fracture susceptibility in a compensatory manner. We also conduct nanoindentation tests to map out elastic modulus and hardness of sea otter and human molars through a section thickness, and microindentation tests to measure toughness. We find that while sea otter enamel is just as stiff elastically as human enamel, it is a little softer and tougher. The role of these material factors in the capacity of dentition to resist fracture and deformation is considered. From such comparisons, we argue that early hominin species like Paranthropus most likely consumed hard food objects with substantially higher biting forces than those exerted by modern humans.

Cement distribution, volume, and compliance in vertebroplasty: some answers from an anatomy-based nonlinear finite element study

STUDY DESIGN: The biomechanics of vertebral bodies augmented with real distributions of cement were investigated using nonlinear finite element (FE) analysis. OBJECTIVES: To compare stiffness, strength, and stress transfer of augmented versus nonaugmented osteoporotic vertebral bodies under compressive loading. Specifically, to examine how cement distribution, volume, and compliance affect these biomechanical variables. SUMMARY OF BACKGROUND DATA: Previous FE studies suggested that vertebroplasty might alter vertebral stress transfer, leading to adjacent vertebral failure. However, no FE study so far accounted for real cement distributions and bone damage accumulation. METHODS: Twelve vertebral bodies scanned with high-resolution pQCT and tested in compression were augmented with various volumes of cements and scanned again. Nonaugmented and augmented pQCT datasets were converted to FE models, with bone properties modeled with an elastic, plastic and damage constitutive law that was previously calibrated for the nonaugmented models. The cement-bone composite was modeled with a rule of mixture. The nonaugmented and augmented FE models were subjected to compression and their stiffness, strength, and stress map calculated for different cement compliances. RESULTS: Cement distribution dominated the stiffening and strengthening effects of augmentation. Models with cement connecting either the superior or inferior endplate (S/I fillings) were only up to 2 times stiffer than the nonaugmented models with minimal strengthening, whereas those with cement connecting both endplates (S + I fillings) were 1 to 8 times stiffer and 1 to 12 times stronger. Stress increases above and below the cement, which was higher for the S + I cases and was significantly reduced by increasing cement compliance. CONCLUSION: The developed FE approach, which accounts for real cement distributions and bone damage accumulation, provides a refined insight into the mechanics of augmented vertebral bodies. In particular, augmentation with compliant cement bridging both endplates would reduce stress transfer while providing sufficient strengthening.

Numerical study on the curling and warping of hardened rigid pavement slabs

In-service hardened concrete pavement suffers from environmental loadings caused by curling and warping of the slab. Traditionally, these loadings are computed on the basis of treating the slab as an elastic material, and of evaluating separately the curling and warping components. This dissertation simulates temperature distribution and moisture distribution through the slabs by use of a developed numerical model that couples the heat transfer and moisture transport. The computation of environmental loadings treats the slab as an elastic-viscous material, which considers the relaxation behavior and Pickett effect of the concrete. The heat transfer model considers the impacts of solar radiation, wind speed, air temperature, pavement slab albedo, etc. on the pavement temperature distribution. This dissertation assesses the difference between documented models that aim to predict pavement temperature, highlighting their pros and cons. The moisture transport model is unique for the documented models; it mimics the wetting and drying events occurring at the slab surface. These events are estimated by a proposed statistical algorithm, which is verified by field rainfall data. Analysis of the predicted results examines on the roles of the local air RH (relative humidity), wind speed, rainy pattern in the moisture distribution through the slab. The findings reveal that seasonal air RH plays a decisive role on the slab‘s moisture distribution; but wind speed and its daily variation, daily RH variation, and seasonal rainfall pattern plays only a secondary role. This dissertation sheds light on the computation of environmental loadings that in-service pavement slabs suffer from. Analysis of the computed stresses centers on the stress relaxation near the surface, stress evolution after the curing ends, and the impact of construction season on the stress‘s magnitude. An unexpected finding is that the total environmental loadings at the cyclically-stable state divert from the thermal stresses. At such a state, the total stress at the daytime is roughly equal to the thermal stress; whereas the total stress during the nighttime is far greater than the thermal stress. An explanation for this phenomenon is that during the night hours, the decline of the slab‘s near-surface temperature leads to a drop of the near-surface RH. This RH drop results in contraction therein and develops additional tensile stresses. The dissertation thus argues that estimating the environmental loadings by solely computing the thermally-induced stresses may reach delusive results. It recommends that the total environmental loadings of in-service slabs should be estimated by a sophisticated model coupling both moisture component and temperature component.

Embedding of human vertebral bodies leads to higher ultimate load and altered damage localisation under axial compression

Computer tomography (CT)-based finite element (FE) models of vertebral bodies assess fracture load in vitro better than dual energy X-ray absorptiometry, but boundary conditions affect stress distribution under the endplates that may influence ultimate load and damage localisation under post-yield strains. Therefore, HRpQCT-based homogenised FE models of 12 vertebral bodies were subjected to axial compression with two distinct boundary conditions: embedding in polymethylmethalcrylate (PMMA) and bonding to a healthy intervertebral disc (IVD) with distinct hyperelastic properties for nucleus and annulus. Bone volume fraction and fabric assessed from HRpQCT data were used to determine the elastic, plastic and damage behaviour of bone. Ultimate forces obtained with PMMA were 22% higher than with IVD but correlated highly (R2 = 0.99). At ultimate force, distinct fractions of damage were computed in the endplates (PMMA: 6%, IVD: 70%), cortex and trabecular sub-regions, which confirms previous observations that in contrast to PMMA embedding, failure initiated underneath the nuclei in healthy IVDs. In conclusion, axial loading of vertebral bodies via PMMA embedding versus healthy IVD overestimates ultimate load and leads to distinct damage localisation and failure pattern.