Strength Of Skeleton Research Articles

Characterization and comparison of uniform hydrophilic/hydrophobic transparent silica aerogel beads: skeleton strength and surface modification

This preparation method of skeleton improvement of wet silica beads by ambient pressure drying is suitable for economic and large-scale industrial production of silica aerogel beads.

Study of soil structures strength and stiffness loss based on thermodynamics and continuum mechanics

Based on the theory of damage mechanics and porous medium continuum mechanics, a solid skeleton strength degradation model for internal erosion of earth structure is presented in this paper. Saturated soil is considered as a mixture composed of matrix skeleton and porous space, the latter being filled by fluid which consists of a mixture of water and eroded particles. With these eroded particles being carried out with fluid, porous space in earth enlarges, and the effective stress area of solid skeleton decreases, which leads the effective stress acting on the solid skeleton to increase. This process also involves earth structure stiffness loss and strength degradation. This paper presents a constitutive model and sets up the relations between the strain and the internal erosion damage variable using thermodynamics and damage mechanics.

Resilience of branching and massive corals to wave loading under sea level rise – A coupled computational fluid dynamics-structural analysis

Measurements of coral structural strength are coupled with a fluid dynamics-structural analysis to investigate the resilience of coral to wave loading under sea level rise and a typical Great Barrier Reef lagoon wave climate. The measured structural properties were used to determine the wave conditions and flow velocities that lead to structural failure. Hydrodynamic modelling was subsequently used to investigate the type of the bathymetry where coral is most vulnerable to breakage under cyclonic wave conditions, and how sea level rise (SLR) changes this vulnerability. Massive corals are determined not to be vulnerable to wave induced structural damage, whereas branching corals are susceptible at wave induced orbital velocities exceeding 0.5m/s. Model results from a large suite of idealised bathymetry suggest that SLR of 1m or a loss of skeleton strength of order 25% significantly increases the area of reef flat where branching corals are exposed to damaging wave induced flows.

Teriparatide Increases Strength of the Peripheral Skeleton in Premenopausal Women With Idiopathic Osteoporosis: A Pilot HR-pQCT Study

In premenopausal women with idiopathic osteoporosis (IOP), treatment with teriparatide leads to substantial improvement in bone density and quality at central skeletal sites. The effects of teriparatide may differ on cortical and trabecular bone and also at the central and the peripheral skeleton. The objective of the study was to determine whether teriparatide was associated with improvements in compartmental volumetric bone mineral density (BMD), bone microarchitecture, and estimated bone strength of the distal radius and tibia as assessed by high-resolution peripheral quantitative computed tomography. Premenopausal women (n = 20, age 41 ± 5 y) with IOP (low trauma fractures and/or Z-scores ≤ -2.0) were scanned with high-resolution peripheral quantitative computed tomography at baseline and after 18 months of teriparatide treatment. Cortical and trabecular volumetric BMD and microarchitecture were measured by both standard and advanced techniques, including individual trabecula segmentation, and bone strength was estimated by finite element analysis. The total volumetric BMD and homogeneous bone stiffness were measured. Trabecular volumetric BMD increased significantly by 2.6% (1.8, 6.2) [median (interquartile range)] at the radius and 2.5% (1.1, 3.6) at the tibia. In addition, trabecular plate bone volume fraction increased by 9.1% (2.1, 17.1) at the radius and 7.6% (1.0, 9.7) at the tibia. Cortical thickness and volumetric density did not change; however, cortical porosity increased at the radius but not at the tibia. Despite these changes, whole-bone stiffness and failure load estimated by finite element analysis increased at both the radius and tibia. In premenopausal women with IOP, 18 months of teriparatide was associated with increases in trabecular volumetric BMD, improved trabecular microarchitecture, and estimated bone strength at both the radius and tibia.

Mechanical properties of silica aerogels prepared from a mixture of TEOS and organo-alkoxysilanes of type R1SiX3

Silica aerogels were prepared from a mixture of tetraethylorthosilicate and organoalkoxysilanes. The effects of organo-alkoxysilanes on the mechanical properties of the silica aerogels were studied. The flexibility of silica aerogels was significantly improved by incorporation of organo-alkoxysilanes. When MTES and TEOS were combined as precursors of silica areogels, with the increased amount of MTES, the apparent elastic modulus and apparent compressive strength monotonously rose. At the same organoalkoxysilanes to TEOS ratio, the size of alkyl groups of the organo-alkoxysilanes had little effect on the mechanical properties. In series of MTES and TEOS, the lowest elastic modulus of silica skeleton and the highest compressive strength of silica skeleton were observed at MTES to TEOS ratio of around 50:50. At a certain organo-alkoxysilanes to TEOS ratio, the elastic modulus of silica skeleton increased and the compressive strength of silica skeleton decreased with the size increase of the alkyl groups.

Factors influencing the selected body parameters and hippometric indexes in donkey's population

The main focus of our work was to collect basic body measurements of donkey population in Czech republic and determine the factors that influence these body measurements and hipometric indexes. The following measurements were recorded: height at withers, chest circumference and metacarpus interference. Based on the collected data, we were able to calculate the hipometric indexes: index of boniness, skeleton strength index, body mass index and coup height index. From a total of 331 individuals of donkey species living in Czech republic we managed to collect 50 samples. These were subjected to a general linear model (GLM) and multiplex comparison statistical analysis. We managed to prove a statistically significant difference between donkeys born in Czech republic and the ones born abroad for all the measurements. Specifically the metacarpus circumference the gender dependency was also proved, having its impact on the hipometric indexes as well; the boniness index and skeleton strength index were also proved to be gender – dependent.

The preparation and characterization graphene-cross-linked phenol–formaldehyde hybrid carbon xerogels

A new synthesis route based on polycondensation of phenol and formaldehyde cross-linked by graphene oxide (GO) was developed. Wet gel after gelation was converted into an organic xerogel by ambient pressure drying to obtain GO-cross-linked phenol–formaldehyde (PF) organic xerogels (GOCPFOX). Graphene-cross-linked PF carbon xerogels (GCPFCX) were produced by carbonization. The morphology and chemical structure of GOCPFOX and GCPFCX were analyzed. The electrochemical behavior of GCPFCX as an electrode material in electric double-layer capacitors (EDLCs) was investigated. Results show that the high mechanical strength of GO increased the gel skeleton strength; thus, organic xerogels exhibit very low drying shrinkage. Scanning electron micrographs indicated that addition of GO altered the gel structure. Thus, when GO was added into the PF solution, the PF molecular chains were anchored on the surface of GO by chemical and physical interaction. The GCPFCX-10 sample achieved the highest specific surface area, mesoporous volume, and specific capacity with 378 m2/g, 0.56 cm3/g, and 116 F/g, respectively. Hence, GCPFCX is a potential material for EDLCs owing to its low production cost and ability to avoid supercritical drying.

Graphene cross-linked phenol–formaldehyde hybrid organic and carbon xerogel during ambient pressure drying

A new method of synthesizing hybrid organic and carbon xerogel using graphene oxide as the cross-linking agent in the polycondensation of phenol and formaldehyde is presented. The organic xerogel is dried under ambient conditions, and the graphene cross-linked phenol–formaldehyde hybrid carbon xerogel (GCPFCX) is obtained through carbonization. Mechanically strong graphene oxide (GO) increases gel skeleton strength, giving organic xerogel very low drying shrinkage, low density and high mechanical property. The GCPFCX exhibits a layered structure, indicating a change in the gel structure resulting from the addition of GO. The PF molecular chains possibly grow along the GO surface because of strong interactions between the two compounds.

Large Mesopore Generation in an Amorphous Silica-Alumina by Controlling the Pore Size with the Gel Skeletal Reinforcement and Its Application to Catalytic Cracking

Tetraethoxy orthosilicate (TEOS) was used not only as a precursor of silica, but also as an agent which reinforces the skeleton of silica-gel to prepare an aerogel and resultant silica and silica-alumina with large pore size and pore volume. In this gel skeletal reinforcement, the strength of silica aerogel skeleton was enhanced by aging with TEOS/2-propanol mixed solution to prevent the shrink of the pores. When silica aerogel was reinforced by TEOS solution, the pore diameter and pore volume of calcined silica could be controlled by the amount of TEOS solution and reached 30 nm and 3.1 cm3/g. The results from N2 adsorption measurement indicated that most of pores for this silica consisted of mesopores. Silica-alumina was prepared by the impregnation of an aluminum tri-sec-butoxide/2-butanol solution with obtained silica. Mixed catalysts were prepared by the combination of β-zeolite (26 wt%) and prepared silica-aluminas with large mesopore (58 wt%) and subsequently the effects of their pore sizes on the catalytic activity and the product selectivity were investigated in catalytic cracking of n-dodecane at 500 °C. The mixed catalysts exhibited not only comparable activity to that for single zeolite, but also unique selectivity where larger amounts of branched products were formed.

On Using Anisotropic Diffusion for Skeleton Extraction

We present a novel and effective skeletonization algorithm for binary and gray-scale images, based on the anisotropic heat diffusion analogy. We diffuse the image in the direction normal to the feature boundaries and also allow tangential diffusion (curvature decreasing diffusion) to contribute slightly. The proposed anisotropic diffusion provides a high quality medial function in the image: it removes noise and preserves prominent curvatures of the shape along the level-sets (skeleton features). The skeleton strength map, which provides the likelihood of a point to be part of the skeleton, is defined by the mean curvature measure. Finally, thin and binary skeleton is obtained by non-maxima suppression and hysteresis thresholding of the skeleton strength map. Our method outperforms the most related and the popular methods in skeleton extraction especially in noisy conditions. Results show that the proposed approach is better at handling noise in images and preserving the skeleton features at the centerline of the shape.

Détection du micro-endommagement dans le tissu osseux trabéculaire par une méthode d’acousto-élasticité dynamique

Osteoporosis affects the whole skeleton strength leading to an actual fracture risk. Associated to a high level of morbidity, it is a critical public health issue. During the last decades, several X-rays and ultrasound devices have been developed to help the clinicians in their diagnosis. They are essentially related to bone mass while several factors are responsible for this pathology. Among them, microdamage has an interesting place. Nonlinear acoustic methods have already shown their ability to detect microcracks in different geophysical and industrial materials. We present a dynamic acousto-elastic testing (interaction of a very low frequency tone burst and high frequency pulses) to measure viscoelastic and dissipative nonlinearities. Applied to trabecular bone samples (human defatted calcanei), this method has shown a high level of nonlinearity in very dense regions of the calcanei. However, native microdamage is often at the limit of the method sensibility. To better evaluate this parameter, we have performed acousto-elastic measurements before and after inducing microdamage thanks to a compression fatigue test. We observed higher nonlinearity after induced damage. Moreover, the level of acoustic nonlinearity has been correlated to actual damage accumulation thanks to confocal microscopy analysis. However, acousto-elasticity measurements repeatability is weak. Correct reproducibility is observed for low level of nonlinearity (low level of microcracks). For high level of nonlinearity, quite different nonlinear behaviors are usually observed from one measurement to the next one.

Mechanical properties of polymer-modified silica aerogels dried under ambient pressure

Silica gels prepared by copolymerizing tetraethylorthosilicate with 3-aminopropyltriethoxy-silane were modified using polymer derived from toluene diisocyanate and dried under ambient pressure. The successful preparation of silica aerogels depended on the effective control of shrinkage during drying. The resulting material, polymer-modified silica aerogel, was then characterized by thermogravimetric analysis and uniaxial compression tests. Results indicated that the apparent elastic modulus and compressive strength of the polymer-modified silica aerogels decreased with increasing amounts of incorporated polymer because of decreasing shrinkage and density, while the strains at the surface cracking point and the final failure point increased significantly during compression tests. The strength and modulus of the silica skeleton could be calculated from the apparent strength and modulus of the silica aerogels respectively. It was interestingly shown that the elastic modulus of the silica skeleton of the silica aerogels increased because of the incorporated polymers, while the polymers had no effects on the compressive strength of the silica skeleton. In addition, the relationships between the apparent elastic modulus or the apparent compressive strength of the polymer-modified silica aerogels and their shrinkage were quantitatively expressed.

The Mechanical Coupling of Fluid-Filled Granular Material Under Shear

The coupled mechanics of fluid-filled granular media controls the physics of many Earth systems, for example saturated soils, fault gouge, and landslide shear zones. It is well established that when the pore fluid pressure rises, the shear resistance of fluid-filled granular systems decreases, and, as a result, catastrophic events such as soil liquefaction, earthquakes, and accelerating landslides may be triggered. Alternatively, when the pore pressure drops, the shear resistance of these geosystems increases. Despite the great importance of the coupled mechanics of grain–fluid systems, the basic physics that controls this coupling is far from understood. Fundamental questions that must be addressed include: what are the processes that control pore fluid pressurization and depressurization in response to deformation of the granular skeleton? and how do variations of pore pressure affect the mechanical strength of the grains skeleton? To answer these questions, a formulation for the pore fluid pressure and flow has been developed from mass and momentum conservation, and is coupled with a granular dynamics algorithm that solves the grain dynamics, to form a fully coupled model. The pore fluid formulation reveals that the evolution of pore pressure obeys viscoelastic rheology in response to pore space variations. Under undrained conditions elastic-like behavior dominates and leads to a linear relationship between pore pressure and overall volumetric strain. Viscous-like behavior dominates under well-drained conditions and leads to a linear relationship between pore pressure and volumetric strain rate. Numerical simulations reveal the possibility of liquefaction under drained and initially over-compacted conditions, which were often believed to be resistant to liquefaction. Under such conditions liquefaction occurs during short compactive phases that punctuate the overall dilative trend. In addition, the previously recognized generation of elevated pore pressure under undrained compactive conditions is observed. Simulations also show that during liquefaction events stress chains are detached, the external load becomes completely supported by the pressurized pore fluid, and shear resistance vanishes.

Analysis of the interaction of acoustic waves with hard and soft corals in the near field of a source.

Hard and soft corals exist in tropical and sub‐tropical regions usually within 25–70 m of the surface. They are invertebrates with a mouth, tentacles, nematocysts, and simple sensory organs and nervous systems. Reef‐building corals live in bottom‐attached colonies and depend on moving water for transport of nutrients and removal of waste products. The physical characteristics of their bodies that promote interaction with flowing water also enhance fluid dynamic forces. Thus in the near field of a powerful acoustic source, the instantaneous drag, lift, and acceleration forces imposed on a coral reef have the potential to cause injury. An analysis of the fluid dynamic forces generated by an air gun blast was used to estimate stresses induced in stony coral skeleton and polyp tissues as a function of colony size. The stress at which injury is expected was calculated by applying a factor of safety of 2 to available values for rupture strength of stony coral skeleton and longitudinal strength of polyp connective tissue. Results indicate that polyps in colonies with characteristic length of about 5 m are likely to be injured by an air gun blast when the peak‐to‐peak received level exceeds 260 dB re 1 μPa.

Dietary Protein Supplementation Increases Peak Bone Mass Acquisition in Energy-Restricted Growing Rats

Peak bone mass is a major determinant of osteoporosis pathogenesis during aging. Respective influences of energy and protein supplies on skeletal growth remains unclear. We investigated the effect of a 5-mo dietary restriction on bone status in young rats randomized into six groups (n = 10 per group). Control animals were fed a diet containing a normal (13%) (C-NP) or a high-protein content (26%) (C-HP). The other groups received a 40% protein energy-restricted diet (PER-NP and PER-HP) or a 40% energy-restricted diet (ER-NP and ER-HP). High-protein intake did not modulate bone acquisition, although a metabolic acidosis was induced and calcium retention impaired. PER and ER diets were associated with a decrease in femoral bone mineral density. The compensation for protein intake in energy-restricted conditions induced a bone sparing effect. Plasma osteocalcin (OC) and urinary deoxypyridinoline (DPD) assays revealed a decreased OC/DPD ratio in restricted rats compared with C animals, which was far more reduced in PER than in ER groups. Circulating IGF-1 levels were lowered by dietary restrictions. In conclusion, both energy and protein deficiencies may contribute to impairment in peak bone mass acquisition, which may affect skeleton strength and potentially render individuals more susceptible to osteoporosis.

Open-Tip Approach

Modifications and innovations in open-structure rhinoplasty that have occurred as this technique has evolved are discussed. In addition, the philosophy and fundamentals of open-tip approach in rhinoplasty are reexamined. A retrospective review of representative patients in a hospital practice setting was performed. All surgical procedures were conducted in a department of plastic surgery of the University of Rome Tor Vergata. The preoperative and long-term results of each patient are compared to demonstrate the effectiveness of the described techniques. The fundamental philosophy of open-tip rhinoplasty is the maintenance of the integrity and strength of the nasal skeleton. Modifications of tip grafting techniques, along with additional domal grafting techniques, and a stronger focus on domal suturing techniques result in a softer contour and lack of tip tensions while maintaining structural support.

Processing and Characterization of Cr-Cu Alloys through Liquid Phase Sintering for Vacuum Circuit Breakers

Powder metallurgical processing of Cr-Cu has advantages over other processes.Vacuum Cirbuit Breakers are well known as vacuum interrupters (VI).The essential properties required for materials used in VI are high electrical conductivity, good skeleton strength and spark erosion resistance.The effect of sintering temperature, compaction pressure and composition on microstructure, sintered density, mechanical properties (tensile strength, hardness) electrical conductivity and skeleton strength of Cu-Cr contacts was investigated.The effect of microstructure on net-shape consolidation and macrostructure evolution during sintering are also detailed.Liquid phase sintering of Cr-Cu alloys resulted in better density without any significant shape distortion.Tensile strength increased with compaction pressure and chromium content.Higher compaction pressure also led to increased bulk hardness.Electrical conductivity increased with increasing compaction pressure and Cu content.

Mechanical limitations of reef corals during hydrodynamic disturbances

[Extract] During hydrodynamic disturbances such as cyclones and tsunamis, coral colonies are partially damaged whereby colony branches or segments are removed or dislodged from the substrate altogether (Woodley et al. 1981; Connell et al. 1997). Afterwards, those coral fragments that are unable to reattach to the substrate (Smith and Hughes 1999) are tumbled about by ambient water motion, resulting in extensive mortality regimes (Knowlton et al. 1981; Woodley et al. 1981). Despite the well-known role of hydrodynamic disturbance in structuring coral reef communities (Connell 1978), the fate of different colonial morphologies is unknown because researchers are unable to observe the reef during such destructive disturbances. To circumvent this obstacle, the present study uses a classical engineering approach to demonstrate the likely consequences for coral colonies when pushed to their mechanical limits by water motion. Contrary to common belief (Chamberlain 1978; Schuhmacher and Plewka 1981; Vosburgh 1982), this study finds that the overall mechanical integrity of coral colonies is highly unlikely to be determined by the strength of their carbonate skeletons, but rather by the highly variable and significantly weaker strength of the reef substrate to which they are attached. Furthermore, as the hydrodynamic force increases, the engineering model predicts that the pruning of colony branches is unlikely to occur before whole-colony dislodgement. It is suggested therefore that the superior strength of coral skeleton, which is found to be increasingly stronger in more mechanically vulnerable morphologies, may be an evolutionary solution for reducing the likelihood of branch removal by localized impacts of waterborne debris during hydrodynamic disturbances.

Sexual dimorphism of the femoral neck during the adolescent growth spurt: a structural analysis

Before puberty, there are only small sex differences in body shape and composition. During adolescence, sexual dimorphism in bone, lean, and fat mass increases, giving rise to the greater size and strength of the male skeleton. The question remains as to whether there are sex differences in bone strength or simply differences in anthropometric dimensions. To test this, we applied hip structural analysis (HSA) to derive strength and geometric indices of the femoral neck using bone densitometry scans (DXA) from a 6-year longitudinal study in Canadian children. Seventy boys and sixty-eight girls were assessed annually for 6 consecutive years. At the femoral neck, cross-sectional area (CSA, an index of axial strength), subperiosteal width (SPW), and section modulus (Z, an index of bending strength) were determined, and data were analyzed using a hierarchical (random effects) modeling approach. Biological age (BA) was defined as years from age at peak height velocity (PHV). When BA, stature, and total-body lean mass (TB lean) were controlled, boys had significantly higher Z than girls at all maturity levels ( P < 0.05). Controlling height and TB lean for CSA demonstrated a significant independent sex by BA interaction effect ( P < 0.05). That is, CSA was greater in boys before PHV but higher in girls after PHV. The coefficients contributing the greatest proportion to the prediction of CSA, SPW, and Z were height and lean mass. Because the significant sex difference in Z was relatively small and close to the error of measurement, we questioned its biological significance. The sex difference in bending strength was therefore explained by anthropometric differences. In contrast to recent hypotheses, we conclude that the CSA–lean ratio does not imply altered mechanosensitivity in girls because bending dominates loading at the neck, and the Z –lean ratio remained similar between the sexes throughout adolescence. That is, despite the greater CSA in girls, the bone is strategically placed to resist bending; hence, the bones of girls and boys adapt to mechanical challenges in a similar way.

A comparison of mechanical properties derived from multiple skeletal sites in mice

Laboratory mice provide a versatile experimental model for studies of skeletal biomechanics. In order to determine the strength of the mouse skeleton, mechanical testing has been performed on a variety of bones using several procedures. Because of differences in testing methods, the data from previous studies are not comparable. The purpose of this study was to determine which long bone provides the values closest to the published material properties of bone, while also providing reliable and reproducible results. To do this, the femur, humerus, third metatarsal, radius, and tibia of both the low bone mass C57BL/6H (B6) and high bone mass C3H/HeJ (C3H) mice were mechanically tested under three-point bending. The biomechanical tests showed significant differences between the bones and between mouse strains for the five bones tested ( p<0.05). Computational models of the femur, metatarsal, and radius were developed to visualize the types of measurement error inherent in the three-point bending tests. The models demonstrated that measurement error arose from local deformation at the loading point, shear deformation and ring-type deformation of the cylindrical cross-section. Increasing the aspect ratio (bone length/width) improved the measurement of Young's modulus of the bone for both mouse strains ( p<0.01). Bones with the highest aspect ratio and largest cortical thickness to radius ratio were better for bending tests since less measurement error was observed in the computational models. Of the bones tested, the radius was preferred for mechanical testing because of its high aspect ratio, minimal measurement error, and low variability.