Livres sur le sujet « Load and structure nonlinearities »

Intrinsic disturbances are processes that have occurred on an evolutionary time scale, and include fire, wind-damage, digging or burrowing by fossorial mammals, defoliation, and trampling by native large mammals. Grassland species evolved with intrinsic disturbances, and they can be important in maintaining grassland community structure and functioning. Adaptations to fire include short herbaceous stature, high allocation belowground, ability to resprout, and smoke-induced seed germination. Fire interacts with grazing because grazing reduces litter (fuel) load, and fires affect forage quality. Plants can tolerate some level of herbivory in most grasslands. Adaptations that enable grassland plants to resist grazing are similar to plant adaptations to fire. Drought can affect grasslands at a variety of time scales. Vegetative reproduction can allow rapid recolonization after droughts have ended. Plowing is the most common disturbance affecting grasslands, and it has been used to transform native grasslands into crop fields and simplified pasture.

Project Vesta was a comprehensive research project to investigate the behaviour and spread of high-intensity bushfires in dry eucalypt forests with different fuel ages and understorey vegetation structures. The project was designed to quantify age-related changes in fuel attributes and fire behaviour in dry eucalypt forests typical of southern Australia. The four main scientific aims of Project Vesta were: To quantify the changes in the behaviour of fire in dry eucalypt forest as fuel develops with age (i.e. time since fire); To characterise wind speed profiles in forest with different overstorey and understorey vegetation structure in relation to fire behaviour; To develop new algorithms describing the relationship between fire spread and wind speed, and fire spread and fuel characteristics including load, structure and height; and to develop a National Fire Behaviour Prediction System for dry eucalypt forests. These aims have been addressed through a program of experimental burning and associated studies at two sites in the south-west of Western Australia.

This chapter focuses on myocardial remodelling, a process that affects the heart’s shape, structure, and function, following myocardial injury (MI). Post-MI remodelling can be divided into three phases, with the first phase 0–72 hours beginning at the time of ischaemic injury, the second phase 72 hours to 6 weeks, and the third and last phase 6 weeks and beyond. During post-infarction remodelling, hypertrophy is an adaptive response that compensates for the increased load, reduces the effect of progressive dilatation, and balances contractile function. The chapter discusses the factors involved in ventricular remodelling and its association with heart failure progression. The effects of therapies designed to prevent or attenuate post-infarction left ventricular remodelling, with reference to the pathophysiological mechanisms involved, are then considered. Therapies specifically discussed include angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), β‎-adrenoreceptor blockers, and aldosterone receptor antagonists.

Under physiological conditions, the subchondral bone of diarthrodial joints such as the hip, knee, and phalanges forms an integrated biocomposite with the overlying calcified and hyaline articular cartilage that is optimally organized to transfer mechanical load. During the evolution of the osteoarthritic process both the periarticular bone and cartilage undergo marked changes in their structural and functional properties in response to adverse biomechanical and biological signals. These changes are mediated by bone cells that modify the architecture and properties of the bone through active cellular processes of modelling and remodelling. These same biomechanical and biological factors also affect chondrocytes in the cartilage matrix altering the composition and structure of the cartilage and further disrupting the homeostatic relationship between the cartilage and bone. This chapter reviews the structural alterations and cellular mechanisms involved in the pathogenesis of osteoarthritis bone pathology and discusses potential approaches for targeting bone remodelling to attenuate the progression of the osteoarthritic process.

The right atrium (RA) is located on the upper right-hand side of the heart and has relatively thin walls. From an anatomical point of view, the RA comprises three basic parts, the appendage, the vestibule of the tricuspid valve, and the venous component (superior and inferior vena cava, and the coronary sinus) receiving the deoxygenated blood. The RA is a dynamic structure dedicated to receive blood and to assist right ventricular (RV) filling. The three components of atrial function are the reservoir function during ventricular systole, the conduit function which consists in passive blood transfer from veins to the RV in diastole, and the booster pump function in relation to atrial contraction in late diastole to complete ventricular filling. Right atrial function depends on cardiac rhythm (sinus or atrial fibrillation), pericardial integrity, RV load and function, and tricuspid function. Right atrial dimension assessment is limited in two-dimensional (2D) echocardiography. Right atrial planimetry in the apical four-chamber view is commonly used with an upper normal value of 18-20 cm2. Minor and major diameters can also be measured. Three-dimensional (3D) echocardiography could overcome the limitation of conventional echocardiography in assessing RA size. Right atrial function has been poorly explored by echocardiography both in physiological and pathological contexts. Although tricuspid inflow and tissue Doppler imaging of tricuspid annulus can be used in the exploration of RA function, 2D speckle tracking and 3D echocardiography appear promising tools to dissect RA function and to overcome the limitations of standard echocardiography.

This research aimed to develop conceptually the pretensioned and stiffened membrane structures, using an experimental approach and computer simulation. The physical method of form finding included the pretensioned fabric with the glued grid made of the wooden sticks. Relaxation of the stressed membrane contributed to forming the specific anticlastic hyparic surface by energy release. The influence of the rigid elements pattern, intensity and direction of pretensioning on the final shape was investigated. The tensegrity structures were also built applying the same form finding way. These experiments led to the modelling of resulting samples with parametric design tools, namely Rhino and Grasshopper. Optimization of the final shape was carried out by changing parameters such as stiffenings configuration and membrane strength. This digital approach demonstrated successful simulation and rationalization of considered structures. Moreover, the final models can be used for further structural analysis and BIM. Considered membrane structures have very efficient load-bearing behavior. They are characterized by small weight, high light transmission and the ability to create large usable spaces free from columns. The most dangerous loads for membrane structures are wind and ponding. In practice, PTFE coated glass-fibre fabric and PVC coated polyester fabric are most suitable for pretensioned and stiffened membrane structures. The role of stiff elements can be played by steel profiles or metal tubes. The average time for the construction of a membrane structure is 6-15 months. Resulted pretensioned and stiffened membrane structures can be used as pavilions, roofs and awnings. They are distinguished by spectacular architectural view and very effective structural system. In addition, membrane tensile structures are characterized by high eco-efficiency and sustainability compared to other types of construction.

Bones are multifunctional passive organs of movement that supports soft tissue and directly attached muscles. They also protect internal organs and are a reserve of calcium, phosphorus and magnesium. Each bone is covered with periosteum, and the adjacent bone surfaces are covered by articular cartilage. Histologically, the bone is an organ composed of many different tissues. The main component is bone tissue (cortical and spongy) composed of a set of bone cells and intercellular substance (mineral and organic), it also contains fat, hematopoietic (bone marrow) and cartilaginous tissue. Bones are a tissue that even in adult life retains the ability to change shape and structure depending on changes in their mechanical and hormonal environment, as well as self-renewal and repair capabilities. This process is called bone turnover. The basic processes of bone turnover are: • bone modeling (incessantly changes in bone shape during individual growth) following resorption and tissue formation at various locations (e.g. bone marrow formation) to increase mass and skeletal morphology. This process occurs in the bones of growing individuals and stops after reaching puberty • bone remodeling (processes involve in maintaining bone tissue by resorbing and replacing old bone tissue with new tissue in the same place, e.g. repairing micro fractures). It is a process involving the removal and internal remodeling of existing bone and is responsible for maintaining tissue mass and architecture of mature bones. Bone turnover is regulated by two types of transformation: • osteoclastogenesis, i.e. formation of cells responsible for bone resorption • osteoblastogenesis, i.e. formation of cells responsible for bone formation (bone matrix synthesis and mineralization) Bone maturity can be defined as the completion of basic structural development and mineralization leading to maximum mass and optimal mechanical strength. The highest rate of increase in pig bone mass is observed in the first twelve weeks after birth. This period of growth is considered crucial for optimizing the growth of the skeleton of pigs, because the degree of bone mineralization in later life stages (adulthood) depends largely on the amount of bone minerals accumulated in the early stages of their growth. The development of the technique allows to determine the condition of the skeletal system (or individual bones) in living animals by methods used in human medicine, or after their slaughter. For in vivo determination of bone properties, Abstract 10 double energy X-ray absorptiometry or computed tomography scanning techniques are used. Both methods allow the quantification of mineral content and bone mineral density. The most important property from a practical point of view is the bone’s bending strength, which is directly determined by the maximum bending force. The most important factors affecting bone strength are: • age (growth period), • gender and the associated hormonal balance, • genotype and modification of genes responsible for bone growth • chemical composition of the body (protein and fat content, and the proportion between these components), • physical activity and related bone load, • nutritional factors: – protein intake influencing synthesis of organic matrix of bone, – content of minerals in the feed (CA, P, Zn, Ca/P, Mg, Mn, Na, Cl, K, Cu ratio) influencing synthesis of the inorganic matrix of bone, – mineral/protein ratio in the diet (Ca/protein, P/protein, Zn/protein) – feed energy concentration, – energy source (content of saturated fatty acids - SFA, content of polyun saturated fatty acids - PUFA, in particular ALA, EPA, DPA, DHA), – feed additives, in particular: enzymes (e.g. phytase releasing of minerals bounded in phytin complexes), probiotics and prebiotics (e.g. inulin improving the function of the digestive tract by increasing absorption of nutrients), – vitamin content that regulate metabolism and biochemical changes occurring in bone tissue (e.g. vitamin D3, B6, C and K). This study was based on the results of research experiments from available literature, and studies on growing pigs carried out at the Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences. The tests were performed in total on 300 pigs of Duroc, Pietrain, Puławska breeds, line 990 and hybrids (Great White × Duroc, Great White × Landrace), PIC pigs, slaughtered at different body weight during the growth period from 15 to 130 kg. Bones for biomechanical tests were collected after slaughter from each pig. Their length, mass and volume were determined. Based on these measurements, the specific weight (density, g/cm3) was calculated. Then each bone was cut in the middle of the shaft and the outer and inner diameters were measured both horizontally and vertically. Based on these measurements, the following indicators were calculated: • cortical thickness, • cortical surface, • cortical index. Abstract 11 Bone strength was tested by a three-point bending test. The obtained data enabled the determination of: • bending force (the magnitude of the maximum force at which disintegration and disruption of bone structure occurs), • strength (the amount of maximum force needed to break/crack of bone), • stiffness (quotient of the force acting on the bone and the amount of displacement occurring under the influence of this force). Investigation of changes in physical and biomechanical features of bones during growth was performed on pigs of the synthetic 990 line growing from 15 to 130 kg body weight. The animals were slaughtered successively at a body weight of 15, 30, 40, 50, 70, 90, 110 and 130 kg. After slaughter, the following bones were separated from the right half-carcass: humerus, 3rd and 4th metatarsal bone, femur, tibia and fibula as well as 3rd and 4th metatarsal bone. The features of bones were determined using methods described in the methodology. Describing bone growth with the Gompertz equation, it was found that the earliest slowdown of bone growth curve was observed for metacarpal and metatarsal bones. This means that these bones matured the most quickly. The established data also indicate that the rib is the slowest maturing bone. The femur, humerus, tibia and fibula were between the values of these features for the metatarsal, metacarpal and rib bones. The rate of increase in bone mass and length differed significantly between the examined bones, but in all cases it was lower (coefficient b <1) than the growth rate of the whole body of the animal. The fastest growth rate was estimated for the rib mass (coefficient b = 0.93). Among the long bones, the humerus (coefficient b = 0.81) was characterized by the fastest rate of weight gain, however femur the smallest (coefficient b = 0.71). The lowest rate of bone mass increase was observed in the foot bones, with the metacarpal bones having a slightly higher value of coefficient b than the metatarsal bones (0.67 vs 0.62). The third bone had a lower growth rate than the fourth bone, regardless of whether they were metatarsal or metacarpal. The value of the bending force increased as the animals grew. Regardless of the growth point tested, the highest values were observed for the humerus, tibia and femur, smaller for the metatarsal and metacarpal bone, and the lowest for the fibula and rib. The rate of change in the value of this indicator increased at a similar rate as the body weight changes of the animals in the case of the fibula and the fourth metacarpal bone (b value = 0.98), and more slowly in the case of the metatarsal bone, the third metacarpal bone, and the tibia bone (values of the b ratio 0.81–0.85), and the slowest femur, humerus and rib (value of b = 0.60–0.66). Bone stiffness increased as animals grew. Regardless of the growth point tested, the highest values were observed for the humerus, tibia and femur, smaller for the metatarsal and metacarpal bone, and the lowest for the fibula and rib. Abstract 12 The rate of change in the value of this indicator changed at a faster rate than the increase in weight of pigs in the case of metacarpal and metatarsal bones (coefficient b = 1.01–1.22), slightly slower in the case of fibula (coefficient b = 0.92), definitely slower in the case of the tibia (b = 0.73), ribs (b = 0.66), femur (b = 0.59) and humerus (b = 0.50). Bone strength increased as animals grew. Regardless of the growth point tested, bone strength was as follows femur > tibia > humerus > 4 metacarpal> 3 metacarpal> 3 metatarsal > 4 metatarsal > rib> fibula. The rate of increase in strength of all examined bones was greater than the rate of weight gain of pigs (value of the coefficient b = 2.04–3.26). As the animals grew, the bone density increased. However, the growth rate of this indicator for the majority of bones was slower than the rate of weight gain (the value of the coefficient b ranged from 0.37 – humerus to 0.84 – fibula). The exception was the rib, whose density increased at a similar pace increasing the body weight of animals (value of the coefficient b = 0.97). The study on the influence of the breed and the feeding intensity on bone characteristics (physical and biomechanical) was performed on pigs of the breeds Duroc, Pietrain, and synthetic 990 during a growth period of 15 to 70 kg body weight. Animals were fed ad libitum or dosed system. After slaughter at a body weight of 70 kg, three bones were taken from the right half-carcass: femur, three metatarsal, and three metacarpal and subjected to the determinations described in the methodology. The weight of bones of animals fed aa libitum was significantly lower than in pigs fed restrictively All bones of Duroc breed were significantly heavier and longer than Pietrain and 990 pig bones. The average values of bending force for the examined bones took the following order: III metatarsal bone (63.5 kg) <III metacarpal bone (77.9 kg) <femur (271.5 kg). The feeding system and breed of pigs had no significant effect on the value of this indicator. The average values of the bones strength took the following order: III metatarsal bone (92.6 kg) <III metacarpal (107.2 kg) <femur (353.1 kg). Feeding intensity and breed of animals had no significant effect on the value of this feature of the bones tested. The average bone density took the following order: femur (1.23 g/cm3) <III metatarsal bone (1.26 g/cm3) <III metacarpal bone (1.34 g / cm3). The density of bones of animals fed aa libitum was higher (P<0.01) than in animals fed with a dosing system. The density of examined bones within the breeds took the following order: Pietrain race> line 990> Duroc race. The differences between the “extreme” breeds were: 7.2% (III metatarsal bone), 8.3% (III metacarpal bone), 8.4% (femur). Abstract 13 The average bone stiffness took the following order: III metatarsal bone (35.1 kg/mm) <III metacarpus (41.5 kg/mm) <femur (60.5 kg/mm). This indicator did not differ between the groups of pigs fed at different intensity, except for the metacarpal bone, which was more stiffer in pigs fed aa libitum (P<0.05). The femur of animals fed ad libitum showed a tendency (P<0.09) to be more stiffer and a force of 4.5 kg required for its displacement by 1 mm. Breed differences in stiffness were found for the femur (P <0.05) and III metacarpal bone (P <0.05). For femur, the highest value of this indicator was found in Pietrain pigs (64.5 kg/mm), lower in pigs of 990 line (61.6 kg/mm) and the lowest in Duroc pigs (55.3 kg/mm). In turn, the 3rd metacarpal bone of Duroc and Pietrain pigs had similar stiffness (39.0 and 40.0 kg/mm respectively) and was smaller than that of line 990 pigs (45.4 kg/mm). The thickness of the cortical bone layer took the following order: III metatarsal bone (2.25 mm) <III metacarpal bone (2.41 mm) <femur (5.12 mm). The feeding system did not affect this indicator. Breed differences (P <0.05) for this trait were found only for the femur bone: Duroc (5.42 mm)> line 990 (5.13 mm)> Pietrain (4.81 mm). The cross sectional area of the examined bones was arranged in the following order: III metatarsal bone (84 mm2) <III metacarpal bone (90 mm2) <femur (286 mm2). The feeding system had no effect on the value of this bone trait, with the exception of the femur, which in animals fed the dosing system was 4.7% higher (P<0.05) than in pigs fed ad libitum. Breed differences (P<0.01) in the coross sectional area were found only in femur and III metatarsal bone. The value of this indicator was the highest in Duroc pigs, lower in 990 animals and the lowest in Pietrain pigs. The cortical index of individual bones was in the following order: III metatarsal bone (31.86) <III metacarpal bone (33.86) <femur (44.75). However, its value did not significantly depend on the intensity of feeding or the breed of pigs.