Changes In Cross-sectional Geometry Research Articles

Effects of Reeling on Pipe Structural Performance—Part I: Experiments

The winding and unwinding of a pipeline in the reeling installation process involve repeated excursions into the plastic range of the material, which induce ovality, elongation, and changes to the mechanical properties. The reeling/unreeling process involves some back tension required to safeguard the pipe from local buckling. This study examines the effects of winding/unwinding a pipe on a reel at different values of tension on the induced ovality and elongation and the resulting degradation in collapse pressure. In Part I, a model testing facility is used to simulate the reeling/unreeling process in the presence of tension. The combination of reel and tube diameters used induces a bending strain of 1.89%. A set of experiments involving three reeling/unreeling cycles at different levels of tension is performed on tubes with diameter-to-thickness ratios (D/t) of 20 and 15.5 in which the progressive changes in cross-sectional geometry and elongation are recorded. Both ovalization and elongation are shown to increase significantly as the back tension increases. A second set of experiments on the same two tube D/ts is performed in which following a reeling/unreeling cycle at a chosen level of tension, the tubes are collapsed under external pressure. The collapse pressure is shown to decrease significantly with tension, which is primarily caused by the reeling/unreeling-induced ovality. Part II presents models for simulating reeling and the induced structural degradation. The experimental results in Part I are used to evaluate the performance of the models.

The geomorphic impacts of culverts at paved forest roads: Examples from Carpathian headwater channels, Czech Republic

Road-stream crossings constructed with culverts have the potential to alter geomorphic processes in adjacent stream channels. We examined changes in channel geometry and bed sediments in longitudinal profiles related to culverts at five paved forest road crossings with perennial headwater streams and two gullies initiated by point releases of water through ditches. A dendrogeomorphic approach was used for dating of exposed tree roots and estimation of bank erosion rates in incised cross-sections downstream of road crossings. The studied forest road crossings concentrate surface runoff from the road net, act as stabilizing elements in stream longitudinal profiles and decelerate bedload transport in the case of culvert clogging, which caused notable upstream and downstream changes in fluvial processes. Notable fining of the coarsest fraction in upstream cross-sections was observed only for two culverts with the highest depositional tendencies. Much lower width-depth ratios (<4) and typically higher channel slopes were measured in channel reaches downstream of the culverts, compared with upstream cross-sections. Two road-induced gullies typically had very low width/depth ratios close to 2. At five of a total of seven studied culverts, the highest documented erosion rates occurred immediately downstream of these structures. The mean annual erosion rates reconstructed from cross-sections at the positions of individual tree root samples ranged from 0.2 to 6.5cm·year−1, and the erosion occurred over 2–5year intervals, depending on the studied location. The highest number of observed changes in cross-sectional geometry caused by channel erosion were connected with relatively high-magnitude flow events (with recurrence intervals >10years; specific discharge >1500l·s·km−2), whereas more frequent flows (with recurrence intervals of 2–10years) were not always recorded by exposed tree roots.

Channel bed adjustment to over bankfull discharge magnitudes of the flysch gravel-bed stream – case study from the channelized reach of the Olše River (Czech Republic)

The rivers draining the Czech part of the Flysch Carpathians have deeply incised their beds over the last 60 years. This paper focuses on the Olše River in the Czech part of the Flysch Carpathians and summarises the results of the increased kinetic energy of flowing water of contemporary channel based on the analyse of hydraulic parameters of channel. The comparison of geodetic measurements from 1960 and 2003 was used together with the assessment of aerial photos from 1950s and present. The average width of the studied reach of the active Olše R. channel narrowed from 35 m in 1955 to 24 m in 2010. In some locations, the original river bed has lowered as much as 2.3 m between the years 1960 and 2003. Morphology of the Olše River channel has accelerated these erosion processes. The main reason for this is an adjustment of water flow dynamics. The unit stream power and hydraulic radius values have increased two to three times from 1960 to 2003 for 5, 20, 50 and 100-recurrence interval discharge. Incision of channel greater than 0.10–0.21m in the studied period may reflect change in cross-sectional geometry and lower than 0.10–0.21m may reflect other factors such as sediment disruption operating in the basin (e.g.with land-use changes, gravel mining etc.).

Identifying donkey domestication through changes in cross-sectional geometry of long bones

The initial phases of donkey domestication are difficult to identify in the archaeological record due to late and inconsistent changes in morphology and body size in the earliest domestics. Use of donkeys for load carrying and the management of captive herds resulted in a distinctive behavioral shift away from the free-ranging speed and mobility characteristic of wild asses toward slower, more steady pacing. Given the ability of bone to adapt to its mechanical environment, bone remodeling in the limbs of wild asses and donkeys are evaluated using cross-sectional geometry to determine whether weight bearing or locomotor differences between the wild and domestic forms may be used to recognize early domestication. Cross-sectional data were collected on the humeri, radii, metacarpals and metatarsals of eight wild ass and six donkey skeletons. Wild ass forelimbs have greater overall strength and more cylindrical humeral diaphyses, indicating better resistance to a varied locomotor repertoire. These results demonstrate that analyses of shaft geometry can provide information on changes in locomotor behavior during domestication. Our finding that shifts in gait had greater effects on the morphology of early domestic donkeys than did load-carrying places a new emphasis on understanding selection for gait changes in domestication dynamics.

Growth-dependent effects of dietary protein concentration and quality on the biomechanical properties of the diaphyseal rat femur

ObjectivesThis study compares the effects of feeding growing rats with increasing concentra-tions of casein (C) and wheat gluten (G), proteins that show different biological qualities, on the morphometrical and biomechanical properties of the femoral diaphysis. Materials and methodsFemale rats were fed with one of ten diets containing different con-centrations (5–30%) of C and G between the 30th and 90th days of life (Control = C-20%). Biomechanical structural properties of the right femur middiaphysis were estimated using a 3-point bending mechanical test with calculation of some indicators of bone material properties. ResultsBody weight and length were affected by treatments, values being highest in rats fed the C-20% diet. G diets affected negatively both parameters. Changes in cross-sectional geome-try (mid-diaphyseal cross-sectional and cortical areas, femoral volume, and rectangular moment of inertia) were positively related to the C content of the diet, while they were severely and negatively affected by G diets. Similar behaviors were observed in the bone structural properties (fracture load, yielding load, diaphyseal stiffness and elastic energy absorption). When values of strength and stiffness were normalized for body weight, the differences disappeared. The bone material quality indicators (elastic modulus, yielding stress, elastic energy absorption/volume) did not differ significantly among all studied groups. Femoral calcium concentration in ashes was not significantly different among groups. ConclusionThe clear differences in strength and stiffness of bone beams induced by dietary protein concentration and quality seemed to be the result of an induced subnormal gain in bone structural properties as a consequence of a correlative subnormal gain in bone growth and mass, yet not in bone material properties.

Growth-dependent effects of dietary protein concentration and quality on the biomechanical properties of the diaphyseal rat femur

Objectives This study compares the effects of feeding growing rats with increasing concentrations of casein (C) and wheat gluten (G), proteins that show different biological qualities, on the morphometrical and biomechanical properties of the femoral diaphysis. Materials and methods Female rats were fed with one of ten diets containing different concentrations (5–30%) of C and G between the 30th and 90th days of life (Control = C-20%). Biomechanical structural properties of the right femur middiaphysis were estimated using a 3-point bending mechanical test with calculation of some indicators of bone material properties. Results Body weight and length were affected by treatments, values being highest in rats fed the C-20% diet. G diets affected negatively both parameters. Changes in cross-sectional geometry (mid-diaphyseal cross-sectional and cortical areas, femoral volume, and rectangular moment of inertia) were positively related to the C content of the diet, while they were severely and negatively affected by G diets. Similar behaviors were observed in the bone structural properties (fracture load, yielding load, diaphyseal stiffness and elastic energy absorption). When values of strength and stiffness were normalized for body weight, the differences disappeared. The bone material quality indicators (elastic modulus, yielding stress, elastic energy absorption/volume) did not differ significantly among all studied groups. Femoral calcium concentration in ashes was not significantly different among groups. Conclusion The clear differences in strength and stiffness of bone beams induced by dietary protein concentration and quality seemed to be the result of an induced subnormal gain in bone structural properties as a consequence of a correlative subnormal gain in bone growth and mass, yet not in bone material properties.

Early Growth Response Gene 1 Regulates Bone Properties in Mice

Transcriptional regulation of the postnatal skeleton is incompletely understood. Here, we determined the consequence of loss of early growth response gene 1 (EGR-1) on bone properties. Analyses were performed on both the microscopic and molecular levels utilizing micro-computed tomography (micro-CT) and Fourier transform infrared imaging (FTIRI), respectively. Mice deficient in EGR-1 (Egr-1 (-/-)) were studied and compared to sex- and age-matched wild-type (wt) control animals. Femoral trabecular bone in male Egr-1 (-/-) mice demonstrated osteopenic characteristics marked by reductions in both bone volume fraction (BV/TV) and bone mineral density (BMD). Morphological analysis revealed fewer trabeculae in these animals. In contrast, female Egr-1 (-/-) animals had thinner trabeculae, but BV/TV and BMD were not significantly reduced. Analysis of femoral cortical bone at the mid-diaphysis did not show significant osteopenic characteristics but detected changes in cross-sectional geometry in both male and female Egr-1 (-/-) animals. Functionally, this resulted in decreased resistance to three-point bending as indicated by a reduction in maximum load, failure load, and stiffness. Assessment of compositional bone properties, including mineral-to-matrix ratio, carbonate-to-phosphate ratio, crystallinity, and cross-linking, in femurs by FTIRI did not show any significant differences or an appreciable trend between Egr-1 (-/-) and wt mice of either sex. Unexpectedly, rib bone from Egr-1 (-/-) animals displayed distinct osteopenic traits that were particularly pronounced in female mice. This study provides genetic evidence that both sex and skeletal site are critical determinants of EGR-1 activity in vivo and that its site-specific action may contribute to the mechanical properties of bone.

Sediment transport modeling for Kulim River – A case study

Rapid urbanization has accelerated impact on the catchment hydrology and geomorphology. This rapid development which takes place in river catchment will result in higher sediment yield and affect river morphology and river channel stability; it also becomes the main cause for serious flooding in urban areas. Therefore, it is necessary to predict and evaluate the river channel stability due to the existing and future developments. This study proceeds at Kulim River in Kedah state, a natural stream in Kedah, Malaysia. The FLUVIAL-12 model, an erodible-boundary model which simulates inter-related changes in channel-bed profile, width variation and changes in bed topography was selected for this study. Engelund-Hansen formula and roughness coefficient n = 0.030 were found to be the best combination to represent the sediment transport activity in the study reach, where good agreements were obtained for both water level and bed profiles between the measured data and predicted results by FLUVIAL-12 model. The model simulation results for existing conditions, future conditions and long-term modeling show that the sediment size and channel geometry in Kulim River changed significantly. However, modeled results show that future changes in cross sectional geometry will be limited and erosion along the reach will slow down from 2006 to 2016, thus Kulim River was predicted to be stable at most locations.

Effects of eccentric exercise training on cortical bone and muscle strength in the estrogen-deficient mouse

The purpose of this study was to determine whether eccentrically biased exercise training could attenuate changes in muscle and bone function associated with estrogen deficiency in the mouse model. Four groups of ICR mice were used: control (Con), sham ovariectomized (Sham), ovariectomized (OVX), and ovariectomized + high-force resistance training (OVX+Train). All groups except Con were implanted with a nerve cuff surrounding the peroneal nerve to stimulate the left ankle dorsiflexors. Training consisted of 30 stimulated eccentric contractions of the left ankle dorsiflexors at approximately 150% of peak isometric torque every third day for 8 wk. After the training period, groups were not significantly different with regard to peak torque or muscle size. However, the tibial midshaft of the trained leg in the OVX+Train mice exhibited greater stiffness (+15%) than that in the untrained OVX mice, which could not be explained by changes in cross-sectional geometry of the tibia. Scaling of bone mechanical properties to muscle strength were not altered by ovariectomy or training. These data indicate that eccentric exercise training in adult mice can significantly increase bone stiffness, despite the absence of ovarian hormones.

Changes in cross‐sectional geometry of the distal femoral metaphysis associated with inflammatory arthritis are reduced by a bisphosphonate (zoledronate)

An increased risk of fracture is a feature of rheumatoid arthritis and of animal models of inflammatory arthritis. We examined geometrical changes in the metaphyseal cortex of the distal femur in an animal model of inflammatory arthritis. Additionally, we examined the effect of a bisphosphonate in preventing these changes. Five groups of rabbits were studied: normal controls, those with inflammatory arthritis, and three groups with arthritis treated with bisphosphonate. To determine geometrical properties, image analysis was performed on digitized cross sections of the femoral metaphyseal cortices. The results demonstrated that the posterior cortical wall was significantly less thick in rabbits with arthritis than in normal rabbits and in the rabbits in the three bisphosphonate treatment groups (p < 0.05). Moment of inertia about the lateral-medial axis was reduced in rabbits with arthritis compared with normal rabbits (p < 0.05). Cross-sectional area was not significantly different between groups. The changes suggest a mechanism of weakening of bone in arthritis; when the results are coupled with results of previous porosity studies, severe directional weakness is apparent. Bisphosphonate was effective in preserving bone integrity in inflammatory arthritis.

Bone size and mechanics at the femoral diaphysis across age and sex

The reasons for the increase in fracture rates with age are not fully understood. It is known that there is a decrease in bone mass with a presumed loss of strength. This decrease may possibly be compensated for by changes in cross-sectional geometry. Previous studies, which have been limited by lack of information on subjects’ heights and weights, were not able to resolve this issue. In this study, measurements of cross-sectional geometry (area and second moments of area) from 107 specimens of human femoral diaphysis from subjects aged 21–92 years were analysed. Mathematical models of the variation in bone geometry with age were developed. These models included the effects of sex, height and weight. Values of parameters from these models were then used in a biomechanical analysis of the static stresses at the mid-shaft of the femur. Results indicate that although there was a reduction in cortical area in old age, bone tissue was redistributed so that neither bending stresses in the coronal plane nor torsional stresses were higher in old age than in young adulthood. An additional finding was that at any age women had smaller bones, less cortical bone area and higher bone stresses than men. This finding may have some bearing on the higher fracture incidence seen in older women.

Calculation of cross-sectional geometry of bone from CT images with application in postmenopausal women.

The objectives of this study were to develop a software program that calculates bone cross-sectional area (CSA) and moments of inertia from digital images, test the computations for accuracy, and implement the software in a study of longitudinal changes in bone properties in a large group of postmenopausal women. A program called SLICE was adapted to use computed tomography (CT) bone images as input. The main outcome variables of the resulting program, SLICE_CT, were bone CSA, areal moments of inertia, and mass-weighted moments of inertia. SLICE_CT was tested for accuracy using representative arrays of CT numbers that approximate cross-sections of cortical bone. Then the technique was applied to images from a 3 year longitudinal study of the radius in 86 postmenopausal women who underwent quantitative CT of the dominant radius at 30% the distance from the wrist to the elbow. The mean age of the subjects at entry into the study was 57 years. Images at baseline and at 3 years were analyzed, and the null hypothesis of no change in cross-sectional geometry was tested by a paired difference two-tailed t test. The error of SLICE_CT was < 1% with proper segmentation, using half-maximal height as the threshold. In the longitudinal study of postmenopausal women, the mean change of CSA of the radius was -1.4% (SD = 3.0%; p < 0.001). However, there was a compensatory 2.4% increase in the cross-sectional second polar moment of inertia (SD = 3.7%; p < 0.001). SLICE_CT is an accurate method with which to determine cross-sectional geometry of digital images and can be used to detect changes in cross-sectional geometry of the radius with age in postmenopausal women. The results indicate that the radius remodels to compensate for bone loss and decreasing material properties of bone associated with aging.

Changes in Activities with the Shift to Agriculture in the Southeastern United States

Changes in Activities with the Shift to Agriculture in the Southeastern United States

Anisotropy in spun single-mode fibres

It is shown that the dominant process for the reduction of birefringence in a spun fibre is the averaging of the local fibre anisotropy by the rapid procession of the axes of asymmetry along the fibre. No significant change in cross-sectional geometry occurs.