The influence of geometry and wall character of pores on the permeation of ions and water through desalination membranes

The transport of water and ions across mimicked nanotube membranes with pseudo atoms is studied using molecular dynamics simulations under equilibrium conditions and hydrostatic pressure. Different pore surface properties are constructed by assigning partial charges on the sites of specified atoms to explore the influence of charges and polarity. The energetics of water and ion transports through the nanopores was calculated to evaluate their filterability to water. The simulation results show that the free energy barriers to water and ion conductions much depend on the charges at the pore entrance and the dipole within the pore. The membranes with hydrophobic pores and negatively charged entrances would be very efficient in the water transport and ion rejection. The charges and dipoles of the pore wall and the aligned dipoles of water molecules in the pore can create a significant force on ions.

The effects of repetitive loading on bone mass and geometry in young male tennis players : a quantative study using magnetic resonance imaging

Pre- and early puberty seem to be the most opportune times for exercise to  improve bone strength in girls, but few studies have addressed this issue in boys. This study investigated the site-, surface-, and maturity-specific exercise-induced changes in bone mass and geometry in young boys. The osteogenic effects of loading were analyzed by comparing the playing and nonplaying humeri of 43 male pre-, peri-, and postpubertal competitive tennis players 10-19 yr of age. Total bone area, medullary area, and cortical area were determined at the mid (40-50%) and distal humerus (60-70%) of both arms using MRI. Humeral bone mass (BMC) was derived from a whole body DXA scan. In prepubertal boys, BMC was 17% greater in the playing compared with nonplaying arm (p < 0.001), which was accompanied by a 12-21% greater cortical area, because of greater periosteal expansion than medullary expansion at the midhumerus and periosteal expansion associated with medullary contraction at the distal humerus. Compared with prepuberty, the side-to-side differences in BMC (27%) and cortical area (20-33%) were greater in peripuberty (p < 0.01). No differences were found between peri- and postpuberty despite longer playing history in the postpubertal players.The osteogenic response to loading was greater in peri- compared with prepubertal boys, which is in contrast with our previous findings in girls and may be caused by differences in training history. This suggests that the window of opportunity to improve bone mass and size through exercise may be longer in boys than in girls.

On the geometry of localization, tracking and navigation

The thesis characterizes the geometry of certain localization, tracking and navigation problems. For instance, the potential localization performance of certain multi-sensor systems is measurably linked to the relative sensor-target geometry. Additionally, several optimal and robust algorithms for localization and tracking are designed which exploit the underlying geometry of the problem considered.

Gaussian vault geometry : digital design and fabrication of scaled prototypes

This paper reports on three approaches to the translation of Gaussian surface models into scaled physical prototype models. Using the geometry of Eladio Dieste's Gaussian Vaults, the paper reports on the aspects encountered in the process of digital to physical prototype fabrication. The primary focus of the paper is on exploring the design geometry, investigating methods for preparing the geometry for fabrication and constructing physical prototypes. Three different approaches in the translation from digital to physical models are investigated: rapid prototyping, two dimensional surface models in paper and structural component models using Computer Numerical Controlled (CNC) fabrication. The three approaches identify a body of knowledge in the design and prototyping of Gaussian vaults. Finally the paper discusses the digital to. fabrication translation processes with regards to the characteristics, benefits and limitations of the three approaches of prototyping the ruled surface geometry of Gaussian Vaults.

Muscle determinants of bone mass, geometry and strength in prepubertal girls

Purpose: The aim of this study was to compare the relative contribution of peak muscle force (isokinetic peak torque) with surrogate estimates of muscle force, including leg lean tissue mass (LTM) and vertical jump height (VJH), on bone mass, geometry and strength in healthy prepubertal girls (n = 103).

Methods: Total leg and FN BMC and leg LTM were measured by DXA; the hip strength analysis program was used to assess FN diameter, cross-sectional area (CSA) and section modulus (Z). Isokinetic peak torque of the knee extensors and flexors (60°·s-1) were used as direct measures of peak muscle force. VJH was measured as an estimate of neuromuscular function. Total leg length or femoral length was used as a surrogate measure of moment arm length.

Results: All estimates of muscle function, except VJH, were positively associated with leg BMC (r = 0.72 - 0.90) and FN BMC, geometry and strength (r = 0.35-0.65) (all, P < 0.001). Multiple linear regression analyses revealed that leg LTM and isokinetic peak torque were independently and equally predictive of leg BMC and FN BMC, bone geometry and strength, explaining 8 to 28% of the variance in each of the bone traits after accounting for moment arm length. When isokinetic peak torque was corrected for both leg LTM and moment arm length, it remained an independent predictor of BMC, CSA and Z, but only accounted for an additional 2 to 5% of the variance.

Conclusion: These data suggest that DXA-derived leg LTM can be used as a reasonable surrogate for isokinetic peak muscle forces when assessing bone strength in relation to muscular function in healthy pre-pubertal girls.

Cross-sectional geometry of weight-bearing tibia in female athletes subjected to different exercise loadings

Summary The association of long-termsport-specific exercise loading with cross-sectional geometry of the weight-bearing tibia was evaluated among 204 female athletes representing five different exercise loadings and 50 referents. All exercises involving ground impacts (e.g., endurance running, ball games, jumping) were associated with thicker cortex at the distal and diaphyseal sites of the tibia and also with large diaphyseal cross-section, whereas the high-magnitude (powerlifting) and non-impact (swimming) exercises were not. Introduction Bones adapt to the specific loading to which they are habitually subjected. In this cross-sectional study, the association of long-term sport-specific exercise loading with the geometry of the weight-bearing tibia was evaluated among premenopausal female athletes representing 11 different sports.

Methods A total of 204 athletes were divided into five exercise loading groups, and the respective peripheral quantitative computed tomographic data were compared to data obtained from 50 physically active, non-athletic referents. Analysis of covariance was used to estimate the between-group differences.

Results At the distal tibia, the high-impact, odd-impact, and repetitive low-impact exercise loading groups had ~30% to 50% (p<0.05) greater cortical area (CoA) than the referents. At the tibial shaft, these three impact groups had ~15% to 20% (p<0.05) greater total area (ToA) and ~15% to 30% (p<0.05) greater CoA. By contrast, both the high-magnitude and repetitive non-impact groups had similar ToA and CoA values to the reference group at both tibial sites.

Conclusions High-impact, odd-impact, and repetitive lowimpact exercise loadings were associated with thicker cortex at the distal tibia. At the tibial shaft, impact loading was not only associated with thicker cortex, but also a larger cross-sectional area. High-magnitude exercise loading did not show such associations at either site but was comparable to repetitive non-impact loading and reference data. Collectively, the relevance of high strain rate together with moderate-to-high strain magnitude as major determinants of osteogenic loading of the weight-bearing tibia is implicated.

Direction-specific diaphyseal geometry and mineral mass distribution of tibia and fibula: A pQCT study of female athletes representing different exercise loading types

Bones adapt to prevalent loading, which comprises mainly forces caused by muscle contractions. Therefore, we hypothesized that similar associations would be observed between neuromuscular performance and rigidity of bones located in the same body segment. These associations were assessed among 221 premenopausal women representing athletes in high-impact, odd-impact, highmagnitude, repetitive low-impact, and repetitive nonimpact sports and physically active referents aged 17–40 years. The whole group mean age and body mass were 23 (5) and 63 (9) kg, respectively. Bone cross sections at the tibial and fibular mid-diaphysis were assessed with peripheral quantitative computed tomography (pQCT). Density-weighted polar section modulus (SSI) and minimal and maximal crosssectional moments of inertia (Imin, Imax) were analyzed. Bone morphology was described as the Imax/Imin ratio. Neuromuscular performance was assessed by maximal power during countermovement jump (CMJ). Tibial SSI was 31% higher in the high-impact, 19% in the odd-impact, and 30% in the repetitive low-impact groups compared with the reference group (P\0.005). Only the high-impact group differed from the referents in fibular SSI (17%, P\0.005). Tibial morphology differed between groups (P = 0.001), but fibular morphology did not (P = 0.247). The bone-bygroup interaction was highly significant (P\0.001). After controlling for height, weight, and age, the CMJ peak power correlated moderately with tibial SSI (r = 0.31, P\0.001) but not with fibular SSI (r = 0.069, P = 0.313). In conclusion, observed differences in the association between neuromuscular performance and tibial and fibular traits suggest
that the tibia and fibula experience different loading

Needleless electrospinning : influences of fibre generator geometry

The fibre generator shape and dimension are key factors affecting the needleless electrospinning process and fibre fineness. In this work, cylinder with rounded rim, disc and ball were used as spinnerets to electrospin polyvinyl alcohol and polyacrylonitrile solutions. A finite element method was used to analyse how the spinneret geometry affected the electric field generated during electrospinning and the associated changes in fibre diameter and productivity. For cylinder spinnerets, increasing the rim radius reduced the discrepancy of electric field intensity between the cylinder end and middle area, which affected the fibre productivity. The electrospinning failed to operate when the rim radius was over 20 mm. With decreasing cylinder diameter, the electric field intensity in the middle area increased, improving the fibre productivity. Thinner disc spinnerets increased the electric field intensity, resulting in finer nanofibres and higher productivities. Ball spinnerets produced evenly distributed electric field, but failed to electrospin fibres when the diameters were below 60 mm. It has been found that strong and narrowly distributed electric field in the fibre-generating area can significantly facilitate the mass production of quality nanofibres.

Repulsive interaction between coplanar cracks in the double–cantilever geometry

Experiments on thin mica sheets are used to demonstrate that coplanar cracks in double-cantilever beam specimens do not universally attract each other, as conventionally portrayed, but, at long range, actually repel. An elasticity analysis explains the repulsion in terms of a compression zone, 0.35 times the beam half-thickness ahead of the crack tip, generated by bending moments from the cantilever arms on the remaining specimen section.

Computation and construction of vault geometry prototypes

Physical models and scaled prototypes of architecture play an important role in design. They enable architects and designers to investigate the formal, functional, and material attributes of the design. Understanding digital processes of realizing scaled prototypes is a significant problem confronting design practice. This paper reports on three approaches to the translation of Gaussian surface models into scaled physical prototype models. Based on the geometry of Eladio Dieste’s Gaussian Vaults, the paper reports on the aspects encountered in the process of digital to physical construction using scaled prototypes. The primary focus of the paper is on computing the design geometry, investigating methods for preparing the geometry for fabrication and physical construction. Three different approaches in the translation from digital to physical models are investigated: rapid prototyping, two-dimensional surface models in paper and structural component models using CNC fabrication. The three approaches identify a body of knowledge in the design and prototyping of Gaussian vaults. Finally the paper discusses the digital to fabrication translation processes with regards to the characteristics, benefits and limitations of the three approaches of prototyping the ruled surface geometry of Gaussian Vaults. The results of each of three fabrication processes allowed for a better understanding of the digital to physical translation process. The use of rapid prototyping permits the production of form models that provide a representation of the physical characteristics such as size, shape and proportion of the Gaussian Vault.