Computer aided stress analysis of the femur with prosthetic hip stem utilizing computed tomography

A computer aided design and analysis method, utilizing computed tomography (CT) is developed, which together with a finite element program determines the stress and deformation patterns in the femur with hip prosthesis. The CT scan data file provides the geometry and the material parameters for the generated finite element model. The three-dimensional finite element model of the femur with hip prosthesis is automatically generated from the CT data file by a preprocessing procedure. The preprocessor includes a CT image display, edge detector, nodes generation, prosthesis simulator, mesh generator and model display. The loading conditions applied on the finite element model are determined from existing gait analysis including joint force and muscle force. Formatted input data for ANSYS (Swanson Analysis Systems Inc.) finite element program is generated by the preprocessor. In this research, the influence on the stress pattern of different prosthetic materials and fixation, such as cobalt-chromium alloy or titanium alloy prosthesis, also cemented or porous-coated prosthesis are studied. A comparison of the stress patterns for the three different femora is made and a radiographic follow-up study in two cases is carried out at 14 months and 12 months postoperation for analyzing the bone remodeling process. As a result of the calculated stress patterns in the femur with prosthesis, it is found that the cobalt-chromium alloy prosthesis unloads the calcar cortical bone and the titanium alloy prosthesis decreases the stress within the prosthetic stem except for the proximal side. The highest calculated stress is approximately 12% of the fatigue limit for cobalt-chromium alloy prosthesis, and approximately 4% for the titanium alloy prosthesis. Comparing the porous coating model with the cemented model, the porous coating model leads to decreased bone stresses, reduced stress concentrations in bone surrounding the prosthesis and more uniformly distributed stress to the surrounding bone tissue. For the effect of stiffness and Poisson\u27s ratio of the porous coating layer, lower elastic modulus and Poisson\u27s ratio will reduce the interface stress between cancellous bone and the porous coating layer. The average stress of the fractured femur with prosthesis is approximately twice the amount of the femur with prosthesis in the proximal and distal side of the prosthetic stem. Furthermore the average stress of the male femur with prosthesis is about 4% lower than the female femur with prosthesis. In regards to stress changes in the postoperative femur, the bone remodeling results indicate that bone resorption of the cortex around the proximal prosthesis would increase the stress in the proximal prosthetic stem and femoral surface slightly while decreasing the stress of the midregion. Bone hypertrophy around the distal prosthesis would decrease the stress up to 35% in the distal prosthetic stem and femoral surface

Biodiversity shapes tree species aggregations in tropical forests

Spatial patterns of conspecific trees are considered as the consequences of biological interactions and environmental influences. They also reflect species interactions in plant communities. However, biological attributes are often neglected while deliberating the factors shaping species distributions. As rising attentions are paid to spatial patterns of tropical forest trees, we noticed that seven Center of Tropical Forest Sites and four Forest Dynamic Plots in Asia and America have presented analogously high proportions of species with aggregated conspecific individuals coincidently. This phenomenon is distinctive and repudiates fundamental ecology hypotheses which suggested dispersed distributions of conspecific tropical trees due to intensive density and natural enemy pressures in tropical forests. We believe that similar aggregation patterns shared by these tropical forests implies the existence of structuring forces in biogeographical scale instead of habitat heterogeneity in local community scales as scientists have considered. To approach the factors contributing to this cross-continent spatial pattern of trees, we obtained and reviewed ecosystem attributes, including topography, temperature, precipitation, biodiversity, density, and biomass, of these forests. Here we show that the proportions of aggregated species are actually constants independent of any ecosystem attributes regardless the nature of these tropical forests. However, local biodiversity are the major factor determining the number of aggregated species and the aggregation of large individuals of these forests. Aggregation of large trees declines along rising biodiversity, while the numbers of aggregated species increase permanently along lifting biodiversity. We propose a possible equilibrium and saturated status of the tropical forests in accommodating aggregated species. Furthermore, the tight correlations of biodiversity and species aggregation strongly imply the importance of overlooked biological interactions in shaping the spatial patterns in the tropical forests

Is Per Capita Real GDP Stationary? Evidence from Selected African Countries Based on More Powerful Nonlinear (Logistic) Unit Root Tests

In this study we use a more powerful nonlinear (logistic) unit root test advanced by Leybourne et al. (1998) to investigate the time-series propertities of per capita real GDP for 26 selected African countries for the period 1960-2000. We strongly reject the null of unit root process for over one-third the countries. These empirical results have important policy implications for selected African countries.

THE EFFECT OF INNOVATION STRATEGY ON POST-M&A INNOVATION PERFORMANCE: AN EVIDENCE FROM PHARMACEUTICAL INDUSTRY

M&A is a popular strategy for pharmaceutical industry due to high R&D risk and costs. Prior research related to post-M&A performance mainly focused on the financial and technology resource perspectives. This study aims to provide a new perspective of innovation strategy which is inspired by the research of March (1991), who noted the difference between exploration and exploitation. Moreover, we build the bridge between M&A and innovation strategy by applying the resource-based view theory. We argue that the acquirer’s exploration strategy will negatively influence the post-M&A innovation performance and the innovation strategy similarity between the acquirer and the target is beneficial for future innovation. Furthermore, we hypothesize that there is a negatively moderating effect caused by the acquirer’s exploration strategy on the effect of innovation strategy similarity. On the basis of 89 M&A deals in the pharmaceutical industry, our empirical results suggest two important findings. First, post- M&A innovation performance is influenced by acquirer’s innovation strategy, more specifically, acquirer’s exploration is harmful for post-M&A innovation. Second, the similarity effect is moderated by acquirer’s innovation strategy. Precisely, acquirer’s exploration will diminish the positive effect of similarity

Is Contract Farming More Profitable and Efficient Than Non-Contract Farming-A Survey Study of Rice Farms In Taiwan

Trade liberalization and globalization has modernized the food retail sector in Taiwan, affecting consumers, producers and trade patterns. These changes have placed significant pressures on farmers and processors including more stringent quality control and product varieties. The government has launched a rice production-marketing contract program in 2005 to assist rice farmers and the agro-business sector to work together as partners. The minimum scale for each contract is 50 hectares of adjacent rice paddies with 50 participants including rice farmers, seedling providers, millers and marketing agents. In order to evaluate the outcome of this program, a survey is conducted in the summer of 2005 after the first (spring) crop is harvested. Information of price and value of output and major variable and fixed inputs are collected along with characteristics of the farmers and farms. The survey results show that the average revenue of a contract farm is about 11 percent higher than an average non-contract farm. The per hectare cost of production in a contract farm is about 13 percent lower and as a result the average profit margin under contract is more than 50 percent above those without contract. A swtiching regression profit frontier model is adopted to further investigate their efficiency performance. The result indicates that an average contract farms is 20 percent more efficient than an average non-contract farm in a comparable operating environment. The result also suggests that although contract farming has potential to improve the profit of smallholders, it is not a sufficient condition for such improvement.Land Economics/Use,