Soft and Hard Implant Fabrication Using 3D-Bioplotting TM

At the Freiburger Materialforschungszentrum we have developed a new process (3DBioplotting TM) that permits most kind of polymers and biopolymers to be used in 3D scaffold design, including hydrogels (e.g. collagen, agar), polymer melts (e.g. PLLA, PGA, PCl) and twocomponent systems (e.g. chitosan, fibrin). Cells can be incorporated within the construction process, making this an ideal Rapid Prototyping technique for Organ Printing. Tailor-made biodegradable soft or hard scaffolds can so be fabricated in a short time using individual computer-tomography data from the patient. In-vitro tests showed promising results and in-vivo experiments are now under observation.Mechanical Engineerin

Freeform Extrusion of High Solids Loading Ceramic Slurries, Part I: Extrusion Process Modeling

A novel solid freeform fabrication method has been developed for the manufacture of ceramic-based components in an environmentally friendly fashion. The method is based on the extrusion of ceramic slurries using water as the binding media. Aluminum oxide (Al2O3) is currently being used as the part material and solids loading as high as 60 vol. % has been achieved. This paper describes a manufacturing machine that has been developed for the extrusion of high solids loading ceramic slurries. A critical component of the machine is the deposition system, which consists of a syringe, a plunger, a ram actuated by a motor that forces the plunger down to extrude material, and a load cell to measure the extrusion force. An empirical, dynamic model of the ceramic extrusion process, where the input is the commanded ram velocity and the output is the extrusion force, is developed. Several experiments are conducted and empirical modeling techniques are utilized to construct the dynamic model. The results demonstrate that the ceramic extrusion process has a very slow dynamic response, as compared to other non-compressible fluids such as water. A substantial amount of variation exists in the ceramic extrusion process, most notably in the transient dynamics, and a constant ram velocity may either produce a relatively constant steady-state extrusion force or it may cause the extrusion force to steadily increase until the ram motor skips. The ceramic extrusion process is also subjected to significant disturbances such as air bubble release, which causes a dramatic decrease in the extrusion force, and nozzle clogging, which causes the extrusion force to slowly increase until the clog is released or the ram motor skips.Mechanical Engineerin

Freeform Extrusion of High Solids Loading Ceramic Slurries, Part II: Extrusion Process Control

Part I of this paper provided a detailed description of a novel fabrication machine for high solids loading ceramic slurry extrusion and presented an empirical model of the ceramic extrusion process, with ram velocity as the input and extrusion force as the output. A constant force is desirable in freeform extrusion processes as it correlates with a constant material deposition rate and, thus, good part quality. The experimental results in Part I demonstrated that a constant ram velocity will produce a transient extrusion force. In some instances the extrusion force increased until ram motor skipping occurred. Further, process disturbances, such as air bubble release and nozzle clogging that cause sudden changes in extrusion force, were often present. In this paper a feedback controller for the ceramic extrusion process is designed and experimentally implemented. The controller intelligently adjusts the ram motor velocity to maintain a constant extrusion force. Since there is tremendous variability in the extrusion process characteristics, an on-off controller is utilized in this paper. Comparisons are made between parts fabricated with and without the feedback control. It is demonstrated that the use of the feedback control reduces the effect of process disturbances (i.e., air bubble release and nozzle clogging) and dramatically improves part quality.Mechanical Engineerin

Overtraining or burnout : a training and psycho-behavioural case study

The aim of this article is to present case study data that challenges the popular conception that athlete burnout represents the ultimate outcome of overtraining. A young male triathlete (22 yrs) completed a comprehensive training diary, along with the Athlete Burnout Questionnaire (ABQ) and the Multi-component Training Distress Scale (MTDS) weekly from the commencement of pre-season training, until the end of the competitive season 45 weeks later. Results were analysed retrospectively upon completion of the season and followed up with semi-structured interviews with the coach and athlete. These longitudinal observations are the first to document an athlete who appears to have simultaneously become overtrained and developed athlete burnout as measured by the ABQ. Thus we are advocating a need for future research to clarify differences between these two training-stress syndromes, specifically in relation to their aetiology, to avoid misdiagnosis and to ensure appropriate treatment for athletes experiencing these conditions is provided

Settlement of the Acorn Barnacle Balanus From Mobile Bay and Weeks Bay, Alabama

Barnacle cyprids and metamorphosed settlers were collected using glass slides as artificial substrates at six sites in the Mobile Bay area. Three sites were located in Weeks Bay, Alabama, where the highest settlement concentration occurred near the entrance to Mobile Bay. Two sites in the north end of Weeks Bay near the Fish River had very reduced settlement. The remaining three locations were on the north shore of Dauphin Island, Alabama. Settlement at Dauphin Island was most abundant at the deeper of two sites at the Dauphin Island Sea Lab boat dock, possibly because the substrates were exposed to less wave action. The other two sites at Dauphin Island were shallow and relatively unsettled when compared with the deep site. Adult barnacles recovered from the Weeks Bay and Dauphin Island locations include Balanus eburneus, B. venustus, B. improvisus, and B. subalbidus. Our data indicate two primary settlement periods for these species, late winter to spring and late summer to fall, with the highest settlement occurring in Feb. and March

Ciliated Protozoan Colonization of Substrates From Weeks Bay, Alabama

Ciliated protozoan colonization of artificial substrates was examined during a 12-mo period from Jan. to Dec. 2001 in Weeks Bay, Alabama. Artificial substrates (glass slides) were suspended in the water at three locations in the Bay for a period of I wk/mo, and the population density of the stalked peritrich Vorticella was determined. Environmental data collected during the colonization period were compared with the population results. There was a positive correlation between colonization and water temperature at two sites and between phosphate and colonization at one site. Additionally, a negative correlation was determined between colonization and dissolved oxygen at two sites, between colonization and nitrate at one site, and between colonization and pH at one site. The protozoan assemblage varied from month to month, although the overall dominance of Vorticella was maintained. Although the size of the population of Vorticella is likely influenced by a number of different variables, we believe that temperature and bacterial abundance are the likely controlling factors

Training Evaluation in Virtual Worlds: Development of a Model

Many organizations have adopted virtual worlds (VWs) as a setting for training programs; however, research on appropriate evaluation of training in this new setting is incomplete. In this article, we address this gap by first exploring the unique issues relevant to evaluation faced by training designers working in VWs. At the macro-organizational level, the primary issue faced is an organizational culture unreceptive to or otherwise skeptical of VWs. At the micro-organizational level, two major issues are identified: individual trainees unreceptive to VWs and general lack of experience navigating VWs. All three of these challenges and their interrelationships may lead to poor reactions, learning, and transfer from VW-based training despite strong, pedagogically sound training design. Second, we survey the training evaluation research literature, identifying the most well-supported training evaluation models, discussing the suitability of each for evaluating VW-based training. Third, we propose a new integrative model based upon this literature, incorporating solutions to the unique issues faced in VWs with the most relevant portions of the models discussed earlier. Fourth, broad thematic implications of this model are identified and applied to prior VW literature. Finally, we provide specific recommendations to practitioners and researchers to evaluate their VW-based training fully

Aqueous-Based Extrusion Fabrication of Ceramics on Demand

Aqueous-Based Extrusion Fabrication is an additive manufacturing technique that extrudes ceramic slurries of high solids loading layer by layer for part fabrication. The material reservoir in a previously developed system has been modified to allow for starting and stopping of the extrusion process on demand. Design pros and cons are examined and a comparison between two material reservoir designs is made. Tests are conducted to determine the optimal deposition parameters for starting and stopping the extrudate on demand. The collected test data is used for the development of a deposition strategy that improves material deposition consistency, including reduced material buildup at sharp corners. Example parts are fabricated using the deposition strategy and hardware design.Mechanical Engineerin

Bacterial Communities on the Northern Gulf of Mexico Continental Shelf are Influenced by Sediment Characteristics Affected by the Mississippi River

Benthic bacteria in the Gulf of Mexico serve the base of the sediment food chain as a food source for various marine organisms. In this paper, we analyzed the bacterial community and sediment characteristics from 14 sediment samples collected along the continental shelf of the northern Gulf of Mexico. Using the bacterial community to assess relationships among our sites, the data revealed groupings of sites that correlated to the sediment characteristics, generally grouped as western sites in Louisiana near the outflow of the Mississippi River and eastern Florida sites more distant from the outflow. Cluster analysis and multidimensional scaling demonstrated significant groupings of Louisiana vs Florida bacterial communities, and distance-based redundancy analysis related these groupings to sediment characteristics. Given the directions of currents around the Mississippi River, our data suggested that the outflow of the river is a major factor affecting the benthic bacterial community in the northern Gulf of Mexico