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

Electrodynamics of Amorphous Media at Low Temperatures

Amorphous solids exhibit intrinsic, local structural transitions, that give rise to the well known quantum-mechanical two-level systems at low temperatures. We explain the microscopic origin of the electric dipole moment of these two-level systems: The dipole emerges as a result of polarization fluctuations between near degenerate local configurations, which have nearly frozen in at the glass transition. An estimate of the dipole's magnitude, based on the random first order transition theory, is obtained and is found to be consistent with experiment. The interaction between the dipoles is estimated and is shown to contribute significantly to the Gr\"{u}neisen parameter anomaly in low $T$ glasses. In completely amorphous media, the dipole moments are expected to be modest in size despite their collective origin. In partially crystalline materials, however, very large dipoles may arise, possibly explaining the findings of Bauer and Kador, J. Chem. Phys. {\bf 118}, 9069 (2003).Comment: Submitted for publication; April 27, 2005 versio

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

Development of Bone Targeting Drugs.

The skeletal system, comprising bones, ligaments, cartilage and their connective tissues, is critical for the structure and support of the body. Diseases that affect the skeletal system can be difficult to treat, mainly because of the avascular cartilage region. Targeting drugs to the site of action can not only increase efficacy but also reduce toxicity. Bone-targeting drugs are designed with either of two general targeting moieties, aimed at the entire skeletal system or a specific cell type. Most bone-targeting drugs utilize an affinity to hydroxyapatite, a major component of the bone matrix that includes a high concentration of positively-charged Ca(2+). The strategies for designing such targeting moieties can involve synthetic and/or biological components including negatively-charged amino acid peptides or bisphosphonates. Efficient delivery of bone-specific drugs provides significant impact in the treatment of skeletal related disorders including infectious diseases (osteoarthritis, osteomyelitis, etc.), osteoporosis, and metabolic skeletal dysplasia. Despite recent advances, however, both delivering the drug to its target without losing activity and avoiding adverse local effects remain a challenge. In this review, we investigate the current development of bone-targeting moieties, their efficacy and limitations, and discuss future directions for the development of these specific targeted treatments

Distribution of total mercury and methylated mercury species in Central Arctic Ocean water and ice

The central Arctic Ocean remains largely unexplored when it comes to the presence and cycling of mercury and its methylated forms including mono- and dimethylmercury (MMeHg and DMeHg, respectively). In this study, we quantified total Hg (HgT) and methylated Hg species in seawater, ice cores, snow, brine, and water from melt ponds collected during the SWEDARCTIC 2016 expedition to the Amerasian and Eurasian side of the Lomonosov Ridge. In the water column, concentrations of HgT, MMeHg and DMeHg ranged from 0.089 to 1.5 pM, <25 to 520 fM and from <1.6 to 160 fM, respectively. HgT was enriched in surface waters while MMeHg and DMeHg were low at the surface (i.e. in the polar mixed layer) and enriched at a water depth of around 200–400 m. A 1:2 ratio of DMeHg to MMeHg was observed in the water column suggesting a lower ratio in the central parts of the Arctic Ocean than what has previously been reported from other parts of the Arctic Ocean. At the ice stations, average HgT ranged from 0.97 \ub1 1.2 pM in the ice cores to 27 \ub1 17 pM in melt pond waters and average MeHgT (total MeHg) from 28 \ub1 15 fM in brine to 130 \ub1 18 fM in melt pond water. The HgT observed in melt ponds and brine was an order of magnitude greater than HgT observed in surface waters and HgT in the upper part of the ice-cores was ~4–8 times higher HgT in comparison to lower layers. Our study suggests that ice may act as a source of HgT to surface waters but not to be a likely source of the methylated Hg forms. Unlike elemental Hg, DMeHg did not enrich in surface waters covered by ice. Concentrations of DMeHg observed in the ice cores and other samples collected from the ice stations were low, suggesting ice to not act as a source of DMeHg to the atmosphere nor to surface waters

Japanese multinationals in the post-bubble era:new challenges and evolving capabilities

Since the bursting of Japan's bubble economy, from 1990 onwards, Japanese multinational companies (MNCs) have faced new competitive challenges and questions about the management practices on which they had built their initial success in global markets. Japanese engagement in the international economy has undergone a number of phases. In the period before the Second World War, Japanese companies learnt from foreign MNCs in trading, shipping, and manufacturing, frequently through strategic alliances, and leveraged their capabilities to succeed in overseas and largely Asian markets. In the immediate post-war decades, during the Japanese ‘economic miracle’, there were notable examples of MNC investment in raw materials and labour intensive production, but both inward and outward foreign direct investment were not significant. Japanese companies achieved leadership in management and technology, in order to support a strategy of export-orientated industrialization. Changes in government policies in the developed economies of the US and Western Europe forced leading Japanese manufacturers to convert themselves into MNCs and to transfer their home-grown capabilities to overseas subsidiaries. The period after 1990 marked declining Japanese competitiveness and it asked questions about the ability of Japanese MNCs to be more responsive and global in their strategies, organization and capabilities.No Full Tex

Antiplatelet and anticoagulant therapy for non-ST-elevation acute coronary syndromes in a general hospital

Aim: To audit compliance with the 2011 European Society of Cardiology (ESC) guidelines for prescribing antiplatelet and anticoagulant therapy in patients diagnosed with non-ST-elevation acute coronary syndromes (NSTE-ACS). Methods: Five-month audit at Cardiac Catheterisation Suite, Mater Dei Hospital, Malta. A data collection form for inpatients diagnosed with NSTE-ACS was developed, psychometrically evaluated and completed for each patient by the investigator. Comparative analysis to assess whether these patients were being managed according to the guidelines was undertaken. Results: 165 patients were recruited; 73% were male, 37% were between 66 and 75 years and 44% were active smokers. The most common risk factors for cardiovascular disease in these patients were hypertension (27%), dyslipidemia and obesity (both 16%). 41% of the patients underwent a percutaneous coronary intervention, either ad hoc (34%) or elective (7%). Compliance to guidelines for prescription of aspirin and clopidogrel 300mg loading dose was 95% and 88% respectively. Compliance to guidelines for prescription of aspirin and clopidogrel 75mg daily maintenance dose was 97% and 96% respectively. Compliance to guidelines for prescription of proton pump inhibitors (PPIs) in patients receiving dual antiplatelet therapy (DAPT) was only 19%; 81% of the patients were prescribed omeprazole against guideline recommendations. Compliance to guidelines for prescription of anticoagulation therapy was 95% with respect to prescription of heparin treatment in combination with DAPT. Compliance to guidelines for prescription of enoxaparin was 81%. Compliance to guidelines for other antiplatelet and anticoagulant drugs recommended in the guidelines, including ticagrelor, prasugrel, glycoprotein IIb/IIIa receptor antagonists, fondaparinux and bivalirudin, was not measured. Conclusions: Prescription of antiplatelet and anticoagulant therapy for NSTE-ACS in Malta is predominantly in accordance with ESC guidelines. Alternative antiplatelet and anticoagulant drugs and PPIs should be included in the Maltese hospital formulary to improve NSTE-ACS management in line with guideline recommendations.peer-reviewe