Metal solid freeform fabrication using semi-solid slurries

A new process for the direct solid freeform fabrication (SFF) of metallic prototypes and components offers a significant advantage over most other metal-SFF processes: it does not involve the use of powders, thus minimizing porosity and shrinkage distortion. This process utilizes the unique rheological and thermophysical properties of semi-solid-metal (SSM) slurries to build a near-netshape metallic component in one step, without the need of sintering, molds, roughmachining, or post-processing operations. A stream of semi-solid is deposited over a moving substrate that follows a three-dimensional pattern. The high viscosity of semi-solid slurries and their particular rheology allows the stream to be deposited over previous layers in a controlled fashion, without traces of an interface. Because the rate of deposition is an order of magnitude faster than in other SFF processes, manufacturing is also faster. In addition, distortion problems characteristic of other processes involving fully molten metal are significantly reduced because the material deposited is already partially solid. In this paper, the first implementation of this technology is presented in detail. Eventually, this process could be useful in the production of a small series of large metallic components that would otherwise be produced by casting or machining. Those processes cost more and result in lower-quality components. For more information, contact P.F. Mendez, Massachusetts Institute of Technology, Department of Materials Science and Engineering, Room 4-133, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139; (617) 253-3204; fax (801) 729-6929; e-mail pat@mit.edu.     

Loaded and nonloaded titanium versus hydroxyapatite-coated threaded implants in the canine mandible

A commercially pure titanium threaded implant was compared to a hydroxyapatite-coated threaded implant of similar geometric design and dimensions in the canine model. Bilateral posterior implants supported fixed prostheses, and some implants in the same mandibles served as unloaded control implants. Implants were evaluated clinically, radiographically, and histomorphometrically at the light microscope level to detect any differences in bone response to loaded conditions. No statistically significant differences were found between the two implant designs under loaded or nonloaded conditions with regard to mobility, probing depth, percentage of osseointegration, and crestal bone position.     

Fiber-optic digital video multiplexing using optical CDMA

The use of laser pulsing in the form of code-division multiple access (CDMA) to multiplex a set of digital video signals over a fiber network is proposed. The laser pulsing is used to generate unique code sequence addresses which identify each source, and the video data are modulated on these sequences. Digital encoding using pulse position modulation (PPM) is proposed, having advantages that permit efficient integration of optical and electronic processing. Data recovery is achieved by optical correlation for sequence recognition, followed by standard electronic PPM decoding. The relation between key system parameters of the encoding, decoding, and optics is derived, and indicates that compressed video rates between 5 and 20 Mb/s/channel, with 25-50 channels, is possible with relatively standard hardware. Experimental breadboard results being carried out at USC on this system indicate the feasibility of the CDMA concept for fiber multiplexing     

Examining market oriented aspects of cost of quality

This paper examines the market-oriented aspects of cost of quality that have not been examined by current research. Using data from the automotive industry, we study the relationship between unit cost and economies of scale, experience curve effects, and imputed cost of quality in a specific context. Estimating these effects on unit cost explicitly has been problematic either due to unavailability of data or the imprecision of available data. Further, if a firm wishes to benchmark itself against its principal competitors along these cost dimensions, unavailability of data on competitors renders estimation impossible. In this paper, we propose and illustrate a method based on the iterative optimization of a dynamic model that has been presented in the literature. The results for a specific, illustrative case confirm the anticipated effects of experience curve advantages and economies of scale, lending validity to the proposed methodology. The results show that there is a positive relationship between unit cost and quality improvements; this possibility has also been raised by other researchers in the literature. The use of the methodology and implications for managerial use are discussed     

Parvovirus B19 infection-related complications in renal transplant recipients: treatment with intravenous immunoglobulin

BACKGROUND: Chronic red cell aplasia can develop in immunocompromised patients including transplant recipients infected with parvovirus B19 (PV B19). Renal involvement with PV B19 infection is not well-recognized. METHODS: We diagnosed erythroid hypoplasia associated with PV B19 infection in three renal transplant recipients; one of them developed de novo collapsing glomerulopathy. These patients were treated with intravenous immunoglobulin (IVIG). RESULTS: In two patients, anemia responded promptly to IVIG therapy. One of them had recurrence of anemia that responded to a second course of IVIG. Despite IVIG treatment, persistent infection with PV B19, recurrent anemia, and de novo collapsing glomerulopathy leading to allograft failure developed in the third patient, who had received the most intense immunosuppression. CONCLUSIONS: These findings indicate that PV B19 infection in transplant recipients can cause chronic red cell aplasia that generally responds to IVIG therapy. In some patients, particularly those who are heavily immunosuppressed, infection may persist despite treatment. As the cellular receptor for PV B19 is expressed in the kidney, persistent infection may result in development of glomerulopathies in these patients.     

Risks of transplanting kidneys from hepatitis B surface antigen-negative, hepatitis B core antibody-positive donors

OBJECTIVES: An indirect inguinal hernia is a common cause of inguinoscrotal swelling in young boys. We describe 3 cases of an extremely unusual entity that has a similar clinical presentation to more commonly diagnosed intrascrotal processes. METHODS: Two patients presented with acute hemiscrotal enlargement and pain, and a third patient presented with scrotal enlargement only. All patients underwent a scrotal ultrasound evaluation and subsequent inguinoscrotal exploration. RESULTS: All patients had a multiseptated peritesticular fluid-filled mass on ultrasound evaluation. Subsequent inguinoscrotal exploration revealed a torsion of the indirect hernia sac in each case. A high ligation and excision of the sac was curative. CONCLUSIONS: Torsion of a hernia sac is an extremely rare entity, and current sonographic imaging fails to clearly diagnose this unusual phenomenon. Because pediatric urologists are commonly called to evaluate a child with an acutely swollen scrotum, awareness of this diagnosis is important.     

Synthesis of glycerol-derived diallyl spiroorthocarbonates and the study of their antishrinking properties in acrylic dental resins

In this work was evaluated the efficiency of an antishrinkage additive in a dental resin. This additive was a mixture 1:1 of five and six-membered ring spiroorthocarbonates functionalized with allylic groups (SOC DA). The aim of this study was to reduce the shrinkage of a typical dental resin composed of a blend of the dimethacrylates, Glycerolate bisphenol A dimethacrylate (Bis-GMA)/2-[(3,5,5-trimethyl-6-[2-(2-methyl prop-2-enoyloxy) ethoxycarbonylamino] hexyl) carbamoyloxy] ethyl, 2-methyl prop-2-enoate, (UDMA)/triethyleneglycol dimethacrylate (TEGDMA) in a 50:30.20 molar ratio, and silicon dioxide as filler. SOC DA was added at 5, 10 and 20 mol% to the already mentioned formulation. It was found that the addition of 20 mol% of SOC DA decreased 53 % the shrinkage of the cured composite material, in comparison with a formulation where it was not added the antishrinkage additive. Besides, the kinetics of photopolymerization determined by Real-Time infrared spectroscopy, demonstrated that the addition of increasing concentration of SOC DA improved the conversion of double bonds of dimethacrylates. Additionally, the presence of SOC DA at 10 % mol, helped to increase the flexural strength and the compressive strength of the composite, as a consequence of the augment of the crosslink density, induced by the ring opening polymerization of SOC DA.     

Production,characterization and application of protein isolates from shark. Part 4. Application of protein isolates in different food systems

The supplementation of spaghetti, white bread, meat emulsion, and minced meat with protein isolates from shark flesh was studied. The results show that such isolates can partially replace conventional proteins in meat products and wheat flour in spaghetti and white bread without negatively altering the properties of the supplemented foods.     

Ping-pong player prototype

In this paper, a low-cost robot capable of playing ping-pong against human opponent using a vision system to detect the ball is presented. In the subsequent sections, the three main subsystems of the robot, i.e., the vision system, mechanical structure, and the control systems, are described. A prototype has been designed with lightweight and resistant materials to increase the response time and accurateness of the shot. One of the important features of this system is that it uses only one camera to detect the ball, thus reducing the computational time and hardware requirements. To detect the location of the ball, the robot combines the information about the ball and about the shadow it casts on the table. The expert module control defines the game strategy. Orienting the bat in order to return the ball to the desired position on the table does this. In these experiments, the success rate in returning balls was greater than 80%.