Precipitation Coating of Monazite on Woven Ceramic Fibers: II. Effect of Processing Conditions on Coating Morphology and Strength Retention of Nextel™ 610 and 720 Fibers

Woven cloths of Nextel^™ 610 and 720 fibers were coated with monazite by precipitation. The cloths were first saturated with concentrated precursor solutions, and then submerged in warm water to initiate precipitation onto the fiber surfaces. Coatings were characterized by scanning electron microscopy, and transmission electron microscopy; thermogravimetric analysis was performed on LaPO₄ owders precipitated in solution under the same conditions as the coatings were deposited. Coating thickness distributions were measured and analyzed. Coated fiber strength was measured following heat treatment for 2 h at 1200°C. Processing conditions which retain a substantial fraction of the uncoated fiber strength are identified, and are discussed in the context of current understanding of strength degradation in coated fibers. Strength retention of coated Nextel^™ 610 fibers following heat treatment was broadly insensitive to precursor solution chemistry and was more strongly affected by intercoat firings which govern the final coating microstructure. For fixed processing conditions, more strength degradation was observed in Nextel^™ 720 due to higher residual stresses in the fiber.     

Evaluation of SiC/SiC minicomposites with yttrium disilicate fiber coating

Hi‐Nicalon‐S/α‐Y₂Si₂O₇/SiC minicomposites were formed by polymer infiltration pyrolysis (PIP) and characterized by TEM, SEM fractography, tensile testing, and fiber push‐in testing. All minicomposites with α‐Y₂Si₂O₇ fiber coatings had strengths significantly higher than the control samples without fiber coatings. Extensive fiber pullout with debonding at the coating‐fiber interface or within the coating itself was observed in minicomposites with Y₂Si₂O₇ fiber coatings, but no debonding was observed in minicomposites without fiber coatings. Debond energies of 4.5 ± 3, 4.6 ± 3 J/m² and average sliding stresses of 91 ± 40, 94 ± 40 MPa were measured by fiber push‐in tests.     

An application‐ and management‐based approach to ATM scheduling

Two frame‐based ATM scheduling strategies, Delayed Frame Queueing (DFQ) and Virtual Frame Queueing (VFQ), are described for real‐time network applications. Both strategies guarantee explicit upper bounds on delay and jitter on a per virtual connection (VC) basis without relying on per‐VC queueing. They also resolve the disadvantages often associated with other frame‐based schedulers. The DFQ scheduler employs Resource Management cells to enable work‐conserving forwarding at intermediate nodes while retaining the option for non‐work‐conserving forwarding at terminal nodes. This allows delay bounds to be uncoupled from jitter bounds. The VFQ scheduler requires no such overhead cell transmissions, but is more limited in its ability to uncouple these two types of bounds. ATM network simulation results indicate that both proposed disciplines offer favorable multiplexing performance in comparison to a well documented high performance service discipline. Finally, we contrast our proposal against the significant difficulties that alternative scheduling strategies based on bandwidth guarantees will face with regard to network management and network synthesis issues. This revised version was published online in June 2006 with corrections to the Cover Date.     

Real-time multimedia scheduling policies for end-to-end delayjitter and loss guarantees across ATM satellite systems

We propose a simple first-in first-out (FIFO)-based service protocol which is appropriate for a multimedia ATM satellite system. The main area of interest is to provide real-time traffic with upper bounds on the end-to-end delay, jitter, and loss experienced at various service queues within a satellite network. Various service protocols, each based on a common underlying strategy, are developed in light of the requirements and limitations imposed at each of the satellite's subsystems. These subsystems include the uplink (UL) earth station (ES) service queue, on-board processing (OBP) queues, and the downlink (DL) ES service queue feeding into a wireline ATM network or directly to an end-user application. Numerous network simulation results demonstrate the tractability, efficiency, and versatility of the underlying service discipline. Key features of our strategy are its algorithmic and architectural simplicity, its non-ad-hoc scheduling approach, and its unified treatment of all real-time streams at all service queues. In addition, the delay and jitter bounds are uncoupled. In this way, end-to-end jitter can be tightly controlled even if medium access requires long indeterminate waiting durations     

Copper Chelants and Antioxidants in Laundry Detergent Formulations Reduce Formation of Malodor Molecules on Fabrics

For consumers who use laundry detergents, a top unmet need is to reduce malodor that can persist on fabrics, even after washing and drying. A known source of odor is autoxidation of residual sebum on fabric, leading to the generation of an array of odiferous compounds. To prevent this oxidation process, two technologies were evaluated: (i) antioxidants to scavenge radicals and (ii) metal chelants to inhibit the involvement of copper ions as catalysts in the autoxidation process. Copper is a common component of sweat, soil, and municipal water supplies, especially where copper piping is involved, which is typical in many US homes and businesses. For the evaluations, swatches of fabric were treated with artificial sebum, then washed in commercial washing machines with tap water containing laundry detergent, and dried using commercial dryers. Copper added to the wash at a level representative of consumer homes substantially increased the formation of known malodor molecules. Copper chelants [in particular, diethylenetriamine (DETA)] added to the wash were effective in inhibiting the formation of malodor molecules. In combination with antioxidants [in particular, methyl 3-(3, 5-di-tert-butyl-4-hydroxyphenyl)propanoate (MtBHPP)], the inhibitory effect was greater. Even at low concentrations (<1%), DETA and MtBHPP were effective at inhibiting the generation of known malodor molecules on fabrics. As DETA and MtBHPP meet performance, cost, and stability considerations, they hold promise for use in high-quality commercial laundry detergent products designed to eliminate malodor on consumer fabrics.     

The case for speech synthesis: An experiment in human engineering

Despite expected widespread use of computer speech synthesis in manufacturing and production applications, no one has yet determined the effects of synthesized speech on task performance. This laboratory study introduced speech synthesis in replicating parts of two previous experiments that had used human-voice feedback. Both instructions and productivity feedback were examined for their effect on arithmetic manipulation tasks. Findings show that there are interaction effects; it appears necessary to develop profiles of persons and conditions which predict how computer speech synthesis may be used most productively. We must attempt to determine the way that speech synthesizers may replace and enhance the communication process, while maintaining high motivation of people who interact with these machines.     

Modelling Heterogeneous Slurry Flows at High Velocities

Experiments have been conducted with sand slurries of median diameter 0.09 mm and 0.27 mm in a laboratory test pipeline 0.103 m in diameter. In addition to pressure gradient measurements as functions of mean velocity and in‐situ solids concentration, concentration and velocity profiles have been obtained. The measurements show that the pipeline friction is lower than expected at high velocities. This deviation is of the type that has been predicted in recent theoretical work by Wilson and coworkers. A correlation for the slurry friction at high velocities has been obtained. This correlation has been used to modify the model for predicting friction of heterogeneous slurries at velocities above the deposition condition.     

Fabrication of a Multilayered Low-Temperature Cofired Ceramic Micro-Plasma-Generating Device

Plasma technology is currently being used in innumerable industrial applications. Some of the common uses of this technology include surface cleaning and treatment, sputtering and etching of semiconductor devices, excitation source for chemical analyses, cutting, environmental cleanup, sterilization, and phototherapy. The harsh conditions that these devices must endure require robust refractory materials systems for their fabrication and reliability. Low-temperature cofired ceramic (LTCC) material systems provide a durable and cost-effective platform for the manufacture of such devices, and allow for possible integration into meso-scale microsystems. Our designs are based on RF microstriplines that capacitively couple and ionize small gas discharge sites over the top electrode. In this paper, we have built several iterations of this micro-plasma generating device using LTCC material systems. The impact of electrode ink selection and processing, lamination methods, dielectric layer thickness, and electrode design has been investigated. Several micro-plasma-generating devices were then evaluated for power requirements, output stability, and long-term reliability.     

Effects of cell-to-cell fuel mal-distribution on fuel cell performance and a means to reduce mal-distribution using MEMS micro-valves

Achieving uniform flow among the cells of a fuel cell stack plays a significant role in being able to operate at maximum capability and efficiency. This paper presents experimental data showing the importance of cell-to-cell fuel flow balancing on fuel cell performance, and a fuel cell energy management (FCEM) technique that has demonstrated the ability to improve stack performance. In a specially instrumented four-cell polymer electrolyte fuel cell that allows external control of the air, fuel, and water-cooling flows to each cell, fuel to a single cell was reduced. V–I curves collected under these unbalanced conditions are compared to curves collected when the fuel flow to each cell was balanced. Reducing the fuel flow to a single cell by 11% decreased the V–I curve cutoff load by 10%—demonstrating the degree of negative effect that unbalanced fuel flows can have on stack performance. Typical fuel cell stacks have no dynamic means to keep flows in the stack balanced between the cells, but through the use of custom-built, piezoelectric micro-valves, a simple flow control strategy, and this custom four-cell laboratory stack, the positive effects of FCEM flow balancing at three different fuel flow rates was demonstrated.     

Presintering effects on ground-based and microgravity liquid phase sintering

Tungsten heavy alloys are an ideal system for liquid phase sintering studies. The sintering behavior and postsintering microstructure depend to a large degree on the processing conditions. While grain growth, final microstructures, and mechanical properties are fairly well understood, the role of presintering conditions is poorly documented. This article discusses presintering condition effects on the subsequent liquid phase sintering densification and distortion during both ground-based and microgravity sintering. It provides unique insight into the events accompanying densification and shape distortion, such as solid-liquid segregation and pore stability. Solid-liquid segregation is closely connected to densification. Presintering conditions play an important role in the mobility and the location of the pores in the sample, which can be explained in terms of the interfacial energy between different phases. In ground-based sintering, the cold-isostatically pressed sample has the most uniform solid-liquid distribution with the largest shrinkage. In microgravity sintering, the vacuum-presintered sample shows the largest degree of densification and elimination of pores.