Design and characterization of a low-profile micropositioning stage

This paper discusses the design and characterization of a new, single-axis, low-profile, piezo-driven vertical motion micropositioning stage for use in laser welding applications. A low-profile configuration is attained by mounting the piezo actuator horizontally and using a novel lever arrangement to transfer the horizontal motion of the actuator into the desired vertical motion. An analytical model for the static and dynamic behavior of the stage is presented, along with finite element (FE) modeling verification. A 200 μm motion-range stage was built, and tests show that the stage has a vertical stiffness of 6.0 N/μm and a resonance frequency of 364 Hz. The results are in very close agreement to those predicted by the model.     

Computer Integration for Robotic Masonry

Abstract: Computers are essential in the development of robotic systems for construction. The introduction of such systems creates many challenges to researchers, equipment manufacturers, and users alike. This paper presents a new initiative to study critical issues related to the establishment of a robotic masonry system. In particular, the paper discusses three major problem areas: (1) design automation, (2) automated mortar application, and (3) adaptive control of brick placement. The data presented have been generated using standard PC computers which control and integrate design tools with real-time machinery and sensory devices.     

Polymeric pseudocrown ethers. III. The complexation with iron(III) in phosphoric—hydrochloric acid mixtures

Polymeric pseudocrown ethers, incorporating oxyethylene and oxypropylene units, extract FeCl₄^? from mixed hydrochloric and phosphoric acids. The complexation depends on hydrochloric acid concentration and becomes efficient when the HCl concentration exceeds 4 M. The regeneration of the polymers is accomplished with water. Column tests have been shown to separate iron very efficiently from phosphoric acid, which is recovered quantitatively. In comparison, Amberlyst A-21, a weak-base anion exchanger, shows affinity for phosphoric acid, making the separation between iron and phosphorus difficult.     

Computer simulation of injection molding

The injection-molding process consists of three consecutive stages: filling, packing, and cooling. In order to obtain some insight into the phenomena involved in the process, and particularly in order to evaluate the moldability of certain resins and to predict the microstructure and properties of products molded therefrom, a number of workers have employed a variety of techniques based on mathematical simulation of the process. Mathematical simulation involves writing the relevant continuity, momentum, and energy equations governing the system, with appropriate boundary and initial conditions representing the prevailing conditions in the cavity and delivery channels. In order to obtain meaningful solutions to the above equations, detailed information is required regarding the thermodynamic, thermal, and rheological properties of the resin. Moreover, the prediction of the microstructure and ultimate properties of the molded article requires a knowledge of the morphological, crystallization, and orientation phenomena that take place under the influence of the thermo-mechanical history experienced by the resin. The complexity of the equations involved results in the utilization of a number of simplifying assumptions and the resort to computer simulation and numerical solutions of these equations. A variety of numerical schemes based on finite difference and finite element methods has been employed by various researchers.     

Water binding and irreversible dehydration processes in cellulose acetate membranes

The relative amounts of freezing and nonfreezing water in various water-wet cellulose acetate (CA) membranes were determined by NMR techniques, from the initial heights of the water component in the free induction decay (MNR intensity). The results suggest that (1) a significant fraction of the water in various wet CA membranes does not freeze, probably because of strong interaction with the polymer; (2) the relaxation times T₂ of the nonfreezing water are of the order of milliseconds indicating that they are still highly mobile compared with ice; (3) all the water contained in dense CA films or in membranes equilibrated at relative humidity of 0.93 does not freeze upon cooling the membranes from room temperature to ?60°C; (4) the amounts of nonfreezing bound water in membranes is higher than the total amount of water absorbed from liquid water by a dense film of the same polymer. However, the amounts of nonfreezing water in various CA membranes as calculated from the “relative NMR intensities” is substantially lower than those calculated from DSC melting endotherms by assuming the heat of fusion of water in membranes to be identical to that of pure water. Various possible reasons for this discrepancy are discussed. Measurements on the first desorption-adsorption cycle of wet CA membranes have also been performed. They suggest that during the first dehydration process, irreversible changes are induced in the structure of the membrane which result in a significantly lower accessibility of the polymer to interact with water. The extent of these irreversible changes in membrane structure is dependent on the details of the dehydration process being more pronounced at higher temperatures.     

Capillary viscometry: A complete analysis including pressure and viscous heating effects

Capillary viscometers have been used extensively, because of their simplicity and reliability, to measure the viscosity of fluids over a wide range of shear rates. However, in capillary flow, the shear rate is not uniform throughout the capillary, a pressure gradient is established in the direction of flow, and the temperature of the fluid is nonuniform due to viscous dissipation. In the present work, a general, simple and practical method is proposed for correcting for the effects of pressure variation and viscous dissipation in determining the viscosity of polymer melts at high pressures. The method essentially involves the estimation of temperature, pressure, shear rate, and shear stress under a variety of experimental conditions at a predetermined point in the capillary. As such, it may be considered as a generalized extension of the classical Rabinowitsch-Mooney method for estimating true viscosity in capillary flow.     

A software reliability engineering practice

A recently adopted best current practice (BCP) at AT&T involving performing software reliability engineering (SRE) tasks over the software life cycle is discussed. Software reliability is defined as the capability of a software product to operate failure-free for a given period under specified operating conditions. The support mechanisms for the SRE BCP are described     

Effect of carbohydrate supplementation provided through drinking water during feed withdrawal on meat and liver colours in broilers

BACKGROUND: The effect of saccarose supplementation provided through drinking water during feed withdrawal on meat and liver colour was investigated in a total of 50 broilers (five floor pens with 10 broilers) at 43 days. Treatments consisted of: (1) full‐fed control broilers fed the standard broiler diet and water for the full 10 h (control); (2) fasted broilers receiving only water (FW); (3) 1 g (0.01SW); (4) 2 g (0.02SW); and (5) 3 g (0.03SW) saccarose L^?1 supplemented water for the 10 h. The CIE colour values representing lightness (L*), redness (a*), and yellowness (b*) were measured on raw livers, breast and thigh meats. RESULTS: Full‐fed broilers had lower dressing percentage, higher abdominal fat and liver yield and lighter thigh meat coloration than the FW birds (P < 0.05). The 0.02SW and 0.03SW resulted in live shrinks that were lower (P < 0.05) than those found in FW broilers. The 0.02SW and 0.03SW resulted in liver colours that were lighter than those found in FW and 0.01SW birds but darker than from control birds (P < 0.05). CONCLUSION: It was concluded that saccarose supplementation during feed withdrawal appears to have a measurable impact on live shrink, and lightness of liver and thigh meat colour in broilers. Copyright © 2007 Society of Chemical Industry