Identification of delay dominant recycle systems

A new identification method for single-input–single-output delay dominant recycle systems is presented in this paper. Identification of recycle systems is similar to that of closed loop systems. However, identification of recycle systems poses certain challenges in that the input-equivalent signal in the closed loop identification is not available for recycle systems. Therefore, special identification routines are required to ensure consistency of recycle and forward models. It is shown that consistent estimates of delay dominant recycle systems can be obtained by treating a delayed output as one of the inputs. Asymptotic variance expressions for the estimates of forward and recycle models are provided. These are then used in designing an optimal excitation signal for recycle systems. The results are illustrated through an industrial example.     

Low-level (PPB) determination of cisplatin in cleaning validation (rinse water) samples. I. An atomic absorption spectrophotometric method

Suitable analytical methods are required for quantitative determination of trace levels of ingredients in samples obtained for purposes of cleaning validation. We describe below an atomic absorption method for the quantitation of cisplatin, an antineoplastic agent, in aqueous samples. Cisplatin was reacted with diethyldithiocarbamic acid (DDTC), sodium salt, to yield a platinum-DDTC (Pt-DDTC) complex. The Pt-DDTC chelate was extracted into methylene chloride, the extract was mixed with acetonitrile, and the platinum content was then determined using a Zeeman atomic absorption (AA) spectrophotometer. The extraction conditions and AA experimental conditions were set up such that the detection level could be extended to 0.5 ng/ml. Reproducible results were obtained at a quantitative working standard concentration of 5 PPB. The absorbance response was found to be a linear function of cisplatin concentration in the region between 0.5 PPB and 20 PPB, which is about 10% to 400% of the target analyte concentration of 5 PPB. The target analyte concentration was set at 5 PPB such that it was at least 10 times the detection limit of about 0.5 PPB.     

Caffeine in Coffee: Its Removal. Why and How?

The popularity of coffee as a beverage is ever increasing despite the fact that there are reports antagonized to its consumption. Of the several factors cited, the alkaloid caffeine present in coffee can cause addiction and stimulate the central nervous system. It has an effect on the cardiovascular system with a slight increase in blood pressure and heart output. It undergoes biotransformation in the human body to form methylated derivatives of uric acid. In recent times, much effort has gone into the research on the removal of caffeine in coffee, resulting in a specialty product called decaffeinated coffee. Decaffeination methods mainly employ organic solvents or water or supercritical carbon dioxide. These methods with their attendant advantages and disadvantages are reviewed in this article.     

An unslotted multichannel channel‐access protocol for distributed direct‐sequence networks

A multichannel reservation-based channel-access protocol is investigated in this paper. The available system bandwidth is divided into distinct frequency channels. Under the protocol, one channel (the control channel) is used to exchange reservation messages and the remaining channels (the traffic channels) are used for information-bearing traffic. The performance of this scheme is compared to that of a single-channel reservation-based protocol. A simple contention-based slotted-Aloha protocol is also considered. Performance results take into account the effects of multiple-access interference on acquisition and packet errors. Results show that the reservation-based approach is advantageous under conditions of high traffic. In addition, a pacing mechanism that mitigates multiple-access interference and promotes fairness is described, and results are presented that demonstrate its effectiveness. This revised version was published online in June 2006 with corrections to the Cover Date.     

A kinetic model for the hydrochloric acid leaching of kaolinite clay in the presence of fluoride ions

The dissolution of kaolinite clay in hydrochloric acid solutions has been carried out in the presence of fluoride ions. Leaching in the presence of fluoride ions activates the clay for leaching, making higher extractions possible at lower roasting and leaching temperatures. The activation energy for the leaching of clay calcined at 540°C is decreased from 71 kJ/mol to 23 kJ/mol in the presence of fluoride ions. Dissolution in the presence of fluoride appears to fit a second-order reaction mechanism.     

Convergent beam diffraction analysis of dispersoids in oxide dispersion strengthened alloys

Convergent Beam Diffraction (CBD) analysis was conducted on two of the four yttrium-aluminum oxide particles in a commercial dispersion strengthened alloy. Diffraction analysis on yttrium-aluminum garnet, YAG (5A1₂O₃ • 3Y₂O₃), and yttrium-aluminum perovskite, YAP (A1₂O₃ • Y₂O₃), indicated that diffraction effects in the High Order Laue Zones and symmetry information from the CBD patterns are extremely useful in obtaining additional information about the crystal structure from a single pattern. It was also shown that double diffraction effects in the zero layer can explain the presence of the kinematically forbidden reflections. The results of the analysis are discussed.