Iron determination by FAAS in fish feed and feces after ultrasound-assisted extraction

This paper proposes a method to determine iron in samples of fish feed and feces using ultrasound in the extraction of the analyte and in subsequent quantification by flame atomic absorption spectrometry. Using HCl 0.10 mol L⁻¹ as the extraction solution, the optimal conditions of extraction were found to be: granulometry of the sample <60 μm; a sonication time of five cycles of 10 s and sonication power of 136 W. The method was applied in studies of the availability of iron in four food sources used in the diet of Nile Tilapia. The results obtained with the proposed extraction method allowed us to calculate the coefficients of apparent digestibility of iron in the food sources, which was not possible when using results obtained from samples mineralized by acid digestion.     

Pricing mechanism for interconnection between phone operators and virtual mobile VoIP operators

Lately software based virtual mobile voice over Internet Protocol (VMVoIP) services have become available to end-users which may endanger profit of regular telephone operators from phone calls. In this situation, telephone operators should decide on a proper mechanism for interconnection with such VMVoIP operators which secures mutual benefit of both operators. In this paper, we study both monopolistic and oligopolistic markets of VMVoIP in which a single VMVoIP and several VMVoIP operators available in the market respectively. We model the interaction among a phone operator, VMVoIP operators and end-users as a leader-follower dynamic game and find a sub-game perfect Nash equilibrium (SPNE) for the game. The SPNE shows the phone operator’s best pricing strategy (i.e., wholesale price for VMVoIP operators and retail price for end-users) and its best decision on the interconnection with VMVoIP operators. We further study economic interpretation of the SPNE. We show that in specific end-users’ demands, the phone operator may increase its total profit by allowing the interconnection and taking right price discrimination strategy.     

Determination of Activity Coefficients of Semi-Volatile Organic Aerosols Using the Integrated Volume Method

We demonstrate the use of the Integrated Volume Method (IVM) to estimate activity coefficients of semi-volatile organic compounds pertinent to ambient/atmospheric aerosols in binary mixtures. We generate binary solution aerosols with different mole fractions of individual components; for each mixture, we measure total change in aerosol volume upon heating from 25 ^○ C to 35 ^○ C, with the aerosols being at equilibrium in both states. The change in aerosol volume, or in other words, the partitioning between the particle phase and the gas phase, is used to determine activity coefficients of the compounds as a function of their mole fraction in the mixture. We demonstrate this method using the following four model systems. System 1: adipic acid–pimelic acid, which illustrates polar organic–polar organic interactions. Non-ideal behavior was observed with activity coefficients around three at infinite dilution. System 2: adipic acid–dioctyl sebacate, which illustrates polar organic–non-polar organic interactions. The compounds in this experiment did not form a solution. System 3: adipic acid–ammonium sulfate, which illustrates polar organic–inorganic interactions. The compounds in this experiment did not form a solution. System 4: adipic acid–ambient extracts, which illustrates the potential use of the method to study partitioning behavior of individual components in a complex matrix approximating that of real ambient aerosol. The measured activity coefficients of adipic acid were less than unity for the tested range of mixing ratios, indicating suppression of volatility of this compound in ambient organic matrix.     

The Nyquist robust sensitivity margin for uncertain closed‐loop systems

The Nyquist robust sensitivity margin is proposed as a new scalar indicator of robust stability that also provides a meaningful quantitative assessment of the worst sensitivity realized by the uncertain closed loop. After formulating and discussing in detail the underlying optimization problem required for the calculation of the margin, the approach is applied to the characterization of the robust stability of a closed‐loop featuring a linear system with an affine uncertainty structure and a parametric uncertainty set described by a real rectangular polytope. The capabilities of the methodology are illustrated through examples, which include an approach for quantifying alternative robustness margins, such as a parametric stability margin. The computational algorithm is systematic and can be carried out with high numerical precision. Copyright © 2005 John Wiley & Sons, Ltd.     

An approach for high-yield requirements capture for e-commerce and its application

Web-based e-commerce software is typically real-time, responsive, and distributed software that must meet high quality requirements. Moreover, because of its Internet-based operating environment, e-commerce software must deal with concurrency, synchronization, and non-deterministic issues (such as delays) primarily caused by the heavy usage load and underlying network conditions. In this paper, we introduce a generic, cost-effective approach to optimize requirements capture (and subsequent development and testing) with respect to functional coverage and customer perception of quality. This high-yield approach is presented and illustrated by application to an e-commerce online shopping system and used to explain the principles of use-case requirements captured in the unified modeling language. Published online: 25 July 2001     

Effect of dead space on gain and noise ofdouble-carrier-multiplication avalanche photodiodes

The effect of dead space on the statistics of the gain in a double-carrier-multiplication avalanche photodiode (APD) is determined using a recurrence method. The dead space is the minimum distance that a newly generated carrier must travel in order to acquire sufficient energy to become capable of causing an impact ionization. Recurrence equations are derived for the first moment, the second moment, and the probability distribution function of two random variables that are related, in a deterministic way, to the random gain of the APD. These equations are solved numerically to produce the mean gain and the excess noise factor. The presence of dead space reduces both the mean gain and the excess noise factor of the device. This may have a beneficial effect on the performance of the detector when used in optical receivers with photon noise and circuit noise     

Dissolution Rates of Commercial Phenylbutazone Tablets: Inter-And Intra-Brand Effects

A study has been carried out to investigate the dissolution rate profiles of twelve batches of sugar-coated phenylbutazone tablets belonging to four commercial brands. Using the rotating basket method, significant inter-brand and inter-batch variations in dissolution rates were found. Only two batches of one brand passed the B.P. dissolution limit whilst other batches had percentages dissolution between 0.3 and 58 after 45 min. Batches with poor dissolution characteristics exhibited significant tablet-to-tablet variations in dissolution rates; a finding which was not observed in the relatively fast-dissolving batches. When the paddle method was substituted for the B.P. basket method, the dissolution rates were relatively faster but similar dissolution failure was found. However, the tablet-to-tablet dissolution variability was decreased in some of the batches. The observed differences in dissolution rates of the batches examined were unrelated to their disintegration times. Inspite of the poor dissolution characteristics of most of the batches studied, no apparent chemical degradation was found. It is recommended that when evaluating the dissolution rates of brands of phenylbutazone tablets, a number of batches from each brand should be tested.     

Isolated agenesis of the mastoid antrum

The first isolated case of agenesis of the mastoid antrum, previously only described in association with the congenital syndromes trisomy 13 and mandibulofacial dysostosis, is reported. The loss of this important surgical landmark may result in disorientation and iatrogenic trauma. The surgeon must be aware of its existence, and where it is suspected the middle fossa dura should be exposed and followed posteriorly until the lateral sinus is encountered.     

Real-Time Testing of WPT-Based Protection of Three-Phase VS PWM Inverter-Fed Motors

This paper presents an experimental testing of a wavelet packet transform (WPT)-based technique for protecting and controlling three-phase voltage-source (VS) pulse-width modulated (PWM) inverters under extreme load conditions. The proposed technique is based on a two-level multiresolution analysis (MRA) applied on output currents of a 3Phi VS PWM inverter. The MRA aims to extract certain signatures, which are the second level highest frequency subband coefficients. These coefficients take a nonzero value for any signal that is short-duration, nonperiodic and nonstationary with impulse-super imposed high frequencies. Such a signal perfectly matches a current arising from any typical fault occurring in either the inverter legs or on the load side. The proposed technique is realized using a -code hosted and executed by a dSPACE ds1102 controller board. The tested inverter supplies loads that include a 3Phi Y-connected R - L load, a 3Phi squirrel-cage induction motor and a 3Phi synchronous reluctance motor. The extreme load conditions include inverter open-leg, motor starting currents and different faults in motor stator windings. The experimental test results show accurate, fast, and effective response to all disturbances including fault currents by the proposed WPT-based technique.