A note on high-Q active networks

Levi's and Zeheb's approach for approximating a high-Q second-order section by n sections with lower Q's is compared with the optimal solution of this problem proposed by Khazanov. Tables relating the maximum error in the approximation to the values of n and the achievable Q-reduction (QR) are also given. They should prove useful to the designer. Finally, some comments on sensitivities are added.     

Power limits for secondary devices operating on TV white spaces

The use of TV white spaces as an alternative to overcome spectrum scarcity is a huge opportunity for new telecommunication systems and services. While being attractive for its desirable propagation characteristics, this part of the spectrum imposes a major difficulty from design and regulatory perspectives: how to optimize the use of spectrum and to ensure the protection of primary users, TV systems for example, at the same time. This paper discusses strategies to be adopted by geo-location database operators to calculate adaptive maximum permitted power levels for secondary devices, according to permissible levels of interference into the digital terrestrial television primary system.     

Pre-emptive versus non-pre-emptive real time scheduling in intelligent mobile robotics

Autonomous and semi-autonomous mobile robots have to perform a multiplicity of concurrent activities in order to carry out useful tasks in unstructured human-populated environments. Even if it is commonly accepted that a successful accomplishment of assigned tasks requires some sort of real time capability to quickly react and adapt to environmental changes, it is not clear which operating system support is best suited for the scheduling and synchronizing of concurrent activities with different timing requirements. This paper discusses this problem, comparing two different real time scheduling policies for autonomous robot applications: pre-emptive rate monotonic and non pre-emptive Earliest Deadline First (EDF). Experimental results are presented and evaluated.     

Photochemical grafting of acrylated azo dyes onto polymeric surfaces. VII. Kinetics and mechanism of dye-sensitized photoinitiation of some diacrylates

Photoinitiated grafting and graft polymerization of liquid mixtures, adsorbed onto polypropylene, polycaprolactam, and poly(ethylene terephthalate) films, containing one of four acryloxy-substituted aromatic diazenes and one of four diacrylate comonomers, in the presence of 1,2-diphenyl-2,2-dimethoxyethanone as photoinitiator, were investigated kinetically at 30 ± 2°C. Irradiation was carried out polychromatically, with impinging photoenergy from 2.1 × 10^?8 to 20.5 × 10^?8 einstein s^?1 cm^?2; in some of the runs the ultraviolet radiation was filtered. The ratio R between the molar concentration of photoinitiator and the sum of concentrations of dye and diacrylate varied between 0.005 and 0.095; the ratio M between the molar concentration of dye and diacrylate varied between 0.005 and 0.046. The moles of dye and diacrylate n initially deposited per unit apparent polymeric surface S varied between 2 and 74 μmol cm^?2. No selective effect was shown by the presence of dyes in the comonomer mixture. The surface density of grafted molecules at the end of the grafting process was not affected by the photoinitiator concentration (for 0.030 < R < 0.095), by diacrylate or dye concentrations, or by the kind of polymer substrate. This parameter, on the contrary, clearly depended on n/S, and linearly up to n/S ? 30 μmol cm^?2. Quantum efficiencies for the two consecutive kinetic processes of grafting and graft polymerization (Φ₁ and Φ₂, respectively) were evaluated. The dependency of Φ₁ on R, as well as of Φ₂ on n/S, are critically discussed on the basis of the proposed mechanism involving grafting of an oligomeric chain (Φ₁ values up to the order of 10²) followed by a step-by-step graft polymerization (Φ₂ limiting values of the order of unity). The sensitizing effect of acryloxy-substituted aromatic diazenes on both Φ₁ and Φ₂ is evidenced.     

Integral transform solution for hyperbolic heat conduction in a finite slab

An analytical integral transformation of the thermal wave propagation problem in a finite slab is obtained through the generalized integral transform technique (GITT). The use of the GITT approach in the analysis of the hyperbolic heat conduction equation leads to a coupled system of second order ordinary differential equations in the time variable. The resulting transformed ODE system is then numerically solved by Gear's method for stiff initial value problems. Numerical results are presented for the local and average temperatures with different Biot numbers and dimensionless thermal relaxation times, permitting a critical evaluation of the technique performance. A comparison is also performed with previously reported results in the literature for special cases and with those produced through the application of the Laplace transform method (LTM), and the finite volume-Gear method (FVGM).     

Coupled Environmental-Mechanical Damage Model of RC Structures

The evaluation of strength reduction of RC structures subjected to mechanical damage process and chemical attack is carried out, with regard to concrete deterioration and steel corrosion. A coupled environmental-mechanical damage model, developed as an extension of that previously published is presented. Two independent scalar mechanical damage parameters are introduced, each of them representing the degradation mechanisms occurring under tensile and compressive stress conditions. The stiffness recovery upon loading reversal, which is manifest when passing from tension into compression, is fully captured by the proposed model. The environmental damage is strongly related to the diffusion process, as well as to the evolution of the chemical reaction between pollutant and cementitious constituents. An enhanced local method is proposed to regularize the problem of nonobjectivity of the finite-element solution due to the strong strain softening behavior of concrete material. The splitting test of a concrete specimen and a static analysis of an RC frame subjected to mechanical loads and chemical attacks are carried out, and the damage evolution is analyzed in detail.     

Development of a Four-Channel Potentiostat for Amperometric Detection in Flow Injection Analysis

Abstract

A four-channel multipotentiostat has been developed for simultaneous voltammetric measurements with microelectrode arrays. To reduce the complexity of electrochemical cell, only one reference and one auxiliary electrode are used. The potential ranges of the four working electrodes may be independently controlled, but they are synchronously scanned by only one DAC. This is accomplished through a microcomputer interfaced with a PCL-711B data acquisition board, which allows the continuous monitoring of the currents and actual potentials of the working electrodes.

The system has been applied to the simultaneous determination of ascorbic and uric acids in synthetic samples. The measurements were carried out with gold microelectrodes modified by deposition of noble metals, which enhance the electrocatalysis and provide an anticipation and a better definition of the oxidation potentials. Recuperation of 98.2% and 97.8% for ascorbic and uric acids, respectively, was obtained by using amperometry.     

Time Resolved Infrared Spectroscopic Analysis of Aerosol Formed by Photo-Oxidation of 1,3,5-Trimethylbenzene and α-Pinene

Secondary organic aerosol generated from the photo-oxidation of 1,3,5-trimethylbenzene and α-pinene in a smog chamber was investigated. Fourier Transform Infrared Spectroscopy (FT-IR) was used to monitor the time dependent change of five different functional groups in the aerosol (carboxylic acids, alcohols, organonitrates, ketones/aldehydes═carbonyls, and aliphatic carbon) sampled with an impactor on zinc-selenide discs. Based on model compounds for oxidation products of 1,3,5-trimethylbenzene and α-pinene, calibration factors for the different functional groups were calculated, and relative molar fractions of the functional groups were estimated from the analysis of the FT-IR spectra of the smog chamber samples. We show chemical evolutions of secondary organic aerosol on a time scale of up to 20 h. Time series with up to eight measurements per experiment show a strong increase in the relative amounts of carboxylic acid groups and a moderate increase of alcohol and carbonyl groups, whereas the relative amounts of organonitrates and the aliphatic carbon decrease. These findings support the assumption that the chemical composition of the aerosol continues to change for a long time after the particle formation has considerably slowed down. According to these observed changes with time, average, sum formulas of the molecules in the secondary organic aerosol are suggested.