Input-output stability degrees for undamped constant coefficients linear partial differential equations

It is an established fact that systems which have transfer matrices with poles converging to the imaginary axis cannot have exponentially stable time responses. Recently it was proved that for a class of partial differential equations with such a structure of poles it is possible to have a fast decay in time, uniformly in space, as arbitrary polynomials if the initial conditions are smooth enough and with an appropriate decay at infinity. The non-homogeneous version of this result which we present here can be summarized as follows: 'arbitrary regularity in space of the input function leads to arbitrary polynomial convergence in time towards the steady state'. The relation between the properties of the input function and the rate of convergence of the poles to the imaginary axis is quantitative and we indicate methods for computing this rate. We also provide conditions for exponential stability in this context. Due to some limitations in exponential stabilization by feedback a natural alternative to stability enhancement is this polynomial one. Therefore it is useful to investigate when it can be recovered in more practical situations (bounded space, boundary control, etc). Possible applications include the control of distributed oscillatory phenomena (e.g. in large flexible structures, plates), and more recently the control of some advanced materials.     

The Emergence of Clusters in the Global Telecommunications Network

Studies of international telecommunication networks in past years have found increases in density, centralization, and integration. More recent studies, however, have identified trends of decentralization and regionalization. The present research examines these structural changes in international telephone traffic among 110 countries between 1989 and 1999. It examines the competing theoretical models of core–periphery and cluster structures. The initial results show lowered centralization and inequality in the network of international telecommunications traffic. Statistical p * procedures demonstrate significant interactions within countries in blocks of similar economic development status, geographic region, and telecommunications infrastructure development status. Specifically, countries with less developed economic and telecommunications status showed significant increases in tendencies to connect to each other and to reciprocate ties. Altogether, the result supports the idea that the global telecommunications network is moving toward a more diversified structure with the emergence of cohesive and interconnected subgroups. The findings have implications for global digital divide and developmental gap issues.     

Catalytic wet peroxide oxidation of phenol over Fe-exchanged pillared beidellite

This study presents an evaluation of the catalytic performances of a Fe-exchanged Al-pillared synthetic beidellite for the wet hydrogen peroxide oxidation of phenolic aqueous wastes. The catalyst was prepared by a cation doping technique, its properties being determined by DRX, BET and chemical analysis techniques. All the tests were performed on a laboratory scale set-up.Important factors affecting catalyst activity and phenol removal efficiencies were studied, i.e. the effect of pH, temperature, catalyst concentration and the stability of the catalyst. The experimental results indicate that the use of this catalyst allows a total elimination of phenol and a significant removal of chemical oxygen demand, without significant leaching of Fe ions. Thus, considering the lowest Fe concentrations in solution after oxidation, at pH=5, 50 degrees C, and 180 min. COD removal efficiency of 87.9% was obtained. It was also observed that by using this catalyst, it is possible to extend the range of pH values for which Fenton-type oxidations can occur.     

2.5 V 35 dBm IIP3 75 MHz sixth-order active RC filter

A differential sixth-order Butterworth Sallen-Key lowpass filter in 0.25 mum SiGe BiCMOS, using a 2.5 V supply, is presented. The filter has a 75 MHz cutoff frequency and an attenuation of more than 20 dB at a stopband frequency of 148 MHz. The third-order intercept point (IIP3) is 35 dBm, providing excellent linearity.     

The relation between electrochemical tests and in vitro evaluation of titanium alloy biocompatibility

In this paper, the electrochemical behaviour of the titanium and Ti‐6Al‐7Nb alloy in artificial saliva (Tani&Zucchi and Carter–Brugirard), ion release tests and in vitro biocompatibility of human osteoblasts (HOB) were studied. Titanium and its implant Ti‐6Al‐7Nb alloy present self‐passivation and very stable passive films in Tani&Zucchi artificial saliva of pH = 2.5; 5; 6.7; 9; the total quantity of ions released in the artificial saliva and corrosion rates are very low, proving a very good corrosion resistance and very low toxicity. In undoped and doped Carter–Brugirard saliva, the open circuit potentials have highly electropositive values, denoting passive state and good stability; the open circuit potential gradients, simulating the non‐uniformity of the saliva composition, show very low values, no danger for the implant integrity. The in vitro cytotoxicity of Ti‐6Al‐7Nb alloy was evaluated on the basis of cell morphology and cell viability. The results obtained revealed a high biocompatibility between HOB and Ti‐6Al‐7Nb alloy.     

Porous indium oxide thin films deposited by electrostatic spray deposition technique

This paper presents the preparation process of porous indium oxide (In₂O₃) films using a novel deposition technique, i.e., electrostatic spray deposition (ESD). The films were deposited on platinum-coated alumina substrates using as precursor solution indium chloride in ethanol and acetic acid. The films were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and Raman spectroscopy. The nanocrystalline structure of the films was evidenced by TEM and also by XRD studies. The Raman spectroscopy and XRD measurements revealed the cubic phase of In₂O₃ films. Considering the obtained results, we conclude that the ESD technique is an efficient, cheap and successful method for the preparation of porous indium oxide films.     

Tungsten trioxide thin films prepared by electrostatic spray deposition technique

Tungsten trioxide (WO₃) thin films deposited on a Pt-coated alumina substrate using the electrostatic spray deposition (ESD) technique is reported in this paper. As precursor solution, tungsten (VI) ethoxide in ethanol was used. The morphology and the microstructure of the films were studied using scanning electron microscopy coupled with energy dispersive X-ray analysis, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Dense to porous morphologies were obtained by tuning the deposition temperature. Impedance spectroscopy and current-voltage measurements were used to study the electrical behaviour of the films in air, in temperature range 300-500 °C. The activation energy was estimated from Arrhenius plots. Considering the obtained results, the ESD technique proved to be an effective technique for the fabrication of porous tungsten trioxide thin films.     

Preparation and characterization of Ce-doped BaTiO3 thin films by r.f. sputtering

Ce-doped BaTiO₃ thin films prepared on silicon-platinium by r.f. sputtering has been investigated. BaTiO₃ doped with 5.5 mol%CeO₂ thin film was deposited at 550°C substrate temperature in an Ar atmosfere. The crystal structure and shape were examined by X-ray diffraction and scanning electron microscopy with EDAX. Analysis by X-ray diffraction patterns show that the crystalline film with a cubic structure of BaTiO₃, was obtained. The surface morphology (roughness, the grain size and the droplet size) of the thin film surface was examined by atomic force microscopy (AFM). The grain size is about 160 nm, the droplet size is about 0.675 m and the roughness is 36.88 nm. EDAX analysis established a composition of the film to be identical with that of the target (BaTiO₃ doped with 5.5 mol%CeO₂). The broad peak in the capacitance versus temperature curve at the Curie point indicate that the r.f. sputtered Ce-doped BaTiO₃ film is ferroelectric. The values of the capacitance of the thin film at 1 KHz were found to be 86 pF and the loss dielectric was tan = 0.0875. The film exibits a dielectric anomaly peak at 23°C showing ferroelectric to paraelectric phase transition.     

Analysis of thorium and its progeny by gamma ray spectrometry and alpha track methods

Samples originating from an EU sponsored intercomparison exercise were analysed by gamma ray spectrometry (a thorium solution sample, a zircon sand sample and a thorium ore sample). An alpha track method was also used to analyse the solution sample. The detection efficiency calibration for the gamma ray spectrometry measurements on the solid samples was established using an in-house standard of thorium nitrate. A GESPECOR Monte Carlo simulation program was utilised in the analysis of the solution sample. The in-house thorium nitrate standard was also used to prepare standards for the alpha track method. The relative differences between the 232Th activity concentration values determined in these intercomparison samples and values supplied by the NPL, UK, were found to be less than 5% when determined by the gamma ray spectrometry method and less than 8% when determined by the alpha track method.