Contact wetting angle as a characterization technique for processing CdTe/CdS solar cells

The feasibility of measuring contact wetting angles to characterize processing induced changes to thin film semiconductors in CdTe/CdS solar cells is evaluated. The contact angles of water and formamide are used to determine the polar and dispersive surface energies of the thin films using two analysis methods. Changes in surface energies resulting from processing are correlated to changes in surface chemistry and structure detected by glancing incidence X‐ray diffraction (GIXRD), X‐ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Surface energies are evaluated for sputtered In₂O₃:SnO₂, chemical surface‐deposited CdS, and physical vapor‐deposited (PVD) CdTe thin films under as‐deposited and treated conditions. Treatments include thermal anneal in air, argon, and CdCl₂ ambient as well as surface etching. Indium tin oxide (ITO) and CdS films exhibit increased polar surface energy corresponding to enhanced crystallization of surfaces resulting from processing and increasing CdS growth temperature. Native oxidation of PVD CdTe (111)‐oriented film surfaces occurs rapidly and is readily detected by changes in contact angle. Surface energies of PVD (111)‐oriented CdTe stored under various humidities prior to processing are energetically similar due to native oxidation. The polar energy of CdTe surfaces is affected by the addition or removal of crystalline surface oxides during film processing. Copyright © 2006 John Wiley & Sons, Ltd.     

Voltammetric studies of titanium (IV) phosphate modified with copper hexacyanoferrate and electroanalytical determination of <Emphasis Type="Italic">N</Emphasis>-acetylcysteine

Titanium (IV) Phosphate copper hexacyanoferrate composite (TiPhCuHCF) was prepared using a new methodology for the synthesis. A preliminary characterization of the precursor and resulting materials was defined using spectroscopic and chemical techniques. The cyclic voltammogram of the modified electrode containing TiPhCuHCF exhibited two redox couples. The first and second redox couples present a formal potential (E ^θ′) of 0.18 and 0.76 V and were ascribed to the Cu^+/Cu²⁺ (E ^θ′)₁ and Fe²⁺(CN)₆/Fe³⁺(CN)₆ (E ^θ′)₂ processes, respectively. In a preliminary study, the peak located at 0.76 V displays a sensitive response to N-acetylcysteine. The modified graphite paste electrode showed a linear range from 1.0 × 10⁻⁵ to 7.0 × 10⁻⁴ mol L⁻¹ for the determination of N-acetylcysteine with a limit detection of 6.96 × 10⁻⁵ mol L⁻¹ and relative standard deviation of ± 5% (n = 3) and amperometric sensitivity of 24.79 × 10⁻³ A mol L⁻¹. The modified electrode was electrochemically stable and showed good reproducibility.     

Exploiting a new electrochemical sensor for biofilm monitoring and water treatment optimization

Bacterial biofilm development is a serious problem in many fields, and the existing biofilm monitoring sensors often turn out to be inadequate. In this perspective, a new sensor (ALVIM) has been developed, exploiting the natural marine and freshwater biofilms electrochemical activity, proportional to surface covering. The results presented in this work, obtained testing the ALVIM system both in laboratory and in an industrial environment, show that the sensor gives a fast and accurate response to biofilm growth, and that this response can be used to optimize cleaning treatments inside pipelines. Compared to the existing biofilm sensors, the proposed system show significant technological innovations, higher sensitivity and precision.     

Defects and strains at magnetic and semiconductor interfaces

Defects and strains at surfaces and interfaces are examined with respect to how they can be measured and how they affect resulting magnetic, electronic or mechanical properties. Emphasis is on MnZn ferrite, GaAs and PbS with deformation being examined by selected area channeling pattern (SACP), transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) techniques. Damage produced during preparation of magnetic surfaces is examined by broadening of lines in SACP patterns while epitaxial strains and their relaxations by dislocations are estimated using both line shifts of SACP patterns and direct imaging by TEM. Of particular importance is that a new SACP method with accuracy approaching 0.1 percent has been developed for non-destructive examination of epitaxial strains in InGaAs/GaAs. Also, for the first time microcrack features in a low band gap semiconductor have been examined with STM.     

A statistical estimation method for segmentation of sonar range data

In this paper, we describe how to deal with an important sensorial activity that ultrasonic echo-locating systems for mobile robot navigation have often to perform, namely the extraction of straight line segments from range data and the accurate localization of the corresponding planar targets. It is commonplace that range data segmentation starts with using least squares interpolation algorithms for obtaining straight line segments: it is our goal to prove that caution must be called for in order to avoid somewhat misleading results. The case study concerns the use of a linear array formed by three ultrasonic transducers in a 2D specular environment composed of line and point acoustic targets.The segmentation algorithm we propose is subdivided into two functionally distinct modules, namely identification and localization. The identification module is based on a sequential hypothesis testing between alternative hypotheses that explain the sonar range data as originated from line or point targets. With regard to the localization module, we demonstrate that widely used approaches to sensor modeling are, to some extent, deceptively simple: the estimation accuracy for the localization of planar objects may be decreased by the inability of some traditional sonar sensor models to take properly into account the specularity of reflections. A physically based model of acoustic range sensors acting in specular environments allows us to design a localization module which is capable of producing accurate and unbiased estimates of the parameters of a planar geometric feature.The proposed theoretical framework is validated by the results of some experiments carried out with a spatial locating system consisting of a rotating linear array of three ultrasonic transducers.     

Symmetry and reversibility in materials with hidden variables

Consequences of microscopic reversibility on the constitutive equations of materials with hidden variables are deduced by taking the view that the expectation value of the fluctuations is determined through the macroscopic behaviour of the body. As a result it is shown that reciprocity relations hold for after effect matrices connecting variables which are conjugate at equilibrium. In particular, the usual relaxation function of the linearised isothermal theory of viscoelasticity is found to be symmetric.     

A comparison of egotism, negativity, and learned helplessness as explanations for poor performance after unsolvable problems.

After people work on unsolvable problems, they often perform poorly on a subsequent task. Egotism explains this decrement as the result of a strategy of low effort designed to blunt an attribution of poor ability should failure occur on the new task. The egotism explanation predicts that adding an element alleged to inhibit performance allows Ss to try without fear of an attribution of low ability. In contrast, learned helplessness predicts that adding an allegedly inhibitory element should lower the expectancy of control, making performance worse than usual. A 3rd explanation is "negativity." Like egotism, it predicts improved performance if an element said to inhibit performance is introduced, but for a different reason: to produce results opposite to the experimenter's suggestion. Unlike egotism, the negativity hypothesis predicts that adding an allegedly facilitating element will worsen performance. 50 college students were given either solvable or unsolvable concept formation problems and then worked on anagrams with or without music said to be distracting. In addition, there was a 5th condition in which Ss were given unsolvable problems followed by music said to facilitate performance. The performance decrement occurred only in the no-music condition, supporting the egotism explanation. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analyses of operational transients in the TRADE experimental program

The TRiga Accelerator Driven Experiment (TRADE) consisted of the coupling of an external proton accelerator to a target in a subcritical core configuration of the TRIGA reactor at the ENEA Casaccia Research Center. In the frame of the safety-related evaluations of the TRIGA reactor a large number of experimental transients induced by reactivity insertions were performed in a critical configuration. Power and fuel temperature experimental transients were analysed by several tools and calculated results showed a reasonable agreement with experiments. Meaningful discrepancies in the simulated temperature trends were found systematically in the 300–600 kW power range. In the paper experimental results in this power range are reported and analysed by means of the TIESTE-MINOSSE code. Investigations lead to suppose the existence of the clad superheating phenomenon at the boiling onset (i.e. boiling delay). On the basis of the studies performed in the past about this subject, the code was improved to take into account this phenomenon. The new simulation results showed a reasonable agreement with the experimental fuel temperature. Results also clearly indicate the local origin of this phenomenon.     

Effect of minor constituents and additives upon peroxidation of oil in peanut butter

Metalloproteins and ionic iron and copper salts are major catalysts of fatty acid peroxidation, but chelating agents, such as ethylenediaminetetraacetic acid and citric acid in water, can retard or reduce this catalytic effect. To extend shelf-life and retain the high quality of peanut butter, methods to prevent or decrease the catalytic effect of these metalloproteins and salts were conducted. Chelating agents suspended in inert solvents (mineral oil) were not as effective as when they were added in water. Depending upon the concentration, water can act as a prooxidant or an antioxidant in peanut butter.     

Energy savings from solid urban waste disposal systems in Italy

The economical recovery of solid urban waste has been made more urgent by the growing scarcity of energy and raw materials resources. Some of the systems used to dispose of urban waste allow, directly or indirectly, the recovery of energy. We examine these technologies with reference to Italy.