Alkyl chain modified sulfonated poly(ether sulfone) for fuel cell applications

A new alkyl chain modified sulfonated poly(ether sulfone) (mPES) was synthesized and formed into membranes. The MEAs were tested in the PEMFC and evaluated systematically in the DMFC by varying the methanol concentration from 0.5 to 5.0 M at 60 °C and 70 °C. The synthesized mPES copolymer has been characterized by nuclear magnetic resonance spectroscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. The proton conductivity of the resulting membrane is higher than the threshold value of 10⁻² S cm⁻¹ at room temperature for practical PEM fuel cells. The membrane is insoluble in boiling water, thermally stable until 250 °C and shows low methanol permeability. In the H₂/air PEMFC at 70 °C, a current density of 600 mA cm⁻² leads to a potential of 637 mV and 658 mV for 50 μm thick mPES 60 and Nafion NRE 212, respectively. In the DMFC, mPES 60's methanol crossover current density is 4 times lower than that for Nafion NRE 212, leading to higher OCV values and peak power densities. Among all investigated conditions and materials, the highest peak power density of 120 mW cm⁻² was obtained with an mPES 60 based MEA at 70 °C and a methanol feed of 2 M.     

Influence of thermal ageing on the stability of polymer bulk heterojunction solar cells

A new approach is presented in order to improve the thermal stability of polymer: [6-6]-phenyl C₆₁ butyric acid methyl ester (PCBM) bulk heterojunction solar cells. The central idea in this approach is the use of a polymer with high glass transition temperature (T_g), well above the normal operating temperatures of the devices. In this paper, a PPV-derivative with a T_g of 150 °C was used as an electron donor and the thermal stability of the obtained solar cells was compared with solar cells based on the reference material poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) with a T_g of 45 °C. The use of the material with higher glass transition temperature resulted in a significant improvement of the thermal stability of the photovoltaic parameters. Furthermore, a systematic transmission electron microscope (TEM) study demonstrates that the better thermal stability of performance coincides with a more stable active layer morphology. Both improvements are attributed to the reduced free movement of the electron donor material (PCBM) within the active layer of the solar cell.     

A Comparison of Organically and Conventionally Grown Foods—Results of a Review of the Relevant Literature

This review is concerned with the summary and evaluation of the results from more than 150 investigations comparing the quality of conventionally and organically produced food or of foods produced with the aid of different fertilisation systems. Cereals, potatoes, vegetables, fruits, wine, beer, bread, cakes and pastries, milk, meat, eggs and honey, as well as products made from them, have been included in the review. Most of the studies evaluated are physico-chemical investigations of concentrations of desirable and undesirable ingredients, pesticide residues, contaminants, sensory analyses and feed experiments with animals. Nutritional studies in humans and experiments which used holistic methods of analysis are also included. Since different methods of sampling were used in the investigations, a summary evaluation of individual results is extremely difficult. Even when the sampling methods are of the same type, a great many factors have to be taken into consideration which are not directly related to the production system but which do influence food quality to a large degree. Despite the heterogeneity of the sample material, some differences in quality between products from conventional and organic farming or foods produced with the aid of different fertilisation systems have been identified. © 1997 SCI     

Relation between perceived and measured workload obtained by long-term inclinometry among dentists

Dentists reported high perceived physical work conditions. Working postures and movements of the head and upper extremities during dental work were registered with inclinometry measurements during four hours. The aim was to clarify the relationship between measured working postures/movements and perceived physical work conditions. Dentists worked with elevated arms and a rather steep forward inclination of the head. Correlations (r = −0.52 to -0.66) between inclination velocity and perceived workload on VAS scales were found, but there were only weak correlations between observed working postures. The different tasks involved in dental work provide limited variation in work movements and postures, measured by inclinometry. By alternating between sitting and standing, it might be possible to achieve variation in physical workload during dental work.     

Die Vorratsdatenspeicherung aus datenschutzrechtlicher Sicht

Mit dem „Gesetz zur Neuregelung der Telekommunikationsüberwachung und anderer verdeckter Ermittlungsma?nahmen sowie zur Umsetzung der Richtlinie 2006/24/EG“ wurde zum 1.1.2008 die Vorratsdatenspeicherung von Telekommunikationsverbindungsdaten eingeführt. Gegen diese gesetzliche Regelung führt der vorliegende Beitrag nicht nur erhebliche verfassungsrechtliche Bedenken, sondern auch Vorbehalte gegen bestehende Regelungsdefizite ins Feld.     

Passwörter — fünf Mythen und fünf Versäumnisse

Bis heute wird der Zugriff auf Daten und Anwendungen überwiegend durch einen Passwortschutz kontrolliert. Oft ist dieser Passwortschutz jedoch unzureichend, weil sich für die Gestaltung von und den Umgang mit Passworten hartn?ckig unrichtige überzeugungen halten und die falschen Priorit?ten gesetzt werden.     

Organized Nanostructured Complexes of Polyoxometalates and Surfactants that Exhibit Photoluminescence and Electrochromism

A variety of functional nanostructured organic/inorganic hybrid materials from the europium‐exchanged derivative of a Preyssler‐type polyoxometalate (POM), [EuP₅W₃₀O₁₁₀]^12?, and functional organic surfactants were prepared by the ionic self‐assembly (ISA) route. The effect of organic surfactants on the structure, photoluminescent, electrochemical and electrochromic properties of the POM anions was investigated in detail. All obtained hybrid materials are amphotropic, i.e., exhibit both thermotropic and lyotropic liquid‐crystalline phase behaviour. Investigations of their photophysical properties have shown that the interactions of the various surfactants with the polyanions influence the coordination environments and site symmetry of Eu³⁺ in different ways. The functional groups in the organic surfactants significantly influence the electrochromic properties and photoluminescence of POMs. Different from normal and pyridine‐containing complexes, no photoluminescence and no electrochromism were observed from the ferrocene‐containing complexes. This may be explained in view of charge transfer between the POM anion and the ferrocenyl group.