Step-Scan T-Cell Fourier Transform Infrared Photoacoustic Spectroscopy (FTIR-PAS) for Monitoring Environmental Air Pollutants

Air pollutants have adverse effects on the Earth’s climate system. There is an urgent need for cost-effective devices capable of recognizing and detecting various ambient pollutants. An FTIR photoacoustic spectroscopy (FTIR-PAS) method based on a commercial FTIR spectrometer developed for air contamination monitoring will be presented. A resonant T-cell was determined to be the most appropriate resonator in view of the low-frequency requirement and space limitations in the sample compartment. Step-scan FTIR-PAS theory for regular cylinder resonator has been described as a reference for prediction of T-cell vibration principles. Both simulated amplitude and phase responses of the T-cell show good agreement with measurement data Carbon dioxide IR absorption spectra were used to demonstrate the capacity of the FTIR-PAS method to detect ambient pollutants. The theoretical detection limit for carbon dioxide was found to be 4 ppmv. A linear response to carbon dioxide concentration was found in the range from 2500 ppmv to 5000 ppmv. The results indicate that it is possible to use step-scan FTIR-PAS with a T-cell as a quantitative method for analysis of ambient contaminants.     

Imaging of Polarons in Ferromagnetic Bilayered Manganites by Scanning Tunnelling Microscopy

We report scanning tunnelling microscopy images of polaronic charge ordered patch on the layered ferromagnet La_2−2x Sr_1+2x Mn₂O₇, x=0.32. The spectroscopic investigation shows that the material is gapped above and below the critical temperature, where the gap changes from 500 to 800 mV, giving evidence for polaronic transport behaviour. This work has been supported by European Project No. 517039 CoMePhS (Controlling Mesoscopic Phase Separation).     

Vibrations of Layered Beams under Conditions of Damaging and Slipping Interfaces

A nonlinear laminate layerwise beam theory is developed to simulate the effect of inelastic interlayer slip on the stiffness degradation of layered beam structures. Layerwise continuous and linear in-plane displacement fields are implemented. It is shown that by definition of an effective cross-sectional rotation the complex problem reduces to the simpler case of a homogenized shear-deformable beam with effective stiffness and a corresponding set of boundary conditions. Inelastic defects of the interlayer material are equivalent to eigenstrains in an identical but unlimited elastic background structure of the homogenized beam with proper effective virgin stiffness. Cross-sectional resultants of these eigenstrains are defined. Since the incremental response of the background to the given load and to the properly imposed eigenstrain increments is considered to be linear within a given time step, effective solution methods of the linear theory of flexural vibrations become applicable. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrocarbons as refrigerants in small heat pump and refrigeration systems – A review

Due to the concern for the effects of the release of HFC refrigerants on the global environment caused by the high global warming potential of these substances, there is a large interest in Europe and elsewhere for the use of hydrocarbons as refrigerants. This article presents a comparison of the properties and performance of hydrocarbons as refrigerants in small-size heat pump and refrigeration systems (<20 kW cooling). A listing of several commercially available systems is also presented. The designs, safety precautions and performances of some of these systems are described.As a general conclusion, it is shown that using hydrocarbons will result in COPs equal to, or higher than, those of similar HFC systems. It is also shown that components suitable for hydrocarbon systems are available on the market, even though the number of large-size hermetic compressors is limited. A major concern, which should not be taken lightly, is the safety issue. Reduced charge through indirect systems and compact heat exchangers, outdoor placing of the unit, hydrocarbon sensors and alarms and forced ventilation are all steps which may be applied to reduce the risks under normal operation.     

eIDs und Identitätsmanagement

Zusammenfassung  Mit der Einführung des elektronischen Personalausweises steht in Deutschland eine eID-L?sung mit potentiell sehr weiter Verbreitung vor der Tür. Der Beitrag diskutiert, wie solche L?sungen im Identit?tsmanagement eingesetzt und wie sie in Zukunft verbessert werden k?nnen. Dr. Christoph Sorge Research Scientist, NEC Laboratories Europe, Heidelberg. T?tigkeitsschwerpunkt: Forschung im Bereich der Netzsicherheit, u.a. Identit?tsmanagement Dr. Dirk Westhoff Chief Researcher, NEC Laboratories Europe, Heidelberg. T?tigkeitsschwerpunkt: Forschung in den Bereichen mobile drahtlose Sicherheit, Identit?tsmanagement