Systematic approach to the synthesis of continuous-time cascaded sigma–delta modulators

This paper deals with a systematic approach to the synthesis of continuous-time cascaded sigma–delta modulators. Based on a system-theoretical model, a detailed derivation of the digital cancelation filters for continuous-time cascaded architectures is presented in order to achieve maximum signal-to-noise ratio together with optimal anti-aliasing performance. By using the same model, an exact equation for the performance loss of any cascaded architecture is derived. The latter is due to the scaling for stability and given relative to an ideal high-pass filter of the overall modulator order. Finally, an analytical calculation of optimal scaling coefficients in between the stages is performed, resulting in a limited search-space for these coefficients. Theoretical results are verified by simulations.     

MEtreePOLIS 1901-2111

As the natural world continues to change, it is clear that people would rather employ technology to adapt to shifting circumstances rather than alter their lifestyles to suit nature's demands. MEtreePolis is a timeline of crucial historical developments that explores the dichotomy of nature and technology. Commencing in 1901, it shoots past the present and into the future, closing in 2111. By providing an imaginative vision of tomorrow, Matthias Hollwich and Marc Kushner provide an entertaining argument for human manipulation of the environment, suggesting that it will inadvertently trigger ‘ecological salvation’ and ‘social utopia’. Copyright © 2010 John Wiley & Sons, Ltd.     

High quality extrudates from aluminum chips by new billet compaction and deformation routes

The effects of different billet preparation techniques as well as selection of various deformation routes and their influence on the final mechanical properties in chip extrusion was studied. The AA6060 chips were compacted into billets using various techniques and then extruded through the flat-face, porthole and ECAP dies to create different deformation routes. The microstructures and the mechanical properties of the chip extruded profiles were compared to cast billets extruded through the flat-face die under the same conditions. The proposed technology shows very promising results in terms of energy savings and production of the high quality engineered aluminum profiles.     

Effect of residual stress on the bending of aluminium

Skin passing or temper rolling introduces a strain gradient through the thickness of the sheet which, in turn, results in a residual stress profile through the thickness. These residual stresses can have a major effect on the elastic-plastic transition in bending operations, but the effect of residual stresses on downstream forming has yet to be determined.In this work, a commercial aluminium alloy, AA6063, was reduced in thickness by rolling in a laboratory mill to introduce residual stresses into the material. The strips were then tested in tension and pure bending and the material behaviour close to the elastic-plastic transition investigated. Substantial lowering of the elastic-plastic transition in the bending moment was observed while the opposite trend was found in the tensile test. The rolling process was analyzed using finite element analysis and the distribution of residual stresses determined; theoretical moment curvature characteristics were obtained using the output of this analysis as the input to the modelling for pure bending. The results show qualitatively how the material is softened in bending after rolling and demonstrate that this is partly due to the residual stress gradients in the material.     

Leistungsfähige Spiegel für solarthermische Kraftwerke

High efficient mirrors for Concentrating Solar Power plants Mirrors are an essential component of CSP plants. Wet chemically coated silver mirrors supplied by Flabeg GmbH achieve an average specular and solar weighted reflectivity of 94.4%. Almost 30 years of field experience prove the durability of the coating. First surface mirrors could provide higher reflectivity, but so far either the necessary durability is not met or the costs are not competitive. Another approach to increase reflectivity is to equip the mirror with an antisoiling coating. This type of mirror is currently under field testing, showing already promising results. New paint systems for silvered mirrors will expand the locations for power plants to the shore or into tropical regions.     

Quenched solid density functional theory and pore size analysis of micro-mesoporous carbons

We present a new model of adsorption on micro-mesoporous carbons based on the quenched solid density functional theory (QSDFT). QSDFT quantitatively accounts for the surface geometrical inhomogeneity in terms of the roughness parameter. We developed the QSDFT models for pore size distribution calculations in the range of pore widths from 0.4 to 35 nm from nitrogen at 77.4 K and argon at 87.3 K adsorption isotherms. The QSDFT model improves significantly the method of adsorption porosimetry: the pore size distribution (PSD) functions do not possess gaps in the regions of ∼1 nm and ∼2 nm, which are typical artifacts of the standard non-local density functional theory (NLDFT) model that treats the pore walls as homogeneous graphite-like plane surfaces. The advantages of the QSDFT method are demonstrated on various carbons, including activated carbons fibers, coal based granular carbon, water purification adsorbents, and mirco-mesoporous carbon CMK-1 templated on MCM-48 silica. The results of PSD calculations from nitrogen and argon are consistent, however, argon adsorption provides a better resolution of micropore sizes at low vapor pressures than nitrogen adsorption.     

The Structural Diversity of Acidic Lipopeptide Antibiotics

Resisting resistance : Acidic lipopeptide antibiotics are very effective in fighting multidrug‐resistant Gram‐positive bacteria, including methicillin‐resistant Staphylococcus aureus and vancomycin‐resistant enterococci. The structural diversity of these lipopeptides, including daptomycin, which is already in clinical use, is depicted in this review. Engineering approaches to yield novel lipopeptides and tailoring events facilitating structural variety are presented.

     

Two Base Pair Duplexes Suffice to Build a Novel Material

Tetrahedral DNA hybrids with tetrakis(p‐hydroxyphenyl)methane cores hybridize in a sequence‐specific fashion at much higher temperatures than isolated linear duplexes. Dinucleotide DNA arms suffice to induce the formation of a solid at room temperature; this demonstrates the strength of multivalent binding. The graphic shows a view of a modeled assembly.