An alternative method for controlling two-output DC-to-DCconverters using saturable core inductor

The method proposed in this paper is an alternative to the use of a conventional magnetic amplifier in the control of a second output in buck derived DC-to-DC power converters. This method avoids the use of linear devices in the magnetic amplifier and improves the power converter dynamic response. It is very simple and it is based on the use of a saturable core and in the double switching frequency and duty cycle modulation in the power transistor     

Synopses of some recent published studies of the design process and designer behaviour

This series of synopses first appeared as Appendix II in ‘Design decision making and recommendations for design aids’ a report commissioned by the British Building Research Establishment. It was felt that this special issue on Designing for Behaviour provided a unique opportunity to republish these extremely relevant summaries to reach a wider audience of interested and involved parties. These synopses might also reveal to environmental design human behaviour researchers some of the problems that designers have in incorporating findings in their design processes and may perhaps suggest ways in which research publications might overcome these barriers to the transfer of information.     

Deckschichtbildung auf verschiedenen Stahlarten unter den Bedingungen des Hochdruck-Wasser-Dampfkreislaufes in Kraftwerken

Scale formation on different types of steel under the conditions of high pressure water/steam circulation in power stations The protective layer formed on steel in hot water and steam has predominantly spinel structure and consists of two strata. One of them is below the original steel surface and is formed by topotactic growth, while the other is above the original metal surface and is formed by epitactic growth. Their composition depends from the diffusivity of the heavy metal ions present. The mobility of the individual ions is different and is considerably higher in ferritic than in austenitic steels. The epitactic layer is more porous and less resistant than the topotactic layer. The topography of the spinel surface plays an important role with respect to flow resistance; crater type pits may be formed in the surface according to a mechanism yet unknown.     

Steering molecular organization and host-guest interactions using two-dimensional nanoporous coordination systems

Metal-organic coordination networks (MOCNs) have attracted wide interest because they provide a novel route towards porous materials that may find applications in molecular recognition, catalysis, gas storage and separation. The so-called rational design principle-synthesis of materials with predictable structures and properties-has been explored using appropriate organic molecular linkers connecting to metal nodes to control pore size and functionality of open coordination networks. Here we demonstrate the fabrication of surface-supported MOCNs comprising tailored pore sizes and chemical functionality by the modular assembly of polytopic organic carboxylate linker molecules and iron atoms on a Cu(100) surface under ultra-high-vacuum conditions. These arrays provide versatile templates for the handling and organization of functional species at the nanoscale, as is demonstrated by their use to accommodate C(60) guest molecules. Temperature-controlled studies reveal, at the single-molecule level, how pore size and chemical functionality determine the host-guest interactions.     

Microcontact printing of DNA molecules

The controlled placement of DNA molecules onto solid surfaces is the first step in the fabrication of DNA arrays. The sequential deposition of tiny drops containing the probe DNA fragments using arrays of spotting needles or ink jet nozzles has become a standard. However, a caveat of liquid spotting is the drying of the deposited drop because this creates the typical inhomogeneities, i.e., rims around the spot. Another drawback is that each DNA array is an original and has to be fabricated individually. Microcontact printing is a versatile technique to place proteins onto different target surfaces in uniformly patterned monolayers with high lateral resolution. Here, we show for the first time that DNA can also be printed with equally high resolution in the submicrometer range using an elastomeric stamp with chemically tailored surface. Two regimes for the transfer of the molecules were observed. Finally, microcontact printing of an array of DNA probes onto a solid support and its use in a subsequent hybridization assay was demonstrated.     

Gas-liquid equilibria in mixtures of hydrogen and thianaphthene

Gas-liquid equilibrium conditions in binary mixtures of hydrogen and thianaphthene were experimentally determined at temperatures of 190 to 430°C and pressures to 250 atm in a flow apparatus. The same apparatus was also employed to measure the vapor pressure of thianaphthene. Comparisons of the new mixture data with Chao-Seader and Grayson-Streed correlations show that both correlations predict the thianaphthene equilibrium ratios well but are in error by up to about 45 and 35% respectively for K-values of hydrogen.     

Molecular weight characteristics of humic substances from different environments as determined by size exclusion chromatography and their statistical evaluation

Recorded molecular weights (MWs) for humic substances (HS) range from a few hundred to millions of daltons. For purposes of defining HS as a specific class of chemical compounds, it is of particular importance to ascertain if this broad range of MWs can be attributed to actual variability in molecular properties or is simply an artifact of the analytical techniques used to characterize HS. The main objectives of this study were (1)to establish if a preferential range of MWs exists for HS and (2) to determine any consistent MW properties of HS. To reach the goal, we have undertaken an approach to measure under standardized conditions the MW characteristics of a large set of HS from different natural environments. Seventy-seven humic materials were isolated from freshwater, soil, peat, and coal, such that each possessed a different fractional composition: humic acid (HA), fulvic acid (FA), and a nonfractionated mixture of HA and FA (HF). Size exclusion chromatography (SEC) was used as the analytical technique to determine molecular weight characteristics. The MW distributions were characterized by number (Mn) and weight (Mw) average MW, and by polydispersity. The complete range of Mw values varied within 4.7-30.4 kDa. The maximum Mw values were observed for peat HF and soil HA, whereas the smallest weights were measured for river water HF. Maximum values of polydispersity (3.5-4.4) were seen for peat HF and soil HA, while much lower values (1.6-3.1) were found for all preparations isolated with XAD-resins. Statistical evaluation showed consistent Mw and Mn variations with the HS source, while polydispersity was mostly a function of the isolation procedure used. A conclusion was made that HS have a preferential range of MW values that could characterize them as a specific class of chemical compounds.