Interactions of hydrophobic fractions of dissolved organic matter with Fe(3+) - and Cu(2+)-montmorillonite

Interactions of dissolved organic matter (DOM) with clays can significantly affect a variety of soil processes. We studied adsorption and fractionation of hydrophobic acid (HoA) and hydrophobic neutral (HoN) fractions of DOM on Cu(2+)- and Fe(3+)-montmorillonite. Adsorption of both samples was higher on Fe(3+)-montmorillonite than on Cu(2+)-montmorillonite. A pH increase of about one unit was recorded followed by HoA adsorption by Fe(3+)-montmorillonite. This suggested exchange of negatively charged DOM groups on surface hydroxyl groups of Fe(3+)-montmorillonite surfaces. Adsorption of HoA on Cu(2+)-montmorillonite and HoN on Fe(3+)- and Cu(2+)-montmorillonites was governed mainly by van der Waals interactions. Spectroscopic analyses showed a distinct HoA fractionation by molecular size and aromaticity only by Fe(3+)-montmorillonite. On the basis of the pH measurements (increase in pH following adsorption of acid components) and enhanced DOM fractionation by molecular size and aromaticity we suggest that DOM reacted with Fe(3+)-montmorillonite similar to goethite.     

Electronic Contact Deposition onto Organic Molecular Monolayers: Can We Detect Metal Penetration?

Using a semiconductor as the substrate to a molecular organic layer, penetration of metal contacts can be clearly identified by the study of electronic charge transport through the layer. A series of monolayers of saturated hydrocarbon molecules with varying lengths is assembled on Si or GaAs and the junctions resulting after further electronic contact is made by liquid Hg, indirect metal evaporation, and a “ready‐made” metal pad are measured. In contrast to tunneling characteristics, which are ambiguous regarding contact penetration, the semiconductor surface barrier is very sensitive to any direct contact with a metal. With the organic monolayer intact, a metal–insulator–semiconductor (MIS) structure results. If metal penetrated the monolayer, the junction behaves as a metal–semiconductor (MS) structure. By comparing a molecule‐free interface (MS junction) with a molecularly modified one (presumably MIS), possible metal penetration is identified. The major indicators are the semiconductor electronic transport barrier height, extracted from the junction transport characteristics, and the photovoltage. The approach does not require a series of different monolayers and data analysis is quite straightforward, helping to identify non‐invasive ways to make electronic contact to soft matter.     

FREP: Energy proportionality for disk storage using replication

Energy saving has become a crucial concern in datacenters as several reports predict that the anticipated energy costs over a three year period will exceed hardware acquisition. In particular, saving energy for storage is of major importance as storage devices (and cooling them off) may contribute over 25 percent of the total energy consumed in a datacenter. Recent work introduced the concept of energy proportionality and argued that it is a more relevant metric than just energy saving as it takes into account the tradeoff between energy consumption and performance. In this paper, we present a novel approach, called FREP (Fractional Replication for Energy Proportionality), for energy management in large datacenters. FREP includes a replication strategy and basic functions to enable flexible energy management. Specifically, our method provides performance guarantees by adaptively controlling the power states of a group of disks based on observed and predicted workloads. Our experiments using a set of real and synthetic traces show that FREP dramatically reduces energy requirements with a minimal response time penalty.     

Virus concentration using hollow fiber membranes—II

An asymmetric polysulphone hollow fiber membrane permeator was used to concentrate polio I virus from 5 and 50-L of deionized- and tap-water. The objective of the study was to evaluate the effect of several independent variables—membrane type and morphology, initial virus concentration, initial feed volume, feed water type and backwash recovery of virus—on process performance. Also, it was the purpose of this study to compare performance for the asymmetric polysulphone and semidense symmetric cellulose acetate hollow fiber membranes (Belfort, Rotem and Katzenelson, 1975). From the results presented here and from a general chemical and biological stability point of view, the polysulphone membranes were superior for virus concentration. The module tested here proved to be versatile and continuously reusable. Finally, in no case and under all conditions studied was polio I virus detected in the permeate.     

Fatigue and residual strength of composite laminates

The mechanics of fatigue failure of laminated composite materials are completely different from that of conventional materials. The mechanics of fatigue failure of conventional materials involve the initiation and propagation of a single crack, which causes the material to fail. Laminated composite material can arrest the propagating crack to within a single lamina, thus avoiding immediate failure. Only after accumulation of cracks the laminate fails. The fatigue life of the laminate is best described by S-N curves. A theory for residual strength is developed which is based on a cumulative damage theory. The theory predicts that the static strength of the laminate is maintained almost to the final failure by fatigue. Experimental results verify this phenomenon.     

Determining the load-time history of fibre composite materials by acoustic emission

Acoustic emission was monitored during the axial loading of unidirectional fibre composite tensile specimens. The material consisted of strong, brittle fibres (E glass) embedded in a viscoelastic matrix (epoxy). It was found that when the load was held constant the acoustic emission output continued, but at a decreasing rate with time at load. As the load level was increased, the acoustic emission output at load continued for a longer period. It is suggested that the acoustic emission under constant load is a result of fibre fracture which continues after loading ceases because of the viscoelastic nature of the matrix which allows stress redistribution with time. The experimental results from acoustic emission are compared with computer calculations for fibre fracture based on theoretical considerations. Good agreement is noted between the theoretical and experimental results.