Treatment of Humic Waters By Ozone

Two different generators for ozone were tested, a traditional electrical discharge generator and a generator based upon UV–irradiation of air at 150–180 nm. It was demonstrated that the traditional generator gave slightly higher reductions in levels of color for equivalent ozone dosages. Both gases affected the molecular weight distribution in the way that the bigger molecules were broken down to smaller ones. No significant difference between the molecular weight reduction efficiency of the gases was found.     

The effect of backbone fluorination on the carrier mobility in alkoxy and alkyl substituted conducting polymers of the poly(phenylenevinylene) type

Summary We report the synthesis of some new backbone fluorinated polymers of the poly(phenylenevinylene) type. The new polymers were characterised by NMR, SEC and X-ray powder diffraction. The charge carrier mobilities were determined using pulse radiolysis time resolved microwave conductivity (PR-TRMC) and the carrier mobilities were compared to the similar non-fluorinated analogues. The changes in charge carrier mobilities as a function of molecular substitution pattern is discussed in terms of other materials properties such as electronic structure and absorption properties. The major result is that it was found possible for this type of material to alter the electronic energy levels by molecular substitution without imparting significant changes in the magnitude of the charge carrier mobilities and the optical properties.     

Preparation of flat-polished specimens for SEM-backscattered electron imaging and X-ray microanalysis—importance of epoxy impregnation

Representative and quantitative microstructural information of cement-based materials can be obtained in the backscattered electron and X-ray modes of the scanning electron microscope (SEM). One prerequisite, of several, is to use flat specimens. Microstructures that are minimally affected by the grinding and polishing necessary to produce the flat surface can be obtained. It is essential to fill the pores of the specimen with epoxy resin prior to grinding and polishing. After hardening, the epoxy stabilizes the microstructure and enables it to withstand the stresses of grinding and polishing without alteration. In the present paper, we describe a preparation technique that we consider to have produced excellent polished specimens. The importance of epoxy impregnation is demonstrated.     

Cracking tendency of HSC: Tensile strength and self generated stress in the period of setting and early hardening

It is well known that horizontal surfaces of high strength concrete (HSC) are susceptible to cracking in the time before and during setting. It appears that there are two critical time periods for such cracking: An early period ranging from placing to an hour or two, and a late period that covers the setting time and early hardening. The latter is considered here. In this period, the cracking risk may be assessed from the ratio between strain (the volume change) and tensile strain capacity, or from the ratio between stress generated from the volume change at restraint, and the tensile strength. All these parameters were measured. It is shown that relatively moderate volume changes of HSC-surfaces caused by drying plus cooling, generate restraining stress that may exceed the tensile strength, and thus, generate failure. The results indicate that crack risk assessment from stress/strength is more reliable than using strain/strain capacity. The starting point of tensile strength evolution of hardened concrete seems to coincide fairly well with the initial setting time. Also, the tensile strain capacity reaches a low level at this point, but continues descending for another hour or more.     

An executable subset of VDM-SL in an SA/RT framework

In this article we present the executable specification language IPTES Meta-IV based on the formal specification language VDM-SL. The language has been fitted to work in an SA/RT framework and the article presents how it supports the specification of the data transformation part of SA/RT. Furthermore we present some of the advanced constructs of the language seen as an executable specification language in its own right. Finally we present how an IPTES Meta-IV interpreter is used in combination with a high-level timed Petri net executor to execute SA/RT models.     

Effect of grain refinement on the fluidity of two commercial Al-Si foundry alloys

The effect of grain refinement on the fluidity of AlSi7Mg and AlSi11Mg has been investigated by spiral tests. Two different types of grain refiners have been evaluated. An AlTi5Bl master alloy was added to different Ti contents. Since the commercial alloys had a high initial content of titanium, model alloys were made to investigate the fluidity at low grain refiner additions. Commercial alloys grain refined only by boron additions have also been investigated. The results from the fluidity measurements have been verified by measuring the dendrite coherency point of the different cast alloys. Although different, the two methods show similar trends. The spirals from each fraction grain refiner cast were subsequently investigated metallographically at the tip of the spirals and at a reference point a distance behind, but no obvious difference in structure was observed. For both alloys, an increase in fluidity is observed as the content of grain refiner increases above 0.12 pct Ti, while the fluidity is impaired with increased grain refinement below 0.12 pct Ti. The alloys grain refined with ~0.015 pct B show the highest fraction solid at dendrite coherency, the smallest grain size, and the best fluidity.     

The Danish Twin Apartment Study – Part II: Mathematical modeling of the relative strength of sources of indoor air pollution

Abstract This study deals with the modeling of air pollution in apartments from laboratory measurements of source strengths, using formaldehyde and Total Volatile Organic Compounds (TVOCs) as model pollutants. The sources in two test apartments were grouped into two: building-related sources and occupant-related sources. The measured source strengths and ventilation rates were used for the prediction of concentrations expected in the apartments. These predictions were compared to measurements in the apartment over 12 months. The conclusions were that the model predictions based on emission rates measured in the laboratory can be used to predict the long-term concentration of the two model pollutants in the apartments. Considering the measured differences in ventilation between the apartments, an occupant emission rate of between 0.2 and 0.3 mg/h/kg body weight could be estimated. Based on previous suggested limits of acceptable exposures of humans to VOCs, an acceptable average emission rate of VOCs from building materials in general was estimated to be about 30 (μ/m²/h. The modeling showed that during the first 200 days, building materials dominated the emissions. After this, sources relating to the occupants dominated. On average about half of the VOC pollution originated from the building materials.     

Simulating Ramsey-Type Fringes in a Pulsed Microwave-Driven Classical Josephson Junction

We present evidence for a close analogy between the nonlinear behaviour of a pulsed microwave-driven Josephson junction at low temperature and the experimentally observed behaviour of Josephson systems operated below the quantum transition temperature under similar conditions. We specifically address observations of Ramsey-type fringe oscillations, which can be understood in classical nonlinear dynamics as results of slow transient oscillations in a pulsed microwave environment. Simulations are conducted to mimic experimental measurements by recording the statistics of microwave-induced escape events from the anharmonic potential well of a zero-voltage state. Observations consistent with experimentally obtained Ramsey-type oscillations are found in the classical model. An erratum to this article can be found at     

An Operator-integration-factor splitting method for time-dependent problems: Application to incompressible fluid flow

In this paper we present a simple, general methodology for the generation of high-order operator decomposition (splitting) techniques for the solution of time-dependent problems arising in ordinary and partial differential equations. The new approach exploits operator integration factors to reduce multiple-operator equations to an associated series of single-operator initial-value subproblems. Two illustrations of the procedure are presented: the first, a second-order method in time applied to velocity-pressure decoupling in the incompressible Stokes problem; the second, a third-order method in time applied to convection-Stokes decoupling in the incompressible Navier-Stokes equations. Critical open questions are briefly described.