The influence of contact zone configuration on the flow structure in a dissolved air flotation pilot plant

The dissolved air flotation process is used in water and wastewater treatment. Among many parameters the fluid dynamics determine the capacity of the process. The contact zone is assumed to be important for the removal function, as it is believed to be the location for the aggregation of bubbles and flocs. This paper presents an experimental study on the flow structure in a contact zone of a DAF pilot tank and the influence of contact zone configuration. The flow structure in the contact zone was examined for different horizontal lengths of the zone and for different heights and inclinations of the shaft wall. The hydraulic surface loading was 11 m/h over the total tank surface area and the recycle rate was constant at 10% of the main flow. The examined hydraulic surface loading over the contact zone ranged from 40 to 98 m/h. Water velocities in the longitudinal, central section of the tank were measured with an acoustical Doppler velocimeter in a grid net for the different contact zone configurations, giving an insight into the flow structure. The result showed that the flow structure in the contact zone was characterised by a turbulent lower region and a plug-flow higher region. The hydraulic surface loading, a function of the length of the contact zone, seemingly determined the extension of the turbulent region. A higher hydraulic surface loading decreased the turbulent region while the lower loading increased it. A hydraulic surface loading of 65 m/h was suggested for design. It was not possible to determine the turbulent intensity quantitatively due to the measurement method. The height and inclination of the shaft wall did not seem to have a significant influence on the turbulent region. However, an increased height of the contact zone enhanced the higher, plug flow region and a recommended height of 0.81 m or higher for the recommended hydraulic surface loading was suggested when both mixing and plug-flow are desired. The separation zone was characterised by a stratified flow structure, mainly influenced by the cross-flow velocity that is a function of the distance between the shaft wall top and the water surface. A cross-flow velocity of 37m/h or higher resulted in a clearly defined stratification, believed to be crucial for an efficient separation of flocs. Finally, the extension of the lower, denser plug-flow region in the separation zone increased when the shaft wall height increased.     

Asymptotically optimal smoothing of averaged LMS estimates for regression parameter tracking

The sequence of estimates formed by the LMS algorithm for a standard linear regression estimation problem is considered. It is known since earlier that smoothing these estimates by simple averaging will lead to, asymptotically, the recursive least-squares algorithm. In this paper, it is first shown that smoothing the LMS estimates using a matrix updating will lead to smoothed estimates with optimal tracking properties, also in case the true parameters are slowly changing as a random walk. The choice of smoothing matrix should be tailored to the properties of the random walk. Second, it is shown that the same accuracy can be obtained also for a modified algorithm, SLAMS, which is based on averages and requires much less computations.     

'Mini small worlds' of shortest link paths crossing domain boundaries in an academic Web space

Summary Combining webometric and social network analytic approaches, this study developed a methodology to sample and identify Web links, pages, and sites that function as small-world connectors affecting short link distances along link paths between different topical domains in an academic Web space. The data set comprised 7669 subsites harvested from 109 UK universities. A novel corona-shaped Web graph model revealed reachability structures among the investigated subsites. Shortest link path netsfunctioned as investigable small-world link structures - 'mini small worlds' - generated by deliberate juxtaposition of topically dissimilar subsites. Indicative findings suggest that personal Web page authors and computer science subsites may be important small-world connectors across sites and topics in an academic Web space. Such connectors may counteract balkanization of the Web into insularities of disconnected and unreachable subpopulations.     

Unprejudiced optimal open loop input design for identification of transfer functions

The problem to estimate transfer functions of linear systems is considered. The quality of the resulting estimate depends, among other things, on the input used during the identification experiment. We measure the quality using a quadratic norm in the frequency domain. The problem to determine optimal inputs, i.e. inputs that minimize the chosen norm, subject to constrained input variance, has long been studied. We point out that such procedures may involve a prejudice (that the system is to be found in a certain model set) that may have some surprising effects. We discuss how such a prejudice can be reduced by allowing the possibility that the true system cannot be exactly described in the chosen model set. We also calculate explicit expressions for the resulting “unprejudiced” optimal inputs. These expressions relate the signal-to-noise ratio (as a function of frequency) to the chosen weighting function in the quadratic norm. We also point out the role of the employed noise model for the design.     

An interpretation of probability in the law of evidence based on pro-et-contra argumentation

The purpose of this paper is to improve on the logical and measure-theoretic foundations for the notion of probability in the law of evidence, which were given in my contributions Åqvist [ (1990) Logical analysis of epistemic modality: an explication of the Bolding–Ekelöf degrees of evidential strength. In: Klami HT (ed) Rätt och Sanning (Law and Truth. A symposium on legal proof-theory in Uppsala May 1989). Iustus Förlag, Uppsala, pp 43–54; (1992) Towards a logical theory of legal evidence: semantic analysis of the Bolding–Ekelöf degrees of evidential strength. In: Martino AA (ed) Expert systems in law. Elsevier Science Publishers BV, Amsterdam, North-Holland, pp 67–86]. The present approach agrees with the one adopted in those contributions in taking its main task to be that of providing a semantic analysis, or explication, of the so called Bolding–Ekelöf degrees of evidential strength (“proof-strength”) as applied to the establishment of matters of fact in law-courts. However, it differs from the one advocated in our earlier work on the subject in explicitly appealing to what is known as “Pro-et-Contra Argumentation”, after the famous Norwegian philosopher Arne Naess. It tries to bring out the logical form of that interesting kind of reasoning, at least in the context of the law of evidence. The formal techniques used here will be seen to be largely inspired by the important work done by Patrick Suppes, notably Suppes [(1957) Introduction to logic. van Nostrand, Princeton and (1972) Finite equal-interval measurement structures. Theoria 38:45–63].     

The effect of temperature on the pulsed current processing behaviour and structural characteristics of porous ZSM-5 and zeolite Y monoliths

Hierachically porous monoliths of ZSM-5 and Y zeolites have been prepared by pulsed current processing (PCP). The densification behaviour and structural characteristics during rapid thermal treatment of the zeolites have been determined and related to the influence of the Si:Al ratio on the thermal stability of the zeolites. Monoliths of macroscopic shape can be prepared with an insignificant loss of surface area and micropore volume when the PCP-treatment was performed at temperatures below a critical maximum PCP temperature (T_PCP). Full-profile fittings of the powder X-ray diffraction patterns showed that the lattice strain of zeolite Y increases rapidly above the critical T_PCP while the ZSM-5 zeolites undergo a phase transition from orthorhombic to monoclinic. The use of a novel ceramic processing route for the production of the zeolite monoliths that do not significantly influence the structural characteristics and surface area of the starting materials has a potential to be of importance in catalysis and gas separation applications.     

Density Measurements of Single Granules Using the Atomic Force Microscope

The density of single spray-dried granules has been determined with a new method based on atomic force microscopy (AFM). Spherical granules with a well-defined diameter are attached to the AFM cantilever, which acts as a beam-type spring, and the mass of a granule is estimated from the shift in the resonant frequency. The error of the measurements associated with the method was estimated to vary between 1% and 5%, depending on the size and shape of the granule. Density measurements of spray-dried WC–Co granules are presented, and the effect of a polymeric binder and dispersant on the consolidation during drying is discussed.     

Regressor selection with the analysis of variance method

Identification of non-linear dynamical models of a black box nature involves both structure decisions, i.e., which regressors to use, the selection of a regressor function, and the estimation of the parameters involved. The typical approach in system identification seems to be to mix all these steps, which for example means that the selection of regressors is based on the fits that is achieved for different choices. Alternatively one could then interpret the regressor selection as based on hypothesis tests (F-tests) at a certain confidence level that depends on the data. It would in many cases be desirable to decide which regressors to use independently of the other steps.In this paper we investigate what the well-known method of analysis of variance (ANOVA) can offer for this problem. System identification applications violate many of the ideal conditions for which ANOVA was designed and we study how the method performs under such non-ideal conditions.ANOVA is much faster than a typical parametric estimation method, using e.g. neural networks. It is actually also more reliable, in our tests, in picking the correct structure even under non-ideal conditions. One reason for this may be that ANOVA requires the data set to be balanced, that is, all parts of the regressor space are weighted equally. Just applying tests of fit for the recorded data may give, for structure identification, improper weight to areas with many, or few, samples.