Order Modeling Techniques Research Articles

Airborne fluoride contamination of soils and olive trees near an aluminum plant. Measurements and simulations

Data from a multimedia survey on fluoride contamination in the vicinity of an aluminum plant are presented and applied along with multimedia‐based simulation modeling techniques in order to investigate the long term response of fluoride in soils and seasonal trends of accumulation by olive trees. Results from the modeling analysis are in fair agreement with observed data. Soils show elevated fluoride concentrations that decrease with distance from the source and depth below the surface. Fluoride is largely retained in the upper 5 cm of soil. Sensitivity analyses showed that accumulation of fluoride is dominated by atmospheric loading. The strong retention of fluoride in the calcareous soils of the area with high organic matter and clay content, is also an important factor for controlling its accumulation in these soils. In the case of olive tree leaves, direct deposition is the main source for fluoride accumulation during the year; washoff is the dominant sink during the wet months; during dry months, however, physical processes such as wind removal, growth dilution, etc appear to be the dominant sinks controlling fluoride accumulation in vegetation. In general, the modeling effort provides a plausible description of the long term response of fluoride in soils and also of the seasonal dynamics of its accumulation in vegetation.

Aspects of an expert design system for the wastewater treatment industry

A new computer aided design program has been created, which uses computer modelling and simulation techniques in order to automatically generate a design solution for a High Recirculation Airlift Reactor (HRAR) wastewater treatment plant. This program replaces a set of programs which could only be used by process design experts, as many decisions had to be made whilst using the design system. A new expert system is being created to automatically integrate expert knowledge into the design process. This expert system will sit above the design program and control the design process. The objective of the new work presented here was to investigate methods for implementing this new expert system onto the new design program. This consisted of creating prototype software in order to demonstrate the advantages of applying expert systems methods to the design of the HRAR treatment process. This paper introduces the approach taken to acquiring and formulating the expert knowledge, and presents simple software to demonstrate the approach.

“Global Change” related and other atmospheric aerosol research at the university of Gent, and the role of PIXE therein

The PIXE technique plays an essential role in the “Global Change” related and regional atmospheric aerosol studies that are being conducted at the University of Gent. It is the only analytical technique used for detailed examinations of elemental mass size distributions in Greenland and the Norwegian Arctic, which aim at improving our understanding of the transfer of particulate species from air to snow. PIXE also provides concentration data for key elements in multi-sample, multi-species stacked filter unit data sets that are examined by receptor modeling techniques in order to identify the contributing aerosol types, to apportion the particulate mass and the various aerosol constituents to these aerosol types, and to determine the extent of the anthropogenic perturbation. Results are presented from such work in equatorial/tropical regions, where the emphasis is placed on assessing the impact of biomass buring on the climatically important fine aerosol. PIXE is also extensively used in aerosol studies around and above the North Sea. Results are presented from a Lagrangian transport experiment that aimed at examining the changes in concentrations and characteristics of gaseous and particulate species in air masses as they move over the North Sea. Finally, preliminary results are presented from long-term aerosol collections in southern Norway.

A Longitudinal Analysis of Sibling Relationships as Mediators of the Link between Family Processes and Youths' Best Friendships

The importance of peers in influencing young people's decisions has long been recognized by both local youth programs (e.g., through schools and social service agencies) and national campaigns (e.g., Just Say No) established to prevent behavior that is potentially dangerous to the youths and to others. Although teaching youths how to resist peer pressure to engage in behavior that they would otherwise reject is important, it may also be advantageous to teach young people how to form friendships in which negative peer pressure would be minimized. Such relationships would be based on mutual trust, respect, and caring (Youniss & Smollar, 1985), thus enabling the youths to feel a greater sense of equality in the friendship (Berndt & Savin-Williams, 1993; Furman & Robbins, 1985), which minimizes unwanted influence. The extent to which these attributes characterize youths' friendships varies, and the factors in young people's lives that are likely to be associated with their establishment of such friendships has yet to be fully identified. The purpose of this article is to identify characteristics of young people and their families that are important to the establishment of strong best friend ships. Although a number of researchers have examined the impact of individual and familial factors on youths' peer relationships (Cohn, 1990; Dekovic & Janssens, 1992; Dishion, 1990; Gold & Yanof, 1985; Lewis & Feiring, 1989; Patterson, Kupersmidt, & Griesle, 1990; Putallaz, 1987; Roff, Sells, & Golden, 1972; Winder & Rau, 1962), most have taken a bivariate approach, with youths' popularity within their school classrooms as the outcome. In the present study, we examined the predictive links between youths' individual temperaments, several of the relationship systems within their families, and the quality of their best friendships. We used a structural equation modeling technique in order to consider both the direct and indirect effects of the different predictors. We were particularly interested in the contribution of youths' sibling relationships to those factors that predict strong best friendships. In several studies (Abramovitch, Corter, Pepler, & Stanhope, 1986; Berndt & Bulleit, 1985; East & Rook, 1992; Stocker & Dunn, 1990; Vandell, Minnett, Johnson, & Santrock, cited in Dunn & McGuire, 1992), researchers have considered the link between youths' sibling and peer relationships; however, the findings regarding both the magnitude and role of that link have been inconsistent. In the present study, we looked beyond the direct effects of youths' sibling relationships on their best friendships, hypothesizing that youths' sibling relationships may assume a mediating role in which youths translate their familial experiences into behaviors that are generalized to interactions with age mates outside the home. THE CONCEPTUAL MODEL We tested a social learning model (Patterson, 1986) in which children learn specific interaction patterns in their relationships with other family members, which are then generalized to their peer relations. Thus, we expected the quality of youths' best friendships to be positively associated with warmth, and negatively associated with conflict, in their sibling relationships. We also examined the mediational role that youths' sibling relationships play in the links between the quality of their best friendships and several individual and family variables: youths' temperaments, the quality of their relationships with their parents, and their exposure to conflict in their parents' marital relationship. Figure 1 presents the conceptual model that we tested and the predicted relations among the constructs. (Figure 1 omitted) Sibling relationship quality. Sibling relationships provide children and adolescents with experiences that are different from those they have with both parents and peers (Azmitia & Hesser, 1993; Brody, Stoneman, & MacKinnon; 1982; Whiting & Whiting, 1975). …

Simulations of regional atmospheric flows on small scale topographical models

This paper presents various aspects on how to adapt existing physical modelling techniques in order to simulate regional atmospheric flows on small scale topographical models. The possibilities and limitations of such models are described, based on those considerations relevant to similarity and, by comparing models with different scales. Several practical aspects of model construction are underlined.