The salt wedge position in a bar-blocked estuary subject to pulsed inflows

A series of laboratory experiments were carried out to investigate the response of a bar-blocked, saltwedge estuary to the imposition of both steady freshwater inflows and transient inflows that simulate storm events in the catchment area or the regular water releases from upstream reservoirs. The trapped salt water forms a wedge within the estuary, which migrates downstream under the influence of the freshwater inflow. The experiments show that the wedge migration occurs in two stages, namely (i) an initial phase characterized by intense shear-induced mixing at the nose of the wedge, followed by (ii) a relatively quiescent phase with significantly reduced mixing in which the wedge migrates more slowly downstream.

Provided that the transition time t_T between these two regimes satisfies t_T>g′h⁴L/q³α, as was the case for all our experiments and is likely to be the case for most estuaries, then the transition occurs at time t_T=1.2(gα³L⁶/g′³q²)^1/6, where g′=gΔρ/ρ0 is the reduced gravity, g the acceleration due to gravity, Δρ the density excess of the saline water over the density ρ₀ of the freshwater, q the river inflow rate per unit width, and L and α are the length and bottom slope of the estuary, respectively.

A simple model, based on conversion of the kinetic energy of the freshwater inflow into potential energy to mix the salt layer, was developed to predict the displacement xw over time t of the saltwedge nose from its initial position. For continuous inflows subject to t<t_T, the model predicts the saltwedge displacement as x_w/h=1.1 (t/τ)^1/3, where the normalizing length and time scales are h=(q²/g)^1/3 and τ=g′α²h4L/q³, respectively. For continuous inflows subject to t>tT, the model predicts the displacement as xw/h=0.45N1/6(t/τ)1/6/α, where N=q²/g′h²L is a non-dimensional number for the problem. This model shows very good agreement with the experiments. For repeated, pulsed discharges subject to t<t_T, the saltwedge displacement is given by (xw/h)3−(x0/h)(xw/h)2=1.3t/τ, where x₀ is the initial displacement following one discharge event but prior to the next event. For pulsed discharges subject to t>t_T, the displacement is given by (xw/h)⁶−(x0/h)(xw/h)⁵=0.008N(t/τ)/α⁶. This model shows very good agreement with the experiments for the initial discharge event but does systematically underestimate the wedge position for the subsequent pulses. However, the positional error is less than 15%.

Control loop for finding initial translator position of linear synchronous motor

This article presents a simple and reliable method for controlling the relative orientation between the two magnetic fields of a permanent magnet synchronous motor. Finding the initial (at motor powering- up time) value of this relative location is essential for the proper operation of the motor. After showing the system controllability, the utilized feedback control loop finds this initial relative orientation quickly and accurately. Further, using the proposed method allows considerable cost saving, as a transducer that is usually used for this purpose can be eliminated. The cost saving is most obvious in the case of linear motors and angle motors with large diameters. The way the problem is posed is an essential part of this work, and it is the reason behind the apparent simplicity of the solution. The method proposed relies on a single sensor, and it was tested when a relative encoder was used.

The position of Australian community sporting organisations in the third sector: membership profiles, characteristics and attitudes

Australian community sporting organisations have been relatively underresearched within the wider study of voluntary associations, yet their membership base is large and constitutes a sizable proportion of the population. This paper analyses data from the Australian Survey of Social Attitudes (AuSSA) 2003 (Gibson et al. 2004), initially to describe characteristics ofmembers ofcommunity sporting organisations in Australia (n=948). It goes on to compare attitudinal dimensions between members of sporting and other major third-sector organisations. On the basis of these comparisons three groupings of associations are suggested: social change, individual/social progress and individual/social maintenance. Sporting organisations form part of the latter category, and the paper briefly discusses the likely nature of social capital production associated with each.

What is the position/contribution of biology in environmental education

In this paper I intend to argue that biological science education and environmental education have traditionally represented fundamentally different discourses - that they have explicitly or implicitly adopted different epistemologies and ontologies - and that this difference has had implications for the conduct of research in these fields. I will draw on recent developments in theory, policy and practice in the field of environmental education to argue that this field tends to be located within a social discourse - that there is a foundation in policy and practice for considering environmental issues as fundamentally social and ethical in nature, rather than in some sense objectively existing. I then consider a rising topic in biology education (that of Biotechnology) as one which while tending to be treated within a scientific discourse, would be more fully explored educationally within a social discourse. I conclude by suggesting that in biology education research we need to consider a reconciliation of these historically differing perspectives.

Marketing position taxonomies : an empirical analysis

Despite the continuing need for an empirically validated classification of marketing positions, for theoretical and practical purposes, it appears that no such schema exists. This study contributes to the development of such a taxonomy through an empirical examination of marketing positions. Specifically, the research extends an existing taxonomy by empirically investigating personal selling marketing activities. Based on the taxonomy developed by Darmon (1998), data were collected about the information load, information complexity, and time and relationship management activities of marketers. Various analytical techniques were used to investigate specific features of the instrument and the taxonomy, as well as to provide convergence for the conclusions drawn by the researchers. It was established that sales positions can be more meaningfully identified, and, therefore, better categorised, by six dimensions than by job title or job role. Further, it appears that marketers in the same selling position vary significantly on these dimensions. These findings have important implications for marketing theory, applied research and management. However, future research should refine the instrument used in this study, since some anomalies emerged in the findings, and extend the study by investigating a wider range of marketing positions. Such research may also explore whether the dimensions identified in this study influence the performance and job satisfaction of marketers, and the extent to which marketing managers account for these variations.

On the effect of path loss rates on the optimal receiver position in sensor networks

In this paper we examine the problem of finding an optimal position for a receiver node in a single-hop sensor network. The basic idea is to minimize the network energy consumption according to a particular network cost function. Our contribution is to simply show the effect of signal path loss rates and sensor weighting on the optimal receiver position.

Adolescent home food environments and socioeconomic position

Many adolescents have diets that are less than optimal, particularly adolescents of low socioeconomic position (SEP). The determinants of SEP differences in adolescent dietary intake are poorly understood. This study examined the home food environments of adolescents and specifically investigated whether low SEP adolescents have less supportive home local environments, fewer eating rules and poorer home availability of fruit and vegetables than adolescents of high SEP. A cross-sectional, self-reported survey was administered to 3,264 adolescents in years 7 and 9, from 37 secondary schools in Victoria, Australia. Adolescent perceptions of the home meal environment, eating rules and home food availability were described and compared across SEP, which was measured using maternal education. Maternal education was linked to various aspects of the home meal environment, as well as home food availability, but not to eating rules. Low SEP adolescents were more likely to report that they were always allowed to watch television during meal times, and that unhealthy foods were always or usually available at home. In contrast, high SEP adolescents were more likely to report that vegetables were always served at dinner, that the evening meal was never an unpleasant time and always or usually a time for family connectedness, and that fruit was always or usually available at home. This study highlights aspects of the home food environment that might explain SEP variation in adolescent diets. Feasible ways of increasing home availability of healthy foods, and encouraging home meal environments to be supportive of healthy eating should be explored, particularly in households of low SEP adolescents.

Primary mathematics practice : the Victorian position

In order to establish what constitutes current primary practice in Victoria, video and other data were collected from a stratified random sample of ten year 3 and 4 classrooms in Victoria. Three video vignettes, representing the contrasting pedagogical flows captured on the videotapes, were produced to stimulate discussion in three separate Focus Groups of randomly selected teachers, principals, and mathematics teacher educators and consultants. This paper reports on their views of what constitutes current Victorian practice in primary mathematics

Reducing position error of cantilevered loads in motion systems

The positioning error of a large cantilevered mass that is actuated at its supported end is minimized as this mass travels at challenging high speeds and accelerations. An integrated approach is adopted to realize the task. After selecting the appropriate actuator that would provide higher rigidity, the system is viewed as a multi-degree of freedom system, and hence the concept of system-generated disturbance is introduced. This allows the use of appropriate mechanical design considerations and a proper generation of the kinematics commands to minimize such disturbance. A disturbance observer is then designed to detect and compensate the remaining disturbance, hence minimizing the positioning error.

Confirming the position of a nasogastric tube what does the literature say?

Nasogastric tubes are a medical device that can be used for a number of purposes. The process of inserting them however can be complicated. Nurses must therefore use an evidence based approach to confirm the correct position of nasogastric tubes and there are three main techniques described in the literature to do so. To date, one group of authors has published the majority of the studies on these techniques. This paper reviews their work.