Energy-based nonlinear control of ship roll gyro-stabiliser with precession angle constraints

In this paper, we consider a passivity-based approach for the design of a control law of multiple ship-roll gyro-stabiliser units. We extend previous work on control of ship roll gyro-stabilisation by considering the problem within a nonlinear framework. In particular, we derive an energy-based model using the port-Hamiltonian theory and then design an active precession controller using passivity-based control interconnection and damping assignment. The design considers the possibility of having multiple gyro-stabiliser units, and the desired potential energy of the system (in closed loop) is chosen to behave like a barrier function, which allows us to enforce constraints on the precession angle of the gyros.

Constraints and characteristics of flexible work arrangements in small not-for-profit firms

There is a great deal of research that examines flexible working arrangements, but this work tends to be concentrated in large organisations. This research examines the approach taken to flexible working arrangements in five small community based, not for profit organisations. We present three propositions that aim to understand the constraints and the characteristics of flexible work in this rarely studied sector.

An observation about circular shortest paths: Dealing with additional constraints using branch and bound

Circular shortest paths represent a powerful methodology for image segmentation. The circularity condition ensures that the contour found by the algorithm is closed, a natural requirement for regular objects. Several implementations have been proposed in the past that either promise closure with high probability or ensure closure strictly, but with a mild computational efficiency handicap. Circularity can be viewed as a priori information that helps recover the correct object contour. Our "observation" is that circularity is only one among many possible constraints that can be imposed on shortest paths to guide them to a desirable solution. In this contribution, we illustrate this opportunity under a volume constraint but the concept is generally applicable. We also describe several adornments to the circular shortest path algorithm that proved useful in applications. © 2011 IEEE.

Conceptualisation and enactment of critical literacy for senior high school EAL learners in Queensland, Australia : commitments, constraints and contradictions

This case study examined four teachers' understandings and teaching of Critical Literacy with senior English as an Additional Language (EAL) learners in two Queensland high schools. Despite continuous, rapid curriculum change in Australia and efforts to diminish Critical Literacy, the four teachers continued to feature it successfully in their teaching with often marginalised learners. They used critical literacy to provide access to and critique dominant language codes, and to draw on learners' diverse experiences. To a lesser extent, the teachers created opportunities for redesigning dominant texts. Implications are important for policy production and interpretation, school planning and teacher professional development.

Innovate triple constraints model for better construction projects results

The continuous changing impacts appeared in all solution understanding approaches in the projects management field (especially in the construction field of work) by adopting dynamic solution paths. The paper will define what argue to be a better relational model for project management constraints (time, cost, and scope). This new model will increase the success factors of any complex program / project. This is a qualitative research adopting a new avenue of investigation by following different approach of attributing project activities with social phenomena, and supporting phenomenon with field of observations rather than mathematical method by emerging solution from human, and ants' colonies successful practices. The results will show the correct approach of relation between the triple constraints considering the relation as multi agents system having specified communication channels based on agents locations. Information will be transferred between agents, and action would be taken based on constraint agents locations in the project structure allowing immediate changes abilities in order to overcome issues of over budget, behind schedule, and additional scope impact. This is complex adaptive system having self organizes technique, and cybernetic control. Resulted model can be used for improving existing project management methodologies.

Impact of Mobility Constraints on Epidemic Broadcast in DTNs

In this paper, we investigate the effect of mobility constraints on epidemic broad-cast mechanisms in DTNs (Delay-Tolerant Networks). Major factors affecting epidemic broadcast performances are its forwarding algorithm and node mobility. The impact of forwarding algorithm and node mobility on epidemic broadcast mechanisms has been actively studied in the literature, but those studies use generally unconstrained mobility models. The objective of this paper is therefore to quantitatively investigate the effect of mobility constraints on epidemic broadcast mechanisms. We evaluate the performances of P-BCAST (PUSH-based BroadCast), SA-BCAST (Self-Adaptive BroadCast), and HP-BCAST (History-based P-BCAST) with a random waypoint mobility model with mobility constraints.

Impact of mobility constraints on epidemic broadcast mechanisms in delay-tolerant networks

In this paper, we investigate the effect of mobility constraints on epidemic broadcast mechanisms in DTNs (Delay-Tolerant Networks). Major factors affecting epidemic broadcast performances are its forwarding algorithm and node mobility. The impact of forwarding algorithm and node mobility on epidemic broadcast mechanisms has been actively studied in the literature, but those studies generally use unconstrained mobility models. The objective of this paper is therefore to quantitatively investigate the effect of mobility constraints on epidemic broadcast mechanisms. We evaluate the performances of three classes of epidemic broadcast mechanisms - P-BCAST (PUSH-based BroadCast), SA-BCAST (Self-Adaptive BroadCast), and HP-BCAST (History-based P-BCAST) - with a random waypoint mobility model with mobility constraints. Our finding includes that the existence of mobility constraints significantly improves the reach ability and dissemination speed of epidemic broadcast mechanisms while degrading their efficiency.

Grassland productivity limited by multiple nutrients

Terrestrial ecosystem productivity is widely accepted to be nutrient limited1. Although nitrogen (N) is deemed a key determinant of aboveground net primary production (ANPP)2,3, the prevalence of co-limitation by N and phosphorus (P) is increasingly recognized4,​5,​6,​7,​8. However, the extent to which terrestrial productivity is co-limited by nutrients other than N and P has remained unclear. Here, we report results from a standardized factorial nutrient addition experiment, in which we added N, P and potassium (K) combined with a selection of micronutrients (K+μ), alone or in concert, to 42 grassland sites spanning five continents, and monitored ANPP. Nutrient availability limited productivity at 31 of the 42 grassland sites. And pairwise combinations of N, P, and K+μ co-limited ANPP at 29 of the sites. Nitrogen limitation peaked in cool, high latitude sites. Our findings highlight the importance of less studied nutrients, such as K and micronutrients, for grassland productivity, and point to significant variations in the type and degree of nutrient limitation. We suggest that multiple-nutrient constraints must be considered when assessing the ecosystem-scale consequences of nutrient enrichment.

A case study of short-sale constraints and limits to arbitrage

This paper uses a unique data set of trades in a unique pair of securities that enables the precise identification of individual broker activity and the trade direction of that activity. We find direct evidence that the imposition (removal) of short-sale constraints limits (generates) trading activity consistent with brokers exploiting apparent mispricing.

The constraints of relevance on prevocational curriculum

This paper reflects on how relevance has been invoked as a curricular principle, both by students and teachers, in curriculum documents and in curriculum theory, to explore its variously conceived parameters and conditions. By posing the questions ‘relevant to whom?’, ‘relevant to what?’, ‘relevant how?’ and ‘relevant when?’ this paper exposes relevance as both a curricular virtue and a curricular constraint. It draws on an empirical project undertaken in the prevocational curriculum offered in Australia’s recently extended compulsory schooling for students in non-academic pathways. Data vignettes offer windows into two settings to exemplify the different ways relevance can be interpreted, stretched or contested. Using Bernstein’s distinction between vertical and horizontal discourses and knowledge structures, the analysis identifies what is gained and what is lost when relevance, variously defined, serves as a principle for curricular selection.

Effects of different instructional constraints on task performance and emergence of coordination in children

The objectives of this study were to determine the impact of different instructional constraints on standing board jump (sbj) performance in children and understand the underlying changes in emergent movement patterns. Two groups of novice participants were provided with either externally or internally focused attentional instructions during an intervention phase. Pre- and post-test sessions were undertaken to determine changes to performance and movement patterns. Thirty-six primary fourth-grade male students were recruited for this study and randomly assigned to either an external, internal focus or control group. Different instructional constraints with either an external focus (image of the achievement) or an internal focus (image of the act) were provided to the participants. Performance scores (jump distances), and data from key kinematic (joint range of motion, ROM) and kinetic variables (jump impulses) were collected. Instructional constraints with an emphasis on an external focus of attention were generally more effective in assisting learners to improve jump distances. Intra-individual analyses highlighted how enhanced jump distances for successful participants may be concomitant with specific changes to kinematic and kinetic variables. Larger joint ROM and adjustment to a comparatively larger horizontal impulse to a vertical impulse were observed for more successful participants at post-test performance. From a constraints-led perspective, the inclusion of instructional constraints encouraging self-adjustments in the control of movements (i.e., image of achievement) had a beneficial effect on individuals performing the standing broad jump task. However, the advantage of using an external focus of attentional instructions could be task- and individual-specific.