Instructional leadership in centralised systems: evidence from Greek high-performing secondary schools

This paper examines the enactment of instructional leadership (IL) in high-performing secondary schools (HPSS), and the relationship between leadership and learning in raising student outcomes and encouraging teachers’ professional learning in the highly centralised context of Greece. It reports part of a comparative research study focused on whether, and to what extent, IL has been embraced by Greek school leaders. The study is exploratory, using a qualitative multiple case design to examine two HPSS in Athens. The research design involved a qualitative approach using several different methods, including semi-structured interviews with school principals, deputy heads, subject teachers and subject advisers, plus observation of leadership practice and meetings and scrutiny of relevant policy documents. The findings show that IL is conceptualised as an informal collaborative leadership practice, interwoven with the official multi-dimension role of Greek principals and their ‘semi-IL’ role. In the absence of official IL ‘actors’, teachers’ leadership has been expanding

Multi-vessel cooperative speed regulation for ship manipulation in towing scenarios

This paper proposes a multi-agent control scheme for multiple physically interconnected tugboats performing a ship towing process. These tugs are coordinated by two control layers. In the higher layer, the supervisory controller outputs the desired towing forces and reference trajectories for the tugs. This information is used by a tug's local controller in the lower layer to calculate the thruster forces and moment for manipulating the ship. The control strategy is based on the model predictive control concept, with the performance function designed by using the position and velocity error to make the ship follow waypoints and speed profile. A distributed control architecture is designed based on the alternating direction method of multipliers (ADMM) to reach a consensus between the predicted position generated by the tug controllers and the reference trajectory generated by the supervisory controller. Simulation experiments illustrate that the proposed method ensures the smooth and efficient maneuverability of the towing process.Transport Engineering and Logistic

MPC-based COLREGS Compliant Collision Avoidance for a Multi-Vessel Ship-Towing System

Collision avoidance plays a vital role in autonomous vehicle systems. As the complexity and scale of missions increase, multi-vehicle systems are adopted in practice. However, there is limited research on collision avoidance of a physically interconnected multi-vessel system. This paper proposes a control scheme for tugboats to tow a ship in congested port areas ensuring collision avoidance that is compliant with COLREGS. The Model Predictive Control (MPC) strategy is used to optimize the towing angles, towing forces, and tugboats’ thruster forces and moment. The COLREGS rules are integrated into the ship reference system by altering predefined waypoints to guide the towing system in a safe and lawful way. By designing the cost function for the ship and tugboats in the MPC controller system, the proposed control scheme makes the ship-towing system stay away from the obstacles and follow the calculated waypoints, achieving collision avoidance. Simulation experiments indicate that the proposed method can deal with static and dynamic obstacle situations in complex water traffic environments, and the collision avoidance operations comply with the COLREGS rules.Accepted Author ManuscriptTransport Engineering and Logistic

COLREGS-Compliant collision avoidance for physically coupled multi-vessel systems with distributed MPC

This paper proposes a distributed control scheme for autonomous tugboats to tow a ship in a restricted water traffic environment ensuring collision avoidance while being compliant with maritime regulation called COLREGS. The complex problem is cooperatively solved by addressing three sub-optimization problems. The first is to optimize the towing forces and angles for solving ship waypoint following and collision avoidance problems. The second is to optimize the tug thruster forces and moment for solving the tug online trajectory tracking and collision avoidance problems. The third is to optimize the Lagrange Multipliers for solving the consensus problem between the ship and tugs. The distributed control architecture follows the Model Predictive Control (MPC) strategy using the Altering Direction Method of Multipliers (ADMM). Simulation experiments indicate that the proposed control scheme can deal with static and dynamic obstacles in restricted waterways for a physically interconnected multi-vessel system executing the towing process, and the collision avoidance complies with COLREGS rules.Transport Engineering and Logistic

How does attention spread across objects oriented in depth?

Previous evidence suggests that attention can operate on object-based representations. It is not known whether these representations encode depth information and whether object depth, if encoded, is in viewer- or object-centered coordinates. To examine these questions, we employed a spatial cuing paradigm in which one corner of a 3-D object was exogenously cued with 75% validity. By rotating the object in depth, we can determine whether validity effects are modulated by 2-D or 3-D cue-target distance and whether validity effects depend on the position of the viewer relative to the object. When the image of a 3-D object was present (Experiments 1A and 1B), validity effects were not modulated by changes in 2-D cue-target distance, and shifting attention toward the viewer led to smaller validity effects than did shifting attention away from the viewer. When there was no object in the display (Experiments 2A and 2B), validity effects increased linearly as a function of 2-D cue-target distance. These results demonstrate that attention spreads across representations of perceived objects that encode depth information and that the object’s orientation in depth is encoded in viewer-centered coordinates.</p

Successes and failures in producing attentional object-based cueing effects

Over 30 years of research using Posner’s spatial cueing paradigm has shown that selective attention operates on representations of spatial locations, leading to space-based theories of attention. Manipulations of stimuli and methods have shown this paradigm to be sensitive to several types of object-based representations—providing evidence for theories incorporating object-based attentional selection. This paper critically evaluates the evidence demanding object-based explanations that go beyond positing spatial representations alone, with an emphasis on identifying and interpreting successes and failures in obtaining object-based cueing effects. This overview of current evidence is used to generate hypotheses regarding critical factors in the emergence and influence of object representations—their generation, strength, and maintenance—in the modulation of object-based facilitatory and inhibitory cueing effects.</p