Decision Support Models for Composing and Navigating through e-Learning Objects

Libraries of learning objects may serve as basis for deriving course offerings that are customized to the needs of different learning communities or even individuals. Several ways of organizing this course composition process are discussed. Course composition needs a clear understanding of the dependencies between the learning objects. Therefore we discuss the metadata for object relationships proposed in different standardization projects and especially those suggested in the Dublin Core Metadata Initiative. Based on these metadata we construct adjacency matrices and graphs. We show how Gozinto-type computations can be used to determine direct and indirect prerequisites for certain learning objects. The metadata may also be used to define integer programming models which can be applied to support the instructor in formulating his specifications for selecting objects or which allow a computer agent to automatically select learning objects. Such decision models could also be helpful for a learner navigating through a library of learning objects. We also sketch a graph-based procedure for manual or automatic sequencing of the learning objects.

A mixed-integer linear programming approach to the optimization of event-bus schedules: a scheduling application in the tourism sector

This paper deals with “The Enchanted Journey,” which is a daily event tour booked by Bollywood-film fans. During the tour, the participants visit original sites of famous Bollywood films at various locations in Switzerland; moreover, the tour includes stops for lunch and shopping. Each day, up to five buses operate the tour. For operational reasons, however, two or more buses cannot stay at the same location simultaneously. Further operative constraints include time windows for all activities and precedence constraints between some activities. The planning problem is how to compute a feasible schedule for each bus. We implement a two-step hierarchical approach. In the first step, we minimize the total waiting time; in the second step, we minimize the total travel time of all buses. We present a basic formulation of this problem as a mixed-integer linear program. We enhance this basic formulation by symmetry-breaking constraints, which reduces the search space without loss of generality. We report on computational results obtained with the Gurobi Solver. Our numerical results show that all relevant problem instances can be solved using the basic formulation within reasonable CPU time, and that the symmetry-breaking constraints reduce that CPU time considerably.

Bilateral impairment of concurrent saccade programming in hemispatial neglect

When healthy observers make a saccade that is erroneously directed toward a distracter stimulus, they often produce a corrective saccade within 100ms after the end of the primary saccade. Such short inter-saccadic intervals indicate that programming of the secondary saccade has been initiated prior to the execution of the primary saccade and hence that the two saccades have been programmed concurrently. Here we show that concurrent saccade programming is bilaterally impaired in left spatial neglect, a strongly lateralized disorder of visual attention resulting from extensive right cerebral damage. Neglect patients were asked to make saccades to targets presented left or right of fixation while disregarding a distracter presented in the opposite hemifield. We examined those experimental trials on which participants first made a saccade to the distracter, followed by a secondary (corrective) saccade to the target. Compared to healthy and right-hemisphere damaged control participants the proportion of secondary saccades directing gaze to the target instead of bringing it even closer to the distracter was bilaterally reduced in neglect patients. In addition, the characteristic reduction of secondary saccade latency observed in both control groups was absent in neglect patients, whether the secondary saccade was directed to the left or right hemifield. This pattern is consistent with a severe, bilateral impairment of concurrent saccade programming in left spatial neglect.

Knowing the future: partial foreknowledge effects on the programming of prosaccades and antisaccades

Foreknowledge about the demands of an upcoming trial may be exploited to optimize behavioural responses. In the current study we systematically investigated the benefits of partial foreknowledge--that is, when some but not all aspects of a future trial are known in advance. For this we used an ocular motor paradigm with horizontal prosaccades and antisaccades. Predictable sequences were used to create three partial foreknowledge conditions: one with foreknowledge about the stimulus location only, one with foreknowledge about the task set only, and one with foreknowledge about the direction of the required response only. These were contrasted with a condition of no-foreknowledge and a condition of complete foreknowledge about all three parameters. The results showed that the three types of foreknowledge affected saccadic efficiency differently. While foreknowledge about stimulus-location had no effect on efficiency, task foreknowledge had some effect and response-foreknowledge was as effective as complete foreknowledge. Foreknowledge effects on switch costs followed a similar pattern in general, but were not specific for switching of the trial attribute for which foreknowledge was available. We conclude that partial foreknowledge has a differential effect on efficiency, most consistent with preparatory activation of a motor schema in advance of the stimulus, with consequent benefits for both switched and repeated trials.

Trial history biases the spatial programming of antisaccades

The historical context in which saccades are made influences their latency and error rates, but less is known about how context influences their spatial parameters. We recently described a novel spatial bias for antisaccades, in which the endpoints of these responses deviate towards alternative goal locations used in the same experimental block, and showed that expectancy (prior probability) is at least partly responsible for this 'alternate-goal bias'. In this report we asked whether trial history also plays a role. Subjects performed antisaccades to a stimulus randomly located on the horizontal meridian, on a 40° angle downwards from the horizontal meridian, or on a 40° upward angle, with all three locations equally probable on any given trial. We found that the endpoints of antisaccades were significantly displaced towards the goal location of not only the immediately preceding trial (n - 1) but also the penultimate (n - 2) trial. Furthermore, this bias was mainly present for antisaccades with a short latency of <250 ms and was rapidly corrected by secondary saccades. We conclude that the location of recent antisaccades biases the spatial programming of upcoming antisaccades, that this historical effect persists over many seconds, and that it influences mainly rapidly generated eye movements. Because corrective saccades eliminate the historical bias, we suggest that the bias arises in processes generating the response vector, rather than processes generating the perceptual estimate of goal location.

[Fetal programming of cardiovascular disease: new causes and underlying mechanisms]

There exists an association between pathologic events occurring during early life and the development of cardiovascular disease in adulthood. For example, transient perinatal hypoxemia predisposes to exaggerated hypoxic pulmonary hypertension and preeclampsia predisposes the offspring to pulmonary and systemic endothelial dysfunction later in life. The latter finding offers a scientific basis for observations demonstrating an increased risk for premature cardiovascular morbidity in this population. Very recently, we showed that offspring of assisted reproductive technologies also display generalized vascular dysfunction and early arteriosclerosis. Studies in animal models have provided evidence that oxidative stress and/or epigenetic alterations play an important pathophysiological role in the fetal programming of cardiovascular disease.

[Pulmonary hypertension and lung edema at high altitude. Role of endothelial dysfunction and fetal programming]

High altitude constitutes an exciting natural laboratory for medical research. While initially, the aim of high-altitude research was to understand the adaptation of the organism to hypoxia and find treatments for altitude-related diseases, over the past decade or so, the scope of this research has broadened considerably. Two important observations led to the foundation for the broadening of the scientific scope of high-altitude research. First, high-altitude pulmonary edema (HAPE) represents a unique model which allows studying fundamental mechanisms of pulmonary hypertension and lung edema in humans. Secondly, the ambient hypoxia associated with high-altitude exposure facilitates the detection of pulmonary and systemic vascular dysfunction at an early stage. Here, we review studies that, by capitalizing on these observations, have led to the description of novel mechanisms underpinning lung edema and pulmonary hypertension and to the first direct demonstration of fetal programming of vascular dysfunction in humans.