Modelling the effects of dam removal on migratory walleye (Sander vitreus) early life‐history stages

Many dams in the USA have outlived their intended purpose and an increasing number are being considered for removal. Yet, quantitative studies of the potential physical, biological and ecological responses are needed to assess dam removal decisions. In this paper, the responses of migratory walleye (Sander vitreus) to increased spawning habitat availability as a result of dam removal was studied by comparing scenarios with and without a high‐head dam in the Sandusky River (Ohio), a major tributary to Lake Erie. A conceptual, ecological model was proposed to define the relationship between hydrodynamics and walleye spawning, egg hatching, larval drift and survival. A mathematical, ecological model of the early life‐history stages was then developed and coupled with time series of depth and velocity predictions over the spawning grounds from a 1‐D hydrodynamic model. Model simulations were run for 1984–1993 for both the with‐ and without‐dam scenarios to assess the potential benefit of dam removal. The simulation results demonstrated that velocity, depth and water temperature are major factors influencing adult walleye spawning success. Without the dam, 10 times the amount of spawning habitat would be available for walleye to spawn. This increase in spawning habitat area resulted in up to five times the total egg deposition and seven times the larval output to the nursing grounds, based on the assumption that 5% of the walleye population of Lake Erie migrated up the Sandusky River to spawn. We concluded that the spawning habitat in the current condition (with the dam) is limiting and additional spawning habitat upstream could significantly increase the number of larval walleye drifting to Lake Erie. The model sensitivity analysis showed that the number of walleye migrating up the river in spring is the dominant factor for larval recruitment to the lake. Copyright © 2006 John Wiley & Sons, Ltd.     

Molecular Mechanisms of Fetal Tendon Regeneration Versus Adult Fibrous Repair

Tendinopathies are painful, disabling conditions that afflict 25% of the adult human population. Filling an unmet need for realistic large-animal models, we here present an ovine model of tendon injury for the comparative study of adult scarring repair and fetal regeneration. Complete regeneration of the fetal tendon within 28 days is demonstrated, while adult tendon defects remained macroscopically and histologically evident five months post-injury. In addition to a comprehensive histological assessment, proteome analyses of secretomes were performed. Confirming histological data, a specific and pronounced inflammation accompanied by activation of neutrophils in adult tendon defects was observed, corroborated by the significant up-regulation of pro-inflammatory factors, neutrophil attracting chemokines, the release of potentially tissue-damaging antimicrobial and extracellular matrix-degrading enzymes, and a response to oxidative stress. In contrast, secreted proteins of injured fetal tendons included proteins initiating the resolution of inflammation or promoting functional extracellular matrix production. These results demonstrate the power and relevance of our novel ovine fetal tendon regeneration model, which thus promises to accelerate research in the field. First insights from the model already support our molecular understanding of successful fetal tendon healing processes and may guide improved therapeutic strategies.     

Reasoning with graph constraints

Graph constraints were introduced in the area of graph transformation, in connection with the notion of (negative) application conditions, as a form to limit the applicability of transformation rules. However, we believe that graph constraints may also play a significant role in the area of visual software modelling or in the specification and verification of semi-structured documents or websites (i.e. HTML or XML sets of documents). In this sense, after some discussion on these application areas, we concentrate on the problem of how to prove the consistency of specifications based on this kind of constraints. In particular, we present proof rules for two classes of graph constraints and show that our proof rules are sound and (refutationally) complete for each class. In addition, we study clause subsumption in this context as a form to speed up refutation.     

Group awareness and self-presentation in computer-supported information exchange

A common challenge in many situations of computer-supported collaborative learning is increasing the willingness of those involved to share their knowledge with other group members. As a prototypical situation of computer-supported information exchange, a shared-database setting was chosen for the current study. This information-exchange situation represented a social dilemma: while the contribution of information to a shared database induced costs and provided no benefit for the individual, the entire group suffered when all members decided to withhold information. In order to alleviate the information-exchange dilemma, a group-awareness tool was employed. It was hypothesized that participants would use group awareness for self-presentational purposes. For the examination of this assumption, the personality variable ‘protective self-presentation’ (PSP) was measured. An interaction effect of group awareness and PSP was found: when an awareness tool provided information concerning the contribution behavior of each individual, this tool was used as a self-presentation opportunity. In order to understand this effect in more detail, single items of the PSP-scale were analyzed.     

The need for considering multilevel analysis in CSCL research—An appeal for the use of more advanced statistical methods

Per definition, CSCL research deals with the data of individuals nested in groups, and the influence of a specific learning setting on the collaborative process of learning. Most well-established statistical methods are not able to analyze such nested data adequately. This article describes the problems which arise when standard methods are applied and introduces multilevel modelling (MLM) as an alternative and adequate statistical approach in CSCL research. MLM enables testing interactional effects of predictor variables varying within groups (for example, the activity of group members in a chat) and predictors varying between groups (for example, the group homogeneity created by group members’ prior knowledge). So it allows taking into account that an instruction, tool or learning environment has different but systematic effects on the members within the groups on the one hand and on the groups on the other hand. The underlying statistical model of MLM is described using an example from CSCL. Attention is drawn to the fact that MLM requires large sample sizes which are not provided in most CSCL research. A proposal is made for the use of some analyses which are useful.     

Gadolinium-enhanced magnetic resonance angiography of the pelvis in patients with erectile impotence

This study evaluted the potential of contrast-enhanced digital-subtraction magnetic resonance angiography (CE-DS-MRA) for noninvasive angiographic delineation of the arterial supply of the penis in patients with erectile dysfunction. After induction of an erection with prostaglandin E, a three-dimensional fast imaging with steady-state precision (FISP) sequence with TE of 1.8–2 milliseconds, TR of 4.4–5 milliseconds, and flip angle of 40°–60° was used to obtain high-resolution angiograms of the pelvis and penis during the injection of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) 0.3 mmol/kg body weight, within 30–50 seconds. DS maximum intensity projections (MIPs) and multiplanar reconstructions (MPRs) were compared with clinical work-up and directional Doppler ultrasound in 11 patients. In all 11 patients (100%), the arterial supply of the penis could be delineated from the aortic bifurcation via the iliac and internal pudendal arteries to the dorsal and deep penile arteries. Of the 22 internal pudendal arteries, 6 (27%) were occluded on CE-DS-MRA and 5 (23%) had stenoses, of which 4 (18%) were greater than 50%. In 7 patients (64%) good correlation between CE-DS-MRA and clinical findings and/or Doppler ultrasound was found; in 2 patients (18%), the correlation was moderate, and in 2 patients (18%) results were discrepant. In 6 patients (55%), MRA provided additional information to the clinical and Doppler ultrasound work-up. CE-DS-MRA can delineate small sessels such as the internal pudendal and penile arteries and thus has the potential to become a noninvasive angiography method in the work-up of erectile impotence. Supported by Siemens Medical Systems, Erlangen; Schering AG, Berlin; and Agfa-Gevaert AG, Leverkusen.