Grundlagen des Burrows-Wheeler-Kompressionsalgorithmus

Zusammenfassung. Der Burrows-Wheeler-Kompressionsalgorithmus hat als ein universelles Kompressionsverfahren in den letzten Jahren aufgrund seiner hervorragenden Kompressionsraten und hohen Verarbeitungsgeschwindigkeiten eine bemerkenswerte Beachtung erfahren. Das Herzstück des Algorithmus stellt die sogenannte Burrows-Wheeler-Transformation dar. Es handelt sich bei dieser Transformation um eine Permutation der Eingabedaten, welche Zeichen mit ähnlichem Kontext nahe beieinander anordnet. Die Transformation sowie die zugehörige Rücktransformation werden zusammen mit den weiteren Stufen des Algorithmus in einer gegenüber der Standardversion verbesserten Variante vorgestellt und die Ergebnisse mit denen anderer Datenkompressionsalgorithmen verglichen. Eingegangen am 12. April 2003, Angenommen am 7. November 2003CR Subject Calssification: E4, H1.1     

Food restriction alters salivary cortisol and α-amylase responses to a simulated weightlifting competition without significant performance modification

The aim of this investigation was to evaluate the effect of a 6-day food restriction period on the physiological responses and performance of 11 high-level weightlifters. After a period of weight maintenance (T₂), they were assigned into two groups depending on whether they lost (Diet group, n = 6) or maintained their body weight (Control group, n = 5) during the course of those 6 days. An evaluation of performance and the measurement of salivary cortisol concentrations and salivary α-amylase (sAA) activity were performed during a simulated weightlifting competition which took place at T₂, after a 6-day period of food restriction (T₃). Dietary data were collected using a 6-day diet record. We noted a 41.8% decrease in mean energy intake during the dietary restriction period, leading to a 4.34% weight loss for the Diet group. Dietary restriction did not modify absolute performance levels, whilst a significant improvement was noted for the Control group. Furthermore, we noted a response of decreased salivary cortisol and increased sAA activity to the simulated competition stress at T₃ for the Diet group. These results may indicate that dietary reduction led to a dissociation of the hypothalamo-pituitary-adrenal axis and the sympatho-adreno-medullary system, which could impair training adaptations and absolute performance development.     

Kinematics and kinetics of handcycling propulsion at increasing workloads in able-bodied subjects

In Paralympic sports, biomechanical optimisation of movements and equipment seems to be promising for improving performance. In handcycling, information about the biomechanics of this sport is mainly provided by case studies. The aim of the current study was (1) to examine changes in handcycling propulsion kinematics and kinetics due to increasing workloads and (2) identify parameters that are associated with peak aerobic performance. Twelve non-disabled male competitive triathletes without handcycling experience voluntarily participated in the study. They performed an initial familiarisation protocol and incremental step test until exhaustion in a recumbent racing handcycle that was attached to an ergometer. During the incremental test, tangential crank kinetics, 3D joint kinematics, blood lactate and ratings of perceived exertion (local and global) were identified. As a performance criterion, the maximal power output during the step test (P_max) was calculated and correlated with biomechanical parameters. For higher workloads, an increase in crank torque was observed that was even more pronounced in the pull phase than in the push phase. Furthermore, participants showed an increase in shoulder internal rotation and abduction and a decrease in elbow flexion and retroversion. These changes were negatively correlated with performance. At high workloads, it seems that power output is more limited by the transition from pull to push phase than at low workloads. It is suggested that successful athletes demonstrate small alterations of their kinematic profile due to increasing workloads. Future studies should replicate and expand the test spectrum (sprint and continuous loads) as well as use methods like surface electromyography (sEMG) with elite handcyclists.     

An ideology critique of global citizenship education

ABSTRACT

In the last two decades, global citizenship education (GCE) has become a catchphrase used by international and national educational agencies, as well as researchers, to delineate the increasing internationalisation of education, framed as an answer to the growing globalisation and the high values of citizenship. These developments, however, have created issues, due to the presence of two conflicting discourses. While the discourse of critical democracy highlights the importance of ethical values, social responsibility and active citizenry, a neoliberal discourse privileges instead a market-rationale, focused on self-investment and enhanced profits. These two discourses are not separated; they rather appear side by side, causing a confusing effect. This article aims to analyse GCE as an ideology, unveiling not only its hidden (discursive) content but also the role played by non-discursive elements in guaranteeing the coexistence of antagonistic discourses. It will be argued that not only the critical democratic discourse does not offer any resistance or threat to the neoliberal structuring of higher education, but also this discourse can function as an apologetic narrative that exculpates all of us who still want to work in universities, notwithstanding our dissatisfaction with their current commodification.     

French football referees: an exploratory study of the conditions of access and employment for referees in terms of level and gender

This essay attempts to explore the conditions of access and employment for football referees in France in terms of gender and refereeing level, based on processing 148 questionnaires. It shows that the social stratum from which the ‘body’ of referees is recruited appears to be higher for correspondingly higher levels of refereeing, and also seems to be clustered around individuals who have had a family sports background (even involving refereeing) and experience in playing football, while the conditions of access for women are less socially selective and less discriminatory in terms of experience in playing football. It also shows that, in terms of a level of education that increases in direct relation to the level of refereeing, referees carry out their activities alongside professional management roles, which are most often at a lower level than that at which they officiate as referees.     

Effect of a congested match schedule on immune-endocrine responses,technical performance and session-RPE in elite youth soccer players

ABSTRACT

This study investigated the effects of a congested match schedule (7 matches played in 7 days) on steroid hormone concentrations, mucosal immunity, session rating of perceived exertion (S-RPE) and technical performance in 16 elite youth soccer players (14.8 ± 0.4 years; 170.6 ± 9.4 cm; 64.9 ± 7 kg). No change was observed for salivary cortisol concentration across match time points (P = 0.33; effect size [ES] = 0.13–0.48). In contrast, there was a decrease in salivary testosterone and salivary IgA (SIgA) concentrations from the 1st compared with the last time point (P = 0.01 and 0.001, ES = 0.42 and 0.67, respectively). The SIgA concentration varied across time points (P < 0.001) with the highest value observed at the 3rd time point (rest day) (3rd vs all time point; ES = 0.47–0.73). No changes were observed for S-RPE across time points (P > 0.05). A higher number of tackles and interceptions were observed during the 4th match vs 1st and 7th matches (P < 0.001; ES = 2.25 and 1.90, respectively). The present data demonstrate that accumulated fatigue related to participation in a congested match schedule might induce a decrease in testosterone concentration in youth players and negatively affect their mucosal immunity and capacity to perform certain technical actions.     

Trust as an antecedent to knowledge sharing in virtual communities of practice

This study focusses on the role of trust in knowledge sharing within the context of virtual communities of practice. Trust is widely accepted as an important enabler of knowledge management (KM) processes. We conceptualise trust across three dimensions, namely: competence, integrity and benevolence; we test hypotheses as to the effect of these facets of trust on knowledge sharing by surveying an intra-organisational global virtual community of practitioners. The results indicate that all three dimensions of trust are positively related to knowledge-sharing behaviour. Trust based on the perceived integrity of the community was found to be the strongest predictor of knowledge-sharing behaviour. Our findings suggest that the dimensions of trust buttress each other; although they are theoretically distinct, they appear to be empirically inseparable. We propose that in order for knowledge sharing to be enabled, trust must concurrently exist in all three dimensions. Implication to organisations in their recruitment policy is to include competence, integrity and benevolence in their sought-for attributes of new employees. KM practitioners also have to encourage these attributes in existing employees, who are potential members of on-line communities of practice. Knowledge sharing itself was conceptualised with three components – quantity (frequency), quality (usefulness or value) and focus (the degree to which an individual feels that they engage in knowledge sharing). Of the three components, focus exhibits the most significant relationship with trust factors. This finding makes knowledge sharing less tangible than perhaps would be expected. It suggests that establishing whether knowledge has been shared is more than counting the frequency or trying to evaluate the usefulness of the shared knowledge. These aspects are important especially to management, but to the individual who shares knowledge, her feelings of having shared knowledge appear to be more important. With the current understanding that knowledge sharing is more of a human activity than technology, it is important that any information system should be assistive in boosting users’ confidence that they are indeed sharing knowledge. If the systems do not re-enforce the users’ knowledge-sharing orientation, knowledge sharing may be discouraged. Notwithstanding the point made about knowledge-sharing focus, it is necessary to take into consideration all the components of knowledge sharing to fully capture the concept. This was well indicated when the combined variable of all (rather than individual) knowledge-sharing items had the strongest correlation with trust factors.