Using the QR Factorization to swiftly update least squares problems

In this paper we study how to update the solution of the linear system Ax = b after the matrix A is changed by addition or deletion of rows or columns. Studying the QR Factorization of the system, more specifically, the factorization created by the Householder reflection algorithm, we find that we can split the algorithm in two parts. The result from the first part is trivial to update and is the only dependency for calculating the second part. We find that not only can this save a considerable amount of time when solving least squares problems but the algorithm is also very easy to implement

Are the playoffs different from the regular season? A comparison of in-game statistics in Icelandic elite handball

There are many axioms in sport that are taken at face value. One of them is that the playoffs are somehow totally different from the regular season. The aim of this study was to test that axiom by comparing in-game statistics during the regular season and the playoffs in the semi-professional Icelandic elite men’s handball league. Data from 724 games (648 regular season games and 76 playoff games; 1448 data points) across five seasons were analysed using a two-level logistic regression analysis. The variables of interest were pace, fast breaks, legal stops, penalty throws given, 2-minute suspensions, and saves. The results indicated no meaningful differences in fast breaks, penalty throws given or number of saves, but did find signs of added intensity during the playoffs with a higher pace, more legal stops and more 2-minute suspensions. While the differences were not particularly large, they have the possibility of being practically meaningful and were in line with the axiom. Possible explanations were discussed but more research is needed to determine whether these findings are context- or sport-specific.publishedVersio

Is Left-Handedness Associated With Greater Success From the 7-Meter Line? An Analysis of 7-Meter Records Across Various Handball Competitions

While left-handers have been overrepresented among 7-meter shooters in handball, previous investigators have not found success from the 7-meter line to be related to handedness. Drawing on previous handedness research in sport, we performed two studies to examine possible negative frequency-dependent advantages to left-handedness during 7-meter throws among elite players. In Study I, we analyzed the records of 974 7-meter shooters from Danish and Norwegian elite divisions (485 males and 489 females) and found that left-handed males were overrepresented compared to the prevalence of left-handers in these two leagues, but left-handed females were not. An analysis of covariance showed no statistically significant associations between throwing arm or sex, and success from the 7-meter line. In Study II, we analyzed the records of 899 7-meter shooters at 41 major championships for both males and females between 2007-2023 (442 males and 457 females). We again found left-handed males to be overrepresented compared to their prevalence at the championships, but left-handed females were not. Also, in alignment with Study I, an analysis of covariance found no associations between throwing arm or sex, and success from 7-meter throws. These findings further underline the complexities associated with lateral biases in sports, where there appear to be benefits for left-handed males in the selection process that are not evident during performance execution.publishedVersio

Identity leadership and cohesion in elite sport: The mediating role of intra-team communication

One perspective on leadership that has recently gained increased attention in sport is identity leadership; however, research on elite sport teams is still in its infancy. Thus, the main purpose of this research is to investigate identity leadership in elite team sports in relation to task cohesion, and subsequently to explore the mediating role of the intra-team communication dimensions of acceptance and distinctiveness. A cross-sectional design was employed and 441 elite athletes from division 1 and division 2 in handball and ice hockey participated in the present study. Structural equation modeling was used to assess relationships between identity leadership and task cohesion, and the mediating role of acceptance and distinctiveness. Results revealed that identity leadership positively predicted task cohesion, and that this relationship was mediated by intrateam communication acceptance. In conclusion, findings in the present study expand our understanding of performance-related benefits of identity leadership in elite sport.Identity leadership and cohesion in elite sport: The mediating role of intra-team communicationpublishedVersio

Put Some Music on: The Effects of pre-Task Music Tempo on Arousal, Affective State, Perceived Exertion, and Anaerobic Performance

publishedVersio

A stepwise regression procedure applied to an international production study - a multiple inference solution

The aim of this paper is to apply a certain procedure for stepwise regression analysis to a problem included in a study of integrated international production. The question, which factors are important for the transnational company's trade behaviour in certain respects, have been analysed by means of traditional methods. Hence the more interesting findings on the subject are likely to be reported already and the results here are only to be regarded as supplementary ones. Comparisons between old and new outcomes, and to some extent the interpretations of them, is however one point here

Spegeldämpande filter för L-band

I detta examensarbete presenteras två olika konstruktionslösningar för ett spegeldämpande filter till en heterodynmottagare för L-bandet. Båda filtren är uppbyggda av distribuerade element i mikrostripsteknik. Filtertyper som behandlas är combline med kapacitansdioder för avstämning samt filter med element av typen commensurate length transmissionsledning. Nödvändig teori om mikrostripteknik och distribuerade element behandlas. Konstruktionen av filtren beskrivs steg för steg från filterkrav till färdig mönsterlayout. Layouterna har simulerats med em™ simulatorprogram

A Comparison Between Foam Rolling and Dynamic Stretch on Throwing Velocity and Accuracy Among Male Handball Players

The monotonous and strenuous shoulder moving pattern during throwing may result in microtrauma and fibrous adhesions between the layers of fascia among athletes. In the last decade, self myofascial release (SMR) has gained good reputation as a way to treat these adhesions. However, there is limited data demonstrating the effects on upper body performance among athletes. PURPOSE: The purpose was to examine the effects from an acute bout of upper body SMR or from dynamic stretch (DS), on shoulder range of motion (ROM), throwing velocity and throwing accuracy. Also to examine correlations between shoulder ROM and throwing velocity/accuracy and between playing experience (PE) and changes in throwing velocity/accuracy and ROM. METHODS: 20 elite male handball players (age 20 ± 5 years, weight 84 ± 9 kg) were included in the study. The study had an experimental cross-over design in which participants first performed baseline measures. They also performed SMR and DS in two different trials. The trials were supervised and separated by 14 days. During SMR, the athletes performed a series of foam rolling exercises during two minutes for the muscles surrounding the shoulder joint. The same muscles were stretched for two minutes during the DS trial. Directly after foam rolling and DS, shoulder ROM, throwing velocity and throwing accuracy were measured using a gravity reference goniometer, radar gun and a high speed videocamera. ANOVA with repeated measures and t-tests were used to analyze differences between and within groups. RESULTS: There were no statistically significant differences in either shoulder ROM, throwing velocity or throwing accuracy between the three trials. There was a moderate correlation between shoulder extension and mean accuracy (r = 0.62; p = 0.004) after DS. When dividing the group into high and low experienced players, among the players in the PE-low group, the most experienced players elicited the greatest increase in peak throwing velocity after DS (r = 0.58; p = 0.10). Change in peak accuracy showed moderate but conflicting correlations after SMR (r = -0.53; p = 0.09) and DS (r = 0.50; p = 0.11) for the players in the PE-high group, indicating a better result after SMR. CONCLUSION: An acute bout of upperbody SMR does not affect ROM and does not improve throwing velocity or throwing accuracy compared to baseline or DS among elite male handball players. Nor could any correlation between ROM and throwing velocity or throwing accuracy be observed. The associations between PE and throwing performance was inconclusive. Further studies is needed to define if PE should be taken into consideration when using SMR or DS in order to improve throwing performance

Hunger does not indicate dietary energy availability in healthy humans : A meal intervention study

Bakgrund En mer stillasittande livsstil med ett högre kaloriintag ökar riskerna för övervikt och andra metabola sjukdomar. För att förebygga och behandla dessa sjukdomar behöver vi bland annat förstå hur hungerkänslor regleras hos människan. Hur stor inverkan blodglukosnivåer har på hungerregleringen är dock omdiskuterat. Syfte Syftet med denna studie var att undersöka hur hungerkänslor och blodglukosnivåer förändras efter en måltid, jämfört med fasta. Kan den upplevda hungern påverkas genom periodisk fas-ta? Hur påverkar en invand måltidsrytm hungern? Hur påverkas hunger och blodglukos i för-väntan på en måltid? Metod Tolv friska testpersoner (7 män, 5 kvinnor) där sju stycken var vana vid periodisk fasta och fem inte var det, randomiserades in i två grupper där ena gruppen (Pi) fick äta en 600 kcal pizza medan den andra gruppen fick fasta (F). Blodglukosvärden och hungeruppskattningar registrerades var 30:e minut, förutom första värdet som registrerades 15 minuter innan pizzor-na serverades. Testpersonerna visste inte vilken grupp de skulle hamna i förrän 10 minuter innan pizzorna serverades. Resultat Fem timmar efter måltiden kunde ingen signifikant skillnad i blodglukossänkning observeras mellan grupperna. Hungern skiljde sig inte heller signifikant mellan grupperna. Endast Pi ökade dock signifikant i hunger (P = 0,05) jämfört med sina startvärden. Fastevana bidrog inte till en förbättrad hungerkontroll. Beskedet om vilken grupp testpersonerna skulle hamna i resulterade i att blodglukosnivåerna skiljde sig signifikant mellan grupperna (P = 0,05) när pizzorna serverades. Då sänktes blodglukosnivåerna hos Pi samtidigt som de höjdes hos F. Fyra av fem testpersoner i F och en testperson i Pi blev tydligt hungrigare vid tidpunkter då de vanligtvis brukade äta på. Slutsats Samband mellan absoluta blodglukosnivåer och hunger kunde inte hittas. Stark hunger kunde uppstå fastän dietär energi sannolikt fortfarande absorberades i tarmarna.Våra resultat indikerade därför att akut energitillgänglighet utgör en relativt liten del i den totala hungersignaleringen. En invand måltidsrytm såg ut att påverka hungern mer än vad måltiden i den här studien gjorde. Större fokus vid hungerreglering bör därför ligga på en re-gelbunden måltidsrytm.Background The increasingly sedentary lifestyle of our society combined with a constantly rising caloric intake has elevated the risk of developing obesity and other metabolic diseases. There is a need to understand the underlying mechanisms of hunger regulation to effectively prevent and treat these diseases. The magnitude of which an active regulation of blood glucose has an influence on hunger regulation is rather controversial. Objective The objective of this study was to investigate how the changes in hunger and blood glucose levels may differ after a mixed meal compared to the fasting state. Research questions include: Does intermittent fasting reduce general hunger? How does an entrenched meal-pattern affect hunger? How does hunger and blood glucose change in anticipation of a meal? Method Twelve healthy subjects (7 men, 5 women), of which seven subjects regularly practiced intermittent fasting and the remaining five did not, were randomized into two groups, one group was eating pizza (Pi), and the other group was fasting (F). Blood glucose levels and hunger ratings were collected every 30 minutes, with exception of initial values that were collected 15 minutes prior to the serving of the pizzas. The subjects were unaware of which group they would be designated to until 10 minutes prior to the serving of the pizzas. Results Decline in blood glucose did not significantly differ between groups during the 5 hour window following the meal ingestion. Hunger ratings differed significantly between individuals but not between groups. However, only Pi had significantly elevated hunger ratings in the end of the test period compared to their initial ratings. In anticipation of the meal a significant change in blood glucose was observed between the groups (P = 0.05), where values dropped for Pi and rose for F. Four out of five subjects in F and one subject in Pi were considerably hungrier during time periods they reported as habitual eating occasion. Conclusion Correlations between absolute blood glucose levels and hunger could not be found. An equal rise in hunger appear regardless if subjects were fed or fasting, meaning significant hunger can appear although dietary energy still is absorbed into the blood stream. Thus our results indicate that the acute availability of dietary energy is only a relatively small part of the total hunger signaling process. A disrupted meal pattern seemed to affect hunger feelings more than the ingestion of the served meal. Thus we conclude that more research should focus on meal-pattern regulation to enable better hunger control

Born to Score? The Relationship between Left-Handedness and Success from the 7-Meter Line

An asymmetry in the prevalence of left-handedness vs. right-handedness in society has supposedly resulted in negative frequency-dependent advantages for left-handers in interactive sports. The aim of this study was to test whether these advantages apply to handball by examining whether being left-handed is beneficial when executing 7 m shots, a highly unimanual movement. All 1,625 7 m shots at the men’s 2016–2022 European championships were analyzed using a Bayesian two-level analysis. While the results did not indicate that left-handers were more likely to score from any single 7 m shot, left-handers were overrepresented among the designated shooters compared to both the population as a whole (38% vs. 11.6%) and left-handers on any given handball team (38% vs. 25%). The implication here was that handedness plays no role in the outcome of 7 m shots at the world-class level, but handedness does appear to play a role in who becomes a world-class 7 m shooter