Criticality for branching processes in random environment

We study branching processes in an i.i.d. random environment, where the associated random walk is of the oscillating type. This class of processes generalizes the classical notion of criticality. The main properties of such branching processes are developed under a general assumption, known as Spitzer's condition in fluctuation theory of random walks, and some additional moment condition. We determine the exact asymptotic behavior of the survival probability and prove conditional functional limit theorems for the generation size process and the associated random walk. The results rely on a stimulating interplay between branching process theory and fluctuation theory of random walks.Comment: Published at http://dx.doi.org/10.1214/009117904000000928 in the Annals of Probability (http://www.imstat.org/aop/) by the Institute of Mathematical Statistics (http://www.imstat.org

DEVELOPMENT OF A NOVEL DEVICE FOR MEASUREMENT OF PEDAL FORCE IN CYCLING

A device was developed to be mounted between a cycling shoe and cleat with the ability to measure force perpendicular to the pedal. The device consists of a PolyPower force sensor placed in between two aluminium plates connected by three bolts. Furthermore, a mechanism allowing pulling forces to be measured is explained. The device was comparable to a golden standard when pushed upon, but did not provide valid measurements of pulling forces. In order to function as a valid and reliable power meter or a device capable of measuring pedal forces, the sensor´s recovery rate should be improved along with the pulling mechanism of the device while angular sensors could be added for assessment of pedal kinematics

The one-ski-method:effects of an alternative teaching approach on selected movement patterns in alpine skiing

Teaching methods in skiing have marginally developed within the last decades. An intervention comparing the conventional approach (SP) and the One-Ski-Method (OSM) is proposed in which the main body actions are first trained on one ski and successively transferred to two skis. The OSM teaches the main body actions towards a proper position on parallel skis. The snowplow gets avoided as it implies obstructive body actions. Two groups were trained using each method. Video footage from the first and the fifth day were evaluated by experts following selected criteria. OSM learners showed significantly larger improvements compared to SP. Results indicate a faster acquisition of key elements of alpine skiing and provide a foundation for further investigations of the OSM method

ANALYSIS OF SKIER KINETICS DURING THE START AND KINEMATICS OVER THE FIRST FEATURES DURING A SKI CROSS RUN

The aim of this study was to analyse the start and the skiing technique in Ski Cross, and relate them to the performance. The project consisted of two parts: an indoor test was conducted to relate the impulse applied by the skiers on the start handles to their velocity at handle release. Further, an outdoor test was conducted to study the skiers’ kinematics over the first features of a Ski Cross run, and relate it to completion time of the first section (~30 m). Five athletes from the Swedish National Team were tested on several occasions using an instrumented start gate, an inertial motion unit (IMU) based suit and a differential global navigation satellite system (GNSS). Results showed marked differences in starting technique leading to distinct velocities after handle release. These differences did not immediately relate to time used to cover the first feature (Wu-Tang) in the run. The data demonstrate that the generation of centre of mass velocity during the start is not the main criterion for a successful performance in the initial section of a ski cross run

Upper and lower space-time envelopes for oscillating random walks conditioned to stay positive

We provide integral tests for functions to be upper and lower space time envelopes for random walks conditioned to stay positive. As a result we deduce a 'Hartman-Winter' Law of the Iterated Logarithm for random walks conditioned to stay positive under a third moment assumption. We also show that under a second moment assumption the conditioned random walk grows faster than n^½ (log n)^(-(1+e)) for any e > 0. The results are proved using three key facts about conditioned random walks. The first is the step distribution obtained in Bertoin and Doney (1994), the second is the pathwise construction in terms of excursions in Tanaka (1998) and the third is a new Skorohod type embedding of the conditioned process in a Bessel-3 process

EFFECTS OF MEDIAL WEDGE INSOLES WHEN WALKING ON DIFFERENT SURFACES

Shoe inserts are often used to correct for foot misalignment or overloading during walking and running. To understand the interaction of medial wedge insoles and different surface hardness and geometry, we investigated plantar pressure and rearfoot movement. Twentyeight subjects with normal feet were tested when walking with and without insole on all combinations of hard and soft surface and level and upstairs walking. The main changes in load distribution and rearfoot movement were found between wearing insoles and not wearing them while differences between surfaces were small. In conclusion, surface hardness did not change the general effects of the insoles

SNOWBOARDER'S FRACTURE: CHANGING JOINT MECHANICS BY FOOT POSITION DURING A SIMULATED LANDING TASK

A high proportion of fractures to the lateral process of the talus (LPT) has been reported in snowboarding, which accounted for 34% of all ankle fractures (Kirkpatrick et al., 1998). A fracture to the LPT is an injury unique to snowboarders and is often misdiagnosed by physicians as an anterolateral ankle sprain. LPT fractures often involve the articular surface of the subtalar joint and it has been shown that misdiagnosis may lead to severe degeneration of the ankle joint and long term morbidity (Boon et aI., 1999). The mechanism of this injury has been studied intensively. LPT fractures are high impact injuries, landing after aerial manoeuvres is thought to be the major cause of LPT fractures (Boon et aI., 1999). In a cadaver study no fractures to the LPT were recorded under purely dorsalflexed conditions but in six of the eight specimens fractures occurred with the addition of 20° external rotation. An axial load of 2200 -8900 N was required to produce a fracture (LPT) in this position. It was proposed by Boon and colleagues tr.at the subsequent 'opening' of the ankle joint seen with heel inversion and external rotation of the talus results in the lateral process shifting upwards on the posterior articular process of the calcaneus. The purpose of this study was to simulate a snowboard landing in the laboratory with using an inverse dynamics approach to calculate effective joint loading for different binding alignments. It was hypothesised that the 'stance' chosen will affect loading and that an optimum foot alignment will help to minimise joint load