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Willem J. Briels - One of the best experts on this subject based on the ideXlab platform.

  • Kayaking and wagging of liquid crystals under shear:comparing director and mesogen motions
    EPL (Europhysics Letters), 2009
    Co-Authors: Yu-guo Tao, W. K. Den Otter, Willem J. Briels
    Abstract:

    Rod-like colloids in dense solutions perform collective orientational motions under shear flow. The periodic tumbling motions of the director, i.e. the average orientation of the rods, are commonly characterized as Kayaking, wagging and flow-aligning, in order of increasing shear rate. Our event-driven Brownian dynamics simulations of rigid spherocylinders reproduce these three distinct director motions, but also clearly show, for the first time, that the individual mesogens are Kayaking at all shear rates. The synchrony of the mesogens's motions gradually decreases with increasing shear rate, which at a critical shear rate causes a transition of the apparent collective motion from Kayaking to wagging. The rods's persistent Kayaking also explains the continuity of the tumbling period at this transition and the smooth change from wagging to flow-aligning observed at higher shear rates.

  • Kayaking and wagging of rods in shear flow
    Physical Review Letters, 2005
    Co-Authors: Yu-guo Tao, W Den K Otter, Willem J. Briels
    Abstract:

    For the first time, we have simulated the periodic collective orientational motions performed by rigid liquid-crystalline polymers with large aspect ratio in the nematic state in shear flow. In order to be able to do so, we developed a new, event-driven Brownian dynamics technique. We present the results of simulations of rods with aspect ratios L/d ranging from 20 to 60 at volume fractions phi given by Lphi/d=3.5 and 4.5. By studying the path of the director, i.e., the average direction of the rods, we observe Kayaking, wagging, flow aligning, and log-rolling type of orbits, depending on the parameters of the simulation and the initial orientation. We find that the tumbling periods depend on Lphi/d and the shear rate but not on the type of motion. Our simulation results qualitatively confirm theoretical predictions and are in good agreement with the experimental measurements of tumbling times of fd viruses.

Petra Molnar - One of the best experts on this subject based on the ideXlab platform.

  • tracing prehistoric activities musculoskeletal stress marker analysis of a stone age population on the island of gotland in the baltic sea
    American Journal of Physical Anthropology, 2006
    Co-Authors: Petra Molnar
    Abstract:

    The skeletal remains from the Middle Neolithic (2750-2300 BC) burial ground at Ajvide, Gotland, are analyzed in order to explore musculoskeletal patterns and to attempt to trace general as well as three specific prehistoric activities (archery, harpooning, and Kayaking) that are likely to have been performed in this marine setting of fishing, hunting, and gathering. Scoring of muscular and ligament attachments is performed using the scoring method of Hawkey and Merbs ([1995] Int. J. Osteoarchaeol. 5:324-338) for muskuloskeletal stress markers (MSM). The skeletal material consists of 24 male and 15 female adult individuals divided into three age groups: young ( 40 years). Thirty upper body MSM sites, on both the left and right sides, are scored and form the basis of the study. Results show that males most frequently have higher mean MSM scores than females. Bilateral asymmetry was noted as low in both sexes. Age proved to be a contributing factor to increased MSM scores, with a greater age-related increase in females. MSM patterns were analyzed statistically in muscle groups associated with the three investigated activities. Significant positive correlations were observed in male individuals in muscle groups associated with archery and to some extent harpooning, an indication that these activities would mainly have been performed by men. Correlations in Kayaking muscles were not evidently consistent with the Kayaking motion. Furthermore, the costoclavicular ligament, often referred to in connection with "kayaker's clavicle," showed no positive statistical correlation with the Kayaking muscles.

  • Tracing prehistoric activities: Musculoskeletal stress marker analysis of a stone‐age population on the Island of Gotland in the Baltic sea
    American journal of physical anthropology, 2005
    Co-Authors: Petra Molnar
    Abstract:

    The skeletal remains from the Middle Neolithic (2750-2300 BC) burial ground at Ajvide, Gotland, are analyzed in order to explore musculoskeletal patterns and to attempt to trace general as well as three specific prehistoric activities (archery, harpooning, and Kayaking) that are likely to have been performed in this marine setting of fishing, hunting, and gathering. Scoring of muscular and ligament attachments is performed using the scoring method of Hawkey and Merbs ([1995] Int. J. Osteoarchaeol. 5:324-338) for muskuloskeletal stress markers (MSM). The skeletal material consists of 24 male and 15 female adult individuals divided into three age groups: young ( 40 years). Thirty upper body MSM sites, on both the left and right sides, are scored and form the basis of the study. Results show that males most frequently have higher mean MSM scores than females. Bilateral asymmetry was noted as low in both sexes. Age proved to be a contributing factor to increased MSM scores, with a greater age-related increase in females. MSM patterns were analyzed statistically in muscle groups associated with the three investigated activities. Significant positive correlations were observed in male individuals in muscle groups associated with archery and to some extent harpooning, an indication that these activities would mainly have been performed by men. Correlations in Kayaking muscles were not evidently consistent with the Kayaking motion. Furthermore, the costoclavicular ligament, often referred to in connection with "kayaker's clavicle," showed no positive statistical correlation with the Kayaking muscles.

Yu-guo Tao - One of the best experts on this subject based on the ideXlab platform.

  • Kayaking and wagging of liquid crystals under shear:comparing director and mesogen motions
    EPL (Europhysics Letters), 2009
    Co-Authors: Yu-guo Tao, W. K. Den Otter, Willem J. Briels
    Abstract:

    Rod-like colloids in dense solutions perform collective orientational motions under shear flow. The periodic tumbling motions of the director, i.e. the average orientation of the rods, are commonly characterized as Kayaking, wagging and flow-aligning, in order of increasing shear rate. Our event-driven Brownian dynamics simulations of rigid spherocylinders reproduce these three distinct director motions, but also clearly show, for the first time, that the individual mesogens are Kayaking at all shear rates. The synchrony of the mesogens's motions gradually decreases with increasing shear rate, which at a critical shear rate causes a transition of the apparent collective motion from Kayaking to wagging. The rods's persistent Kayaking also explains the continuity of the tumbling period at this transition and the smooth change from wagging to flow-aligning observed at higher shear rates.

  • Kayaking and wagging of rods in shear flow
    Physical Review Letters, 2005
    Co-Authors: Yu-guo Tao, W Den K Otter, Willem J. Briels
    Abstract:

    For the first time, we have simulated the periodic collective orientational motions performed by rigid liquid-crystalline polymers with large aspect ratio in the nematic state in shear flow. In order to be able to do so, we developed a new, event-driven Brownian dynamics technique. We present the results of simulations of rods with aspect ratios L/d ranging from 20 to 60 at volume fractions phi given by Lphi/d=3.5 and 4.5. By studying the path of the director, i.e., the average direction of the rods, we observe Kayaking, wagging, flow aligning, and log-rolling type of orbits, depending on the parameters of the simulation and the initial orientation. We find that the tumbling periods depend on Lphi/d and the shear rate but not on the type of motion. Our simulation results qualitatively confirm theoretical predictions and are in good agreement with the experimental measurements of tumbling times of fd viruses.

Allison Inkster - One of the best experts on this subject based on the ideXlab platform.

G S Palmer - One of the best experts on this subject based on the ideXlab platform.

  • prediction of 200 m sprint Kayaking performance
    Canadian Journal of Applied Physiology-revue Canadienne De Physiologie Appliquee, 2003
    Co-Authors: Ken A Van Someren, G S Palmer
    Abstract:

    The aim of this study was to determine the anthropometric and physiological profile of 200-m sprint kayakers and to examine relationships with 200-m race performance. Twenty-six male kayakers who were categorised in two ability groups, international (Int) and national (Nat) level, underwent a battery of anthropometric and physiological tests and a 200-m race. Race time was significantly lower in Int than Nat (39.9 +/- 0.8 s and 42.6 +/- 0.9 s, respectively). Int demonstrated significantly greater measures of mesomorphy, biepycondylar humeral breadth, circumferences of the upper arm, forearm and chest, peak power and total work in a modified Wingate test, total work in a 2-min ergometry test, peak isokinetic power, and peak isometric force. Significant relationships were found between 200-m time and a number of anthropometric variables and anaerobic and dynamometric parameters. Stepwise multiple regression revealed that total work in the modified Wingate alone predicted 200-m race time (R2 = 0.53, SEE = 1.11 s) for all 26 subjects, while biepycondylar humeral breadth alone predicted race time (R2 = 0.54, SEE = 0.52 s) in Int. These results demonstrate that superior upper body dimensions and anaerobic capacities distinguish international-level kayakers from national-level athletes and may be used to predict 200-m performance.

  • comparison of physiological responses to open water Kayaking and kayak ergometry
    International Journal of Sports Medicine, 2000
    Co-Authors: K A Von Someren, G R W Phillips, G S Palmer
    Abstract:

    This study compared the physiological responses of simulated Kayaking on a K1 ERGO kayak ergometer with open water paddling. Nine well-trained male kayakers (VO2peak 4.27 +/- 0.58 L x min(-1), age 24 +/- 4 yr, mass 77.3 +/- 6.4 kg, height 179.5 +/- 5.3 cm; [mean +/- SD]) performed two 4 min exercise bouts on open water (OW) and on an air braked kayak ergometer (Erg). During exercise, expired air and heart rate (HR) were continuously measured. The distance covered during OW (992 +/- 47.1 m) was highly correlated (r2 = 0.86) with the total work performed in Erg (47.64 +/- 7.67 kJ). There were no differences between trials for oxygen uptake, carbon dioxide production or estimated carbohydrate oxidation. However, during OW, minute ventilation was significantly higher at 60 and 90 s (104.2 +/- 16.4 vs. 92.6 +/- 20.4 L x min(-1) and 120.5 +/- 15.8 vs. 111.7 +/- 17.6 L x min(-1) for 60 and 90 s, respectively, p < 0.05), and HR was higher in OW during the first minute (120 +/- 20 vs. 104 +/- 19 beats x min(-1), 164 +/- 8 vs. 147 +/- 18 beats x min(-1) and 178 +/- 6 vs. 170 +/- 7 beats x min(-1) for 0, 30, and 60 s, respectively, p < 0.05). There were no differences in peak VO2 between OW and Erg (4.10 +/- 0.49 vs. 4.09 +/- 0.53 L x min(-1), respectively) nor in post-exercise blood (lactate) (6.43 +/- 1.47 vs. 6.59 +/- 0.99 mmol x L(-1), respectively). We conclude that the K1 ERGO accurately simulates the physiological demands of short-term, high-intensity Kayaking.