To compare the velocity characteristics of wheelchair propulsion with and without the use of a tennis racquet, eight male wheelchair tennis players performed a series of 20m sprints from a stationary start. The maximum velocities reached on average 4.39 ± 0.74 m/s; however, they were reduced by 0.18 ± 0.06 m/s during the racquet condition. Furthermore, when wheeling under the racquet condition, the velocities achieved during the first three pushes were significantly reduced. The reduction in maximum velocity and relative velocity contributions while holding a tennis racquet may have been due to an ineffective push technique resulting in low effectiveness of force application. The relation of these parameters and trunk stability is discussed.
Abstract. Differential Power Analysis (DPA) attacks find a statistical correlation between the power consumption of a cryptographic device and intermediate values within the computation. Randomization via (Boolean) masking of intermediate values breaks this statistical dependence and thus prevents such attacks (at least up to a certain order). Especially for software implementations, (first-order) masking schemes are popular in academia and industry, albeit typically not as the sole countermeasure. The current practice then is to manually 'insert' Boolean masks: essentially software developers need to manipulate low-level assembly language to implement masking. In this paper we make a first step to automate this process, at least for first-order Boolean masking, allowing the development of compilers capable of protecting programs against DPA.
Exposure to vibration has traditionally been associated with compromised perfusion. This study investigated whether blood supply during whole body vibration (WBV), as an exercise modality, is in proportion to the metabolic demand by the contracting musculature. As a secondary aim, serum levels of vascular endothelial growth factor (VEGF) were assessed. Ten young healthy males performed WBV and dynamic shallow squatting (Squat) exercise at comparable levels of oxygen uptake for 3 min. Changes in oxygenated, deoxygenated and total haemoglobin (O(2)Hb, HHb and tHb, respectively) along with tissue oxygenation index (TOI) were measured continuously before, during and after the exercise by near-infrared spectroscopy (NIRS, Portamon, Artinis Medical Systems, Zetten, The Netherlands). Vascular endothelial growth factor-A blood levels before and after exercise were assessed by ELISA. Oxygen uptake was comparable in Squat and WBV (11.4 and 10.7 ml kg(-1) min(-1)), respectively, P = 0.49), as were all other cardiopulmonary variables. Near-infrared spectroscopy data were found to be non-stationary during and shortly after WBV, but stationary in Squat. There was an increase in O(2)Hb and TOI, and a decrease in HHb during the first 30 s of WBV, but no significant change was observed during Squat. No group difference was found in VEGF serum levels. These results suggest that oxygen supply during WBV is sufficient, and oxygenation is even enhanced during the first approximately 30 s. Most likely, the transient response is because of local vascular regulatory mechanisms and due to muscle contraction mechanics. This might become clinically relevant under pathological conditions, e.g. in vascular disorders.
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