A circle swimmer at low Reynolds number

Swimming in circles occurs in a variety of situations at low Reynolds number. Here we propose a simple model for a swimmer that undergoes circular motion, generalising the model of a linear swimmer proposed by Najafi and Golestanian (Phys. Rev. E 69, 062901 (2004)). Our model consists of three solid spheres arranged in a triangular configuration, joined by two links of time-dependent length. For small strokes, we discuss the motion of the swimmer as a function of the separation angle between its links. We find that swimmers describe either clockwise or anticlockwise circular motion depending on the tilting angle in a non-trivial manner. The symmetry of the swimmer leads to a quadrupolar decay of the far flow field. We discuss the potential extensions and experimental realisation of our model.Comment: 9 pages, 9 Figure

Comment on the article by J. Elgeti, U. B. Kaupp, and G. Gompper : hydrodynamics of sperm cells near surfaces

A recent study by Elgeti et al. used multiparticle collision dynamics to simulate a long-standing problem: the approach of sperm to surfaces, and subsequent accumulation. The authors highlight differences in their predictions with those of the earlier Stokes flow simulations of Smith et al. attributing the differences to methodological flaws in the earlier article. In this Comment, we discuss the criticisms leveled in detail, and review some recently published work that shows how species-specific details of cell morphology provides a more likely explanation for the differing predictions of the two studies. We also highlight experimental work that supports the study of Smith et al

Dynamic Load Balancing for a Grid Application

Grids functionally combine globally distributed computers and information systems for creating a universal source of computing power and information. A key characteristic of grids is that resources (e.g., CPU cycles and network capacities) are shared among numerous applications, and therefore, the amount of resources available to any given application highly fluctuates over time. In this paper we analyze the impact of the fluctuations in the processing speed on the performance of grid applications. Extensive lab experiments show that the burstiness in processing speeds has a dramatic impact on the running times, which heightens the need for dynamic load balancing schemes to realize good performance. Our result

Arbitrary picosecond pulse shaping in a radially polarized Yb-fiber MOPA beyond 10 W

We demonstrate simultaneous spatial and arbitrary temporal pulse-shaping with a picosecond Yb-doped fiber laser system generating an output power > 10 W. By using a self-developed feed-back control algorithm on a single polarization optical pulse shaper, we obtained arbitrary complex pulse structures in the time domain with high accuracy and at high power level. Meanwhile, the pulse shaping in the spatial domain has been achieved using an in-house S-waveplate to change the linearly polarized fundamental mode into doughnut modes with different polarizations each at a time. This new capability enhances the versatility of ultrashort fiber laser systems for high precision material processing. Directly amplifying the radially polarized doughnut-mode avoids complex beam conversion at the output and provides an efficient route for power-scaling

Validity of the comprehensive assessment of prospective memory (CAPM) for use with adults with traumatic brain injury

Objective: To expand upon the existing psychometric properties of the Comprehensive Assessment of Prospective Memory (CAPM) for use with adults with traumatic brain injury by examining concurrent and criterion validity. Method: Participants were 45 adults with a traumatic brain injury. Participants and their relatives completed Section A of the CAPM and a measure of psychosocial integration. Participants were also administered two neuropsychological tests of prospective memory, the Cambridge Prospective Memory Test (CAM-PROMPT) and the Memory Intentions Screening Test (MIST). Concurrent validity was measured by comparing scores on the CAPM with scores on the CAM-PROMPT and MIST. Criterion validity was examined by correlating CAPM scores with level of psychosocial integration. Results: Participant self-reports on the CAPM were not significantly correlated with the CAM-PROMPT or MIST, but were significantly correlated with level of psychosocial integration. Relative reports on the CAPM were correlated significantly with total score on the MIST and CAM-PROMPT and level of psychological integration. Conclusions: The findings indicate that the concurrent validity of the self-report version of CAPM is low suggesting that selfreports alone do not provide an objective measure for assessing prospective memory function. The relative report version however, demonstrated reasonable concurrent and criterion validity, suggesting that the relative report version of the Section A of the CAPM is a useful means of evaluating frequency of prospective memory failure in adults with traumatic brain injury