We demonstrate experimentally a gating ratchet with cold rubidium atoms in a driven near-resonant optical lattice. A single-harmonic periodic modulation of the optical potential depth is applied, together with a single-harmonic rocking force. Directed motion is observed as a result of the breaking of the symmetries of the system. DOI: 10.1103/PhysRevLett.100.040603 PACS numbers: 05.60.Cd, 05.40.ÿa, 05.45.ÿa, 05.70.Ln The rectification of Brownian motion in the absence of net applied bias forces is an intriguing phenomenon, termed the ratchet effect, which has recently attracted much attention in different fields [1][2][3][4][5][6][7][8]. In fact, ratchets have been implemented in a variety of physical systems [9][10][11][12][13][14][15] ranging from solid state devices and optical trap setups to granular gases and nanopores in polymer films. All the different implementations of the ratchet effect can be traced back to two main elements. First, the system has to be driven out of equilibrium, so to overcome the restrictions imposed by the second principle of thermodynamics. Second, the relevant symmetries of the system, which would otherwise inhibit directed motion, have to be broken.In the rocking ratchet [2], particles in a periodic potential experience also an applied ac force. The applied force is zero average and time symmetric. However, there is an eventual net flux due to the symmetry-breaking anisotropy of the potential. The same effect can be obtained for a spatially symmetric potential and a biharmonic drive, with the time symmetry of the system controlled by the symmetry of the drive [4 -7,11].In the gating ratchet [16], particles experience an oscillating potential which is spatially symmetric. A zeroaverage and time-symmetric ac force is also applied. A current can be generated following a gating effect, with the lowering of the potential barriers synchronized with the motion produced by the additive force. This mechanism has to be contrasted with the previously demonstrated acdriven ratchets with additive biharmonic driving [11], in which the underlying mechanism is harmonic mixing [17].In this work we present the experimental demonstration of a gating ratchet with cold rubidium atoms in a dissipative optical lattice. We demonstrate that the gating mechanism can indeed lead to the generation of a current and show that such a current generation is controlled by the symmetries of the system.Before presenting the experimental results, it is important to carry out the symmetry analysis for the gating ratchet. This will serve as a guide for the experimental work. We consider a weakly damped particle in an amplitude modulated symmetric potential Vx1 mt. A rocking force Ft is also applied. The Langevin equation for the particle of mass M isHere x is the position of the particle at the time t, and and are the damping coefficient and a stationary Gaussian noise, respectively. Both the amplitude modulation mt and the rocking force Ft are single-harmonic fields:For the symmetry analysis, the noise term t ca...

Robotic devices are traditionally actuated by hydraulic systems or electric motors. However, with the desire to make robotic systems more compact and versatile, new actuator technologies are required. In this paper, the control of ionic polymer metal composite actuators is investigated from a practical perspective. The actuator characteristics are examined though the unblocked maximum displacement and blocked force output. Open-loop position control then closed-loop position proportional, integral, and derivative (PID) control is then applied to a strip of actuators. Finally, the performance of the polymer is investigated when implementing an impedance controller (force/position control).

This article reflects the proceedings of a workshop session, Postgraduate Education and Knowledge Translation, at the 2007 Academic Emergency Medicine Consensus Conference on knowledge translation (KT) in emergency medicine (EM). The objective was to develop a research strategy that incorporates KT into EM graduate medical education (GME). To bridge the gap between the best evidence and optimal patient care, Pathman et al. suggested a multistage model for moving from evidence to action. Using this theoretical knowledge-to-action framework, the KT consensus conference group focused on four key components: acceptance, application, ability, and remembering to act on the existing evidence. The possibility that basic familiarity, along with the pipeline by Pathman et al., may improve KT uptake may be an initial starting point for research on GME and KT. Current residents are limited by faculty GME role models to demonstrate bedside KT principles. The rapid uptake of KT theory will depend on developing KT champions locally and internationally for resident physicians to emulate. The consensus participants combined published evidence with expert opinion to outline recommendations for identifying the barriers to KT by asking four specific questions: 1) What are the barriers that influence a resident's ability to act on valid health care evidence? 2) How do we break down these barriers? 3) How do we incorporate this into residency training? 4) How do we monitor the longevity of this intervention? Research in the fields of GME and KT is currently limited. GME educators assume that if we teach residents, they will learn and apply what they have been taught. This is a bold assumption with very little supporting evidence. This article is not an attempt to provide a complete overview of KT and GME, but, instead, aims to create a starting point for future work and discussions in the realm of KT and GM. ACADEMIC EMERGENCY MEDICINE 2007; 14:1008-1014 ª 2007 by the Society for Academic Emergency MedicineKeywords: graduate medical education, residents, emergency medicine, knowledge translation, core competency T he task of theme IIIa of this consensus conference on knowledge translation (KT) was to develop a research framework describing how medical education strategies can promote evidence implementation by emergency medicine (EM) resident physicians.KT skills should be appreciated and utilized by medical students, residents, and postgraduate physicians. Yet, each of these groups has a unique baseline skill set and appreciation for the capacity of KT to enhance EM clinical practice. Accordingly, KT education will need to be

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