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[en] This paper describes an educational analysis of a first year physics experiment on standing waves for engineering students. The educational analysis is based on the ACELL (Advancing Chemistry by Enhancing Learning in the Laboratory) approach which includes a statement of educational objectives and an analysis of student learning experiences. The experiment is likely to be found in many physics departments, hence is appropriate to illustrate the ACELL approach in physics. The concepts associated with standing waves are difficult; however, they are underpinned by mathematical formulation which lend themselves to be visualized in experiments. The challenge is to strike a balance between these two for the particular student cohort. In this study, this balance is achieved by using simple equipment and providing appropriate scaffolds for students to associate abstract concepts with concrete visuals. In essence the experiment is designed to adequately manage cognitive resources. Students work in pairs and are questioned and assisted by demonstrators and academic staff during a 2 h practical class. Students were surveyed using the ACELL instrument. Analysis of the data showed that by completing the practical students felt that their understanding of physics had increased. Furthermore, students could see the relevance of this experiment to their engineering studies and that it provided them with an opportunity to take responsibility for their own learning. Overall they had a positive learning experience. In short there is a lot of dividend from a small outlay of resources.
[en] In this reply we respond to comments made by Repetto et al and by Butokov on our letter (Burko 2010 Eur. J. Phys. 31 L71-7), in which we discussed two different results for the elastic potential energy of a string element. One derived from the restoring force on a stretched string element and the other from the work done to bring the string to a certain distorted configuration. We argue that one cannot prefer from fundamental principles the former over the latter (or vice versa), and therefore one may apply either expression to situations in which their use contributes to insight. The two expressions are different by a boundary term which has a clear physical interpretation. For the case of standing waves, we argue that the latter approach has conceptual clarity that may contribute to physical understanding. (letters and comments)
[en] Simple apparatus is described which demonstrates wave propagation in a infinitely long periodic structure. The structure consists of a toroidal transmission line with periodic variation of the wave phase velocity around the line. Results are presented to illustrate the effect of the periodic perturbation on the resonant frequencies of the system
[en] We recently demonstrated that strings of trapped atoms inside a standing wave optical dipole trap can be rearranged using optical tweezers [Y. Miroshnychenko et al., Nature 442, 151 (2006)]. This technique allows us to actively set the interatomic separations on the scale of the individual trapping potential wells. Here, we use such a distance-control operation to insert two atoms into the same potential well. The detected success rate of this manipulation is 16-3+4%, in agreement with the predictions of a theoretical model based on our experimental parameters
[en] The analysis of the peculiarities of the anomalous coherent scattering of thee-level atoms in the field of standing waves is presented. It is shown that at the anomalous scattering (occurring in strong fields) the diffraction pattern undergoes qualitative changes (an asymmetry occurs and a partial inhibition trapping takes place) which would be taken into account when projecting effective schemes for atomic selection or beam-splitting. 11 refs
[en] Theory and experiment show that two electromagnetic modes are necessary and sufficient to determine the field nonuniformity within a parallel-plate rf capacitive plasma reactor. These two modes give rise to the standing wave effect and the telegraph effect. The standing wave effect is associated with high frequencies in large reactors where the reactor size is larger than about a tenth of the vacuum wavelength of the rf excitation. The telegraph effect is associated with asymmetric electrode areas, which necessitates the redistribution of rf current along the plasma to maintain rf current continuity
[en] Charged particle accelerators generally include a pre-grouping or pre-accelerating structure associated with the accelerator structure itself. But pre-grouping or pre-accelerating structures of known type (Patent application No. 70 39261 for example) present electric and dimensional characteristics that rule them out for accelerators working at high frequencies (C or X bands for example), since the distance separating the interaction spaces becomes very small in this case. The accelerator structure mentioned in this invention can be used to advantage for such accelerators
[fr]Les accelerateurs de particules chargees comportent generalement une structure de pregroupement ou de preacceleration associee a la structure acceleratrice proprement dite. Or les structures de pregroupement ou de preacceleration de type connu (Brevet de la Demanderesse no. 70 39261 par exemple) presentent des caracteristiques electriques et dimensionnelles telles qu'elles ne sont plus utilisables pour des accelerateurs fonctionnant a frequences elevees (bande C ou bande X par exemple). En effet, la distance separant les espaces d'interaction devient, dans ce cas tres faible. La structure acceleratrice objet de la presente invention peut etre utilisee avantageusement pour de tels accelerateurs
[en] Complex modes and traveling waves in axially moving Timoshenko beams are studied. Due to the axially moving velocity, complex modes emerge instead of real value modes. Correspondingly, traveling waves are present for the axially moving material while standing waves dominate in the traditional static structures. The analytical results obtained in this study are verified with a numerical differential quadrature method.
[en] Acoustic tweezers are gaining increasing attention as a noncontact method that is capable of handling microparticles and nanoparticles in a controllable manner. By designing the acoustic field, objects, such as cells, bacteria, exosomes, and even worms, could be precisely and flexibly manipulated by the acoustic radiation force. With the advantages of non-invasiveness, label-free operation, and low power consumption, acoustic tweezers have been proven to be crucially important for a diverse range of applications, particularly in the biomedical domain. In this paper, we review the historical development and the current state of the theory of the acoustic radiation force. Furthermore, we introduce recent advancements in acoustic tweezers based on the standing wave, travelling wave, single beam, and arbitrary wave fields; its mechanism and potential applications are also presented. Finally, some perspectives referring to the future development of acoustic tweezers are discussed. (topical review)