26 research outputs found
Normal and lateral Casimir force: Advances and prospects
We discuss recent experimental and theoretical results on the Casimir force
between real material bodies made of different materials. Special attention is
paid to calculations of the normal Casimir force acting perpendicular to the
surface with the help of the Lifshitz theory taking into account the role of
free charge carriers. Theoretical results for the thermal Casimir force acting
between metallic, dielectric and semiconductor materials are presented and
compared with available experimental data. Main attention is concentrated on
the possibility to control the magnitude and sign of the Casimir force for
applications in nanotechnology. In this respect we consider experiments on the
optical modulation of the Casimir force between metal and semiconductor test
bodies with laser light. Another option is the use of ferromagnetic materials,
specifically, ferromagnetic dielectrics. Under some conditions this allows to
get Casimir repulsion. The lateral Casimir force acting between sinusoidally
corrugated surfaces can be considered as some kind of noncontact friction
caused by zero-point oscillations of the electromagnetic field. Recent
experiments and computations using the exact theory have demonstrated the role
of diffraction-type effects in this phenomenon and the possibility to get
asymmetric force profiles. Conclusion is made that the Casimir force may play
important role in the operation of different devices on the nanoscale.Comment: 27 pages, 13 figures; Invited keynote lecture at the 2nd
International Conference on Science of Friction, Ise-Shima, Mie, Japan,
September 13-18, 2010; to appear in J. Phys.: Conf. Se
Transport matrix for particles and momentum in collisional drift waves turbulence in linear plasma devices
International audienceThe relationship between the physics of turbulent transport of particles and azimuthal momentum in a linear plasma device is investigated using a simple model with a background density gradient and zonal flows driven by turbulent stresses. Pure shear flow driven Kelvin-Helmholtz instabilities (k∥=0) relax the flow and drive an outward (down gradient) flux of particles. However, instabilities at finite k∥ with flow enhanced pumping can locally drive an inward particle pinch. The turbulent vorticity flux consists of a turbulent viscosity term, which acts to reduce the global vorticity gradient and the residual vorticity flux term, accelerating the zonal flows from rest. Moreover, we use the positivity of the production of fluctuation potential enstrophy to obtain a constraint relation, which tightly links the vorticity transport to the particle transport. This relation can be useful in explaining the experimentally observed correlation between the presence of E×B flow shear and the measured inward particle flux in various magnetically confined plasma devices
Casimir rack and pinion
As the technological advances lead to miniaturization of mechanical devices, engineers face new challenges that are brought about by the fundamentally different rules that apply at small scales. One of the biggest problems in small machines is the excessive wear of the many surfaces that work in contact with each other, which severely constrains the durability of such machine parts. Here, a force that is caused by the quantum fluctuations of electromagnetic field - known as the lateral Casimir force - is employed to propose a design for a potentially wear-proof rack and pinion with no contact, which can be miniaturized to nano-scale. We demonstrate that both uniform and harmonic lateral motion of the rack can be converted into unidirectional rotation of the pinion. The robustness of the design is studied by exploring the relation between the pinion velocity and the rack velocity in the different domains of the parameter space. The effects of friction and added external load are also examined. © 2007 IOP Publishing Ltd
Automatic detection of epileptic seizure using time-frequency distributions
The aim of this work is to introduce a new method based on time frequency distribution for classifying the EEG signals. Some parameters are extracted using time-frequency distribution as inputs to a feed-forward backpropagation neural networks (FBNN). The proposed method had better results with 98.25% accuracy compared to previously studied methods such as wavelet transform, entropy, logistic regression and Lyapunov exponent
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Spontaneous profile self-organization in a simple realization of drift-wave turbulence
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Spontaneous profile self-organization in a simple realization of drift-wave turbulence
We report the observation of a transport bifurcation that occurs by spontaneous self-organization of a drift-wave and shear flow system in a linear plasma device. As we increase the magnetic field above a threshold (BCr = 1200 G), a global transition occurs, with steepening of mean density and ion pressure profiles, onset of strong E × B shearing, a reduction of turbulence, and improved turbulent radial particle transport. An abrupt transition appears in the graph of turbulent particle flux versus density gradient. Hysteresis in the density gradient further confirms this transport bifurcation. The total Reynolds work on the flow sharply increases above threshold. This correlates with the increase of density steepness, which suggests the Reynolds stress-driven flow that plays an essential role in density steepening and transport bifurcation. A change in turbulence feature from drift waves (DWs) to a mix of DWs and ion temperature gradients also coincides with the transport bifurcation. Interesting phenomena related to the transport bifurcation are also reported; a local inward particle flux, the co-existence of ion and electron features, and a self-sustained axial flow absent momentum input