5,643 research outputs found
One-point statistics and intermittency of induced electric field in the solar wind
The interplanetary induced electric field e=vxb is studied, using solar wind
time series. The probability distribution functions (PDFs) of the electric
field components are measured from the data and their non-gaussianity is
discussed. Moreover, for the first time we show that the electric field
turbulence is characterized by intermittency. This point is addressed by
studying, as usual, the scaling of the PDFs of field increments, which allows a
quantitative characterization of intermittency.Comment: Accepted for publication on Europhysics Letters, April 22th, 200
Photon spin-to-orbital angular momentum conversion via an electrically tunable -plate
Exploiting electro-optic effects in liquid crystals, we achieved real-time
control of the retardation of liquid- crystal-based -plates through an
externally applied voltage. The newly conceived electro-optic -plates can be
operated as electrically driven converters of photon spin into orbital angular
momentum, enabling a variation of the orbital angular momentum probabilities of
the output photons over a time scale of milliseconds.Comment: 4 pages, 5 figures, submitte
The Solar Wind as a Turbulence Laboratory
In this review we will focus on a topic of fundamental importance for both astrophysics and plasma physics, namely the occurrence of large-amplitude low-frequency fluctuations of the fields that describe the plasma state. This subject will be treated within the context of the expanding solar wind and the most meaningful advances in this research field will be reported emphasizing the results obtained in the past decade or so. As a matter of fact, Helios inner heliosphere and Ulysses' high latitude observations, recent multi-spacecrafts measurements in the solar wind (Cluster four satellites) and new numerical approaches to the problem, based on the dynamics of complex systems, brought new important insights which helped to better understand how turbulent fluctuations behave in the solar wind. In particular, numerical simulations within the realm of magnetohydrodynamic (MHD) turbulence theory unraveled what kind of physical mechanisms are at the basis of turbulence generation and energy transfer across the spectral domain of the fluctuations. In other words, the advances reached in these past years in the investigation of solar wind turbulence now offer a rather complete picture of the phenomenological aspect of the problem to be tentatively presented in a rather organic way
Sign Singularity of the Magnetic Helicity from in Situ Solar Wind Observations
Some turbulent signed measures show a singularity related to extreme oscillations in sign, the scaling behavior of cancellations between positive and negative contributions being characterized by the cancellation exponent Îș. Using in situ observations of magnetic fluctuations in the solar wind, we show that magnetic helicity is sign singular, a property that underlies the dominance of a single sign of polarization of fluctuations at small scales. We recover a statistical correlation between Îș and the bulk solar wind speed when any correlation has been found between Îș and the distance from the Sun. Even if the usual models of magnetic fluctuations based on random phases are able to reproduce (in a statistical sense) the gross features of helicity fluctuations, they cannot reproduce the behavior of sign singularity
Tracking Fractures of Deformable Objects in Real-Time with an RGB-D Sensor
This paper introduces a method able to track in real-time a 3D elastic deformable objects which undergo fractures, using the point cloud data provided by an RGB-D sensor. Our framework relies on a prior visual segmentation of the object in the image. The segmented point cloud is registered by non-rigidly fitting the mesh, based on the Finite Element Method to physically model elasticity, and on geometrical point-to-point correspondences to compute external forces exerted on the mesh. Fractures are handled by processing the stress tensors computed on the mesh of the FEM model, in order to detect fracturable nodes. Local remeshing around fracturable nodes is then performed to propagate the fracture. The real-time performance of the system is demonstrated on real data involving various deformations and fractures
Nonprehensile Dynamic Manipulation: A Survey
Nonprehensile dynamic manipulation can be reason- ably considered as the most complex manipulation task. It might be argued that such a task is still rather far from being fully solved and applied in robotics. This survey tries to collect the results reached so far by the research community about planning and control in the nonprehensile dynamic manipulation domain. A discussion about current open issues is addressed as well
Real-time tracking of 3D elastic objects with an RGB-D sensor
This paper presents a method to track in real-time a 3D textureless object which undergoes large deformations such as elastic ones, and rigid motions, using the point cloud data provided by an RGB-D sensor. This solution is expected to be useful for enhanced manipulation of humanoid robotic systems. Our framework relies on a prior visual segmentation of the object in the image. The segmented point cloud is registered first in a rigid manner and then by non-rigidly fitting the mesh, based on the Finite Element Method to model elasticity, and on geometrical point-to-point correspondences to compute external forces exerted on the mesh. The real-time performance of the system is demonstrated on synthetic and real data involving challenging deformations and motions
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