Silvia Perri, V. Carbone · Physical Review E · 2008
We investigate the dynamics of a realization of the stochastic Fermi acceleration mechanism. The model consists of test particles moving between two oscillating magnetic clouds and differs from the usual Fermi-Ulam model in two ways. (i) Particles can penetrate inside clouds before being reflected. (ii) Particles can radiate a fraction of their energy during the process. Since the Fermi mechanism is at work, particles are stochastically accelerated, even in the presence of the radiated energy. Furthermore, due to a kind of resonance between particles and oscillating clouds, the probability density function of particles is strongly modified, thus generating beams of accelerated particles rather than a translation of the whole distribution function to higher energy. This simple mechanism could account for the presence of beamlets in some space plasma physics situations.
Cited by 1
Xiaoming Huo · Encyclopedia of Statistical Sciences · 2005
Abstract Beamlets is a data structure to be used to analyze linear or curvilinear features in two dimensional space. Beamlets are a collection of dyadically organized line segments, taking a range of positions, orientations, and having various lengths. The key advantage of such a data structure is that it forms a multiscale framework for linear and curvilinear features. This data structure enables new methods in statistical modeling, statistic estimation, denoising, data reduction, and compression. The new methods are both computationally efficient and theoretically optimal. The derived methods are particularly suitable for large size data.
Cited by 1
Byers, D. C., Banks, B. A. · NASA STI Repository (National Aeronautics and Space Administration)
Ion beamlets of predetermined configurations are formed by shaped apertures in the screen grid of an ion thruster having a double grid accelerator system. A plate is placed downstream from the screen grid holes and attached to the accelerator grid. When the ion thruster is operated holes having the configuration of the beamlets formed by the screen grid are sputtered through the plate at the accelerator grid.
Cited by 0Open access
2008
Abstract—A multiscale coder for curves and boundaries is presented. It utilizes a multiscale structure—beamlets—that is designed primarily for linear and curvilinear features. The coder is composed of three main components: 1) a rate-distortion optimized beamlet-based representation, 2) a tree-based coding from a beamlet representation to a symbol stream, and 3) an entropy coder. This coder is named “JBEAM. ” Taking advantage of its multiscale property, we utilized tree-based coding to make it progressive. The derived coder has a low order of computational complexity. Simulations demonstrate an advantage over the state-of-the-art industrial standard: JBIG 2. A software package, which includes an implementation of JBEAM, is made available. Variations and potential improvements of this method will be discussed. This work may inspire more activities in this line of research, improving curve coding. Index Terms—Beamlet, curve coding, tree-based coding. I.
Cited by 0
Jian Mao, Ru‐Shan Wu · 2007
In this paper, we develop an efficient method of directional illumination analysis in the local angle domain using local exponential beamlets. To get the local angle information, the wave field is decomposed by local exponential beamlets, which is implemented by a combination of local cosine and sine transforms. As the local cosine/sine transforms have fast algorithms, this method has much better efficiency than the Gabor‐Daubechies frame method. We calculated the directional illumination map and the acquisition dip response (ADR) for the 2D SEG/EAGE salt model to demonstrate the validity of our method.
Cited by 24
Xiaoming Huo, Jihong Chen · IEEE Transactions on Image Processing · 2005
A multiscale coder for curves and boundaries is presented. It utilizes a multiscale structure--beamlets--that is designed primarily for linear and curvilinear features. The coder is composed of three main components: 1) a rate-distortion optimized beamlet-based representation, 2) a tree-based coding from a beamlet representation to a symbol stream, and 3) an entropy coder. This coder is named "JBEAM." Taking advantage of its multiscale property, we utilized tree-based coding to make it progressive. The derived coder has a low order of computational complexity. Simulations demonstrate an advantage over the state-of-the-art industrial standard: JBIG 2. A software package, which includes an implementation of JBEAM, is made available. Variations and potential improvements of this method will be discussed. This work may inspire more activities in this line of research, improving curve coding.
Cited by 42
Yangjian Cai, Qiang Lin · Optics & Laser Technology · 2004
Cited by 5
UMCS Library (Maria Curie-Skłodowska University) · 2004
Cited by 0
Kruit, P., Van Bruggen, M.J. · Research Repository (Delft University of Technology) · 2006
Cited by 0Open access
Jonathan Edwards, J. F. Nicholson, Simon O’Keefe · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2005
Beamlet processing is a powerful and flexible approach to the identification of line based structures in data. The processing method is efficient (<i>O</i>(<i>n</i><sup>2</sup>)) and also robust to variation in direction of the line continuation. This paper identifies two weaknesses with the current approach: the inability to identify lines at variable intensity, and with variation in width. These are addressed with a simple modification to the process used in selecting the salient beamlets called <b>maxbeam2</b>. This is demonstrated on a line image with variation in signal intensity and line width. The technique appears to correct the above weaknesses with only a small amount of extra processing, and hence make beamlets more generally applicable.
Cited by 0
Ru‐Shan Wu, Ling Chen · WORLD SCIENTIFIC eBooks · 2002
Cited by 18
Grigorenko, E., A. Fedorov, E. Budnik et al. · HAL (Le Centre pour la Communication Scientifique Directe) · 2005
Cited by 0
Xiaoming Huo, Jihong Chen, David L. Donoho · 2004
Beamlets are combined with zero-tree coding algorithm to create a new coding method, particularly suitable for lines and curves. Beamlets are a multiscale collection of line segments at a range of scales, location, having a variety of lengths and orientations. The new coding scheme - named JBEAM is more efficient - in terms of bit rates - in coding binary curvy images in simulations.
Cited by 6
Е. Е. Григоренко, A. Fedorov, E. Yu. Budnik et al. · Planetary and Space Science · 2004
Cited by 4
M. Cavenago, G. Serianni, P. Veltri et al. · AIP conference proceedings · 2018
After installation of Mo liners in the source NIO1 (Negative Ion Optimization phase 1), hydrogen plasmas in a continuous regime operation (much longer than one hour) are routinely maintained, with more than 1 kW rf power and 0.5 Pa pressure, allowing a systematic investigation of pure H− volume effect, which requests a much lower acceleration voltage Vs ≅ 12 kV than future Cs operations at Vs ≅ 60 kV. A new extraction grid EG was installed (replacing some eroded insulators) and preliminary beam images are compared to old EG ones, discussing effects of different deflection field strength and need of intermediate values. Large improvements in beam diagnostics and the effect of installation of a cryogenic pump are also reported.
Cited by 2Open access
Irina Robu, Erhard W. Rothe · Journal of Flow Visualization and Image Processing · 2005
We describe the creation of sets of 633-nm beamlets and their bending by supercritical СО2. Small temperature gradients within a cell that contains the fluid resulted in large density gradients that, in turn, are almost proportional to gradients of the optical refractive index. The paths of such beamlets can be described quantitatively. Beamlets were made with a He−Ne laser-beam that impinged on an array of apertures. The transmitted light forms Fraunhofer diffraction patterns whose shapes depend upon the arrangement of the apertures. The beamlets traversed a 7.62-cm-long cell and were deflected downward to a degree that depended upon the spatial distribution of CO2 density. The deflection is as much as 0.25 m at a distance of 2 m.
Cited by 0
Christiansen, Peter Leth, Rasmussen, Kim, Berge, L et al. · Technical University of Denmark, DTU Orbit (Technical University of Denmark, DTU) · 1997
Cited by 0
Low, Russell J., England, Jonathan, Krause, Stephen E. et al. · Surrey Research Insight Open Access (The University of Surrey) · 2009
Techniques for preventing parasitic beamlets from affecting ion implantation are disclosed. In one particular exemplary embodiment, the techniques may be realized as an apparatus for preventing parasitic beamlets from affecting ion implantation. The apparatus may comprise a controller that is configured to scan a spot beam back and forth, thereby forming an ion beam spanning a predetermined width. The apparatus may also comprise an aperture mechanism that, if kept stationary, allows the spot beam to pass through. The apparatus may further comprise a synchronization mechanism, coupled to the controller and the aperture mechanism, that is configured to cause the aperture mechanism to move in synchronization with the scanned spot beam, allowing the scanned spot beam to pass through but blocking one or more parasitic beamlets associated with the spot beam.
Cited by 0
A. Morace, Natsumi Iwata, Y. Sentoku et al. · Nature Communications · 2019
Increasing the laser energy absorption into energetic particle beams represents a longstanding quest in intense laser-plasma physics. During the interaction with matter, part of the laser energy is converted into relativistic electron beams, which are the origin of secondary sources of energetic ions, γ-rays and neutrons. Here we experimentally demonstrate that using multiple coherent laser beamlets spatially and temporally overlapped, thus producing an interference pattern in the laser focus, significantly improves the laser energy conversion efficiency into hot electrons, compared to one beam with the same energy and nominal intensity as the four beamlets combined. Two-dimensional particle-in-cell simulations support the experimental results, suggesting that beamlet interference pattern induces a periodical shaping of the critical density, ultimately playing a key-role in enhancing the laser-to-electron energy conversion efficiency. This method is rather insensitive to laser pulse contrast and duration, making this approach robust and suitable to many existing facilities.
Cited by 23Open access
Morace, A., Iwata, N., Sentoku, Y. et al. · TIB Repositorium · 2019
Increasing the laser energy absorption into energetic particle beams represents a longstanding quest in intense laser-plasma physics. During the interaction with matter, part of the laser energy is converted into relativistic electron beams, which are the origin of secondary sources of energetic ions, γ-rays and neutrons. Here we experimentally demonstrate that using multiple coherent laser beamlets spatially and temporally overlapped, thus producing an interference pattern in the laser focus, significantly improves the laser energy conversion efficiency into hot electrons, compared to one beam with the same energy and nominal intensity as the four beamlets combined. Two-dimensional particle-in-cell simulations support the experimental results, suggesting that beamlet interference pattern induces a periodical shaping of the critical density, ultimately playing a key-role in enhancing the laser-to-electron energy conversion efficiency. This method is rather insensitive to laser pulse contrast and duration, making this approach robust and suitable to many existing facilities.
Cited by 0Open access