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Optical manipulation of particles of all shapes and sizes (Vol. 46 No. 2)
A new study of how particles may respond to the mechanical effects of light helps improve optical manipulation and remote sensing of non-spherical particles.
Manipulation of small objects by light has gained in popularity in the past few years. Now, scientists have performed the first systematic analysis of the behaviour of ellipsoidal particles manipulated by laser beams. The work shows that such particles are constantly moving in and out of the reach of an optical beam, creating oscillations. These findings have been obtained by the authors. This work could help understand the unusual behaviour of rod-like particles manipulated by optical tweezers. Ultimately, the theoretical part of this work could contribute numerical models of how complicated shapes and large sizes scatter laser light. Numerous applications exist in fluid engineering and remote sensing methods.
B. M. Mihiretie, P.Snabre, J.-C. Loudet and B. Pouligny, "Optically driven oscillations of ellipsoid particles. Part I: Experimental observations", Eur. Phys. J. E 37, 124 (2014)
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J.C. Loudet, B. M. Mihiretie and B. Pouligny, "Optically driven oscillations of ellipsoidal particles. Part II: Ray-Optics calculations", Eur. Phys. J. E 37, 125 (2014)
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Mechanisms of two-proton emission seen in three-body correlations (Vol. 46 No. 2)
Hitherto three-body correlations between decay products of nuclear resonances, unstable to the emission of two neutrons have been a very effective tool in the analysis of GSI-experiments on 5H, 10He, 13Li, and 14Be. Here the first report is given about the mechanisms for two-proton emission from states in 16Ne, representing the presently most complete study of this nucleus. One-neutron knockout from 17Ne populated the 16Ne(g.s.) (Er=1.39 MeV, Γ=0.08 MeV) above the 14O+p+p threshold, and resonances at Er=3.22 MeV and 7.57 MeV. The decay mechanisms were revealed analysing three-body energy correlations in the 14O+p+p system. It was found that the 16Ne(g.s.) undergoes a democratic three-body decay. In contrast to this, the 16Ne(21+) state emits protons through the 15F(g.s.) sequentially. The decay of 7.57 MeV state is well-described assuming emission of a proton from the d5/2 shell to 15F(5/2+), which decays by d5/2 proton emission to 14O(g.s.). By using R-matrix analysis and mirror symmetry this state was unambiguously identified as the third 2+ state in 16Ne.
J. Marganiec et al. (+ 58 co-authors), “Studies of continuum states in 16Ne using three-body correlation techniques”, Eur. Phys. J. A 51, 9 (2015)
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Efficient Lattice-Boltzmann simulation techniques for nonlinear thermoacoustic engines (Vol. 46 No. 2)
Thermoacoustics is the physics of the interaction of thermal and acoustic fields. The nonlinear acoustic effect and low Mach number compressible flow in thermoacoustic engines make the theoretical analysis of such systems extremely complicated. A new study investigates the nonlinear self-excited thermoacoustic onset in a Rijke tube via the lattice Boltzmann method (LBM), which simulates the fluid flow by tracking the evolution of particles and obtains flow stream and heat transfer patterns from the kinetic level. The adopted LBM model, which was developed by the authors, convincingly simulates the Navier-Stokes-Fourier equations, treating accurately the nonlinear process of wave excitation of coupled fields and providing reliable estimates for pressure, density, velocity and temperature in such a finite geometry.
A nonlinear self-excited standing wave in the Rijke tube is observed from simulations. Agreement is obtained with theoretical predictions when they exist. Instantaneous velocity fields and temperature fields are discussed. The maximal Mach number in the Rijke tube is about 0.035, indicating that the air flow under the limit cycle is the low Mach number compressible flow.
Y. Wang, D.-K. Sun, Y.-L. He, and W.-Q. Tao, “Lattice Boltzmann study on thermoacoustic onset in a Rijke tube”, Eur. Phys. J. Plus, 130, 9 (2015)
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New experimental approach for near–edge ultrafast EUV absorption spectroscopy (Vol. 46 No. 2)
Time resolved pump-probe spectroscopy in the extreme ultraviolet (EUV) spectral range offers the opportunity to study properties and structure of the electron subsystem in condensed materials under non-equilibrium conditions rapidly changing in the sub-ps time scale. New frontiers studies can be accomplished thanks to the availability of new generation sources such as free electron lasers (FEL). The breakthrough research interest in the EUV radiation–matter interactions requires the development of pivotal optical elements able to manipulate short wavelength beams. Conventional single layers coated mirrors provide negligible reflectance in the extreme ultraviolet spectral range, therefore knowledge coming from other disciplines is required to overcome such technological limits. The development of the multilayer coated mirrors has been intensively driven by the microelectronics industry in view of their application in EUV lithographic apparatus. The same technology has been used to develop a novel broadband multilayer coated mirror conceived specifically for near-edge ultrafast absorption spectroscopy. Such an optical element has been inserted in the EIS-TIMEX end-station at FERMI@ELETTRA FEL. The design of the device has been optimised in order to manipulate the FEL pulses preserving their temporal and wavefront properties in the wavelength range required by the ultrafast absorption spectroscopy at L(2,3)-edge of silicon (see figure).
A. J. Corso, P. Zuppella, E. Principi, E. Giangrisostomi, F. Bencivenga, A. Gessini, S. Zuccon, C.
Masciovecchio, A. Giglia, S. Nannarone and M. G. Pelizzo, "Broadband multilayer optics for ultrafast EUV absorption spectroscopy with free electron laser radiation", J. Opt. 17, 025505 (2015)
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