Search results for "Focu"
showing 10 items of 1182 documents
An Ultrasonic Lens Design Based on Prefractal Structures
2016
The improvement in focusing capabilities of a set of annular scatterers arranged in a fractal geometry is theoretically quantified in this work by means of the finite element method (FEM). Two different arrangements of rigid rings in water are used in the analysis. Thus, both a Fresnel ultrasonic lens and an arrangement of rigid rings based on Cantor prefractals are analyzed. Results show that the focusing capacity of the modified fractal lens is better than the Fresnel lens. This new lens is believed to have potential applications for ultrasonic imaging and medical ultrasound fields.
Actinic Flux and Net Flux Calculations in Radiative Transfer—A Comparative Study of Computational Efficiency
2001
Abstract The accuracy and speed of three well-known computational techniques (DISORT, the δ–four-stream approximation, and the two-stream approximation), and the matrix inversion method, which is less well known, have been investigated. Results are presented for both broadband actinic and net fluxes over a range of parameters including solar zenith cosine, relative humidity, and altitude for two different surface/aerosol systems: terrestrial and oceanic. The matrix inversion method can only calculate actinic fluxes; therefore, this is the main focus of this paper. Investigations into the comparative accuracy of the four techniques for the oceanic model with and without a cloud layer include…
Target states and control of molecular alignment in a dissipative medium
2006
Received 17 August 2006; published 14 November 2006We investigate how and to what extent molecular alignment can be controlled in a dissipative medium by asuitable train of laser pulses. We focus primarily on the extension of a scheme of control originally constructedfor unitary evolution. The procedure is applied to control the alignment of CO molecules in an Ar gas. Theparameters of the train of kicks—i.e., the intensity of each kick and the delay between them—are eitherobtained by a systematic procedure maximum strategy or by optimization by evolutionary algorithms.DOI: 10.1103/PhysRevA.74.053411 PACS number s : 32.80.Lg, 33.80. b, 42.50.Hz
On the lower bound on the exchange-correlation energy in two dimensions
2010
We study the properties of the lower bound on the exchange-correlation energy in two dimensions. First we review the derivation of the bound and show how it can be written in a simple density-functional form. This form allows an explicit determination of the prefactor of the bound and testing its tightness. Next we focus on finite two-dimensional systems and examine how their distance from the bound depends on the system geometry. The results for the high-density limit suggest that a finite system that comes as close as possible to the ultimate bound on the exchange-correlation energy has circular geometry and a weak confining potential with a negative curvature. Fil: Räsänen, Esa. Universi…
Top-seesaw assisted technicolor model with 126 GeV Higgs boson
2013
We discuss a model which involves the top quark condensation and the walking technicolor. We focus on the scalar boson in such a model from the viewpoint of the observed scalar boson at the LHC.
Resonant Plasmon-Soliton Interaction
2008
We describe an effective resonant interaction between two localized wave modes of different nature: a plasmon-polariton at a metal surface and a self-focusing beam (spatial soliton) in a non-linear dielectric medium. Propagating in the same direction, they represent an exotic coupled-waveguide system, where the resonant interaction is controlled by the soliton amplitude. This non-linear system manifests hybridized plasmon-soliton eigenmodes, mutual conversion, and non-adiabatic switching, which offer exciting opportunities for manipulation of plasmons via spatial solitons.
Transverse nonlinear optics in heavy-metal-oxide glass
2008
6 pags. ; 9 figs.
Linear inverse filtering improves spatial separation of nonlinear brain dynamics: a simulation study.
2000
We examined topographic variations in nonlinear measures based on scalp voltages, which were generated by two simulated current dipoles each placed in a different hemisphere of a spherical volume conductor (three-shell model). Dipole dynamics were that of a three-torus and the x-component of the Lorenz-system and scalp voltage were calculated for a configuration of 29 electrode positions. Although estimates for correlation dimension D2 and Lyapunov exponent L1 were close to the theoretical values for the original time series, the simulated scalp voltage data showed almost no topographic resolution of dipole positions. In order to enhance topographic differentiation, we constructed linear in…
Plasma instability in the afterglow of electron cyclotron resonance discharge sustained in a mirror trap
2012
The work presented in this article is devoted to time-resolved diagnostics of non-linear effects observed during the afterglow plasma decay of a 14 GHz electron cyclotron resonance ion source operated in pulsed mode. Plasma instabilities that cause perturbations of the extracted ion current during the decay were observed and studied. It is shown that these perturbations are associated with precipitation of high energy electrons along the magnetic field lines and strong bursts of bremsstrahlung emission. The effect of ion source settings on the onset of the observed instabilities was investigated. Based on the experimental data and estimated plasma properties, it is assumed that the instabil…
Experimental evidence of E × B plasma rotation in a 2.45 GHz hydrogen discharge
2015
An experimental observation of a rotating plasma structure in a 2.45 GHz microwave-driven hydrogen discharge is reported. The rotation is presumably produced by E × B drift. The formation of the rotating plasma structure is sensitive to the strength of the off-resonance static magnetic field. The rotation frequency is on the order of 10 kHz and is affected by the neutral gas pressure and applied microwave power.