From X- to O-shaped spatiotemporal spectra of light filaments in water

We show that the angle-wavelength spectra of light filaments excited by ultrashort pulses experience a transition from X- to O-like structures when their carrier wavelengths are switched from normal to anomalous dispersion. Calculations confirm that the O-shaped conical emission follows the elliptic geometry of the nonlinear Schr?dinger equation with anomalous dispersion.     

Focused array transducer for two-dimensional optoacoustic tomography

Optoacoustic (OA) imaging utilizes short laser pulses to create acoustic sources in tissue and time resolved detection of generated pressure profiles for image reconstruction. The ultrasonic transients provide information on the distribution of optical absorption coefficient that can be useful for early cancer diagnostics. In this work a new design of wide-band array transducer is developed and tested. The array consists of 32 focused piezo-elements made of PVDF slabs imposed on a cylindrical surface. A single array element response to an OA signal coming from arbitrarily located point source is investigated theoretically and experimentally. The measured signals correspond well to numerically calculated ones. Focal zone maps of the elements with aperture angles 30 degrees and 60 degrees are presented and discussed; the resolution in direction perpendicular to the imaging plane is determined. Point spread function of the whole array is calculated using experimentally obtained signals from the sources located at different distances from the array. Backprojection algorithm is employed for reconstruction of the optoacoustic images. It is shown that the spatial resolution of the images yielded by the proposed array increases significantly compared to previous transducer designs.     

Nonlinear unbalanced bessel beams: stationary conical waves supported by nonlinear losses

Nonlinear losses accompanying self-focusing substantially impact the dynamic balance of diffraction and nonlinearity, permitting the existence of localized and stationary solutions of the 2D + 1 nonlinear Schr?dinger equation, which are stable against radial collapse. These are featured by linear, conical tails that continually refill the nonlinear, central spot. An experiment shows that the discovered solution behaves as a strong attractor for the self-focusing dynamics in Kerr media.     

Peak dispersion and contributions to plate height in nonaqueous capillary electrophoresis at high electric field strengths: propanol as background electrolyte solvent

Peak dispersion effects in nonaqueous capillary electrophoretic separations of aromatic anionic analytes were investigated in a propanolic background electrolyte solution. Poly(glycidylmethacrylate-co-N-vinylpyrrolidone) coating was applied to the capillary to suppress the electroosmotic flow and to improve the repeatability of the migration times. Electrical field strengths up to 2000 Vcm(-1) were applied in separations and the separation efficiencies were compared with theoretical values calculated on the basis of plate height theory. The contributions to the total plate height were calculated for injection plug length, diffusion, Joule heating, electromigration dispersion, analyte adsorption to the capillary wall, and detector slit aperture length. Analyte diffusion coefficients were measured by Taylor dispersion method, while distribution constants were measured chromatographically. Agreement between the calculated and empirical results was fairly good even though some approximations were required. In most cases the longitudinal diffusion contribution governed the total plate height, while the contribution of Joule heating was insignificant even at exceptionally high field strengths used. The relatively long detection slit aperture was found to influence the separation efficiency strongly, while the other dispersion sources that were investigated were of minor importance, except for adsorption in the case of one analyte. With all analytes, the dispersive effect of longitudinal diffusion was reduced as the field strength was increased, leading to enhanced migration velocities and faster separations.     

Torus actions on symplectic orbi-spaces

Which -dimensional orbi-spaces have effective symplectic - torus actions? As shown by Lerman and Tolman (1997) and Watson (1997), this question reduces to that of characterizing the finite subgroups of centralizers of tori in the real symplectic group . We resolve this question, and generalize our method to a calculation of the centralizers of all tori in .

     

Pulse correction to monochromatic light-beam propagation

The problem of diffraction of few-cycle light pulses is solved by means of a perturbative technique. The propagated field is expressed as a series of correction terms to the field obtained from diffraction laws for many-cycle pulses. The features previously reported for diffraction of ultrashort pulses are reproduced by first- and second-order corrections.     

Diffraction-free and dispersion-free pulsed beam propagation in dispersive media

The diffraction of pulsed beams of light is formulated as an anomalously dispersive phenomenon. In a dispersive material, the effects of material group-velocity dispersion and diffraction on pulsed beam propagation can mutually cancel if the transverse profile of the pulse is suitably chosen.     

Equations of Hurwitz schemes in the infinite Grassmannian

The main result proved in the paper is the computation of the explicit equations defining the Hurwitz schemes of coverings with punctures as subschemes of the Sato infinite Grassmannian. As an application, we characterize the existence of certain linear series on a smooth curve in terms of soliton equations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

First emission studies of Tc2X8(2-) systems (X = Cl, Br)

The emission spectra of the solids [n-Bu(4)N](2)Tc(2)X(8) (X = Cl, Br) have been investigated at room temperature and 77 K. In each case, the emission originates in the (1)δ-δ* excited state, as with the rhenium homologues, but has a shorter lifetime.