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61.
Victor H. Hamity Oscar A. Reula Jeffrey Winicour 《General Relativity and Gravitation》1990,22(1):81-95
Several methods of prescribing initial data for gravitational and matter fields, which are intended to eliminate extraneous radiation that is not produced by the matter source, are analysed in a simple exactly soluble radiating model. The model consists of an harmonic oscillator coupled to a scalar field along future light cones of Minkowski space time. In particular we analyze the asymptotic regime of the oscillator and find it is characterized essentially by two distinct decay modes. They differ in the way they behave both in the limit of small coupling constant and in a certain Newtonian limit. As a criterion to select initial data for the field with no extra radiation, we require that these initial data sets should put the oscillator from the start into the asymptotic regime. The underlying hypothesis here is that initial transients result from excitation of the oscillator by incoming radiation. We then see that the requirement of a uniform Newtonian limit leads to unique data for the scalar field for each arbitrary data set for the oscillator. We further find that this unique data set indeed satisfies our criterion. 相似文献
62.
We discover that a spatially localized gain supports stable vortex solitons in media with cubic nonlinearity and two-photon absorption. The interplay between nonlinear losses and gain in amplifying rings results in the suppression of otherwise ubiquitous azimuthal modulation instabilities of radially symmetric vortex solitons. We find that the topology of the gain profile imposes restrictions on the maximal possible charge of vortex solitons. Symmetry breaking occurs at high gain levels, resulting in the formation of necklace vortex solitons composed of asymmetric bright spots. 相似文献
63.
We find an interpretation of the complex of variational calculus in terms of the Lie conformal algebra cohomology theory.
This leads to a better understanding of both theories. In particular, we give an explicit construction of the Lie conformal
algebra cohomology complex, and endow it with a structure of a
\mathfrakg{\mathfrak{g}}-complex. On the other hand, we give an explicit construction of the complex of variational calculus in terms of skew-symmetric
poly-differential operators. 相似文献
64.
Modulo some natural generalizations to noncompact spaces, we show in this Letter that Moyal planes are nonunital spectral triples in the sense of Connes. The action functional of these triples is computed, and we obtain the expected result, i.e. the noncommutative Yang–Mills action associated with the Moyal product. In particular, we show that Moyal gauge theory naturally fits into the rigorous framework of noncommutative geometry. 相似文献
65.
Fluorescent optical imaging of tumors deep within tissue depends on specific binding of antibodies to the tumors' surface markers. These fluorescent antibodies propagating in the vicinity of the tumor can be attached to and (or) diffused away from it. We illustrate application of a new tool, based on the random-walk theory in turbid media, for extracting the pharmacokinetics of these fluorescent antibodies by data deconvolution, excluding the effect of upper turbid tissue layers. 相似文献
66.
Yang VX Munce N Pekar J Gordon ML Lo S Marcon NE Wilson BC Vitkin IA 《Optics letters》2004,29(15):1754-1756
High-resolution optical coherence tomography demands a large detector bandwidth and a high numerical aperture for real-time imaging, which is difficult to achieve over a large imaging depth. To resolve these conflicting requirements we propose a novel multifocus fiber-based optical coherence tomography system with a micromachined array tip. We demonstrate the fabrication of a prototype four-channel tip that maintains a 9-14-microm spot diameter with more than 500 microm of imaging depth. Images of a resolution target and a human tooth were obtained with this tip by use of a four-channel cascaded Michelson fiber-optic interferometer, scanned simultaneously at 8 kHz with geometric power distribution across the four channels. 相似文献
67.
Kozhushko V Khokhlova T Zharinov A Pelivanov I Solomatin V Karabutov A 《The Journal of the Acoustical Society of America》2004,116(3):1498-1506
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. 相似文献
68.
We address the phenomenon of soliton self-bending in Kerr-type nonlocal nonlinear media with an imprinted transverse periodic modulation of the linear refractive index. We show that the imprinted optical lattice makes possible to control the mobility of soliton by varying the depth and the frequency of the linear refractive index modulation. 相似文献
69.
Morfill GE Rubin-Zuzic M Rothermel H Ivlev AV Klumov BA Thomas HM Konopka U Steinberg V 《Physical review letters》2004,92(17):175004
Fluid flow around an obstacle was observed at the kinetic (individual particle) level using "complex (dusty) plasmas" in their liquid state. These "liquid plasmas" have bulk properties similar to water (e.g., viscosity), and a comparison in terms of similarity parameters suggests that they can provide a unique tool to model classical fluids. This allows us to study "nanofluidics" at the most elementary-the particle-level, including the transition from fluid behavior to purely kinetic transport. In this (first) experimental investigation we describe the kinetic flow topology, discuss our observations in terms of fluid theories, and follow this up with numerical simulations. 相似文献
70.
Volodymyr Malyutenko Vitalii Borblik Victor Vainberg 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):563
An all-optical approach to convert terahertz radiation (THz, wavelength λ1) into infrared (IR, peak wavelength λ2) is presented. We show that this up-conversion process is due to the photon drag effect induced by the THz radiation in intrinsic narrow-gap semiconductors followed by spatial redistribution of current carriers and band-to-band radiative recombination. The process results in non-selective high-speed (ns range rise/fall times) IR imaging of positive (conventional luminescence) and/or negative (negative luminescence) contrasts. Estimates made for an InSb pixelless converter at 300 K and moderate THz intensity (kW/cm2) show that this up-conversion process (with λ1/λ2>102) can be observed with a conventional thermal imaging camera. 相似文献