An extrapolation method for projection data fltration in pulsed X-ray tomography

This paper deals with an inverse problem that consists of an attenuation coefficient identification for the non-stationary radiation transfer equation. To solve the problem, we propose a method that uses several pulses of radiation to extrapolate ideal projection data corresponding to a non-scattering medium. Numerical experiments on the Shepp-Logan phantom show that the method proposed improves the reconstruction quality.

Внутридопплеровские резонансы затухания свободной поляризации в ультратонких газовых ячейках

The linear-optical effect of the free polarization decay (FPD) in an ultrathin gas cell, the internal thickness of which is less than or of the order of the wavelength of the exciting monochromatic laser radiation, transmitted orthogonally to the plane-parallel walls of this cell, is theoretically investigated. The considered coherent FPD signal is emitted immediately after an abrupt interruption of such a relatively weak stationary radiation. Sub-Doppler resonances arising at the central frequencies of the studied quantum transitions in the spectra of the intensity and energy of the FPD as a result of the transit-time relaxation of atoms in the gas cell are established and analyzed. A significant dependence of these resonances and the dynamics of the FPD on the ratio of the inner thickness of the ultrathin cell to the wavelength of the exciting monochromatic radiation is shown. The narrow, high-contrast sub-Doppler resonances of the FPD detected and investigated in the linear-optical regime can be used in ultrahigh-resolution atomic (molecular) spectroscopy, as well as references for compact frequency standards.

New Theoretical Model of the Irradiance Distribution in Water from a Unidirectional Point Source

Formulas are presented for calculating the irradiance field, which is formed in a turbid medium with a narrow scattering phase function and homogeneous optical properties when an infinitely narrow light beam passes through it. The calculations are based on a new mathematical model of the stationary radiation field of an omnidirectional point source and relationships enabling one to represent the irradiance distribution in a continuous or modulated light beam through this field. The obtained formulas, in contrast to the previously known ones, permit taking into account the temporal spreading of a pulsed light beam in the sea without a significant decrease in the accuracy of describing its spatial structure.

Coplanar Stripline Loaded Reconfigurable Loop Antenna for WLAN and WiMAX Applications

In this paper, a loop antenna loaded with coplanar strip (CPS) line is proposed as a multiband antenna. The CPS line is added with two switches to vary the antenna perimeter to cover seven different bands. The CPS line introduced into the loop is not only useful in reconfiguring antenna dimensions but also provides stationary radiation patterns for the all the covered bands. The proposed antenna works in single and dual-band modes. When the proposed antenna works as a single band antenna, it produces a band from 4.2GHz to 5.7GHz. Under dual-band operation, it produces bands from 3.75GHz to 4.7GHz and from 6.4GHz to 7.8GHz. The other dual-band mode ranges from 3.5GHz to 3.8GHz and from 5.58GHz to 7.4 GHz. The simulated and measured results are in good agreement and the proposed antenna can be used satisfactorily for W-LAN and WiMax applications. The proposed technique can also be used for size reduction of loop antennas.

Modeling of Earth's limb infrared radiation

The study proposes some methods of engineering calculation of outgoing infrared radiation on the basis of the solution of the energy transfer equation for a stationary radiation field in the Earth surface – atmosphere system with allowance for permissible approximations. According to the experimental data, a mathematical model has been developed and verified, which makes it possible to calculate the spectral distributions and integral values of the infrared radiation intensity for a given angular position of the observer outside the atmosphere.