Radio Wave Propagation Phenomena from GPS Occultation Data Analysis

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Reconstruction of internal gravity wave parameters from radio occultation retrievals of vertical temperature profiles in the Earth's atmosphere

A new method for the reconstruction of internal gravity wave (IGW) parameters from a single vertical temperature profile measurement in the Earth's atmosphere has been developed. This method does not require any additional information not contained in the profile and may be used for the analysis of profiles measured by various techniques. The criterion for the IGW identification has been formulated and argued. In the case when this criterion is satisfied, then analyzed temperature fluctuations can be considered as wave-induced. The method is based on the analysis of relative amplitude thresholds of the temperature wave field and on the linear IGW saturation theory in which amplitude thresholds are restricted by dynamical (shear) instability processes in the atmosphere. When the amplitude of an internal gravity wave reaches the shear instability limit, energy is assumed to be dissipated in such a way that the amplitude is maintained at the instability limit as the wave propagates upwards. In order to approbate the method we have used data of simultaneous high-resolution balloon measurements of the temperature and wind velocity in the Earth's stratosphere over France where a long-period inertia-gravity wave has been detected. Using the radiosonde temperature data only, we have reconstructed all wave parameters, which were determined by radiosondes, with relative deviations not larger than 30%. An application of the method to the radio occultation (RO) data has given the possibility to identify the IGWs in the Earth's stratosphere and to determine the magnitudes of key wave parameters such as the intrinsic frequency, amplitudes of vertical and horizontal perturbations of the wind velocity, vertical and horizontal wavelengths, intrinsic vertical and horizontal phase (and group) speeds, kinetic and potential energy, vertical fluxes of the wave energy and horizontal momentum. The obtained results of internal wave studies in the Earth's stratosphere deduced from the COSMIC and CHAMP GPS occultation temperature profiles are presented and discussed

Integrated fiber-based transverse mode converter

A transverse mode converter based on a binary microrelief implemented directly on the end-face of a few-mode fiber was numerically investigated. The results of numerical simulation demonstrated the converter to form LP-11 and LP-21 modes with high efficiency, providing a more-than 92 % mode purity. Transformations of modes excited by a fiber microbending were also numerically investigated. The excited beams were shown to save their mode purity even in a strong bending as the arising parasitical modes were mostly unguided by the fiber. The resulting beam power and mode content were also demonstrated to depend on the beam and bending mutual orientation for beams with strong rotational symmetry.This work was partly supported by the Ministry of Education and Science of the Russian Federation (project 16.7894.2017/6.7)

Radio Occultation Method for Remote Sensing of the Atmosphere and Ionosphere

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Exciton and Hole-Transfer Dynamics in Polymer:Fullerene Blends

Ultrafast hole transfer dynamics from fullerene derivative to polymer in bulk heterojunction blends are studied with visible-pump – IR-probe spectroscopy. The hole transfer process is found to occur in 50/300 fs next to the interface, while a longer 15-ps time is attributed to exciton diffusion towards interface in PC71BM domains. High polaron generation efficiency in P3HT blends indicates excellent intercalation between the polymer and the fullerene even at highest PC71BM concentration thereby yielding a valuable information on the blend morphology

Synthesis of silicon nanowires using plasma chemical etching process for solar cell applications

Recently, research on silicon nanowire solar cells has been developed rapidly and is one of the very young research field. The production of highly oriented long silicon nanowires is an challenging problem. Here, in this article we report the optimization of successful synthesis of highly oriented, long silicon nanowires on silicon substrates by plasma chemical etching process. The produced silicon structures were first examined using scanning electron microscopy (SEM). The SEM results clearly shows the highly oriented nanowires on the silicon substrate. The flowing carrier gas, temperature, pressure and voltage are main parameters responsible for the formation of the silicon nanowires. The successful synthesis of silicon nanowires shows bright perspectives for further research on silicon nanostructure properties