Computational algorithms for simulations in atmospheric optics.

A computer simulation technique for atmospheric and adaptive optics based on parallel programing is discussed. A parallel propagation algorithm is designed and a modified spectral-phase method for computer generation of 2D time-variant random fields is developed. Temporal power spectra of Laguerre-Gaussian beam fluctuations are considered as an example to illustrate the applications discussed. Implementation of the proposed algorithms using Intel MKL and IPP libraries and NVIDIA CUDA technology is shown to be very fast and accurate. The hardware system for the computer simulation is an off-the-shelf desktop with an Intel Core i7-4790K CPU operating at a turbo-speed frequency up to 5 GHz and an NVIDIA GeForce GTX-960 graphics accelerator with 1024 1.5 GHz processors.

Causes of non-Kolmogorov turbulence in the atmosphere.

In the present work, we briefly describe a model for atmospheric turbulence energy on the basis of experimental data obtained in Siberia. A series of new studies is considered and the results of our long-term experimental observations are summarized. The results of these studies form the basis for an explanation of some effects in interactions between optical waves and atmospheric turbulence. Our numerous experimental results point to the possible generation of so-called coherent turbulence in the atmosphere. When analyzing the problem, we proceeded based on our own experimental data and comprehension that the coherent turbulence is a result of the action of self-organizing nonlinear processes, which run in continuous media, including atmospheric air. The experimental data confirmed the effect of attenuation of light fluctuations in coherent turbulence.

Features of optical image jitter in a random medium with a finite outer scale.

For more than 40 years, we have studied the effect of the low-frequency spectral range of atmospheric turbulence on optical characteristics. We also have looked at the influence of the turbulence models as well as an outer scale of turbulence on the parameters of telescopes and systems of laser beam formations. This question is important mainly for ground-based astronomy. Here we propose what we believe is a new optical method that uses the phase fluctuations of optical image jitter to estimate both the integral (along an atmospheric path) value of the structure parameter of atmospheric turbulence and effective outer scales of turbulence.

Comparison of Kolmogorov's and coherent turbulence.

Features of optical wave fluctuations while propagating through a randomly inhomogeneous turbulent medium with a finite outer scale are considered, including conditions when areas with dominating influence of one large-scale coherent structure are observed in the atmosphere, for which the spectrum of atmospheric turbulence can differ significantly from the Kolmogorov model spectrum. Using an approximate model of the spectrum for coherent turbulence, described earlier in our works, the variance of jitter of an optical image is calculated (under the applicability condition for the smooth perturbation method). The comparison of these equations with known similar equations for Kolmogorov turbulence has shown that the variance of fluctuations is significantly weaker in coherent turbulence than in the Kolmogorov theory under similar conditions. This means that phase fluctuations of optical radiation decrease significantly in coherent turbulence. The importance of this conclusion is noted for interpretation of the results of optical sounding of atmospheric turbulence.

Optical correlation algorithm for reconstructing phase skeleton of complex optical fields for solving the phase problem.

We propose an optical correlation algorithm illustrating a new general method for reconstructing the phase skeleton of complex optical fields from the measured two-dimensional intensity distribution. The core of the algorithm consists in locating the saddle points of the intensity distribution and connecting such points into nets by the lines of intensity gradient that are closely associated with the equi-phase lines of the field. This algorithm provides a new partial solution to the inverse problem in optics commonly referred to as the phase problem.

Dynamics of adaptive optical systems.

Dynamic (time) characteristics of adaptive systems are analyzed. A common adaptive system with a finite frequency band (or a finite response time) is described as a dynamic constant time-delay system, where time delay is to be much shorter than the time of coherence radius transfer through an optical beam by a mean wind speed. The questions of coherent beam formation are considered with use of the reference source. The analytical calculation of the Strehl parameter is made on basis of the generalized Huygens-Kirchhoff principle. An adaptive system is considered where the correcting phase is calculated with the use of both its derivatives and the signal, as well as adaptive systems using different time-predicting algorithms of the correcting signal for future time points. The use of a predicted phase front of the correcting wave allows much longer time delays. The stronger the phase distortions in the optical wave, the higher the time gain in comparison with common (with constant time delay) adaptive systems.

Partial correction for turbulent distortions in telescopes.

To provide complete compensation for turbulent distortions in the visible range at aperture dimensions typical for modern telescopes (6-10 m), one needs to develop adaptive systems with hundreds of control channels. More simple adaptive systems that provide complete compensation in the infrared range can give an essential advantage in angular resolution in the visible range too. In this case the image brightness characterized by the Strehl ratio remains much less than that in the diffraction-limited case, i.e., the system provides only partial compensation. We present the results of numerical calculations of the partially corrected point-spread function and discuss possible approaches to composing the adaptive system configuration.

Monostatic and bistatic schemes and an optimal algorithm for tilt correction in ground-based adaptive telescopes.

It has been pointed out that the two terms effective scattering volume and laser guide star are scientific synonyms. The first term was introduced by the end of 1970 by specialists in atmospheric optics and laser sounding. Information has also been given concerning fluctuations of waves reflected from an object and waves passed twice through atmospheric inhomogeneities. A corresponding mathematical apparatus allows one to estimate correlation characteristics of a laser guide star. The mutual correlation function of random angular displacements of a plane-wave image and the centroid displacements of a focused Gaussian laser beam are considered. The algorithm of optimal correction is introduced in which a priori information is used. Based on this algorithm, the variance of residual jitter of a star image obtained with the use of a laser guide star is evaluated.

[Comparative evaluation and current views on the treatment of trochanieric fractures of the femur in middle-aged and elderly patients]. / Sravnitel'naia otsenka i sovremennye vzgliady na lechenie vertel'nykh perelomov bedrennoi kosti u pozhilykh i starykh liudei.

The methods of treatment of trochanteric fractures of the femur depend on both on the peculiarities of the fracture of this part of the bone and on the general state of elderly and old people aggravated with accompanying diseases of the inner organs. The immobilization-free method was used in extremely severe cases. The mortality rate in the patients of this group was the highest. Skeletal traction still remains the main method of treating trochanteric fractures. However, this method is connected with a long period of bed rest, a danger of the development of hypostatic complications, and requires a long rehabilitation period. Surgical treatment with immersion osteosunthesis using a two or three flange nail with diaphyseal application is rather traumatic and does not allow the patients to move with a full load on the extremity at early terms, although it permits to mobilize them at earlier terms. The mortality rate is almost the same as in the treatment with skeletal traction. External perosseous osteosynthesis is low traumatic and allows to walk with a full load on the extremity at early terms, yet it requires regular observation and dressings, which prolongs the in-patient treatment period. The most prospective method of treatment of trochanteric fractures in elderly and old people is intramedullary osteosynthesis after Ender or Lezius.

[Surgical treatment of recent injuries of the internal lateral ligament of the knee joint]. / Operativnoe lechenie svezhikh povrezhdenii vnutrennei bokovoi sviazki kolennogo sustava.

The authors describe their experience in surgical treatment of fresh injuries of the interior lateral ligament in 25 patients, in 15 of whom autoplasty of the injured ligament was performed by making use of the tendon of musculus semitendinosus which was shifted without being cut off into the projection of the ligament location and sewn to the joint capsule by interrupted sutures.

Dynamic characteristics of optical adaptive systems.

The effect of time delay on characteristics of an optical adaptive system is considered. Classification of the optical adaptive systems as dynamic feedback systems has been made. Systems with constant delay, a highspeed adaptive system as well as a new class of systems, i.e., predicting adaptive systems, are investigated.

Optical wave phase fluctuations.

This paper presents a series of studies on the effect of low-frequency fluctuations of the atmospheric refractive index on phase fluctuations of space-limited optical beams. Theoretical calculations have been made in the approximation of a smooth perturbation method. Numerous experimental data on statistical characteristics of optical wave phase fluctuations are given. These are used to verify the theoretical conclusions and to solve an inverse problem on the determination of the atmospheric turbulence characteristics.