Nanodomain structures formation during polarization reversal in uniform electric field in strontium barium niobate single crystals

We have studied the ferroelectric nanodomain formation in single crystals of strontium barium niobate Sr 0.61Ba 0.39Nb 2O 6 using piezoelectric force microscopy and Raman confocal microscopy. The nanodomain structures have been created by application of the uniform electric field at room temperature. Four variants of nanodomain structure formation have been revealed: (1) discrete switching, (2) incomplete domain merging, (3) spontaneous backswitching, and (4) enlarging of nanodomain ensembles. Kinetics of the observed micro- and nanodomain structures has been explained on the basis of approach developed for lithium niobate and lithium tantalate crystals. © 2012 American Institute of Physics

Nanodomain structures formation during polarization reversal in uniform electric field in strontium barium niobate single crystals

We have studied the ferroelectric nanodomain formation in single crystals of strontium barium niobate Sr 0.61Ba 0.39Nb 2O 6 using piezoelectric force microscopy and Raman confocal microscopy. The nanodomain structures have been created by application of the uniform electric field at room temperature. Four variants of nanodomain structure formation have been revealed: (1) discrete switching, (2) incomplete domain merging, (3) spontaneous backswitching, and (4) enlarging of nanodomain ensembles. Kinetics of the observed micro- and nanodomain structures has been explained on the basis of approach developed for lithium niobate and lithium tantalate crystals. © 2012 American Institute of Physics

Polarization reversal by tip of scanning probe microscope in SBN

We present the results of experimental study of the influence of initial domain state on the shape and size of isolated domains created by the conductive tip of scanning probe microscope during local polarization reversal in relaxor ferroelectric strontium barium niobate doped with nickel and cerium. The domain radius was found to increase with increasing voltage and time and depend on the initial polarization direction. Circular domains of the opposite sign were found to appear due to polarization backswitching. The obtained results can be used for practical applications of domain and domain wall engineering in ferroelectrics

Recording and light scattering on dynamic holographic gratings in Sr0.61Ba0.39Nb2O6: 0.002 wt.% CeO2 crystal

This work was supported by VolkswagenStiftung, Grant No. Az. 90.261 and Presidium RAS Program No. 5: “Photonic technologies in probing inhomogeneous media and biological objects”

Tip-induced domain growth in the non-polar cuts of SBN:Ce single crystals

The local switching by conductive tip of scanning probe microscope was studied in the non-polar cuts of Ce-doped Sr0.61Ba0.39Nb2O6 single crystals after creation of the single-domain state. The switched domains possessed the egg-shaped heads and wedge-like tails. The dependences of lengths of the domain head and tail and width of the domain head on the voltage and pulse duration were derived. The start voltage for growth of the domain tail was revealed. The fast relaxation of the domain head and slow relaxation of the domain tail were observed. The model of the forward domain growth by step generation and kink motion was used for explanation of the experimental results. The obtained knowledge can be used for the domain engineering in ferroelectrics. © Published under licence by IOP Publishing Ltd.Russian Science Foundation, RSF: 19-72-00008The equipment of the Ural Centre for Shared Use “Modern nanotechnology” Ural Federal University was used. The research was made possible by the Russian Science Foundation (grant № 19-72-00008)

Supplemental technologies of liver ultrasound investigation at the 1-st type tyrosinemia in pediatrics

Aim of investigation. To carry out objective estimation of liver parenchyma state in children with the 1-st type hereditary tyrosinemia (НТ-1) by ultrasound method with quantitative estimation of hepatic parenchyma pattern.Material and methods. Overall 14 children with the 1-st type tyrosinemia aged 3 months to 14 years (6 — with acute and subacute forms and 8 — with chronic form) were studied. Traditional ultrasound investigation and innovative non-invasive ultrasound technique of quantitative analysis of liver parenchyma acoustic pattern — Acoustic Structure Quantification (ASQ) were applied. Traditional US-investigation of hemodynamic parameters of portal system blood flow reveals early US-signs of portal hypertension. Color mapping (ASQ technique) allows visual estimation of fibrosis severity and amount of functioning parenchyma. Plotting of histograms and density probability functions of various zones of liver parenchyma allows to establish the stage of fibrosis. The density index provides quantitative characteristic of fibrosis stage.Results. Neither absence of fibrosis or minimal and moderately severe fibrosis was observed in children with НТ-1. The density index range at severe fibrosis stage was 2,62 (2,62-2,72) (2,62-2,72), at stage of liver cirrhosis — 3,37 (3,21–3,80) (3,00–4,58). In the areas of normal liver parenchyma no significant differences from the control group were found and the range was equal to 1,10–1,35.Conclusion. Obtained data may be used for objective estimation of the process stage in children with the 1-st type tyrosinemia when liver biopsy is contraindicated

Mathematical modeling of the refractive effect of SMILE surgery in high degree myopia correction

The aim of the study. To develop a mathematical model of changes in corneal refraction during femtosecond laser-assisted lenticule extraction through a small surgical incision and, on this basis, to propose a technology for modified calculation of surgical parameters and to prove its effectiveness. Material and methods. The study included 191 patients with high myopia. They were divided into two groups: group  1 consisted of 55  patients who  were  had  SMILE (SMall Incision Lenticule Extraction) surgery with standard calculations; group  2 included 136 patients who had SMILE surgery with a modified calculation of surgical parameters based on the developed mathematical model of the refractive effect of the surgery. Results. When assessing the refractive effect of patients who were operated using standard technology, it was found that it was possible to achieve a refraction different from emmetropia for ± 0.5 D only in 51 % of cases; in the remaining patients, the planned residual refractive effect was obtained and averaged –1.96 ± 0.29 D. In patients operated using the modified technology, a statistically significantly better refractive result was achieved already on the first day. A refractive error of more than ± 1.0 D was obtained in only 1 % of cases; a deviation from the calculated refraction of ± 0.5 D was achieved in 82 % of cases, with the average values by 1 year –0.24 ± 0.57 D. Conclusions. The developed technology of a modified calculation of the parameters of the SMILE surgery for high myopia correction makes it possible to obtain an optimal refractive effect in compliance with safety rules when the structural and functional parameters of the eye are initially unfavorable for refractive surgery

The High–Low Arctic boundary: How is it determined and where is it located?

Geobotanical subdivision of landcover is a baseline for many studies. The High–Low Arctic boundary is considered to be of fundamental natural importance. The wide application of different delimitation schemes in various ecological studies and climatic scenarios raises the following questions: (i) What are the common criteria to define the High and Low Arctic? (ii) Could human impact significantly change the distribution of the delimitation criteria? (iii) Is the widely accepted temperature criterion still relevant given ongoing climate change? and (iv) Could we locate the High–Low Arctic boundary by mapping these criteria derived from modern open remote sensing and climatic data? Researchers rely on common criteria for geobotanical delimitation of the Arctic. Unified circumpolar criteria are based on the structure of vegetation cover and climate, while regional specifics are reflected in the floral composition. However, the published delimitation schemes vary greatly. The disagreement in the location of geobotanical boundaries across the studies manifests in poorly comparable results. While maintaining the common principles of geobotanical subdivision, we derived the boundary between the High and Low Arctic using the most up‐to‐date field data and modern techniques: species distribution modeling, radar, thermal and optical satellite imagery processing, and climatic data analysis. The position of the High–Low Arctic boundary in Western Siberia was clarified and mapped. The new boundary is located 50–100 km further north compared to all the previously presented ones. Long‐term anthropogenic press contributes to a change in the vegetation structure but does not noticeably affect key species ranges. A previously specified climatic criterion for the High–Low Arctic boundary accepted in scientific literature has not coincided with the boundary in Western Siberia for over 70 years. The High–Low Arctic boundary is distinctly reflected in biodiversity distribution. The presented approach is appropriate for accurate mapping of the High–Low Arctic boundary in the circumpolar extent