Influence of tree-crown density on dominant plant species of the herb-shrub stratum in the zone of mixed forests

Forest ecosystems are among the most complex and dynamic biological systems of our planet. They play an important role in sustaining biodiversity, regulating the climate, and preserving water resources. Furthermore, they serve as natural filters, improving the quality of soil and air, and also preventing erosive processes. Forests create unique conditions for life of various species of plants and animals, which contributes to maintenance of the natural biodiversity and supports the stability of the ecosystem. Likewise, forests are important for the carbon cycle. They absorb a large amount of carbon, thus hindering global warming. Therefore, forest ecosystems are of paramount ecological value and their preservation is crucial for a balanced functioning of the planet. Our studies were carried out in the forest ecosystems of the Desna-Starohutskyi National Park, which is in the Ukrainian Polissia. The materials and methods of the study included systematic collection of the data on density of tree crowns, and also records of diversity of plants of the herb-shrub stratum in the chosen forest areas. Those data were analyzed using statistical methods. The study results revealed that the crown density has a significant effect on diversity of herb-shrub plants in the lower forest strata. Increase in crown density correlated with decrease in the light availability in the herb-shrub stratum. Change in the crown density towards increase significantly altered the conditions for competition between herbaceous and shrub species. Decrease in light availability led to shift in the competition ratio between the species, promoting dominance of more shade-loving species. Increase in crown density, which often reached 100%, made the competition more severe, especially for key resources (light, water, and nutrients). Because of this, species diversity in the herb-shrub stratum of the forest ecosystems was observed to decrease, and less adapted species were extruded. In general, change in tree-crown density in the forest ecosystem had a significant effect on the dynamics of herbaceous and shrub species, changing competitive relations and the structure of those plant communities. The results we obtained expand the knowledge about interactions between crown density and the structure of herb-shrub stratum, which gives perspectives for more efficient management of forest resources, and can also improve scientific identification and implementation of measures for protection of forest ecosystems

Photoinduced 3D orientational order in side chain liquid crystalline azopolymers

We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced 3D orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, correspondingly. Using irradiation with the polarized light of two different wavelengths we find that the kinetics of photoinduced anisotropy can be dominated by either photo-reorientation or photoselection mechanisms depending on the wavelength. We formulate the phenomenological model describing the kinetics of photoinduced anisotropy in terms of the isomer concentrations and the order parameter tensor. We present the numerical results for absorption coefficients that are found to be in good agreement with the experimental data. The model is also used to interpret the effect of changing the mechanism with the wavelength of the pumping light.Comment: uses revtex4 28 pages, 10 figure

Dielectric studies of dispersions of carbon nanotubes in liquid crystal 5CB

The frequency dependences of the imaginary ε″ and real ε′ parts of complex dielectric permittivity inherent to planarly aligned layers of nematic liquid crystals 5CB doped with multiwalled carbon nanotubes (CNT) were investigated in a wide range of frequencies (f = 10⁻²-10⁶ Hz) and CNT concentrations (c = 0-0.25 wt.%). It has been shown that the studied frequency range can be divided in three parts according to behavior of ε′ (f) and ε″ (f) curves. The low-frequency range (10⁻² < f < 10¹ Hz) reflects the near-electrode processes in the cell. The ratio ε″/ε′ used to characterize these processes sharply grows if the concentration of CNT exceeds 0.05 wt.%. The moderate frequency range (10¹ < f < 10⁵ Hz) corresponds to the alternating current conductivity, σАС. At the nanotubes concentration less than 0.025 wt.%, σАС does not depend on the frequency that implies its ionic origin. In its turn, at the c ≥ 0.025 wt.%, σАС is a power function of the frequency that is typical for electronic hopping mechanism. The transition from the ionic to electronic conductivity can be explained by the percolation theory with the critical concentration of nanotubes 0.031 wt.% and percolation parameter 2.5. The high-frequency range (10⁵ < f < 10⁶ ) is mainly attributed to dipole volume polarization. For c < 0.05 wt.% such polarization is well described by the Debye equation. The time of dielectric relaxation in this frequency range increases with nanotubes content. This is explained by effective interaction of nanotubes with 5CB molecules

Factors in liquid crystal photoalignment on polymer films: photoorientation versus self-assembly

We demonstrate that photostimulated self-assembly, running in parallel with molecular photoorientation in the top layer of the aligning polymer film, breaks the bulk molecular order mainly determined by the symmetry of irradiation. This may substantially modify liquid crystal (LC) alignment. Depending on the chemical composition of the liquid crystal, the self-assembled layers may influence either homeotropic or planar LC alignment with extremely weak azimuthal anchoring. Effective self-assembly occurs in polymers having side chain chromophores with flexible spacers and polar terminal groups

ИСПОЛЬЗОВАНИЕ ВЕЙВЛЕТ-АНАЛИЗА В ИЗУЧЕНИИ РЕЛЬЕФА ДНА ЗАЛИВА ПЕТРА ВЕЛИКОГО ЯПОНСКОГО МОРЯ

The paper provides an example of the application of wavelet analysis to the bottom topography of the Peter the Great Bay of the Sea of Japan and the depth slope. The bottom micro- and mesorelief is formed by hydrodynamic processes. Thus, the study of various landforms and their position can show where the dynamics of internal gravity waves is most pronounced. A digital model of the relief of the bay, depth dump and adjacent land has been created. The digital model of the seabed and land elevation is based on the available global databases GEBKO and ASTER, as well as bathymetric measurements obtained using the ship's echo sounder. The preparation of bathymetric data on the bottom of the bay for further application of mathematical methods is considered. Interpolation with regression of Gaussian processes was used at the first stage of creating a digital elevation model. Further, smoothing was carried out due to linear interpolation and an increase in the cell size of the digital elevation model. Due to the coarsening of the model, the measurement error has decreased. On the basis of wavelet analysis and the method of natural orthogonal functions, various groups of landforms were identified and contoured according to their height characteristics. Sedimentary waves were identified in the bay. The height of sedimentary waves does not exceed 8 m, and the distances between the peaks vary within 1 km. The structural parameters of the bottom topography for each profile of the wavelet analysis are identified. Differences are observed in the shape of the wavelet patterns for different types of sedimentary waves. So, for small sedimentary waves (up to 2 m high) are evenly distributed along the profile and they are having even bifurcations. Sedimentary waves with a height of more than 2 m are grouped in the central part of the bay and in the wavelet analysis they are also distinguished by local bifurcations, but with a higher dimension.В работе приводится пример применения вейвлет-анализа к рельефу дна залива Петра Великого Японского моря и свала глубин. Микро- и мезорельеф дна формируются современными гидродинамическими процессами. Таким образом, изучение различных форм рельефа и их положение может показать, где наиболее выражена динамика внутренних гравитационных волн. Создана цифровая модель рельефа залива, свала глубин и прилегающей суши. Цифровая модель рельефа дна и суши базируется на доступных глобальных базах данных GEBKO и ASTER, а также данных батиметрических измерений, полученных с помощью эхолота судна. Рассматривается подготовка батиметрических данных дна залива для дальнейшего применения математических методов. На первом этапе создания цифровой модели рельефа использовалась интерполяция с помощью регрессии на основе гауссовских процессов. Далее проводилось сглаживание за счет линейной интерполяции и увеличение размера ячейки цифровой модели рельефа. За счет загрубления модели уменьшилась погрешность измерений. На основе вейвлет-анализа и метода естественных ортогональных функций были выделены и оконтурены различные группы форм рельефа по их высотным характеристикам. Были определены осадочные волны в заливе. Высота осадочных волн не превышает 8 м, а расстояния между вершинами колеблются в пределах 1 км. Выделены структурные параметры рельефа дна для каждого профиля вейвлет-анализа. Наблюдаются различия в облике вейвлет-картин для разного вида осадочных волн. Так, для небольших осадочных волн, высотой до 2 м, они равномерно распределены по профилю, имея ровные «вилочки» – раздвоения. Осадочные волны высотой более 2 м сгруппированы в центральной части залива и в вейвлет-анализе также выделяются локальными раздвоениями, но с большей размерностью. Литература: Астафьева Н.М. Вейвлет-анализ: основы теории и применение // Успехи физических наук. 1996. Т. 166. № 11. С. 1145–1170. DOI:&nbsp;10.3367/UFNr.0166.199611a.1145. Бурнаев Е.В., Панов М.Е., Зайцев А.А. Регрессия на основе нестационарных гауссовских процессов с байесовской регуляризацией // Информационные процессы. 2015. Т.15. № 3. С.&nbsp;298–313. Девдариани А.С. Математический анализ в геоморфологии / под ред. В.В. Лонгинова. М.:&nbsp;Недра, 1967. 156 с. Долгих Г.И., Новотрясов В.В., Самченко А.Н., Ярощук И.О. Об одном механизме образования осадочных волн на шельфе Японского моря // Доклады академии наук. 2015. Т. 465. № 5. С.&nbsp;593–597. DOI: 10.7868/S0869565215350169. Дремин И.М., Иванов О.В., Нечитайло В.А. Вейвлеты и их использование // Успехи физических наук. 2001. Т.171. № 5. С.465–501. DOI: 10.3367/UFNr.0171.200105a.0465. Коротченко Р.А., Самченко А.Н., Ярощук И.О. Применение многомерного ЕОФ-анализа в геоинформатике // Цифровая обработка сигналов. 2013. № 3. C. 17–20. Коротченко Р.А., Самченко А.Н., Ярощук И.О. Применение статистических методов в изучении рельефа шельфовой зоны на примере залива Посьета (Японское море) // Вестник Дальневосточного отделения Российской академии наук. 2011. № 6 (160). С. 54–59. Коротченко Р.А., Самченко А.Н., Ярощук И.О. Пространственно-временной анализ геоморфологии океанического дна залива Петра Великого (Японское море) // Океанология. 2014. Т. 54. № 4. С. 538–545. DOI:&nbsp;10.7868/S0030157414030046. Левченко О.В., Росляков А.Г., Поляков А.С., Зверев А.С., Мерклин Л.Р. Новые данные об осадочных волнах на западном континентальном склоне Каспийского моря // Доклады академии наук. 2008. т.420. № 4. C.&nbsp;537–542. Самченко А.Н. 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Ordering of droplets and light scattering in polymer dispersed liquid crystal films

Abstract We study the effects of droplet ordering in initial optical transmittance through polymer dispersed liquid crystal (PDLC) films prepared in the presence of an electrical field. The experimental data are interpreted by using a theoretical approach to light scattering in PDLC films that explicitly relates optical transmittance and the order parameters, characterizing both the orientational structures inside bipolar droplets and orientational distribution of the droplets. The theory relies on the Rayleigh-Gans approximation and uses the PercusYevick approximation to take into account the effects due to droplet positional correlations