221 research outputs found

    Methods to calibrate and scale axial distances in confocal microscopy as a function of refractive index

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    Accurate distance measurement in 3D confocal microscopy is important for quantitative analysis, volume visualization and image restoration. However, axial distances can be distorted by both the point spread function and by a refractive-index mismatch between the sample and immersion liquid, which are difficult to separate. Additionally, accurate calibration of the axial distances in confocal microscopy remains cumbersome, although several high-end methods exist. In this paper we present two methods to calibrate axial distances in 3D confocal microscopy that are both accurate and easily implemented. With these methods, we measured axial scaling factors as a function of refractive-index mismatch for high-aperture confocal microscopy imaging. We found that our scaling factors are almost completely linearly dependent on refractive index and that they were in good agreement with theoretical predictions that take the full vectorial properties of light into account. There was however a strong deviation with the theoretical predictions using (high-angle) geometrical optics, which predict much lower scaling factors. As an illustration, we measured the point-spread-function of a point-scanning confocal microscope and showed that an index-matched, micron-sized spherical object is still significantly elongated due to this PSF, which confirms that single micron-sized spheres are not well suited to determine accurate axial calibration nor axial scaling.Comment: 8 pages, 5 figure

    Исследование устойчивости функционирования региональных природно-промышленных систем и принятие оптимальных управленческих решений

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    Предложена математическая модель, описывающая поведение горного массива при воздействии на него массовых сил. Найдены условия параметров задачи, при которых возможны геотектонические нарушения. Предложена методика исследований, заключающаяся в системном подходе решения вопроса, который состоит в выделении рассматриваемой системы, определении составляющих ее компонентов, определение связей между ними. Определяющим моментом методики исследования является наличие базы данных по факторам влияния. Рассматривается математическая модель, позволяющая описать слоистую структуру горного массива с учетом наличия геологических нарушений и техногенных воздействий. Исследование ее устойчивости базируется на анализе энергетического баланса внешнего и внутреннего потенциалов, комплексно воздействующих на горный массив, на котором расположен рассматриваемый регион. Выведены критерии (на основании дисбаланса потенциалов), позволяющие делать пространственно-временной прогноз возможных чрезвычайных горно-геологических процессов. Достоверность критериев устойчивости усиливается коэффициентом системности, который может рассчитываться как для всей природно-промышленной системы, так и для отдельных ее компонентов.Запропоновано математичну модель, яка описує поведінку гірничого масиву під час впливу на нього масових сил. Знайдено умови параметрів задачі, за яких можливі геотектонічні порушення. Пропонується методика досліджень, яка полягає у системному підході вирішення питання, яке складається у виділенні розглянутої системи, визначенні складових її компонентів, зв’язків між ними. Визначним моментом методики досліджень є наявність бази даних по факторам впливу. Розглядається математична модель, яка дозволяє описати шарову структуру гірничого масиву з обліком наявності геологічних порушень і ехногенних впливів. Дослідження її стійкості базується на аналізі енергетичного балансу зовнішнього і внутрішнього потенціалів, які комплексно впливають на гірничий масив, на якому розташовано регіон, що розглядається. Виведено критерії (на основі дисбалансу потенціалів), які дозволяють робити просторо-часовий прогноз можливих надзвичайних гірничо-геологічних процесів. Достовірність критеріїв стійкості посилюється коефіцієнтом системності, який може розраховуватись як для всієї природно-промислової системи, так і для окремих її компонентів.A mathematical model, which describes the behavior of the rock mass during it is affected by mass forces, is proposed. Conditions are found for the parameters of the problem, where geotectonic violation is possible. A method of study, which consists in systematic approach to problem solution (separate the system, determination of its components, the definition of relationships between components) is proposed. The key defining of research methods is the availability of a database on the factors of influence. A mathematical model that allows to describe the layered structure of the rock mass based on the availability of geological faults and technogenic impacts, is considered. Research of its stability is based on the analysis of the energy balance of internal and external potentials, the complex influence of the mountain range, which is located in this region. The criteria (based on the imbalance of potentials), which allow the space-time prediction of possible extreme geological processes, are derived. The reliability of stability criteria is enhanced by systemic factor that can be calculated for the entire faculty, and for the individual components

    Nature of an Electric-Field-Induced Colloidal Martensitic Transition

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    We study the properties of a solid-solid close-packed to body-centered tetragonal transition in a colloidal suspension via fluorescence confocal laser scanning microscopy, in three dimensions and in real space. This structural transformation is driven by a subtle competition between gravitational and electric dipolar field energy, the latter being systematically varied via an external electric field. The transition threshold depends on the local depth in the colloidal sediment. Structures with order intermediate between close-packed and body-centered tetragonal were observed, with these intermediate structures also being stable and long lived. This is essentially a colloidal analogue of an ‘‘atomiclevel’’ interfacial structure. We find qualitative agreement with theory (based purely on energetics). Quantitative differences can be attributed to the importance of entropic effects

    Colloid-oil-water-interface interactions in the presence of multiple salts: charge regulation and dynamics

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    We theoretically and experimentally investigate colloid-oil-water-interface interactions of charged, sterically stabilized, poly(methyl-methacrylate) colloidal particles dispersed in a low-polar oil (dielectric constant ϵ=510\epsilon=5-10) that is in contact with an adjacent water phase. In this model system, the colloidal particles cannot penetrate the oil-water interface due to repulsive van der Waals forces with the interface whereas the multiple salts that are dissolved in the oil are free to partition into the water phase. The sign and magnitude of the Donnan potential and/or the particle charge is affected by these salt concentrations such that the effective interaction potential can be highly tuned. Both the equilibrium effective colloid-interface interactions and the ion dynamics are explored within a Poisson-Nernst-Planck theory, and compared to experimental observations.Comment: 13+2 pages, 5+3 figures; V2: small clarifications in the tex

    Morphology-Controlled Growth of Crystalline Ag-Pt-Alloyed Shells onto Au Nanotriangles and Their Plasmonic Properties

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    The surface plasmon resonance of noble-metal nanoparticles depends on nanoscale size, morphology, and composition, and provides great opportunities for applications in biomedicine, optoelectronics, (photo)catalysis, photovoltaics, and sensing. Here, we present the results of synthesizing ternary metallic or trimetallic nanoparticles, Au nanotriangles (Au NTs) with crystalline Ag-Pt alloyed shells, the morphology of which can be adjusted from a yolk-shell to a core-shell structure by changing the concentration of AgNO3 or the concentration of Au NT seeds, while the shell thickness can be precisely controlled by adjusting the concentration of K2PtCl4. By monitoring the growth process with UV-vis spectra and scanning transmission electron microscopy (STEM), the shells on the Au NT-Ag-Pt yolk-shell nanoparticles were found to grow via a galvanic replacement synergistic route. The plasmonic properties of the as-synthesized nanoparticles were investigated by optical absorbance measurements

    Вимоги до матеріалів, що приймаються до друку в збірнику наукових праць «Сучасна українська політика. Політики і політологи про неї»

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    Whereas bulk zinc oxide (ZnO) exhibits the wurtzite crystal structure, nanoscale ZnO was recently synthesized in the rock salt structure by addition of Mg. Using first-principles methods, we investigated two stabilization routes for accessing rock salt ZnO. The first route is stabilization by Mg addition, which was investigated by considering ZnO-MgO mixed phases. The second route is through size effects, as surface energies become dominant for small nanocrystal sizes. We discovered that the surface energy of rock salt ZnO is surprisingly low at 0.63 J m-2, which is lower than those of wurtzite and zinc blende ZnO and lower than that of rock salt MgO. We predict that pure rock salt ZnO is stable for nanocrystals smaller than 1.6 nm, and that Mg additions can greatly extend the size range in which the rock salt phase is stable. Both mixed-phase and core-shell models were considered in the calculations. The present approach could be applied to predict the stabilization of many other nanocrystal phases in deviating crystal structures

    Non-equilibrium sedimentation of colloids on the particle scale

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    We investigate sedimentation of model hard sphere-like colloidal dispersions confined in horizontal capillaries using laser scanning confocal microscopy, dynamical density functional theory, and Brownian dynamics computer simulations. For homogenized initial states we obtain quantitative agreement of the results from the respective approaches for the time evolution of the one-body density distribution and the osmotic pressure on the walls. We demonstrate that single particle information can be obtained experimentally in systems that were initialized further out-of-equilibrium such that complex lateral patterns form.Comment: to be published in Phys. Rev. Let
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