Моделювання еволюції надпотужних конвективних утворень над Кримом під час проходження смерчів

Предметом даного дослідження були умови формування осередків надпотужних вертикальних рухів, сильних вихорів та надпотужних конвективних утворень під час проходження смерчів над центральною частиною Криму 22 липня 2002 р. Тривимірні прогностичні мікрофізичні моделі фронтальних систем хмар з урахуванням та без урахування складного рельєфу, розроблені в УкрНДГМІ, було адаптовано до умов розвитку хмарності в екстремальних умовах розвитку смерчів. Проведено декілька серій чисельних експериментів для пошуку ключових параметрів, які спричиняли та визначали характер розвитку вихрових утворень і процесів, що їх супроводжують.Предметом исследования в работе были условия формирования ячеек сверхмощных вертикальных движений, сильных вихрей, сверхмощных конвективных образований во время прохождения смерчей над центральной частью Крыма 22 июля 2002 года. Трехмерные прогностические микрофизические модели с учетом и без учета орографии, разработанные в УкрНИГМИ, были адаптированы для условий эволюции фронтальных облачных систем в экстремальных условиях развития смерчей. Проведено несколько серий численных экспериментов с целью поиска ключевых параметров, определяющих характер развития вихревых образований и сопровождающих их явлений

Complex Colloidal Structures by Self-assembly in Electric Fields

The central theme of this thesis is exploiting the directed self-assembly of both isotropic and anisotropic colloidal particles to achieve the fabrication of one-, two-, and three-dimensional complex colloidal structures using external electric fields and/or a simple in situ thermal annealing method. Colloids are typically defined as objects having at least one dimension in the size range of a few nanometers to several micrometers that form a dispersed phase when suspended in a continuum phase. As a result of Brownian motion, the colloidal particles are able to explore configurational space, and eventually reach the equilibrium configuration that minimizes the free energy. An important feature of the colloidal particles is the possibility of controlling the size, shape, and composition. The assembly of colloidal particles has long been a rich and continuously growing area of materials science, with great potential for a broad range of applications including electronics, optics, and biotechnology. Within this field, the bulk of the research has been devoted to studying the assembly of isotropic spherical particles. Recently, there has been growing interest in the design of more complex structures to see how such a change in microstructure could influence certain material properties, especially optical properties, but also to answer the demand for more realistic model systems for molecular analogues. In this thesis, we used external electric fields to impart anisotropy into systems consisting of both isotropic and an-isotropic particles. If there is a mismatch in permittivity between the particles and the suspending medium, the colloids acquire an induced dipole moment. A major advantage of this approach is that the interactions are tunable and fully reversible. Moreover, a large number of parameters can be used to control and tune particle interactions and subsequent self-assembly in AC electric fields, including field strength and frequency, particle shape, particle and solvent dielectric properties. Interestingly, the relatively simple anisotropic dipolar interaction already gives rise to several new phases in a uniaxial field. We developed methods to produce model systems that are essentially colloidal analogues of polymer chains in all three stiffness regimes that can be observed on a single particle level, even in concentrated systems without using molecular tracers. Moreover, we obtained control over the length, and the flexibility of the bead chains. We exploited our simple thermal sintering method further for bonding polymeric colloidal particles after they have been assembled into various three-dimensional structures. Next, we discussed the generality of our method by implementing this method to close and non-close packed structures. We used our thermal annealing method to synthesize more complex shape particles such as rhombic dodecahedron particles and also we discuss the stability of the particles. We controlled the lateral position of the strings of particles with micrometer-scale precision by a combination of structured wall and electric dipoles. We investigated the self-assembly of gold nano-sheets as a function of salt in electric fields. Finally, we studied the effect of external electric fields on the phase behavior of sharp-edged colloidal cubes using optical microscopy and Monte Carlo simulations

Self-assembly of colloidal particles into strings in a homogeneous external electric or magnetic field

Colloidal particles with a dielectric constant (magnetic susceptibility) mismatch with the surrounding solvent acquire a dipole moment in a homogeneous external electric (magnetic) field. The resulting dipolar interactions can lead to aggregation of the particles into string-like clusters. Recently, several methods have been developed to make these structures permanent. However, especially when multiple particle sizes and/or more complex shapes than single spheres are used, the parameter space for these experiments is enormous. We therefore use Monte Carlo simulations to investigate the structure of the self-assembled string-like aggregates in binary mixtures of dipolar hard and charged spheres, as well as dipolar hard asymmetric dumbbells. Binary mixtures of spheres aggregate in different types of clusters depending on the size ratio of the spheres. For highly asymmetric systems, the small spheres form ring-like and flame-like clusters around strings of large spheres, while for size ratios closer to 1, alternating strings of both large and small spheres are observed. For asymmetric dumbbells, we investigate both the effect of size ratio and dipole moment ratio, leading to a large variety of cluster shapes, including chiral clusters

Bonding assembled colloids without loss of colloidal stability

In recent years the diversity of self-assembled colloidal structures has strongly increased, as it is fueled by a wide range of applications in materials science and also in soft condensed-matter physics.[1–4] Some potential applications include photonic bandgap (PBG) crystals, materials for plasmonic devices, high-efficiency energy conversion and storage, miniature diagnostic systems, desalination, and hierarchically structured catalysts.[1–4] Three dimensional colloidal crystals with mostly close-packed (randomly or face-centered cubic (fcc) stacked) structures have been fabricated via various methods, some of which are able to impose the orientation of these crystals, e.g., sedimentation,[5] colloidal epitaxy,[6] evaporative or “flow controlled” deposition,[7] shear flow,[8,9] and spin-coating.[10] Fewer methods have been reported to generate non-close-packed colloidal crystal structures, for instance, by a physical or chemical immobilization of colloidal arrays with a readily polymerizable monomer, which is dissolved in the dispersion,[11–14] and by a combination of thermal sintering and etching of close-packed colloidal crystals.[15] Many methods are currently being developed further to fabricate more diverse crystal symmetries and non-close-packed structures by tuning the interaction between the particles, e.g., oppositely charged interactions,[16,17] external electric fields,[18–20] and/or non-spherical shapes.[21,22] However, the structures thus formed are vulnerable to capillary forces that arise when the solvent is evaporated and to many other post-treatment steps, especially when the particles are non-close-packed.[1–4] For example, to obtain a PBG in the near infrared, the artificial opals must be dried, then infiltrated with a high-refractive-index material, and the spheres must subsequently be selectively removed by chemical etching[15,23] or a thermal treatment (calcination or pyrolysis).[1,2,4,14,24 Here, we present a facile and flexible one-step, in situ, thermal annealing method to permanently fix non-close-packed and close-packed polymeric structures so that they easily survive a subsequent drying step without loss of colloidal stability. We first demonstrate the concept with fluorescently labeled and sterically stabilized polymethylmethacrylate (PMMA) particles[25] because this system can be readily index and density matched, allowing us to compare their structures in 3D real-space before and after the treatment by means of confocal laser scanning microscopy. In unrelated work, we have already demonstrated this method for creating 1D colloidal bead chains by the application of an external electric field,[26] but it is shown in the present paper that the method presented is quite general and can be applied on many other self-assembly schemes. Moreover, we show that the shape and volume fraction of the particles after bonding can be changed by varying the heating time. Here, we implement our method to three different non-close-packed assemblies and one close-packed structure: i) ionic colloidal crystals of oppositely charged particles with a CsCl morphology, ii) external electric field induced body-centered tetragonal (bct) crystal structures, iii) labyrinthine or maze-like sheet structures induced by external electric fields, and iv) random hexagonal close-packed crystals

Directed Self-Assembly of Micron-Sized Gold Nanoplatelets into Oriented Flexible Stacks with Tunable Interplate Distance

A growing demand for control over the interparticle spacing and the orientation of anisotropic metallic particles into self-assembled structures is fuelled by their use in potential applications such as in plasmonics, catalysis, sensing, and optoelectronics. Here, we present an improved high yield synthesis method to fabricate micron- and submicron-sized gold nanoplatelets with a thickness less than 20 nm using silver nanoplatelets as seeds. By tuning the depth of the secondary minimum in the DLVO interaction potential between these particles, we are able to assemble the platelets into dynamic and flexible stacks containing thousands of platelets arranged face-to-face with well-defined spacing. Moreover, we demonstrate that the length of the stacks, and the interplate distance can be controlled between tens and hundreds of nm with the ionic strength. We use a high frequency external electric field to control the orientation of the stacks and direct the stacks into highly organized 2D and 3D assemblies that strongly polarize light

Self-organization of the bacterial cell-division protein FtsZ in confined environments

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