The history of constructivism in the Urals: 21st-century studies

The article was submitted on 28.07.2016.Статья посвящена научному обзору и анализу трудов современных исследователей по истории архитектуры конструктивизма на Урале. Наличие в крупных и малых городах Урала различных экспериментальных градостроительных решений и приемов квартальной застройки, типологического разнообразия общественных, жилых, производственных зданий и сооружений, реализованных в стилистических формах конструктивизма, существенно выделяет Уральский регион от других районов страны. По решению ЦИК СССР в 1923 г. была создана Уральская область с целью увеличения промышленно-хозяйственного потенциала страны, и попутно с целью решения основных проблем реконструкции «культуры и быта». Внедрение современных строительных материалов и конструкций, новаторские поиски в архитектуре объемно-пространственных решений, различных по типологии объектов в рациональной стилистике широко использовалось в застройке таких городов как Пермь, Челябинск, Магнитогорск, Курган, Нижний Тагил, Свердловск, Златоуст, Надеждинск и др. Социальная и художественная направленность современного по тем годам творческого течения повлияла на формирование новой структуры уральских городов, преобразовала архитектурный язык и облик построек, позволила создать новые, ранее не встречающиеся в архитектурной практике типы зданий, изменила представление людей об удобстве, стиле и качестве жизни. С середины 1930-х до начала 1990-х гг. многие уральские города решением правительства страны были закрыты для зарубежных исследователей советской авангардной архитектуры, а на публикации книг и статей об объектах конструктивизма в стране было наложено табу. Поэтому одни из первых серьезных публикаций конструктивистских объектов, сооруженных в уральских городах, появились только на рубеже ХХ–ХХΙ вв. С начала нового века стала складываться научная школа истории уральской авангардной архитектуры, известными представителями которой являются А. А. Барабанов, Е. В. Конышева, Л. Н. Смирнов, А. А. Стариков, Л. И. Токменинова, Л. П. Холодова и другие ученые.The article features a comprehensive review of recent research on the history of Constructivism in the Urals. Various experimental urban solutions in Ural cities and towns, innovative models of quarter planning, and the typological diversity of public, residential, and industrial buildings built in Constructivist style makes Ural region distinct from other parts of the country. The introduction of contemporary building materials and designs and novel research into the usage of space can be seen in diverse buildings in Perm, Chelyabinsk, Magnitogorsk, Kurgan, Nizhny Tagil, Sverdlovsk, Zlatoust, Nadezhdinsk, and others. The social and artistic direction of Constructivism as an ultra-modern creative movement greatly influenced the new architectural look of cities in the Urals. It also transformed the language of architecture and the visual imagery of buildings: it allowed for the creation of new, unprecedented architectural types and changed people’s ideas about convenience, style, and quality of life. From the mid-1930s until the early 1990s, many towns in the Urals were closed off to foreign researchers: the publication of books and articles about Constructivism was also prohibited. This is why the first serious publications about the Constructivist heritage of the Urals appeared only at the beginning of the 21st century. Thus began a rise in scholarship on this subject

Natural FLRW metrics on the Lie group of nonzero quaternions

It is shown that the Lie group of invertible elements of the quaternion algebra carries a family of natural closed Friedmann-Lemaitre-Robertson-Walker metrics.Comment: A slightly more technical version of "Natural geometry of nonzero quaternions" IJTP 46 (2) (2007) 251-25

Piezoelectric nonlinearity and frequency dispersion of the direct piezoelectric response of BiFeO3 ceramics

We report on the frequency and stress dependence of the direct piezoelectric d33 coefficient in BiFeO3 ceramics. The measurements reveal considerable piezoelectric nonlinearity, i.e., dependence of d33 on the amplitude of the dynamic stress. The nonlinear response suggests a large irreversible contribution of non-180{\deg} domain walls to the piezoelectric response of the ferrite, which, at present measurement conditions, reached a maximum of 38% of the total measured d33. In agreement with this interpretation, both types of non-180{\deg} domain walls, characteristic for the rhombohedral BiFeO3, i.e., 71{\deg} and 109{\deg}, were identified in the poled ceramics using transmission electron microscopy (TEM). In support to the link between nonlinearity and non-180{\deg} domain wall contribution, we found a correlation between nonlinearity and processes leading to deppining of domain walls from defects, such as quenching from above the Curie temperature and high-temperature sintering. In addition, the nonlinear piezoelectric response of BiFeO3 showed a frequency dependence that is qualitatively different from that measured in other nonlinear ferroelectric ceramics, such as "soft" (donor-doped) Pb(Zr,Ti)O3 (PZT); possible origins of this dispersion are discussed. Finally, we show that, once released from pinning centers, the domain walls can contribute extensively to the electromechanical response of BiFeO3; in fact, the extrinsic domain-wall contribution is relatively as large as in Pb-based ferroelectric ceramics with morphotropic phase boundary (MPB) composition, such as PZT. This finding might be important in the search of new lead-free MPB compositions based on BiFeO3 as it suggests that such compositions might also exhibit large extrinsic domain-wall contribution to the piezoelectric response.Comment: 38 pages, 11 figure

Electronic structure study by means of X-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet

The electronic structure of the single molecule magnet system M[Fe(L)2]3*4CHCl3 (M=Fe,Cr; L=CH3N(CH2CH2O)2) has been studied using X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, soft X-ray emission spectroscopy, and density functional calculations. There is good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 eV and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O,N) exhibit a magnetic polarisation yielding effective spin S=5/2 per iron atom, giving a high spin state molecule with a total S=5 effective spin for the case of M = Fe.Comment: Fig.2 replaced as it will appear in J. Chem. Phy

Analysis of patterns formed by two-component diffusion limited aggregation

We consider diffusion limited aggregation of particles of two different kinds. It is assumed that a particle of one kind may adhere only to another particle of the same kind. The particles aggregate on a linear substrate which consists of periodically or randomly placed particles of different kinds. We analyze the influence of initial patterns on the structure of growing clusters. It is shown that at small distances from the substrate, the cluster structures repeat initial patterns. However, starting from a critical distance the initial periodicity is abruptly lost, and the particle distribution tends to a random one. An approach describing the evolution of the number of branches is proposed. Our calculations show that the initial patter can be detected only at the distance which is not larger than approximately one and a half of the characteristic pattern size.Comment: Accepted for publication in Physical Review

First-principles study of hydrogen dynamics in monoclinic TiO

The existence of intrinsic vacancies in cubic (monoclinic) TiO suggests opportunity for hydrogen absorption, which was addressed in recent experiments. In the present work, based on first principle calculations, the preferences are studied for the hydrogen absorption sites and diffusion paths between them. The oxygen vacancies are found to be primary hydrogen traps with absorption energy of -2.87 eV. The plausible channels for hydrogen diffusion between adjacent vacancy sites (ordered in the monoclinic TiO structure) are compared with the help of calculations done with the nudge elastic band method. Several competitive channels are identified, with barrier heights varying from 2.87 to 3.71 eV, that is high enough to ensure relative stability of trapped hydrogen atoms at oxygen vacancy sites. Moreover, the possibility of adsorption of molecular hydrogen was tested and found improbable, in the sense that the H2 molecules penetrating the TiO crystal are easily dissociated (and released atoms tend to proceed towards oxygen vacancy sites). These results suggest that hydrogen may persist in oxygen vacancy sites up to high enough temperatures.Comment: updated and enlarged version, accepted for publication in Journal of Physical Chemistry C (June 2023