More Like this

1. Effective Ultrapowers and Applications; Aspects of Computation and Automata Theory with Applications

   https://doi.org/10.1142/9789811278631_0008  

   Dimitrov, Rumen D; Harizanov, Valentina (November 2023, WORLD SCIENTIFIC)

   Greenberg, Noam; Jain, Sanjay; Ng, Keng Meng; Schewe, Sven; Stephan, Frank; Wu, Guohua; Yang, Yue (Ed.)

   We give a systematic account of the current state of knowledge of an e↵ective analogue of the ultraproduct construction. We start with a product of a uniformly computable sequence of computable structures indexed by the set of natural numbers. The equality of elements and sat- isfaction of formulas are defined modulo a subset of the index set, which is cohesive, i.e., indecomposable with respect to computably enumerable sets. We present an analogue of Lo ́s’s theorem for e↵ective ultraprod- ucts and a number of results on definability and isomorphism types of the e↵ective ultrapowers of the field of rational numbers, when the com- plements of cohesive sets are computably enumerable. These e↵ective ultraproducts arose naturally in the study of the automorphisms of the lattice of computably enumerable vector spaces. Previously, a number of authors considered related constructions in the context of nonstandard models of fragments of arithmetic. 

   more » « less
2. Finite Element Analysis of 3D Woven Composites Using Consumer Graphical Processing Units

   https://doi.org/10.12783/asc35/34923  

   Drach, Borys (September 2020, Proceedings of the 35th ASC Technical Conference, Hoboken, NJ, USA, 2020)

   null (Ed.)

   The focus of this paper is application of a Graphical Processing Unit (GPU) based solver to linearly elastic finite element analysis (FEA) of composites with threedimensional (3D) woven reinforcements. Aspects specific to this material system including local material orientations, high contrast between elastic properties of constituents, large number of degrees of freedom, and simulation runtimes are discussed. Speedups offered by parallelization via GPUs and regularity of structured grids enable matrix-free implementation of FEA, which requires reassembly of the global stiffness at every iteration of solution of the system of linear equations, but in turn significantly reduces memory requirements. This makes linear analysis of composite structures with explicit reinforcement representation (tens of millions of degrees of freedom) possible on personal computers. Potential applications of this procedure include fast calculation of effective properties for design of novel 3D woven architectures and efficient solution of problems with high degrees of material nonlinearity requiring frequent stiffness matrix updates. 

   more » « less
3. The long-term optical activity of the propellers AE Aquarii and AR Scorpii

   https://doi.org/10.1093/pasj/psaa012  

   Šimon, Vojtěch (April 2020, Publications of the Astronomical Society of Japan)

   Abstract This analysis of the long-term optical activity of the propellers AE Aqr and AR Sco uses data from the Catalina Real-time Transient Survey, DASCH, and AAVSO. The site and character of the emissions from the phenomena caused by the magnetic field of the white dwarf (WD) vary from system to system. The histogram of intensities of the ensemble of flares of AE Aqr suggests that the long-term activity consists of a large variety of the peak magnitudes of the flares, with the probability of their detection gradually decreasing with increasing intensity. Any increase of activity only leads to an increase of the number of blobs of the transferring matter. We also detected a season with a transient decrease or even a cessation of the mass outflow from the donor to the lobe of the WD. The very strong orbital modulation of AR Sco is most stable in the phases of the extrema of brightness for about a century; its minor changes suggest that the trailing side of the synchrotron-emitting region is more unstable than the leading side. 

   more » « less
4. Generalized characteristic sets and new multivariate difference dimension polynomials

   https://doi.org/10.1007/s00200-023-00628-0  

   Levin, Alexander (October 2023, Applicable Algebra in Engineering, Communication and Computing)

   We introduce a new type of characteristic sets of difference polynomials using a generalization of the concept of effective order to the case of partial difference polynomials and a partition of the basic set of translations σ. Using properties of these characteristic sets, we prove the existence and outline a method of computation of a multivariate dimension polynomial of a finitely generated difference field extension that describes the transcendence degrees of intermediate fields obtained by adjoining transforms of the generators whose orders with respect to the components of the partition of σ are bounded by two sequences of natural numbers. We show that such dimension polynomials carry essentially more invariants (that is, characteristics of the extension that do not depend on the set of its difference generators) than previously known difference dimension polynomials. In particular, a dimension polynomial of the new type associated with a system of algebraic difference equations gives more information about the system than the classical univariate difference dimension polynomial. 

   more » « less
5. Assessing the availability of green infrastructure to residents of an Arctic city (on the example of Nadym) [Оценка обеспеченности зеленой инфраструктурой жителей арк­тического города (на примере Надыма)]

   https://doi.org/10.25283/2223-4594-2022-4-475-490  

   Sizov, O.S.; Fedorov, R.Y.; Pechkina, Y.A.; Michugin, M.S.; Kuklina, V.V.; Soromotin, A.V.; Fedash, A.V. (December 2022, Arctic: Ecology and Economy)

   Based on remote sensing data, the authors consider the features of the formation and use of green spaces in the city of Nadym (Yamalo-Nenets Autonomous Area). They give a detailed assessment of the availability of green infrastructure for the inhabitants of Nadym based on a comparison of the spatial distribution of vegetation and the urban population. During the construction of the city, there was a dramatic reduction in the area of vegetation cover, which reached its maximum during active construction in the 1980s. After the completion of the main construction stage and until now, there has been a steady increase in the share of vegetation, which is explained by active landscaping activities against the backdrop of climate softening. The authors have find out that while maintaining the high availability of open green spaces within the city, the main lack of vegetation is observed within the residential development of microdistricts. The methodology for the integrated use of medium and ultra-high resolution space images, UAV surveys, detailed mapping of residential buildings and field geobotanical descriptions tested during the study can be used in a detailed analysis of the state of the green infrastructure of other cities in the north of Western Siberia. In general, the assessment of the green infrastructure availability in the Arctic cities is of great importance for urban planning, allowing to fully take into account the regional environmental needs of local residents, in the context of the heterogeneity of their distribution. 

   more » « less