On direct numerical treatment of hypersingular integral equations arising in mechanics and acoustics

In this paper we present a treatment of hypersingular integral equations, which have relevant applications in many problems of wave dynamics, elasticity and fluid mechanics with mixed boundary conditions. The main goal of the present work is the development of an efficient direct numerical collocation method. The paper is completed with two examples taken from crack theory and acoustics: the study of a single crack in a linear isotropic elastic medium, and diffraction of a plane acoustic wave by a thin rigid screen.Comment: accepted by Acta Mechanica, 19 pages, 3 figure

Nucleation barrier reconstruction via the seeding method in a lattice model with competing nucleation pathways

We study a three-species analogue of the Potts lattice gas model of nucleation from solution in a regime where partially disordered solute is a viable thermodynamic phase. Using a multicanonical sampling protocol, we compute phase diagrams for the system, from which we determine a parameter regime where the partially disordered phase is metastable almost everywhere in the temperature–fugacity plane. The resulting model shows non-trivial nucleation and growth behaviour, which we examine via multidimensional free energy calculations. We consider the applicability of the model in capturing the multi-stage nucleation mechanisms of polymorphic biominerals (e.g., CaCO3). We then quantitatively explore the kinetics of nucleation in our model using the increasingly popular “seeding” method. We compare the resulting free energy barrier heights to those obtained via explicit free energy calculations over a wide range of temperatures and fugacities, carefully considering the propagation of statistical error. We find that the ability of the “seeding” method to reproduce accurate free energy barriers is dependent on the degree of supersaturation, and severely limited by the use of a nucleation driving force ∆µ computed for bulk phases. We discuss possible reasons for this in terms of underlying kinetic assumptions, and those of classical nucleation theory. C 2016 Author(s

Spatio-temporal feature representations of reactivated memories

How does the human brain recover memories of past events? The neural processes of memory retrieval are still not fully uncovered. This doctoral thesis is concerned with the spatio-temporal feature representations of reactivated episodic memories. Classical theories and empirical evidence suggest that the revival of memory representations in the brain is initiated in the hippocampus, before activity patterns in cortical regions reactivate to represent previously experienced events. The current doctoral project tests the assumption that the neural processing cascade during retrieval is reversed with respect to perception. This general framework predicts that semantic concepts and modality-independent information is reconstructed before modality-specific sensory details. This backward information flow is also assumed to affect the neural representations when memories are recalled repeatedly, enhancing the integration of new information into existing conceptual networks. The first two studies investigate the neural information flow during retrieval with respect to the reactivated mnemonic representations. First, simultaneous EEG-fMRI is used to track the presumed reversed reconstruction from abstract modality-independent to sensory-specific visual and auditory memory representations. The second EEG-fMRI project then zooms in on the recall of visual memories, testing whether the visual retrieval process propagates backwards along the ventral visual stream transferring from abstract conceptual to detailed perceptual representations. The reverse reconstruction framework predicts that conceptual information, due to its prioritisation, should benefit more from repeated recall than perceptual information. Hence, the last, behavioural study investigated whether retrieval strengthens conceptual representations over perceptual ones and thus promotes the semanticisation of episodic memories. Altogether, the findings offer novel insights into retrieval-related processing cascades, in terms of their temporal and spatial dynamics and the nature of the reactivated representations. The results also provide an understanding of memory transformations during the consolidation processes that are amplified through repeated retrieval

Feature-specific reaction times reveal a semanticisation of memories over time and with repeated remembering

Memories are thought to undergo an episodic-to-semantic transformation in the course of their consolidation. We here test if repeated recall induces a similar semanticisation, and if the resulting qualitative changes in memories can be measured using simple feature-specific reaction time probes. Participants studied associations between verbs and object images, and then repeatedly recalled the objects when cued with the verb, immediately and after a two-day delay. Reaction times during immediate recall demonstrate that conceptual features are accessed faster than perceptual features. Consistent with a semanticisation process, this perceptual-conceptual gap significantly increases across the delay. A significantly smaller perceptual-conceptual gap is found in the delayed recall data of a control group who repeatedly studied the verb-object pairings on the first day, instead of actively recalling them. Our findings suggest that wake recall and offline consolidation interact to transform memories over time, strengthening meaningful semantic information over perceptual detail

Factors and Trends of Increasing Role of Mass Media in Democratic Elections in Kazakhstan

The article discusses some features of information technologies used by Kazakh media during election campaigns of different years. The purpose of this work is to analyze the peculiarities and factors behind the increasing role of the Kazakh media in the process of democratic elections. The article shows that since 1991-1996 transitional phases, Kazakhstan has been undergoing an intensive procedure of incorporating the media into its constantly evolving democratic set-up and putting up a media monitoring system of the political process in place. Kazakhstan mass media has successfully coped with this task bringing in changes within and taking into account public mentality and technologies at hand. The article presents a comparative analysis of the use of various information technologies in Kazakh election campaigns of different years, with particular attention on the presidential election of 2019

“Westlessness” as an Obstacle to Constructive Interaction with Liberaldemocratic Western States

The results of the Munich Security conference held in February, 2020 identified a number of critical points that Western countries are currently facing. At the heart of this year’s conference was the term “Westlessness”, which is marked in the Munich Security Report. In this work, the indicated term is analyzed, as well as its role in changing the nature of international relations and the importance for a possible study of the crisis of liberal democracy.По результатам прошедшей в феврале 2020 года Мюнхенской конференции по безопасности был выявлен ряд критических точек, с которыми сталкиваются страны Запада в настоящее время. В центре внимания прошедшей конференции был термин «Westlessness », обозначенный в Мюнхенском докладе по безопасности. В данной работе анализируется указанный термин, а также его роль в изменении характера межгосударственных отношений и значение для возможного исследования кризиса либеральной демократии

Statistical detection of cooperative transcription factors with similarity adjustment

Motivation: Statistical assessment of cis-regulatory modules (CRMs) is a crucial task in computational biology. Usually, one concludes from exceptional co-occurrences of DNA motifs that the corresponding transcription factors (TFs) are cooperative. However, similar DNA motifs tend to co-occur in random sequences due to high probability of overlapping occurrences. Therefore, it is important to consider similarity of DNA motifs in the statistical assessment

Reconstructing Spatio-Temporal Trajectories of Visual Object Memories in the Human Brain

How the human brain reconstructs, step-by-step, the core elements of past experiences is still unclear. Here, we map the spatio-temporal trajectories along which visual object memories are reconstructed during associative recall. Specifically, we inquire whether retrieval reinstates feature representations in a copy-like but reversed direction with respect to the initial perceptual experience, or alternatively, this reconstruction involves format transformations and regions beyond initial perception. Participants from two cohorts studied new associations between verbs and randomly paired object images and subsequently recalled the objects when presented with the corresponding verb cue. We first analyse multivariate fMRI patterns to map where in the brain high- and low-level object features can be decoded during perception and retrieval, showing that retrieval is dominated by conceptual features, represented in comparatively late visual and parietal areas. A separately acquired EEG dataset is then used to track the temporal evolution of the reactivated patterns using similarity-based EEG-fMRI fusion. This fusion suggests that memory reconstruction proceeds from anterior fronto-temporal to posterior occipital and parietal regions, in line with a conceptual-to-perceptual gradient, but only partly following the same trajectories as during perception. Specifically, a linear regression statistically confirms that the sequential activation of ventral visual stream regions is reversed between image perception and retrieval. The fusion analysis also suggests an information relay to fronto-parietal areas late during retrieval. Together, the results shed light onto the temporal dynamics of memory recall, and the transformations that the information undergoes between the initial experience and its later reconstruction from memory. We combined EEG and fMRI to investigate which features of a visual object are reactivated when recalled from episodic memory, and how the memory reconstruction stream unfolds over time and across the brain. Our findings suggest that relative to perception, memory retrieval follows a backwards information trajectory along a conceptual-to-perceptual gradient, and additionally relays retrieved information to multimodal fronto-parietal brain regions. These findings address the fundamental question of whether memories are more or less truthful reconstructions of past events, or instead are subject to systematic biases that prioritise some types of features over others. Our data suggests that episodic memory retrieval is a dynamic and highly reconstructive process with clear prioritisation of abstract-conceptual over detailed-perceptual information. [Abstract copyright: Copyright © 2024 Lifanov-Carr et al.

CORECLUST: identification of the conserved CRM grammar together with prediction of gene regulation

Identification of transcriptional regulatory regions and tracing their internal organization are important for understanding the eukaryotic cell machinery. Cis-regulatory modules (CRMs) of higher eukaryotes are believed to possess a regulatory ‘grammar’, or preferred arrangement of binding sites, that is crucial for proper regulation and thus tends to be evolutionarily conserved. Here, we present a method CORECLUST (COnservative REgulatory CLUster STructure) that predicts CRMs based on a set of positional weight matrices. Given regulatory regions of orthologous and/or co-regulated genes, CORECLUST constructs a CRM model by revealing the conserved rules that describe the relative location of binding sites. The constructed model may be consequently used for the genome-wide prediction of similar CRMs, and thus detection of co-regulated genes, and for the investigation of the regulatory grammar of the system. Compared with related methods, CORECLUST shows better performance at identification of CRMs conferring muscle-specific gene expression in vertebrates and early-developmental CRMs in Drosophila

Binding site number variation and high-affinity binding consensus of Myb-SANT-like transcription factor Adf-1 in Drosophilidae

There is a growing interest in the evolution of transcription factor binding sites and corresponding functional change of transcriptional regulation. In this context, we have examined the structural changes of the ADF-1 binding sites at the Adh promoters of Drosophila funebris and D. virilis. We detected an expanded footprinted region in D. funebris that contains various adjacent binding sites with different binding affinities. ADF-1 was described to direct sequence-specific DNA binding to sites consisting of the multiple trinucleotide repeat . The ADF-1 recognition sites with high binding affinity differ from this trinucleotide repeat consensus sequence and a new consensus sequence is proposed for the high-affinity ADF-1 binding sites. In vitro transcription experiments with the D. funebris and D. virilis ADF-1 binding regions revealed that stronger ADF-1 binding to the expanded D. funebris ADF-1 binding region only moderately lead to increased transcriptional activity of the Adh gene. The potential of this regional expansion is discussed in the context of different ADF-1 cellular concentrations and maintenance of the ADF-1 stimulus. Altogether, evolutionary change of ADF-1 binding regions involves both, rearrangements of complex binding site cluster and also nucleotide substitutions within sites that lead to different binding affinities