Microtubules: Montroll's kink and Morse vibrations

Using a version of Witten's supersymmetric quantum mechanics proposed by Caticha, we relate Montroll's kink to a traveling, asymmetric Morse double-well potential suggesting in this way a connection between kink modes and vibrational degrees of freedom along microtubulesComment: 2pp, twocolum

Augmenting Weak Semantic Cognitive Maps with an “Abstractness” Dimension

The emergent consensus on dimensional models of sentiment, appraisal, emotions, and values is on the semantics of the principal dimensions, typically interpreted as valence, arousal, and dominance. The notion of weak semantic maps was introduced recently as distribution of representations in abstract spaces that are not derived from human judgments, psychometrics, or any other a priori information about their semantics. Instead, they are defined entirely by binary semantic relations among representations, such as synonymy and antonymy. An interesting question concerns the ability of the antonymy-based semantic maps to capture all “universal” semantic dimensions. The present work shows that those narrow weak semantic maps are not complete in this sense and can be augmented with other semantic relations. Specifically, including hyponym-hypernym relations yields a new semantic dimension of the map labeled here “abstractness” (or ontological generality) that is not reducible to any dimensions represented by antonym pairs or to traditional affective space dimensions. It is expected that including other semantic relations (e.g., meronymy/holonymy) will also result in the addition of new semantic dimensions to the map. These findings have broad implications for automated quantitative evaluation of the meaning of text and may shed light on the nature of human subjective experience

Dynamics of Neural Networks with Continuous Attractors

We investigate the dynamics of continuous attractor neural networks (CANNs). Due to the translational invariance of their neuronal interactions, CANNs can hold a continuous family of stationary states. We systematically explore how their neutral stability facilitates the tracking performance of a CANN, which is believed to have wide applications in brain functions. We develop a perturbative approach that utilizes the dominant movement of the network stationary states in the state space. We quantify the distortions of the bump shape during tracking, and study their effects on the tracking performance. Results are obtained on the maximum speed for a moving stimulus to be trackable, and the reaction time to catch up an abrupt change in stimulus.Comment: 6 pages, 7 figures with 4 caption

Этапы становления сельскохозяйственного производства республики: К 100-летию образования Министерства сельского хозяйства и продовольствия Республики Беларусь

There are several stages associated with fundamental changes in arrangement and production technologies for the development of agricultural production in the Republic of Belarus. Each of the stage was associated with achievements of scientific and technological progress and had important social and economic consequences. The paper dwells on the stages of agriculture development in the Republic of Belarus since 1919 to the present days. The basic transformations of the Ministry of Agriculture and Food as a body for state administration of agriculture are covered. It is shown that nowadays the Ministry of Agriculture and Food of the Republic of Belarus performs absolutely greater part of functions in the field of state agriculture management, in particular: administration, economic regulation, legal regulation, state agricultural policy, state control. It is known that high level of agro-industrial complex development guarantees the food security of the state, therefore, political independence and sovereignty as well. Over the years of the sovereign existence, the Republic of Belarus has been able to restore and develop agriculture, ensuring the country’s food security, as well as become an important exporter of food and agricultural products. Thus, the achieved results of agricultural production confirm the right chosen course aimed at intensive methods of work based on achievements of science and technology.В развитии сельскохозяйственного производства Республики Беларусь можно выделить несколько этапов, связанных с коренными изменениями организации и технологий производства. Каждый из этапов был связан с достижениями научно-технического прогресса и имел важные социально-экономические последствия. В статье представлены этапы развития сельского хозяйства в Республике Беларусь с 1919 г. по настоящее время. Освещены основные преобразования Министерства сельского хозяйства и продовольствия как органа государственного управления сельским хозяйством. Показано, что в настоящее время Министерство сельского хозяйства и продовольствия Республики Беларусь выполняет абсолютное большинство функций в сфере государственного управления сельским хозяйством, в частности: администрирование, экономическое регулирование, нормативно-правовое регулирование, проведение государственной политики в сельскохозяйственной сфере, государственный контроль. Известно, что высокий уровень развития агропромышленного комплекса является гарантом продовольственной безопасности государства, следовательно, политической независимости и суверенитета. За годы своего суверенного существования Республика Беларусь смогла возродить и развить сельское хозяйство, которое обеспечивает продовольственную безопасность страны, а также стать важным экспортером продуктов питания и сельскохозяйственной продукции. Таким образом, достигнутые результаты сельскохозяйственного производства подтверждают правильность выбранного курса на интенсивные методы работы на основе достижений науки и техники

Dynamical model of sequential spatial memory: winnerless competition of patterns

We introduce a new biologically-motivated model of sequential spatial memory which is based on the principle of winnerless competition (WLC). We implement this mechanism in a two-layer neural network structure and present the learning dynamics which leads to the formation of a WLC network. After learning, the system is capable of associative retrieval of pre-recorded sequences of spatial patterns.Comment: 4 pages, submitted to PR

An associative network with spatially organized connectivity

We investigate the properties of an autoassociative network of threshold-linear units whose synaptic connectivity is spatially structured and asymmetric. Since the methods of equilibrium statistical mechanics cannot be applied to such a network due to the lack of a Hamiltonian, we approach the problem through a signal-to-noise analysis, that we adapt to spatially organized networks. The conditions are analyzed for the appearance of stable, spatially non-uniform profiles of activity with large overlaps with one of the stored patterns. It is also shown, with simulations and analytic results, that the storage capacity does not decrease much when the connectivity of the network becomes short range. In addition, the method used here enables us to calculate exactly the storage capacity of a randomly connected network with arbitrary degree of dilution.Comment: 27 pages, 6 figures; Accepted for publication in JSTA

A first principle (3+1) dimensional model for microtubule polymerization

In this paper we propose a microscopic model to study the polymerization of microtubules (MTs). Starting from fundamental reactions during MT's assembly and disassembly processes, we systematically derive a nonlinear system of equations that determines the dynamics of microtubules in 3D. %coexistence with tubulin dimers in a solution. We found that the dynamics of a MT is mathematically expressed via a cubic-quintic nonlinear Schrodinger (NLS) equation. Interestingly, the generic 3D solution of the NLS equation exhibits linear growing and shortening in time as well as temporal fluctuations about a mean value which are qualitatively similar to the dynamic instability of MTs observed experimentally. By solving equations numerically, we have found spatio-temporal patterns consistent with experimental observations.Comment: 12 pages, 2 figures. Accepted in Physics Letters

A Comparative Computer Simulation of Dendritic Morphology

Computational modeling of neuronal morphology is a powerful tool for understanding developmental processes and structure-function relationships. We present a multifaceted approach based on stochastic sampling of morphological measures from digital reconstructions of real cells. We examined how dendritic elongation, branching, and taper are controlled by three morphometric determinants: Branch Order, Radius, and Path Distance from the soma. Virtual dendrites were simulated starting from 3,715 neuronal trees reconstructed in 16 different laboratories, including morphological classes as diverse as spinal motoneurons and dentate granule cells. Several emergent morphometrics were used to compare real and virtual trees. Relating model parameters to Branch Order best constrained the number of terminations for most morphological classes, except pyramidal cell apical trees, which were better described by a dependence on Path Distance. In contrast, bifurcation asymmetry was best constrained by Radius for apical, but Path Distance for basal trees. All determinants showed similar performance in capturing total surface area, while surface area asymmetry was best determined by Path Distance. Grouping by other characteristics, such as size, asymmetry, arborizations, or animal species, showed smaller differences than observed between apical and basal, pointing to the biological importance of this separation. Hybrid models using combinations of the determinants confirmed these trends and allowed a detailed characterization of morphological relations. The differential findings between morphological groups suggest different underlying developmental mechanisms. By comparing the effects of several morphometric determinants on the simulation of different neuronal classes, this approach sheds light on possible growth mechanism variations responsible for the observed neuronal diversity

A simple rule for axon outgrowth and synaptic competition generates realistic connection lengths and filling fractions

Neural connectivity at the cellular and mesoscopic level appears very specific and is presumed to arise from highly specific developmental mechanisms. However, there are general shared features of connectivity in systems as different as the networks formed by individual neurons in Caenorhabditis elegans or in rat visual cortex and the mesoscopic circuitry of cortical areas in the mouse, macaque, and human brain. In all these systems, connection length distributions have very similar shapes, with an initial large peak and a long flat tail representing the admixture of long-distance connections to mostly short-distance connections. Furthermore, not all potentially possible synapses are formed, and only a fraction of axons (called filling fraction) establish synapses with spatially neighboring neurons. We explored what aspects of these connectivity patterns can be explained simply by random axonal outgrowth. We found that random axonal growth away from the soma can already reproduce the known distance distribution of connections. We also observed that experimentally observed filling fractions can be generated by competition for available space at the target neurons--a model markedly different from previous explanations. These findings may serve as a baseline model for the development of connectivity that can be further refined by more specific mechanisms.Comment: 31 pages (incl. supplementary information); Cerebral Cortex Advance Access published online on May 12, 200