Unjamming of active rotators

Active particle assemblies can exhibit a wide range of interesting dynamical phases depending on internal parameters such as density, adhesion strength or self-propulsion. Active self-rotations are rarely studied in this context, although they can be relevant for active matter systems, as we illustrate by analyzing the motion of Chlamydomonas reinhardtii algae under different experimental conditions. Inspired by this example, we simulate the dynamics of a system of interacting active disks endowed with active torques and self-propulsive forces. At low packing fractions, adhesion causes the formation of small rotating clusters, resembling those observed when algae are stressed. At higher densities, the model shows a jamming to unjamming transition promoted by active torques and hindered by adhesion. We also study the interplay between self-propulsion and self-rotation and derive a phase diagram. Our results yield a comprehensive picture of the dynamics of active rotators, providing useful guidance to interpret experimental results in cellular systems where rotations might play a role

Problems of Asset Valuation in the Process of Bank Liquidation

The aim of the article is to identify problematic issues of valuation of property (assets) of banks that are in the process of liquidation, and substantiate proposals for the desired solution, taking into account the need to protect the rights of bank creditors. Although the bankruptcy of banks causes significant economic and moral losses, the processes of removing insolvent banks from the market, their reorganization or liquidation are constantly taking place. Therefore, regulators and banks that have been declared insolvent face many questions, including the adequate valuation of banking assets and the determination of the liquidation estate. The article discusses approaches to asset valuation and features of their application in Ukrainian practice, as well as peculiarities of the sale of assets of banks in liquidation according to the Dutch auction model. It is noted that the imperfection of management of banks’ assets in the process of their functioning leads to discrepancies in the valuation of these low-quality assets in the liquidation procedure. It is determined that the ratio between the estimated value of assets and their book value for banks declared insolvent is on average 26.2 %, and the median value is 22.3 % This leads to a number of problems, including the inability of the Deposit Guarantee Fund (DGF) to ensure the repayment of part of the bank’s liabilities, which could be repaid in case of timely acceptance of tender offers at market value. It is noted that the most liquid assets, which are real estate and property, occupy an insignificant share in the structure of the liquidation mass – about 5 %, and the conversion rate in the sale of real estate quite often reaches 200 %. It is proposed, in accordance with European practice, to empower the Fund to monitor the assets of banks in the process of their functioning. The expediency of valuating assets not from the position of doing business «as usual» but from the point of view of the objective need to sell assets, focusing on the quick sale of assets at a market price, is emphasized. In order to improve the process of valuating the assets of an insolvent bank and focusing on the quick and transparent sale of the bank’s assets, it is proposed to implement the international experience of using loss-sharing agreements into domestic practice

MicroRNA-222 Regulates Melanoma Plasticity

Melanoma is one of the most aggressive and highly resistant tumors. Cell plasticity in melanoma is one of the main culprits behind its metastatic capabilities. The detailed molecular mechanisms controlling melanoma plasticity are still not completely understood. Here we combine mathematical models of phenotypic switching with experiments on IgR39 human melanoma cells to identify possible key targets to impair phenotypic switching. Our mathematical model shows that a cancer stem cell subpopulation within the tumor prevents phenotypic switching of the other cancer cells. Experiments reveal that hsa-mir-222 is a key factor enabling this process. Our results shed new light on melanoma plasticity, providing a potential target and guidance for therapeutic studies

Dense active matter model of motion patterns in confluent cell monolayers

Epithelial cell monolayers show remarkable displacement and velocity correlations over distances of ten or more cell sizes that are reminiscent of supercooled liquids and active nematics. We show that many observed features can be described within the framework of dense active matter, and argue that persistent uncoordinated cell motility coupled to the collective elastic modes of the cell sheet is sufficient to produce swirl-like correlations. We obtain this result using both continuum active linear elasticity and a normal modes formalism, and validate analytical predictions with numerical simulations of two agent-based cell models, soft elastic particles and the self-propelled Voronoi model together with in-vitro experiments of confluent corneal epithelial cell sheets. Simulations and normal mode analysis perfectly match when tissue-level reorganisation occurs on times longer than the persistence time of cell motility. Our analytical model quantitatively matches measured velocity correlation functions over more than a decade with a single fitting parameter.Comment: updated version accepted for publication in Nat. Com

Metamaterial architecture from a self-shaping carnivorous plant

As meticulously observed and recorded by Darwin, the leaves of the carnivorous plant Drosera capensis L. slowly fold around insects trapped on their sticky surface in order to ensure their digestion. While the biochemical signaling driving leaf closure has been associated with plant growth hormones, how mechanical forces actuate the process is still unknown. Here, we combine experimental tests of leaf mechanics with quantitative measurements of the leaf microstructure and biochemistry to demonstrate that the closure mechanism is programmed into the cellular architecture of D. capensis leaves, which converts a homogeneous biochemical signal into an asymmetric response. Inspired by the leaf closure mechanism, we devise and test a mechanical metamaterial, which curls under homogeneous mechanical stimuli. This kind of metamaterial could find possible applications as a component in soft robotics and provides an example of bio-inspired design

Active wetting of epithelial tissues

Development, regeneration and cancer involve drastic transitions in tissue morphology. In analogy with the behavior of inert fluids, some of these transitions have been interpreted as wetting transitions. The validity and scope of this analogy are unclear, however, because the active cellular forces that drive tissue wetting have been neither measured nor theoretically accounted for. Here we show that the transition between 2D epithelial monolayers and 3D spheroidal aggregates can be understood as an active wetting transition whose physics differs fundamentally from that of passive wetting phenomena. By combining an active polar fluid model with measurements of physical forces as a function of tissue size, contractility, cell-cell and cell-substrate adhesion, and substrate stiffness, we show that the wetting transition results from the competition between traction forces and contractile intercellular stresses. This competition defines a new intrinsic lengthscale that gives rise to a critical size for the wetting transition in tissues, a striking feature that has no counterpart in classical wetting. Finally, we show that active shape fluctuations are dynamically amplified during tissue dewetting. Overall, we conclude that tissue spreading constitutes a prominent example of active wetting --- a novel physical scenario that may explain morphological transitions during tissue morphogenesis and tumor progression

SULFUR ABUNDANCE IN THE GALACTIC DISC STARS

The  sulfur abundance was determined by the synthetic spectrum method in the stars with metallicity close to that of the Sun. The comparison with the results of other authors, as well as the nucleosynthesis  computations were made.The  sulfur abundance was determined by the synthetic spectrum method in the stars with metallicity close to that of the Sun. The comparison with the results of other authors, as well as the nucleosynthesis  computations were made

THE FORMATION OF EFFECTIVE MANAGEMENT OF TECHNICAL-GEOLOGICAL SYSTEMS IN GEOLOGICAL SUBSOIL: REALITY AND PERSPECTIVES

A technical-geological system (TGS) consists of geological environment, man-made objects (techno-sphere) and management system, which are divided into a number of individual components. This all can be considered as natural - anthropogenic complex. The effective functioning of such complex set as TGS is provided by perfect theory, management methodology and by the degree of information fullness and its reliability. We study the “mining deposit-geological environment” systems as technical-geological system (TGS) with the following constituents: geological object rated as deposit facility with defined economic assessment, technical equipment for the conduction of extraction works and management system of all processes in TGS. The investigation of mineral deposits as TGS has three practical aspects: 1) it refers to the study of the geological environment as the environment of human living; 2) it is associated with the study of geological bodies as natural resources; 3) it is associated with retrospective research based on the study of dynamical systems, as well as with determination of the forecast of mineral resources exploration. Mastering of mining deposit should be provided with such information capabilities that match the complexity of the TGS, in order to be able to control its condition, relationships, and flows of matter, energy and information. Accordingly, this situation will provide TGS management the capacity to bring economic development in the fields of deposit development to order. The basis of management is the development of the impact of the managing institution on the object of management, which is revealed sin formation process that provides acquisition, processing and analysis of obtained data to build a model of TGS state, using the estimated parameters, develop­ment of recommendations for the implementation of managing in flounce. This approach can be considered as theoretical basis of rational subsoil use. The effective management of the TGS resource potential has to be a flexible system that will change, adapt to market conditions, thus ensuring maximum utilization of mineral resources while preserving the environment. Based on this, the systematic approach to effectively manage resource potential TGS is proposed. The economic evaluation of reserves and mineral resources should be conducted on each stage of the development of the mineral resources complex for the purposes of increasing the validity of decisions and formulation of a comprehensive development strategy based on the standards of international level of the system CRIRSCO (Committee for Mineral Reserves International Reporting Standards). CRIRSCO implementation is held starting with the assessment of the efficiency of the industry as a whole and should serve as a basis for the selection of priority directions of its development at all stages of geological prospecting and operation of mineral resources

From jamming to collective cell migration through a boundary induced transition

Cell monolayers provide an interesting example of active matter, exhibiting a phase transition from flowing to jammed states as they age. Here we report experiments and numerical simulations illustrating how a jammed cellular layer rapidly reverts to a flowing state after a wound. Quantitative comparison between experiments and simulations shows that cells change their self-propulsion and alignment strength so that the system crosses a phase transition line, which we characterize by finite-size scaling in an active particle model. This wound-induced unjamming transition is found to occur generically in epithelial, endothelial and cancer cells