Revisiting the stability of spatially heterogeneous predator-prey systems under eutrophication

We employ partial integro-differential equations to model trophic interaction in a spatially extended heterogeneous environment. Compared to classical reaction-diffusion models, this framework allows us to more realistically describe the situation where movement of individuals occurs on a faster time scale than the demographic (population) time scale, and we cannot determine population growth based on local density. However, most of the results reported so far for such systems have only been verified numerically and for a particular choice of model functions, which obviously casts doubts about these findings. In this paper, we analyse a class of integro-differential predator-prey models with a highly mobile predator in a heterogeneous environment, and we reveal the main factors stabilizing such systems. In particular, we explore an ecologically relevant case of interactions in a highly eutrophic environment, where the prey carrying capacity can be formally set to 'infinity'. We investigate two main scenarios: (i) the spatial gradient of the growth rate is due to abiotic factors only, and (ii) the local growth rate depends on the global density distribution across the environment (e.g. due to non-local self-shading). For an arbitrary spatial gradient of the prey growth rate, we analytically investigate the possibility of the predator-prey equilibrium in such systems and we explore the conditions of stability of this equilibrium. In particular, we demonstrate that for a Holling type I (linear) functional response, the predator can stabilize the system at low prey density even for an 'unlimited' carrying capacity. We conclude that the interplay between spatial heterogeneity in the prey growth and fast displacement of the predator across the habitat works as an efficient stabilizing mechanism.Comment: 2 figures; appendices available on request. To appear in the Bulletin of Mathematical Biolog

Evolution of a Polydisperse Ensemble of Ellipsoidal Crystals with Fluctuating Growth Rates in Supercooled Melts

In this paper, an analytical solution to the model of the evolution of ellipsoidal crystals with fluctuating growth rates at the intermediate step of bulk phase transition is presented. A complete system of integrodifferential equations describing the problem was derived and analytically solved using the Laplace integral method. The kinetics of supercooling removal in melts has been found. The particle-volume distribution function represents a pike-shaped curve decreasing its maximum with time. It is demonstrated the differences in the distribution function for ellipsoidal and spherical crystals. © 2021 Institute of Physics Publishing. All rights reserved.This work was supported by the Russian Science Foundation (grant no. 18-19-00008)

Features of the structure of addictive identity in adolescence

© Authors. The relevance of the study of this problem is due to the lack of reliable information about the psychological mechanisms, phenomenology and psychological structure of addictive behavior of a personality in adolescence, which is the main cause of insufficient effectiveness for implementation of corrective measures. In this regard, this article aims to study addictive identity structure in the chemical (alcohol and drug) addiction both at the level of structural components of identity in adolescence and that of their structural organization. The leading methods of the problem study are the empirical methods of studying the structural components of addictive identity. The experiment involved 96 young men at the age of 18-24 years old. Of them 55 people are with alcohol dependence, 41 people with drug (opioid) addiction. The study found that addictive identity of young persons with chemical dependence (alcohol and drug) at the level of structural components is characterized by simple undifferentiated cognitive constructs meaningfully related to the object of addiction; flattened motivational profile, as well as a discrepancy at the level of the valuable component of identity. Identified in the study features allow to state that at the level of structural organization an addictive identity of young persons, both at alcohol and drug dependence, is characterized by disintegrated structural organization of identity. Clinical and psychological diagnosis of addictive identity structure with alcohol and drug addiction should be viewed as prognostic basis in the process of socio-psychological rehabilitation of young men with chemical addiction. The identified structural features of addictive identity serve as predictors in determining the risk groups by the given deviant status

Mathematical modeling of the growth of ellipsoidal crystals in metastable melts and solutions

The evolution of individual crystals of ellipsoidal shape in supercooled one-component and binary melts as well as in supersaturated solutions is studied theoretically. The crystal volume growth rate is derived using the prolate ellipsoidal coordinates. We show that this rate is a function of the current crystal volume and supercooling/supersaturation of the ambient liquid. Also, we demonstrate that the particle growth rate increases with increasing the volume of ellipsoidal crystals and supercooling. © 2020 John Wiley & Sons, Ltd.Russian Science Foundation, RSF: 18-19-00008This work was supported by the Russian Science Foundation (Grant no. 18-19-00008)

A complete analytical solution to the integro-differential model describing the nucleation and evolution of ellipsoidal particles

In this paper, a complete analytical solution to the integro-differential model describing the nucleation and growth of ellipsoidal crystals in a supersaturated solution is obtained. The asymptotic solution of the model equations is constructed using the saddle-point method to evaluate the Laplace-type integral. Numerical simulations carried out for physical parameters of real solutions show that the first four terms of the asymptotic series give a convergent solution. The developed theory was compared with the experimental data on desupersaturation kinetics in proteins. It is shown that the theory and experiments are in good agreement. © 2021 John Wiley & Sons, Ltd.Ministry of Education and Science of the Russian Federation, Minobrnauka: FEUZ-2020-0057; Russian Science Foundation, RSF: 18-19-00008This work was supported by the Russian Science Foundation (grant no. 18-19-00008).This article contains two parts: (i) a new theory of the growth of an ensemble of ellipsoidal crystals in a metastable liquid and (ii) a computational simulation of crystal growth based on the developed theory. Part (i) was supported by the Russian Science Foundation (grant no. 18-19-00008), whereas part (ii) was made possible due to the financial support from the Ministry of Science and Higher Education of the Russian Federation (project no. FEUZ-2020-0057)

Osteoarthritis: Key elements in its pathogenesis and current agents for pathogenetic therapy

Three main areas can be arbitrarily identified in the modern concept of treatment for osteoarthritis (OA); these are: 1) an impact on the progression of joint destruction; 2) suppression of peripheral pain mechanisms; and 3) inhibition of the central processes involved in the formation of pain sensation. Glucosamine and chondroitin sulfate (CS) have become the first agents that are able to retard the development of cartilage degeneration. They have been used in medical practice for more than 40 years. A number of clinical trials of these drugs have yielded favorable results during their use in patients with OA. Another agent containing amino sugars and CS – sea fish cartilage hydrolysate has more recently emerged. Clinical trials have demonstrated that it is able to significantly relieve OA-induced pain. To date, the main agent for the analgesic therapy of OA is considered to be nonsteroidal anti-inflammatory drugs (NSAIDs) that act on the peripheral mechanisms of pain and are widely used to treat diseases that are accompanied by chronic pain. However, a large-scale meta-analysis dealing with the experience with NSAIDs used to treat OA has shown that pain relief due to this therapy averaged only about 10 mm on a 100-mm visual analogue scale. To enhance the efficiency of therapy for OA, drug and non-drug treatments that affect the central mechanisms of pain in this disease are also used

Intercomparison of five nets used for mesozooplankton sampling

Intercomparison of nets commonly used for mesozooplankton sampling in the Black and Mediterranean seas was attempted within SESAME (Southern European Seas: Assessing and Modelling Ecosystem Changes) project. Five nets were compared: three Juday nets equipped with 150 μm, 180 μm and 200 μm mesh size, Nansen net (100 μm mesh size) and WP2 (200 μm mesh size). Replicated samples were collected at one station in the western Black Sea offshore waters in April 2009. Collected samples were analyzed at species level (except for meroplankton), stages (for copepods) and size length. A decrease of total abundance values was observed with increasing mesh size, due to the significantly higher numbers of animals smaller than 1 mm in the samples obtained by fine mesh size than with coarser nets. Few comparisons were revealed significant for the abundance of animals with 1-2 mm length, while no significance was detected for specimens larger than 2 mm. The above differences resulted in discripancies between nets regarding species and stages composition. Biomass values did not differ significantly between nets, due to the strong contribution to total biomass of the large animals fraction (Calanus euxinus). The smallest and the largest animals revealed high variability between replicates collected by Nansen, Juday- 200 μm and WP2 nets. Correction factors were calculated for the conversion of abundance values between each couple of nets. The detected differences between nets regarding the abundance and biomass, the community taxonomic composition and size structure, as well as the estimated correction factors, provide useful information for the harmonization of data obtained by the above nets in the Black Sea