РЕГУЛЮВАННЯ СТІЙКОСТІ РІДКИХ МІКРОСТРУМЕНІВ ПОЛІПРОПІЛЕНУ В МАТРИЦІ СПІВПОЛІАМІДУ ЗА РАХУНОК НАНОДОБАВОК

Goal. Investigation of the effect of the concentration of nanoparticles of aluminum oxide (Al2O3) and alumina modified with silver (Ag/Al2O3) on the decomposition kinetics of liquid microjets of polypropylene (PP) in a copolyamide (CPA) matrix and the possibility of controlling the microfibrillar morphology of the PP/CPA blend.Methodology. The components of the blend were mixed on a screw-disk extruder. The kinetics of the disintegration of liquid microjets was studied using a technique based on the theory of destabilization of a liquid cylinder under the action of capillary waves. The degree of dispersion of polypropylene in the matrix was evaluated by photomicrographs of cross sections of the extrudates of the blends.Results. Nanoadditives of the original and silver-modified aluminum oxide with a content of (0.1 ÷ 3.0) wt.% In the blend increase the compatibility of the components: the surface tension (γαβ) in the compositions of all compositions decreases. Ag/Al2O3 nanoparticles are more effective than aluminum oxide nanoparticles - the γαβ value decreases by 9.6 and 5.3 times, respectively, which ensures a high degree of dispersion of the dispersed phase component in the matrix. The disintegration resistance of polypropylene microjets is increasing, as evidenced by a decrease in the instability coefficient (q) and an increase in the microjet lifetime (tl). The curves of q and tl dependence on the additive content have an extreme character. The minimum values of the instability coefficient of microjets and the maximum values of their lifetime are achieved at a nanoparticle concentration corresponding to the lowest interfacial tension.Scientific novelty. The positive effect of the investigated nanoadditives on the kinetics of the decomposition of liquid microjets of polypropylene in the copolyamide matrix has been established. The highest modifying effect in the presence of Ag/Al2O3 nanoparticles is due to their amphiphilic nature, which ensures the predominant localization of nanoparticles at the interface and a synergistic increase in the degree of compatibility in the PP/CPA system.Practical significance. The regularities of increasing the stability of liquid microjets to disintegration in polymer blends filled with nanoparticles have been established, which will make it possible to determine the parameters of the processes of mixing and forming fibers and films, in which the microfibrillar structure arising during the flow of the melt will remain unchanged in the products.

Longtime behaviour and bursting frequency, via a simple formula, of FitzHugh–Rinzel neurons

The longtime behaviour of the FitzHugh–Rinzel (FHR) neurons and the transition to instability of the FHR steady states, are investigated. Criteria guaranteeing solutions boundedness, absorbing sets, in the energy phase space, existence and steady states instability via oscillatory bifurcations, are obtained. Denoting by $$ \lambda ^{3} + \sum\nolimits_{{k = 1}}^{3} {A_{k} } (R)\lambda ^{{3 - k}} = 0 $$ λ 3 + ∑ k = 1 3 A k ( R ) λ 3 - k = 0 , with R bifurcation parameter, the spectrum equation of a steady state $$m_0$$ m 0 , linearly asymptotically stable at certain value of R, the frequency f of an oscillatory destabilizing bifurcation (neuron bursting frequency), is shown to be $$ f=\displaystyle \frac{\sqrt{A_2(R_\mathrm{H})}}{2\pi } $$ f = A 2 ( R H ) 2 π with $$R_\mathrm{H}$$ R H location of R at which the bifurcation occurs. The instability coefficient power (ICP) (Rionero in Rend Fis Acc Lincei 31:985–997, 2020; Fluids 6(2):57, 2021) for the onset of oscillatory bifurcations, is introduced, proved and applied, in a new version.

TRANSCUTANEOUS MULTICHANNEL ELECTROGASTROGRAPHY: NORMAL PARAMETERS IN A BRAZILIAN POPULATION

ABSTRACT BACKGROUND: Electrogastrography (EGG) is a noninvasive technique for the assessment of gastric myoelectrical activity using electrodes placed on the abdominal surface. Changes in gastric myoelectrical activity may be associated with diseases such as gastroparesis, functional dyspepsia, nausea, and recurrent vomiting. In Brazil, no studies to date have assessed gastric myoelectrical activity using multichannel EGG in healthy individuals. OBJECTIVE: To establish normal values of transcutaneous multichannel EGG in healthy Brazilian individuals. METHODS: This was a prospective study including 20 healthy individuals who underwent EGG. Recording was performed during two periods: a preprandial recording was performed for 30 minutes, and a postprandial recording was performed for 30 minutes after a soft-solid meal of 400 kcal (20 grams of proteins, 60 grams of carbohydrates, and 9 grams of fat). RESULTS: We assessed dominant frequency (DF) parameters, %DF distribution, the instability coefficient, and the power ratio (PR). A total of 20 individuals (11 women and 9 men) with a mean age of 39.5±7.4 years were included. Mean DF (95%CI) ranged from 2.4 to 3.1 cpm in the resting phase and 2.6 to 3.2 cpm in the postprandial period. The %DF in normogastria range was >70% in all healthy individuals. We identified that only one individual did not present a positive response to the test meal, and the other 19 individuals showed a PR greater than 1. The instability coefficient did not change significantly with meal intake. CONCLUSION: Multichannel EGG may be applied in future studies to evaluate gastric motility disorders in the Brazilian population.

Short Cantilever Rock Beam Structure and Mechanism of Gob-Side Entry Retaining Roof in Reuse Period

In the reuse stage of a gob-side entry retaining, failure of the structure and stability of the main roof have a significant effect on the safety of the advanced support and ventilation space at the working face. In this study, field investigation, theoretical analysis, and industrial experimentation were performed to analyse the fracture characteristics and formation process of the gob-side entry retaining roof during the reuse period. A dynamic-equilibrium mechanical model of the main roof structure is presented and the formation mechanisms of different types of short cantilever rock beam structures are clarified. The following major conclusions are drawn: (1) Three types of short cantilever rock beam structures occur in the main roof of a gob-side entry retaining during the reuse period, namely, the “short cantilever-articulated rock beam” structure, “short cantilever step rock beam (type I)” structure, and “short cantilever step rock beam (type II)” structure. (2) The stability criterion for these three short cantilever rock beam structures was also determined; that is, when the sliding instability coefficient K ≥ 1, the short cantilever-articulated rock beam structure will form, and when the sliding instability coefficient K < 1, the short cantilever step rock beam (type I or II) will form. (3) The governing law for the thicknesses of the main roof, immediate roof, and coal seam of the short cantilever rock beam structure was clarified; namely, the K-value gradually increases with increases in the thickness of the coal seam, drops sharply and then decreases gradually with increases in the thickness of the main roof, and decreases slowly with increases in the thickness of the immediate roof. The research results were validated at the gob-side entry retaining project in the Huainan mining area and have theoretical significance and reference value for roadway support projects with similar conditions.

Emotional Dysregulation Mechanisms in Psychosomatic Chronic Diseases Revealed by the Instability Coefficient

In the present work, we analyzed some emotional mechanisms (emotion dysregulation—ED, negative affect—NA, and emotional vulnerability) involved in chronic diseases by means of an interdisciplinary approach. We started from the conceptualization of emotions as a complex dynamic system that can be investigated and understood within a framework inspired by Chaos Theory. An “instability coefficient” Δ was computed to analyze ED mechanisms, NA, and emotional vulnerability in different disease groups (blood cancer, breast cancer, hypertension) as well as in healthy persons. This coefficient, recently defined by our group, computes the Euclidian distance between the pairs of vectors whose components are similar or reverted items of a test measuring ED. The emotional and somatic systems were considered as two complex dynamical systems in interaction. Due to this interaction, and as a result of the laws of complexity, a small perturbation in an inner state of the emotional system could generate an important reaction in the somatic system in time. The emotional vulnerability reflected by high values of Δ was associated with the chronic disease condition. The differences between illness groups and healthy persons, as well as between the three disease groups in Δ values, were analyzed. The results showed that there were significant differences between the chronic disease groups in Δ values. The most highly significant differences in Δ values were reported between the breast cancer group and the healthy group on one hand and between the breast cancer group and the blood cancer group on the other hand. The less significant differences in Δ values were noticed between the hypertension group and the control group. Δ was significant in predicting ED and NA. Compared to the classical approaches, the original contribution of our research is that these results encourage us to propose this interdisciplinary method of assessment as a challenging, valid tool of investigation and understanding of complex phenomena that occur in the emotional and somatic system.

FEATURES OF FINANCIAL STRATEGY OF THE ENTERPRISE IN CONDITIONS OF ECONOMIC INSTABILITY

This article defines and systematizes the main factors that generate the instability of the external financial environment of the enterprise. In particular, an independent group of global factors of the external financial environment of the company, which are generated by the development of the global economy as a whole, is singled out. Among the factors of this group are primarily considered those that determine the cyclical nature of financial crises. The main principles of estimation and forecasting of certain parameters of the instability of the external financial environment of the enterprise are considered, namely the standard deviation indicator, coefficient of variation, risk value, instability coefficient. The main forms of taking into account the influence of the instability of the external financial environment on the individual processes of developing the financial strategy of the enterprise are determined. Phases of the overall process of financial strategy development: diagnosis of strategic opportunities of financial development of the enterprise; development of a complex of strategic financial decisions of the enterprise; realization of the developed financial strategy of the enterprise.

An Approach to Robustness Evaluation for Sequential Testing under Functional Distortions in L1-metric

The problem of sensitivity analysis for the sequential probability ratio test under func- tional distortions of the observation probability distribution is considered. For the situa- tion where distorted densities of the log likelihood ratio statistic belong to ?-neighborhoods of hypothetical centers in the L1-metric the least favorable distributions that maximize the conditional error probabilities are constructed. The instability coefficient is obtained to enable robustness evaluation for the sequential probability ratio test and its modification – trimmed sequential probability ratio test.