Stability Threshold Research Articles

Freezing of a soft-core fluid in a one-dimensional potential: Predictions based on a pressure-balance equation.

Using concepts from classical density functional theory, we investigate the freezing of a two-dimensional system of ultrasoft particles in a one-dimensional external potential, a phenomenon often called laser-induced freezing (LIF). In the first part of the paper, we present numerical results from free minimization of a mean-field density functional for a system of particles interacting via the GEM-4 potential. We show that the system does indeed display a LIF transition, although the interaction potential is markedly different from the cases studied before. We also introduce a suitably defined effective density within the potential wells ρ[over ¯]_{eff} as a control parameter of LIF, rather than the amplitude of the external potential as in the common LIF scenario. In the second part, we suggest a theoretical description of the onset of LIF which is based on the pressure-balance equation relating the pressure tensor and the external potential. Evaluating this equation for the modulated liquid phase at effective density ρ[over ¯]_{eff} and combining it with the (known) stability threshold of the corresponding bulk fluid, we can predict the critical effective density or, equivalently, the potential amplitude related to the onset of LIF. Our approach yields very good results for the model at hand and it is transferable, in principle, to other model systems.

Localized outbreaks in an S-I-R model with diffusion.

We investigate an SIRS epidemic model with spatial diffusion and nonlinear incidence rates. We show that for small diffusion rate of the infected class [Formula: see text], the infected population tends to be highly localized at certain points inside the domain, forming K spikes. We then study three distinct destabilization mechanisms, as well as a transition from localized spikes to plateau solutions. Two of the instabilities are due to coarsening (spike death) and self-replication (spike birth), and have well-known analogues in other reaction-diffusion systems such as the Schnakenberg model. The third transition is when a single spike becomes unstable and moves to the boundary. This happens when the diffusion of the recovered class, [Formula: see text] becomes sufficiently small. In all cases, the stability thresholds are computed asymptotically and are verified by numerical experiments. We also show that the spike solution can transit into an plateau-type solution when the diffusion rates of recovered and susceptible class are sufficiently small. Implications for disease spread and control through quarantine are discussed.

Dynamic Contest Games with Time Delays

Dynamic asymmetric contest games are examined under the assumption that the assessed value of the prize by each agent depends on the total effort of all agents, and each agent has only delayed information about the efforts of the competitors. Assuming gradient dynamics with continuous time scales, first the resulting one-delay model is investigated. Then, assuming additional delayed information about the agents’ own efforts, a two-delay model is constructed and analyzed. In both cases, first the characteristic equation is derived in the general case, and then two special cases are considered. First, symmetric agents are assumed and then general duopolies are examined. Conditions are derived for the local stability of the equilibrium including stability thresholds and stability switching curves.

Narrative instabilities

AbstractTaking Nabokov’sPale Fireas its tutor text, this chapter seeks to demonstrate that narrative functions as a complex or dynamic system. Due to the novel’s nonlinear and multiply configured format, a series of dissipative structures is provoked whereby states near equilibrium, on reaching states far from equilibrium under the weight of multiple causality, putting the system “beyond the threshold of stability” and “at the edge of chaos,” perpetually self-organize. Taking a cue from nonequilibrium thermodynamics, instabilities, it is argued, are inherent to narrative discourse. This calls into question the pertinence of the logic of linearity (“event A causes event B”) as well as the scope of such postulates as the isomorphic relation between sequence and narrative as a whole, a postulate that frames narrative as a closed system following the principle of conservation of energy in classical mechanics. As the poem “Pale Fire” in Nabokov’s novel advances linearly, it is constantly disrupted by the “Commentary” which is related to the poem only tangentially, each text fragmenting the other and self-organizing into new meanings. The effect is to render salient in narrative discourse the complexity science principles (in addition to those mentioned above) of irreversibility (the “arrow of time”) vs. reversibility, sensitivity to initial conditions, negative vs. positive feedback and the symmetry-breaking effects of bifurcation. The manifestation of these principles in Nabokov’s novel raises fundamental questions about the structuring of narrative, but also about the conceptual framework through which narrative at large might be approached.

Performance potential of gas foil journal bearings enhanced with micro taper-grooves on top foil

PurposeTo improve the load capacity and stability of gas foil journal bearings (GFJB), this paper aims to propose a novel GFJB with taper-grooved top foil.Design/methodology/approachA modified bump stiffness model is established considering rounding and friction. By considering the variation of clearance in the circumferential and axial direction, the static and dynamic characteristics of the novel bearing are calculated using the finite difference method, and perturbation method, respectively. The bearing performance under different groove parameters is studied and compared to the traditional bearings.FindingsThe results show that this novel GFJB can bring multi-extra local dynamic pressure and decrease the gas end leakage, which improves the static and dynamic properties. Moreover, as the increment of groove depth, the load capacity and direct stiffness are reinforced. There is an optimal groove width to maximize the load capacity, and the taper-groove is more beneficial to the improvement of bearing performance than other groove shapes. For the novel GFJB (Ng = 6, Hg = 10µm), the load capacity and direct stiffness increase by about 6.67 and 13.5 per cent, respectively. The stability threshold speed (STS) of a rotor supported by the novel bearings is also increased.Originality/valueThe performance of the presented novel GFJB is enhanced immensely compared to the traditional bearings, and the results are expected to be helpful to bearing designers, researchers and academicians concerned.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0307.

1.88 μm laser emission from Tm3+ doped fluorosilicate glass microspheres with excellent stability and high damage threshold

In this letter, high Q factor microsphere resonators with excellent stability and high damage threshold are fabricated from Tm3+ doped fluorosilicate glasses using the traditional melt-quenching and fiber heating techniques. Intense 1.88 μm photoluminescence and single mode laser emission are obtained under the excitation of an 808 nm laser. The Q factor of the microsphere resonator is measured to be as high as 1.4 × 106. Models for photoluminescence and lasing are proposed using spectroscopic data from the absorption and emission spectra. The excellent resistance to humidity and temperature are characterized from the transmittance spectra under different environmental conditions. Differential thermal analysis (DTA), measured in four different glass samples proves the high damage threshold. The proposed glass microsphere resonator laser can find application in optical sensors and micro lasers, especially in complex environments.

Advancing Therapeutic Protein Discovery and Development through Comprehensive Computational and Biophysical Characterization

Therapeutic protein candidates should exhibit favorable properties that render them suitable to become drugs. Nevertheless, there are no well-established guidelines for the efficient selection of proteinaceous molecules with desired features during early stage development. Such guidelines can emerge only from a large body of published research that employs orthogonal techniques to characterize therapeutic proteins in different formulations. In this work, we share a study on a diverse group of proteins, including their primary sequences, purity data, and computational and biophysical characterization at different pH and ionic strength. We report weak linear correlations between many of the biophysical parameters. We suggest that a stability comparison of diverse therapeutic protein candidates should be based on a computational and biophysical characterization in multiple formulation conditions, as the latter can largely determine whether a protein is above or below a certain stability threshold. We use the presented data set to calculate several stability risk scores obtained with an increasing level of analytical effort and show how they correlate with protein aggregation during storage. Our work highlights the importance of developing combined risk scores that can be used for early stage developability assessment. We suggest that such scores can have high prediction accuracy only when they are based on protein stability characterization in different solution conditions.

The state of agrolandscapes of the forest-steppe zone of the Krasnoyarsk Territory

The landscape concept should give a fundamental assessment of the intensification extent of agricultural prospects. A detailed agroecological examination of all components of the natural-territorial complex, the creation of simulation models of their dynamics and the adoption of optimal decisions based on the results of forecasts should be carried out. The purpose of landscape analysis of natural resources is a comprehensive assessment of climatic, soil, plant and animal factors, establishing the relationship of landscape components with farming systems. Any landscape in the process of its development is exposed to impacts, and its stability has its limits. The stability threshold, expressed through the preservation by the landscape of its parameters and properties, and the critical impact quantities are determined in each case. General criteria for the natural stability of geosystems are their high organization, intensive functioning and geosystems functions balance, including biological productivity and renewability of vegetation cover. These qualities are determined by the optimum ratio of heat and moisture and are expressed by the development of soil cover, and ultimately, soil fertility. Landscape-ecological analysis of the territory makes it possible to establish the composition of agricultural and non-agricultural land, taking into account the heterogeneity and stability of a particular landscape, the occurrence of geochemical and biological processes in it, as well as to link the system of agriculture, land reclamation and specialization of the agricultural organization. The main element of Novosyolovo district landscape is agricultural land; the lands of the forest fund are the second largest area of natural geosystems. The degree of change in agrolandscapes is estimated on the basis of the existing structural and functional organization of agricultural lands, their quality state. It was established that plowing is low and it does not exceed the allowable limit, the forest cover of the district is close to optimal.

ВЛИЯНИЕ ЭКОЛОГИЧЕСКИХ И СОЦИАЛЬНОЭКОНОМИЧЕСКИХ ФАКТОРОВ НА ФОРМИРОВАНИЕ ЛЕСОВ ПОДМОСКОВЬЯ

Changes in forest management tasks in the Moscow region over 120 years from the end of the XIX century are considered. The analysis of forest exploitation from 1946 to 2018 is given. The principles of forest management have changed conceptually at least three times over the past 120 years. As a result of assigning all the forests of the Moscow region to protective categories, legally imposed restrictive measures have been introduced in forest territories that are largely occupied by artificial plantings, which initially characterized by a simplified structure and reduced thresholds of natural stability. There is an increase in the average age of plantings, the accumulation of standing volume of mature and overmature stands, particularly vulnerable to environmental hazards, the frequency and intensity of which will increase due to projected climate change. Currently, the forests of the Moscow region are losing their protective properties, and their environmental, sanitary, and recreational potential is decreasing. Standing volume of ripe and overmature forests increased 7 times over 50 years before the mass dying off and breakdown of stands related to the 2010 drought, including 25 times in coniferous forests. At the same time, the average age of plantings has almost doubled: from 36 years in 1966 to 62 years in 2016. In the case of mass dying off forests in large areas, forestry is not able to quickly solve the problems that arise. This leads to significant losses of wood, which has time to completely lose its liquidity before it is harvested by sanitary logging, and to large costs for the disposal of this wood. Variants of forest management and reforestation aimed at the formation of sustainable protective forest stands are proposed. The expediency of using natural regeneration in reforestation is proved. On the example of research on stationary objects in the National park "Losiny Ostrov" and “Shchelkovsky” educational and experimental forestry district shows a tendency to a significant increase in the natural renewal of broad-leaved species, primarily linden and Norway maple. In recent decades, complex spruce forests have been replaced by broad-leaved communities in National park "Losiny Ostrov". In General, in "Losiny Ostrov" since 1891, the area of stands with the dominance of linden trees, their age and standing volume are constantly growing. The initial stages of changing spruce forests linden ones are also marked on the territory of the “Shchelkovsky” educational and experimental forestry district. These trends should be taken into account when drawing up long-term forest management plans.

稀土掺杂光功能玻璃及器件应用（特邀）

The luminescence and laser properties of rare earth are produced by the transition of 4f electrons between different energy levels. Due to its special properties, rare earth ions doped optical-functional glass have played important roles in high power laser system, whether as active or passive components. Nd3+, Er3+ doped phosphate laser glass, which have high rare earth ion doping concentration, preparation characteristics with large size and high uniformity, can be used in high energy laser as an important gain medium material; Volume Bragg grating based on Ce3+-doped Photo-Thermo-Refractive glass, is a multifunctional optical components in high power laser system, owing to its excellent wavelength and angular selectivity, high diffraction efficiency, high thermal stability and high damage threshold. In this paper the latest progress of Nd3+, Er3+ doped phosphate laser glass and Volume Bragg grating base on Ce3+-doped Photo-Thermo-Refractive glass were reported.

On the Theory of the Mandelstam–Brillouin Scattering in a Plasma Layer

The evolution of a perturbation from a local source upon the Mandelstam–Brillouin scattering in a plasma layer of a finite thickness and infinite length is examined analytically. It is shown that, in the course of time, the perturbation can either leave the scattering region through one of the two layer boundaries or propagate along the layer with a velocity that is lower than the velocity of propagation of the sound wave and with the amplitude that either exponentially increases or decreases. In the particular case of strictly backward scattering (the scattering angle is π), this propagation velocity is zero. The instability threshold fields and instability increments are calculated taking into account both convective losses and collisional damping of waves. It is shown that the instability threshold for scattering at an arbitrary angle can be lower than that for strictly backward scattering, and, if the intensity threshold of the pump wave is exceeded little, the scattering increment at an angle can also be higher than the increment for backward scattering. If the threshold is exceeded greatly, so that convective losses can be neglected, the greatest increment is observed for backward scattering.

МОДЕЛИРОВАНИЕ И БИФУРКАЦИОННЫЙ АНАЛИЗ УСТОЙЧИВОСТИ ГЕОТЕХНИЧЕСКОЙ СИСТЕМЫ В УСЛОВИЯХ ВОЗДЕЙСТВИЯ ВИБРАЦИОННЫХ ФАКТОРОВ

The automation of control processes for the stability of geotechnical systems is a great challenge involving the development of methods for multivariate analyzing and forecasting the stability with the subject to the nonlinearity of material stiffness parameters. The aim of the study is to improve the efficiency of automated control systems for geotechnical stability by developing an approach to detect negative changes in bifurcation diagrams of vibration displacement parameters of object structures. The authors present a mathematical model of the dynamic behavior of structural elements of an object as an elementary unit of a geotechnical system that describes a response to an external vibration action. An algorithm of bifurcation analysis is presented, which allows authors to determine the initial transition stage of the object structure to an unstable state by the acceleration values of forced oscillations exceeding the model parameters. A bifurcation diagram of stability changes in the structure of object at the displacement resulting from the load increase under vibration action has been constructed. This diagram, which type of codimension-one bifurcations is merging, enabled to determine the critical load values resulting in an unstable state transition of a system due to the influence of a combination of vibration factors. The efficiency evaluation of the proposed approach was carried out by the comparison with the results of construction stability calculations obtained by the use of the dynamic coefficient. The difference between the values of the maximum object displacement without loss of the stability under vibration action, obtained by the standard calculation method and using the developed model, is 32.5%, and it is significant in the theory of structure stability. When exogenous vibration noise is used as a source of a sounding signal, the application of the developed approach in automated control systems for geotechnical stability enable to change the permissible stability thresholds of objects being exploited depending on the level and combination of influencing factors.

Численное моделирование несоосных цилиндрических оболочек, частично заполненных жидкостью

Работа посвящена численному анализу динамического поведения горизонтально ориентированных несоосных оболочек, кольцевой зазор между которыми полностью или частично заполнен текущей жидкостью. Решение задачи осуществляется в трeхмерной постановке с использованием метода конечных элементов. При моделировании упругих тел предполагается, что их криволинейная поверхность достаточно точно аппроксимируется совокупностью плоских сегментов, деформации в которых определяются с помощью соотношений классической теории пластин. Движение идеальной сжимаемой жидкости описывается волновым уравнением, которое совместно с условием непроницаемости и соответствующими граничными условиями преобразуется с помощью метода Бубнова-Галeркина. Математическая постановка задачи динамики тонкостенных конструкций основана на вариационном принципе возможных перемещений. Оценка устойчивости базируется на вычислении и анализе комплексных собственных значений связанной системы уравнений. Верификация модели произведена для случая неподвижной жидкости путeм сопоставления результатов с известными решениями. Представлен анализ влияния величины кольцевого зазора и уровня его заполнения жидкостью при различном значении эксцентриситета между осями вращения жeстко закреплeнных с обоих краeв оболочек на границы гидроупругой устойчивости. Показано, что для несоосных оболочек уменьшение уровня заполнения приводит к повышению границ устойчивости. Продемонстрирована зависимость критической скорости течения жидкости от отклонения внутренней оболочки от соосного положения.

Short wavelength ion temperature gradient mode in tokamak plasmas with hollow density profiles

By the gyrokinetic integral eigenmode equation, we numerically investigate the short-wavelength ion-temperature-gradient (SWITG) mode in tokamak plasmas with hollow density profiles. This paper finds that the critical ion temperature gradient (ITG) R/LTiC exists for the hollow density profile. Over such a gradient, the SWITG mode is unstable. The R/LTiC for a hollow density profile is slightly lower than that for a peaked density profile, though far away from the threshold, the mode in the latter case is more unstable. Furthermore, the scaling of the ITG threshold increasing with ion-to-electron temperature ratio Ti/Te has been calculated, suggesting that the SWITG mode is more difficult to excite in hot ion plasmas as compared with that in hot electron plasmas. For the slightly hollow density profiles, it is shown that in the case of flat (peaked) electron temperature profiles, the SWITG modes are destabilized (stabilized) by the trapped electrons. For the steep hollow density profiles, however, the trapped electrons reduce the growth rate substantially, and thus, the SWITG stability threshold is raised significantly. In addition, the dependence of the threshold on local plasma parameters is analyzed in detail. It is found that the SWITG modes become more unstable for the high safety factor, small Larmor radius, weak magnetic shear, and high electron-to-ion temperature ratio.

К теории рассеяния Мандельштама-Бриллюэна в плазменном слое

The evolution of a perturbation from a local source for Mandel'shtam-Brillouin scattering in a plasma layer with unlimited length is calculated. Perturbation over time in this case can either leave the scattering region through one of the two boundaries, or propagate along the layer at a speed below sound wave propagation speed, with an exponential growth, or a fall in perturbation amplitude. In the particular case of strictly backward scattering (the scattering angle is π), this propagation velocity is zero. The paper calculates the threshold instability fields and the instability increments, taking into account both convective losses and collisional attenuation of waves. It is shown that the instability threshold for scattering at an arbitrary angle can be lower than for strictly backwards scattering and when the threshold is exceeded by the intensity of the pump wave; the scattering increment at an angle can also be higher than the increment for backscattering. When the threshold is greatly exceeded, the convective losses can be neglected, and the largest increment is observed for backward scattering.

Spot patterns of the Schnakenberg reaction–diffusion system on a curved torus

For the Schnakenberg activator-inhibitor model on a torus, in the singularly perturbed regime of small activator to inhibitor diffusivity ratio , we derive a reduced ODE describing the influence of curvature on the the slow drift dynamics of a single localised spot, and also stability thresholds to fast amplitude instabilities of one- and two-spot patterns. By way of a hybrid asymptotic-numerical analysis, we obtain the results in terms of certain quantities associated with the Green’s function for both the Laplace–Beltrami () and Helmholtz () operators on the torus. To this end, we introduce a new analytic-numerical method for computing Green’s functions on surfaces that requires only the numerical solution of a problem that is as regular as is desired. This allows properties of Green’s functions at the location of the singularity to be determined to a high degree of accuracy. The method is applicable to operators of the form for any metric tensor g, first order differential operator X, and smooth potential . It centers on a microlocal approach for analytically determining the coefficients of all singular terms of the local behavior of a Green’s function inside a region around the singular point. Remaining terms of the Green’s function are solved for numerically using finite differences. The primary purpose of this paper is to both introduce the theoretical underpinnings of this technique and to numerically demonstrate its ability to accurately yield properties of a Green’s function on a curved surface. All results are confirmed by numerical finite element solutions of the Schnakenberg reaction–diffusion system on the torus.

Numerical simulation of streamwise fluidelastic instability of tube bundles subjected to two-phase cross flow

This work aims to develop and validate a numerical model to simulate the flow-structure interaction in tube bundles subjected to two-phase flow. The model utilizes a mixture multiphase module in which a drift flux formulation is used to account for the slip between the phases. Two methods of numerical flow-structure interaction are used to predict the onset of fluidelastic instability (FEI) in the streamwise direction for a two-phase air–water flow mixture in parallel triangular tube bundles. These models are the hybrid analytical-flow field model and the direct numerical flow/structure coupling model. This work investigates the effects of void fractions in the range of 20% to 80% and several pitch-to-diameter ratios (P/D) in the range of 1.3 to 1.7. The results of the fluidelastic forces and the stability threshold are validated against the experimental data available in the literature and show an excellent agreement. The streamwise FEI threshold shows a significant dependency on the pitch-to-diameter ratio while the void fraction exhibits a lesser effect. Generally, the stability threshold increases as the pitch-to-diameter ratio increases. The model that was developed paves the way for devising of more reliable prediction tools for FEI in steam generators.

Exploring ultrafast threshold switching in In3SbTe2 phase change memory devices

Phase change memory (PCM) offers remarkable features such as high-speed and non-volatility for universal memory. Yet, simultaneously achieving better thermal stability and fast switching remains a key challenge. Thus, exploring novel materials with improved characteristics is of utmost importance. We report here, a unique property-portfolio of high thermal stability and picosecond threshold switching characteristics in In3SbTe2 (IST) PCM devices. Our experimental findings reveal an improved thermal stability of amorphous IST compared to most other phase change materials. Furthermore, voltage dependent threshold switching and current-voltage characteristics corroborate an extremely fast, yet low electric field threshold switching operation within an exceptionally small delay time of less than 50 picoseconds. The combination of low electric field and high speed switching with improved thermal stability of IST makes the material attractive for next-generation high-speed, non-volatile memory applications.

The relationship between political instability and financial inclusion: Evidence from Middle East and North Africa

AbstractWhat is the effect of political instability on financial inclusion (FI) in the Middle East and North Africa region? Using data for 2011, 2014, and 2017, from the Global Findex database, we test the asymmetry relationship between political instability and FI using the probit model with sample selection and a multiplicative interaction test of the asymmetric model. We also propose and test a political stability threshold model that may trigger FI. We find that (a) political instability positively correlates with lower degrees of FI with higher levels of persistence; (b) higher incomes and higher education are associated with higher degrees of FI; (c) a lack of documentation required by formal financial institutions proves to be a major barrier to FI; and (d) inefficient mechanisms to determine real interest rates, corruption, oil reliance, unemployment, and religious tensions also negatively affect FI. Further, we calculate the political stability threshold level that will trigger FI to be ‐0.960 for the Middle East and North Africa region. The policymakers could enhance and promote FI and economic well‐being by targeting the minimum threshold value of political stability.

Stability Analysis of Rotating Systems Supported by Textured Journal Bearings

Abstract Fluid-induced instability in rotating systems due to the presence of hydrodynamic journal bearings consists of an undesirable phenomenon with a considerable destructive potential. Surface texturing of journal bearings is currently investigated as a possible approach to improve the stability characteristics of rotating systems. Thereby, this work aims to evaluate the influence of textured journal bearings in the stability threshold and unstable vibration mode of rotating systems. The classical Reynolds equation is used to model the pressure distribution inside the bearing, being solved by the finite volume method (FVM). The rotating system evaluated in this work is a steam turbine that is modeled using the finite element method (FEM). Numerical results show that textured geometric parameters, i.e., shape, area density, and maximum depth, are capable of changing the stability threshold (for worse or better) as well as the corresponding unstable vibration mode. Moreover, the present study also indicates that a full texturing of journal bearings is desirable to achieve a better improvement in the stability threshold when compared with partial texturing. Based on the results obtained in this work, the textured journal bearings represent a promising and feasible tool to improve the stability conditions of rotating systems in industrial applications.