Instability Zones Research Articles

Power dissipation efficiency and temperature sensitivity coefficient of 2024Al/Al18B4O33w composite deformed at strain rate up to 10.0 s−1

AbstractPower dissipation efficiency and temperature sensitivity coefficient of 2024Al/Al18B4O33w composite under high strain rate (>0.01 s−1) at elevated temperature is studied. The composite has two instability zones with the one under low temperature and high strain rate. The power dissipation efficiency of composite from 0.08 to 0.30 is lower than that of unreinforced 2024Al alloy, showing the poorer hot forgeability of composite.

푸틴주의와 한반도 - 2000년 이후 러시아의 한반도 정책 변화

Since 2000, Russia has sought to secure partnerships in Northeast Asia to return to its status as a great power and form a multipolar system. On the Korean Peninsula it has maintained the “equidistant diplomacy with North and South” and began to engage limitedly in securing strategic stability. In order to strengthen the partnership for the formation of a multipolar system by expanding cooperation with China in the political and economic fields, and to explore the possibility of full-scale cooperation through solving territorial problems with Japan, it was necessary to restore strategic influence and secure strategic stability on the Korean Peninsula. During this period, Russia regarded the Korean Peninsula as a strategic instability zone threatening the security of its eastern borders, and tried to secure strategic stability by resolving the North Korean nuclear problem while maintaining the “equidistant diplomacy with North and South”. In other words, at the time Russia paid attention to the meaning of the Korean Peninsula in the security dimension, specifically the security level of Asia or the whole of Northeast Asia. Since 2012, when Putin returned to the presidency, Russia has sought to secure support from Northeast Asia for the development of Far East and Siberia in to consolidate its status as a great power. On the Korean Peninsula, unlike the past, it attempted to actively engage in strategic stability and economic benefits. The development of the Far East and Siberia began in earnest with the launch of the 3rd Putin government. Therefore it has become essential to expand economic cooperation with North and South Korea to complement economic cooperation with China, which needs certain checks at the economic level, and Japan, with which the possibility of full-scale cooperation disappears. Russia has been actively working to establish a new foundation for expanding economic cooperation with the two Koreas, while trying to maintain North Koreas existing regime and prevent military conflicts. In conclusion, since 2012, in Putinist diplomacy, the Korean Peninsula has had an important meaning not only in the security dimension but also in the economic dimension.

Bodily and Spiritual Borders in the Parsi Males of Rohinton Mistry’s Tales from Firozsha Baag

Abstract In this essay, I am going to read the bodies of the Parsi male characters in Rohinton Mistry’s Tales from Firozsha Baag (1987) through the lens of Julia Kristeva’s theories of the abject. According to Kristeva, the abject refers to the human reaction (horror, vomit) to a threatened breakdown in meaning caused by the loss of the distinction between subject and object or between self and other, a reaction elicited by bodily fluids such as excrement, blood or even semen. The bodies of the Parsi males in Tales of Firozsha Baag are a site of awareness in which the “bodily borders” (Moreno-Álvarez 2014: 39) explode. In the first section of the essay, I will discuss the stories “One Sunday”, “The Collectors” and “Exercisers”. In the second section, I will delve into Mistry’s Canadian trilogy — ”Squatter”, “Lend Me Your Light” and “Swimming Lessons” — whose main subject is the young Parsi male striving for happiness and individual liberation (moksha) through emigration to North America. I will conclude that these Parsi men have difficulties integrating themselves in their Indian and North American contexts because the realms of the corporeal and the spiritual are, quoting Frantz Fanon’s phrase, “zones of occult instability” (Fanon 1967: 21).

Characterization of Ti-25.5Al-13.5Nb-2.8Mo-1.8Fe Alloy Hot Deformation Behavior Through Processing Map

The isothermal compression tests of Ti-25.5Al-13.5Nb-2.8Mo-1.8Fe (at.%) alloys were executed under the deformation temperature ranges of 950-1100 C with the strain rate ranges of 0.001-1 s-1, for total height reduction of 0.5. The isothermal compression deformation behavior was investigated based on flow stress curves, dynamic model analysis. The processing map of Ti-25.5Al-13.5Nb-2.8Mo-1.8Fe alloy was obtained for the optimum hot process parameters. The calculated value of Q (activation energy) was 634.5 kJ/mol. The constitutive model of the alloy was constructed. Based on DMM and the Prasad flow instability criteria, the hot processing map was established with strain of 0.7. The deformation mechanisms were interpreted by microstructural observation within both stable and instability zones. Processing map showed a stable region under the deformation temperature ranges of 950-1100 C with the strain rate ranges of 0.001-1 s-1. One certain maximum power dissipation efficiency value was approximately 43 % occurred at 950 C/0.001 s-1. Another peak power dissipation efficiency value was about 58 % at 1050 C/0.001 s-1. Both areas were the optimum processing regions. Furthermore, while the strain rate value exceeded 1 s-1, the alloy sustained deformation instability phenomenon, such as shearing band or flow localization.

High temperature deformation and dynamic recrystallization behavior of AlCrCuFeNi high entropy alloy

The high temperature deformation and dynamic recrystallization characteristics of multicomponent AlCrCuFeNi high entropy alloy, composed of simple FCC and BCC phases were studied in detail in the temperature range of 900–1050 °C and in the strain rate range of 0.001–1 s−1 by generating contour maps of multiple models using a high temperature thermomechanical simulator test. The processing maps consisting of dissipation and instability maps show that the suitable areas for TMP are at 900–920 °C/10−1.5–10−3s−1 and 1000–1050 °C/10−2.5–10−3s−1. In contrast, two instability zones at (900–920 °C/10−0.75~1s−1 and 1000–1050 °C/10−0.5~1s−1) should be avoided during hot processing. EBSD analysis indicates that the volume fraction of dynamic recrystallization decreases with increasing deformation rate after hot compressive deformation at 1050 °C for different strain rates.

Dynamic Behavior of Earth Dam under Non-Stationary Kinematic Effect

In connection with the large-scale design, construction and operation of earth dams (the number of which exceeds 50), in the Republic of Uzbekistan which is situated in a seismic region, the mechanics are faced with the task of improving the design methods for calculating main and dynamic loads, including seismic ones. This paper presents a solution to the non-stationary dynamic problem for a particular earth dam taking into account the elastic and inelastic characteristics of soil, the methods used are revealed, instability zones are identified, and the use of the numerical finite element method to solve such problems is justified. The purpose of this work is the development of the methods for solving dynamic problems for earth hydro-technical structures (dams, levees, reservoirs) in a plane statement taking into account the elastic and inelastic properties of soil material. The calculation results make it possible to predict the stress-strain state and determine the vulnerable zones of an earth dam, where loss of stable operation of the structure under dynamic load is possible.

Dynamic Instability Analysis of Axially Compressed Castellated Columns

This paper presents an analytical study on the dynamic instability of castellated columns subjected to axial excitation loading. By assuming the instability modes, the kinetic energy and strain energy of the columns and the loss of the potential of the axially applied load are evaluated, from which the mass matrix, stiffness matrix, and geometric stiffness matrix of the system are derived. These matrices are then used for deriving dynamic equations and carrying out the analysis of dynamic instability of castellated columns by using Bolotin’s method. The analytical expression for determining the critical excitation frequency of the columns is derived, which takes account for not only the shear influence of web openings but also the rotary inertia effect on the transverse vibration of the columns. Numerical examples are also provided for illustrating the dynamic instability behaviour of castellated columns when subjected to axial excitation loading. The results show that the consideration of the shear effect in castellated columns results in a shaft of the dynamic instability zone to low frequency side and a reduction of the width of the dynamic instability zone. The shear effect on the dynamic instability zone becomes more significant in the short column than in the long column, and in the wide flange column than in the narrow flange column.

Effects of subterranean termite nest architectures on earth embankment seepage and stability

Subterranean termites (Odontotermes formosanus Shiraki) that build nests in the soil matrices of earth embankments may adversely affect the stability of these structures in paddy farming regions of southern China. An adult termite nest comprises a primary chamber, fungus gardens, passageways, and other shelter tubes. These porous architectures enable high hydraulic conductivity and rapid groundwater flow. In this study, we performed a field survey to characterize these termite nest architectures and proposed a simulation method that estimates seepage and associated stability in termite-infested earth embankments. Three types of nest architectures—straight, siphon, and string—were investigated in situ. Groundwater flow and its relationship with earth embankment stability were analyzed using a numerical model based on the two-dimensional Richards equation in the HYDRUS software package. Results indicated that the presence of termite nests affected seepage zone geometry and substantially affected its phreatic line, seepage flux, and global and local stabilities of the earth embankment. In the cases examined here, the presence of termite nests resulted in a maximum factor of safety reduction of 17% along the downstream slope. The local instability zones of earth embankment, resulting from clogged termite nest passageways along the downstream slope, were also assessed.

Comparative Hot Workability Characteristics of an Al–Si/SiCp Aluminium Matrix Composite Hybrid Reinforced with Various TiB2 Additions

Hot compression tests were conducted on Al–Si/SiCp + TiB2 hybrid aluminium matrix composites with various TiB2 contents at temperatures from 350 to 500 °C and strain rates from 0.001 to 1 s−1. The hot workability characteristics and deformation mechanisms were investigated by combining constitutive equations, processing maps and microstructural observations through scanning electron microscopy and transmission electron microscopy measurements. The results showed that there were small differences in the peak stresses when the contents of TiB2 were 3% and 5%, while the peak stress increased when the content of TiB2 reached 8%. The contents of TiB2 had little influence on the activation energy but affected the processing maps to a certain extent. The areas of the instability zones were observed to gradually increase with increased TiB2 additions. The optimal deformation conditions of the studied materials migrated from a low temperature and high strain rate to a high temperature and low strain rate with increasing TiB2 content. In addition, the flow softening mechanism transformed from dynamic recrystallization + dynamic recovery to dynamic recovery with increasing TiB2 content.

Afrasian Zone of Instability and The Riddles of the Russian Strategy Planning

Afrasian Zone of Instability and The Riddles of the Russian Strategy Planning

Static and Dynamic Stability Analysis of an Asymmetric Rotating Tapered Sandwich Beam Subjected to Pulsating Axial Load with Thermal Gradient

The static and dynamic stability of an asymmetric rotating tapered sandwich beam subjected to pulsating axial load in temperature environment is studied under two different boundary conditions. The non-dimensional equations of motion and the boundary conditions are derived by applying Hamilton's energy principle. A coupled Hill's equations with complex coefficients are derived from the non-dimensional equations of motion by the application of the generalized Galerkin method. By the application of the Saito-Otomi conditions, zones of instabilities are obtained and presented graphically. For the calculation of the Young's module for the elastic layers, the effect of temperature has been taken in to consideration by means of a uniform thermal gradient along the longitudinal axes for both the upper and lower elastic layers. The effects of the taper parameter, core loss factor, thermal gradient, rotational speed, hub radius, and core density parameter on the static buckling loads and the regions of instability are investigated.

Numerical and microcontroller simulations, and electronic circuit realisation of Minorsky’s equation

This work deals with the mathematical analysis, numerical and microcontroller simulations and electronic circuit realisation of the dynamics of Minorsky’s equation. We consider the model including the nonlinear derivative feedback with delay. The study of stability is done by linearising the equation. An alternation between the zones of stability and instability as a function of the values of the delay is found. The bifurcation diagrams allowed us to validate the analytical predictions. These bifurcation diagrams show Hopf bifurcations and complex dynamics of the system. The analog and microcontroller simulations together with the experimental analysis were carried out in order to validate the theoretical analysis.

Multistability and Stochastic Phenomena in the Distributed Brusselator Model

Abstract An influence of random disturbances on the pattern formation in reaction–diffusion systems is studied. As a basic model, we consider the distributed Brusselator with one spatial variable. A coexistence of the stationary nonhomogeneous spatial structures in the zone of Turing instability is demonstrated. A numerical parametric analysis of shapes, sizes of deterministic pattern–attractors, and their bifurcations is presented. Investigating the corporate influence of the multistability and stochasticity, we study phenomena of noise-induced transformation and generation of patterns.

Rheological Law and Mechanism for Superplastic Deformation of Ti-6Al-4V.

The behaviors of and mechanisms acting in Ti–6Al–4V alloy during low-temperature superplastic deformation were systematically studied by using a Gleeble-3800 thermocompression simulation machine. Focusing on the mechanical behaviors and microstructure evolution laws during low-temperature superplastic compression tests, we clarified the changing laws of the strain rate sensitivity index, activation energy of deformation, and grain index at varying strain rates and temperatures. Hot working images based on the dynamic material model and the deformation mechanism maps involving dislocation quantity were plotted on the basis of PRASAD instability criteria. The low-temperature superplastic compression-forming technique zone and the rheological instability zone of Ti–6Al–4V were analyzed by using hot processing theories. The dislocation evolution laws and deformation mechanisms of the grain size with Burgers vector compensation and the rheological stress with modulus compensation during the low-temperature superplastic compression of Ti–6Al–4V were predicted by using deformation mechanism maps.

Zone of genetic instability in polyploide hybrid spined loaches (Cypriniformes, Cobitidae, Cobitis) in the Middle Dnieper

Zone of genetic instability in polyploide hybrid spined loaches (Cypriniformes, Cobitidae, Cobitis) in the Middle Dnieper

Experimental study on the pressure drop oscillation characteristics of the flow boiling instability with FC-72 in parallel rectangle microchannels

Experiments of the pressure drop instability of flow boiling with FC-72 in 8 parallel rectangle microchannels with a hydraulic diameter of 88 μm were conducted in this study. The mass flux ranges from 578.2 to 2310.9 kg/m2 s, the heat flux ranges from 0 to 1200 kW/m2 and the measured pressure drop ranges from 13 to 275 kPa. The compressive volume in a nitrogen vessel before the test microchannels is set as 0, 5 and 15 ml in the experiments. The experimental results of heat transfer, pressure drop and the corresponding flow patterns are presented and analyzed. Furthermore, the critical vapour qualities at the onset of the flow boiling instability (OFBI) are predicted by a theoretical model considering the local pressure and the frictional pressure resistances. The calculated and experimental results indicate that the instable zones in a flow boiling stability map expand with increasing the compressive volume and decreasing the two types of resistances. The critical vapour quality at OFBI changes from 0.65 to 1 when the local pressure resistance combination coefficient is increased to 7.33 × 10−3 or the frictional pressure resistance combination coefficient is increased to 0.532. The physical mechanisms behind the phenomena are discussed according to the experimental results.

Dynamics of summer monsoon current around Sri Lanka

From June–September, the summer monsoon current (SMC) flows eastward south of Sri Lanka and bends northeastward to form a swift jet that enters the Bay of Bengal (BoB). This part of SMC serves as the major component of the water exchange between the Arabian Sea and the BoB, maintaining the salt and freshwater of the North Indian Ocean. The processes that determine the evolution, intensification, and meandering of the SMC involve both local and remote forcing by winds. Interactions of the SMC with westward-propagating Rossby waves and eddies are only partly understood. In this study, we investigate these processes using an Indian Ocean general circulation model (MOM4p1) that is capable of simulating the SMC realistically. Because eddies and meanders are smoothed out in the climatology, our analyses focus on a single year of 2009, a period when a strong anticyclonic bend in the SMC was observed. An eddy-kinetic-energy budget analysis shows the region to be a zone of significant eddy activity, where both barotropic and baroclinic instabilities are active. Based on the analysis, we classify the evolution of SMC into stages of onset, intensification, anticyclonic bend, anticyclonic vortex formation, meandering, and termination. In addition, analysis of eddy-potential-vorticity flux and eddy-enstrophy decay reveal when, where, and how the eddies tend to drive the mean flow. Rossby waves and westward-propagating eddies arriving from the east energize the SMC in June and accelerate the mean flow through an up-gradient eddy-potential-vorticity flux. At the same time, local winds also strengthen the flow, by increasing its mean near-surface kinetic energy and raising isopycnals, the latter building up available potential energy (APE). The baroclinic instability that takes place in late July and early August releases APE, thereby generating the SMC meanders.

What Shapes the Absorption Measure Distribution in AGN Outflows?

The Absorption Measure Distribution (AMD) in the X-ray outflows of Seyfert active galactic nuclei (AGN) describes the distribution of absorbing column density as a function of ionization parameter. Up to now, AMD has been measured only for seven objects with high-resolution X-ray data that contain absorption lines from ionized heavy elements. Even though the number of measured AMDs is not large, they display a universal broad shape containing a prominent dip, for which the absorbing column drops by around two orders of magnitude. In this paper, we tested a range of photoionization models against the overall shape of the AMD as observed in Seyferts. In particular, we demonstrate that the shape of the AMD depends both on the spectral energy distribution (SED) of radiation which enters the outflow, and the density of the warm absorber (WA). The model that best reproduces the observed shape of the AMD is one wherein the gas density of the WA is of the order of $10^{12}$ cm$^{-3}$, irradiated by an SED whose optical/UV luminosity is 100 times higher than the X-ray luminosity. When the cloud density is higher than $\sim 10^{11}$ cm$^{-3}$, free-free heating dominates the entire absorber, and only one instability zone occurs, which is in agreement with observations.

Assessment of the correlation between grain angularity parameter and friction index of sand containing low plastic fines

ABSTRACT This paper describes a fundamental research to explore the impact of grain angularity on theinstability and steady state friction angles of binary mixtures through laboratory triaxial compression tests performed on three different sands named as Chlef sand “CS”, Fontainebleau sand “FS” and Hostun sand “HS” mixed with low plastic Chlef silt in the range of Fc=0% to 30%. The silty sand samples were prepared with dry funnel pluviation and subjected to three different initial confining pressures (P’c=100 kPa, 200 kPa and 300 kPa). The obtained test results indicate that the low plastic fines content has a significant influence on the instability friction angle (φins), steady state friction angle (φss) and angularity ratio (Ar=Ahs/Amix) of the used materials. New proposed parameter named as friction index (FI= (φss- φins)/ φss) is suggested to evaluate the instability zone of the tested materials. Indeed, the friction index increases with the increase of fines content for the silty sand soils. Moreover, the obtained results demonstrate clearly that the instability and steady state friction angles could be correlated with the angularity ratio and friction index. The angularity ratio and friction index appear as appropriate parameters to identify the undrained instability zones of silty sand.

Modelling of glacially-induced stress changes in Latvia, Lithuania and the Kaliningrad District of Russia

We model the change of Coulomb Failure Stress (δCFS) during the Weichselian glaciation up until today at 12 locations in Latvia, Lithuania and Russia that are characterised by soft-sediment deformation structures (SSDS). If interpreted as seismites, these SSDS may point to glacially-induced fault reactivation. The δCFS suggests a high potential of such reactivation when it reaches the instability zone. We show that δCFS at all 12 locations reached this zone several times in the last 120,000 years. Most notably, all locations exhibit the possibility of reactivation after ca. 15 ka BP until today. Another time of possible activity likely happened after the Saalian glaciation until ca. 96 ka BP. In addition, some models suggest unstable states after 96 ka BP until ca. 28 ka BP at selected locations but with much lower positive δCFS values than during the other two periods. For the Valmiera and Rakuti seismites in Latvia, we can suggest a glacially-induced origin, whereas we cannot exactly match the timing at Rakuti. Given the (preliminary) dating of SSDS at some locations, at Dyburiai and Ryadino our modelling supports the interpretation of glacially-induced fault reactivation, while at Slinkis, Kumečiai and Liciškėnai they likely exclude such a source. Overall, the mutual benefit of geological and modelling investigations is demonstrated. This helps in identifying glacially-induced fault reactivation at the south-eastern edge of the Weichselian glaciation and in improving models of glacial isostatic adjustment.