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In contrast to long standing view on predator–prey interactions that predators have only direct effect on prey by killing, recent field experimentation on terrestrial vertebrates showed that indirect effect of predators' fear may alter the behavioral changes on prey, including foraging and reproduction. Usually, prey perceive the signals from predators (chemical and/or vocal cues) and change their life-history and behavior to reduce the probability of being killed. Recently, Wang et al. (J Math Biol 73:1179–1204, 2016) proposed and analyzed a predator–prey model by considering the fear effect on prey population. They concluded that the model dynamics may exhibit both supercritical and subcritical Hopf bifurcation, while the classical predator–prey model exhibits only supercritical Hopf bifurcation. The cost of fear on prey may dramatically reduce foraging and reproduction, which may change the ecosystem stability. In the present investigation, we explore the possible applications of fear in prey due to predators' signals and error based Z-control mechanism by manipulating the abundance of predator population. Our results suggest that by manipulating or controlling the abundance of predator one can achieve a desired prey population density. We also observe that Z-control mechanism has the property to produce a stable steady-state or a stable limit cycle by excluding the bi-stability situation as observed by Wang et al. We perform extensive numerical simulations to illustrate our analytical findings. [ABSTRACT FROM AUTHOR]

In this paper, we study the dynamics of a predator–prey system under the combined effects of fear, migration and switching phenomena. This study is new in the sense that the dynamics of such system was studied either through fear or migration, or switching, but the combined effects of such three factors are yet to be explored. We observe oscillatory behavior of the system in the absence of fear, migration and switching, whereas the system shows stable dynamics if anyone of these three factors is introduced. After analyzing the behavior of system with fear, migration and switching, we find that the system does not possess periodic solution whenever the predator population experiences intraspecies competition, but in the absence of intraspecies competition among predator population, fear of predators destabilizes the system, whereas on increasing the migration rates, the system first undergoes subcritical Hopf-bifurcation and then supercritical Hopf-bifurcation settling the system to stable coexistence. Existence of multiple limit cycles is also observed. Our results show that switching behavior of predator population supports the survival of prey and predator populations. We extend our model by assuming the fear parameters as time dependent. We find that the nonautonomous system exhibits periodic solutions, whereas the corresponding autonomous system shows stable focus. Moreover, we observe that if the autonomous system undergoes a Hopf-bifurcation through limit cycle oscillations, the corresponding nonautonomous system shows higher periodic solutions. Almost periodic behavior of the system is also observed by setting the fear parameters as almost periodic functions of time. [ABSTRACT FROM AUTHOR]

The increasing input of environmental toxins in aquatic systems raises concerns regarding the environmental exposure and impact of toxins on natural aquatic environments. Phytoplankton and zooplankton appear to be among the most sensitive aquatic organisms to environmental toxins. Moreover, toxin-producing phytoplankton plays an important role in regulating the real aquatic ecosystems. In this paper, the combined effects of these factors on the dynamics of phytoplankton–zooplankton interactions are investigated. The phytoplankton grows logistically, but their growth rate is suppressed due to the presence of environmental toxins. The zooplankton is assumed to be generalist and follows logistic growth in the absence of phytoplankton. Also, it is considered that toxicants in the environment are increased constantly due to different natural and human behaviors. Global sensitivity analysis helps to identify the most significant parameters that reduce the environmental toxins in the system. Among these, the input rate of environmental toxins, contact rate between phytoplankton and environmental toxins, and environmental toxins-induced growth suppression of phytoplankton have destabilizing effect on the dynamics of system, while the depletion rate of environmental toxins has stabilizing effect. Therefore, it is imperative to modulate the depletion rate of environmental toxins to prevent the crash of the aquatic food web system. Further, we incorporate seasonal variations in the model, letting the parameters become functions of time. Sufficient conditions for the existence and stability of positive periodic solutions are obtained. We also derive conditions for existence, uniqueness and stability of a positive almost periodic solution. Large values of time-dependent toxin release by phytoplankton and input rate of environmental toxins induce periodic solutions of the nonautonomous system while the corresponding autonomous system exhibits a stable focus. Interestingly, our nonautonomous system exhibits bursting patterns for two slow rationally related excitation frequencies. Finally, we convert our deterministic autonomous model into stochastic model by introducing additive noise term. We find that the stability of the system gets disturbed in the presence of environmental fluctuation. [ABSTRACT FROM AUTHOR]

Metal injection moulding (MIM) is a near-net shape manufacturing technology for producing intricate parts, cost-effectively. MIM comprises combined techniques of plastic injection moulding and powder metallurgy. The present study focused on the development of the binder and fabrication of defect free MIM component. A wax-based binder system consisting of paraffin wax (PW), low density polyethylene (LDPE), polyethylene glycol (PEG-600) and stearic acid was established for MIM of NiCrSiB (70% Wt.) + Cr3C2-NiCr (30% Wt.) nickel based metal matrix composite (NMMC) powder. The feedstock was characterised through rheological properties at different temperatures. Injection temperature was determined from the rheological investigation of the feedstock having the 56% powder loading and 44% binder by volume. Sintering process was carried out with the temperature cycle in the range of 1250-1300 ∘C under hydrogen purged atmosphere. The MIM components showed good and acceptable shrinkage in linear dimensions. The mechanical properties and wear behaviour of NMMC was studied using a pin-on-disc apparatus with alumina disc.Tests were performed under dry sliding conditions at room temperature and elevated temperatures of 200 and 400 ∘C. Results shows that wear rate is maximum at 400 ∘C for 40 N and lowest at room temperature for 10 N. Further wear mechanism was analysed using scanning electron microscope (SEM). [ABSTRACT FROM AUTHOR]

In the present paper, we present an experimentally validated 3D multiphase and multiscale solidification model to understand the transport processes involved during slurry generation with a cooling slope. In this process, superheated liquid alloy is poured at the top of the cooling slope and allowed to flow along the slope under the influence of gravity. As the melt flows down the slope, it progressively loses its superheat, starts solidifying at the melt/slope interface with formation of solid crystals, and eventually exits the slope as semisolid slurry. In the present simulation, the three phases considered are the parent melt as the primary phase, and the solid grains and air as secondary phases. The air phase forms a definable air/liquid melt interface as the free surface. After exiting the slope, the slurry fills an isothermal holding bath maintained at the slope exit temperature, which promotes further globularization of microstructure. The outcomes of the present model include prediction of volume fractions of the three different phases considered, grain evolution, grain growth, size, sphericity and distribution of solid grains, temperature field, velocity field, macrosegregation and microsegregation. In addition, the model is found to be capable of making predictions of morphological evolution of primary grains at the onset of isothermal coarsening. The results obtained from the present simulations are validated by performing quantitative image analysis of micrographs of the rapidly oil-quenched semisolid slurry samples, collected from strategic locations along the slope and from the isothermal slurry holding bath. [ABSTRACT FROM AUTHOR]

In this present article, we propose and analyze a cannibalistic predator-prey model with disease in the predator population. We consider two important factors for the dynamics of predator population. The first one is governed through cannibalistic interaction, and the second one is governed through the disease in the predator population via cannibalism. The local stability analysis of the model system around the biologically feasible equilibria are investigated. We perform global dynamics of the model using Lyapunov functions. We analyze and compare the community structure of the system in terms of ecological and disease basic reproduction numbers. The existence of Hopf bifurcation around the interior steady state is investigated. We also derive the sufficient conditions for the permanence and impermanence of the system. The study reveals that the cannibalism acts as a self-regulatory mechanism and controls the disease transmission among the predators by stabilizing the predator-prey oscillations. [ABSTRACT FROM AUTHOR]

The present paper deals with an eco-epidemiological model consisting of susceptible prey, infected prey and predator. We assume that the recruitment of prey follows the saturating functional form due to habitat saturation. We make a general assumption of the non-restricted conversion rate of the predator population due to consumption of the infected prey population. We study the existence and stability criteria of the equilibrium points. Our results suggest that the predator population may be eliminated from the system due to the negative effect of infected prey; however, the negative impact can be buffered by the alternative food. Alternative food helps predator population to survive and makes the system disease free. The outcomes from the model are verified numerically by taking a set of biologically feasible parameter values. [ABSTRACT FROM AUTHOR]

Biporous media having clusters of size range 300 - 425 μm, 425 - 600 μm, > 600 μm have been sintered at 950 °C, 180 min using gas atomized spherical particles (D50 of 90 microns) of pure copper in reducing atmosphere of pure hydrogen gas. MicroCT scan of biporous samples have been performed to and then images have been reconstructed to 3D CAD models, which further have been discretised into tetrahedral mesh using image processing and reconstruction software Avizo Fire 8.0. Direct numerical simulations have been performed to obtain Evaporative heat transfer coefficient (EHTC) over the surface of these biporous clusters. The transient evaporation phenomena and effect of cluster size on evaporation has been investigated in this paper. These results have been compared with the experimental results available in literature for evaporative heat transfer coefficient for biporous media. [ABSTRACT FROM AUTHOR]

In this article, an eco-epidemiological system with weak Allee effect and harvesting in prey population is discussed by a system of delay differential equations. The delay parameter regarding the time lag corresponds to the predator gestation period. Mathematical features such as uniform persistence, permanence, stability, Hopf bifurcation at the interior equilibrium point of the system is analyzed and verified by numerical simulations. Bistability between different equilibrium points is properly discussed. The chaotic behaviors of the system are recognized through bifurcation diagram, Poincare section and maximum Lyapunov exponent. Our simulation results suggest that for increasing the delay parameter, the system undergoes chaotic oscillation via period doubling. We also observe a quasi-periodicity route to chaos and complex dynamics with respect to Allee parameter; such behavior can be subdued by the strength of the Allee effect and harvesting effort through period-halving bifurcation. To find out the optimal harvesting policy for the time delay model, we consider the profit earned by harvesting of both the prey populations. The effect of Allee and gestation delay on optimal harvesting policy is also discussed. [ABSTRACT FROM AUTHOR]

In the present work, microstructure evolution during semi-solid slurry generation of Al-Si-Cu-Fe alloy, using a cooling slope, was studied and the effect of microstructural morphology of the slurry on its rheological behavior was investigated. Microstructure evolution during melt flow along the slope was studied by extracting samples from various locations of the slope and performing rapid oil quenching experiments. Quantitative investigation was performed to evaluate primary phase shape and size for different process conditions of the semi-solid slurry, and subsequently rheological investigations were performed to correlate slurry morphology with its flow behavior. Three different types of rheological experiments were performed: isothermal test, shear jump test, and shear time test, in order to investigate rheological behavior of the semi-solid slurry. In addition, effect of melt treatment, by adding modifier (0.1 wt pct of Al-10Sr) and grain refiner (0.15 wt pct of Al-5Ti-1B), on the microstructure evolution during slurry generation, flow behavior of the slurry, and intermetallics formation was studied. [ABSTRACT FROM AUTHOR]

In this article, an eco-epidemiological model with strong Allee effect in prey population growth is presented by a system of delay differential equations. The time lag in terms of the delay parameter corresponds to the predator gestation period. We inspect elementary mathematical characteristic of the proposed model such as uniform persistence, stability and Hopf bifurcation at the interior equilibrium point of the system. We execute several numerical simulations to illustrate the proposed mathematical model and our analytical findings. We use basic tools of nonlinear dynamic analysis as first return maps, Poincare sections and Lyapunov exponents to identify chaotic behavior of the system. We observe that the system exhibits chaotic oscillation due to the increase of the delay parameter. Such chaotic behavior can be suppressed by the strength of Allee effect. [ABSTRACT FROM AUTHOR]

The present work discusses the findings obtained from simulations of semi solid die filling of a steering knuckle, prior to actual component development using in-house developed rheo pressure die casting system. Die filling capability of A356 Al alloy at semi-solid state has been investigated using commercial software Flow-3Dcast to optimise the pouring temperature of semi-solid slurry into the die cavity, while all other variables such as gating design, die preheat temperature and injection velocity are kept constant based on the prior knowledge obtained from trial numerical simulations and experimentation. Efforts have been made to nullify the essence of costly, time consuming experiments towards obtaining high-quality castings out of the findings obtained from numerical simulations. The optimum pouring temperature identified in the present study is 610 °C, which facilitates smoother slurry flow, minimum surface defect concentration, uniform temperature field and solid fraction distribution within the component cavity. [ABSTRACT FROM AUTHOR]

In this paper, we propose a prey-predator system with disease in both the prey and predator populations. We also consider that the predator population is cannibalistic in nature and the disease spread in the predator population through cannibalism. Local stability of the system around the biologically feasible equilibria are studied. We also analyze the community structure of the system in terms of ecological and disease basic reproduction numbers. We observe that cannibalism in predator population stabilized the prey-predator oscillations. It is also observed that cannibalism can control the disease in the system. The existence of Hopf bifurcation is investigated by choosing the appropriate bifurcation parameter, and also derive the conditions for the permanence of the system. Furthermore, applying the normal form theory and central manifold theorem, the direction of Hopf bifurcation, the stability and the period of bifurcating periodic solutions are derived. Finally extensive numerical experiments are performed to validate analytical findings. [ABSTRACT FROM AUTHOR]

In recent years, semisolid manufacturing has emerged as an attractive option for near net shape forming of components with aluminum alloys. In this class of processes, the key to success lies mainly in the understanding of rheological behavior of the semi-solid slurry in the temperature range between liquidus and solidus. The present study focuses on the non-Newtonian flow behavior of the pseudo plastic slurry of Al-7Si-0.3Mg alloy for a wide shear range using a high-temperature Searle-type rheometer. The rheological behavior of the slurry is studied with respect to relevant process variables and microstructural features such as shear rate, shear duration, temperature history, primary particle size, shape, and their distribution. The experiments performed are isothermal tests, continuous cooling tests, shear jump tests, and shear time tests. The continuous cooling experiments are aimed toward studying the viscosity and shear stress evolution within the slurry matrix with increasing solid fraction at a constant shear rate. Three different cooling rates are considered and their effect on flow behavior of the slurry was studied under iso-shear condition. Descending shear jump experiments are performed to understand the viscous instability of the slurry. [ABSTRACT FROM AUTHOR]

Cooling slope (CS) has been used in this study to prepare semi-solid slurry of A356 Al alloy, keeping in view of slurry generation on demand for Rheo-pressure die casting process. Understanding the physics of microstructure evolution during cooling slope slurry formation is important to satisfy the need of semi-sold slurry with desired shape, size and morphology of primary Al phase. Mixture of spherical and rosette shaped primary Al phase has been observed in the samples collected during melt flow through the slope as well as in the cast (mould) samples compared to that of dendritic shape, observed in case of conventionally cast A356 alloy. The liquid melt has been poured into the slope at 650 °C temperature and during flow it falls below the liquidus temperature of the said alloy, which facilitates crystallization of α-Al crystals on the cooling slope wall. Crystal separation due to melt flow is found responsible for nearly spherical morphology of the primary Al phase. [ABSTRACT FROM AUTHOR]

The current study aims to assess the impact of rheocast's input variables (cooling slope techniques) on its mechanical properties. The rheocast experiment was carried out by varying the input variables of slope angle (30º, 45º, and 60º), slope length (400, 500, and 600 mm), and pouring temperature (580, 585, and 590 °C). The effect of input variables on responses (ultimate tensile strength and elongation) and the factor interaction graph of responses have been evaluated by analysis of variance (ANOVA) and response surface methodology. The experimental findings showed that optimum response values (ultimate tensile strength, 181 MPa; elongation, 6.19%) were obtained at the following series of input variables: 585 °C pouring temperature, 500 mm slope length, and 45º slope angles. Analysis of variance results infers that pouring temperature is the most significant input variable, which highly influences the response factors. A confirmation experiment was performed at a 95% confidence level to ensure that the obtained values of response factors fall within permissible limits. [ABSTRACT FROM AUTHOR]

An attempt has been made to simulate the mold filling behavior of semi-solid slurry of Al–10.5Si–1.7Cu alloy for rheo-pressure die casting (RPDC) with additional emphasis on the speed range of plunger of a die casting unit. The numerical results attained are then validated with subsequent experiments using the in-house-developed RPDC system. The software Flow-3D Cast™ is deployed to simulate the process of die filling at different speed ranges of plunger. Rheological parameters of Al–10.5Si–1.7Cu cast Al alloy used in the simulation study are measured experimentally with Anton™ Rheo meter. Semi-solid metal processing for the experiments is carried out using an indigenously developed coupled cooling slope and pressure die-cast system. The results from the simulation study indicate that plunger movement at higher speeds causes void formation, largely due to the air entrapment in the overflow region. However, when filling at slow speeds, this effect is mitigated simply by ensuring the final temperature of the slurry is above the solidus temperature; thus, the mold is completely filled with no void formation. By comparing the formed appearance of parts in experiments and simulations, as well as observing the X-ray films and flow field obtained in simulation,f it is clear that simulation and experiment agree quite well. [ABSTRACT FROM AUTHOR]

The main aim of this study is to understand the microstructure characterization, mechanical properties and wear behavior of in situ processed A356/5%TiB2 rheocast metal matrix composite. This investigation deals with an aluminum-based in situ composite wherein the reinforcement, TiB2, was synthesized in the molten alloy via reaction of salts between K2TiF6 and KBF4. The paper shall cover a few aspects of this new generation of composites, such as the development of in situ composite and distribution pattern (grain structure), size and number of TiB2 in cast ingot of A356 aluminum alloy with 5% TiB2. The obtained results revealed that cast condition of A356/TiB2 composite, primary phase of aluminum alloy and eutectic Si phase are normally in the refined shape and TiB2 particles are mostly in the hexagonal or near spherical shape, with the size ranging from size 1 to 5 µm uniformly distributed throughout the microstructure. It has been found that the mechanical properties of rheocast composite material are enhanced with addition of TiB2 particles. The wear rate of the composites improves significantly with the TiB2 content. Analysis of the worn surfaces suggests that adhesion and ploughing are the predominant wear mechanisms. [ABSTRACT FROM AUTHOR]

The present study investigates the structure-property relationship of gravity die-cast and rheocast in situ processed 1wt%TiB2/Al-3.5Mg-0.15Sc-0.075Zr composites. The reinforcement was synthesized via the reaction of fluoride salts (K2TiF6 and KBF4) in the melt at 750 °C for an hour. The cooling slope technique was used for rheocasting, wherein the melt (pouring temperature of 700 °C) was allowed to flow over the cooling slope at an angle of 60°. Thereafter, all samples (gravity die cast and rheocast) were aged at 300 °C for 5 h. Microstructural characterization, hardness measurements, tensile tests, and fractography were necessary supplements to this investigation. The results obtained from this investigation infer: (a) The presence of nano-TiB2 particles increases the ductility (15%) of the gravity die-cast specimens; (b) rheocasting increases the strength of the specimen due to transformation from dendritic to equiaxed dendritic morphology and uniform particle distribution (reduced agglomeration). (c) Rheocast and aged specimens show maximum strength and adequate ductility due to the combined effects of structure refinement, reduced agglomeration, and the formation of fine precipitates. [ABSTRACT FROM AUTHOR]