Narrow Results

We study the combined effects of aging and links removal on epidemic dynamics in the Barabási–Albert scale-free networks. The epidemic is described by a susceptible-infected-refractory (SIR) model. The aging effect of a node introduced at time t_i is described by an aging factor of the form (t-t_i)^-β in the probability of being connected to newly added nodes in a growing network under the preferential attachment scheme based on popularity of the existing nodes. SIR dynamics is studied in networks with a fraction 1-p of the links removed. Extensive numerical simulations reveal that there exists a threshold p_c such that for p≥p_c, epidemic breaks out in the network. For p<p_c, only a local spread results. The dependence of p_c on β is studied in detail. The function p_c(β) separates the space formed by β and p into regions corresponding to local and global spreads, respectively.

Investigated in this study are precipitate evolution with and without addition of W, Co, and B in two kinds of 9-12% Cr steels (named as A and B) used for power plants after various aging time and temperature using OM, SEM, TEM, etc. Three kinds of precipitates (Cr-rich M₂₃C₆, Nb-rich and V-rich MX, W-rich and Mo-rich Laves phase) were observed and investigated in the two alloys. Upon aging, the area fraction of M₂₃C₆ increased whereas that of Laves phases decreased despite of increase in size. The area fraction of W-rich Laves phase was much higher than that of Mo-rich Laves phase, indicating that W addition, compared to that of Mo addition, is more powerful in the formation of Laves phase precipitation (specimen A). The martensitic microstructure of specimen B was more stable than that of specimen A due to the addition of cobalt and boron. The tensile test and impact test were measured and studied in relation to the long term aging effect.

The precipitation phenomena and the related hardening in an Al–Cu–Mg–Si alloy were studied by calorimetry, X-ray diffraction analysis and microhardness measurements. The main calorimetric peaks were identified to be due to β^′′, θ′ and Q′ phases precipitation. The hardening during aging at room temperature and 160°C, was respectively, explained by atomic clusters and GP zones formation and by GP zones and β^′′/θ′ phases coprecipitation. Although the mechanical properties variation during aging at 200°C is simple, the corresponding microstructural evolution is complex: on the basis of the DSC results, the increasing of microhardness values, is mainly due to the coprecipitation of GP zones and β^′′/θ′ phases, however, the maximum hardening is explained by the coexistence of β^′′/θ′ and θ^′′ phases. Another important conclusion is that during aging at 160°C and 200°C, the θ′ phase is essentially developed from GP zones.

The microstructures and mechanical properties of as-extruded Mg–2.3Zn–0.18Y–$x$Zr ($x$ = 0.03, 0.06 and 0.13 at.%) alloys and aged Mg–2.3Zn–0.18Y–0.13Zr alloy were studied. The results revealed that the microstructures of as-extruded Mg–2.3Zn–0.18Y–$x$Zr alloys are typical bimodal structures. The coarse $\alpha$-Mg grains are surrounded by fine dynamically recrystallized $\alpha$-Mg grains. The average size of $\alpha$-Mg grains decreases with increasing Zr content. Moreover, the addition of Zr (at.%) can improve the mechanical properties of alloy. The as-extruded Mg–2.3Zn–0.18Y–0.13Zr alloy has the best mechanical properties with ultimate tensile strength (UTS) and yield strength (YS) of 346 MPa and 292 MPa, respectively, and an elongation of 26.7%, which can be attributed to the grain refining effect and precipitate strengthening. The UTS and elongation of Mg–2.3Zn–0.18Y–0.13Zr alloy changed slightly after aging treatment, but the YS increases remarkably, with the maximum increase of 30 MPa. The fracture surfaces of all alloys consist of many tearing ridges and dimples.

This paper’s aim is to describe the results of the phase transformation of BCuAl₉Fe₄ alloy after casting, quenching and aging. After casting, the microstructure of this alloy consists of $\alpha$ phase with grain size about 100 $\mu$m, mixture $(\alpha +\gamma )$ and the inter-metallic phase Fe₃Al. However, the proportion of the $\alpha$ phase in the casting alloy is coarse. The alloy was heated at $850^{\circ }$C for 2 h then quickly cooling in water. After quenching, the microstructure of alloy shows that the grain size reduced to about 40 $\mu$m. After quenching, the alloy was aged at $350^{\circ }$C for 2 h, the martensite phase of this alloy decomposed into order phase ($\alpha +{\gamma }_2)$ with fine grain size, dispersed in the matrix. The intermetallic phase was fine and evenly dispersed in the matrix. By TEM analysis, after heat treatment, the structure of martensite and the inter-metallic phase in this alloy which had small grain size were formed.

The aging behavior of the random n-vector model with long-range interaction decaying as r^-(d+σ) (where d is the dimensionality), is investigated by the theoretic renormalization-group approach. The system initially disordered at a high temperature is firstly quenched to the critical temperature T_c and then released to an evolution with model A dynamics. The aging properties are studied by the short-time expansions. The scaling behavior of two-time response and correlation functions are obtained in a frame of the expansion in ∊ = 2σ-d. In dimensions d < 2σ, the long-time limit of the critical fluctuation dissipation ratio X^∞ is calculated up to one-loop order. The simulation of X^∞ is discussed.

A series of Y₂O₃ nanoparticles of average particle size 19–37 nm are synthesized by a glycine-nitrate method. Room temperature ferromagnetism is observed in all samples. The magnetization of these samples decreases with increasing annealing temperature, showing a size-dependent ferromagnetism. Vacuum-heating effect on the ferromagnetism is also investigated, which indicates that the observed ferromagnetism is possibly associated with oxygen defects. Interestingly, an aging behavior of the ferromagnetism is observed when the sample is exposed to air or immersed in ethanol. These results further support the oxygen-vacancy-mediated ferromagnetism mechanism.

Wide bandgap II–VI semiconductor quantum dots embedded in glass matrix have shown great potential for opto-electronic device applications. The current problem is to achieve low size dispersion, high volume fraction, and better control over the size of the quantum dots in glass matrix. In this work, a modified growth method has been proposed to achieve a greater control over the size of quantum dots, to reduce their size dispersion and to increase their volume fraction. A theoretical model has been developed to quantitatively estimate the various parameters of the quantum dots. The effects of aging on various parameters of quantum dots in Semiconductor-Doped Glass (SDG) samples have also been discussed in the present work.

Different time-dependent mechanisms such as creep, environmental surface oxidation or internal material degradation due to aging and irradiation will subject structures to the possibility of premature failures. In this paper a micro-scale finite element mesh consisting of multiple elements encased in ~50–150μm sized grains with designated grain boundaries is used to replicate shapes and dimensions to simulate an isotropic metallic microstructure. The grains are encased in pseudo-grain boundary element sets which can have different material and damage parameters compared to the grains. In this type of mesh random crack paths for intergranular and transgranular cracking conditions are allowed. It is shown that creep cracking using a uniaxial ductility constraint-based model coupled with a functionally distributed time-dependent environmentally assisted corrosion/oxidation/material degradation damage model acting on surface or internally can be realistically predicted using this model. It is also evident material properties input data have scatter especially at the sub-grain level where the measurement methods are new and not always standardised. This is dealt with in the model by employing a normal distributive probabilistic method to allow for statistically varied random damage and crack growth development. In this way it is possible to take into account the inherent variability in material input properties at the analysis stage without the need to change material properties following each run. The method could negate the need for knowing the exact material properties, which in any case is impossible to derive at the microstructural level, as results of each run can be varied using a statistically distributed critical damage criterion specified for each element.

A simple and general thermodynamic theory is applied to describe the irreversible aspects of the continuous process of functional efficiency loss, which occurs in dissipative biological structures after they reach maturity. Following Prigogine [G. Nicolis and I. Prigogine, Self-organization in Nonequilibrium Systems (Wiley, New York, 1997), pp. 2–3], this theory considers that these dissipative structures perform their functions carrying out cyclic processes per se since they are self-organized far from equilibrium. Starting from the theoretical fact that after biological dissipative systems reach adulthood, the functionality of their organs decreases linearly over time. We show that cumulative damage leads to the exponential law of increasing mortality rate with age for population groups, known as Gompertz’s law. The theory was applied to the determination of functional efficiency loss parameter, $\alpha$, for 71 living beings as a function of mass covering 18 orders of magnitude. The mathematical adjustment allowed us to conclude that there is a minimum in the value of the $\alpha$ parameter for a 23.3 kg mass which is close enough to the Homo sapiens one. We obtained useful expressions to describe the $\alpha$ parameter for smaller masses than those of saccharomyces cerevisiae, so perhaps this theory may contribute to the study of the evolution of some dissipative pre-biological structures.

The accelerated aging test of SBR-based absorption materials in heat seawater were carried in laboratory. The elongation at break of the materials in aging time was investigated. Two methods were adopted to forecast the life expectancy of the materials. Mathematical model was applied through MATLAB software programming to gain the forecasted life expectancy is 10.98y in seawater at 25 ℃. The time-temperature superposition method was applied to gain the life expectancy, which is 12.08y in seawater at 25 ℃.