Dynamical stability of radiation-induced C15 clusters in iron

Density functional theory predicts clusters in the form of the C15 Laves phase to be the most stable cluster of self-interstitials in iron at small sizes. The C15 clusters can form as a result of irradiation, but their prevalence and survival in harsh irradiation conditions have not been thoroughly studied. Using a new bond-order potential optimised for molecular dynamics simulations of radiation damage, we explore the dynamical stability of the C15 clusters in iron under irradiation conditions. We find that small C15 clusters make up 5–20% of the interstitial clusters formed directly in cascades. In continuous irradiation, C15 clusters are frequently formed, after which they remain highly stable and grow by absorbing nearby single interstitial atoms. Growth of C15 clusters ultimately leads to collapse into dislocation loops, most frequently into 1/2⟨111⟩ loops and only rarely collapsing into ⟨100⟩ loops at low temperatures. The population, size, and collapse of C15 clusters during continuous irradiation correlates well with their formation energies relative to dislocation loops calculated at zero Kelvin.Peer reviewe

Genetic uniqueness and socio-cultural conservation values of the endangered Yakutian Cattle

At the local level the values of the cattle were more related to everyday livelihood strategies of single households and families, whereas the representatives of the republic, in line with the newspapers, highlighted the importance of the cattle for Sakha's food production and for national identity. Thus, individuals at different levels were in favour of conserving the cattle, but for different reasons. The local residents and experts were more concerned about developing economically sustainable cattle production, whereas the experts in Yakutsk were concerned about the conservation of genetic resources. The genetic studies have indicated that Yakutian Cattle show genetic distinctiveness and have genetic value for the maintenance of cattle diversity

Effect of random surface orientation on W sputtering yields

In this study, we investigate the sputtering yield of tungsten surfaces by energetic particles, focusing on the effect of surface orientation and the incoming irradiation angle, by means of molecular dynamics. We develop a simulation approach to simulate sputtering from completely random surface orientations. This allows obtaining the sputtering yields averaged over a sufficiently large number of orientations, to obtain statistically significant yields representative of a polycrystalline sample with random grain orientations. We find that the total sputtering yield is dependent on the surface orientation, and that the results for random surfaces are clearly different from that of any of the low-index ones or their average. The different low index surfaces and the random surfaces also showed that the sputtering yield is dependent on the incoming angle of the ion. The outgoing angle of the sputtered tungsten atoms was observed to be very sensitive to the surface orientation. Different features on the tungsten surface were observed to drastically affect the sputtering yield at certain angles.Peer reviewe

Effects of the short-range repulsive potential on cascade damage in iron

Recent work has shown that the repulsive part of the interatomic potential at intermediate atomic separations strongly affects the extent and morphology of the damage produced by collision cascades in molecular dynamics simulations. Here, we modify an existing embedded atom method interatomic potential for iron to more accurately reproduce the threshold displacement energy surface as well as the many-body repulsion at intermediate and short interatomic distances. Using the modified potential, we explore the effects of an improved repulsive potential on the primary damage production and the cumulative damage accumulation in iron. We find that the extent of the damage produced by single cascades, in terms of surviving Frenkel pairs, directly correlates with the change in threshold displacement energies. On the other hand, the damage evolution at higher doses is more dependent on the formation and stability of different defect clusters, defined by the near-equilibrium part of the interatomic potential.Peer reviewe

Defect accumulation and evolution during prolonged irradiation of Fe and FeCr alloys

The understanding of materials' behaviour during continuous irradiation is of great interest for utilizing materials in environments where harsh radiation is present, like nuclear power plants. Most power plants, both current and future ones, are based, at least partially, on Fe or FeCr alloys. In this study, we investigate the response of BCC Fe and several FeCr alloys to massively overlapping cascades. The effect of the added chromium on the defect accumulation and defect evolution was studied. Both a bulk setup, for observing the evolution deep inside the material far from grain boundaries and surfaces, and a setup with a nearby open surface, to investigate the effect of a permanent defect sink, were studied. We found that the primary defect production is similar in all materials, and also the build-up before serious overlap is comparable. When cascade overlap starts, we found that different sized clusters are formed in the different materials, depending on the setup. The defect cluster evolution was followed and could be related to the dislocation reactions in the materials. We found that the irradiation mixing was specific to the different chromium concentrations, the low chromium-containing alloy showed ordering, whereas the highest chromium-containing sample showed segregation. (C) 2019 The Authors. Published by Elsevier B.V.Peer reviewe

Memory Effect, Rejuvenation and Chaos Effect in the Multi-layer Random Energy Model

We introduce magnetization to the Multi-layer Random Energy Model which has a hierarchical structure, and perform Monte Carlo simulation to observe the behavior of ac-susceptibility. We find that this model is able to reproduce three prominent features of spin glasses, i.e., memory effect, rejuvenation and chaos effect, which were found recently by various experiments on aging phenomena with temperature variations.Comment: 10 pages, 14 figures, to be submitted to J. Phys. Soc. Jp

CASCADE DEBRIS OVERLAP MECHANISM OF <100> DISLOCATION LOOP FORMATION IN Fe AND FeCr

Two types of dislocation loops are observed in irradiated alpha-Fe, the 1/2 loop and the loop. Atomistic simulations consistently predict that only the energetically more favourable 1/2 loops are formed directly in cascades, leaving the formation mechanism of loops an unsolved question. We show how loops can be formed when cascades overlap with random pre-existing primary radiation damage in Fe and FeCr. This indicates that there are no specific constraints involved in the formation of loops, and can explain their common occurrence. Copyright (C) EPLA, 2017Peer reviewe

Scaling Law and Aging Phenomena in the Random Energy Model

We study the effect of temperature shift on aging phenomena in the Random Energy Model (REM). From calculation on the correlation function and simulation on the Zero-Field-Cooled magnetization, we find that the REM satisfies a scaling relation even if temperature is shifted. Furthermore, this scaling property naturally leads to results obtained in experiment and the droplet theory.Comment: 8 pages, 7 figures, to be submitted to J. Phys. Soc. Jp

Aging, rejuvenation, and memory effects in short-range Ising spin glass: Cu0.5_{0.5}Co0.5_{0.5}Cl2_{2}-FeCl3_{3} graphite bi-intercalation compound

Non-equilibrium aging dynamics in 3D Ising spin glass Cu$_{0.5}$Co$_{0.5}$Cl$_{2}$-FeCl$_{3}$ GBIC has been studied by zero-field cooled (ZFC) magnetization and low frequency AC magnetic susceptibility ($f = 0.05$ Hz), where $T_{g} = 3.92 \pm 0.11$ K. The time dependence of the relaxation rate $S(t) = (1/H)$d$M_{ZFC}/$d$\ln t$ for the ZFC magnetization after the ZFC aging protocol, shows a peak at a characteristic time $t_{cr}$ near a wait time $t_{w}$ (aging behavior), corresponding to a crossover from quasi equilibrium dynamics to non-equilibrium. The time $t_{cr}$ strongly depends on $t_{w}$, temperature ($T$), magnetic field ($H$), and the temperature shift ($\Delta T$). The rejuvenation effect is observed in both $\chi^{\prime}$ and $\chi^{\prime\prime}$ under the $T$-shift and $H$-shift procedures. The memory of the specific spin configurations imprinted during the ZFC aging protocol can be recalled when the system is re-heated at a constant heating rate. The aging, rejuvenation, and memory effects observed in the present system are discussed in terms of the scaling concepts derived from numerical studies on 3D Edwards-Anderson spin glass model.Comment: 14 pages, 14 figures; Eur. Phys. J. B accepted for publicatio

Numerical Study of Aging in the Generalized Random Energy Model

Magnetizations are introduced to the Generalized Random Energy Model (GREM) and numerical simulations on ac susceptibility is made for direct comparison with experiments in glassy materials. Prominent dynamical natures of spin glasses, {\it i.e.}, {\em memory} effect and {\em reinitialization}, are reproduced well in the GREM. The existence of many layers causing continuous transitions is very important for the two natures. Results of experiments in other glassy materials such as polymers, supercooled glycerol and orientational glasses, which are contrast to those in spin glasses, are interpreted well by the Single-layer Random Energy Model.Comment: 8 pages, 9 figures, to be submitted to J. Phys. Soc. Jp