We give a theoretical description of avalanche-like dynamics of magnetic flux in the critical state of discrete superconductors using a one-dimensional model of a multijunction SQUID. We show that ...the system under consideration demonstrates the self-organized criticality. The avalanches of vortices manifest themselves as jumps of the total magnetic flux in the sample. The sizes of these jumps have a power-law distribution. We argue that similarities in the behavior of discrete and usual type-II superconductors allows to extend our results for description of avalanche-like dynamics in type-II superconductors with strong pinning.
The model of a superconducting metamaterial, which is a disordered lattice of Josephson junctions, has been studied theoretically and by computer simulation. The aim of this work is to reveal and ...analyze the conditions under which the generation frequencies of constituting junctions are locked in the system under study placed in a spatially nonuniform magnetic field. The main result is the demonstration of the possibility of locking of the generation frequencies of junctions in individual layers of the system under study. This result is particularly important in view of the possibility of the use of superconducting metamaterials for the creation of devices, in particular, generators capable of working in the terahertz frequency range.
The influence of neutron irradiation on the amorphous Ti40.7Hf9.5Ni44.8Cu5 and Ti50Ni25Cu25 thin ribbons, their crystallization behaviour and martensitic transformations that occur after ...crystallization have been studied. The critical fluence value of 1⋅1019 cm−2 was found. If the fluence was 1⋅1019 cm−2 or less, the crystallization parameters and the temperatures of the martensitic transformation that took place alloy after crystallization hardly changed. Otherwise, a huge increase in the crystallization temperature and enthalpy occurred and the degradation of the martensitic transformation in crystallized samples was observed.
Freshwater inflow has a strong impact on the biological, chemical and physical characteristics of estuaries, which in turn affect the distribution and abundance of estuarine organisms. Increased ...climatic variability associated with climate change is predicated to modify precipitation patterns, which will likely intensify floods in estuaries. The demersal fish assemblage of the freshwater-dominated Great Fish Estuary, South Africa, was sampled using beam trawls, monthly, from December 2013 to November 2014. The first six months of the study were characterised by river flooding and high flow, with estuarine conditions found only in the mouth region; this was followed by six months of intermediate flow, with estuarine conditions recorded up to 10 km from the mouth. River flooding and subsequent reduced salinity resulted in a decrease in species richness and abundances of fishes in the estuary, with only two estuarine species (Glossogobius callidus and Psammogobius knysnaensis) and one marine migrant (Solea turbynei) recorded following river flooding (201 m
3
s
−1
), in January 2014. The greatest species richness and abundances among both marine and estuarine fishes were recorded during intermediate flow conditions. We conclude that although freshwater inflow into estuaries is important for the nursery function of these systems, flooding-especially in freshwater-dominated estuaries-may cause a temporary decline in the abundance of most marine and estuarine fish species, including important bentho-pelagic marine migrant fishery species, such as Argyrosomus japonicus and Pomadasys commersonnii.
The theory of the bulk-SQUID effect in discrete superconductors is constructed for the first time. It is shown that the bulk-SQUID effect emerges in the system of 2D intrinsically stochastic ...multijunction SQUID (i.e., with random values of critical currents of the junctions, injection currents, and the coupling coefficients between the junction) due to generation frequency locking in all junctions. It is demonstrated that the bulk-SQUID effect occurs in a wide range of random parameters of the system. This domain of variation of the system parameters can be divided into three subdomains. The first one is the subdomain of coherent dynamics of phases at the junctions, the second is the subdomain of incoherent dynamics, in which the phases of the junctions are not locked, but the bulk-SQUID effect persists, and the third is the subdomain of transient dynamics, in which coherent dynamics and the bulk-SQUID effect are observed in parts. A simple mathematical model of noninteracting junctions, which correctly describes basic features of the dynamics of the initial system and makes it possible to calculate some of its statistical characteristics, is proposed and analyzed.
We tested the effects of marine reserve status on the reproductive biology and recruitment rates of two commonly exploited (Helcion concolor, Scutellastra longicosta) and two rarely exploited ...(Cellana capensis, Scutellastra granularis) limpet species using two reserve and two non-reserve sites on the south coast of South Africa. Because densities of commonly exploited species are lower outside reserves, we hypothesised that limpets outside reserves will: (i) mature earlier; and (ii) show higher individual reproductive output. Rarely exploited species should show no such effects. For recruitment, we hypothesised that if recruits are attracted to adults or survive better where there are more adults, then commonly exploited (but not rarely exploited) species should show higher recruitment inside reserves. Analyses of gonadosomatic indices produced significant Month × Reserve interactions for all species (ANCOVA, p < 0.05), indicating inconsistent reserve effects even for exploited species, although months with significant differences occurred more often in the commonly exploited species, giving weak support to the hypothesis regarding reproductive output. Reserve status had no significant effect on sex ratios or size at sexual maturity for either sex of any species. Accordingly, reserves had only a minor influence on reproduction in these species, which might reflect an indirect effect of poor policing. The timing of major recruitment events differed among species, with two broad patterns: recruitment was sporadic for C. capensis and S. longicosta and protracted for H. concolor and S. granularis. Recruit densities showed strong site effects. Highest recruitment occurred at the exploited site, Xhora, with no reserve effects, except in a single month for C. capensis, indicating that recruitment is independent of whether the site is protected or not. Therefore, reserves do not enhance recruitment directly, but because these populations appear to be open on scales of tens of kilometres, generally higher densities of limpets within reserves could enhance overall recruitment, because of greater gamete output by the population. Accordingly, reserves might have an indirect 'spillover' effect on recruitment, if not a direct one.
Marine reserves are commonly used to conserve living resources, but their effectiveness where policing is difficult is unclear. We compared monthly population density and size structure data ...collected over 20 months for two rarely and two commonly exploited intertidal limpets inside and outside reserves in South Africa. Densities were greater inside reserves, but significantly so in very few months. Unexpectedly, no significant reserve effect was detected for the territorial Scutellastra longicosta, shown by surveys to be favoured by harvesters. Reserve effects for the rarely exploited S. granularis probably result from indirect effects of higher barnacle cover in reserves where trampling is reduced, while interviews indicated that Cellana capensis is not targeted but large individuals are sometimes misidentified and hence are harvested outside the reserve. There were few reserve effects on mean or mean maximum size. The results indicate a gradient of exploitation among species and sites. One non-reserve site was more heavily exploited than the other, while one reserve experienced more poaching than the other. The effectiveness of marine reserves thus differed between reserves and among species. Exploited limpets were generally larger and at higher densities in reserves, but these effects were rarely statistically significant, indicating that reserve effects are weak compared to natural variability, probably reflecting ineffective policing.
Efforts to meet the Millennium Development Goal 1 (MDG1), which was to reduce by half the proportion of the population living below the poverty line by 2015, and the demands of democratization in ...South Africa have directed attention at the agricultural sector's potential for reducing poverty. Expectedly, agriculture has attracted considerable interest and public investment. This article explores the linkages between public spending in agriculture, agricultural growth, and poverty in the Eastern Cape Province of South Africa. The identification of the critical linkages will contribute to improving decision making on the use of public funds in agriculture. Methodologically, the study simulates the required agricultural investment and required agricultural growth rate that is sufficient to meet MDG1 by 2025 by employing partial equilibrium modeling based on the System Dynamics Analyses approach. This entailed the application of growth decomposition technique and growth elasticity of poverty concepts with a specific emphasis on policy interventions for promoting agricultural growth. The drivers and cause-effect relationships between agriculture and poverty reduction were investigated. The employed models allowed for an exploration of plausible future growth in public spending in agriculture, agricultural growth elasticity of poverty, and the possibility of reducing poverty levels in the province while evaluating strategies for meeting the MDG1 by 2025. Estimates for the required agricultural growth rate and the increase in public spending on agriculture required in order to reach MDG1 by 2025 were calculated for each district municipality in the Eastern Cape Province. All the district municipalities were then evaluated in terms of their need to increase public investment in agriculture and the ability to achieve MDG1 by 2025 and beyond. Estimates for both the required public spending and the required agricultural growth were then calculated following both the business-as-usual scenario and the best-case scenario.
The effect of the structure of a complex network on the properties of avalanche dynamical process on it has been analyzed for the first time. It has been shown that the assortativity ...(disassortativity) degree, which is a structure characteristic of the network and is numerically characterized by the assortativity coefficient
r
, is a control parameter governing the properties of the dynamical process on the network. The structure of individual avalanches on networks with various
r
values has been studied. It has been shown that the number of nodes involved in an avalanche is a periodic function of the time.
The effect of the structure of a complex network on the properties of an avalanche dynamical process on it has been studied. It has been found that such a structural characteristic of the network as ...the degree of its assortativity (disassortativity), which is numerically expressed by the assortativity coefficient
r
, is a control parameter determining the properties of the dynamical process on the network.
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