Structural adjustment and the contemporary sub-Saharan African city

Although it has been suggested that structural adjustment policies have slowed Third World urban growth and have stimulated a spatial deconcentration of economic activity, this paper argues that African cities continue to grow and mainly through peri-urban development. This investment comes mainly from domestic sources and migrants' remittances, and tends to he in consumption rather than production. Reasons include cultural factors lack of confidence in the national economy and in the state's long-term economic objectives, an increasing demand for housing, improvements in intraurban transport, and a desire to spread investment risk among a range of alternatives including housing

Rare earth geochemistry of Arenig cherts from the Ballantrae Ophiolite and Leadhills Imbricate Zone, southern Scotland: implications for origin and significance to the Caledonian Orongeny

Rare earth element (REE) data from low to mid-Arenig cherts are used to test competing models for the early Ordovician evolution of the Laurentian margin in the northern British Isles. Cherts from the Ballantrae Ophiolite Complex have chondrite-normalized REE patterns typical of continental margin settings with LREE enrichment, a slight negative Eu(anom) and shale and chondrite-normalized La/Yb values of 0.97-1.41 and 7.78-11.4 respectively. This pattern, together with a large positive chondrite-normalized Ce(anom) (1.44-1.70), is virtually identical to that found in radiolarian chert of the Gascoyne Abyssal Plain, in the Timor Sea. Cherts from the Raven Gill Formation within the Leadhills Imbricate Zone, Northern Belt, Southern Uplands have typical continental margin REE patterns, chondrite-normalized Ce(anom) (0.9-1.21) and Eu(anom) (0.61-0.79) values indicating that they formed closer to the continental margin than those from Ballantrae. Shale and chondrite-normalized and La/Yb values of 0.95-1.27 and 4.92-13.88 respectively confirm this interpretation. It is concluded that the Ballantrae ophiolite formed in a rifted-arc basin above a northwards dipping, intra-oceanic subduction zone. The modest depth of burial of the Raven Gill Formation precludes it being part of a marginal basin which was subsequently trapped as the Ballantrae Ophiolite was obducted in the late Arenig. The Arenig rocks of the Leadhills Imbricate Zone represent an allochthonous terrane accreted to the western extension of the Midland Valley in Ireland in pre-Caradoc times. Here it formed the basement to the Southern Uplands basin. Palaeontological evidence places this basin adjacent to Pomeroy, Co. Tyrone in the early Caradoc. Sinistral strike-slip faulting, from the late Ashgill transported the Southern Uplands Terrance to its present location, a distance of less than 250 km

Early maternal experience shapes offspring performance in the wild

Both the environments experienced by a mother as a juvenile and an adult can affect her investment in offspring. However, the implications of these maternal legacies, both juvenile and adult, for offspring fitness in natural populations are unclear. We investigated whether the juvenile growth rate and adult reproductive traits (length, body condition, and reproductive investment at spawning) of female wild Atlantic salmon (Salmo salar) were related to the growth and survival of their offspring. Adult salmon captured on their upstream migration were used to create experimental full-sib clutches of eggs, which were mixed and then placed in artificial nests in a natural stream that lacked salmon due to a migration barrier. Four months later we resampled the stream to obtain family-level estimates of offspring size and survival. Mothers that had grown slowly as juveniles (as determined by scalimetry) but had invested heavily in reproduction (egg production for a given body length) and were in relatively poor body condition (somatic mass for a given body length) at spawning produced the largest eggs. Larger eggs resulted in larger juveniles and higher juvenile survival. However, after controlling for egg size, offspring growth was positively related to maternal juvenile growth rate and reproductive investment. The predictors of offspring survival (i.e., reproductive success) varied with the juvenile growth rate of the mother: If females grew slowly as juveniles, their reproductive success was negatively related to their own body condition. In contrast, the reproductive success of females that grew quickly as juveniles was instead related positively to their own body condition. Our results show that maternal influences on offspring in the wild can be complex, with reproductive success related to the early life performance of the mother, as well as her state at the time of breeding

Evaluation of the Effects of Point and Nonpoint Source Phosphorus Loads Upon Water Quality in the Highland Lakes

Texas Department of Water Resources Interagency Cooperation Contract IAC (84-85)-0896Center for Water and the Environmen

Interactions between parental traits, environmental harshness and growth rate in determining telomere length in wild juvenile salmon

A larger body size confers many benefits, such as increased reproductive success, ability to evade predators and increased competitive ability and social status. However, individuals rarely maximise their growth rates, suggesting that this carries costs. One such cost could be faster attrition of the telomeres that cap the ends of eukaryotic chromosomes and play an important role in chromosome protection. A relatively short telomere length is indicative of poor biological state, including poorer tissue and organ performance, reduced potential longevity and increased disease susceptibility. Telomere loss during growth may also be accelerated by environmental factors, but these have rarely been subjected to experimental manipulation in the natural environment. Using a wild system involving experimental manipulations of juvenile Atlantic salmon Salmo salar in Scottish streams, we found that telomere length in juvenile fish was influenced by parental traits and by direct environmental effects. We found that faster-growing fish had shorter telomeres and there was a greater cost (in terms of reduced telomere length) if the growth occurred in a harsher environment. We also found a positive association between offspring telomere length and the growth history of their fathers (but not mothers), represented by the number of years fathers had spent at sea. This suggests that there may be long term consequences of growth conditions and parental life history for individual longevity

Photoionization of H₂ using the molecular R-matrix with time approach

We present results of the first calculations using the variational ab initio molecular R-matrix with time approach. We have calculated two and four-photon ionization cross sections for H2 and studied the effects of electron correlation and choice of the Gaussian atomic basis sets. Our results are compared with earlier calculations

Ab initio many-body calculations on infinite carbon and boron-nitrogen chains

In this paper we report first-principles calculations on the ground-state electronic structure of two infinite one-dimensional systems: (a) a chain of carbon atoms and (b) a chain of alternating boron and nitrogen atoms. Meanfield results were obtained using the restricted Hartree-Fock approach, while the many-body effects were taken into account by second-order M{\o}ller-Plesset perturbation theory and the coupled-cluster approach. The calculations were performed using 6-31$G^{**}$ basis sets, including the d-type polarization functions. Both at the Hartree-Fock (HF) and the correlated levels we find that the infinite carbon chain exhibits bond alternation with alternating single and triple bonds, while the boron-nitrogen chain exhibits equidistant bonds. In addition, we also performed density-functional-theory-based local density approximation (LDA) calculations on the infinite carbon chain using the same basis set. Our LDA results, in contradiction to our HF and correlated results, predict a very small bond alternation. Based upon our LDA results for the carbon chain, which are in agreement with an earlier LDA calculation calculation [ E.J. Bylaska, J.H. Weare, and R. Kawai, Phys. Rev. B 58, R7488 (1998).], we conclude that the LDA significantly underestimates Peierls distortion. This emphasizes that the inclusion of many-particle effects is very important for the correct description of Peierls distortion in one-dimensional systems.Comment: 3 figures (included). To appear in Phys. Rev.

Atomic and molecular suite of R-matrix codes for ultrafast dynamics in strong laser fields and electron/positron scattering

Synopsis: We describe and illustrate a number of recent developments of the atomic and molecular ab initio R-matrix suites for both time-dependent calculations of ultrafast laser-induced dynamics and time-independent calculations of photoionization and electron scattering

Atomic and molecular suite of R-matrix codes for ultrafast dynamics in strong laser fields and electron/positron scattering

We describe and illustrate a number of recent developments of the atomic and molecular ab initio R-matrix suites for both time-dependent calculations of ultrafast laser-induced dynamics and time-independentcalculations of photoionization and electron scattering. © 2019 Published under licence by IOP Publishing Ltd

Self-optimization, community stability, and fluctuations in two individual-based models of biological coevolution

We compare and contrast the long-time dynamical properties of two individual-based models of biological coevolution. Selection occurs via multispecies, stochastic population dynamics with reproduction probabilities that depend nonlinearly on the population densities of all species resident in the community. New species are introduced through mutation. Both models are amenable to exact linear stability analysis, and we compare the analytic results with large-scale kinetic Monte Carlo simulations, obtaining the population size as a function of an average interspecies interaction strength. Over time, the models self-optimize through mutation and selection to approximately maximize a community fitness function, subject only to constraints internal to the particular model. If the interspecies interactions are randomly distributed on an interval including positive values, the system evolves toward self-sustaining, mutualistic communities. In contrast, for the predator-prey case the matrix of interactions is antisymmetric, and a nonzero population size must be sustained by an external resource. Time series of the diversity and population size for both models show approximate 1/f noise and power-law distributions for the lifetimes of communities and species. For the mutualistic model, these two lifetime distributions have the same exponent, while their exponents are different for the predator-prey model. The difference is probably due to greater resilience toward mass extinctions in the food-web like communities produced by the predator-prey model.Comment: 26 pages, 12 figures. Discussion of early-time dynamics added. J. Math. Biol., in pres