The political economy of power generation in Zimbabwe since 1980

This article presents a historical analysis of the power generation choices in Zimbabwe since independence in 1980; their causes and consequences. In the early 1980s, the electricity supply choices of the country were dictated by a policy of self-sufficiency, and least-cost supply options (e.g. imports and hydropower) were rejected at a not negligible economic cost. At the end of the 1980s, a new political environment and pressures from the World Bank prompted substantial changes towards least-cost alternatives. In the early 1990s, security of supply motives still played an important role and financial constraints were severe. At present, however, there is little evidence that imported power is still as cheap a source of electricity as it was about 15 years ago. This situation together with the ongoing trend towards higher discount rates imply that thermal power, in particular coal-fired power, will dominate future electricity supply investments in Zimbabwe.     

Effects of aircraft noise and speech on prose memory: What role for working memory capacity?

Previous research indicates that aircraft noise and meaningful background speech are particularly detrimental to school adolescents' ability to remember what they read, but until now the effects from aircraft noise and speech have never been compared directly in an experiment. Furthermore, individual differences in susceptibility to these effects are not well understood. The present investigation addressed these two issues. Adolescents attending upper secondary school were recruited as participants and the data collection was made in their ordinary classrooms. The results from two experiments revealed that speech is more detrimental to prose memory than is aircraft noise, and individual differences in working memory capacity contributes more to individual differences in susceptibility to the effects of aircraft noise on prose memory than to the effects of speech. Some applied implications of those findings to noise abatement interventions are suggested.     

The adsorption of short single-stranded DNA oligomers to mineral surfaces

We studied the adsorption of short single-stranded deoxyribonucleic acid (ssDNA) oligomers, of approximately 30 nucleotides (nt) in length, of varying sequence, adenine + guanine + cytosine (AGC) content, and propensity to form secondary structure, to equal surface area samples of olivine, pyrite, calcite, hematite, and rutile in 0.1 M NaCl, 0.05 M pH 8.1 KHCO₃ buffer. Although the mineral surfaces have widely varying points of zero charge, under these conditions they show remarkably similar adsorption of ssDNA regardless of oligomer characteristics. Mineral surfaces appear to accommodate ssDNA comparably, or ssDNA oligomers of this length are able to find binding sites of comparable strength and density due to their flexibility, despite the disparate surface properties of the different minerals. This may partially be due charge shielding by the ionic strength of the solutions tested, which are typical of many natural environments. These results may have some bearing on the adsorption and accumulation of biologically derived nucleic acids in sediments as well as the abiotic synthesis of nucleic acids before the origin of life.     

The constitutively active Ah receptor (CA-AhR) mouse as a model for dioxin exposure - effects in reproductive organs

The dioxin/aryl hydrocarbon receptor (AhR) mediates most toxic effects of dioxins. In utero/lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) impairs fetal/neonatal development and the developing male reproductive tract are among the most sensitive tissues. TCDD causes antiestrogenic responses in rodent mammary gland and uterus and in human breast cancer cell lines in the presence of estrogen. Also, more recently an estrogen-like effect of TCDD/AhR has been suggested in the absence of estrogen. A transgenic mouse expressing a constitutively active AhR (CA-AhR) was developed as a model mimicking a situation of constant exposure to AhR agonists. Male and female reproductive tissues of CA-AhR mice were characterized for some of the effects commonly seen after dioxin exposure. Sexually mature CA-AhR female mice showed decreased uterus weight, while an uterotrophic assay in immature CA-AhR mice resulted in increased uterus weight. In immature mice, both TCDD-exposure and CA-AhR increased the expression of the estrogen receptor target gene Cathepsin D. When co-treated with 17β-estradiol no increase in Cathepsin D levels occurred in either TCDD-exposed or CA-AhR mice. In sexually mature male CA-AhR mice the weights of testis and ventral prostate were decreased and the epididymal sperm reserve was reduced. The results of the present study are in accordance with previous studies on dioxin-exposed rodents in that an activated AhR (here CA-AhR) leads to antiestrogenic effects in the presence of estrogen, but to estrogenic effects in the absence of estrogen. These results suggest the CA-AhR mouse model as a useful tool for studies of continuous low activity of the AhR from early development, resembling the human exposure situation.     

Declining coastal piscivore populations in the Baltic Sea: Where and when do sticklebacks matter?

Intraguild predation interactions make fish communities prone to exhibit alternative stable states with either piscivore or prey fish dominance. In the Baltic Sea, local declines of coastal piscivores like perch (Perca fluviatilis) have been observed to coincide with high densities of sticklebacks (Gasterosteus aculeatus). Mechanisms behind this shift between piscivore and stickleback dominance were studied both experimentally and in field. Results showed that predation by sticklebacks has a strong negative effect on perch larvae survival, but this effect rapidly decreases with increasing perch size, likely due to gape limitations and digestion constraints in sticklebacks. Large spatial and temporal variations in patterns of stickleback migration into perch spawning sites were observed. Whether or not high density of sticklebacks will cause declines in coastal piscivore populations is suggested to depend on the availability of spawning sites in which sticklebacks do not migrate into or arrive late in the reproduction season of coastal piscivores.     

Occurrence and sorption properties of arsenicals in marine sediments

The content of total arsenic, the inorganic forms: arsenite (As(III)) and arsenate (As(V)), the methylated forms: monomethylarsonic acid and dimethylarsinic acid (DMA), trimethylarsenic oxide, tetramethylarsenonium ion and arsenobetaine was measured in 95 sediment samples and 11 pore water samples from the Baltic Sea near the island of Bornholm at depths of up to 100 m. As(III+V) and DMA were detected in the sediment and As(III+V) was detected in the sediment pore water. Average total As concentration of 10.6?±?7.4 mg/kg dry matter (DM) in the sediment corresponds to previously reported values in the Baltic Sea and other parts of the world. Existing data for on-site measurements of sorption coefficients (Kd) of arsenicals in marine and freshwater sediments show large variability from <1 to >1,000 L/kg. In this work, calculated sorption coefficients (Kd and Koc) for As(III+V) showed significant correlation with depth, dissolved oxygen (DO), salinity and sediment classification; for depths <70 m, salinity <11 %, DO >9 mg/L and sand/silt/clay sediments the Kd was 118?±?76 L/kg DM and for depths >70 m, salinity >11 %, DO?<?9 mg/L and muddy sediments the Kd was 513?±?233 L/kg DM. The authors recommend using the found Kd value for arsenic in marine sediments when conditions are similar to the Baltic Sea. At locations with significant anthropogenic point sources or where the local geology contains volcanic rock and sulphide mineral deposits, there may be significantly elevated arsenic concentrations, and it is recommended to determine on-site Kd values.     

Levels and possible sources of PCDD/PCDF in sediment and pike samples from Swedish lakes and rivers. (Part one)

One goal of the Swedish survey project is to discover possible sources of PCDD/F. Bottom sediment and pike were sampled at various sites near different types of industries along the coast line of two lakes and one river. The results show background levels of PCDD/F in some lakes which can only be explained by atmospheric input. In some lakes paper mill emissions of chlorinated PCDD/F give high levels of local contamination (≈1 ng/g IG) within short distances (<1 km) from the source. PCDD/F from paper mill effluents are transported long distances and traces can be detected over the entire lake area. The PCDD/F levels in pike are correlated with levels in the underlying sediment.     

评价农场尺度上养分和微量元素动态变化的一个系统方法:以(O)jebyn奶牛场的研究为例

通过把全面的农田试验和矿质风化释放养分以及微量元素循环具体研究结合起来,用一个系统分析方法来评价农场尺度上的养分和微量元素可持续性.为了比较有机和常规农业管理方式,在瑞典北部的Ojebyn奶牛场进行了一个包括磷、钾和锌在内的农场尺度上的实例研究.通过结合不同的元素平衡法(农场总体尺度、畜舍尺度和农田尺度)以及进一步把这些方法应用到FARMFLOw模型,我们能够把子系统内质量流和库结合起来并建立子系统之间联系,来进行农场尺度上的预测.研究发现农场内部的元素流动大,而且农场有内部源(锌)和损失项(钾).在Ojebyn奶牛场形成并得到验证的方法是很有前途的,认为可以应用到任何农场.     

A systems approach to assess farm-scale nutrient and trace element dynamics: a case study at the Ojebyn dairy farm

A systems analysis approach was used to assess farmscale nutrient and trace element sustainability by combining full-scale field experiments with specific studies of nutrient release from mineral weathering and trace-element cycling. At the Ojebyn dairy farm in northern Sweden, a farm-scale case study including phosphorus (P), potassium (K), and zinc (Zn) was run to compare organic and conventional agricultural management practices. By combining different element-balance approaches (at farmgate, barn, and field scales) and further adapting these to the FARMFLOW model, we were able to combine mass flows and pools within the subsystems and establish links between subsystems in order to make farm-scale predictions. It was found that internal element flows on the farm are large and that there are farm internal sources (Zn) and loss terms (K). The approaches developed and tested at the Ojebyn farm are promising and considered generally adaptable to any farm.