African Land Ecology: Opportunities and Constraints for Agricultural Development

Current agriculture in Sub-Sahara Africa is undeveloped and the Green Revolution has left the continent largely untouched. Poor performance is often related to a number of socio-economic factors. In this paper we argue that there are also some specifities of natural resources, namely local homogeneity and spatial diversity of the pre-dominant Basement Complex soils, that imply that simple fertilizer strategies may not produce the yield increases obtained elsewhere. Keywords: Sub-Sahara Africa, Agro-Ecology, Land use, Land resources, Basement Complex, Green Revolution, Micronutrients, Fertilizer Policy

Analysis of distortion in pulse modulation converters for switching radio frequency power amplifiers

High-efficiency linear radio frequency (RF) power amplifiers are needed for today’s wireless communication systems. Switch mode techniques have the potential for high efficiency but require a pulse drive signal. The generation of pulse width modulated signals and pulse position modulated signals by sigma delta modulators can introduce unwanted spectral components. Third order and image components are the dominant distortions generated in the pulse position modulation circuit. The authors identify the cause of distortion and mathematically quantify its amplitude and frequency. In a single carrier environment, an increase in offset frequency increases the unwanted spectral components. Calculations, simulations and measurements show that offsets less than 1% of the carrier frequency are required to keep unwanted components 40 dB below the signal level. Simulations and measurements show that the effect on a multichannel orthogonal frequency division multiplexing (OFDM) system is less detrimental. Nonetheless, unacceptable noise increases of up to 20 dB are observed in odd harmonic channels when the transmission is not centred on the nominal carrier frequency

Food photographs in nutritional surveillance: errors in portion size estimation using drawings of bread and photographs of margarine and beverages consumption

Food photographs are widely used as instruments to estimate portion sizes of consumed foods. Several food atlases are available, all developed to be used in a specific context and for a given study population. Frequently, food photographs are adopted for use in other studies with a different context or another study population. In the present study, errors in portion size estimation of bread, margarine on bread and beverages by two-dimensional models used in the context of a Belgian food consumption survey are investigated. A sample of 111 men and women (age 45–65 years) were invited for breakfast; two test groups were created. One group was asked to estimate portion sizes of consumed foods using photographs 1–2 d after consumption, and a second group was asked the same after 4 d. Also, real-time assessment of portion sizes using photographs was performed. At the group level, large overestimation of margarine, acceptable underestimation of bread and only small estimation errors for beverages were found. Women tended to have smaller estimation errors for bread and margarine compared with men, while the opposite was found for beverages. Surprisingly, no major difference in estimation error was found after 4 d compared with 1–2 d. Individual estimation errors were large for all foods. The results from the present study suggest that the use of food photographs for portion size estimation of bread and beverages is acceptable for use in nutrition surveys. For photographs of margarine on bread, further validation using smaller amounts corresponding to actual consumption is recommended

Late Holocene landscape instability in the Breckland (England) drift sands

This research investigates the landscape instability associated with the drift sands, which are widespread across north-western Europe. It focuses on Breckland, UK using new sites along with existing geomorphic, archaeological and historical data. This shows landscape instability of drift sands occurred at 5240 ± 1040 years BCE, 600 ± 100, 1150 ± 50, 1600 and ~1790 CE. Comparison of these phases to climate records show no clear patterns with drifting occurring during dry/wet as well as cold/warm periods. Additionally, similar climatic shifts lead to diverging reactions of landscapes in different regions throughout Europe. At the regional scale, land usage and population pressures also may not be the direct cause of sand drifting, suggesting that complex responses or different triggers at different times were responsible. Within this, society's unawareness of the inherent landscape instability and the threat posed by the sand hazard may have been important as it affected whether mitigation measures were or could be implemented. In Breckland, initial instability may have been due to the establishment of the open field system on virgin soil. Later changes in land ownership and associated power within the society, led to an inability of communities to implement mitigation measures and large land owners abstaining from tackling the sand hazard. Whilst the widespread coversands and climatic extremes provide the underlying susceptibility to sand drifting, it would appear that drift sands of the last 2000 years may provide less of a sedimentary archive of Late Holocene climatic changes and more a record of land management changes

Adult Pelvic Sarcomas: A Heterogeneous Collection of Sarcomas?

Introduction. Adult pelvic soft tissue sarcomas are a rare group of heterogeneous malignancies. These sarcomas differ from extremity and trunk soft tissue sarcomas in presentation, characteristics and response to treatment

Complete mitochondrial genomes and updated divergence time of the two freshwater clupeids endemic to Lake Tanganyika (Africa) suggest intralacustrine speciation

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