131,327 research outputs found
Improved fallows in Eastern Zambia: history, farmer practice and impacts
No full text"The decline in soil fertility in smallholder systems is a major factor inhibiting equitable development in much of sub-Saharan Africa. Some areas fallow in order to strength soil fertility for later planting, but as populations increase, demand follows and continuous cropping becomes the norm and there is a reduction in yields. This case study summarizes the development of improved tree fallows by researchers and farmers in eastern Zambia to help solve the problem of poor soil fertility. Many farmers are finding that by using improved fallows, they can substitute relatively small amounts of land and labor for cash, which they would need to buy mineral fertilizer. The study has three phases: the historical background (phase 1); an assessment of problems, description of the technology, and how it was developed (phase 2); and how the improved fallows practices were disseminated and spread (phase 3). This paper will describe each phase, the goals, and results." Authors' AbstractSouthern Africa, africa south of sahara, Crop yields,
Thinking Making and Living Architecture in an Ageing Society
No full textAgeing society anew demographic structure, has emerged in contemporary society which is driving the adoption of societal policies that focus on active ageing. This change is not inclusive to all groups of older adults, such as people with dementia, not being inclusive can lead to segregation and stigmatisation.. Inclusion both social and economic positively impacts on older-adults’ mental and physical wellbeing. Taking this into consideration and being aware of an increasing amount of publications on design philosophies that promote inclusion; the aim of this paper is to describe and formalize the three phases of an inclusive design process: the thinking, making, and living of architecture. In addition, this paper will outline a robust methodology based on these phases. This methodology will be used as a 'tool' for the analysis of existing architectural urban models over a three year study period. The intended outcome of this study will be to provide a comprehensive theory on these models can promote social and economic inclusion for older adults
Developments in the use of EISCAT for interplanetary scintillation
No full textThe antennas of EISCAT have been used for interplanetary scintillation (IPS) studies of the solar wind for many years. The main science found from these studies is obtained through the cross-correlation of signals from antennas having the longest baseline, providing more accurate information on the different solar wind streams which may be present in the line of sight. The development of dual-frequency IPS observations between the 1.4 GHz receivers at the remote sites and Tromso, has allowed the use of the EISCAT Svalbard Radar for IPS, increasing the available baselines to the extent that three solar wind streams can sometimes be identified in the cross-correlation functions. A weak-scattering model incorporating three possible solar wind streams and dual observing frequencies is discussed and some results presented. A recent study found that the current sampling bandwidth limits the sensitivity of IPS observations at EISCAT. Methods of increasing the sensitivity, and the results of trials, are discussed
Factors influencing adoption of agroforestry among smallholder farmers in Zambia
No full textAgroforestry technologies have been extensively researched and introduced to smallholder farmers in Zambia for over two decades. Despite the research and extension effort over this period, not many farmers have adopted these technologies. The purpose of this paper is to determine why agroforestry technologies are not being taken up by examining factors that influence the adoption of agroforestry practices. Based on data obtained from 388 farming households, statistical analysis show an association between adoption of both improved fallows and biomass transfer technologies with knowledge of the technology, availability of seed, and having the appropriate skills. In addition some household characteristics are found to be linked to the incidence of adoption. However, the strength of association between these variables is low, giving an indication that there might be other factors at play limiting agroforestry adoption. It is anticipated that these findings will point to other areas beyond the household and community level that need further exploration in order to understand factors limiting agroforestry adoption.Agroforestry adoption, smallholder farmers, limitations to adoption, chi-square tests of independence analysis, Zambia, Agricultural and Food Policy, Community/Rural/Urban Development, Crop Production/Industries, Environmental Economics and Policy, Land Economics/Use,
An evaluation of exciterless topologies for medium power wound-field synchronous generators
No full textThe wound field synchronous machine has widespread use both as a motor and a generator, due to its low cost, wide power range and its consolidated history built over decades of operation. A critical aspect of these machines is the method of excitation to the field winding. Typically, the choice is between a static excitation system using slip-rings and a rotating excitation system using a brushless exciter. An alternative is that of removing the classical exciter completely and thus feed the field winding through more advanced 'exciterless' solution. The potential to reduce component count and improve power density has resulted in increasing interest in exciterless solutions, over the last couple of decades. This paper thus gives an overview of these methods, assessing and comparing their advantages and disadvantages. A particular focus is on medium power applications, which traditionally have dominated the market of synchronous generators and associated generating sets, and where significant improvements in terms of cost minimisation, power quality, and ease of design are always required
Simultaneous interplanetary scintillation and Heliospheric Imager observations of a coronal mass ejection
No full textWe describe simultaneous Interplanetary Scintillation (IPS) and STEREO Heliospheric Imager (HI) observations of a coronal mass ejection (CME) on 16 May 2007. Strong CME signatures were present throughout the IPS observation. The IPS raypath lay within the field-of-view of HI-1 on STEREO-A and comparison of the observations shows that the IPS measurements came from a region within a faint CME front observed by HI-1A. This front may represent the merging of two converging CMEs. Plane-of-sky velocity estimates based on time-height plots of the two converging CME structures were 325 kms?1 and 550 kms?1 for the leading and trailing fronts respectively. The plane-of-sky velocities determined from IPS ranged from 420 ± 10 kms?1 to 520 ± 20 kms?1. IPS results reveal the presence of micro-structure within the CME front which may represent interaction between the two separate CME events. This is the first time that it has been possible to interpret IPS observations of small-scale structure within an interplanetary CME in terms of the global structure of the event
Harmonic reduction methods for electrical generation: a review
No full textThis paper provides a comprehensive literature review of techniques for harmonic related power quality improvement of electrical generation systems. An increasing interest in these aspects is due to the ever more stringent power quality requirements, deriving from new grid codes and compliancy standards, aimed at limiting waveform harmonic distortion at all points of the distribution network. Although a wealth of literature is available for such techniques, it has never been compiled into a handbook incorporating all the solutions aimed at both electrical machine and power systems engineers
Power quality improvement by pre-computed modulated field current for synchronous generators
No full textAlthough power quality aspects of electrical machines have been extensively studied and investigated for a large number of years, room for improvement still exists in the field of classic, wound-field, synchronous generators. This paper proposes an innovative method of power quality improvement for single-phase synchronous generators in which the usual DC field current is replaced by a calculated current waveform. The optimised field current waveform is designed in such a way that harmonics created by the machine geometry and the winding configuration are significantly reduced
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