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Search Results: 1 - 10 of 140578 matches for " Torbjorn K. Nielsen "
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Hydropower in the Context of Sustainable Energy Supply: A Review of Technologies and Challenges
Chiyembekezo S. Kaunda,Cuthbert Z. Kimambo,Torbjorn K. Nielsen
ISRN Renewable Energy , 2012, DOI: 10.5402/2012/730631
Abstract:
Potential of Small-Scale Hydropower for Electricity Generation in Sub-Saharan Africa
Chiyembekezo S. Kaunda,Cuthbert Z. Kimambo,Torbjorn K. Nielsen
ISRN Renewable Energy , 2012, DOI: 10.5402/2012/132606
Abstract:
Hydropower in the Context of Sustainable Energy Supply: A Review of Technologies and Challenges
Chiyembekezo S. Kaunda,Cuthbert Z. Kimambo,Torbjorn K. Nielsen
ISRN Renewable Energy , 2012, DOI: 10.5402/2012/730631
Abstract: Hydropower is an important renewable energy resource worldwide. However, its development is accompanied with environmental and social drawbacks. Issues of degradation of the environment and climate change can negatively impact hydropower generation. A sustainable hydropower project is possible, but needs proper planning and careful system design to manage the challenges. Well-planned hydropower projects can contribute to supply sustainable energy. An up-to-date knowledge is necessary for energy planners, investors, and other stakeholders to make informed decisions concerning hydropower projects. This is basically a review paper. Apart from using expert knowledge, the authors have also consulted extensively from journals, conference papers, reports, and some documents to get secondary information on the subject. The paper has reviewed the world energy scenario and how hydropower fits in as the solution to the global sustainable energy challenge. Issues of hydropower resource availability, technology, environment and climate change have been also discussed. Hydropower is sensitive to the state of environment, and climate change. With global climate change, though globally the potential is stated to slightly increase, some countries will experience a decrease in potential with increased risks. Adaptation measures are required to sustainably generate hydropower. These are also discussed in the paper. 1. Introduction 1.1. World Energy Scenario and Sustainable Energy In this era, concerns about environment and climate change management influence choices investors and international financing institutions make concerning energy projects [1]. The word “environment” can be defined in many ways depending on the discipline; but it is broadly understood to refer to surroundings that interact with life on earth. The surroundings can be divided into nonliving and living components. The important point concerning environment, according to Gorshkov and Makarieva [2], is that it provides resources, such as energy, that support life on earth. Since energy is sourced and processed into a usable form from the environment, activities pertaining to its extraction, transportation, conversion, and utilisation impact the environmental system. The impacts are pronounced in thermal energy systems. For fossil fuel energy systems, it is also not possible to totally avoid emissions and environmental setbacks because of combustion. During the combustion process, energy is converted from chemical into heat and the gaseous products of combustion are ejected from the system at a higher
Potential of Small-Scale Hydropower for Electricity Generation in Sub-Saharan Africa
Chiyembekezo S. Kaunda,Cuthbert Z. Kimambo,Torbjorn K. Nielsen
ISRN Renewable Energy , 2012, DOI: 10.5402/2012/132606
Abstract: The importance of renewable energy such as small hydropower for sustainable power generation in relation to its capacity to contribute towards alleviating acute shortage of rural electricity supply in the sub-Saharan African region has been discussed. A relatively comprehensive small hydropower technology review has been presented. Rural electricity supply scenario in the region has been presented and, in general, the region has very low electricity access levels coupled with various challenges. Small hydropower technology has been discussed as one of the promising decentralised power generation system for rural electricity supply in the region. Despite challenges in data acquisition, this paper has shown that the SSA has significant hydropower resources, but the level of installation is very low. Challenges hampering SHP technology development in the region have been identified and discussed, such as those concerning technology, climate change, finance, and policy. This is basically a paper where the authors consulted a wide range of literature including journals, conference proceedings, and reports as well as expert knowledge in the area. It is hoped that this paper contributes to the information base on SHP technology which is quite lacking in the region. 1. Introduction Sustainable electricity supply not only supports social and economic development processes but also environmental and global climate change management and hence its importance in attainment of the Millennium Development Goals. Currently, there is an increasing electricity demand in industry, household, and services sectors in developing countries to support social-economic development activities. If this electricity is generated unsustainably and the trend is not controlled, it could lead to exacerbation of environmental and climate change management problems which the world is currently experiencing. The energy supply sector (mainly for generation of electricity), according to the Intergovernmental Panel on Climate Change (IPCC), is the largest contributor to the global human-induced greenhouse gas (GHG) emissions (responsible for global warming—main cause of climate change); in 2004, energy supply sector contributed to around 26% of global GHG emissions, followed by forestry (17%), agriculture (13%), and transport (13%) [1]. Developing countries, especially those from sub-Saharan African (SSA) countries (sub-Saharan Africa as a geographical term refers to the area of the continent of Africa that lies south of the Sahara. The countries in the sub-Saharan African region are Angola,
Explicit construction of constrained instantons
Morten Nielsen,N. K. Nielsen
Physics , 1999, DOI: 10.1103/PhysRevD.61.105020
Abstract: Instantons in massless theories do not carry over to massive theories due to Derrick's theorem. This theorem can, however, be circumvented, if a constraint that restricts the scale of the instanton is imposed on the theory. Constrained instantons are considered in four dimensions in phi^4 theory and SU(2) Yang-Mills-Higgs theory. In each of these theories a calculational sceme is set up and solved in the lowest few orders in the mass parameter in such a way that the need for a constraint is exhibited clearly. Constrained instantons are shown to exist as finite action solutions of the field equations with exponential fall off only for specific constraints that are unique in lowest order in the mass parameter in question.
Alternative approaches to the Casalbuoni-Brink-Schwarz Superparticle
Morten Nielsen,N. K. Nielsen
Physics , 2000, DOI: 10.1006/aphy.2000.6083
Abstract: Wigner's method of induced representations is applied to the N=1 super-Poincare group, and by using a state corresponding to the basic vector of the little group as a Clifford vacuum we show that the spin operator of a supersymmetric point particle obeys Wigner's constraints. As dynamical variables for the particle we use canonical coordinates on the symmetry group manifold. The physical phase space is then constructed using a vielbein formalism. We find that the Casalbuoni-Brink-Schwarz superparticle appears as a special case of our general construction. Finally, the theory is reformulated as a gauge theory where the gauge freedom corresponds to the choice of spin constraints or, equivalently, the free choice of relativistic center of mass. In a special case the gauge symmetry reduces to the well known kappa-symmetry.
Positive attitudes towards priority setting in clinical guidelines among Danish general practitioners: A web based survey  [PDF]
Ann Nielsen, Benedicte Carlsen, Pia K. Kjellberg
Health (Health) , 2013, DOI: 10.4236/health.2013.52026
Abstract:

Aims: Increasing focus on improvement and optimisation of the treatment in primary care and reduction of healthcare costs emphasize the need to understand which factors determines adherence and non-adherence to clinical guidelines. In the present study, we examined attitudes towards clinical guidelines in Danish general practitioners (GPs). Methods: We conducted a survey among Danish GPs from all five regions of Denmark. In total, 443 GPs answered the web-based questionnaire that contained questions about attitudes and barriers to clinical guidelines. Results: More than 90% of the GPs reported that they have good knowledge of the guidelines and in general follows the guidelines. A majority of the GPs (81%) found it acceptable that economic considerations are part of the guidelines. The most important factors for non- adherence to guidelines were “need of adjustment to clinical practice” and “lack of confidence in guidelines”. The attitudes to clinical guidelines were not significantly associated with practice characteristics such as gender, years of experience, practice organisation and localisation. Conclusions: Our findings show that clinical guidelines are an integrated or internalised part of everyday practice among GPs in Denmark. Furthermore, the findings indicate that Danish GPs are positive towards applying priority setting in their practice. This is decisive in the light of rising healthcare costs due to development of new expensive technologies and ageing populations that puts pressure on the healthcare system in general and primary healthcare in particular.

Corn and Soybean Responses to Two Tillage Systems in a Cool Growing Season  [PDF]
Jesper K. V. Nielsen, Howard J. Woodard
Open Journal of Soil Science (OJSS) , 2015, DOI: 10.4236/ojss.2015.58016
Abstract: A field study in 2014 documented corn and soybean biomass and nutrient responses between conventional-till and no-till tillage systems at Beresford, SD during cooler than normal weather conditions with adequate soil moisture. The overall study was established in 1992. Each treatment plot was monitored weekly from June to August for soil moisture, temperature, and plant growth stages. Biomass was harvested during and at the end of the growing season for yield and nutrient content. Soil moisture measured throughout the early and middle part of the growing season was determined to be sufficient for crop growth, since precipitation was much greater than normal in June (33.2 cm). However, air temperature was below normal early in the growing season and lowered Growing Degree Days (939°C) compared to the 30-year average (139°C). Soil temperatures (5 cm depth) were not significant between tillage treatments in the corn plots during the growing season for 12 observation dates (range 16.3°C - 28.0°C). Plant growth was not significantly different between tillage treatments, reflecting the lack of soil temperature differences (5 cm depth) between tillage treatments. The mid-season plant tissue and crop residue at harvest nutrient content (P, K, and Zn) were not significant between tillage treatments. Corn grain yields were 10.3 T·ha-1 and 10.1 T·ha-1 for conventional tillage and no-till, respectively. Soybean grain yields were 3.9 T·ha-1?and 3.3 T·ha-1 for conventional tillage and no-till, respectively. These results would more than likely have been
PYTHIA 5.7 and JETSET 7.4 Physics and Manual
Torbjorn Sjostrand
Physics , 1995,
Abstract: This is the latest edition of the physics description and manual of the PYTHIA and JETSET programs for event generation in High Energy Physics.
QCD Physics Lessons of Z0 Decay
Torbjorn Sjostrand
Physics , 1995,
Abstract: This talk contains a subjective selection of interesting results on Z$^0$ decays, presented by the LEP and SLC groups. The emphasis is on soft and semihard QCD physics. Results are put in a theoretical context, and the limits of our current understanding are stressed. Topics covered include event measures, prompt photons, coherence and string effects, data and theory for particle rates and spectra, particle correlations and Bose--Einstein effects.
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