197,815 research outputs found
Spin decoherence and manipulation in quantum dots : the role of the spin-orbit interaction
No full textSolid state based quantum information processing is focused on physical implementation of all necessary elements of quantum computation and quantum information in solid state systems, mainly due to their scalability compared to e.g. optical systems. Among many proposals to realize these types of devices, such as quantum dots as charge qubits or Josephson junction circuits, we study here one of the most promising candidates, i.e., the spin of an electron confined to a quantum dot as a qubit. Experimentally, it has been shown that the relaxation rate of this two level system can be pushed above few seconds in low magnetic fields. Moreover, using spin echo techniques,
the spin dephasing time can be maximized up to milliseconds with the current technology. This long spin decay time is one of the main reasons that make this system desirable for quantum computation and quantum information purposes.
We reexamined the recent measurement based proposal called one-way quantum computation which exploits entanglement and local measurements as tools to perform quantum computation on N qubits. Although it was suggested in the original work to entangle the qubits via the nearest neighbor Ising interaction, we investigated how one can generate the so-called cluster states with the Heisenberg interaction. We extended our method to include more general forms of Heisenberg interaction such as asymmetric coupling of adjacent qubits. These forms of couplings, rather than Ising interaction, are more encountered in solid state devices, and therefore make it possible to perform one-way quantum computation with electron spins in quantum dots coupled via exchange interaction to their adjacent spins.
Chapters II, III, and IV of my thesis are devoted to the study of the spin-orbit interaction in heterostructure quantum dots and its effect on the spin dynamics. We observed that one can actually use spin-orbit interaction to manipulate the spin state of an electron on time scales much smaller than the spin dephasing time. Specifically, in chapter II, we studied the effect of a nearby functioning quantum point contact (QPC) on the relaxation of the electron spin and show that the charge fluctuations in QPC lead to spin relaxation of the confined electron in the presence of spin-orbit interactiom and an applied magnetic field. We also addressed the relation of this rate to the microscopic parameters of the system and found some geometrical dependence of the spin relaxation time on the orientation of the QPC on the substrate. Moreover, we showed in chapters III and IV that the spin-orbit interaction can play a positive role, in order to rotate the spin around the Bloch sphere. We considered different mechanisms, particularly, Electron Dipole Spin Resonance (EDSR) and holonomic unitary gates in quantum dots. We verified that these mechanisms of spin manipulation can be realized in solid state systems with the state of the art semiconductor technologies.
Chapter V of the thesis covers a slightly different topic and focuses on the role of the Coulomb interaction in electronic transport. There, we reviewed the non-analytic corrections to the Fermi liquid behavior and their consequences on the momentum occupation number of the electrons in a two dimensional electron gas (2DEG). As an example, we calculated the tunneling rate from an interacting electron reservoir onto a quantum dot and compared our result to the corresponding case for electron tunneling between bilayer 2DEGs. Moreover, within RPA approximation, we found that the electron-plasmon coupling leads to a quadratic frequency dependence of the electron self-energy at low frequencies at the Fermi surface. This correction suppresses the same order corrections due to the particle-hole bubble
Methane emissions from wastewater management
No full textGreenhouse gas emissions in the form of methane and carbon dioxide are produced when municipal and industrial wastewater and their residual solid by-product (sludge) are handled under or subject to anaerobic conditions, thus contributing to the global warming potential or the greenhouse effect. This paper presents estimation methods used for determining methane emissions from the management of wastewater. Applications for estimating countrywide methane gas emissions from wastewater management are presented with the country of Lebanon as an example. The relative significance of these emissions is assessed in comparison with methane emissions from developing and developed countries. Uncertainty associated with the estimation process and mitigation measures to reduce potential impacts of methane emissions from wastewater management are also discussed.<br/
Particulate matter in urban areas: health based economic assessment
No full textThe interest in the association between human health and air pollution has grown substantially in recent years. Based on epidemiological studies in several countries, there is conclusive evidence of a link between particulate air pollution and adverse health effects. Considering that particulate matter may be the most serious pollutant in urban areas and that pollution-related illness results in financial and non-financial welfare losses, the main objective of this study is to assess the economic benefits of reducing particulate air pollution in Lebanese urban areas. Accordingly, the extent and value of health benefits due to decreasing levels of particulate in the air are predicted. Health impacts are expressed in both physical and monetary terms for saved statistical lives, and productivity due to different types of morbidity endpoints. Finally, the study concludes with a range of policy options available to mitigate particulate air pollution in urban areas.<br/
Effectiveness of wastewater management in rural areas of developing countries: A case of Al-Chouf Caza in Lebanon
No full textAlike many developing countries, Lebanon lacks a national wastewater management strategy that can effectively protect public health and environmental quality. This has led the local communities and municipalities to plan and implement their own arrangements for wastewater treatment systems. However, most municipalities still lack the human and financial resources, management capabilities, and environmental awareness necessary to implement wastewater management in an environmentally sound manner. As such, the effectiveness of these systems, particularly with regard to the quality of the treated effluent, warrants evaluation. Accordingly, a performance evaluation of the treatment-disposal systems, taking three villages in Al-Chouf Caza in Lebanon as a case study, was carried out. The conducted field work, visual assessment, and laboratory analyses of effluent discharges revealed that the existing systems for wastewater treatment in the three villages are either not properly functioning or operational but ineffective and, consequently, hardly achieve any treatment higher than primary. Although developing countries are being encouraged to implement wastewater treatment systems with the promise of financial aid from developed nations, it is important that local conditions are considered carefully to make full use of any aid. It is very crucial to take into account the economic status of the community and the municipality in question. There is no point in adopting the most advanced technology for wastewater treatment if there is no mechanism to ensure maximum efficiency. © 2009 Springer Science+Business Media B.V.APHA-AWWA-WEF, 1998, STAND METH EX WAT WA; Bakir HA, 2001, J ENVIRON MANAGE, V61, P319, DOI 10.1006-jema.2000.0414; Bazza M, 2003, WA SCI TECHNOL, V3, P33; Chernicharo CAL, 2001, WATER SCI TECHNOL, V44, P221; ELFADEL M, 2001, SCREENING IMPA UNPUB; Engin GO, 2006, J ENVIRON MANAGE, V79, P357, DOI 10.1016-j.jenvman.2005.07.011; Florencio L, 2001, WATER SCI TECHNOL, V44, P71; Jurdi M, 2002, ENVIRON MONIT ASSESS, V77, P11, DOI 10.1023-A:1015781930601; Massoud MA, 2003, OCEAN COAST MANAGE, V46, P875, DOI 10.1016-S0964-5691(03)00068-1; Massoud MA, 2006, SCI TOTAL ENVIRON, V362, P31, DOI 10.1016-j.scitotenv.2005.09.056; Massoud MA, 2006, SCI TOTAL ENVIRON, V362, P15, DOI 10.1016-j.scitotenv.2005.09.079; Oron G, 1999, AGR WATER MANAGE, V38, P223, DOI 10.1016-S0378-3774(98)00066-3; Rocky Mountain Institute, 2004, VAL DEC WAST TECHN C; *SOER MOE, 2000, STAT ENV REP LEB 199; USEPA, 2002, EPA625R00008 OFF WAT; *WHO CEHA, 2001, TECHN EXP CONS INN W; World Bank, 1996, SCARC SEC AV WAT CRI43
Public-private partnership for solid waste management services
No full textThe increasing cost of municipal solid waste (MSW) management has led local governments in numerous countries to examine if this service is best provided by the public sector or can better be provided by the private sector. Public–private partnerships have emerged as a promising alternative to improve MSW management performance with privately owned enterprises often outperforming publicly owned ones. In Lebanon, several municipalities are transforming waste management services from a public service publicly provided into a public service privately contracted. In this context, a regulated private market for MSW management services is essential. The present study examines a recent experience of the private sector participation in MSW management in the Greater Beirut Area. The results of a field survey concerning public perception of solid waste management are presented. Analysis of alternatives for private sector involvement in waste management is considered and management approaches are outlined. <br/
GHG Emissions from solid waste and wastewater management: mitigation perspectives in developing vs. developed countries
No full textComparative assessment of methodologies for methane emissions estimation from MSW landfills
No full textMethane emissions from landfills: a methodology comparative assessment
No full textClimate change from greenhouse gas emissions has been at the forefront of current research in the past decade. Anthropogenic emissions of greenhouse gases, over the past 100 years led to a considerable increase in the concentration of these gases in the atmosphere. Methane emissions, of which municipal solid waste landfilling is one of its major anthropogenic sources, make a significant contribution to the greenhouse effect. This paper considers the influence of municipal solid waste management, particularly landfilling on climate change, presents a brief review of methane formation mechanisms in municipal solid waste landfills, describes estimation methods used in determining methane emissions, and compares results and associated uncertainties that are typically obtained with each method. Applications for estimating country-wide (with the country of Lebanon as an example) methane gas emissions from solid waste are presented using the approach adopted by the Intergovernmental Panel on Climate Change. The relative significance of these emissions is assessed in comparison with methane emissions from developing and developed countries. Mitigation measures to reduce the potential impacts of methane emissions taking into consideration country specific economic and technological conditions are also discussed. <br/
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