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‣ Energy benchmarking of South Australian WWTPs

Krampe, J.
Fonte: IWA Publishing Publicador: IWA Publishing
Tipo: Artigo de Revista Científica
Publicado em //2013 Português
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Optimising the energy consumption and energy generation of wastewater treatment plants (WWTPs) is a topic with increasing importance for water utilities in times of rising energy costs and pressures to reduce greenhouse gas (GHG) emissions. Assessing the energy efficiency and energy optimisation of a WWTP are difficult tasks as most plants vary greatly in size, process layout and other influencing factors. To overcome these limits it is necessary to compare energy efficiency with a statistically relevant base to identify shortfalls and optimisation potential. Such energy benchmarks have been successfully developed and used in central Europe over the last two decades. This paper demonstrates how the latest available energy benchmarks from Germany have been applied to 24 WWTPs in South Australia. It shows how energy benchmarking can be used to identify shortfalls in current performance, prioritise detailed energy assessments and help inform decisions on capital investment.; J. Krampe

‣ Key role for nuclear energy in global biodiversity conservation

Brook, B.W.; Bradshaw, C.J.A.
Fonte: Wiley Publicador: Wiley
Tipo: Artigo de Revista Científica
Publicado em //2015 Português
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Modern society uses massive amounts of energy. Usage rises as population and affluence increase, and energy production and use often have an impact on biodiversity or natural areas. To avoid a business-as-usual dependence on coal, oil, and gas over the coming decades, society must map out a future energy mix that incorporates alternative sources. This exercise can lead to radically different opinions on what a sustainable energy portfolio might entail, so an objective assessment of the relative costs and benefits of different energy sources is required. We evaluated the land use, emissions, climate, and cost implications of 3 published but divergent storylines for future energy production, none of which was optimal for all environmental and economic indicators. Using multicriteria decision-making analysis, we ranked 7 major electricity-generation sources (coal, gas, nuclear, biomass, hydro, wind, and solar) based on costs and benefits and tested the sensitivity of the rankings to biases stemming from contrasting philosophical ideals. Irrespective of weightings, nuclear and wind energy had the highest benefit-to-cost ratio. Although the environmental movement has historically rejected the nuclear energy option, new-generation reactor technologies that fully recycle waste and incorporate passive safety systems might resolve their concerns and ought to be more widely understood. Because there is no perfect energy source however...

‣ Towards a Sustainable Global Energy Supply Infrastructure: Net Energy Balance and Density Considerations

KESSIDES, Ioannis N.; WADE, David C.
Fonte: Instituto Universitário Europeu Publicador: Instituto Universitário Europeu
Tipo: Trabalho em Andamento Formato: application/pdf; digital
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This paper employs a framework of dynamic energy analysis to model the growth potential of alternative electricity supply infrastructures as constrained by innate physical energy balance and dynamic response limits. Coal- red generation meets the criteria of longevity (abundance of energy source) and scalability (ability to expand to the multi-terawatt level) which are critical for a sustainable energy supply chain, but carries a very heavy carbon footprint. Renewables and nuclear power, on the other hand, meet both the longevity and environmental friendliness criteria. However, due to their substantially di¤erent energy densities and load factors, they vary in terms of their ability to deliver net excess energy and attain the scale needed for meeting the huge global energy demand. The low power density of renewable energy extraction and the intermittency of renewable ows limit their ability to achieve high rates of indigenous infrastructure growth. A signi cant global nuclear power deployment, on the other hand, could engender serious risks related to proliferation, safety, and waste disposal. Unlike renewable sources of energy, nuclear power is an unforgiving technology because human lapses and errors can have ecological and social impacts that are catastrophic and irreversible. Thus...

‣ Aggregate Economic Implications of New Technologies in Energy Industry

Zhang, Xinya
Fonte: Universidade Rice Publicador: Universidade Rice
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This thesis studies technological progress in the energy sector and the transition path from fossil fuels to renewable energy, with a particular emphasis on the conse- quences to the whole economy. Currently, there is an active discussion regarding sub- sidizing renewable energy sources, which are often portrayed as the sole future source of energy and the driver of signi cant employment and economic growth. However, innovation in the fossil fuel sector and its continuing development can also be a game changer and should not be ignored. In the rst chapter, we use a dynamic general equilibrium model with endogenous technological progress in energy production to study the optimal transition from fossil fuels to renewable energy in a neoclassical growth economy. We emphasize the importance of modeling technology innovation in the fossil fuel sector, as well as in the renewable energy industry. Advancements in the development of shale oil and gas increase the supply of fossil fuel. This implies that the parity cost target" for renewables is a moving one. We believe that this important observation is often neglected in policy discussions. Our quantitative analysis nds that these advancements allow fossil fuels to remain competitive for a longer period of time. While technological breakthroughs in the fossil fuel sector have postponed the full transition to renewable energy...

‣ Modeling of hydraulic and energy efficiency indicators for water supply systems

Nogueira Vilanova, Mateus Ricardo; Perrella Balestieri, Jose Antonio
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 540-557
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 2013/07287-3; The present work approaches the necessity of the hydraulic and energetic efficiency indicator development for the management and decision making of water supply systems (WSSs) that can enable the comparison between the current situation of the system with its optimal technical condition regarding the energy and hydraulic terms. Such indicators must consider and represent the physical and operational components which integrate the hydraulic and energetic conversion processes in WSSs. The optimal technical condition refers to the target-value of the analyzed variable, which makes possible the lowest consumption/demand of electricity and hydraulic head, or their better use, simultaneously meeting the operational requirements of the system. The literature registers the lack of efficiency indicators for the analysis of WSSs, since the existing indicators only address the energy situation of these systems, which are not related with the energy efficiency and conservation potentials. The evaluation of the global energy efficiency of WSSs depends on the individual and separated analysis of the various physical components and energy conversion processes. In order to sustain the decision making...

‣ Valoração probabilística de empreendimentos de geração de energia elétrica a partir de bagaço de cana-de-açúcar em leilão de energia de reserva; Probabilistic valuation model for generation projects that use sugar cane bagasse and commercialize energy in reserve energy auctions

Viviana Andrea Contreras Medellin
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/07/2015 Português
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A geração de energia elétrica a partir de fontes renováveis constitui uma alternativa interessante para a diversificação da matriz energética de um país. No Brasil, o programa de incentivo às fontes alternativas de energia elétrica (Proinfa), instituído em 2004, teve como objetivo promover a diversificação da matriz energética, buscar alternativas para aumentar a segurança no abastecimento de energia elétrica e permitir a valorização das características e potencialidades regionais e locais. Dentre as fontes renováveis de geração de energia, o destaque deste trabalho é para a biomassa, utilizando o bagaço da cana-de-açúcar. O bagaço da cana é produzido em grandes quantidades no Brasil e possui 1/3 do conteúdo energético da cana. Este recurso permite a geração de energia descentralizada. No setor elétrico brasileiro, a contratação de energia proveniente de empreendimentos de geração a partir do bagaço da cana-de-açúcar pode ser formalizada por meio dos leilões de energia de reserva. A análise de projetos para empreendimentos deste tipo envolve duas variáveis estocásticas: a geração de energia (que depende da disponibilidade do recurso ¿ período sazonal) e o valor da energia no mercado de curto prazo (que depende das condições hidrológicas). Portanto...

‣ How Perspective Impacts Policy: A Comparison of the Social, Scientific, and Political Perspectives on Native Forest Waste Utilization as a Renewable Energy Source in the United States and Australia

Caldwell, Mandi
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Relatório
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This report compares the political, social and scientific perspectives of native forest utilization between the United States and Australia. The report focuses on the perspectives of using native forest waste from harvesting and management for renewable energy ce11ificates (REC). Methods for comparison include extensive research and discussions with a broad range of stake holders (Appendix A). A standard set of questions were used to initiate discussions (Appendix B). There is a growing emphasis on encouraging renewable energy research and use, driven by a multitude of factors including concerns of climate change, dwindling resources and increasing emphasis on recycling and efficient resource use. Generating energy by burning wood is one of the suites of renewable energy options available for many countries. According to the United States Environmental Protection Agency, renewable energy is d~fined as an energy source that can be "continuously replenished" on the planet (US EPA 2007). Australia and the United States have active forestry industries that produce by-product, or waste. This waste may be created at any stage in the process of converting wood to useable items such as timber and furniture. However, there is debate regarding the eligibility of certain wood wastes for REC. The social perspective for the United States and Australia are very similar: both want to protect the environment. This is not unusual in more affluent countries...

‣ From Crisis to Stability in the Armenian Power Sector : Lessons Learned from Armenia's Energy Reform Experience

Sargsyan, Gevorg; Balabanyan, Ani; Hankinson, Denzel
Fonte: Washington, DC: World Bank Publicador: Washington, DC: World Bank
Tipo: Publications & Research :: Publication; Publications & Research :: Publication
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In the wake of the Soviet Union's collapse, Armenia, like other former Soviet republics, began to struggle with the implications of its newfound independence. In the electricity sector, this meant learning how to manage and sustain a fragment of a system that had never been designed to function as a stand-alone grid. Armenia's electricity system-and, indeed, its entire energy supply system-had been designed to operate as part of a much larger, integrated Trans-Caucasus system. Plants were built to run on fuel imported from thousands of miles away, from neighbors who, with the Soviet Union gone, could offer little certainty that such supply would continue under terms that Armenia could afford. The problems with this system began to show in 1992. The start of the war over Nagorno Karabakh, and the resulting imposition by Azerbaijan and Turkey of an economic blockade, cut off Armenia's only source of gas and oil for its thermal plants. Four years prior to that, a massive earthquake had forced a shut down of the Medzamor nuclear power plant...

‣ Energy Considerations for Pipe Replacement in Water Distribution Systems

Prosser, MONICA
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
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Water utilities are facing pressure to continue to provide high-quality potable water in an increasingly energy constrained world; managing the ageing infrastructure that exists in many countries is a challenge in and of itself, but recently this has been coupled with political and public attention to the environmental impacts of the distribution system. Utility managers need to take a holistic approach to decision-making in order to determine all of the impacts of their plans. The intention of this thesis is to present a set of considerations for utility planners and managers to provide clarity to the trade-offs associated with any pipe replacement decision. This research has examined the energy relationships between operational energy reduction and the embodied energy tied to replacing deteriorated pipes in water distribution networks. These relationships were investigated through the development and application of a life-cycle energy analysis (LCEA) for three different pipe replacement schedules developed with the intent to reduce leakage in the system. The results showed that the embodied energy for pipe replacement is significant even when compared against the large amount of energy required to operate a large-scale water utility. The annual operational energy savings of between 8.9 and 9.6 million kWh achieved by 2070 through pipe replacement comes at a cost; 0.88-2.05 million kWh/mile for replacement with ductile iron pipes with diameters of 6” to 16” respectively. This imbalance resulted in a maximum energy payback period of 17.6 years for the most aggressive replacement plan in the first decade. Some of the assumptions that were used to complete the LCEA were investigated through a sensitivity analysis; specific factors that were numerically queried in this chapter include the break rate forecasting method...

‣ Strategies to Improve Industrial Energy Efficiency

O'Rielly, Kristine Marita
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
Português
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A lack of technical expertise, fueled by a lack of positive examples, can lead to companies opting not to implement energy reduction projects unless mandated by legislation. As a result, companies are missing out on exceptional opportunities to improve not only their environmental record but also save considerably on fuel costs. This study investigates the broad topic of energy efficiency within the context of the industrial sector by means of a thorough review of existing energy reduction strategies and a demonstration of their successful implementation. The study begins by discussing current industrial energy consumption trends around the globe and within the Canadian manufacturing sector. This is followed by a literature review which outlines 3 prominent energy efficiency improvement strategies currently available to companies: 1) Waste heat recovery, 2) Idle power loss reduction and production rate optimization, and lastly 3) Auxiliary equipment operational performance. Next, a broad overview of the resources and tools available to organizations looking to improve their industrial energy efficiency is provided. Following this, several case studies are presented which demonstrate the potential benefits that are available to Canadian organizations looking to improve their energy efficiency. Lastly...

‣ Geographies of biomass and solar energy: Spatial decision support for regional energy sustainability

Calvert, KIRBY
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
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This thesis applies concepts and techniques in geography in order to contribute to our understanding of the opportunities and challenges associated with the transition toward renewable energy. The work is best understood as the sum of two parts. In the first part, the methodological and philosophical underpinnings of the field of energy geography are explored in order to situate the research in the broader constellation of geographical practices surrounding energy. I make the case that energy transitions are not merely shifts in energy supply but are also simultaneously fundamental shifts in prevailing spatial relations, so that energy transition management is best conceived as a spatial strategy with emphasis on regional level land-energy planning. In the second part of the thesis, I aim to provide decision support in favour of this spatial strategy. This begins in Chapter 4 with a comprehensive critical review of how GIScience and remote sensing has been applied in RE assessments and spatial planning. The next three chapters engage key gaps in this literature and are the analytical contributions of the thesis. The focus of the research is on biomass and solar energy in (eastern) Ontario. In Chapter 5 I develop geographically explicit supply-cost curves for forestry and agricultural biomass and assess the relative merits of a mixed biomass feedstock stream. In Chapter 6 I recognize and address the issue that developers of dedicated bioenergy crops and ground-mount solar PV systems prefer the same type of land. Land-energy trade-offs are modeled and their implications in the context of incentivizing RE development are discussed. In Chapter 7 I explore ways in which targeted facility siting can capture ancillary benefits related to RE production. I argue that focusing on the benefits as well as the costs of system siting is critical to linking developer and public interests. Ontario’s feed-in tariff program is evaluated in the light of this claim. Chapter 8 concludes with a summary of key findings and describes the ways in which this thesis can be used as a platform upon which a broader research program can be raised.; Thesis (Ph.D...

‣ Modelos para análises de sistemas energéticos industriais aplicados a estudos de eficiência energética; Models for analysis of industrial energy systems applied to energy efficiency studies

Rafael Rodrigues da Silva
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 15/02/2013 Português
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Sistemas industriais consumidores de energia são, em geral, complexos. Metodologias e ferramentas que facilitem o cálculo de potenciais de economia no consumo de energia térmica e elétrica são, portanto, de extrema importância. Nesse contexto, modelos de simulação de sistemas energéticos são bastante úteis para explicar o comportamento de sistemas complicados, que estão além da capacidade do cérebro humano compreender integralmente todas as suas características relevantes. Esse trabalho apresenta o contexto brasileiro de oportunidades para uso de softwares que se propõem a realizar a modelagem de sistemas energéticos industriais em alguns dos seus principais sistemas consumidores de energia: força motriz, ar comprimido, calor de processo, aquecimento direto, refrigeração e resfriamento, sistemas de bombeamento e sistemas de ventilação. São consideradas duas fontes de disponibilização desse tipo de ferramenta. A primeira é o Programa Nacional de Conservação de Energia Elétrica (Procel), que possui softwares nacionais, em língua portuguesa, para análises de alguns dos sistemas listados anteriormente. A segunda é o U.S. Department of Energy (DOE), pela tradição do país no uso deste tipo de ferramenta com profissionais habilitados formalmente...

‣ Urubu: energy scavenging in wireless sensor networks

Ribeiro, Rui Filipe de Sá
Fonte: Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto Publicador: Instituto Politécnico do Porto. Instituto Superior de Engenharia do Porto
Tipo: Dissertação de Mestrado
Publicado em //2010 Português
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For the past years wireless sensor networks (WSNs) have been coined as one of the most promising technologies for supporting a wide range of applications. However, outside the research community, few are the people who know what they are and what they can offer. Even fewer are the ones that have seen these networks used in real world applications. The main obstacle for the proliferation of these networks is energy, or the lack of it. Even though renewable energy sources are always present in the networks environment, designing devices that can efficiently scavenge that energy in order to sustain the operation of these networks is still an open challenge. Energy scavenging, along with energy efficiency and energy conservation, are the current available means to sustain the operation of these networks, and can all be framed within the broader concept of “Energetic Sustainability”. A comprehensive study of the several issues related to the energetic sustainability of WSNs is presented in this thesis, with a special focus in today’s applicable energy harvesting techniques and devices, and in the energy consumption of commercially available WSN hardware platforms. This work allows the understanding of the different energy concepts involving WSNs and the evaluation of the presented energy harvesting techniques for sustaining wireless sensor nodes. This survey is supported by a novel experimental analysis of the energy consumption of the most widespread commercially available WSN hardware platforms.; Há já alguns anos que as redes de sensores sem fios (do Inglês Wireless Sensor Networks - WSNs) têm sido apontadas como uma das mais promissoras tecnologias de suporte a uma vasta gama de aplicações. No entanto...

‣ Energy saving innovations, non-exhaustible sources of energy and long-run: what would happen if we run out of oil?

Zuleta, Hernando
Fonte: Facultad de Economía Publicador: Facultad de Economía
Tipo: info:eu-repo/semantics/book; info:eu-repo/semantics/acceptedVersion Formato: application/pdf
Publicado em //2008 Português
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We formulate and solve a model of factor saving technological improvement considering three factors of production: labor, capital and energy. The productive activities have three main characteristics: first, in order to use capital goods firms need energy; second, there are two sources of energy: non-exhaustible and exhaustible; third, capital goods can be of different qualities and the quality of these goods can be changed along two dimensions -reducing the need of energy or changing the source of energy used in the production process. The economy goes through three stages of development after industrialization. In the first, firms make use of exhaustible energy and the e¢ ciency in the use of energy is constant. In the second stage, as the price of energy grows the e¢ ciency in its use is increased. In the third stage, the price of exhaustible sources is so high that firms have incentives to use non-exhaustible sources of energy. During this stage the price of energy is constant. In this set up, the end of the oil age has level effects on consumption and output but it does not cause the collapse of the economic system.

‣ A mathematical programming/economic equilibrium model for the quantitative analysis of the stability of Japan's energy system

Oyama, Tatsuo
Fonte: MIT Energy Lab Publicador: MIT Energy Lab
Tipo: Trabalho em Andamento Formato: 2028561 bytes; application/pdf
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Japan's energy supply-demand system is fully dependent on the import of primary energy resources from foreign countries. So the availability of primary energy, including crude oil and coal, is a very important factor for the stability of our energy system. In order to measure our energy system's stability under an uncertain future availability of energy resources, we built a mathematical programming / economic equilibrium model based upon linear programming techniques. In the model analysis uncertain future availability of primary energy resources is expressed as random variables with a given probability distribution, and the economic equilibrium point is obtained by iterative convergent computation. From our numerical results we know an optimal energy supply-demand structure with equilibrium prices of primary energy resources at the future target year, and obtain supply stability and instability probabilities of our energy system. Furthermore, applicability of decomposition techniques to our energy model analysis and necessary and sufficient conditions for the stability of our energy system are discussed.

‣ Energy-pressure relation for low-dimensional gases

Mancarella, Francesco; Mussardo, Giuseppe; Trombettoni, Andrea
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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A particularly simple relation of proportionality between internal energy and pressure holds for scale invariant thermodynamic systems, including classical and quantum Bose and Fermi ideal gases. One can quantify the deviation from such a relation by introducing the internal energy shift as the difference between the internal energy of the system and the corresponding value for scale invariant gases. We discuss general thermodynamic properties associated to the scale invariance, provide criteria for which the internal energy shift density is a bounded function of temperature. We then study the internal energy shift and deviations from the energy-pressure proportionality in low dimensional models of gases interpolating between the ideal Bose and the ideal Fermi gases, focusing on the Lieb-Liniger model in 1d and on the anyonic gas in 2d. In 1d the internal energy shift is determined from the thermodynamic Bethe ansatz integral equations and an explicit relation for it is given at high temperature. Our results show that the internal energy shift is positive, it vanishes in the two limits of zero and infinite coupling (respectively the ideal Bose and the Tonks Girardeau gas) and it has a maximum at a finite, temperature depending, value of the coupling. Remarkably...

‣ Medium-induced jet evolution: wave turbulence and energy loss

Fister, Leonard; Iancu, Edmond
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/09/2014 Português
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We study the gluon cascade generated via successive medium-induced branchings by an energetic parton propagating through a dense QCD medium. We focus on the high-energy regime where the energy $E$ of the leading particle is much larger than the characteristic medium scale $\omega_c=\hat q L^2/2$, with $\hat q$ the jet quenching parameter and $L$ the distance travelled through the medium. In this regime the leading particle loses only a small fraction $\sim\alpha_s(\omega_c/E)$ of its energy and can be treated as a steady source of radiation for gluons with energies $\omega\le\omega_c$. For this effective problem with a source, we obtain exact analytic solutions for the gluon spectrum and the energy flux. The solutions exhibit wave turbulence: the basic physical process is a continuing fragmentation which is `quasi-democratic' (i.e. quasi-local in energy) and which provides an energy transfer from the source to the medium at a rate (the energy flux $\mathcal{F}$) which is quasi-independent of $\omega$. The locality of the branching process implies a spectrum of the Kolmogorov-Obukhov type, i.e. a power-law spectrum which is a fixed point of the branching process and whose strength is proportional to the energy flux: $D(\omega)\sim\mathcal{F}/\sqrt\omega$ for $\omega\ll\omega_c$. Via this turbulent flow...

‣ Energy Density-Flux Correlations in an Unusual Quantum State and in the Vacuum

Ford, L. H.; Roman, Thomas A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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In this paper we consider the question of the degree to which negative and positive energy are intertwined. We examine in more detail a previously studied quantum state of the massless minimally coupled scalar field, which we call a ``Helfer state''. This is a state in which the energy density can be made arbitrarily negative over an arbitrarily large region of space, but only at one instant in time. In the Helfer state, the negative energy density is accompanied by rapidly time-varying energy fluxes. It is the latter feature which allows the quantum inequalities, bounds which restrict the magnitude and duration of negative energy, to hold for this class of states. An observer who initially passes through the negative energy region will quickly encounter fluxes of positive energy which subsequently enter the region. We examine in detail the correlation between the energy density and flux in the Helfer state in terms of their expectation values. We then study the correlation function between energy density and flux in the Minkowski vacuum state, for a massless minimally coupled scalar field in both two and four dimensions. In this latter analysis we examine correlation functions rather than expectation values. Remarkably, we see qualitatively similar behavior to that in the Helfer state. More specifically...

‣ Dynamics of dark energy in the gravitational fields of matter inhomogeneities

Novosyadlyj, B.; Kulinich, Yu.; Tsizh, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We study the dynamical properties and space distribution of dark energy in the weak and strong gravitational fields caused by inhomogeneities of matter in the static world of galaxies and clusters. We show that the dark energy in the weak gravitational fields of matter density perturbations can condense or dilute, but amplitudes of its perturbations remain very small on all scales. We illustrate also how the "accretion" of the phantom dark energy onto the matter overdensity forms the dark energy underdensity. We analyze the behavior of dark energy in the gravitational fields of stars and black holes with the Schwarzschild metric. It is shown that, in the case of stars, the static solution of the differential equations for energy-momentum conservation exists and describes the distribution of density of dark energy inside and outside of a star. We have found that for stars and galaxies its value differs slightly from the average and is a bit higher for the quintessential scalar field as dark energy and a bit lower for the phantom one. The difference grows with the decrease of the effective sound speed of dark energy and is large in the neighborhood of neutron stars. We obtain and analyze also the solutions of equations that describe the stationary accretion of the dark energy as a test component onto the Schwarzschild black hole. It is shown that the rate of change of mass of the dark energy is positive in the case of quintessential dark energy and is negative in the case of the phantom one.; Comment: 13 pages...

‣ Casimir Energy for a Coupled Fermion-Kink System and its stability

Gousheh, Siamak Sadat; Mohammadi, Azadeh; Shahkarami, Leila
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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We compute the Casimir energy for a system consisting of a fermion and a pseudoscalar field in the form of a prescribed kink. This model is not exactly solvable and we use the phase shift method to compute the Casimir energy. We use the relaxation method to find the bound states and the Runge-Kutta-Fehlberg method to obtain the scattering wavefunctions of the fermion in the whole interval of $x$. The resulting phase shifts are consistent with the weak and strong forms of the Levinson theorem. Then, we compute and plot the Casimir energy as a function of the parameters of the pseudoscalar field, i.e. the slope of $\phi(x)$ at x=0 ($\mu$) and the value of $\phi(x)$ at infinity ($\theta_0$). In the graph of the Casimir energy as a function of $\mu$ there is a sharp maximum occurring when the fermion bound state energy crosses the line of E=0. Furthermore, this graph shows that the Casimir energy goes to zero for $\mu\rightarrow 0$, and also for $\mu\rightarrow \infty$ when $\theta_0$ is an integer multiple of $\pi$. Moreover, the graph of the Casimir energy as a function of $\theta_0$ shows that this energy is on the average an increasing function of $\theta_0$ and has a cusp whenever there is a zero fermionic mode. We finally compute the total energy of a system consisting of a valence fermion in the ground state. Most importantly...