Página 48 dos resultados de 476117 itens digitais encontrados em 0.039 segundos

## ‣ Systematic analysis of the incoming quark energy loss in cold nuclear matter

Song, Li-Hua; Duan, Chun-Gui; Liu, Na
Tipo: Artigo de Revista Científica
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The investigation into the fast parton energy loss in cold nuclear matter is crucial for a good understanding of the parton propagation in hot-dense medium. By means of four typical sets of nuclear parton distributions and three parametrizations of quark energy loss, the parameter values in quark energy loss expressions are determined from a leading order statistical analysis of the existing experimental data on nuclear Drell-Yan differential cross section ratio as a function of the quark momentum fraction. It is found that with independence on the nuclear modification of parton distributions, the available experimental data from lower incident beam energy rule out the incident-parton momentum fraction quark energy loss. Whether the quark energy loss is linear or quadratic with the path length is not discriminated. The global fit of all selected data gives the quark energy loss per unit path length {\alpha} = 1.21\pm0.09 GeV/fm by using nuclear parton distribution functions determined only by means of the world data on nuclear structure function. Our result does not support the theoretical prediction: the energy loss of an outgoing quark is three times larger than that of an incoming quark approaching the nuclear medium. It is desirable that the present work can provide useful reference for the Fermilab E906/SeaQuest experiment.

## ‣ Baryon Production at LHC and Very High Energy Cosmic Ray Spectra

Piskounova, Olga I.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The spectra of baryons at LHC can explain the features of the proton spectra in cosmic rays (CR). It seems important to study all baryon data that are available from collider experiments in wide range of energies. Transverse momentum spectra of baryons from RHIC ($\sqrt(s)$=62 and 200 GeV) and from LHC ($\sqrt(s)$=0.9 and 7 TeV) have been considered. It is seen that the slope of distributions at low $p_T$'s is changing with energy. The QGSM fit of these spectra gives the average transverse momenta which behave as $s^{0.06}$ that is similar to the previously observed behavior of $\Lambda^0$ hyperon spectra. The change in average transverse momenta that are slowly growing in VHE hadron interactions at CR detectors cannot cause the "knee" in measured cosmic ray proton spectra. In addition, the available data on heavy quark hadron production from LHC-b at $\sqrt{s}$=7 TeV were also studied. The preliminary dependence of hadron average transverse momenta on their masses at LHC energy is presented. The possible source of cosmic ray antiparticle-to-particle ratios that are growing with energy was analyzed in the framework of QGSM, where the growing ratios are the result of local leading asymmetry between the production spectra of baryons and antibaryons in the kinematical region of proton target fragmentation. In the laboratory system of cosmic ray measurements this spectrum asymmetry will be seen as growing ratio of secondary antiparticle-to-particle spectra until the certain energy of secondaries. This conclusion makes the particle production at the sources of very high energy cosmic protons important...

## ‣ Study of the High Energy Gamma-ray Emission from the Crab Pulsar with the MAGIC telescope and Fermi-LAT

Saito, Takayuki
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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My thesis deals with a fundamental question of high energy gamma-ray astronomy. Namely, I studied the cut-off shape of the Crab pulsar spectrum to distinguish between the leading scenarios for the pulsar models. Pulsars are celestial objects, which emit periodic pulsed electromagnetic radiation (pulsation) from radio to high energy gamma-rays. Two major scenarios evolved in past 40 years to explain the pulsation mechanism: the inner magnetosphere scenario and the outer magnetosphere scenario. Both scenarios predict a high energy cut-off in the gamma-ray energy spectrum, but with different cut-off sharpness. An exponential cut-off is expected for the outer magnetosphere scenario while a super-exponential cut-off is predicted for the inner magnetosphere scenario. Therefore, one of the best ways to confirm or rule out these scenarios is to measure the energy spectrum of a pulsar at around the cut-off energy, i.e., at energies between a few GeV and a few tens of GeV. All past attempts (>10) to measure pulsars with ground-based instruments have failed while satellite-borne detectors had a too small area to study detailed spectra in the GeV domain. In this thesis, the gamma-ray emission at around the cut-off energy from the Crab pulsar is studied with the MAGIC telescope. The public data of the satellite-borne gamma-ray detector...

## ‣ Neutrino Dark Energy

Guendelman, E. I.; Kaganovich, A. B.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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There exist field theory models where the fermionic energy-momentum tensor contains a term proportional to g_{\mu\nu}\bar{\Psi}\Psi which can be responsible for a dark matter to dark energy transmutation. We study some cosmological aspects of the new field theory effect where nonrelativistic neutrinos are obliged to be drawn into cosmological expansion (by means of dynamically changing their own parameters). This becomes possible as the magnitudes of the cold neutrino and vacuum energy densities are comparable. Some of the features of such Cosmo-Low Energy Physics (CLEP) state in the toy model of the late time universe filled with homogeneous scalar field and uniformly distributed nonrelativistic neutrinos: neutrino mass increases as a^{3/2} ($a=a(t)$ is the scale factor); its energy density scales as a sort of dark energy and its equation-of-state approaches w=-1 as a\to\infty; the total energy density of such universe is less than it would be in the universe free of fermionic matter at all. CLEP state can be realized in the framework of an alternative gravity and matter fields theory. The latter is reduced to canonical General Relativity when the fermionic matter built of the first two fermion families is only taken into account. In this case also the 5-th force problem is resolved automatically.; Comment: 8 pages...

## ‣ Testing fundamental principles with high-energy cosmic rays

Gonzalez-Mestres, Luis
Tipo: Artigo de Revista Científica
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It is not yet clear whether the observed flux suppression for ultra-high energy cosmic rays (UHECR) at energies above \simeq 4.10E19 eV is a signature of the Greisen-Zatsepin-Kuzmin (GZK) cutoff or corresponds, for instance, to the maximum energies available at the relevant sources. Both phenomena can be sensitive to violations of standard special relativity modifying cosmic-ray propagation or acceleration at very high energy, and would in principle allow to set bounds on Lorentz symmetry violation (LSV) parameters. But the precise phenomenological analysis of the experimental data is far from trivial, and other effects can be present. The effective parameters can be directly linked to Planck-scale physics or to physics beyond Planck scale. If a vacuum rest frame (VRF) exists, LSV can modify the internal structure of particles at very high energy. Conventional symmetries may also cease to be valid at energies close to the Planck scale. Other possible violations of fundamental principles and conventional basic hypotheses (quantum mechanics, quark confinement, energy and momentum conservation, vacuum homogeneity and "static" properties, effective space dimensions...) can also be considered and possibly tested in high-energy cosmic-ray experiments. Even below UHE (ultra-high energy)...

## ‣ Energy loss effects on charm and bottom production in high-energy heavy-ion collisions

Lin, Ziwei; Vogt, Ramona; Wang, Xin-Nian
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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We study the effect of energy loss on charm and bottom quarks in high-energy heavy-ion collisions including longitudinal expansion and partial thermalization. We find that high $p_\perp$ heavy quarks are greatly suppressed, and consequently, high-mass dileptons from heavy quark decays are also suppressed. We consider in detail the detector geometry and single lepton energy cuts of the PHENIX detector at the Relativistic Heavy Ion Collider (RHIC). Because of the longitudinal expansion, the suppressions of $ee, e\mu$ and $\mu\mu$ pairs resulting from the heavy quark energy loss are very different due to the different rapidity coverages and energy cuts. The assumed energy loss rate, on the order of 1 GeV/fm, results in a large suppression on dielectrons, and dielectrons from heavy quark decays become comparable or even lower than the Drell-Yan yield. It is thus possible to probe the energy loss rate of the medium using dileptons from heavy quark decays.; Comment: Revtex, 30 pages including 12 figures, using epsf, discussions added on the uncertainty of dE/dx

## ‣ Negative Energy Seen By Accelerated Observers

Ford, L. H.; Roman, Thomas A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The sampled negative energy density seen by inertial observers, in arbitrary quantum states is limited by quantum inequalities, which take the form of an inverse relation between the magnitude and duration of the negative energy. The quantum inequalities severely limit the utilization of negative energy to produce gross macroscopic effects, such as violations of the second law of thermodynamics. The restrictions on the sampled energy density along the worldlines of accelerated observers are much weaker than for inertial observers. Here we will illustrate this with several explicit examples. We consider the worldline of a particle undergoing sinusoidal motion in space in the presence of a single mode squeezed vacuum state of the electromagnetic field. We show that it is possible for the integrated energy density along such a worldline to become arbitrarily negative at a constant average rate. Thus the averaged weak energy condition is violated in these examples.This can be the case even when the particle moves at non-relativistic speeds. We use the Raychaudhuri equation to show that there can be net defocussing of a congruence of these accelerated worldlines. This defocussing is an operational signature of the negative integrated energy density. These results in no way invalidate nor undermine either the validity or utility of the quantum inequalities for inertial observers. In particular...

## ‣ Study Medium-induced Parton Energy Loss in Gamma+jet Events of High-Energy Heavy-Ion Collisions

Wang, Xin-Nian; Huang, Zheng
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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The effect of medium-induced parton energy loss on jet fragmentation is studied in high-energy heavy-ion collisions. It is shown that an effective jet fragmentation function can be extracted from the inclusive $p_T$ spectrum of charged particles in the opposite direction of a tagged direct photon with a fixed transverse energy. We study the modification of the effective jet fragmentation function due to parton energy loss in AA as compared to pp collisions, including $E_T$ smearing from initial state radiations for the photon-tagged jets. The effective fragmentation function at $z=p_T/E_T^\gamma\sim 1$ in pA collisions is shown to be sensitive to the additional $E_T$ smearing due to initial multiple parton scatterings whose effect must be subtracted out in AA collisions in order to extract the effective parton energy loss. Jet quenching in deeply inelastic lepton-nucleus scatterings as a measure of the parton energy loss in cold nuclear matter is also discussed. We also comment on the experimental feasibilities of the proposed study at the RHIC and LHC energies and some alternative measurements such as using $Z^0$ as a tag at the LHC energy.; Comment: RevTex files with 14 embedded psfigures. A few typos are corrected in this reviesed version

## ‣ Energy dependence of Normal Branch Oscillation in Scorpius X-1

Wang, J.; Chang, H. -K.; Liu, C. -Y.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
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We report the energy dependence of normal branch oscillations (NBOs) in Scorpius X-1, a low-mass X-ray binary Z-source. Three characteristic quantities (centroid frequency, quality factor, and fractional root-mean-squared (rms) amplitude) of a quasi-periodic oscillation signal as functions of photon energy are investigated. We found that, although it is not yet statistically well established, there is a signature indicating that the NBO centroid frequency decreases with increasing photon energy when it is below 6-8 keV, which turns out to be positively correlated with the photon energy at the higher energy side. In addition, the rms amplitude increases significantly with the photon energy below 13 keV and then decreases in the energy band of 13-20 keV. There is no clear dependence on photon energy for the quality factor. Based on these results, we suggest that the NBO originates mainly in the transition layer.; Comment: 6 pages, 4 figures

## ‣ Exploring the dynamics of the world energy system : an agent-based - system dynamics model

Kooshknow, S.A.R Mir Mohammadi; Ghorbani, Amineh; Dijkema, Gerard P.J.
Tipo: Conferência ou Objeto de Conferência Formato: application/pdf
Relevância na Pesquisa
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Due to limitation of some energy resources, there are concerns whether the world energy system (WES) can supply sufficient energy for societies in the future. Scientists develop models to gain insights into the system. GEMBA is a system dynamics model developed by Dale to explore the global energy supply using biophysical economics approach. Biophysical economics theory analyzes the economy based on the physical properties and structures of real economic systems and it considers natural resources and their impacts on the economic processes. GEMBA like other system dynamics models adopt a top-down view on the WES. The top-down view assumes that all elements of a system have global knowledge about the system. Many of such models do not capture some characteristics of a WES such as geographical resource distribution and demand diversity. In addition, it is often not possible to analyze the emergent effects from variations in low-level elements on the system behavior in top-down analysis. We developed an exploratory agent-based model, by taking a biophysical economics lens, for bottom-up analysis of a WES and relevant natural resources. We decomposed the world into a number of geographical regions to capture resource distribution and demand diversity in the WES. Our Multi-Region World Energy Model (MRWEM) combines the GEMBA with the concept of energy-return-on-investment (EROI) for imported energy. So...

## ‣ A dynamic link speed mechanism for energy saving in interconnection networks

Hoang Hai, Nguyen
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis; info:eu-repo/semantics/publishedVersion Formato: application/pdf
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## ‣ Energy intensity in road freight transport of heavy goods vehicles in Spain

Tipo: Trabalho em Andamento Formato: application/pdf
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This paper examines the factors that have influenced the energy intensity of the Spanish road freight transport of heavy goods vehicles over the period 1996–2012. This article aims to contribute to a better understanding of the factors behind the energy intensity change of road freight and also to inform the design of measures to improve energy efficiency in road freight transport. The paper uses both annual single-period and chained multi-period multiplicative LMDI-II decomposition analysis. The results suggest that the decrease in the energy intensity of Spanish road freight in the period is explained by the change in the real energy intensity index (lower energy consumption per tonne-kilometre transported), which is partially offset by the behaviour of the structural index (greater share in freight transport of those commodities the transportation of which is more energy intensive). The change in energy intensity is analysed in more depth by quantifying the contribution of each commodity through the attribution of changes in Divisia indices.

## ‣ The role of policy in energy transitions: lessons from the energy liberalisation era

Pollitt, Michael G.
Fonte: Faculty of Economics, University of Cambridge, UK Publicador: Faculty of Economics, University of Cambridge, UK
Tipo: Trabalho em Andamento
Português
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The aim of this paper is to discuss the period of energy privatisation and liberalisation which began in the 1980s within its wider historical context. The key issues are: what has been learned from this recent period, and how significant is it in the light of an energy transition to low carbon energy system by 2050? Energy liberalisation has led to positive and globally widespread but modest efficiency gains but a lack of clearly visible direct benefits to households in many countries. It has significantly improved the governance of monopoly utilities (via independent regulators), the prospects for competition and innovation, and the quality of policy instruments for environmental emissions control (through the emergence of trading mechanisms). We conclude that it is not liberalisation per se that will determine the movement towards a low carbon energy transition, but the willingness of societies to bear the cost, which will be significant no matter what the extent of liberalisation.

## ‣ An assessement of global energy resource economic potentials

Mercure, Jean-Francois; Salas, Pablo
Fonte: Department of Land Economy, University of Cambridge Publicador: Department of Land Economy, University of Cambridge
Tipo: Article; draft
Português
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This paper presents an assessment of global economic energy potentials for all major natural energy resources. This work is based on both an extensive literature review and calculations based onto natural resource assessment data. Economic potentials are presented in the form of cost-supply curves, in terms of energy flows for renewable energy sources, or fixed amounts for fossil and nuclear resources, using consistent energy units that allow direct comparisons to be made. These calculations take into account, and provide a theoretical framework for considering uncertainty in resource assessments, providing a novel contribution aimed at enabling the introduction of uncertainty into resource limitations used in energy modelling. The theoretical details and parameters provided in tables enable this extensive natural resource database to be adapted to any modelling framework for energy systems.; This work was supported by the Three Guineas Trust, Conicyt (Comisio ?n Nacional de Investigacio ?n Cient ??fica y Tec- nolo ?gica, Gobierno de Chile) and the Ministerio de Energie, Gobierno de Chile.

## ‣ Local energy policy and managing low carbon transition: The case of Leicester, UK

Lemon, M.; Pollitt, M.; Steer, S.
Tipo: Article; published version
Português
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This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.esr.2015.02.001; National and local energy policies are implemented within a complex energy landscape that makes any evaluation of their impacts far from straightforward. Drawing upon a case study of Leicester this paper argues that the ability of local authorities to deliver significant energy savings within this landscape is questionable, albeit with other additional benefits being realised (e.g. job creation, community engagement). It examines existing domestic energy demand and multiple deprivation data for Leicester and neighbouring cities and combines this with a qualitative description of the transition process. The paper identifies the need for a more systematic analysis of how national energy policy translates to the local level and concludes that it is problematic even for a leading, pro-active and innovative local authority to have a statistically meaningful energy policy. Even where energy policies are favourable, carbon reduction is less easy to realise than other ? more local - co-benefits and that in the light of significant financial and co-ordination constraints more attention needs to be given to how local communities can be more effectively supported in their desire to meet (or exceed) national targets.; We wish to thank Laura Platchkov for her research assistance on this paper. We acknowledge the financial assistance of the EPSRC Flexnet award (EP/E0411X/1) and all of the Leicester based contributors to the project...

## ‣ LEED vs. ENERGY STAR: A Cost/Benefit Analysis of Sustainability Labels for Commercial Buildings

Hiser, Stephen
Tipo: Masters' project
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Existing commercial buildings are at the forefront of efforts to address climate change through the implementation of energy efficiency upgrades and other sustainability measures. These efforts have been supported by both public and private organizations, and appear to be gaining momentum as the United States continues to search for ways to make its existing and future infrastructure more sustainable. As a result of the push for more green buildings, many real estate investors have elected to pursue sustainability labels for their existing building portfolios, including the ENERGY STAR rating and Leadership in Energy and Environmental Design - Existing Buildings: Operations & Maintenance (LEED-EBOM) certification. These labels are designed to certify and verify a commercial building’s operating efficiency with respect to sustainability and environmental impact. There is much industry speculation over whether these labels contribute to overall building value for the investor, and if other intangible benefits exist for owners/operators and/or building occupants. This project attempts to provide institutional real estate investors, such as real estate investment trusts (REITs), with general guidelines for selecting one of the aforementioned sustainability labels based on its potential contribution to building value and possible reductions in carbon dioxide emissions attributable to building operations. Analyses were conducted using fundamental real estate valuation models and industry data to evaluate financial and environmental costs and benefits associated with the ENERGY STAR and LEED-EBOM building labels. Financial costs and benefits were analyzed using the direct capitalization valuation model...

## ‣ Dynamics of Electromagnetic Systems for Energy Harvesting and Filtering

Owens, Benjamin Andrew Michael
Tipo: Dissertação
Relevância na Pesquisa
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The focus of this dissertation is on the dynamics of electromagnetic systems for energy harvesting and filtering applications. The inclusion of magnets into systems generates nonlinearity due to the nature of electromagnetic interactions. In this work, magnetic nonlinearity manifests in tip interactions for cantilever beams, coupling effects for electromagnetic transduction, and bistable potential wells for a two beam system. These electromagnetic interactions are used to add non-contact coupling effects for the creation of bistable oscillators or arrays of coupled beams for energy filtering.

Nonlinearity at the tip of cantilever beams acts to change the dynamic and static behavior of the system. In this dissertation, these interactions are analyzed both with and without the nonlinear tip interactions. A linear analysis of the system without the tip interaction first provides insight into the shifting frequencies of the first four natural oscillation modes when considering a rigid body tip mass with rotational inertia and a center of mass that is offset from the tip of the beam. Then, the characterization of the nonlinearities in the beam stiffness and magnetic interaction provide insight into the static and dynamic behavior of the beam. The analytical and numerical investigations...

## ‣ The Impact of Electricity Storage on Energy Sector Emissions

Keaveny, Brian
Tipo: Masters' project
Relevância na Pesquisa
325.37043%
The composition of the U.S. electrical power system reflects competing objectives, as investments are driven by ratepayers who demand access to electricity that is both low cost and reliable. Maintaining generation ready for fluctuations in demand currently requires the inefficient use of generation assets, driving up total energy system costs. During the night, low demand for electricity can force the underutilization of wind farms and baseload coal-fired plants. During the day, load-following natural gas-fired plants are often operated at partial capacity so they can be ramped up to track changing demand. One means to address these two issues is electricity storage. Electricity storage technologies are capable of shifting surplus low cost nighttime electricity to times of higher daytime demand. Whether time-shifting electricity storage technologies may enable lower energy system costs depends upon the parameters of these technologies and future conditions. In this study, a least-cost optimization energy model (MARKAL) managed by U.S. EPA is used to explore the potential future role of electricity storage under varying conditions. Scenarios model a stricter national renewable portfolio standard (RPS), varying natural gas prices, and a national limit on CO2 emissions from the energy system. Scenario results are analyzed to discern the impact of electricity storage on generation output and on the associated energy sector emissions of CO2...

## ‣ Control of Vibratory Energy Harvesters in the Presence of Nonlinearities and Power-Flow Constraints

Cassidy, Ian Lerner
Tipo: Dissertação
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Over the past decade, a significant amount of research activity has been devoted to developing electromechanical systems that can convert ambient mechanical vibrations into usable electric power. Such systems, referred to as vibratory energy harvesters, have a number of useful of applications, ranging in scale from self-powered wireless sensors for structural health monitoring in bridges and buildings to energy harvesting from ocean waves. One of the most challenging aspects of this technology concerns the efficient extraction and transmission of power from transducer to storage. Maximizing the rate of power extraction from vibratory energy harvesters is further complicated by the stochastic nature of the disturbance. The primary purpose of this dissertation is to develop feedback control algorithms which optimize the average power generated from stochastically-excited vibratory energy harvesters.

This dissertation will illustrate the performance of various controllers using two vibratory energy harvesting systems: an electromagnetic transducer embedded within a flexible structure, and a piezoelectric bimorph cantilever beam. Compared with piezoelectric systems, large-scale electromagnetic systems have received much less attention in the literature despite their ability to generate power at the watt--kilowatt scale. Motivated by this observation...

Kayani, Mahrukh