424 research outputs found
Use of floating PV plants for coordinated operation with hydropower plants: Case study of the hydroelectric plants of the Sao Francisco River basin
[EN] In recent years, the Brazilian electricity sector has seen a considerable reduction in hydroelectric production and an increase in dependence on the complementation of thermoelectric power plants to meet the energy demand. This issue has led to an increase in greenhouse gas emissions, which has intensified climate change and modified rainfall regimes in several regions of the country, as well as increased the cost of energy. The use of floating PV plants in coordinated operation with hydroelectric plants can establish a mutual compensation between these sources and replace a large portion of the energy that comes from thermal sources, thereby reducing the dependence on thermoelectric energy for hydropower complementation. Thus, this paper presents a procedure for technically and economically sizing floating PV plants for coordinated operation with hydroelectric plants. A case study focused on the hydroelectric plants of the Sao Francisco River basin, where there has been intense droughts and increased dependence on thermoelectric energy for hydropower complementation. The results of the optimized design show that a PV panel tilt of approximately 3 degrees can generate energy at the lowest cost (from R 312.00/MWh, depending on the geographical location of the FLOATING PV platform on the reservoir). From an energy perspective, the average energy gain generated by the hydroelectric plant after adding the floating PV generation was 76%, whereas the capacity factor increased by 17.3% on average. In terms of equivalent inflow, the PV source has a seasonal profile that compliments the natural inflow of the river. Overall, the proposed coordinated operation could replace much of the thermoelectric generation in Brazil.The authors would like to thank the Brazilian National Council for Scientific and Technological Development (Conselho Nacional de Desenvolvimento CientĂfico e TecnolĂłgico, CNPq; in Portuguese) for granting a productivity in research scholarship to Prof. Regina Mambeli Barros (PQ2, Process number: 301986/2015-0) and Prof. Geraldo LĂșcio Tiago Filho and to the Brazilian Coordination for the Improvement of Higher Education Personnel (Coordenação de Aperfeiçoamento de Pessoal de NĂvel Superior, Capes; in Portuguese) for granting the Master of Science scholarship to Naidion Motta SilvĂ©rio and the Doctorate scholarship to Ivan Felipe da Silva dos Santos.Silverio, N.; Barros, R.; Tiago Filho, GL.; RedĂłn-SantafĂ©, M.; Silva Dos Santos, IF.; De Mello Valerio, VE. (2018). Use of floating PV plants for coordinated operation with hydropower plants: Case study of the hydroelectric plants of the Sao Francisco River basin. Energy Conversion and Management. 171:339-349. https://doi.org/10.1016/j.enconman.2018.05.095S33934917
Search for fingerprints of disoriented chiral condensates in cosmic ray showers
Although the generation of disoriented chiral condensates (DCCs), where the
order parameter for chiral symmetry breaking is misaligned with respect to the
vacuum direction in isospin state, is quite natural in the theory of strong
interactions, they have so far eluded experiments in accelerators and cosmic
rays. If DCCs are formed in high-energy nuclear collisions, the relevant
outcome are very large event-by-event fluctuations in the neutral-to-charged
pion fraction. In this note we search for fingerprints of DCC formation in
observables of ultra-high energy cosmic ray showers. We present simulation
results for the depth of the maximum () and number of muons on the
ground, evaluating their sensitivity to the neutral-to-charged pion fraction
asymmetry produced in the primary interaction.Comment: 7 pages, 4 figure
Method to compute the stress-energy tensor for the massless spin 1/2 field in a general static spherically symmetric spacetime
A method for computing the stress-energy tensor for the quantized, massless,
spin 1/2 field in a general static spherically symmetric spacetime is
presented. The field can be in a zero temperature state or a non-zero
temperature thermal state. An expression for the full renormalized
stress-energy tensor is derived. It consists of a sum of two tensors both of
which are conserved. One tensor is written in terms of the modes of the
quantized field and has zero trace. In most cases it must be computed
numerically. The other tensor does not explicitly depend on the modes and has a
trace equal to the trace anomaly. It can be used as an analytic approximation
for the stress-energy tensor and is equivalent to other approximations that
have been made for the stress-energy tensor of the massless spin 1/2 field in
static spherically symmetric spacetimes.Comment: 34 pages, no figure
The fraction of cancer attributable to ways of life, infections, occupation, and environmental agents in Brazil in 2020
Many human cancers develop as a result of exposure to risk factors related to the environment and ways of life. The aim of this study was to estimate attributable fractions of 25 types of cancers resulting from exposure to modifiable risk factors in Brazil. The prevalence of exposure to selected risk factors among adults was obtained from population-based surveys conducted from 2000 to 2008. Risk estimates were based on data drawn from metaanalyses or large, high quality studies. Population-attributable fractions (PAF) for a combination of risk factors, as well as the number of preventable deaths and cancer cases, were calculated for 2020. The known preventable risk factors studied will account for 34% of cancer cases among men and 35% among women in 2020, and for 46% and 39% deaths, respectively. The highest attributable fractions were estimated for tobacco smoking, infections, low consumption of fruits and vegetables, excess weight, reproductive factors, and physical inactivity. This is the first study to systematically estimate the fraction of cancer attributable to potentially modifiable risk factors in Brazil. Strategies for primary prevention of tobacco smoking and control of infection and the promotion of a healthy diet and physical activity should be the main priorities in policies for cancer prevention in the country. \ua9 2016 Azevedo e Silva et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
Search for First Harmonic Modulation in the Right Ascension Distribution of Cosmic Rays Detected at the Pierre Auger Observatory
We present the results of searches for dipolar-type anisotropies in different
energy ranges above eV with the surface detector array of
the Pierre Auger Observatory, reporting on both the phase and the amplitude
measurements of the first harmonic modulation in the right-ascension
distribution. Upper limits on the amplitudes are obtained, which provide the
most stringent bounds at present, being below 2% at 99% for EeV
energies. We also compare our results to those of previous experiments as well
as with some theoretical expectations.Comment: 28 pages, 11 figure
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