1,702 research outputs found
Optimal Operation of a Distributed Generation Microgrid based on the Multi-Objective Genetic Algorithms
This document describes the application of multi-objective genetic algorithms as techniques and tools to optimize generation and distribution in small microgrids. In this way, genetic algorithms have been used for the allocation of distributed generation to reduce losses and improve the voltage profile. The IEEE14 network has been taken as a study and analysis model. This smart grid has 14 nodes and integrates several generation units, both conventional and renewable, transformers, and multiple loads. In this way, a multi-objective metaheuristic algorithm is proposed with the purpose of planning the power distribution grid based on a series of conditions such as the optimal generation configuration, the minimization of power losses in the lines, power transfer capacity, the reduction of CO2 emissions, and the optimization of the benefits obtained in renewable generation. The overall purpose is the development of an intelligent microgrid management system that is capable of determining the optimal configuration, by estimating demand, energy costs, and operating costs. © 2022, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved
Is the Fast Evolution Scenario for Virialized Compact Groups Really Compelling? The Role of a Dark Massive Group Halo
We report on results of N-body simulations aimed at testing the hypothesis
that galaxies in X-ray emitting (i.e., virialized) Compact Groups are not
tidally stripped when they are embedded in a common, massive, quiescent dark
matter halo. To disentangle the effects of interactions from spurious effects
due to an incorrect choice of the initial galaxy model configurations, these
have been chosen to be tidally-limited King spheres, representing systems in
quasi-equilibrium within the tidal field of the halo. The potential of the halo
has been assumed to be frozen and the braking due to dynamical friction
neglected. Our results confirm the hypothesis of low rates of tidal stripping
and suggest a scenario for virialized Compact Group evolution in their
quiescent phases with only very moderate tidally induced galaxy evolution can
be generally expected. This implies the group stability, provided that the
dynamical friction timescales in these systems are not much shorter than the
Hubble time. We discuss briefly this possibility, in particular taking account
of the similarity between the velocity dispersions of a typical virialized
Compact Groups and the internal velocity dispersion of typical member galaxies.
A number of puzzling observational data on Compact Groups can be easily
explained in this framework. Other observations would be better understood as
the result of enhanced merging activity in the proto-group environment, leading
to virialized Compact Group formation through mergers of lower mass halos, as
predicted by hierarchical scenarios of structure formation.Comment: 18 pages, 1 postscript file, 2 tables, to be published in ApJLet
Ellipticals at z=0 from Self-Consistent Hydrodynamical Simulations: Clues on Age Effects in their Stellar Populations
We present results of a study of the stellar age distributions in the sample
of elliptical-like objects (ELOs) identified at z=0 in four simulations
operating in the context of a concordance cosmological model. The simulations
show that the formation of most stars in each ELO of the sample is a
consequence of violent dynamical events, either fast multiclump collapse at
high z, or mergers at lower z. This second way can explain the age spread as
well as the dynamical peculiarities observed in some ellipticals, but its
relative weight is never dominant and decreases as the ELO mass at the halo
scale, , increases, to such an extent that some recent mergers
contributing an important fraction to the total ELO mass can possibly
contribute only a small fraction of new born stars. More massive objects have
older means and narrower spreads in their stellar age distributions than less
massive ones. The ELO sample shows also a tight correlation between
and the central stellar l.o.s. velocity dispersion, . This gives
a trend of the means and spreads of ELO stellar populations with
that is consistent, even quantitatively, with the age effects observationally
detected in the stellar populations of elliptical galaxies. Therefore, these
effects can be explained as the observational manifestation of the intrinsic
correlations found in the ELO sample between and the properties of
the stellar age distribution, on the one hand, and and
, on the other hand. These correlations hint, for the first time,
at a possible way to reconcile age effects in ellipticals, and, particularly,
the increase of ratios with , with the
hierarchical clustering paradigm.Comment: 13 pages, 2 figures, accepted for publication in Astrophysical
Journal Letter
Ocean Wave Energy Converters: Analysis, Modeling, and Simulation. Some case studies
Wave energy has much more potential and benefits than other forms of renewable energy. It is more predictable, consistent, and controllable than wind or solar energy. In this way, an adequate infrastructure can be an alternative and also sustainable system for power supply. In this paper, different wave energy conversion mechanisms (buoys, Pelamis, and oysters) have been described. These models are implemented and simulated using the Design Modeller, ANSYS-AQWA, and WEC-SIM applications. The purpose has been to develop a complete simulation of the wave energy converter and discuss its operation. The analysis has been developed in Matlab-Simulink and both regular and irregular waves have been considered. For this, an approximation to the linear waves theory has been used. The results obtained indicate the energy absorbed from the sea waves and also the energy supplied to the power grid. The simulation results estimated with the different WEC models are comparable to the results shown by other research papers. © 2022, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved
Low-cost variable-speed wind turbines design by recycling small electrical machines. Arrangement of permanent magnets in the rotor
This paper describes the design of low-cost variable-speed wind turbines by recycling small electrical machines. In this way, electrical machines such as automobile claw-pole alternators, induction motors for domestic applications, or simply electric motors for some industrial applications are studied, considering their reuse as permanent magnet synchronous generators (PMSG) in small wind turbines or hydro-power turbines. The main purpose is the integration of hybrid energy conversion systems (wind and hydraulic turbines) in small stand-alone microgrids within the rural environment. Likewise, in order to optimize the design, the arrangement of the permanent magnets in the rotor is analyzed. The analysis has been carried out using the FluxMotor simulation software, which is based on the 2D finite element method. At the same time, the FEM software provides a lot of information about the optimization of the electrical machine and its multiple design options and topologies. Suggested designs have similar performance as well as a similar size and weight. The purpose has been to explore different topologies and select the most efficient designs. In this way, it is shown that it is possible to reuse an electrical generator easily, without losing much of the general performance. © 2022, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved
Leadership, management, quality, and innovation in organ donation: 2019 Kunming recommendations for One Belt & One Road countries
The findings and recommendations of the 2019 consensus conference in organ donation, held in Kunming, China, are here reported. The main objective of the conference was to gather relevant information from experts involved in the field. The data and opinions provided allowed to propose a series of recommendations for “One Belt & One Road Countries” on how to achieve self-sufficiency in organ donation. Leadership in organ donation should be results-oriented and goal-driven based on the principles of excellence, empowerment, and engagement, providing the means, resources, and strategies necessary to reach the goal in earnest. Management includes good governance and transparency of a national registry of patients in the waiting list, donors, transplants, transplant teams, quality, and safety programs with continuous educational training of health care professionals. Mandatory monitoring, auditing and evaluation of quality must be incorporated into donation practices as relevant points in innovation, as well as the adoption of already established and novel processes and technologies. Achievement of self-sufficiency in organ donation is a crucial step to fight against transplant tourism and to prevent organ trafficking. Based on recommendations arising from the conference, each country could review and develop individualized action plans adjusted to its own circumstances and reality
Strength distribution of solar magnetic fields in photospheric quiet Sun regions
The magnetic topology of the solar photosphere in its quietest regions is
hidden by the difficulties to disentangle magnetic flux through the resolution
element from the field strength of unresolved structures. The observation of
spectral lines with strong coupling with hyperfine structure, like the observed
MnI line at 553.7 nm, allows such differentiation.
The main aim is to analyse the distribution of field strengths in the network
and intranetwork of the solar photosphere through inversion of the MnI line at
553.7 nm.
An inversion code for the magnetic field using the Principal Component
Analysis (PCA) has been developed. Statistical tests are run on the code to
validate it. The code has to draw information from the small-amplitude spectral
feature oppearing in the core of the Stokes V profile of the observed line for
field strengths below a certain threshold, coinciding with lower limit of the
Paschen-Back effect in the fine structure of the involved atomic levels.
The inversion of the observed profiles, using the circular polarization (V)
and the intensity (I), shows the presence of magnetic fields strengths in a
range from 0 to 2 kG, with predominant weak strength values. Mixed regions with
mean strength field values of 1130 and 435 Gauss are found associated with the
network and intranetwork respectively.
The MnI line at 553 nm probes the field strength distribution in the quiet
sun and shows the predominance of weak, hectoGauss fields in the intranetwork,
and strong, kiloGauss fields in the network. It also shows that both network
and intranetwork are to be understood at our present spatial resolutions as
field distributions of which we hint the mean properties.Comment: 10 pages, 6 figure
Artificial intelligence in wind speed forecasting: a review
Wind energy production has had accelerated growth in recent years, reaching an annual increase of 17% in 2021. Wind speed plays a crucial role in the stability required for power grid operation. However, wind intermittency makes accurate forecasting a complicated process. Implementing new technologies has allowed the development of hybrid models and techniques, improving wind speed forecasting accuracy. Additionally, statistical and artificial intelligence methods, especially artificial neural networks, have been applied to enhance the results. However, there is a concern about identifying the main factors influencing the forecasting process and providing a basis for estimation with artificial neural network models. This paper reviews and classifies the forecasting models used in recent years according to the input model type, the pre-processing and post-processing technique, the artificial neural network model, the prediction horizon, the steps ahead number, and the evaluation metric. The research results indicate that artificial neural network (ANN)-based models can provide accurate wind forecasting and essential information about the specific location of potential wind use for a power plant by understanding the future wind speed values
Active surveillance in prostate cancer: role of available biomarkers in daily practice
Prostate cancer (PCa) is the most commonly diagnosed cancer in men. The diagnosis is currently based on PSA levels, which are associated with overdiagnosis and overtreatment. Moreover, most PCas are localized tumours; hence, many patients with low-/very low-risk PCa could benefit from active surveillance (AS) programs instead of more aggressive, active treatments. Heterogeneity within inclusion criteria and follow-up strategies are the main controversial issues that AS presently faces. Many biomarkers are currently under investigation in this setting; however, none has yet demonstrated enough diagnostic ability as an independent predictor of pathological or clinical progression. This work aims to review the currently available literature on tissue, blood and urine biomarkers validated in clinical practice for the management of AS patients
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