5,058 research outputs found
Calculation of nuclear matrix elements in neutrinoless double electron capture
We compute nuclear matrix elements for neutrinoless double electron capture
on Gd, Er and W nuclei. Recent precise mass
measurements for these nuclei have shown a large resonance enhancement factor
that makes them the most promising candidates for observing this decay mode. We
use an advanced energy density functional method which includes beyond
mean-field effects such as symmetry restoration and shape mixing. Our
calculations reproduce experimental charge radii and values predicting
a large deformation for all these nuclei. This fact reduces significantly the
values of the NMEs leading to half-lives larger than years for the
three candidates
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Floating Offshore Wind Turbines Oscillations Damping.
This article deals with the modelling and control of oscillations that appear on floating offshore wind turbines (FOWT). First, these offshore wind energy systems, located in deep waters, are described and the modeling approach is presented. Secondly, the traditional structural control strategies based on tuned mass-damper (TMD) systems for oscillations reduction are complemented with a passive mechanism called inerter in order to improve the performance of the structural controller. This work is based on a previous work by the authors in which the inerter was located in parallel to an existing TMD in the nacelle of the FOWT. In this work, the inerter is located between the tower and the barge and results are compared to those obtained previously showing better performance. The results here presented are promising in terms of oscillations damping, both in amplitude and frequency, and constitute preliminary results of the ongoing current research of the authors
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Modelling and control of floating offshore wind turbines
This tutorial deals with the modeling and control of floating marine wind turbines. First, these offshore wind energy systems, located on the high seas, in deep waters are described; some modeling approaches are discussed. The power control of these turbines is presented in detail, explaining the different types of control that seek to maximize the energy. The issue of unstable dynamics that can appear in the floating platform due to the wind turbine rotor control is highlighted, something that other types of offshore and onshore turbines do not share. An example shows the reduction of vibrations by applying structural control strategies; results prove that a passive device that is complemented with a mechanism called inerter eliminates the oscillations of the floatin
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From local to global control
In this paper the authors study the problem of the existence of multiple local operating points in control systems. In particular, they consider a method of going from local to global control, i.e. given a number of local, linearized systems, from which global system do they come, and, can global controllers be determined in this case
Influential Article Review - Assessing Company Growth Using Kosovo Businesses Data
This paper examines business. We present insights from a highly influential paper. Here are the highlights from this paper: This paper provides evidence on the impact of the business environment on the growth of firms in less-developed countries, with evidence from Kosovo firms. The theoretical perspective used is growth diagnostics. The data used to test the hypotheses were obtained from two different sources: international surveys and a manager survey dataset. The findings show that the business environment in Kosovo provides little incentive for firm growth. Further, empirical evidence shows that the business environment in Kosovo is characterised by low appropriability, with a high cost of capital, and in which complementary factors in the form of human capital are scarce. For our overseas readers, we then present the insights from this paper in Spanish, French, Portuguese, and German
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Helicopter flap/lag energy exchange study
This paper presents a study on the energy exchange taking place on articulated helicopter main rotor blades. The blades are hinged, and the flap/lag modes are highly coupled. These dynamical couplings existing between the two degrees of freedom are clearly identifiable as the nonlinear terms that appear in the equations of motion are key to understand the energy exchange process. The work here conducted is carried out using VehicleSim, a multibody software specialized in modelling mechanical systems composed by rigid bodies. A spring pendulum system is also studied in order to examine its nonlinear behaviour and to establish existing analogies with the rotor blade nonlinear dynamics. The nonlinear couplings of both systems are compared to each other, and commensurability condition is analysed by means of short-time Fourier transform methods as well as the flap and lag amplitudes spectrum. Simulations are carried out, and the obtained results show clear analogies in the energy exchange process taking place in both systems. The stability of these modes is also studied using Poincare’ map method
Graph Element Networks: adaptive, structured computation and memory
We explore the use of graph neural networks (GNNs) to model spatial processes
in which there is no a priori graphical structure. Similar to finite element
analysis, we assign nodes of a GNN to spatial locations and use a computational
process defined on the graph to model the relationship between an initial
function defined over a space and a resulting function in the same space. We
use GNNs as a computational substrate, and show that the locations of the nodes
in space as well as their connectivity can be optimized to focus on the most
complex parts of the space. Moreover, this representational strategy allows the
learned input-output relationship to generalize over the size of the underlying
space and run the same model at different levels of precision, trading
computation for accuracy. We demonstrate this method on a traditional PDE
problem, a physical prediction problem from robotics, and learning to predict
scene images from novel viewpoints.Comment: Accepted to ICML 201
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