18,904 research outputs found
A Comparative Analysis of Self-Rectifying Turbines for the Mutriku Oscillating Water Column Energy Plant
Oscillating Water Column (OWC) based devices are arising as one of the most promising technologies for wave energy harnessing. However, the most widely used turbine comprising its power take-off (PTO) module, the Wells turbine, presents some drawbacks that require special attention. Notwithstanding different control strategies are being followed to overcome these issues; the use of other self-rectifying turbines could directly achieve this goal at the expense of some extra construction, maintenance, and operation costs. However, these newly developed turbines in turn show diverse behaviours that should be compared for each case. This paper aims to analyse this comparison for the Mutriku wave energy power plant.This work was supported by the MINECO through the
Research Project DPI2015-70075-R (MINECO/FEDER, UE)
and in part by the University of the Basque Country
(UPV/EHU) through PPG17/33. The authors would like to
thank the collaboration of the Basque Energy Agency (EVE)
through Agreement UPV/EHUEVE23/6/2011, the Spanish
National Fusion Laboratory (EURATOM-CIEMAT) through
Agreement UPV/EHUCIEMAT08/190, and EUSKAMPUSCampus
of International Excellence
Pendulum Integration and Elliptic Functions
Revisiting canonical integration of the classical pendulum around its
unstable equilibrium, normal hyperbolic canonical coordinates are constructe
Introducing the concept of first and last value to aid lean design: learning from social housing projects In Chile
Value for the customer through efficient production processes is a fundamental principle of Lean. In Lean Construction, Value to customers is largely delivered through project planning and control activities only. Thus, it can be argued that Lean Construction overlooks the opportunity to address Value from the early stages of a project. Aimed at improving this, Lean Design arose as a new approach for design management promoting customer and end user involvement from the early stage of projects. However, even here environmental & social issues are postponed over individual requirements. As a result, Lean potential in general skips the opportunity to address Value from a wider perspective in which the return of Value from the construction industry to society is considered. This paper proposes dividing the wider understanding of the performance of the (global) built environment from the particular (local) project requirements calling the former First Value and the latter Last Value. The theory is triangulated through observation of how a developing country (Chile) is resolving social issues through the use of the built environment. The work described develops Lean Design Management by providing a clearer vision of Value to reduce waste and aid sustainability in the built environment
The role of rotation on Petersen Diagrams. The period ratios
The present work explores the theoretical effects of rotation in calculating
the period ratios of double-mode radial pulsating stars with special emphasis
on high-amplitude delta Scuti stars (HADS). Diagrams showing these period
ratios vs. periods of the fundamental radial mode have been employed as a good
tracer of non-solar metallicities and are known as Petersen diagrams (PD).In
this paper we consider the effect of moderate rotation on both evolutionary
models and oscillation frequencies and we show that such effects cannot be
completely neglected as it has been done until now. In particular it is found
that even for low-to-moderate rotational velocities (15-50 km/s), differences
in period ratios of some hundredths can be found. The main consequence is
therefore the confusion scenario generated when trying to fit the metallicity
of a given star using this diagram without a previous knowledge of its
rotational velocity.Comment: A&A in pres
Inconsistencies in the application of harmonic analysis to pulsating stars
Using ultra-precise data from space instrumentation we found that the
underlying functions of stellar light curves from some AF pul- sating stars are
non-analytic, and consequently their Fourier expansion is not guaranteed. This
result demonstrates that periodograms do not provide a mathematically
consistent estimator of the frequency content for this kind of variable stars.
More importantly, this constitutes the first counterexample against the current
paradigm which considers that any physical process is described by a contin-
uous (band-limited) function that is infinitely differentiable.Comment: 9 pages, 8 figure
Symmetries in Fluctuations Far from Equilibrium
Fluctuations arise universally in Nature as a reflection of the discrete
microscopic world at the macroscopic level. Despite their apparent noisy
origin, fluctuations encode fundamental aspects of the physics of the system at
hand, crucial to understand irreversibility and nonequilibrium behavior. In
order to sustain a given fluctuation, a system traverses a precise optimal path
in phase space. Here we show that by demanding invariance of optimal paths
under symmetry transformations, new and general fluctuation relations valid
arbitrarily far from equilibrium are unveiled. This opens an unexplored route
toward a deeper understanding of nonequilibrium physics by bringing symmetry
principles to the realm of fluctuations. We illustrate this concept studying
symmetries of the current distribution out of equilibrium. In particular we
derive an isometric fluctuation relation which links in a strikingly simple
manner the probabilities of any pair of isometric current fluctuations. This
relation, which results from the time-reversibility of the dynamics, includes
as a particular instance the Gallavotti-Cohen fluctuation theorem in this
context but adds a completely new perspective on the high level of symmetry
imposed by time-reversibility on the statistics of nonequilibrium fluctuations.
The new symmetry implies remarkable hierarchies of equations for the current
cumulants and the nonlinear response coefficients, going far beyond Onsager's
reciprocity relations and Green-Kubo formulae. We confirm the validity of the
new symmetry relation in extensive numerical simulations, and suggest that the
idea of symmetry in fluctuations as invariance of optimal paths has
far-reaching consequences in diverse fields.Comment: 8 pages, 4 figure
Probing the Stellar Surface of HD 209458 from Multicolor Transit Observations
Multicolor photometric observations of a planetary transit in the system HD
209458 are analyzed. The observations, made in the Stromgren photometric
system, allowed a recalculation of the basic physical properties of the
star-planet system. This includes derivation of linear limb-darkening values of
HD 209458, which is the first time that a limb-darkening sequence has
observationally been determined for a star other than the Sun. As the derived
physical properties depend on assumptions that are currently known with limited
precision only, scaling relations between derived parameters and assumptions
are given. The observed limb-darkening is in good agreement with theoretical
predictions from evolutionary stellar models combined with ATLAS model
atmospheres, verifying these models for the temperature (Teff ~ 6000K), surface
gravity (log g ~ 4.3) and mass (~ 1.2 Msol) of HD 209458.Comment: 16 pages, 8 figures, uses elsart.cls, accepted for New Astronom
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