Liking to be in America: Puerto Rico’s Quest for Difference in the United States

The interaction between wind turbines in simple wind farm layouts is investigated with the purpose of observing the influence of wake loss phenomenon on the energy production of downwind turbines. Following an intensive exploration stage about wind farm aerodynamics and wake modeling subjects, several tests cases are designed to represent various wind farm configurations, consisting of different number of wind turbines. These cases are simulated by using DNV GL WindFarmer software which provides the opportunity of performing simulations with two different wake modeling techniques, namely Modified PARK and Eddy Viscosity. Various terrain and ambient turbulence intensity conditions are considered during the test cases. Also three different turbine types having different hub heights, rotor diameters and power-thrust coefficients are used in order to observe the effect of turbine characteristics on wake formation. Besides WindFarmer, WAsP and MATLAB tools are used in some simulation stages in order to generate input data such as wind and terrain conditions or farm layout configurations; and to process the data obtained in the end of these test cases. Simulations which are executed in the presence of a predominant wind direction from a narrow direction bin indicate that, even though there exists no significant interaction between the turbines placed in abreast configurations, successive turbine rows affect each other strongly due to the existence of the wake region of upwind turbines. It is observed that downwind spacing between turbine rows required to recover wake deficit up to a certain level changes depending on terrain and ambient turbulence intensity conditions together with turbine characteristics. For instance increasing surface roughness length (or ambient turbulence intensity) of a given site by keeping all the other parameters constant can provide up to 20% (or 30%) decrease in the required downstream distance to reduce wake loss to 5% level in a simple tandem layout consisting of two wind turbines. Further test cases are executed with various numbers of wind turbines in different configurations to observe the effect of partial, full and multiple wake regions on total farm efficiency. The results obtained from these cases are used in order to have a comparison between several farm layouts and evaluate their advantages and drawbacks

ac driven sine-Gordon solitons: dynamics and stability

The ac driven sine-Gordon equation is studied analytically and numerically, with the aim of providing a full description of how soliton solutions behave. To date, there is much controversy about when ac driven dc motion is possible. Our work shows that kink solitons exhibit dc or oscillatory motion depending on the relation between their initial velocity and the force parameters. Such motion is proven to be impossible in the presence of damping terms. For breathers, the force amplitude range for which they exist when dissipation is absent is found. All the analytical results are compared with numerical simulations, which in addition exhibit no dc motion at all for breathers, and an excellent agreement is found. In the conclusion, the generality of our results and connections to others systems for which a similar phenomenology may arise are discussed.Comment: 10 pages, latex, PostScript figures included with epsfig, to appear in European Physical Journal B, see GISC homepage at http://valbuena.fis.ucm.es/ for related wor

Innovative research in the design and operation of large telescopes for space: Aspects of giant telescopes in space

The capability and understanding of how to finish the reflector surfaces needed for large space telescopes is discussed. The technology for making very light glass substrates for mirrors is described. Other areas of development are in wide field imaging design for very fast primaries, in data analysis and retrieval methods for astronomical images, and in methods for making large area closely packed mosaics of solid state array detectors

Massive star formation in Wolf-Rayet galaxies. IV: Colours, chemical composition analysis and metallicity-luminosity relations

(Abridged) We performed a multiwavelength analysis of a sample of starburst galaxies that show the presence of a substantial population of very young massive (WR) stars. Here we present the global analysis of the derived photometric and chemical properties. We compare optical/NIR colours and the physical properties (reddening coefficient, equivalent widths of the emission and underlying absorption lines, ionization degree, electron density, and electron temperature) and chemical properties with previous observations and galaxy evolution models. Attending to their absolute B-magnitude many of them are not dwarf galaxies, but they should be during their quiescent phase. We found that both C(Hb) and Wabs increase with increasing metallicity. We detected a high N/O ratio in objects showing strong WR features. The ejecta of the WR stars may be the origin of the N enrichment in these galaxies. We compared the abundances provided by the direct method with those obtained using empirical calibrations, finding that (i) the Pilyugin method is the best suitable empirical calibration, (ii) the relations between the oxygen abundance and the N2 or the O3N2 parameters provided by Pettini & Pagel (2004) give acceptable results for objects with 12+log(O/H)>8.0, and (iii) the results provided by empirical calibrations based on photoionization models are systematically 0.2-0.3 dex higher than the values derived from the direct method. The O and N abundances and the N/O ratios are related to the optical/NIR luminosity; the dispersion is consequence of the differences in the star-formation histories. Galaxies with redder colours tend to have higher oxygen and nitrogen abundances. Our detailed analysis is fundamental to understand the nature of galaxies showing strong starbursts, as well as to know their star formation history and the relationships with the environment.Comment: 30 pages, 22 figures, accepted to A&A. Updated with the final version

On a conjecture regarding Fisher information

Fisher's information measure plays a very important role in diverse areas of theoretical physics. The associated measures as functionals of quantum probability distributions defined in, respectively, coordinate and momentum spaces, are the protagonists of our present considerations. The product of them has been conjectured to exhibit a non trivial lower bound in [Phys. Rev. A (2000) 62 012107]. We show here that such is not the case. This is illustrated, in particular, for pure states that are solutions to the free-particle Schr\"odinger equation. In fact, we construct a family of counterexamples to the conjecture, corresponding to time-dependent solutions of the free-particle Schr\"odinger equation. We also give a new conjecture regarding any normalizable time-dependent solution of this equation.Comment: 4 pages; revised equations, results unchange

The Laplacian spectral excess theorem for distance-regular graphs

The spectral excess theorem states that, in a regular graph G, the average excess, which is the mean of the numbers of vertices at maximum distance from a vertex, is bounded above by the spectral excess (a number that is computed by using the adjacency spectrum of G), and G is distance-regular if and only if equality holds. In this note we prove the corresponding result by using the Laplacian spectrum without requiring regularity of G