Opportunities for and challenges to further reductions in the “specific power” rating of wind turbines installed in the United States

A wind turbine’s “specific power” rating relates its capacity to the swept area of its rotor in terms of Watt per square meter. For a given generator capacity, specific power declines as rotor size increases. In land-rich but capacity-constrained wind power markets, such as the United States, developers have an economic incentive to maximize megawatt-hours per constrained megawatt, and so have favored turbines with ever-lower specific power. To date, this trend toward lower specific power has pushed capacity factors higher while reducing the levelized cost of energy. We employ geospatial levelized cost of energy analysis across the United States to explore whether this trend is likely to continue. We find that under reasonable cost scenarios (i.e. presuming that logistical challenges from very large blades are surmountable), low-specific-power turbines could continue to be in demand going forward. Beyond levelized cost of energy, the boost in market value that low-specific-power turbines provide could become increasingly important as wind penetration grows

Strings in gravity with torsion

A theory of gravitation in 4D is presented with strings used in the material action in $U_4$ spacetime. It is shown that the string naturally gives rise to torsion. It is also shown that the equation of motion a string follows from the Bianchi identity, gives the identical result as the Noether conservation laws, and follows a geodesic only in the lowest order approximation. In addition, the conservation laws show that strings naturally have spin, which arises not from their motion but from their one dimensional structure.Comment: 16 page

Dilute Bose gases interacting via power-law potentials

Neutral atoms interact through a van der Waals potential which asymptotically falls off as r^{-6}. In ultracold gases, this interaction can be described to a good approximation by the atom-atom scattering length. However, corrections arise that depend on the characteristic length of the van der Waals potential. We parameterize these corrections by analyzing the energies of two- and few-atom systems under external harmonic confinement, obtained by numerically and analytically solving the Schrodinger equation. We generalize our results to particles interacting through a longer-ranged potential which asymptotically falls off as r^{-4}.Comment: 7 pages, 4 figure

Promoting independent learning skills using video on digital language laboratories

This is the author's PDF version of an article published in Computer assisted language learning ©2006. The definitive version is available at http://www.informaworld.com/The article discusses the potential for developing independent learning skills using the digital language laboratory with particular reference to exploiting the increasingly available resource of digital video. It investigates the potential for recording and editing video clips from online sources and digitalising clips from analogue recordings and reflects on the current status quo regarding the complex copyright regulations in this area. It describes two pilot self-access programmes based on video clips which were undertaken with University College Chester undergraduates and reflects on the value of the experience for students in developing a wide range of language skills as well as independent learning skills using their feedback on the experience

Fermion Helicity Flip Induced by Torsion Field

We show that in theories of gravitation with torsion the helicity of fermion particles is not conserved and we calculate the probability of spin flip, which is related to the anti-symmetric part of affine connection. Some cosmological consequences are discussed.Comment: 6 pages, to appear in Europhysics Letter

Pressure-induced diamond to beta-tin transition in bulk silicon: a near-exact quantum Monte Carlo study

The pressure-induced structural phase transition from diamond to beta-tin in silicon is an excellent test for theoretical total energy methods. The transition pressure provides a sensitive measure of small relative energy changes between the two phases (one a semiconductor and the other a semimetal). Experimentally, the transition pressure is well characterized. Density-functional results have been unsatisfactory. Even the generally much more accurate diffusion Monte Carlo method has shown a noticeable fixed-node error. We use the recently developed phaseless auxiliary-field quantum Monte Carlo (AFQMC) method to calculate the relative energy differences in the two phases. In this method, all but the error due to the phaseless constraint can be controlled systematically and driven to zero. In both structural phases we were able to benchmark the error of the phaseless constraint by carrying out exact unconstrained AFQMC calculations for small supercells. Comparison between the two shows that the systematic error in the absolute total energies due to the phaseless constraint is well within 0.5 mHa/atom. Consistent with these internal benchmarks, the transition pressure obtained by the phaseless AFQMC from large supercells is in very good agreement with experiment.Comment: 9 pages, 5 figure

Two-dimensional molecular para-hydrogen and ortho-deuterium at zero temperature

We study molecular para-hydrogen (p-${\rm H_{2}}$) and ortho-deuterium (o-${\rm D_{2}}$) in two dimensions and in the limit of zero temperature by means of the diffusion Monte Carlo method. We report energetic and structural properties of both systems like the total and kinetic energy per particle, radial pair distribution function, and Lindemann's ratio in the low pressure regime. By comparing the total energy per particle as a function of the density in liquid and solid p-${\rm H_{2}}$, we show that molecular para-hydrogen, and also ortho-deuterium, remain solid at zero temperature. Interestingly, we assess the quality of three different symmetrized trial wave functions, based on the Nosanow-Jastrow model, in the p-${\rm H_{2}}$ solid film at the variational level. In particular, we analyze a new type of symmetrized trial wave function which has been used very recently to describe solid $^{4}$He and found that also characterizes hydrogen satisfactorily. With this wave function, we show that the one-body density matrix $\varrho_{1} (r)$ of solid p-${\rm H_{2}}$ possesses off-diagonal long range order, with a condensate fraction that increases sizably in the negative pressure regime.Comment: 11 pages, 9 figure

Professional training and participatory research: Combined actions for developing organic rice farming in the Camargue region of France

In 2006 and 2007, INRA’s Joint Research Unit, Innovation, was a partner in a European professional training project within the framework of the Leonardo da Vinci programme. The objective of this project was to help develop organic rice farming in the major European rice-growing regions where rice is mainly cultivated in ecologically-sensitive areas. In France, the rate of conversion to organic production is much lower that what would be expected, since organic rice farming presents particular technical problems. The availability of expert support is critical to successful conversion and no structured training was available in the past. This is the reason why we developed a participatory training method that helps rice growers and stakeholders to convert to organic farming and to improve their organic rice production. Different training sessions were organised. The participants shared their thoughts about technical problems encountered and identified possible solutions. Some of the topics developed were weeds, soils and fertility, and varieties. At the end of these sessions, a motivated workgroup was set up. Some of its members even proposed to assess the efficiency of some of the techniques that were discussed during the work sessions in fields on their own farms. Furthermore, field visits were organised in the Camargue region of France and in Spain. Scientists and group members hope to be able to continue to work together after the O.R.P.E.S.A. project is over. In order to make this possible, we are now planning to initiate new research and development actions using the same approach

Simulating The Doppler-Free Fluorescence Spectrum For The Potassium D1 Transitions

Radiation theory (absorption, spontaneous emission, and stimulated emission) is applied to Potassium (39K and 41K) to examine details of the D1 lines, Figure 1, in the near IR at 770 nm. When examining the resonance fluorescence from two counter-propagation laser beams in a K cell, Figure 2, three prominent “Doppler-free” features—dips at the D1a and D1b resonances and spikes at their crossover frequencies—stand out superposed on the fluorescence background. They are examined with a detailed simulation, Figures 3 and 4, and compared to observations, Figure 5. Parametric studies of the Doppler-free features, Figures 6–8, indicate how to maximize their prominence, and thus their importance as frequency references for laboratory and atmospheric observations

Few-body resonances of unequal-mass systems with infinite interspecies two-body s-wave scattering length

Two-component Fermi and Bose gases with infinitely large interspecies s-wave scattering length $a_s$ exhibit a variety of intriguing properties. Among these are the scale invariance of two-component Fermi gases with equal masses, and the favorable scaling of Efimov features for two-component Bose gases and Bose-Fermi mixtures with unequal masses. This paper builds on our earlier work [D. Blume and K. M. Daily, arXiv:1006.5002] and presents a detailed discussion of our studies of small unequal-mass two-component systems with infinite $a_s$ in the regime where three-body Efimov physics is absent. We report on non-universal few-body resonances. Just like with two-body systems on resonance, few-body systems have a zero-energy bound state in free space and a diverging generalized scattering length. Our calculations are performed within a non-perturbative microscopic framework and investigate the energetics and structural properties of small unequal-mass two-component systems as functions of the mass ratio $\kappa$, and the numbers $N_{1}$ and $N_2$ of heavy and light atoms. For purely attractive Gaussian two-body interactions, we find that the $(N_1,N_2)=(2,1)$ and $(3,1)$ systems exhibit three-body and four-body resonances at mass ratios $\kappa = 12.314(2)$ and 10.4(2), respectively. The three- and four-particle systems on resonance are found to be large. This suggests that the corresponding wave function has relatively small overlap with deeply-bound dimers, trimers or larger clusters and that the three- and four-body systems on resonance have a comparatively long lifetime. Thus, it seems feasible that the features discussed in this paper can be probed experimentally with present-day technology.Comment: 17 pages, 17 figure