2,312 research outputs found
Effect of wind turbine generator model and siting on wind power changes out of large WECS arrays
Methods of reducing the WECS generation change through selection of the wind turbine model for each site, selection of an appropriate siting configuration, and wind array controls are discussed. An analysis of wind generation change from an echelon and a farm for passage of a thunderstorm is presented. Reduction of the wind generation change over ten minutes is shown to reduce the increase in spinning reserve, unloadable generation and load following requirements on unit commitment when significant WECS generation is present and the farm penetration constraint is satisfied. Controls on the blade pitch angle of all wind turbines in an array or a battery control are shown to reduce both the wind generation change out of an array and the effective farm penetration in anticipation of a storm so that the farm penetration constraint may be satisfied
Measurements and comparison of primary biological aerosol above and below a tropical forest canopy using a dual channel fluorescence spectrometer
Original article can be found at: http://www.atmos-chem-phys.net/10/issue10.html Copyright - the authors. Authors grant any third party the right to use the article freely as long as its original authors and citation details are identified. The article and any associated published material is distributed under the Creative Commons Attribution 3.0 License.Aerosol particle size distributions were measured below and above a tropical rainforest canopy in Borneo, Malaysia, in June/July 2008 using the WIBS-3: a single particle dual channel fluorescence spectrometer. Material in the size range 0.8–20 μm was characterized according to optical equivalent diameter (DP), morphology and fluorescence at 310–400 nm and 400–600 nm following excitation at 280 nm and 370 nm respectively. Particles fluorescent after both excitations are likely to be fluorescent primary biological aerosol particles (FBAP). Measured FBAP number concentration (NFBAP) at both sites exhibited clear diurnal cycles. The largest variability was observed in the understorey, where NFBAP reached a minimum of 50–100 L−1 in late morning. In mid afternoon it exhibited strong transient fluctuations as large as 4000 L−1 that were followed by sustained concentrations of 1000–2500 L−1 that reduced steadily between midnight and sunrise. Above the canopy FBAP number ranged from 50–100 L−1 during the daytime to 200–400 L−1 at night but did not exhibit the transient enhancements seen in the understorey. The strong FBAP fluctuations were attributed to the release of fungal spores below the canopy and appeared to be linked to elevated relative humidity. The mean FBAP number fraction in the size range 0.8 μm<DP<20 μm was 55% in the understorey and 28% above canopy. A size mode at 2 μm<DP<4 μm appears at both sites and is primarily FBAP, which dominated the coarse (DP≥2.5 μm) number concentration at both sites, accounting for 75% in the understorey and 57% above the canopy. In contrast, the concentration of non-fluorescent particles (NNON) at both sites was typically 200–500 L−1, the majority of which occupied a size mode at 0.8<DP<1.5 μm. Enhanced understorey NNON was observed daily in mid-afternoon and also at midday on three occasions: the former coincided with the FBAP enhancements and measured approximately 10% of their magnitude; the latter occurred independently of the NFBAP diurnal cycle and comprised particles smaller than 2 μm. Particle diameter of 3–5 μm is consistent with smaller fungal spores, though absolute identification of biological species is not possible with the UV-LIF technique. Based on the measured FBAP and non-fluorescent particle abundances and their observed recovery times following rain showers, FBAP originated beneath the canopy while the non-fluorescent material was transported from further away. It is concluded that these separate sources contributed the majority of the aerosol measured by the WIBS-3 at both sites.Peer reviewe
Czochralski crystal growth: Modeling study
The modeling study of Czochralski (Cz) crystal growth is reported. The approach was to relate in a quantitative manner, using models based on first priniciples, crystal quality to operating conditions and geometric variables. The finite element method is used for all calculations
Static and dynamic properties of crystalline phases of two-dimensional electrons in a strong magnetic field
We study the cohesive energy and elastic properties as well as normal modes
of the Wigner and bubble crystals of the two-dimensional electron system (2DES)
in higher Landau levels. Using a simple Hartree-Fock approach, we show that the
shear moduli ('s) of these electronic crystals show a non-monotonic
behavior as a function of the partial filling factor at any given
Landau level, with increasing for small values of , before
reaching a maximum at some intermediate filling factor , and
monotonically decreasing for . We also go beyond previous
treatments, and study how the phase diagram and elastic properties of electron
solids are changed by the effects of screening by electrons in lower Landau
levels, and by a finite thickness of the experimental sample. The implications
of these results on microwave resonance experiments are briefly discussed.Comment: Discussion updated - 16 pages, 10 figures; version accepted for
publication in Phys. Rev.
Anisotropic states of two-dimensional electrons in high magnetic fields
We study the collective states formed by two-dimensional electrons in Landau
levels of index near half-filling. By numerically solving the
self-consistent Hartree-Fock (HF) equations for a set of oblique
two-dimensional lattices, we find that the stripe state is an anisotropic
Wigner crystal (AWC), and determine its precise structure for varying values of
the filling factor. Calculating the elastic energy, we find that the shear
modulus of the AWC is small but finite (nonzero) within the HF approximation.
This implies, in particular, that the long-wavelength magnetophonon mode in the
stripe state vanishes like as in an ordinary Wigner crystal, and not
like as was found in previous studies where the energy of shear
deformations was neglected.Comment: minor corrections; 5 pages, 4 figures; version to be published in
Physical Review Letter
Luttinger Liquid in the Core of Screw Dislocation in Helium-4
On the basis of first-principle Monte Carlo simulations we find that the
screw dislocation along the hexagonal axis of an hcp He4 crystal features a
superfluid core. This is the first example of a regular quasi-one-dimensional
supersolid, and one of the cleanest cases of a regular Luttinger-liquid system.
In contrast, the same type of screw dislocation in solid Hydrogen is
insulating.Comment: replaced with revised versio
Deployable-erectable trade study for space station truss structures
The results of a trade study on truss structures for constructing the space station are presented. Although this study was conducted for the reference gravity gradient space station, the results are generally applicable to other configurations. The four truss approaches for constructing the space station considered in this paper were the 9 foot single fold deployable, the 15 foot erectable, the 10 foot double fold tetrahedral, and the 15 foot PACTRUSS. The primary rational for considering a 9 foot single-fold deployable truss (9 foot is the largest uncollapsed cross-section that will fit in the Shuttle cargo bay) is that of ease of initial on-orbit construction and preintegration of utility lines and subsystems. The primary rational for considering the 15 foot erectable truss is that the truss bay size will accommodate Shuttle size payloads and growth of the initial station in any dimension is a simple extension of the initial construction process. The primary rational for considering the double-fold 10 foot tetrahedral truss is that a relatively large amount of truss structure can be deployed from a single Shuttle flight to provide a large number of nodal attachments which present a pegboard for attaching a wide variety of payloads. The 15 foot double-fold PACTRUSS was developed to incorporate the best features of the erectable truss and the tetrahedral truss
Travelling waves in a drifting flux lattice
Starting from the time-dependent Ginzburg-Landau (TDGL) equations for a type
II superconductor, we derive the equations of motion for the displacement field
of a moving vortex lattice without inertia or pinning. We show that it is
linearly stable and, surprisingly, that it supports wavelike long-wavelength
excitations arising not from inertia or elasticity but from the
strain-dependent mobility of the moving lattice. It should be possible to image
these waves, whose speeds are a few \mu m/s, using fast scanning tunnelling
microscopy.Comment: 4 pages, revtex, 2 .eps figures imbedded in paper, title shortened,
minor textual change
Fluctuation conductivity in superconductors in strong electric fields
We study the effect of a strong electric field on the fluctuation
conductivity within the time-dependent Ginzburg-Landau theory for the case of
arbitrary dimension. Our results are based on the analytical derivation of the
velocity distribution law for the fluctuation Cooper pairs, from the Boltzmann
equation. Special attention is drawn to the case of small nonlinearity of
conductivity, which can be investigated experimentally. We obtain a general
relation between the nonlinear conductivity and the temperature derivative of
the linear Aslamazov-Larkin conductivity, applicable to any superconductor. For
the important case of layered superconductors we derive an analogous relation
between the small nonlinear correction for the conductivity and the
fluctuational magnetoconductivity. On the basis of these relations we provide
new experimental methods for determining both the lifetime constant of
metastable Cooper pairs above T_c and the coherence length. A systematic
investigation of the 3rd harmonic of the electric field generated by a harmonic
current can serve as an alternative method for the examination of the
metastable Cooper-pair relaxation time.Comment: 18 pages, REVTeX, submitted to Phys. Rev.
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