User\u27s Guide to MBC3: Multi-Blade Coordinate Transformation Code for 3-Bladed Wind Turbine

The dynamics of wind turbine rotor blades are conventionally expressed in rotating frames attached to the individual blades. The tower-nacelle subsystem though, sees the combined effect of all rotor blades, not the individual blades. Also, the rotor responds as a whole to excitations such as aerodynamic gusts, control inputs, and tower-nacelle motion—all of which occur in a nonrotating frame. Multi-blade coordinate transformation (MBC) helps integrate the dynamics of individual blades and express them in a fixed (nonrotating) frame. MBC involves two steps: transforming the rotating degrees of freedom and transforming the equations of motion. Reference 1 details the MBC operation. This guide summarizes the MBC concept and underlying transformations

Comment on "Froehlich Mass in GaAs-Based Structures"

The results of recent measurements of the cyclotron resonance (CR) spectra for a GaAs quantum well are interpreted in terms of the resonant magnetopolaron effect. Owing to this effect, the CR peaks split near the TO-phonon frequency and also change their positions with respect to those obtained without electron-phonon interaction. The theoretical peak positions of the CR spectra calculated within the many-polaron approach compare well with experimental data, as distinct from the CR energies calculated without electron-phonon interaction, which show no particular features in the region of the optical-phonon frequencies. We conclude that the Froehlich polaron concept is valid and even necessary to interpret the CR spectra of quantum wells.Comment: 1 page, 1 figure, E-mail addresses: [email protected], [email protected]

Room temperature spin coherence in ZnO

Time-resolved optical techniques are used to explore electron spin dynamics in bulk and epilayer samples of n-type ZnO as a function of temperature and magnetic field. The bulk sample yields a spin coherence time T2* of 20 ns at T = 30 K. Epilayer samples, grown by pulsed laser deposition, show a maximum T2* of 2 ns at T = 10 K, with spin precession persisting up to T = 280 K.Comment: 3 pages, 3 figure

Strong charge-transfer excitonic effects and Bose-Einstein exciton-condensate in graphane

Using first principles many-body theory methods (GW+BSE) we demonstrate that optical properties of graphane are dominated by localized charge-transfer excitations governed by enhanced electron correlations in a two-dimensional dielectric medium. Strong electron-hole interaction leads to the appearance of small radius bound excitons with spatially separated electron and hole, which are localized out-of-plane and in-plane, respectively. The presence of such bound excitons opens the path on excitonic Bose-Einstein condensate in graphane that can be observed experimentally.Comment: 8 pages, 6 figure

Imaging spin flows in semiconductors subject to electric, magnetic, and strain fields

Using scanning Kerr microscopy, we directly acquire two-dimensional images of spin-polarized electrons flowing laterally in bulk epilayers of n:GaAs. Optical injection provides a local dc source of polarized electrons, whose subsequent drift and/or diffusion is controlled with electric, magnetic, and - in particular - strain fields. Spin precession induced by controlled uniaxial stress along the axes demonstrates the direct k-linear spin-orbit coupling of electron spin to the shear (off-diagonal) components of the strain tensor.Comment: 5 pages, 5 color figure

Spin-Hall effect in two-dimensional mesoscopic hole systems

The spin Hall effect in two dimensional hole systems is studied by using the four-terminal Landauer-B\"{u}ttiker formula with the help of Green functions. The spin Hall effect exists even when there are {\em not} any correlations between the spin-up and -down heavy holes (light holes) and when the $\Gamma$-point degeneracy of the heavy hole and light hole bands is lifted by the confinement or recovered by the strain. When only a heavy hole charge current without any spin polarization is injected through one lead, under right choice of lead voltages, one can get a pure heavy (light) hole spin current, combined with a possible impure light (heavy) hole spin current from another two leads. The spin Hall coefficients of both heavy and light holes depend on the Fermi energy, devise size and the disorder strength. It is also shown that the spin Hall effect of two dimensional hole systems is much more robust than that of electron systems with the Rashba spin-orbit coupling and the spin Hall coefficients do not decrease with the system size but tend to some nonzero values when the disorder strength is smaller than some critical value.Comment: 5 pages, 4 figure

User's Guide to PreComp (Pre-Processor for Computing Composite Blade Properties)

PreComp (Pre-processor for computing Composite blade structural properties) was developed to compute the stiffness and inertial properties of a composite blade. The code may also be used to compute the structural properties of a metallic blade by treating it as a special case of an isotropic composite material. This guide provides step-by-step instructions on how to prepare input files (specify blade external geometry and internal structural layup of composite laminates), how to execute the code, and how to interpret the output properties. PreComp performs extensive checks for completeness, range, and viability of input data; these are also discussed in this manual. The code runs fast, usually in a fraction of a second, and requires only a modest knowledge of the composites and laminates schedule typically used in blades

Effective Hamiltonian of Strained Graphene

Based on the symmetry properties of graphene lattice, we derive the effective Hamiltonian of graphene under spatially non-uniform acoustic and optical strains. We show that with the proper selection of the parameters, the obtained Hamiltonian reproduces the results of first-principles spectrum calculations for acoustic strain up to 10%. The results are generalized for the case of graphene with broken plane reflection symmetry, which corresponds, for example, to the case of graphene placed at a substrate. Here, essential modifications to the Hamiltonian give rise, in particular, to the gap opening in the spectrum in the presence of the out of plane component of optical strain, which is shown to be due to the lifting of the sublattice symmetry. The developed effective Hamiltonian can be used as a convenient tool for analysis of a variety of strain-related effects, including electron-phonon interaction or pseudo-magnetic fields induced by the non-uniform strain

Theory of exciton fine structure in semiconductor quantum dots: quantum dot anisotropy and lateral electric field

Theory of exciton fine structure in semiconductor quantum dots and its dependence on quantum dot anisotropy and external lateral electric field is presented. The effective exciton Hamiltonian including long range electron-hole exchange interaction is derived within the k*p effective mass approximation (EMA). The exchange matrix elements of the Hamiltonian are expressed explicitly in terms of electron and hole envelope functions. The matrix element responsible for the "bright" exciton splitting is identified and analyzed. An excitonic fine structure for a model quantum dot with quasi- two-dimensional anisotropic harmonic oscillator (2DLAHO) confining potential is analyzed as a function of the shape anisotropy, size and applied lateral electric field

Exciton spin decay modified by strong electron-hole exchange interaction

We study exciton spin decay in the regime of strong electron-hole exchange interaction. In this regime the electron spin precession is restricted within a sector formed by the external magnetic field and the effective exchange fields triggered by random spin flips of the hole. Using Hanle effect measurements, we demonstrate that this mechanism dominates our experiments in CdTe/(Cd,Mg)Te quantum wells. The calculations provide a consistent description of the experimental results, which is supported by independent measurements of the parameters entering the model.Comment: 5 pages, 3 figure