637 research outputs found
Model-based Aeroservoelastic Design and Load Alleviation of Large Wind Turbine Blades
This paper presents an aeroservoelastic modeling approach for dynamic load alleviation
in large wind turbines with trailing-edge aerodynamic surfaces. The tower, potentially on a
moving base, and the rotating blades are modeled using geometrically non-linear composite
beams, which are linearized around reference conditions with arbitrarily-large structural
displacements. Time-domain aerodynamics are given by a linearized 3-D unsteady vortexlattice
method and the resulting dynamic aeroelastic model is written in a state-space
formulation suitable for model reductions and control synthesis. A linear model of a single
blade is used to design a Linear-Quadratic-Gaussian regulator on its root-bending moments,
which is finally shown to provide load reductions of about 20% in closed-loop on the full
wind turbine non-linear aeroelastic model
Linear scaling between momentum and spin scattering in graphene
Spin transport in graphene carries the potential of a long spin diffusion
length at room temperature. However, extrinsic relaxation processes limit the
current experimental values to 1-2 um. We present Hanle spin precession
measurements in gated lateral spin valve devices in the low to high (up to
10^13 cm^-2) carrier density range of graphene. A linear scaling between the
spin diffusion length and the diffusion coefficient is observed. We measure
nearly identical spin- and charge diffusion coefficients indicating that
electron-electron interactions are relatively weak and transport is limited by
impurity potential scattering. When extrapolated to the maximum carrier
mobilities of 2x10^5 cm^2/Vs, our results predict that a considerable increase
in the spin diffusion length should be possible
Keratinocyte footprint assay discriminates antilaminin-332 pemphigoid from all other forms of pemphigoid diseases
Background Antilaminin-332 mucous membrane pemphigoid is a chronic severe pemphigoid disease characterized by autoantibodies to laminin-332. At present no commercial assay is available to demonstrate antilaminin-332 antibodies, and diagnosis relies on in-house techniques with limited sensitivities. Objectives In order to move, keratinocytes cultured in vitro secrete laminin-332 to attach to the culture dish. In that way, they leave behind a unique footprint trail of laminin-332. We aimed to develop a sensitive and specific laboratory assay to determine antilaminin-332 autoantibodies in patient serum based on binding of patient IgG to these unique footprints. Methods Normal human keratinocytes were grown on glass coverslips and incubated with patient or control serum for 1 h. The binding of IgG was then investigated by immunofluorescence. After validating the test for its ability to identify antilaminin-332 autoantibodies it was converted into a daily available test based on binding of IgG to dried coverslips that can be stored frozen. The staining patterns of sera from patients with antilaminin-332 pemphigoid were then compared with those of sera from patients with other autoimmune bullous diseases and normal human sera. Results IgG of all antilaminin-332 pemphigoid sera (n = 16) bound to laminin-332 footprints, while all normal human controls (n = 55) were negative. From the sera of patients with other diseases (n = 72) four sera tested positive. The footprint assay was also positive for sera that were negative by salt-split skin analysis, demonstrating that it is a very sensitive technique. Conclusions The keratinocyte footprint assay is a fast and specific assay to confirm or rule out the presence of antilaminin-332 autoantibodies. What's already known about this topic? Antilaminin-332 mucous membrane pemphigoid is a severe form of pemphigoid, and patients may have an increased risk of malignancies. The diagnosis of antilaminin-332 mucous membrane pemphigoid is complicated by the lack of specific commercial tests for antilaminin-332 antibodies and can be confirmed only in specialized laboratories. Keratinocytes in culture need laminin-332 for adhesion and migration and therefore deposit it on the bottom of the culture dish. What does this study add? The keratinocyte footprint assay detects antilaminin-332 autoantibodies in patient serum using the native laminin-332 produced by cultured keratinocytes. What is the translational message? The keratinocyte footprint assay is a fast and specific assay to confirm or rule out the presence of antilaminin-332 autoantibodies
Large yield production of high mobility freely suspended graphene electronic devices on a PMGI based organic polymer
The recent observation of fractional quantum Hall effect in high mobility
suspended graphene devices introduced a new direction in graphene physics, the
field of electron-electron interaction dynamics. However, the technique used
currently for the fabrication of such high mobility devices has several
drawbacks. The most important is that the contact materials available for
electronic devices are limited to only a few metals (Au, Pd, Pt, Cr and Nb)
since only those are not attacked by the reactive acid (BHF) etching
fabrication step. Here we show a new technique which leads to mechanically
stable suspended high mobility graphene devices which is compatible with almost
any type of contact material. The graphene devices prepared on a
polydimethylglutarimide based organic resist show mobilities as high as 600.000
cm^2/Vs at an electron carrier density n = 5.0 10^9 cm^-2 at 77K. This
technique paves the way towards complex suspended graphene based spintronic,
superconducting and other types of devices.Comment: 14 pages, 4 figure
Electronic spin transport in graphene field effect transistors
Spin transport experiments in graphene, a single layer of carbon atoms,
indicate spin relaxation times that are significantly shorter than the
theoretical predictions. We investigate experimentally whether these short spin
relaxation times are due to extrinsic factors, such as spin relaxation caused
by low impedance contacts, enhanced spin flip processes at the device edges or
the presence of an aluminium oxide layer on top of graphene in some samples.
Lateral spin valve devices using a field effect transistor geometry allowed for
the investigation of the spin relaxation as a function of the charge density,
going continuously from metallic hole to electron conduction (charge densities
of cm) via the Dirac charge neutrality point (). The results are quantitatively described by a one dimensional spin
diffusion model where the spin relaxation via the contacts is taken into
account. Spin valve experiments for various injector/detector separations and
spin precession experiments reveal that the longitudinal (T) and the
transversal (T) relaxation times are similar. The anisotropy of the spin
relaxation times and , when the spins are injected
parallel or perpendicular to the graphene plane, indicates that the effective
spin orbit fields do not lie exclusively in the two dimensional graphene plane.
Furthermore, the proportionality between the spin relaxation time and the
momentum relaxation time indicates that the spin relaxation mechanism is of the
Elliott-Yafet type. For carrier mobilities of 2-5 cm2^/Vs and
for graphene flakes of 0.1-2 m in width, we found spin relaxation times of
the order of 50-200 ps, times which appear not to be determined by the
extrinsic factors mentioned above.Comment: 11 pages, 13 figure
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Incorporation of Multi-Member Substructure Capabilities in FAST for Analysis of Offshore Wind Turbines: Preprint
FAST, developed by the National Renewable Energy Laboratory (NREL), is an aero-hydro-servo-elastic tool widely used for analyzing onshore and offshore wind turbines. This paper discusses recent modifications made to FAST to enable the examination of offshore wind turbines with fixed-bottom, multi-member support structures (which are commonly used in transitional-depth waters).; This paper addresses the methods used for incorporating the hydrostatic and hydrodynamic loading on multi-member structures in FAST through its hydronamic loading module, HydroDyn. Modeling of the hydrodynamic loads was accomplished through the incorporation of Morison and buoyancy loads on the support structures. Issues addressed include how to model loads at the joints of intersecting members and on tapered and tilted members of the support structure. Three example structures are modeled to test and verify the solutions generated by the modifications to HydroDyn, including a monopile, tripod, and jacket structure. Verification is achieved through comparison of the results to a computational fluid dynamics (CFD)-derived solution using the commercial software tool STAR-CCM+
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