3,807 research outputs found
Design and evaluation of low cost blades for large wind driven generating systems
The development and evaluation of a low cost blade concept based on the NASA-Lewis specifications is discussed. A blade structure was designed and construction methods and materials were selected. Complete blade tooling concepts, various technical and economic analysis, and evaluations of the blade design were performed. A comprehensive fatigue test program was conducted to provide data and to verify the design. A test specimen of the spar assembly, including the root end attachment, was fabricated. This is a full-scale specimen of the root end configuration, 20 ft long. A blade design for the Mod '0' system was completed
Impurity corrections to the thermodynamics in spin chains using a transfer-matrix DMRG method
We use the density matrix renormalization group (DMRG) for transfer matrices
to numerically calculate impurity corrections to thermodynamic properties. The
method is applied to two impurity models in the spin-1/2 chain, namely a weak
link in the chain and an external impurity spin. The numerical analysis
confirms the field theory calculations and gives new results for the crossover
behavior.Comment: 9 pages in revtex format including 5 embedded figures (using epsf).
To appear in PRB. The latest version in PDF format can be found at
http://fy.chalmers.se/~eggert/papers/DMRGimp.pd
Edge Logarithmic Corrections probed by Impurity NMR
Semi-infinite quantum spin chains display spin autocorrelations near the
boundary with power-law exponents that are given by boundary conformal field
theories. We show that NMR measurements on spinless impurities that break a
quantum spin chain lead to a spin-lattice relaxation rate 1/T_1^edge that has a
temperature dependence which is a direct probe of the anomalous boundary
exponents. For the antiferromagnetic S=1/2 spin chain, we show that 1/T_1^edge
behaves as T (log T)^2 instead of (log T)^1/2 for a bulk measurement. We show
that, in the case of a one-dimensional conductor described by a Luttinger
liquid, a similar measurement leads to a relaxation rate 1/T_1^{edge} behaving
as T, independent of the anomalous exponent K_rho.Comment: 4 pages, 1 encapsulated figure, corrected typo
Numerical Evidence for Multiplicative Logarithmic Corrections from Marginal Operators
Field theory calculations predict multiplicative logarithmic corrections to
correlation functions from marginally irrelevant operators. However, for the
numerically most suitable model - the spin-1/2 chain - these corrections have
been controversial. In this paper, the spin-spin correlation function of the
antiferromagnetic spin-1/2 chain is calculated numerically in the presence of a
next nearest neighbor coupling J2 for chains of up to 32 sites. By varying the
coupling strength J2 we can control the effect of the marginal operator, and
our results unambiguously confirm the field theory predictions. The critical
value at which the marginal operator vanishes has been determined to be at J2 =
0.241167 +/- 0.000005J.Comment: revised paper with extended data-analysis. 5 pages, using revtex with
4 embedded figures (included with macro). A complete postscript file with all
figures + text (5 pages) is available from
http://FY.CHALMERS.SE/~eggert/marginal.ps or by request from
[email protected]
Design and evaluation of low-cost stainless steel fiberglass foam blades for large wind driven generating systems
A low cost wind turbine blade based on a stainless steel fiberglass foam Budd blade design concept, was evaluated for its principle characteristics, low cost features, and its advantages and disadvantages. A blade structure was designed and construction methods and materials were selected. A complete blade tooling concepts, various technical and economic analysis, and evaluations of the blade design were performed. A comprehensive fatigue test program is conducted to provide data to verify the design stress allowables
Universal alternating order around impurities in antiferromagnets
The study of impurities in antiferromagnets is of considerable interest in
condensed matter physics. In this paper we address the elementary question of
the effect of vacancies on the orientation of the surrounding magnetic moments
in an antiferromagnet. In the presence of a magnetic field, alternating
magnetic moments are induced, which can be described by a universal expression
that is valid in any ordered antiferromagnet and turns out to be independent of
temperature over a large range. The universality is not destroyed by quantum
fluctuation, which is demonstrated by quantum Monte Carlo simulations in the
two-dimensional Heisenberg antiferromagnet. Physical predictions for finite
doping are made, which are relevant for experiments probing Knight shifts and
the order parameter.Comment: 5 pages, 2 figures. The most recent version in PDF format can be
found at http://www.physik.uni-kl.de/eggert/papers
Phase diagram of an impurity in the spin-1/2 chain: two channel Kondo effect versus Curie law
We consider a magnetic s=1/2 impurity in the antiferromagnetic spin chain as
a function of two coupling parameters: the symmetric coupling of the impurity
to two sites in the chain and the coupling between the two sites .
By using field theory arguments and numerical calculations we can identify all
possible fixed points and classify the renormalization flow between them, which
leads to a non-trivial phase diagram. Depending on the detailed choice of the
two (frustrating) coupling strengths, the stable phases correspond either to a
decoupled spin with Curie law behavior or to a non-Fermi liquid fixed point
with a logarithmically diverging impurity susceptibility as in the two channel
Kondo effect. Our results resolve a controversy about the renormalization flow.Comment: 5 pages in revtex format including 4 embedded figures (using epsf).
The latest version in PDF format is available from
http://fy.chalmers.se/~eggert/papers/phase-diagram.pd
Universal cross-over behavior of a magnetic impurity and consequences for doping in spin-1/2 chains
We consider a magnetic impurity in the antiferromagnetic spin-1/2 chain which
is equivalent to the two-channel Kondo problem in terms of the field
theoretical description. Using a modification of the transfer-matrix density
matrix renormalization group (DMRG) we are able to determine local and global
properties in the thermodynamic limit. The cross-over function for the impurity
susceptibility is calculated over a large temperature range, which exhibits
universal data-collapse. We are also able to determine the local
susceptibilities near the impurity, which show an interesting competition of
boundary effects. This results in quantitative predictions for experiments on
doped spin-1/2 chains, which could observe two-channel Kondo physics directly.Comment: 5 pages in revtex format including 3 embedded figures (using epsf).
The latest version in PDF format is available from
http://fy.chalmers.se/~eggert/papers/crossover.pdf . Accepted by PR
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