2,890 research outputs found
Residual Stresses in Layered Manufacturing
Layered Manufacturing processes accumulate residual stresses during materialbuildup. These stresses may cause part warping and layer delamination. This paper presents
work done on investigating residual stress accumulation andp(i,rt distortion of Layered
Manufactured artifacts. A simple analyticaLmodel was developed and used to determine how the number of layers and the layer thickness influences part warping. Resllits
show that thin layers produce lower part deflection as compared with depositing fewer
and thicker layers. In addition to the analytical work, a finite element model wasdeveloped and used to illvestigate the deposition pattern's influence on. the part deflection.
Finite element model and corresponding experimental analysis showed that the geometry of the deposition pattern significantly affects the resulting part distortion. This
finite element model was also used to investigate an inter-layer surface defect,. known
as the Christmas Thee Step, that is associated with Shape Deposition Manufacturing.
Results indicate that the features of this defect are influenced only by the material
deposited close. to the part·surface and the particular material deposited. The step is
not affected by the deposition pattern.Mechanical Engineerin
Accuracy of circular polarization as a measure of spin polarization in quantum dot qubits
A quantum dot spin LED provides a test of carrier spin injection into a
qubit, as well as a means of analyzing carrier spin injection in general and
local spin polarization. The polarization of the observed light is, however,
significantly influenced by the dot geometry so the spin may be more polarized
than the emitted light would naively suggest. We have calculated carrier
polarization-dependent optical matrix elements using 8-band strain-dependent
k.p theory for InAs/GaAs self-assembled quantum dots (SAQDs) for electron and
hole spin injection into a range of quantum dot sizes and shapes, and for
arbitrary emission directions. The observed circular polarization does not
depend on whether the injected spin-polarized carriers are electrons or holes,
but is strongly influenced by the SAQD geometry and emission direction.
Calculations for typical SAQD geometries with emission along [110] show light
that is only ~5% circularly polarized for spin states that are 100% polarized
along [110]. Therefore observed polarizations [Chye et al. PRB 66, 201301(R)]
of ~1% imply a spin polarization within the dot of ~20%. We also find that
measuring along the growth direction gives near unity conversion of spin to
photon polarization, and is the least sensitive to uncertainties in SAQD
geometry.Comment: 4 pages, 6 figure
Interaction Effects in Conductivity of Si Inversion Layers at Intermediate Temperatures
We compare the temperature dependence of resistivity \rho(T) of Si MOSFETs
with the recent theory by Zala et al. This comparison does not involve any
fitting parameters: the effective mass m* and g*-factor for mobile electrons
have been found independently. An anomalous increase of \rho with temperature,
which has been considered a signature of the "metallic" state, can be described
quantitatively by the interaction effects in the ballistic regime. The in-plane
magnetoresistance \rho(B) is qualitatively consistent with the theory; however,
the lack of quantitative agreement indicates that the magnetoresistance is more
susceptible to the sample-specific effects than \rho(T).Comment: 4 pages, 5 figures. References update
A Mesoscopic Quantum Eraser
Motivated by a recent experiment by Buks et al. [Nature 391, 871 (1998)] we
consider electron transport through an Aharonov-Bohm interferometer with a
quantum dot in one of its arms. The quantum dot is coupled to a quantum system
with a finite number of states acting as a which-path detector. The
Aharonov-Bohm interference is calculated using a two-particle scattering
approach for the joint transitions in detector and quantum dot. Tracing over
the detector yields dephasing and a reduction of the interference amplitude. We
show that the interference can be restored by a suitable measurement on the
detector and propose a mesoscopic quantum eraser based on this principle.Comment: 7 pages, 2 figures, to appear in Europhys. Lett., uses EuroPhys.sty
and EuroMacro.tex (included
Reply to Comment on "Weak anisotropy and disorder dependence of the in-plane magnetoresistance in high mobility (100) Si-inversion layers"
Reply to the Comment by V.T. Dolgopolov and A.V. Gold [cond-mat/0203276].Comment: 2 page
Tuning of the Gap in a Laughlin-Bychkov-Rashba Incompressible Liquid
We report on our investigation of the influence of Bychkov-Rashba spin-orbit
interaction (SOI) on the incompressible Laughlin state. We find that
experimentally obtainable values of the spin-orbit coupling strength can induce
as much as a 25% increase in the quasiparticle-quasihole gap Eg at low magnetic
fields in InAs, thereby increasing the stability of the liquid state. The
SOI-modulated enhancement of Eg is also significant for filling factors 1/5 and
1/7, where the FQH state is usually weak. This raises the intriguing
possibility of tuning, via the SO coupling strength, the liquid to solid
transition to much lower densities.Comment: 4 pages, 3 figure
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