2,309 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
Quantum Dot as Spin Filter and Spin Memory
We consider a quantum dot in the Coulomb blockade regime weakly coupled to
current leads and show that in the presence of a magnetic field the dot acts as
an efficient spin-filter (at the single-spin level) which produces a
spin-polarized current. Conversely, if the leads are fully spin-polarized the
up or down state of the spin on the dot results in a large sequential or small
cotunneling current, and thus, together with ESR techniques, the setup can be
operated as a single-spin memory.Comment: 4 pages, 3 figures, REVTe
Polarized Magnetic Wire Induced by Tunneling Through a Magnetic Impurity
Using the zero mode method we compute the conductance of a wire consisting of
a magnetic impurity coupled to two Luttinger liquid leads characterized by the
Luttinger exponent . We find for resonance conditions, in which
the Fermi energy of the leads is close to a single particle energy of the
impurity, the conductance as a function of temperature is , whereas for off-resonance conditions the conductance is
. By applying a gate voltage and/or
a magnetic field, one of the spin components can be in resonance while the
other is off-resonance causing a strong asymmetry between the spin-up and
spin-down conductances.Comment: 8 pages, submitted to PR
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
An extreme ultraviolet spectrometer experiment for the Shuttle Get Away Special Program
An extreme ultraviolet (EUV) spectrometer experiment operated successfully during the STS-7 mission in an experiment to measure the global and diurnal variation of the EUV airglow. The spectrometer is an F 3.5 Wadsworth mount with mechanical collimator, a 75 x 75 mm grating, and a bare microchannel plate detector providing a spectral resolution of 7 X FWHM. Read-out of the signal is through discrete channels or resistive anode techniques. The experiment includes a microcomputer, 20 Mbit tape recorder, and a 28V, 40 Ahr silver-zinc battery. It is the first GAS payload to use an opening door. The spectrometer's 0.1 x 4.2 deg field of view is pointed vertically out of the shuttle bay. During the STS-7 flight data were acquired continuously for a period of 5 hours and 37 minutes, providing spectra of the 570 A to 850 A wavelength region of the airglow. Five diurnal cycles of the 584 A emission of neutral helium and the 834 A emission of ionized atomic oxygen were recorded. The experiment also recorded ion events and pressure pulses associated with thruster firings. The experiment is to fly again on Mission 41-F
Superlattice properties of carbon nanotubes in a transverse electric field
Electron motion in a (n,1) carbon nanotube is shown to correspond to a de
Broglie wave propagating along a helical line on the nanotube wall. This
helical motion leads to periodicity of the electron potential energy in the
presence of an electric field normal to the nanotube axis. The period of this
potential is proportional to the nanotube radius and is greater than the
interatomic distance in the nanotube. As a result, the behavior of an electron
in a (n,1) nanotube subject to a transverse electric field is similar to that
in a semiconductor superlattice. In particular, Bragg scattering of electrons
from the long-range periodic potential results in the opening of gaps in the
energy spectrum of the nanotube. Modification of the bandstructure is shown to
be significant for experimentally attainable electric fields, which raises the
possibility of applying this effect to novel nanoelectronic devices.Comment: 7 pages, 3 figure
Tunneling of Bloch electrons through vacuum barrier
Tunneling of Bloch electrons through a vacuum barrier introduces new physical
effects in comparison with the textbook case of free (plane wave) electrons.
For the latter, the exponential decay rate in the vacuum is minimal for
electrons with the parallel component of momentum , and
the prefactor is defined by the electron momentum component in the normal to
the surface direction. However, the decay rate of Bloch electrons may be
minimal at an arbitrary (``hot spots''), and the prefactor
is determined by the electron's group velocity, rather than by its
quasimomentum.Comment: 4 pages, no fig
Optical Signatures of Spin-Orbit Interaction Effects in a Parabolic Quantum Dot
We demonstrate here that the dipole-allowed optical absorption spectrum of a
parabolic quantum dot subjected to an external magnetic field reflects the
inter-electron interaction effects when the spin-orbit interaction is also
taken into account. We have investigated the energy spectra and the
dipole-allowed transition energies for up to four interacting electrons
parabolically confined, and have uncovered several novel features in those
spectra that are solely due to the SO interaction.Comment: 4 pages, 3 figure
Coulomb interaction effects in spin-polarized transport
We study the effect of the electron-electron interaction on the transport of
spin polarized currents in metals and doped semiconductors in the diffusive
regime. In addition to well-known screening effects, we identify two additional
effects, which depend on many-body correlations and exchange and reduce the
spin diffusion constant. The first is the "spin Coulomb drag" - an intrinsic
friction mechanism which operates whenever the average velocities of up-spin
and down-spin electrons differ. The second arises from the decrease in the
longitudinal spin stiffness of an interacting electron gas relative to a
noninteracting one. Both effects are studied in detail for both degenerate and
non-degenerate carriers in metals and semiconductors, and various limiting
cases are worked out analytically. The behavior of the spin diffusion constant
at and below a ferromagnetic transition temperature is also discussed.Comment: 9 figure
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