8,203 research outputs found
Functional requirements for onboard management of space shuttle consumables, volume 1
A study was conducted to determine the functional requirements for onboard management of space shuttle consumables. A generalized consumable management concept was developed for application to advanced spacecraft. The subsystems and related consumables selected for inclusion in the consumables management system are: (1) propulsion, (2) power generation, and (3) environmental and life support
Dynamics of a classical Hall system driven by a time-dependent Aharonov--Bohm flux
We study the dynamics of a classical particle moving in a punctured plane
under the influence of a strong homogeneous magnetic field, an electrical
background, and driven by a time-dependent singular flux tube through the hole.
We exhibit a striking classical (de)localization effect: in the far past the
trajectories are spirals around a bound center; the particle moves inward
towards the flux tube loosing kinetic energy. After hitting the puncture it
becomes ``conducting'': the motion is a cycloid around a center whose drift is
outgoing, orthogonal to the electric field, diffusive, and without energy loss
Magnetic quantum critical point and superconductivity in UPt3 doped with Pd
Transverse-field muon spin relaxation measurements have been carried out on
the heavy-fermion superconductor UPt3 doped with small amounts of Pd. We find
that the critical Pd concentration for the emergence of the large-moment
antiferromagnetic phase is ~0.6 at.%Pd. At the same Pd content,
superconductivity is completely suppressed. The existence of a magnetic quantum
critical point in the phase diagram, which coincides with the critical point
for superconductivity, provides evidence for ferromagnetic spin-fluctuation
mediated odd-parity superconductivity, which competes with antiferromagnetic
order.Comment: 4 pages (includes 3 figures); postscript fil
Magnetic quantum critical point and superconductivity in UPt3 doped with Pd
Transverse-field muon spin relaxation measurements have been carried out on
the heavy-fermion superconductor UPt3 doped with small amounts of Pd. We find
that the critical Pd concentration for the emergence of the large-moment
antiferromagnetic phase is ~0.6 at.%Pd. At the same Pd content,
superconductivity is completely suppressed. The existence of a magnetic quantum
critical point in the phase diagram, which coincides with the critical point
for superconductivity, provides evidence for ferromagnetic spin-fluctuation
mediated odd-parity superconductivity, which competes with antiferromagnetic
order.Comment: 4 pages (includes 3 figures); postscript fil
Local oxidation of Ga[Al]As heterostructures with modulated tip-sample voltages
Nanolithography based on local oxidation with a scanning force microscope has
been performed on an undoped GaAs wafer and a Ga[Al]As heterostructure with an
undoped GaAs cap layer and a shallow two-dimensional electron gas. The oxide
growth and the resulting electronic properties of the patterned structures are
compared for constant and modulated voltage applied to the conductive tip of
the scanning force microscope. All the lithography has been performed in
non-contact mode. Modulating the applied voltage enhances the aspect ratio of
the oxide lines, which significantly strengthens the insulating properties of
the lines on GaAs. In addition, the oxidation process is found to be more
reliable and reproducible. Using this technique, a quantum point contact and a
quantum wire have been defined and the electronic stability, the confinement
potential and the electrical tunability are demonstrated to be similar to the
oxidation with constant voltage.Comment: 7 pages, 7 figures, accepted by J. Appl. Phy
Cu -edge Resonant Inelastic X-Ray Scattering in Edge-Sharing Cuprates
We present calculations for resonant inelastic x-ray scattering (RIXS) in
edge-shared copper oxide systems, such as CuGeO and LiCuO,
appropriate for hard x-ray scattering where the photoexcited electron lies
above oxygen 2p and copper 3d orbital energies. We perform exact
diagonalizations of the multi-band Hubbard and determine the energies, orbital
character and resonance profiles of excitations which can be probed via RIXS.
We find excellent agreement with recent results on LiCuO and
CuGeO in the 2-7 eV photon energy loss range.Comment: Updated with new data, expanded 9 pages, 9 figure
Are there nodes in LaFePO, BaFe(AsP), and KFeAs ?
We reexamined the experimental evidences for the possible existence of the
superconducting (SC) gap nodes in the three most suspected Fe-pnictide SC
compounds: LaFePO, BaFe(AsP), and KFeAs. We
showed that while the -linear temperature dependence of the penetration
depth of these three compounds indicate extremely clean nodal gap
superconductors, the thermal conductivity data unambiguously showed that LaFePO and
BaFe(AsP) are extremely dirty, while KFeAs
can be clean. This apparently conflicting experimental data casts a serious
doubt on the nodal gap possibility on LaFePO and
BaFe(AsP).Comment: 11 pages, 5 figures A new section "4. Remark on the quantum
oscillation (QO) experiments" is adde
Quantum response of dephasing open systems
We develop a theory of adiabatic response for open systems governed by
Lindblad evolutions. The theory determines the dependence of the response
coefficients on the dephasing rates and allows for residual dissipation even
when the ground state is protected by a spectral gap. We give quantum response
a geometric interpretation in terms of Hilbert space projections: For a two
level system and, more generally, for systems with suitable functional form of
the dephasing, the dissipative and non-dissipative parts of the response are
linked to a metric and to a symplectic form. The metric is the Fubini-Study
metric and the symplectic form is the adiabatic curvature. When the metric and
symplectic structures are compatible the non-dissipative part of the inverse
matrix of response coefficients turns out to be immune to dephasing. We give
three examples of physical systems whose quantum states induce compatible
metric and symplectic structures on control space: The qubit, coherent states
and a model of the integer quantum Hall effect.Comment: Article rewritten, two appendices added. 16 pages, 2 figure
Microwave Conductivity of a High Purity d-wave Superconductor
The cusp-like behavior of the microwave conductivity observed in clean
ortho-II YBCuO at low temperature and low frequency is
shown to be related directly to a linear in frequency dependence of the
impurity scattering rate with a negligibly small value at zero frequency. In
the weak scattering limit, the conductivity decreases linearly with the
frequency. In the vortex state, assuming a random (Gaussian) distribution of
vortices, we show that the magnetic field profoundly alters the impurity
scattering rate, which now acquires a finite zero frequency value. As a
consequence, we predict a Drude-like line shape in the microwave conductivity
at low frequency.Comment: 3 figure
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