180 research outputs found
Differential stiffness effects
Differential stiffness as developed in NASTRAN is a linear change in stiffness caused by applied loads. Examples of differential stiffness are the stiffening effects of gravity forces in a pendulum, centrifugal forces in rotor blades and pressure loading of shell structures. In cases wherein this stiffness caused by a load is destabilizing, the differential stiffness concept lends itself to nonlinear structural analysis. Rigid Formats 4 (static analysis with differential stiffness) and 13 (normal modes with differential stiffness) are specifically designed to account for such stiffness changes. How pressure loading may be treated in these rigid formats is clarified. This clarification results from modal correlation of Ground Vibration Test (GVT) results from the empty and pressurized Filament Wound Case (FWC) quarter-scale Space Shuttle solid rocket booster (QSSRB). A sketch of the QSSRB cantilevered to the floor by its external tank attachments is shown
In-situ growth of superconducting NdFeAs(O,F) thin films by Molecular Beam Epitaxy
The recently discovered high temperature superconductor F-doped LaFeAsO and
related compounds represent a new class of superconductors with the highest
transition temperature (Tc) apart from the cuprates. The studies ongoing
worldwide are revealing that these Fe-based superconductors are forming a
unique class of materials that are interesting from the viewpoint of
applications. To exploit the high potential of the Fe-based superconductors for
device applications, it is indispensable to establish a process that enables
the growth of high quality thin films. Efforts of thin film preparation started
soon after the discovery of Fe-based superconductors, but none of the earlier
attempts had succeeded in an in-situ growth of a superconducting film of
LnFeAs(O,F) (Ln=lanthanide), which exhibits the highest Tc to date among the
Fe-based superconductors. Here, we report on the successful growth of
NdFeAs(O,F) thin films on GaAs substrates, which showed well-defined
superconducting transitions up to 48 K without the need of an ex-situ heat
treatment
Growth of a smooth CaF 2 layer on NdFeAsO thin film
We studied the method to grow a smooth and flat CaF 2 layer on NdFeAsO thin films since CaF 2 is a promising candidate material for the barrier layer of a superconducting junction. When the CaF 2 layer was grown at 800°C, the surface was very rough because {111} facets had grown preferentially. However, when CaF 2 was grown at lower temperatures and post-annealed in situ at 800°C for 30 min the facets were eliminated and a CaF 2 layer with a smooth surface was obtained. Fluorine diffusing from CaF 2 into NdFeAsO was observed when CaF 2 was grown at high temperatures, but the diffusion was suppressed by lowering the growth temperature to 400°C
Analysis of interdiffusion between SmFeAsO0.92F0.08 and metals for ex situ fabrication of superconducting wire
We demonstrate the fabrication of superconducting SmFeAsO1-xFx (Sm-1111)
wires by using the ex-situ powder-in-tube technique. Sm-1111 powder and a
binder composed of SmF3, samarium arsenide, and iron arsenide were used to
synthesize the superconducting core. Although the F content of Sm-1111 is
reduced in the process of ex-situ fabrication, the binder compensates by
sufficiently supplementing the F content, thereby preventing a decrease in the
superconducting transition temperature and a shrinking of the superconducting
volume fraction. Thus, in the superconducting Sm-1111 wire with the binder, the
transport critical current density reaches the highest value of ~4000 A/cm2 at
4.2 K
Noise-free scattering of the quantized electromagnetic field from a dispersive linear dielectric
We study the scattering of the quantized electromagnetic field from a linear,
dispersive dielectric using the scattering formalism for quantum fields. The
medium is modeled as a collection of harmonic oscillators with a number of
distinct resonance frequencies. This model corresponds to the Sellmeir
expansion, which is widely used to describe experimental data for real
dispersive media. The integral equation for the interpolating field in terms of
the in field is solved and the solution used to find the out field. The
relation between the in and out creation and annihilation operators is found
which allows one to calculate the S-matrix for this system. In this model, we
find that there are absorption bands, but the input-output relations are
completely unitary. No additional quantum noise terms are required.Comment: Revtex, submitted to Physical Review
DC superconducting quantum interference devices fabricated using bicrystal grain boundary junctions in Co-doped BaFe2As2 epitaxial films
DC superconducting quantum interference devices (dc-SQUIDs) were fabricated
in Co-doped BaFe2As2 epitaxial films on (La, Sr)(Al, Ta)O3 bicrystal substrates
with 30deg misorientation angles. The 18 x 8 micro-meter^2 SQUID loop with an
estimated inductance of 13 pH contained two 3 micro-meter wide grain boundary
junctions. The voltage-flux characteristics clearly exhibited periodic
modulations with deltaV = 1.4 micro-volt at 14 K, while the intrinsic flux
noise of dc-SQUIDs was 7.8 x 10^-5 fai0/Hz^1/2 above 20 Hz. The rather high
flux noise is mainly attributed to the small voltage modulation depth which
results from the superconductor-normal metal-superconductor junction nature of
the bicrystal grain boundary
Theory of Pseudomodes in Quantum Optical Processes
This paper deals with non-Markovian behaviour in atomic systems coupled to a
structured reservoir of quantum EM field modes, with particular relevance to
atoms interacting with the field in high Q cavities or photonic band gap
materials. In cases such as the former, we show that the pseudo mode theory for
single quantum reservoir excitations can be obtained by applying the Fano
diagonalisation method to a system in which the atomic transitions are coupled
to a discrete set of (cavity) quasimodes, which in turn are coupled to a
continuum set of (external) quasimodes with slowly varying coupling constants
and continuum mode density. Each pseudomode can be identified with a discrete
quasimode, which gives structure to the actual reservoir of true modes via the
expressions for the equivalent atom-true mode coupling constants. The quasimode
theory enables cases of multiple excitation of the reservoir to now be treated
via Markovian master equations for the atom-discrete quasimode system.
Applications of the theory to one, two and many discrete quasimodes are made.
For a simple photonic band gap model, where the reservoir structure is
associated with the true mode density rather than the coupling constants, the
single quantum excitation case appears to be equivalent to a case with two
discrete quasimodes
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