53 research outputs found
Using a MEMS pendulum to measure the gravity gradient in orbit: a new concept for a miniaturized Earth sensor
AbstractWe present the fabrication and test results of a novel inertial sensor for use onboard satellites, to obtain the Earth vector. Current state-of-the-art Earth sensors determine the Earth vector by imaging the Earthâs horizon in the IR. This requires multiple optical heads on different faces of the satellite, with associated mounting and thermal considerations. The MEMS-based approach reported here is based on measuring the gravity gradient vector by measuring the gravity gradient torque on a 4 cm long Si-pendulum. This approach eliminates the need for multiple external access ports, allowing a compact sensor to be situated anywhere inside the spacecraft
Discrete breathers in dc biased Josephson-junction arrays
We propose a method to excite and detect a rotor localized mode
(rotobreather) in a Josephson-junction array biased by dc currents. In our
numerical studies of the dynamics we have used experimentally realizable
parameters and included self-inductances. We have uncovered two families of
rotobreathers. Both types are stable under thermal fluctuations and exist for a
broad range of array parameters and sizes including arrays as small as a single
plaquette. We suggest a single Josephson-junction plaquette as an ideal system
to experimentally investigate these solutions.Comment: 5 pages, 5 figure, to appear June 1, 1999 in PR
Analytical results for coupled map lattices with long-range interactions
We obtain exact analytical results for lattices of maps with couplings that
decay with distance as . We analyze the effect of the coupling
range on the system dynamics through the Lyapunov spectrum. For lattices whose
elements are piecewise linear maps, we get an algebraic expression for the
Lyapunov spectrum. When the local dynamics is given by a nonlinear map, the
Lyapunov spectrum for a completely synchronized state is analytically obtained.
The critical lines characterizing the synchronization transition are determined
from the expression for the largest transversal Lyapunov exponent. In
particular, it is shown that in the thermodynamical limit, such transition is
only possible for sufficiently long-range interactions, namely, for , where is the lattice dimension.Comment: 4 pages, 2 figures, corrections included. Phys. Rev. E 68, 045202(R)
(2003); correction in pres
Aharonov-Bohm spectral features and coherence lengths in carbon nanotubes
The electronic properties of carbon nanotubes are investigated in the
presence of disorder and a magnetic field parallel or perpendicular to the
nanotube axis. In the parallel field geometry, the -periodic
metal-insulator transition (MIT) induced in metallic or semiconducting
nanotubes is shown to be related to a chirality-dependent shifting of the
energy of the van Hove singularities (VHSs). The effect of disorder on this
magnetic field-related mechanism is considered with a discussion of mean free
paths, localization lengths and magnetic dephasing rate in the context of
recent experiments.Comment: 22 pages, 6 Postscript figures. submitted to Phys. Rev.
Structural and Electronic Properties of a Carbon Nanotorus: Effects of Delocalized Vs Localized Deformations
The bending of a carbon nanotube is studied by considering the structural
evolution of a carbon nanotorus from elastic deformation to the onset of the
kinks and eventually to the collapse of the walls of the nanotorus. The changes
in the electronic properties due to {\it non-local} deformation are contrasted
with those due to {\it local} deformation to bring out the subtle issue
underlying the reason why there is only a relatively small reduction in the
electrical conductance in the former case even at large bending angles while
there is a dramatic reduction in the conductance in the latter case at
relatively small bending angles.Comment: 10 pages, 6 figure
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo
Electrical transport in rings of single-wall nanotubes: one- dimensional localization
We report low-temperature magnetoresistance (MR) measurements on rings of single-wall carbon nanotubes. Negative MR characteristic of weak one-dimensional localization is clearly observed from 3.0 to 60 K, and the coherence length LÏ is obtained as a function of temperature. The dominant dephasing mechanism is identified as electron-electron scattering. Below 1 K, we observe a transition from weak to strong localization, and below 0.7 K a weak antilocalization is induced by spin-orbit scattering.
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