1,639 research outputs found
Electrical rotary joint apparatus for large space structures
A structural array and electrical rotary joint for transmitting an electrical power between large space structures having relative rotational movement is disclosed which includes large support framework structures which rotate relative to one another about a common axis of rotation. A rotary interface joint is defined between the structures. A cylindrical hub member is carried by one structure and a cylindrical hub member is carried by a support structure with a third hub member being concentrically within a fourth hub member for relative rotation. Tension connecting cables connect hub members with their associated outer structures whereby relative rotational movement between the structures is transmitted to the cylindrical hub members for unitary motion therewith. Electrical conductor brush members are carried by one hub and electrical contact rings are carried by another hub member in sliding electrical contact with the brushes for transmission of electrical power during relative rotational movement between the two support structures
Transport and recombination through weakly coupled localized spin pairs in semiconductors during coherent spin excitation
Semi-analytical predictions for the transients of spin-dependent transport
and recombination rates through localized states in semiconductors during
coherent electron spin excitation are made for the case of weakly spin-coupled
charge carrier ensembles. The results show that the on-resonant Rabi frequency
of electrically or optically detected spin-oscillation doubles abruptly as the
strength of the resonant microwave field gamma B_1 exceeds the Larmor frequency
separation within the pair of charge carrier states between which the transport
or recombination transition takes place. For the case of a Larmor frequency
separation of the order of gamma B_1 and arbitrary excitation frequencies, the
charge carrier pairs exhibit four different nutation frequencies. From the
calculations, a simple set of equations for the prediction of these frequencies
is derived
Analytical description of spin-Rabi oscillation controlled electronic transitions rates between weakly coupled pairs of paramagnetic states with S=1/2
We report on an analytical description of spin-dependent electronic
transition rates which are controlled by a radiation induced spin-Rabi
oscillation of weakly spin-exchange and spin-dipolar coupled paramagnetic
states (S=1/2). The oscillation components (the Fourier content) of the net
transition rates within spin-pair ensembles are derived for randomly
distributed spin resonances with account of a possible correlation between the
two distributions that correspond to the two individual pair partners. The
results presented here show that when electrically or optically detected Rabi
spectroscopy is conducted under an increasing driving field B_ 1, the Rabi
spectrum evolves from a single resonance peak at s=\Omega_R, where
\Omega_R=\gamma B_1 is the Rabi frequency (\gamma is the gyromagnetic ratio),
to three peaks at s= \Omega_R, s=2\Omega_R, and at low s<< \Omega_R. The
crossover between the two regimes takes place when \Omega_R exceeds the
expectation value \delta_0 of the difference of the Zeeman energies within the
pairs, which corresponds to the broadening of the magnetic resonance lines in
the presence of disorder caused by hyperfine field or distributions of Lande
g-factors. We capture this crossover by analytically calculating the shapes of
all three peaks at arbitrary relation between \Omega_R and \delta_0. When the
peaks are well-developed their widths are \Delta s ~ \delta_0^2/\Omega_R.Comment: 10 page, 5 figure
Using coherent dynamics to quantify spin-coupling within triplet-exciton/polaron complexes in organic diodes
Quantifying the spin-spin interactions which influence electronic transitions
in organic semiconductors is crucial for understanding their
magneto-optoelectronic properties. By combining a theoretical model for three
spin interactions in the coherent regime with pulsed electrically detected
magnetic resonance experiments on MEH-PPV diodes, we quantify the spin-coupling
within complexes comprising three spin-half particles. We determine that these
particles form triplet-exciton:polaron pairs, where the polaron:exciton
exchange is over 5 orders of magnitude weaker (less than 170 MHz) than that
within the exciton. This approach providing a direct spectroscopic approach for
distinguishing between coupling regimens, such as strongly bound trions, which
have been proposed to occur in organic devices.Comment: 5 pages, 4 figure
Slow Hopping and Spin Dephasing of Coulombically Bound Polaron Pairs in an Organic Semiconductor at Room Temperature
Polaron pairs are intermediate electronic states that are integral to the optoelectronic conversion process in organic semiconductors. Here, we report on electrically detected spin echoes arising from direct quantum control of polaron pair spins in an organic light-emitting diode at room temperature. This approach reveals phase coherence on a microsecond time scale, and offers a direct way to probe charge recombination and dissociation processes in organic devices, revealing temperature-independent intermolecular carrier hopping on slow time scales. In addition, the long spin phase coherence time at room temperature is of potential interest for developing quantum-enhanced sensors and information processing systems which operate at room temperature
CO2 emission reduction potential of large-scale energy efficiency measures in power generation from fossil fuels in China, India, Brazil, Indonesia and South Africa
We quantify the theoretical potential for energy-efficiency CDM projects using best available technology in coal, natural gas or oil fuelled power generation in China, India, Brazil, Indonesia and South Africa, looking at new power plants or retrofit measures. We then discuss the likelihood of the potential emission reductions materialising under CDM. Our results are very sensitive to choices of baseline and project efficiencies and the level of electricity generation from potential emission reduction projects until 2020. The highest emission reduction potential can be achieved from using supercritical power plants in China (275 Mt CO2), India (130 Mt) and Indonesia (41 Mt), followed by retrofit measures in China (<62 Mt), India (<31 Mt). In Brazil, new gas power plants offer the most emission reduction potential (36 Mt), while in South Africa the complete refurbishments of currently mothballed 4 GW coal-fired power plants offer a moderate potential (<13 Mt). Especially the chances for natural gas power projects to qualify as CDM projects are slim due to their very high economic attractiveness. In India both new supercritical coal-fired power plants as well as refurbishment of coal power plants stand a fair chance to pass the additionality test as supercritical power plants have not been commissioned so far and (international) financing for power projects is harder to procure than in China
Electrical detection of 31P spin quantum states
In recent years, a variety of solid-state qubits has been realized, including
quantum dots, superconducting tunnel junctions and point defects. Due to its
potential compatibility with existing microelectronics, the proposal by Kane
based on phosphorus donors in Si has also been pursued intensively. A key issue
of this concept is the readout of the P quantum state. While electrical
measurements of magnetic resonance have been performed on single spins, the
statistical nature of these experiments based on random telegraph noise
measurements has impeded the readout of single spin states. In this letter, we
demonstrate the measurement of the spin state of P donor electrons in silicon
and the observation of Rabi flops by purely electric means, accomplished by
coherent manipulation of spin-dependent charge carrier recombination between
the P donor and paramagnetic localized states at the Si/SiO2 interface via
pulsed electrically detected magnetic resonance. The electron spin information
is shown to be coupled through the hyperfine interaction with the P nucleus,
which demonstrates the feasibility of a recombination-based readout of nuclear
spins
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