2,257 research outputs found
Quantum-coherent phase oscillations in synchronization
Recently, several studies have investigated synchronization in
quantum-mechanical limit-cycle oscillators. However, the quantum nature of
these systems remained partially hidden, since the dynamics of the oscillator's
phase was overdamped and therefore incoherent. We show that there exist regimes
of underdamped and even quantum-coherent phase motion, opening up new
possibilities to study quantum synchronization dynamics. To this end, we
investigate the Van der Pol oscillator (a paradigm for a self-oscillating
system) synchronized to an external drive. We derive an effective quantum model
which fully describes the regime of underdamped phase motion and additionally
allows us to identify the quality of quantum coherence. Finally, we identify
quantum limit cycles of the phase itself.Comment: 6 pages + Supplemental Materia
Biogenesis of mitochondrial ubiquinol
The precursor proteins to the subunits of ubiquinol:cytochrome c reductase (cytochrome bc1 complex) of Neurospora crassa were synthesized in a reticulocyte lysate. These precursors were immunoprecipitated with antibodies prepared against the individual subunits and compared to the mature subunits immunoprecipitated or isolated from mitochondria. Most subunits were synthesized as precursors with larger apparent molecular weights (subunits I, 51,500 versus 50,000; subunit II, 47,500 versus 45,000; subunit IV (cytochrome c1), 38,000 versus 31,000; subunit V (Fe-S protein), 28,000 versus 25,000; subunit VII, 12,000 versus 11,500; subunit VIII, 11,600 versus 11,200). Subunit VI (14,000) was synthesized with the same apparent molecular weight. The post-translational transfer of subunits I, IV, V, and VII was studied in an in vitro system employing reticulocyte lysate and isolated mitochondria. The transfer and proteolytic processing of these precursors was found to be dependent on the mitochondrial membrane potential. In the transfer of cytochrome c1, the proteolytic processing appears to take place in two separate steps via an intermediate both in vivo and in vitro. In vivo, the intermediate form accumulated when cells were kept at 8 degrees C and was chased into mature cytochrome c1 at 25 degrees C. Both processing steps were energy- dependent
General linearized theory of quantum fluctuations around arbitrary limit cycles
The theory of Gaussian quantum fluctuations around classical steady states in
nonlinear quantum-optical systems (also known as standard linearization) is a
cornerstone for the analysis of such systems. Its simplicity, together with its
accuracy far from critical points or situations where the nonlinearity reaches
the strong coupling regime, has turned it into a widespread technique, which is
the first method of choice in most works on the subject. However, such a
technique finds strong practical and conceptual complications when one tries to
apply it to situations in which the classical long-time solution is time
dependent, a most prominent example being spontaneous limit-cycle formation.
Here we introduce a linearization scheme adapted to such situations, using the
driven Van der Pol oscillator as a testbed for the method, which allows us to
compare it with full numerical simulations. On a conceptual level, the scheme
relies on the connection between the emergence of limit cycles and the
spontaneous breaking of the symmetry under temporal translations. On the
practical side, the method keeps the simplicity and linear scaling with the
size of the problem (number of modes) characteristic of standard linearization,
making it applicable to large (many-body) systems.Comment: Constructive suggestions and criticism are welcom
Puzzling subunits of mitochondrial cytochrome reductase
The ubiquinol-cytochrome c reductase complex, like the other proton-pumping respiratory complexes of mitochondria, is an assembly of many different subunits. However, only a few of these subunits participate directly in the electron transfer and proton translocation. The roles of the other subunits are largely unknown. We discuss here some intriguing features of two of these subunits
Incorporating Risk into Control Design for Emergency Operation of Turbo-Fan Engines
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90650/1/AIAA-2011-1591-262.pd
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