42 research outputs found
Quantum Mechanics on the cylinder
A new approach to deformation quantization on the cylinder considered as
phase space is presented. The method is based on the standard Moyal formalism
for R^2 adapted to (S^1 x R) by the Weil--Brezin--Zak transformation. The
results are compared with other solutions of this problem presented by
Kasperkovitz and Peev (Ann. Phys. vol. 230, 21 (1994)0 and by Plebanski and
collaborators (Acta Phys. Pol. vol. B 31}, 561 (2000)). The equivalence of
these three methods is proved.Comment: 21 pages, LaTe
A New Non-Perturbative Approach to Quantum Theory in Curved Spacetime Using the Wigner Function
A new non-perturbative approach to quantum theory in curved spacetime and to
quantum gravity, based on a generalisation of the Wigner equation, is proposed.
Our definition for a Wigner equation differs from what have otherwise been
proposed, and does not imply any approximations. It is a completely exact
equation, fully equivalent to the Heisenberg equations of motion. The approach
makes different approximation schemes possible, e.g. it is possible to perform
a systematic calculation of the quantum effects order by order. An iterative
scheme for this is also proposed. The method is illustrated with some simple
examples and applications. A calculation of the trace of the renormalised
energy-momentum tensor is done, and the conformal anomaly is thereby related to
non-conservation of a current in d=2 dimensions and a relationship between a
vector and an axial-vector current in d=4 dimensions.
The corresponding ``hydrodynamic equations'' governing the evolution of
macroscopic quantities are derived by taking appropriate moments. The emphasis
is put on the spin-1/2 case, but it is shown how to extend to arbitrary spins.
Gravity is treated first in the Palatini formalism, which is not very
tractable, and then more successfully in the Ashtekar formalism, where the
constraints lead to infinite order differential equations for the Wigner
functions.Comment: LaTeX2e (uses amssymb), 36 page
Decoherence of molecular wave packets in an anharmonic potential
The time evolution of anharmonic molecular wave packets is investigated under
the influence of the environment consisting of harmonic oscillators. These
oscillators represent photon or phonon modes and assumed to be in thermal
equilibrium. Our model explicitly incorporates the fact that in the case of a
nonequidistant spectrum the rates of the environment induced transitions are
different for each transition. The nonunitary time evolution is visualized by
the aid of the Wigner function related to the vibrational state of the
molecule. The time scale of decoherence is much shorter than that of
dissipation, and gives rise to states which are mixtures of localized states
along the phase space orbit of the corresponding classical particle. This
behavior is to a large extent independent of the coupling strength, the
temperature of the environment and also of the initial state.Comment: 7 pages, 4 figure
Quantum Tunneling in the Wigner Representation
Time dependence for barrier penetration is considered in the phase space. An
asymptotic phase-space propagator for nonrelativistic scattering on a one -
dimensional barrier is constructed. The propagator has a form universal for
various initial state preparations and local potential barriers. It is
manifestly causal and includes time-lag effects and quantum spreading. Specific
features of quantum dynamics which disappear in the standard semi-classical
approximation are revealed. The propagator may be applied to calculation of the
final momentum and coordinate distributions, for particles transmitted through
or reflected from the potential barrier, as well as for elucidating the
tunneling time problem.Comment: 18 pages, LATEX, no figure
Characterisation of Innate Fungal Recognition in the Lung
The innate recognition of fungi by leukocytes is mediated by pattern recognition receptors (PRR), such as Dectin-1, and is thought to occur at the cell surface triggering intracellular signalling cascades which lead to the induction of protective host responses. In the lung, this recognition is aided by surfactant which also serves to maintain the balance between inflammation and pulmonary function, although the underlying mechanisms are unknown. Here we have explored pulmonary innate recognition of a variety of fungal particles, including zymosan, Candida albicans and Aspergillus fumigatus, and demonstrate that opsonisation with surfactant components can limit inflammation by reducing host-cell fungal interactions. However, we found that this opsonisation does not contribute directly to innate fungal recognition and that this process is mediated through non-opsonic PRRs, including Dectin-1. Moreover, we found that pulmonary inflammatory responses to resting Aspergillus conidia were initiated by these PRRs in acidified phagolysosomes, following the uptake of fungal particles by leukocytes. Our data therefore provides crucial new insights into the mechanisms by which surfactant can maintain pulmonary function in the face of microbial challenge, and defines the phagolysosome as a novel intracellular compartment involved in the innate sensing of extracellular pathogens in the lung
An optimaly coupled 5 GHz quadrature LC oscillator
A 5 GHz quadrature LC oscillator is realized which is based on a new architecture for multi-phase LC oscillators. Each section in the oscillator is coupled with an explicit phase shift of 180 degrees divided by the number of sections. Analysis on behavioral level shows that this maximizes the quality factor, and as a result, the carrier-to-noise ratio and robustness. An effective quality factor is derived which quantizes the degradation in phase noise performance if the sections of a multiphase LC oscillator are non-optimally coupled. The realized 5 GHz quadrature LC oscillator demonstrates that even at high frequencies the additional complexity of the proposed architecture yields a CNR improvement. The oscillator is realized in a BiCMOS process with a cut-off frequency of 30 GHz using an LC resonator with a quality factor of 4. A tuning range from 4.91 to 5.23 GHz is obtained with a CNR better than 113 dBc/Hz at 2 MHz offset. The VCO core power dissipation is only 21.2 mW at 2.7 V supply voltage