19,819 research outputs found
Pseudo-Einstein and Q-flat metrics with eigenvalue estimates on CR-hypersurfaces
Let be the smooth boundary of a bounded strongly pseudo-convex
domain in a complete Stein manifold . Then (1) For ,
admits a pseudo-Eistein metric; (2) For , admits
a Fefferman metric of zero CR Q-curvature; and (3) for a compact strictly
pseudoconvex CR embeddable 3-manifold , its CR Paneitz operator is a
closed operator
A Unified Stochastic Formulation of Dissipative Quantum Dynamics. I. Generalized Hierarchical Equations
We extend a standard stochastic theory to study open quantum systems coupled
to generic quantum environments including the three fundamental classes of
noninteracting particles: bosons, fermions and spins. In this unified
stochastic approach, the generalized stochastic Liouville equation (SLE)
formally captures the exact quantum dissipations when noise variables with
appropriate statistics for different bath models are applied. Anharmonic
effects of a non-Gaussian bath are precisely encoded in the bath multi-time
correlation functions that noise variables have to satisfy. Staring from the
SLE, we devise a family of generalized hierarchical equations by averaging out
the noise variables and expand bath multi-time correlation functions in a
complete basis of orthonormal functions. The general hiearchical equations
constitute systems of linear equations that provide numerically exact
simulations of quantum dynamics. For bosonic bath models, our general
hierarchical equation of motion reduces exactly to an extended version of
hierarchical equation of motion which allows efficient simulation for arbitrary
spectral densities and temperature regimes. Similar efficiency and exibility
can be achieved for the fermionic bath models within our formalism. The spin
bath models can be simulated with two complementary approaches in the presetn
formalism. (I) They can be viewed as an example of non-Gaussian bath models and
be directly handled with the general hierarchical equation approach given their
multi-time correlation functions. (II) Alterantively, each bath spin can be
first mapped onto a pair of fermions and be treated as fermionic environments
within the present formalism.Comment: 31 pages, 2 figure
Efficient DCT-MCM Detection for Single and Multi-Antenna Wireless Systems
The discrete cosine transform (DCT) based multicarrier modulation (MCM) system is regarded as one of the promising transmission techniques for future wireless communications. By employing cosine basis as orthogonal functions for multiplexing each real-valued symbol with symbol period of T, it is able to maintain the subcarrier orthogonality while reducing frequency spacing to 1/(2T) Hz, which is only half of that compared to discrete Fourier transform (DFT) based multicarrier systems. In this paper, following one of the effective transmission models by which zeros are inserted as guard sequence and the DCT operation at the receiver is replaced by DFT of double length, we reformulate and evaluate three classic detection methods by appropriately processing the post-DFT signals both for single antenna and multiple-input multiple-output (MIMO) DCT-MCM systems. In all cases, we show that with our reformulated detection approaches, DCT-MCM schemes can outperform, in terms of error-rate, conventional OFDM-based systems
- …