1,201 research outputs found
Unconventional Homogeneous and Heterogeneous Asymmetric Organocatalysis
This work describes developments of i) a catalytic asymmetric protonation reaction of ketene dithioacetals
using a chiral Brønsted acid as a catalyst and ii) a heterogeneous catalysis using textiles as solid support
materials. First, for an asymmetric protonation reaction of ketene dithioacetals, we have disclosed a facile
preparation of various lactones and hydrocoumarins. The formation and application of ketene dithioacetals
was well demonstrated and fully chracterized. The key enantiodetermining step, an asymmetric protonation
reaction, was smoothly catalyzed by BINOL‐based Brønsted acids. The desired dithioacetal protected
hydrocoumarins were obtained in good yields and high enantioselectivities. The utility of the obtained
enantioenriched products were further demonstrated by synthesizing a natural product and conducting a large
scale reaction. Secondly, we have successfully demonstrated a facile preparation of textile‐immobilized
heterogeneous catalysts. As a general method, photochemical reaction conditions can provide diverse solidsupported
organocatalysts within one‐step from inexpensive starting materials. Further applications and
mechanistic studies revealed the high efficiency and application potential of the presented methodology
Separation in Stability Analysis of Piecewise Linear Systems in Discrete Time
Abstract. Stability analysis of piecewise linear systems, without affine terms, consists of the problem of finding maximal stabilizing sets of switching paths among possible system coefficients and that of obtaining a sequence of state-space partitions in the order of increasing refinement. Exploiting the fact that these two problems can be solved separately, one can find subsets of the state space such that the piecewise linear system restricted to these sets is uniformly exponentially stable
Loophole-free Bell test for continuous variables via wave and particle correlations
We derive two classes of multi-mode Bell inequalities under local realistic
assumptions, which are violated only by the entangled states negative under
partial transposition in accordance with the Peres conjecture. Remarkably, the
failure of local realism can be manifested by exploiting wave and particle
correlations of readily accessible continuous-variable states, with very large
violation of inequalities insensitive to detector-efficiency, which makes a
strong case for a loophole-free test.Comment: 4 pages, published versio
Reply to the comment on "Loophole-free Bell test for continuous variables via wave and particle correlations"
In a recent note, Cavalcanti and Scarani (CS) constructed a counter
local-hidden-variable model to explain the violation of our inequalities in
Phys. Rev. Lett. 105, 170404 (2010). Here, we briefly discuss some issues in
response to the comments raised by CS.Comment: published versio
Proposal for direct measurement of concurrence via visibility in a cavity QED system
An experimental scheme is proposed that allows direct measurement of the
concurrence of a two-qubit cavity system. It is based on the cavity-QED
technology using atoms as flying qubits and relies on the identity of the
two-particle visibility of the atomic probability with the concurrence of the
cavity system. The scheme works for any arbitrary pure initial state of the
two-qubit cavity system.Comment: To appear in Physical Review A as a Rapid Comminicatio
Adaptive channel estimation in WCDMA STTD systems
The receiver performance with the use of a space
time transmit diversity (STTD) scheme is more susceptible to
the accuracy of channel estimate than that without the use of
the STTD scheme since the despreading signals suffer from the
effect of crosstalk and the transmit power is equally divided
into multiple transmit antennas. As a result, the efficiency of
channel estimation in the WCDMA STTD system becomes an
important issue more than that in the non-STTD system. In this
paper, an adaptive channel estimator (ACE) is designed to
mitigate the performance degradation due to inaccurate
channel estimation. Numerical results show that the
performance improvement significantly increases with the use
of the proposed ACE, particularly when the channel condition
becomes worse
Optimum pilot pattern for channel estimation in OFDM systems
The performance of channel estimation in orthogonal frequency division multiplexing (OFDM) systems significantly depends on the pilot signal, which is usually scattered in time and frequency domains. For a given pilot density, the authors optimally design the pilot pattern so as to minimize the mean squared error (MSE) of the channel estimate with the use of a general interpolator. The analytic results are verified by computer simulation
Optimum pilot pattern for MMSE channel estimation in single-carrier MIMO systems
The minimum mean squared error (MMSE)
channel estimator (CE) can provide receiver performance better
than the least square (LS) CE. However, the MMSE CE usually
uses a pilot pattern optimally designed for the LS CE. In this
paper, we derive an optimum pilot pattern for the MMSE CE in
single-carrier MIMO systems assuming that both the transmitter
and receiver know the average channel information, such as the
channel correlation matrix and signal to interference and noise
power ratio. Analytic and simulation results show that the
MMSE CE with the use of the proposed pilot pattern can reduce
the MSE compared to the use of one optimized for the LS CEThis work was supported (in part) by the Ministry of Information
& Communications, Korea, under the Information Technology
Research Center (ITRC) Support Program
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