44,524 research outputs found
Dimerization-assisted energy transport in light-harvesting complexes
We study the role of the dimer structure of light-harvesting complex II (LH2)
in excitation transfer from the LH2 (without a reaction center (RC)) to the LH1
(surrounding the RC), or from the LH2 to another LH2. The excited and
un-excited states of a bacteriochlorophyll (BChl) are modeled by a quasi-spin.
In the framework of quantum open system theory, we represent the excitation
transfer as the total leakage of the LH2 system and then calculate the transfer
efficiency and average transfer time. For different initial states with various
quantum superposition properties, we study how the dimerization of the B850
BChl ring can enhance the transfer efficiency and shorten the average transfer
time.Comment: 11 pages, 6 figure
Entanglement of separate nitrogen-vacancy centers coupled to a whispering-gallery mode cavity
We present a quantum electrodynamical model involving nitrogen-vacancy
centers coupled to a whispering-gallery mode cavity. Two schemes are considered
to create W state and Bell state, respectively. One of the schemes makes use of
the Raman transition with the cavity field virtually excited; The other enables
the Bell state preparation and quantum information transfer by virtue of dark
state evolution and adiabatic passage, which is tolerant to ambient noise and
experimental parameter fluctuations. We justify our schemes by considering the
experimental feasibility and challenge using currently available technology.Comment: 8 pages and 5 figure
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Bias adjustment of satellite-based precipitation estimation using gauge observations: A case study in Chile
Satellite-based precipitation estimates (SPEs) are promising alternative precipitation data for climatic and hydrological applications, especially for regions where ground-based observations are limited. However, existing satellite-based rainfall estimations are subject to systematic biases. This study aims to adjust the biases in the Precipitation Estimation from Remotely Sensed Information using Artificial Neural NetworksâCloud Classification System (PERSIANN-CCS) rainfall data over Chile, using gauge observations as reference. A novel bias adjustment framework, termed QM-GW, is proposed based on the nonparametric quantile mapping approach and a Gaussian weighting interpolation scheme. The PERSIANN-CCS precipitation estimates (daily, 0.04°Ă0.04°) over Chile are adjusted for the period of 2009â2014. The historical data (satellite and gauge) for 2009â2013 are used to calibrate the methodology; nonparametric cumulative distribution functions of satellite and gauge observations are estimated at every 1°Ă1° box region. One year (2014) of gauge data was used for validation. The results show that the biases of the PERSIANN-CCS precipitation data are effectively reduced. The spatial patterns of adjusted satellite rainfall show high consistency to the gauge observations, with reduced root-mean-square errors and mean biases. The systematic biases of the PERSIANN-CCS precipitation time series, at both monthly and daily scales, are removed. The extended validation also verifies that the proposed approach can be applied to adjust SPEs into the future, without further need for ground-based measurements. This study serves as a valuable reference for the bias adjustment of existing SPEs using gauge observations worldwide
Determination of optimal reversed field with maximal electrocaloric cooling by a direct entropy analysis
Application of a negative field on a positively poled ferroelectric sample
can enhance the electrocaloric cooling and appears as a promising method to
optimize the electrocaloric cycle. Experimental measurements show that the
maximal cooling does not appear at the zero-polarization point, but around the
shoulder of the P-E loop. This phenomenon cannot be explained by the theory
based on the constant total entropy assumption under adiabatic condition. In
fact, adiabatic condition does not imply constant total entropy when
irreversibility is involved. A direct entropy analysis approach based on work
loss is proposed in this work, which takes the entropy contribution of the
irreversible process into account. The optimal reversed field determined by
this approach agrees with the experimental observations. This study signifies
the importance of considering the irreversible process in the electrocaloric
cycles
Highly tunable spin-dependent electron transport through carbon atomic chains connecting two zigzag graphene nanoribbons
Motivated by recent experiments of successfully carving out stable carbon
atomic chains from graphene, we investigate a device structure of a carbon
chain connecting two zigzag graphene nanoribbons with highly tunable
spin-dependent transport properties. Our calculation based on the
non-equilibrium Green's function approach combined with the density functional
theory shows that the transport behavior is sensitive to the spin configuration
of the leads and the bridge position in the gap. A bridge in the middle gives
an overall good coupling except for around the Fermi energy where the leads
with anti-parallel spins create a small transport gap while the leads with
parallel spins give a finite density of states and induce an even-odd
oscillation in conductance in terms of the number of atoms in the carbon chain.
On the other hand, a bridge at the edge shows a transport behavior associated
with the spin-polarized edge states, presenting sharp pure -spin and
-spin peaks beside the Fermi energy in the transmission function. This
makes it possible to realize on-chip interconnects or spintronic devices by
tuning the spin state of the leads and the bridge position.Comment: 7 pages, 9 figure
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