3,494 research outputs found
The adjustment-stabilization method for constrained systems
For constrained system which has several independent first integrals, we give
a new stabilization method which named adjustment-stabilization method. It can
stabilize all known constants of motion for a given dynamical system very well
instead of the stabilization and post-stabilization methods which only
conserves one of all first integrals. Further more, new method can improve
numerical accuracy too. We also point out the post-stabilization is just a
simplest case of the new method.Comment: 6 pages, 5 figure
Efficient Downlink Channel Reconstruction for FDD Multi-Antenna Systems
In this paper, we propose an efficient downlink channel reconstruction scheme
for a frequency-division-duplex multi-antenna system by utilizing uplink
channel state information combined with limited feedback. Based on the spatial
reciprocity in a wireless channel, the downlink channel is reconstructed by
using frequency-independent parameters. We first estimate the gains, delays,
and angles during uplink sounding. The gains are then refined through downlink
training and sent back to the base station (BS). With limited overhead, the
refinement can substantially improve the accuracy of the downlink channel
reconstruction. The BS can then reconstruct the downlink channel with the
uplink-estimated delays and angles and the downlink-refined gains. We also
introduce and extend the Newtonized orthogonal matching pursuit (NOMP)
algorithm to detect the delays and gains in a multi-antenna multi-subcarrier
condition. The results of our analysis show that the extended NOMP algorithm
achieves high estimation accuracy. Simulations and over-the-air tests are
performed to assess the performance of the efficient downlink channel
reconstruction scheme. The results show that the reconstructed channel is close
to the practical channel and that the accuracy is enhanced when the number of
BS antennas increases, thereby highlighting that the promising application of
the proposed scheme in large-scale antenna array systems
Tailoring excitonic states of van der Waals bilayers through stacking configuration, band alignment and valley-spin
Excitons in monolayer semiconductors have large optical transition dipole for
strong coupling with light field. Interlayer excitons in heterobilayers, with
layer separation of electron and hole components, feature large electric dipole
that enables strong coupling with electric field and exciton-exciton
interaction, at the cost that the optical dipole is substantially quenched (by
several orders of magnitude). In this letter, we demonstrate the ability to
create a new class of excitons in transition metal dichalcogenide (TMD) hetero-
and homo-bilayers that combines the advantages of monolayer- and
interlayer-excitons, i.e. featuring both large optical dipole and large
electric dipole. These excitons consist of an electron that is well confined in
an individual layer, and a hole that is well extended in both layers, realized
here through the carrier-species specific layer-hybridization controlled
through the interplay of rotational, translational, band offset, and
valley-spin degrees of freedom. We observe different species of such
layer-hybridized valley excitons in different heterobilayer and homobilayer
systems, which can be utilized for realizing strongly interacting
excitonic/polaritonic gases, as well as optical quantum coherent controls of
bidirectional interlayer carrier transfer either with upper conversion or down
conversion in energy
The effects of large extra dimensions on associated production at linear colliders
In the framework of the large extra dimensions (LED) model, the effects of
LED on the processes \rrtth and \eetth at future linear colliders are
investigated in both polarized and unpolarized collision modes. The results
show that the virtual Kaluza-Klein (KK) graviton exchange can significantly
modify the standard model expectations for these processes with certain
polarizations of initial states. The process \rrtth with
allows the effective scale to be probed up to 7.8 and 8.6 TeV in
the unpolarized and , J=2 polarized collision
modes, respectively. For the \eetth process with , the upper
limits of to be observed can be 6.7 and 7.0 TeV in the unpolarized
and , , polarized collision modes,
respectively. We find the \rrtth channel in J=2 polarized photon collision mode
provides a possibility to improve the sensitivity to the graviton tower
exchange.Comment: To be appeard in Physical Review
N-Cyclohexyl-3-(4-hydroxy-6-oxo-1,6-dihydropyrimidin-5-yl)-3-p-tolylpropanamide
In the molecule of the title compound, C20H25N3O3, the aromatic rings are oriented at a dihedral angle of 88.36 (3)°. The cyclohexane ring adopts a chair conformation. In the crystal structure, intermolecular N—H⋯O and O—H⋯N hydrogen bonds link the molecules. C—H⋯π interactions are also present
First-Principles Investigation of Anistropic Hole Mobilities in Organic Semiconductors
We report a simple first-principles-based simulation model (combining quantum mechanics with Marcus−Hush theory) that provides the quantitative structural relationships between angular resolution anisotropic hole mobility and molecular structures and packing. We validate that this model correctly predicts the anisotropic hole mobilities of ruberene, pentacene, tetracene, 5,11-dichlorotetracene (DCT), and hexathiapentacene (HTP), leading to results in good agreement with experiment
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