954 research outputs found
NONCOMMUTATIVE DIFFERENTIALS ON POISSON-LIE GROUPS AND PRE-LIE ALGEBRAS
We show that the quantisation of a connected simply-connected Poisson-Lie
group admits a left-covariant noncommutative differential structure at lowest
deformation order if and only if the dual of its Lie algebra admits a pre-Lie
algebra structure. As an example, we find a pre-Lie algebra structure
underlying the standard 3D differential structure on \C_q[SU_2]. At the
noncommutative geometry level we show that the enveloping algebra U(\cm) of a
Lie algebra \cm, viewed as quantisation of \cm^*, admits a connected
differential exterior algebra of classical dimension if and only if \cm
admits a pre-Lie algebra. We give an example where \cm is solvable and we
extend the construction to the quantisation of tangent and cotangent spaces of
Poisson-Lie groups by using bicross-sum and bosonization of Lie bialgebras. As
an example, we obtain natural 6D left-covariant differential structures on the
bicrossproduct \C[SU_2]\lrbicross U_\lambda(su_2^*).Comment: Expanded result on bicrossproduct construction, added 6D
left-covariant differential calculi on \C[SU_2]\lrbicross U_\lambda(su_2^*)
as an example, and improved structure of the paper, 40 pages Latex, no
figure
Cosmological constant from quantum spacetime
http://dx.doi.org/10.1103/PhysRevD.91.124028© 2015, Physical Review
Constraints on Ho\v{r}ava-Lifshitz gravity from GRB 170817A
In this work we focus on a toy model: (3+1)-dimensional Ho\v{r}ava-Lifshitz
gravity coupling with an anisotropic electromagnetic (EM) field which is
generated through a Kaluza-Klein reduction of a (4+1)-dimensional
Ho\v{r}ava-Lifshitz gravity. This model exhibits a remarkable feature that it
has the same velocity for both gravitational and electromagnetic waves. This
feature makes it possible to restrict the parameters of the theory from GRB
170817A. In this work we use this feature to discuss possible constraints on
the parameter in the theory, by analyzing the possible Lorentz
invariance violation effect of the GRB 170817A. This is achieved by analyzing
potential time delay of gamma-ray photons in this event. It turns out that it
places a stringent constraint on this parameter. In the most ideal case, it
gives .Comment: 21 pages, 2 tables. Accepted for publication in EPJ
(E)-2-{3-[4-(Diphenylamino)styryl]-5,5-dimethylcyclohex-2-enylidene}malononitrile
In the title compound, C31H27N3, the cyclohexene ring has an envelope configuration. In the crystal structure, there is an 34 Å3 void around the inversion center, but the low electron density (0.13 e Å−3) in the difference Fourier map suggests no solvent molecule occupying this void. No hydrogen bonding is found in the crystal structure
Determining layer number of two dimensional flakes of transition-metal dichalcogenides by the Raman intensity from substrate
Transition-metal dichalcogenide (TMD) semiconductors have been widely studied
due to their distinctive electronic and optical properties. The property of TMD
flakes is a function of its thickness, or layer number (N). How to determine N
of ultrathin TMDs materials is of primary importance for fundamental study and
practical applications. Raman mode intensity from substrates has been used to
identify N of intrinsic and defective multilayer graphenes up to N=100.
However, such analysis is not applicable for ultrathin TMD flakes due to the
lack of a unified complex refractive index () from monolayer to bulk
TMDs. Here, we discuss the N identification of TMD flakes on the SiO/Si
substrate by the intensity ratio between the Si peak from 100-nm (or 89-nm)
SiO/Si substrates underneath TMD flakes and that from bare SiO/Si
substrates. We assume the real part of of TMD flakes as that of
monolayer TMD and treat the imaginary part of as a fitting
parameter to fit the experimental intensity ratio. An empirical ,
namely, , of ultrathin MoS, WS and WSe
flakes from monolayer to multilayer is obtained for typical laser excitations
(2.54 eV, 2.34 eV, or 2.09 eV). The fitted of MoS has
been used to identify N of MoS flakes deposited on 302-nm SiO/Si
substrate, which agrees well with that determined from their shear and
layer-breathing modes. This technique by measuring Raman intensity from the
substrate can be extended to identify N of ultrathin 2D flakes with N-dependent
. For the application purpose, the intensity ratio excited by
specific laser excitations has been provided for MoS, WS and
WSe flakes and multilayer graphene flakes deposited on Si substrates
covered by 80-110 nm or 280-310 nm SiO layer.Comment: 10 pages, 4 figures. Accepted by Nanotechnolog
Superior gas-sensing performance of amorphous CdO nanoflake arrays prepared at room temperature
Highly sensitive and selective detection of volatile organic compounds (VOCs) with fast response time is imperative based on safety requirements, yet often remains a challenge. Herein, we propose an effective solution, preparing a novel gas sensor comprised of amorphous nanoflake arrays (a-NFAs) with specific surface groups. The sensor was produced via an extremely simple process in which a-NFAs of CdO were deposited directly onto an interdigital electrode immersed in a chemical bath under ambient conditions. Upon exposure to a widely used VOC, diethyl ether (DEE), the sensor exhibits excellent performance, more specifically, the quickest response, lowest detection limit and highest selectivity ever reported for DEE as a target gas. The superior gas-sensing properties of the prepared a-NFAs are found to arise from their open trumpet-shaped morphology, defect-rich amorphous nature, and surface CO groups
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