9,923 research outputs found
Raman fingerprint of semi-metal WTe2 from bulk to monolayer
Tungsten ditelluride (WTe2), a layered transition-metal dichalcogenide (TMD),
has recently demonstrated an extremely large magnetoresistance effect, which is
unique among TMDs. This fascinating feature seems to be correlated with its
special electronic structure. Here, we report the observation of 6 Raman peaks
corresponding to the A_2^4, A_1^9, A_1^8, A_1^6, A_1^5 and A_1^2 phonons, from
the 33 Raman-active modes predicted for WTe2. This provides direct evidence to
distinguish the space group of WTe2 from that of other TMDs. Moreover, the
Raman evolution of WTe2 from bulk to monolayer is clearly revealed. It is
interesting to find that the A_2^4 mode, centered at ~109.8 cm-1, is forbidden
in a monolayer, which may be attributable to the transition of the point group
from C2v (bulk) to C2h (monolayer). Our work characterizes all observed Raman
peaks in the bulk and few-layer samples and provides a route to study the
physical properties of two-dimensional WTe2.Comment: 19 pages, 4 figures and 2 table
Holographic R\'enyi entropy for CFT with symmetry
In this paper we investigate the holographic R\'enyi entropy of two disjoint
intervals on complex plane with small cross ratio for conformal field
theory with symmetry in the ground state, which could be dual to a higher
spin AdS gravity. We focus on the cases of and symmetries. In
order to see the nontrivial contributions from the fields, we calculate the
R\'enyi entropy in the expansion of to order in both the gravity and
the CFT sides. In the gravity side the classical contributions to the
entanglement entropy is still given by the Ryu-Takayanagi area formula under
the reasonable assumption, while the 1-loop quantum corrections have to take
into account of the contributions not only from massless gravitons, but also
from massless higher spin fields. In the CFT side we still use the operator
product expansion of twist operators in the small interval limit, but now we
need to consider the quasiprimary fields constructed from fields, besides
the ones from Virasoro Verma module. In the large central charge limit, we
obtain the classical, 1-loop, 2-loop, and 3-loop parts of the R\'enyi entropy.
The classical and 1-loop results in the gravity and the CFT sides are in exact
match. This confirms the higher spin gravity/CFT correspondence, and also
supports the holographic computation of R\'enyi entanglement entropy, including
the quantum correction, in both the AdS gravity and the higher spin AdS
gravity.Comment: 32 pages, published versio
Hidden Conformal Symmetry of Extremal Black Holes
We study the hidden conformal symmetry of the extremal black holes. We
introduce a new set of conformal coordinates to write the generators.
We find that the Laplacian of the scalar field in many extremal black holes
could be written in terms of the quadratic Casimir. This suggests
that there exist dual CFT descriptions of these black holes. From the conformal
coordinates, the temperatures of the dual CFTs could be read directly. For the
extremal black hole, the Hawking temperature is vanishing. Correspondingly,
only the left (right) temperature of the dual CFT is non-vanishing and the
excitations of the other sector are suppressed. In the probe limit, we compute
the scattering amplitudes of the scalar off the extremal black holes and find
perfect agreement with the CFT prediction.Comment: 16 pages; Published versio
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Prediction of microbial communities for urban metagenomics using neural network approach.
BACKGROUND:Microbes are greatly associated with human health and disease, especially in densely populated cities. It is essential to understand the microbial ecosystem in an urban environment for cities to monitor the transmission of infectious diseases and detect potentially urgent threats. To achieve this goal, the DNA sample collection and analysis have been conducted at subway stations in major cities. However, city-scale sampling with the fine-grained geo-spatial resolution is expensive and laborious. In this paper, we introduce MetaMLAnn, a neural network based approach to infer microbial communities at unsampled locations given information reflecting different factors, including subway line networks, sampling material types, and microbial composition patterns. RESULTS:We evaluate the effectiveness of MetaMLAnn based on the public metagenomics dataset collected from multiple locations in the New York and Boston subway systems. The experimental results suggest that MetaMLAnn consistently performs better than other five conventional classifiers under different taxonomic ranks. At genus level, MetaMLAnn can achieve F1 scores of 0.63 and 0.72 on the New York and the Boston datasets, respectively. CONCLUSIONS:By exploiting heterogeneous features, MetaMLAnn captures the hidden interactions between microbial compositions and the urban environment, which enables precise predictions of microbial communities at unmeasured locations
The Electromagnetic Decays of
We calculate the electromagnetic (EM) decay widths of the
meson, which is observed recently by the ATLAS Collaboration. The main EM decay
channels of this particle are and , which, in
literature, are estimated to have the branching ratio of about . In this
work, we get the partial decay widths: keV,
keV and keV. In the
calculation, the instantaneous approximated Bethe-Salpeter method is used. For
the -wave mesons, the wave functions are given by mixing the
and states. Within the Mandelstam formalism, the decay amplitude is
given, which includes the relativistic corrections.Comment: 9 pages, 3 figures, 3 table
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