224 research outputs found
Privacy-preserving communication and power injection over vehicle networks and 5G smart grid slice
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A Score-based Geometric Model for Molecular Dynamics Simulations
Molecular dynamics (MD) has long been the \emph{de facto} choice for modeling
complex atomistic systems from first principles, and recently deep learning
become a popular way to accelerate it. Notwithstanding, preceding approaches
depend on intermediate variables such as the potential energy or force fields
to update atomic positions, which requires additional computations to perform
back-propagation. To waive this requirement, we propose a novel model called
ScoreMD by directly estimating the gradient of the log density of molecular
conformations. Moreover, we analyze that diffusion processes highly accord with
the principle of enhanced sampling in MD simulations, and is therefore a
perfect match to our sequential conformation generation task. That is, ScoreMD
perturbs the molecular structure with a conditional noise depending on atomic
accelerations and employs conformations at previous timeframes as the prior
distribution for sampling. Another challenge of modeling such a conformation
generation process is that the molecule is kinetic instead of static, which no
prior studies strictly consider. To solve this challenge, we introduce a
equivariant geometric Transformer as a score function in the diffusion process
to calculate the corresponding gradient. It incorporates the directions and
velocities of atomic motions via 3D spherical Fourier-Bessel representations.
With multiple architectural improvements, we outperforms state-of-the-art
baselines on MD17 and isomers of C7O2H10. This research provides new insights
into the acceleration of new material and drug discovery
Ultrafast Charge Transfer in Atomically Thin MoS2/WS2 Heterostructures
Van der Waals heterostructures have recently emerged as a new class of
materials, where quantum coupling between stacked atomically thin
two-dimensional (2D) layers, including graphene, hexagonal-boron nitride, and
transition metal dichalcogenides (MX2), give rise to fascinating new phenomena.
MX2 heterostructures are particularly exciting for novel optoelectronic and
photovoltaic applications, because 2D MX2 monolayers can have an optical
bandgap in the near-infrared to visible spectral range and exhibit extremely
strong light-matter interactions. Theory predicts that many stacked MX2
heterostructures form type-II semiconductor heterojunctions that facilitate
efficient electron-hole separation for light detection and harvesting. Here we
report the first experimental observation of ultrafast charge transfer in
photo-excited MoS2/WS2 heterostructures using both photoluminescence mapping
and femtosecond (fs) pump-probe spectroscopy. We show that hole transfer from
the MoS2 layer to the WS2 layer takes place within 50 fs after optical
excitation, a remarkable rate for van der Waals coupled 2D layers. Such
ultrafast charge transfer in van der Waals heterostructures can enable novel 2D
devices for optoelectronics and light harvesting
Amplitude- and phase-resolved nano-spectral imaging of phonon polaritons in hexagonal boron nitride
Phonon polaritons are quasiparticles resulting from strong coupling of
photons with optical phonons. Excitation and control of these quasiparticles in
2D materials offer the opportunity to confine and transport light at the
nanoscale. Here, we image the phonon polariton (PhP) spectral response in thin
hexagonal boron nitride (hBN) crystals as a representative 2D material using
amplitude- and phase-resolved near-field interferometry with broadband mid-IR
synchrotron radiation. The large spectral bandwidth enables the simultaneous
measurement of both out-of-plane (780 cm-1) and in-plane (1370 cm-1) hBN phonon
modes. In contrast to the strong and dispersive in-plane mode, the out-of-plane
mode PhP response is weak. Measurements of the PhP wavelength reveal a
proportional dependence on sample thickness for thin hBN flakes, which can be
understood by a general model describing two-dimensional polariton excitation
in ultrathin materials
Proteomic and Physiological Analyses Reveal Putrescine Responses in Roots of Cucumber Stressed by NaCl
Investigating Graph Structure Information for Entity Alignment with Dangling Cases
Entity alignment (EA) aims to discover the equivalent entities in different
knowledge graphs (KGs), which play an important role in knowledge engineering.
Recently, EA with dangling entities has been proposed as a more realistic
setting, which assumes that not all entities have corresponding equivalent
entities. In this paper, we focus on this setting. Some work has explored this
problem by leveraging translation API, pre-trained word embeddings, and other
off-the-shelf tools. However, these approaches over-rely on the side
information (e.g., entity names), and fail to work when the side information is
absent. On the contrary, they still insufficiently exploit the most fundamental
graph structure information in KG. To improve the exploitation of the
structural information, we propose a novel entity alignment framework called
Weakly-Optimal Graph Contrastive Learning (WOGCL), which is refined on three
dimensions : (i) Model. We propose a novel Gated Graph Attention Network to
capture local and global graph structure similarity. (ii) Training. Two
learning objectives: contrastive learning and optimal transport learning are
designed to obtain distinguishable entity representations via the optimal
transport plan. (iii) Inference. In the inference phase, a PageRank-based
method is proposed to calculate higher-order structural similarity. Extensive
experiments on two dangling benchmarks demonstrate that our WOGCL outperforms
the current state-of-the-art methods with pure structural information in both
traditional (relaxed) and dangling (consolidated) settings. The code will be
public soon
Pre-training of Equivariant Graph Matching Networks with Conformation Flexibility for Drug Binding
The latest biological findings observe that the traditional motionless
'lock-and-key' theory is not generally applicable because the receptor and
ligand are constantly moving. Nonetheless, remarkable changes in associated
atomic sites and binding pose can provide vital information in understanding
the process of drug binding. Based on this mechanism, molecular dynamics (MD)
simulations were invented as a useful tool for investigating the dynamic
properties of a molecular system. However, the computational expenditure limits
the growth and application of protein trajectory-related studies, thus
hindering the possibility of supervised learning. To tackle this obstacle, we
present a novel spatial-temporal pre-training method based on the modified
Equivariant Graph Matching Networks (EGMN), dubbed ProtMD, which has two
specially designed self-supervised learning tasks: an atom-level prompt-based
denoising generative task and a conformation-level snapshot ordering task to
seize the flexibility information inside MD trajectories with very fine
temporal resolutions. The ProtMD can grant the encoder network the capacity to
capture the time-dependent geometric mobility of conformations along MD
trajectories. Two downstream tasks are chosen, i.e., the binding affinity
prediction and the ligand efficacy prediction, to verify the effectiveness of
ProtMD through linear detection and task-specific fine-tuning. We observe a
huge improvement from current state-of-the-art methods, with a decrease of 4.3%
in RMSE for the binding affinity problem and an average increase of 13.8% in
AUROC and AUPRC for the ligand efficacy problem. The results demonstrate
valuable insight into a strong correlation between the magnitude of
conformation's motion in the 3D space (i.e., flexibility) and the strength with
which the ligand binds with its receptor
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