3,263 research outputs found
A review of creep deformation and rupture mechanisms of low Cr-Mo alloy for the development of creep damage constitutive equations under lower stress
Accurate Reproduction of 161 Small-Molecule Complex Crystal Structures using the EUDOC Program: Expanding the Use of EUDOC to Supramolecular Chemistry
EUDOC is a docking program that has successfully predicted small-molecule-bound protein complexes and identified drug leads from chemical databases. To expand the application of the EUDOC program to supramolecular chemistry, we tested its ability to reproduce crystal structures of small-molecule complexes. Of 161 selected crystal structures of small-molecule guest-host complexes, EUDOC reproduced all these crystal structures with guest structure mass-weighted root mean square deviations (mwRMSDs) of <1.0 Å relative to the corresponding crystal structures. In addition, the average interaction energy of these 161 guest-host complexes (−50.1 kcal/mol) was found to be nearly half of that of 153 previously tested small-molecule-bound protein complexes (−108.5 kcal/mol), according to the interaction energies calculated by EUDOC. 31 of the 161 complexes could not be reproduced with mwRMSDs of <1.0 Å if neighboring hosts in the crystal structure of a guest-host complex were not included as part of the multimeric host system, whereas two of the 161 complexes could not be reproduced with mwRMSDs of <1.0 Å if water molecules were excluded from the host system. These results demonstrate the significant influence of crystal packing on small molecule complexation and suggest that EUDOC is able to predict small-molecule complexes and that it is useful for the design of new materials, molecular sensors, and multimeric inhibitors of protein-protein interactions
Enhancing Deep Neural Networks Testing by Traversing Data Manifold
We develop DEEPTRAVERSAL, a feedback-driven framework to test DNNs.
DEEPTRAVERSAL first launches an offline phase to map media data of various
forms to manifolds. Then, in its online testing phase, DEEPTRAVERSAL traverses
the prepared manifold space to maximize DNN coverage criteria and trigger
prediction errors. In our evaluation, DNNs executing various tasks (e.g.,
classification, self-driving, machine translation) and media data of different
types (image, audio, text) were used. DEEPTRAVERSAL exhibits better performance
than prior methods with respect to popular DNN coverage criteria and it can
discover a larger number and higher quality of error-triggering inputs. The
tested DNN models, after being repaired with findings of DEEPTRAVERSAL, achieve
better accurac
MDPFuzz: Testing Models Solving Markov Decision Processes
The Markov decision process (MDP) provides a mathematical framework for
modeling sequential decision-making problems, many of which are crucial to
security and safety, such as autonomous driving and robot control. The rapid
development of artificial intelligence research has created efficient methods
for solving MDPs, such as deep neural networks (DNNs), reinforcement learning
(RL), and imitation learning (IL). However, these popular models for solving
MDPs are neither thoroughly tested nor rigorously reliable.
We present MDPFuzzer, the first blackbox fuzz testing framework for models
solving MDPs. MDPFuzzer forms testing oracles by checking whether the target
model enters abnormal and dangerous states. During fuzzing, MDPFuzzer decides
which mutated state to retain by measuring if it can reduce cumulative rewards
or form a new state sequence. We design efficient techniques to quantify the
"freshness" of a state sequence using Gaussian mixture models (GMMs) and
dynamic expectation-maximization (DynEM). We also prioritize states with high
potential of revealing crashes by estimating the local sensitivity of target
models over states.
MDPFuzzer is evaluated on five state-of-the-art models for solving MDPs,
including supervised DNN, RL, IL, and multi-agent RL. Our evaluation includes
scenarios of autonomous driving, aircraft collision avoidance, and two games
that are often used to benchmark RL. During a 12-hour run, we find over 80
crash-triggering state sequences on each model. We show inspiring findings that
crash-triggering states, though look normal, induce distinct neuron activation
patterns compared with normal states. We further develop an abnormal behavior
detector to harden all the evaluated models and repair them with the findings
of MDPFuzzer to significantly enhance their robustness without sacrificing
accuracy
Estimating Individualized Decision Rules with Tail Controls
With the emergence of precision medicine, estimating optimal individualized
decision rules (IDRs) has attracted tremendous attention in many scientific
areas. Most existing literature has focused on finding optimal IDRs that can
maximize the expected outcome for each individual. Motivated by complex
individualized decision making procedures and popular conditional value at risk
(CVaR) measures, we propose a new robust criterion to estimate optimal IDRs in
order to control the average lower tail of the subjects' outcomes. In addition
to improving the individualized expected outcome, our proposed criterion takes
risks into consideration, and thus the resulting IDRs can prevent adverse
events. The optimal IDR under our criterion can be interpreted as the decision
rule that maximizes the ``worst-case" scenario of the individualized outcome
when the underlying distribution is perturbed within a constrained set. An
efficient non-convex optimization algorithm is proposed with convergence
guarantees. We investigate theoretical properties for our estimated optimal
IDRs under the proposed criterion such as consistency and finite sample error
bounds. Simulation studies and a real data application are used to further
demonstrate the robust performance of our method
4,4′-[8b,8c-Bis(ethoxycarbonyl)-4,8-dioxo-2,3,5,6-tetraÂhydro-1H,4H-2,3a,4a,6,7a,8a-hexaÂazacycloÂpentaÂ[def]fluorene-2,6-diyl]dipyridinium bisÂ(tetraÂfluoridoÂborate)
In the title compound, C26H32N8O6
2+·2BF4
−, the cation is built up from four fused rings, viz. two nearly planar imidazole rings and two triazine rings exhibiting chair conformations. One ethÂoxy group is disordered between two positions in an approximate ratio 3:2. The F atoms of the two anions are each rotationally disordered between two orientations in the same 3:2 ratio. The crystal structure is stabilized by interÂmolecular N—H⋯O, C—H⋯F and N—H⋯F interÂactions
Solving Einstein equations using deep learning
Einstein field equations are notoriously challenging to solve due to their
complex mathematical form, with few analytical solutions available in the
absence of highly symmetric systems or ideal matter distribution. However,
accurate solutions are crucial, particularly in systems with strong
gravitational field such as black holes or neutron stars. In this work, we use
neural networks and auto differentiation to solve the Einstein field equations
numerically inspired by the idea of physics-informed neural networks (PINNs).
By utilizing these techniques, we successfully obtain the Schwarzschild metric
and the charged Schwarzschild metric given the energy-momentum tensor of
matter. This innovative method could open up a different way for solving
space-time coupled Einstein field equations and become an integral part of
numerical relativity.Comment: 18 pages, 4 figure
- …