Aiming at the common problem of low learning effect in single structure learning of a Bayesian network, a new algorithm EF-BNSL integrating ensemble learning and frequent item mining is proposed. ...Firstly, the sample set is obtained by sampling the original dataset using Bootstrap, which is mined using the Apriori algorithm to derive the maximum frequent items and association rules so that the black and white list can be determined. Secondly, considering that there may be wrong edges in the black and white list, the black and white list is used as the penalty term of the BDeu score and the initial network is obtained from the hill climbing algorithm. Finally, repeat the above steps 10 times to obtain 10 initial networks. The 10 initial networks were integrated and learned by the integrated strategy function to obtain the final Bayesian network. Experiments were carried out on six standard networks to calculate F1 score and HD. The results show that the EF-BNSL algorithm can effectively improve F1 score, reduce HD, and learn the network structure that is closer to the real network.
Based on first principle calculations, a graphene monolayer shows a complicated deformation behavior under uniaxial tension. The maximum stress of graphene is reached when the bond stretching ratio ...is far less than its breaking value, which means that graphene shows the typical "ductile-like" behavior but not the conventionally considered "brittle-like" behavior. Although the graphene monolayer shows isotropic behavior in strength, it is strongly anisotropic in deformation (
i.e.
, the ultimate strain is highly different along the different directions). Under uniaxial tension along the zigzag/armchair direction, the overall deformation is only supported by the C-C bonds in one orientation, whereas the C-C bonds in the other orientation and the C-C-C bond angle have almost no contribution, which cannot be correctly predicted by the empirical potential simulations. The complicated bond deformation means that the conventional constitutive model (
σ
=
E
+
D
2
) cannot accurately describe the tensile behavior of the graphene monolayer. According to the bond deformation under uniaxial tension, graphene can be simplified as a spring-network including both nonlinear springs (resisting both the tensile and compressive load) and a very strong compressive angle-spring (resisting the decrease of the C-C-C bond angle).
Under uniaxial tension, the deformation of graphene monolayer is only supported by the C-C bonds in one orientation, whereas the C-C bonds in the other orientation and the C-C-C bond angle have almost no contribution, which cannot be correctly predicted by the empirical potential simulations.
Using molecular dynamics simulations, we investigated the reusable performance of the nanofluidic energy absorption system (NEAS) to dissipate the impact energy created by a drop hammer (simulated by ...a carbon plate with an initial velocity and mass). The effects of nanopore flexibility and surface roughness on the reusable performance of NEAS are also considered. The results clearly shown that NEAS can only convert the mechanical energy into the solid–liquid interfacial energy (i.e., store it in the system) in the loading stage; the stored interfacial energy is gradually released and finally dissipated as heat by the solid–liquid interaction in the unloading stage. Therefore, the unloading response of NEAS decides whether or not the system can be reused for energy absorption, which is sensitive to the loading condition. Although NEAS behaves as a one-time used energy absorption material under quasi-static loading condition, it can be reused under dynamic loading condition. In addition, the nanopore surface roughness also affects the unloading behavior of NEAS. To the best of our knowledge, this is the first time to theoretically validate the reusable performance of NEAS.
The finite element method is used to investigate the indentation behavior of two-dimensional (2D) materials mounted on a substrate. The overall indentation response of the composite structure of ...2D-material/substrate is highly sensitive to the elastic modulus ratio of the 2D-material to its substrate (
λ
). When
λ
is small (e.g.,
λ
<
100
), the overall indentation load–displacement relationship agrees with the classic indentation model (e.g., the Hertz model), whereas with a large
λ
(e.g.,
λ
≥
10
3
), the indentation behavior of the composite structure will deviate from the manner predicted by the classic indentation model. In addition, with a small
λ
, the overall indentation modulus of the composite structure is very close to that of the pure substrate (i.e., the 2D-material has a very weak contribution to the overall indentation modulus), and thus, the elastic modulus of the 2D-material cannot be effectively determined from the overall indentation modulus. The contribution of the 2D-material rapidly increases with
λ
, and when
λ
>
10
4
, it is possible to accurately determine the elastic modulus of the 2D-material from the overall indentation response by the inverse analysis.
Two dimensional (2D) materials are usually assumed to be continuum thin films to study their mechanical behavior. Freestanding indentation testing and pressure bulge testing are two standard ...techniques for characterizing the mechanical properties of thin films. Compared with the former, the latter is far less often used to characterize the elastic moduli of 2D materials, even though there is no solid evidence to show that the former is more effective than the latter. In the present work, the effectiveness of the analytical models adopted in both approaches on determining the elastic moduli of 2D materials are investigated using numerical analysis, which can be evaluated based upon the accuracy of the determined elastic moduli, and the effects of Poisson’s ratio and the applied loading range are also considered. To account for the effect of the adhesive boundary condition of freestanding 2D materials in the testing, the numerical simulations of the initially unstressed samples, pre-stretched samples and slack samples are all analyzed in the present work. It is found that the bulge testing model is actually more effective than the indentation model on determining the mechanical properties of 2D materials.
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Nanofluidic behavior has been used to produce a high energy absorption system which can transfer the mechanical work (done by impact or blast) into the solid–liquid interfacial energy. Increasing the ...liquid interface area by using nanoporous particles with high specific surface area is the typical way to increase the energy absorption density of system. In present work, we found that the energy absorption density is also highly sensitive to the species of liquid selected in a nanofluidic system. Using molecular dynamics (MD) simulations, the performance of nanofluidic energy absorption system (NEAS) based on glycerol solutions with different concentrations is investigated, and the effects of nanochannel size and loading rate on the system performance are also considered. With the increase of the concentration of glycerol (ϕ), the energy absorption density of NEAS can be significantly increased; e.g., when the liquid changes from water (ϕ = 0) to pure glycerol (ϕ = 1), the energy absorption density of NEAS can be increased by up to three times.
Graphene is the stiffest membrane and PDMS is one of the very compliant materials. The indentation response of a graphene monolayer mounted on a PDMS substrate (graphene/PDMS) is studied by both ...experimental and computational investigations. Due to the huge elastic modulus ratio between membrane and substrate (∼106) and the very large ratio of indentation depth to membrane thickness (∼103), the indentation deformation of graphene in the graphene/PDMS structure is analogous to that of free-standing (F-S) graphene but just with a relatively smaller indentation depth (i.e., the graphene deformation is insensitive to the appearance of PDMS substrate); the graphene can create a screening effect, which causes the PDMS substrate deformation to be insensitive to the tip geometry. In addition, with the aid of finite element method (FEM), the elastic modulus of graphene monolayer can be accurately determined from the overall indentation response of graphene/PDMS using an inverse analysis, which is determined as 0.982TPa (very close to previously reported values). The present approach can be also extended to other 2D materials.
Sustainably feeding the world's growing population is a challenge, and closing yield gaps (that is, differences between farmers' yields and what are attainable for a given region) is a vital strategy ...to address this challenge. The magnitude of yield gaps is particularly large in developing countries where smallholder farming dominates the agricultural landscape. Many factors and constraints interact to limit yields, and progress in problem-solving to bring about changes at the ground level is rare. Here we present an innovative approach for enabling smallholders to achieve yield and economic gains sustainably via the Science and Technology Backyard (STB) platform. STB involves agricultural scientists living in villages among farmers, advancing participatory innovation and technology transfer, and garnering public and private support. We identified multifaceted yield-limiting factors involving agronomic, infrastructural, and socioeconomic conditions. When these limitations and farmers' concerns were addressed, the farmers adopted recommended management practices, thereby improving production outcomes. In one region in China, the five-year average yield increased from 67.9% of the attainable level to 97.0% among 71 leading farmers, and from 62.8% to 79.6% countywide (93,074 households); this was accompanied by resource and economic benefits.
We propose to measure the elastoplastic properties of micro- and nano-fibers by a normal indentation technique in which the vertically aligned fibers are embedded in an elastic matrix. Measurements ...are taken at two different indentation depths, which represent different levels of the matrix effects and lead to the establishment of two independent equations that correlate the fiber/matrix properties with the indentation responses. Effective reverse analysis algorithms are proposed, and by following which the desired fiber properties can be determined from a sharp indentation test. Comprehensive analysis is also carried out to verify the effectiveness and error sensitivity of the presented method. The extracted material properties agree well with those measured from the parallel experiments on human hair and glass fibers.
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