A high‐performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high‐pressure solid‐phase compression molding. Superior ...shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO loading owning to multi‐facet segregated architecture with rGO selectively located on the boundaries among PS multi‐facets. This special architecture not only provides many interfaces to absorb the electromagnetic waves, but also dramatically reduces the loading of rGO by confining the rGO at the interfaces. Moreover, the mechanical strength of the segregated composite is dramatically enhanced using high pressure at 350 MPa, overcoming the major disadvantage of the composite made by conventional‐pressure (5 MPa). The composite prepared by the higher pressure shows 94% and 40% increment in compressive strength and compressive modulus, respectively. These results demonstrate a promising method to fabricate an economical, robust, and highly efficient EMI shielding material.
The rGO/PS composite with segregated architecture is realized via high‐pressure solid‐phase compression molding for efficient EMI shielding. The highest EMI SE of 45.1 dB among rGO based polymer composites is achieved with only 3.47 vol% rGO loading. The high‐pressure molded composite shows 94% and 40% enhancement in compressive strength and modulus compared to conventional‐pressure molded composite.
Many organizations are using knowledge management systems (KMSs) to facilitate knowledge sharing. However, few studies have empirically investigated how individual characteristics and organizational ...work practices influence knowledge sharing. Based on accountability theory, the person–situation interactional psychology perspective, and the five-factor model of personality, this study uses a quasi-experimental design to investigate how two accountability-inducing management practices—evaluation and evaluation plus reward—and their interactions with personality characteristics influence knowledge sharing using a KMS. One hundred employees from a Chinese software company participated in the study. The authors found that both evaluation and evaluation plus reward had a positive relationship with knowledge sharing. Greater levels of knowledge sharing occurred in the evaluation-plus-reward condition compared with the evaluation condition. Also, knowledge sharing was influenced by the interaction between evaluation plus reward and conscientiousness, neuroticism, and openness to experience. Implications of the study results for research and practice are discussed.
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We initiate a systematic study of precision calculation of the inflation correlators at the 1-loop level, starting in this paper with bosonic 1-loop bispectrum with chemical-potential ...enhancement. Such 1-loop processes could lead to important cosmological collider observables but are notoriously difficult to compute due to the lack of symmetries. We attack the problem from a direct numerical approach based on the real-time Schwinger-Keldysh formalism and show full numerical results for arbitrary kinematics containing both the oscillatory “signals” and the “backgrounds”. Our results show that, while the non-oscillatory part can be one to two orders of magnitude larger, the oscillatory signal can be separated out by applying appropriate high-pass filters. We have also compared the result with analytic estimates typically adopted in the literature. While the amplitude is comparable, there is a non-negligible deviation in the frequency of the oscillatory part away from the extreme squeezed limit.
•The AdaBoost algorithm is adopted to predict the compressive strength of concrete.•1030 sets of data is collected to train the model and reaches an accuracy of 98%.•Different algorithms are compared ...to show the superior of the proposed model.•Key factors and in the AdaBoost and influence of input variables are investigated.
In this paper, an intelligent approach based on the machine learning technique is proposed for predicting the compressive strength of concrete. This approach employs the adaptive boosting algorithm to construct a strong learner by integrating several weak learners, which can find the mapping between the input data and output data. The weak learner whose predicting error is small will have a larger weight in the entire system, thus the overall accuracy of the strong learner will be enhanced. A total of 1030 sets of concrete compressive strength tests is collected to train and test the learners, in which the concrete mixture components (e.g., coarse/fine aggregates, cement, water, additive, etc.) and the curing time are set as the input data while the compressive strength value is set as the output data. The proposed approach is validated through a 10-fold cross validation method, and reaches an average accuracy of over 95% in sense of determination coefficient. In addition, a new dataset of 103 samples for concrete compressive strength is also adopted to demonstrate the generalization power of the proposed mode. The proposed approach is also compared to some other individual machine learning techniques that are already applied in this field, e.g., artificial neural network (ANN) and support vector machine (SVM), and shows superior advantages over these methods. Finally, the influence of some key factors in the adaptive boosting approach is also investigated, e.g., the amount of training data, the choice of weak learner, and the influence of the sensitivity and number of the input parameters. It is shown that using 80% of the total data for training can obtain acceptable prediction results and decision tree is the best choice for the weak learner in the boosting framework. Also, the importances of different input variables are obtained based on the sensitivity analysis results.
Three Zn(II) metal-organic frameworks (Zn-MOFs), Zn2(tib)(HL(1))(H2L(1))0.5·2H2O (1), Zn2(tib)(L(2))·H2O (2) and Zn3(tib)(L(3))2(H2O)6·2 H2O (3), have been prepared by reactions of ...1,3,5-tris(1-imidazolyl)benzene (tib), and biphenyl-3,3',4,4'-tetracarboxylic acid (H4L(1)), 4,4'-oxydiphthalic acid (H4L(2)), or benzene-1,3,5-tricarboxylic acid (H3L(3)) with corresponding Zn(II) salts, respectively. Single crystal structure analyses reveal that 1 and 2 are constructed by Zn-centered polyhedra, tib and multidentate tetracarboxylate ligands to form 3-dimensional frameworks. In contrast, when the tetracarboxylate ligands were replaced by tricarboxylate ligand, layered structure of 3 is produced. These compounds are further characterized by powder X-ray diffraction, element analyses, thermogravimetric analyses and photoluminescent spectroscopy. The luminescent properties of three Zn-MOFs dispersed in different solvents have been investigated systematically, demonstrating high sensitivity for the detection of nitro compounds via a fluorescence quenching mechanism.
Excellent electromagnetic interference (EMI) shielding ability, light weight, and good heat resistance are highly required for practical applications of EMI shielding materials, such as in areas of ...aerospace, aircraft, and automobiles. Herein, a lightweight and robust carbon nanotube (CNT)/polyimide (PI) foam was developed for efficient and heat-resistant EMI shielding. Thanks to poly(vinyl pyrrolidone) (PVP) as a surfactant that not only promotes the uniform dispersion of CNTs to form perfect CNT conductive networks but also can be removed in situ during the polymerization process, the density of resultant CNT/PI foam is only 32.1 mg·cm–3, and the EMI shielding effectiveness (EMI SE) is up to 41.1 dB, which represents one of the highest EMI SE values compared to previously reported polymer-based foams. The CNT/PI foam also achieves the absorption coefficient (A) of up to 82.3%, which is very impressive in CNT/polymer foams at comparable EMI SE levels. The PI matrix endows the foam with excellent heat resistance. The as-prepared CNT/PI foam presents a higher EMI SE than 35 dB even after being subjected to the flame of an alcohol burner. Moreover, the compressive strength and compressive modulus are up to 240.9 and 323.9 kPa. These results indicate its certain application potential in the harsh requirement of aeronautics and aerospace industries as a highly efficient and lightweight EMI shielding material.
Prolonged exposure to negative stressors could be harmful if a subject cannot respond appropriately. Strategies evolved to respond to stress, including repetitive displacement behaviours, are ...important in maintaining behavioural homoeostasis. In rodents, self-grooming is a frequently observed repetitive behaviour believed to contribute to post-stress de-arousal with adaptive value. Here we identified a rat limbic di-synaptic circuit that regulates stress-induced self-grooming with positive affective valence. This circuit links hippocampal ventral subiculum to ventral lateral septum (LSv) and then lateral hypothalamus tuberal nucleus. Optogenetic activation of this circuit triggers delayed but robust excessive grooming with patterns closely resembling those evoked by emotional stress. Consistently, the neural activity of LSv reaches a peak before emotional stress-induced grooming while inhibition of this circuit significantly suppresses grooming triggered by emotional stress. Our results uncover a previously unknown limbic circuitry involved in regulating stress-induced self-grooming and pinpoint a critical role of LSv in this ethologically important behaviour.
The XENON1T collaboration has observed an excess in electronic recoil events below 5 keV over the known background, which could originate from beyond-the-standard-model physics. The solar axion is a ...well-motivated model that has been proposed to explain the excess, though it has tension with astrophysical observations. The axions traveling from the Sun can be absorbed by the electrons in the xenon atoms via the axion-electron coupling. Meanwhile, they can also scatter with the atoms through the inverse Primakoff process via the axion-photon coupling, which emits a photon and mimics the electronic recoil signals. We found that the latter process cannot be neglected. After including the keV photon produced via the inverse Primakoff process in the detection, the tension with the astrophysical constraints can be significantly reduced. We also explore scenarios involving additional new physics to further alleviate the tension with the astrophysical bounds.
Designing lightweight polyimide (PI) foam with low density, high heat resistance, excellent electromagnetic interference (EMI) shielding ability and good compressibility is urgent in practical ...application of aeronautics and aerospace. However, to guarantee high EMI shielding effectiveness (EMI SE), high conductive filler content was always required, which would lead to high stiffness and poor compressibility of the composite foam, because of the agglomerations and the limitation of the interaction force between conductive filler and PI matrix. Herein, desirable CNT dispersion could be achieved with the assistant of the functional group on graphene oxide surface and the “π-π” conjugation between graphene and CNT. The resultant composite foam exhibits an average EMI SE of 28.2 dB and specific EMI SE (SSE) of 7050 dB cm2 g−1 at an only 0.02 g cm−3 density. Meanwhile, the multi-layer structure formed in cell wall and chemical bonding between PI matrix and graphene flakes endow the composite foam with good cycling compression stability. Moreover, the high decomposition temperature (Td, 10%) of 630.9 °C exhibits great competition with other previously reported PI-based composites. These features confirm the potential of the CNT/graphene/PI foam as a lightweight, compressive, heat-resistant material for efficient EMI shielding and electromagnetic wave absorption.
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•A facile approach for developing lightweight polyimide foam with uniform dispersion of carbon nanotube was designed.•Desirable dispersibility of carbon nanotube in polyimide matrices was achieved with the aid of graphene oxide.•The as-prepared polyimide foam exhibits excellent electromagnetic wave shielding ability and good compressibility.
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