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      • Stability, Molecular Sieving, and Ion Diffusion Selectivity of a Lamellar Membrane from Two-Dimensional Molybdenum Disulfide

        Deng, Mengmeng,Kwac, Kijeong,Li, Meng,Jung, Yousung,Park, Hyung Gyu American Chemical Society 2017 Nano letters Vol.17 No.4

        <P>Two-dimensional (2D) subnanometer channels allow unique mass transport promising for molecular sieving. New 2D channels of MoS2 nanosheets allow one to understand molecular transmission and separation, unlike the graphene oxide counterpart containing various defects and cationic metal contaminants. Membranes from layered MoS2 platelets show extraordinary stability in an aqueous environment and compatibility with polymer filters, both beneficial to efficient manufacturing. Sharing gas-tightness and unimpeded water vapor permeation with a graphene oxide membrane, our lamellar MoS2 membrane demonstrates a molecular sieving property for organic vapor for the first time. The MoS2 membrane also reveals diffusion selectivity of aqueous ions, attributable to the energy penalty in bulk-to-2D dimensional transition. These newly revealed properties of the lamellar membrane full of angstrom-sized 2D channels point to membrane technology applications for energy and environment.</P>

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        Distributed Fuzzy Resilient Tracking for Nonlinear MASs Under DoS Attacks

        Shu-Huan Gao,Mengmeng Chen,Chao Deng 제어·로봇·시스템학회 2023 International Journal of Control, Automation, and Vol.21 No.10

        In this paper, the distributed fuzzy resilient tracking problem for a class of second-order nonlinear multiagent systems (MASs) under denial-of-service (DoS) attacks is addressed. Compared with the existing distributed fuzzy tracking results, a more general class of second-order MASs with DoS attacks under combined output observable situation are considered in this paper. Under DoS attacks, the second-order derivative of the traditional distributed observer does not exist, while this signal is necessary to solve the distributed fuzzy tracking problem for second-order MASs when using the backstepping method. To solve the problem, a hierarchical control method that consists of a cooperative resilient observer and a distributed controller is proposed. Specifically, a new distributed resilient observer state with a second-order derivative and also the function of defending network attacks is designed based on a combined output observable condition. By using the backstepping technique, decentralized fuzzy adaptive resilient controllers are designed to achieve distributed tracking under DoS attacks. It is shown that the distributed fuzzy resilient tracking problem can be solved under our designed method. Finally, second-order nonlinear MASs are provided to verify the effectiveness of our method.

      • KCI등재

        Numerical Investigation and Design of Cold-formed Steel Angle Columns with Complex Edges under Axial Compression

        Jun-Feng Zhang,Mengmeng Feng,En-Feng Deng,Shiyun Pang 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.2

        Currently, cold-formed steel (CFS) is widely used in fabricated steel structures for high strength-to-weight ratio and ease for installation. However, limited research is available in the literature on the CFS angle columns with complex edges under axial compression. In this paper, the axial compressive capacity of the CFS angle columns with complex edges was numerically studied. The distortional buckling characteristics of 1008 CFS angle sections with complex edges were analyzed by finite strip software CUFSM. Detailed non-linear finite element model (FEM) was developed based on finite element program ABAQUS and verified by comparing with test results. The verification indicated that the developed FEM could well predict the ultimate strength and failure model of the specimens. Using the validated FEM, an extensive parametric study comprised of 330 models was conducted. The influences of the specimen length, the edge ratio and the limb-width ratio of the angle section on the axial compressive capacity of CFS angle columns with complex edges were evaluated. Then an improved direct strength method (DSM) was proposed based on the existing DSM. The evaluations based on tests and FEA results showed that using the modified DSM to predict the load-bearing capacity of the CFS angle columns with complex edges was feasible.

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        그래핀에 기초한 막의 구조와 물질 전달 성질 개관

        Jakob Buchheim,Roman M. Wyss,Chang-Min Kim,Mengmeng Deng,Hyung Gyu Park 한국막학회 2016 멤브레인 Vol.26 No.4

        최근 2차원 나노 물질을 응용하여 수처리 막의 성능을 향상시킬 수 있는가에 대한 연구가 활발하다. 그 노력의 한 가운데에 원자 두께를 가지고 있으면서 손쉽게 구할 수 있고 층으로 쌓을 수도 있는 2차원 물질인 그래핀이 자리하고 있다. 이 총설에서 우리는 그래핀으로부터 만들 수 있는 두 가지 막 구조에 관한 기초 물질 전달 현상을 최근 연구 성과를 중심으 로 다룬다. 그 물질 자체로 이미 물질 전달 차단성을 갖는 그래핀에 정확히 제어된 크기의 구멍을 뚫을 수 있다면 아마도 원 자 크기 수준으로 얇은 두께 때문에 그래핀 막은 같은 기공 크기의 어느 막보다도 빠른 궁극적 투과도를 나타낼 것이며, 이 로부터 선택도를 담보할 수 있다면 다양한 막 분리 공정에 적용할 수 있을 것이다. 그 한 예로, 나노미터 이하의 기공을 가정 한 초박막 침투성 그래핀 막에 대한 분자동역학 연구와 몇몇 초기 실험 결과들이 해수담수화 막으로서의 가능성을 보인 점은 주목할 만하다. 그래핀 물질로부터 다른 구성을 가진 막을 설계할 수 있는데, 이 막은 적당히 산화된 그래핀 마이크로 판들을 무작위로 적층함으로써 구현할 수 있다. 그래핀 판 적층 간격을 나노미터 이하로 쉽게 제어할 수 있기 때문에 이 구조 역시 수처리 및 해수담수화 막으로서의 가능성을 시사한다. 기존 막기술에 존재하지 않던 구조와 물질 전달 성질을 가짐으로써 두 종류의 그래핀 막은 앞으로 수처리 기술을 비롯한 다양한 막 기술의 응용분야에서 효과적으로 기여할 가능성이 충분하다. Two-dimensional materials offer unique characteristics for membrane applications to water technology. With its atomic thickness, availability and stackability, graphene in particular is attracting attention in the research and industrial communities. Here, we present a brief overview of the recent research activities in this rising topic with bringing two membrane architecture into focus. Pristine graphene in single- and polycrystallinity poses a unique diffusion barrier property for most of chemical species at broad ambient conditions. If well designed and controlled, physical and chemical perforation can turn this barrier layer to a thinnest feasible membrane that permits ultimate permeation at given pore sizes. For subcontinuum pores, both molecular dynamics simulations and experiments predict potential salt rejection to envisage a seawater desalination application. Another novel membrane architecture is a stack of individual layers of 2D materials. When graphene- based platelets are chemically modified and stacked, the interplanar spacing forms a narrow transport pathway capable of separation of solvated ions from pure water. Bearing unbeknownst permeance and selectivity, both membrane architecture - ultrathin porous graphene and stacked platelets - offer a promising prospect for new extraordinary membranes for water technology applications.

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