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Zhengqing Shi,Chuan Zhou,Jian Guo 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.5
This paper investigates the consensus tracking problem with predefined performances requirements for a class of unknown nonlinear multi-agent systems with hysteresis quantizer and external disturbances under a directedgraph topology. Neural network observers are designed to estimate unmeasurable states and the the consensus tracking problem with performance requirements is transformed to a stabilization problem by prescribed performanceerror transformation schemes. The novel consensus protocol can be applied to a more general class of nonlinearmulti-agent systems since the Lipschitz condition is avoided and state information is not required. It is strictlyproved that all signals in the closed-loop systems are cooperatively uniformly ultimately bounded and both thetransient and steady performances of the consensus tracking satisfy prescribed performance requirements. Finally,two numerical examples are presented to validate the effectiveness of the proposed strategy.
Zhengqing Zhang,Tianfeng Li,Guanghui Tang 한국응용곤충학회 2018 Journal of Asia-Pacific Entomology Vol.21 No.1
Atrijuglans hetaohei Yang (Lepidoptera: Gelechioidea) is a kind of walnut pest, which mainly damage Juglans regia(Juglandales: Juglandaceae) and is widely distributed in China. The information of microRNAs, e.g., the conservedand novel miRNAs of this species is still unknown. In the present study, the miRNAs in larval and adultstages of A. hetaohei were identified by high throughput sequencing with reference to the genome database of theBombyx mori. A total of 132 conserved miRNAs belonging to 64 families and seven novel miRNAs were obtained,among which 118 miRNAs were identified in both libraries, 4 and 17 miRNAs were only detected to adultspecificand larval-specific libraries, respectively. The most abundant miRNAs in A. hetaohei were miR-1a-3p, let-7, miR-2766 and miR-184. Comparative analysis revealed that 4 novel miRNAs and 47 conserved miRNAs weredifferentially expressed (P < 0.05) between two libraries. Abundance changes of miRNAs were observed fromlarva to adult: 19 miRNAs were up-regulated and 21 miRNAs were down-regulated. The metamorphosis andapoptosis associated miRNAs including miR-1a-3p, miR-133, let-7, miR-2766, miR-184 and miR-34 were discussedfor their predicted functions in insect development. The different expressions of these miRNAs wererelevant to dorso-ventral axis formation, phototransduction, insect hormone biosynthesis, circadian rhythm andmitogen-activated protein kinase (MAPK) signaling pathway. qRT-PCR analysis of ten miRNAs showed similarexpression patterns as high throughput analysis, most miRNAs were highly expressed in adult stage, while miR-8-3p, miR-305-3p and miR-2766 were highly expressed in larvae. The results preliminarily revealed the characterizationof conserved and novel miRNAs in different development stages of A. hetaohei. The different expressionsand associated functions of these miRNAs will provide a basis for understanding post-transcriptionallevel during A. hetaohei development and growth.
Zhang, Zhengqing,Matin, Mohammad A.,Ha, Man Yeong,Jang, Joonkyung American Chemical Society 2016 Langmuir Vol.32 No.37
<P>This paper reports a large scale molecular dynamics (MD) simulation study of the wettability of a gold surface engraved with (hemi)spherical cavities. By increasing the depth of cavities, the contact angle (CA) of a water droplet on the surface was varied from a hydrophilic (69 degrees) to a hydrophobic value (>109 degrees). The nonmonotonic behavior of the CA vs the depth of the cavities was consistent with the Cassie-Baxter theory, as found in the experiment by Abdelsalam et al. (Abdelsalam, M. E.; Bartlett, P. N.; Kelf, T.; Baumberg, J. Wetting of Regularly Structured Gold Surfaces. Langmuir 2005, 21, 1753-1757). Depending on the depth of cavities, however, the droplet existed not only in the Cassie-Baxter state, but also in the Wenzel or an intermediate state, where the cavities were penetrated partially by the droplet.</P>
Thermal Healing of the Nanometer-Wide Lines of Self-Assembled Monolayer
Zhang, Zhengqing,Ahn, Yoonho,Son, Jong Yeog,Jang, Joonkyung American Chemical Society 2016 The Journal of Physical Chemistry Part C Vol.120 No.28
<P>The structural and thermal properties of the nanometer-wide lines of a self-assembled monolayer (SAM) were investigated using molecular dynamics simulations. When grown by contact printing, a linear SAM contained a significant portion (8%) of unbound molecules that are inverted among upright molecules. This paper proposes thermal annealing (300-400 K) as an efficient method to remove the unbound molecules and improve the quality of the linear SAM. The partial melting of the SAM during heating enabled the unbound molecules to flip and adsorb. With subsequent cooling, the linear SAM recovered its compact ordered structure. The molecular mechanisms and activation energies involved in the thermal annealing were elucidated.</P>
Thermal Healing of a Mixed-Thiol Monolayer at the Nanoscale
Zhang, Zhengqing,Lim, Manho,Ahn, Yoonho,Jang, Joonkyung American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.23
<P>Using molecular dynamics simulation, we study the thermal healing of a mixed-thiol monolayer grown by contact printing. By simulating the monolayers with various compositions of octadecanethiol and decanethiol molecules, we show that a mixed-thiol monolayer grown by contact printing contains a significant portion of unbound molecules which fail to bind their sulfur atoms to the underlying gold surface. A subsequent thermal annealing (300-370 K) however removes the unbound thiol molecules and gives an ordered and compact monolayer. We uncover the molecular pathways behind the removal of the unbound molecules during thermal annealing.</P> [FIG OMISSION]</BR>
Correlating Atomic Structure and Transport in Suspended Graphene Nanoribbons
Qi, Zhengqing John,Rodrí,guez-Manzo, Julio A.,Botello-Mé,ndez, André,s R.,Hong, Sung Ju,Stach, Eric A.,Park, Yung Woo,Charlier, Jean-Christophe,Drndić,, Marija,Johnson, A. T. Ch American Chemical Society 2014 NANO LETTERS Vol.14 No.8
<P/><P>Graphene nanoribbons (GNRs) are promising candidates for next generation integrated circuit (IC) components; this fact motivates exploration of the relationship between crystallographic structure and transport of graphene patterned at IC-relevant length scales (<10 nm). We report on the controlled fabrication of pristine, freestanding GNRs with widths as small as 0.7 nm, paired with simultaneous lattice-resolution imaging and electrical transport characterization, all conducted within an aberration-corrected transmission electron microscope. Few-layer GNRs very frequently formed bonded-bilayers and were remarkably robust, sustaining currents in excess of 1.5 μA per carbon bond across a 5 atom-wide ribbon. We found that the intrinsic conductance of a sub-10 nm bonded bilayer GNR scaled with width as <I>G</I><SUB>BL</SUB>(<I>w</I>) ≈ 3/4(<I>e</I><SUP>2</SUP><I>/h</I>)<I>w</I>, where <I>w</I> is the width in nanometers, while a monolayer GNR was roughly five times less conductive. Nanosculpted, crystalline monolayer GNRs exhibited armchair-terminated edges after current annealing, presenting a pathway for the controlled fabrication of semiconducting GNRs with known edge geometry. Finally, we report on simulations of quantum transport in GNRs that are in qualitative agreement with the observations.</P>
Molecular features of hydration layers probed by atomic force microscopy
Zhang, Zhengqing,Ryu, Seol,Ahn, Yoonho,Jang, Joonkyung The Royal Society of Chemistry 2018 Physical chemistry chemical physics Vol.20 No.48
<P>Structurally-ordered layers of water are universally formed on a solid surface in aqueous solution or under ambient conditions. Although such hydration layers are commonly probed <I>via</I> atomic force microscopy (AFM), the current understanding on how the hydration layers manifest themselves in an AFM experiment is far from complete. By using molecular dynamics simulation, we investigate the hydration layers on a hydrophilic or hydrophobic surface probed by a nanoscale tip. We study the density and molecular orientation of water, the free energy, and the force on the tip by varying the tip-surface distance. The force-distance curve oscillates due to the transition between the mono-, bi-, and tri-layers of water confined between the tip and the surface. If both the tip and the surface are hydrophobic, water confined between the tip and the surface evaporates due to the dewetting transition, giving a hydrophobic force without oscillation. The periodicity of oscillation in the force differs from the structural periodicity of water. With a close proximity of the tip, the molecular dipoles align parallel to the surface, regardless of whether the tip and the surface are hydrophilic or hydrophobic.</P>