Size- and Chirality-Dependent Structural and Mechanical Properties of Single-Walled Phenine Nanotubes

Phenine nanotubes (PNTs) have recently been synthesized as a promising new onedimensional material for high-performance electronics. The periodically distributed vacancy defects in PNTs result in novel semiconducting properties, but may also compromise their mechanical properties. However, the role of these defects in modifying the structural and mechanical properties is not yet well understood. To address this, we conducted systematic molecular dynamics simulations investigating the structural evolution and mechanical responses of PNTs under various conditions. Our results demonstrated that the twisting of linear carbon chains in both armchair and zigzag PNTs led to interesting structural transitions, which were sensitive to chiralities and diameters. Additionally, when subjected to tensile and compressive loading, PNTs’ cross-sectional geometry and untwisting of linear carbon chains resulted in distinct mechanical properties compared to carbon nanotubes. Our findings provide comprehensive insights into the fundamental properties of these new structures while uncovering a new mechanism for modifying the mechanical properties of one-dimensional nanostructures through the twisting–untwisting of linear carbon chain

One Dimensional Twisted Van der Waals Structures Constructed by Self-Assembling Graphene Nanoribbons on Carbon Nanotubes

Twisted van der Waals heterostructures were recently found to possess unique physical properties, such as superconductivity in magic angle bilayer graphene. Owing to the nonhomogeneous stacking, the energy of twisted van der Waals heterostructures are often higher than their AA or AB stacking counterpart, therefore, fabricating such structures remains a great challenge in experiments. On the other hand, one dimensional (1D) coaxial van der Waals structures has less freedom to undergo phase transition, thus offer opportunity for fabricating the 1D cousin of twisted bilayer graphene. In this work, we show by molecular dynamic simulations that graphene nanoribbons can self-assemble onto the surface of carbon nanotubes driven by van der Waals interactions. By modifying the size of the carbon nanotubes or graphene nanoribbons, the resultant configurations can be controlled. Of particular interest is the formation of twisted double walled carbon nanotubes whose chiral angle difference can be tuned, including the 1.1° magic angle. Upon the longitudinal unzipping of such structures, twisted bilayer graphene nanoribbons can be obtained. As the longitudinal unzipping of carbon nanotubes is a mature technique, we expect the strategy proposed in this study to stimulate experimental efforts and promote the fast growing research in twistronics

Competition between Hydration Shell and Ordered Water Chain Induces Thickness-Dependent Desalination Performance in Carbon Nanotube Membrane

Exploring new reverse osmosis (RO) membranes that break the permeability-selectivitytrade-off rule is the ultimate goal in seawater desalination. Both nanoporous monolayer graphene(NPG) and carbon nanotube (CNT) channels have been proposed to be promising candidates forthis purpose. From the perspective of membrane thickness, both NPG and CNT can be classifiedinto the same category, as NPG is equivalent to the thinnest CNT. While NPG has the advantage ofa high water flux rate and CNT is excellent at salt rejection performance, a transition is expectedin practical devices when the channel thickness increases from NPG to infinite-sized CNTs. Byemploying molecular dynamics (MD) simulations, we find that as the thickness of CNT increases,the water flux diminishes but the ion rejection rate increases. These transitions lead to optimaldesalination performance around the cross-over size. Further molecular analysis reveals that thisthickness effect originates from the formation of two hydration shells and their competition withthe ordered water chain structure. With the increase in CNT thickness, the competition-dominatedion path through CNT is further narrowed. Once above this cross-over size, the highly confinedion path remains unchanged. Thus, the number of reduced water molecules also tends to stabilize,which explains the saturation of the salt rejection rate with the increasing CNT thickness. Our resultsoffer insights into the molecular mechanisms of the thickness-dependent desalination performancein a one-dimensional nanochannel, which can provide useful guidance for the future design andoptimization of new desalination membrane

Size- and Chirality-Dependent Structural and Mechanical Properties of Single-Walled Phenine Nanotubes

Phenine nanotubes (PNTs) have recently been synthesized as a promising new one-dimensional material for high-performance electronics. The periodically distributed vacancy defects in PNTs result in novel semiconducting properties, but may also compromise their mechanical properties. However, the role of these defects in modifying the structural and mechanical properties is not yet well understood. To address this, we conducted systematic molecular dynamics simulations investigating the structural evolution and mechanical responses of PNTs under various conditions. Our results demonstrated that the twisting of linear carbon chains in both armchair and zigzag PNTs led to interesting structural transitions, which were sensitive to chiralities and diameters. Additionally, when subjected to tensile and compressive loading, PNTs’ cross-sectional geometry and untwisting of linear carbon chains resulted in distinct mechanical properties compared to carbon nanotubes. Our findings provide comprehensive insights into the fundamental properties of these new structures while uncovering a new mechanism for modifying the mechanical properties of one-dimensional nanostructures through the twisting–untwisting of linear carbon chains

Crossing Generative Adversarial Networks for Cross-View Person Re-identification

Person re-identification (\textit{re-id}) refers to matching pedestrians across disjoint yet non-overlapping camera views. The most effective way to match these pedestrians undertaking significant visual variations is to seek reliably invariant features that can describe the person of interest faithfully. Most of existing methods are presented in a supervised manner to produce discriminative features by relying on labeled paired images in correspondence. However, annotating pair-wise images is prohibitively expensive in labors, and thus not practical in large-scale networked cameras. Moreover, seeking comparable representations across camera views demands a flexible model to address the complex distributions of images. In this work, we study the co-occurrence statistic patterns between pairs of images, and propose to crossing Generative Adversarial Network (Cross-GAN) for learning a joint distribution for cross-image representations in a unsupervised manner. Given a pair of person images, the proposed model consists of the variational auto-encoder to encode the pair into respective latent variables, a proposed cross-view alignment to reduce the view disparity, and an adversarial layer to seek the joint distribution of latent representations. The learned latent representations are well-aligned to reflect the co-occurrence patterns of paired images. We empirically evaluate the proposed model against challenging datasets, and our results show the importance of joint invariant features in improving matching rates of person re-id with comparison to semi/unsupervised state-of-the-arts.Comment: 12 pages. arXiv admin note: text overlap with arXiv:1702.03431 by other author

Three-dimensional transverse vibration of microtubules

A three-dimensional (3D) transverse vibration was reported based on the molecular structural mechanics model for microtubules (MTs), where the bending axis of the cross section rotates in an anticlockwise direction and the adjacent half-waves oscillate in different planes. Herein, efforts were invested to capturing the physics behind the observed phenomenon and identifying the important factors that influence the rotation angle between two adjacent half waves. A close correlation was confirmed between the rotation of the oscillation planes and the helical structures of the MTs, showing that the 3D mode is a result of the helicity found in the MTs. Subsequently, the wave length-dependence and the boundary condition effects were also investigated for the 3D transverse vibration of the MTs. In addition, the vibration frequency was found to remain the same in the presence or absence of the bending axis rotation. This infers that the unique vibration mode is merely due to the bending axis rotation of the cross section, but no significant torsion occurs for the MTs

Mechanistic pathway of water adsorption to impact on the nonlinear elasticity of single-crystalline ZnO NWs

Surface modification via adsorbates is significant for property prediction in nanostructures where surface effect is dominant. This is especially vital for zinc oxide (ZnO) nanowires (NWs) which has no native passivation layer. As water is an ubiquitous environmental factor and its aggregation on ZnO surface is favoured, molecular statics (MS) simulations are used to study the deformation of ZnO with surface water adsorption in the finite strain regime (up to 0.1). Three types of water covered surface structures are considered to examine their effects on the size-dependence of linear () and nonlinear () elastic moduli. The pathway of adsorption to impact NWs is identified by revealing the radial distribution of , and residual stress for the NWs. The physical origins of the water adsorption effects are further discussed in terms of the layer-wise equilibrium structure and potential energy variation