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Based on AIREBO (Adaptive Intermolecular Reactive Empirical Bond Order) potential, molecular dynamics simulations (MDs) are performed to study the mechanical behavior of AB- and AA-stacked bi-layer graphene films (BGFs) under tension. Stress–strain relationship is established and deformation mechanism is investigated via morphology analysis. It is found that AA-stacked BGFs show wavy folds, i.e. the structural instability, and the local structure of AB-stacked BGFs transforms into AA-stacked ones during free relaxation. The values of the Young's modulus obtained for AA-stacked zigzag and armchair BGFs are 797.2 GPa and 727.4 GPa, and those of their AB-stacked counterparts are 646.7 GPa and 603.5 GPa, respectively. In comparison with single-layer graphene, low anisotropy is observed for BGFs, especially AB-stacked ones. During the tensile deformation, hexagonal cells at the edge of BGFs are found to transform into pentagonal rings and the number of such defects increases with the rise of tensile strain.

A novel sensing probe, 2-(perfluorophenyl)-1H-imidazo[4,5-b]phenazine (PFIPZ) containing imidazole and phenazine units, has been successfully synthesized and can identify picric acid over other electron-deficient compounds or strong acids.

Molecular dynamics (MD) simulations were performed to stretch the rectangular graphene sheets doped with silicon, nitrogen or boron atoms. Young's modulus, ultimate stress (strain) and energy absorption were measured for the graphene sheets with the doping concentration (DC) ranging from 0 to 5%. The emphasis was placed on the distinct effects of each individual dopant on the fundamental mechanical properties of graphene. The results indicated that incorporating the dopants into graphene led to an almost linear decrease in Young's modulus. Monotonic reductions in ultimate strength, ultimate strain and energy absorption were also observed. Such doping effects were found to be most significant for silicon, less pronounced for boron, and small or negligible for nitrogen. The outputs provide an important guidance for the development and optimization of novel nanoscale devices, and facilitate the development of graphene-based M/NEMS.

Organic π-conjugated small molecules have attracted much attention for developing high performance organic photovoltaics (OPVs) due to their well-defined molecular structure, easily controlled energy levels and absorption, and more accurate simulation-experiment match. A novel small molecule combing a N-heteroacene (acceptor moiety) and benzo[1,2-b:4,5-b′]dithiophene (donor unit) together through a π-conjugated bridge (3,3″-dioctyl-2,2′:5′,2″-terthiophene), has been synthesized and characterized. The blended films of this small molecule with different acceptors have a wide absorption in visible region, which makes it possible for application in OPVs. The as-fabricated devices with PEDOT:PSS as an anode buffer layer show the power conversion efficiency at around 1%. By replacing PEDOT:PSS with MoO3, the power conversion efficiency is almost doubled up to 1.97%. AFM images and XRD patterns are employed to investigate the morphologies of the active layer. Consistent with the J–V curves and EQE spectra, the higher power conversion efficiency probably comes from the good alignment of the HOMO energy level of the small molecule with the work function of anode buffer layer and reduced chemical interactions between active layer and anode buffer layer.

This Letter reports the effect of an internal residual stress and the local geometric nonlinearity on the vibration of piezoelectric nanowires (NWs). A dynamic equation is derived based on Hamilton's principle, which enables one to capture the above-mentioned effects and the influence of all lateral surfaces of a rectangular NW. Vibration frequencies are obtained for the NWs under an electrical voltage and compared with those given by the existing Young–Laplace model where zero internal stress, a linear strain and the effects of top and bottom surfaces of rectangular NWs are considered. It is found that the internal residual stress can extinguish the effect of the surface-induced residual stress and substantially down shift the frequency or qualitatively alter the size-dependence of the frequency. In addition, with a nonlinear strain the piezoelectric effect is found to be able to exert a direct impact on the bending stiffness of piezoelectric NWs.

Molecular dynamics simulations of ZnO nanowires (NWs) [22] show that the structural relaxation (SR) leads to the distribution of Young's modulus ( Y ) different from the assumption of the core–shell ( C–S ) model. It is thus of interest to validate the C–S model in measuring the equivalent Young's modulus and evaluate the effect of SR on the piezoelectric potential of bent ZnO NWs. To this end, a layer-wise model with the actual Y- distribution is developed and compared with the C–S model in the virtual experiments performed via the finite-element simulations. It is found that, in the tensile test, the C–S model can still be used to predict the Young's modulus as it happens to reflect a quadratic polynomial law of the SR-induced excess strain energy density. In addition, the strong effect of SR is achieved for the piezoelectric potential of the bent NWs, where the redistributed piezoelectric property plays a predominant role.

Increasing the length of N-heteroacenes or their analogues is highly desirable because such materials could have great potential applications in organic electronics. In this report, the large p-conjugated N-heteroquinone 6,10,17,21- tetra-((triisopropylsilyl)ethynyl)-5,7,9,11,16,18,20,22-octaaza- nonacene-8,19-dione (OANQ) has been synthesized and characterized. The as-prepared OANQ shows high stability under ambient conditions and has a particularly low LUMO level, which leads to it being a promising candidate for air- stable n-type field-effect transistors (FETs). In fact, FET devices based on OANQ single crystals have been fabricated and an electron mobility of up to 0.2 cm 2 V 1 s 1 under ambient conditions is reported. More importantly, no obvious degra- dation was observed even after one month. Theoretical calculations based on the single crystal are consistent with the measured mobility.

Realizing the control of emission colors of single molecules is very important in the development of full-color emitting materials. Herein, three novel phenazine derivatives (2,3,7,8-tetrakis(decyloxy)phenazine (2a), 2,3-didecyloxy-5,14-diaza-7,12-dioxo-9,10- dicyanopentacene (2b), and 2,3,13,14-tetradecyloxy-5,11,16,22-tetraaza-7,9,18,20-tetraoxo-8,19-dicyanoenneacene (2c)) have been successfully synthesized and fully characterized. Compound 2c can emit blue light in toluene solution (450 nm), green light in the powder/film state (502/562 nm), and red light in the 2c/TFA state (610 nm). The OLED with 2c emits a strong green light at a peak of 536 nm with a maximum luminance of the OLED of about 8600 cd m(-2), which indicates that 2c could be a promising fluorescent dye for OLED applications.

Gallium nitride (GaN) nanowires (NWs) hold technological significance as functional components in emergent nano-piezotronics. However, the examination of their mechanical responses, especially the mechanistic understanding of behavior beyond elasticity (at failure) remains limited due to the constraints of in situ experimentation. We therefore performed simulations of the molecular dynamics (MD) of the mechanical behavior of [Formula: see text]-oriented GaN NWs subjected to tension or compression loading until failure. The mechanical properties and critical deformation processes are characterized in relation to NW sizes and loading conditions. Detailed examinations revealed that the failure mechanisms are size-dependent and controlled by the dislocation mobility on shuffle-set pyramidal planes. The size dependence of the elastic behavior is also examined in terms of the surface structure determined modification of Young's modulus. In addition, a comparison with c-axis NWs is made to show how size-effect trends vary with the growth orientation of NWs.

In cells, the protein cross-linkers lead to a distinct buckling behavior of microtubules (MTs) different from the buckling of individual MTs. This paper thus aims to examine this issue via the molecular structural mechanics (MSM) simulations. The transition of buckling responses was captured as the two-dimensional-linkers were replaced by the three-dimensional (3D) ones. Then, the effects of the radial orientation and the axial density of the 3D-linkers were examined, showing that more uniform distribution of the radial orientation leads to the higher critical load with 3D buckling modes, while the inhomogeneity of the axial density results in the localized buckling patterns. The results demonstrated the important role of the cross-linker in regulating MT stiffness, revealed the physics of the experimentally observed localized buckling and these results will pave the way to a new multi-component mechanics model for whole cells.

Piezoelectric nanowires (NWs) or nanotubes (NTs) are a vital component in nano-electromechanical and piezo-electronic device development. With various cross-sectional geometries achievable, the piezoelectric property-cross sectional shape relation is of fundamental interest. As existing studies (primarily based on first-principles calculations) are limited to ultrathin NWs or analysis based on continuum theories, the present work employs molecular statics (MS) simulation, which enables the examination of NWs/NTs up to cross-sectional size of 20.6 nm and elucidation of the underlying mechanisms at the atomic level. Analyses are carried out for NWs/NTs with experimentally observed geometry by comparing their size-dependence of effective piezoelectric constant and the radial distribution of the average dipole moment change with strain. The fraction of strain-sensitive dipoles, initial volume contraction and surface piezoelectricity were shown to control the shape effect on the piezoelectricity of ZnO nanostructures.

A novel larger heteroacene, 2,3,15,16-tetradecyloxy-5,8,10,13,18,21,23,26-octaaza-7,11,20,24-tetraoxohendecacene (8N8O) with two different types of heteroatoms (O and N) and eleven linearly fused rings, has been successfully synthesized and can identify iodide over other anions.

One-dimensional (1D) organic semiconductor micro/nano-structures (e.g. wires and tubes) have received increasing attention because these highly-ordered structures possess intriguing optical and electronic properties. Here, we reported a novel and easily-processed method to fabricate a large amount of ultralong polymer/small molecule hybrid microstructures based on classical donor poly(3-hexyl)thiophene (P3HT) and acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ). This simple solution-process via evaporating mixed solutions of P3HT/TCNQ with different ratios can generate the desired 1D microstructure with lengths of up to several centimeters. The performance of field-effect transistors based on these as-fabricated microstructures indicated that the charge-transport properties can be controlled by simply adjusting the mixture ratio, resulting in p-type, ambipolar or barely non-charge transport features. Our approach would provide a new tool to understand the growth mechanism and rational control of the ratios of appropriate materials, which is instructive to enhance the performance of organic semiconductor devices.

Organic resistance memory has attracted a lot of attention due to its high scalability, flexibility, easy processing, low fabrication cost, etc. Organic small molecules, which possess well-defined structures and more accurate experiment-simulation matching, have been widely explored as active materials for application in organic resistance memory. In addition, inorganic–organic hybrid polymers are expected to have charming resistive switching properties because they can potentially combine the advantages of both inorganic materials and organic polymers. This review presents the recent progress of organic resistance memory based on several families of organic small molecules and some typical inorganic–organic hybrid polymers, and discussion of their structure–property relationships.

Eco-friendly solvents are very important in the green fabrication of organic electronic devices. However, their use in the preparation of organic nonvolatile memories (ONVMs) is rare. In this article, three water-soluble donor–acceptor conjugated polymers (WSCPs) have been synthesized, which can be used as switching layers to prepare ONVM devices with water as a solvent. The as-fabricated memory devices show large ON/OFF ratios, good endurance and long retention. Our success could provide a green way to fabricate high-performance ONVMs.

A novel D–A conjugated polymer (PIBT-BDT) with 7-perfluorophenyl-6H-[1,2,5]thiadiazole[3,4-g]benzoimidazole is synthesized by the Stille coupling reaction. A memory device with PIBT-BDT as the active layer shows a large on/off ratio (>105), good endurance (>100 cycles), and long retention (>104 s). Through simulating the I–V curves and analysing energy barriers in the device structure, we suggest that the memory effect of Au/PIBT-BDT/ITO originates from the charge transfer between the strong acceptor (IBT) units and the donor BDT units.

In this paper, we focused on how the film morphology changes can affect the memory performance based on phenazine derivatives because the performance of many devices is strongly dependent on the morphology of organic molecules in the as-prepared films. To address this point, two phenazine derivatives, 7,8-bis(decyloxy)-3-(2-hydroxy-4,5-dinitrophenoxy)phenazin-2-ol (2OHPz) and 7,8-bis(decyloxy)-3-(2-(decyloxy)-4,5-dinitrophenoxy)phenazin-2-ol (1OHPz), have been successfully synthesized and characterized. These two compounds have the same electron-withdrawing groups (nitro and pyrazine) and molecular backbone, but different terminal substituted groups, which would be very helpful for us to understand how substituted groups affect the morphology and device performance. In fact, the sandwich-structured memory devices based on ITO/2OHPz/Al exhibited excellent ternary memory behavior with high ON2/ON1/OFF current ratios of 108.8/103/1 at switching threshold voltages of −1.80 V/−3.62 V while the memory devices based on ITO/1OHPz/Al displayed binary memory behavior with ON/OFF current ratios of 107.5/1 at a switching threshold voltage of −3.0 V. The different memory behaviors are attributed to the different molecular packing in the two phenazine derivatives, which is confirmed by AFM, XRD and UV-vis absorption. The AFM height image of the 2OHPz film thermally evaporated onto the ITO surface indicates the formation of self-organized fibril structures, which is in sharp contrast to that of the 1OHPz film. This variation suggests different degrees of aggregation in these films, which is also in accordance with the XRD and UV-vis absorption results. There is one diffraction peak at 2θ 16.11° for the film of 2OHPz, indicating the formation of a more ordered structure in the thin film. In contrast, there is no obvious diffraction peak in the film of 1OHPz. Moreover, the UV-vis absorption wavelength of the thin film of 2OHPz is blue-shifted by ∼10 nm more than that of 1OHPz film compared to those in dichloromethane.

Methylthionation on benzo[1,2-b:4,5-b′]dithiophene (BDT) was examined as a promising molecular functionalization strategy to tune the packing structure and molecular orientation on the substrates. β-Methylthionated BDT with a rubrene-like “pitched” π-stacking showed higher mobility than its α-counterpart with a herringbone packing in single-crystal organic field-effect transistors (SC-OFETs).

d-xylose, the main building block of plant biomass, is a pentose sugar that can be used by bacteria as a carbon source for bio-based fuel and chemical production through fermentation. In bacteria, the first step for d-xylose metabolism is signal perception at the membrane. We previously identified a three-component system in Firmicutes bacteria comprising a membrane-associated sensor protein (XylFII), a transmembrane histidine kinase (LytS) for periplasmic d-xylose sensing, and a cytoplasmic response regulator (YesN) that activates the transcription of the target ABC transporter xylFGH genes to promote the uptake of d-xylose. The molecular mechanism underlying signal perception and integration of these processes remains elusive, however. Here we purified the N-terminal periplasmic domain of LytS (LytSN) in a complex with XylFII and determined the conformational structures of the complex in its d-xylose–free and d-xylose–bound forms. LytSN contains a four-helix bundle, and XylFII contains two Rossmann fold-like globular domains with a xylose-binding cleft between them. In the absence of d-xylose, LytSN and XylFII formed a heterodimer. Specific binding of d-xylose to the cleft of XylFII induced a large conformational change that closed the cleft and brought the globular domains closer together. This conformational change led to the formation of an active XylFII-LytSN heterotetramer. Mutations at the d-xylose binding site and the heterotetramer interface diminished heterotetramer formation and impaired the d-xylose–sensing function of XylFII-LytS. Based on these data, we propose a working model of XylFII-LytS that provides a molecular basis for d-xylose utilization and metabolic modification in bacteria.

In plants, geranylgeranyl diphosphate (GGPP) is produced by plastidic GGPP synthase (GGPPS) and serves as a precursor for vital metabolic branches, including chlorophyll, carotenoid, and gibberellin biosynthesis. However, molecular mechanisms regulating GGPP allocation among these biosynthetic pathways localized in the same subcellular compartment are largely unknown. We found that rice contains only one functionally active GGPPS, OsGGPPS1, in chloroplasts. A functionally active homodimeric enzyme composed of two OsGGPPS1 subunits is located in the stroma. In thylakoid membranes, however, the GGPPS activity resides in a heterodimeric enzyme composed of one OsGGPPS1 subunit and GGPPS recruiting protein (OsGRP). OsGRP is structurally most similar to members of the geranyl diphosphate synthase small subunit type II subfamily. In contrast to members of this subfamily, OsGRP enhances OsGGPPS1 catalytic efficiency and specificity of GGPP production on interaction with OsGGPPS1. Structural biology and protein interaction analyses demonstrate that affinity between OsGRP and OsGGPPS1 is stronger than between two OsGGPPS1 molecules in homodimers. OsGRP determines OsGGPPS1 suborganellar localization and directs it to a large protein complex in thylakoid membranes, consisting of geranylgeranyl reductase (OsGGR), light-harvesting-like protein 3 (OsLIL3), protochlorophyllide oxidoreductase (OsPORB), and chlorophyll synthase (OsCHLG). Taken together, genetic and biochemical analyses suggest OsGRP functions in recruiting OsGGPPS1 from the stroma toward thylakoid membranes, thus providing a mechanism to control GGPP flux toward chlorophyll biosynthesis.

In this paper, with the Hausdorff measure, the Hausdorff integral on fractal sets with one or lower dimension is firstly introduced via measure theory. Then the definition of the integral on fractal sets in [Formula: see text] is given. With the variable substitution theorem in the Riemann integral generalized to the integral on fractal sets, the integral on fractal manifolds is defined. As a result, with the generalization of Gauss’ theorem, Stokes’ theorem is generalized to the integral on fractal manifolds in [Formula: see text].

We report on mechanical properties of blue phosphorus nanotubes (BluePNTs) from systematic molecular dynamics simulations, adopting a Stillinger-Weber potential with parameters determined by fitting to energetic and structural data from first-principles calculations. Our results corroborate the previously reported bending poison effect and size-dependent buckling behaviors. Under axial compression, current simulations predict a shell-to-column buckling mode transition for BluePNTs with increasing aspect ratios; further compression of BluePNTs with large aspect ratios results in a column-to-shell buckling mode transition. Associated critical buckling strains can be described by the continuum mechanics theory. We also simulated buckling behavior of black phosphorus nanotubes (BlackPNTs) and found that the buckling modes of BluePNTs exhibit much less chirality dependence compared to BlackPNTs, stemming from subtle structural differences between these two closely related yet distinct systems. The present results offer insights into key structural and mechanical properties of BluePNTs for fundamental understanding and potential applications of this relatively new member of the large and diverse nanotube family of materials.

A new tetraazatetracene derivative, 2,3-[4,4'-bis(N,N-diphenylamino)benzyl]-5,12-bis[(triisopropylsilyl)ethynyl]-1,4,6,11-tetraazatetracene (TPAs-BTTT), displays rewritable multilevel memory behavior, which is probably induced by multielectron intramolecular charge transfer (CT).

The friction coefficient and wear resistance of non-smooth surface with different conditions are studied in this work. First, the effects of groove spacing on the friction behavior and wear resistance of the non-smooth surface are investigated. Second, the effects of massive laser shock peening (LSP) impact on the dry sliding wear performance of the non-smooth surface manufactured by laser surface texture (LST) are evaluated. In addition, the worn surfaces and typical microstructure in the top surface layer of all samples were characterized by field emission scanning electron microscope (SEM) with an EDS elemental analysis and transmission electron microscopy (TEM). The influence process of groove spacing and LSP on the friction behavior and wear resistance of T9 tool steel are also analyzed and discussed.

Although Li-oxygen batteries offer extremely high theoretical specific energy, their practical application still faces critical challenges. One of the main obstacles is the high charge overpotential caused by sluggish kinetics of charge transfer that is closely related to the morphology of discharge products and their distribution on the cathode. Here, a series of noble metal nanoparticles (Pd, Pt, Ru and Au) are encapsulated inside end-opened carbon nanotubes (CNTs) by wet impregnation followed by thermal annealing. The resultant cathode materials exhibit a dramatic reduction of charge overpotentials compared to their counterparts with nanoparticles supported on CNT surface. Notably, the charge overpotential can be as low as 0.3 V when CNT-encapsulated Pd nanoparticles are used on the cathode. The cathode also shows good stability during discharge–charge cycling. Density functional theory (DFT) calculations reveal that encapsulation of “guest” noble metal nanoparticles in “host” CNTs is able to strengthen the electron density on CNT surfaces, and to avoid the regional enrichment of electron density caused by the direct exposure of nanoparticles on CNT surface. These unique properties ensure the uniform coverage of Li2O2 nanocrystals on CNT surfaces instead of localized distribution of Li2O2 aggregation, thus providing efficient charge transfer for the decomposition of Li2O2.

The grain boundaries (GBs) in polycrystalline graphene (PG) lead to distinctive mechanical and electronic properties relative to their single-crystalline counterparts. In particular, local buckling occurs in the presence of GBs, resulting in arched structures promising for high frequency nanoresonators with raised quality (Q) factor. In this paper such arched PG structures were studied by using software Avogadro and their fundamental vibrations were simulated based on a molecular structure model. The frequency and Q factor of the PG nanoresonators were found to be largely increased due to the GB-induced buckling. The major factors controlling such GB effects were also captured, including the inflection angle of the arched PG, the crystal orientation of its GB and the constraints on its boundaries. The study suggests that the presence of GB may lead to a novel strategy to enhance the structure stiffness of graphene for their potential applications in high performance nanoresonators and nanosensors.

The OmpR/PhoB subfamily protein GlnR of actinomycetes is an orphan response regulator that globally coordinates the expression of genes related to nitrogen metabolism. Biochemical and genetic analyses reveal that the functional GlnR from Amycolatopsis mediterranei is unphosphorylated at the potential phosphorylation Asp(50) residue in the N-terminal receiver domain. The crystal structure of this receiver domain demonstrates that it forms a homodimer through the α4-β5-α5 dimer interface highly similar to the phosphorylated typical response regulator, whereas the so-called "phosphorylation pocket" is not conserved, with its space being occupied by an Arg(52) from the β3-α3 loop. Both in vitro and in vivo experiments confirm that GlnR forms a functional homodimer via its receiver domain and suggest that the charge interactions of Asp(50) with the highly conserved Arg(52) and Thr(9) in the receiver domain may be crucial in maintaining the proper conformation for homodimerization, as also supported by molecular dynamics simulations of the wild type GlnR versus the deficient mutant GlnR(D50A). This model is backed by the distinct phenotypes of the total deficient GlnR(R52A/T9A) double mutant versus the single mutants of GlnR (i.e. D50N, D50E, R52A and T9A), which have only minor effects upon both dimerization and physiological function of GlnR in vivo, albeit their DNA binding ability is weakened compared with that of the wild type. By integrating the supportive data of GlnRs from the model Streptomyces coelicolor and the pathogenic Mycobacterium tuberculosis, we conclude that the actinomycete GlnR is atypical with respect to its unphosphorylated conserved Asp residue being involved in the critical Arg/Asp/Thr charge interactions, which is essential for maintaining the biologically active homodimer conformation.

Continuous-variable position-momentum entanglement (or Einstein-Podolsky-Rosen entanglement) of two particles has played important roles in the fundamental study of quantum physics as well as in the progress of quantum information. In this paper, we propose a scheme to generate Einstein-Podolsky-Rosen (EPR) position-momentum entangled photon pairs efficiently via spontaneous four-wave mixing (SFWM) process in a hot rubidium gas cell. The EPR entanglement between the photon pair is measured and characterized by using the ghost interference and the ghost imaging method. Due to the simplicity of the experimental setup and the high photon pair generation rate, our EPR entangled photon source may has potential applications in quantum imaging, hyperentanglement preparation and atomic ensemble based quantum information processing and quantum communication protocols.

Cloud computing takes the network technology, virtualization technology, and distributed computing technology as the foundation. The business model of cloud computing is based on its own need and has formed a new application mode with the characteristics of dynamic extension, resource sharing, and others. The cloud computing environment refers to the integration of terminal devices, such as computers distributed on the Internet, to realize hardware and software resources by means of some kind of network calculation. The basic components include the application layer, platform layer, resource layer, user access and management, and technology and take all kinds of cloud computing services as the core. Under such an environment, the user’s data and resources in cloud computing are wholly dependent on the unreliable network communication and partially trusted cloud storage server, which makes the users question the safety of the cloud computing environment, and resulting the arrested development of cloud computing. In this paper, network security risks and current common computer network attack method in cloud computing environment were discussed in detail and the network security protection technologies were proposed to improve the security of network of cloud computing environment.

We theoretically study the angular rotation displacement based on the hybrid interferometers, which contain a beam splitter (BS) and an optical parameter amplication (OPA) for beam splitting and recombination. Two schemes with different orders of an OPA and a BS are discussed and both of them can realize the super resolving and sensitive angular rotation displacement. The sensitivity of angular rotation displacement can surpass the shot noise limit 12l N with the orbital angular momentum input beams. The squeezing strength of an OPA and the reflectivity of the BS play a decisive role on the resolutions and sensitivities while the losses play a negative effect on the sensitivity.

Helical poly(isocyanide)s are an important class of synthetic polymers possessing a static helical structure. Since their initial discovery, numerous examples of these helices have been fabricated. In this contribution, the synthesis of a chiral, azobenzene (azo)-containing isocyanide monomer is reported. Upon polymerization with nickel(II) catalysts, a well-defined circular dichroism (CD) trace is obtained, corresponding to the formation of a right-handed polymeric helix. The helical polymer, dissolved in chloroform and irradiated with UV light (365 nm), undergoes a cis to trans isomerization of the azobenzene side-chains. After the isomerization, a change in conformation of the helix occurs, as evidenced by CD spectroscopy. When the solution is irradiated with LED light, the polymer returns to a right-handed helical conformation. To open up the possibility for chain-end post-polymerization modification of this light-responsive system, an alkyne-functionalized nickel(II) catalyst is also used in the polymerization of the azobenzene monomer, resulting in a stimuli-responsive, terminal-alkyne-containing helical poly(isocyanide).

This letter aims to study the electromechanical vibration of microtubules submerged in cytosol. The microtubule-cytosol interface is established in molecular dynamics simulations, and the electrically excited vibrations of microtubules in cytosol are studied based on a molecular mechanics model. The simulations show that the solid-liquid interface with a nanoscale gap significantly reduces the viscous damping of cytosol on microtubule vibration. Specifically, as far as the radial breathing modes are concerned, cytosol behaves nearly as a rigid body and thus has a very small damping effect on the radial breathing mode of microtubules. This distinctive feature of the radial breathing modes arises from its extremely small amplitude (

Gold nanoparticle (AuNP)-polymer composite has attracted considerable attention due to its high stretchability, metal-like electrical conductivity and substantial piezoresistivity. In the nanocomposite, the effect of the van der Waals (vdW) interaction increases greatly between AuNPs, which may significantly change its overall mechanical and electrical properties. In examining this issue, the nanocomposite with randomly distributed AuNPs is constructed by Monte Carlo method, tensile tests on the material are then performed via molecular dynamics simulations and finally, its piezo-resistivity is studied based on an effective resistor model. The effects of AuNP interaction are examined for the mechanics, dynamics and piezoresistivity of the nanocomposite by comparing the results obtained in the presence and absence of the vdW interaction. It is found that the AuNP attraction tends to hold the AuNPs together, leading to enhanced Young’s modulus, yield and fracture stress even at the low volume fraction 5% to 10% of AuNPs. The piezoresistive effect of the composite is also improved as the AuNP attraction substantially affects AuNP dynamics in large deformation. It is expected that similar effects of NP vdW interaction can also be obtained for the nanocomposites based on copper or silver NPs embedded in polymer.

This study demonstrates variations in the vascular anatomy of the parapharyngeal space (PPS) as seen from the transoral approach compared with the transcervical approach. The PPS was dissected in injected cadaveric specimens. Anatomical measurements, including those of branches of the external and internal carotid arteries (ECA and ICA) and the styloglossus and stylopharyngeus muscles, were recorded and analyzed. In 67% (8/12) of cases, the ascending palatine artery (APA) originated from the facial artery and crossed the styloglossus muscle. The diameter of the APA at its origin was 1.4 ± 0.3mm. In 75% (9/12) of cases, the ascending pharyngeal artery (aPA) arose from the medial surface of the ECA near its origin. In 58% (7/12) of cases, the aPA ascended vertically between the ICA and the lateral pharynx to the skull base, along the longus capitus muscle. The aPA crossed the styloglossus muscle 12.6 ± 3.9mm from the insertion into the tongue. In 92% (11/12) of cases, the ECA and ICA were separated by the styloid diaphragm and pharyngeal venous plexus. In 8% (1/12), the ECA bulged into the parapharyngeal fat between the styloglossus and stylopharyngeus muscles adjacent to the pharyngeal constrictors. Knowledge of the precise anatomy of the PPS is important for transoral robotic surgery (TORS). Control of the vessels that supply and traverse the PPS can help the TORS surgeon avoid those critical structures and reduce surgical morbidity and potential hemorrhage. Clin. Anat. 27:1016–1022, 2014. © 2014 Wiley Periodicals, Inc.

N-substituted heteroacenes have been widely used as electroactive layers in organic electronic devices, and only a few of them have been investigated in organic resistive memory devices. Here, a novel N-substituted heteroacene 2-(4′-(diphenylamino)phenyl)-4,11-bis((triisopropylsilyl)ethynyl)-1H-imidazo[4,5-b]phenazine (DBIP) has been designed, synthesized, and characterized. Sandwich-structure memory devices based on DBIP have been fabricated and the devices show non-volatile and stable memory character with good endurance performance.

Although organic multilevel resistance memories have attracted much attention for potential realization of the exponentially-increasing density of data storage, the ambiguous structure–property relationship and the unclear switching mechanism impeded further development of multilevel resistance memory devices. Therefore, it is very urgent to ingeniously design multilevel memory materials with a certain switching mechanism. In this contribution, we have employed a multi-redox (multiple barriers) polyoxometalate-based inorganic–organic hybrid polymer (whose effective carriers are electrically controllable) to realize a ternary resistance switching memory (multilevel memories). We do believe that the as-designed inorganic–organic polymer can integrate the multi-redox states of the POM and the processability of flexible polymers together. The as-fabricated multilevel memory devices exhibit rewriteable switching properties among three redox states by applying different RESET voltages, good endurance with distinct operation windows, and long retention. Our results could provide a new strategy to design controllable multilevel resistance memories with excellent performance. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

To achieve ultra-high density memory devices with a capacity of 3n or larger, a novel larger and stable oxacalix[4]arene, 4N4OPz, is reported. 4N4OPz exhibited excellent ternary memory behavior with high ON2/ON1/OFF current ratios of 108.7/104.2/1, low switching threshold voltage of −1.80 V/−2.87 V, and good stability for these three states.

The purpose of this paper is to discuss agent risk taking and efforts in the context of multiple heterogeneous references. We focus on two key references in terms of performance target and aspiration income. And we also introduce them into the principal-agent model. By the method of numerical simulation, our results show that performance target and the gap of psychological reference income have complex interaction influences on agent risk taking and efforts. In addition, profit-sharing coefficient plays moderating role in these complex relationships. Our results also provide good evidence and supplement to Pepper and Gore’s proposition.

Piezoelectric nanofilms (PNFs) are often subject to compression in their applications. Bulking thus occurs for those with a thin thickness. In this paper we have conducted a comprehensive study of the bucking behaviors of PNFs which are treated as sandwich-plates to account for the effect of the surface elasticity and piezoelectricity. The results from the analytic formulae show that the surface and piezoelectric effects influence not only the critical buckling load but also the associated modes. Specifically the two effects depend strongly on the nature of the residual surface stress and the direction of the voltage applied on PNFs.

The piezoelectric constant e33 is calculated using molecular dynamic simulations for square gallium nitride (GaN) nanowires (NWs). Its magnitude is found to decrease significantly with increasing cross-section and temperature. An attempt is made to understand the physics behind the size- and temperature dependence of e33. Specifically, a constant surface piezoelectric coefficient e 33 s = 0.52 × 10 - 9 C/m is achieved for square GaN NWs independent of the geometric size of their cross-sections.

This paper aims to identify a well-defined effective diameter of Nanowires (NWs) in evaluating their Young's modulus and to investigate the physical mechanisms behind the achieved surface elasticity. To this end, GaN NWs were considered for which a layer-wise model was developed and the tensile tests were performed based on molecular statics simulations (MSS). It was shown that two previously defined effective diameters result in opposing effects of the surface elasticity and reversed size-dependence of the overall Young's modulus. Subsequently, a proper effective diameter was decided for the NWs, which enables one to correctly interpret atomistic simulations in terms of continuum mechanics concepts. In particular, clear evidence was attained showing that the bond loss on the NW surface results in around 43% surface softening relative to the NW interior and bulk material.

Length-dependent flexural rigidity (FR) is observed experimentally for microtubules (MTs) subjected to certain boundary conditions. To shed some light on this unique feature, we have studied the FR of MTs with different boundary conditions. A molecular structural mechanics method is employed to accurately describe the real boundary conditions imposed on MTs in experiments. Some of component protofilaments of MTs are blocked at the ends while others are free. In addition, linked kinesin is treated as an elastic body rather than a rigid body. Our simulations show that for relatively long MTs having a length comparable to those measured in experiments the length-dependent rigidity is detected only for those with fixed–free and fixed–fixed ends, which is consistent with the experimental observation. To capture the physics leading to the above phenomenon, Timoshenko beam model is adopted accounting for both transverse shear effect (TSE) and imperfect boundary effect (IBE). Comparison between TSE and IBE indicates that the boundary condition-selective length-dependence achieved for the FR of relatively long MTs is primarily a result of the influence of IBE rather than TSE.

Vibration responses were investigated for a viscoelastic Single-walled carbon nanotube (visco-SWCNT) resting on a viscoelastic foundation. Based on the nonlocal Euler-Bernoulli beam model, velocity-dependent external damping and Kelvin viscoelastic foundation model, the governing equations were derived. The Transfer function method (TFM) was then used to compute the natural frequencies for general boundary conditions and foundations. In particular, the exact analytical expressions of both complex natural frequencies and critical viscoelastic parameters were obtained for the Kelvin-Voigt visco-SWCNTs with full foundations and certain boundary conditions, and several physically intuitive special cases were discussed. Substantial nonlocal effects, the influence of geometric and physical parameters of the SWCNT and the viscoelastic foundation were observed for the natural frequencies of the supported SWCNTs. The study demonstrates the efficiency and robustness of the developed model for the vibration of the visco-SWCNT-viscoelastic foundation coupling system.

In this paper a beat phenomenon is reported in molecular dynamics simulations for vibrating boron nitride-carbon nanotubes (BN-CNTs) and then analysed based on a continuum mechanics theory. It was shown that the distinctive dynamic behaviour is a result of the superposition of two orthogonal transverse vibrations whose frequencies are slightly different due to the oval cross-section of the hybrid nanotubes. In particular, the interaction between the two vibrations in BN-CNTs will facilitate to resolve the fundamental issue in developing mass nanosensors for atomic-scale mass measuring. To reach this goal, efforts should be made to maintain high quality factor of the BN-CNT oscillating system by minimising the damping effect of its surrounding environment. This issue turns out to be essential for the beat mode-based nanosensors as large damping will reduce the hybrid nanotubes to conventional resonators with only one transverse vibration same as that reported for homogeneous nanotubes.

The importance of macrocyclic shape-persistency in novel host–guest systems for the highly efficient template-directed synthesis of rotaxanes has been revealed., Examples of using two-dimensional shape-persistent macrocycles, i.e. those having noncollapsible and geometrically well-defined skeletons, for constructing mechanically interlocked molecules are scarce, which contrasts the many applications of these macrocycles in molecular recognition and functional self-assembly. Herein, we report the crucial role played by macrocyclic shape-persistency in enhancing multipoint recognition for the highly efficient template-directed synthesis of rotaxanes. Cyclo[6]aramides, with a near-planar conformation, are found to act as powerful hosts that bind bipyridinium salts with high affinities. This unique recognition module, composed of two macrocyclic molecules with one bipyridinium ion thread through the cavity, is observed both in the solid state and in solution, with unusually high binding constants ranging from ∼1013 M–2 to ∼1015 M–2 in acetone. The high efficacy of this recognition motif is embodied by the formation of compact [3]rotaxanes in excellent yields based on either a “click-capping” (91%) or “facile one-pot” (85%) approach, underscoring the great advantage of using H-bonded aromatic amide macrocycles for the highly efficient template-directed synthesis of mechanically interlocked structures. Furthermore, three cyclo[6]aramides bearing different peripheral chains 1–3 demonstrate high specificity in the synthesis of a [3]rotaxane from 1 and 2, and a [2]rotaxane from 3 via a “facile one-pot” approach, in each case as the only isolated product. Analysis of the crystal structure of the [3]rotaxane reveals a highly compact binding mode that would be difficult to access using other macrocycles with a flexible backbone. Leveraging this unique recognition motif, resulting from the shape-persistency of these oligoamide macrocycles, in the template-directed synthesis of compact rotaxanes may open up new opportunities for the development of higher order interlocked molecules and artificial molecular machines.

Rifampin (RIF) is a first-line drug used for the treatment of tuberculosis and other bacterial infections. Various RIF resistance mechanisms have been reported, and recently an RIF-inactivation enzyme, RIF phosphotransferase (RPH), was reported to phosphorylate RIF at its C21 hydroxyl at the cost of ATP. However, the underlying molecular mechanism remained unknown. Here, we solve the structures of RPH from Listeria monocytogenes (LmRPH) in different conformations. LmRPH comprises three domains: an ATP-binding domain (AD), an RIF-binding domain (RD), and a catalytic His-containing domain (HD). Structural analyses reveal that the C-terminal HD can swing between the AD and RD, like a toggle switch, to transfer phosphate. In addition to its catalytic role, the HD can bind to the AD and induce conformational changes that stabilize ATP binding, and the binding of the HD to the RD is required for the formation of the RIF-binding pocket. A line of hydrophobic residues forms the RIF-binding pocket and interacts with the 1-amino, 2-naphthol, 4-sulfonic acid and naphthol moieties of RIF. The R group of RIF points toward the outside of the pocket, explaining the low substrate selectivity of RPH. Four residues near the C21 hydroxyl of RIF, His825, Arg666, Lys670, and Gln337, were found to play essential roles in the phosphorylation of RIF; among these the His825 residue may function as the phosphate acceptor and donor. Our study reveals the molecular mechanism of RIF phosphorylation catalyzed by RPH and will guide the development of a new generation of rifamycins.

Two metallothionein genes (HsMT1 and HsMT2) were first identified and described from Hyriopsis schlegelii. The open reading frame of HsMT1 and HsMT2 were 216 and 222 bp, encoding a protein of 71 and 73 amino acid residues. The deduced amino acid sequences showed they contained parts of typical MT characteristics, apart from HsMT2 lacked Cys–Cys motifs. The phylogenetic tree showed HsMT1 shared a high similarity with that of other molluscs, but HsMT2 was split into a distinct group separated from known molluscan MTs. HsMT1 exhibited constitutive expression in all examined tissues and the highest expression occurred in hepatopancreas, however, nearly all HsMT2 was just detected in gonad. After Cd exposure, their mRNA levels presented similar expression patterns. The transgenic bacteria of HsMT1 showed higher tolerance than HsMT2 in Cd environment. It was implied that HsMT1 and HsMT2 were involved in metal response but HsMT2 might have other physiological functions.