Formation Of Linear Structures Research Articles

Evolution of 2D MoO3 Layer Structures on Pd(100): Interplay of Interfacial Interactions and Polarity

Abstract We explore the structural evolution of two-dimensional (2D) MoO3 films beyond the monolayer, which have been prepared by physical vapor deposition and post-oxidation onto a Pd(100) surface, and characterized by the tools of surface science and density functional theory (DFT) calculations. According to DFT, the most stable oxide layers are stoichiometric, and derive their energetic stability from the low cost of creating 2D freestanding layers from the orthorhombic bulk phase, good matching to Pd, and the particularly strong adhesion to the substrate. The observed 2D MoO3 layers are distinguished by well-ordered linear defects, such as domain boundaries in the monolayer, and misfit dislocations in the bilayer. Applying reactive oxidation preparation conditions results in the formation of ordered arrays of nanostructures, nanowires and nanoclusters, in the MoO3 bilayer. The formation of such linear structures is accounted for in the DFT by models of missing row defects of various orientations and stoichiometries. Their relative stability is rationalized in terms of the number of broken Mo-O bonds, the polar character of the nanostructure edges and the interaction strength with the Pd substrate. Comparison with similar WO3 layers on Pd(100) is provided.

Natural formation of linear defect structures in MoS2

Near surface defects can significantly impact the quality of metallic interconnects and other interfaces necessary to create device structures incorporating two-dimensional materials. Furthermore, the impact of such defects can strongly depend on their organization. In this study, we present scanning tunneling microscopy images and tunneling spectroscopy of point and linear defects near the surface of natural MoS2. The point defects share similar structural and electronic characteristics and occur with comparable frequency as subsurface sulfur vacancies observed previously on natural MoS2. The linear defects observed here occur less frequently than the point defects but share the same depth profile and electronic structure. These data indicate that the linear defects are actually a one-dimensional organization of subsurface sulfur vacancies. Our density functional calculations agree with this assessment in that, for sufficient local defect concentrations, it is energetically more favorable for the defects to be organized in a linear fashion rather than as clusters or even isolated single point defects. Given these measurements were taken from naturally formed MoS2, this organization likely occurs during crystal formation. Considering the impact of one-dimensional organization on the local properties of layered materials, and the potential for them to be introduced purposefully during crystal formation, research into the formation mechanism and properties of these defects could enable new paths for defect engineering in MoS2-based systems.

Physical multiple shock solutions to the integrability of linear structures of Burgers hierarchy

This work is concerned with the formation of linear structures of components of Burgers' hierarchy. The integrability of some linear systems of two or more parts is investigated. A linear arrangement of five elements is studied by using the Painlevé analysis. The simplified Hirota's method provides a trustworthy cure for the proposed linear design of the five components, where multiple kink solutions are formally derived for this constructed system. Our findings can help many researchers interested in fluid mechanics and plasma physics.

Inertial Alfvén waves with polarization force in a dusty plasma

The properties of dust inertial Alfvén waves (DIAWs) in a dusty plasma with the effects of polarization force are investigated. First, the dispersion equation is obtained from the fluid equations by considering the polarization force. Then, the energy balance equation is deduced by applying the Sagdeev pseudopotential method. It is shown that the polarization force affects the characteristics of DIAWs as well as the pseudopotential significantly. In addition, the existence of the polarization force changes the width of DIAWs. The present results may be helpful in further understanding the effect of polarization forces on the formation of linear and nonlinear structures of Alfvén waves in the laboratory plasma, astrophysical dusty plasma systems, planetary ring systems, cometary tails, etc.

Construction of a Helical Structure with a Parallel Alignment of Molecular Dipoles in Crystals by Utilizing a Halogen-3 Synthon and a Bulky Silyl Spacer

The arrangement of dipoles in a molecular crystal is one of the most important factors determining the electronic and photophysical properties in the solid state. However, it remains a significant challenge to design the dipole arrangement in crystals because of the difficulty in predicting the crystal structure. Herein, we report the formation of linear structures with antiparallel dipoles and helical structures with parallel dipoles in crystals by introducing halogen substituents. Polar 2,3-difluorophenylene derivatives 1–3 consist of a bulky triisopropylsilyl moiety on one side as a spacer and a hydrogen (4-H, 1) or halogen substituent (4-Br, 2; 4-I, 3) at the para-position of the silyl group. Single-crystal X-ray diffraction studies revealed that crystals 2 and 3 form triangle “halogen-3 synthon” by halogen bonding among Br or I substituents, resulting in helical structures with parallel alignment of the dipoles, whereas the dipoles are in antiparallel alignment in linear structures to cancel their polarity in crystal 1.

Synthesis of Contorted Polycyclic Conjugated Hydrocarbons via Regioselective Activation of Cyclobutadienoids.

Contorted carbon structures have drawn much attention in the past decade for their rich three-dimensional geometries, enhanced solubility, and tunable electronic properties. We report a modular method to synthesize contorted polycyclic conjugated hydrocarbons containing helical moieties in controlled topologies. This strategy leverages our previously reported streamlined synthesis of π-systems containing four-membered cyclobutadienoids (CBDs), whose catalyzed cycloaddition with alkynes affords helical structures. Interestingly, we observed exclusive nonbay region regioselectivity in the C-C bond activation of CBDs in our system, which is opposite to the scarce previous examples of [N]phenylene activation that led to the formation of linear phenacene structures. The quantitative and regioselective nonbay region alkyne cycloaddition yielded a variety of helical carbon structures with their topologies predetermined by the CBD-containing precursor hydrocarbons. The cycloaddition can be inhibited by methyl substituents exocyclic to the four-membered ring, thus allowing selective activation of only certain desired CBD units while leaving the others intact. Calculation elucidated the basis for the observed regioselectivity. The described method provides a new route to multihelical aromatic hydrocarbons with complex yet defined geometries, facilitating the further exploration of such fascinating carbon structures.

Poly acrylic acid stabilized magnetic nanoemulsions for visual defect detection: Effect of pH on detection sensitivity and colloidal stability

Magnetic field assisted tunable colour contrast in magnetic nanoemulsions is exploited for visual detection of defects in ferromagnetic components. We demonstrate an enhanced defect detection sensitivity by stabilizing oil-in-water magnetic nanoemulsion with poly acrylic acid (PAA) at varying pH. In this detection technique, the variation of magnetic permeability, in the vicinity of the defects, causes magnetic flux leakage, which results in a distinct colour contrast on the magnetic nanoemulsion sensor due to the formation of anisotropic periodic structures, parallel to the external field direction, where the inter-droplet spacing within the linear chains depends on the effective magnetic flux. By exploiting this colour and magnetic flux dependence, severity of the defects is assessed by observing the colour contrast. Our studies indicate that defect detection sensitivity decreases with increasing pH due to globule-to-coil conformational transition of the interfacial PAA molecules. With increasing pH, the PAA network swells due to mobile counter-ions induced osmotic pressure and electrostatic repulsion between the charged monomer units, leading to a solvated coil-like configuration, which is confirmed from the increase in hydrodynamic diameter and zeta potential. The inter-droplet force measurements show an increase in decay length by ~3.5 times, when pH is increased from ~1.5 to ~4.0. The lower decay length at pH ~ 1.5 indicates the formation of linear chain-like structures with smaller inter-droplet spacing near the defect edges, where the magnetic flux leakage is maximum. This results in a fewer number of randomly oriented droplets at the defect centre, thereby enhancing the defect detection sensitivity at lower pH. However, nanoemulsions stabilized at pH > 3 show increased colloidal stability, as compared to pH ~ 1.5. Our studies indicate that nanoemulsions at pH ~ 3.5 exhibit an optimum colloidal stability with good defect detection sensitivity. The obtained results are beneficial for developing high sensitivity, reliable and reusable magnetic nanoemulsion sensors for naked eye visualization of defects in ferromagnetic components.

On Separation of Charges and Formation of Linear Structures in the Nuclei of Dislocations in Metals

In metals, the non-adiabatic mechanism of charge separation into the electron, cation, and vacancy chains is considered. It includes: 1) the photoelectric effect caused by bremsstrahlung caused by the scattering of conduction electrons by impurity ions lying at the ends of these chains and oscillating with the frequency of the local phonon mode; 2) knocking out from the metal cations of the matrix, sufficiently slow (in comparison with the conduction electrons) photoelectrons that pull these cations from the nodes, thereby not violating the electroneutrality condition in the model of a free electron gas as with the static state of the chains and at their motion (slipping, recrawling) in the absence of a thermal field; 3) induced radiation along the line of chains; 4) the formation of linear structures in the spatial lattice of octahedral interstitial sites. The conditions for the formation of quasistable bound states in the dislocation core are considered. A hypothesis is advanced that the latent energy in the dislocation cores contains a component that is of an electromagnetic nature.

433 Pemphigus vulgaris patient disease severity correlates with in vitro assessments of desmosomal function

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease characterized by severe epidermal blistering and mucous membrane erosions. PV is caused by antibodies directed against the desmosomal cadherin desmoglein 3 (Dsg3), and in cases involving the skin, both Dsg3 and Dsg1. PV can be assessed clinically using the Pemphigus Disease Area Index (PDAI) and using an ELISA for Dsg IgG titers in patient sera. In vitro, PV IgG activity can be investigated by incubating normal human keratinocytes with PV patient IgG and monitoring changes in desmosomal protein organization and overall strength of cell-cell adhesion using a dispase-based cell-cell dissociation assay. However, the relationship between clinical PV assessments and in vitro activity of patient IgG have not been reported. In the present study, we compared the relationship between the in vitro pathogenicity of PV IgG from 23 patients to their PDAI score and ELISA titers. Overall, Dsg1 ELISA values showed a stronger correlation with PDAI scores (p<0.01) when compared to Dsg3 ELISA (p<0.02). However, the sum of Dsg3 and Dsg1 ELISA values exhibited a highly significant correlation to PDAI (p<0.0005). In vitro, treatment of keratinocytes with patient IgG resulted in a range of alterations in desmosomal protein organization that included Dsg3 clustering, the formation of linear array-like structures, and endocytosis of Dsg3-PV IgG complexes. Interestingly, the loss of cell-cell adhesion strength as assessed using in vitro dispase cell dissociation assays exhibited a positive correlation with Dsg3 ELISA titers (p<0.005), supporting the validity of the dispase assay as a measure of PV pathogenicity . These findings confirm the association of Dsg ELISA values with PDAI and establish a relationship between Dsg IgG titers in patients and loss of adhesion in cultured keratinocytes.

Interfacial Self-Assembly and Oriented Attachment in the Family of PbX (X = S, Se, Te) Nanocrystals.

The realization of materials with new optoelectronic properties draws much scientific attention toward the field of nanocrystal superstructures. Low-dimensional superstructures created by interfacial assembly and oriented attachment of PbSe nanocrystals are a striking example because theory showed that PbSe sheets with a honeycomb geometry possess non-trivial flat bands and Dirac cones in the valence and conduction bands. Here, we report on the formation of one-dimensional linear and zigzag structures and two-dimensional (2D) square and honeycomb structures for the entire lead chalcogenide family: PbX (X = S, Se, Te). We observe that PbTe, with a lower bulk melting temperature and enthalpy of formation than those of PbSe, shows a higher nanocrystal surface reactivity, such that the surface must be passivated and the reaction conditions moderated to obtain reasonably ordered superstructures. The present findings constitute a step forward in the realization of a larger family of atomically coherent 2D superstructures with variable IV–VI and II–VI compositions and with electronic properties dictated by the nanogeometry.

A Modular System for the Design of Stimuli‐Responsive Multifunctional Nanoparticle Aggregates by Use of Host–Guest Chemistry

A self-assembly approach for the design of multifunctional nanomaterials consisting of different nanoparticles (gold, iron oxide, and lanthanide-doped LiYF4 ) is developed. This modular system takes advantage of the light-responsive supramolecular host-guest chemistry of β-cyclodextrin and arylazopyrazole, which enables the dynamic and reversible self-assembly of particles to spherical nanoparticle aggregates in aqueous solution. Due to the magnetic iron oxide nanoparticles, the aggregates can be manipulated by an external magnetic field leading to the formation of linear structures. As a result of the integration of upconversion nanoparticles, the aggregates are additionally responsive to near-infrared light and can be redispersed by use of the upconversion effect. By varying the nanoparticle and linker concentrations the composition, size, shape, and properties of the multifunctional nanoparticle aggregates can be fine-tuned.

A Density Functional Theory Investigation of Nin , Pdn , and Ptn Clusters (n=1-4) Adsorbed on Buckminsterfullerene.

In this study, we examine the adsorptions of Ni, Pd, and Pt clusters on C60 by using a computational approach. Our calculation results show that the base structure of C60 can host Nin /Pdn /Ptn (n=1-4) clusters with good adsorption stability and the complexes establish either two or no unpaired electrons. The binding energy of Pd and Pt clusters increases as the number of metal atoms increases, implying that the coverage of C60 with Pd or Pt preferentially establishes a large-size metal cluster. A single metal atom favorably occupies the C-C bridge site. For dimer clusters, the three metals of interest share a similar binding fashion, in which two metal atoms establish direct interactions with the C-C bridge sites. For trimer adsorptions, the formation of linear and triangular structures is observed. Both Pt3 and Ni3 preferably constitute isosceles triangles on C60 , whilst Pd3 favorably establishes a linear shape. Finally, for each of the Ni4 and Pd4 adsorption cases, we observed three stable binding configurations: rhombus, tetrahedron, and Y-form. Whereas Ni4 establishes a tetrahedral form, Pd4 attains the most stable form with the Y-shape geometry on C60 . Overall, we observe that the trend of Pd binding to C60 tends to go beyond the fashion of Ni and Pt. In terms of magnetic alignment, the Pdn -C60 systems seem to be non-magnetic in most cases, unlike the Ni and Pt cases, the structures of which possess magnetic moments of 2 μB in their most stable forms.

Composition, structure, origin, and evolution of off-axis linear volcanic structures of the Brazil Basin, South Atlantic

The paper considers the conditions and mechanisms of the formation of linear volcanic structures in the Brazil Basin, South Atlantic. Among these objects, those related to the ascent of deep mantle plumes predominate. It is shown that the ascent of melts from plume sources leads to the formation of (a) hot spot tracks in the form of linear volcanic ridges and (b) active hot lines in the form of submarine mountain chains with trends differing from those of hot spot tracks and with a more variable character of the age distribution of volcanic rocks. Fault tectonics affects the character of plume activity. In addition, plume material from a hot spot area is dragged by a moving plate as a flow or a sublithospheric lens, which leads to the long-term existence of particular independent segments of linear structures and sometimes to late volcanism reactivation within their limits. Decompression melting of the asthenospheric mantle in zones where thin lithosphere undergoes tension causes the formation of passive hot lines. The main mantle source for the considered volcanic rocks was a mixture of DMM and HIMU mantle components, with the latter abruptly dominating. In marginal oceanic regions, the EM1 component is also present (the EM2 component is found more rarely) within fragments of tectonically delaminated continental mantle that was trapped by the oceanic mantle during the breakup of Gondwana.

Impact of cordon‐bleu expression on actin cytoskeleton architecture and dynamics

Cordon‐bleu (COBL) is a multifunctional WASP‐Homology 2 (WH2) domain‐containing protein implicated in a wide variety of cellular functions ranging from dendritic arborization in neurons to the assembly of microvilli on the surface of transporting epithelial cells. In vitro biochemical studies suggest that COBL is capable of nucleating and severing actin filaments, among other activities. How the multiple activities of COBL observed in vitro contribute to its function in cells remains unclear. Here, we used live imaging to evaluate the impact of COBL expression on the actin cytoskeleton in cultured cells. We found that COBL induces the formation of dynamic linear actin structures throughout the cytosol. We also found that stabilizing these dynamic structures with the parallel actin‐bundling protein espin slows down their turnover and enables the robust formation of self‐supported protrusions on the dorsal cell surface. Super‐resolution imaging revealed a global remodeling of the actin cytoskeleton in cells expressing these two factors. Taken together, these results provide insight as to how COBL contributes to the assembly of actin‐based structures such as epithelial microvilli. © 2016 Wiley Periodicals, Inc.

Assembly of Branched Colloidal Nanocrystals in Polymer Films Leads to Enhanced Viscous Deformation Resistance.

Progress in the integration of nanocrystals with polymers has enabled the creation of materials for applications ranging from photovoltaics to biosensing. However, controlling the nanocrystal segregation and aggregation in the polymer phase remains a challenging task, especially because nanocrystals tend to form amorphous clusters inside the polymer matrix. Here, we present the ability of octapod-shaped particles to overcome their strong entropy-driven tendency to aggregate disorderly and form instead centipede-like linear arrays that are randomly oriented and fully embedded in polystyrene films upon controlled solvent evaporation. This behavior cannot be entirely described by short-range van der Waals interactions between the octapods in the polymer solution. An important role here is played by the increment of the viscosity of the medium during the evaporation of the solvent, which prevents disaggregation of the chains once they are formed. We show that increasing the octapod loading in the blends does not impact the length of the linear arrays beyond a critical length, while it favors instead chain demixing to form self-segregated regions of parallel interlocked chains. Our experiments evidence that softening of the polymer matrix by ex situ heating of the films induces a tail-to-tail coupling of the preformed chains and leads to the formation of longer linear structures of octapods, up to 2 μm long. The presence of 1D arrays of octapods in free-standing polystyrene films improves the creep response by a remarkable 37%, owing to an octapod pinning effect of the polymer matrix.

Endothelial pattern formation in hybrid constructs of additive manufactured porous rigid scaffolds and cell-laden hydrogels for orthopedic applications

Vascularization of tissue engineering constructs (TECs) in vitro is of critical importance for ensuring effective and satisfactory clinical outcomes upon implantation of TECs. Biomechanical properties of TECs have remarkable influence on the in vitro vascularization of TECs. This work utilized in vitro experiments and finite element analysis to investigate endothelial patterns in hybrid constructs of soft collagen gels and rigid macroporous poly(ε-caprolactone)-β-tricalcium phosphate (PCL-β-TCP) scaffold seeded/embedded with human umbilical vein endothelial cells (HUVECs) for bone tissue engineering applications. We first fabricated and characterized well-defined porous PCL-β-TCP scaffolds with identical pore size (500µm) but different strut sizes (200 and 400µm) using additive manufacturing (AM) technology, and then assessed the HUVEC׳s proliferation and morphogenesis within collagen, PCL-β-TCP scaffold, and the collagen-scaffold hybrid construct. Results showed that, in the hybrid construct, the cell population in the collagen component dropped by day 7 but then increased by day 14. Also, cells migrated onto the struts of the scaffold component, proliferated over time, and formed networks on the thinner struts (i.e., 200µm). Also, the thinner struts resulted in formation of long linear cellular cords structures within the pores. Finite element simulation demonstrated principal stress patterns similar to the observed cell-network pattern. It is probable that the scaffold component modulated patterns of principal stresses in the collagen component as biomechanical cues for reorganization of cell network patterns. Also, the scaffold component significantly improved the mechanical integrity of hydrogel component in the hybrid construct for weight-bearing applications. These results have collectively indicated that the manipulation of micro-architecture of scaffold could be an effective means to further regulate and guide desired cellular response in hybrid constructs.

Impact of cordon-bleu expression on actin cytoskeleton architecture and dynamics.

Cordon-bleu (COBL) is a multifunctional WASP-Homology 2 (WH2) domain-containing protein implicated in a wide variety of cellular functions ranging from dendritic arborization in neurons to the assembly of microvilli on the surface of transporting epithelial cells. In vitro biochemical studies suggest that COBL is capable of nucleating and severing actin filaments, among other activities. How the multiple activities of COBL observed in vitro contribute to its function in cells remains unclear. Here, we used live imaging to evaluate the impact of COBL expression on the actin cytoskeleton in cultured cells. We found that COBL induces the formation of dynamic linear actin structures throughout the cytosol. We also found that stabilizing these dynamic structures with the parallel actin-bundling protein espin slows down their turnover and enables the robust formation of self-supported protrusions on the dorsal cell surface. Super-resolution imaging revealed a global remodeling of the actin cytoskeleton in cells expressing these two factors. Taken together, these results provide insight as to how COBL contributes to the assembly of actin-based structures such as epithelial microvilli. © 2016 Wiley Periodicals, Inc.

Fabrication and surface enhanced Raman spectroscopy of single Au@SiO2 dimers linked by benzenedithiol

Metal nanoparticle dimers with controllable gap distance have attracted considerable attention because of their promising application in plasmonics. Generally, gaps with nanometer or subnanometer dimensions generate localized surface plasmon resonance (LSPR) coupling effect, thus contributing to a strong electromagnetic field for improving surface enhanced Raman scattering (SERS) effect. Here, we developed a facile approach to fabricate Au@SiO2 dimers through the steric hindrance effect, in which the SiO2 shell functioned as a block and a rigid dithiol molecule was employed as linker. The thickness of the SiO2 shell played a critical role in improving the yield of dimers. The dimerization efficiency increased significantly as the shell thickness decreased to ~1 nm. When 1,4‐benzenedithiol was used as linker molecule, the yield of dimers was ~30%. Few dimers were obtained when mecaptobenzonic acid was used as linker. A thicker shell is associated with a low yield of dimer, whereas a thinner shell resulted in the formation of multimers and linear structures. The low number of linker molecules on the exposed area of monodisperse single nanoparticles and the lack of LSPR coupling effect (‘hot spots’) resulted in the disappearance of SERS signals of the linkers. The estimated SERS enhancement factor was about eight fold because of the strong coupling effect in the gap of the dimer with the distance of the dithiol molecular length. From the above results, SERS combined with SEM could be developed into powerful tools for monitoring the formation of dimers and positioning of single dimers. It may aid the control of assembly of Au nanoparticles and in probing key issues about SERS enhancements. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Synthesis and conformation of 3,6-connected cyclohexadiene chains.

3,6-Connected cyclohexadienes as precursors for polyphenylenes are synthesized and characterized by mass spectrometry and NMR spectroscopy. Pure fractions of trimers, hexamers, and nonamers are collected after separation of the product mixture by recycling GPC. The anticipated formation of rigid linear structures, due to the trans-configuration of the monomeric units, is supported by density functional theory and experimentally confirmed by dynamic light scattering from dilute solution at low scattering angles. The obtained translational diffusion coefficients are represented by rigid rod-like or prolate ellipsoid-like molecular shapes. The measurements of diffusion coefficients reveal a length-dependent ratio of 1:2:3 between the three oligomers, which directly correlates to the expected length extension from trimer to nonamer.

Supramolecular Structure and Renaturation of a (1→3)-β-d-Glucan Compared with Curdlan and Scleroglucan

A (1→3)-β-d-Glucan produced by Lactobacillus suebicus CUPV221 strain was investigated by tapping mode atomic force microscopy (TM-AFM), to compare its supramolecular structure and conformation with two commercial polysaccharides: curdlan and scleroglucan. It was found that the β-d-Glucan was a (1→3)(1→2)-β-d-Glucan and at room temperature formed three-dimensional networks by entanglements between strands, as does scleroglucan. However, (1→3)(1→2)-β-d-Glucan strands seemed to be more stiff than those of scleroglucan. It was also observed that curdlan samples deposited from 5 mM NaOH aqueous solution showed supermolecular assemblies, recognized in the literature as micelles, which are controlled by hydrophobic hydration. The (1→3)(1→2)-β-d-Glucan in alkaline aqueous solutions produced different supramolecular structures depending on pH, and at 0.4 M NaOH (pH 13.16), denaturation took place. After neutralizing the alkaline solution with HCl, the formation of short linear, circular, and hairpin structures was observed.