Distinct Structural Types Research Articles

Morphological structure and mechanical properties of epoxy/polysulfone/cellulose nanofiber ternary nanocomposites

Despite some work on epoxy resin/cellulose nanofiber (CNF) system, it remains unclear how CNF affects microstructure and mechanical properties of epoxy/polysulfone (PSF) binary blends so far. We herein introduced CNF into the blends via a combination of solvent exchange and melt mixing. Results show that epoxy/PSF binary blends display three distinct types of phase separated structures but slightly affecting mechanical properties because of poor interfacial adhesion. However, only adding small amount of CNF can enhance impact toughness and tensile strength due to improved interfacial adhesion, probably arising from hydrogen bonding interactions between CNF surfaces and matrix polymers, and penetrating and bridging effects of CNF between different phases. For example, compared with the epoxy/PSF blends, adding 0.2 wt% of CNF can increase impact strength by ∼49%. Additionally, 0.3 wt% of CNF can increase the glass transition temperature by ∼18 °C relative to the epoxy resin.

Unified total synthesis of the natural products endiandric acid A, kingianic acid E, and kingianins A, D, and F.

A measure of the strength of a synthetic strategy is its versatility: specifically, whether it allows structurally distinct targets to be prepared. Herein we disclose a unified approach for the total synthesis of natural products of three distinct structural types, all of which occur naturally as racemic mixtures. The point of divergence involves the terminal alkylation of a conjugated tetrayne, and culminates in a significantly shortened synthesis of endiandric acid A (8 steps), the first total synthesis of kingianic acid E (8 steps), and a second-generation synthesis of kingianins A, D, and F (11 steps). Evidence for redox catalysis in the biosynthesis of kingianic acid E is presented.

Free-stream coherent structures in parallel boundary-layer flows

AbstractOur concern in this paper is with high-Reynolds-number nonlinear equilibrium solutions of the Navier–Stokes equations for boundary-layer flows. Here we consider the asymptotic suction boundary layer (ASBL) which we take as a prototype parallel boundary layer. Solutions of the equations of motion are obtained using a homotopy continuation from two known types of solutions for plane Couette flow. At high Reynolds numbers, it is shown that the first type of solution takes the form of a vortex–wave interaction (VWI) state, see Hall & Smith (J. Fluid Mech., vol. 227, 1991, pp. 641–666), and is located in the main part of the boundary layer. On the other hand, here the second type is found to support an equilibrium solution of the unit-Reynolds-number Navier–Stokes equations in a layer located a distance of $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}O(\ln \mathit{Re})$ from the wall. Here $\mathit{Re}$ is the Reynolds number based on the free-stream speed and the unperturbed boundary-layer thickness. The streaky field produced by the interaction grows exponentially below the layer and takes its maximum size within the unperturbed boundary layer. The results suggest the possibility of two distinct types of streaky coherent structures existing, possibly simultaneously, in disturbed boundary layers.

Lanthanide coordination polymers: Synthesis, diverse structure and luminescence properties

The new semirigid exo-bidentate ligand incorporating furfurysalicylamide terminal groups, namely, 1,4-bis{[(2′-furfurylaminoformyl)phenoxyl]methyl}-2,5-bismethylbenzene (L) was synthesized and used as building blocks for constructing lanthanide coordination polymers with luminescent properties. The series of lanthanide nitrate complexes have been characterized by elemental analysis, IR spectroscopy, and X-ray diffraction analysis. The semirigid ligand L, as a bridging ligand, reacts with lanthanide nitrates forming three distinct structure types: chiral noninterpenetrated two-dimensional (2D) honeycomblike (6,3) (hcb, Schläfli symbol 63, vertex symbol 666) topological network as type I, 1D zigzag chain as type II and 1D trapezoid ladder-like chain as type III. The structural diversities indicate that lanthanide contraction effect played significant roles in the structural self-assembled process. The luminescent properties of EuIII, TbIII and DyIII complexes are discussed in detail. Due to the good match between the lowest triplet state of the ligand and the resonant energy level of the lanthanide ion, the lanthanide ions in EuIII, TbIII and DyIII complexes can be efficiently sensitized by the ligand.

Resiliency of an Interior Ponderosa Pine Forest to Bark Beetle Infestations Following Fuel-Reduction and Forest-Restoration Treatments

Mechanical thinning and the application of prescribed fire are commonly used to restore fire-adapted forest ecosystems in the Western United States. During a 10-year period, we monitored the effects of fuel-reduction and forest-restoration treatments on levels of tree mortality in an interior ponderosa pine, Pinus ponderosa Dougl. ex Laws., forest in California. Twelve experimental plots, ranging in size from 77–144 ha, were established to create two distinct forest structural types: mid-seral stage (low structural diversity; LoD) and late-seral stage (high structural diversity; HiD). Following harvesting, half of each plot was treated with prescribed fire (B). A total of 16,473 trees (8.7% of all trees) died during the 10-year period. Mortality was primarily attributed to bark beetles (Coleoptera: Curculionidae, Scolytinae) (10,655 trees), specifically fir engraver, Scolytus ventralis LeConte, mountain pine beetle, Dendroctonus ponderosae Hopkins, western pine beetle, D. brevicomis LeConte, pine engraver, Ips pini (Say), and, to a much lesser extent, Jeffrey pine beetle, D. jeffreyi Hopkins. Trees of all ages and size classes were killed, but mortality was concentrated in the smaller-diameter classes (19–29.2 and 29.3–39.3 cm at 1.37 m in height). Most mortality occurred three to five years following prescribed burns. Higher levels of bark beetle-caused tree mortality were observed on LoD + B (8.7%) than LoD (4.2%). The application of these and other results to the management of interior P. ponderosa forests are discussed, with an emphasis on the maintenance of large trees.

Biotemplate synthesis of carbon nanostructures using bamboo as both the template and the carbon source

A series of carbon nanostructures were prepared via a biotemplate method by catalytic decomposition of bamboo impregnated with ferric nitrate. The natural nanoporous bamboo was used as both the green carbon source and the template for the in situ growth of carbon nanostructures. Scanning electron microscope, field emission transmission electron microscope and energy dispersive X-ray spectroscope were used to characterize the product. Four distinct structural types of carbon nanostructures have been identified, namely nanofibers, hollow carbon nanospheres, herringbone and bamboo-shaped nanotubes. The effect of reaction temperature (from 600 to 900°C) on the growth behavior of carbon nanostructures was investigated and the corresponding growth mechanism was proposed. At low temperature the production of nanofibers was favored, while higher temperature led to bamboo-shaped nanostructures.

Repairing a Medieval Door

The main doors of medieval buildings or building complexes such as cathedrals or palaces are substantial structures, often weighing as much as one tonne per leaf. A survey of medieval English doors shows several distinct structural types whose different structural actions will be considered. All must develop some form of in plane action through the interaction of their components to transmit their weight back to their supports. However their complexity often allows several different modes of action, each of which will be differently affected by moisture movement within the timber, so that more than one mode of action will often need to be considered. The recent need to repair the early sixteenth century main doors of Trinity College, Cambridge involved the detailed analysis of one of these types whose structure comprised a dense grid of relatively slender muntins and ledges set within a much more substantial frame, carrying decorated boarding and mouldings on the outside face. The intention was that by understanding this structure we would be able to restore the original structural action of the door. In this case earlier interventions and permissions, and the extent of deterioration at the lower hinges, made this impossible. However, the exercise suggests an approach that might be valuable in the restoration of other doors of this type.

Effects of Ga accumulation on the microstructure of Cu(In1−x,Gax)Se2 thin films during selenization

Cu(In1−x,Gax)Se2 (CIGS) thin films were prepared by the sputtering of CuInGa (CIG) alloy precursors and CuGa/In stacked precursors followed by selenization. The effects of the using CIG precursors prepared by various methods and that of use of various selenization temperatures on the microstructural characteristics of CIGS thin films were investigated and the nature of phase transformation and Ga accumulation are discussed. Observation of the cross section morphologies revealed that the CIGS thin films prepared from CIG alloy precursors show two distinct types of structure. In addition, Ga was found to accumulate in high concentrations in the films. The X-ray diffraction (XRD) patterns of the films indicated the coexistence of CuInSe2 (CIS) and CIGS phases at low selenization temperatures. However, the CIGS phase seemed to disappear when the selenization temperature was increased to 580°C. In comparison, the films prepared from CuGa/In stacked precursors also showed Ga accumulation after selenization. Surprisingly, the distinct structure of the films improved when the selenization temperature was increased to 580°C. The XRD patterns of the films showed that the CIS and Ga-rich CIGS phases coexisted at low selenization temperatures. When the selenization temperature was increased to 580°C, the positions of the CIS and Ga-rich CIGS peaks seemed to mix and shift to the position of Cu(In0.7,Ga0.3)Se2.

Catalytic Synthesis of Carbon Nanotube and Nanofilament Over Oxidized Diamond-Supported Catalysts

Carbon nanotube and filament could be obtained by the decomposition of C2H4 using oxidized diamond-supported metal catalysts with three distinct structural types. Oxidized diamond is proposed as a novel catalytic means for the synthesis of nanocarbons. Oxidized diamond may catalyze unique reactions of importance in carbon nanotube and filament synthesis.

3D numerical modelling of graben interaction and linkage: a case study of the Canyonlands grabens, Utah

AbstractGraben systems in extensional settings tend to be segmented with evidence of segment interaction. To gain a better understanding of the evolution of structures formed during graben growth and interaction, we here study the Grabens area of Canyonlands National Park, Utah, where a wide range of such structures is well exposed. With the aid of 3D numerical models, we attempt to reproduce structures observed in that region and to understand controls on the structural style of graben interaction by varying the spacing between pre‐existing structures. The sensitivity of the system to the thickness of the salt layer is also tested. Four distinct types of structures are observed when the spacing between inherited weak zones is varied: (1) grabens connecting in a relay zone divided by a narrow central horst; (2) graben segments interacting via a secondary stepover graben; (3) grabens propagating alongside each other with limited segment interaction; and (4) an abandoned graben segment in a system of multiple competing grabens. The presence of a basal salt layer (Paradox Member) promotes efficient graben propagation. A comparison between the observed structures and the numerical model results indicates that the detachment salt layer is relatively thin in the study area.

Case study of an ice void structure in polar mesospheric clouds

The Cloud Imaging and Particle Size (CIPS) instrument aboard the Aeronomy of Ice in the Mesosphere (AIM) mission produces detailed images of Polar Mesospheric Clouds (PMCs) from space and has revealed several distinct types of cloud structures. One such commonly observed structure is an ‘ice void’—a nearly circular ice-free region with diameter varying from tens to thousands of kilometers. We document the morphology of large ice voids (diameter of ∼500–1000km) as seen by CIPS in the northern hemisphere 2007 PMC season. The meteorology of the mesosphere when these voids occur is described by the Navy Operational Global Atmospheric Prediction System–Advanced Level Physics High Altitude (NOGAPS–ALPHA) forecast/assimilation system. A comprehensive study of dynamics and transport in the mesosphere using NOGAPS–ALPHA during the occurrence of a large ice void observed by CIPS on 19 July 2007 indicates that warmer temperatures (warmer than the frost point temperature of ∼144K) at the location of the void may be related to increased tidal activity and transport of warm air from low latitudes. However, a detailed analysis of all identified voids is necessary to generalize the factors that could be responsible for the formation of an ice void.

An orthorhombic Mo3VOxcatalyst most active for oxidative dehydrogenation of ethane among related complex metal oxides

Four distinct structural types (orthorhombic, trigonal, tetragonal and amorphous) of Mo3VOx catalyst were each synthesized by a hydrothermal method as a single phase, characterized structurally and tested for oxidative dehydrogenation of ethane. A common structural feature of the catalysts is that the materials are a layer-type structure and constructed with pentagonal {Mo6O21} units. The arrangement of the pentagonal units can form heptagonal channels to create different structural features. The orthorhombic Mo3VOx catalyst has microporosity due to the open heptagonal channels adsorbing nitrogen molecules and showed the highest activity for the reaction among four distinct catalysts. Furthermore, this phase appeared to be most active, currently, compared to other complex metal oxide catalysts reported. An observed positive relation between the microporosity and the oxidation activity suggests that the catalytic oxidation takes place at the heptagonal channels.

Proton transfer or hemibonding? The structure and stability of radical cation clusters

The basin hopping search algorithm in conjunction with second-order Møller-Plesset perturbation theory is used to determine the lowest energy structures of the radical cation clusters (NH3)n˙(+), (H2O)n˙(+), (HF)n˙(+), (PH3)n˙(+), (H2S)n˙(+) and (HCl)n˙(+), where n = 2-4. The energies of the most stable structures are subsequently evaluated using coupled cluster theory in conjunction with the aug-cc-pVTZ basis set. These cationic clusters can adopt two distinct structural types, with some clusters showing an unusual type of bonding, often referred to as hemibonding, while other clusters undergo proton transfer to give an ion and radical. It is found that proton transfer based structures are preferred by the (NH3)n˙(+), (H2O)n˙(+) and (HF)n˙(+) clusters while hemibonded structures are favoured by (PH3)n˙(+), (H2S)n˙(+) and (HCl)n˙(+). These trends can be attributed to the relative strengths of the molecules and molecular cations as Brønsted bases and acids, respectively, and the strength of the interaction between the ion and radical in the ion-radical clusters.

The size of the metal ion controls the structures of the coordination polymers of benzo-2,1,3-selenadiazole

The products of the combination of benzo-2,1,3-selenenadiazole with chloride salts of divalent Mn, Fe, Co, Ni, and Cd crystallize from DMSO in two distinct structural types. While the smaller ions form infinite chains of metal atoms N,N′-bridged by the heterocycle, the larger ions stabilize infinite chains of metal atoms bridged by μ2 halide ions. In the latter case, two heterocycle molecules cap each metal ion and are able to establish a link to the next chain in the lattice through the [Se–N]2 supramolecular synthon. Despite the large (>9.2 A) distance between the [M(μ-Cl)2]∞ chains, the manganese derivative is only paramagnetic.

Karyotypic variability of human multiple myeloma cell lines

Cytogenetic analysis of human multiple myeloma (MM) cell lines L363, Karpas 707, RPMI 8226, and U-266 was carried out. During long-term existence in vitro, the number of chromosomes in the cell lines was shown to be preserved at the near-diploid level (L363, Karpas 707, U-266) or to increase up to the hypotriploid level (RPMI 8226). There were complexly rearranged karyotypes with abnormalities of chromosomes of all pairs in all cell lines; however, no identical chromosomal translocations have been revealed. Loci of chromosomes involved in structural rearrangements in these cell lines often coincided with sites of DNA copy number imbalances characteristic for MM in vivo. Distinct types of the karyotypic structure of cell populations differing in the combination of cells with the main and additional structural variants of karyotype and of cells with nonclonal chromosome rearrangements were found in MM cell lines. In general, the karyotypic variability of the MM cell lines corresponds to the dynamics of karyotype of myeloma cells in vivo and, hence, has a tumor-specific character.

Emergence of Long Range One-Dimensional Nanostructures in a Disordered Two-Dimensional System: Mn-Doped Ti1+δS2

Multiple microscopic techniques have been employed to study Mn-intercalated Ti1+δS2 at different length scales. The introduction of Mn intercalates resulted in the formation of two distinct types of one-dimensional structures; both exhibited extremely high aspect ratios, with lengths exceeding hundreds of micrometers. The smaller of the two features were only a few nanometers wide, while the larger one-dimensional structures had widths on the order of magnitude of one hundred nanometers. The one-dimensional structures were detected on samples with a range of Mn-doping levels but were especially common in samples with a 15% Mn-doping concentration. In these samples, a high density of parallel linear structures could be found at lengths ranging from the nanometer to micrometer scale. One-dimensional structures were never found in Ti1+δS2 samples without Mn dopants. We utilized Monte Carlo simulations to better understand these structures, which arise from interactions between the two species of intercalates in the system: Mn ions and excess Ti ions bound to intercalation sites. While the arrangement of intercalated ions has no long-range order, interactions between various nanoscale domains leads to the formation of domain-wall-like structures extending over macroscopic distances.

Ciliated sensory hair cell formation and function require the F-BAR protein syndapin I and the WH2 domain-based actin nucleator Cobl

During development, general body plan information must be translated into distinct morphologies of individual cells. Shaping cells is thought to involve cortical cytoskeletal components and Bin-Amphiphysin-Rvs167 (BAR) superfamily proteins. We therefore conducted comprehensive side-by-side loss-of-function studies of zebrafish orthologs of the F-BAR protein syndapin I and the actin nucleator Cobl. Zebrafish syndapin I associates with Cobl. The loss-of-function phenotypes of these proteins were remarkably similar and suggested a common function. Both cobl- and syndapin I-morphant fish showed severe swimming and balance-keeping defects, reflecting an impaired organization and function of the lateral line organ. Their lateral line organs lacked several neuromasts and showed an impaired functionality of the sensory hair cells within the neuromasts. Scanning electron microscopy revealed that sensory hair cells of both cobl- and syndapin I-morphant animals showed defects in the formation of both microtubule-dependent kinocilia and F-actin-rich stereocilia. Consistent with the kinocilia defects in sensory hair cells, body length was shortened and the development of body laterality, a process depending on motile cilia, was also impaired. Interestingly, Cobl and syndapin I both localized to the base of forming cilia. Rescue experiments demonstrated that proper formation of ciliated sensory hair cell rosettes relied on Cobl's syndapin I-binding Cobl homology domain, the actin-nucleating C-terminus of Cobl and the membrane curvature-inducing F-BAR domain of syndapin I. Our data thus suggest that the formation of distinct types of ciliary structures relies on membrane topology-modulating mechanisms that are based on F-BAR domain functions and on complex formation of syndapin I with the actin nucleator Cobl.

Microstructure and Crystallization Kinetics of Polyurethane Thermoplastics Containing Trisilanol Isobutyl POSS

The synthesis of thermoplastic polyurethanes (TPU) from the reaction of a NCO group‐containing prepolymer and 0, 1.14, 1.71, and 2.28 wt% of trisilanol isobutyl polyhedral oligomeric silsesquioxane (POSS) was carried out in an instrumented batch mixer. The samples were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). SEM analysis shows that the incorporation of POSS promoted strongly aggregation through physical interactions (formation of POSS‐rich domains). Modifications in the TPU microstructure and the reduction in the crystal size were observed in the XRD diffractograms. The incorporation of POSS equally altered the TPU crystallization, and samples bearing higher concentrations of POSS formed two distinct types of crystalline structures. The kinetics of crystallization showed that nucleation strongly depends on the balance between TPU crystal formation and POSS‐rich domains.

Leader–member exchange, subordinate stewardship, and hierarchical governance

In this article, by integrating the institutional theory, leader–member exchange (LMX) theory, and stewardship theory, we propose a model of subordinate stewardship behaviors in organizational hierarchies and the resultant hierarchical governance structures. First, we develop propositions suggesting that the quality of LMX (supervisor–subordinate) is determined by three antecedents: leader characteristics, subordinate characteristics, and internal organizational context. The quality of LMX, in turn, affects the subordinate stewardship behaviors. Second, by integrating institutional theory and stewardship theory, we propose that the interaction between isomorphic pressures and the level of subordinate stewardship behaviors may result in four distinct types of hierarchical governance structures: isomorphic stewardship, isomorphic controls, firm-specific controls, and firm-specific stewardship. These governance mechanisms reflect the internal drive toward subordinate stewardship, while complying with the external norms of isomorphism. Thus, different types of governance structures may exist between and within firms. Implications of this model are discussed here.

Context-sensitive detection of local community structure

Local methods for detecting community structure are necessary when a graph’s size or node-expansion cost make global community detection methods infeasible. Various algorithms for local community detection have been proposed, but there has been little analysis of the circumstances under which one approach is preferable to another. This paper describes an evaluation comparing the accuracy of five alternative vertex selection policies in detecting two distinct types of community structures—vertex partitions that maximize modularity, and link partitions that maximize partition density—in a variety of graphs. In this evaluation, the vertex selection policy that most accurately identified vertex-partition community structure in a given graph depended on how closely the graph’s degree distribution approximated a power-law distribution. When the target community structure was partition-density maximization, however, an algorithm based on spreading activation generally performed best, regardless of degree distribution. These results indicate that local community detection should be context-sensitive in the sense of basing vertex selection on the graph’s degree distribution and the target community structure.