Self-assembled one-dimensional nanostructure arrays

A range of proposed devices relies on the electronic, optical or magnetic properties of one-dimensional (1D) chains of nanoparticles. Here, well-controlled 1D arrays have been formed by templating a spherical-morphology block copolymer within a narrow groove. Significantly, the domains are distorted into ellipses with aspect ratio and major axis orientation controlled by the groove width. This technique gives unprecedented control over the period, particle size, aspect ratio, and orientation of nanoparticles in 1D arrays, making it valuable for creating self-assembled masks for the fabrication of novel devices.     

Advances and perspectives on one-dimensional nanostructure electrode materials for potassium-ion batteries

Potassium-ion batteries (PIBs) have aroused considerable interest as a promising next-generation advanced large-scale energy storage system due to the abundant potassium resources and high safety. However, the K⁺ with large ionic radius brings restricted diffusion kinetics and severe volume expansion in electrode materials, resulting in inferior actual rate characteristics and rapid capacity fading. Designing electrode materials with one-dimensional (1D) nanostructure can effectively enhance various electrochemical properties due to the well-guided electron transfer pathways, short ionic diffusion channels and high specific surface areas. In this review, we summarize the recent research progress and achievements of 1D nanostructure electrode materials in PIBs, especially focusing on the development and application of cathode and anode materials. The nanostructure, synthetic methods, electrochemical performances and structure-performance correlation are discussed in detail. The advanced characterizations on the reaction mechanisms of 1D nanostructure electrode materials in PIBs are briefly summarized. Furthermore, the main future research directions of 1D nanostructure electrode materials are also predicted, hoping to accelerate their development into the practical PIBs market.     

Fiber template approach toward preparing one-dimensional silica nanostructure with rough surface

Silica nanofibers were grown on the surface of chitosan nanofibers used as templates by coating the surface with silica derived from the hydrolysis and condensation of tetraethoxysilane using ammonium hydroxide as a catalyst. This was followed by the decomposition of the chitosan template. The relationship between different processing factors (type of templates as well as amounts of catalyst and template) and the formation of silica nanofibers was examined. Varying the processing factors was found to be effective in controlling the morphology of the silica nanofibers. The use of chitosan nanofibers effectively led to the formation of one-dimensional silica nanofibers as the positively charged chitosan nanofibers promoted the deposition of the negatively charged silica nanoparticles through electrostatic attractive forces. Therefore, the chitosan nanofibers acted as good deposition sites for interacting with silica nanoparticles. Although a large amount of catalyst promoted the sol-gel reaction, the silica nanoparticles grew excessively in the solvent. Therefore, the surface structure of the prepared silica nanofibers could be controlled by varying the amount of chitosan template as this also varied the formation mechanism of the silica nanofibers. The resultant samples had a rough silica wall composed of densely assembled silica nanoparticles, with a high specific surface area (338 m²/g).     

Stepwise current-driven release of attogram quantities of copper iodide encapsulated in carbon nanotubes

Encapsulated nanograins of copper iodide have been sequentially discharged from individual carbon nanotubes. Using a high resolution electron microscope equipped with a two-terminal electrical measurements unit, it was possible to manipulate the filling contents with precisions of a few attograms at a time. Changes in electrical resistance and filling ratio were followed in tandem and in real-time. It is shown that the pulsed release of the halide is directly related to the overall conductance of the filled nanotube.     

Electrochemical deposition of the cobalt nanostructure by double template and pulse current methods

An electrochemical pulse method and the principles of the so-called double template deposition have been developed to prepare a cobalt nanomaterial. Atomic force microscopy (AFM) analysis reveal a material with double structure; fibers that grow from the bottom of the pores in the aluminum oxide membrane present many subdivision due to the lyotropic liquid crystal template. The small-scale images show parallel lines with regular periodicity formed by cobalt on the surface of the Al₂O₃/Al working electrode. The distance between the two consecutive lines is about 10 nm, this value is close to the diameter of the column of liquid crystal. Depending on the experimental condition, the axis of the column of liquid crystal can be parallel to the plan of the electrode surface.     

An approach for synthesizing various types of tungsten oxide nanostructure

Various types of tungsten oxide nanostructures, including nanowires, nanobundles, and three-dimensional nanowire networks, have been synthesized on large-area silicon substrates by simply heating an array of tungsten filaments in a vacuum chamber. The fine structure and components of as-prepared products can been controlled by changing the tungsten filament temperature. This approach is free of catalysts and templates, and provides an economical method for large-scale preparation of various types of tungsten oxide nanostructures for applications.     

Fabrication and mechanical properties of suspended one-dimensional polymer nanostructures: polypyrrole nanotube and helical polyacetylene nanofibre

Mechanical properties of suspended quasi-one-dimensional polymer nanostructures were investigated using atomic force microscopy (AFM). A recently developed new acid-free etch method combined with electron beam lithography was used to fabricate suspended polypyrrole (PPy) nanotubes and helical polyacetylene (HPA) nanofibres. The elastic modulus of each suspended structure was obtained by AFM force-distance measurements. The estimated modulus value of the PPy nanotube (HPA nanofibre) was 0.96?GPa (0.5?GPa). Using this acid-free method, all-organic flexible NEMS devices can be fabricated in the future.     

An encapsulated drug delivery system for recalcitrant urinary tract infection

One of the hallmarks of urinary tract infection, a serious global disease, is its tendency to recur. Uropathogenic bacteria can invade cells lining the bladder, where they form longer-term intracellular reservoirs shielded from antibiotics, re-emerging at a later date to initiate flare-ups. In these cases, only lengthy systemic antibiotic treatment can eradicate all the reservoirs. Yet, long courses of antibiotics are not ideal, as they can lead to side effects and an increase in antibiotic resistance. Moreover, most antibiotics lose some potency by the time they reach the bladder, and many cannot permeate cells, so they cannot access intracellular reservoirs. Here, using coaxial electrohydrodynamic forming, we developed novel core–shell capsules containing antibiotics as a prototype for a future product that could be infused directly into the bladder. Gentamicin was encapsulated in a polymeric carrier (polymethylsilsesquioxane) and these capsules killed Enterococcus faecalis, a common chronic uropathogen, in vitro in a dose-responsive, slow-release manner. Capsules containing a fluorescent tracer dye in place of gentamicin penetrated human bladder cells and released their dye cargo with no apparent toxicity, confirming their ability to successfully permeate cells. These results suggest that such antibiotic capsules could prove useful in the treatment of recalcitrant UTI.     

Corundum nanostructure ITO film fabrication: An approach for physical properties assessment

Corundum (hexagonal) structure indium tin oxide (h-ITO) nanocrystals have been synthesized by subjecting an aqueous solution of In and Sn chlorides (Sn/In 8 wt.%) to a hydrothermal process followed by annealing at 450 °C in forming gas for 1 h. The annealing temperature was selected based on thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) of the dried precipitated powder, which showed a stable weight and phase at temperatures above 420 °C. X-ray diffraction (XRD) patterns showed the formation of orthorhombic InOOH precipitates that is transformed, after annealing, into h-ITO nanocrystals with 32 nm average crystal size. For nanostructure film deposition, dispersed sols of the prepared nanocrystals were spun coated on glass substrates. The films were densified by UV irradiation, whilst four-probe method was used to measure its sheet resistance. A sheet resistance as low as 10.6 kΩ □ have been reached. Scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM) showed that the films have high surface roughness and nanopores. The transmittance spectra of the nanostructure films were measured in the UV–vis–NIR wavelength range. In addition to its low resistivity, nanostructure h-ITO films showed a wide range of transparency.     

冷轧变形纳米晶钴的X射线衍射研究

对冷轧变形前后纳米金属钴的微观应变。晶格常数以及晶粒尺寸的变化进行了研究，对X射线衍射图谱进行了分析计算，结果表明，变形过后晶体内部存有残余内应力并导致了微观应变，应变大小为ε=1．412×10q；对变形前后的晶格常数进行计算，得到变形后的晶格常数为a=0．25241nm；c=0．40782nm；透射电镜的观察和衍射谱线的计算表明变形后纳米金属钴的晶粒大小与形状基本未发生变化，平均晶粒尺寸为18．8nm。有可能是空位的活动降低了变形过程中的晶界迁移几率，使得变形后的晶粒尺寸基本没有发生变化。     

An application of least squares to one-dimensional transient problems

The method of ‘least squares’, which falls under the category of weighted residual processes, is applied as a time-stepping algorithm to one-dimensional transient problems including the heat conduction equation, diffusion-convection equation, and a non-linear unsaturated flow equation. Comparison is made with other time-stepping algorithms, and the least squares method is seen to offer definite advantages.     

Local feedback mode of scanning electrochemical microscopy for electrochemical characterization of one-dimensional nanostructure: theory and experiment with nanoband electrode as model substrate

Local feedback mode is introduced as a novel operation mode of scanning electrochemical microscopy (SECM) for electrochemical characterization of a single one-dimensional (1D) nanostructure, for example, a wire, rod, band, and tube with 1-100-nm width and micrometer to centimeter length. To demonstrate the principle, SECM feedback effects under diffusion limitation were studied theoretically and experimentally with a disk probe brought near a semi-infinitely long band electrode as a geometrical model for a conductive 1D nanostructure. As the band becomes narrower than the disk diameter, the feedback mechanism for tip current enhancement is predicted to change from standard positive feedback mode, to positive local feedback mode, and then to negative local feedback mode. The negative local feedback effect is the only feedback effect that allows observation of a 1D nanostructure without serious limitations due to small lateral dimension, available tip size, or finite electron-transfer rate. In line-scan and approach-curve experiments, an unbiased Pt band electrode with 100-nm width and 2.6-cm length was detectable in negative local feedback mode, even using a 25-microm-diameter disk Pt electrode. Using a 2-microm-diameter probe, both well-defined and defected sites were observed in SECM imaging on the basis of local electrochemical activity of the nanoband electrode. Noncontact and spatially resolved measurement is an advantage of this novel SECM approach over standard electrochemical approaches using electrodes based on 1D nanostructure.     

An explicit unconditionally stable variable time-step method for one-dimensional stefan problems

Modelling of heat conduction processes with phase changes benefits from the application of variable time-step methods when the behaviour of the moving boundary is not known a prioiri. Due to convergence and stability constraints only implicit difference equations have been used with these methods. Implicit methods show a significant loss of accuracy and exhibit convergence difficulties when used for relatively slow or rapid moving-boundary problems. To overcome these problems an improved explicit variable time-step method which combines the explicit exponential difference equation and a variable time-step grid network with virtual subspace increments around the moving boundary is presented and tested for both a solidification and a melting problem. A virtual subinterval time-step elimination technique is incorporated to ensure that stability is automatically maintained for any mesh size. Unlike the implicit variable time-step methods, the accuracy of the resulting method is not affected by the velocity of the moving boundary. For both test problems numerical results are in better agreement with known analytical solutions than results predicted by other numerical methods.     

Osteogenic behavior of alginate encapsulated bone marrow stromal cells: An in vitro study

Sodium alginate is a useful polymer for the encapsulation and immobilization of a variety of cells in tissue engineering because it is biocompatible, biodegradable and easy to process into injectable microbeads. Despite these properties, little is known of the efficacy of calcium cross-linked alginate gel beads as a biodegradable scaffold for osteogenic cell proliferation and differentiation. In this study, we investigated the ability of rabbit derived bone marrow cells (BMCs) to proliferate and differentiate in alginate microbeads and compared them with BMCs cultured in poly-l-lysine (PLL) coated microbeads and on conventional 2D plastic surfaces. Results show that levels of proliferation and differentiation in microbeads and on tissue culture plastics were comparable. Cell proliferation in microbeads however diminished after fortification with a coating layer of PLL. Maximum cell numbers observed were, 3.32 × 10⁵ ± 1.72 × 103; 3.11 × 10⁵ ± 1.52 × 10³ and 3.28 × 10⁵ ± 1.21 × 10³ for the uncoated, PLL coated and plastic surface groups respectively. Alkaline phosphatase and protein expressions reflected the stage of cell differentiation. We conclude that calcium cross-linked alginate microbeads can act as a scaffold for BMC proliferation and osteogenic differentiation and has potential for use as 3D degradable scaffold.     

An alternative one-dimensional study of dynamic crack growth in DCB test specimens

Crack propagation in a double cantilever beam is studied analytically and numerically. The specimen is modelled as a pair of Timoshenko-beams in direct contact along the prospective crack path. An alternative to previous models assuming some type of elastic interlayer is thus presented.

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Résumé On étudie de manière analytique et de manière numérique la propagation d'une fissure dans une poutre double Cantilever. L'éprouvette est représentée par une paire de poutres de Timoschenko en contact direct le long du chemin probable de la fissure. On présente donc une alternative aux modèles précédents qui suppose un certain type de couche intermédiaire élastique.

     

An inverse boundary problem for one-dimensional heat equation with a multilayer domain

In this paper, we propose a regularization method for determining a moving boundary from Cauchy data in one-dimensional heat equation with a multilayer domain. The numerical scheme is based on the use of the method of fundamental solutions and a discrete Tikhonov regularization technique. The generalized cross validation rule for the choice of a regularization parameter is applied to obtain a stable numerical approximation to the moving boundary. Numerical experiments for five examples show that our proposed method is effective and stable.     

External field-assisted laser ablation in liquid: An efficient strategy for nanocrystal synthesis and nanostructure assembly

Laser ablation in liquid (LAL) has received considerable attention over the last decade, and is gradually becoming an irreplaceable technique to synthesize nanocrystals and fabricate functional nanostructures because it can offer effective solutions to some challenges in the field of nanotechnology. The goal of this review is to offer a comprehensive summary of recent developments of LAL in nanocrystal synthesis and nanostructure fabrication. First, we will introduce the fundamental processes of microsecond, nanosecond, and femtosecond LAL, and how the active species act differently in plasma, cavitation bubbles, and droplets in the different LAL processes. Second, a variety of LAL-based techniques for nanomaterials synthesis and processing are presented, such as electric-, magnetic-, and temperature-field LAL, as well as electrochemically assisted LAL, pulsed laser deposition in liquid, and laser writing of nanopatterns in liquid. Third, new progress in LAL-generated nanomaterials is described. Fourth, we emphasize five applications of LAL-generated nanomaterials that have emerged recently in the fields of optics, magnetism, environment, energy, and biomedicine. Finally, we consider the core advantages of LAL, the limitations of LAL and corresponding solutions, and the future directions in this promising research area.     

An automatic method for generating carbon nanostructure atomistic models using hexagonal meshes with properly distributed defects

Atomistic models, which are crucial for performing molecular dynamics simulations of carbon nanostructures, consist of virtual hexagonal meshes with defects properly distributed in the intersectional areas. Currently, atomistic models are created mostly by hand, which is a notably tedious and time‐consuming process. In this paper, we develop a method that produces atomistic models automatically. Because a hexagonal mesh and triangulation represent dual graphs, our work focuses on the creation of proper triangulation. The edge lengths of the triangulation should be compatible with the lengths of the C–C bonds, and vertices with valences other than 6 (due to the defects in the hexagonal mesh) should be properly arranged around the boundaries of the different components of a carbon nanostructure. Two techniques play important roles in our method: (1) sphere packing is used to place the nodes for triangulation that produces nearly constant edge lengths of the triangles and (2) the movement and editing of defects is used to control the number and positions of the defects. We subsequently develop a computer program based on this method that can create models much easier and faster than the current handwork method, thereby reducing the operation time significantly. Copyright © 2016 John Wiley & Sons, Ltd.     

An elementary theory of one-dimensional rod penetration using a new estimate for pressure

In this paper, a new pressure law is proposed to replace the modified Bernoulli equation of Tate in 1967 and 1969. It is achieved by decomposing the equation of motion, which was proposed by Jones et al. in 1987, into two parts and incorporating the kinematic equation by Wilson et al. in 1989. The new pressure law takes the effect of mushroom strain into account. From two different considerations, the pressure law is applied to the one-dimensional penetration modeling. First, by assuming that the rod/target interface pressure is approximately constant during the quasi-steady state, the governing equations can be analytically integrated to give a closed form solution for the penetration depth. The prediction is reasonably good in the low velocity regime. Secondly, a velocity-dependent interface pressure is added. A so-called shape factor, which was first introduced without physical interpretation by Alekseevskii in 1966, is substantiated. With this factor, the governing equations can be numerically integrated to give very accurate predictions for the impact velocity range from 1 km/s to 4 km/s.