Single-layer Tube Research Articles

Nonself-Sustained Microwave Discharge in a System for Hydrocarbon Decomposition and Generation of Carbon Nanotubes

This paper deals with the investigation of a method for sustainment of high-power microwave discharge in the installation for natural-gas decomposition. The essence of the method is to provide a generation of auxiliary discharge plasma in the area where the main microwave plasma torch burns. The design of the electrode system of auxiliary discharge resembles that for a coaxial plasmatron that consumes an average current of about 0.1 A. Then, the nonself-sustained microwave discharge with a frequency of 2.45 GHz has been obtained at a power level from 1 to 3 kW. Such a discharge has been used in the installation for natural-gas decomposition and generation of the carbon nanotubes. With a typical gas flow of 1 m3/h, the natural-gas conversion achieves 40%-80%. Three types of nanotubes are contained in the final product: multilayer tubes, single-layer tubes, and onion-type tubes.

Ultrastructure and mineral composition of serpulid tubes (Polychaeta, Annelida)

We have studied the tube ultrastructure of 44 recent species from 36 serpulid genera. Twelve distinct ultrastructures are identified. Serpulids possess very diverse tube ultrastructures, in contrast with the traditional point of view. Most species show single-layered tubes, but 34% of these species have between two and four ultrastructurally different layers. Tubes are mostly bimineralic, and are composed of aragonite and calcite; however, one of the polymorphs is always dominant. All the studied single-layered tubes with a lamello fibrillar tube ultrastructure are exclusively calcitic; prismatic structures, both in regular or irregular orientation, are either calcitic or aragonitic in composition. There is no correlation between tube mineralogy, and ultrastructure, and marine, brackish, and freshwater environments. We find that 47% of the serpulid species studied possess a unique combination of tube structure characters.

Suture-reinforced electrospun polydioxanone–elastin small-diameter tubes for use in vascular tissue engineering: A feasibility study

This study characterizes the cross-linking of electrospun elastin and the mechanical properties of suture-reinforced 1.5 mm internal diameter electrospun tubes composed of blended polydioxanone (PDO) and soluble elastin. Several tube configurations were tested to assess the effects of reinforcement on tube mechanical properties. Between the electrospun layers of each double-layered prosthetic, zero, one or two 6-0 sutures were wound, maintaining 1 mm spacing with a pitch of 9°. Single-layered tubes without suture were also examined. Samples were cross-linked and tested for compliance and burst strength. Compliance decreased significantly ( p < 0.05) and burst strength significantly increased ( p < 0.01) with reinforcement. Uncross-linked tubes were also tested to determine the effects of cross-linking. Results demonstrated that cross-linking significantly decreases burst strength ( p < 0.01), while decreases in compliance for cross-linked tubes were not significant. Cross-linked suture-reinforced PDO–elastin tubes had burst pressures more than 10 times greater than normal systolic pressures and exhibited a range of compliance values, including those matching native artery. These tubes display many characteristics of the “ideal” small-diameter graft, having mechanical properties that can be tailored to match those desired in vascular replacement applications.

Form follows function: developmental and physiological view on ventricular myocardial architecture

The arrangement of myocytes within the ventricle is critical for its contractile performance, as evidenced by significant functional impairment seen in cardiomyopathies associated with myofiber disarray or post-infarction remodeling. A review on this topic by Anderson and associates provides anatomical insight gained from a multitude of approaches, and concludes that the best concept is that of syncytial continuum with supporting collagenous matrix. The overall arrangement is in the form of several intertwined helices, and the authors find no support for a recently suggested ventricular myocardial band hypothesis. This commentary aims at providing a developmental and physiological perspective on this purely anatomical concept. Unlike some other organ systems, the developing heart has to function since very early stages to support the oxygen and nutrition demands of the growing embryo, thus putting some constraints on heart development. The ventricular myocardial architecture transforms from a single-layered tube through trabeculated stages into a mature form that relies on a multi-layered compact zone. The first evidence of helical patterns is found in trabeculated hearts during ventricular contraction, and layers with different helix pitch develop during later fetal stages as the compact zone thickens. The second major point determining ventricular contraction is the sequence of its electrical activation. The ventricular activation sequence changes concomitantly with its morphology, from slow peristaltoid through base-to-apex pattern found in looped trabeculated hearts, to mature apex-to-base direction. Thus, adult ventricular myocardial architecture is best understood when one also considers the way it developed together with its electrical activation sequence and contraction pattern.

Structures of Boron Nitride Nanotubes with Single-Layer and Multilayers Produced by Arc Discharge

Nanoscale materials created from boron nitride (BN) by arc discharge between ZrB2 electrodes in an N2 atmosphere have been investigated by electron microscopy. BN nanotubes were formed together with Zr-compound nanoparticles encapsulated in BN cages. Most of the tubes were multilayered and had diameters from 3 to 40 nm and lengths on the order of 100 nm. Single-layer tubes with diameters of 2 to 5 nm were also formed as a minority. Concerning the helical structures of BN tubes, a variety of chiral angles, including the zigzag and the armchair types, were observed. The morphology of the tube tips suggests the presence of pentagons and heptagons which are energetically less favorable compared with squares (four-membered rings).

Growth of single-layer carbon tubes assisted with iron-group metal catalysts in carbon arc

Single-layer (SL) carbon tubes were produced by arc evaporation of graphite rods containing iron-group metals (Fe, Co, Ni, Fe/Co, Co/Ni, Fe/Ni) under He and Ar gas. Transmission electron microscopy (TEM) revealed that these elemental and binary metals, excluding Fe which need a special atmosphere (a mixture of Ar and CH4), showed catalytic activity producing SL tubes under pure inactive gases. Fe/Ni alloy was the most effectual catalysts for producing SL tubes. The highest abundance of SL tubes in raw soot was estimated to be ∼ 10% from TEM observation. Smoke particles directly caught on TEM grids near an evaporation source during arcburning were also investigated, and it was suggested that small metal particles were first formed in the gas phase and then SL tubes grew from them.

Carbon nanocapsules and single-layered nanotubes produced with platinum-group metals (Ru, Rh, Pd, Os, Ir, Pt) by arc discharge

Encapsulation of platinum-group metals (Ru, Rh, Pd, Os, Ir, Pt) within carbon nanocapsules and synthesis of single-layered (SL) carbon nanotubes by arc evaporation of metal/carbon composites have been studied. Transmission electron microscopy revealed that all the platinum-group metals, forming small particles (10–200 nm in diameter), were encapsulated within multilayered graphitic cages. Particles trapped in the cages were single-domain crystallites in normal metallic phases. Rh, Pd, and Pt showed catalytic activity for growing SL carbon tubes, but the other metals did not. Bundles of dense SL tubes with diameter 1.3–1.7 nm were extruding radially from metal particles for Rh and Pd; the sizes of core particles were 20–30 nm for Rh, and 50–200 nm for Pd. In the case of Pt, one or a few SL tubes (typically 1.3–2.0 nm in diameter and sometimes ∼3 nm) grew from a tiny particle (∼10 nm).

Carbon nanotubes with single-layer walls

Macroscopic quantities of single-layer carbon nanotubes have recently been synthesized by cocondensing atomic carbon and iron group or lanthanide metal vapors in an inert gas atmosphere. The nanotubes consist solely of carbon, sp 2 -bonded as in graphene strips rolled to form closed cylinders. The structure of the nanotubes has been studied using high-resolution transmission electron microscopy. Iron group catalysts, such as Co, Fe, and Ni, produce single-layer nanotubes with diameters typically between 1 and 2 nm and lengths on the order of micrometers. Groups of shorter nanotubes with similar diameters can grow radially from the surfaces of lanthanide carbide nanoparticles that condense from the gas phase. If the elements S, Bi, or Pb (which by themselves do not catalyze nanotube production) are used together with Co, the yield of nanotubes is greatly increased and tubules with diameters as large as 6 nm are produced. Single-layer nanotubes are anticipated to have novel mechanical and electrical properties, including very high tensile strength and one-dimensional conductivity. Theoretical calculations indicate that the properties of single-layer tubes will depend sensitively on their detailed structure. Other novel structures, including metallic crystallites encapsulated in graphitic polyhedra, are produced under the conditions that lead to nanotube growth.

Stresses and Deformations in Composite Tubes Due to a Circumferential Temperature Gradient

This paper presents a linear elasticity solution for determining the response of composite tubes subjected to a circumferential temperature gradient of the form ΔTo+ ΔT1 cos(θ). The temperature does not vary with distance along the tube nor through the wall. Temperature-independent material properties are assumed and a displacement approach is used. The results are limited to tubes with the fibers in each layer oriented axially or circumferentially, so-called cross-ply tubes. It is shown that for both single layer and multiple layer tubes, one constant characterizes overall bending of the tube and one constant characterizes overall axial deformation. Numerical results show that fiber orientation strongly influences the stresses in a single layer tube. When the fibers are aligned axially, all components of stress in the tube are small. When the fibers are aligned circumferentially, the hoop stress becomes large. This is due to the large difference between the radial and circumferential coefficients of thermal expansion when the fibers are oriented circumferentially. Also, for a single layer tube constructed of a material with no thermal expansion in the axial direction, the overall change of length of the tube due to the temperature gradient will be zero only if the material is transversely isotropic. However, even if the material is transversely isotropic, the tube will still experience overall bending.