Tube Axis Research Articles

Addition of borazine to boron nitride nanotubes: [2+2] cycloaddition or bond cleavage

We have studied the addition of borazine to different armchair and zigzag BNNTs to investigate the chemoselectivity (BN bond cleavage vs. [2+2] cycloaddition) and regioselectivity (parallel vs. oblique addition) of the reaction. Based on our results, the borazine can either selectively break a B–N bond of the BN nanotubes, expanding the hexagonal ring of the tube to larger one at the surface, or undergo a [2+2]-cycloaddition on the BNNT surfaces. Both of these reactions exhibit a dependence on the chirality and active site of the tubes. Diagonal BN bonds of the zigzag BN tubes, either at the edges or at the middle of the tubes, are cleaved; but BN bonds parallel to the tube axis undergo [2+2] cycloaddition reactions. In contrast, diagonal BN bonds of the armchair BNNTs prefer cycloaddition, and BN bonds perpendicular to the tube axis follow BN bond cleavage and expansion ring. Overall, the B–N bond cleavage and expansion ring reactions of the borazine and the BN nanotubes are exothermic while [2+2] cycloaddition reactions of the BN nanotubes and borazine are endothermic. Reaction energies decrease with the increase of the diameter of the tube. [2+2] cycloadditions decrease the band gaps of the BNNTs by only about 4.3–19.9% while bond cleavage process increases the band gaps of the BNNTs, by about 1.4–7.9%.

Extensions of Johnson’s Theory of Backward-Wave Oscillations in a Traveling-Wave Tube

This paper extends Johnson’s classical theory [Johnson, Proc. IRE 43, 684 (1955)] for the threshold of backward-wave oscillation (BWO) in a traveling-wave tube by considering the effects of: 1) small random variations of the circuit phase velocity along the tube axis and 2) end reflections. We find that both the BWO threshold and BWO frequency are minimally affected by random variations of the phase velocity, but we find that the oscillation threshold depends sensitively on the magnitude and phase of the composite reflection coefficients.

Energy Absorption Characteristic of Compress-Expand Tensile Mechanism Using Finite Element Analysis.

Thin-walled tube was applicable as energy absorption in impact structural. Deformation ideally flows along tube’s axis in compression direction resulted plastic deformation. The deformation required external energy which taken from excessive source. Limitation of thin-walled tube was at collapse direction flows only in compression condition parallel to tube axis. Distortion of direction will trigger unstable collapse which reduce and blocked deformation flow. In real condition it is difficult to create perfect collapse deformation due to misalignment of flow. Compress-expand thin walled tube has wide stable area of collapse deformation compared with several tubes in compression direction. This research introduces conversion mechanism to thin-walled structure to adapt tensile direction which release from its service limitation. Tensile mechanism which called as tensile crash box using compress-expand cylindrical thin-walled tube consist of three main parts are able to absorb energy of deformation in tensile direction. Result from finite element analysis of tensile crash box was obtained that geometric parameter of compress-expand tube was highly influenced to energy absorption of tensile crash box.

Zebrafish prdm12b acts independently of nkx6.1 repression to promote eng1b expression in the neural tube p1 domain

BackgroundFunctioning of the adult nervous system depends on the establishment of neural circuits during embryogenesis. In vertebrates, neurons that make up motor circuits form in distinct domains along the dorsoventral axis of the neural tube. Each domain is characterized by a unique combination of transcription factors (TFs) that promote a specific fate, while repressing fates of adjacent domains. The prdm12 TF is required for the expression of eng1b and the generation of V1 interneurons in the p1 domain, but the details of its function remain unclear.MethodsWe used CRISPR/Cas9 to generate the first germline mutants for prdm12 and employed this resource, together with classical luciferase reporter assays and co-immunoprecipitation experiments, to study prdm12b function in zebrafish. We also generated germline mutants for bhlhe22 and nkx6.1 to examine how these TFs act with prdm12b to control p1 formation.ResultsWe find that prdm12b mutants lack eng1b expression in the p1 domain and also possess an abnormal touch-evoked escape response. Using luciferase reporter assays, we demonstrate that Prdm12b acts as a transcriptional repressor. We also show that the Bhlhe22 TF binds via the Prdm12b zinc finger domain to form a complex. However, bhlhe22 mutants display normal eng1b expression in the p1 domain. While prdm12 has been proposed to promote p1 fates by repressing expression of the nkx6.1 TF, we do not observe an expansion of the nkx6.1 domain upon loss of prdm12b function, nor is eng1b expression restored upon simultaneous loss of prdm12b and nkx6.1.ConclusionsWe conclude that prdm12b germline mutations produce a phenotype that is indistinguishable from that of morpholino-mediated loss of prdm12 function. In terms of prdm12b function, our results indicate that Prdm12b acts as transcriptional repressor and interacts with both EHMT2/G9a and Bhlhe22. However, bhlhe22 function is not required for eng1b expression in vivo, perhaps indicating that other bhlh genes can compensate during embryogenesis. Lastly, we do not find evidence for nkx6.1 and prdm12b acting as a repressive pair in formation of the p1 domain – suggesting that prdm12b is not solely required to repress non-p1 fates, but is specifically needed to promote p1 fates.

Electronic and optical characteristics of phosphorus-doped carbon nanotubes: a first principle study

The electronic and optical properties of pure, phosphorus doped infinite and finite single walled carbon nanotubes (n, 0) (n = 4, 5 and 6) with different doping degree were investigated with the combination of density functional theory (DFT) and Non-Equilibrium Green’s function (NEGF) formalisms at room temperature. It was found that depending on the chirality, phosphorus atoms may eliminate the Van Hove Singularity energy or increase the density of states (DOS) at Fermi level. Also, replacing the carbons by phosphorus atoms increases DOS at Fermi level. The π bonds between carbon and phosphorus are responsible for extraordinary DOS at Fermi level as well. Moreover, each P atom in the simulated tubes contains about 2.62e-2.94e. Replacing carbon atoms by phosphorus eventuates in the reduction of optical susceptibility and the statics refractive index. Last but not least, despite pure SWCNTs, the doping results in the lower static refractive index as well as the increment of an intraband optical gap for the parallel to tube axis polarization through P-SWCNTs.

Fabrication of an ultra‐thick‐oriented 3C‐SiC coating on the inner surface of a graphite tube by high‐frequency induction‐heated halide chemical vapor deposition

AbstractCubic SiC (3C‐SiC) is a promising material for nuclear industry applications due to its excellent properties. In this report, a highly oriented thick 3C‐SiC coating with good crystallinity was prepared on the inner surface of a monolithic graphite tube via high‐frequency induction‐heated halide chemical vapor deposition using SiCl4, CH4, and H2 as precursors. The texture coefficient (TC(hkl)), microstructure, and deposition rate along the tube axis was studied. 3C‐SiC coating with a high (111) orientation and crystallinity was obtained. Along the tube axis, TC(111) was consistent with the temperature distribution. The surficial morphology of the 3C‐SiC coating changed from pebble‐like to hexangular facet and then to hemispherical. The deposition rate and coating thickness were 300 μm/h and 615 μm, respectively, which is sufficiently rapid and thick enough to obtain free‐standing SiC tubes for nuclear reactors.

Reconnection of vortex tubes with axial flow

This paper addresses the interaction of initially anti-parallel vortex tubes containing an axial flow that induces a twisting of the vortex lines around the tube axes, using numerical simulations. Vortex tube configurations with both the same and opposite senses of twist -- corresponding to same and opposite signs of kinetic helicity density -- are considered. It is found that the topology of the reconnection process is very different between the two cases. For tubes with the same sense of twist, the reconnection is fully three-dimensional (3D): vortex lines reconnect at a finite angle, and 3D vortex null points may be created. Following reconnection the vortex line topology in both bridge and thread structures exhibits a high degree of complexity. For oppositely-twisted tubes the reconnection is locally two-dimensional, occurring along vorticity null lines, that in contrast to the untwisted case are not perpendicular to the tube axes. This leads to a break in the symmetry between the two vortex bridges generated during reconnection. For all cases studied, increasing the twist in the vortex tubes leads to a later, faster, and more complete reconnection process.

Comparative prediction of binding affinity of Hydroxyurea anti-cancer to boron nitride and carbon nanotubes as smart targeted drug delivery vehicles

In this study, the adsorption of Hydroxyurea (HU) onto the inner and outer surfaces of boron nitride and carbon nanotubes (CNTs) was investigated using the density functional theory calculations and molecular dynamics (MDs) simulations in aqueous solution. The values of the adsorption energy show that HU molecule is preferentially adsorbed inside of boron nitride and CNTs with the molecular axis parallel to the tubes axis, which means that the cavity of nanotubes is favorable for encapsulation of this drug. Also, it was found that the HU/boron nitride nanotube (BNNT) system is more stable than the HU/CNT system. The stability of the complexes of HU/ BNNT attributed to the formation of the intermolecular hydrogen bonds between the H atoms of HU molecule and the N atoms of BNNT, which is confirmed by Bader’s quantum theory of atoms in molecules. The natural bond orbital analysis shows the charge transfers occur from HU molecule to nanotubes in all complexes. Moreover, the adsorption of HU molecule on the surfaces of the nanotubes was investigated by explicit water models. Also, the adsorption behavior of HU on the functionalized boron nitride and CNTs is investigated to design and develop new nanocarriers for biomedical applications. Furthermore, MDs simulations are examined in the presence of one and two drug molecules. The obtained results illustrate that the lowest value of Lennard–Jones (L–J) energy between drug and nanotubes exist in the simulation system with two drug molecules.

Numerical investigation of heat transfer for elliptical tube in granular flow using DEM

Moving bed heat exchangers take important part in terms of extracting heat from granular materials. Circular tube is main part of heat exchanger in most studies and implements. Two heat transfer deterioration zone for circular tubes in granular flow is found and results in a low heat transfer coefficient. Elliptic tubes receive increase attention recent years for their better heat transfer performance for fluid. In this work numerical investigation based on DEM has been produced to obtain heat transfer performance of elliptic tubes in granular flow with different axis ratio. The result shows that elliptic tubes with axis ratio from 1.2 to 2.0 have a narrower area of heat transfer deterioration in granular flow and consequently a higher effective heat transfer coefficient from than circular tube (axis ratio =1.0) with the same long axis.

A high precision 3D reconstruction method for bend tube axis based on binocular stereo vision.

Previous stereo-vision based methods for measuring bent tube axis usually approximate the centerlines of image contours as the axis projection, inevitably resulting in reconstruction errors. This phenomenon is more significant as the tube diameter increases. In this paper, a perspective projection model for any cross section of bent tube was established. Based on this model, a way to locate the precise projected position on image planes of points laying on axis was proposed and 3D coordinates of axis points are reconstructed by binocular stereo vision. We measured three bent tubes with different diameters. Compared with classical approaches, this method effectively reduces the reconstruction errors with measurement accuracy practically independent of diameter.

How external buoyancy controls the Marangoni convection for a volatile meniscus inside a pore

In this experimental investigation we use a localised heating source on the bottom side of a horizontally positioned square capillary tube of 1 mm side length, inside which an ethanol meniscus pinned at one of the tube mouth undergoes evaporation in still air. We use Infra-Red thermography to map the temperature distribution along the meniscus interface and Particle Image Velocimetry in the meniscus liquid phase to characterise the fluid motion. As already reported in the literature, the unheated case shows that there is an asymmetry in the temperature profile in vertical cross sections of the tube and this in turn distorts the Marangoni vortex structure. This asymmetry brought by gravity was thought to operate along the meniscus interface inside the tube; instead, we show in this study that the descending cold plume that develops around the capillary tube seems to be ultimately responsible for the temperature distribution at the meniscus wedge around the tube. When we impose a localised heating on the bottom side of the capillary tube, the temperature profile along the vertical diametrical section of the tube becomes symmetrical and the resulting flow pattern becomes also symmetrical with respect to the tube axis, as confirmed by the particle image velocimetry measurements. When more heating is introduced at the bottom side of the tube, the symmetry in the flow is lost again and the toroidal Marangoni vortex spins in the direction opposite to that of the unheated case.This heat and mass transfer problem seems to be diffusion controlled by the amount of vapor in the air surrounding the capillary tube for what concerns the evaporation; the shape and intensity of the Marangoni vortex in the meniscus liquid phase seems also dictated by what happens around the tube rather than inside of it.

Modeling and simulation for cross-sectional ovalization of thin-walled tubes in continuous rotary straightening process

Cross-sectional ovalization of thin-walled circular steel tube caused by large plastic bending usually occurs at initial large bending stage in tube's continuous rotary straightening process. When the bending loads have been removed, there must be residual ovalization kept on the tube's cross-section during the whole straightening process, to induce the poor roundness and the reduction of the tube flexural stiffness. So the maximal residual cross-sectional ovalization should be predict accurately in order to be controlled under the allowable limit during the straightening process. In this paper, this issue is studied by the approaches of simulations and theoretical modeling. Firstly the finite element (FE) simulations for thin-walled tube straightening process are carried out on stainless steel tubes with different geometric parameters under different working rolls' bending radii, to measure the residual cross-sectional ovalization along the circumferential direction. The results imply that the profile of deformed cross-section is not standard ellipse and the appearance of the maximum residual ovalization is usually found in the direction perpendicular to the tube's centroid axis. Secondly the theoretical modeling procedure is carried out as follows. First of all, the normal strain and stress components are derived using the thin-shell large deformation kinematics. Then the cross-sectional ovalization in loading process is analyzed by the principle of virtual work. And then using the general geometric description without the elliptical assumption, a rational model is derived by the classic unloading rule to predict the maximal residual cross-sectional ovalization of thin-walled tube in straightening process. It is solved iteratively using Matlab ode23s function. The theoretical results are compared with the simulation ones. The relative errors are lower than 10%, which validates the effectiveness of the new model. Meanwhile the influences of tube's material, thickness and bending radius on maximum residual ovalization are found.

Analysis of AGP contribution to the dynamic assembly and mechanical properties of cell wall during pollen tube growth

Arabinogalactan proteins as cell wall structural proteins are involved in fundamental processes during plant development and growth. The aim of this study was to evaluate AGP function in the distribution of pectin, cellulose and callose along Fragaria x ananassa pollen tube and to associate the cell wall structure with local mechanical properties. We used Yariv reagent which interacts with AGPs and allows the observation of the assembly of cell walls without AGPs performing their function. Cytochemical, immunofluorescence labelling and atomic force microscope have been used to characterize the changes in cell wall structure and stiffness. It was shown that disordering of the structure of AGP present in cell walls affects the localization of cellulose, pectins and the secretion of callose. Changes in cell wall assembly are relevant to pollen tube mechanical properties. The stiffness gradient lengthwise through the axis of the pollen tube has demonstrated a significantly higher Young’s modulus of the shank region than the growth zone. It has been revealed that the apex of the pollen tube cultured in the presence of Yariv reagent is stiffer (1.68 MPa) than the corresponding region of the pollen tube grown under control conditions (0.13-0.27 MPa). AGP affects the structure of the cell wall by changing the distribution of other components and the modification of their localization, and hence it plays a significant role in the mechanical properties of the cell wall.

Incremental forming characteristics of hollow parts with grooves

Incremental profile forming (IPF) is a new plastic processing technology developed in recent years. The new profile manufacturing technology is mainly used to produce tubular parts with variable cross sections along the axis of tube. The parts with different cross sections produced by this technology satisfy the lightweight and high strength requirements of the tubular parts. The IPF method is very flexible and can form diverse complex-shaped parts. Because no special machine is available for this technology, depending on the shapes of formed tubular parts, the forming tool and forming method should be designed. Thus, this study proposes a new method to form the annular groove and tube wall groove. Using a special tool and servo drive system of spinning machine, it is possible to form an annular groove and tube wall groove on the surface of tubular part. This is a typical IPF method for tubes. The process of different grooves on the surface of tubes was systematically studied in this paper. Through experiments and finite element simulations, different process parameters influencing the forming quality of groove were studied. It was concluded that the tool’s single feed and spindle speed significantly affect the forming quality and forming limit.

Effect of Non-uniform Convection on Entropy Generation and Enthalpy for the Laminar Developing Pipe Flow of a High Prandtl Number Fluid

In a boundary wall of a pipe for developed laminar flow, to find the best example in which the least enthalpy and entropy are created, non-uniform distribution of convective flow in wall is studied. Some factors are simulated for transfer coefficient heat variations of moving the pipe. Distribution of temperature, entropy and enthalpy along the radius and distribution of generated entropy and enthalpy along the tube axis are shown. Entropy and enthalpy are reduced along the axis. Entropy, except some areas close to the wall, is increasing along the radius. Temperature and enthalpy, approaching the wall along the radius, have increased.

Electro-osmotic pumping through a bumpy microtube: Boundary perturbation and detection of roughness

To machine precision, a micro-duct cannot be fabricated without producing surface roughness. It is of essential importance to examine the effects and predict the level of roughness on electro-osmotic (EO) pumping for ducts of fundamental shapes. In this study, we consider a bumpy microtube with its wall shape modeled by the product of two sinusoidal functions. Boundary perturbation is carried out with respect to the amplitude roughness ε (relative to the Debye length) up to the second-order by considering the Debye-Hückel approximation and viscous Stokes equation for the electrolyte transport. Besides the amplitude roughness ε, the key parameters include the azimuthal wave number n and the axial wave number α of the bumpiness, as well as the non-dimensional electrokinetic width K. It is shown that the EO pumping rate Q is modified by a second-order term −ε2πχ, namely, Q = Q0 − ε2πχ, where Q0 denotes the pumping rate through the smooth tube. The net effect χ = χ1 + χ2 comprises two components: χ1 = χ1(K) < 0 increases with increasing K, representing a pure gain, while χ2 has no definite sign and is a complex function of K, n, and α. In particular, χ is negative at small α whilst being positive at large α, and the dividing line of signs also depends on K. For small α (<1), χ increases with increasing n at all K, while for large α (>1), χ decreases with increasing n at large K (>20). For a given number of oscillations Ac = nα (>1), there exists an intermediate n at which the EO pumping rate is maximized at small K (<20). Moreover, we identify a long-wavelength limit singularity in the EO pumping rate as α → 0 for all n, i.e., in the longitudinal sense. In addition, the velocity component along the tube axis is modified by a second-order term of the roughness, though the same velocity component near the wavy wall exhibits periodic behaviors in phase with the wall roughness. Physical reasoning is given to all the derived mathematical results, and their implication in practical applications as a model for predicting tube roughness is explained. As the tube shape represents a conduit of practical use, a particular emphasis is placed upon potential applications of the derived result.

Spin—Orbital Optical Minigaps in Silicon Nanotubes Si (n, n)

The electron structure of silicon metal nanotubes Si (n, n) was calculated by the linearized augmented cylindrical wave (LACW) method with account for spin—orbital coupling. The calculations predict the formation of minigaps in hexagonal silicon nanotubes with energies of 1.89 ≥ Eg ≥ 0.34 meV for 5 ≤ n ≤ 20 due to the coupling of the electron spin with the electron orbital moment associated with the rotation of electrons around the tube axis.

Mass-growth of a finite tube reinforced by a pair of helical fibres

Several types of tube-like fibre-reinforced tissue, including the layers of arteries and veins, different kinds of muscle, biological tubes as well as plants and trees, are reinforced by a pair of helical fibres wound symmetrically around the tube axis in opposite directions. In many cases, this kind of biological structures grow in an axially symmetric manner that preserves their own shape as well as the direction and shape of their embedded pair of helical fibres. This study considers and investigates the influence that preservation of fibre direction exerts on pseudo-elastic (elastic-like) mass-growth modelling of the described fibre-reinforced structure. Complete sets of necessary conditions that enable the implied axisymmetric tube mass-growth to take place are sought, found and presented. These hold in addition to, and simultaneously with standard kinematic relations and equilibrium equations met in conventional hyperelasticity. They thus render this mass-growth mathematical model the properties of an apparently overdetermined boundary value problem. However, the additional information they provide leads to identification of admissible classes of strain energy densities for growth that enable realisation of the implied type of tube mass-growth. The analysis is applicable to several different types of mass-growth of tube-like tissue reinforced by a pair of symmetrically wound helical fibres. This is demonstrated with an application which considers that mass-growth of the fibre-reinforced tube takes place in an incompressible manner; namely, in a non-isochoric manner that along with fibre direction, it also preserves the material density of the growing tube.

Effect of Fiber Angles on Hybrid Double‐Tube Concrete Columns under Monotonic Axial Compression

Hybrid double‐tube concrete columns (hybrid DTCCs) are a novel form of hybrid columns that combine fiber‐reinforced polymer (FRP) composites with two traditional construction materials (i.e., concrete and steel). Hybrid DTCCs consist of an outer FRP tube and an inner steel tube aligned concentrically, with the space between the two tubes and inside of the steel tube filled with concrete. The three materials (i.e., FRP, concrete, and steel) in hybrid DTCCs are combined optimally to deliver excellent performances, such as excellent ductility and remarkable corrosion resistance. Recently, hybrid DTCCs have received increasing research attention on their compressive behavior. Existing studies, however, are focused on hybrid DTCCs with fibers of the FRP tube oriented in the hoop direction or close to the hoop direction. Against this background, this paper presents a series of monotonic axial compression tests on hybrid DTCCs with a particular focus on the effect of fiber angles (i.e., the angle of the fiber orientations to the longitudinal axis of the FRP tube). Three types of fiber angles (i.e., ±45°, ±60°, or ±80°) and two FRP tube thicknesses (i.e., 4 mm and 8 mm) were employed in the present study. Experimental results show that the concrete in hybrid DTCCs is well confined by both the FRP tube and the steel tube, leading to excellent ductility; the confinement effect of the FRP tube increases with the increase of the absolute value of fiber angles, whereas the ultimate axial strain decreases with the increase of the absolute value of fiber angles. An existing analysis‐oriented model, which considers the different confining states of the concrete between the two tubes and that inside of the steel tube, is verified using the present test results. The model is capable of providing accurate predictions for hybrid DTCCs with a ±80° FRP tube. For hybrid DTCCs with a ±45° or ±60° FRP tube, the model yields reasonable accurate predictions for the peak axial load but underestimates the ultimate axial strain consistently.

A Numerical Study on Jet Structure and Noise Emission of Underexpanded Radial Jet

In this study, an underexpanded radial jet issuing from a small gap between two circular tubes facing each other is investigated numerically. Radial jet is formed, for example, downstream of high-pressure valves in piping system and of poppet valves in engines, and causes many industrial problems such as the noise generation and the fatigue failure of structure. In this study, the jet issuing from a small gap between two tubes with same diameter is numerically simulated. The flow field is assumed to be axisymmetric against the central axis of tubes and to be symmetric against the intermediate plane between the exits of two tubes. The axisymmetric Euler equations are solved using symmetric TVD (Total Variation Diminishing) scheme. The effects of nozzle pressure ratio and of diameter of circular tubes on the structure and the behavior of jets are examined. Typical cell structure of underexpanded jet appears in radial jet and the length of cell becomes smaller in downstream region because the jet spreads radially like a disc. The length and width of first cell are larger with higher nozzle pressure ratio. Many vortices are generated one after another near the jet boundary and move downstream, which cause the oscillation of jet. Outside of jet, two types of density waves are observed. One of them propagates toward the nozzle (toward the upstream region) and the other propagates in opposite direction. Focusing on the pressure change caused by the former waves, which is related to well-known screech, dominant frequency obtained by FFT analysis was found to become lower with higher pressure ratio and smaller diameter of tube.