Function Of Tube Length Research Articles

OPTIMIZING DIAMETER, LENGTH, AND WATER IMMERSION IN FLOW RESISTANT TUBE VOCALIZATION

The objective was to quantify the range of airflow resistance and oral pressure attainable with variation of length, diameter, and water immersion depth of tubes and straws. Pressure-flow equations for tubes, determined previously for variable tube geometries, were used to calculate oral pressure ranges. Human subjects were then recruited to use the variable tube geometries to produce oral pressures, which were quantified with commercial manometers. Nomograms for airflow resistances and oral pressures are plotted as a function of tube length, tube diameter, and water insertion depth. It is shown that tube diameters in the range of 2.5-3.0 mm with tube lengths of 10-40 cm produce oral pressures in the range of 10-40 cm H2O. Insertion of the distal end into water adds a pressure in the amount of the depth of insertion. Maximum power transfer with different tube geometries is discussed.

Benchmark study of ionization potentials and electron affinities of armchair single-walled carbon nanotubes using density functional theory

The intrinsic parameters of carbon nanotubes (CNTs) such as ionization potential (IP) and electron affinity (EA) are closely related to their unique properties and associated applications. In this work, we demonstrated the success of optimal tuning method based on range-separated (RS) density functionals for both accurate and efficient prediction of vertical IPs and electron affinities (EAs) of a series of armchair single-walled carbon nanotubes C20nH20 (n = 2–6) compared to the high-level IP/EA equation-of-motion coupled-cluster method with single and double substitutions (IP/EA-EOM-CCSD). Notably, the resulting frontier orbital energies (–εHOMO and –εLUMO) from the tuning method exhibit an excellent approximation to the corresponding IPs and EAs, that significantly outperform other conventional density functionals. In addition, it is suggested that the RS density functionals that possess both a fixed amount of exact exchange in the short-range and a correct long-range asymptotic behavior are suitable for calculating electronic structures of finite-sized CNTs. Next the performance of density functionals for description of various molecular properties such as chemical potential, hardness and electrophilicity are assessed as a function of tube length. Thanks to the efficiency and accuracy of this tuning method, the related behaviors of much longer armchair single-walled CNTs until C200H20 were studied. Lastly, the present work is proved to provide an efficient theoretical tool for future materials design and reliable characterization of other interesting properties of CNT-based systems.

On The Energy Absorption of Natural Woven Silk/Epoxy Composite Tube

In this study the energy absorption response and load carrying capability of Bombyx mori (B. mori) natural silk fibre/Epoxy composite cylindrical tubes under an axial quasi-static compression was investigated. The composite tubes were prepared using mandrel assisted hand lay-up technique. The tube was fabricated using 24 layers of B. mori natural silk fibre, fully wetted with epoxy matrix. The tube was then cut into varied lengths of 50 mm, 80 mm, and 120 mm, respectively. Three specimens were tested in each category. The experimental results were analysed by measuring maximum peak load (Pmax), specific absorbed energy (SAE), and total energy absorption (TE) as a function of tube length. Findings show results being varied according to tube length in unpredictable manners. Failure fragmentation of the tubes was analysed from photographs obtained during the test using high resolution camera, which showed micro cracks induced by compression load as the predominant source of failure.

Harmonic Content in the Beam Current in a Traveling-Wave Tube

In a klystron, charge overtaking of electrons leads to an infinity of ac current on the electron beam. This paper extends the klystron theory of orbital bunching to a traveling-wave tube (TWT). We calculate the harmonic content of the beam current in a TWT that results from an input signal of a single frequency. We assume that the electron orbits are governed by Pierce’s classical three-wave, linear theory. The crowding of these linear orbits may lead to charge overtaking and, therefore, harmonic generation on the beam current, as in a klystron. We analytically calculate the buildup of harmonic content as a function of tube length from the input, and compare the results with the CHRISTINE code. Good agreement is found. Also found is the surprisingly high level of harmonic contents in the electron beam current, even when the TWT operates in the small signal regime. A dimensionless bunching parameter for a TWT, $X={(2P_{\rm{ in}}/(P_{b} C))}^{1/2}$ , is identified, which characterizes the harmonic content in the ac beam current, where $P_{{\textrm {in}}}$ is the input power of the signal, $P_{b}$ is the dc beam power, and $C$ is Pierce’s gain parameter.

Transport behavior of functionalized multi-wall carbon nanotubes in water-saturated quartz sand as a function of tube length

A series of one-dimensional column experiments was conducted to examine the effects of tube length on the transport and deposition of 4-ethoxybenzoic acid functionalized multi-wall carbon nanotubes (MWCNTs) in water-saturated porous media. Aqueous MWCNTs suspensions were prepared to yield three distributions of tube lengths; 0.02–1.3 μm (short), 0.2–7.5 μm (medium), and 0.2–21.4 μm (long). Results of the column studies showed that MWCNT retention increased with increasing tube length. Nevertheless, more than 76% of the MWCNT mass delivered to the columns was detected in effluent samples under all experimental conditions, indicating that the functionalized MWCNTs were readily transported through 40–50 mesh Ottawa sand. Examination of MWCNT length distributions in the effluent samples revealed that nanotubes with lengths greater than 8 μm were preferentially deposited. In addition, measured retention profiles exhibited the greatest MWCNT deposition near the column inlet, which was most pronounced for the long MWCNTs, and decreased sharply with travel distance. Scanning electron microscope (SEM) images showed that MWCNTs were deposited on sand surfaces over the entire column length, while larger MWCNT bundles were retained at grain intersections and near the column inlet. A mathematical model based on clean bed filtration theory (CBFT) was unable to accurately simulate the measured retention profile data, even after varying the weighting function and incorporating a nonuniform attachment rate coefficient expression. Modification of the mathematical model to account for physical straining greatly improved predictions of MWCNT retention, yielding straining rate coefficients that were four orders-of-magnitude greater than corresponding attachment rate coefficients. Taken in concert, these experimental and modeling results demonstrate the potential importance of, and need to consider, particle straining and tube length distribution when describing MWCNT transport in water-saturated porous media.

Effect of Ending Surface on Energy and Young's Modulus of an Armchair Single-Walled Carbon Nanotubes

The energy and Young's modulus as a function of tube length for (10, 10) armchair single-walled carbon nanotubes (SWCNTs) are investigated by using a linear scaling self-consistent-charge density functional tight binding (SCC-DFTB) method. It is found that the formula derived from total energy for a zigzag SWCNT [Physica B404, 3930 (2009)] can be also used to explain these calculated length-dependent properties. Moreover, a transition occurs from fast change of length-dependent properties of the SWCNT to their slow change. This transition corresponds to the SWCNT's length of about 5 nm. The length for the armchair SWCNT is about one half of that of the corresponding Zigzag SWCNTs. In addition, a definition of volume for a short SWCNT is discussed.

Comparison of different current collecting modes of anode supported micro-tubular SOFC through mathematical modeling

A two-dimensional model comprising fuel channel, anode, cathode and electrolyte layers for anode-supported micro-tubular solid oxide fuel cell (SOFC), in which momentum, mass and charge transport are considered, has been developed. By using the model, tubular cells operating under three different modes of current collection, including inlet current collector (IC), outlet current collector (OC) and both inlet and outlet collector (BC), are proposed and simulated. The transport phenomena inside the cell, including gas flow behavior, species concentration, overpotential, current density and current path, are analyzed and discussed. The results depict that the model can well simulate the diagonal current path in the anode. The current collecting efficiency as a function of tube length is obtained. Among the three proposed modes, the BC mode is the most effective mode for a micro-tubular SOFC, and the IC mode generates the largest current density variation at z-direction.

Electron Transport and Velocity Oscillations in a Carbon Nanotube

We report Monte Carlo (MC) simulation results showing applied bias dependent spatial velocity oscillations for semiconducting single-walled zig-zag carbon nanotubes (CNTs). MC simulations show velocity oscillations in CNTs at different lengths due to high scattering rates associated with optical phonon emissions in the one-dimensional CNT system. The frequencies of these oscillations are as high as 30 THz. In addition, we investigate average ensemble electron velocities as a function of tube length.

Numerical Simulation of Light Propagation Through Highly-Ordered Titania Nanotube Arrays: Dimension Optimization for Improved Photoabsorption

Propagation of electromagnetic waves in the ultraviolet-visible range (300 to 600 nm) through a unique highly-ordered titania nanotube array structure is studied using the computational technique of Finite Difference Time Domain (FDTD). Through numerical simulation the transmittance, reflectance and absorbance of the nanotube-arrays are obtained as a function of tube length and diameter. The nanotube-arrays are found to completely absorb light having wavelengths less than approximately 330 nm. For wavelengths above 380 nm absorption increases as a function of nanotube length, while above 435 nm absorption increases with decreasing pore size. Computational simulations closely match experimental measurements, indicating the suitability of the computational technique for guiding material optimization.

Effects of subglottal acoustics on phonation onset

The effect of subglottal acoustic loading on the vocal fold vibration was investigated using a self-oscillating mechanical model of the folds. Although the influence of the supraglottal tract on vocal fold vibration has received more attention than the subglottal system, the influence of the subglottal system on vocal fold vibration is also potentially significant, and merits investigation. In this study, the subglottal system consisted of a uniform tube connected to an expansion chamber on the flow supply end (e.g., a pseudo-lung). The length of the subglottal tube was varied systematically over a relatively large range in order to investigate the influence of subglottal acoustics on vocal fold vibration. Phonation onset and offset pressures were measured in the subglottal tube as a function of tube length. Over the range of investigation, the fundamental frequency of phonation was found to be negatively correlated with the subglottal tube length. However, both phonation onset and offset pressure were positively correlated with subglottal tube length, with the onset pressure increasing faster than the offset pressure. This hysteresis effect vanished and the two pressures merged at a small value of the subglottal tube length, indicating a change in the onset behavior from a subcritical Hopf bifurcation to a supercritical Hopf bifurcation (a codimension-2 bifurcation point). In addition, phonation did not exist below a critical subglottal tube length.

Finite-Size Effect and Wall Polarization in a Carbon Nanotube Channel

The electronic structure and dielectric screening of finite-length armchair carbon nanotubes are studied in view of their technical applications. For this purpose, a self-consistent tight-binding method, which captures the periodic oscillation pattern of the finite band gap as a function of tube length, is applied. We find the parallel screening constant E| to grow nearly linearly with the length L and to show little dependence on the band gap. In contrast, the perpendicular screening constant E┴ is strongly related to the band gap and converges for L >1 0 R (radius) to its bulk value. Our description is employed to study the wall polarization in a short (6,6) nanotube filled with six water molecules, a situation that arises with technical uses of carbon nanotubes as channels. Single-walled carbon nanotubes (SWNTs) can be classified as metallic, quasi-metallic, or semiconducting, depending on how they are wrapped up from graphene layers. 1 When SWNTs are shortened, their energy levels become quantized, which makes them suitable for applications such as quantum dots and single-electron transistors. 2 It has also been proposed that the small size and stable structure make short SWNTs good candidates for artificial nanoscale channels for transport of water, 3-6 protons, 7,8 ions, 9 or polymers. 10 Recent experiments using X-ray diffraction 11 and neutron scattering 12 provided insight into the properties of nanotube-confined water. The observations revealed a chain of water molecules wrapped by a shell of water, all encapsulated inside SWNTs with diameter around 1.4 nm. 12 These experiments confirm an earlier prediction that water can enter the hydrophobic interior of narrow SWNTs. 3-6 From the modeling point of view, artificial SWNT channels have been studied by means of molecular dynamics (MD) simulations, focusing on both filling and transport properties. 3-6 In the previous simulations, the interaction between water and the SWNT was usually treated through a short-range van der Waals potential, and little attention was paid to the polarizable nature of the SWNT. Unlike many biological channels, SWNTs are highly polarizable due to their delocalized ﷿-electrons, which respond strongly to external fields. A study of screening effects of infinitely long SWNTs to an external point charge impurity has revealed that metallic nanotubes can effectively screen out the longrange Coulomb potential along the axial direction, while screening effects in semiconducting tubes are weaker. 13 Neglecting the polarization of SWNTs could be misleading because the filling and transport properties of water are sensitive to the water-SWNT interaction. 3 Therefore, knowl

Charge distribution and stability of charged carbon nanotubes.

Density-functional calculations of charge distribution on negatively and positively charged nanotubes result in charge density profiles characterized by a significant increase of charge density at the tube ends. These results are in quantitative agreement with classical electrostatic analysis, which assumes constant electrostatic potential on the conductive tube surface. At high charging levels, the tube ends are observed to be unstable due to Coulomb repulsion. By combining ab initio calculations with classical electrostatics, we determine, as a function of tube length and geometry of the tube end, the critical voltage beyond which nanotubes are unstable.

Prediction of dissolved oxygen and carbon dioxide concentration profiles in tubular photobioreactors for microalgal culture

A model is developed for prediction of axial concentration profiles of dissolved oxygen and carbon dioxide in tubular photobioreactors used for culturing microalgae. Experimental data are used to verify the model for continuous outdoor culture of Porphyridium cruentum grown in a 200-L reactor with 100-m long tubular solar receiver. The culture was carried out at a dilution rate of 0.05 h-1 applied only during a 10-h daylight period. The quasi-steady state biomass concentration achieved was 3.0 g. L-1, corresponding to a biomass productivity of 1.5 g. L-1. d-1. The model could predict the dissolved oxygen level in both gas disengagement zone of the reactor and at the end of the loop, the exhaust gas composition, the amount of carbon dioxide injected, and the pH of the culture at each hour. In predicting the various parameters, the model took into account the length of the solar receiver tube, the rate of photosynthesis, the velocity of flow, the degree of mixing, and gas-liquid mass transfer. Because the model simulated the system behavior as a function of tube length and operational variables (superficial gas velocity in the riser, composition of carbon dioxide in the gas injected in the solar receiver and its injection rate), it could potentially be applied to rational design and scale-up of photobioreactors. Copyright 1999 John Wiley & Sons, Inc.

Prediction of dissolved oxygen and carbon dioxide concentration profiles in tubular photobioreactors for microalgal culture

A model is developed for prediction of axial concentration profiles of dissolved oxygen and carbon dioxide in tubular photobioreactors used for culturing microalgae. Experimental data are used to verify the model for continuous outdoor culture of Porphyridium cruentum grown in a 200-L reactor with 100-m long tubular solar receiver. The culture was carried out at a dilution rate of 0.05 h−1 applied only during a 10-h daylight period. The quasi-steady state biomass concentration achieved was 3.0 g · L−1, corresponding to a biomass productivity of 1.5 g · L−1 · d−1. The model could predict the dissolved oxygen level in both gas disengagement zone of the reactor and at the end of the loop, the exhaust gas composition, the amount of carbon dioxide injected, and the pH of the culture at each hour. In predicting the various parameters, the model took into account the length of the solar receiver tube, the rate of photosynthesis, the velocity of flow, the degree of mixing, and gas-liquid mass transfer. Because the model simulated the system behavior as a function of tube length and operational variables (superficial gas velocity in the riser, composition of carbon dioxide in the gas injected in the solar receiver and its injection rate), it could potentially be applied to rational design and scale-up of photobioreactors. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 62: 71–86, 1999.

Geometric boundary effects on the electronic properties of finite carbon nanotubes

Quantum finite-size effects in carbon nanotubes are studied as a function of tube length L and of the type of end structure used to terminate the tube. The “end” structures considered are: tori, open tubes terminated with H atoms, and various caps formed from hemispherical pieces of fullerenes. With different geometric boundaries there arise distinct asymptotic band-gap behaviors as a function of L: damped oscillations decaying as 1/ L, monotonic 1/ L decay, exponentially decaying, and constant. These asymptotic scaling behaviors are categorized and explained in terms of general characteristics of the frontier orbitals. Implications for nanoscale devices are briefly discussed.

Tube-worm-sediment relationships in populations of Pectinaria gouldii (Polychaeta: Pectinariidae) from Barnegat Bay, New Jersey, USA

Pectinaria gouldii (Verrill), which lives for 1 year in Barnegat Bay, New Jersey, constructs over its lifetime a conical tube of increasingly large sand grains, regardless of surrounding sediment characteristics. However, the rate of increase of mean grain size of the tube and the population density of the worm vary with sediment type. The distribution of this species is limited by sediment composition. Worms of equal length will always have equal anterior tube apertures, although the thickness of the tube walls may be unequal. Tube surface-area, worm dry weight, and tube weight all increase as a power function of tube length. The conical shape and increasing mass of the tube impose an upper limit to worm growth, but do not interfere with worm mobility.