Increasing Tube Length Research Articles

A relationship between tube length and intra‐ocular pressure after glaucoma drainage implant surgery cannot be explained by Poiseuille's law – author's reply

We thank Dr. Jansonius for his interest and thoughtful comments on our paper (Jung et al. 2013). We investigated the relationship between the tube length and intra-ocular pressure (IOP) from understanding the Poiseuille's equation. As a result, the tube length was significantly correlated with final IOP in subgroups with two glaucoma medications. That finding has to be explained in many aspects including cellular and molecular response as well as physical equation. We agree that an increase in IOP per mm increase in tube length is not huge by computing the equation as you calculated. However, Poiseuille's law definitely supports the direction of the relationship between the tube length and IOP in our study, even though the effect of it is not great. Postoperative IOP may be determined by aqueous flow both through tube and the bleb surrounding the endplate (Schwartz et al. 2006; Minckler et al. 2008). The tube made of silicone may cause cellular response and inflammation in anterior chamber or changes in the composition of the aqueous humour after glaucoma drainage valve implantation (Fiore et al. 1989; McDermott et al. 1993). Quantitatively, long tubes may develop more aggressive inflammatory cellular reaction in aqueous humour. That aqueous humour can flow to the endplate and induce severe fibrosis of bleb. That is, there is a possibility that the tube length affects the wound healing response of the bleb, although it is just an assumption. We suggest that the correlation between the tube length and IOP should be interpreted physically and biologically. Jansonius et al. mentioned that different tube lengths in eyes with various characteristics yielded our observation. We tried to find the confounding factor, but there was no significant association between tube length and diagnosis, age, axial length or preoperative IOP. We agree that surgeons should consider the tube retraction when trimming the tube. As we mentioned in our study, customization of the tube length for individual patient is definitely important for clinical application of glaucoma drainage valve. However, there is also a need to contemplate that too long tube is not unconditionally better to postoperative outcome physically and biologically. Further study will be needed to determine the effects of long tube on cellular events in anterior chamber and wound healing response of the bleb.

Proton transfer and the diffusion of H+ and OH− ions along water wires

Hydrogen and hydroxide ion transport in narrow carbon nanotubes (CNTs) of diameter 8.1 Å and lengths up to 582 Å are investigated by molecular dynamics simulations using a dissociating water model. The diffusion coefficients of the free ions in an open chain are significantly larger than in periodically replicated wires that necessarily contain D or L end defects, and both are higher than they are in bulk water. The free hydroxide ion diffuses faster than the free hydronium ion in short CNTs, unlike diffusion in liquid water, and both coefficients increase and converge to nearly the same value with increasing tube length. The diffusion coefficients of the two ions increase further when the tubes are immersed in a water reservoir and they move easily out of the tube, suggesting an additional pathway for proton transport via OH(-) ions in biological channels.

A relationship between tube length and intraocular pressure after glaucoma drainage implant surgery cannot be explained by Poiseuille's law

Jung et al. (2013) studied the effect of tube length on the intraocular pressure (IOP) after glaucoma drainage implant surgery. Referring to Poiseuille's law, they hypothesized higher IOPs in eyes with longer tubes. They tested this hypothesis in retrospective clinical data. However, this hypothesis can be tested much more directly, with a quantitative approach. With Q = 150 μl per hour (4 × 10−11 m3/s; Caprioli 1992), η = 1 × 10−3 Ns/m2 (assuming the viscosity of aqueous to be equal to that of water, which is 1 × 10−3 Ns/m2 at 20°C and somewhat lower at body temperature; Weast et al. 1984) and R = 1 × 10−4 m (a lower limit estimated from the fact that a 3–0 prolene suture, which has a diameter of 0.2 mm, fits in the tube; Rietveld & van der Steen 2004), Eqn (2) yields a change in pressure drop per unit change in tube length of 1 × 103 Pa/m, which equals 7.6 × 10−3 mmHg per mm. In other words, according to Poiseuille's law, an increase in tube length of 1 mm causes an increase in IOP of <0.01 mmHg. Jung et al. (2013) observed an increase in IOP of about 1 mmHg per mm increase in tube length. Obviously, their observation cannot be explained by Poiseuille's law. A possible explanation for their observation is that surgeons use different tube lengths in eyes with different characteristics, yielding confounding in their observational study design. In conclusion, there is no physical basis for a relationship between tube length and intraocular pressure after glaucoma drainage implant surgery. Because tube retraction is not a rare complication, surgeons should keep this in mind when trimming the tube.

Compatible and incompatible pollination and the senescence and ovary growth of Dendrobium flowers

The pollinia from five cultivars of Dendrobium (‘Miss Teen’, ‘Karen’, ‘Sakura’, ‘Willie’, and ‘Pompadour’) were placed on the stigma of openflowers of Dendrobium ‘Miss Teen’ (or ‘Kenny’). The ethylene production and post-pollination development of cross-pollinated flowerswere monitored. The pollinated flowers showed two different development patterns depending upon pollination compatibility. The firstgroup, which was pollinated with incompatible pollen from flowers of ‘Karen’ and ‘Miss Teen’, did not exhibit post-pollination symptomsand ovary growth. The second group, which was pollinated with compatible pollen from flowers of ‘Pompadour’, ‘Sakura’ and ‘Willie’,showed premature perianth senescence and induced ovary growth within a day. Compatible pollination of ‘Miss Teen’ flowers resulted inan immediate burst in the production of ethylene and a rapid ovary growth followed by an increase in pollen tube length. In contrast,when ‘Miss Teen’ flowers were self-pollinated or pollinated with ‘Karen’ pollinia, these changes did not occur. In the pollinia of ‘Pompadour’,‘Sakura’ and ‘Willie’ there were higher levels of auxin and 1-aminocyclopropane-1-carboxylic acicd (ACC ) than in those of ‘Miss Teen’and ‘Karen’. Compatible pollination also resulted in higher ACC synthase and ACC oxidase activities within 12 h after pollination than afterpollination with incompatible pollen. There was a low level of ACC oxidase activity in non-pollinated flowers and a higher ACC oxidaseactivity in the column plus pedicel than petal plus sepal and lip.

ROLE OF THREE-PHONON AND FOUR-PHONON PROCESSES IN THERMAL TRANSPORT OF SINGLE-WALLED CARBON NANOTUBES

Thermal conductivity of single-walled carbon nanotubes has been calculated considering the three-phonon and four-phonon processes. The contribution of the acoustic modes and optical modes in the relaxation rate of the phonon–phonon interaction and hence to the thermal conductivity have been considered. The thermal conductivity has been calculated for the (8, 0), (10, 0), (11, 0) and (13, 0) zigzag semiconducting nanotubes having different radii. It is found that the thermal conductivity increases linearly at low temperatures which is nearly T2 below 30 K and after reaching a peak, it decreases as aT-1 - bT-2 where a and b are constants and b &gt; a at higher temperatures. It is also found that the thermal conductivity increases with increasing radius of the tube due to the independent effect of three-phonon process and four-phonon process. The thermal conductivity is also found to decrease with increasing tube length due to four-phonon process.

Abstract 5093: Tumor angiogenesis: The role of Cathepsin L and its therapeutic intervention by the small molecule inhibitor KGP94.

Abstract Angiogenesis, the process of new blood vessel formation from pre-existing ones, is crucial to tumor growth and progression. Understanding the interplay between tumor cells and surrounding vasculature is of significant interest towards the identification of novel pro-angiogenic factors and the development of anti-angiogenic therapies. Cathepsin L (CTSL) is a cysteine protease that is up regulated in a wide range of human cancers. In transformed cells extracellular CTSL levels can increase up to 200-fold and comprise up to 40% of total secreted proteins. The role of CTSL in promoting tumor metastasis is supported by recent studies in our laboratory which have shown that treatment with the small molecule CTSL inhibitor 3-bromophenyl-3-hydroxyphenyl-ketone thiosemicarbazone (KGP94) significantly impairs the metastatic phenotype of prostate and breast cancer cells. However, the contribution of CTSL to tumor angiogenesis remains less well explored. Thus, the goal of the present studies was to evaluate the role of tumor cell secreted CTSL in tumor cell induced angiogenesis and to determine whether KGP94 treatment could inhibit this process. Upon activation by pro-angiogenic stimuli, endothelial cells migrate and invade through the interstitium to form tubes. The effect of CTSL on the migratory, invasive and tube formation capacity of endothelial cells was therefore investigated. Stimulation of human micro-vascular endothelial cells of the lung (HMVEC-L) with purified human CTSL led to a dose dependent increase in endothelial cell invasion (1.5 fold at 10ng/ml and 2 fold at 100ng/ml). Furthermore, CTSL (100ng/ml) increased the tube forming ability of endothelial cells as demonstrated by an increase in total tube length, average length of individual tube and number of tubes formed. Tumor cells secrete high levels of CTSL; therefore the effect of tumor cell conditioned media on endothelial cell migratory and invasive potential was evaluated. Incubation of HMVEC-L with conditioned media from MDA-MB-231 breast cancer cells, led to a significant increase in their migration, invasion and tube formation capacity (migration 1.3 fold; invasion 2.5 fold). These pro-angiogenic endothelial cell functions were significantly impaired in HMVEC-L treated with 10 or 25μM KGP94. For example, there was a 55% reduction in conditioned media stimulated invasiveness at 10μM and a 68% reduction at 25μM. Similarly, KGP94 treatment also significantly impaired purified CTSL and conditioned media stimulated tube formation. Interestingly, KGP94 treatment alone, did not affect the migratory or invasive capacity of unstimulated endothelial cells, suggesting that this agent might selectively impede tumor induced angiogenesis. Citation Format: Dhivya R. Sudhan, Dietmar W. Siemann. Tumor angiogenesis: The role of Cathepsin L and its therapeutic intervention by the small molecule inhibitor KGP94. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5093. doi:10.1158/1538-7445.AM2013-5093

Free vibration analysis of single-walled carbon nanotubes using a higher-order gradient theory

Free vibration characteristics of single-walled carbon nanotubes (SWCNTs) with various constraints, tube chiralities, lengths and diameters are examined using a higher-order gradient theory. The theory describes deformations of C–C bond vectors at the atomic level and links to the continuum level. The capture of curved effects of C–C bond vectors makes the established constitutive model accords extremely well with physical behaviors. Numerical simulations have been conducted using the mesh-free computational framework based on the moving Kriging interpolation. It reveals that the present method gives a good prediction of atomistic simulation results, especially in the treatment of a larger system. SWCNTs of various types of chirality are investigated and computational results reveal that the fundamental frequency increases as the tube diameter increases, until it reaches a critical diameter beyond which it decreases. As the diameter continues to increase, the change of fundamental frequency becomes smaller and smaller and converges to that of counterpart graphite sheet. The critical diameter is largely dependent on tube lengths and constraints but independent of chiralities. It is found that the increase of tube length gives rise to an increase of critical diameter. As far as constraints are concerned, the critical diameter of fixed–free style is much larger than that of the fixed–fixed style.

Molecular dynamics study on buckling of single-wall carbon nanotube-based intramolecular junctions and influence factors

Carbon nanotube-based intramolecular junctions can function as rectifying diodes and switches in circuits and thus possesses the promising potential to be applied in nano-scale electronic devices. Due to their slender and unsymmetrical geometry, intramolecular junctions are prone to buckling under compression and the resulting structural instability will eventually leads to structural or electrical failure. Thus, it is important to explore the mechanical behaviors of intramolecular junctions subject to compressive loads. In this study, molecular dynamical simulations are carried out to investigate the compressive behaviors of intramolecular junctions at finite temperature, while carbon nanotubes are also studied as reference. The simulation results indicate that the strain rate effect is negligible within relatively low loading-rate range but the critical strain increases significantly under higher loading rate. At an extremely high strain rate, the intramolecular junctions will crush immediately. It is also predicted that local deformation will be introduced at high environmental temperature. Moreover, with increasing tube length, the instability mode of the intramolecular junctions transfers from shell buckling to column buckling and the critical aspect ratio is lower than that of carbon nanotubes due to presence of the Stone–Wales defects.

Axial heat transfer correlations in a circulating fluidized bed riser

Experiments were conducted to determine the total (gas convective plus particle convective component) tube to suspension surface-average heat transfer coefficients for several vertical tubes placed in the core of a 5.5 m tall, 100 mm × 100 mm square Circulating Fluidized Bed (CFB) riser. The tubes carrying hot water were made of copper having 9.6 mm outside diameter and 0.6 mm thickness. The influence of axial location of the tube on heat transfer was studied using a 0.6 m high vertical tube placed along the riser axis at distances of 0.97, 1.62, 3.0, 4.0 and 5.3 m above the distributor plate. The effect of tube length on heat transfer was investigated using 0.6, 1.2, 2.0 and 2.5 m vertical tubes placed axially at four positions in the CFB riser, the tube mid-points being 5.2, 4.9, 4.5 and 4.25 m above the distributor plate respectively. The tubes are thus occupied about 10–45% of the riser height from the top. Sand was used as the bed material with mean diameter of 143 μm, 256 μm and 363 μm with respective densities of 2631, 2564 and 2740 kg/m3. The fluidizing air velocity and solid recycle flux were varied in the range of 4–8 m/s and 21–72 kg/m2 s respectively resulting in the average cross-sectional suspension density of 10–42 kg/m3, which is the range usually obtained in commercial boilers. It was found that the tube length and location strongly influenced the heat transfer. Heat transfer coefficients decreased with increasing tube length and with increasing axial locations from the distributor plate. Two empirical correlations for average heat transfer coefficient were developed in terms of relevant design and operating parameters including new-non-dimensional parameters for tube length (Ht/dp) and axial location (Hd/Hb). A semi-empirical heat transfer model for core tube to gas–solid suspension flow in a CFB riser in terms of Nusselt and Reynolds numbers with effective suspension properties was also presented. The semi-empirical predicts the present experimental data within ±20% and when other published data was included, the deviation was ±30%. While the modeling approach seems satisfactory, it needs refinement to improve its accuracy and consolidate all data in a more comprehensive way.

Leptin induces tube formation in first-trimester extravillous trophoblast cells

To study the roles of leptin on tube formation (as a measure of cellular angiogenesis) and expression of associated genes in first-trimester human extravillous trophoblast cells. The effects of leptin on tube formation and fatty acid uptake in first trimester extravillous placental trophoblast cells, HTR8/SVneo, were investigated. We also investigated the effects of leptin on the expression of genes involved in angiogenesis and lipid metabolism in these cells. Leptin at 25 ng/ml maximally stimulated tube formation in the first trimester placental trophoblast cells, HTR8/SVneo, by increasing tube length as well as numbers (10,100 ± 150 pixels) compared with those of control cells (2900 ± 50 pixels) p>0.05. Leptin-induced tube formation was not inhibited by the selective inhibitor of VEGF, indicating that its action was independent of VEGF. Leptin, however, significantly increased the expression of genes those are involved in angiogenesis pathways such as PECAM1, JAG1, CDH5, IL8, NRP1, SPHK1, S1PR1, CXCL 1 and 6, FGF1, EFNA3 and AKT1, as determined by PCR array. Leptin did not, however, stimulate expression of the primary angiogenic factors known in placenta such as VEGF or ANGPTL4, as determined by both qRTPCR and PCR array assays. Leptin increased 7-fold expression of FABP4, which is known to be involved in VEGF-mediated angiogenesis in endothelial cells. In addition, leptin treatment resulted a 48% increase in the uptake of docosahexaenoic acid, 22:6n-3 (DHA) which also stimulates tube formation in these cells. Leptin may play an important role in early placentation by stimulating several genes involved in angiogenic signalling pathway and fatty acid metabolism.

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.

ANALYSIS OF ENTROPY GENERATION, PUMPING POWER, AND TUBE WALL TEMPERATURE IN AQUEOUS SUSPENSIONS OF ALUMINA PARTICLES

In the present paper, the practical efficiency of using aluminaminus;water nanofluid was evaluated numerically by the method of entropy generation; pumping power and tube wall temperature were analyzed. Laminar forced convection by water-based nanofluid flow through a uniformly heated circular tube is considered. A single-phase fluid approach is adopted to investigate the behavior of nanofluid and numerical results are compared with the experimental data. Good agreement is achieved in the developed region. The aim of the present study is to investigate the influence of volume fraction, duct length, Reynolds number, and tube diameter on pumping power, entropy generation, and tube wall temperature to evaluate the nanofluid overall efficiency. The results indicated that increasing volume fraction of nanofluid for heat performance increases the pumping power exponentially and decreases the entropy generation and tube wall temperature linearly, so this suggests that using nanofluid with high volume fraction is not reasonable due to the cost of pumping power. Since it was observed that entropy generation and pumping power increase and tube wall temperature decreases relative to the duct length, this suggests that increasing tube length will reduce the overall efficiency of nanofluids. However, to avoid high wall temperature, duct length cannot be too short. Also, the results showed that increasing tube diameter will decrease entropy generation and pumping power and tube wall temperature remains constant, so it can be concluded that increasing pipe diameter will enhance the overall efficiency of nanofluids. Since the product of the diameter and length is constant, the tube diameter has the maximum value at the point which shows the maximum wall temperature; also, the duct length is minimum at this point, too. Therefore, it can be concluded that the overall efficiency of nanofluid is maximum at this point.

Finite-Length Effect of Carbon Nanotubes on the Encapsulation and Decomposition of Nitromethane: ONIOM Calculation

To understand the confinement effect of carbon nanotubes (CNTs) on energetic compounds, the encapsulation and thermal decomposition of nitromethane (NM) confined inside finite armchair (5,5) single-walled CNTs of various lengths (C30+10nH20) were investigated on the basis of ONIOM calculations. It was found that NM was not encapsulated by CNT(5,5) of n ≤ 5, while CNT(5,5) of n≥ 6 were able to encapsulate NM. The NM confined inside the CNT(5,5) displayed different structural characteristics in contrast to the isolated NM. The activation energy barriers of the C-N thermal decomposition for the confined NM were found to be about 5˜15 kcal/mol lower than that of the isolated NM, suggesting that CNT confinement enabled the C-N thermal decomposition of NM to take place more easily. In addition, our computations showed that a distinct oscillation of the activation energy barriers was correlated to tube length increase, especially when n≤ 10. This indicated that the energy barrier was highly dependent on CNT length. Keywords: Carbon nanotube, Nitromethane, Thermal decomposition, Confinement effect, Bond dissociation energy, Ab initio, encapsulation, ONIOM calculation, energetic compounds, energy barrier

Anisotropy and Transport Properties of Tubular C-BN Janus Nanostructures

By use of density functional theory and nonequilibrium Green’s function technique we have studied the electronic structure and transport properties of tubular Janus structures composed of hybridized carbon (C) and boron-nitride (BN) nanotubes (NTs) with carbon caps at both ends. The effect of chirality was probed by focusing on (5, 5) armchair and (9, 0) zigzag structures, both of which have similar radii and are metallic in the infinite length limit. The study has revealed a number of interesting properties: (1) The highest-occupied molecular orbital (HOMO)–lowest-unoccupied molecular orbtial (LUMO) gap is decreased when BN patch is inserted to zigzag structure but increased when it is inserted in the arm chair structure and graphene sheet. (2) The zigzag edges of the heterojunctions lead to anisotropy of frontier orbital distribution where the HOMO and LUMO are respectively predominated by B–C and N–C bonding states. Consequently, one side or one end becomes more reactive than the other. (3) The current in tubular Janus structures is reduced from that in pristine carbon nanotubes. At low bias, the current in the zigzag structure increases with increasing tube length while reverse is the case with the arm chair structure.

Far infrared thermal detectors for laser radiometry using a carbon nanotube array

We present a description of a 1.5 mm long, vertically aligned carbon nanotube array (VANTA) on a thermopile and separately on a pyroelectric detector. Three VANTA samples, having average lengths of 40 μm, 150 μm, and 1.5 mm were evaluated with respect to reflectance at a laser wavelength of 394 μm(760 GHz), and we found that the reflectance decreases substantially with increasing tube length, ranging from 0.38 to 0.23 to 0.01, respectively. The responsivity of the thermopile by electrical heating (98.4 mA/W) was equal to that by optical heating (98.0 mA/W) within the uncertainty of the measurement. We analyzed the frequency response and temporal response and found a thermal decay period of 500 ms, which is consistent with the specific heat of comparable VANTAs in the literature. The extremely low (0.01) reflectance of the 1.5 mm VANTAs and the fact that the array is readily transferable to the detector's surface is, to our knowledge, unprecedented.

Laminar Flow Analysis of Low Temperature Propellant Flowing through Pipes of Filling System

With aiming at the problem of liquid hydrogen flowing through filling system in space launch site, the author set up a math model of laminar flow and coupled with the analysis of laminar flow condition of liquid hydrogen in tube. Based on the computational fluid dynamics, the flow field was studied according to the numerical simulation method. Then, the changes of flow parameters i.e. pressure and velocity at the tube were observed. Simulation results showed that, in the inlet-section, there existed boundary-layer, besides, the velocity and pressure which changed continually was not stable until the liquid hydrogen flowed through on-way. In addition, the velocity distributed in the form of rotary parabolic surface whose axis was the tube’s axis itself in water-carrying section of on-way. The velocity near the surface of the tube was about zero and the pressure turned to smaller with the increase of tube length. As a result of the pressure drop, there existed the loss of on-way. The above simulation results which provided the theoretical basis for liquid hydrogen study accorded with the actual condition.

Turbulence Flow Analysis of Low Temperature Propellant Flowing through Pipes of Filling System

With aiming at the problem of liquid hydrogen flowing through filling system in space launch site, the author set up a turbulence model and coupled with the analysis of turbulence condition of liquid hydrogen in tube. Based on the computational fluid dynamics, the flow field was studied according to the numerical simulation method. Then, the changes of flow parameters i.e. pressure and velocity at the tube were observed. Simulation results showed that, in the inlet-section, there existed boundary-layer, besides, the velocity and pressure which changed continually was not stable until the liquid hydrogen flowed through on-way. In addition, in water-carrying section of turbulence flow, the velocity distribution was even and there was no obvious delamination which explained that the mix was intense. The velocity near the surface of the tube was about zero and the pressure turned to smaller with the increase of tube length. As a result of the pressure drop, there existed the loss of on-way. The above simulation results which provided the theoretical basis for liquid hydrogen study accorded with the actual condition.

Fabrication of TiO 2 nanotube arrays by electrochemical anodization in an NH 4F/H 3PO 4 electrolyte

Highly ordered TiO 2 nanotube arrays were fabricated by electrochemical anodization of titanium in an NH 4F/H 3PO 4 electrolyte. A TiO 2 crystal phase was identified by X-ray diffraction, and the morphology, length and pore diameter of the TiO 2 nanotube arrays were determined by field-emission scanning electron microscopy (FE-SEM). The anodization parameters including the rate of magnetic stirring, F − concentration, calcination temperature, anodization voltage and anodization time were investigated in detail. The results show that the as-prepared TiO 2 nanotube arrays possessed good uniformity, a well-aligned morphology with a length of 750 nm and an average pore diameter of 62 nm at a 150 rpm rate of magnetic stirring for 120 min at 20 V in an electrolyte mixture of 0.2 M H 3PO 4 and 0.3 M NH 4F with a 500 °C calcination to obtain 100% anatase phase. The adsorption of N-719 dye at different tube lengths was determined by UV-vis analysis and found to increase with increasing tube length. We also discuss the formation mechanism of the TiO 2 nanotube arrays. The findings indicate that the formation of the TiO 2 nanotube arrays proceeds by the combined action of the electrochemical etching and chemical dissolution.

Density functional theory study on nitrogen-doped carbon nanotubes with and without oxygen adsorption: the influence of length and diameter

Finite nitrogen-doped carbon nanotubes (NCNTs) with and without adsorbed O2 were systematically investigated using the B3LYP/6-31G* method. NCNTs with 10 different lengths and 9 different diameters were considered. The charge carried by the N atom and its circumjacent C atoms, the HOMO–LUMO gap, the O2 binding energy and the C–O bond length oscillate periodically as the tube length increases, whereas these values show a monotonic increase or decrease as the tube diameter is enlarged. All of the adsorbed oxygen investigated here is activated. Enlarging the tube diameter has a complicated influence on the catalytic ability of the NCNT. First, O2 adsorption becomes increasingly difficult on the surface of the NCNT, and the reactivity of the Oa atom becomes lower and lower as the tube diameter is enlarged, which reduces the reactivity of the NCNT. Second, enlarging the tube diameter creates more active centers for the adsorption and activation of oxygen, which will increase the reactivity of the NCNT.

Thermal analysis of internal condensation process in a horizontal tube of falling film evaporation

Internal condensation in a horizontal tube of falling film evaporation is of great importance in the process of low-temperature multi-effect distillation (LT-MED). Thermal analysis of internal condensation in a horizontal tube is investigated within the practical operating parameters in a LT-MED desalination plant. The analysis takes into account of the effect of interfacial shear, axial pressure gradient, saturation condensation temperature, heat transfer temperature difference, and non-condensable gas (NCG) on heat transfer characteristics of internal condensation. It is done to obtain the exact correlations that different methods to calculate axial pressure drop gradient and heat transfer coefficient are compared. The results indicate that reducing condensation temperature and increasing temperature difference contribute to improving the condensation rate of unit length for certain values of the tube length and inlet steam velocity, and that the tube length depends on the heat transfer temperature difference. The analytical results also show that the effect of interfacial shear stress on condensation rate is important while that was usually neglected in previous research, and that very small mass fraction of NCG can significantly increase the tube length as the presence of NCG reduces local temperature difference along the tube length. Besides, an increase in tube length compensates the negative effect of interfacial shear stress and NCG on internal condensation.