Increasing Tube Length Research Articles

Effect of tubular chiralities of single-walled ZnO nanotubes on electronic transport

The electronic transport properties of single-walled ZnO nanotubes with different chiralities are investigated by nonequilibrium Green's function combined with density functional theory. In this paper we consider three representative ZnO nanotubes, namely (3, 3) armchair, (5, 0) zigzag, and (4, 2) chiral, with a similar diameter of about 5.4Å. Short nanotubes exhibit good conductance behavior. As the tube length increases, the conductance decreases at low bias and the nanotubes indicate semiconducting behavior. The current-voltage characteristics of the nanotubes longer than 3nm depend weakly on the length of the tubes. The armchair and chiral ZnO nanotubes with the same length and diameter have almost overlapped current-voltage curves. The electron transport behaviors are analyzed in terms of the transmission spectra, density of states and charge population of these nanotubes. The results indicate that the resonant peaks above the Fermi level are responsible for electric currents. However, the zigzag ZnO nanotubes exhibit asymmetric current-voltage curves attributed to the built-in polarization field and give larger current than the armchair and chiral nanotubes at the same bias. The features explored here strongly suggest that the ZnO nanotubes are stable, flexible structures, which are valuable in Nano-Electromechanical System.

Numerical investigation of a CO2 loop thermosyphon in an integrated air conditioning system for free cooling of data centers

Free cooling based on loop thermosyphon is ideal energy-saving method for data centers. Most working fluids presently used in this field will cause greenhouse effect or destroy the ozone layer. It is necessary to investigate the applicability of environment friendly fluids. A distributed-parameter model of a CO2 loop thermosyphon in an integrated air conditioning system for free cooling is built and validated. The performance is compared with traditional working fluids and the effects of some key geometric parameters are evaluated. The results show that the optimal filling ratios for CO2, R22 and R134a are 120%, 100% and 90%, respectively. The circulation flow rate of CO2 is much smaller than those of R22 and R134a. For CO2 loop thermosyphon, the heat transfer rate decreases with the increase of pipe length, while increases with the increase of riser diameter and height difference. The heat transfer rate increases with the increase of tube number and length of the evaporator, while the increasing rate decreases gradually. The optimal tube number and length are 80 and 0.6m, respectively. The relationships between the above phenomenon and the internal flow state are also analyzed.

Effect of a cross-flow perforated tube on pressure pulsation and pressure loss in a reciprocating compressor piping system

This paper experimentally investigates the effects of a cross-flow perforated tube on the pressure pulsation attenuation and pressure loss in a reciprocating compressor piping network, with particular focus on the structure parameters and installation positions. The results demonstrate that significant pressure fluctuation attenuation and less pressure loss in the whole piping system can be achieved when a well-designed cross-flow perforated tube is installed downstream of the pulsating bottle. The pressure pulsation is reduced as the perforated rate decreases and as the perforated tube length increases, while the hole diameter has little effect upon the pulsation attenuation. In the aspect of reducing pressure loss, the perforated rate should be larger than 0.05 and the hole diameter should be larger than 8 mm. In addition, a pressure pulsation computation model based on the linear acoustic wave theory and transfer matrix method is developed to predict the pulsating pressure in compressor piping systems with an installed cross-flow perforated tube. With favorable agreement between the model prediction and the present experimental results (maximum deviation within 6.8%), the predicted pulsating pressure can be attenuated for the reciprocating compressor piping system with various compressor speeds when a cross-flow perforated tube is reasonably designed and installed.

Experimental study on spontaneous ignition and flame propagation of high-pressure hydrogen release via a tube into air

Spontaneous ignition and subsequent flame propagation of high-pressure hydrogen release via a tube into air are experimentally investigated using pressure records, flame detection and direct high-speed photographs. The study shows that as the burst pressure increases the likelihood of spontaneous ignition increases and the initial ignition is closer to the burst disk. With the increase of tube length, the possibility of spontaneous ignition increases, while the critical release pressure for spontaneous ignition decreases. It is also found that a strong shock wave generated to trigger the ignition and a long tube to promote the growth of the flame are two key factors for the transition from spontaneous ignition inside the tube to jet flame in the air. After the flame exits from the tube, a flame envelope is formed in the front of the hydrogen jet, which gradually splits into upstream and downstream combustion regions. The upstream flame region propagates forward. However, the downstream flame region moves back toward the tube exit. The flame is then stabilized at the tube exit and gradually grows. Noticeable deflagration events were observed to occur successively in the semi-enclosed space. The deflagration leads to a significant increase of pressure in the chamber. And the overpressure of the deflagration is higher than that of the leading shock wave. Both the overpressures of the leading shock wave and the deflagration increase with the release pressure. A stable jet flame is formed outside the tube subsequent to the deflagration. And different jet flame configurations are observed at different controlling mechanisms of flow.

Effect of Ethylene Flow Rate and CVD Process Time on Diameter Distribution of MWCNTs

To date, focus of the research activities in nanoscience was to control the chemical vapor deposition (CVD) growth of carbon nanotubes (CNTs) by changing the precursor pressure and process temperature. The effect of the precursor flow rate and process time on CNTs growth parameters has been overlooked in past studies and therefore is very little known. This study was focused on the optimization of the ethylene flow rate and CVD process time for CNTs growth over Fe2O3/Al2O3 catalyst in a fluidized bed chemical vapor deposition (FBCVD) reactor, operating at atmospheric pressure. Argon and hydrogen were considered as the carrier and supporting gases, respectively. Transmission electron microscope (TEM) and Scanning Electron Microscopy (SEM) were used to investigate the surface morphology, nanostructures, purity and yield of the grown CNTs. In-depth analysis revealed an increase in tube length, yield and the carbon concentration with ethylene flow rate in the range of 50–110 sccm. However, an inverse relationship between flow rate and tube diameter distribution was predicted in the given work. The most favorable results were obtained at an ethylene flow rate of 100 sccm and a CVD process time of 60 minutes. The dense and homogeneous growth of relatively pure nanotubes of increased tube length and narrow diameter distribution, in the range of 20–25 nm, was observed at optimized flow rate and process time.

TiO2 Nanotube arrays: Influence of tube length on the photocatalytic degradation of Paraquat

Highly ordered TiO2 nanotubes have attracted a lot of attention for the photocatalytic removal of organic pollutants. A few studies demonstrated that the tube morphology plays a key role on the photocatalytic activity. However, no studies have been performed to explain the optimal photocatalytic activity observed for a precise tube length. Here we studied how the morphology of the tubes evolves during anodic growth and we evaluated the corresponding photocatalytic activity. In our conditions, the optimal activity was found for 7μm long tubes. The SEM study reveals that short tubes have a small pore opening thus hindering pollutant diffusion into the tubes. On the other hand, tubes longer than 7μm have thinner walls due to etching by the fluoride ions. Consequently the volume of TiO2 decreases strongly in the upper part of the tubes as the tube length increase and light should travel a longer pathway before absorption and production of electron-hole pairs. Hence the organic species have to diffuse further and the photocatalytic activity decreases.

Economy, efficiency, and the evolution of pollen tube growth rates.

Pollen tube growth rate (PTGR) is an important aspect of male gametophyte performance because of its central role in the fertilization process. Theory suggests that under intense competition, PTGRs should evolve to be faster, especially if PTGR accurately reflects gametophyte quality. Oddly, we know remarkably little about how effectively the work of tube construction is translated to elongation (growth and growth rate). Here we test the prediction that pollen tubes grow equally efficiently by comparing the scaling of wall production rate (WPR) to PTGR in three water lilies that flower concurrently: Nymphaea odorata, Nuphar advena and Brasenia schreberi. Single-donor pollinations on flower or carpel pairs were fixed just after pollen germination (time A) and 45 min later (time B). Mean PTGR was calculated as the average increase in tube length over that growth period. Tube circumferences (C) and wall thicknesses (W) were measured at time B. For each donor, WPR = mean (C × W) × mean PTGR. Within species, pollen tubes maintained a constant WPR to PTGR ratio, but species had significantly different ratios. N. odorata and N. advena had similar PTGRs, but for any given PTGR, they had the lowest and highest WPRs, respectively. We showed that growth rate efficiencies evolved by changes in the volume of wall material used for growth and in how that material was partitioned between lateral and length dimensions. The economics of pollen tube growth are determined by tube design, which is consequent on trade-offs between efficient growth and other pollen tube functions.

Axial vibration of single-walled carbon nanotubes using doublet mechanics

This paper investigates the axial vibration of single-walled carbon nanotubes based on doublet mechanics with a length scale parameter. A forth-order partial differential equation that governs the axial vibration mode of single-walled carbon nanotubes is derived. Using doublet mechanics, the relation between natural frequency and length scale parameter is derived in the axial mode of vibration. It is shown that length scale parameter plays significant roles in the axial vibration behavior of single-walled carbon nanotubes. Such effect decreases the natural frequency compared to the predictions of the classical continuum mechanics models. However, with increasing tube length, the scale effect on the natural frequency decreases.

Hydrogen physisorption and selectivity in single-walled silicon carbon nanotubes: a grand canonical Monte-Carlo study

We report grand canonical Monte-Carlo simulations of pure hydrogen physisorption and its binary mixtures with nitrogen and methane H/N2H2/CH4 in single-walled silicon carbon nanotubes (SWSiCNTs). We investigate the effect of temperature, pressure, tube diameter and the influence of the presence of the second molecule on the adsorption of hydrogen. Some obtained results have compared with that of boron nitride and carbon nanotubes and it shows that the SWSiCNT has more hydrogen adsorbable than single-walled boron nitride (SWBNNT) and carbon nanotube (SWCNT) in same chirality of nanotube and same thermodynamic conditions. Furthermore, the influence of tube length on hydrogen adsorption capacity has been illustrated in various SWSiCNT, SWBNNT and SWCNT and the calculations show that the hydrogen adsorption holds the line when the tube length increases. In addition, pure hydrogen adsorption is investigated in rhombic and square SWSiCNT arrays, while the results of this investigation illustrate that rhombic and square SWSiCNT arrays have gravimetric hydrogen capacities between rhombic and square silicon and carbon nanotube arrays, in same thermodynamics conditions and same tube diameters. The simulation data of pure hydrogen fit to Langmuir, Freundlich and Langmuir–Freundlich equations and the Langmuir–Freundlich equation has the best behavior fitting to hydrogen adsorption data; it emphasizes that the multi-layer pure hydrogen adsorptivity occurs more prominently in SWSiCNTs. Also, the excess and delivery isotherms of hydrogen were calculated for various SWSiCNTs, SWBNNTs and SWCNTs. Furthermore, the adsorption selectivity in different mole fractions of hydrogen/methane and hydrogen/nitrogen mixtures in SWSiCNTs has investigated at 77 and 298 K on (8,8) and (15,15) SWSiCNTs, and results show that selectivity-based adsorption decreases at 298 K in both mixtures while increasing pressure and temperature can increase selectivities and the selectivity is not related to the diameter of nanotubes.

Vertical Mode Gas Sensing Performance of TiO2 Nanotube Array by Tuning of Surface Area and Carrier Transport Length

1-D oxide nanostructures-based metal-insulator–metal structures represent potential gas sensor devices, owing to their vertical electron transport feature. In this paper, we demonstrate that for achieving optimum gas sensing by a TiO2 nanotube (NT) array in vertical mode, tuning of NTs (1-D) surface area as well as carrier transport path length by tailoring the NT length can be a valuable approach. For anodization times of 1, 4, 8, 12, and 16 h, the corresponding NT length was found to be 280–320, 506–514, 1730–1790, 2000–2200, and 2380–2420 nm, respectively, with almost no variation in tube diameters or separations. The carrier concentrations of the NTs were found to be decreasing with increasing tube length. The vertical device structure, employing NT arrays of different lengths as the sensing layer, was investigated in the temperature range of 50 °C–250 °C for sensing acetone, as a test gas/vapor, in the concentration range of 10–1000 ppm. The response magnitude of the sensor was increased with increased NT length, possibly owing to the availability of larger amounts of gas interaction sites due to higher surface area at increased length. The response time and recovery time of the developed sensor also increased with increasing tube length and became excessively sluggish after the critical tube length exceeded 2250 nm owing to slower adsorption/desorption and diffusion kinetics.

Effect of design parameters on thermodynamic losses of the heat transfer process in LT-MEE desalination plant

Thermodynamic losses caused by the flow resistances and the boiling point elevation (BPE) in low-temperature multi-effect evaporation (LT-MEE) desalination plant were investigated. The purpose is to provide detailed considerations for the design and modeling of LT-MEE process. Design parameters were analyzed to evaluate their effects on thermodynamic losses. Results indicate that on the premise of constant distillate production, as the sequence number of evaporator/condenser increases, each flow resistance decreases first and then increases, while the variation of corresponding temperature depression always performs a rising tendency. With the increase of tube length, the proportion of saturated temperature depression caused by the in-tube condensation flow resistance increases, and that caused by the inter-tube flow resistance decreases. The tube length for the lowest temperature depression occurs when two temperature depressions are in similar proportions. The thermodynamic losses caused by the flow resistances and the BPE account for considerable percentages, especially when under smaller temperature difference. The operating characteristics of LT-MEE desalination plant are summarized based on the analysis.

Abstract 4185: Role of Cathepsin L in breast cancer angiogenesis

Abstract Recognition of the dependence of angiogenesis on proteolytic enzymes has raised significant interest in evaluation of proteases as potential targets to disrupt tumor angiogenesis. While the role of cysteine proteases in tumor metastasis is well understood, their contribution to tumor angiogenesis remains less explored. Cysteine cathepsins, in particular cathepsin L (CTSL) gets are upregulated 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. 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. Similarly, 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). Compared to parental MDA-MB-231 breast cancer cells, CTSL knockdown cells that were inoculated intradermally into ventral skin flaps of female nude mice showed a significant reduction in their ability to induce blood vessel formation (3.5-fold).These proangiogenic endothelial cell functions were accompanied by a significant increase in endothelial cell proliferation upon stimulation with purified CTSL (2-fold). Microarray analyses revealed a significant upregulation of cell cycle related genes by CTSL. Western blot analyses further confirmed upregulation of members of the cyclin family by CTSL. In conclusion, our findings suggest that in addition to its pro-metastatic function, CTSL might further contribute to tumor progression by eliciting various pro-angiogenic endothelial cell functions. Citation Format: Dhivya Sudhan, Belen Rabaglino, Charles Wood, Dietmar Siemann. Role of Cathepsin L in breast cancer angiogenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4185. doi:10.1158/1538-7445.AM2015-4185

Long Vertically Aligned TiO2 Nanotube Electrodes Prepared via Two‐Step Anodization for Highly Efficient Photovoltaics

AbstractVertically aligned long TiO2 nanotube (NT) electrodes with optimized structures for photovoltaic application were prepared by a two‐step anodization method. The structures of the conventional TiO2 NT electrodes prepared by one‐step anodization became severely bundled and disordered for tube lengths exceeding 20 μm. On the other hand, two‐step anodization resulted in uniform and bundle‐free TiO2 NT electrodes, with tube lengths of up to 38 μm. When used in dye‐sensitized solar cells (DSSCs) as photoanodes, the two‐step TiO2 NT electrodes exhibited enhanced short‐circuit current density (Jsc) with increasing tube length, owing to an increased roughness factor, which resulted in high dye loading. However, the dark current and open‐circuit voltage decay (OCVD) curves confirmed that the electron recombination rate increased, and the electron lifetime decreased, with increasing tube length. This reduced electron lifetime resulted in sharp reductions in the open‐circuit voltage (Voc) with increasing tube length. Owing to the trade‐off between the enhanced current density and the reduced electron lifetime, an optimal conversion efficiency of 4.56 % was obtained for a tube length of 29 μm.

P61 * CATHEPSIN K IN AN IN VITRO MODEL OF GLIOMA ANGIOGENESIS

INTRODUCTION: Cathepsin K, a cysteine protease expressed in osteoclasts, involved in bone resorption is expressed in other cells including brain cells. Reports suggest that cathepsin K may be involved in cancers associated with bone metastasis. Little is known about its expression in brain tumours. There is evidence of a potential interaction of cathepsin K with stromal cell derived factor 1 (SDF-1) in haemapoietic stem cell motility. Because of the importance of SDF-1 in brain tumour angiogenesis and recruitment of glioma like stem cells to vascular niches, we investigated cathepsin K in an in vitro model of angiogenesis. METHOD: Brain endothelial cells (hCMEC) and glioma cell lines (SNB-19 and UP-007) cultured under normoxic and hypoxic conditions were analysed using flow cytometry and western blotting. Angiogenesis was assessed using an in vitro model of brain endothelial cell tube formation. Brain endothelial tube length, number of tube projections and number of branch points were measured. RESULTS: Under hypoxic conditions, there is a significant decrease in cathepsin K expression in brain endothelial cells when compared to normoxic conditions (P ≤ 0.05). Addition of Odanacatib, a cathepsin K inhibitor, to the angiogenesis assay revealed that inhibition of cathepsin K resulted in a significant increase in endothelial tube length in normoxic conditions (p < 0.05). CONCLUSION: The decrease in cathepsin K expression in endothelial cells under hypoxia, coupled with the increase in tube length following inhibition of cathepsin K, suggests an involvement of cathepsin K with angiogenesis. These data provide rationale and basis for further study into the function of cathepsin K and its relationship with SDF-1 in gliomas.

Analysis of electrostatic powder charging for fractionation of foods

Electrostatic separation based on different tribo-electric charging behaviours of components has emerged as a novel, sustainable dry fractionation process. This study aims to characterise charging behaviour of single-component particles in nitrogen gas flowing through aluminium tubes. Experiments were carried out with polystyrene (PS) particles and wheat gluten as model particles. Results indicated that specific charge increased linearly with gas velocity up to 28 m/s for both materials. It was found that surface charge densities of different-sized PS particles overlapped for laminar gas flow, whereas for higher stronger gas flow rates, surface charge density of the smallest particles deviated from that of larger particles. Specific charge of PS particles increased linearly with increasing tube length from 125 to 225 mm. Additionally, charging of PS particles was unaffected by relative humidity (RH) of gas; however, specific charge of wheat gluten decreased for RH > 80%. Concluding, these results provide insight in critical parameters affecting charging behaviour, thus facilitating the development of electrostatic separation processes to fractionate food ingredients.

바이오가스용 소형 열교환기 연구

Our lab designs a heat exchangers for air and carbondioxide gas. Coolant is water, thus it is very difficult to determine heat transfer parameters in this gas-liquid system. Repeated experiments gives overdesign value 35%, overall heat transfer coefficient 33.8 (kcal/m2-hr-°C) for carbondioxide. Another series of experiments determine overdesign 18.7%, overall heat transfer coefficient 21.4 (kcal/m2-hr-°C) for Air. These parameters are in same range of literature. Overdesign is increasing as tube length increases, also increases as wall thickness of heat exchanger increases. To get proper fluid linear velocity in heat exchanger, we change the diameter of tube and finally we can have optimum fluid linear velocity in the heat exchanger.

Viscosity and rheological behavior of microbubbles in capillary tubes

The viscosity of microbubbles has been measured in capillary tubes. Experiments were conducted in tubes of different diameters and lengths, with a constant microbubble concentration. The effects of bubble void fraction and size distribution on the viscosity of microbubbles were also investigated. Microbubbles demonstrate shear‐thinning non‐Newtonian behavior. The viscosity of microbubbles decreases with a decrease in tube diameter and bubble void fraction, and with an increase in tube length. Although viscosity changes with tube dimensions, the flow index (n′) is only influenced by the microbubble void fraction. It is also found that bubble size distribution in the range (1–12 µm) used in this study does not affect the viscosity of microbubbles. The data were then used to develop a correlation to predict viscosity of microbubbles, which represents the experimental viscosity data with an absolute average relative deviation less than 1.3%. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2660–2669, 2014

Experimental investigation of the effects of heat transport pipeline configurations on the performance of a passive phase-change cooling system

The separate-type passive phase-change cooling systems provide considerable flexibility in the placement of the evaporator and condenser. An experimental study of flow characteristics and heat transfer during condensation inside the connecting section, i.e. heat transport pipeline, was conducted. Measurements were made in round tubes with diameters ranging from 20 to 38mm, lengths from 1 to 6m, and inclination angles from 0° to 30°. Distilled water was used as the working fluid. The study primarily took into account the effect of various parameters (inner diameter, length and inclination angle) on the performance of a cooling system. Flow visualization showed that at all operating conditions the flow pattern was the droplet flow. Heat transfer coefficient increased with increasing tube length, inner diameter and inclination angle. The system pressure drop also increased with an increase in the tube length while decreased with increasing inclination angle. For a constant heat load, an obvious decrease of evaporator temperature was observed for longer tubes. Moreover, the cooling system needed a certain time (defined as “delayed time”, represented the robustness of the system) to reach the steady-state again when the heat load increased. Different tube configurations can result in different “delayed time”.

The spin-dependent transport of Co-encapsulated Si nanotubes contacted with Cu electrodes

Unlike carbon nanotubes, silicon ones are hard to form. However, they could be stabilized by metal-encapsulation. Using first-principles calculations, we investigate the spin-dependent electronic transport of Co-encapsulated Si nanotubes, which are contacted with Cu electrodes. For the finite tubes, as the tube-length increases, the transmission changes from spin-unpolarized to spin-polarized. Further analysis shows that, not only the screening of electrodes on Co's magnetism but also the spin-asymmetric Co-Co interactions are the physical mechanisms. As Cu and Si are the fundamental elements in semiconductor industry, our results may throw light on the development of silicon-based spintronic devices.

The energy-absorbing characteristics of polymer foams reinforced with bamboo tubes

This paper investigates for the first time, the energy-absorbing characteristics of a range of lightweight bamboo-reinforced foam structures. Initial attention focuses on characterizing the energy-absorbing characteristics of the individual bamboo tubes and assessing the influence of tube geometry on energy absorption. Here, it has been shown that the specific energy absorption of the bamboo tubes decreases with increasing tube length as a result of axial splitting associated with barreling of the samples under compressive loading. The influence of the tube inner diameter/thickness (D/t) ratio was also investigated using a number of tube sizes, where it was shown that there is a small increase in specific energy absorption with decreasing D/t. The tubes were then embedded in crosslinked PVC foams in order to investigate the influence of varying degree of external support applied to the reinforcement on the failure modes in the tubes as well as the measured specific energy absorption values. Finally, alternative techniques for enhancing the energy-absorbing capacity of the tubes were investigated. Here, tubes of different length were wrapped circumferentially in epoxy-impregnated kenaf fibers to enhance their resistance to axial spitting. It was shown that reinforcing the tubes in this manner can significantly enhance the ability of the tubes to absorb energy under conditions of axial quasi-static crushing.