Tube In Presence Research Articles

Magnetic flux response of non-Hermitian topological phases

We derive the response of non-Hermitian topological phases with intrinsic point gap topology to localized magnetic flux insertions. In two spatial dimensions, we identify the necessary and sufficient conditions for a flux skin effect that localizes an extensive number of in-gap modes at a flux core. In three dimensions, we furthermore establish the existence of: a flux spectral jump, where flux tube insertion fills up the entire point gap only at a single parallel crystal momentum; a higher-order flux skin effect, which occurs at the ends of flux tubes in presence of pseudo-inversion symmetry; and a flux Majorana mode that represents a spectrally isolated mid-gap state in the complex energy plane. We uniquely associate each non-Hermitian symmetry class with intrinsic point gap topology with one of these cases or a trivial flux response, and discuss possible experimental realizations.

Kink oscillations of magnetic flux tubes in presence of resistivity

ABSTRACTKink oscillations in the solar coronal flux tubes are among the best seismological tools for estimating the unknown parameters of the solar corona. Here, we study the effect of resistivity on the linear evolution of magnetohydrodynamic (MHD) kink waves in magnetic flux tubes with transverse inhomogeneity in the plasma density. In thin tube thin boundary approximation, we obtain the well-known resistive spectrum of Alfvén continuum modes with a semi-analytical method and study the relative importance of the eigenmodes in the spectrum. As shown in previous studies, the quasi-mode solution of ideal MHD appears in the spectrum. Results show that while the internal and external homogeneous regions of the flux tube oscillate dominantly in quasi-mode in the inhomogeneous region in each magnetic surface a different combination of resistive eigenmodes contributes to the perturbations. Comparing the results obtained here with those obtained previously in the same configuration for a viscous plasma shows that resistivity is less efficient than viscosity in transforming the energy of the wave to heat.

A COMPARATIVE STUDY OF MICROSCOPIC TYMPANOPLASTY VERSUS ENDOSCOPIC TYMPANOPLASTY IN MANAGEMENT OF INACTIVE MUCOSAL VARIETY OF CHRONIC OTITIS MEDIA

Chronic Otitis Media (COM) is defined as the chronic inflammation of the middle ear cleft including the middle ear, mastoid air cell system and the eustachian tube in presence of a permanent abnormality of the pars tensa or flaccida, most likely as a result of earlier acute otitis media, negative middle ear pressure or otitis media with effusion. As COM is not necessarily a result of the gathering of pus, the classic term chronic suppurative otitis media (CSOM) is no longer advocated.

Instability of liquid film flow inside of a vertical tube in presence of an interfacial surfactant.

Liquid film coating inside a tube becomes unstable to surface-tension-driven Rayleigh-Plateau (RP) instability. The presence of interfacial surfactant reduces the growth rate of RP instability but is unable to completely eliminate it. Further, it is known that the surfactant mode, an eigenmode emerging because of the presence of surfactant, remains stable for such liquid films. However, the above two observations hold true only when the liquid film remains stationary (i.e., in the absence of base flow). Here, we investigate the linear stability of surfactant-laden liquid film inside of the tube with base flow included in the analysis. We observed a complete suppression of Rayleigh-Plateau instability because of the presence of surfactant when the basic flow is included in the analysis. However, the surfactant mode, which otherwise remains stable in the absence of base flow, is found to be unstable when the basic flow is taken into account in the stability analysis. More importantly, depending on the base flow strength, the wave number corresponding to maximum growth rate and cutoff wave number for surfactant mode are greater than unity for a wide variety of parameters. This is unlike the (RP) instability observed for surfactant-covered stationary films where the cutoff wave number is always less than unity. Further, we show that the growth rate observed for this surfactant-mode instability in the presence of sufficiently strong basic flow is significantly higher than the growth rate of RP instability observed for a stationary liquid film. These observations imply that depending on the strength of basic flow, the effect of presence of surfactant is destabilizing for such film flows as opposed to a stabilizing effect observed for stationary liquid films in earlier studies.

Evaluation of weighted residual methods for thermal radiation on nanofluid flow between two tubes in presence of magnetic field

The current paper deals with the problem of convective heat transfer for a nanofluid flow between two tubes in the presence of a horizontal magnetized field. Two novel analytical methods, called the method of moments (MOM) and the least square method (LSM), are employed to mathematical model the problem. Also, the thermal radiation parameter (Rd) is considered, and the KKL model is used for the thermal conductivity and viscosity of the nanofluid. Besides solving nonlinear problem by present methods without grid generation difficulties, a reasonable agreement is observed with numerical technique. After that, the effects of Reynolds (Re), Hartmann (Ha), and Eckert (Ec) numbers on heat convection and velocity related to the flow of the fluid are analyzed. The results show that an increment of Ec number leads to 46% rise in temperature pattern at the same radial position. In addition, the 11.3% reduction on temperature profile is observed due to Rd parameter increment.

Heat and Fluid Flow in an Open Agricultural Greenhouse in Presence of Plants

Flow convection in agriculture greenhouse is one of the most important factors on the growth and fruiting of plants. The present work focused on natural convection in an open greenhouse heated by ridge tubes in presence of plants. Analyses are performed for different boundary conditions imposed at the roof such as constant temperature, convective heat flux, and convective and radiative heat flux. The governing equations comprising continuity, momentum and energy equations are solved by Ansys-Fluent software. In each case, the average velocity and temperature of the air are determined. The obtained results are presented in terms velocity and temperature profiles. Isothermal lines and velocity vectors showed that by increasing the convective heat transfer coefficient, the average temperature and average airflow velocity decrease. The outcomes of this study help build greenhouses with dimensions and materials to suitable for the given external conditions.

Experimental investigation of thermal-hydraulic characteristics of finned oval tube bundles in cross-flow arrangements

Enhancement of heat transfer using finned circular tubes arranged in counter-flow configurations are accompanied by high pressure losses. To obviate these problems, finned oval tubes are introduced which can enhance heat transfer while keeping pressure losses minimum. In this paper, different configurations of finned oval tubes which are called tube bundles are experimentally investigated using a thermal camera and a smoke wind tunnel (1800 <Re∞<8200). Given that thermal performance and hydraulic behavior of the tube bundles have reciprocal effects on each other, flow patterns, shedding behavior, and temperature distribution on the finned oval tubes in presence of a heat flux are visualized experimentally for the first time in order to monitor wake zones and their corresponding sizes and impacts on the heat transfer performance of finned oval tube bundles. Effects of diagonal tube pitch and angle of tubes arranged in the staggered configurations on the flow regime, heat transfer rate and pressure loss are studied and the Chilton–Colburn J-factor and friction coefficient f are investigated. Following these investigations, three distinct flow patterns are identified. Based on the results, recirculation regions formed behind the central tube and the dead zone between upper tubes imposes negative effects on the flow behavior leading to a bad thermal performance. Based on the results, for the studied Reynolds numbers and arrangements, smaller tube diagonal pitches are the most desirable in staggered configurations of finned oval tubes. Nusselt number is almost 25% higher for smaller tube pitches in relation to the larger one. Bundles with smaller tube pitches have also higher efficiency indices. Accordingly, at all configurations, finned oval tube bundles perform better at low and high Reynolds numbers from the efficiency index point of view. Therefore, it is better to use these kinds of tubes at low Reynolds numbers in the industry.

Comparison of Heat Transfer Performance for Condensation in Corrugated Low Finned Tube and Smooth Tube with Air

The existence of air served as non-condensable gas makes it difficult to design effective titanium condenser in PTA plant. In this paper, the heat transfer characteristic for condensation inside corrugated low finned tube and smooth tube in presence of air was compared. The local heat transfer performance was studied by comparing bulk temperature and local heat transfer rate. The effect of non-condensable gas mass fraction on overall heat transfer performance was also analysed. The results indicated that both the bulk temperature and the local heat transfer rate decreased along the axial direction due to the reduction of steam partial pressure and temperature difference. The average heat transfer coefficient and total heat transfer rate decreased with the increase of inlet non-condensable gas mass fraction. And the corrugated low finned tube could reduce the impact of non-condensable gas by reducing the thickness of gas film and condensate film.

Mechanism of Condensation Enhancement by Corrugated Low Finned Tubes in Presence of Noncondensable Gas

Corrugated tubes are the most convenient reinforcement techniques to enhance intube condensation. In this paper, the average condensation heat transfer coefficients inside the corrugated low finned tube and smooth tube were firstly introduced. The distribution of local heat transfer coefficient was presented at lower and higher inlet noncondensable gas mass fractions. The results show that the major heat transfer resistance is the thermal resistance of liquid film at lower inlet gas fraction. So the mechanism of condensation enhancement by corrugated low finned tubes is the increase of liquid film condensation coefficient. But at higher inlet gas fraction gas layer mass transfer resistance becomes the control thermal resistance. The spiral ribs inside corrugated low finned tube can thinner not only the gas layer thickness but also the liquid film thickness. The mechanism of condensation enhancement is the increase of both gas layer and liquid film condensation coefficient.

102 Application of Liquid-Impregnated Surfaces on Gastrointestinal Devices to Reduce Device-Associated Complications

INTRODUCTION: Plastic stents can occlude and require reintervention in up to 75% of cases and this has contributed to more frequent use of much more expensive metal stents. Efforts to increase the duration of plastic stent patency, such as antibacterial stent and hydrophilic coating or design modifications, have met limited success. We hypothesize that a biocompatible liquid-impregnated surface (LIS) coating combining a textured substrate with a liquid lubricant creates a lubricious surface that reduces cell attachment and biofilm formation. Our aim is to determine the ability of LIS coating in an in vitro model to reduce thrombus formation and lumen occlusion. METHODS: A polyethylene (PE) tube, made with the same material and size as a 10 Fr biliary stent, is coated with a LIS coating. A Chandler loop assay with freshly harvested bovine blood is used to analyze cell attachment and thrombus formation. Pressure buildup within either PE tubes or 5 Fr polyurethane tubes in presence of whole blood is tested with an occlusion assay. The coated devices are challenged with bile extract solution at 38 °C up to 35 days. The surface composition is analyzed by Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR). RESULTS: LIS-coated tubes demonstrated a 100% thrombus reduction using the Chandler loop assay (Figure 1a). The coating remained stable on the surface up to 35 days both in air and in the bile acid solution (Figure 1b,c). LIS-coated tubes were observed to remain patent after 12 hours of swine bile infusion, compared to controls that were completely obstructed. The coated surfaces also reduced occlusion rates in bovine blood (Figure 2). CONCLUSION: With a formulation developed through thermodynamic and hydrodynamic validation, a biocompatible LIS coating was applied on a model GI device both internally and externally. In addition to the anti-thrombogenic and antimicrobial performance, the slippery characteristics of the coating can reduce friction, facilitate device deployment during implantation. The coating has the potential to be applied on a GI device such as a biliary stent for a further product development.

Numerical investigation of flow boiling heat transfer in helically coiled tube under constant heat flux

Numerical study of subcooled and saturated flow boiling in the curved and helically coiled tubes in presence of phase change is one of the challenging area of CFD studies. In this paper, the CFD modeling of the nucleate and convective flow boiling in the small helically coiled tube at low vapor quality (up to the 18.93 percent) region is studied. A proper Eulerian-based mathematical model is used for interphase exchange forces and heat transfer between two phases in CFD modeling using Bulk boiling model. The results show that, the inner and the bottom wall of the helically coiled tube have the lowest and the highest heat transfer coefficient, respectively. The effect of change in coil diameter, helical pitch and tube diameter is investigated on the counters of vapor volume fraction. It is seen that at low vapor quality flows, the heat transfer coefficient is enhanced by decreasing in coil diameter, tube diameter and increasing in coil pitch of helically coiled tube.

Multiple Stenotic Effect on Blood Flow Characteristics in Presence of Slip Velocity

The aim of the present analysis is to study the effect of slip velocity on blood flow through an arterial tube in presence of multiple stenosis. The effects of length of stenosis, shape parameter, parameter γ on resistance to flow and shear stress have been incorporated here. The results have been shown in graphical form and discussed.

Preparation and characterization of the rod-shaped stibnite

Stibnite (Sb2S3) micro-wires have been grown on glass substrates by sulfuration of Sb thermal evaporated film in a vacuum sealed tube in presence of sulfur powder at 300°C for 6h. X-ray diffraction and Raman spectroscopy techniques indicate that the synthesized micro-wires have an orthorhombic structure. SEM micrographs show rod-shaped micro-wires with a typical length of several tens of micrometers and a diameter of the order of 0.5μm. The absorption coefficient dependence on the photon energy in the UV–visible range revealed the existence of a direct transition with an energy band gap of about 1.7eV. Moreover, the band tails and localized states which are related to the level of defects in the material will be presented. These parameters were determined from the exponential absorption profile. All these results have been evaluated and discussed in terms of alteration of band gap edge and electrical measurements.

Turbulent film condensation in a vertical tube in presence of non condensable gas

This paper presents the simulation of the condensation of methanol vapour in the presence of non-condensable gas in turbulent flows in a vertical tube. The liquid and gas stream are approached by two coupled turbulent boundary layer. For solving the coupled governing equations for liquid film and gas flow together with the interfacial matching conditions an implicit finite difference method is employed. The effect of the influencing parameters are studied so the effect of inlet Reynolds number, the effect of temperature gradient, mass fraction are illustrated. The numerical results demonstrate that an important concentration of no-condensable gas reduces the heat transfer coefficient and film thickness considerably. The local heat flux and film thickness increase as tube surface temperature decreases at any bulk concentration of non-condensable gas. Moreover, inlet velocity increases as film thickness decreases and heat flux increases.

Electrochemically controlled in-tube solid phase microextraction

We report a new in-tube solid phase microextraction approach named electrochemically controlled in-tube solid phase microextraction (EC in-tube SPME). This approach, which combined electrochemistry and in-tube SPME, led to decrease in total analysis time and increase in sensitivity. At first, pyrrole was elctropolymerized on the inner surface of a stainless steel tube. Then, the polypyrrole (PPy)-coated in-tube SPME was coupled on-line to liquid chromatography (HPLC) to achieve automated in-tube SPME–HPLC analysis. After the completion of EC-in-tube SPME–HPLC setup, the PPy-coated tube was used as working electrode for uptake of diclofenac as target analyte. Extraction ability of the tube in presence and in absence of applied electrical field was investigated. It was found that, under the same extraction conditions, the extraction efficiency could be greatly enhanced by using the constant potential. Important factors are also optimized. The detection limit (S/N=3) and precision were 0.1μgL−1 and 4.4%, respectively.

English

This paper presents an analytical study of pulsatile flow of blood with micro-organisms through stenosed tubes in presence of transverse magnetic field.The effect of externally applied magnetic field on velocity, flow rate is studied.The analytical solutions for the velocity, volumetric flow rate are obtained using finite Hankel and Laplace transforms,and their natures are shown graphically for different values of involved parameters.

Safety and efficacy of percutaneous endoscopic gastrostomy tube placement in patients with malignant peritoneal carcinomatosis induced bowel obstruction.

e14012 Background: Percutaneous Endoscopic Gastrostomy (PEG) tube placement in advanced peritoneal carcinomatosis with bowel obstruction is a feasible palliative procedure to help patients with obstructive symptoms. We describe the safety and efficacy of using PEG tube for decompression in patients with large peritoneal masses. Methods: A consecutive case series of 62 patients (Apr-08 to Jun-11) with advanced abdominal carcinomatosis induced bowel obstruction. All patients were extensively treated for their cancer. None of them were surgical candidates due to extensive peritoneal involvement. All patients had symptoms of nausea, vomiting and pain at the time of PEG tube placement. All patients had a 28F (Bard) PEG tube placed for drainage. The primary outcomes of interest were complications and symptom resolution due to PEG tube placement. Frequency of nausea, vomiting and severity of pain was recorded daily in patient charts. Results: 16 were males and 46 females. The mean age was 50.5 years. Most common cancers were ovary, pancreas, colon and stomach. Of 62 patients, 57 patients had expired at the time of this analysis. Of those 57 expired, 49 had PEG tube at the time of death, while 8 had complete resolution of symptoms with PEG tube removed before death. The 5 out of 62 patients who are alive still have the PEG tube for drainage (average 70.4 days). The average duration of PEG tube placement for all patients combined was 70.9 days (range 6-312 days). Relief of nausea, vomiting and pain was observed in 53 (85.5%), 55 (88.7%) and 35 (56.5%) patients respectively. Of a total of 43 patients who had PEG tube placed for &gt;= 30 days, 24 (56%) could continue with their chemotherapy cycles because of symptom resolution. Non life threatening complications of PEG tube placement were observed in 9 (14.5%) patients. 3 had infection at the insertion site, 2 had bleeding and 3 had leaking at the PEG tube site while 1 had aspiration. 6 (9.7%) patients required replacement of the PEG tube due to occlusion. Conclusions: Placement of PEG tube in presence of advanced peritoneal carcinomatosis is safe and effective in relieving obstructive symptoms as well as extending the period of active cancer therapy.

Investigation of breakdown voltage and electrical breakdown time delay in air-filled tube in presence of combined gas and vacuum breakdown mechanism

This paper presents the experimental data of breakdown voltage and electrical breakdown time delay for air-filled tube at p = 0.7 mbar pressure. The breakdown voltage was measured for product p·d (d is inter-electrode gap) from 0.005 to 0.2 mbar cm, i.e. when breakdown was a consequence of gas and vacuum mechanisms combined. It was shown that the static breakdown voltage, which was determined from experimental data of the dynamic breakdown voltage, retains approximately constant value. The shape of the memory curve, which displays the mean value of electrical breakdown time delay t¯d vs. relaxation time τ, is very similar to that previously obtained in the case of breakdown induced by Townsend's mechanism alone. UV and gamma radiation lead to the decrease of t¯d values for values τ > 30 ms and this decrease is larger in the presence of UV radiation. UV and gamma radiation shorten the relaxation time needed for memory curve to reach saturation. On the basis of exponential and Gaussian distributions of experimental data, the contribution of the statistical time delay and the formative time to total electrical breakdown time delay for different values of relaxation time is considered.

Fatigue limit assessment on seamless tubes in presence of inhomogeneities: Small crack model vs. full scale testing experiments

The existence of crack-like flaws cannot be excluded in pressure vessels and piping due to the presence of non-metallic inclusions and surface imperfections. These inhomogeneities reduce the fatigue strength of the pressure vessel. In this work, the detrimental effect of the surface quality on the fatigue strength of cylinder housings is analyzed by means of a fatigue model available in the literature using values obtained by crack propagation tests. The comparison in terms of fatigue limit between model and experimental full scale (FS) tests has shown an underestimation of the fatigue strength if the prediction based on ΔKth,LC values for long cracks is used. This is due to a flattening effect of the ΔKth,LC values at high stress ratios R under full scale tests that the standard crack propagation tests do not anticipate. Further investigations need to be carried out for more realistic prediction by the mentioned model. In order to obtain an accurate and more realistic fatigue limit, an alternative small scale (SS) fatigue test has been implemented. The goal was to reproduce as much as possible the real condition of a full scale (FS) state during the small scale (SS) fatigue limit test; and this has led to a good agreement between the FS and SS fatigue limit tests.

Film condensation heat transfer on a horizontal tube in presence of a noncondensable gas

The double boundary layer model has been developed to study the behavior of film condensation heat transfer outside a horizontal tube in presence of air treated as a noncondensable gas. And the coupled heat and mass transfer on a smooth horizontal tube is numerically solved with the finite difference method. The local mass concentration of the noncondensable gas, the distributions of velocity and temperature in the boundary layers are presented and discussed. The numerical results have shown that the mass concentration and velocity of the noncondensable gas increase from the bulk mixture to the interface while the temperature decreases from the bulk mixture to the interface. Although the mass concentration of the noncondensable gas in the bulk mixture could be small, the reduction in average heat transfer coefficient is obvious. The comparisons of heat transfer coefficient show that the numerical predictions agree well with available experimental data. ► We develop the double boundary layer model. ► We examine film condensation heat transfer in presence of noncondensable gas. ► We present local mass concentration, velocity and temperature in boundary layers. ► Low noncondensable gas causes large reduction of condensation heat transfer. ► Good agreement for heat transfer is achieved between numerical and experimental data.