Presence Of Air Pockets Research Articles

Dosimetric Study to Estimate Deviations in Delivered Radiation Dose due to Occluded Air Spaces in Vaginal Vault Brachytherapy Applications.

To develop a dosimetric tool to estimate the dose delivered in the presence of air pockets with EBT3 film while simulating the conditions of vaginal vault brachytherapy (VVBT) with 3.0 diameter cylindrical applicator at a prescription dose distance of 5mm from the surface of it. Six acrylic plates (10 cm x 10 cm, 0.5 cm thick) with four different types of slots were designed and produced locally. They can hold a cylindrical vaginal brachytherapy applicator in the centre, air equivalent material from the applicator's surface [(sizes 4.5 mm (A), 3.0 mm (B), and 2.0 mm (C)], EBT3 film at the prescribed dose distance, and holder rods. Plates were layered together with acrylic rods and assembled in a holding box in a water phantom. Three treatment plans done in TPS with prescription doses of 2 Gy, 3 Gy, and 4 Gy at 5.0 mm with a treatment length of 6 cm, and were executed in Co-60-based HDR brachytherapy unit (M/s SagiNova, Germany) with & without the placement of air equivalent material, and the dose received at slot locations A, B, & C were noted. The mean percentage deviation of measured dose without and with presence of air pocket at A, B and C was 13.9%, 11.0% and 6.4% respectively for all dose prescriptions. As the air pocket size expanded radially from 2.0 mm to 4.5 mm, the increase in dosage ranged from 6.4% to 13.9% which was due to the fact that the film was held at dosage prescription distance and the lack of attenuation of photons radially through air pocket. The present study can be carried out with a 3D printed phantom that simulates VVBT application having air pockets of different dimensions at different locations and also can be analyzed with Monte Carlo simulations.

Dosimetric Impact of Air Pockets in the Vaginal Cuff Brachytherapy Using Model-based Dose Calculation Algorithm.

Endometrial cancer is the most common disease of the female reproductive system. Vaginal cuff brachytherapy (VCB) has intrinsic advantages compared to external beam therapy when treated with radiation. A single-channel cylinder is a standard applicator in VCB. The present study aims to estimate a change in the dose to vaginal mucosa due to air pockets between the cylinder and vaginal mucosa by calculating with the Acuros BV algorithm and comparing it to the Task Group 43 (TG-43) algorithm. Patients who presented with air packets were included retrospectively. For each patient, three plans were created: the first plan used TG-43, the second plan used dose recalculation with Acuros BV, and the third plan was generated by re-optimization by Acuros BV. On the same axial computed tomography image, the point doses at the cylinder's surface and the displaced mucosa were recorded and the ratios were then estimated. The average volume of air pockets was 0.08 cc (range of 0.01-0.3 cc), and 84% of air pockets displaced the vaginal mucosa by ≥0.2 cm. The average ratios of dose were 0.77 ± 0.09 (1 standard deviation [SD]) and 0.78 ± 0.09 (1 SD) for TG-43 and Acuros BV algorithms, respectively. Due to the air pocket, mucosa received a reduced dose by an average of 22.72% and an average of 23.29% for TG-43 and Acuros BV, respectively. The maximum displacement of mucosa and the ratio of doses were negatively correlated for both. In the Optimized Acuros BV plan, total dwell time increased by 1.8% but no considerable change in the dose ratios. The calculated dose of mucous membrane forced out of the cylinder surface by air pockets by the Acuros BV algorithm was nonsignificantly different from TG-43. Therefore, even in the presence of air pockets, the TG-43 algorithm for calculating the VCB dose is appropriate.

Anti-icing strategies of plant surfaces: the ice formation on leaves visualized by Cryo-SEM experiments

This paper presents an experimental study on surface icing on leaves in six plant species having different surface micromorphology and wettability properties. Contrary to previous studies on ice crystallization, which have been mainly performed by using infrared video thermography, we applied a Cryo-SEM approach allowing not only characterization of plant surfaces in their native conditions but also visualization of ice crystal formation on the native plant surfaces at the micro- and nanoscales. The Cryo-SEM was also used as an experimental device to freeze water vapor, thaw ice crystals, and freeze fluid water on the plant surface again. The experiments clearly demonstrate that trichome coverage (especially with several distinct layers) and 3D wax projections can be recognized as anti-icing strategies of plants. Trichomes can prevent and delay ice formation by being nucleation points for the formation of ice from vapor and protect the plant surface from overcooling, when fluid water freezes in contact with the leaf surface. The study shows for the first time two important effects that might reduce plant cell freezing rate: the presence of air pockets between wax projections that protect from direct contact between ice crystals and the plant cuticle and elimination of fluid water after thawing and preventing further re-freezing on the surface. The detailed knowledge obtained here is not only important for plant ecology, evolution, and plant protection but also for looking for potential biomimetic strategies that reduce/avoid icing of cultural plants and artificial technical surfaces.Graphical

Porosity formation during atmospheric ice accretion: measurements using micro-computed tomography

AbstractAtmospheric ice accretion results from the exposure of technical equipment or facilities to cold and humid environments. Supercooled droplets in a cloud can impact an airplane's surface and quickly form an ice layer. The presence of air pockets in such a layer is well known and explains the white appearance of some of the accretions. However, estimation of its porosity values and studies on the pore formation mechanics remain limited. In this study, we performed tests in an icing wind tunnel and scans with micro-computed tomography to address these issues. Here, we show that the accretion has closed porosity below 1%, which is mostly produced by the interaction between a spray-like impact on the water surface. The insights we provide here are important to improve ice accretion modelling techniques and establish a different approach to address the interaction between the cloud and the surfaces exposed to atmospheric icing.

Simulating alveoli-inspired air pockets in a ZnO/NiMoO4/C3N4 catalyst filter for toluene entrapment and photodecomposition

Here, we propose an alveoli–inspired catalyst to address the susceptibility of photocatalytic air oxidation systems to fluctuations in volatile organic contaminant (VOC) loads. An alveoli structure was fabricated by covering ZnO nanorods grown on a stainless–steel mesh (SSM) with a porous NiMoO4/C3N4 layer. The alveoli catalyst regulates VOC mass transfer from the air to the catalyst surface using air pockets that capture VOC molecules by diffusion driven by a concentration gradient. Air pockets act as localized reservoirs of molecules that prevent scarcity and congestion at the catalyst surface at low and high VOC loads, respectively. The presence of air pockets in the catalyst assembly and its potential to capture VOC was confirmed by a distinct bimodal adsorption configuration. A ZnO/NiMoO4/C3N4@SSM (ZNC@SSM) catalyst with air pockets achieved a high degree of toluene adsorption (6.1 μmol·m–2). Toluene selectivity of ZnO controlled the delivery of molecules to active catalyst sites, resulting in 95% toluene conversion in 90 min. Synergetic toluene adsorption in air pockets and degradation on catalytic sites helped achieve a quantum yield of 4.14 × 10–05 molecules/photon. A figure of merit reflecting fundamental system parameters was compared with previous photocatalytic systems to evaluate the practicality of ZNC@SSM.

2530 An Unusual Cause of Abdominal Pain From Salmonella enteritidis (SE): Guess Where the Bug Was?

INTRODUCTION: Aortitis, an inflammatory entity with high mortality that is usually due to a rheumatologic etiology; however, an infectious etiology is sometimes the cause. We present a rare case of aortitis secondary to Salmonella septicemia treated with 6 weeks of antibiotics. Endovascular surgical repair (EVAR) with antibiotics (abx) is the preferred treatment. CASE DESCRIPTION/METHODS: A 76 year-old male with HTN, DM and CAD s/p CABG 3 months prior, presented to the ED c/o 7-day hx of suprapubic abdominal pain radiating to the lower quadrants and lower back, associated with fever, chills, night sweats, and chest pain. There was no recent history of a diarrheal illness. VS: T 101 F, BP 100/60, RR 18 and pulse of 100. PE revealed costochondral erythema and tenderness, as well as manubrial and suprapubic tenderness. Labs showed WBC 31000, ESR 100, CRP 150, CT abdomen revealed perineural fibrosis of the aorta just above the ostium of the IMA; the presence of air pockets was concerning for infectious aortitis. Patient refused surgery. Blood C&S were sent and patient was started on IV Cefipime, Linezolid and metronidazole. Sternal osteomyelitis was suspected. Bone scan revealed increased uptake in the region of the manubrium and upper body of the sternum. CTA confirmed aortitis. Blood C&S and sternal biopsy grew SE and abx were switched to IV ceftriaxone for 6 weeks. There was clinical and radiographic improvement without complications. DISCUSSION: Salmonella aortitis carries a high mortality even with best treatment options, making prompt diagnosis crucial for survival. Risk factors for Salmonella aortitis include vascular pathologies, CAD, HTN, DM, immunosuppression, seronegative C2 Infections, rheumatological diseases and hematological malignancies. The best treatment for infectious aortitis is EVAR with long-term abx. Treatment with abx alone is controversial; however, their use is the mainstay of therapy. Review of literature revealed that patients treated solely with abx without surgery did not survive. Duration of abx is also controversial with some experts suggesting lifelong treatment. In this case, the patient refused surgery and received abx for 6 weeks only, with resultant clinical and radiological remission.

Monte Carlo study of the impact of a magnetic field on the dose distribution in MRI-guided HDR brachytherapy using Ir-192

In the process of developing a robotic MRI-guided high-dose-rate (HDR) prostate brachytherapy treatment, the influence of the MRI scanner’s magnetic field on the dose distribution needs to be investigated. A magnetic field causes a deflection of electrons in the plane perpendicular to the magnetic field, and it leads to less lateral scattering along the direction parallel with the magnetic field. Monte Carlo simulations were carried out to determine the influence of the magnetic field on the electron behavior and on the total dose distribution around an Ir-192 source. Furthermore, the influence of air pockets being present near the source was studied. The Monte Carlo package Geant4 was utilized for the simulations. The simulated geometries consisted of a simplified point source inside a water phantom. Magnetic field strengths of 0 T, 1.5 T, 3 T, and 7 T were considered. The simulation results demonstrated that the dose distribution was nearly unaffected by the magnetic field for all investigated magnetic field strengths. Evidence was found that, from a dose perspective, the HDR prostate brachytherapy treatment using Ir-192 can be performed safely inside the MRI scanner. No need was found to account for the magnetic field during treatment planning. Nevertheless, the presence of air pockets in close vicinity to the source, particularly along the direction parallel with the magnetic field, appeared to be an important point for consideration.

Controlling air solubility to maintain “Cassie” state for sustained drag reduction

“Cassie” state of wetting can be established by trapping air pockets on the crevices of textured hydrophobic surfaces, leading to significant drag reduction. However, this drag reduction cannot be sustained due to gradual dissolution of trapped air into water. In this paper, we explore the possibility of sustaining the underwater Cassie state of wetting in a microchannel by controlling the solubility of air in water; the solubility being changed by controlling the local absolute pressure near the surface. We show that using this method, we can in fact make the water locally supersaturated with air thus encouraging the growth of trapped air pockets on the surface. In this case, the water acts as a pumping medium, delivering air to the crevices of the hydrophobic surface in the microchannel, where the presence of air pockets is most beneficial from the drag reduction perspective. In our experiments, the air trapped on a textured surface is visualized using total internal reflection based technique, at different local absolute pressures with the pressure drop (or drag) also being simultaneously measured. We find that, by controlling the pressure and hence the solubility close to the surface, we can either shrink or grow the trapped air bubbles, uniformly over a large surface area. The experiments show that, by precisely controlling the pressure and hence the solubility we can sustain the “Cassie state” over extended periods of time. This method thus provides a means of getting sustained drag reduction from a textured hydrophobic surface in channel flows.

Modeling Vaporous Cavitation in Transient Pipe Flow Using the Zielke’s Friction Model

This study provides a theoretical and numerical modeling of transient vaporous cavitation in a horizontal pipeline, anchored to the upstream reservoir. The model approach is, essentially, based on that of the column separation model (CSM). The basic system of partial differential equations to solve is a hyperbolic type and adapts perfectly to the method of characteristics. This code, allows us, taking into account the unsteady part of the friction term, to determine at any point of the pipe, and at each instant, the average piezometric head, the average discharge and the change in volume of the vapour cavity. This study illustrates the effect of the presence of air pockets, resulting in cavitation, on the amplitude of the pressure wave. The calculation results are in good agreement with those reported in the literature

Assessment of air pockets in high-dose-rate vaginal cuff brachytherapy using cylindrical applicators.

PurposeTo retrospectively assess the incidence and magnitude of air pockets around vaginal cylinders and its impact on dose distribution in vaginal cuff image-guided high-dose-rate (HDR) brachytherapy.Material and methodsFifty endometrial carcinoma patients treated by postoperative HDR vaginal cuff brachytherapy were included in the study. The average age of patients was 58.3 ± 11.8 years (range: 31-87 years). Brachytherapy was performed using cylindrical applicators, and the dose prescribed to 0.5 cm from the applicator's surface, over a length of 5 cm from the applicator's tip. Computed tomography (CT) simulation was used for each brachytherapy fraction. The incidence, vaginal mucosa displacement, volume, and dosimetric effect of air pockets around the vaginal cylinder were evaluated.ResultsA total of 78 air pockets were found in 29/50 patients (58%) and 45/135 (33%) brachytherapy plans. They were located at the apex: 16/78 (20%) and lateral to the applicator: 62/78 (80%). The volume of air pockets ranged between 0.01 and 2.1 cm3 (mean: 0.15 cm3 ± 0.36 cm3), and the maximum displacement of vaginal mucosa from cylinder surface was between 0.1 and 1.09 cm (mean: 0.34 cm ± 0.2 cm). The dose reduction to the vaginal mucosa generated by the air pockets ranged from 0.5 to 66% (mean: 26.4% ± 13.9%).ConclusionsThe presence of air pockets around vaginal cylinder applicators is frequently noticed in post-operative vaginal cuff brachytherapy. The dose to the vaginal mucosa is reduced, as a result of displacement generated by air pockets. The effect on the clinical outcome of this dose reduction is yet to be determined.

Effect on Auditory Threshold of Air and Water Pockets Bordering the Pathway between Soft Tissue Stimulation Sites and the Cochlea

Auditory sensation can be elicited by applying a bone conduction vibrator to skin sites on the head, neck, and thorax over soft tissues. This is called soft tissue conduction (STC). We hypothesized that introducing substances with acoustic impedances that sharply deviate from those of soft tissues, such as air pockets, into the soft tissues beneath soft tissue stimulation sites would have an effect on the auditory threshold to stimulation at skin sites over soft tissue. In human subjects, we assessed the auditory threshold with a bone vibrator applied to several STC sites, especially the cheek, and to several bone conduction sites on the skull. The subjects were equipped with bilateral earplugs. The subject then filled his or her cheek with either air or water, and the auditory threshold was again determined. We also recorded the auditory brain stem response to STC stimulation under the chin in fat sand rats in the absence and presence of subcutaneous air or saline solution pockets (0.4 mL) under the chin. In humans, the threshold to stimulation on the cheek was elevated (13 to 18 dB) in the presence of an air-inflated cheek, but not with a water-filled cheek. In animals, in the presence of an air pocket, the auditory brain stem response threshold was elevated by 10 to 20 dB; no threshold change occurred with a saline solution pocket. The introduction of air (but not water) into the soft tissues beneath the soft tissue stimulation sites led to a threshold elevation in both humans and animals. This was not the case when an identical volume of water was introduced, which would also have interrupted a possible parallel bone conduction pathway. These results provide evidence that soft tissue stimulation at low intensities induces tissue vibrations that are transmitted to the cochlea along a series of soft tissues with similar acoustic impedances.

Pressure and partial wetting effects on superhydrophobic friction reduction in microchannel flow

Friction reduction in microchannel flows can help alleviate the inherently taxing pumping power requirements associated with the dimensions involved. One possible way of achieving friction reduction is through the introduction of surface microtexturing that can lead to a superhydrophobic Cassie-Baxter state. The Cassie-Baxter state is characterized by the presence of air pockets within the surface microtexturing believed to act as an effective “shear free” (or at least shear reduced) layer, decreasing the overall friction characteristics of the surface. Most work in this area has concentrated on optimizing the surface microtexturing geometry to maximize the friction reduction effects and overall stability of the Cassie-Baxter state. However, less attention has been paid to the effects of partially wetted conditions induced by pressure and the correlation between the liquid-gas interface location within the surface microtexturing and the microchannel flow characteristics. This is mainly attributed to the difficulty in tracking the interface shape and location within the microtexturing in the typical top-down view arrangements used in most studies. In this paper, a rectangular microchannel with regular microtexturing on the sidewalls is used to visualize and track the location of the air-water interface within the roughness elements. While visually tracking the wetting conditions in the microtextures, pressure drops versus flow rates for each microchannel are measured and analyzed in terms of the non-dimensional friction coefficient. The frictional behavior of the Poiseuille flow suggests that (1) the air-water interface more closely resembles a no-slip boundary rather than a shear-free one, (2) the friction is rather insensitive to the degree of microtexturing wetting, and (3) the fully wetted (Wenzel state) microtexturing provides lower friction than the non-wetted one (Cassie state), in corroboration with observations (1) and (2).

Corrosion and Oxidation Behavior of Zr58Cu22Fe4Co4Al12 Metallic Glass

The pitting corrosion behavior of melt spun ribbon made at a wheel speed of 20 ms in 3.5 wt% NaCl solution and nonisothermal and isothermal oxidation behavior of 2 mm diameter rod samples of newly developed Zr58Cu22Fe4Co4Al12 bulk metallic glass have been studied. The pitting corrosion is more on the air side as compared to the wheel side mainly due to the presence of air pockets. The pitted regions are enriched with copper suggesting dealloying effect due to its noble nature. The alloy shows very good oxidation resistance compared to some of the exiting bulk metallic glass forming alloys. The oxidation leads to the formation of mainly tetragonal ZrO2 with the presence of monoclinic ZrO2, mixture of CuO and Cu2O and Al2O3. Copper in the alloy oxidized progressively with the appearance of white flowery globule shape which later forms interconnected faceted CuO network.

"Air - Bubble" Sign - An uncommon presentation of a common disease

Sir, A 33-year-old female presented with right-sided pleuritic chest pain and expectoration of mucopurulent, foul-smelling, and salty sputum for one year. There was a history of close contact with a pet dog for last two years. General survey and systemic examination revealed no abnormality. Absolute eosinophil count was 800/cmm. Sputum microscopy for acid fast bacilli was negative. A homogenous opacity in right lower lobe was seen in chest radiogram [Figure 1]. Contrast enhanced computed tomography (CECT) scan of thorax showed two rounded, heterogenous opacities (1 × 1 cm and 1.5 × 2 cm, respectively) with presence of air pockets within the lesions—the “air – bubble sign” [Figure 2]. Ultrasonography (USG) of thorax revealed loculated collection of fluid with echogenic organization inside. USG-guided aspiration of the lesion revealed viscid material. Cytology of the smear showed fragmented membranous structures with lamination along with aggregates of degenerated inflammatory cells in a background of proteinaceous fluid [Figure 3]. Fiberoptic bronchoscopy did not reveal any endobronchial lesion. USG of whole abdomen did not reveal cyst in intra-abdominal organs. Serum anti-echinococcal IgG level was 26.41 U/ml (normal value: <8 U/ml, ELISA method). A diagnosis of infected hydatid cyst in right lung was made and albendazole tablet, 400 mg twice daily, was started. The patient was referred to the department of cardiothoracic surgery for further management and follow up.Figure 1: Chart X-ray—PA and right lateral view showing homogenous opacity in right lower lobe with sparing of right costophrenic angleFigure 2: CECT thorax showing “Air – bubble” signFigure 3: FNAC showing fragmented membranous structures with laminationEchinococcosis, a zoonosis caused by Echinococcus granulosus is endemic in India, mostly involving liver and lungs. Most pulmonary cysts are asymptomatic and become clinically evident as a result of complications like cyst rupture and secondary infection. Pulmonary cysts are characteristically solitary and involve single lobe, mainly the lower lobe, and more common on the right.[1] Structurally, the cysts consist of pericyst, exocyst, and endocyst from outside inwards. Echinococcal cysts carry high risk of rupture with subsequent seeding to the other viscera[2] and secondary infection. The rupture may lead to anaphylactic reaction.[2] Most common respiratory symptoms of ruptured hydatid cyst are cough with fetid expectoration.[2] CECT scan of thorax is the diagnostic modality of choice for pulmonary hydatid cyst. Most of intact pulmonary cysts present as solid lesions of fluid density on CECT thorax. But ruptured cysts almost always present with a variety of radiological appearances due to different combinations of collapsed membrane, air, and fluid, making its diagnosis difficult. Sometimes, secondary bacterial infection supervenes on the ruptured cyst with subsequent increase in attenuation numbers in CECT thorax.[3] Because of solid density of the cyst, the differentiation from a pulmonary neoplasm is usually impossible. Serological test like anti-echinococcal IgG is helpful in most patients for final diagnosis, but measurable immunological response may not develop in few patients. Pulmonary hydatid cyst may rupture through pericyst only or through pericyst, exocyst, and endocyst with expulsion intracystic contents within airways. A number of radiological signs of ruptured cysts are described which include crescent sign, water lily sign, daughter cyst, double arch sign, ring within a ring sign, serpent or snake sign, and spin or whirl sign.[4] When there is dissection of air between the pericyst and parasitic membrane, due to erosion of a bronchiole by an expanding cyst, “airbubble” sign is seen. The “air bubble” sign which is a relatively newly recognized radiological sign is reported to be very sensitive and specific (85.7% sensitivity and 96.6% specificity) in establishing diagnosis of ruptured, infected hydatid cyst.[5] Air bubble sign is best seen in mediastinal window as single or multiple small, rounded radiolucent areas with sharp margins within the periphery of a solid mass lesion.

Vapor Stabilizing Substrates for Superhydrophobicity and Superslip

The success of rough substrates designed for superhydrophobicity and superslip relies crucially on the presence of air pockets in the roughness grooves. This air is supplied by the surrounding environment. However, if the rough substrates are used in enclosed configurations, such as in fluidic networks, the air pockets may not be sustained in the roughness grooves and may diffuse out. In this work, a design approach based on sustaining a vapor phase of the liquid in the roughness grooves, instead of relying on the presence of air, is explored. The resulting surfaces, referred to as vapor stabilizing substrates, are deemed to be more robust against wetting transition even if no air is present.

Superplastic forming of Zr based metallic glass ribbons under equibiaxial tension

In this paper, the superplastic forming behaviour of a Zr based metallic glass ribbon at different die diameters is examined. The wall thickness distribution and the relative bulging height values of the ribbon are experimentally determined, and the results are in reasonably good agreement with the finite element method (FEM) findings. The ribbon demonstrated early failure in both tensile tests and gas pressure forming. It is considered that the presence of air pockets in the as cast ribbon is one of the reasons for this. The FEM results also demonstrate that the air pockets may develop into localised regions which may eventually lead to failure of the ribbon. The differential scanning calorimeter curves of the as cast and deformed specimens show that the onset temperature of crystallisation is changed after deformation. This change is related to its change of microstructure. More work is needed to improve the formability of the ribbon and to study the post-deformed properties of the metallic glass.

Foamability and foam stability at high pressures and temperatures. I. Instrument validation

An instrument was designed and assembled with the aim of measuring macroscopic properties of foams (such as foamability and stability) under high pressures and moderate temperatures (up to 105 bar and 425 K, respectively). The device makes use of infrared sensors to detect the foam forefront position as it is generated by gas sparging in the foaming solution. The measurement makes use of a modified dynamic Bikerman protocol to estimate the foamability and stability of the studied solution. Traditional direct observation used in foam experiments at ambient conditions is therefore circumvented and the instrument can be set up in an appropriate place and monitored remotely so as to reduce the risks involved in high-pressure, high-temperature operations. Data from the infrared system allows not only following the dynamics of foam phenomena but also the relative foam quality along the column, and the presence of air pockets in the case of unstable or pulsating foams. A series of fluorosurfactants (cationic, anionic, and nonionic) were used to validate the instrument and the effect of temperature on foamability, foam stability and foam quality is discussed. Finally, synergistic effects were observed with respect to the foam behavior of different mixtures of the studied surfactants.

Response to the comments of D. R. Blackman and Y. Peleg (JRA 14, 411-14)

The comments on my article (JRA 13,104-32) by Blackman and Peleg, which are much appreciated, reflect prevailing discussions on Roman hydraulic engineering practices as well as on the relevant paragraphs of Vitruvius (8.6). Blackman focuses mainly on technical aspects, while Peleg aims at archaeological arguments.Blackman starts with a discussion of the term ‘siphon’, which he regrets being used as it could lead to misunderstanding: ‘siphon’ would represent a “real” siphon, not an “inverted” siphon, suggesting that I must have meant that there was a real siphon at Aspendos. However, in archaeology “siphon” is generally accepted to represent an inverted siphon. There is no misunderstanding: at Aspendos we have an inverted siphon, and since real siphons are not known in classical aqueduct systems, there is no objection to using ‘siphon’ and ‘inverted siphon’ for one and the same notion. Subsequently he states: “The presence of air pockets and so on is almost irrelevant to operations [of siphons] if no point in the system lies above the Hydraulic Gradient Line; were it not so, no garden hose would work reliably” This is a misconception. It is only due to the fact that our garden hoses are connected to supplies with elevated pressures that we get water from them. If we would connect the hose to a low-pressure source (e.g., to a rainwater container standing at ground level), we have to straighten out the coils before water will emerge. If the hose is coiled up, for example, on a wall support but positioned below the free water surface in the container to which it is connected, while we are holding the free end somewhere near the ground, we have nothing but an inverted siphon with high points. If air pockets are irrelevant, water should come out, but it does not if air is in the hose. For problems associated with air pockets in gravity-driven closed conduit systems (which classical siphons must be considered to be), see G. Corcos, Air in water pipes (1989) and H. T. Falvey, Air-water flow in hydraulic structures (1980).

Two sets of technical comments on P. Kessener, “The aqueduct at Aspendos,” JRA 13

Kessener's comprehensive and scholarly contribution, which bravely tackles the basic science in some detail and which will surely be an enduring reference, nevertheless perpetuates some technical misunderstandings that recur in the literature. I begin with the term “siphon”. It is unfortunate that this term continues to be used. The term applies to the situation when, at some point in a closed conduit, the hydrostatic pressure is less than atmospheric. It is not just that the overwhelming proportion of the innumerable pipe systems in the world never know sub-atmospheric pressure and should not be confused with this unusual arrangement, which warrants a technical term of its own (indeed, many modern textbooks do not mention siphons); but to introduce the term inappropriately also leads to misleading reporting and misconceptions. When we reach the discussion of the hydraulics of this system, real siphons find their way into the argument (p. 125), though the evidence shows that there was no siphon at Aspendos. The presence of air pockets and so on is almost irrelevant to operations if no point in the system lies above the Hydraulic Grade Line; were it not so, no garden hose would work reliably.It is quite true that the problems of getting a siphon to start and to keep it running are significant: even without leaks, air tends to come out of solution and will eventually destroy the liquid column. But in a pipe system which does not go sub-atmospheric, the inverse (if we might dare to use the word) applies: air trapped at a high point will tend to be taken into solution, and the confused internal flow at such a point will be very efficient at entraining and so removing air. Just as a garden hose may splutter when first turned on, very rapidly all air is expelled from the system and there is no question that flow will eventually be established without further intervention.

EFFECT OF AIR POCKETS ON PIPELINE SURGE PRESSURE.

Through a series of analytical examples, it is demonstrated how the presence of air pockets can severely exacerbate surge peaks during pump shut-down in single water pipeline systems when operating unprotected against transient pressures. Single air pockets of small size and the multiple presence of air pockets are shown to be especially problematic. It is suggested that such behaviour may trigger pipe failures in circumstances where normal surge analysis may not predict such collapse.