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The aim of this study was to evaluate the sulphur hexafluoride (SF6) tracer technique for methane (CH4) emission measurement in sheep. Ten cryptorchid Romney sheep were involved in two indoor trials (T1 and T2), where daily CH4 emissions were individually measured both by the SF6 tracer ('tracer CH4') and by the indirect calorimetry chamber ('chamber CH4') techniques while fed on lucerne hay at 1.2 times maintenance requirements. Separate sets of permeation tubes with pre-calibrated permeation rates ('pre-calibrated PRs') were used in the two trials (for tracer CH4) and at the time of T1 and T2 these tubes had been deployed in the rumen for 250 and 30 days, respectively. The tracer CH4 measurements were carried out for 2 (T1) and 5 (T2) days in digestibility crates housed within a building (T1) or a well-ventilated covered yard (T2). Sheep were transferred to calorimetry chambers for 3 days acclimatisation, followed by measurement of CH4 emission for 7 (T1) and 3 (T2) days. In T1 samples from the chamber, outflow and inflow (collected over ∼22 h) were analysed for CH4 and SF6 concentrations using the tracer protocol. Thus, PRs of SF6 at the time of the trials ('calculated PRs') could be inferred and the corresponding CH4 emissions are then calculated using either the pre-calibrated PR or calculated PR. Permeation tubes were recovered at the end of the animal trials and their 'post-recovery PR' determined. In trial T1, the tracer CH4 estimates (based on the pre-calibrated PR) were much higher and more variable than the chamber CH4 values. In this trial, the calculated PR and the post-recovery PR were similar from each other but smaller than the pre-calibrated PR, and when the calculated PR was used in place of the pre-calibrated PR the CH4 emission estimates agreed well with the chamber CH4 values. This suggested that the discrepancy was due to a declining PR during the long deployment time of the tubes in T1, an observation reported elsewhere. When the long intra-ruminal deployment was avoided in T2, good agreement between the techniques for CH4 emission measurement was observed.

Ruminant husbandry is a major source of anthropogenic greenhouse gases (GHG). Filling knowledge gaps and providing expert recommendation are important for defining future research priorities, improving methodologies and establishing science-based GHG mitigation solutions to government and non-governmental organisations, advisory/extension networks, and the ruminant livestock sector. The objectives of this review is to summarize published literature to provide a detailed assessment of the methodologies currently in use for measuring enteric methane (CH) emission from individual animals under specific conditions, and give recommendations regarding their application. The methods described include respiration chambers and enclosures, sulphur hexafluoride tracer (SF) technique, and techniques based on short-term measurements of gas concentrations in samples of exhaled air. This includes automated head chambers (e.g. the GreenFeed system), the use of carbon dioxide (CO) as a marker, and (handheld) laser CH detection. Each of the techniques are compared and assessed on their capability and limitations, followed by methodology recommendations. It is concluded that there is no ‘one size fits all’ method for measuring CH emission by individual animals. Ultimately, the decision as to which method to use should be based on the experimental objectives and resources available. However, the need for high throughput methodology e.g. for screening large numbers of animals for genomic studies, does not justify the use of methods that are inaccurate. All CH measurement techniques are subject to experimental variation and random errors. Many sources of variation must be considered when measuring CH concentration in exhaled air samples without a quantitative or at least regular collection rate, or use of a marker to indicate (or adjust) for the proportion of exhaled CH sampled. Consideration of the number and timing of measurements relative to diurnal patterns of CH emission and respiratory exchange are important, as well as consideration of feeding patterns and associated patterns of rumen fermentation rate and other aspects of animal behaviour. Regardless of the method chosen, appropriate calibrations and recovery tests are required for both method establishment and routine operation. Successful and correct use of methods requires careful attention to detail, rigour, and routine self-assessment of the quality of the data they provide., This review is part of the FACCE-JPI ‘Global Network’ project. Authors acknowledge national funding from the Departmentfor Environment, Food and Rural Affairs (UK), INIA (Spain, project MIT01-GLOBALNET-EEZ), the Ministry of Economic Affairs(The Netherlands; project Global Research Alliance on Agricultural Greenhouses Gases, BO-20-007-006), USDA-NIFA (USA),French National Research Agency through the FACCE-JPI program, Agricultural GHG Research Initiative for Ireland (AGRI-I),Academy of Finland, Helsinki, Finland (Project 281337), and BLW (Switzerland).

The aim of this study was to determine if methane emissions from young farmed deer increase with age. Methane emissions of 20 red deer stags grazing permanent perennial rye grass-based pasture were measured four times post-weaning, at 4.5, 6.5, 9 and 11.5 months of age, using the sulphur hexafluoride technique. Methane production and methane yield increased with age (P＜0.05) and appeared lower (26％) than previous measurements from adult deer on similar pasture. These results imply that total methane emissions from young deer recorded in the New Zealand Greenhouse Gas Inventory are likely to be overestimated if values are based on adult methane emissions only.

Estimates of methane (CH4) production from grazing animals are routinely made using the sulphur hexafluoride (SF6) tracer technique. While this technique is generally regarded as useful, some investigators report a higher variability in measurements when compared with calorimetry. The SF6 technique is a marker dilution method in which a known release rate of SF6 from an intra-ruminal permeation tube is used to calculate CH4 emissions from the ratio of SF6:CH4 in expired breath. The release rate of SF6 is unique for each tube, and although calculated CH4 emissions should be independent of SF6 release rate, an analysis of research conducted in New Zealand has suggested a possible influence of SF6 release rate upon calculated CH4 emissions. A modified cross-over design, with two groups of six steers given either one (2.878 mg SF6 d-1) or two (7.336 mg SF6 d-1) permeation tubes and offered either energy maintenance (M) or 2 × M levels of feed intake was undertaken to determine the effect of SF6 release rate and intake on calculated CH4 emissions. A high SF6 release rate elevated the calculated CH4 emission per day (P < 0.001) and per kg dry matter intake (kg DMI) by 19% (P < 0.001) irrespective of the level of intake. Release rate of SF6 can affect the calculated CH4 emissions from animals when employing the SF6 tracer technique. Key words: Methane, SF6 tracer technique, cattle, variability, feeding level

The aim of this article is to present Paschen characteristic formulae with appropriate constants for most of the common gases used in high voltage technology. This aim is achieved by choosing two appropriate well-separated values on the Paschen characteristic, and this enables the two physical-engineering constants B and C in formula to be determined.

Electrical equipment using SF6 forms an integral part of the electricity networks, providing a safe and reliable power supply throughout the world including most European countries. SF6-emissions potentially occur in all lifecycle-phases of electrical equipment—manufacture, use and decommissioning. A study summarized in this paper finds that SF6 emissions throughout the life-cycle have substantially been reduced since the mid-nineties. Almost all available and economically feasible reduction options have been accessed at least partly. The study demonstrates that, until 2020, further reductions can be achieved if these reduction options are fully implemented throughout Europe. This paper gives an overview of reduction potentials and costs, as well as the real and projected emission development between 1995–2020.

Fourier transform infrared spectrometry has been used to retrieve the total column abundances of SF 6 at three locations in the northern hemisphere, i.e., the Ny– Alesund site in Spitsbergen/Norway at 79 ∘ N , the Jungfraujoch observatory in Switzerland at 47 ∘ N and the Kitt Peak observatory in Arizona, USA, at 32 ∘ N . The total column results have been converted to average tropospheric mixing ratios. The mean increases in these mixing ratios have been found to be equal to 0.31 ± 0.08 pptv yr - 1 at Ny Alesund, 0.24 ± 0.01 pptv yr - 1 at the Jungfraujoch and 0.28 ± 0.09 pptv yr - 1 at Kitt Peak for the common period March 1993 to March 2002, in agreement with corresponding CMDL data ( 0.21 ± 0.0002 pptv yr - 1 ) at the surface. The limited accuracy of the Ny Alesund and Kitt Peak data results from strong tropospheric water vapour interferences at these lower altitude sites. Observations at all three locations show that SF 6 is still accumulating in the atmosphere. Extrapolations of linear and second-order fits to the Jungfraujoch data predict tropospheric mixing ratios of SF 6 , respectively equal to 16.4 ± 0.5 and 14.7 ± 0.6 in 2050, and 28.2 ± 0.9 and 22.2 ± 0.8 pptv in 2100, significantly lower than those reported in the literature so far.

Bulk age determinations, based upon chlorofluorocarbons and sulphur hexafluoride measurements of samples from twenty-one chalk groundwater supplies in southern England, Indicate that waters of relatively recent age predominate In both unconfined and partially confined situations. Water from pumping stations located on chalk below Palaeogene cover can be distinguished hydrochemically, and a likely interpretation is that these supplies are receiving a small proportion of recharge via induced via induced leakage. Whilst water which is abstracted from the chalk always involves mixing processes, for a sub-set of confined supplies, ‘piston’ flow could be inferred as a dominant mechanism - resulting in bulk groundwater ages of a few decades. Other supplies are the product of complex mixing. Although low-level chlorofluorocarbon enrichment was encountered for half the catchments sampled, they and sulphur hexafluoride appear to provide independent corroboration to microbiological indicators of the presence of rapid recharge.

The aim of the study was to assess how deep into the acinar region the airway response to cold dry-air hyperventilation challenge (CACh) reaches in subjects with asthma of different severity. Peripheral airway function was measured using a single-breath sulphur hexafluoride (SF 6 ) and helium (He) washout test and overall airway function by forced expiratory volume in one second (FEV 1 ) at rest, after CACh and β 2 -therapy in 55 adults with a history of asthma. The normalised phase-III slopes (Sn III ) for SF 6 and He were used to assess peripheral airway obstruction and the (SF 6 -He) Sn III difference to indicate where obstruction occurred. While a greater He versus SF 6 slope increase indicates a response close to the acinar entrance, the reverse indicates a response deeper into the acinar airspaces. Twelve subjects had a major fall in FEV 1 (≥20%) after CACh, 16 a minor fall (10–19%), and 27 did not react. Resting He and SF 6 Sn III were significantly greater in major responders with respect to minor and nonresponders, while resting FEV 1 did not differ between the three groups. The major responders showed marked increases of He and SF 6 Sn III after CACh, with greater increase for He resulting in a negative (SF 6 -He) Sn III difference. To conclude, airways close to the acinar entrance participate in the overall airway response to cold-air challenge in asthmatic adults with marked airway hyperresponsiveness to cold, dry air.

Comprehensive ( p , ρ , T ) measurements on pure ethylene (83 values), pure ethane (168 values), and pure sulphur hexafluoride (220 values) have been carried out in the homogeneous gas and liquid phases for temperatures from 235 K to 520 K at pressures up to 30 MPa. The measurements were performed by means of an accurate single-sinker densimeter based on the Archimedes’ buoyancy principle. The total uncertainty of the measurements in density ρ was estimated to be ±(0.02 to 0.025)%. The measurements have been compared with results of other experimentalists and with values calculated from current equations of state.

A solid analytic procedure of Gas insulated switchgear condition checking is utilized in this studies as a part of exploration for the detection of sulphur hexafluoride gas (SF 6 ) decomposition by-product because of its high affectability, reliability and anti-electromagnetic obstruction. This is known as chemical decomposition by-product method. A simulated coaxial deterioration chamber was designed and used on the high voltage electrode to re-enact the decomposition of SF 6 under the impact of protrusion defect that generates partial discharge in the coaxial chamber at a pressure of 0.2MPa.The chamber is energised at 50kv for the period of 50 hours and the generated partial discharge simulate the decomposition of SF 6 gas. The deterioration decomposition products SO 2 , SOF 2 , SO 2 F 2 , SO 2 F 10 , SiF 4 , CO, C 3 F 8 , C 2 F 6 were detected offline by FTIR spectrometer. These deteriorated items and its concentration can be utilized to recognize and distinguish the type and the magnitude of fault in gas insulated switchgear (protrusion fault) before failure occur for the aim of preventive maintenance.

The requirement to tackle anthropogenic greenhouse gas (GHG) emissions has become increasingly urgent as understanding of the risks of climate change has advanced. The scientific community has been developing mechanisms to bring about a reduction in the quantities of anthropogenic GHG emissions in order that responsibility for anthropogenic climate forcing may be equitably assigned and specific, pragmatic emissions reduction targets can be set and progress measured. The ‘carbon footprint’ is increasingly being recognised as a valuable indicator in the field of GHG emissions management. For ease of application the definition the “carbon footprint” has been limited to the inclusion of emissions of carbon dioxide (CO2) and methane (CH4) by Wright et al. (2011). However, in some cases a more complete measure is needed that includes the full array of Kyoto “basket” GHGs – CO2, CH4, nitrous oxide (N2O), sulphur hexafluoride (SF6), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs). Outside of the academic literature the conventional approach is to term this metric a “GHG inventory” (UN, 1998; Ranganathan et al., 2004). However, in the academic literature the term “GHG inventory” has been used to account for various different collections of GHGs and other climate-influencing gases, leading to confusion over the definition of the “GHG inventory”. Consequently, an alternative term, the “climate footprint”, has been proposed (Wiedmann and Minx, 2008; Wright et al., 2011) which aims to eliminate this confusion. The question is: should we continue using the commonly-used term, “GHG inventory”, and endeavour to impose and promote a strict definition or should we introduce a new, rigorously defined term, the “climate footprint”

Daily methane emission from 12 Romney‐cross‐bred ewes and 10 lactating Friesian dairy cows, rotationally grazed on perennial ryegrass/white clover dominant pastures, was measured during four seasons of a year (September, November, March, and June/July). Methane emission was measured from each animal for 5 consecutive days in each measurement period using the sulphur hexafluoride tracer gas technique. The pastures varied significantly in chemical composition between seasons, generally decreasing in protein, soluble sugars, and digestibility and increasing in acid detergent fibre (ADF) and neutral detergent fibre (NDF) as the grasses flowered in November, with an increase in protein and a decrease in soluble sugars in March, a trend that continued through to June/July. Methane emission (g/day) from dairy cows was significantly different (P < 0.001) between seasons, being high at peak lactation in September (430.6) and declining with milk yield and feed intake in November (247.6) and March (181.5) a...

Methane (CH4) and carbon dioxide (CO2) production from six crossbred yearling beef heifers (400 ± 13.0 kg) were measured, using the sulphur hexafluoride (SF6) tracer gas technique (Tracer) and open-circuit hood calorimetry (Cal) to validate the former in estimating rumen CH4 and CO2 production in the field. Animals were individually fed a diet consisting of 50% barley concentrate and 50% alfalfa cubes at 1.3 &times ;maintenance requirements daily. Hifers were divided into two groups for individual animal 24- h gas measurements by each method. Each group of heifers was rotated between the Cal and Tracer techniques for 6 consecutive days in an incomplete block design. Methane production ranged from 108 to 145 L d-1 (mean 130 ± 4.0 L d-1) using the Cal technique, and 90 to 167 L d-1 (mean 137 ± 4.0 L d-1) using the Tracer technique. The mean CH4 production (L d-1) was not different (P = 0.24) between the two methods. Carbon dioxide production with the Tracer technique was 20% higher than CO2 production with the Cal technique (P < 0.01). The range of CO2 production was 1574 to 2049 L d-1 (mean 1892 ± 74.0 L d-1) by Cal, and 1541 to 3330 L d-1 (mean 2353 ± 74.0 L d-1) by Tracer. Day-to-day variation in CH4 production was not different within each method (P > 0.05); however, animal-to-animal variation (11.7%) was significant for the Tracer technique (P = 0.04), but not for the Cal technique (P = 0.53). Comparison of the equality of variance between the two methods showed that there were no differences in variations (P > 0.05) between Cal and Tracer for CH4 production. On the other hand, variations in CO2 production were not equal (P > 0.05) between methods. Day-to-day variation in CO2 production was significant using Cal, but not Tracer (P > 0.05). Animal-to-animal variation in CO2 production was 1.6 and 11.8% by Cal and Tracer techniques, respectively. It can be concluded that the SF6 tracer technique accurately estimated rumen CH4 production, but CO2 production was 20% higher. The study suggests that for CH4 measurements using the SF6 tracer technique, more animal numbers are needed than for Cal to reduce animal-to-animal variation. Key words: Methane, carbon dioxide, SF6 tracer technique, validation, cattle

Magnesium metal in its molten state will oxidise rapidly in air, leading to burning on the melt surface. In order to process molten magnesium safely, the melt is protected from oxidation by blanketing the surface with a cover gas. The cover gas reacts with the metal and forms a protective film on the melt surface. Sulphur hexafluoride (SF 6 ) is widely used by the magnesium industry as a component of cover gas mixtures. However, the use of SF 6 has come under increased scrutiny due to its high cost and, more importantly, its significant impact on the greenhouse effect. To optimise the use of SF 6 , a detailed knowledge of its role in protecting molten magnesium is required. This paper describes the characterisation of the surface films formed on molten magnesium protected by cover gas mixtures containing SF 6 . Sensitive surface analysis techniques have been used to quantitatively determine the chemical attributes of the films. XPS showed that the film contains only MgO and MgF 2 . No sulphur compounds were detected. AES depth profiling indicated film thickness to be in the range 0.1–1 μm.

Experimental studies have been undertaken, involving in situ observations of the interaction between cover gas mixtures and molten magnesium. It has been shown that, in the presence of sulphur hexafluoride (SF6), the contact angle between solid MgO and molten magnesium is reduced, resulting in the wetting of MgO by magnesium metal. In contrast, it was observed that the absence of SF6 results in a large contact angle, poor wetting of the MgO by magnesium metal and a non-adherent surface film. It is proposed that the formation of an adherent, protective surface film under a cover gas mixture containing SF6 is due to capillary forces acting within the film.

Gas insulated switchgear (GIS) plays a vital role in high voltage transmission of electrical energy due to its advantages of high reliability and performance, compact in dimensions and outstanding compatibility with the environment. It uses sulphur hexafluoride gas as its insulant and coolant because of its high dielectric strength and excellent arc quenching ability. Gas insulated switchgear in operation suffers the challenge of its insulation decomposition and eventually failure due to the activities of partial discharge that arouses from defects. This failure is catastrophic and it will lead to entire power out stage that will affect all categories of human activities, so there is a need for Gas insulated switchgear condition monitoring and diagnoses in order to carry out preventive maintenance. This paper reviews diagnostic techniques and methods for Gas insulated switchgear insulation degradation caused by partial discharge for the purpose of carrying out preventive maintenance to avert its failure.

The need for compact substations in the densely populated areas has led to the development of gas insulated substations (GIS) which offer a best alternative to conventional air insulated substation in technical, environmental and operational features. The entire parts of these substations are housed in earthed metallic enclosures filled with sulphur hexafluoride gas (SF 6 ). Further research in the field of GIS helps in developing HVDC transmission of power through Gas insulated transmission. The major problem associated with the Gas insulated substations is the particle contamination which generally arises due to manufacturing or operational cycles. The understanding of the particle movement is of vital importance as these tend to increase the breakdown chances of gas insulation. The present work focuses on the determination of lift off fields on commonly encountered metallic particle contaminants in gas insulated busducts working on DC voltages. New dimensions of the busduct are proposed in order to reduce the electrostatic fields on the particles thereby reducing the chances of the breakdown.

Gas insulated substations have found their applications in the modern day power industry due to their low space requirement and higher reliability of operation. Their major components include busducts, circuit breakers, transformers that are placed in enclosures filled with sulphur hexafluoride gas. The major component of GIS is the gasinsulated busduct which has conductors enclosed in anearthed metallicenclosure filled with a high electronegative gas sulphur hexafluoride, SF 6 . Though GIS are highly reliable, the major reason for the breakdown is due to the metallic particle contamination which arises due to manufacturing and operational functions. Among the contaminants, Aluminium particles are of prime concern as they are lighter and hence move freely when compared to the other metallic particle contaminants.In this paper, the critical dimensions of Aluminium wire like particle contaminants are determined which may lead to breakdown using the conventional field calculation method. The simulation results show that the particles with higher lengths and with lower radii are more responsible for breakdown in busducts.

We use FUND 3.5 to estimate the social cost of carbon dioxide, methane, nitrous oxide, and sulphur hexafluoride emissions. We show the results of a range of sensitivity analyses, focusing on the impact of carbon dioxide fertilization. Ignored in previous studies of the social cost of greenhouse gas emissions, carbon dioxide fertilization has a positive effect at the margin, but only for carbon dioxide. Because of this, the ratio of the social cost of a greenhouse gas to that of carbon dioxide (the global damage potential) is higher - that is, previous papers underestimated the importance of reducing non-carbon dioxide greenhouse gas emissions. When leaving out carbon dioxide fertilization, our estimate of the social cost of methane is comparable to previous estimates. Our estimate of the global damage potential of methane is close to the estimates of the global warming potential because discounting roughly cancels carbon dioxide fertilization. Our estimate of the social cost of nitrous oxide is higher than previous estimates, also when omitting carbon dioxide fertilization. This is because, in FUND, vulnerability to climate change falls over time (with development) while in the long run carbon dioxide is a more potent greenhouse gas than nitrous oxide. Our estimate of the global damage potential of nitrous oxide is larger than the global warming potential because of carbon dioxide fertilization, discounting, and rising atmospheric concentrations of both gases. Our estimate of the social cost of sulphur hexafluoride is similar to the one previous estimate. Its global damage potential is higher than the global warming potential because of carbon dioxide fertilization, discounting, and rising concentrations.

With special respect to HVDC transmission, an artificial protrusion is investigated experimentally in compressed sulphur hexafluoride (SF 6 ) gas. Varied test parameters are voltage waveform and gas pressure. Corona inception and breakdown voltages are measured at DC and AC. Lightning and switching impulse breakdown voltages are evaluated at repeated constant amplitude stress. Composite voltage stress consisting of lightning impulse superimposed to DC bias is further examined. In this case, no significant reduction of lightning impulse breakdown voltage was observed at high gas pressure.

In ruminants, methane (CH4) is a by-product of digestion and contributes significantly to the greenhouse gas emissions attributed to agriculture. Grazed grass is a relatively cheap and nutritious feed but herbage species and nutritional quality vary between pastures, with management, land type and season all potentially impacting on animal performance and CH4 production. The objective of this study was to evaluate performance and compare CH4 emissions from cattle of dairy and beef origin grazing two grassland ecosystems: lowland improved grassland (LG) and upland semi-natural grassland (UG). Forty-eight spring-born beef cattle (24 Holstein–Friesian steers, 14 Charolais crossbred steers and 10 Charolais crossbred heifers of 407 (s.d. 29), 469 (s.d. 36) and 422 (s.d. 50) kg BW, respectively), were distributed across two balanced groups that grazed the UG and LG sites from 1 June to 29 September at stocking rates (number of animals per hectare) of 1.4 and 6.7, respectively. Methane emissions and feed dry matter (DM) intake were estimated by the SF6 tracer and n-alkane techniques, respectively, and BW was recorded across three experimental periods that reflected the progression of the grazing season. Overall, cattle grazed on UG had significantly lower (P0.05) in CH4 emissions per unit of feed intake when expressed either on a DM basis (20.7 and 21.6 g CH4 per kg DM intake for UG and LG, respectively) or as a percentage of the gross energy intake (6.0% v. 6.5% for UG and LG, respectively). However, cattle grazing UG had significantly (P

The combination of ultrasound (US) and microbubbles (MB) is a promising physical method for improving the nanoparticles (NPs) delivery efficiency. However, few concerns over comparable delivery effect of the passive or active targeting property's NPs mediated by US and MB have limited their translation towards further application. For this, we prepared small interfering RNA (siRNA)-loaded mPEG-PLGA-PLL (siRNA/mPPP) NPs with passive targeting property and siRNA-loaded mPEG-PLGA-PLL-cRGD (siRNA/mPPPR) NPs with active targeting property, and evaluated the effect of US and MB for their delivery efficiency. The experimental results demonstrated that US and MB effectively enhance the siRNA delivery efficiency of the mPPP NPs compared with the mPPP NPs alone. In contrast, an improved delivery efficiency of siRNA was not observed in PC-3 cells treated with the mPPPR NPs mediated by US and MB, suggesting that the delivery efficiency of NPs mediated US and MB also depend on its targeting properties.

International audience; Boiling phenomena in the two-phase region of SF6 close to its critical point have been observed using the high-quality thermal and optical environment of the CNES dedicated facility ALI-DECLIC on board the International Space Station (ISS). The weightlessness environment of the fluid, which cancels buoyancy forces and favorites the three-dimensional spherical shape of the gas bubble, is proven to be an irreplaceable powerful tool for boiling studies. To identify each key mechanism of the boiling phenomena, the ALI-DECLIC experiments have benefited from (i) the well-adapted design of the test cells, (ii) the high-fidelity of the ALI insert teleoperation when long-duration experiment in stable thermal and microgravity environment are required and (iii) the high repeatability of the controlled thermal disturbances. These key mechanisms were observed by light transmission and interferometry technique independently with two sample cells filled with pure SF6 at a near-critical density. The fluid samples are driven away from thermal equilibrium by using a heater directly implemented in the fluid, or a surface heater on a sapphire optical window. In the interferometry cell, the bulk massive heater distinguishes two symmetrical two-phase domains. The modification of the gas bubble shape is observed during heating. In the direct observation cell, the gas bubble is separated by a liquid film from the thin layered transparent heater deposited on the sapphire window. The liquid film drying and the triple contact line motion during heating are observed using light transmission. The experiments have been performed in a temperature range of 10 K below the critical temperature T c, with special attention to the range View the MathML source0.1mK≤Tc−T≤3mK very close to the critical temperature. The unique advantage of this investigation is to provide opportunities to observe the boiling phenomena at very low heat fluxes, thanks to the fine adjustment of the liquid-vapor properties, (e.g. surface tension), by precise control of the distance to the critical point. We present the new observations of the gas bubble spreading over the heating surface which characterizes the regime where vapor bubbles nucleate separately and grow, as well as liquid drying, vapor film formation, triple contact line motion, which are the key mechanisms at the origin of the boiling crisis when the formed vapor film reduces the heat transfer drastically at the heater wall.

Electron energy loss spectroscopy (EELS) has been used to study the photo-absorption spectrum of trifluoromethyl sulphur pentafluoride (SF5CF3) for the first time. Comparison is made with the EELS spectrum of sulphur hexafluoride (SF6). The photolysis of the compound is discussed with relevance to estimated lifetimes in the atmosphere. It is estimated that the lifetime of SF5CF3 is of the order of 1000 years.

The aims of this study were to assess the validity and reliability of body volume and percent body fat determined by sulphur hexafluoride dilution, using underwater weighing as the criterion method, and to determine the influence of the magnitude of body volume. Thirty-one healthy Japanese individuals aged 18-27 years (16 males: height 1.70 +/- 0.06 m, mass 64.8 +/- 7.7 kg; 15 females: height 1.60 +/- 0.05 m, mass 55.2 +/- 6.2 kg; mean +/- s) participated in the study. Sulphur hexafluoride dilution measures the concentration of sulphur hexafluoride gas in the chamber (BSF-200, Shimazu Corp.). Underwater weighing was performed five times using a weight scale (AD-6204, AD) after residual volume had been determined (System9, Minato Medical Corp.). There were no significant differences in the mean between two trials for body volume, body density or percent body fat determined by sulphur hexafluoride dilution. The intra-class correlation coefficient of these variables ranged from 0.985 to 0.999. The results suggest that sulphur hexafluoride dilution is a reliable method for assessing body composition. There was no significant difference in body volume or percent body fat between sulphur hexafluoride dilution (males: 61.3 +/- 7.6 litres, 18.4 +/- 6.7%; females: 52.8 +/- 6.9 litres, 21.0 +/- 8.9%) and underwater weighing (males: 60.6 +/- 7.0 litres, 15.6 +/- 3.5%; females: 53.0 +/- 6.5 litres, 23.7 +/- 6.1%) and there was a high correlation between the two (r = 0.997, P0.05). A Bland-Altman plot of the difference between percent body fat estimated by underwater weighing and sulphur hexafluoride dilution versus average percent body fat by the two methods showed no systematic difference (mean difference = -0.12 +/- 6.6 kg). The upper and lower limits of agreement were 13.2% and -13.4%, respectively. Determination by sulphur hexafluoride dilution resulted in both over- and underestimations in body volume and the difference between the two body volumes (determined by underwater weighing and by sulphur hexafluoride dilution) was inversely proportional to the mean body volume by the two methods. This suggests that improvements need to be made to the device or to the technique to maintain a constant volume of sulphur hexafluoride in the chamber.

Conducting particles in transmission and switching equipment insulated by compressed sulphur hexafluoride (SF6) can re- sult in loss of as much as 90% of the gas dielectric strength. Particles in practical systems can exist in a wide variety of shapes and sizes, and of materials of different densities. In this letter, the effect of particle size on the probability of SF6 breakdown is discussed. Theoretical and ex- perimental results are presented.

This study compares the characteristics of two tracer gases — sulphur hexafluoride (SF 6 ), and nitrous oxide (N 2 O) — whose densities are different from that of air (i.e. 5.11 and 1.53, respectively). The study is based on exclusively experimental work; and concerns the behaviour of the two gases with regard to their distribution and dispersion in an experimental cell, incorporating into the comparison method an index that is intended to characterise the ventilation of an enclosed space, namely ventilation effectiveness, ϵ C .

Charge, fired strip multiplicity distributions for the induced signal were investigated for the 2 mm gap RPC operating with several tetrafluoroethane (C2H2F4) based mixtures with variation of isobutane (iC4H10) and sulphur hexafluoride (SF6) concentrations. Suppression of the large fast charges for the mixtures containing SF6 in comparison with the binary C2H2F4/iC4H10 mixture was confirmed. Exclusion of isobutane from the mixture with 2% of SF6 does not change charge distributions.

Currents trends in indoor air quality involve prevention as well as the need for specific legislation (norms) to protect people’s health and to achieve greater levels of comfort. It is currently one of the most important areas of study [5] , [6] , [10] . The existence of different indoor air quality norms and standards depending on the country involved has made it difficult to determine when these standards really ensure low levels of indoor pollutants. The requirements of the future European ventilation norm (prENV 1752) make a detailed study on the energy implications of the problem essential. This work represents an original study in this field, where the results obtained from a series of practical indoor air quality and ventilation measurements are explored. These results have been obtained using photoacoustic spectroscopy (PAS) and the trace gas (sulphur hexafluoride) technique in a series of Spanish office buildings with varying climatisation systems. The results obtained in ventilation flows as well as an analysis for comparison purposes with data on Spanish, American (ASHRAE 62R) and European norms (prENV 1752) are presented. The conclusions which may be drawn are also offered. Finally, the work shows a ventilation flow which achieves high environmental indoor air quality in offices while at the same time offering compatibility with high energy saving.

The paper reports further results from an investigation into partial discharge degradation of mica – an important component of many insulation systems. Further to work investigating axial stressing, transverse partial discharges have been applied across the surface of two forms of mica: ruby-muscovite and amber-phlogopite. The partial discharges were generated under AC, both polarities of DC, and both polarities of impulse electrical stressing. Three gaseous atmospheres (air, nitrogen (N2) and sulphur hexafluoride (SF6)) have been utilised to obtain degradation mechanisms for most practical environments. A discharge degradation mechanism, based on the effects of particle bombardment and chemical by-product formation, is hypothesised. This hypothesis is consistent with the experimental results.

Choroidal neovascular membrane (CNVM) is one of the most common causes of submacular hemorrhage (SMH). Conventional treatment involves management of the SMH with pneumatic displacement with or without tissue plasminogen activator (TPA) followed by intravitreal injection of bevacizumab in a second sitting. We decided to assess the efficacy of treating SMH secondary to CNVM with pneumatic displacement using sulphur hexafluoride (SF6) gas and intravitreal bevacizumab. Four patients with SMH secondary to CNVM were included in this study. Intravitreal bevacizumab, 0.05 ml, along with 0.5 ml of SF6 was injected through the pars plana into the vitreous cavity. Postoperative best corrected visual acuity improved in all eyes with complete or partial displacement of SMH out of the foveal area.

We show that the addition of small amounts of sulphur hexafluoride, SF 6 , to the present ATLAS baseline gas mixture C 2 H 2 F 4 /C 4 H 10 has a very strong e⁄ect in suppressing the avalanche-to-streamer transition. An RPC of 50]50 cm2 area, 2 mm gas gap was operated in pure avalanche, streamer-free mode in a voltage range of about 1 kV. The results of the test suggest that the observed fast signal could be interpreted as the sum of contributions of a number of primary saturated avalanches. ( 1998 Elsevier Science B.V. All rights reserved.

The fluorinated compounds sulphur hexafluoride (SF 6 ), perfluorocarbons (CF 4 , C 2 F 6 ) and hydrofluorocarbons (HFCs) are atmospheric trace gases with extremely high global warming potentials (GWP). The study examines the real emissions of these compounds in Germany between 1990 and 1995, and develops projections for the years up to 2020. These projections indicate that annual perfluorocarbon releases will drop between the years 1990 and 2000 from 335 t/34 t to 100 t/10 t due to automation measures at the main source (aluminium smelting). Sulphur hexafluoride emissions, however, will remain in the range between 200 and 300 t per annum until the year 2020. By far the largest emitters are car tyres and sound-insulation glazing, non-electrical swithgear, the latter being relatively well sealed and linked to management and reprocessing concepts for used gas. As concerns hydrofluorocarbons which have only been used since 1990 with the specific intention of substituting chlorofluorocarbons (CFCs), an increasing degree of CFC substitution in stationary and mobile refrigeration technology, in canned PUR foams and in asthma sprays must be expected to lead to steeply rising emissions to levels exceeding 9,700 t/a from the year 2007 onwards, if halogen-free alternatives are not used more strongly. Assuming these trends, the cumulative emissions of the stated fluorinated compounds will correspond to a global warming impact of 25 million t CO 2 (GWP time horizon: 100 years) by the year 2020.

International audience; An inter-laboratory comparison exercise involving the environmental tracers used for groundwater dating was organized in 2012 in France. This paper focuses on SF6 and CFC tracers. Sampling and analytical protocols were compared in three different exercises using: (1) groundwater from a homogeneous aquifer, (2) groundwater from a fractured heterogeneous aquifer and (3) an air standard. The results show good agreement between laboratories (except some outliers) for the aquifers and air standard. Variation in the SF6 results on the air standard was low (RSD = 2%) compared to CFCs (RSD 3–7%), even though its concentration was two orders of magnitude lower. Results obtained on recent groundwater (recharged post 1980) show that the inter-laboratory uncertainty for groundwater dating with SF6 is 3–4 years. This large uncertainty is mainly due to sampling and/or analytical problems. For CFCs, the uncertainties obtained from all laboratories were less than 2 years for groundwater recharged between 1965 and 1996. A higher RSD was observed for CFCs with the air standard analysis, as compared to groundwater measurement, which could indicate an additional uncertainty due to inadequate standardization. Different sampling protocols were used by the laboratories (glass bottles, steel cylinders, etc.) but no systematic effect on measurement uncertainty could be attributed to any of these protocols for either CFCs or SF6. The better precisions obtained through these exercises indicate that, except for CFC-11 and SF6, the corresponding uncertainty in recharge date determination on recent groundwater (1993 – present) is higher than the commonly assumed 1–2 years (i.e., 7 years for CFC-12 and 4 years for CFC-113). These results confirm the need for regular inter-laboratory comparison exercises to improve the analytical and sampling procedures used in groundwater dating.

The aim of this study was to compare the diagnostic accuracy of the late phase of CEUS and the hepatobiliary phase of CE-MR with Gd-BOPTA in the characterization of focal liver lesions in terms of benignity and malignancy. A total of 147 solid focal liver lesions (38 focal nodular hyperplasias, 1 area of focal steatosis, 3 regenerative nodules, 8 adenomas, 11 cholangiocarcinomas, 36 hepatocellular carcinomas and 49 metastases) were retrospectively evaluated in a multicentre study, both with CEUS, using sulphur hexafluoride microbubbles (SonoVue, Bracco, Milan, Italy) and CE-MR, performed with Gd-BOPTA (Multihance, Bracco, Milan, Italy). All lesions thought to be malignant were cytohistologically proven, while all lesions thought to be benign were followed up. Sensitivity, specificity, positive (PPV) and negative (NPV) predictive values and accuracy were calculated for the late phase of CEUS and the hepatobiliary phase of CE-MRI, respectively, and in combination. Analysis of data revealed 42 benign and 105 malignant focal liver lesions. We postulated that all hypoechoic/hypointense lesions on the two phases were malignant. The diagnostic errors were 13/147 (8.8%) by CEUS and 12/147 (8.2%) by CE-MR. Sensitivity, specificity, PPV, NPV and accuracy of the late phase of CEUS were 90%, 93%, 97%, 80% and 91%, 93%, 97%, 81% and 92% for the hepatobiliary phase of CE-MRI, respectively. If we considered both techniques, the misdiagnosis diminished to 3/147 (2%) and sensitivity, specificity, PPV, NPV and accuracy were 98%, 98%, 99%, 95% and 98%. The combination of the late phase of CEUS and the hepatobiliary phase of CE-MR in the characterization of solid focal liver lesions in terms of benignity and malignancy is more accurate than the two techniques used separately.

When electrical discharges occur in sulphur hexafluoride gas (SF6) lower fluorides are produced within the discharge, and they in turn react readily with impurities, insulators and the electrodes. The final stable compounds formed include sulphur oxyfluorides and sulphur oxides. The aim of the present work was to optimize an analytical method for determining the decomposition products, and finding the dependence of the reaction route followed on the reaction conditions (input energy, contaminants present in the system). By performing model experiments and using various GC/MS techniques, several decomposition products were identified and correlations found between the abundances of the individual components and the decomposition conditions © 1997 John Wiley & Sons, Ltd.

In a bulk-glass triangular Faraday current sensor, the stringent conditions required to provide critical-angle reflection at each reflecting surface are difficult to achieve. High tolerances for both the optical geometry of the sensor and the wavelength of the laser source are required. Here we present a method of essentially tuning the sensor for optimum operation by matching the angle of reflection at each surface to the wavelength of the laser source. This is done by controlling the gaseous environment external to each of the reflecting surfaces. The technique is demonstrated using sulphur hexafluoride (SF6), which has the advantage of a relatively large refractive index.

SUMMARY The efficacy and side effects of sulphur hexafluoride (SF6) in the reformation of the flat anterior chamber (AC) after standard trabeculectomies were studied. Ten patients with lenticulocorneal touch following trabeculectomy were enrolled. All had water-tight conjunctival wounds with overflowing fistulas. In 5, one to four surgical attempts to reform the AC were unsuccessful. Two to seven days after trabeculectomy, the AC was reformed by a single injection of SFt/air mixture (20-40%). Gas was injected through the limbus at 3 or 9 o'clock. The AC remained deep after absorption of the gas in 2-7 days. All patients had stromal oedema in the first 4 days. This resolved and specular microscopy did not show any abnormality. After a mean follow-up of 2.5 years, all had normal intraocular pressure, 3 with one topical antiglaucoma treatment. Three patients developed cataracts before and 3 after reformation of the AC. The latter 3 were not anterior capsular cataracts as induced by gases. SFt/air mixture (20-40%) is inert and kind to the cornea and, as it is absorbed in less than 7 days, it exerts minimal damage to the crystalline lens. It is effective in the reformation of flat A Cs.

In order to determine the quantity of methane (CH4) produced by steers on pasture, 16 steers with a mean weight of 356 ± 25 kg were randomly selected from a larger group of cattle (n = 48) to evaluate the effects of grazing management and monensin controlled release capsule (CRC) administration on ruminal CH4 production using the sulphur hexafluoride (SF6) tracer-gas technique. Pasture management treatments consisted of two grazing systems (continuous stocking or 10-paddock rotational stocking) at each of two stocking rates (low, 1.1 steer ha−1 or high, 2.2 steers ha−1) with two replications of each pasture treatment. Half of the animals on each pasture treatment were administered a monensin CRC delivering 270 mg d−1, and untreated animals served as controls. During the 140-d grazing season, one steer from each treatment-replicate combination was sampled to determine daily intake and CH4 production on four occasions. The chemical composition of diets differed between grazing management treatments and sampling periods. Voluntary intake and CH4 production, adjusted for differences in body weight, were unaffected by grazing management, sampling period or by monensin CRC administration and averaged 0.69 ± 0.1 L kg BW−1 d−1 across all grazing management treatments. The energy lost through eructation of CH4 averaged 4.5 ± 1.4% of gross energy intake. Key words: Methane, cattle, environment, digestion efficiency, pasture, forage

Sulphur hexafluoride (SF6) gas-insulated substations (GIS) are exposed to the same types of overvoltages as conventional substations, such as lightning overvoltages, switching overvoltages and temporary overvoltages. Possible means to limit overvoltages in a GIS are active gap (SiC) surge arresters and metal oxide (ZnO) surge arresters. The objective of this work is to study the effects of the system configuration on the performance of these two types of overvoltage limiting devices. The results obtained from the study are presented and discussed, and some general conclusions are suggested.

One of the major issues for users and potential users of magnesium is magnesium melt protection. This is particularly so with the use of sulphur hexafluoride coming under increased scrutiny, as it is now recognised as a very potent greenhouse gas. It has been demonstrated that sulphur hexafluoride prevents molten magnesium from oxidation by adding fluorine into the unprotective magnesium oxide surface film. The hydrofluorocarbon gas 1,1,1,2-tetrafluoroethane (HFC-13a) has been recently developed for magnesium melt protection by the Cooperative Research Centre for Cast Metals Manufacturing (CAST) in Australia. This gas has a global warming potential 18 times lower than sulphur hexafluoride and has been shown to be an effective replacement for SF in many applications. HFC-134a has also been shown to have some unique properties resulting in more possible applications for magnesium melt protection than sulphur hexafluoride. Recent experience with HFC-134a in laboratory and plant trials is discussed as well as the global implications of replacing sulphur hexafluoride with hydrofluorocarbons.

This chapter introduces the subject of gaseous insulation and provides information relating to the application of gaseous insulants to high-voltage systems. It examines atmospheric air and compressed gases and illustrates how, by linking available experimental test data from such sources with a knowledge of the 'effectiveness' of various practical gas-gap clearances, the designer can achieve reliable insulation design. The chapter also briefly discusses the need for extra high-voltage (EHV) and ultra high-voltage (UHV) test areas or laboratories. Evidence is presented of how laboratory studies, on representative insulation systems and electrode arrangements, provide the designer with choices relating to electrical stresses, clearance levels, service performance and testing procedures. Gas-insulated substations (GIS) using sulphur hexafluoride (SF6) gaseous insulation have been used in transmission systems worldwide for more than 45 years. The service reliability of this class of equipment is of paramount importance. In addition, the chapter presents a large amount of experimental breakdown information on SF6 and briefly reviews the application of field computation strategies in support of GIS and other equipment designs. Several of the major factors influencing the insulation design and in-service behaviour and reliability of SF6 gaseous and epoxy resin support insulations, as used in GIS equipment, will also be considered.

In this paper, we take the strategy of direct laser interference technology to modify the silicon surface under air and sulphur hexafluoride (SF6) gas ambiance conditions. With the investigation of optical properties, the silicon spike structures (known as black silicon) which were fabricated in the SF6 ambiance showed the excellent ability of reducing light reflection with a broadband spectrum. For comparison, well-defined microcone structures were fabricated in the air ambiance. After hydrofluoric (HF) acid wiping off the oxides on the surface, micro cone structures have shown the anti-reflection function as well and its reflective behaviour was dependent on the structural depth relatively. Due to a high impurities concentration of spike structures obtained in the SF6 ambiance, applications of sulphur-doped black silicon would be limited. To obtain large-scale uniform structures, direct laser interference technology in the air ambiance could be an alternative.