Electrical Breakdown in Water Vapor

In this paper investigations of the voltage required to break down water vapor are reported for the region around the Paschen minimum and to the left of it. In spite of numerous applications of discharges in biomedicine, and recent studies of discharges in water and vapor bubbles and discharges with liquid water electrodes, studies of the basic parameters of breakdown are lacking. Paschen curves have been measured by recording voltages and currents in the low-current Townsend regime and extrapolating them to zero current. The minimum electrical breakdown voltage for water vapor was found to be 480 V at a pressure times electrode distance (pd) value of around 0.6 Torr cm (similar to 0.8 Pa m). The present measurements are also interpreted using (and add additional insight into) the developing understanding of relevant atomic and particularly surface processes associated with electrical breakdown.

Time-Resolved DRIFTS, MS, and Resistance Study of SnO2 Materials: The Role of Surface Hydroxyl Groups in Formation of Donor States

Time-resolved DRIFTS, MS, and resistance measurements were used to study the interaction of undoped and Pd-doped SnO2 with H-2 in air and argon at 300 degrees C. Using first-order kinetics, we compare the time constants for the resistance drop and its partial recovery with those of the surface hydroxyl evolution and water formation in the gas phase upon exposure to hydrogen. In the case of the undoped oxide, resistance and bridging hydroxyls (BOHs) evolve similarly, manifesting a fast main drop followed by recovery at a similar rate. The rate of water formation for this material was found to be much slower than that of the main drop in both the resistance and BOHs. In contrast, the resistance change for SnO2-Pd appeared to be similar to that of water formation, and no correlation was found between the evolution of resistance and surface OHs. Isotopic exchange on both materials revealed that water formation occurs via fast and slow hydrogen transfer to surface oxygen species. While the former originates from just-adsorbed hydrogen, the latter appears to proceed from the preadsorbed OHs. Both surfaces exhibit close interaction between chemisorbed oxygen and existing bridging OH groups, indicating that the latter is an intermediate in the hydrogen oxidation and generation of donor states on the surface.

Selective deuterium ion acceleration using the Vulcan petawatt laser

We report on the successful demonstration of selective acceleration of deuterium ions by target-normal sheath acceleration (TNSA) with a high-energy petawatt laser. TNSA typically produces a multi-species ion beam that originates from the intrinsic hydrocarbon and water vapor contaminants on the target surface. Using the method first developed by Morrison et al. [Phys. Plasmas 19, 030707 (2012)], an ion beam with >99% deuterium ions and peak energy 14 MeV/nucleon is produced with a 200 J, 700 fs, > 10 20 W/cm 2 laser pulse by cryogenically freezing heavy water (D<inf>2</inf>O) vapor onto the rear surface of the target prior to the shot. Within the range of our detectors (0°-8.5°), we find laser-to-deuterium-ion energy conversion efficiency of 4.3% above 0.7 MeV/nucleon while a conservative estimate of the total beam gives a conversion efficiency of 9.4%.

Assessment of the effectiveness of the guard ring in obtaining a uni-directional flow in an in situ water permeability test

The non-destructive evaluation of the water permeability of concrete structures is a long standing challenge, principally due to the difficulty of achieving a uni-direction flow for computing the water permeability coefficient. The use of a guard ring (GR) was originally proposed for the in situ sorptivity test, but little information can be found for the water permeability test. In this study, the effect of a GR was carefully examined through the flow simulation, which was verified by carrying out experiments. It was observed that the GR can confine the flow near the surface, but cannot achieve a uni-directional flow across the whole depth of flow. To achieve a better performance, it is essential to consider the effects of the size of the inner seal and the GR and the significant interaction between these two. The analysis of the experimental data has indicated that the GR influences the flow for porous concretes, but there is no significant effect for dense concretes. Further investigation, validated using the flow-net theory, has shown a strong correlation between the water permeability coefficients obtained with the GR (K w-GR) and without it (K w-No GR), suggesting that one dimensional flow is not essential for interpreting data for site tests. Another practical issue was that more than 30 % of the tests with GR failed due to the difficulty of achieving a good seal between the inner and the outer chambers. Based on the work reported in this paper, a new water permeability test is proposed.

Repeatability and reliability of new air and water permeability tests for assessing the durability of high-performance concretes

This paper reports on the accuracy of new test methods developed to measure the air and water permeability of high-performance concretes (HPCs). Five representative HPC and one normal concrete (NC) mixtures were tested to estimate both repeatability and reliability of the proposed methods. Repeatability acceptance was adjudged using values of signal-noise ratio (SNR) and discrimination ratio (DR), and reliability was investigated by comparing against standard laboratory-based test methods (i.e., the RILEM gas permeability test and BS EN water penetration test). With SNR and DR values satisfying recommended criteria, it was concluded that test repeatability error has no significant influence on results. In addition, the research confirmed strong positive relationships between the proposed test methods and existing standard permeability assessment techniques. Based on these findings, the proposed test methods show strong potential to become recognized as international methods for determining the permeability of HPCs.

The influence of reusing ‘Formtex’ controlled permeability

The effects of the reuse of ‘Formtex’ Controlled Permeability Formwork (CPF) liner on strength and durability properties of concrete were investigated at two different water-cement ratios and the results are reported in this paper. Test blocks were cast using the CPF on one side and impermeable formwork (IF) on the opposite side of the mould so that direct comparisons could be made between the two. The strength was assessed using the Limpet pulloff tester and both the air permeability and the water absorption (sorptivity) were measured using the Autoclam Permeability System. Both these instruments measured the ‘covercrete’ properties. In addition, cores cut from the test specimens were subjected to an accelerated carbonation test and a chloride exposure test. The results showed that the ‘Formtex’ CPF increases the surface strength and the durability of concrete compared to the IF. There was an almost complete elimination of blowholes. The permeability of concrete decreased and its resistance to the ingress of both carbon dioxide and chlorides increased when CPF was used. The beneficial effects of the Formtex CPF were most evident in concrete of higher water-cement ratio. With the reuse of the Formtex liner twice, that is a total of three uses, the performance of the CPF to improve the properties of concrete remained almost the same. In this research the CPF liner was cleaned thoroughly between each use, which must be adhered to for site applications for reproducing the beneficial effects observed in the laboratory.

Anatase thin films on glass from the chemical vapor deposition of titanium(IV) chloride and ethyl acetate

Thin (50-500 nm) films of TiO2 may be deposited on glass substrates by the atmospheric pressure chemical vapor deposition (APCVD) reaction of TiCl4 with ethyl acetate at 400600 C. The TiO2 films are exclusively in the form of anatase, as established by Raman microscopy and glancing angle X-ray diffraction. X-ray photoelectron spectroscopy gave a 1:2 Ti:O ratio with Ti 2P(3/2) at 458.6 eV and O 1s is at 530.6 eV. The water droplet contact angle drops from 60degrees to

A field study assessing the impact of on-site wastewater treatment systems on surface water quality in a Co. Monaghan catchment

Poorly functioning on-site wastewater treatment systems (OSWTS) can be among the many sources of pollution to groundwater and surface water, which are of critical concern owing to potential human and ecological health risks. An investigation into the effects of on-site wastewater treatment systems (OSWTS) on surface water quality has been undertaken at several sites within a catchment in Co. Monaghan. The study sites were located in areas of 'low’ permeability, suggesting that run-off usually dominates over infiltration. Poor treatment performance of OSWTS within the catchment were found to be the result of several factors, including location in areas with unsuitable soil and site characteristics, incorrect installation, poor maintenance and inappropriate operation by the home owner.

A comparison of nitogen fate and transport in catchments underlain by high and low permeability aquifers using chemical and isotopic tools.

Variability in nitrogen fate and transport in different catchments types is often not considered. This research considers the importance of such nitrogen processes within groundwater pathways in two agricultural catchments in Ireland; a well drained catchment, underlain by karstified Carboniferous limestone, and a poorly drained catchment, underlain by Silurian greywacke.
Depth specific low-flow groundwater sampling was used to evaluate the hydrochemical stratification in groundwater. Groundwater samples, as well as surface water samples, along river courses were analysed for nitrogen species (NO3, NH4 and NO2) and nitrate isotopes (d15N and d18O) as well as field parameters and major ions
.
The dominant nitrate (NO3) groundwater pathway in the poorly drained greywacke catchment is through the shallow weathered bedrock, as indicated by transmissivity values and the ionic and isotopic signatures, and a clear reduction in NO3 concentration is observed with depth. A similar chloride trend would suggest dilution is a major factor, however d15N and d18O isotopic values producing an enrichment ratio of 1.8 indicate that denitrification is also an important process involved in the fate of the NO3 within the groundwater flow system. This consistent trend with depth is in contrast to the stratification pattern observed in the karstified catchment. NO3 was not detected in the shallow groundwater pathway; the dominant groundwater pathway is in the deeper groundwater where there is little change in the nitrate isotope values with depth (d15N values range between 4.1 and 4.6 ‰). This deeper groundwater contributes the dominant proportion of the river flow through a number of springs. As a result, the deeper groundwater, springs and river have a similar ionic signature and NO3 concentration range (23 ± 3 mg/l). Despite this pattern, the NO3 isotopes show a distinct difference in isotopic values between the deeper groundwater in the diffuse karst and the springs indicating some denitrification is occurring during groundwater discharge into the river. Furthermore the isotopes give an indication of the variability of the spatial extent of the springs and the complexities of the fissures through which they are fed. The results of this study clearly show the importance of the geology in the fate and transport of NO3 in agricultural catchments.

Influence of a pore-forming agent on swelling, network parameters, and permeability of poly(ethylene glycol)-crosslinked poly(methyl vinyl ether-co-maleic acid) hydrogels:Application in transdermal delivery systems

We characterized hydrogels, prepared from aqueous blends of poly(methyl vinyl ether-co-maleic acid) (PMVE/MA) and poly(ethylene glycol) (PEG 10,000 Daltons) containing a pore-forming agent (sodium bicarbonate, NaHCO ). Increase in NaHCO content increased the equilibrium water content (EWC) and average molecular weight between crosslinks (M ) of hydrogels. For example, the %EWC was 731, 860, 1109, and 7536% and the M was 8.26, 31.64, 30.04, and 3010.00 × 10 g/mol for hydrogels prepared from aqueous blends containing 0, 1, 2, and 5% w/w of NaHCO , respectively. Increase in NaHCO content also resulted in increased permeation of insulin. After 24 h, percentage permeation was 0.94, 3.68, and 25.71% across hydrogel membranes prepared from aqueous blends containing 0, 2, and 5% w/w of NaHCO , respectively. Hydrogels containing the pore-forming agent were fabricated into microneedles (MNs) for transdermal drug delivery applications by integrating the MNs with insulin-loaded patches. It was observed that the mean amount of insulin permeating across neonatal porcine skin in vitro was 20.62% and 52.48% from hydrogel MNs prepared from aqueous blends containing 0 and 5% w/w of NaHCO . We believe that these pore-forming hydrogels are likely to prove extremely useful for applications in transdermal drug delivery of biomolecules. © 2012 Wiley Periodicals, Inc.

Measurement of permeability using a bench-top centrifuge

The commonly used British Standard constant head triaxial permeability test for testing of fine-grained soils is relatively time consuming. A reduction in the required time for soil permeability testing would provide potential cost savings to the construction industry, particularly in the construction quality assurance of landfill clay liners. The purpose of this paper is to evaluate an alternative approach of measuring permeability of fine-grained soils benefiting from accelerated time scaling for seepage flow when testing specimens in elevated gravity conditions provided by a centrifuge. As part of the investigation, an apparatus was designed and produced to measure water flow through soil samples under conditions of elevated gravitational acceleration using a small desktop laboratory centrifuge. A membrane was used to hydrostatically confine the test sample. A miniature data acquisition system was designed and incorporated in the apparatus to monitor and record changes in head and flow throughout the tests. Under enhanced gravity in the centrifuge, the flow through the sample was under ‘variable head' conditions as opposed to ‘constant head' conditions as in the classic constant head permeability tests conducted at 1 g . A mathematical model was developed for analysis of Darcy's coefficient of permeability under conditions of elevated gravitational acceleration and verified using the results obtained. The test data compare well with the results on analogous samples obtained using the classical British Standard constant head permeability tests.

Investigation of moisture condition and Autoclam sensitivity on air permeability measurements for both normal concrete and high performance concrete

While on site measurement of air permeability provides a useful approach for assessing the likely long term durability of concrete structures, no existing test method is capable of effectively determining the relative permeability of high performance concrete (HPC). Lack of instrument sensitivity and the influence of concrete moisture are proposed as two key reasons for this phenomenon. With limited systematic research carried out in this area to date, the aim if this study was to investigate the influence of instrument sensitivity and moisture condition on air permeability measurements for both normal concrete and HPC. To achieve a range of moisture conditions, samples were dried initially for between one and 5 weeks and then sealed in polythene sheeting and stored in an oven at 50 C to internally distribute moisture evenly. Moisture distribution was determined throughout using relative humidity probe and electrical resistance measurements. Concrete air permeability was subsequently measured using standardised air permeability (Autoclam) and water penetration (BS EN: 12390-8) tests to assess differences between the HPCs tested in this study. It was found that for both normal and high performance concrete, the influence of moisture on Autoclam air permeability results could be eliminated by pre-drying (50 ± 1 C, RH 35%) specimens for 3 weeks. While drying for 5 weeks alone was found not to result in uniform internal moisture distributions, this state was achieved by exposing specimens to a further 3 weeks of sealed pre-conditioning at 50 ± 1 C. While the Autoclam test was not able to accurately identify relative HPC quality due to low sensitivity at associated performance levels, an effective preconditioning procedure to obtain reliable air permeability of HPC concretes was identified. © 2013 The Authors

Influence of testing on permeability of compacted fine soils

The British standard constant-head triaxial test for measuring the permeability of fine-grained soils takes a relatively long time. A quicker test could provide savings to the construction industry, particularly for checking the quality of landfill clay liners. An accelerated permeability test has been developed, but the method often underestimates the permeability values compared owing to structural changes in the soil sample. This paper reports on an investigation
into the accelerated test to discover if the changes can be limited by using a revised procedure. The accelerated test is assessed and compared with the standard test and a ramp-accelerated permeability test. Four different finegrained materials are compacted at various water contents to produce analogous samples for testing using the three different methods. Fabric analysis is carried out on specimens derived from post-test samples using mercury intrusion porosimetry and scanning electron microscopy to assess the effects of testing on soil structure. The results show that accelerated testing in general underestimates permeability compared with values derived from the standard test, owing to changes in soil structure caused by testing. The ramp-accelerated test is shown to provide an improvement in terms of these structural changes.