Mitigation of gas and vapour cloud explosions using fine water sprays

For the past fifty years or so, there has been a great deal of interest in the use of water based explosion suppression systems, designed to mitigate or reduce the impact of thermal explosions and their consequential overpressures, which may be as high as 2MPa in outdoor environments. This level of interest has been heightened in more recent years due to a number of high loss explosion events including, Flixborough, UK (1974), Piper Alpha, North Sea (1998) and Buncefield, UK (2005).All of the previous research has focused on the suppression and mitigation proficiency of existing or new water deluge systems, which deploy sprays containing droplets 200≤D32≤1000μm. Where a high speed flame propagates through a region of spray containing such droplets, the flow ahead of the flame will hydrodynamically break up the droplets into fine mist, which in turn will act as a heat sink in the flame, with a resulting degree of suppression. These studies concluded that in most cases, existing deluge systems contributed to a global reduction in flame speed and thus caused a decrease in the resultant damaging overpressures.This present study however, is focused on the mitigation of slow moving deflagrations with resulting speeds of ≤30m/s. A flame travelling at such low relative speeds will not possess the inertia to inflict secondary atomisation by hydrodynamic break up. Consequently, the droplets within the spray must be small enough to extract heat in the short finite moments that the flame and droplets interact (approximately 0.03ms for a representative 1mm thick flame front). Previous theoretical studies have suggested that droplets, D32, in the order of 10μm - 20μm will be required to successfully mitigate combustion without relying on further droplet break up. To date, there have been no other published experimental studies in this area.An innovative high pressure atomiser known as a Spill Return Atomiser (SRA) was selected, which contained a unique swirl chamber and was originally developed for decontamination and disinfection. The efficient atomisation of the SRA produced fine sprays containing droplets, D32, 15μm - 20μm. A series of „cold trials‟ were conducted to further develop the single SRA, which manifested in the creation of several exclusive single and multiple spray options in counter, parallel and cross flow, with the direction of the propagating flame. These new configurations were supplied with deionised water at a liquid pressure of 13MPa and were qualitatively analysed using High Definition (HD) imagery and quantitatively characterised using non-intrusive laser techniques. During the development stages of this study the SRA spray cone angle was increased from 34.7˚ to 49.2˚and the exit orifice flow rate was raised from 0.295 L/min to 1.36 L/min. The increase in flow rate provided a number of spray options ranging from 17≤D32≤29μm, with liquid volume flux of 0.011 cm3/s/cm2 - 0.047cm3/s/cm2 and mean droplet velocity of 0m/s - 21.4m/s, with the resulting characteristics giving way to complete explosion mitigation qualities.The second phase of this study was to conceive, design and build a suitable apparatus capable of producing slow representative flame speeds within the range of 5 m/s - 30m/s. In excess of 250 mitigation „hot trials‟ were performed using the unique conformations produced during the „cold trials‟, whereby a configuration consisting of 4 x SRA‟s in cross flow (X/F) configuration, successfully and repeatedly, completely mitigated homogeneous methane-air mixtures throughout the whole flammable range E.R. 0.5≤(ϕ)1.0≤ 1.69 (5 - 15%), with flame speeds ranging from 5 - 30m/s. The combined spray configuration consisted of four SRA‟s which were 105mm apart and each opposed by 120˚, thus providing a total spray region of 315mm (spray centre to centre). As the sprays did not overlap or converge, the liquid volume flux remained as 0.047cm3/s/cm2.With droplets, D32, ≤30μm generally requiring impact velocities of approximately ≥142.83m/s to break up further, the flame speeds experienced in these trials of ≤30m/s would not have caused hydrodynamic break up of the droplets in the sprays. Therefore, due to the flame speeds and drop sizes utilised in this study, the droplets entering the flame front would have been in their original form.Although some comparisons were made using the experimental data with Computational Fluid Dynamics (CFD), it proved to be an extremely complicated phenomenon. This was due to the presence and interaction of the complexities of the combustion process and other variables such as water droplet dynamics and heat transfer modes. As such, a set of recommendations have therefore been proposed in pursuing this work in future project

A review of the electrical properties of semiconductor nanowires: Insights gained from terahertz conductivity spectroscopy

Accurately measuring and controlling the electrical properties of semiconductor nanowires is of paramount importance in the development of novel nanowire-based devices. In light of this, terahertz (THz) conductivity spectroscopy has emerged as an ideal non-contact technique for probing nanowire electrical conductivity and is showing tremendous value in the targeted development of nanowire devices. THz spectroscopic measurements of nanowires enable charge carrier lifetimes, mobilities, dopant concentrations and surface recombination velocities to be measured with high accuracy and high throughput in a contact-free fashion. This review spans seminal and recent studies of the electronic properties of nanowires using THz spectroscopy. A didactic description of THz time-domain spectroscopy, optical pump–THz probe spectroscopy, and their application to nanowires is included. We review a variety of technologically important nanowire materials, including GaAs, InAs, InP, GaN and InN nanowires, Si and Ge nanowires, ZnO nanowires, nanowire heterostructures, doped nanowires and modulation-doped nanowires. Finally, we discuss how THz measurements are guiding the development of nanowire-based devices, with the example of single-nanowire photoconductive THz receivers.The authors gratefully acknowledge EPSRC (UK) for research funding. H J Joyce gratefully acknowledges the Royal Commission for the Exhibition of 1851 for her research fellowship.This is the final version of the article. It first appeared from IOP via https://doi.org/10.1088/0268-1242/31/10/10300

Large-scale latitudinal and vertical distributions of NMHCs and selected halocarbons in the troposphere over the Pacific Ocean during the March-April 1999 Pacific Exploratory Mission (PEM-Tropics B)

Nonmethane hydrocarbons (NMHCs) and selected halocarbons were measured in whole air samples collected over the remote Pacific Ocean during NASA's Global Tropospheric Experiment (GTE) Pacific Exploratory Mission-Tropics B (PEM-Tropics B) in March and early April 1999. The large-scale spatial distributions of NMHCs and C2Cl4 reveal a much more pronounced north-south interhemispheric gradient, with higher concentrations in the north and lower levels in the south, than for the late August to early October 1996 PEM-Tropics A experiment. Strong continental outflow and winter-long accumulation of pollutants led to seasonally high Northern Hemisphere trace gas levels during PEM-Tropics B. Observations of enhanced levels of Halon 1211 (from developing Asian nations such as the PRC) and CH3Cl (from SE Asian biomass burning) support a significant southern Asian influence at altitudes above 1 km and north of 10° N. By contrast, at low altitude over the North Pacific the dominance of urban/industrial tracers, combined with low levels of Halon 1211 and CH3Cl, indicate a greater influence from developed nations such as Japan, Europe, and North America. Penetration of air exhibiting aged northern hemisphere characteristics was frequently observed at low altitudes over the equatorial central and western Pacific south to ∼5° S. The relative lack of southern hemisphere biomass burning sources and the westerly position of the South Pacific convergence zone contributed to significantly lower PEM-Tropics B mixing ratios of the NMHCs and CH3Cl south of 10° S compared to PEM-Tropics A. Therefore the trace gas composition of the South Pacific troposphere was considerably more representative of minimally polluted tropospheric conditions during PEM-Tropics B. Copyright 2001 by the American Geophysical Union

Utilization of fine water sprays in explosion mitigation : cold trial

For the past fifty years, there has been a great deal of interest using water-based explosion suppression systems in mitigating/reducing the impact of thermal explosions and their consequential overpressures. Previous research focused on the suppression and mitigation with sprays containing droplets 200µm ≤ D32 ≤ 1000µm. The present study is focused on the mitigation of slow-moving deflagrations with speeds of less than or equal to 30 m/s. Consequently, the droplets within the spray must be small enough to extract heat in the short finite moments that the flame and droplets interact at about 0.03 ms for a 1 mm thick flame front. An apparatus was thus designed to simulate ‘partly confined and/or vented’ conditions, venting upstream of the propagating flame. Previous theoretical studies have suggested that droplets in the order of 10 µm to 20 µm will enable to mitigate combustion without relying on further droplet break up. This investigation, herewith, is presenting the full details of qualitative and quantitative analysis of using Spill Return Atomiser (SRA) to provide fine water spray. The spray cone angle was increased from 34.7˚ to 49.2˚and the exit orifice flow rate was raised from 0.295 l/min to 1.36 l/min. Increasing the flow rate provided a number of spray options ranging from 17µm ≤ D32 ≤ 29µm, with liquid volume flux of 0.011 cm³/s/cm² to 0.047 cm³/s/cm² and mean droplet velocity of 0 to 21.4 m/s, with the resulting of complete explosion mitigation qualities

Modulation of terahertz polarization on picosecond timescales using polymer-encapsulated semiconductor nanowires

© OSA 2017. We exploit the photoconductivity of semiconductor nanowires to achieve ultrafast broad-bandwidth modulation of THz pulses. A modulation depth of -8 dB was exhibited by a polarizer consisting of 14 layers of nanowires encapsulated in polymer

Comparison of Cross-Sectional and Daily Reports in Studying the Relationship Between Depression and Use of Alcohol in Response to Stress in College Students

Alcohol use in response to stress in college students may be affected by the presence of symptoms of depression. However, this is a challenging issue to study due to the various methodologies used as well as the possible effect of depressed mood on the accuracy of self-report. This study focused on methodological issues as possible sources of equivocal findings regarding the relationship between depressed mood and alcohol use in response to stress in a college student population. Findings may differ when these variables are examined cross-sectionally versus longitudinally. Methods : Depressed mood and alcohol coping were assessed both cross-sectionally and repeatedly over time in 125 college students. Participants were assessed at baseline using a diagnostic self-report measure of depression as well as a measure of typical coping style. In addition, daily measures of stress, symptoms of depression, and coping were completed for 45 consecutive days. Results : Different relationships between depressed mood and alcohol coping were found when depressed individuals were analyzed separately from those who were not depressed. Although a significant correlation between daily use of alcohol coping and daily depressed mood was found, there were no differences between depressed and nondepressed participants (as assessed at baseline) on daily alcohol coping. Conclusions : These findings have implications for research design as well as clinical assessment regarding the relationships between mood and use of alcohol for coping; the findings suggest that cross-sectional measures of mood and alcohol use may obscure differences as assessed repeatedly over time. In addition, these findings support the utility of frequent assessment of depressive symptoms when implementing or evaluating programs that target coping skills in college students.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65757/1/j.1530-0277.2000.tb04552.x.pd

Commensal bacteria augment Staphylococcus aureus infection by inactivation of phagocyte-derived reactive oxygen species

Staphylococcus aureus is a human commensal organism and opportunist pathogen, causing potentially fatal disease. The presence of non-pathogenic microflora or their components, at the point of infection, dramatically increases S. aureus pathogenicity, a process termed augmentation. Augmentation is associated with macrophage interaction but by a hitherto unknown mechanism. Here, we demonstrate a breadth of cross-kingdom microorganisms can augment S. aureus disease and that pathogenesis of Enterococcus faecalis can also be augmented. Co-administration of augmenting material also forms an efficacious vaccine model for S. aureus. In vitro, augmenting material protects S. aureus directly from reactive oxygen species (ROS), which correlates with in vivo studies where augmentation restores full virulence to the ROS-susceptible, attenuated mutant katA ahpC. At the cellular level, augmentation increases bacterial survival within macrophages via amelioration of ROS, leading to proliferation and escape. We have defined the molecular basis for augmentation that represents an important aspect of the initiation of infection

"Textural analysis of multiparametric MRI detects transition zone prostate cancer"

OBJECTIVES: To evaluate multiparametric-MRI (mpMRI) derived histogram textural-analysis parameters for detection of transition zone (TZ) prostatic tumour. METHODS: Sixty-seven consecutive men with suspected prostate cancer underwent 1.5T mpMRI prior to template-mapping-biopsy (TPM). Twenty-six men had 'significant' TZ tumour. Two radiologists in consensus matched TPM to the single axial slice best depicting tumour, or largest TZ diameter for those with benign histology, to define single-slice whole TZ-regions-of-interest (ROIs). Textural-parameter differences between single-slice whole TZ-ROI containing significant tumour versus benign/insignificant tumour were analysed using Mann Whitney U test. Diagnostic accuracy was assessed by receiver operating characteristic area under curve (ROC-AUC) analysis cross-validated with leave-one-out (LOO) analysis. RESULTS: ADC kurtosis was significantly lower (p < 0.001) in TZ containing significant tumour with ROC-AUC 0.80 (LOO-AUC 0.78); the difference became non-significant following exclusion of significant tumour from single-slice whole TZ-ROI (p = 0.23). T1-entropy was significantly lower (p = 0.004) in TZ containing significant tumour with ROC-AUC 0.70 (LOO-AUC 0.66) and was unaffected by excluding significant tumour from TZ-ROI (p = 0.004). Combining these parameters yielded ROC-AUC 0.86 (LOO-AUC 0.83). CONCLUSION: Textural features of the whole prostate TZ can discriminate significant prostatic cancer through reduced kurtosis of the ADC-histogram where significant tumour is included in TZ-ROI and reduced T1 entropy independent of tumour inclusion. KEY POINTS: MR textural features of prostate transition zone may discriminate significant prostatic cancer; Transition zone (TZ) containing significant tumour demonstrates a less peaked ADC histogram; TZ containing significant tumour reveals higher post-contrast T1-weighted homogeneity; The utility of MR texture analysis in prostate cancer merits further investigation