Accounting for the effect of concentration fluctuations on toxic load for gaseous releases of carbon dioxide.

Research Highlights • An approach to account for the effect of concentration fluctuations on toxic load is investigated in the context of land-use planning for major hazard sites. • For momentum-dominated free-jets of CO 2 gas, the approach is shown to be conservative. • For low-momentum dense CO 2 plumes, the validity of the approach is uncertain • Recommendations are provided for additional analysis of experimental data and numerical simulations in order to address this uncertainty. • Measurements of concentration fluctuations in large-scale CO 2 release experiments would be beneficial Abstract In Great Britain, advice on land-use planning decisions in the vicinity of major hazard sites and pipelines is provided to Local Planning Authorities by the Health and Safety Executive (HSE), based on quantified risk assessments of the risks to the public in the event of an accidental release. For potential exposures to toxic substances, the hazard and risk is estimated by HSE on the basis of a "toxic load". For carbon dioxide (CO 2 ), this is calculated from the time-integral of the gas concentration to the power eight. As a consequence of this highly non-linear dependence of the toxic load on the concentration, turbulent concentration fluctuations that occur naturally in jets or plumes of CO 2 may have a significant effect on the calculated hazard ranges. Most dispersion models used for QRA only provide estimates of the time-or ensemble-averaged concentrations. If only mean concentrations are used to calculate the toxic load, and the effects of concentration fluctuations are ignored, there is a danger that toxic loads and hence hazard ranges will be significantly under-estimated. This paper explores a simple and pragmatic modification to the calculation procedure for CO 2 toxic load calculations. It involves the assumption that the concentration fluctuates by a factor 3 of two with a prescribed square-wave variation over time. To assess the validity of this methodology, two simple characteristic flows are analysed: the free jet and the dense plume (or gravity current). In the former case, an empirical model is used to show that the factor-oftwo approach provides conservative estimates of the hazard range. In the latter case, a survey of the literature indicates that there is at present insufficient information to come to any definite conclusions. Recommendations are provided for future work to investigate the concentration fluctuation behaviour in dense CO 2 plumes. This includes further analysis of existing dense gas dispersion data, measurements of concentration fluctuations in ongoing large-scale CO 2 release experiments, and numerical simulations. Keywords Concentration fluctuations, carbon dioxide, toxic load, free jet, dense plume, land-use planning Introduction In Great Britain, advice on land-use planning decisions in the vicinity of major hazard sites and pipelines is provided to Local Planning Authorities by the Health and Safety Executive (HSE), based on Quantified Risk Assessments (QRA) for the risks to the public in the event of an accidental release. For potential exposures to toxic substances, QRA is based on estimates of individual or societal risk for exposures to amounts of substances that would result in certain levels of toxicity. The toxicological hazard is determined by HSE, based on the duration of exposure as specified according to the Toxic Load (TL) (HSE, 2008). Risk estimates are based on the likelihood of a hypothetical individual receiving an exposure equal to or greater than a threshold level of TL known as the Specified Level of Toxicity (SLOT). The TL relating to the mortality of 50% of an exposed population is also specified by a threshold level known as the Significant Likelihood of Death (SLOD). Further information on the SLOT and SLOD concepts is provided by To calculate the TL, HSE uses the well-known formula of ten Berge (ten where c is the instantaneous gas concentration at a point in space, T is the duration of exposure and n is the ten Berge toxic load exponent, which is specific to the particular substance released. Values of n together with SLOT and SLOD levels are provided for chemicals of major hazard interest by HSE (2008). For a review of alternative toxic load models, see for example 4 However, for substances where n is greater than unity, fluctuations in concentration over time can have a significant effect on the toxic load. In the study of chlorine releases by For carbon dioxide, the ten Berge exponent n is eight (HSE, 2008), reflecting the highly nonlinear response to exposure. A factor of two increase in CO 2 concentration therefore produces a factor of 256 increase in the toxic load. Any fluctuations in concentration above the mean level will very quickly tend to increase the toxic load. Basing TL calculations for CO 2 solely on the mean concentration could therefore lead to a significant under-estimate of the hazard range. In practically all foreseeable releases of CO 2 , the dispersion of the gas will involve some fluctuations in concentration over time due to turbulence. Turbulence is produced from the strong shear layers induced by high-momentum jets, from frictional effects from a dense current rolling along the ground, or from turbulence already present in the atmosphere. Even if gas is produced at the source at a constant rate, an observer at some distance downstream will in nearly all circumstances be subjected to a time-varying concentration. This phenomenon is very well known and has been the subject of extensive study, e.g. Many dispersion models used for risk assessment purposes are unable to provide reliable estimates of the concentration fluctuations over time. A notable exception is the FROST software developed by GL Noble Denton (P. Cleaver, Personal Communication, January 2011) which assumes profiles for both peak and mean concentrations, and hence allows the effects of concentration fluctuations to be included in a simple manner. Although some models, such as DRIFT To provide a practical and simple means of moving forward, the present paper examines a simple and pragmatic modification to the calculation procedure for CO 2 toxic load. It involves the assumption that the concentration fluctuates by a factor of two with a prescribed squarewave variation over time, i.e. it is assumed that the concentration is twice the mean for half of the time, and zero for the remaining time. This rudimentary approach is not intended to provide a realistic reflection of actual turbulent fluctuations, but is merely aimed at incorporating the effects of fluctuations on the toxic load to a very basic degree. The utility of such an approach is that it can be readily implemented in simple dispersion models and therefore provides a practical solution methodology at the present time. In the future, more robust scientifically-based models will no doubt be proposed for use in risk assessment. 5 The notion of a factor of two variation about the mean to account for turbulent concentration fluctuations is not a new concept. It is commonly used in the context of flammable vapour clouds, where hazard ranges are often defined as the location where the predicted average gas concentration reaches half of the Lower Flammability Limit (50% LFL), e.g. To analyse whether the methodology involving a factor-of-two variation about the mean is valid for CO 2 toxic load calculations, two idealised scenarios are examined in the present work: the free jet and the dense plume (or gravity current). Free Jets The empirically-based toxic load model for free jets examined here is derived from the flammability factor model of To calculate the toxic load requires two simple modifications of the flammability factor model. Firstly, the concentration Probability Distribution Function (PDF) is integrated between concentration volume fraction limits of zero and one (rather than just between the flammable limits) and, secondly, the concentration is raised to the ten Berge toxic load exponent, as follows: where ( ) c p~is the concentration PDF, and the time-varying concentration, c , is expressed as a volume fraction. In the model of • The mean concentration along the jet centreline is determined from empirical profiles from 6 The present model was implemented in MatLab and the integration of Equation The results show, as expected, that the smallest hazard range is produced if concentration fluctuations are ignored and only the mean concentration is used to determine the toxic load. Assuming a factor-of-two variation about the mean produces the largest hazard range. The distance from the jet source to the SLOT or SLOD is approximately 50% higher when the factor-of-two model is adopted, compared to the approach where concentration fluctuations are ignored. Results from the PDF model suggest that the factor-of-two approach is conservative in terms of the distance to the SLOT and SLOD on the centreline of the jet. Since the intensity of the fluctuations increases towards the periphery of the jet, the PDF model predicts the toxic effect to extend over a wider area near the base of the jet than the other two model results, which are based solely on the mean concentration contours. The results shown in The PDF on which the present model is based was derived from experimental measurements of gas concentration in free jets by The results shown here are for free jets in a quiescent environment. Commonly, risk assessments consider releases in non-zero wind-speeds. The present model is not valid under these conditions. Gas jets in a cross flow were studied experimentally by Low-Momentum Dense Plumes Although CO 2 is likely to be stored and transported at high pressure, perhaps in the supercritical or dense-phase state As the dense CO 2 vapour cloud spreads along the ground away from the source it will entrain fresh air and dilute. However, unlike many toxic gases such as chlorine, which remains toxic down to very low concentrations, the short-term exposure levels for CO 2 are relatively high. Its Immediately Dangerous to Life and Health (IDLH) concentration is 4% vol/vol (40,000 ppm) compared to just 0.001% vol/vol (10 ppm) for chlorine (NIOSH, 1995). If it is assumed that the source of CO 2 gas is at its sublimation temperature at atmospheric pressure (-78.5 ˚C), and the ambient temperature is 0˚C, then by the time that the CO 2 has diluted to 4% vol/vol, the CO 2 -air mixture will have a density 5% greater than ambient. At a higher CO 2 concentration of 10% vol/vol, which causes unconsciousness after 30 minutes exposure (NORSOK, 2001), the gas mixture will be 11% denser than ambient. Therefore, over the range of concentrations of practical interest, it is likely that a large, low-momentum CO 2 release will exhibit gravity effects. The CO 2 cloud will not behave as a passive or neutral tracer gas. Dense gas clouds exhibit different dispersion behaviour to those of neutrally-buoyant gases. Gravitational forces act to accelerate the cloud, whilst the vertical density gradient tends to suppress turbulence and reduce dilution. Concentrations inside the spreading dense plume tend to be more uniform than those in the equivalent passive plume. Therefore, as the dense plume meanders it produces lower intensity fluctuations in the core and higher intensity fluctuations on the periphery as compared to equivalent passive plumes (see Britter, 1988, and The bulk of research efforts to analyse concentration fluctuations in gas dispersion have been undertaken for passive, neutrally-buoyant plumes. Early work in this area includes that of 8 Further work on concentration fluctuations has been undertaken by Wilson and co-workers at the University of Alberta A significant body of research on concentration fluctuations has been undertaken over the last 30 years by Chatwin, Mole, Nielsen and co-workers at Sheffield University and Risø National Laboratory Research into concentration fluctuations with more focus on practical models for risk assessment has been undertaken by Other related work in this field includes the statistical analysis of concentration in dense gas clouds by None of the work examined as part of this literature review was found to provide a model for concentration fluctuations in dispersing dense gas clouds that could be used to calculate the toxic load. However, some previously reported studies provide anecdotal evidence of the potential magnitude of certain relevant parameters. Statistical analysis by Future Directions The literature survey has not revealed any further useful insight into concentration fluctuations in dense gas releases, to validate the proposed factor-of-two model. Three potential avenues for future work are as follows: Firstly, a thorough assessment of previous field-scale dense gas dispersion experiments involving time-resolving gas concentration measurements could be undertaken. The measurements need to have been taken at a rate equal to, or faster, than the human breathing rate (approx. 0.3 Hz). In some cases, it may be possible to infer concentration values from thermocouple measurements of fluctuating temperature, using an approach similar to that adopted by Witcofksi and Chirivella (1984). It has already been established that dense gas experiments exhibit a degree of scatter due to the stochastic nature of the flow Secondly, if sufficient concentration fluctuation data does not yet exist, it could be generated by new field-scale experiments. There are difficulties in interpreting data from reduced scale wind tunnel tests due to the need to scale dimensionless parameters for both buoyancy and turbulence simultaneously. Often, wind tunnel tests are performed at lower Reynolds numbers, which do not feature the full range of turbulence scales, or the slow changes in conditions which are present in the atmosphere. At the present time, a number of field-scale CO 2 releases are planned in order to support the risk assessment of planned carbon capture, 10 transport and storage infrastructure. This includes the medium-scale and field-scale tests to be undertaken as part of the EU-funded CO 2 PipeHaz project 1 , and the large-scale tests to be undertaken as part of the National Grid COOLTRANS project. In view of this, it would be advantageous to maximise the potential benefits from these large and costly experiments by recording time-varying CO 2 concentrations (or at least temperatures), which could subsequently be used to develop concentration PDFs. Thirdly, the matter could be investigated by numerical simulations, using methods in which time-varying concentrations are resolved. The most promising avenue is to use Large-Eddy Simulation (LES). This approach has previously been used to assess concentration fluctuations in passive and buoyant plumes by Once these analyses have been performed, it would be beneficial to revisit the factor-of-two square-wave model proposed here. If it was shown to be significantly under-or overconservative, other alternatives could be investigated, such as the use of prescribed triangular or sinusoidal variations in concentration over time. Discussion and Conclusions The present work has examined the validity of a simple approach to account for the effect of concentration fluctuations in calculating the toxic load for atmospheric CO 2 releases. It is based on the assumption that the concentration at any point in space fluctuates by a factor of two with a prescribed square-wave variation over time. Analysis of free jets of CO 2 using a PDF-based model originally derived to predict the ignition probability of flammable gas jets has shown that this factor-of-two approach produces conservative predictions of the hazard range, in terms of the maximum distance to the SLOT and SLOD. For low-momentum plumes of dense CO 2 gas, a review of the literature has shown that, at present, it is not possible to establish the validity of the factor-of-two model. Suggestions have been provided for future work to address this matter, involving analysis of existing data, new field-scale measurements and numerical simulations using LES. It is clear from the literature review and analysis presented in the current work that if only mean concentrations are used to calculate the toxic load, hazard ranges for CO 2 releases are likely to be significantly under-predicted. Given the current state of knowledge, it is unclear whether in all circumstances the proposed factor-of-two model will always give rise to conservative predictions. However, at the very least this approach provides a step in the right direction, and incorporates the effect of fluctuations on the toxic load in a way that can be easily adopted using the current generation of quantified risk assessment models. Impact analysis will show whether or not the approach leads to untenable (over-conservative) hazard ranges in scenarios of practical interest. As scientific understanding develops, and more 1 http://www.co2pipehaz.eu 11 sophisticated, practical models are developed, it will be necessary to reassess this methodology

Urban tourism and population change: Gentrification in the age of mobilities

The prepandemic unbridled growth of tourism has triggered a significant debate regarding the future of cities; several authors suggest that neighbourhood change produced by tourism should be conceived as a form of gentrification. Yet research on population shifts—a fundamental dimension of gentrification—in such neighbourhoods is scarce. Our exploration of the Gòtic area in Barcelona, using quantitative and qualitative techniques, reveals a process of population restructuring characterised by a decrease of long-term residents and inhabited dwellings, and the arrival of young and transnational gentrifiers that are increasingly mobile and form a transient population. We then use some insights from the mobilities literature to make sense of these results. In the gentrification of the Gòtic, the attractiveness of the area for visitors and for a wider palette of transnational dwellers feeds one another, resulting in an uneven negotiation whereby more wealthy and ‘footloose’ individuals gain access and control of space and housing over less mobile and more dependent populations.info:eu-repo/semantics/publishedVersio

Airbnb and crime in Barcelona (Spain): testing the relationship using a geographically weighted regression

The existence of works proving the possible relationship empirically that Airbnb lodgings could have with crime in Spain is not known. This research analyzes the relationship between Airbnb lodgings and crimes against the properties and people in Barcelona’s neighbourhoods. To achieve this, we use an ordinary least squares regression model and a geographically weighted regression model. The results show a significant and positive relationship between the higher density of Airbnb lodgings and the higher crime rates in the neighbourhoods, especially of patrimonial nature. Divided by type of leased space, the Airbnb homes, in which the guest shares a room with other guests, show a higher relationship with crimes against property and people. The results of the local model show a spatial heterogeneity in all variables used, indicating the need to address non-stationary spatial processes that reveal hidden patterns. However, the only variable that shows statistically significant local variability is the total Airbnb lodgings variable. Finally, we discussed some unexpected results, proposing some future lines of research. © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group, on behalf of Nanjing Normal University

Effect of UVA Fluence Rate on Indicators of Oxidative Stress in Human Dermal Fibroblasts

During the course of a day human skin is exposed to solar UV radiation that fluctuates in fluence rate within the UVA (290-315 nm) and UVB (315-400 nm) spectrum. Variables affecting the fluence rate reaching skin cells include differences in UVA and UVB penetrating ability, presence or absence of sunscreens, atmospheric conditions, and season and geographical location where the exposure occurs. Our study determined the effect of UVA fluence rate in solar-simulated (SSR) and tanning-bed radiation (TBR) on four indicators of oxidative stress---protein oxidation, glutathione, heme oxygenase-1, and reactive oxygen species--in human dermal fibroblasts after receiving equivalent UVA and UVB doses. Our results show that the higher UVA fluence rate in TBR increases the level of all four indicators of oxidative stress. In sequential exposures when cells are exposed first to SSR, the lower UVA fluence rate in SSR induces a protective response that protects against oxidative stress following a second exposure to a higher UVA fluence rate. Our studies underscore the important role of UVA fluence rate in determining how human skin cells respond to a given dose of radiation containing both UVA and UVB radiation

‘Sell[ing] what hasn’t got a name’: An exploration of the different understandings and definitions of ‘community engagement’ work in the performing arts

Widely known to promote broader involvement in the processes which define the arts and culture (Webster, 1997), community engagement work in the performing arts — despite employing a set of commonly recognised norms — has tended to be conceptualised differently both historically and contemporarily. Drawing on ethnographic research — particularly semi-structured qualitative interview accounts of numerous British practitioners with a track record of work in the sector, the article explores these different conceptualisations. The article finds that it is the actual ‘work that matters’ and not what it is named, and that the diversity of understandings and definitions among sectoral practitioners is reflective of evolving thinking, values and practice, something that may be destabilising for better or worse

A preliminary investigation of materialism and impulsiveness as predictors of technological addictions among young adults

Background and aims: The primary objective of the present research is to investigate the drivers of technological addiction in college students — heavy users of Information and Communication Technology (ICT). The study places cell phone and instant messaging addiction in the broader context of consumption pathologies, investigating the influence of materialism and impulsiveness on these two technologies. Clearly, cell phones serve more than just a utilitarian purpose. Cell phones are used in public and play a vital role in the lives of young adults. The accessibility of new technologies, like cell phones, which have the advantages of portability and an ever increasing array of functions, makes their over-use increasingly likely. Methods: College undergraduates (N = 191) from two U.S. universities completed a paper and pencil survey instrument during class. The questionnaire took approximately 15–20 minutes to complete and contained scales that measured materialism, impulsiveness, and mobile phone and instant messaging addiction. Results: Factor analysis supported the discriminant validity of Ehrenberg, Juckes, White and Walsh's (2008) Mobile Phone and Instant Messaging Addictive Tendencies Scale. The path model indicates that both materialism and impulsiveness impact the two addictive tendencies, and that materialism's direct impact on these addictions has a noticeably larger effect on cell phone use than instant messaging. Conclusions: The present study finds that materialism and impulsiveness drive both a dependence on cell phones and instant messaging. As Griffiths (2012) rightly warns, however, researchers must be aware that one's addiction may not simply be to the cell phone, but to a particular activity or function of the cell phone. The emergence of multi-function smart phones requires that research must dig beneath the technology being used to the activities that draw the user to the particular technology

Embryonic and adult isoforms of XLAP2 form microdomains associated with chromatin and the nuclear envelope

Laminin-associated polypeptide 2 (LAP2) proteins are alternatively spliced products of a single gene; they belong to the LEM domain family and, in mammals, locate to the nuclear envelope (NE) and nuclear lamina. Isoforms lacking the transmembrane domain also locate to the nucleoplasm. We used new specific antibodies against the N-terminal domain of Xenopus LAP2 to perform immunoprecipitation, identification and localization studies during Xenopus development. By immunoprecipitation and mass spectrometry (LC/MS/MS), we identified the embryonic isoform XLAP2γ, which was downregulated during development similarly to XLAP2ω. Embryonic isoforms XLAP2ω and XLAP2γ were located in close association with chromatin up to the blastula stage. Later in development, both embryonic isoforms and the adult isoform XLAP2β were localized in a similar way at the NE. All isoforms colocalized with lamin B2/B3 during development, whereas XLAP2β was colocalized with lamin B2 and apparently with the F/G repeat nucleoporins throughout the cell cycle in adult tissues and culture cells. XLAP2β was localized in clusters on chromatin, both at the NE and inside the nucleus. Embryonic isoforms were also localized in clusters at the NE of oocytes. Our results suggest that XLAP2 isoforms participate in the maintenance and anchoring of chromatin domains to the NE and in the formation of lamin B microdomains

Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C−H Bond Activation

Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct functionalization of nitrogen heterocycles through C−H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes our work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. We initially discovered an intramolecular Rh-catalyzed C-2 alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. We then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, we discovered that a novel substrate-derived Rh−N-heterocyclic carbene (NHC) complex was involved as an intermediate. We then synthesized analogous Rh−NHC complexes directly by treating precursors to the intermediate [RhCl(PCy3)2] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazoline, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy3)2 fragment coordinates to the heterocycle before intramolecular activation of the C−H bond occurs. The resulting Rh−H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid cocatalysts accelerate the alkylation, we developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. We demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, we developed conditions to directly arylate these heterocycles with aryl halides. Our initial conditions that used PCy3 as a ligand were successful only for aryl iodides. However, efforts designed to avoid catalyst decomposition led to the development of ligands based on 9-phosphabicyclo[4.2.1]nonane (phoban) that also facilitated the coupling of aryl bromides. We then replicated the unique coordination environment, stability, and catalytic activity of this complex using the much simpler tetrahydrophosphepine ligands and developed conditions that coupled aryl bromides bearing diverse functional groups without the use of a glovebox or purified reagents. With further mechanistic inquiry, we anticipate that researchers will better understand the details of the aforementioned Rh-catalyzed C−H bond functionalization reactions, resulting in the design of more efficient and robust catalysts, expanded substrate scope, and new transformations