Critical Analysis of Longwall Ventilation Systems and Removal of Methane

Bleeder systems are an important component for ventilation and the control of methane. The bleeder system of a coal mine contains a mixing zone for methane-laden air from the mined-out portions of the seam to mix with fresh air and the methane concentrations in the bleeders can often be elevated. Bleeders also provides a pathway for coalbed methane-laden ventilation air to quickly flow out of the mine through low resistance airways of a mine, such as supported gateroads, along the un-compacted outer perimeter of the gob, etc. Substantial quantities of coalbed methane are typically removed from underground workings. Although it is a relatively simple task to determine the methane quantities exiting the mine through direct measurements, a clear understanding of the exact manner and associated concentrations in which bleeder entries accumulate and transport methane-air mixtures is not known. The benefit of this improved understanding will decrease the likelihood of an explosion due to unknown accumulations of explosive gases in the bleeder entries, thereby improving worker safety.;In order to provide a better understanding of how a bleeder system works in moving methane through the mine, several field monitoring studies have been designed and completed using a tube bundle system and tracer gas releases. The tube bundle system was installed at a bleederless (progressively sealed) underground coal mine. The tube bundles monitoring points were located at different critical locations surrounding the longwall to specifically monitor gas concentrations and barometric pressures on a 30 minute interval for a period of two years. The tracer gas studies, on the other hand, were conducted at an underground coal operation with a traditional bleeder system. The objectives of these tracer tests were to determine transportation pathways and retention times of tracer gasses to better understand the exact gas movements in longwall gobs. The tracer gas was sampled from different headgate and tailgate entries through sample tubes of different lengths using vacutainers. The gas samples were analyzed using gas chromatography for determining concentration measurements for tracer and other gasses, including methane.;The tube bundle system results showed that falling barometric atmospheric pressure can cause the caved material to outgas higher concentrations of contaminants into the bleeder system. During prolonged atmospheric pressure drops, the gas concentrations leaving the caved material via the bleederless system were measured to increase by over two times the average values. These results strongly suggest that to effectively monitor and detect these outgassing events, the bleeder system requires collecting data more often than the once-a-week regulation stated in the 30 CFR Part §75.364.;The tracer gas testing showed locations of high methane in the bleeders, but the practice in multi panel longwall districts of use premixing of the airflow exiting the longwall panels with cleaner airflow to dilute the methane concentrations to below allowable levels before passing through bleeder evaluation points masked the high methane concentrations. Specifically, samples with methane concentration above 4% were collected from the middle entry of the tailgate, but these airflows were diluted to below 2% just before reaching the bleeder evaluation points, and the mine was unaware of the higher methane levels. This result indicates that premixing of explosive airflow as soon possible, as it exits from the tailgate entries in this case, is beneficial to reducing possible explosions, sampling locations need to be closer to the caved material to better monitor and record the actual conditions existing within the inaccessible bleeder locations.;The explosive mixtures of methane in the bleeder are not theoretical but exist and are measurable with direct and indirect methods within both bleeder and bleederless ventilation system. Obtaining measurements of these mixtures is the first step to be able to better engineer longwall ventilation safety.;The conclusions for this research are: 1) Long duration atmospheric pressure drops of a day or more in length are the controlling factor in increased emission from the caved material. 2) The practice of pre-mixing airflows leaving the middle entries between longwall panels with low methane airflow before reaching the bleeder evaluation points, can mask the existence of explosive mixtures of methane at other locations in the bleeders. 3) Without knowledge of the precise locations of high methane in the bleeder entries, the bleeder system cannot be optimized for minimizing explosive methane concentrations and improve miner safety. To solve the atmospheric pressure drop issue it is recommended that a continuous monitoring system should be installed on surface to record these mine-wide changes in total methane emissions. It is also recommended that bleeder evaluation points should be moved closer to the caved material or the sample tubes should be used to monitor critical locations before mixing occurs. Both of these recommendations will improve the understanding of the nature of gas transportation within the bleeder system and thereby lead to improved worker safety

The role of age and mode of delivery in the STEPS intervention: a longitudinal pilot-study in treatment of posttraumatic stress symptoms in Danish survivors of sexual assault

Background: The STEPS programme has been succesfully implemented as a group-based treatment of trauma symptoms after rape for adolescents. The STEPS intervention was translated from Dutch to Danish and offered to adults in addition to adolescents as well as an individual intervention in addition to a group-based intervention at a Danish Centre for Rape Victims through 2011 to 2014. The programme was translated from Dutch to Danish and expanded to adults in addition to adolescents as well as to an individual intervention in addition to a group-based intervention at a Danish Centre for Rape Victims through 2011 to 2014. Objective: The present study observes  development in trauma symptoms and ICD-11 diagnostic status during an adapted version of the intervention programme ‘STEPS’ for survivors of sexual assault. Methods: A prospective uncontrolled study was conducted, monitoring symptoms of posttraumatic stress and other trauma-related symptomatology before treatment, after treatment and at 6 and 12 months' follow up for 103 referrals receiving individual or group-based STEPS. Tentative diagnoses of posttraumatic stress disorder (PTSD) and complex PTSD were assigned to participants according to the ICD-11 to observe the development in diagnostic status across time, and multilevel modelling was used to assess the development of symptom severity and to assess the moderating effect of age-group and mode of delivery. Results: A loglinear function representing large and statistically significant decline in symptomatology over time provided the best fit for all measures of trauma-related symptomatology. The decline was not moderated by age-group or mode of intervention. Dropout rates were independent of mode of intervention and age. Conclusion: The adaption of the STEPS programme to adults and as an individual intervention is feasible and maintains effect sizes comparable to those observed in the original intervention. Further research using randomized controlled trials is needed to ascribe the observed effect to the STEPS programme

Instability of the Northeast Greenland Ice Stream over the last 45,000 years

The outlet glaciers that comprise the Northeast Greenland Ice Stream (NEGIS) have experienced accelerated retreat in recent years, yet their longterm stability remains unclear. Here, via cosmogenic surface exposure and radiocarbon ages, the authors investigate the stability of the NEGIS for the past 45 kyr

Dealing with a traumatic past: the victim hearings of the South African truth and reconciliation commission and their reconciliation discourse

In the final years of the twentieth and the beginning of the twenty-first century, there has been a worldwide tendency to approach conflict resolution from a restorative rather than from a retributive perspective. The South African Truth and Reconciliation Commission (TRC), with its principle of 'amnesty for truth' was a turning point. Based on my discursive research of the TRC victim hearings, I would argue that it was on a discursive level in particular that the Truth Commission has exerted/is still exerting a long-lasting impact on South African society. In this article, three of these features will be highlighted and illustrated: firstly, the TRC provided a discursive forum for thousands of ordinary citizens. Secondly, by means of testimonies from apartheid victims and perpetrators, the TRC composed an officially recognised archive of the apartheid past. Thirdly, the reconciliation discourse created at the TRC victim hearings formed a template for talking about a traumatic past, and it opened up the debate on reconciliation. By discussing these three features and their social impact, it will become clear that the way in which the apartheid past was remembered at the victim hearings seemed to have been determined, not so much by political concerns, but mainly by social needs

The racist bodily imaginary: the image of the body-in-pieces in (post)apartheid culture

This paper outlines a reoccurring motif within the racist imaginary of (post)apartheid culture: the black body-in-pieces. This disturbing visual idiom is approached from three conceptual perspectives. By linking ideas prevalent in Frantz Fanon’s description of colonial racism with psychoanalytic concepts such as Lacan’s notion of the corps morcelé, the paper offers, firstly, an account of the black body-in-pieces as fantasmatic preoccupation of the (post)apartheid imaginary. The role of such images is approached, secondly, through the lens of affect theory which eschews a representational ‘reading’ of such images in favour of attention to their asignifying intensities and the role they play in effectively constituting such bodies. Lastly, Judith Butler’s discussion of war photography and the conditions of grievability introduces an ethical dimension to the discussion and helps draw attention to the unsavory relations of enjoyment occasioned by such images

Lichens facilitate seedling recruitment in alpine heath

Abstract Questions How do mat thickness, physical structure and allelopathic properties of terricolous mat-forming lichens affect recruitment of vascular plants in dwarf-shrub and lichen heath vegetation?. Location The mountains of Dovrefjell, central Norway. Methods In autumn, seeds of ten vascular plant species were collected and sown in a common garden experiment with mats of six lichen species and bare-soil controls as experimental treatments. We recorded growing season soil temperature and moisture, and seedling recruitment and growth after one year. The effect of lichen secondary compounds on germination was tested in a growth chamber experiment and compared to the lichen-plant interactions detected under field conditions. Results The lichen mats buffered extreme soil temperatures and soil drying in dry weather, with soils below the thickest mats (Cladonia stellaris and C. rangiferina) experiencing the lowest temperature fluctuations. Seedling recruitment and seedling growth in the field and seed germination in the lab were species-specific. Seedling recruitment rates were overall higher within lichen mats than on bare soil, but the c. 6.5 cm thick mats of C. stellaris reduced recruitment of many species. The lab experiment suggested no overall strong effect of lichen allelopathy on seed germination, and effects on seed germination were only moderately correlated with the lichen-plant interactions observed for seedling recruitment in the field. Conclusions In harsh environments like alpine dwarf-shrub and lichen heaths, the presence of lichens and the resulting amelioration of the microclimate seems more important for vascular plant recruitment than are allelopathic effects often reported in lab experiments. We might therefore expect most terricolous lichens, depending on the plant species in focus, to facilitate rather than hamper the early stages of plant recruitment into lichen-dominated arctic-alpine heath vegetation. This article is protected by copyright. All rights reserved.Peer reviewe

Reaction Time Variability in Children Is Specifically Associated With Attention Problems and Regional White Matter Microstructure

Background Increased intraindividual variability (IIV) in reaction times (RTs) has been suggested as a key cognitive and behavioral marker of attention problems, but findings for other dimensions of psychopathology are less consistent. Moreover, while studies have linked IIV to brain white matter microstructure, large studies testing the robustness of these associations are needed. Methods We used data from the Adolescent Brain Cognitive Development (ABCD) Study baseline assessment to test the associations between IIV and psychopathology (n = 8622, age = 8.9–11.1 years) and IIV and white matter microstructure (n = 7958, age = 8.9–11.1 years). IIV was investigated using an ex-Gaussian distribution analysis of RTs in correct response go trials in the stop signal task. Psychopathology was measured by the Child Behavior Checklist and a bifactor structural equation model was performed to extract a general p factor and specific factors reflecting internalizing, externalizing, and attention problems. To investigate white matter microstructure, fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity were examined in 23 atlas-based tracts. Results Increased IIV in both short and long RTs was positively associated with the specific attention problems factor (Cohen’s d = 0.13 and d = 0.15, respectively). Increased IIV in long RTs was also positively associated with radial diffusivity in the left and right corticospinal tract (both tracts, d = 0.12). Conclusions Using a large sample and a data-driven dimensional approach to psychopathology, the results provide novel evidence for a small but specific association between IIV and attention problems in children and support previous findings on the relevance of white matter microstructure for IIV.publishedVersio