Numerical simulation of air ventilation in super-large underground developments

Recent advancements in engineering technology have enabled the construction of super-large underground engineering projects in China. Currently, the ventilation requirements and standards of normal-size underground spaces are used for super-large underground excavating engineering projects in China. For example, the minimum air velocity of 0.15 m/s is the standard velocity for normal-size underground spaces; however, this value is also used as the required air velocity for diluting underground contaminants in super-large underground developments. This paper aims to examine the minimum ventilation requirements for super-large underground developments (S > 100 m²). A three-dimensional computational domain representing a full-scale underground space has been developed. The pertinent parameters such as dust concentration, smoke density, oxygen concentration and air temperature have been simulated. The results show that at some specific underground conditions, the ventilation air velocity of 0.15 m/s is sufficient to control the dust level, provide required oxygen concentration and maintain the air temperature at acceptable levels during development; however, it is not sufficient to bring the CO concentration below an acceptable safe limit. This must be considered by the ventilation system designers of super-large underground developments.     

Floor dust erosion during early stages of coal dust explosion development

An ignition of methane and air can generate enough air flow to raise mixtures of combustible coal and rock dust. The expanding high temperature combustion products ignite the suspended dust mixture and will continue to propagate following the available combustible fuel supply. If the concentration of the dispersed rock dust is sufficient, the flame will stop propagating. Large-scale explosion tests were conducted within the National Institute for Occupational Safety and Health (NIOSH) Lake Lynn Experimental Mine (LLEM) to measure the dynamic pressure history and the post-explosion dust scour depth. The aim of this effort is to provide quantitative data on depth of dust removal during the early stages of explosion development and its relationship to the depth of floor dust collected for assessing the incombustible content most likely to participate in the combustion process. This experimental work on dust removal on is not only important for coal mine safety but also for industrial dust explosions.     

Distribution of Salmonella clonal groups in four Brazilian feed mills

Feed is one of the major vehicles for Salmonella transmission to pigs, and its spread during the milling process may play an important role in feed contamination. Therefore, a cross-sectional study was carried out in four feed mills in order to evaluate the frequency of Salmonella isolation at various stages of feed production and to track the spread of genotypically related isolates grouped by pulsed-field gel electrophoresis (PFGE). From a total of 1269 analyzed samples, 63 (4.96%) showed the presence of Salmonella. Evaluated feed mills (A, B, C and D) presented 3.5% (n = 11/317), 1.7% (n = 5/289), 7.5% (n = 23/308) and 7.0% (n = 25/355) positive samples, respectively. Twenty-three serovars were identified, with the most frequently detected being Montevideo (n = 14, 22.2%), Anatum (n = 8, 12.7%) and Senftenberg (n = 8, 12.7%). The isolation of Salmonella was significantly higher (p = 0.002) in samples with the presence of total coliforms (36/489; 7.36%) than in the coliform-negative samples (27/780; 3.46%). Conveyors (OR = 4.43, 95% CI: 2.43–8.09) were the most likely sites of Salmonella isolation, followed by dust settled on the feed mill's floor (OR = 2.88, 95% CI: 1.41–5.33). Isolates indistinguishable on PFGE or belonging to pulsotypes with a high similarity (>95%) were identified in serovars Agona, Infantis, Montevideo, Orion, Senftenberg and Worthington. In particular, clonal groups of serovars Montevideo and Senftenberg were found to be disseminated among different sample types (ingredients, dust collected from the premise's floor and complete feed) or to be endemic in the feed mills. The dissemination of Salmonella clonal groups demonstrates the importance of control measures to avoid dust and debris accumulation on equipment surfaces.     

Experimental and computational study on the separation performance of an electrostatic precipitator with curved transvers collecting plates

Aiming at the problems of low collection efficiency of fine particulate matter and large area occupied by existing electrostatic precipitators (ESP), a new type of horizontal electrode ESP is proposed. It has the advantages of accelerating turbulent coalescence, increasing the effective dust collecting area and increasing the particle driving speed. The performance of the new type of ESP is systematic studied through simulation and experiment at the same time, and the results matches well. By comparing the dust removal effect of the horizontal electrode ESP and the conventional ESP, it can be concluded that the horizontal electrode ESP has a better dust removal efficiency, and can still maintain a better dust removal effect under high air velocity. The dust removal efficiency of new ESP can reach above 98% under the experimental conditions.     

Dust particle detection in traffic surveillance video using motion singularity analysis

Dust particle detection in video aims to automatically determine whether the video is degraded by dust particle or not. Dust particles are usually stuck on the camera lends and typically temporally static in the images of a video sequence captured from a dynamic scene. The moving objects in the scene can be occluded by the dusts; consequently, the motion information of moving objects tends to yield singularity. Motivated by this, a dust detection approach is proposed in this paper by exploiting motion singularity analysis in the video. First, the optical model of dust particle is theoretically studied in by simulating optical density of artifacts produced by dust particles. Then, the optical flow is exploited to perform motion singularity analysis for blind dust detection in the video without the need for ground truth dust-free video. More specifically, a singularity model of optical flow is proposed in this paper using the direction of the motion flow field, instead of the amplitude of the motion flow field. The proposed motion singularity model is further incorporated into a temporal voting mechanism to develop an automatic dust particle detection in the video. Experiments are conducted using both artificially-simulated dust-degraded video and real-world dust-degraded video to demonstrate that the proposed approach outperforms conventional approaches to achieve more accurate dust detection.     

The Cut and the Continuum: Sophie Ristelhueber’s Anatomical Atlas

From her early photographs of the ruinous aftermath of the Lebanon War in Beirut (1982) to her more recent images of bomb craters in Eleven Blowups (2006), the French artist Sophie Ristelhueber has been intent to maintain, in her own metaphor, ‘the analytical distance of an anatomy lesson’. Exhibiting the evidence of warfare but withholding their explanation, Ristelhueber’s provocative gesture of making art of war, removing human conflicts from their political contexts to render them as still-lifes, ready-mades, earthworks, or surrealist poems, is patently anti-journalistic. In keeping with the artist’s surgical analogy, this article explores Ristelhueber’s aesthetic mode of address as one that shares its fundamental operation with that of photography – namely, to make a cut. Retracing the morphology of recurring imprints and injuries that appear across the terrestrial and corporeal expanses traversed in her work, the article considers the ways in which these cuts pertain to the transformative power of violence and images alike.     

Validation of coastal sea and lake surface temperature measurements derived from NOAA/AVHRR data

An interactive validation monitoring system is being used at the NOAA/NESDIS to validate the sea surface temperature (SST) derived from the NOAA-12 and NOAA-14 polar orbiting satellite AVHRR sensors for the NOAA CoastWatch program. In 1997, we validated the SST in coastal regions of the Gulf of Mexico, Southeast US and Northeast US and the lake surface temperatures in the Great Lakes every other month. The in situ     

Resuspension of carbon dust collected in Tore Supra and exposed to turbulent airflow: Controlled experiments and comparison with model

This work presents the results of experiments conducted with carbon microparticles collected in the tokamak Tore Supra in order to characterize their resuspension behaviour from a stainless-steel substrate when exposed to turbulent airflow. Experiments were conducted in a wind tunnel with controlled velocity profiles and monitored environmental conditions. A consequent amount of dust has been collected in the vessel of the tokamak and a bimodal particle size distribution of samples is first demonstrated. Comparison with resuspension of alumina powders with equivalent particle size distributions under turbulent airflow is also discussed. Results for both carbon and alumina microparticles are then compared to a theoretical resuspension model. Data reveal that exposing multilayer deposits with bimodal particle size distributions to low-speed flows (i.e. 3–10 m/s) induces a significant reduction of the mobilized fractions compared to what was predicted by the model. In addition, results helped to highlight some limitations in the model to physically describe changes in the adhesive strength that can occur with a polydisperse deposit.     

煤矸石电厂除尘系统改造设计

以演马电厂的除尘系统改造为例,提出了以电除尘器代替原有的水膜除尘器的改遣方案,通过计算,确定电除尘器的相关系数。