也谈矿井提升钢丝绳的合理选择问题

关于矿井提升钢丝绳的合理选择问题,在《煤炭科学技术》刊物上曾发表过两篇专题文章,根据实践经验,介绍了提升钢丝绳合理选择的一些基本原则。现结合国产钢丝绳和矿井提升机的产品规格,谈一些看法,作为上述文章的补充。 一、应该优先选用金属断面系数大的钢丝绳。《煤矿安全规程》规定了矿井提升机的滚筒(对于摩擦式提升机则为摩擦轮)直径与提升钢丝绳直径的比值。对于不同结构品种的钢丝绳而言,如果直径及抗拉强度是相同的,则金属断面系数越大,其全部钢丝的破断拉力总和值也越大。当绳端的荷重为定值时,相应的安全系数也越大,这对于延长钢丝绳的使用寿命是极其有利的。     

Adsorptive removal of phenol from aqueous solutions on activated carbon prepared from tobacco residues: equilibrium, kinetics and thermodynamics

This study consists of producing high surface area activated carbon from tobacco residues by chemical activation and its behavior of phenol removal from aqueous solutions. K(2)CO(3) and KOH were used as chemical activation agents and three impregnation ratios (50, 75 and 100 wt.%) were applied on biomass. Maximum BET surface areas of activated carbons were obtained from impregnation with 75 wt.% of K(2)CO(3) and 75 wt.% of KOH as 1635 and 1474 m(2)/g, respectively. Optimum adsorption conditions were determined as a function of pH, adsorbent dosage, initial phenol concentration, contact time and temperature of solution for phenol removal. To describe the equilibrium isotherms the experimental data were analyzed by the Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherm models. Pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models were used to find out the kinetic parameters and mechanism of adsorption process. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated for predicting the nature of adsorption. According to the experimental results, activated carbon prepared from tobacco residue seems to be an effective, low-cost and alternative adsorbent precursor for the removal of phenol from aqueous solutions.     

Lead levels in Eurasian otters decline with time and reveal interactions between sources, prevailing weather, and stream chemistry

The uptake of contaminants by biota varies spatially and temporally due to a complex range of interacting environmental variables, but such complexities are typically disregarded in studies of temporal change. Here, we use linear modeling to explore spatial and temporal variation in bone Pb levels measured in samples taken from 329 Eurasian otters (Lutra lutra) found dead in southwest England. Between 1992 and 2004 Pb levels in otters fell by 73%, following UK legislative control of Pb emissions implemented since the mid 1980s. Spatial variation in bone Pb was positively correlated with modeled Pb emissions and stream sediment Pb, which interacted negatively with wind-speed and sediment Ca, respectively. Opportunistic collection of samples from wildlife mortalities provided a valuable opportunity for monitoring environmental contamination, interpretation of which was aided by spatially explicit analysis of environmental variables.     

Prevalence of Clostridium difficile in retailed meat in the Netherlands

Recent reports indicate that a large proportion of community-acquired Clostridium difficile infections (CA-CDI) are not linked to recent antibiotic therapy, older age, significant comorbidity or previous hospitalization. Possible community sources for CA-CDI include animals and food, and therefore a surveillance study on the prevalence of C. difficile in meat was performed. Samples of different meat species were collected from the retail trade and analyzed for the presence of C. difficile using a method that included selective enrichment in C. difficile broth, subsequent alcohol shock-treatment and plating onto C. difficile selective medium. C. difficile isolates were tested for the presence of toxin genes and were typed using PCR ribotyping. Of 500 samples tested, 8 (1.6%) were positive for the presence of C. difficile: 1 from lamb (6.3%) and 7 from chicken meat (2.7%). The isolated strains belonged to PCR ribotypes different from those that are currently most frequently found in patients with CDI in the Netherlands, except for C. difficile PCR ribotype 001 which was found in one chicken meat sample. This observation suggests that other matrices than meat may serve as a source for CA-CDI.     

A lysimeter study of nitrate leaching, optimum fertilisation rate and growth responses of corn (Zea mays L.) following soil amendment with water-saving super-absorbent polymer

BACKGROUND: Nitrate leaching and the resulting groundwater contamination from intensive cereal production has become a major concern for long‐term farmland efficiency and environmental sustainability in northern China. The aim of this study was to evaluate a water‐saving super‐absorbent polymer (SAP) for minimising NO₃^? leaching from soil and optimising corn growth and yield. Thirty‐six undisturbed soil lysimeters were installed in a field lysimeter facility in drought‐affected northern China to study the growth and yield characteristics of summer corn (Zea mays L.) as well as the amount of NO₃–leaching losses under different fertiliser (standard, medium or 75% and low, or 50% of conventional fertilisation rate) and SAP (control, 0; level‐1, 15 kg ha^?1 and level‐2, 30 kg ha^?1) treatments. RESULTS: Corn yield fell by 19.7% under medium and 37.7% under low fertilisation; the application of SAP increased yield significantly by 44.4% on level‐1 and 80.3% on level‐2. Similarly, plant height, leaf area, number of grains as well as protein, soluble sugar and starch contents in the grain also increased with SAP treatment. Application of SAP at 30 kg ha^?1 plus half of conventional fertilisation can reduce maximum (64.1%) nitrate leaching losses from soil. CONCLUSIONS: Application of SAP at 30 kg ha^?1 plus only half the amount of conventional fertiliser rate (150 kg urea, and 50 kg each of superphosphate and potassium sulfate) would be a more appropriate practice both for minimising nitrate leaching and sustainable corn production under the arid and semiarid conditions of northern China. Copyright © 2011 Society of Chemical Industry     

Infrared hollow waveguide sensors for simultaneous gas phase detection of benzene, toluene, and xylenes in field environments

Simultaneous and molecularly selective parts-per-billion detection of benzene, toluene, and xylenes (BTX) using a thermal desorption (TD)-FTIR hollow waveguide (HWG) trace gas sensor is demonstrated here for the first time combining laboratory calibration with real-world sample analysis in field. A calibration range of 100-1000 ppb analyte/N(2) was developed and applied for predicting the concentration of blinded environmental air samples within the same concentration range, and demonstrate close agreement with the validation method used here, GC-FID. The analyte concentration prediction capability of the TD-FTIR-HWG trace gas sensor also compares well with the industrial standard and other experimental techniques including GC-PID, ultrafast GC-FID, and GC-DMS, which were simultaneously operated in the field. With the advent of a quantum cascade laser with emission frequencies specifically tailored to efficiently overlap benzene absorption as the most relevant analyte, the overall sensor footprint could be considerably reduced to ultimately yield hand-held trace gas sensors facilitating direct and real-time detection of BTX in air down to low ppb levels.     

Individual safety performance in the construction industry: development and validation of two short scales

In the current research a short measure of safety performance is developed for use in the construction industry and the relationships between different components of safety performance and safety outcomes (e.g., occupational injuries and work-related pain) are explored within the construction context. This research consists of two field studies. In the first, comprehensive measures of safety compliance and safety participation were shortened and modified to be appropriate for use in construction. Evidence of reliability and validity is provided. Both safety compliance and safety participation were negatively related to occupational injuries, yet these two correlations were not statistically different. In the second study, we investigated the relationships between these two components of safety performance and work-related pain frequency, in addition to replicating Study 1. Safety compliance had a stronger negative relationship with pain than safety participation. Implications for research are discussed.     

A 265-base DNA sequencing read by capillary electrophoresis with no separation matrix

Electrophoretic DNA sequencing without a polymer matrix is currently possible only with the use of some kind of "drag-tag" as a mobility modifier. In free-solution conjugate electrophoresis (FSCE), a drag-tag attached to each DNA fragment breaks linear charge-to-friction scaling, enabling size-based separation in aqueous buffer alone. Here we report a 265-base read for free-solution DNA sequencing by capillary electrophoresis using a random-coil protein drag-tag of unprecedented length and purity. We identified certain methods of protein expression and purification that allow the production of highly monodisperse drag-tags as long as 516 amino acids, which are almost charge neutral (+1 to +6) and yet highly water-soluble. Using a four-color LIF detector, 265 bases could be read in 30 min with a 267-amino acid drag-tag, on par with the average read of current next-gen sequencing systems. New types of multichannel systems that allow much higher throughput electrophoretic sequencing should be much more accessible in the absence of a requirement for viscous separation matrix.     

Spatially resolved laser-induced breakdown spectroscopy in methane-air diffusion flames

A new setup for spatially resolved laser-induced breakdown spectroscopy (SR-LIBS) is used for the first time to analyze methane-air diffusion flames. Using this configuration, background continuum emission is reduced, signal-to-background noise ratio is increased up to eight times, and spatial resolution is enhanced. The local equivalence ratio is also quantitatively estimated and the width of the secondary combustion region at a specified height above the burner is determined for two different methane flow rates. Furthermore, the threshold energy for spark formation is measured for regions inside and outside the flame. The results show that threshold energy is larger at the secondary combustion region, near the border of the flame, than inside the flame.