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171.
Five aromatic hydrocarbons (benzene, toluene, and three isomeric xylenes) were monitored in indoor and outdoor air of 7 public buildings and 54 private homes, located in Barcelona City metropolitan area and in several rural areas of Catalonia. The sampling was carried out over four periods: spring-summer and winter of 2000, and summer and winter of 2001. Passive ORSA 5 Dra¨ger samplers were used for benzene, toluene, and xylenes (BTX) adsorption. BTX were extracted with carbon disulphide and analysed using ... 相似文献
172.
Gabi N. Waite Stéphane J. P. Egot-Lemaire Walter X. Balcavage 《The Environmentalist》2011,31(2):107-113
Over the past decades, strong evidence has accumulated that low-frequency electromagnetic fields (EMFs) can be useful in treating
human pathologies, such as bone fractures, soft tissue illnesses, and pain. Common strategies for the design of commercial
therapeutic devices are to generate EMFs that simulate body endogenous EMFs, or EMFs that resonate with a particular biological
process, such as the natural motions of ions. We recently came across a biologically active commercial EMF signal that seems
to be different. The signal is generated by summing the fundamental frequencies and harmonics of several periodic base signals
which remain proprietary to the company. When first examined in the time domain, the signal resembled electronic noise; however,
when critically analyzed, the signal is not identical with noise. Rather, it is a highly complex waveform exhibiting a very
wide range of values for the time derivative of the magnetic field density (dB/dt) and a beat frequency in the Extremely Low-Frequency
range. In this paper, we speculate on the mechanism of action of this and similar signals. We consider it less likely that
cells, or cell components, act like filters to extract and couple with individual signals that make up the complex EMF signal.
Consequently, we favor the possibility that with the signal discussed here cells respond to the very complex signal and that
the biological response can be modified by the presence of a beat in the signal, in this case a low-frequency beat. More generally,
this would suggest the hypothesis that biological processes can be regulated by noise-like signals and that the effects of
a noisy signal can be modified by the presence of signal repetition patterns, such as beats. Given the very small energy that
signals like these can transduce into a biological system, biological effects can be expected only when the molecular processes
involved are poised so that the available energy leads to molecular reactions that achieve the activation state for the reaction. 相似文献
173.
Development of a coupled reservoir operation and water diversion model: Balancing human and environmental flow requirements 总被引:2,自引:0,他引:2
X.A. YinZ.F. Yang 《Ecological modelling》2011,222(2):224-231
Maintaining a natural flow regime helps preserve the health of riverine ecosystems. Conventional studies on reservoir operations have focused mainly on identifying optimal operational schemes for satisfying human water demands. To systematically reflect the ecological effects of both natural and human-induced hydrologic alterations, water diversions downstream of the reservoirs should be considered as well. This research focused on a coupled reservoir operation and water diversion (CROWD) model, created through the integration of a reservoir operation model and a water diversion model. The proposed model considers both human and environmental flow requirements, and represents a compromise that balances ecological protection (preservation of the natural flow regime of a river) and human needs (reduced water shortages). In the reservoir operation model, the reservoir space is divided into three zones and different operating rules are developed for directing reservoir operation when water levels are in different zones; in the water diversion model, different water users are assigned different supply priorities with the instream flows no more than the minimum environmental flows having the highest priority; and the two models are coupled by the water mass balance between the two hydraulic facilities. The non-dominated-sorting genetic algorithm II (NSGA-II) was used to determine the parameters of the developed CROWD model and the model was applied to support the joint operational management of the Tanghe Reservoir and the Liaoyang Diversion in the Tang river basin, China. The resulting reservoir operation and water diversion schemes indicate that the CROWD model is useful for optimizing the operation of reservoirs and water diversion schemes. Moreover, it helps to analyze tradeoffs between human and environmental water needs, resulting in solutions that reduce the risk of water shortages and minimize ecological integrity disturbances. 相似文献
174.
J.X. Wen A. HeidariS. Ferraris V.H.Y. Tam 《Journal of Loss Prevention in the Process Industries》2011,24(2):187-193
A modelling strategy has been developed for consequence analysis of medium and large scale gaseous detonation. The model is based on the solution of Euler equations with one-step chemistry. The Van Leer flux limited method which is a total variation diminishing scheme is used for shock capturing. Preliminary calculations were firstly conducted for small domains with fine grids which resolve the wave, relatively coarse grids which have less than 10 grids across the wave and coarse grids in which the minimum grid size is larger than the wave thickness to ensure that the reaction scheme has been properly tuned to capture the correct detonation pressure, temperature and velocity in the resolutions used in the different cases. The model was firstly tested against a medium scale detonation test in a shock tube with U-bends. Reasonably good agreement is achieved on detonation pressure and mean shock wave velocities at different measuring segments of the tube. Following the validation, the detonation of a hypothetical planar propane-air cloud is simulated. The predictions uncovered some interesting features of such large scale detonation phenomena which are of significance in the safety context, especially for accidental investigations. The findings from the present analysis are in line with the forensic evidence on damages in some historic accidents and challenges previous analysis of a major accident in which forensic evidence suggested localised detonation but was considered as the consequence of fire storms by the investigation team. 相似文献
175.
Gallego E Roca FJ Perales JF Guardino X 《Journal of environmental monitoring : JEM》2011,13(9):2612-2622
The effect of different sampling exposure times and ambient air pollutant concentrations on the performance of Radiello? samplers for analysis of volatile organic compounds (VOCs) is evaluated. Quadruplicate samples of Radiello? passive tubes were taken for 3, 4, 7 and 14 days. Samples were taken indoors during February and March 2010 and outdoors during July 2010 in La Canonja (Tarragona, Spain). The analysis was performed by automatic thermal desorption (ATD) coupled with capillary gas chromatography (GC)/mass spectrometry detection (MS). The results show significant differences (t-test, p < 0.05) between the amounts of VOCs obtained from the sum of two short sampling periods and a single equivalent longer sampling period for 65% of all the data. 17% of the results show significantly larger amounts of pollutant in the sum of two short sampling periods. Back diffusion due to changes in concentrations together with saturation and competitive effects between the compounds during longer sampling periods could be responsible for these differences. The other 48% of the results that are different show significantly larger amounts in the single equivalent longer sampling period. The remaining 35% of the results do not show significant differences. Although significant differences are observed in the amount of several VOCs collected over two shorter sampling intervals compared to the amount collected during a single equivalent longer sampling period, the ratios obtained are very close to unity (between 0.7 and 1.2 in 75% of cases). We conclude that Radiello? passive samplers are useful tools if their limitations are taken into account and the manufacturer's recommendations are followed. 相似文献
176.
Yang SX Li JT Yang B Liao B Zhang JT Shu WS 《Journal of environmental monitoring : JEM》2011,13(7):1876-1883
Previous studies have shown that the application of soil amendments is efficient in reducing acidity and heavy metal bioavailability in mine soils. However, it remains a challenge for environmentalists to predict accurately and control economically the re-acidification in re-vegetated mine soils. In this study, net acid generation (NAG) test and bioassay technique were employed to assess the effectiveness of the amendments [including lime, N-P-K (nitrogen, phosphorous and potassium) fertilizer, phosphate and river sediment] on re-acidification and heavy metal immobilization in an extremely acid (pH < 3) mine soil. Our results suggested that NAG test was a rapid and accurate approach to assess the effectiveness of the amendments on re-acidification potential of the mine soil. Interestingly, it was found that phosphate and river sediment played quite specific roles in preventing the re-acidification in the mine soil. In addition, the results also indicated that the addition of 25 t ha(-1) lime combined with river sediment (30%) might be an economical method to successfully control the acidification and re-acidification in the extremely acid mine soil, allowing the re-establishment of the plants. Collectively, our results implied that the combined use of NAG test and bioassay assessment was effective in evaluating a reclamation strategy for extremely acidic mine soils. 相似文献
177.
In order to further expound the effect of soil nematodes on litter decomposition in urban forest, this study investigated the responses of soil nematodes communities to litter decomposition by litterbags technology at different mesh sizes in Dalian National Forest Park. Soil nematodes community composition, decomposition rate of litter and nutrient release were also analyzed. It found a total of 4 418 nematodes from 39 genera. Higher relative density of soil nematodes was found in the bags with 0.1 mm mesh size (1.55 individuals and 7.34 orders per g of dry litter) compared to the bags with 0.02 mm mesh size (0.21 individuals and 0.49 orders per g of dry litter). There were very few soil nematodes in the 0.02 mm litter bags. Thus we regarded that soil nematodes only affected the 0.1 mm litter bags. The mass loss rates as well as C and P release rates was higher in litter bags with 0.1 mm mesh size than in those with 0.02 mm mesh size, indicating a significant influence of soil nematodes on mass loss and nutrient release. The contribution of soil nematodes to the litter mass loss was about 24%. The effect of soil nematodes on the nutrient release rates differed among elements. The soil nematodes had a bigger influence on the release rate of N than that of other elements, whereas the influence on K release rate was the lowest. The results showed that soil nematodes communities has a significant effect on the litter decomposition and nutrient release of the forest litter in Dalian city, especially promoting the mass loss rates and N release rates. 相似文献
178.
Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C2HCl3 (k(1)) and C2Cl4 (k2) over an extended temperature range at 740+/-10 Torr in a He bath gas. These absolute rate measurements were accomplished using a laser photolysis/laser-induced fluorescence (LP/LIF) technique under slow flow conditions. The simple Arrhenius equation adequately describes the low temperature data for k1 (<650 K) and the entire data set for k2 and is given by (in units of cm3 molecule(-1) s(-1)): k1(291 - 650 K) = (9.73+/-1.15) x 10(-13) exp (158.7+/-44.0)/T, k2(293 - 720 K ) = (1.53+/-0.14) x 10(-12) exp (-688.2+/-67.5)/T. Error limits are 2sigma values. The room temperature values for k1 and k2 are within +/-2sigma of previous data using different techniques. The Arrhenius activation energies for k1 and k2 are a factor of 2-3 lower than previously reported values. The experimental measurements for both k1 and k2 in conjunction with transition state and variation transition state theory calculations infer an OH addition mechanism. The lack of a measurable kinetic isotope effect for k1 is consistent with this mechanism. Insight into the subsequent reactions of the chemically activated intermediate are presented in the form of potential energy diagrams derived from ab initio calculations. 相似文献
179.
Experimental results from an isothermal laminar flow reactor at atmospheric pressure are presented on the chemical composition in the post-oxidative region of two sooting fuel-rich pre-mixed mixtures diluted in nitrogen. A base case composed of n-heptane and O2 in N2 at 1425 K with a C/O of 2.85 was perturbed by substituting 10% of the carbon in n-heptane with carbon as CH4. While these changes would intuitively reduce aromatics and soot formation by increasing H2 and decreasing C2H2 concentrations, we observe the opposite. The concentrations of individual aromatic species are observed to actually increase by up to 50% and the soot yield increases by 80%. 相似文献
180.
农田恶性杂草相比普通杂草的传播更为迅速且难以有效防治,对农业生产危害严重.明确典型恶性杂草当前潜在分布面积及未来气候变化下对耕地的潜在入侵风险对农业生产管理具有重要意义.以广泛分布于青藏高原农田中的3种常见恶性杂草,即野燕麦(Avena fatua L.)、一年生早熟禾(Poa annua L.)和狗尾草[Setaria viridis(L.)P.Beauv.]为研究对象,利用广义增强模型(GBM)、广义线性模型(GLM)、人工神经网络(ANN)、最大熵(MaxEnt)、随机森林(RF)及多元自适应回归样条(MARS)算法集合预测上述3种杂草在青藏高原的潜在地理分布以及驱动其变化的关键因子,以评估其对耕地的入侵风险.未来气候场景采用最新的第六次国际耦合模式比较计划(CMIP6)框架下2050年的4种共享经济路线(SSP1-2.6、2-4.5、3-7.0、5-8.5).结果显示:野燕麦适宜分布区面积约为3.5912×10^(5) km^(2),主要分布于四川西南部及青海东部,零星分布于甘肃、西藏和新疆;一年生早熟禾和狗尾草的适宜分布区面积约为4.3046×10^(5) km^(2)和2.0036×10^(5) km^(2),均主要分布于四川西南部和西藏东南部,零星分布于青海东部和甘肃南部.年均温是3种杂草分布的最主要驱动因子.此外,人类足迹和土壤有效氮是影响野燕麦分布的相对重要因子;土壤酸碱度、最暖季降水量是影响一年生早熟禾分布的重要因子;温度季节性、最暖季降水量是影响狗尾草分布的重要因子.预计至2050年,3种杂草在4种情境下均会出现不同程度的扩张,狗尾草的扩张面积表现出随辐射强迫的增强呈先升高后趋于稳定的趋势,而另两种杂草则呈先升后降的趋势.预计3种杂草的潜在分布面积在耕地中的占比与扩张面积的变化趋势一致,且在主产区的占比高于非主产区.模拟结果表明,未来气候变化下,随着3种恶性杂草的适宜分布区面积的扩张,其对青藏高原耕地的入侵风险将增加,尤其是粮食主产区所面临威胁更为严峻,建议应重点关注青藏高原粮食主产区恶性杂草的生理生态、迁移扩散和防治技术研究.(图6表2参61) 相似文献