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291.
This study examined the levels of seven heavy metals (namelyzinc, copper, cadmium, chromium, lead, manganese and iron) andtheir associations with magnetic properties in playground dustof Hong Kong. Results showed that the playground dust containedhigh concentrations of Zn (mean = 1883 g g-1), Cu(mean = 143 g g-1) and Cr (mean = 263 g g-1).Qualitative examination of dust samples under microscope indicated local traffic as one of the important pollutant sources. Magnetic measurements indicated that these anthropogenicpollutants mainly consisted of coarse-grained multidomain (MD) ferrimagnetic minerals. Superparamagnetic (SP), stable single domain (SSD) ferrimagnetic grains and non-ferrimagnetic mineralswere present in relatively small amounts. Significant correlations between heavy metals and various magnetic parametersindicated a strong affinity of heavy metals to magnetic minerals hence pointed out the potential of magnetic properties for simpleand rapid proxy indications of heavy metal pollution in playground dust. 相似文献
292.
Synthesis of a block copolymer of poly(3-hydroxybutyrate) and poly(ethylene glycol) and its application to biodegradable polymer blends 总被引:2,自引:0,他引:2
A block copolymer {P[(R,S)-HB-b-EG]} of atactic poly[(R,S)-3-hydroxybutyrate] {P[(R,S)-HB]} and poly(ethylene glycol) (PEG) was prepared by the ring-opening polymerization of -butyrolactone in the presence of a macroinitiator (PEG/ZnEt2/H2O) which had been produced by the reaction of ,-dihydroxy PEG (
n=3000) with ZnEt2/H2O (1/0.6) catalyst. The block copolymer (
n=10,500,
w/
n=1.2) was an A-B-A triblock copolymer comprising atactic P[(R,S)-HB] (A) and PEG (B) segments. The miscibility, physical properties, and biodegradability of binary blends of microbial poly[(R)-3-hydroxybutyrate] {P[(R)-HB]} with the block copolymer P[(R,S)-HB-b-EG] has been studied. The glass-transition temperature (T
g) data showed that the P[(R)-HB]/P[(R,S)-HB-b-EG] blend was miscible in the amorphous state. The P[(R)-HB] film became flexible and tough by means of blending with P[(R,S)-HB-b-EG] block copolymer. The enzymatic degradation of blend films was carried out at 37°C and pH 7.4 in a 0.1M phosphate solution of an extracellular PHB depolymerase fromAlcaligenes faecalis. The enzymatic degradation took place solely on the surface of the blend films. 相似文献
293.
294.
295.
Ramsis B. Salama Richard Silberstein Daniel Pollock 《Water, Air, & Soil Pollution: Focus》2005,5(1-2):3-26
The flow pathways of water in the soils of the Gnangara Mound are highly irregular and depend upon the moisture content, the
repellency and preferential wettability potential of the soils. The occurrence of preferential flow is more evident in dry
soils. As the soil wets during the rainy season, the water repellence and differential wettability decreases, the fingering
and the preferential flow paths disappear. Most of the agricultural sites in the Spearwood Sands which showed more irregular
flow than the Bassendean Sands are under continuous irrigation during cultivation season. As the repellency problems are chemically
treated, it is therefore expected that the flow will be more uniform all the year round. Landuse is mainly responsible for
variation in recharge rates; however, the hydraulic properties control aquifer response and water level pattern to a greater
degree. Water levels in the mid 1970s were in a semi steady state. Since that time, a combination of increasing water use
by pine plantations, heavy pumping from private boreholes in market gardens and private homes and intensive pumping from the
Gnangara Mound for the metropolitan water supply have caused water levels to continually decline in the Superficial aquifer.
Nitrate and phosphate concentrations in the regional Superficial aquifer are generally very low. None of the tested pesticides
(atrazine, diazinon, dimethoate, endosulfan, fenamiphos, iprodione, malathion and chlorpyrifos) were detected in the groundwater
samples collected from the monitoring bores. 相似文献
296.
Stefano Cordiner Renato Baciocchi Marina Attinà 《Water, Air, & Soil Pollution: Focus》2002,2(5-6):573-585
The prediction of the atmospheric concentration of ozoneand of other photochemical pollutants represents one of themajor scientific challenges in the study of urban airquality. To this aim, photochemical models are widelyapplied as support tools for regulatory purposes, but theirresults are known to be affected by several uncertainties,in boundary conditions, geographical and meteorologicaldata and the chemical composition of emission and ambientair as well. Also the mechanism selected to describe theurban chemistry may lead to large differences in the modelresults. In this work, the influence of ambient air composition onthe results of photochemical model has been studied using a simple Lagrangian trajectory model coupled with different chemical sub-models (CB-IV and a simplified version of EMEP). To this aim a parametric sensitivity study of ozone with respect to its precursors' concentration was performed withreference to the same meteorological conditions and by simulatingdifferent scenarios characterized by specific emitted pollutantsconcentration. Rather than analyzing sensitivity by changing initial composition, an analytical local sensitivity concept has been applied; this allowed evaluation the influence of initial concentration on the predicted ozone concentration andto discriminate between VOC-sensitive and NOx-sensitive kineticregimes. Finally, these results have been successfully comparedwith those obtained applying the concept of photochemical indicators (i.e. O3/NOy and H2O2/HNO3 ratios). 相似文献
297.
Processing and Physical Properties of Plastics Made from Soy Protein Polyester Blends 总被引:6,自引:0,他引:6
Blending soy protein with polyesters using a polyvinyllactam as a compatibilizer successfully made soy protein-based plastics. The polyesters used to produce blends included polycaprolactone (PCL) and Biomax (a commercial biodegradable polyester). The blends were processed by compounding extrusion and injection molding. Blends containing soy protein/Biomax-poly(vinyl alcohol) had tensile strengths ranging from 16–22 MPa, with samples containing larger percentages of the synthetic polymer exhibiting greater strengths. Blends made from soy protein, Biomax, and PCL had tensile strengths ranging from 27–33 MPa. All the blends had high Young's moduli but demonstrated brittle characteristics as evident from their low elongations at break, ranging from 1.8–3.1%. Plastics made from soy protein/polyester blends exhibited low water absorption and had good stability under ambient conditions relative to the plastics made from soy protein alone. Blends made from soy protein flour produced plastics with the lowest water absorption. 相似文献
298.
299.
Soybean protein has been considered as a potential biodegradable polymer in the manufacture of plastics. The purpose of this investigation was to characterize the effect of storage time on thermal and mechanical properties of soybean protein isolate (SPI) plastics. SPI was separated from defatted soy flour, modified with 1M or 2M urea, or plasticized with glycerol, and compression molded into plastics. Plastic made from SPI alone was used as a control. For all SPI plastics, glass transition temperatures and dynamic storage modulus increased and loss tangent decreased during storage. Excess enthalpy of relaxation of all SPI plastics had an exponential relationship with storage time, indicating a fast aging rate at the beginning of storage. All SPI plastics tended to be stiff and brittle during storage. The plastics with glycerol had the slowest aging rate and were fairly stable after 60 days, with about 8.8 MPa tensile strength and 168% strain at break. Plastics with the 2M urea-modification SPI also had a slow aging rate and became relative stable after 60 days, with about 10 MPa tensile strength and 72% elongation. 相似文献
300.
曲靖电厂灰渣性质及其用作水泥混合材的试验研究 总被引:1,自引:0,他引:1
在对粉煤灰及炉渣的主要物理、化学性质进行分析测试的基础上,对它们用作水泥混合材所表现出的性能及存在的问题进行了分析研究。 相似文献