In situ strain monitoring of fiber-reinforced polymers using embedded piezoresistive nanocomposites

Fiber-reinforced polymer (FRP) structures and components are highly susceptible to damage due to delamination, matrix cracking, inter-laminar fracture, and debonding, all of which have potential to cause catastrophic structural failure. While numerous sensing technologies have been developed and embedded in FRP composites for monitoring strain, they serve as defects and can promote damage formation and propagation. Thus, in this study, an alternative technique is proposed for in situ strain monitoring of FRP composites via layer-by-layer multi-walled carbon nanotube-polyelectrolyte thin films deposited directly upon glass fiber weaves. To date, these carbon nanotube-based thin films have been validated for their piezoresistivity. The objective of this study is to characterize the strain sensing performance of different thickness thin films deposited on glass fiber weaves and embedded in FRP specimens using time-domain two-point probe resistance and frequency-domain electrical impedance spectroscopy (EIS) measurements. From the experimental thin film electromechanical response, a new method for fitting using a cubic smoothing spline is implemented and is compared to linear least-squares fitting. The results show that the cubic spline fit is better suited for capturing the strain sensitivities (or gage factors) of these thin films within the time- and frequency-domains along with the variation of strain sensitivity with applied strain. The bulk resistance response is described by the DC resistance measurements, whereas the EIS measurements provide insight of the inter-nanotube response.     

Copper in foods, beverages and waters from South East Spain: influencing factors and daily dietary intake by the Andalusian population

The copper content of 225 food, 49 beverage and twelve potable water samples were determined using atomic absorption spectrometry (AAS). Analyses of NIST and BCR reference materials demonstrated the accuracy of this technique. The highest copper levels were found in dried fruit and legumes, followed by organ meats, molluscs and crustaceans, cephalopods, cereals and sausages, respectively. In cereals, legumes and fruit, copper levels increased significantly with increasing levels of protein and decreasing carbohydrate content (p < 0.001). In meat and meat by-products, copper concentrations found in organ meats were significantly higher (p < 0.01). In fresh fish products, copper levels in shellfish were significantly higher than those measured in fish (p < 0.001). In vegetables, the copper concentrations found in mushrooms were significantly higher (p < 0.005). Mean copper concentrations analysed in cheese were statistically higher than those determined in other dairy products (p < 0.01). In beverages, copper levels determined in rum and juices were significantly higher (p < 0.001). Beverages for which a vegetable component was directly used in their manufacturing process (juices, wines and beers) had statistically higher copper levels when compared with fresh drinks. The daily dietary intake (DDI) of copper in the Andalusian diet was 1979 mug day(-1) per person. Cereals, meat, meat by-products and vegetables are the food categories that are the main source of copper in the daily diet. Taking into account the dietary reference intakes and upper levels (900 and 10, 000 mug Cu day(-1) for healthy adults, respectively), the mean copper DDI found indicate that for most of healthy adult individuals from the area, no adverse effects occur in relation to copper nutrition (deficiency or toxicity). Potable waters supplied 53 mug day(-1), which constitutes on average 0.025% of the maximum tolerable daily intake of this element set by the Joint FAO/WHO Expert Committee.     

Polybrominated diphenyl ethers in peregrine falcon (Falco peregrinus) eggs from the northeastern U.S

A total of 114 peregrine falcon eggs from nests in Connecticut, Massachusetts, Maine, New Hampshire, Rhode Island, and Vermont were analyzed for polybrominanted diphenyl ethers (PBDEs). Eggs were collected from 1996 to 2006, excluding 1997 and 1998. Total PBDE concentrations ranged from 74.5 to 6610 ng/g wet weight, with a median of 440. These levels were generally higher than those observed in European peregrine eggs, but comparable to those in North American seabird eggs. Congener patterns differed from such seabirds and were dominated by BDE-153, followed by BDE-99, -183, -209, -197, -207, -154, -100, and -196; with lesser contributions from BDE-47, -208, -203, -201, -206, -202, -138, and -119. Urban and rural falcon eggs contained similar total PBDE concentrations but different congener profiles. Urban eggs exhibited higher BDE-209 concentrations and greater percentages of other highly brominated congeners. BDE-209 was detectable in all eggs, with concentrations ranging from 1.4 to 420 ng/g wet weight Five octa- and three nona-brominated congeners were also frequently detected, some likely derived from the biodegradation of BDE-209. Temporal analyses indicated no significant changes in concentrations of total PBDEs, or most individual congeners, during the study period. An exception was BDE-209. It exhibited a significant increase, with a doubling time of 5 years. Current PBDE burdens may be insufficient to cause noticeable adverse effects at the population level, as the number of territorial pairs increased in the past decade. However, the high BDE-209 concentrations, short doubling time, and likely biodegradation observed in peregrine eggs from the northeastern U.S. may supportthe need for additional deca-BDE regulations.     

Antarctic research bases: local sources of polybrominated diphenyl ether (PBDE) flame retardants

Contemporary studies of chemical contamination in Antarctica commonly focus on remnants of historical local releases or long-range transport of legacy pollutants. To protect the continent's pristine status, the Antarctic Treaty's Protocol on Environmental Protection prohibits importation of persistent organic pollutants. However, some polybrominated diphenyl ether (PBDE) congeners exhibit similar properties. Many modern polymer-containing products, e.g., home/office furnishings and electronics, contain percent levels of flame retardant PBDEs. PBDE concentrations in indoor dust and wastewater sludge from the U.S. McMurdo and New Zealand-operated Scott Antarctic research bases were high. Levels tracked those in sludge and dust from their respective host countries. BDE-209, the major constituent in the commercial deca-PBDE product, was the dominant congener in sludge and dust, as well as aquatic sediments collected near the McMurdo wastewater outfall. The pattern and level of BDE-209 sediment concentrations, in conjunction with its limited environmental mobility, suggest inputs from local sources. PBDE concentrations in fish and invertebrates near the McMurdo outfall rivaled those in urbanized areas of North America and generally decreased with distance. The data indicate that reliance on wastewater maceration alone, as stipulated by the Protocol, may permit entry of substantial amounts of PBDEs and other chemicals to the Antarctic environment.     

Short communication: Evaluation of the overall accuracy of the DeLaval cell counter for somatic cell count in ovine milk: effect of soak time in diluted and undiluted milk samples

This study evaluated the performance of the DeLaval cell counter (DCC) when analyzing ovine milk with different soak times (defined as the permanence time of samples within the DCC cassette before starting the DCC counting procedure) in diluted and undiluted milk samples in 2 dairy sheep breeds. A total of 101 composite ovine milk samples (50 from Assaf ewes and 51 from Churra ewes), ranging between 50 × 10³ and 2,200 × 10³ cells/mL, were divided into 10 aliquots/milk to be analyzed by DCC. Four undiluted aliquots and 4 aliquots diluted 1:1 in PBS were analyzed by using soak times of 0, 1, 2, and 3 min/aliquot, and the other 2 aliquots were diluted 1:1 in propidium iodide or ethidium bromide staining solutions and analyzed by DCC. Milk samples were also analyzed by the Fossomatic method, as a reference. All analyses were carried out in duplicate. Undiluted milk samples with soak times ≥1 min showed large coefficients of regression (b = 0.96 to 0.98) and correlation (r > 0.99) when compared with the Fossomatic method. In these samples, DCC gave repeatability standard deviations (s_r = 35 to 51 × 10³ cells/mL) lower than other DCC analytical conditions (s_r = 49 to 74 × 10³ cells/mL), and their log SCC means (5.51 to 5.52) were close to the reference value (5.56). The log SCC means corresponding to samples diluted 1:1 in staining solutions (5.55) did not differ from the reference value; however, these aliquots had lower regression coefficients (b: 0.92 to 0.93). Samples diluted 1:1 in PBS and undiluted samples with a 0-min soak time showed a global accuracy similar to or lower than undiluted samples with soak times ≥1 min. Breed did not seem to affect the results. We concluded that undiluted raw milk with a soak time ≥1 min and analyzed by DCC shows suitable overall accuracy in ovine milk compared with the reference method and can be considered as the best option for on-farm use from an operational point of view.     

优质石英岩作为高纯石英原料的提纯试验研究

采用阴极发光显微镜、ICP-OES和SEM-EDS等分析测试手段研究了花脖湾石英岩的矿石性质,以解离并去除白云母为提纯目标进行了浮选和酸浸条件优化试验。结果表明:花脖湾石英岩质地纯净,w(SiO_2)高达99.00%,白云母是主要脉石矿物,优化试验确定的浮选条件为:矿浆pH值2.5,DDA用量140g/t;酸浸条件为:混合酸质量分数30%,温度55℃,时间120min。在超声波辅助作用下提纯获得的细粒级(0.110~0.074mm)石英砂9种杂质元素总含量降低至66.65×10-6,w(SiO_2)达到99.99%。花脖湾石英岩矿经试验证实为一种石英岩型高纯石英原料,作为高纯石英资源应用前景广阔。     

电解工艺参数对铟微粉纯度和粒度的影响(I)

研究了电解工艺制备铟微粉时,铟离子浓度、电流密度和连续电解时间对粉体纯度和粒度的影响。结果表明：当电工艺参数为NaCl浓度80g/L,极距5cm,硫脲浓度0.3g/L,明胶浓度0.5g/L,pH=2.5,添加剂聚乙烯吡咯烷酮用量为0.2g/L时,连续电解时间越长,所得粉体粒度越大;电流密度为130A/m₂时,所得粉体粒度最小,纯度最高;In₃₊浓度对粉体粒度的影响最小,但对纯度影响最大;在此工艺参数和In₃₊浓度为30g/L,电流密度为130 A/cm₂的条件下电解1h,可得到粒度小于100μm的铟微粉,其中粒度小于30μm的占75%。