Enhancing transverse mixing in streams with submerged vanes

In order to maintain the water quality of moving streams, it is essential to know the process of pollutant mixing. The transverse mixing is very important which is needed to be modeled to understand mixing phenomenon. It was observed that transverse mixing is a strong function of secondary currents, thus, submerged vanes, which are aerofoil skewed at angle of 10°–40° with respect to flow, generate transverse circulations that can be utilized to induce secondary currents in the flow to enhance transverse mixing. Present study is an attempt to utilize submerged vanes as an instrument to enhance the transverse mixing by incorporating various vane configurations. In order to study the effect of vane generated circulations on transverse mixing, experimentations were conducted on three vane sizes and for various row arrangements of vanes attached to bed. An attempt is made to investigate the effect of submerged vane size and rows on transverse velocity, concentration profile and transverse mixing coefficient. It was observed by measurement of concentration profile that transverse mixing was more enhanced for submerged vanes of higher height. It was also observed that as the number of rows is proportional to the transverse mixing. By measuring the transverse velocity profile, it was observed that more and more fluid was advected in transverse direction for higher rows of vanes. By utilizing the observed transverse mixing coefficients, number of vane rows and relative height of vane, a predictor was derived to predict transverse mixing coefficient in the presence of submerged vane rows. It was observed that the derived predictor shows a fair amount of agreement in the result predicted.     

Technical efficiency analysis of the conversion of cropland to forestland program in Jiangxi,Shaanxi, and Sichuan

Conversion of Cropland to Forestland Program (CCFP) has greatly impacted China’s agricultural sector, and more specifically rural farmers. While changes in living standards as a result of the implementation of the CCFP have been analyzed, little research has been conducted regarding the impacts of such policies on farming operations. As agriculture contributes nearly 10% of national GDP, it is important to analyze the implications of policies on a national industry. An input-oriented data envelopment analysis (DEA) model was used to examine the technical efficiency of farming operations following implementation of the CCFP, using survey data from farmers in Jiangxi, Shaanxi, and Sichuan provinces. Additionally, the impact of factors such as urbanization, age and education, and land fragmentation was examined with respect to farming operational efficiency. Scale inefficiency was found to have the greatest effect on overall inefficiency in farming operations in comparison to pure technical inefficiency, which was largely influenced by the presence and degree of land fragmentation of land holdings. Findings can be used to inform national land-use policies facilitating land fragmentation in China and address gaps in existing broader level studies that utilize non-parametric approaches to examine the technical efficiency of Chinese farmers affected by the CCFP.     

Physical factors negatively affecting evaluation of long-term biodegradation experiments of polychlorinated biphenyls

Behaviour of PCB added in the form of a technical mixture (Delor 106) and [¹⁴C]PCB 77 into different aqueous model cultivation media in long-term experiments was studied. The work was focused on monitoring PCB recovery from liquid media in the absence of micro-organisms. GC-ECD and radioanalysis were utilised for determination of PCB in the examined systems. Strong relations between duration of experiments, composition of media, degree of chlorination of biphenyls, and recovery of PCB were found. The lowest yields of PCB were observed for the extracts from model solutions based on N-limited cultivation media without veratryl alcohol and Tween 80. The addition of these components, mainly of Tween 80, caused a significant increase of PCB recoveries.     

Accumulation and partition of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in the muscle and liver of fish

The present study monitored fish from sites contaminated for many years, and the data reflected the results of actual, long-term environmental exposure. The sum concentrations and TEQs of PCDD/F in the muscle of common carp (Cyprinus carpio (linnaeus)) and big head (Aristichthys nobilis) from the different site of a heavily polluted lake in China are decreased with decrease of PCDD/F concentration in sediment and water. Concentration in fish can be highly variable, but the concentration is comparable in muscle between different species of fish if the concentrations are normalized by lipid content. PCDD/F accumulate in certain tissues with the highest proportions found in the liver of fish. The concentrations and TEQs in livers were also decreased with concentrations of sediments and water. The concentrations of PCDD/F in muscle are significantly correlated with those in liver. BCFs of 2,3,7,8-substituted PCDD/F calculated directly from water were consistent with that calculated indirectly from sediment. PCDD/F concentrations in sediment are much higher than that in water, therefore the measurement is much easier and the results are more accurate. Estimated BCFs for superhydrophobic chemicals derived from sediment may also serve as acceptable surrogates for "true" bioaccumulation potential.     

Influence of aggregate pre-wetting and fly ash on mechanical properties of lightweight concrete

This study has examined the mechanical properties of lightweight aggregate concrete with a density of 1800 kg/m3. The effects of the following parameters on the concrete properties have been analyzed: the pre-wetting time of the lightweight aggregate and the percentage of pulverized fly ash used as cementitious replacement material. The strength of the lightweight aggregate was found to be the primary factor controlling the strength of high-strength lightweight concrete. An increase in the cementitious content from 420 to 450 kg/m3 does not significantly increase the strength of lightweight aggregate concrete. The relationship between the flexural and compressive strength at 28 days can be represented by the equation fr=0.69/fck. The elastic modulus was found to be much lower than that of normal weight concrete, ranging from 15.0 to 20.3 GPa. The addition of PFA increases the slump and density of lightweight aggregate concrete.