Photocatalytic activity of TiO2 films grown on different substrates

Titanium dioxide films were prepared on glass, indium-tin oxide (ITO) glass and p-type monocrystalline silicon and studied for the photocatalytic degradation of rhodamine B in an aqueous medium. Raman, AFM, and XPS spectroscopic investigations of these films indicated that microstructure of titanium oxide films were greatly affected by the substrate materials. Rutile was confirmed to be easily formed on the surface of ITO glass, and TiO2 tended to grow as closely packed particles that were elongated strips with an average size of 20 nm, and had lovely contrast with the perfectly round particles grown on p-type monocrystalline silicon. Charge transfer between the film and silicon substrate was verified by surface photovoltage spectra. This may be the real reason why the films grown on ITO glass and silicon substrates exhibit higher photocatalytic reactivity than the film on glass substrate. Moreover, the different surface properties also seem to be responsible for the different activity.     

Prevalence of the Crayfish Plague Pathogen Aphanomyces astaci in Invasive American Crayfishes in the Czech Republic

Abstract:  In Central Europe invasive North American crayfishes are carriers of the oomycete Aphanomyces astaci, which causes crayfish plague. This lethal disease currently represents one of the major threats to native European crayfishes. We used molecular methods—species-specific amplification and sequencing of the pathogen DNA—to investigate the prevalence of individuals latently infected with A. astaci in 28 populations of two invasive American crayfish species (6 of the signal crayfish [ Pacifastacus leniusculus ] and 22 of the spiny-cheek crayfish [ Orconectes limosus ]) in the Czech Republic. The pathogen occurred in 17 investigated populations. We recorded a high variation in positive reactions, ranging from 0% to 100%, in populations of O. limosus . In P. leniusculus, however, only one individual out of 124 tested positive for the pathogen. There was a clear relationship between the water body type and pathogen prevalence in O. limosus . Infection ratios in isolated standing waters were usually low, whereas in running waters, pathogen prevalence often exceeded 50%. Other evaluated characteristics of potential plague pathogen carriers (size, sex, and the presence of melanized spots in the cuticle) seemed to be unrelated to infection. Our data suggest that in contrast to other European countries, O. limosus seems to be the primary reservoir of crayfish plague in the Czech Republic. Although all populations of alien American crayfishes may be potential sources of infections and should be managed as such, knowledge on the prevalence of the plague pathogen at various localities may allow managers to focus conservation efforts on the most directly endangered populations of native crayfishes.     

Adsorption of thorium from aqueous solutions by perlite

The use of expanded perlite for the adsorption of thorium from aqueous solution by batch technique is presented. The effects of particle size, pH of the solution, initial thorium concentration, shaking time, V/m ratio and temperature were determined. It was found that the adsorption capacity increases by the increase in the pH of the suspensions. The rate of thorium adsorption on expanded perlite was observed to be fast in the first hour of the reaction time. Adsorption isotherms were expressed by Langmuir and Freundlich adsorption models and the adsorption experiments conducted at 30 ± 1 °C showed that the adsorption isotherms correlated well with the Langmuir model. From the adsorption data, thermodynamic parameters such as ΔG^o, ΔH^o and ΔS^o were calculated as a function of temperature.     

Thermodynamics of interaction of lindane on silty loam and silty clay loam Indian soils

Abstract

Interaction of lindane with silty loam and silty clay loam soils was studied in batch tests at 23, 30 and 37° C. Sorption experiments were carried out at four concentrations and for varying time of contact upto 72 hours. This was followed by desorption studies. No desorption was observed. The sorption data was analysed using sorption equations and evaluating the thermodynamic parameters. The sorption was found to be predominantly entropic in nature and a combined effect of adsorption and chemisorption. The effect of organic matter and other chemical and mineralogical constituents of soils has also been discussed. The sorption with single application of lindane with the two soil types indicates that the insecticide is less likely to reach groundwater.     

Are either sod and catalase or the polyamines involved in the paraquat resistance of Conyza canadensis ?

Abstract

Paraquat/atrazine coresistant (PqAR) and paraquat resistant (PqR) horseweed (Conyza canadensis /L./ Cronq.) plants showed ‐ in the first hour after 0.5 mM paraquat spraying ‐ a decreased catalase activity followed by a slight increase. However, the enzyme activity remained always below the initial value. Sensitive plants showed a significant increase of catalase activity in the first 4 hour after spraying. The transient character of paraquat inhibition, the recovery of photosyn‐thetic activity of the PqAR Conyza plants (characterized by variable fluorescence) after spraying remained unaffected by the Superoxide dismutase (SOD) inhibitor, diethyldithiocarbamate. This indicates that SOD is not involved in the resistance mechanism. Untreated resistant biotypes showed about 2.5 times higher total polyamine and putrescine level than the sensitive one. 100 μM of exogenously added putrescine was observed as having a protecting effect against paraquat in floated leaves of the sensitive biotype only. The resistant leaves were unaffected probably on account of their higher endogenous polyamine level. It is concluded that polyamines may play a role in the paraquat resistance of Conyza canadensis.     

The costs to farmers and estate owners of public access to the countryside

This paper considers the external costs of public access on privately‐owned farm and estate land in Scotland. The increased costs and reductions in income associated with public access are found to be highly variable and site‐specific, with the main effects on land in areas of high population density or high scenic quality, or with recreational attributes. Although costs were on average higher for estates, reflecting their larger area and recreational potential, on a per‐hectare basis the costs of access were greater for the farm sector. Whilst much of the public access exists through de facto rights on open‐access land, there was evidence for an increasing commercialization of open‐air recreation, particularly with respect to more specialized activities. The discussion considers the extent to which the costs of access for land managers are reflected in policies determining the public provision of countryside access.     

Prediction of ambient PM10 and toxic metals using artificial neural networks

In this study, an artificial neural network is employed to predict the concentration of ambient respirable particulate matter (PM10) and toxic metals observed in the city of Jaipur, India. A feed-forward network with a back-propagation learning algorithm is used to train the neural network the behavior of the data patterns. The meteorological variables of wind speed, wind direction, relative humidity, temperature, and time are taken as input to the network. The results indicate that the network is able to predict concentrations of PM10 and toxic metals quite accurately.     

Inhibition of microbial activity of activated sludge by ammonia in leachate

Leachate samples were collected from the West New Territory Landfill (WENT), Hong Kong, and characterized in the laboratory. The analytical results confirmed that it has a typical nature of aged leachate with a low BOD₅/COD ratio of 0.22 and a high strength of ammonia-nitrogen around 5 g/L. A lab-scale study was conducted to investigate the inhibition of microbial activity of the activated sludge. In the first test, glucose-based synthetic wastewater was used in two parallel reactors. The experimental results demonstrated that COD removal declined from 95.1 to 79.1% and the dehydrogenase activity of the sludge decreased from 11.04 to 4.22 μg TF/mg mixed liquor suspended solids (MLSS), when the ammonia-nitrogen concentration increased from 50 mg/L to 800 mg/L progressively. The remaining NH₃⁺-N residue in the treated wastewater increased from 0.58 mg/L to 649 mg/L extensively. In the second test, mixed wastewater samples containing glucose and raw leachate were fed into six parallel biological reactors and operated on batch mode. The experimental results showed COD removal decreased from 97.7 to 78.1% and the dehydrogenase activity decreased from 9.29 to 4.93 μg triphenyl formazon (TF)/mg MLSS, respectively, when the ammonia-nitrogen concentration increased within the same range. Microbial inhibition could also be substantiated by a decrease of specific oxygen uptake rate (SOUR) from 68 to 45 mg O₂/g MLSS. These results suggested leachate containing high-strength ammonia-nitrogen should be pretreated to an acceptable NH₄⁺-N level before it is fed into biological reactors.     

The influence of salinity on the rate of photosynthesis and abundance of some tropical phytoplankton

Several species of phytoplankton were grown in unialgal, but not bacteria-free, cultures. These clones when exposed to varying salinities, from 5 to 35, showed a marked increase in their rates of photosynthesis at low salinities. The optimum requirement of salinity, however, varied in different species. Observations on the relative abundance of phytoplankton in an estuary, where the salinity changes were fairly large, confirmed that, within limits, waters with low salinities support a greater abundance of phytoplankton in nature. The wide adaptability of phytoplankton to changes in salinity corresponds to the conditions brought about by the monsoon system along the southwest coast of India, where large dilutions are associated with the enrichment of water with nutrients.     

Origins and fundamental concepts of the competing-risks problem

The history of problems dealing with competing risks is briefly outlined, beginning with Daniel Bernoulli's 1760 “Mémoir” on mortality due to smallpox and proceeding through the development of actuarial techniques and methods used in clinical research, reliability theory, population dynamics, and other areas of application. A probabilistic formulation of the theory of competing risks is then presented which appears applicable to all these areas. Within the framework of this theory, some fundamental problems are stated and discussed, such as questions of identifiability, choices of estimation procedures, or techniques for testing hypotheses.