The risk of diffuse pollution of groundwater by nitrogen substances from agricultural land is perceived as a result of the interaction of groundwater vulnerability (determined by the characteristics of the environment overlying groundwater in relation to water transport or soil solution) and loading of overlying environment by nitrogen. Index of groundwater vulnerability was assessed on the basis of four parameters, namely, the amount of effective rainfall in the period from October to March, the capacity of soil to accumulate water, the average depth of the groundwater table and the permeability of the rock environment. Assessment of the index of loading of overlying environment by nitrogen was based on two parameters, namely, nitrogen balance and crop cover on agricultural land in the winter half on districts level in 2012, which corresponds with current state of the load. The resulting risk of groundwater pollution by nitrogen was expressed by the formula counting with the transformed values of groundwater vulnerability index and the index of loading of overlying environment by nitrogen. From practical point of view, the above mentioned indexes, as well as the subsequent risk of diffuse groundwater pollution, were spatially expressed via three associated categories. Based on the evaluation of relevant parameters, 5.18% of agricultural land falls into the category of very high and high risk, 42.20% in the medium risk category and 52.62% in the category of low and very low risk of diffuse pollution of groundwater by nitrogen from agricultural land.
The aquatic ecosystem of the Meskiana Valley (wilaya of Oum El Bouaghi) covers a large area with a permanent flow and a semi-arid climate characterized by a strong evapotranspiration. In order to determine the Physico-chemical quality, pollution and salinity of the water of the river of Meskiana and more particularly in its downstream part which is exposed to wastewater discharges, analyses were carried out at the level of three sampling points: witness, the upstream (before spill), downstream (after spill)). In order to prevent the risk of alkalization and salinization of soil, the sodium absorption rate (SAR) and the percentage of sodium were determined and represented on the Wilcox and Riverside diagram. The high concentrations of polluting chemical elements and excessive salinity obtained at the downstream site show a high risk of pollution and salinization.
Water-lubricated bearings of ship propeller shafts - problems, experimental tests and theoretical investigations
In recent years can be met ships whose propeller shaft polymer bearings are lubricated with water. It results from simplicity and associated low cost of such solution which is also environmentally friendly as no risk of pollution is involved. However the solution is not free of disadvantages. The main problem is intensive wear of bush material, occurring in certain cases. It very often results from errors of improper design and machining and mounting operations. Another problem is a limited value of its hydrodynamic load-carrying capacity, resulting from low viscosity of water used as a lubricating medium.
As results from the performed research investigations, bearing of the kind is a highly sensitive unit. Problems of choosing a suitable bearing clearance, designing an optimum bush geometry, selecting a proper bush material are crucial for lifitime of the bearing.
Influence of main design parameters of ship propeller shaft water-lubricated bearings on their properties
In recent years more and more frequently can be met ships in which propeller shaft water-lubricated polymer bearings have been applied. It results from their simplicity and associated relatively low initial and operational cost as compared with the complex classical sealed system based on oil-lubricated bearings. It is worth mentioning that the water-lubricated bearings are also environmentally friendly as no risk of pollution with lubricating oil used in classical systems, is involved. Design procedure of bearings in question based on materials made available by producers is relatively simple. However it turns out that choice of an appropriate sliding material, clearance value and optimum arrangement of lubricating grooves may greatly influence bearing's properties. As results from the performed research investigations, bearing of the kind is a highly sensitive unit. Problems of choosing a suitable bearing clearance, designing an optimum bush geometry, selecting a proper bush material are crucial for life time of the bearing. In particular the problem is in forming hydrodynamical properties of bearing as owing to its operation in the fluid friction regime durability of bearings, the very responsible units of propulsion transmission system, can be greatly extended.
Influence of local bush wear on properties of water lubricated marine stern tube bearings
In recent years more and more frequently can be met ships in which propeller shaft water-lubricated polymer bearings have been applied. It results from their simplicity and associated relatively low initial and operational cost as compared with the complex classical sealed system based on oil-lubricated bearings. It is worth mentioning that the water-lubricated bearings are also environmentally friendly as no risk of pollution with lubricating oil used in classical systems, is involved. Design procedure of bearings in question based on materials available from their producers is relatively simple. However the calculating of such bearings creates many problems. For calculating the hydrodynamic lubricating theory is as a rule used and elastic bush flexibility taken into account. In the case of greater loads when lubricating film is very thin to achieve a proper solution is very difficult.
For this reason is proposed a novel method in which bush local wear effect can be accounted for. Such phenomenon has been observed during experimental tests of heavy-loaded water-lubricated slide bearings. With the use of the applied calculation algorithm bush local wear close to its edges can be taken into account, and - in consequence - a greater bearing capacity can be achieved.
This study aims to evaluate the effect of seed priming for two pepper varieties by extracts of two algae thalli on the performance of growth at vegetative stage. The seeds were soaked in thalli aqueous extracts (at 20, 40, 60, 80 and 100 g/L), for 24 h at 28±2°C, rinsed thoroughly with distilled water and then dried to their initial weight as a first batch (SD), a second batch of seeds was considered, corresponding to seeds placed in Petri dishes to germinate directly after washing (SND). Untreated seeds were the control. The results showed than the priming has improved seedlings growth for both varieties. Seed priming with algae aqueous extracts has improved roots and shoots length. The best stimulations were 220% and 70%, respectively, recorded for seedlings of Baklouti and Chargui varieties, following the priming with the extract of Padina pavonica at 40 g/L concentration. These improvements appear to be related to a better photosynthetic intensity, an increase in the number of leaves and the water content, which were noted in plants from pretreated seeds. Finally, the results indicate that, generally, the plantlets from SND were more vigorous. The results of this work show that algae could be an inexhaustible resource of substances, that can be used as an alternative to chemicals used in the pretreatment of seeds, reducing the risk of pollution and preserving the biological material.
In this work, we propose mathematical models describing the soybean oil bleaching process as a function of its parameters (temperature: 80 – 120 °C, clay dosage: 0.25 – 2 %, contact time: 10 – 30 min). The crude soybean oil visible spectrum shows three values of maximum wavelength (λmax). A value at 426 nm corresponding to the chlorophyll-a, the values at 451 and at 479 nm were assigned to β-carotene pigment. The models were developed using multiple linear regression analysis (MLRA) and were performed with Matlab programming language. The input variables are the temperature (X1), the clay dosage (X2) and the contact time (X3). The output parameter is the bleaching capacity (Y in % uptake). Statistical analysis methods were used to analyze and to confirm the reliability of the selected models. The optimal bleaching conditions for the soybean oil were: temperature 100 °C; clay dosage 2 % w/w and contact time 30 min. The highest bleaching capacity was found to be 81.04 % at 426 nm, 90.60 % at 451 nm and 93.66 % at 479 nm. The developed models allowed predicting the bleaching capacity representing the removal of the β-carotene and chlorophyll-a pigments present in the crude soybean oil at each λmax. Also they allowed a better control of the most influencing parameters on the bleaching step and contribute to the optimization of the spent bleaching clay rejects by optimizing the amount of bleaching clay used in the refining process; consequently, to reduce risks of pollution.
], the authors built on a RDA method which relies on a homomorphic Message Authentication Code scheme and a customized encryption scheme. when the client and server have a shared secret key, the scheme existence riskofpollution attacks. The homomorphic Message Authentication Code cryptosystem protect the scheme avoid the risk and this cryptosystem consists of three parts, namely: sign, combine, and verify. We use the sign algorithm to generate a tag for blocks and then use the homomorphic property to generate a linear combination of tags of the blocks. The