Reaction kinetics and rheological characteristics of ultra-thin P-based triboreactive films

To access the evolving tribochemistry at the contacting asperities, a miniature pin-on-disc tribological apparatus was developed and combined with synchrotron X-ray Absorption Spectroscopy (XAS). The new apparatus makes it possible to study in-situ the transient decomposition reactions of various oil additives on different surfaces under a wide range of realistic operating conditions. The results suggest that the decomposition of ZDDP starts by forming intermediate sulphate species on the steel surface, which are readily reduced to sulphides of discontinuous clusters. The clusters can play different vital roles including binding the subsequently formed phosphate layers with the steel surface. Initially, the phosphate layers consist of short chains due to excess concentration of metal oxides on the steel surface. As the oxides’ concentration decreases in the subsequent layers, the short chains start to polymerise into longer ones. The polymerisation reaction appeared to follow first-order reaction kinetics with two distinctive phases. The first is a fast transient burst phase near the metal surface, whereas the second phase dominates the formation of the layers away from the metal surface and is characterized by slow kinetics. To better understand the origin of the superior antiwear properties of the P-rich tribofilms, an Atomic Force Microscope (AFM) liquid cell was designed to form tribofilms in-situ while examining their textural and rheological properties over time. The obtained results indicate that the tribofilms behave as a molten glass with an average viscosity of 1×1012 Pa.s. This suggests that their superior antiwear properties originate from their intrinsic rheological properties that allow them to flow while formed, which was clear from their ability to maintain local order on the nanoscale through the motion, rearrangement and local reconfiguration of single and multiple patches of the formed tribofilm at the interface. This seems to effectively mitigate the smearing and wearing of the contacting asperities resulting in less wear. The findings of this study open future opportunities for quantitatively analysing the interfacial rheology and reaction kinetics governing a broad range of additives and substrates, which can help build mechanistic models capable of better predicting wear

Hydrography, nutrients and plankton abundance in the hot spot of Abu Qir Bay, Alexandria, Egypt

The hydrography, nutrient levels and plankton abundance were investigated monthly for a complete annual cycle in the southwestern part of Abu Qir Bay, the most polluted and biologically productive area on the Egyptian Mediterranean coast. Intense temporal and spatial variability was observed in all measured parameters characteristic of the effects of several effluents discharged into the bay. Based on the present investigation, the southwestern Bay can be divided ecologically and biologically into two parts: one including the near shore strip, which is directly affected by the waste waters, and a second comprising the southwestern part of the coastal strip and the offshore stations, both of which are relatively far away from the land-based effluents.The Bay water was characterized by low transparency (monthly average: 64-280 cm), dissolved oxygen (monthly average 2.0-6.8 mg/l) and surface salinity (monthly average: 24.8-37.9 ppt), the highest limits usually being in the offshore section. Water fertility and plankton production were high in the Bay indicating an occasionally acute degree of eutrophication, particularly nearshore. Great variations occurred in the concentrations of nutrients throughout the year, with monthly averages of 0.8-50.88 mM for ammonia, 0.42-3.28 mM for nitrite, 1.29-17.36 mM for nitrate, 0.32-3.61 mM for reactive phosphate and 1.09-33.34 mM for reactive silicate. Similarly, the abundance of both phytoplankton and zooplankton showed pronounced temporal and spatial variability, whereas the monthly average chlorophyll-a fluctuated between 2.06 and 52.64 mg/l and zooplankton between 31x103 and 248.6x103 ind./m3. However, the absolute values of all parameters indicated remarkably wider ranges of variations.Significant correlation was found between chlorophyll-a and some ecological parameters like temperature, salinity, transparency, dissolved oxygen, nitrite and between zooplankton and temperature, while there was a significant correlation between nutrient concentrations and salinity changes

Hard-Bottom Polychaetes Exposed to Multiple Human Pressure along the Mediterranean Coast of Egypt

The complex mixture of anthropogenic pressure determines the impact on the marine biota, hampering the ecosystem's functioning. The coast of Alexandria, Egypt, experiences multiple human pressure, including sewage discharge, engineering activities (urbanization) for armoring purposes, and beach nourishment. Hard-bottom polychaete assemblages are demonstrated to reflect coastal areas' environmental status, though their use in monitoring programs is uncommon. The sensitivity of hard-bottom polychaete assemblages in depicting variations in environmental conditions of two sites exposed to the discharge of polluted water and three sites exposed to urbanization was analyzed. The high spatial and temporal variation in species abundance and diversity probably hid differences among the assemblages exposed to the two forms of pressure while highlighting differences among sites exposed to the same impact form. In addition, changes in the algal substrate probably influenced the observed pattern. Temporal variation of salinity and differences in biological oxygen demand (BOD) and the organic matter appeared to indirectly affect polychaete abundance and diversity by favoring tolerant algal taxa such as Ulva sp. Contrary to what was expected, assemblage variation due to site-specific environmental features accounted for more than the variations due to the two forms of human pressure in shaping differences among polychaete assemblages

A simple deterministic plastoelastohydrodynamic lubrication (PEHL) model in mixed lubrication

Most power transmitting components operate under mixed lubrication conditions. Concentrated pressures and smaller lubricant film thickness may cause surface and subsurface stresses to exceed the material yield limit causing permanent geometrical changes. A model was developed to include elastoplastic behaviour within a deterministic unified mixed lubrication framework. Model details are presented and the model is validated against published simulation data. A parametric study to address the effect of material yielding on the contact parameters is performed. It is found that the model successfully produces all the key features of the PEHL contact. The model provides a valuable tool to analyse the PEHL contacts with minimal increase in computational effort and complexity

Statistical and fourier analysis of cyclic changes of zooplankton abundance in the eastern harbor of Alexandria

279-290Time series data of monthly averages, over three stations, for counts of zooplankton groups and species, and some environmental factors (water temperature, salinity and chlorophyll a) were collected from the Eastern Harbor of Alexandria, during the period of 48 months, from October 1999 to November 2003. The spectral density graphics with frequency indicated that inspite of the presence of several peaks for different variables the only significant peak, at 95% confidence limit, was found in case of water temperature. The results of Fourier analysis show that the most common periods that are relatively important and affecting the movement of the time-series of environmental and the biological variables are 12, 9 and 6 months. The 12 months was corresponding to seasonal changes, while periods less than 12 months were due to local changes depending on the hydrological exchange between the Eastern Harbor and the open Mediterranean coastal waters in front of the study area. The time lags of the occurrence of the maxima of each two variables at the important cycles with periods 12, 9 and 6 months were calculated to express the response time of the different groups flourishing relative to the occurrence of the effecting environmental factors. The cluster and correlation analyses of the different variables have also been done to show most correlated ones. The results indicated that the annual cycle is the most important one in most cases. The multiple regression equations between the zooplankton counts and the environmental variables showed the important controlling factor in the different species and groups of zooplankton

Eutrophication problems in the Western Harbour of Alexandria, Egypt

Eutrophication-related problems in the Western Harbour ofA lexandria were studied monthly from April 1999 to March 2000. Variation in salinity appeared to be the key to all changes in water quality and plankton abundance in the harbour. Both at the surface and near the bottom the salinity was lower (annual average: 35.1 and 38.3 PSU respectively) than in the open sea (39 PSU). Dissolved oxygen levels indicated poor aeration conditions along the water column (2.3–3.98 mg l−1). Average pH values were approximately similar in the two layers (8.1 and 8 respectively) but exhibited different ranges ofv ariations. Nutrient salts varied widely, often occurring in high concentrations, with ranges of 0.12–5.7 and 0.06–2.6 μM at the surface and the bottom respectively for phosphate, 0.21–20.46 and 0.25–18.12 μM for nitrate, 0.29–3.3 and 0.23–1.66 μM f or nitrite, 0.56–57.46 and 2.32–43.73 μM for ammonia and 0.3–36.3 and 0.48–38.4 μM for silicate. As a result ofn utrient enrichment, phytoplankton growth was very intensive, reflected by an abnormally high concentration ofc hlorophyll a (annual average: 33.82 μg l−1). At the same time the death ofl arge numbers ofp hytoplankton cells could be inferred from the relatively large amount of phaeopigment (annual average: 10.39 μg l−1). The high levels ofn utrient salts and phytoplankton biomass together serve as a good indicator ofhig h eutrophication levels in the Western Harbour throughout the year. These conditions clearly affected the zooplankton stock, which varied between 5.8–93.6×103 indiv. m−3, although for most of the time values remained at a low level (annual average: 26 728 indiv. m−3)

Protozoa in a stressed area of the Egyptian Mediterranean coast of Damietta, Egypt

AbstractThe Damietta coast is part of the Egyptian Mediterranean coast off the Nile Delta and has recently been polluted as a result of intensive human activities. The environmental parameters and protozoan community in the area were studied biweekly from January to December 2007. The results of the environmental parameters indicated low salinity, oxic and anoxic conditions, high nutrient levels and intensive phytoplankton growth. A total of 69 protozoan species were identified, belonging to Amoebozoa (8 species), Foraminifera (12 species), non-tintinnid ciliates (22 species) and tintinnids (27 species). The numerical density of protozoans was high over the whole area, with annual averages between 8.2×103 cells m−3 and 51.4×103 cells m−3. Spring was the most productive season for protozoans, but several distinct peaks were observed during the year at the sampling sites. The protozoan groups showed clearly different spatial patterns in both composition and abundance: whereas amoebozoans and non-tintinnid ciliates were dominant in the more polluted areas (sites IV and V), tintinnids dominated in the less polluted areas (sites, I, II and III). Several pollution indicators were recorded: amoebozoans – Centropyxis aculeata, Centropyxis sp., Cochliopodium sp., Difflugia sp.; non-tintinnids – Bursaridium sp., Frontonia atra, Holophrya sp., Paramecium sp., Paramecium bursaria, Vasicola ciliata, Vorticella sp., Strombidium sp.; tintinnids – Favella ehrenbergii, Helicostomella subulata, Leprotintinnus nordgvisti, Tintinnopsis beroidea, Stenosemella ventricosa, Tintinnopsis campanula, T. cylindrica, T. lobiancoi, Eutintinnus lusus-undae