A longitudinal assessment of the determinant relationship between employee commitments to the occupation and the organization

A review of the research literature suggested that occupational commitment may be an antecedent to employees' commitment to the organization. Although several studies have assessed the general relationship between occupational and organizational commitment, none have attempted to establish the causal priority between the two constructs. In the present study, occupational commitment was viewed as a causal antecedent to organizational commitment. Based on longitudinal data from 100 management information systems professionals, this view was supported through cross-lagged analysis. Further, we examined a longitudinal causal model of the turnover process in which occupational commitment was placed as an antecedent to organizational commitment. Structural equation analysis supported the fit of this model to the data. Implications of the findings are discussed.     

Ignition and burning rates of segregated waste combustion in packed beds

Recent developments in national recycling and re-use programmes for municipal waste have led to segregation of an increasing proportion of waste to enhance material recovery. Several of the segregated streams contain materials that can not viably be re-used or recycled but can be used for energy recovery. In this study, the combustion of cardboard and waste wood was investigated in a small-scale packed bed reactor in order to provide fundamental data for the design/operation of moving bed furnaces. Key parameters of combustion including the ignition and burning rates were evaluated for various air flowrates and compared to the modelling results. Two successive stages of combustion were identified for both samples: the propagation of ignition front into the bed and combustion of the fuel above the ignition front. The burning rate of cardboard reached a peak of about 300 kg/m(2)h at the air flowrate of 936 kg/m(2)h and decreased at higher air flowrates. For waste wood, both the ignition and burning rates increased in the tested range of the air flowrate up to 702 kg/m(2)h, of which the values were very close to those for the cardboard. The model prediction was in good agreement with the test results for waste wood. However, the burning rate for cardboard was under-predicted due to strongly irregular shapes of the fuel.     

Mathematical modelling of sewage sludge incineration in a bubbling fluidised bed with special consideration for thermally-thick fuel particles

Fluidised bed combustor (FBC) is one of the key technologies for sewage sludge incineration. In this paper, a mathematical model is developed for the simulation of a large-scale sewage sludge incineration plant. The model assumes the bed consisting of a fast-gas phase, an emulsion phase and a fuel particle phase with specific consideration for thermally-thick fuel particles. The model further improves over previous works by taking into account throughflow inside the bubbles as well as the floating and random movement of the fuel particles inside the bed. Validation against both previous lab-scale experiments and operational data of a large-scale industrial plant was made. Calculation results indicate that combustion split between the bed and the freeboard can range from 60/40 to 90/10 depending on the fuel particle distribution across the bed height under the specific conditions. The bed performance is heavily affected by the variation in sludge moisture level. The response time to variation in feeding rate is different for different parameters, from 6min for outlet H(2)O, 10min for O(2), to 34min for bed temperature.     

Scots pine (Pinus sylvestris L.) growth and condition in a polluted environment: from decline to recovery

The results of long-term investigations of Scots pine (Pinus sylvestris L.) growth and condition in the impact zone of one of the biggest air pollution sources in Lithuania--mineral fertilizers plant "Achema" are presented. The main attention is laid to the recovery of damaged stands since annual emissions to air were reduced essentially. The investigations indicated, that the recovery of tree increment was mostly caused by distinct reduction of emissions of nitrogen and sulphur oxides and dust of mineral fertilizers. Despite reduced pollution, crown defoliation of investigated stands has continued to increase for a certain period. After the crown recovery of damaged stands has started, the recovery of most damaged survived trees was most intensive and convergence of defoliated to a different extend stands and trees is characteristic feature of this period. No defoliation threshold has been determined beyond of which recovery of trees would be impossible. Recovery of more than a quarter of damaged trees was registered even in the case of 90% of defoliation. Recovery of dominant trees occurs to be faster of that for suppressed trees within the same level of defoliation. The impact of stand density on the crown recovery rate is negative, the higher density (more intensive competition), the slower recovery of damaged trees. The dependence of growth rate on defoliation was found to be of logistic character: while crown defoliation consists up to 25-30%, tree increment losses are rather inconsiderable, further increase of defoliation leads to the essentially higher increment losses, however having achieved 65-70% defoliation, further increase of defoliation does not result such intensive decrease of radial increment.     

Converting moving-grate incineration from combustion to gasification - numerical simulation of the burning characteristics

Waste incineration is a politically sensitive issue in the UK. The major current technology is based on direct combustion of wastes in a moving-grate furnace. However, general public opinion prefers non-direct burning technologies. Waste gasification is one of those nearest technologies available. By reducing the primary air-flow rate through the grate of a packed-bed system, operation of the existing solid-waste incineration equipment can be easily converted from combustion mode to gasification mode without major modification of the hardware. The potential advantages of this are lower dust carry-over in the flue gases, lower bed temperature (and therefore lower NO(x) formation in the bed), simplified gas-treatment procedures and lower running cost, among other benefits. The major disadvantages are, however, reduced throughput of the wastes and possibly higher carbon in the ash at exit. In this study, numerical simulation of both combustion and gasification of municipal solid wastes in a full-scale moving grate furnace is carried out employing advanced mathematical models. Burning characteristics, including burning rate, gas composition, temperature and burning efficiency as a function of operating parameters are investigated. Detailed comparisons between the combustion mode and gasification mode are made. The study helps to explore new incineration technology and optimise furnace operating conditions.     

Iron-catalyzed oxidation of s(IV) species by oxygen in aqueous solution: Influence of pH on the redox cycling of iron

Redox cycling of Fe(II)/Fe(III) during the catalyzed aqueous S(IV) oxidation by dissolved oxygen in the presence of Fe(II) and/or Fe(III) at an initial pH_i of 4.4, often observed in atmospheric waters, was studied in detail. It has been found that the reaction rate is not considerably affected by the oxidation state of iron at the start of the reaction. An equilibrium between Fe(II) and Fe(III) was established a few minutes after the start of the reaction, regardless of the oxidation state of iron at the beginning of the experiment. The prevailing oxidation state of iron in a particular phase of the reaction depends on the concentration of S(IV) in the reaction solution. It has been found that the formation of polymerized hydroxo Fe(III) species is also included in the mechanism of the Fe-catalyzed oxidation of S(IV). The formation of these species was confirmed by the on-line measurement of Fe(II) and Fe_reac. The results also clearly demonstrate that the pH_i of the solution is a major factor, controlling the concentration of Fe(III) ions, the form of S(IV) species, and consequently the reaction rate of S(IV) oxidation by oxygen.     

Characterisation of particulate matter on the receptor level in a city environment

Airborne particulate matter (PM) has become one of the dominant pollutants with the increasing material and energy demand due to global economic growth. The main objective of this research is to provide a comprehensive receptor level characterisation of the particulate matter collected in a city environment. Particulate matter samples were collected on Tapered Element Oscillating Microbalance (TEOM) filters from five monitoring sites over a period of 1 year. An Andersen eight-stage cascade impactor was also used to collect airborne PM samples from three other locations to compare with the samples collected by TEOM. All the samples were then subjected to individual particle morphology and chemical composition analysis by SEM/EDS. Bulk chemical composition of the samples were also analysed through ICP–OES. Based on these analyses, possible sources of the PM samples were identified. The results showed that the monitoring sites in residential environments were dominated by transportation-derived particles and other migratory particulates. Monitoring sites near the city centre were dominant by particles from transportation, with biological particles abundant for the site closer to a river. The monitoring station located close to the industrial area, despite only 200 m away from a motorway, has low contribution of non-exhaust particulates from vehicles. Instead, the particulates collected from this site were dominated by industrial sources. An air dispersion modelling package was also used to model the particulate matter dispersion in the city area for the period of sampling. The results from the model showed that the points of high emissions were around industrial areas.     

Application of ultrasound irradiation in landfill leachate treatment

Environmental Science and Pollution Research - Landfilling is known to be the most widely used method in municipal solid waste management in many countries. Landfill leachate containing different...     

Tree-ring analysis for the assessment of anthropogenic changes and trends

Investigation of Pine (Pinus sylvestris L.)annual radial increment (width of annual tree rings) was carriedout in the surroundings of one of the largest pollution sources inLithuania – Jonava Nitrogen Fertilizers Plant. The main objectiveof investigation was to analyse different sides of anthropogenictransformations of tree-ring series in the polluted environment:changes in tree growth intensity; variance changes in tree-ringseries; changes in the relations with natural external factors.Three different periods of tree reaction to the environmentalpollution were singled out – fertilization period, depressionperiod and recovery period since annual emissions were essentiallyreduced. The variance of tree-ring series has increased severaltimes in the polluted environment. Reaction of trees to the impactof climatic factors (temperature, precipitation) has changedsignificantly in the polluted environment and their sensitivity hasalso increased.     

Chemometric characterization of soil and plant pollution: Part 1: Multivariate data analysis and geostatistical determination of relationship and spatial structure of inorganic contaminants in soil

Geostatistical and multivariate methods of data analysis are used to describe patterns of soil pollution with inorganic contaminants in Celje County, Slovenia. Groups of contaminants and polluted sites were identified using cluster analysis and confirmed with multidimensional variance and discriminant analysis. Factor analysis yields an identification of not directly observable relationships between the contaminants. The spatial structure and distribution of contaminants were assessed by applying semivariogram analysis and kriging interpolation method. Zinc, Cd and Cu were identified as a pollutant emitted from the zinc smelter, Pb also from other sources, and Cr and Ni mostly from geological parent material.