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Number of results: 44
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Abstract

In this study, the spatial variation of daily and monthly concentration precipitation index and its aggressive-ness were used in 23 rainfall stations in the extreme north-east of Algeria over the period 1970–2010. The trend was analysed by the Mann–Kendall (MK) test. The results show that daily precipitation concentration index (CI) values are noticeably higher in places where the amount of total precipitation is low, the results of MK test show that areas of high precipitation concentration tend to increase. The seasonality and aggressiveness of precipita-tion are high in the eastern and western parts of the study region (eastern and central coastal of Constantine catchments), whereas a moderately seasonal distribution with low aggressiveness is found in the middle of the study area (plains and central Seybouse catchment). As a result, the modified Fournier index (MFI) has a signifi-cant correlation with annual precipitation, whereas the CI and monthly precipitation concentration index (PCI) show an opposite correlation in relation to annual precipitation.
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Abstract

Height, frequency and spatial differentiation of atmospheric precipitation of the summer season for the period 1975-1982 are presented. Results of the respective investigations are compared with atmospheric precipitation in other areas of the western coast of Spitsbergen.
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Abstract

Certain chemical parameters such pH, specific electric conductivity (SpC) and concentrations of chloride ions (Cl-) have been analysed in samples of precipitation collected close to the Polish Polar Station at Hornsund (PPS), SW Spitsbergen. On the basis of seasonal data from years 1993-1994 and 1998-1999, some differences are apparent from the two sets. There is also a marked difference in the seasonal results, especially with respects to pH values; summer precipitation (pH of which can be as low as 3.78) is much more acidic than winter. This was particularly notable in respect of the summer of 1993, and was presumably the result of a relatively unusual atmospheric circulation and a high influx of airborne contaminants from Europe. The wide variation in specific electrical conductivity measurements is considered to be related to variations in wind direction and speed. That precipitation the highest total dissolved salts, of 11.7 mm w.e. (water equivalent), (November 1993), provided 10.7 g of salt per square metre of tundra near the Polish Polar Station. The proximity of the sea, consequently the development of marine aerosols, largely determines the chemical nature of the precipitation. Thus, variations in the chloride ion concentrations during the study periods more or less reflect the variations in the marine aerosol influences on the nature of the polluted precipitation. An analysis of the atmospheric circulation reveals that the most acid precipitation occurs most frequently in the C-8 type of circulation (cyclonic S + SW) and also, less so, for type C-3 (anticyclonic S + SW).
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Abstract

In this paper results of microstructural observations for series of CuZn39Pb2 alloys produced from qualified scraps are presented. The individual alloy melts were differentiated in terms of thermal parameters of continuous casting as well as refining methods and modifications. Structural observations performed by SEM and TEM revealed formation of different types of intermetallic phases including “hard particles”. EDS results show that “hard particles” are enrich in silicon, phosphorus, iron, chromium and nickel elements. Additionally, formation of Al-Fe-Si and Al-Cr in alloy melts was observed as well. It was found that quantity and morphology of intermetallic phases strongly depends upon the chemical composition of raw materials, process parameters, modifiers and refining procedure applied during casting. It was observed that refining process results in very effective refinement of intermetallic phases, whereas modifiers, particularly carbon-based, results in formation of large particles in the microstructure.
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Abstract

Measurements of pollutants scavenged from air masses over southern Svalbard in summer precipitation are presented. Rainfall was sampled in July and August 2002 at Calypsobyen, Bellsund. Specific conductivity (SpC) and pH were measured and ion concentrations were determined by ion chromatography. Ions of marine origin were subtracted, assuming that all chlorides were of marine origin. The FLEXTRA trajectory model was applied to discover the sources of air masses arriving at Svalbard and track the paths of pollutant transport. Average (v/w) rainfall pH was 4.94, mean SpC amounted to 34.8 µS cm-1. Total dissolved solids concentration (TDS) ranged from 12.6 to 67 mg L-1, with ions of marine origin (Cl-, Na+, Mg2+) prevailing. Rains with the highest percentage of marine salts occurred with winds from the East at above average velocities. Non-sea salt (nss) sulphate concentrations ranged from 0.5 µeq L-1 to 23 µeq L-1, (v/w) average was 17 µeq L-1. Nitrate concentrations ranged from 0 to 24 µeq L-1. The highest concentrations of nss-SO42- and NO3- were measured on 25 August, when the highest rainfall occurred (27 mm) and pH was the lowest (4.65). Rainfall at Calypsobyen deposited 194 kg km-2 of acidifying anions and 263 kg km-2 of base cations over the recording period. The polluted air masses were mostly from northern and central Europe. Rainfalls scavenging air masses formed over Greenland and Norwegian Seas displayed similar concentrations, being probably polluted by SOx and NOx from ship emissions.
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Abstract

The paper presents the research results of the influence of the precipitation hardening on hardness and microstructure of selected Al-Si and Al-Cu alloys obtained as 30 mm ingots in a horizontal continuous casting process. The ingots were heat treated in process of precipitation hardening i.e. supersaturation with subsequent accelerated or natural ageing. Moreover in the range of the study it has been carried out investigations of chemical constitution, microscopic metallographic with use of scanning electron microscope with EDS analysis system, and hardness measurements using the Brinell method. On basis of obtained results it has been concluded that the chemical constitution of the investigated alloys enables to classify them into Al alloys for the plastic deformation as EN AW-AlSi2Mn (alternatively cast alloy EN AC-AlSi2MgTi) and as EN AW-AlCu4MgSi (alternatively cast alloy EN AC-AlCu4MgTi) grades. Moreover in result of applied precipitation hardening has resulted in the precipitation from a supersaturated solid solution of dispersive particles of secondary phases rich in alloying element i.e. Si and Cu respectively. In consequence it has been obtained increase in hardness in case of AlSi2Mn alloy by approximately 30% and in case of AlCu4MgSi alloy by approximately 20% in comparison to the as-cast state of continuous ingots.
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Abstract

The high mechanical properties of the Al-Li-X alloys contribute to their increasingly broad application in aeronautics, as an alternative forthe aluminium alloys, which have been used so far. The aluminium-lithium alloys have a lower specific gravity, a higher nucleation andcrack spread resistance, a higher Young’s module and they characterize in a high crack resistance at lower temperatures. The aim of theresearch planned in this work was to design an aluminium alloy with a content of lithium and other alloy elements. The research includedthe creation of a laboratorial melt, the microstructure analysis with the use of light microscopy, the application of X-ray methods to identify the phases existing in the alloy, and the microhardness test.
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Abstract

Because of excellent properties, similar to natural bone minerals, and variety of possible biomedical applications, hydroxyapatite (HAp) is a valuable compound among the calcium phosphate salts. A number of synthesis routes for producing HAp powders have been reported. Despite this fact, it is important to develop new methods providing precise control over the reaction and having potential to scale-up. The main motivation for the current paper is a view of continuous synthesis methods toward medical application of produced hydroxyapatite, especially in the form of nanoparticles.
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Abstract

Temperature and precipitation conditions in the Kaffiøyra region in the summer season (21 July-31 August) for the period from 1975-2014 are described based on data collected during 22 expeditions, in which meteorological measurements were carried out, and complete data series combining both original and reconstructed data. The latter ones were obtained using data from the Ny Ålesund meteorological station, which are strongly correlated with data from the Kaffiøyra region. Seasonal statistics presented for temperature and precipitation based on these two sets of data reveal only slight changes. Summer temperatures in the Kaffiøyra region in the studied period (1975-2014) showed statistically significant strong upward trends, while precipitation totals revealed a downward trend, but not statistically significant. In the studied area, based on 40-years of data, it was demonstrated that the near-surface lapse rates of summer air temperature are slightly lower in glaciated (0.58°C/100 m) than in non-glaciated areas (0.67°C/100 m). Anticyclonic/cyclonic circulation types significantly increase/decrease air temperature on the Waldemar Glacier, while their impact on precipitation is markedly smaller. In summer, close correlations were observed between air temperature and such glacier characteristics as the mass balance and the location of the equilibrium line, while precipitation does not have a great influence on them.
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Abstract

The scope of this work is to investigate the precipitation of two Al-Mg-Si alloys with and without Cu and excess Si by using the differential scanning calorimetry (DSC), transmission electron microscopic (TEM), Vickers hardness measurement and X-ray diffraction. The analysis of the DSC curves found that the excess Si accelerate the precipitation and the alloy contain the excess Si and small addition of copper has higher aging-hardness than that of free alloy (without excess Si and Cu) at the same heat treatment condition. The sufficient holding time for the precipitation of the β'' phase was estimated to be 6 hours for the alloy aged at 100°C and 10 hours for the alloy aged at 180°C. The low Copper containing Al-Mg-Si alloy gives rise to the forming a finer distribution of β (Mg2Si) precipitates which increases the hardness of the alloy. In order to know more about the precipitation reactions, concern the peaks on the DSC curve transmission electron microscopy observation were made on samples annealed at temperatures (250°C, 290°C and 400°C) just above the corresponding peaks of the three phases β'', β' and β respectively.
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Abstract

The paper presents a model of a rapping system of an electrostatic precipitator. The rapping system consists of a set of collecting electrodes hanging on a suspension bar and braced together in a brushing bar. The suspension and brushing bars are modeled using the rigid finite element method, while the collecting plates are modeled using the hybrid method. The method combines the rigid finite element method with the classical finite element method. As a result, the mass matrix is diagonal. Some results of numerical simulations concerning free vibrations of the collecting plates and the influence of the number of elements, into which the plate is divided, on the vibrations of the rapping system are presented.
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Abstract

One type of spheroidal cast iron, with additions of 0.51% Cu and 0.72% Ni, was subjected to precipitation hardening. Assuming that the greatest increase in hardness after the shortest time of ageing is facilitated by chemical homogenisation and fragmentation of cast iron grain matrix, precipitation hardening after pre-normalisation was executed. Hardness (HB), microhardness (HV), qualitative and quantitative metalographic (LM, SEM) and X-ray structural (XRD) tests were performed. The acquired result of 13.2% increase in hardness after ca. 5-hour ageing of pre-normalised cast iron confirmed the assumption.
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Abstract

In the present investigation, the morphology of Ti inclusions in high strength tire cord steel was investigated and their precipitation behavior was discussed using a precipitation and growth model. The results show that Ti inclusions mainly exist in the form of TiN. The two-dimensional characterization of Ti inclusions is square-like with sharp edges and corners, while its three-dimensional shape exhibits a cubic or rectangular-prism morphology. The Ti inclusions do not precipitate when the solid fraction of tire cord during solidification is less than 0.987, and their final radius is closely related to the cooling rate and initial concentration product. The higher the cooling speed, the smaller the final radius, when the cooling speed is constant, the final radius of Ti inclusions is mainly determined by the initial concentration product, w[N]0×w[Ti]0. In order to retard the precipitation and growth of Ti inclusions in tire cord steel, the cooling rate and initial concentration product can be taken into consideration.
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Abstract

The results of studies of W-Ni-Co-Fe experimental alloy, with chemical composition assuring a possibility of producing Ni-based supersaturated solid solution are presented. The alloy was prepared from tungsten, nickel, cobalt and iron powders which were first mixed then melted in a ceramic crucible where they slowly solidified in hydrogen atmosphere. Next specimens were cut from the casting and heated at a temperature 950o C. After solution treatment the specimens were water quenched and then aged for 20 h at a temperature 300o C. The specimens were subjected to microhardness measurements and structure investigations. The latter included both conventional metallography and SEM observations. Moreover, for some specimens X-ray diffractometry studies and TEM investigations were conducted. It was concluded that quenching lead to an increase of tungsten concentration in nickel matrix which was confirmed by Ni lattice parameter increase. Aging of supersaturated solid solution caused strengthening of the Ni-based matrix, which was proved by hardness measurements. The TEM observation did not yield explicit proofs that the precipitation process could be responsible for strengthening of the alloy.
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Abstract

This work presents the results of a study whose aim was to determine the influence of algal blooms on precipitation of heavy metals. The scope of the study covered culture of a mixed population made up of Scenedesmus and Pseudokirchneriella algae in experimental conditions and initiating a metal biosorption process with the use of culture biomass by administering ions of Zn(II) and Ni(II). The process was controlled by assessing the level of biosorption of metals entered at a one-off basis in the form of Zn(II) and Ni(II) salts or in the form of mixture of both ions, in comparison to the control sample, at different exposure times (2 hours and 24 hours). The presence of metals was determined both in the biomass and in the culture medium. The presented results of the study confirm the effectiveness of Chlorophyta in the process of zinc and nickel biosorption. A phenomenon of competitiveness between the metals was observed when they were administered at the same time.
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Abstract

Magnetite nanoparticles have become a promising material for scientific research. Among numerous technologies of their synthesis, co-precipitation seems to be the most convenient, less time-consuming and cheap method which produces fine and pure iron oxide particles applicable to environmental issues. The aim of the work was to investigate how the co-precipitation synthesis parameters, such as temperature and base volume, influence the magnetite nanoparticles ability to separate heavy metal ions. The synthesis were conducted at nine combinations of different ammonia volumes - 8 cm3, 10 cm3, 15 cm3 and temperatures - 30°C, 60°C, 90°C for each ammonia volume. Iron oxides synthesized at each combination were examined as an adsorbent of seven heavy metals: Cr(VI), Pb(II), Cr(III), Cu(II), Zn(II), Ni(II) and Cd(II). The representative sample of magnetite was characterized using XRD, SEM and BET methods. It was observed that more effective sorbent for majority of ions was produced at 30°C using 10 cm3 of ammonia. The characterization of the sample produced at these reaction conditions indicate that pure magnetite with an average crystallite size of 23.2 nm was obtained (XRD), the nanosized crystallites in the sample were agglomerated (SEM) and the specific surface area of the aggregates was estimated to be 55.64 m2·g-1 (BET). The general conclusion of the work is the evidence that magnetite nanoparticles have the ability to adsorb heavy metal ions from the aqueous solutions. The effectiveness of the process depends on many factors such as kind of heavy metal ion or the synthesis parameters of the sorbent.
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