Thermal electron energy distribution measurements in the ionosphere

Results of electron spectrometer and cylindrical Langmuir probe measurements of ionospheric electron energy distribution in the range from about 0·2 eV to 4·0 eV are presented and discussed in this paper.     

Taylor expansion of the theoretical gravity formula

A recurrence relation has been derived to obtain the derivatives required for the Taylor expansion of the theoretical gravity formula in powers of latitude. The computations using the relationship derived can provide easily all required derivatives for any reference ellipsoid.     

A study of the upward continuation of gravity data from a plane surface

Summary A summation method of upward continuation of gravity data has been considered under the assumption that observations are available at regular intervals. The upward continued value has been obtained as the sum of products of individual gravity values and corresponding theoretical coefficients. Besides the usual parameter involving horizontal and vertical distances, the theoretical coefficients have been generalized to be dependent also on i) the order of a low order polynomial assumed to represent the gravity variation around a grid point and ii) the weights assigned to the gravity values at the nearest four grid points used for least-squares determination of the polynomial. Since the observations in practical cases are available over a finite area only, the effect of truncation of the area of the integration has also been discussed separately. The method has been programmed and tested on a three-dimensional model, whose true gravity effects were computed at various levels over a finite area. Upward continued values have been computed under various assumptions about the gravity field in the outside region. Comparisons of these results with the true values indicate that the truncation effect becomes increasingly important for larger values of the ratio of elevation to grid separation and/or when the gravity field is not a local one. It has also been found that the greater is the above ratio, the less important is the effect of weights on the theoretical coefficients and practically vanishes(<10 ^–4 ) when the ratio is greater than5.0.     

Methode zur Bestimmung des Ammoniakstickstoffes in Gewässern

For the spectrophotometrical determination of ammonia in surface water the reaction with hypochlorite and thymol in alkaline solution is used. Compared with other techniques, expenditure is low, the reagents are stable for a long period of time and the reaction is little dependent on external conditions. In 2 cm cuvettes there can be determined 0.05… 0.5 mg/l ammonia nitrogen. Comparative investigations carried out at nine sites in the area of the lake Balaton have revealed concentrations of 0.2… 0.7 mg/l ammonia nitrogen.     

The effect of Al(OH)4 on the dissolution rate of quartz

The influence of Al(OH)₄⁻ on the dissolution rate of quartz at pH 10-13 and 59-89 °C was determined using batch experiments. Al(OH)₄⁻ at concentrations below gibbsite solubility depressed the dissolution rate by as much as 85%, and this effect was greater at lower pH and higher Al(OH)₄⁻ concentration. Dissolution rates increased with increasing temperature; however, the percent decrease in rate due to the presence of Al(OH)₄⁻ was invariant with temperature for a given H⁺ activity and Al(OH)₄⁻ concentration. These data, along with what is known about Al-Si interactions at high pH, are consistent with Al(OH)₄⁻ and Na⁺ co-adsorbing on silanol sites and passivating the surrounding quartz surface. The observed pH dependence, and lack of temperature dependence, of inferred Al(OH)₄⁻ sorption also supports the assumption that the acid-base behavior of the surface silanol groups has only a small temperature dependence in this range. A Langmuir-type adsorption model was used to express the degree of rate depression for a given in situ pH and Al(OH)₄⁻ concentration. Incorporation of the rate data in the absence of aluminate into models that assume a first-order dependence of the rate on the fraction of deprotonated silanol sites was unsuccessful. However, the data are consistent with the hypothesis proposed in the literature that two dissolution mechanisms may be operative in alkaline solutions: nucleophilic attack of water on siloxane bonds catalyzed by the presence of a deprotonated silanol group and OH⁻ attack catalyzed by the presence of a neutral silanol group. The data support the dominance of the second mechanism at higher pH and temperature.     

FTIR characterization of amorphous uranyl-silicates

Ambient-temperature environments in which dissolved silica and U(VI) are present may lack the conditions necessary to readily form crystalline uranyl-silicate phases; however amorphous phases, as defined by the absence of well-defined Bragg reflections in powder X-ray diffraction patterns, are kinetically favored when solution saturation levels are appropriate. Such amorphous uranyl-silicates may be related to the crystalline phases predicted to be thermodynamically stable and influence the mobility of U in the environment. To investigate amorphous uranyl-silicates and their relation to crystalline phases we precipitated solids from solutions containing 0.05 M UO₂(ClO₄)₂ and 0.1 M Na₂SiO₃ adjusted to pH values from 2.2 to 9 and allowed the precipitates to age in their mother liquors for approximately 6 weeks at 22 °C. We compared the chemical composition, X-ray diffraction patterns, and Fourier transform infrared spectra of the precipitates to those of the crystalline phases predicted by thermodynamic modeling. The precipitates were amorphous with U:Si ratios of 0.8 ± 0.1. Their FTIR spectra revealed changes in the UO₂²⁺ and SiO₄⁴⁻ vibrations as a function of pH that are consistent with a shift in mid-range structural linkages from those similar to soddyite to those more like Na-boltwoodite. Structural H₂O, OH, and SiO₃OH³⁻ vibrations do not change as a function of pH and are consistent with a mixture of soddyite-like and Na-boltwoodite-like features. Six weeks of aging at ambient temperature is enough time for the precipitate structures to rearrange and adopt mid-range structural linkages characteristic of crystalline phases predicted by thermodynamic modeling.     

On the relationship between auriferous talc deposits hosted in volcanic rocks and massive sulphide deposits in Egypt

The volcanic-hosted massive sulphide (VHMS) deposits in the Eastern Desert of Egypt (e.g., Um Saki deposit) are associated with Precambrian coarse acid pyroclastic rocks. The upper contacts of the massive sulphide body are sharp and well-defined; while the keel zone to the mineralization is always associated with pervasive alteration, characterized by the presence of septechlorite and talc, associated with variable amounts of carbonate and tremolite. On the other hand, the economic talc deposits in Egypt are hosted intensively altered volcanic rocks. Besides talc, chlorite, carbonates and tremolite that occur in variable amounts in these deposits, anomalously high concentrations of gold are also present.The present study showed that alterations in the talc deposits of Darhib, El Atshan, Abu Gurdi, Egat, Um Selimat and Nikhira are similar to those occurring in the keel zone underlying the VHMS of Um Samuki and that the chemical modifications due to alteration processes (additions of Mg, Fe, Mn and Ca coupled with depletions in silica, alkalies, alumina and titanium) are comparable, even the host rocks are different, thus reflecting a genetic relationship. It is suggested that, the examined localities of talc deposits are hosted in the intensively altered volcanics in the keel zones of volcanogenic massive sulphide deposits. Recently, detailed geophysical prospecting program, including electric (resistivity, self-potential and induced polarization), electromagnetic and magnetic methods, was carried out at Darhib, Abu Gurdi and Um Selimat talc deposits. The quantitative interpretation of these geophysical measurements revealed the presence of subsurface bodies of sulphides. The present distribution of talc and allied minerals in Darhib, El Atshan, Abu Gurdi, Egat, Um Selimat and Nikhira could be explained by a tectonic process in which the coarse acid pyroclastic rocks with massive sulphides have tilted in such way that the footwall rock alterations (talc and allied minerals) are exposed on the present-day surface at these localities. Structural studies are currently under way in an attempt to explain the deformation regime that led to the present situation of talc deposits.Two distinct spatial and mineralogical associations of gold mineralization could be identified in the volcanogenic massive sulphide deposits and their footwall alterations (the keel zone) in the Eastern Desert of Egypt. These are (1) gold–silver–zinc association, and (2) gold–copper association. In the former, gold grades are very low and silver is anomalous. This association occurs typically in the upper levels of the VHMS deposit where low-temperature sulphides are abundant. Gold was deposited because of the mixing between the ascending hot solutions and the sulphate-rich seawater. The upper levels of Um Samuki sulphide body represent this association. Gold–copper association, on the other hand, typically occurs in the footwall altered rocks (the keel zone) and the lowest parts of the massive sulphide body. Gold grades reach up to 5.54 ppm, but the average is 1 ppm. Silver is very low, usually in the range of 4–10 ppm. Lead usually, but not always, accompanies gold in this association. Deposition of gold probably took place due to decreasing of temperature and/or increasing pH of the ascending hot brines. The keel zones at Darhib, Abu Gurdi, El Atshan, Um Selimat, Nikhira and Egat talc mines better represent this association.     

Biogeochemistry of trace metals (Mn, Sr, Rb, Ba, Cu, Zn, Pb and Cd) in a river-wetland-lake system (Balaton Region, Hungary)

Mn, Sr, Ba, Rb, Cu, Zn, Pb and Cd concentrations have been measured seasonally in the water and deposited sediments of the system comprising: Zala river (main input) — Lakes Kis-Balaton 1 and 2 (small artificial lakes created in a former bay of Lake Balaton) — Keszthely bay (hypertrophic part of Lake Balaton). The concentrations of the trace elements together with pH, alkalinity, dissolved cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺), dissolved inorganic ligands (Cl^–, SO₄ ^2–), particulate Al, Ca, inorganic and organic carbon are used to assess the contamination of the study area and biogeochemical processes controlling trace element concentrations. Thermodynamic speciation calculations have also been utilized to enhance our understanding of the system. In the sediments Rb, Ba, Cu and Zn concentrations were mainly controlled by the abundance of the aluminosilicate fraction. Strontium was mainly associated with the calcium carbonate fraction. The aluminosilicate fraction constitutes a major sink for Mn and Cd but the concentration of these elements are also strongly related to calcite precipitation. The main processes that control the dissolved distribution of trace elements in the Balaton system were: solid phase formation (carbonate) for Mn; coprecipitation with calcite for Sr, Ba, Rb and possibly Mn and Cd; adsorption/desorption processes (pH dependent) for Zn and Pb; solubilization of Mn and precipitation of Cd and Cu in reed covered wetland areas where anoxic conditions were probably existing during the warm season. A preliminary budget of atmospheric and river input to Lake Balaton has also been outlined. Although Lake Balaton, is subjected to anthropogenic inputs mainly from agricultural and domestic activities, their impact on trace element concentrations in the Balaton system is very limited due to the efficiency of removal processes (i.e. adsorption and co-precipitation) and to high sedimentation rates and strong sediment re-suspension. Anthropogenic inputs are only detected for Pb.     

Growth and urban differentiation on the urban periphery: A case study from Szeged, Hungary

In late nineteenth century Hungarian cities there were strong contrasts between the inner ‘urban’ core and the rural periphery in terms of housing conditions, accessibility and lifestyle. Rural-urban fringe zones in the Great Plain were quite distinctive because the Turkish period was followed by an outflow of population which resulted in scattered settlement around the urban centres. The fringe could be regarded simply as a zone of transition, but the differences between urban centres and their immediate surroundings were gradually reduced through the industrialisation of the larger towns in the communist period. A study of Szeged examines the expansion of the fringe zone and its gradual urbanisation through the growth of housing as people have moved out from the centre to live among the rural population which increasingly turned from agriculture to commuting. Villages on either side of Szeged's administrative boundary accommodated more migrants from the city during the 1980s and experienced a gradual positive change in the quality of life as people escaped from the decaying residential blocs in the centre. During the years since 1989 there has been further migration, coupled with a growth of small businesses and a big improvement in services (shopping, running water, sewage and telecommunications). Further change may be expected in line with the forces of counterurbanisation. This revised version was published online in July 2006 with corrections to the Cover Date.