Ab initio 2-D periodic Hartree–Fock study of Fe-substituted lizardite 1T– a simplified cronstedtite model

 A 2-D periodic ab initio Hartree–Fock LCAO study was performed on Fe-substituted 1:1 sheet silicate, lizardite. The atomic orbitals were described by large-core pseudopotentials (Fe atoms) and a sp basis set (the other atoms). Calculated atomic charges and the results of bond population analysis indicate that the Fe-O bond was as ionic as the Mg-O. This hypothesis was supported by calculated density of states and electron density maps. Increasing Fe for Mg substitution changed the shape of projected density of states (PDOS) of O(p) orbitals. Received: 27 January 2000 / Accepted: 21 May 2000     

Speleothems and pine trees as sensitive indicators of environmental pollution – A case study of the effect of uranium-ore mining in Hungary

Four decades of U ore production in Hungary provides an opportunity to study the possible environmental effects of mining. The study reveals significant changes in chemical composition of a stalagmite (cave deposit). The good fit between U content changes in the studied deposit and the U ore production rate support the assumption of the relationship with mining activity. An independent chemoenviromental archive, living pine (Pinus sylvestis) trees were also investigated. Data on pine tree cores collected from the same region show different levels of pollution (Cu, Zn, Mn, U) after the 1950s and 1960s, linked to the opening of mines and subsequent dust fallout around the site. Elevated concentrations of detritally derived elements (Si, Al, Th) coupled with a rise in U concentration and change in δ²³⁴U values of the stalagmite suggest increasing amounts of mine-derived dust from 1 to 3 km distance that settled and washed into the karst system. The combined usage of different proxies not only provides historic records for the anthropogenic impact in the environment, but also allows the timing of U concentration increases within the stalagmite and the identification of elemental behavior from the pollution. This study shows that complementary geochemical archives such as stalagmites and tree rings used together can enhance understanding of past environmental contamination.     

Disappearing ionospheres on the nightside of Venus

Instruments on the Pioneer Venus Orbiter have detected a substantial ionosphere on the nightside of Venus during most orbits. However, during some orbits the nightside ionosphere seems to have almost disappeared, existing only as irregular patches of low-density plasma. The solar wind dynamic pressure on these occasions is greater than average. We have correlated data from several instruments (Langmuir probe, ion mass spectrometer, retarding potential analyzer, magnetometer, and plasma analyzer) for a number of orbits during which the nightside ionosphere had disappeared. The magnetic field tends to be coherent, horizontal, and larger than usual, and the electron and ion temperatures are much larger than they usually are on the nightside. We suggest mechanisms which might explain the reasons for the disappearance of the ionosphere when the solar wind dynamic pressure is large.     

Heat wave risk assessment and mapping in urban areas: case study for a midsized Central European city,Novi Sad (Serbia)

Risk assessment and mapping methodologies for heat waves as frequently occurring hazards in central and southeastern Europe were applied in this study, and the impact of heat waves on the mortality of urban populations was determined as part of the assessment. The methodology for conducting the heat wave risk assessment is based on European Commission’s Guidelines for Risk Assessment and Mapping. The Novi Sad (Serbia) urban area was studied during summer 2015, which was one of the hottest summers in the last few decades. In situ air temperature measurements from urban stations and mortality of urban populations were used. Nocturnal urban heat island (UHI) intensity values between the various built-up zones and natural surrounding areas were used for the hazard level calculation. Temperature data from 9 p.m. to 5 a.m. were used because during the night, the UHI intensity reached its maximum values. The average daily number of deaths by LCZs was used to define the impact level of the vulnerability index. Calculations for both hazard levels were completed during two intensive heat waves (in July and August 2015) when it was expected that there may be a high level of risk. The results and maps show that the urban area is complex, and the heat wave risk on the population is not uniform. The most densely built-up areas (LCZs 2, 5 and 6) have very high or high risk values that are influenced by a higher rate of mortality. The obtained results and maps can be used by local authorities to prevent and mitigate climate-related hazards, for medical institutions as well as urban planners and for ancillary local, regional or national services. According to these results, the local authorities could define hot spots where they can place medical and rescue teams and install points with water supplies, etc.     

Intraplate volcanism in the Danube Basin of NW Hungary: 3D geophysical modelling of the Late Miocene Pásztori volcano

International Journal of Earth Sciences - Three-dimensional geophysical modelling of the early Late Miocene Pásztori volcano (ca. 11–10 Ma) and adjacent area in the Little...     

Analysis of soil boundary conditions of flash floods in a small basin in SW Hungary

Flash floods are one of the most significant natural hazards of today. Due to the complexity of flash flood triggering factors, to prevent or mitigate flood triggered losses, numeric model based flood forecasting models are capable tools to predict stream water levels. The main goal of the current research was to reproduce two flow peaks with the HEC-HMS rainfall-runoff model and test the model sensitivity for various input parameters. To obtain sufficient input data, we monitored soil depth, maximum infiltration rate, soil moisture content, rainfall, time of concentration and flow. To obtain input data, parameters were calculated, measured in the Sás Valley experimental watershed (SW Hungary) or optimized with the built in function of the HEC-HMS. Soil moisture was monitored in the 1.7 km2 pilot catchment over the period between September 2008 and September 2009. HEC-HMS had a good performance reproducing the two events, however simulated flow time series are highly influenced by the antecedent soil moisture, infiltration rate and canopy storage. Outflow modeled data were verified for two flood events (June 4, 2008 and July 9, 2009). The HEC-HMS was over-sensitive for input soil moisture and with increasing input rainfall and increasing outflow, larger simulation errors were observed.     

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.