Constraints of archaeomagnetic dating and field intensity determinations in three ancient tile kilns in Belgium     

Souad Ech-Chakrouni  Jozef Hus  Simo Spassov 《Studia Geophysica et Geodaetica》2013,57(4):585-604

The aim of this study is to date by the archaeomagnetic method the last heatingcooling cycle of one Roman and two Medieval tile kilns, discovered in Belgium. The investigation demonstrates the limitations when well-documented local directional secular variation curves of the geomagnetic field in the past are used for dating and the difficulties when trying to determine field intensities from “in situ” baked clays from the kilns. The three kilns yielded very well defined ancient field directions but two possible dating solutions for each of them when no a priori time constraints are taken into account, due to field direction recurrence. As an increase of the dating accuracy and reduction of the number of dating solutions can be expected using the full field vector information, also field intensity determinations on burnt clays from the kilns were attempted. Field intensities from samples of the Roman and of one of the Medieval kilns are quite scattered. On the other hand, results obtained applying the Thellier-Thellier method and the modified method developed by Dekkers and Böhnel on sister samples from the Roman kiln agree fairly well. Rock magnetic properties reveal high variance in the kilns that point to varying spatial heating and cooling conditions in the kilns. Even well burnt material from the kilns shows irreversible changes when heated in air in the laboratory. Reliable field intensities on “in situ” baked materials from kilns themselves can therefore only be obtained when measuring sufficient number of samples from different parts of the kiln, taking into account the spatial-temporal conditions during kiln operation and cooling history. More reference intensity data is needed in our regions in order to improve dating based on directional reference data only.  相似文献   

Effects of land use,slope gradient,and soil and water conservation structures on runoff and soil loss in semi-arid Northern Ethiopia     

Gebeyehu Taye  Jean Poesen  Bas Van Wesemael  Matthias Vanmaercke  Daniel Teka  Jozef Deckers 《自然地理学》2013,34(3):236-259

April lightning production in Richmond County, Georgia, from 1995 to 2003 is considered with regard to the associated risk to golfers and spectators at the Master's Golf Tournament and courses throughout the county. An examination of the April lightning climatology of Georgia, focusing on Richmond County, reveals a minimum in lightning activity during the time of the tournament (the first full week of April). A discriminant analysis of Richmond County lightning production utilizes several meteorological variables in order to discern between three categories of April lightning days: little or no lightning activity, minimal lightning activity, and high lightning activity. The analysis distinguishes relatively well between the categories with only 13.5% of the events misclassified. A composite regional analysis of the three lightning categories illustrates the environmental differences between these events. Although the little or no lightning and high lightning categories are somewhat similar environmentally, the intensity of features separates these events and allows for interpretation. The statistical and synoptic analyses together emphasize the importance of low-level instability and frontal proximity and intensity in enhancing lightning production in thunderstorms during April in and surrounding Richmond County. A multitude of meteorological conditions can lead to thunderstorm development. Localized studies of these environments, especially during times of major outdoor sporting events, are needed to help mitigate the risk associated with lightning.  相似文献   

Soil Microbial and Enzyme Activities Response to Pollution Near an Aluminium Smelter   总被引：2，自引：0，他引：2  

Juan Carlos García‐Gil  Jozef Kobza  Pedro Soler‐Rovira  Soňa Javoreková 《洁净——土壤、空气、水》2013,41(5):485-492

The aim of this research was to assess the impact caused by a long‐term pollution by fluoride and heavy metals in two soils (PS1 and PS2) near an aluminium smelter in Slovakia, on soil microbial biomass C (MBC), basal respiration, metabolic quotient (qCO₂) water‐soluble organic C (WSOC) and enzymes activities involved in the C, N and P biogeochemical cycles. An unpolluted soil was used as control (C0). Results obtained for soil fluoride content reflected a gradient of fluoride exposure in topsoils of contaminated sites. Decreases in microbial and enzymatic activities and in MBC to organic C ratio were found in PS2 site, which is closer to the smelter and exhibited the highest fluoride content. PS1‐soil showed an extreme alkaline pH caused by leaching of waste effluents from the smelter dumping site, higher contents of Zn, Cu, Pb and Cd, significantly larger MBC, qCO₂ and catalase and urease activities, and much larger basal respiration and dehydrogenase activity than PS2 and C0‐soil. Phosphatase, β‐glucosidase and BAA‐protease were negatively correlated with WSOC, basal respiration and dehydrogenase activity, and showed some degree of inhibition in polluted sites. These results may indicate different responses of microbial communities to ecosystem disturbances, caused by the drastic changes in soil's physicochemical properties as result of the long‐term emissions of fly ash with high levels of contaminants that are still affecting soil microbial and enzymatic activities.  相似文献   

Mass distribution in the asteroid belt     

Jozef Klačka 《Earth, Moon, and Planets》1992,56(1):47-52

The dependence of the cumulative number of numbered asteroids (up to 3720) on their absolute magnitude is investigated. The differential mass index k is derived from these relations for fainter asteroids. A steeper slope (2.2 < k < 2.4) is found in the four most populous asteroid familes (Flora, Koronis, Eos and Themis) and a flatter slope (1.3 < k < 1.6) for non-family asteroids. This indicates that there are two different asteroid populations in the asteorid belt. Total masses of the asteroid families may be greater than it is commonly accepted.  相似文献   

A Generalized Structure-Activity Relationship for the Decomposition of (Substituted) Alkoxy Radicals     

Jozef Peeters  Gaia Fantechi  Luc Vereecken 《Journal of Atmospheric Chemistry》2004,48(1):59-80

A novel and readily applicable Structure-Activity Relationship (SAR) for predicting the barrier height E_b to decomposition by C-C scission of (substituted) alkoxy radicals is presented. Alkoxy radicals are pivotal intermediates in the atmospheric oxidation of (biogenic) volatile organic compounds, and their fate is therefore of crucial importance to the understanding of atmospheric VOC degradation mechanisms. The SAR is based on available theoretical energy barriers and validated against barriers derived from experimental data. The SAR is expressed solely in terms of the number(s) N_i of alkyl-, hydroxy- and/or oxo-substituents on the - and -carbons of the breaking bond: E_b(kcal/mol) =17.5 – 2.1 × N(alk) – 3.1 ×N(alk) – 8.0 × N_,(OH) – 8.0 × N(O=) – 12 × N(O=). For barriers below 7 kcal/mol, an additional, second-order term accounts for the curvature. The SAR reproduces the available experimental and theoretical data within 0.5 to 1 kcal/mol. The SAR generally allows conclusive predictions as to the fate of alkoxy radicals; several examples concerning oxy radicals from prominent atmospheric VOC are presented. Specific limitations of the SAR are also discussed. Using the predicted barrier height E_b, the high-pressure rate coefficient for alkoxy decomposition k _diss (298 K) can be obtained from k _diss (298 K) = L ×1.8 × 10¹³ exp(–E_b/RT) s^–1, with L the reaction path degeneracy.  相似文献   

Impact of road building on gully erosion risk: a case study from the Northern Ethiopian Highlands   总被引：1，自引：0，他引：1  

Jan Nyssen  Jean Poesen  Jan Moeyersons  Edith Luyten  Maude Veyret‐Picot  Jozef Deckers  Mitiku Haile  Gerard Govers 《地球表面变化过程与地形》2002,27(12):1267-1283

Although obvious in the field, the impact of road building on hydrology and gullying in Ethiopia has rarely been analysed. This study investigates how road building in the Ethiopian Highlands affects the gully erosion risk. The road between Makalle and Adwa in the highlands of Tigray (northern Ethiopia), built in 1993–1994, caused gullying at most of the culverts and other road drains. While damage by runoff to the road itself remains limited, off‐site effects are very important. Since the building of the road, nine new gullies were created immediately downslope of the studied road segment (6·5 km long) and seven other gullies at a distance between 100 and 500 m more downslope. The road induces a concentration of surface runoff, a diversion of concentrated runoff to other catchments, and an increase in catchment size, which are the main causes for gully development after road building. Topographic thresholds for gully formation are determined in terms of slope gradient of the soil surface at the gully head and catchment area. The influence of road building on both the variation of these thresholds and the modification of the drainage pattern is analysed. The slope gradient of the soil surface at the gully heads which were induced by the road varies between 0·06 and 0·42 m m^?1 (average 0·15 m m^?1), whereas gully heads without influence of the road have slope gradients between 0·09 and 0·52 m m^?1 (average 0·25 m m^?1). Road building disturbed the equilibrium in the study area but the lowering of topographic threshold values for gullying is not statistically significant. Increased gully erosion after road building has caused the loss of fertile soil and crop yield, a decrease of land holding size, and the creation of obstacles for tillage operations. Hence roads should be designed in a way that keeps runoff interception, concentration and deviation minimal. Techniques must be used to spread concentrated runoff in space and time and to increase its infiltration instead of directing it straight onto unprotected slopes. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Reactions of Cl Atoms with Selected VOCs: Kinetics, Products and Mechanisms   总被引：1，自引：0，他引：1  

Gaia Fantechi  Niels R. Jensen  Ole Saastad  Jens Hjorth  Jozef Peeters 《Journal of Atmospheric Chemistry》1998,31(3):247-267

The reactions of isoprene, MBO (2-methyl-3-buten-2-ol) and toluene with chlorine atoms have been studied at 298 ± 5 K and 740 ± 5 Torr with the use of FTIR spectroscopy. Major products of the isoprene-Cl reaction and of the MBO-Cl reaction have been identified and quantified, and reaction mechanisms have been tentatively proposed in order to explain the products formed. The reaction between isoprene and Cl atoms yields mainly HCl, formyl chloride, formic acid, methylglyoxal (pyruvic aldehyde), CO and CO2, while the MBO-Cl reaction forms acetone, HCl, formyl chloride, formic acid, CO, CO2. As products from the reaction between toluene and Cl we identified and quantified HCl and benzaldehyde. The rate constants for the reactions of isoprene and toluene with Cl atoms have also been determined using a relative rate method. The measured values are: kisoprene = (5.5 ± 1.0) × 10–10 cm3 molecule–1 s–1 and ktoluene = (5.6 ± 1.3) × 10–11 cm3 molecule–1 s–1. Atmospheric lifetimes have been estimated from these values.  相似文献   

The biostratigraphy of the Hauterivian/Barremian Boundary Beds in the Krížna Nappe, Western Carpathians (Czechoslovakia)     

Karol Borza  Jozef Michalík  Viera Ga&#x;paríkov  Zdenêk Va&#x;í ek 《Cretaceous Research》1984,5(4):349-356

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The extent of Greater India,II. Palaeomagnetic data from the Ladakh Intrusives at Kargil,northwestern Himalayas     

Chris Klootwijk  Madan Lal Sharma  Jozef Gergan  Biras Tirkey  S.K. Shah  Vinod Agarwal 《Earth and Planetary Science Letters》1979,44(1):47-64

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Hydromagnetic spin-up under conditions of the earth's core-mantle boundary     

Jozef Brestenský  Gustáv Siráň  Reviewer I. Cupal 《Studia Geophysica et Geodaetica》1978,22(3):276-282

Summary The disturbances of the velocity and magnetic fields close to the Earth's core-mantle boundary, caused by sudden irregular changes in the Earth's rotation, are investigated. The problem leads to the investigation of the structure of the Ekman-Hartman hydromagnetic boundary layer, the magnetic diffusive region and the currentless region. Precise Laplacean inversions of the images of all disturbances in the Earth's core-mantle system are obtained for the limiting case of a zero magnetic Prandtl number, =0. The disturbance of the velocity in the direction of the axis of rotation (Ekman suction) in the currentless region has the nature of inertial oscillations with a frequency of 2. Additional disturbances (with respect to the case of =0) of the velocity in the azimuthal and radial directions, particularly for the EHL and MDR region, are determined for the case when 0< « 1. The disturbance in the velocity again has the character of inertial oscillations with the frequency 2, being exponentially damped in EHL asexp (–2²t) and in MDR asexp (–²t).  相似文献