Mineralogical,magnetic and mössbauer data of symthite (Fe9S11)     

Viktor Hoffmann  Helge Stanjek  Enver Murad 《Studia Geophysica et Geodaetica》1993,37(4):366-381

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Orbital interactions in phyllosilicates: Perturbations of an idealized two-dimensional,infinite silicate frame     

William F. Bleam  Roald Hoffmann 《Physics and Chemistry of Minerals》1988,15(4):398-408

The _∞ ² [Si₂O ₅ ²⁻ ] frame in phyllosilicate minerals is distorted through the rotation and tilting of the silicate tetrahedra and interacts with octahedral cations through its apical oxygens. Qualitative perturbation theory and extended Hückel band structure calculations demonstrate that rotation and tilting distortions of the _∞ ² [Si₂O ₅ ²⁻ ] frame have little influence on orbital interactions within the frame. The effects which are observed can be traced to next-nearestneighbor, oxygen-oxygen interactions. Analysis of band widths and crystal-orbital-overlap-populations demonstrate the importance of O(2s) orbitals in the silicate bond. Interactions between Si(3s, 3p) and O(2s) atomic orbitals account for about half of the bonding overlap in the Si-O bond. Crystal orbitals within the _∞ ² [Si₂O ₅ ²⁻ ] frame are perturbed in kaolinite, lizardite, pyrophyllite and talc through interactions of the apical oxygens with octahedrally coordinated Al(III) and Mg(II). These interactions appear to involve states that are non-bonding in an isolated frame, having little effect on the Si-O_apical bond while significantly reducing the apical-oxygen atomic population.  相似文献   

Horizontal ground deformation patterns and magma storage during the Puu Oo eruption of Kilauea volcano,Hawaii: episodes 22–42     

John P Hoffmann  George E Ulrich  Michael O Garcia 《Bulletin of Volcanology》1990,52(7):522-531

Horizontal ground deformation measurements were made repeatedly with an electronic distance meter near the Puu Oo eruption site approximately perpendicular to Kilauea's east rift zone (ERZ) before and after eruptive episodes 22–42. Line lengths gradually extended during repose periods and rapidly contracted about the same amount following eruptions. The repeated extension and contraction of the measured lines are best explained by the elastic response of the country rock to the addition and subsequent eruption of magma from a local reservoir. The deformation patterns are modeled to constrain the geometry and location of the local reservoir near Puu Oo. The observed deformation is consistent with deformation patterns that would be produced by the expansion of a shallow, steeply dipping dike just uprift of Puu Oo striking parallel to the trend of the ERZ. The modeled dike is centered about 800 m uprift of Puu Oo. Its top is at a depth of 0.4 km, its bottom at about 2.9 km, and the length is about 1.6 km; the dike strikes N65° E and dips at about 87°SE. The model indicates that the dike expanded by 11 cm during repose periods, for an average volumetric expansion of nearly 500 000 m³. The volume of magma added to the dike during repose periods was variable but correlates positively with the volume of erupted lava of the subsequent eruption and represents about 8% of the new lava extruded. Dike geometry and expansion values are used to estimate the pressure increase near the eruption site due to the accumulation of magma during repose periods. On average, vent pressures increased by about 0.38 MPa during the repose periods, one-third of the pressure increase at the summit. The model indicates that the dikelike body below Puu Oo grew in volume from 3 million cubic meters (Mm³) to about 10–12 Mm³ during the series of eruptions. The width of this body was probably about 2.5–3.0 m. No net long-term deformation was detected along the measured deformation lines.  相似文献   

Methode zur Bestimmung des Ammoniakstickstoffes in Gewässern     

I. Hoffmann  B. Nagy  J. Schneider 《洁净——土壤、空气、水》1984,12(6):645-651

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.  相似文献   

A Contribution to the Mechanism of Elimination of Dimethylformamide and Dimethylamine by a Heterogenous Culture of Microorganisms     

J. Houser  J. Hoffmann  H. Da&#x;kov  J. Kone ný  J. Kupec  M. Mldek 《洁净——土壤、空气、水》1983,11(4):433-438

In a batch experiment with activated sludge from a large-scale plant the hydrolytical and biochemical degradation of dimethylformamide (DMF) and its reaction product dimethylamine (DMA) and the conversion connected with this under aerobic and anaerobic conditions is investigated. Parallel to the hydrolysis of DMF the biochemical degradation of DMA occurs. The extensive conversion of these substrates is followed by the nitrification of the ammoniumions formed, and under subsequent anaerobic conditions with methanol as the carbon source also denitrification can be achieved. If the oxygen supply of the activated sludge is insufficient, however, also DMA can be used as a carbon source for denitrification, ammonium-ions being released from DMA in addition. In the batch experiment the elimination rates referred to nitrogen were 7 … 14 mg/g · h for DMF, 0.8 … 1.7 mg/g · h for DMA, 0.3 … 0.6 mg/g · h for NH and 0.4 to 1.3 mg/g · h for nitrate in the presence of methanol. DMF and DMA are obviously not suitable as the only carbon source for denitrification.  相似文献   

The role of dust source area and pedogenesis in three loess-palaeosol sections from North Bulgaria: A mineral magnetic study     

V. I. Avramov  D. Jordanova  V. Hoffmann  W. Roesler 《Studia Geophysica et Geodaetica》2006,50(2):259-282

Rock magnetic studies of three loess-palaeosol sections from Bulgaria (Harletz and Orsoja in the NW and Durankulak in the NE at the Black Sea coast) have been carried out. Thermomagnetic analyses of magnetic susceptibility point to magnetite as the major ferrimagnetic carrier in the loess and palaeosol units. Maghemite gives a significant contribution to the total magnetic signal in the recent soils (S₀), while in one of the sections-Orsoja-hematite may also be present. The effective magnetic grain sizes deduced from the hysteresis measurements and the ratios M_rs/M_s and B_cr/B_c fall in the pseudo single domain (PSD) range, but the data distributions in a Day diagram for the three different sections are shifted. This is suggested to be caused by different detrital input (e.g. different dust source areas) and varying degrees of pedogenic modification. The calculated background susceptibilities χ_bg differ significantly as well. The lowest value is obtained for the Durankulak section-χ_bg = 9.95 × 10⁻⁸ m³/kg, which is in accordance with the data from other studies of loess-palaeosol profiles from the Black Sea area. The corresponding background susceptibilities for the other two sections studied-Harletz and Orsoja-are significantly higher (33.1 and 17.75 × 10⁻⁸ m³/kg, respectively). Both parent material and pedogenesis are found to be responsible for the observed differences in the magnetic characteristics.  相似文献   

Remote sensing and GIS in hydrogeology   总被引：1，自引：0，他引：1  

Jörn Hoffmann  Per Sander 《Hydrogeology Journal》2007,15(1):1-3

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Spectral analysis of planetary waves seen in ionospheric total electron content (TEC): First results using GPS differential TEC and stratospheric reanalyses     

C. Borries  N. Jakowski  Ch. Jacobi  P. Hoffmann  A. Pogoreltsev 《Journal of Atmospheric and Solar》2007,69(17-18):2442

The coupling of the neutral atmosphere and the ionosphere through planetary waves (PW) (zonal wavenumber 0–5) is investigated by spherical harmonic analyses of the ionospheric total electron content (TEC). These analyses detect mean variations, standing and travelling waves which are assumed to be signatures of PW. Database used for TEC analyses are 3 years of hourly TEC maps covering the higher middle and polar latitudes. They are regularly produced by DLR Neustrelitz. The obtained results are compared with PW analyses using NCEP/NCAR and Met Office stratospheric reanalyses. Case studies show that signatures of PW occur simultaneously in the middle atmosphere and ionosphere.  相似文献   

A geological record of multiple Pleistocene tsunami inundations in an oceanic island: The case of Maio,Cape Verde     

José Madeira  Ricardo S. Ramalho  Dirk L. Hoffmann  João Mata  Mário Moreira 《Sedimentology》2020,67(3):1529-1552

In the Central Atlantic archipelagos – the Canaries, Cape Verde, Madeira and the Azores – tsunami hazard is often regarded as low, when compared with other extreme wave events such as hurricanes and storms. The geological record of many of these islands, however, suggests that tsunami hazard may be underestimated, notwithstanding being lower than in areas adjacent to subduction zones, such as the margins of the Pacific and Indian oceans. Moreover, tsunamis in oceanic islands are generally triggered by local large-scale volcanic flank collapses, for which little is known about their frequency, making it difficult to estimate the probability of a new occurrence. Part of the problem lies in the fact that tsunami deposits are usually difficult to date, and few islands in the world exhibit evidence for repeated tsunami inundation on a protracted timescale. This study reports on the presence of abundant tsunami deposits (conglomerates and sandstones) on Maio Island (Cape Verde) and discusses their stratigraphy, sedimentological characteristics, probable age and tsunamigenic source. Observations indicate that four distinct inundation events of variable magnitude took place during the Pleistocene. One of the tsunami deposits yielded a high-confidence U/Th age of 78·8 ± 0·9 ka, which overlaps within error with the 73 ± 7 ka age proposed for Fogo volcano's flank collapse, an event known to have had a significant tsunami impact on nearby Santiago Island. This shows that the Fogo tsunami also impacted Maio, resulting in runups in excess of 60 m above coeval sea-level at ca 120 km from the source. Two older deposits, possibly linked to recurrent flank collapses of the Tope de Coroa volcano in Santo Antão Island, yielded lower-confidence ages of 479 to 390 ka and 360 to 304 ka. A younger deposit (<78 ka) remains undated. In summary, the geological record of Maio exhibits well-preserved evidence of repeated tsunami inundation, reinforcing the notion that tsunami hazard is not so low at volcanic archipelagos featuring prominent and highly-active volcanoes such as in Cape Verde.  相似文献   

Midlatitude mesopause region winds and waves and comparison with stratospheric variability     

Ch. Jacobi  P. Hoffmann  R.Q. Liu  P. Krian  J. Las tovi ka  E.G. Merzlyakov  T.V. Solovjova  Yu.I. Portnyagin 《Journal of Atmospheric and Solar》2009,71(14-15):1540-1546

We present time series of January–May mean mesosphere/lower thermosphere (MLT) mean winds and planetary wave (PW) proxies over Europe together with stratospheric stationary planetary waves (SPW) at 50°N and time series of European ozone laminae occurrence. The MLT winds are connected with stratospheric PW and laminae at time scales of several years to decades. There is a tendency for increased wave activity after 1990, together with more ozone laminae and stronger MLT zonal winds. However, possible coupling processes are not straightforward. While mean MLT winds before the 1990s show similar interannual variations than stratospheric PW at 100 hPa, later a tendency towards a connection of the MLT with the middle stratosphere SPW is registered. There is also a tendency for a change in the correlation between lower and middle stratosphere SPW, indicating that coupling processes involving the European middle atmosphere from the lower stratosphere to the mesopause region have changed.  相似文献