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1.
Periodic ab initio Hartree-Fock LCAO calculations have been carried out on the two dimensional sheet of SiO4 tetrahedra, representing one of the basic constituting units of layer silicates, using Huzinaga's DZP basis sets. The influence of the basis set on the chemical bonding picture is characterized by Mulliken atomic charges and by electron density maps. Silicon atomic charges +1.6 ¦e¦ are more realistic than those +2.4 ¦e¦ reported for smaller basis sets. The silicon d orbital population is found to be 0.6 in close agreement with molecular data. Electron density maps indicate the absence of charge density in the center of the ditrigonal cavity. The charge buildup of nonbonding basal oxygen orbitals is directed mainly downwards perpendicular to the sheet plane. 相似文献
2.
The structure of the mid- and high-latitude ionosphere during the November 2004 storm event obtained from GPS observations 总被引：1，自引：1，他引：1
Andrzej Krankowski Irk I. Shagimuratov Lubomir W. Baran Galina Yakimova 《Acta Geophysica》2007,55(4):490-508
GPS data from the International GNSS Service (IGS) network were used to study the development of the severe geomagnetic storm
of November 7–12, 2004, in the total electron content (TEC) on a global scale. The TEC maps were produced for analyzing the
storm. For producing the maps over European and North American sectors, GPS measurements from more than 100 stations were
used. The dense network of GPS stations provided TEC measurements with a high temporal and spatial resolution. To present
the temporal and spatial variation of TEC during the storm, differential TEC maps relative to a quiet day (November 6, 2004)
were created.
The features of geomagnetic storm attributed to the complex development of ionospheric storm depend on latitude, longitude
and local time. The positive, as well as negative effects were detected in TEC variations as a consequence of the evolution
of the geomagnetic storm. The maximal effect was registered in the subauroral/auroral ionosphere during substorm activity
in the evening and night period. The latitudinal profiles obtained from TEC maps for Europe gave rise to the storm-time dynamic
of the ionospheric trough, which was detected on November 7 and 9 at latitudes below 50°N. In the report, features of the
response of TEC to the storm for European and North American sectors are analyzed. 相似文献
3.
Rock displacement and thermal expansion study at historic heritage sites in Slovakia 总被引：1，自引：0，他引：1
Jan Vlcko Vladimir Greif Vladimir Grof Michal Jezny Lubomir Petro Martin Brcek 《Environmental Geology》2009,58(8):1727-1740
The paper discusses the results of the research devoted to the preservation of cultural heritage carried out within last two
decades in Slovakia. The aim of the study depended on monitoring of selected castle rocks showing instability problems due
to extremely slow displacements of creep character. Apart from traditional methods of investigation at one test site (Spis
Castle), authors implemented in their work the study of thermal expansion of the rocks as a result of seasonal periodic temperature
changes having potential influence on displacements and numerical modeling in order to understand better the landslide failure
mechanism. The results obtained from all study sites confirmed that even slow movements have to be implemented into preservation
and stabilization works in order to safeguard the sites of great historic value. 相似文献
4.
Local geometry and orientation of intercalated molecules of formamide (FA) and N-methylformamide (NMFA) in the clay mineral
dickite (D) was studied by means of Density Functional Theory (DFT) calculations. Ten configurations with different orientation
of the intercalated molecule were investigated for both D_FA and D_NMFA intercalates. Four groups of relaxed structures sorted
by the calculated total electronic energy were found in both cases. The experimental geometry of the D_FA intercalate was
denoted as the most stable structure from the investigated models. The differences in the total electronic energy of all D_FA
configurations are within the interval of ∼92 kJ/mol. On one hand FA forms intercalates specifically and a close relation
between the orientation of the FA molecules in the interlayer space and the stability of a particular configuration has been
observed. On the other hand, N-methylformamide forms intercalated structures non-specifically. Small differences in the total
energy, not larger than 18 kJ/mol, are observed for different orientations of the NMFA molecules The reorientation of the
intercalated molecules has only a small effect on the stabilization of the D_NMFA intercalate what is in contrast with the
D_FA intercalate. It was also observed that the experimental D_NMFA configuration is not the most stable. A small variation
of the total electronic energy of different configurations correlates with small changes of the orientation of the dipole
moment of the intercalated NMFA molecule. 相似文献
5.
Stable O and C isotope data of 110 Upper Pliensbachian-Lower Bajocian belemnites have been obtained and used to attempt a reconstruction of palaeotemperature and its variation in two epicontinental depositional environments from the Western Balkan mountains (Bulgaria). The samples were collected from 3 sections with high-resolution ammonite subdivision. Initially taphonomic, cathodoluminescence and geochemical analyses were used for evidence of diagenetic alteration. Non-luminescent parts of the belemnite rostra have been sampled for isotope analyses and 76 samples, having δ18O < −4‰ (PDB), δ13C > −0.5‰ (PDB), Fe < 250 ppm, Mn < 50 ppm, Sr > 950 ppm and Sr/Mn ratio > 80 were used for palaeotemperature interpretations. The O and C isotope data generally exhibit little stratigraphical variability with minor fluctuations, however, there are prominent positive C isotope excursions and coeval negative O isotope shifts detected in the Lower Toarcian Tenuicostatum, Falciferum and Bifrons Zones. The O isotope data, interpreted in terms of palaeotemperature, revealed relatively high seawater temperatures during the Toarcian, Aalenian and Early Bajocian, with detectable temperature rises during the Early Toarcian (maximum value of 29.6 °C). Both C isotope maxima and O isotope minima are used as evidence of the Early Toarcian anoxic event reported from many localities of the same age and in similar facies in Western Europe. In the study the latter is recognized as 3 episodes, which are closely related with the seawater temperature maxima. This isotope record pattern is considered as a consequence of a global Tethyan transgression during the Early Toarcian. 相似文献
6.
Adsorption of H2O, NH3 and C6H6 on H- and alkali metal-exchanged structures of mordenite and on corresponding cations on the smectite layer is investigated
by ab initio density-functional calculations. Proton or an alkali metal cation compensates one Al/Si framework substitution
and resides in the extra-framework position of zeolite or above flat smectite layer close to the Al/Si substitution. Pronounced
similarities between zeolite and smectite are observed in changes of the adsorption energies and location of the external
cation with changing character of the external cation. Calculated adsorption energies exhibit the following trend: E(NH3) > E(H2O) > E(C6H6). Because of looser contact with the framework, zeolitic cations are stronger adsorption centers and calculated adsorption
energies of zeolites are by ~20–30% larger than cations of smectites. The highest adsorption energy is calculated for H-exchanged
structures and down the group of alkali metal cations a decrease of the adsorption energy is observed. Deviations from the
smooth variation of the adsorption energy are caused by: (1) formation of strong hydrogen bonds in H-exchanged structures,
(2) adsorption induced migration of the external Li+ cation, and (3) steric hindrances of the flat C6H6 molecule adsorbed on the cation in the cage of zeolite. 相似文献
7.
Vincenzo Alagna Massimo Iovino Vincenzo Bagarello Jorge Mataix‐Solera Lubomir Lichner 《水文研究》2019,33(4):661-674
The repellency index (RI) defined as the adjusted ratio between soil‐ethanol, Se, and soil‐water, Sw, sorptivities estimated from minidisk infiltrometer experiments has been used instead of the widely used water drop penetration time and molarity of ethanol drop tests to assess soil water repellency. However, sorptivity calculated by the usual early‐time infiltration equation may be overestimated as the effects of gravity and lateral capillary are neglected. With the aim to establish the best applicative procedure to assess RI, different approaches to estimate Se and Sw were compared that make use of both the early‐time infiltration equation (namely, the 1 min, S1, and the short‐time linearization approaches), and the two‐term axisymmetric infiltration equation, valid for early to intermediate times (namely, the cumulative linearization and differentiated linearization approaches). The dataset included 85 minidisk infiltrometer tests conducted in three sites in Italy and Spain under different vegetation habitats (forest of Pinus pinaster and Pinus halepensis, burned pine forest, and annual grasses), soil horizons (organic and mineral), postfire treatments, and initial soil water contents. The S1 approach was inapplicable in 42% of experiments as water infiltration did not start in the first minute. The short‐time linearization approach yielded a systematic overestimation of Se and Sw that resulted in an overestimation of RI by a factor of 1.57 and 1.23 as compared with the cumulative linearization and differentiated linearization approaches. A new repellency index, RIs, was proposed as the ratio between the slopes of the linearized data for the wettable and hydrophobic stages obtained by a single water infiltration test. For the experimental conditions considered, RIs was significantly correlated with RI and WDPT. Compared with RI, RIs includes information on both soil sorptivity and hydraulic conductivity and, therefore, it can be considered more physically linked to the hydrological processes affected by soil water repellency. 相似文献
8.
Abstract This article presents statistical analysis of a selection of data collected under a World Bank survey on Kyoto Protocol capacity-building needs in 16 potential clean development mechanism (CDM) host countries. It focuses on three interrelated issues: perceived barriers to the implementation of the CDM, expert judgment regarding the human, institutional and systemic capacity that must be built to overcome these barriers, and views on the most urgent steps that need to be taken to facilitate CDM implementation. The analysis reveals that in many countries there is a wide diversity of opinion across the group of respondents, which could be caused by a number of factors, including the inherent complexity of the Kyoto flexible mechanisms, limited understanding of their basic functioning and potential in the local context, and the differing needs and interests of stakeholder groups. Despite this, many statistically significant preferences can be identified at the national level. Among nations, two broad groups of countries emerge, which can be traced back to their overall level of capacity development. The statistical analysis presented in this article lends credibility to qualitative conclusions drawn from previous interpretations of the survey data and has implications for the design of capacity-building efforts. However, in evaluating capacity-building needs and the readiness of countries to engage in CDM deals, potential investors and providers of capacity-building services will need to consider not only the results of this type of opinionbased needs assessment, but also the practical experience gained through CDM transactions. 相似文献
9.
José Alexander Chávez Hernandez Jiři Šebesta Lubomir Kopecky Reynaldo López Landaverde 《Natural Hazards》2014,71(3):1323-1354
An erosion hazard map was elaborated using geomorphologic and lithological information; this was the base to characterize the erodibility of the territory. The aim of the proposed methodology is to define the areas where more detailed studies are necessary (e.g., to estimate rates of soil erosion, mitigation measurements, land use) to prevent future problems. Field work and remote sensing data (study of historical aerial photographs and satellite images) were used to understand the geomorphologic evolution and the current processes taking place in an area; this information was used to group the units according to its lithology, dynamic and slope inclination. The map was processed using the geographical information system and categorized in zones of very high, high, moderate, low and null fluvial erosion hazards. The map covers the Metropolitan Area of San Salvador, which is experiencing serious problems of mass wasting processes, collapse and settlements of foundations. Most affected areas belong to the Tierra Blanca Joven tephras which are unsaturated and cover most of the surface; nowadays, the urban projects and infrastructure resting in this material are suffering from extensive damage. The geotechnical information on the tephras shows a decrease in strength and collapsible behavior when saturated. Due to this, the use of Quickdraw tensiometers (suction) and TMS3 (soil moisture content) is proposed for monitoring. The methodology of erosion hazard mapping correlates well with mass wasting reported in the studied area, and for this reason, it could be a good way to protect the natural resources and improve the land use. 相似文献