Land-air boundary environment as recorded by the¹⁸O/¹⁶O and¹³C/¹²C isotope ratios in the shells of land snails     

Mordeckai Magaritz  Jossef Heller  Michal Volokita 《Earth and Planetary Science Letters》1981,52(1):101-106

A yearly cycle of carbon and oxygen isotope composition of shells of the Israeli land snailXeropicta vestalis is presented. The¹⁸O/¹⁶O values indicate that the snails use water from the land-air boundary zone. The¹⁸O/¹⁶O ratio of the shells is in isotopic equilibrium with the water condensate from the vapour during the winter months. During the summer months a contribution to the above water from soil water migrating upwards due to evaporation is noticeable. The δ¹³C values indicate that as in marine molluscs, the carbon isotopic composition in land snails is controlled mainly by the aqueous carbonate compound which is in equilibrium with the land-air boundary CO₂.  相似文献   

Magsat equivalent source anomalies over the southeastern United States: implications for crustal magnetization     

Michal E. Ruder  Shelton S. Alexander 《Earth and Planetary Science Letters》1986,78(1)

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Analytical expression for fresnel volumes and interface fresnel zones of seismic body waves. Part 1: Direct and unconverted reflected waves     

Michal Kvasnička  Vlastislav Červený 《Studia Geophysica et Geodaetica》1996,40(2):136-155

Summary Fresnel volumes, plane-sectional Fresnel zones and interface Fresnel zones of direct and unconverted reflected waves are studied. Exact analytical expressions for various parameters of Fresnel volumes and Fresnel zones are derived and discussed. Among others, these expressions are related to semi-axes of Fresnel zones, to overshooting and penetration distances, and to the off-ray shifts of Fresnel zones.  相似文献   

Total water content thresholds for shallow landslides,Outer Western Carpathians     

Michal Bíl  Richard Andrášik  Pavel Zahradníček  Jan Kubeček  Jiří Sedoník  Petr Štěpánek 《Landslides》2016,13(2):337-347

Shallow landslides are fairly frequent natural processes which emerge as a result of both rainfall and rapid snowmelt in the Flysch Belt of the Outer Western Carpathians. We estimated the total water content thresholds for the previously defined seven phases of increased landsliding which took place between 1939 and 2010 around the Napajedla meteorological station. The time series were reconstructed on the basis of data from surrounding stations. Rainfalls with the highest intensities (>1 mm/min) were removed from the set. Rainfall of such an intensity primarily causes overland flow and soil erosion and does not contribute to landslide threshold. The snow water equivalent was computed on the basis of the snow height, and possible errors were evaluated as interval estimations. An interval of 10 days before a landslide phase was selected for the total water content threshold. The resulting lower boundary (67.0 mm/10 days) and upper boundary (163.3 mm/10 days) thresholds of water infiltrated into soil during an event shall be part of the prepared online warning system in this area.  相似文献   

Spotless flares and type II radio bursts     

Michal Šeršeň  Boris Valníček 《Solar physics》1993,145(2):339-345

Flares accompanied by type II meter radio bursts that occurred in plages with no visible spots are examined in this paper. There have been found 12 such spotless flares observed in the period of January 1981–August, 1990. Six out of all the flares may be said to have not been associated with any filament activation or disruption. A few of these flares have shown features of major events. The study suggests that a filament activation seems not to be the crucial factor for the occurrence of major flares in regions with no visible spots.  相似文献   

Interactive Effects of UV-B Radiation and Chemical Contamination on Physiological Parameters in the Lichen Ramalina lacera     

Jacob Garty  Tal Levin  Haya Lehr  Sharon Tomer  Ayala Hochman 《Journal of Atmospheric Chemistry》2004,49(1-3):267-289

To assess the impact of ultraviolet B (UV-B) radiation under laboratory conditions on lichens from different biomonitoring sites, thalli of the lichen Ramalina lacera were transplanted from a clean air site to nine different polluted sites in Israel. Our objective was to determine the probability of synergistic/antagonistic effects on physiological parameters by considering two stressors: chemical contamination and UV-B. Exposure to both airborne pollutants in the field and subsequent UV-B radiation in the laboratory which led to a severe disintegration of cell membranes, followed by electrolyte leakage, indicate the probability of a synergistic effect. The impairment of the potential quantum yield of electron transfer through photosystem II (PSII) of photosynthesis indicated by a significant decrease of the ratio F_v/F_m, further demonstrated the synergistic effect of both chemical contamination and UV-B radiation. Besides enlarged amounts of stress-ethylene in lichens at contaminated sites, the reduced levels of ethylene production upon UV-B radiation in the present study suggest the likelihood of an antagonistic effect of xenobiotic elements and UV-B radiation as a result of an impaired ethylene-producing system.  相似文献   

A search for acoustic amplitude deficit at the antipodes of sunspots     

Michal L. Peri  Ken G. Libbrecht 《Solar physics》1991,132(2):223-231

We present a search for the acoustic oscillation deficit which may exist at the antipodes of sunspots. Dopplergrams from Big Bear Solar Observatory 1988 helioseismology data were selected for five days on which large sunspots were known to be on the unseen hemisphere of the Sun. Acoustic oscillation amplitudes in the antipodal regions of these sunspots were compared with amplitudes in surrounding quiet-Sun regions. We did not detect a statistically significant acoustic amplitude deficit in our data. Our results indicate that the amplitude deficit at the sunspot antipodal points is limited to no more than 3% of the acoustic amplitude in the region, for solar oscillation modes of spherical harmonic degree l 200. We conclude that no strong acoustic deficit exists at the antipodes of sunspots. A more sensitive search, requiring more elaborate observations than we have performed, would be desirable in order to determine if a weak acoustic amplitude deficit exists at some level at the antipodes of sunspots, perhaps at higher spatial frequencies of oscillation. The noise level in any signals detected by such observations would probably limit their usefulness as seismic probes. However, information on the lifetimes of solar oscillation modes can be deduced even if no acoustic amplitude deficit is detected.  相似文献   

Using external tropospheric corrections to improve GNSS positioning of hot-air balloon     

Pavel Vaclavovic  Jan Dousa  Michal Elias  Jakub Kostelecky 《GPS Solutions》2017,21(4):1479-1489

High accurate global navigation satellite systems (GNSS) require to correct a signal delay caused by the troposphere. The delay can be estimated along with other unknowns or introduced from external models. We assess the impact of the recently developed augmentation tropospheric model on real-time kinematic precise point positioning (PPP). The model is based on numerical weather forecast and thus reflects the actual state of weather conditions. Using the G-Nut/Geb software, we processed GNSS and meteorological data collected during the experiment using a hot-air balloon flying up to an altitude of 2000 m. We studied the impacts of random walk noise setting of zenith total delay (ZTD) on estimated parameters and the mutual correlations, the use of external tropospheric corrections, the use of data from a single or dual GNSS constellation and the use of Kalman filter and backward smoothing processing methods. We observed a significant negative correlation of the estimated rover height and ZTD which depends on constraining ZTD estimates. Such correlation caused a degraded performance of both parameters when estimated simultaneously, in particular for a single GNSS constellation. The impact of ZTD constraining reached up to 50-cm differences in the rover height. Introducing external tropospheric corrections improved the PPP solution regarding: (1) shortened convergence, (2) better overall robustness, particularly, in case of degraded satellite geometry, (3) less adjusted parameters with lower correlations. The numerical weather model-driven PPP resulted in 9–12- and 5–6-cm uncertainties in the rover altitude using the Kalman filter and the backward smoothing, respectively. Compared to standard PPP, it indicates better performance by a factor of 1–2 depending on the availability of GNSS constellations, the troposphere constraining and the processing strategy.  相似文献   

Spatial modelling of summer climate indices based on local climate zones: expected changes in the future climate of Brno,Czech Republic     

Geletič  Jan  Lehnert  Michal  Dobrovolný  Petr  Žuvela-Aloise  Maja 《Climatic change》2019,152(3-4):487-502

Climatic Change - With global climate change ongoing, there is growing concern about future living conditions in urban areas. This contribution presents the modelled spatial distribution of two...  相似文献   

Automated calibration of advanced soil constitutive models. Part II: hypoplastic clay and modified Cam-Clay     

Kadlíček  Tomáš  Janda  Tomáš  Šejnoha  Michal  Mašín  David  Najser  Jan  Beneš  Štěpán 《Acta Geotechnica》2022,17(8):3439-3462

This paper introduces an automated deterministic method for the calibration of the Modified Cam-Clay and hypoplastic clay model. The calibration is structured in a hierarchical order established based on the apriori sensitivity study performed. The proposed method favours the clear physical meaning of the model parameters to a complete optimization of the objective error function. The method requires only basic laboratory experiments and it is currently implemented in the free-to-use online application called ExCalibre.

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