Institute of Geophysics

Institute of Geophysics 197 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Calibration of acoustic emission sensors
Kolář, Petr ; Petružálek, Matěj
Measurement of acoustic emission (AE) during laboratory experiments – rock sample loading - is an important tool for study of material mechanical properties as well as understanding of modes of its failure. For correct data processing it is necessary to calibrate used AE sensors. The calibration constants can depend on property of individual sensors, on their contact conditions, etc. As there can be a deformation induced charge in sensor contact condition, the calibration constants may vary with time. AE sources can be modeled (in the same way as natural earthquakes) as double couple sources with use of moment tensor (MT) formalism (3x3 symmetric tensor, i.e. 6 independent values, the problem is linear). We adopted method, which enable calibration of an individual station of a seismic network. The method is based on simultaneous determination of MTs and calibration constant(s). During the experiment there were repeatedly measured velocities of elastic waves by ultrasonic sounding, when AE sensors cyclically acted as sources. We processed this data and for each cycle determined calibration constant for all the sensors but one, which is supposed to be 1. The source is supposed to be of single force type, which further reduces number of determined parameters. The evaluation was performed cyclically for all the sensors, the final calibration constants are then the mean values.
Reconstruction of the solar activity to 11,000 years BP and possible long-term periodicities
Střeštík, Jaroslav
Observations of solar activity (Wolf sunspot numbers) last only about 250 years, moreover, from sporadic observations the solar activity can be estimated approximately to the year 1500. In addition to the well-known eleven-year period some long-term periods seem to take place. This means that the values at the maxima of 11-yr solar cycles in certain periods are higher than those in other ones. Based on the analysis of dust fallout containing radioactive elements, conserved in glaciers, some authors reconstructed the solar activity first one millennium back, and later more millennia back. The longest series begins 9000 years B. C. and these data are published. Strangely, most authors of these the reconstructions do not look for possible periodicities, or only marginally. Here the possible periodicities obtained from a series of 11,000 years long have been presented. The results suggest a superlong periodicity with the length about 6500 years, on the other hand, they do not confirm variations with the length between 100 and 200 years, which are not persistent.
Verification of model calculations for the Kaplan turbine design
Polák, M. ; Polák, Václav ; Hudousková, M.
In order to design a water turbine, the Theory of the Physical Similarity of Hydraulic Machines is used in technical practice. This principle has been known and used by manufacturers of turbines and pumps, but is not available to general public. This paper describes author's calculation program for turbine design that is well accessible to the widest possible range of users of mainly small hydropower sources. Based on the given hydraulic potential (water head and flowrate), the program determines the most suitable turbine type and calculates its main geometric parameters. In addition to numerical results, the program is also endowed with graphic output which renders in true scale hydraulic profiles of rotor blades and guide blades as well as the hydraulic profile of a spiral casing. The process of the Kaplan turbine design is used as an example in this paper. The comparisons of the calculated results with the verified standard 4-K-69 Kaplan turbine confirm the compliance of numerical results with reality.
Detailed analysis of (selected) West Bohemian earthquakes - results and possible geological consequences
Kolář, Petr
At TCP 2011 and 2013 we informed about Interactive tool for determination of parameters of finite seismic source model using Stopping Phases method. Now the crucial part of software is developed and the Tool is in routine operation: events are analysed, values of investigated parameters are obtained and in addition the harvested results seem to yield also information about detailed geological structure in the foci area - such knowledge cannot be obtained by another way unless the exhaustive and expensive prospecting geophysical methods are applied. Namely we processed sets of events from pronounced seismic swarms which occurred in West Bohemia in yrs. 2000, 2008 and under the investigation are 2011 data (2014 data are the challenge for the future).
The change of the rain factor on the net of stations in the Czech Republic during 1961-2010
Střeštík, Jaroslav ; Rožnovský, J. ; Štěpánek, P. ; Zahradníček, P.
Precipitation totals do not express precisely the humidity conditions in the landscape. Therefore the Lang’s rain factor, constructed from monthly and annual average temperatures and precipitation totals on 267 stations in the Czech Republic during 1961-2010, has been used here. Its values are very different at different stations, the lowest they are at South Moravia and Labe lowlands. Its average for the whole territory displays a slow decrease during the 50 years, supplemented by strong fluctuations. The strongest decrease appears in the Northern boundary mountains. The same factor calculated only for summer displays stronger differences between highlands and lowlands, especially in South Moravian ones. Stronger decrease at North Moravia, especially in mountains, and very weak decrease at other parts takes place.
School vacancies from the point of view of the annual course of selected meteorological parameters
Střeštík, Jaroslav
School vacancies in our country have lasted from July 1st till August 31st since more than hundred years. There is, however, a question, whether this period is the best one. The course of the air temperatures show that the warmest period in the year occurs between the half June and half August. On the other hand, rains are less frequent in August than in June. In view of the fact that the annual course of temperatures in individual years approaches to the long-term one more than that of precipitation, and with respect to some other factors, it results that the most suitable period for school vacancies starts on June 20th. In that case, the vacancies and subsequent school year should start always in Monday.
Methodology for evaluating the soil properties by using magnetic susceptibility , applicable for the assessment of soil degradation due to water erosion
Kapička, Aleš ; Kodešová, R. ; Jakšík, O. ; Klement, A. ; Petrovský, Eduard ; Grison, Hana
This work has been supported by the Ministry of Agriculture of the Czech Republic (Project No. QJ1230319, “Soil water regime within a sloping agricultural area”). The goal was to propose methodology for using the soil magnetic parameters for accessing soil properties and their spatial distribution within agricultural areas affected by water erosion. Methodology includes: choice of sampling design for target area (optimized based on other auxiliary data) and soil sampling (topsoil), soil sample processing (drying, grinding, sieving, etc.), method of magnetic susceptibility measurements (using Bartington MS2 and Kappametr SM400) and procedure to calibrate models of predicting soil properties from soil magnetic properties. Prediction of the oxidable organic carbon from the mass specific magnetic susceptibility determined in the laboratory is shown here as an example of practical application of this methodology for soil properties assessment in certain soil types. In addition close correlation between volume magnetic susceptibility measured directly in the field and mass specific magnetic susceptibility obtained in the laboratory documents that the oxidable organic carbon may be estimated directly from the field measurements.
Increase of annual and seasonal air temperatures in the Czech Republic during 1961-2010
Střeštík, Jaroslav ; Rožnovský, J. ; Štěpánek, P. ; Zahradníček, P.
Using the monthly means of air temperatures at 267 stations in the Czech Republic, the long-term change has been estimated at each station for the last 50 years. Annual mean temperatures for the whole country show a considerable increase, more pronounced than that for global temperature, however, supplemented by strong fluctuations from year to year. Long-term changes in air temperatures at different stations and in different regions vary. Stronger increase in air temperatures can be seen in Bohemia, whereas in Moravia temperature increase is not so significant. This difference is more pronounced in the winter, whereas in the summer, the differences are smaller and perhaps of opposite nature. This means that the continentality of the climate in Moravia increases, while in Bohemia it very slightly decreases. Long-term changes depend only marginally on the absolute values of annual mean temperatures at the respective station. The increase of autumn temperatures is considerably lower than that of other seasons.
Possible correlations between geomagnetic activity and global air temperature
Střeštík, Jaroslav
Annual values of the geomagnetic activity indices aa have been compared with the annual mean values of global air temperature during 1850-2012. Despite of a big noise level a significant positive correlation takes place. However, it only reflects a very similar long-term change occurring in both investigated quantities, which must not have a common origin. Short periodical changes with periods of years or decades are at both quantities quite different and their correlation is negligible. When shorter parts with the length of about some decades have been compared, resulting correlations were different. The significant correlation for the whole period is therefore not persistent. No influence of the geomagnetic activity on global temperature in shorter time dimensions has been proved and therefore it is not possible to use any estimate of a possible course of the geomagnetic activity for a prediction of the global temperature in the future. Using the temperature data from the individual stations instead of the global ones different correlations can be obtained but even these are not persistent. The same result will follow using any other selection of shorter intervals.
The change of annual and seasonal precipitation totals in the Czech Republic during 1961-2012
Střeštík, Jaroslav ; Rožnovský, J. ; Štěpánek, P. ; Zahradníček, P.
Using the monthly values of precipitation totals at 267 stations in the Czech Republic a longterm change has been estimated at each station for the last 50 years. Annual totals for the whole country display a slight increase, however, supplemented by a much stronger fluctuations from year to year. Long-term changes in annual totals at different stations and in different regions are different. In southern and western Bohemia precipitation totals increased more, in Elbe lowlands and in a large part of the Moravia, rather a small decrease in rainfall has been observed. Long-term changes depend only slightly on the total rainfall at the respective station or in the region. Summer precipitation totals increased more than annual averages, while spring precipitation totals decreased, at other times seasons the change is negligible. At the same time, the annual variation changes slightly: maximum precipitation has shifted from June to July and August.

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