Effect of the time factor on the temperature dependence of electrical resistivity of some rocks     

S. I. Shepel  M. Laštovičková 《Studia Geophysica et Geodaetica》1991,35(4):344-353

Summary The electrical AC (10³ Hz) resistivity of some rocks was measured in a dry regime in air and in an argon atmosphere under various heating regimes. It is shown that long-term measurements provide us additional information about factors influencing resistivity and activation energy which cannot be obtained by means of standard measurements.  相似文献   

Some characteristics of quasi-biennial geomagnetic oscillations of solar origin     

Emil M. Apostolov  Vojtěch Letfus  Reviewer J. Laštovička 《Studia Geophysica et Geodaetica》1988,32(2):171-186

Summary The monthly means of the geomagnetic index aa and of the relative sunspot numbers were used to analyse the quasi-biennial oscillations (QBO) in geomagnetic activity related to an analogous variation in solar activity. Statistical methods of time series analysis were applied: autocorrelation and power spectrum, cross-correlation, complex demodulation, and the digital filter technique. The aim of this investigation was not only the detection of QBO in geomagnetic activity, which has been done by various authors, but also the determination of the time variation of the period, phase and amplitude of these oscillations in the given time interval with reference to the results of Apostolov [2] and Apostolov and Letfus [4]. The following main results have been obtained: The characteristic period of QBO in geomagnetic activity is shorter and varies in a narrower interval than that in sunspot activity; the lifetime of the oscillations is about 22 years and roughly coincides with Hale's cycle; the amplitude of QBO in geomagnetic activity has its maximum on the decreasing branch of the sunspot cycle; the QBO in geomagnetic activity follows the analogous variation in sunspot activity with a delay of 2 to 6 months for various solar cycles, as compared with the 3 to 22 moths for the raw, unfiltered data. The causes of the differences in the characteristics of QBO in geomagnetic and sunspot activity are considered and it is shown that these differences do not contradict the solar control of this phenomenon.

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Comparative performance of convolutional neural network,weighted and conventional support vector machine and random forest for classifying tree species using hyperspectral and photogrammetric data     

C. Sothe  C. M. De Almeida  M. B. Schimalski  L. E. C. La Rosa  J. D. B. Castro  R. Q. Feitosa 《地理信息系统科学与遥感》2020,57(3):369-394

ABSTRACT

The classification of tree species can significantly benefit from high spatial and spectral information acquired by unmanned aerial vehicles (UAVs) associated with advanced classification methods. This study investigated the following topics concerning the classification of 16 tree species in two subtropical forest fragments of Southern Brazil: i) the potential integration of UAV-borne hyperspectral images with 3D information derived from their photogrammetric point cloud (PPC); ii) the performance of two machine learning methods (support vector machine – SVM and random forest – RF) when employing different datasets at a pixel and individual tree crown (ITC) levels; iii) the potential of two methods for dealing with the imbalanced sample set problem: a new weighted SVM (wSVM) approach, which attributes different weights to each sample and class, and a deep learning classifier (convolutional neural network – CNN), associated with a previous step to balance the sample set; and finally, iv) the potential of this last classifier for tree species classification as compared to the above mentioned machine learning methods. Results showed that the inclusion of the PPC features to the hyperspectral data provided a great accuracy increase in tree species classification results when conventional machine learning methods were applied, between 13 and 17% depending on the classifier and the study area characteristics. When using the PPC features and the canopy height model (CHM), associated with the majority vote (MV) rule, the SVM, wSVM and RF classifiers reached accuracies similar to the CNN, which outperformed these classifiers for both areas when considering the pixel-based classifications (overall accuracy of 84.4% in Area 1, and 74.95% in Area 2). The CNN was between 22% and 26% more accurate than the SVM and RF when only the hyperspectral bands were employed. The wSVM provided a slight increase in accuracy not only for some lesser represented classes, but also some major classes in Area 2. While conventional machine learning methods are faster, they demonstrated to be less stable to changes in datasets, depending on prior segmentation and hand-engineered features to reach similar accuracies to those attained by the CNN. To date, CNNs have been barely explored for the classification of tree species, and CNN-based classifications in the literature have not dealt with hyperspectral data specifically focusing on tropical environments. This paper thus presents innovative strategies for classifying tree species in subtropical forest areas at a refined legend level, integrating UAV-borne 2D hyperspectral and 3D photogrammetric data and relying on both deep and conventional machine learning approaches.  相似文献   

利用小半径X射线粉末相机鉴定几种造岩矿物          下载免费PDF全文

李达周  叶大年  沈保丰  翟安民 《地质科学》1978,13(4):365-372

自X射线在矿物学中广泛应用以来,很多造岩矿物的成份能够用X射线鉴定了。目前普遍使用的是衍射仪、大半径德拜相机或基尼叶相机,使用小半径相机的还很少。  相似文献   

Changes of electrical conductivity in the vicinity of the curie temperature of basaltic rocks — theoretical model     

Marcela Laštovičková  Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1978,22(1):98-102

Summary Samples of basalts, haematites and magnetites display either temporary or permanent (magnetite) weakening of the increase of the electrical conductivity with increasing temperature in the vicinity of their Curie temperature. Using the second quantization, this paper explains the observed pattern of the electrical conductivity adequately for magnetite and approximately for the other rocks by means of a quantum theory model of ferromagnetic minerals. This theory describes only the electron component of the electrical conductivity, which is responsible for the Curie temperature effect.Dedicated to RNDr. Jan Pícha, CSc., on his 60th Birthday  相似文献   

K-ar ages of the yemen plateau     

Lucia Civetta  Luigi La Volpe  Lucio Lirer 《Journal of Volcanology and Geothermal Research》1978,4(3-4)

The temporal evolution of the Yemen Trap series is examined in the light of K-Ar radiometric data.Rifting and volcanic activity characterize the Yemen plateau between 30 and 20 m.y. confirming a fairly common history of the Afro-Arabian plate on both sides of the Red Sea.  相似文献   

On some sources of uncertainty in the Lyman-α ionization-rate calculation     

Jan Laštovička  Reviewer V. Letfus 《Studia Geophysica et Geodaetica》1976,20(3):273-283

Summary The effect of the uncertainty and variability in the absorption cross-section, ionization cross-section and the Lyman- line shape on the Lyman- ionization-rate calculation is studied. The effect of the variability of the Lyman- line shape seems to be negligible. The effect of the ionization cross-section is rather small. The greatest and very significant effect, particularly at lower altitudes, is due to the discrepancy in the absorption cross-section data. Some ionospheric and atmospheric consequences are briefly discussed.  相似文献   

The dependence of the ionospheric absorption at 2775 kHz on the intensity of ionizing radiation—Ionospheric implications     

J. Laštovička 《Pure and Applied Geophysics》1976,114(3):321-331

Summary The results of comparisons of experimental data on the A3 2775 kHz absorption, X-ray (1–8 Å) flux and Lyman- radiation are compared with model data on ionization-rate and radio-wave absorption height profiles. The Lyman- radiation is found to dominate even in the upper D-region ionization (except flare conditions). A significant increase of usually used nitric oxide concentrations from rocket airglow measurements is required for achieving the best agreement between experimental and model data.  相似文献   

Changes of electric conductivity in the neighbourhood of the curie temperature of basalts     

Marcela Laštovičková  Vladimír Kropáček  Reviewer F. Janák 《Studia Geophysica et Geodaetica》1976,20(3):265-272

Summary In investigating the electric conductivity of rocks as a function of the temperature it was found that rocks containing ferrimagnetic minerals display a change in the slope of the functionlg =f(1/T) in the neighbourhood of the Curie temperature . In order to explain these changes the curveslg =f(1/T) and the Curie temperatures , obtained from the temperature dependence of the saturated magnetization J_s=f(T), were compared. Eight samples of basalts, 2 samples of haematite and magnetite were used to demonstrate the relation between and the changes in the pattern of the electric conductivity, caused by the variations of the exchangeable energy of ferrimagnetic minerals.  相似文献   

Mafic minerals from Punta delle Pietre Nere subvolcanites (Gargano,Southern Italy): Their petrological significance     

Maria De Fino  L. La Volpe  G. Piccarreta 《Mineralogy and Petrology》1983,32(1):69-78

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