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The computation of sparse representations of data on the sphere (e.g. topographical data) is a crucial step for further processing
such as multiple separation, migration, imaging and sparsity promoting data-recovery. The Easy Path Wavelet Transform (EPWT)
is a new tool for sparse data representation that has recently been introduced for image compression. In this paper we consider
the EPWT on spherical triangulations. It is a locally adaptive transform that works along pathways through the array of function
values and exploits the local correlations of the data in a simple appropriate manner. In our approach the usual discrete
one-dimensional orthogonal or biorthogonal wavelet transform can be applied. The EPWT can be used for defining a multiresolution
analysis on the sphere in which the scaling spaces and the wavelet spaces depend adaptively on the data. Issues of implementation
of the EPWT are also considered. 相似文献
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We present a statistical analysis of the relationship between the kinematics of the leading edge and the eruptive prominence
in coronal mass ejections (CMEs). We study the acceleration phase of 18 CMEs in which kinematics was measured from the pre-eruption
stage up to the post-acceleration phase. In all CMEs, the three part structure (the leading edge, the cavity, and the prominence)
was clearly recognizable from early stages of the eruption. The data show a distinct correlation between the duration of the
leading edge (LE) acceleration and eruptive prominence (EP) acceleration. In the majority of events (78%) the acceleration
phase onset of the LE is very closely synchronized (within ± 20 min) with the acceleration of EP. However, in two events the
LE acceleration started significantly earlier than the EP acceleration (> 50 min), and in two events the EP acceleration started
earlier than the LE acceleration (> 40 min). The average peak acceleration of LEs (281 m s−2) is about two times larger than the average peak acceleration of EPs (136 m s−2). For the first time, our results quantitatively demonstrate the level of synchronization of the acceleration phase of LE
and EP in a rather large sample of events, i.e., we quantify how often the eruption develops in a “self-similar” manner. 相似文献
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The present study tests the usefulness of SoLIM software and GIS techniques for the reconstruction of large vegetation formations from the mid-Holocene period in Romania. We used current reference climate data (temperature, precipitation) and the current extent of ecological regions in Romania to derive climate optimality functions for each vegetation formation. The optimality functions were used to simulate current and past distributions of vegetation. The results showed that the current and mid-Holocene simulated spatial distributions of vegetation are quite similar. Changes were found for about 14% of the Romanian territory (33 946 km2), the most important being the retreat of coniferous forests in favor of mixed forests and of mixed forests in favor of forest steppe. The former is validated by previous pollen-based studies showing the transition from coniferous forests to mixed forests that occurred in several areas of the country after the mid-Holocene. The study demonstrates the potential of this methodological approach to reconstruct past vegetation formations, and at the same time that it is a straightforward and expert knowledge-based method. Although our application uses only climate factors, the results can be further refined by incorporating additional drivers (soil and landform information, site-specific pollen and fossil data, wildfire data) for a more accurate inference of paleovegetation. 相似文献
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Rudolf Br��zdil Monika B��l��nov�� Jaroslav Ro?novsky 《Theoretical and Applied Climatology》2011,104(1-2):71-81
Drought forecasting is a critical component of drought risk management. Identification of effective predictors is a major component of forecasting models. Sea surface temperature (SST) and sea level pressure (SLP) are relevant predictors for short- to long-term drought forecasts. However, these datasets are captured globally within a cell-wise network. This paper describes an approach to locate the most effective cells of the SST and SLP datasets using data mining. They are then applied as input to an adaptive neurofuzzy inference system (ANFIS) model to forecast possible droughts 3, 6, and 9?months in advance. Tehran plain was selected as the study area, and drought events are designated using the effective drought index (EDI). In another treatment, past values of the EDI time series were introduced to the ANFIS and the results compared with the previous findings. It was shown that R 2 values were higher for all cases applying the SST/SLP datasets. Additionally, the performance of SST/SLP datasets and the ANFIS model was assessed according to ??drought?? or ??wet?? classification, and it was concluded that more than 90% of the time the ANFIS model detected the drought status correctly or with only a one class error. 相似文献
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The ultimate objective of the research conducted by the authors is to explore the feasibility of determining reliable in situ values of soil modulus as a function of strain. In field experiments, an excitation is applied on the ground surface using large‐scale shakers, and the response of the soil deposit is recorded through receivers embedded in the soil. The focus of this paper is on the simulation and observation of signals that would be recorded at the receiver locations under idealized conditions to provide guidelines on the interpretation of the field measurements. Discrete models are used to reproduce one‐dimensional and three‐dimensional geometries. When the first times of arrival are detected by receivers under the vertical impulse, they coincide with the arrival of the P wave; therefore related to the constrained modulus of the material. If one considers, on the other hand, phase differences between the motions at two receivers, the picture is far more complicated and one would obtain propagation velocities, function of frequency and measuring location, which do not correspond to either the constrained modulus or Young's modulus. It is necessary then to conduct more rigorous and complicated analyses in order to interpret the data. This paper discusses and illustrates these points. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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The prominence which erupted at the SE limb on August 18, 1980 is one of the best observed disparition brusque events: high-resolution monochromatic ground-based observations in the H line were supplemented by the SMM and Solwind satellite coronographic observations; the radio wavelength range was well covered by single-frequency and spectral observations, and the prominence magnetic fields were measured two days before the eruption.The prominence showed a helical-like internal structure from the pre-eruptive phase, up to the late phases of eruption. The pitch angles of the helical-like threads were measured at several positions 31 along the prominence axis, and the evolution of twist was followed during the eruption. These measurements provide an estimate of the parameters which are directly comparable with theoretical models. The pitch angles of the helical threads decreased during the eruption. A redistribution of twist along the prominence axis could not be detected within the accuracy of measurements, although there are indications that the twist was partly transformed into an external kink-type screw of the prominence axis. The value of the total twist did not change during the eruption within the accuracy of the measurements.The kinematics of the process was followed, and accompanying events in the radio-range and soft X-rays are listed. Measurements of the magnetic field vector in the prominence are reviewed briefly. The observations were compared with predictions of cylindrical models, considering the forces acting at the prominence summit. Observational implications and constraints are discussed, and the decrease of the axial electric current and the mass loss are inferred. 相似文献
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