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131.
Gudrun Carl Ingolf Kühn 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(3):315-324
Spatial (two-dimensional) distributions in ecology are often influenced by spatial autocorrelation. In standard regression
models, however, observations are assumed to be statistically independent. In this paper we present an alternative to other
methods that allow for autocorrelation. We show that the theory of wavelets provides an efficient method to remove autocorrelations
in regression models using data sampled on a regular grid. Wavelets are particularly suitable for data analysis without any
prior knowledge of the underlying correlation structure. We illustrate our new method, called wavelet-revised model, by applying
it to multiple regression for both normal linear models and logistic regression. Results are presented for computationally
simulated data and real ecological data (distribution of species richness and distribution of the plant species Dianthus carthusianorum throughout Germany). These results are compared to those of generalized linear models and models based on generalized estimating
equations. We recommend wavelet-revised models, in particular, as a method for logistic regression using large datasets. 相似文献
132.
使用基于伴随方法的反演策略,研制出了南加州地壳的三维地震模型。该模型涉及到16次层析成像迭代,需要6800次波场模拟和总计80万个中心处理单位小时。与南加州地震中心给出的最初三维模型比较,该新的地壳模型揭示了更强的非均匀性,包括±30%的局部变化。模型说明了诸如沉积盆地和横跨断层的构造反差的浅部特征。也揭示了深部的地壳特征,从而帮助重建诸如俯冲捕获洋壳碎块的南加州构造。新模型有助于对地震危险性做出更实际而准确的评估。 相似文献
133.
We propose a method to compensate for the phase lag and the amplitudeattenuation in the cup anemometer signal. These two effects, caused by theinstrument's inertia, are the major flaws of the cup anemometer in additionto over-speeding. Since the instrument's response is invariant in wavenumber (not frequency) representation, we transform the signals to becompensated from the time domain to the spatial domain by using Taylor'shypothesis. In the spatial domain we apply a linear time-invariant filterto eliminate the phase lag and the amplitude attenuation. The proposedprocedure improves instrument performance down to spatial scales equal toor smaller than the distance constant of the anemometer. The method for cupanemometer compensation is presented in detail and later adapted for vanes. 相似文献
134.
Radiation pressure acts to accelerate dust grains and, by transfer of momentum through collisions with the gas, drives the outflows of late-type stars. Some of these dust–gas collisions may be energetic enough to remove atoms from the dust grains. From an assumed initial size distribution for the dust grains, the method of Krüger et al. is used to study the evolution of a sample of spherical amorphous carbon grains under conditions typical of a late-type star. The size distribution of dust grains is presented for various sets of model parameters. One set of models assumes an initial Mathis, Rumpl & Nordsieck (MRN) distribution for the dust grains. The high-luminosity ( L ∗), high-effective temperature ( T eff ) set of parameters has a terminal velocity ( v term ) that is near, but above , the upper limit of observed outflow velocities for carbon stars (∼30 km s−1 for the assumed ̇ of 5×10−6 M⊙ yr−1 ). The low L ∗, T eff model has a v term that lies near, but below , the upper limit of observed velocities. A significant amount of sputtering occurs in the high L ∗, T eff model with ∼40 per cent of the grain mass sputtered. About ∼1 per cent of the dust mass is sputtered in the low L ∗, T eff . Another set of models assumes that the dust forms with a log-normal distribution. Here, v term is nearly the same for the high L ∗, T eff model as for the low L ∗, T eff model. This is a result of the large amount of dust mass loss (∼75 per cent) by sputtering in the high L ∗, T eff model. 相似文献
135.
Carl Troll 《International Journal of Earth Sciences》1944,34(7-8):307-325
Ohne Zusammenfassung 相似文献
136.
Larry Lines Joe Wong Kris Innanen Fereidoon Vasheghani Carl Sondergeld Sven Treitel Tadeusz Ulrych 《Geophysical Prospecting》2014,62(1):190-195
While seismic reflection amplitudes are generally determined by real acoustical impedance contrasts, there has been recent interest in reflections due to contrasts in seismic‐Q. Herein we compare theoretical and modelled seismic reflection amplitudes for two different cases of material contrasts. In case A, we examine reflections from material interfaces that have a large contrast in real‐valued impedance () with virtually no contrast in seismic‐Q. In case B, we examine reflections from material interfaces that have virtually no contrast in but that have very large seismic‐Q contrasts. The complex‐valued reflection coefficient formula predicts non‐zero seismic reflection amplitudes for both cases. We choose physical materials that typify the physics of both case A and case B. Physical modelling experiments show significantly large reflections for both cases – with the reflections in the two cases being phase shifted with respect to each other, as predicted theoretically. While these modelling experiments show the existence of reflections that are predicted by theory, there are still intriguing questions regarding the size of the Q‐contrast reflections, the existence of large Q‐contrast reflections in reservoir rocks and the possible application of Q‐reflection analysis to viscosity estimation in heavy oilfields. 相似文献
137.
Testing a spatially distributed tracer‐aided runoff model in a snow‐influenced catchment: Effects of multicriteria calibration on streamwater ages
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Thea I. Piovano Doerthe Tetzlaff Pertti Ala‐aho Jim Buttle Carl P. J. Mitchell Chris Soulsby 《水文研究》2018,32(20):3089-3107
Integrating stable isotope tracers into rainfall‐runoff models allows investigation of water partitioning and direct estimation of travel times and water ages. Tracer data have valuable information content that can be used to constrain models and, in integration with hydrometric observations, test the conceptualization of catchment processes in model structure and parameterization. There is great potential in using tracer‐aided modelling in snow‐influenced catchments to improve understanding of these catchments' dynamics and sensitivity to environmental change. We used the spatially distributed tracer‐aided rainfall‐runoff (STARR) model to simulate the interactions between water storage, flux, and isotope dynamics in a snow‐influenced, long‐term monitored catchment in Ontario, Canada. Multiple realizations of the model were achieved using a combination of single and multiple objectives as calibration targets. Although good simulations of hydrometric targets such as discharge and snow water equivalent could be achieved by local calibration alone, adequate capture of the stream isotope dynamics was predicated on the inclusion of isotope data in the calibration. Parameter sensitivity was highest, and most local, for single calibration targets. With multiple calibration targets, key sensitive parameters were still identifiable in snow and runoff generation routines. Water ages derived from flux tracking subroutines in the model indicated a catchment where runoff is dominated by younger waters, particularly during spring snowmelt. However, resulting water ages were most sensitive to the partitioning of runoff sources from soil and groundwater sources, which was most realistically achieved when isotopes were included in the calibration. Given the paucity of studies where hydrological models explicitly incorporate tracers in snow‐influenced regions, this study using STARR is an important contribution to satisfactorily simulating snowpack dynamics and runoff generation processes, while simultaneously capturing stable isotope variability in snow‐influenced catchments. 相似文献
138.
The rates and altitudes for the dissociation of atmospheric constituents of Titan are calculated for solar UV, solar wind protons, interplanetary electrons, Saturn magnetospheric particles, and cosmic rays. The resulting integrated synthesis rates of organic products range from 102–103 g cm?2 over 4.5 × 109 years for high-energy particle sources to 1.3 × 104 g cm?2 for UV at , and to 5.0 × 105 g cm?2 if (acting primarily on C2H2, C2H4, and C4H2) is included. The production rate curves show no localized maxima corresponding to observed altitudes of Titan's hazes and clouds. For simple to moderately complex organic gases in the Titanian atmosphere, condensation occurs below the top of the main cloud deck at 2825 km. Such condensates comprise the principal cloud mass, with molecules of greater complexity condensing at higher altitudes. The scattering optical depths of the condensates of molecules produced in the Titanian mesosphere are as great as ~ 102/(particulate radius, μm) if column densities of condensed and gas phases are comparable. Visible condensation hazes of more complex organic compounds may occur at altitudes up to ~ 3060 km provided only that the abundance of organic products declines with molecular mass no faster than laboratory experiments indicate. Typical organics condensing at 2900 km have molecular masses = 100–150 Da. At current rates of production the integrated depth of precipitated organic liquids, ices, and tholins produced over 4.5 × 109 years ranges from a minimum ~ 100 m to kilometers if UV at is important. The organic nitrogen content of this layer is expected to be ~ 10?1?10?3 by mass. 相似文献
139.
Carl L. Devito 《Astrophysics and Space Science》1996,244(1-2):357-369
Some recent astronomical observations [4], and a number of experiments in particle physics, seem to cast doubt on the validity of the standard linear model for time. These results raise two (at least) questions: (1) If time is not a linear continuum (i.e., if the standard model is incorrect), then why does this model work so well in so many areas of science? (2) Whatever the “true nature” of time is, are there any advantages, to science, in replacing the standard model with a more complicated one? The purpose of this paper is to present a non-linear, mathematical model for time that enables us to answer question (1), and to partially answer question (2). Our discussion of question (2) is incomplete, but our results are intriguing. They also show promise of helping us understand some of the observations mentioned above. A rather natural extension of our model brings it into close contact with one that has been used in quantum theory (“Stochastically branching spacetime topology” by Roy Douglas [2]). These points of contact will also be discussed. 相似文献
140.