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261.
How cold was it for Neanderthals moving to Central Europe during warm phases of the last glaciation?
Grzegorz Skrzypek Andrzej Wiśniewski Pauline F. Grierson 《Quaternary Science Reviews》2011,30(5-6):481-487
Precise estimates of mean annual temperature (MAT) for when Neanderthals occupied Central Europe are critical for understanding the role that climatic and associated environmental factors played in Neanderthal migrations and in their ultimate extinction. Neanderthals were continuously present in the relatively warm regions of southern and Western Europe in the Pleistocene but only temporarily settled Central Europe (CE), presumably because of its colder and less hospitable climate. Here, we present a new approach for more spatially and temporally accurate estimation of palaeotemperatures based on the stable oxygen isotope composition of phosphates extracted from animal teeth found at sites linked directly to concurrent Neanderthal occupation. We provide evidence that Neanderthals migrated along the Odra Valley of CE during warmer periods throughout the Upper Pleistocene. The MATs during these migrations were about 6.8 °C for the warm phase of Oxygen Isotope Stage OIS 5a–d (prior to the OIS4 cold event) at ~115–74,000 yr BP and about 6.3 °C during the early OIS 3 warm phase ~59–41,000 yr BP. Our results show that temperatures during these phases peaked 2–4 °C above longer term estimates from ice cores and pollen records. We argue that our approach can provide valuable insights into evaluating the role of climate in human migration patterns in the Pleistocene. 相似文献
262.
Andrzej J. Maciejewski Maria Przybylska Wojciech Szumiński 《Celestial Mechanics and Dynamical Astronomy》2017,127(2):163-184
In this paper we show that the anisotropic Kepler problem is dynamically equivalent to a system of two point masses which move in perpendicular lines (or planes) and interact according to Newton’s law of universal gravitation. Moreover, we prove that generalised version of anisotropic Kepler problem as well as anisotropic two centres problem are non-integrable. This was achieved thanks to investigation of differential Galois groups of variational equations along certain particular solutions. Properties of these groups yield very strong necessary integrability conditions. 相似文献
263.
Kacper Kotulak Adam Froń Andrzej Krankowski German Olivares Pulido Manuel Henrandez-Pajares 《Acta Geophysica》2017,65(1):13-28
In radioastronomy the interferometric measurement between radiotelescopes located relatively close to each other helps removing ionospheric effects. Unfortunately, in case of networks such as LOw Frequency ARray (LOFAR), due to long baselines (currently up to 1500 km), interferometric methods fail to provide sufficiently accurate ionosphere delay corrections. Practically it means that systems such as LOFAR need external ionosphere information, coming from Global or Regional Ionospheric Maps (GIMs or RIMs, respectively). Thanks to the technology based on Global Navigation Satellite Systems (GNSS), the scientific community is provided with ionosphere sounding virtually worldwide. In this paper we compare several interpolation methods for RIMs computation based on scattered Vertical Total Electron Content measurements located on one thin ionospheric layer (Ionospheric Pierce Points—IPPs). The results of this work show that methods that take into account the topology of the data distribution (e.g., natural neighbour interpolation) perform better than those based on geometric computation only (e.g., distance-weighted methods). 相似文献
264.
Recent investigations on the hypoplastic constitutive model for granular materials show that the failure surface can be surpassed by some stress paths. This is contradictory to the conventional definition of failure surface in plasticity, according to which the stress is allowed to move on the failure surface but never across it. In the present paper, the interrelations among the different constitutive models are discussed with special reference to failure and stability. For the hypoplastic constitutive equation, the accessible stress states and the stable stress states are found to be enclosed by a bound surface and a stability surface in the stress space, respectively. Theoretical findings about the bound surface and the stability surface are verified qualitatively by presenting results of triaxial tests on dry sand. © 1997 by John Wiley & Sons, Ltd. 相似文献
265.
Interpretation of tracer tests performed in fractured rock of the Lange Bramke basin, Germany 总被引:1,自引:1,他引:0
Two multitracer tests performed in one of the major cross-fault zones of the Lange Bramke basin (Harz Mountains, Germany)
confirm the dominant role of the fault zone in groundwater flow and solute transport. Tracers having different coefficients
of molecular diffusion (deuterium, bromide, uranine, and eosine) yielded breakthrough curves that can only be explained by
a model that couples the advective–dispersive transport in the fractures with the molecular diffusion exchange in the matrix.
For the scale of the tests (maximum distance of 225 m), an approximation was used in which the influence of adjacent fractures
is neglected. That model yielded nearly the same rock and transport parameters for each tracer, which means that the single-fracture
approximation is acceptable and that matrix diffusion plays an important role. The hydraulic conductivity of the fault zone
obtained from the tracer tests is about 1.5×10–2 m/s, whereas the regional hydraulic conductivity of the fractured rock mass is about 3×10–7 m/s, as estimated from the tritium age and the matrix porosity of about 2%. These values show that the hydraulic conductivity
along the fault is several orders of magnitude larger than that of the remaining fractured part of the aquifer, which confirms
the dominant role of the fault zones as collectors of water and conductors of fast flow.
Received, April 1997 Revised, January 1998, August 1998 Accepted, August 1998 相似文献
266.
Andrzej J. Maciejewski Marek Szydłowski 《Celestial Mechanics and Dynamical Astronomy》1999,73(1-4):17-24
We discuss specific properties of dynamical systems originating from cosmology and relativity. In particular, we present results
of our study of the Bianchi class A cosmological models. We introduce new variables in which the Hamiltonian constraint for
all the class A models is solved algebraically. We present results of dimension reduction of the investigated models.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
267.
268.
Andrzej A. Zdziarski Marek Gierliski A. R. Rao S. V. Vadawale Joanna Mikoajewska 《Monthly notices of the Royal Astronomical Society》2005,360(3):825-838
We present an exhaustive analysis of five broad-band observations of GRS 1915+105 in two variability states, χ and ω, observed simultaneously by the Proportional Counter Array (PCA) and High-Energy X-ray Timing Experiment (HEXTE) detectors aboard the Rossi X-ray Timing Explorer , and the Oriented Scintillation Spectrometer Experiment (OSSE) detector aboard the Compton Gamma-ray Observatory . We find all the spectra well fitted by Comptonization of disc blackbody photons, with very strong evidence for the presence of a non-thermal electron component in the Comptonizing plasma. Both the energy and the power spectra in the χ state are typical of the very high/intermediate state of black hole binaries. The spectrum of the ω state is characterized by a strong blackbody component Comptonized by thermal electrons and a weak non-thermal tail. We then calculate rms spectra (fractional variability as functions of energy) for the PCA data. We accurately model the rms spectra by coherent superposition of variability in the components implied by the spectral fits, namely a less variable blackbody and more variable Comptonization. The latter dominates at high energies, resulting in a flattening of the rms at high energies in most of the data. This is also the case for the spectra of the quasi-periodic oscillations present in the χ state. Then, some of our data require a radial dependence of the rms of the disc blackbody. We also study the distance to the source, and find d ≃ 11 kpc as the most likely value, contrary to a recent claim of a much lower value. 相似文献
269.
270.
A statistical model for estimating the accuracy of event location applied to a network of Scandinavian stations 总被引:1,自引:0,他引:1
A statistical model for estimating the errors of epicenter location and origin time is proposed and applied to the old Fennoscandian seismic network. An average crustal model (Sellevoll andPomeroy, 1968) and P and S wave residuals as a function of azimuth have been used. The calculations are carried out for different maximum detection ranges. The analysis shows relatively, small (1 km) standard errors of epicenter location of strong earthquakes for central Fennoscandia. The largest errors are found in the southern and eastern parts of Fennoscandia.On leave from Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland. 相似文献