Spherically symmetric cosmological perturbations in the de Donder gauge

Cosmological perturbations on a F-R-W background are considered in a modified de Donder gauge. To guarantee the energy-momentum conservation for the perturbations in the de Donder gauge a compatibility condition is obtained. Finally we present the basic equations for the propagation of spherically symmetric perturbations. These equations are the basis for investigating the influence of cosmological epoches on the growing of density contrasts.     

Mechanical and microseismic characteristics of sandstones subject to moderate low-frequency differential cyclic loading (DCL) followed by monotonic loading up to failure

Acta Geotechnica - This work aims to experimentally investigate the behaviour of sandstone drilled from an underground coal mine exposed to low-frequency cyclic loading with distinct...     

Characteristics and generation mechanisms of key infrared radiation signals during damage evolution in sandstone

Acta Geotechnica - Infrared radiation count (IRC) is considered as an indicator for damage evolution of rocks. This new indicator links damage intensity and corresponding infrared radiation...     

Winter-to-spring temperature dynamics in Turkey derived from tree rings since AD 1125

In the eastern Mediterranean in general and in Turkey in particular, temperature reconstructions based on tree rings have not been achieved so far. Furthermore, centennial-long chronologies of stable isotopes are generally also missing. Recent studies have identified the tree species Juniperus excelsa as one of the most promising tree species in Turkey for developing long climate sensitive stable carbon isotope chronologies because this species is long-living and thus has the ability to capture low-frequency climate signals. We were able to develop a statistically robust, precisely dated and annually resolved chronology back to AD 1125. We proved that variability of δ¹³C in tree rings of J. excelsa is mainly dependent on winter-to-spring temperatures (January–May). Low-frequency trends, which were associated with the medieval warm period and the little ice age, were identified in the winter-to-spring temperature reconstruction, however, the twentieth century warming trend found elsewhere could not be identified in our proxy record, nor was it found in the corresponding meteorological data used for our study. Comparisons with other northern-hemispherical proxy data showed that similar low-frequency signals are present until the beginning of the twentieth century when the other proxies derived from further north indicate a significant warming while the winter-to-spring temperature proxy from SW-Turkey does not. Correlation analyses including our temperature reconstruction and seven well-known climate indices suggest that various atmospheric oscillation patterns are capable of influencing the temperature variations in SW-Turkey.     

A Fundamental Plane of Black Hole Activity: Pushing Forward the Unification Scheme

We examine the disc-jet connection in stellar mass and supermassive black holes by investigating the properties of their compact emission in the hard X-ray and radio bands. We compile a sample of ∼100 active galactic nuclei with measured mass, 5 GHz core emission, and 2–10 keV luminosity, together with eight galactic black holes with a total of ∼50 simultaneous observations in the radio and X-ray bands. Using this sample, we study the correlations between the radio (L_R) and the X-ray (L_X) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with both M and L_X, at a highly significant level. We show how this result can be used to extend the standard unification by orientation scheme to encompass unification by mass and accretion rate.     

Asymmetry and variations of solar limb darkening along the diameter defined by diurnal motion in April 1981

Unexpected asymmetries and variations, which showed up in the first, preliminary reductions of new limb-darkening observations made in June 1986, near the present minimum of solar activity, stimulated a re-analysis of our limb-darkening observations made in April 1981 at Kitt Peak (Neckel and Labs, 1984). The results seem to indicate rather definitely that the intensity distribution across the disk varies at all observed wavelengths between 3300 and 6600 Å with amplitudes in the order of 1–2 % and time-scales from minutes to hours. Asymmetries in the intensity distribution with respect to the disk center are a frequent phenomenon. There can be no doubt, that also the absolute disk center intensity undergoes variations with comparable size and modulation, as they were in fact recently observed by Koutchmy and Lebecq (1986). Presumably, the solar oscillations contribute a significant part to the observed effects. However, due to the 5–7 min periodicity of our observations no definite conclusions can be drawn.Examples for widely differing limb darkening curves - at the same wavelength! - are given in Figure 7. Figure 8 illustrates the variations in time by exhibiting the differences between (north-) western and (south-) eastern radius for a larger number of selected, successive scans, regardless of wavelength. Figure 9 displays some differences between observed limb-to-limb distributions and special, symmetric reference curves.