欧洲和远东第四纪陆相堆积的生物地层对比(哺乳动物)

在晚第三纪晚期和第四纪时,欧亚大陆古动物群的面貌受两个陆桥的影响很大,在尽西边有一个复合陆桥,即非洲与欧洲相连,与亚洲沿着非洲西边—伊比利亚半岛连接;中间的非洲—西西里岛陆桥和一个东地中海陆桥(非洲—阿拉伯半岛)连接。     

Kristallisationsschieferung oder Abbildungskristalloblastese?

Ohne Zusammenfassung     

What do streamers in the dust tail tell about the cometary nucleus?

The interrelations between the physical parameters of a cometary nucleus, and the morphology of the dust tail and its streamers are systematically investigated by means of a model developed by Beißer (1990a), involving a rotating nucleus. The analysis of streamers in the tail, using direct modeling and synchrone grids, provides a suitable tool to deduce substantial informations on the nucleus' state of rotation. Opportunities and limitations of this analysis are discussed. Dust emission parameters like the distribution of active regions on the nucleus, or the emission characteristics can only be determined if certain other physical properties of the nucleus have been independently measured before.     

An object within a particle of extraterrestrial origin compared with an object of presumed terrestrial origin

Filamentary objects of submicron size isolated from an extraterrestrial particle and from the Gunflint cherts are compared and shown to have similarities of size, shape and interior structure.     

Binarity of the red-rectangle and other extremely fe-poor (post?)-AGB stars

We present radial velocity measurements proving the binary nature of all the known extremely Fe-deficient Post-ABG stars including HD 44179, the central star of the well known but poorly understood Red-Rectangle nebula. With the observed orbital parameters, it is more likely that the stars represent a particular stage in binary evolution, rather than a typical post-AGB evolutionary stage.     

Algorithms for Stellar Perturbation Computations on Oort Cloud Comets

We investigate different approximate methods of computing the perturbations on the orbits of Oort cloud comets caused by passing stars, by checking them against an accurate numerical integration using Everhart’s RA15 code. The scenario under study is the one relevant for long-term simulations of the cloud’s response to a predefined set of stellar passages. Our sample of stellar encounters simulates those experienced by the Solar System currently, but extrapolated over a time of 10¹⁰ years. We measure the errors of perihelion distance perturbations for high-eccentricity orbits introduced by several estimators – including the classical impulse approximation and Dybczyński’s (1994, Celest. Mech. Dynam. Astron. 58, 1330–1338) method – and we study how they depend on the encounter parameters (approach distance and relative velocity). We introduce a sequential variant of Dybczyński’s approach, cutting the encounter into several steps whereby the heliocentric motion of the comet is taken into account. For the scenario at hand this is found to offer an efficient means to obtain accurate results for practically any domain of the parameter space.     

Principal oscillation pattern analysis of the 30- to 60-day oscillation in the tropical troposphere

The Principal Oscillation Pattern technique is used to derive an index of the 30- to 60-day oscillation in the tropical troposphere. In the 200-mb equatorial velocity potential field, one dominant pair of POPS is found. Its properties compare very well with the properties of the oscillation identified in previous studies. In particular, a good correlation between the time evolution of the POP coefficients and area-averaged outgoing long-wave radiation (ORL) is found. The POPS are derived from a 2-year subinterval of the whole 5-year data set. This leaves independent data for subsequent verification. The patterns and their characteristic numbers are almost unchanged if the whole data set is analysed. Also, the analysis is insensitive to changes of the analysis area: if the analysis is limited to 90°-longitude equatorial sectors, the signal is also identified and its patterns are consistent with the patterns derived from the full data set. Interestingly, the signal is best defined in the eastern hemisphere. The POPS may be used to derive associated correlation patterns of other quantities in winter and summer separately. The path of the oscillation has a marked annual cycle: in northern winter it migrates from the Indian Ocean across northern Australia into the region of the South Pacific Convergence Zone (SPCZ) and in northern summer it moves from the Indian Ocean across South Asia along the intertropical Convergence Zone (ITCZ) to South America. The POP coefficient may be seen as a bivariate index of the state (phase and strength) of the 30- to 60-day oscillation. Since the POP technique incorporates a prediction equation for the phase of the POP coefficients, the POP model allows for the prediction of the complex amplitude of the oscillation. In a sequence of forecast experiments, of which about two-thirds used independent data, the POP forecasts were found to be useful in about half of all cases for lead times of several days. The correlation and RMS skills were calculated for the POP forecast and for persistence. The POP forecast appears to be considerably better with respect to both measures. The correlation skill scores 60% after 7 days. The POP forecast is most skillful in northern winter and if strong signals are present with minima of velocity potential in the eastern hemisphere.     

Leptonic jets from young stellar objects?

Various explanations of the bipolar-flow phenomenon in star-forming regions are compared and confronted with the observed facts. It is concluded that stellar-wind interpretations are inconsistent with the constraints. The exotic property of young stellar objects may be their extreme spin which implies strong magnetic fields and vacuum discharges above thee ^± pair-formation threshold (of 10¹² eV). Pair-plasma jets are thought to be centrifugally driven by young stars during their first 10^4±1 years of rapid rotation.