Modeling of cometary evolution by kinetic theory: Method and first results

Physical evolution of Jupiter family (JF) comets is considered as a simultaneous process of erosion and fading. Dynamical effects are limited to discrete changes of the perihelion distance, that result in changes of the evaporation rate. Assuming that the JF comet population is in a steady state, a distribution function of this population in the two dimensional phase space consisting of radius and active fraction of the nucleus surface is found as the solution of a set of kinetic equations, each one of them for a different perihelion distance. With use of the distribution function some statistical properties of the comet population, like the total number of comets in the considered region of the phase space, the number of objects that evaporate or get dormant per unit time, etc., are obtained. The cumulative distribution function with respect to the absolute brightness is calculated and compared with the observed one as a check on the considered models.     

The recession of the Inland Ice margin during the Holocene climatic optimum in the Jakobshavn Isfjord area of West Greenland

Recent subsurface mapping of parts of the Greenland Inland Ice margin in the region of Jakobshavn Isbræ indicates that the fjord system in the period of at least 2700–4700 calendar yr B.P. was more ice free than at present, and that the front of the glacier was at least 15 km behind the present position. The ¹⁴C-dating of subfossils brought to the present ice margin fit with the climatic records from ice cores and confirm the favourable conditions for Greenland's first settlers, the Sarqaq people, who arrived in the region about 400 yr ago to find hunting grounds 10–20% larger than the present.     

Continuum model and analysis of wick-drained systems

An equivalent homogeneous continuum theory is developed for modelling discretely drained soil stratum. The model accounts for the local horizontal flow to discrete vertical drains such as wick or sand or stone columns as well as direct vertical drainage of the soil and global horizontal flow due to non-uniform horizontal conditions. Calibration curves for the model are presented for the case of no soil smear due to the drain installation and for the case when smear exists. The model is implemented in both analytical and finite element analyses for those cases where no well resistance is present and when it is of importance. The accuracy and applicability of the model is demonstrated for simple one- and two- layered problems including smear and well resistance.     

The dynamical behaviour of aN-shell model for an expanding universe

We consider a homogeneous expanding universe consisting of dust which is represented byN concentric massive spherical shells. We assume an explosive perturbation of the innermost shell at some instant of time. The effect of shell crossing and exchange of energy is investigated by deriving the equations of motion and obtaining their stationary and quasi-stationary solutions. Existing equilibrium stages and the density distribution for theN-shell system are discussed. Gravodynamics is a primary source for an understanding of gravitational clustering.     

The Mbale meteorite shower

Abstract— On 1992 August 14 at 12:40 UTC, an ordinary chondrite of type L5/6 entered the atmosphere over Mbale, Uganda, broke up, and caused a strewn field of size 3 × 7 km. Shortly after the fall, an expedition gathered eye witness accounts and located the position of 48 impacts of masses between 0.1 g and 27.4 kg. Short-lived radionuclide data were measured for two specimens, one of which was only 12 days after the fall. Subsequent recoveries of fragements has resulted in a total of 863 mass estimates by 1993 October. The surfaces of all fragments contain fusion crust. The meteorite shower caused some minor inconveniences. Most remarkably, a young boy was hit on the head by a small specimen. The data are interpreted as to indicate that the meteorite had an initial mass between 400–1000 kg (most likely ～1000 kg) and approached Mbale from Az = 185 ± 15, H = 55 ± 15, and V_∞ = 13.5 ± 1.5/s. Orbital elements are given. Fragmentation of the initial mass started probably above 25 km altitude, but the final catastrophic breakup occurred at an altitude of 10–14 km. An estimated 190 ± 40 kg reached the Earth's surface minutes after the final breakup of which 150 kg of material has been recovered.     

On the Possibility for Action Conservation in the Solar Cycle

The sunspot series are investigated in detail by use of a wavelet transform. By simple arguments, we present a reduced sunspot time-series, which can be argued to be approximately proportional to the magnetic flux density at the coronal surface. This reduced sunspot index correctly reproduces the (average) 22 year solar cycle. Closer scrutiny of the sunspot variation shows that the frequency of the solar cycle and the energy in the magnetic field vary consistently with conservation of action, i.e., energy divided by frequency. The analysis is based on the available data beginning with the year 1700, and analyzed by a wavelet transform. The present results relate to observations reported previously in the literature.