Bayesian active learning for parameter calibration of landslide run-out models

Landslides - Landslide run-out modeling is a powerful model-based decision support tool for landslide hazard assessment and mitigation. Most landslide run-out models contain parameters that cannot...     

Passive Seismic Experiment “13 BB Star” in the Margin of the East European Craton,Northern Poland

The lithosphere-asthenosphere boundary (LAB) is investigated recently very effectively, mostly using seismic methods because of their deep penetration and relatively good resolution. The nature of LAB is still debated, particularly under “cold” Precambrian shields and platforms. Passive experiment “13 BB star” is dedicated to study deep structure of the Earth’s interior in the marginal zone of the East European craton in northern Poland. The seismic network consists of 13 broadband stations on the area of ca. 120 km in diameter. The network is located in the area of well-known sedimentary cover and crustal structure. Good records obtained till now, and expected during next 1-year long recording campaign, should yield images of detailed structure of the LAB, ?410”, “?520”, and ?660” km discontinuities, as well as mantle-core boundary and inner core.     

Monitoring ionospheric scintillations and TEC at the Polish Polar Station on Spitsbergen: instrumentation and preliminary results

As a partial contribution to the International Polar Year, the Space Research Centre of the Polish Academy of Sciences has installed on the Polish Polar Station, located in the region of the Hornsund Bay in southern Spitsbergen, the equipment intended to monitor ionospheric scintillation and total electron content. We describe the equipment setup and the aims of the experiment. As an illustration of data analysis, we present the reconstruction of irregular structure of the ionosphere from the complex amplitude data, and the estimate of the form and drift of diffraction pattern based on the spaced receiver measurements.     

Spacetime is not just space and time

Our physical intuition usually separates space from time, ignoring the spacetime character of the physical reality. In strongly curved spacetimes this may lead to confusion and paradoxes. I present here two examples: (1) in the non-static cosmological spacetimes with flat space sections, the cosmological expansion of space is a true physical effect. Contrary to what the intuition imagines, it cannot be explained as a motion of matter in a non-expanding flat space. (2) Contrary to intuition, for static spacetimes the mathematically simplest 3+1 split is not given by the direct projection as in the standard ADM scheme. The simplest split is defined by a counter intuitive “optical geometry” that redshifts both space and time by the same conformal factor.     

A structure and energy dissipation efficiency of relativistic reconfinement shocks

We present a semi-analytical hydrodynamical model for the structure of reconfinement shocks formed in astrophysical relativistic jets interacting with external medium. We take into account exact conservation laws, both across the shock front and in the zone of the shocked matter, and exact angular relations. Our results confirm a good accuracy of the approximate formulae derived by Komissarov & Falle. However, including the transverse pressure gradient in the shocked jet, we predict an absolute size of the shock to be about twice larger. We calculate the efficiency of the kinetic energy dissipation in the shock and show a strong dependence on both the bulk Lorentz factor and opening angle of the jet.     

Varying Fundamental Constants: A Dynamical Systems Approach

Theory of dynamical systems offers a possibility of investigating the space of all possible solutions. In the context of simple cosmological models such like Varying Speed of Light Friedman-Robertson-Walker (VSL FRW) models there exists a systematic method of reducing field equations to certain two-dimensional dynamical system. One of the features of this reduction is the possibility of representing the model as a Hamiltonian system in which the properties of the potential function V(X) can serve as a tool for qualitative classification of possible evolutions of a(t). Some important features like resolution of the flatness problem, existence of event horizons near the singularity can be visualized as domains on the phase-space. Then one is able to see how large is the class of solutions (labelled by the initial conditions) leading to the desired property. This revised version was published online in July 2006 with corrections to the Cover Date.