An analysis of the derivation of Friedmann's Equation

In the introductive section a deeper specification is made of the physical meaning of the terms in the Friedmann Equation (FE). After that, assuming validity of Mach's Principle, it is deduced (Section 2) that the FE for the radiation-dominated phase of the evolution of the Universe (which is considered to be closed) is valid even for the matter-dominated era. On the other hand, such a form of the FE is shown to be irrelevant when used for deducing how the frequency of the 3K-photons depends on the radius of the Universe. The solution of the dilemma turns out to have its roots in the way in which the relativistic gravitational potentials are composed, together with the fact that the cosmic potential of the closed Universe is equal to –1. Consequently, the equation one uses for the matter-dominated era is shown to be proper for both the main phases of the cosmological evolution (Section 3). In Section 4, the deduction of the critical density-value is revised, and the new result shortly discussed. In Section 5 it is concluded that there is only one possible value for the maximum radius of our Universe, specific for the initial condition due to the FE. Nevertheless, it is not excluded that other smaller universes can exist. In the final section a modified soabubble analogy with the first law of thermodynamics is used to describe the dynamics of the cosmological expansion, and, in this context, the importance of Mach's Principle is pointed out.     

The Friedmann universe and the world potential

In Section 1 of the paper the energy equation of the Friedmann universe, when matter dominates over radiation, is discussed. It is known that the value of the world potential is constant everywhere in the Universe, despite the pulsation motion of the Universe or a possible transformation of pulsation energy into matter or vice versa. The condition for the Universe being closed is deduced. Furthermore, the possibility to define the mass-energy of the Universe is discussed; and the conclusion is arrived at that the mass-energy of the Universe relative to an observer in the non-metric space outside the Universe is equal to zero; i.e. the Universe originated as a vacuum fluctuation. Finally, the view-point of an external observer is described. Such an observer can claim that our closed Universe is a black hole in a non-metric empty space. Besides, the differences between such a black hole and the astrophysical black holes are indicated.In Section 2 the origin of the gravitational force retarding the expansion is discussed, using the properties of the relativistic gravitational potential. In contradiction to Section 1, the view-point of an inner observer (inside the Universe) is used here. It is concluded that the boundary of the closed Universe is an unlocalizable potential barrier.In Section 3 of the paper the apparent discrepancy between Mach's principle and the general theory of relativity is resolved. The solution is based on the fact that, for the Euclidean open universe, the concept of mass is related to the potential of the background equal to –1, but the concept of the mass-energy is related to the zero-potential of the non-metric background. Because the universe is open and a potential barrier (a boundary of the universe) can be localized-i.e. is geometrically existing — by solution of the field equation, we have to refer to the background with zero-potential. The principal idea of the solution is then that the zero-density means the density of mass-energy, when simultaneously the mass density is equal to the critical value for which the Robertson-Walker metric becomes the Euclidean metric of the Minkowski (i.e., flat) space-time. Further a generalization of Newton's law of inertia is formulated, and the properties of nullgeodesics are touched upon. As a conclusion it is stated that this paper and the two previous ones (see Voráek, 1979a, b)de facto express Mach's principle.     

On the nature of bright rims of filaments

A filament with a very bright rim was observed in the H line on May 11, 1989, using the Meudon spectroheliograph. Absolute calibration of the spectroheliogram allows us to express the intensities in particular sites of the filament, in its bright rim and inside the surrounding chromosphere. From a large number of photometric scans, we obtained a histogram of the intensity excess of the bright rim relative to the quiet chromosphere. The mean value of this excess amounts to about 4%. We present a theoretical explanation of bright rims, based on the nature of H radiative diffusion in the filaments. Computed NLTE model of the filament leads to a rim intensity excess which is in good agreement with our observations.     

European Observation Network: Ground - Based Support for Gamma-Ray Satellites

We present first preliminary results obtained with the European Observation Network consisting of 9 observatories in the Czech Republic, Germany and Bulgaria. We also discuss related problems such as the background of unknown variable stars and suggest a strategy for work in this area.     

Sedimentary geochemistry of core PG1351 from Lake El’gygytgyn—a sensitive record of climate variability in the East Siberian Arctic during the past three glacial–interglacial cycles

The ca. 13 m long sediment core PG1351, recovered in 1998 from the central part of Lake El’gygytgyn, NE Siberia, was investigated for lithostratigraphy, water content, dry bulk density (DBD), total organic carbon (TOC), total nitrogen (TN), total sulphur (TS) and biogenic silica (opal) contents, and for TOC stable isotope ratios (δ¹³C_TOC). The event stratigraphy recorded in major differences in sediment composition match variations in regional summer insolation, thus confirming a new age model for this core, which suggests that it spans the last 250 ka BP. Four depositional units of contrasting lithological and biogeochemical composition have been distinguished, reflecting past environmental conditions associated with relatively warm, peak warm, cold and dry, and cold but more moist climate modes. A relatively warm climate, resulting in complete summer melt of the lake ice cover and seasonal mixing of the water column, prevailed during the Holocene and Marine Isotope Stages (MIS) 3, 5.1, 5.3, 6.1, 6.3, 6.5, 7.1–7.3, 7.5, 8.1 and 8.3. MIS 5.5 (Eemian) was characterized by significantly enhanced aquatic primary production and organic matter supply from the catchment, indicating peak warm conditions. During MIS 2, 5.2, 5.4, 6.2 and 6.4 the climate was cold and dry, leading to perennial lake ice cover, little regional snowfall, and a stagnant water body. A cold but more moist climate during MIS 4, 6.6, 7.4, 8.2 and 8.4 is thought to have produced more snow cover on␣the perennial ice, strongly reducing light penetration and biogenic primary production in␣the lake. While the cold–warm pattern during␣the past three glacial–interglacial cycles is probably controlled by changes in regional summer insolation, differences in the intensity of the warm phases and in the degree of aridity (changing snowfall) during cold phases likely were due to changes in atmospheric circulation patterns. This is the seventh in a series of eleven papers published in this special issue dedicated to initial studies of El'gygytgyn Crater Lake and its catchment in NE Russia. JulieBrigham-Grette, Martin Melles, Pavel Minyuk were guest editors of this special issue.     

Are the crustal and mantle conductive zones isotropic or anisotropic?

One of the significant problems of modern deep magnetotellurics is the recognition of anisotropy in the crustal and mantle conductive zones. In the paper we perform numerical experiment comparing several 2D models of crustal and mantle isotropic and anisotropic prismatic conductors. Anisotropy is modeled by alternating horizontal or vertical thin layers of different resistivities (the vertical layers are parallel to the prism strike). Using these models, we examine conditions under which the magnetotelluric and magnetovariational response functions distinguish between isotropy and anisotropy. The resolution of MT and MV studies depends on the sediments conductance, lithosphere resistance and deep conductor width. Calculations show that the most favorable conditions for anisotropy studies are observed in the active regions characterized by small sediments conductance (10–20 S) and moderate lithosphere resistance (10⁸ Ohm·m²). However, in the stable regions, where sediments conductance exceeds 50–100 S and the lithosphere resistance comes up to 10⁹ Ohm·m², the crustal and mantle anisotropic and isotropic conductors manifest themselves in the equivalent magnetotelluric and magnetovariational functions, which cannot distinguish between anisotropy and isotropy and admit both the interpretations.     

Biochemical characteristics of alga-bacterial mats and invertebrates from shallow-water hydrothermal fields of the West Pacific Ocean

In this study we assessed the biochemical adaptations of biotic specimens from the hydrothermal vent fields from different geographical zones. Algabacterial and bacterial mats and specimens of bivalves (9 species) and sea urchins (2 species) from different coastal shallow-water fields of hydrothermal activity along the West Rift zones of the Pacific Ocean were sampled to compare biochemical activities to volcanogenic chemical characteristics. The algabacterial and bacterial mat cells and subcellular fractions of bivalve gills and sea urchin guts were measured for 5-aminolevulinic acid (ALA), cytochromes b, (c + c₁), (a + a₃) and P450 (CYP), and activities of ALA synthetase and CYP-dependent aminopyrine N-demethylase (APND). The algabacterial mats from the Kuril Islands and New Zealand displayed comparable ALA and cytochrome levels and enzyme activities. Similar ALA synthesis, APND activity, and levels of cytochromes b and (c + c₁) were observed in bacterial mats from hydrothermal fields from Kuriles, New Britain Island and New Zealand. More active ALA synthesis, APND activity and enhanced content of cytochromes b and (c + c₁) and lower levels of CYP were found in bacterial mats than in algabacterial mats. Further, all bivalves influenced by hydrothermal discharges had elevated CYP levels and APND activity as well as a significant increase in ALA content and ALA synthesis (P < 0.05). Statistically sufficient (P < 0.05) alterations in ALA synthesis, APND activity and total CYP level were found in sea urchins under hydrothermal influence. Our findings contribute to the global assessment of hydrothermal effluents on biota and indicate that living conditions near hydrothermal vents accelerate metabolism of bivalves and sea urchins in examined hydrothermal zones in the northern and southern West Pacific Ocean.     

The dynamical evolution of stellar superclusters

Recent images taken with the Hubble Space Telescope ( HST ) of the interacting disc galaxies NGC 4038/4039 (the Antennae) reveal clusters of many dozens and possibly hundreds of young compact massive star clusters within projected regions spanning about 100 to 500 pc. It is shown here that a large fraction of the individual star clusters merge within a few tens to a hundred Myr. Bound stellar systems with radii of a few hundred parsecs, masses ≲ 10⁹ M⊙ and relaxation times of 10¹¹ − 10¹² yr may form from these. These spheroidal dwarf galaxies contain old stars from the pre-merger galaxy and much younger stars formed in the massive star clusters, and possibly from later gas accretion events. The possibility that star formation in the outer regions of gas-rich tidal tails may also lead to superclusters is raised. The mass-to-light ratio of these objects is small, because they contain an insignificant amount of dark matter. After many hundred Myr such systems may resemble dwarf spheroidal satellite galaxies with large apparent mass-to-light ratios, if tidal shaping is important.     

Radial Velocities of Six Early Type Evolved Stars

Many early-type main sequence stars are known spectroscopic binaries, while early type spectroscopic binaries with evolved components are rather rare and well-determined masses are available only in some cases. For this reason a program to study stars with suspected variable velocity among early-type evolved stars has been initiated some time ago. In the present paper 54 coudé spectra for a sub-group formed of six early-type stars, namely HD 7902, HD 28446, HD 42087, HD 187983, HD 195592 and HD 208501 have been measured and the results of these plates have been presented.     

Finding the shape of a local heterogeneity by means of a structural inversion with constraints

Various aspects of structural inversion are considered. The aim of the inversion is limited to finding the shape of an isolated 2D homogeneous body, although the technique may be generalized to the case of interfaces with steep fragments, faults or overhangs. The unknown parameters are shifts of border points. The shift directions can be normal to the initial heterogeneity configuration or to another contour. Medium properties (seismic velocities, densities, etc.) within the heterogeneity are assumed to be known. The optimal shape is determined iteratively, a quadratic objective function being minimized at each iteration with the conjugate‐gradient method. Special attention is paid to preventing self‐intersections, for which purpose each unknown parameter is forced to lie within a certain predetermined interval. In order to achieve this, the classical conjugate‐gradient method has been modified accordingly. Three numerical examples are considered. These illustrate how the developed technique can be applied to different practical problems. The first example is devoted to monitoring an oil/steam interface by gravity gradiometry measurements. In the second example, a cross‐hole seismic experiment is simulated. It is shown that a structural inversion can restore the configuration of a local body much more accurately than traditional seismic tomography. In the third example, the shape of a salt dome is reconstructed by joint inversion of refracted traveltimes and gravity measurements. This example demonstrates how different kinds of data, used simultaneously in a structural inversion, can complement each other.