PALAEORUNOFF FROM LAKE LADOGA TO THE BALTIC SEA DURING THE HOLOCENE

The article presents the results of the palaeohydrological analysis of the river system reorganization in the North-West of Russia, the Karelian Isthmus. This study aimed at the hydrological calculation of the runoff through the Heinjoki water connection of Lake Ladoga, the Gulf of Finland and PalaeoVuoksa during different periods of the Holocene. The methods of the equation of water balance, hydraulic-morphometric dependencies and the method of geographical analogy were used in this research. The main result of the carried work is the refinement of the existing regional flow model. In particular, the role of the Heinjoki Strait and the Neva River channel in different stages of the Holocene is considered. The authors came to the conclusion that Lake Ladoga always had a runoff to the Baltic Sea. It is shown that most probably in the period of 10,200-3,500 years ago the runoff was carried out through the Heinjoki waterway. The study underlines that the isostatic factor played a significant role in the forming of the water flow. The change in the runoff direction from the Heinjoki waterway to the Neva River is mainly related to the isostatic uplift of the Karelian Isthmus and the northern part of Lake Ladoga. Quantitative parameters of the Heinjoki palaeoflow (flow rate, annual runoff, runoff layer, runoff coefficient) seem to be roughly equivalent to the modern parameters of the flow of the Neva River. The article is dedicated to our colleague, a talented geographer and teacher, PhD Oleg Borisovich Averichkin (1979-2010) who first performed the calculations of the paleorunoff of Lake LadogaThe article presents the results of the palaeohydrological analysis of the river system reorganization in the North-West of Russia, the Karelian Isthmus. This study aimed at the hydrological calculation of the runoff through the Heinjoki water connection of Lake Ladoga, the Gulf of Finland and PalaeoVuoksa during different periods of the Holocene. The methods of the equation of water balance, hydraulic-morphometric dependencies and the method of geographical analogy were used in this research. The main result of the carried work is the refinement of the existing regional flow model. In particular, the role of the Heinjoki Strait and the Neva River channel in different stages of the Holocene is considered. The authors came to the conclusion that Lake Ladoga always had a runoff to the Baltic Sea. It is shown that most probably in the period of 10,200-3,500 years ago the runoff was carried out through the Heinjoki waterway. The study underlines that the isostatic factor played a significant role in the forming of the water flow. The change in the runoff direction from the Heinjoki waterway to the Neva River is mainly related to the isostatic uplift of the Karelian Isthmus and the northern part of Lake Ladoga. Quantitative parameters of the Heinjoki palaeoflow (flow rate, annual runoff, runoff layer, runoff coefficient) seem to be roughly equivalent to the modern parameters of the flow of the Neva River. The article is dedicated to our colleague, a talented geographer and teacher, PhD Oleg Borisovich Averichkin (1979-2010) who first performed the calculations of the paleorunoff of Lake Ladog

Using the nonlinear layer model for estimation of characteristics of high-power ultrashort laser pulse beams propagating along an aerospace path

The propagation of high-power ultrashort laser pulses on aerospace paths when laser radiation is sent from the Earth into space is analyzed theoretically. Titanium-sapphire and CO2 lasers with femtosecond and picosecond pulse durations, respectively, are considered as radiation sources. The effective intensity and effective radius of curvature of the wavefront of high-power laser beams are estimated on the basis of the nonlinear layer model. It is shown that, on the whole, the use of a CO2 laser makes it possible to achieve more precise focusing of radiation on an object during energy transfer under the conditions of power losses caused by strong molecular absorption. Also, more precise focusing on aerospace paths up to 400 km long is ensured by the use of a laser beam with a lower peak power and a larger initial radius

Condition for stopping the collapse of high-power femtosecond laser pulses during propagation through an optical medium

An intensity collapse stopping criterion is determined in the approximation of the nonlinear Schrödinger equation for the problem of self-focusing of high-power femtosecond laser radiation in an optical medium. Using propagation of a femtosecond laser pulse in air as an example, it is shown that the collapse stops when the role of diffraction increases due to a decrease in the laser beam radius, and this occurs not at a point, but in a segment before a nonlinear focus, where the radiation self-phase modulation due to the plasma nonlinearity prevails over the Kerr effect. The result (collapse stopping criterion) makes it possible to take into account nonlinear effects of optical media during propagation of high-power femtosecond laser pulses through them. In particular, the role of nonlinear absorption is determined under the conditions considere

Numerical simulations of self-channeling and filamentation of spatially pre-modulated high-power femtosecond laser pulse in air

The numerical simulations of propagation of high-power femtosecond laser pulses in air under conditions of superposed spatial phase modulation are carried out on the basis of the reduced form of nonlinear Schrцdinger equation for time-averaged electric field envelope. Initial spatial modulations are applied to pulse wavefront profiling by a staggered phase mask with variable phase jumps between adjacent elements. It is shown that with specific phase modulations, the pulse filamentation region in air can be markedly shifted further and elongated compared to a non-modulated pulse

Propagation of high-power phase-modulated femtosecond laser pulses in air in the self-channeling and filamentation modes

Propagation of high-power phase-modulated femtosecond laser pulses in air is simulated numerically. Spatial modulation of the initial wavefront of the pulse was implemented using a programmable phase mask consisting of checkered zones with a varied phase jump of the wave. Within the framework of the numerical solution of the nonlinear Schrödinger equation for the time-averaged amplitude of the electric field, modes of self-focusing, filamentation, and postfilamentation channeling of radiation for phase-modulating masks with different phase shifts at boundaries of adjacent segments are studied. It is shown that for certain types of phase modulation of the pulse the filamentation domain in air can be significantly shifted (in the coordinate) and elongated as compared with a nonmodulated pulse. In addition, it is established that using phase modulation makes it possible to decrease angular divergence of high-intensity light channels forming at the stage of postfilamentation propagation. This provides the possibility of radiation self-channeling at distances multiple exceeding the Rayleigh length

Self-channeling of spatially modulated femtosecond laser beams in the post-filamentation region

The propagation of high-intensity femtosecond laser pulses in air under conditions of superposed spatial phase modulation is considered theoretically. The numerical simulations are carried out on the basis of the reduced form of a nonlinear Schrödinger equation for a time-averaged electric field envelope. Initial spatial modulations are applied to pulse wavefront profiling by a staggered (TEM22) phase plate, which is simulated numerically. The dynamics of laser pulse self-focusing, filamentation, and post-filamentation self-channeling after the phase plates with variable phase jumps is studied. We show that, with specific phase modulations, the pulse filamentation region in air can be markedly shifted further and elongated compared with a nonmodulated pulse. Moreover, during the post-filamentation propagation of spatially structured radiation, the highly localized light channels are formed, possessing enhanced intensity and reduced angular divergence, which enables post-filamentation pulse self-channeling on the distance multiple exceeding the Rayleigh range

Manipulation of femtosecond laser filamentation by wire mesh amplitude mask

The results of numerical simulation on the propagation of high-power femtosecond laser pulses in air under conditions of the amplitude modulation are presented. Laser pulse amplitude modulation is realized by using the metal mesh-masks, which divide the initial laser beam into lower-energy parts (subbeams). We show that, in general, the beam energy partitioning by metal meshes reduces the total length of beam filamentation region in air, whereas the longitudinal continuity of the laser plasma distribution in the filaments is considerably improved. A strong dependence of the filamentation region parameters (starting coordinate, length, longitudinal continuity) on the position of the mesh-mask relative to the laser beam axis is also revealed. It turns out that under certain conditions, when the beam axis points to the mesh crossing, the spatial position of the filaments can be shifted further along the propagation path by increasing the size of the mesh cells. Alternatively, if the beam center exposes the mesh cell opening, the filamentation start coordinate decreases monotonically when the mesh becomes sparser. Additionally, the parameters of the filamentation region exhibit high sensitivity to the mesh wire thickness that can dominate the influence of mesh position and cell size

Unusual biochemistry of changes in neuron membrane permeability evoked by cAMP

AbstractInfluence of different metabolic poisons on cAMP-evoked neuron membrane permeability is investigated. Drugs preventing cAMP binding with R subunits of protein kinase decrease the cAMP-evoked current, but the inhibitor of the C subunit, H8, has no effect. The cAMP-dependent current is increased by uncouplers and decreased by inhibitors of glycolysis and oxidative phosphorylation. The mechanism of cAMP action on neuron permeability is discussed