5,199 research outputs found
Eccentric Contraction-Induced Muscle Fibre Adaptation
Hard-strength training induces strength increasing and muscle damage, especially after eccentric contractions. Eccentric contractions also lead to muscle adaptation. Symptoms of damage after repeated bout of the same or similar eccentrically biased exercises are markedly reduced. The mechanism of this repeated bout effect is unknown. Since electromyographic (EMG) power spectra scale to lower frequencies, the adaptation is related to neural adaptation of the central nervous system (CNS) presuming activation of slow-non-fatigable motor units or synchronization of motor unit firing. However, the repeated bout effect is also observed under repeated stimulation, i.e. without participation of the CNS. The aim of this study was to compare the possible effects of changes in intracellular action potential shape and in synchronization of motor units firing on EMG power spectra. To estimate possible degree of the effects of central and peripheral changes, interferent EMG was simulated under different intracellular action potential shapes and different degrees of synchronization of motor unit firing. It was shown that the effect of changes in intracellular action potential shape and muscle fibre propagation velocity (i.e. peripheral factors) on spectral characteristics of EMG signals could be stronger than the effect of synchronization of firing of different motor units (i.e. central factors)
Recent trends in state of landscapes and shoreline dynamics in the Bulgarian sector of the Black Sea
The article analyzes the contemporary processes of natural and human-induced shore- line dynamics between cape Kaliakra and cape Emine, Bulgarian Black Sea coastal zone. Main accent is put on the anthropogenic impact on beach morphodynamics, coastal erosion, sediment transport and accretion influenced by land use changes and technogenic load. The stages of recent landscape transformations since the beginning of the XX century are discussed chronologically. Assumptions are made with reference to existing relationships among coastal geomorphic processes, land use dynamics, levels of anthropogenization and coastal landscape change at the investigated area.ΠΡΠΎΠ°Π½Π°Π»ΠΈΠ·ΠΈΡΠΎΠ²Π°Π½ΠΎ ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΡΠ΅ ΠΏΡΠΎΡΠ΅ΡΡΡ Π΅ΡΡΠ΅ΡΡΠ²Π΅Π½Π½ΠΎΠΉ ΠΈ ΠΏΠΎΠ΄Π²Π΅ΡΠΆΠ΅Π½Π½ΠΎΠΉ Π°Π½ΡΡΠΎΠΏΠΎΠ³Π΅Π½Π½ΠΎΠΌΡ Π²Π»ΠΈΡΠ½ΠΈΡ Π΄ΠΈΠ½Π°ΠΌΠΈΠΊΠΈ Π±Π΅ΡΠ΅Π³ΠΎΠ²ΠΎΠΉ Π»ΠΈΠ½ΠΈΠΈ ΠΌΠ΅ΠΆΠ΄Ρ ΠΌΡΡΠΎΠΌ ΠΠ°Π»ΠΈΠ°ΠΊΡΠ° ΠΈ ΠΌΡΡΠΎΠΌ ΠΠΌΠΈΠ½Π΅ Π½Π° Π±ΠΎΠ»Π³Π°ΡΡΠΊΠΎΠΌ ΠΏΠΎΠ±Π΅ΡΠ΅ΠΆΡΠ΅ Π§Π΅ΡΠ½ΠΎΠ³ΠΎ ΠΌΠΎΡΡ. ΠΡΠ½ΠΎΠ²Π½ΠΎΠ΅ Π²Π½ΠΈΠΌΠ°Π½ΠΈΠ΅ ΡΠ΄Π΅Π»Π΅Π½ΠΎ Π²ΠΎΠ·Π΄Π΅ΠΉΡΡΠ²ΠΈΡ Π°Π½ΡΡΠΎΠΏΠΎΠ³Π΅Π½Π½ΡΡ
ΡΠ°ΠΊΡΠΎΡΠΎΠ² Π½Π° Π±Π΅ΡΠ΅Π³ΠΎΠ²ΡΡ ΠΌΠΎΡΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΠΊΡ, ΠΏΡΠΈΠ±ΡΠ΅ΠΆΠ½ΡΡ ΡΡΠΎΠ·ΠΈΡ, ΡΡΠ°Π½ΡΠΏΠΎΡΡΠΈΡΠΎΠ²ΠΊΡ ΠΈ Π°ΠΊΠΊΡΠΌΡΠ»ΡΡΠΈΡ ΠΎΡΠ°Π΄ΠΊΠΎΠ² ΠΏΠΎΠ΄ Π²Π»ΠΈΡΠ½ΠΈΠ΅ΠΌ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΠΉ Π² ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠΈ Π·Π΅ΠΌΠ΅Π»Ρ ΠΈ ΡΠ΅Ρ
Π½ΠΎΠ³Π΅Π½Π½ΠΎΠΉ Π½Π°Π³ΡΡΠ·ΠΊΠΈ. Π‘ΡΠ°Π΄ΠΈΠΈ Π½Π΅Π΄Π°Π²Π½ΠΈΡ
ΠΏΡΠ΅ΠΎΠ±ΡΠ°Π·ΠΎΠ²Π°Π½ΠΈΠΉ Π»Π°Π½Π΄ΡΠ°ΡΡΠ° Ρ Π½Π°ΡΠ°Π»Π° XX ΡΡΠΎΠ»Π΅ΡΠΈΡ ΡΠ°ΡΡΠΌΠΎΡΡΠ΅Π½Ρ Ρ
ΡΠΎΠ½ΠΎΠ»ΠΎΠ³ΠΈΡΠ΅ΡΠΊΠΈ. Π‘Π΄Π΅Π»Π°Π½Ρ Π²ΡΠ²ΠΎΠ΄Ρ ΠΎ Π²Π·Π°ΠΈΠΌΠΎΠΎΡΠ½ΠΎΡΠ΅Π½ΠΈΡΡ
ΠΏΡΠΈΠ±ΡΠ΅ΠΆΠ½ΡΡ
ΠΏΡΠΎΡΠ΅ΡΡΠΎΠ², Π³Π΅ΠΎΠΌΠΎΡΡΠΎΠ»ΠΎΠ³ΠΈΠΈ, Π΄ΠΈΠ½Π°ΠΌΠΈΠΊΠΈ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΡ Π·Π΅ΠΌΠ»ΠΈ, ΡΡΠΎΠ²Π½Ρ Π°Π½ΡΡΠΎΠΏΠΎΠ³Π΅Π½ΠΈΠ·Π°ΡΠΈΠΈ ΠΈ ΠΈΠ·ΠΌΠ΅Π½Π΅Π½ΠΈΡ ΠΏΡΠΈΠ±ΡΠ΅ΠΆΠ½ΠΎΠ³ΠΎ Π»Π°Π½Π΄ΡΠ°ΡΡΠ° Π½Π° ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½Π½ΠΎΠΉ ΡΠ΅ΡΡΠΈΡΠΎΡΠΈΠΈ.ΠΡΠΎΠ°Π½Π°Π»ΡΠ·ΠΎΠ²Π°Π½ΠΎ ΡΡΡΠ°ΡΠ½Ρ ΠΏΡΠΎΡΠ΅ΡΠΈ ΠΏΡΠΈΡΠΎΠ΄Π½ΠΎΡ Ρ Π·Π°Π·Π½Π°Π²ΡΠΎΡ Π°Π½ΡΡΠΎΠΏΠΎΠ³Π΅Π½Π½ΠΎΠ³ΠΎ Π²ΠΏΠ»ΠΈΠ²Ρ Π΄ΠΈΠ½Π°ΠΌΡΠΊΠΈ Π±Π΅ΡΠ΅Π³ΠΎΠ²ΠΎΡ Π»ΡΠ½ΡΡ ΠΌΡΠΆ ΠΌΠΈΡΠΎΠΌ ΠΠ°Π»ΡΠ°ΠΊΡΠ° Ρ ΠΌΠΈΡΠΎΠΌ ΠΠΌΡΠ½Π΅ Π½Π° Π±ΠΎΠ»Π³Π°ΡΡΡΠΊΠΎΠΌΡ ΡΠ·Π±Π΅ΡΠ΅ΠΆΠΆΡ Π§ΠΎΡΠ½ΠΎΠ³ΠΎ ΠΌΠΎΡΡ. ΠΡΠ½ΠΎΠ²Π½Ρ ΡΠ²Π°Π³Ρ ΠΏΡΠΈΠ΄ΡΠ»Π΅Π½ΠΎ Π²ΠΏΠ»ΠΈΠ²Ρ Π°Π½ΡΡΠΎΠΏΠΎΠ³Π΅Π½Π½ΠΈΡ
ΡΠΈΠ½Π½ΠΈΠΊΡΠ² Π½Π° Π±Π΅ΡΠ΅Π³ΠΎΠ²Ρ ΠΌΠΎΡΡΠΎΠ΄ΠΈΠ½Π°ΠΌΡΠΊΡ, ΠΏΡΠΈΠ±Π΅ΡΠ΅ΠΆΠ½Ρ Π΅ΡΠΎΠ·ΡΡ, ΡΡΠ°Π½ΡΠΏΠΎΡΡΡΠ²Π°Π½Π½Ρ ΠΉ Π°ΠΊΡΠΌΡΠ»ΡΡΡΡ ΠΎΡΠ°Π΄ΡΠ² ΠΏΡΠ΄ Π²ΠΏΠ»ΠΈΠ²ΠΎΠΌ Π·ΠΌΡΠ½ Ρ Π²ΠΈΠΊΠΎΡΠΈΡΡΠ°Π½Π½Ρ Π·Π΅ΠΌΠ΅Π»Ρ Ρ ΡΠ΅Ρ
Π½ΠΎΠ³Π΅Π½Π½ΠΎΠ³ΠΎ Π½Π°Π²Π°Π½ΡΠ°ΠΆΠ΅Π½Π½Ρ. Π‘ΡΠ°Π΄ΡΡ Π½Π΅Π΄Π°Π²Π½ΡΡ
ΠΏΠ΅ΡΠ΅ΡΠ²ΠΎΡΠ΅Π½Ρ Π»Π°Π½Π΄ΡΠ°ΡΡΡ Π· ΠΏΠΎΡΠ°ΡΠΊΡ XX ΡΡΠΎΡΡΡΡΡ ΡΠΎΠ·Π³Π»ΡΠ½ΡΡΠΎ Ρ
ΡΠΎΠ½ΠΎΠ»ΠΎΠ³ΡΡΠ½ΠΎ. ΠΡΠΎΠ±Π»Π΅Π½ΠΎ Π²ΠΈΡΠ½ΠΎΠ²ΠΊΠΈ ΠΏΡΠΎ Π²Π·Π°ΡΠΌΠΎΠ²ΡΠ΄Π½ΠΎΡΠ΅Π½Π½Ρ ΠΏΡΠΈΠ±Π΅ΡΠ΅ΠΆΠ½ΠΈΡ
ΠΏΡΠΎΡΠ΅ΡΡΠ², Π³Π΅ΠΎΠΌΠΎΡΡΠΎΠ»ΠΎΠ³ΡΡ, Π΄ΠΈΠ½Π°ΠΌΡΠΊΠΈ Π²ΠΈΠΊΠΎΡΠΈΡΡΠ°Π½Π½Ρ Π·Π΅ΠΌΠ»Ρ, ΡΡΠ²Π½Ρ Π°Π½ΡΡΠΎΠΏΠΎΠ³Π΅Π½ΡΠ·Π°ΡΡΡ ΡΠ° Π·ΠΌΡΠ½ΠΈ ΠΏΡΠΈΠ±Π΅ΡΠ΅ΠΆΠ½ΠΎΠ³ΠΎ Π»Π°Π½Π΄ΡΠ°ΡΡΡ Π½Π° Π΄ΠΎΡΠ»ΡΠ΄ΠΆΠ΅Π½ΡΠΉ ΡΠ΅ΡΠΈΡΠΎΡΡΡ
Thermal Breakage and Self-Healing of a Polymer Chain under Tensile Stress
We consider the thermal breakage of a tethered polymer chain of discrete
segments coupled by Morse potentials under constant tensile stress. The chain
dynamics at the onset of fracture is studied analytically by Kramers-Langer
multidimensional theory and by extensive Molecular Dynamics simulations in 1D-
and 3D-space. Comparison with simulation data in one- and three dimensions
demonstrates that the Kramers-Langer theory provides good qualitative
description of the process of bond-scission as caused by a {\em collective}
unstable mode. We derive distributions of the probability for scission over the
successive bonds along the chain which reveal the influence of chain ends on
rupture in good agreement with theory. The breakage time distribution of an
individual bond is found to follow an exponential law as predicted by theory.
Special attention is focused on the recombination (self-healing) of broken
bonds. Theoretically derived expressions for the recombination time and
distance distributions comply with MD observations and indicate that the energy
barrier position crossing is not a good criterion for true rupture. It is shown
that the fraction of self-healing bonds increases with rising temperature and
friction.Comment: 25 pages, 13 picture
A triple helix model for the structure of chromatin fiber
AbstractA model of chromatin fiber structure is presented in which a repeating unit of a trinucleosome forms a 3-dimensional zigzag. Twisting and compression of the zigzag result in a triple helix structure. The model is built mainly on the flow linear dichroism data showing that (a) nucleosomal disc faces are tilted relative to the fiber axis, (b) the orientation of nucleosomes does not change upon folding and unfolding of chromatin, and (c) the orientation of nucleosomes is maintained by the globular domain of histone HI
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