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.Проанализировано современные процессы естественной и подверженной антропогенному влиянию динамики береговой линии между мысом Калиакра и мысом Емине на болгарском побережье Черного моря. Основное внимание уделено воздействию антропогенных факторов на береговую морфодинамику, прибрежную эрозию, транспортировку и аккумуляцию осадков под влиянием изменений в использовании земель и техногенной нагрузки. Стадии недавних преобразований ландшафта с начала XX столетия рассмотрены хронологически. Сделаны выводы о взаимоотношениях прибрежных процессов, геоморфологии, динамики использования земли, уровня антропогенизации и изменения прибрежного ландшафта на исследованной территории.Проаналізовано сучасні процеси природної і зазнавшої антропогенного впливу динаміки берегової лінії між мисом Каліакра і мисом Еміне на болгарському узбережжі Чорного моря. Основну увагу приділено впливу антропогенних чинників на берегову морфодинаміку, прибережну ерозію, транспортування й акумуляцію осадів під впливом змін у використанні земель і техногенного навантаження. Стадії недавніх перетворень ландшафту з початку XX сторіччя розглянуто хронологічно. Зроблено висновки про взаємовідношення прибережних процесів, геоморфології, динаміки використання землі, рівня антропогенізації та зміни прибережного ландшафту на дослідженій території

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