Regulation of waveform asymmetry in flagella is critical for changes in direction when sperm are swimming, as seen during the chemotaxis of sperm towards eggs. Ca2+ is an important regulator of asymmetry in flagellar waveforms. A calcium sensor protein, calaxin, is associated with the outer arm dynein and plays a key role in the regulation of flagellar motility in a Ca2+-dependent manner. However, the underlying mechanism of regulating asymmetric waves by means of Ca2+ and calaxin remains unclear. To clarify the calaxin-dependent mechanism for generating Ca2+-dependent asymmetric flagellar waveforms, we analyzed the initial step of flagellar bend formation and propagation in the sperm of the ascidian Ciona intestinalis. Our experiment used demembranated sperm cells, which were then reactivated by UV flash photolysis of caged ATP under both high and low Ca2+ concentrations. Here, we show that initial bends in the flagella are formed at the base of the sperm and propagate towards the tip during waveform generation. However, the direction of the initial bend differed between asymmetric and symmetric waves. When a calaxin inhibitor (repaglinide) was applied, it resulted in the failure of asymmetric wave formation and propagation. This was because repaglinide had no effect on initial bend formation, but it significantly inhibited the generation of the subsequent bend in the reverse direction. Switching of dynein sliding activity by mechanical feedback is crucial for flagellar oscillation. Our results suggest that the Ca2+/calaxin mechanism plays an important role in the switching of dynein activity from microtubule sliding in the principal bend into the suppressed sliding in the reverse bend, thereby allowing the sperm to successfully change direction.
Alterations of brain function often result in abnormally slow frequency activity inthe EEG. Pathologic slowing, when localized, often correlates with focal brainlesions; when diffuse, slow activity often signifies an encephalopathy. Epileptiformactivity characteristic of people with epilepsy includes abnormalities such asspikes, sharp waves and spike-wave complexes, (slides21 & 22).
Crack Initiation And Propagation Ppt Slides
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Seizure propagation, the process by which a partialseizure spreads within the brain, occurs when there is sufficient activation torecruit surrounding neurons. This leads to a loss of surroundinhibition and spread of seizure activity into contiguous areasvia local cortical connections, and to more distant areas via long associationpathways such as the corpus callosum.
The propagation of bursting activity is normally prevented by intacthyperpolarization and a region of surrounding inhibition created by inhibitoryneurons. With sufficient activation there is a recruitment of surroundingneurons via a number of mechanisms. Repetitive discharges lead to: 1) anincrease in extracellular K+, which blunts the extent ofhyperpolarizing outward K+ currents, tending to depolarizeneighboring neurons; 2) accumulation of Ca++ inpresynaptic terminals, leading to enhanced neurotransmitter release; and 3)depolarization-induced activation of the NMDA subtype of the excitatory aminoacid receptor, which causes more Ca++ influx andneuronal activation. Of equal interest, but less well understood, is the processby which seizures typically end, usually after seconds or minutes, and whatunderlies the failure of this spontaneous seizure termination in thelife-threatening condition known as status epilepticus(see Clinical Epilepsy syllabus).
In this paper, we present complete evolution of a lightning discharge, from its initiation to ground attachment, which was optically and electromagnetically (RF) observed at the Lightning Observatory in Gainesville (LOG), Florida. This discharge involved a bidirectional leader whose initial extension was predominantly horizontal until the negative end turned toward ground. The dynamics of the positive and negative ends are examined and found to be dramatically different. A simple electrostatic model was used to estimate the electrical characteristics of the bidirectional leader. This study helps to improve our understanding of the initiation of lightning by providing the first high-speed (HS) video records and quantifying the dynamics of a bidirectional leader that resulted in a cloud-to-ground stroke.
Our views of bidirectional leaders in general are as follows. Leaving aside bidirectional leaders originating from metallic objects17,18,19, there appear to be four main scenarios for the formation of bidirectional leaders: (1) initiation of lightning in the cloud [present study; see also Kostinskiy et al.9,20], (2) lightning channel branching process [Montanya et al.2; Warner et al.3], (3) space leader involved in the negative leader step-formation process [Gorin et al.21; Gamerota et al.22], and (4) recoil-leader-type process giving rise to K-changes, dart leaders, and M-components [e.g., Warner et al.10; Mazur et al.23]. The formation of bidirectional leader may occur in virgin air (scenarios 1, 2, and 3) or in decayed channel branches (scenario 4). In the latter case, electrical breakdown is easier to initiate, since it occurs in warm, low-density air which the decayed lightning channel branches are filled with. Creation of bidirectional leader seed in scenario 1 may involve a decayed channel section, with the following extension taking place in virgin air [present study]. The dynamics of positive and negative leader ends in terms of the extension speed and branching can be very different either for the same bidirectional leader or for leaders following different scenarios. Positive end can extend faster22,24 or slower2,3 than the negative end, or the two ends can extend at similar speeds10. In the present study, we observed a pulsating behavior of the positive end, while the negative end extended normally. The spatial scale can vary from meters22 to many kilometers [present study]. Recoil-leader-type processes usually occur in decayed positive leader branches, but can also be formed in decayed negative branches, as recently reported by Montanya et al.25 and Stolzenburg et al.26.
How to cite this article: Tran, M. D. and Rakov, V. A. Initiation and propagation of cloud-to-ground lightning observed with a high-speed video camera. Sci. Rep. 6, 39521; doi: 10.1038/srep39521 (2016).
FIGURE 6. A model for the formation and propagation of the first bend and second bend in symmetric and asymmetric sperm flagellar waves. (A) Schematic representation for the R- and P-sliding in relation to the number of active dynein on doublet microtubule. Based on the studies of sea urchin and mammalian sperm. The formation of P-bends and R-bends is induced by the activation of dyneins on doublet 7 and 3, respectively. (B) A putative mechanism for initial bend formation and its propagation under low and high Ca2+ conditions are shown. Left, formation of a symmetric wave under low Ca2+ conditions. The first bend is formed by R-sliding. In turn, this R-bend induces switching of active dynein to that on the opposite side across the axoneme, resulting in P-sliding to form a P-bend. Right, generation of an asymmetric wave under high Ca2+ conditions. P-bend is first formed by P-sliding. In turn, this P-bend induces the switching of active dynein to that on the opposite side across the axoneme and generates suppressed R-sliding to form a R-bend with smaller curvature, resulting in the propagation of an asymmetric wave. A calaxin inhibitor, repaglinide, suppresses the generation of R-bend, possibly by inhibiting the mechanical transmission from P- to R-sliding.
Citation: Shiba K, Baba SA, Fujiwara E and Inaba K (2023) Calaxin is required for asymmetric bend initiation and propagation in sperm flagella. Front. Cell Dev. Biol. 11:1136404. doi: 10.3389/fcell.2023.1136404
Fatigue behavior of aluminum alloy 5454- H32 was studied under laboratory air and 3 % NaCl solution environment using smooth cylindrical and notched plate specimens. Presence of 3 % NaCl environment during fatigue loading drastically reduced alloy fatigue life. The deleterious effect was pronounced in both types of specimens in the long- life regions, where the fatigue lives were lowered by as much as a factor of 10. However, the sharply notched specimens showed only a modest reduction in fatigue life in corrosive environment. The severe influence of the corrosive environment in the long- life (low- stress) regime cannot be explained merely by the early initiation of the fatigue crack from surface pits; the environmental contribution in the early crack growth regime must also be considered an important factor. Fracture surface studies revealed extensive pitting and some secondary cracking in the crack initiation region. It was shown that lowered fatigue life in Al 5454- H32 occurs by early initiation of fatigue cracks from surface pits. In addition, a corrosion pitting and secondary cracking process may be operative in the small crack growth region. This could have enhanced the early crack growth rate and thus contributed to the lower fatigue life in the long- cycle region.
The introductory slide from the home page, reproduced below, indicates that Controlled/"Living" Radical Polymerization (CRP) procedures can be used for the preparation of copolymers, incorporating a broad spectrum of radically (co)polymerizable monomers forming materials with predetermined molecular weight, and narrow molecular weight distribution.(2) The most recent work on conducting an ATRP with low concentration of transition metals indicates that some control over the breadth of the MWD is also possible.(3) Here, and elsewhere in the text the word "control" and/or "controlled" means that if the polymerization process conditions are selected so that the contributions of the chain breaking processes are insignificant compared to chain propagation, then synthesis of polymers with predetermined molecular weights, low polydispersity and site specific functionalities become a reality. be457b7860
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