排序方式: 共有49条查询结果,搜索用时 9 毫秒
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I. B. Semenov Yu. V. Mitrishkin A. A. Subbotin A. G. Vertinskiĭ N. L. Marusov I. S. Sushin 《Plasma Physics Reports》2006,32(2):114-118
The main parameters of tokamak discharges are known to be limited by large-scale MHD instabilities. Sometimes, the instabilities lead to a rapid (on time scales of tens of microseconds) disruption of the discharge current and to the release of all the energy stored in the plasma column at the discharge chamber wall. This process, which is called the disruptive instability, may have irreversible catastrophic consequences for the operation of a fusion reactor. In the present paper, a study is made of the dynamics of self-oscillations in systems of two and six van der Pol coupled oscillators. A van der Pol coupled-oscillator model is used to develop a multivariable feedback controller based on the combined principle of compensating for internal cross feedbacks within the object and introducing damping feedbacks in each control channel. By using mathematical simulation methods, it is shown that the controller designed guarantees the suppression of self-oscillations in a system of van der Pol oscillators over a fairly broad range of parameters of the object under control (and thereby provides the structural stability of the object). The nonlinear control system model makes it possible to suppress coupled MHD perturbations developing in a tokamak plasma. 相似文献
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Riepsamen AH Gibson T Rowe J Chitwood DJ Subbotin SA Dowton M 《Journal of molecular evolution》2011,72(2):182-192
We assessed the rate of in vitro polymerase errors at polythymidine [poly(T)] tracts in the mitochondrial DNA (mtDNA) of a
heteroderid nematode (Heterodera cajani). The mtDNA of these nematodes contain unusually high numbers of poly(T) tracts, and have previously been suggested to contain
biological poly(T) length variation. However, using a cloned molecule, we observed that poly(T) variation was generated in
vitro at regions containing more than six consecutive Ts. This artefactual error rate was estimated at 7.3 × 10−5 indels/poly(T) tract >6 Ts/cycle. This rate was then compared to the rate of poly(T) variation detected after the amplification
of a biological sample, in order to estimate the ‘biological + artefactual’ rate of poly(T) variation. There was no significant
difference between the artefactual and the artefactual + biological rates, suggesting that the majority of poly(T) variation
in the biological sample was artefactual. We then examined the generation of poly(T) variation in a range of templates with
tracts up to 16 Ts long, utilizing a range of Heteroderidae species. We observed that T deletions occurred five times more
frequently than insertions, and a trend towards increasing error rates with increasing poly(T) tract length. These findings
have significant implications for studies involving genomes with many homopolymer tracts. 相似文献
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Subbotin SA Ragsdale EJ Mullens T Roberts PA Mundo-Ocampo M Baldwin JG 《Molecular phylogenetics and evolution》2008,48(2):491-505
The root lesion nematodes of the genus Pratylenchus Filipjev, 1936 are migratory endoparasites of plant roots, considered among the most widespread and important nematode parasites in a variety of crops. We obtained gene sequences from the D2 and D3 expansion segments of 28S rRNA partial and 18S rRNA from 31 populations belonging to 11 valid and two unidentified species of root lesion nematodes and five outgroup taxa. These datasets were analyzed using maximum parsimony and Bayesian inference. The alignments were generated using the secondary structure models for these molecules and analyzed with Bayesian inference under the standard models and the complex model, considering helices under the doublet model and loops and bulges under the general time reversible model. The phylogenetic informativeness of morphological characters is tested by reconstruction of their histories on rRNA based trees using parallel parsimony and Bayesian approaches. Phylogenetic and sequence analyses of the 28S D2–D3 dataset with 145 accessions for 28 species and 18S dataset with 68 accessions for 15 species confirmed among large numbers of geographical diverse isolates that most classical morphospecies are monophyletic. Phylogenetic analyses revealed at least six distinct major clades of examined Pratylenchus species and these clades are generally congruent with those defined by characters derived from lip patterns, numbers of lip annules, and spermatheca shape. Morphological results suggest the need for sophisticated character discovery and analysis for morphology based phylogenetics in nematodes. 相似文献
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Subbotin VM 《Theoretical biology & medical modelling》2012,9(1):11-22
ABSTRACT: BACKGROUND: An accepted hypothesis states that coronary atherosclerosis (CA) is initiated by endothelial dysfunction due to inflammation and high levels of LDL-C, followed by deposition of lipids and macrophages from the luminal blood into the arterial intima, resulting in plaque formation. The success of statins in preventing CA promised much for extended protection and effective therapeutics. However, stalled progress in pharmaceutical treatment gives a good reason to review logical properties of the hypothesis underlining our efforts, and to reconsider whether our perception of CA is consistent with facts about the normal and diseased coronary artery. Analysis To begin with, it must be noted that the normal coronary intima is not a single-layer endothelium covering a thin acellular compartment, as claimed in most publications, but always appears as a multi-layer cellular compartment, or diffuse intimal thickening (DIT), in which cells are arranged in many layers. If low density lipoprotein cholesterol (LDL-C) invades the DIT from the coronary lumen, the initial depositions ought to be most proximal to blood, i.e. in the inner DIT. The facts show that the opposite is true, and lipids are initially deposited in the outer DIT. This contradiction is resolved by observing that the normal DIT is always avascular, receiving nutrients by diffusion from the lumen, whereas in CA the outer DIT is always neovascularized from adventitial vasa vasorum. The proteoglycan biglycan, confined to the outer DIT in both normal and diseased coronary arteries, has high binding capacity for LDL-C. However, the normal DIT is avascular and biglycan-LDL-C interactions are prevented by diffusion distance and LDL-C size (20 nm), whereas in CA, biglycan in the outer DIT can extract lipoproteins by direct contact with the blood. These facts lead to the single simplest explanation of all observations: (1) lipid deposition is initially localized in the outer DIT; (2) CA often develops at high blood LDL-C levels; (3) apparent CA can develop at lowered blood LDL-C levels. This mechanism is not unique to the coronary artery: for instance, the normally avascular cornea accumulates lipoproteins after neovascularization, resulting in lipid keratopathy. Hypothesis Neovascularization of the normally avascular coronary DIT by permeable vasculature from the adventitial vasa vasorum is the cause of LDL deposition and CA. DIT enlargement, seen in early CA and aging, causes hypoxia of the outer DIT and induces neovascularization. According to this alternative proposal, coronary atherosclerosis is not related to inflammation and can occur in individuals with normal circulating levels of LDL, consistent with research findings. 相似文献
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The survived portion of an organ which topographically can be considered as a part of the lung, as well as a section of muscular tissue, perhaps that of the heart, has been studied. Under weak systems, the portion resembles the lung, spaces resembling alveoles, alveolar ducts and alveolar saccules are seen. "Alveolar" walls are stained dark grey by different methods; "alveoles" contain yellow granules, ferric components are not detected in them. The intestinal wall and that of the large vessel in the mesenteric cavity preserves a fibrillar carcass, fibrillar ultrastructure corresponding to collagen. 相似文献
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Sergei A. Subbotin John J. Chitambar Vlamidir N. Chizhov Jason D. Stanley Renato N. Inserra Marcelo E. Doucet Michael McClure Weimin Ye Dimitre S. Mollov Carolina Cantalapiedra‐Navarrete Nicola Vovlas Esther Van Den Berg Pablo Castillo 《Zoological Journal of the Linnean Society》2014,171(3):475-506
The genus Hemicycliophora (Nematoda: Hemicycliophoridae) contains 132 valid species of plant‐parasitic nematodes, collectively known as ‘sheath nematodes’. Hemicycliophora spp. are characterized morphologically by a long stylet with rounded basal knobs and a cuticular sheath, present in juvenile and adult stages. Populations of 20 valid and 14 putative species of Hemicycliophora and Loofia from several countries were characterized morphologically using light (LM) and scanning electron microscopy (SEM) and molecularly using the D2‐D3 segments of 28S rRNA and internal transcribed spacer (ITS) rRNA gene sequences. LM and SEM observations provided new details on the morphology of these species. PCR‐restriction fragment length polymorphisms (PCR‐RFLPs) of the D2‐D3 of 28S rDNA were proposed for identification of the species. Phylogenetic relationships within populations of 36 species of the genus Hemicycliophora using 102 D2‐D3 of 28S rDNA and 97 ITS rRNA gene sequences as inferred from Bayesian analysis are reconstructed and discussed. Ancestral state reconstructions of diagnostic characters (body and stylet length, number of body annuli, shape of vulval lip and tail), using maximum parsimony and Bayesian inference, revealed that none of the traits are individually reliable characters for classifying the studied sheath nematode. The Shimodaira–Hasegawa test rejected the validity of the genus Loofia. This is the most complete phylogenetic analysis of Hemicycliophora species conducted so far. © 2014 The Linnean Society of London 相似文献
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Nakonechnaya O. V. Gafitskaya I. V. Burkovskaya E. V. Khrolenko Yu. A. Grishchenko O. V. Zhuravlev Yu. N. Subbotin E. P. Kulchin Yu. N. 《Russian Journal of Plant Physiology》2019,66(4):656-663
Russian Journal of Plant Physiology - A study of the effect of various light intensity (75, 135, 230, and 382 µmol/(m2 s)) on the morphogenesis of Stevia rebaudiana (Bertoni) Bertoni in vitro... 相似文献
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