共查询到20条相似文献,搜索用时 31 毫秒
1.
A. A. Skovoroda 《Plasma Physics Reports》2009,35(2):99-111
Invariant local surface equilibrium equations are derived that interrelate the absolute value of the magnetic field B, the absolute value of the gradient of the magnetic flux |?Φ|, the local shear s, and the plasma pressure on nested equilibrium magnetic surfaces in currentless configurations. Examples of applying these equations to analysis of symmetric and isodynamic equilibria are considered. 相似文献
2.
A. V. Gordeev 《Plasma Physics Reports》2006,32(9):780-785
It is shown that relativistic electron current can propagate across the magnetic field B 0 over a distance d much larger than the electron gyroradius, r 0 ? m e v z c/(eB 0) ? d. This current is driven by the Hall electric field, which is generated on a spatial scale equal to the magnetic Debye radius r B = B 0/(4πen e) and causes the electrons to drift in crossed electric and magnetic fields. For a plane equilibrium current configuration, analytic profiles of the electron velocity and electron density are calculated and the electric and magnetic fields are determined. The results obtained are used to explain electron leakages in magnetically insulated transmission lines filled with a plasma expanding from the electrodes. Equations describing an equilibrium configuration of the ions and electrons that drift simultaneously across a strong magnetic field are derived. 相似文献
3.
A quasi-linear prediction of the two-fluid dynamo effect is analyzed with the use of tearing eigenfunctions obtained for force-free equilibrium. In the range of parameters of practical interest, the basic shear Alfvén mode is decoupled from fast compressional Alfvén and slow magneto-acoustic modes. Kinetic Alfvén modification of the shear Alfvén wave drives an instability with a growth rate ∝δ1/3ρ s 2/3 , where δ is the electron skin depth and ρs is the ion-sound gyroradius. A net dynamo effect parallel to the magnetic field is calculated at ρ s ?δ for large values of the stability factor \(\Delta '\rho _s^{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}} \delta ^{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}} \gg 1\). The dynamo effect caused by the j×B Hall term dominates the contribution from the v×B term (the alpha effect) by a factor ∝(ρs/δ)2 in the narrow electron layer, while in the broader ion layer these contributions are comparable. The results are compared with the case of a strong guiding field where ρ s ?δ and the tearing instability is described by resistive MHD. 相似文献
4.
《Fungal Ecology》2008,1(2-3):102-106
The effect of temperature and different solute (Ψs) and matric potentials (Ψm) on growth and sporulation of three aflatoxigenic strains of Aspergillus flavus isolated from contaminated maize in northern Italy was determined. The Ψs of maize-based media were modified ionically (NaCl) and non-ionically (glycerol) and the Ψm with PEG 8000 in the range −1.4 to −21.0 MPa at 25 and 30 °C. Both temperature and Ψs/Ψm stress had statistically significant effects on growth rates of the three strains. Faster growth occurred at 30 °C and −1.4 and −2.8 MPa. A. flavus strains were more sensitive to Ψm than Ψs stress with limits of −9.8 MPa and −14 to−18 MPa, respectively. Sporulation was significantly influenced by Ψs potential, solute type and temperature. This suggests that these aflatoxigenic strains of A. flavus isolated from aflatoxin-contaminated maize are probably able to colonise crop debris rapidly at prevailing temperatures and water stress conditions. This type of information on the ecology of aflatoxin producing A. flavus strains isolated in Italy will contribute to the development of a systems model to predict their activity in crop residue and colonisation of maize grain. 相似文献
5.
K. N. Mitrofanov V. V. Aleksandrov E. V. Grabovski E. A. Ptichkina A. N. Gritsuk I. N. Frolov Ya. N. Laukhin 《Plasma Physics Reports》2014,40(9):679-704
The phenomenon of magnetic flux breakthrough into a wire array during its implosion was studied experimentally at the Angara-5-1 facility. It is shown that breakthroughs develop in the final stage of plasma production from the wire material and occur near the initial wire position. The spatial distributions of the azimuthal magnetic field within tungsten, molybdenum, copper, and aluminum wire arrays were studied using magnetic probes. The distributions of the azimuthal magnetic field B φ(z, t) along the array height in different stages of implosion were measured, and the characteristic dimensions of regions with a nonuniform magnetic field that appear during magnetic flux breakthroughs at the outer boundary of the wire array plasma were determined. The dimensions of these regions are compared with those of the regions with depressed plasma radiation observed in frame and time-integrated X-ray images. The dynamics of the distribution B φ(z, t) in regions with a nonuniform magnetic field during breakthroughs of the azimuthal magnetic flux is compared with that of the spatial distribution of pinch radiation in the frame X-ray images in different stages of implosion. The experimental data on the characteristics of spatially nonuniform breakthroughs of the magnetic flux into the wire array are analyzed using the plasma rainstorm model proposed by V.V. Aleksandrov et al. (JETP 97, 745 (2003)). The plasma density in the region of magnetic flux breakthrough is estimated. 相似文献
6.
Chao-Hsiung Lin Chih-Jen Yu Chu-Hsin Hsieh Ying-Feng Chang 《Analytical biochemistry》2009,385(2):224-3296
Fiber-optic biosensors have been studied intensively because they are very useful and important tools for monitoring biomolecular interactions. Here we describe a fluorescence detection fiber-optic biosensor (FD-FOB) using a sandwich assay to detect antibody-antigen interaction. In addition, the quantitative measurement of binding kinetics, including the association and dissociation rate constants for immunoglobulin G (IgG)/anti-mouse IgG, is achieved, indicating 0.38 × 106 M−1 s−1 for ka and 3.15 × 10−3 s−1 for kd. These constants are calculated from the fluorescence signals detected on fiber surface only where the excited evanescent wave can be generated. Thus, a confined fluorescence-detecting region is achieved to specifically determine the binding kinetics at the vicinity of the interface between sensing materials and uncladded fiber surface. With this FD-FOB, the mathematical deduction and experimental verification of the binding kinetics in a sandwich immunoassay provide a theoretical basis for measuring rate constants and equilibrium dissociation constants. A further measurement to study the interaction between human heart-type fatty acid-binding protein and its antibody gave the calculated kinetic constants ka, kd, and KD as 8.48 × 105 M−1 s−1, 1.7 × 10−3 s−1, and 2.0 nM, respectively. Our study is the first attempt to establish a theoretical basis for the florescence-sensitive immunoassay using a sandwich format. Moreover, we demonstrate that the FD-FOB as a high-throughput biosensor can provide an alternative to the chip-based biosensors to study real-time biomolecular interaction. 相似文献
7.
A. A. Beletskii L. I. Grigor’eva E. L. Sorokovoy V. V. Chechkin Y. L. Sorokovoy Ye. D. Volkov P. Ya. Burchenko A. Ye. Kulaga S. A. Tsybenko A. V. Lozin A. S. Slavnyj Yu. S. Lavrenovich N. V. Zamanov Yu. K. Mironov V. S. Romanov 《Plasma Physics Reports》2009,35(10):818-823
In the l = 3/m = 9 Uragan-3M (U3-M) torsatron (R 0 = 1 m, ā ≈ 0.12 m, ι(ā)/2π ~ 0.3) with an open helical divertor and a plasma produced and heated by RF fields (ω ? ωci), studies of low frequency (5–100 kHz) density and potential fluctuations in the SOL plasma and in the diverted plasma flows (DPFs), have been carried out. It is shown, that in the SOL to more (less) distantly located points relative to the last closed magnetic surface, higher (lower) frequency fluctuations are inherent. Such a spectral splitting in two sub-ranges occurs in the DPFs too. A peculiarity of the spatial distribution of DPF fluctuation spectra is that lower frequency fluctuations dominate on the ion toroidal B × ?B drift side. During L-H-like transition in U-3M simultaneously with strong E r shear formation, a suppression of lower frequency fluctuations and a decrease of local radial turbulent particle flux take place. Results are presented of investigation of plasma density fluctuations in SOL with the use of probability distribution function (PDF) analysis. Evaluations of skewness and kurtosis of fluctuations have been made. The analysis of I s fluctuations in DPF have been carried out in a similar way. 相似文献
8.
A. A. Skovoroda 《Plasma Physics Reports》2009,35(4):269-272
The complete set of universal local relationships between geometrical (the curvature and torsion of the force lines of the magnetic field and the field complementary to it) and magnetic (|B|, |?Φ|, b · (? × b), and the local shear s) quantities in currentless magnetic configurations comprising a system of equilibrium nested magnetic surfaces, including those with several magnetic axes, is derived. Possible applications of these relationships are discussed. 相似文献
9.
The dipole potential (Ψd) constitutes a large and functionally important part of the electrostatic potential of cell plasma membranes. However, its direct measurement is not possible. Herein, new 3-hydroxyflavone fluorescent probes were developed that respond strongly to Ψd changes by a variation of the intensity ratio of their two well-separated fluorescence bands. Using fluorescence spectroscopy with cell suspensions and confocal microscopy with adherent cells, we showed, for the first time, two-color fluorescence ratiometric measurement and visualization of Ψd in cell plasma membranes. Using this new tool, a heterogeneous distribution of this potential within the membrane was evidenced. 相似文献
10.
《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1986,886(1):88-95
The ligand binding properties of folate chemotactic receptors on isolated membranes of Dictyostelium discoideum were analyzed. Three out of the four receptor states (BF, BS and BSS) were detected, showing rate constants and Kd values similar to those obtained for intact cells. Guanine nucleotides changed the proportioning of the receptor states as well as the rates of several conversions. (i) The transformation of BF into BS was inhibited by GDP but not by guanylyl imidodiphosphate (GuaPP[NH]P) or GTP. (ii) The number of BS sites was lowered by GTP and GuaPP[NH]P. (iii) The binding to BSS was lowered by GTP and GDP, but increased by GuaPP[NH]P. (iv) The rate of disappearance of BSS was increased by GTP, but not by GuaPP[NH]P. Effects of guanine nucleotides were not observed after treatment of the membrane preparations with 15 mg/ml bovine serum albumin. This treatment caused the detection of a binding type different from the types described previously. The affinity of this binding site was extremely high (Kd ≤ 0.2 nM for N10-methylfolic acid), while the dissociation was relatively slow (k−1 ≤ 3·10−4 s−1). It is proposed that bovine serum albumin uncouples the folate receptor from a guanine nucleotide regulatory (G) protein in an irreversible manner. A model is presented in which the four receptor states correspond to distinct interactions with a G protein and GDP or GTP. 相似文献
11.
Previous studies suggest that the sensitivity of leaf mitochondrial respiration and the pool of soluble sugars to water stress could influence the response of leaf isoprene emission to drought by affecting the availability of extra-chloroplastic carbon for isoprene synthesis. We measured rates of isoprene emission and CO2 exchange, and the concentration of nonstructural carbohydrates in leaves of Quercus pubescens Willd. seedlings subjected to either normal watering (control plants, C) or drought (droughted plants, D). Stopping of watering caused predawn leaf water potential (Ψpd) to decline between −2.3 and −5.1 MPa among D plants, whereas Ψpd remained higher than −0.45 MPa in C plants. Isoprene emission (Is), net CO2 assimilation (An) and dark mitochondrial respiration (Rd) decreased with increasing water deficit, with declines in these variables relative to the respective means of C plants being An > Is > Rd. This resulted in positive pairwise correlations between the three variables. The concentration of nonstructural carbohydrates did not change between treatments, but the concentration of soluble sugars increased and that of starch decreased in D plants as compared with C plants. As a consequence, there was a negative correlation between Is and the concentration of soluble sugars, which supports a limited use of cytosolic sugars in sustaining isoprene synthesis at high to severe water stress. Our data also indicate that competition between Is and Rd for the same carbon substrates had little importance for isoprene emission at high to severe water stress, as compared to the overall constraint on isoprene metabolism probably imposed by the shortage of photosynthetic carbon, energy and reducing equivalents. 相似文献
12.
Mechanisms for generating current filaments in a dense plasma under the action of focused laser pulses and in a Z-pinch configuration are discussed. The main properties of current filaments with a zero and nonzero electron vorticity Ω e =B?(c/e)?×p e that originate at magnetic fields in the range 4πn e m e c2?B2?4πn i m i c2 are investigated under the conditions of Coulomb explosion at currents below the ion Alfvén current. A study is made of the equilibrium configurations of nonquasineutral current filaments in a purely longitudinal (Bz) and a purely azimuthal (Bθ) magnetic field and also in a more general case of a helical magnetic field, having two components, under conditions such that the charge separation occurs on a spatial scale on the order of the magnetic Debye radius rB ? |B|/(4πene. It is shown that strong electric fields generated in the current filaments are comparable in magnitude to the atomic field and are capable of accelerating ions to energies of several tens of megaelectronvolts. The ion dynamics in strong electric fields of the filaments is calculated numerically and is shown to lead to the formation of collisionless shock waves on time scales on the order of several inverse ion plasma frequencies ω pi ?1 . The possible formation of current filaments on different spatiotemporal scales is considered. 相似文献
13.
Rongsong Li 《Biochemical and biophysical research communications》2009,388(2):406-356
Mitochondrial dysfunction is intimately involved in cardiovascular diseases. Mitochondrial membrane potential (ΔΨm) is coupled with oxidative phosphorylation to drive ATP synthesis. In this study, we examined the effect of physiological pulsatile shear stress (PSS) on ΔΨm and the role of Mn-SOD expression on ΔΨm. Confluent human aortic endothelial cells (HAEC) were exposed to PSS, and ΔΨm was monitored using tetramethylrhodamine methyl ester (TMRM+), a mitochondrial membrane potential probe. PSS significantly increased ΔΨm and the change in ΔΨm was a dynamic process. ΔΨm returned to baseline level after PSS for 2 h followed by static state for 4 h. Mitochondrial Mn-SOD expression and activities were also significantly up-regulated in response to PSS. Silencing Mn-SOD attenuated PSS-mediated ΔΨm increase while adding Mn-SOD mimetic, MnTMPyP, increased ΔΨm to the similar extent as induced by PSS. Our findings suggest that PSS-increased mitochondrial ΔΨm, in part, via Mn-SOD up-regulation. 相似文献
14.
We analyze a decoupled Moran model with haploid population size N, a biallelic locus under mutation and drift with scaled forward and backward mutation rates θ1=μ1N and θ0=μ0N, and directional selection with scaled strength γ=sN. With small scaled mutation rates θ0 and θ1, which is appropriate for single nucleotide polymorphism data in highly recombining regions, we derive a simple approximate equilibrium distribution for polymorphic alleles with a constant of proportionality. We also put forth an even simpler model, where all mutations originate from monomorphic states. Using this model we derive the sojourn times, conditional on the ancestral and fixed allele, and under equilibrium the distributions of fixed and polymorphic alleles and fixation rates. Furthermore, we also derive the distribution of small samples in the diffusion limit and provide convenient recurrence relations for calculating this distribution. This enables us to give formulas analogous to the Ewens-Watterson estimator of θ for biased mutation rates and selection. We apply this theory to a polymorphism dataset of fourfold degenerate sites in Drosophila melanogaster. 相似文献
15.
Owing to the complex nature of V1VO ATPases, identification of neighboring subunits is essential for mechanistic understanding of this enzyme. Here, we describe the links between the V1 headpiece and the VO-domain of the yeast V1VO ATPase via subunit A and d as well as the VO subunits a and d using surface plasmon resonance and fluorescence correlation spectroscopy. Binding constants of about 60 and 200 nM have been determined for the a-d and d-A assembly, respectively. The data are discussed in light of subunit a and d forming a peripheral stalk, connecting the catalytic A3B3 hexamer with VO.
Structured summary
MINT-7012054: d (uniprotkb:P32366) binds (MI:0407) to A (uniprotkb:P17255) by fluorescence correlation spectroscopy (MI:0052)MINT-7012041: d (uniprotkb:P32366) binds (MI:0407) to A (uniprotkb:P17255) by surface plasmon resonance (MI:0107)MINT-7012028: d (uniprotkb:P32366) binds (MI:0407) to a (uniprotkb:P32563) by surface plasmon resonance (MI:0107) 相似文献16.
The equilibrium of a plasma with isotropic pressure in a periodic divertor configuration with a poloidal magnetic field is calculated. The issue of how the plasma equilibrium changes as the parameter β≡8πp/B 2 increases is considered for a fairly representative class of pressure profiles p(ψ) (where ψ is the flux coordinate). It is shown that the plasma can be in equilibrium up to β values (in terms of the vacuum magnetic field at the divertor axis) on the order of unity. 相似文献
17.
Pathogens can cause chronic premature needle abscission in coniferous species. To assess the potential impacts on tree productivity, stomatal regulation was investigated in Douglas fir with chronic stomatal occlusion and defoliation from varying levels of the Swiss needle cast (SNC) fungus, Phaeocryptopus gaeumannii. Levels of SNC disease and subsequent defoliation were manipulated by choosing six sites with varying levels of disease and by foliar applications of fungicides on six trees per site. Diurnal measurements of leaf water potential (Ψleaf), stomatal conductance (g s) and vapor pressure deficit (D) were made on six fungicide treated and six control trees per site. In addition, leaf specific hydraulic conductance was calculated on a single branch (K L_B) from three trees per treatment per site. Stomatal conductance at D=1 kPa (g sref) was negatively correlated with fungal colonization (number of fruiting bodies present in needle stomata) and positively correlated with K L_B. Despite reduced needle retention in diseased trees, K L declined due to a reduction in sapwood area and permeability (i.e., increasing presence of latewood in functional sapwood). In general, stomatal sensitivity to D for all foliage was consistent with stomatal regulation based on a simple hydraulic model [g s=K L(Ψsoil?Ψleaf)/ D], which assumes strict stomatal regulation of Ψleaf. However, when fungal presence reduced maximum g s below the potential maximum supported by hydraulic architecture, stomatal sensitivity was lower than expected based on the theoretical relationship: dg s/dlnD=0.6·g sref. The results indicate that losses in productivity associated with physical blockage of stomata and defoliation are compounded by additional losses in K L and a reduction in g s in remaining functional stomata. 相似文献
18.
Richard B.M. Schasfoort Kiki C. Andree Niels van der Velde Alex van der Kooi Ivan Stojanović Leon W.M.M. Terstappen 《Analytical biochemistry》2016
The values of the affinity constants (kd, ka, and KD) that are determined by label-free interaction analysis methods are affected by the ligand density. This article outlines a surface plasmon resonance (SPR) imaging method that yields high-throughput globally fitted affinity ranking values using a 96-plex array. A kinetic titration experiment without a regeneration step has been applied for various coupled antibodies binding to a single antigen. Globally fitted rate (kd and ka) and dissociation equilibrium (KD) constants for various ligand densities and analyte concentrations are exponentially interpolated to the KD at Rmax = 100 RU response level (KDR100). 相似文献
19.
The radioiodinated pindolol analogs 125I-labeled cyanopindolol ([125I]CYP) and 125I-labeled hydroxybenzylpindolol ([125I]HBP) have been used to study binding to human platelet β-adrenergic receptors. [125I]CYP binds to a saturable class of binding sites on platelet membranes with a dissociation constant (Kd) of 14±3 pM and maximal binding capacity (Bmax) of 18±4 fmol/mg protein. Binding of [125I]CYP is reversible and is characterized by forward and reverse rate constants of 1.8·107 s?1·M?1 and 3.8·10?4 s?1, respectively. [125I]HBP binds to a saturable class of platelet membrane sites with a Kd of 50±10 pM and Bmax of 32±6 fmol/mg protein. [125I]HBP also binds to a saturable class of sites on intact platelets with a Kd of 58±14 pM and Bmax of 24±4 molecules per platelet. Binding of [125I]CYP and [125I]HBP is stereospecifically inhibited by propranolol and epinephrine; the (?) stereoisomers are at least 50-times more potent than the (+) stereoisomers. Binding of both radioligands is inhibited by adrenergic ligands with a potency order of propranolol ? isoproterenol > epinephrine > practolol > norepinephrine > phenylephrine. These observations indicate that [125I]CYP and [125I]HBP bind to platelet sites which have the pharmacological characteristics of β-adrenergic receptors but which are not typical of either the β1 or β2 sub-type. 相似文献
20.
Misako Aida Chikayoshi Nagata Iwao Ohmine Keiji Morokuma 《Journal of theoretical biology》1982,99(3):599-608
In extremely thermophilic tRNA, ribosylthymine is replaced by 2-thioribosylthymine at the key site in tRNA. By means of the ab initio molecular orbital (MO) calculation using the 4–31G basis set, we evaluate how this replacement brings about an increment of stacking energy, and how this increment in stacking energy is responsible for the stability of the thermophile tRNA. Calculated stacking energy for G : s2T : Ψ is larger by 4·85 kJ/mol (1·16 kcal/mol) than that for G : T : Ψ. Taking account of the thermodynamical data of yeast tRNAs by Privalov & Filimonov (1978), such an increment in stacking energy seems to considerably contribute to the increase of the midpoint melting temperature (Tm) in the thermophile tRNA, although other factors such as hydrogen bonding, ribose puckering and magnesium ions can not be excluded. It is found that the dispersion force mainly contributes to the stacking energies for G : T : Ψ and G : s2T : Ψ, especially for the latter. From the decomposition of the SCF energy, electrostatic and charge transfer energies are found to contribute to the stabilization of the thermophile tRNA, though the contribution of the former is larger than the latter. 相似文献