Local surface equilibrium equations for currentless magnetic configurations

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.     

Electron leakage mechanism in a plasma-filled magnetically insulated transmission line

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.     

A hall dynamo effect driven by two-fluid tearing instability

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 ∝δ^1/3ρ _s ^2/3 , where δ is the electron skin depth and ρ_s 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 ∝(ρ_s/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.     

Effect of solute and matric potential on in vitro growth and sporulation of strains from a new population of Aspergillus flavus isolated in Italy

The effect of temperature and different solute (Ψ_s) and matric potentials (Ψ_m) on growth and sporulation of three aflatoxigenic strains of Aspergillus flavus isolated from contaminated maize in northern Italy was determined. The Ψ_s of maize-based media were modified ionically (NaCl) and non-ionically (glycerol) and the Ψ_m with PEG 8000 in the range −1.4 to −21.0 MPa at 25 and 30 °C. Both temperature and Ψ_s/Ψ_m 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 Ψ_m than Ψ_s stress with limits of −9.8 MPa and −14 to−18 MPa, respectively. Sporulation was significantly influenced by Ψ_s 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.     

Study of the termination phase of plasma production and the formation of magnetic flux breakthroughs during wire array implosion

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.     

Quantitative measurement of binding kinetics in sandwich assay using a fluorescence detection fiber-optic biosensor

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 k_a and 3.15 × 10⁻³ s⁻¹ for k_d. 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 k_a, k_d, and K_D 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.     

Spectral and statistical analysis of fluctuations in the SOL and diverted plasmas of the Uragan-3M torsatron

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 ? ω_ci), 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.     

Local geometrical properties of magnetic configurations with nested equilibrium magnetic surfaces

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.     

Two-color fluorescent probes for imaging the dipole potential of cell plasma membranes

The dipole potential (Ψ_d) 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 Ψ_d 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 Ψ_d in cell plasma membranes. Using this new tool, a heterogeneous distribution of this potential within the membrane was evidenced.     

Folate chemotactic receptors in Dictyostelium discoideum II. Guanine nucleotides alter the rates of interconversion and the proportioning of four receptor states

The ligand binding properties of folate chemotactic receptors on isolated membranes of Dictyostelium discoideum were analyzed. Three out of the four receptor states (B^F, B^S and B^SS) were detected, showing rate constants and K_d 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 B^F into B^S was inhibited by GDP but not by guanylyl imidodiphosphate (GuaPP[NH]P) or GTP. (ii) The number of B^S sites was lowered by GTP and GuaPP[NH]P. (iii) The binding to B^SS was lowered by GTP and GDP, but increased by GuaPP[NH]P. (iv) The rate of disappearance of B^SS 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 (K_d ≤ 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.     

Leaf isoprene emission declines in Quercus pubescens seedlings experiencing drought – Any implication of soluble sugars and mitochondrial respiration?

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 (Ψ_pd) to decline between −2.3 and −5.1 MPa among D plants, whereas Ψ_pd remained higher than −0.45 MPa in C plants. Isoprene emission (I_s), net CO₂ assimilation (A_n) and dark mitochondrial respiration (R_d) decreased with increasing water deficit, with declines in these variables relative to the respective means of C plants being A_n > I_s > R_d. 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 I_s 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 I_s and R_d 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.     

Localization of magnetized electrons in current filaments as a fundamental cause of Coulomb explosion

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 (B_z) and a purely azimuthal (B_θ) 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 r_B ? |B|/(4πen_e. 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.     

Pulsatile shear stress increased mitochondrial membrane potential: Implication of Mn-SOD

Mitochondrial dysfunction is intimately involved in cardiovascular diseases. Mitochondrial membrane potential (ΔΨ_m) is coupled with oxidative phosphorylation to drive ATP synthesis. In this study, we examined the effect of physiological pulsatile shear stress (PSS) on ΔΨ_m and the role of Mn-SOD expression on ΔΨ_m. Confluent human aortic endothelial cells (HAEC) were exposed to PSS, and ΔΨ_m was monitored using tetramethylrhodamine methyl ester (TMRM⁺), a mitochondrial membrane potential probe. PSS significantly increased ΔΨ_m and the change in ΔΨ_m was a dynamic process. ΔΨ_m 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 ΔΨ_m increase while adding Mn-SOD mimetic, MnTMPyP, increased ΔΨ_m to the similar extent as induced by PSS. Our findings suggest that PSS-increased mitochondrial ΔΨ_m, in part, via Mn-SOD up-regulation.     

The allele-frequency spectrum in a decoupled Moran model with mutation, drift, and directional selection, assuming small mutation rates

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.     

Association of the eukaryotic V1VO ATPase subunits a with d and d with A

Owing to the complex nature of V₁V_O ATPases, identification of neighboring subunits is essential for mechanistic understanding of this enzyme. Here, we describe the links between the V₁ headpiece and the V_O-domain of the yeast V₁V_O ATPase via subunit A and d as well as the V_O 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 V_O.

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)     

Plasma equilibrium in axisymmetric open divertor configurations

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.     

Stomatal regulation in Douglas fir following a fungal-mediated chronic reduction in leaf area

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 (Ψ_leaf), 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(Ψ_soil?Ψ_leaf)/ D], which assumes strict stomatal regulation of Ψ_leaf. 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.     

Interpolation method for accurate affinity ranking of arrayed ligand–analyte interactions

The values of the affinity constants (k_d, k_a, and K_D) 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 (k_d and k_a) and dissociation equilibrium (K_D) constants for various ligand densities and analyte concentrations are exponentially interpolated to the K_D at R_max = 100 RU response level (K_D^R100).     

Demonstration of human platelet β-adrenergic receptors using 125I-labeled cyanopindolol and 125I-labeled hydroxybenzylpindolol

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 (K_d) of 14±3 pM and maximal binding capacity (B_max) 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 K_d of 50±10 pM and B_max of 32±6 fmol/mg protein. [¹²⁵I]HBP also binds to a saturable class of sites on intact platelets with a K_d of 58±14 pM and B_max 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.     

Ab Initio molecular orbital study on the thermostability of the extreme thermophile tRNA: Role of the base stacking

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 (T_m) 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.