Anomalous Fast-Ion Transport During Neutral Beam Injection on EAST

The fast-ion transport during neutral beam injection on the Experimental Advanced Superconducting Tokamak (EAST) is studied. Based on the NUBEAM and TRANSP codes, it is found that fast-ion transport is anomalous when the minimum safety factor (q_min) is about 2, while it is neoclassical when q_min is around 1. Neutral beam injection heating efficiency, plasma stored energy, and the total heating power are reduced when the fast ion transport is anomalous. The Alfvén continuum spectrum and the mode structures of toroidal Alfvén eigenmodes (AEs) are also calculated for comparison between neoclassical fast-ion transport and anomalous fast-ion transport. High-q_min discharge with anomalous fast-ion transport has more AE activity than that of lower q_min discharge with neoclassical fast-ion transport.     

Formation of a narrow radial density profile of fast ions in the GDT device

The radial density profile of fast ions with a mean energy of 10 keV is measured in experiments with a two-component high-β plasma in the GDT device. Fast ions are produced by injecting neutral beams into a warm plasma. The measured fast-ion density profile is found to be narrower than that calculated with allowance for the neutral beam trapping and Coulomb scattering. Special experiments with a movable limiter have indicated that the formation of a narrow fast-ion density profile in GDT cannot be attributed to the loss of fast ions. Possible mechanisms responsible for this effect are discussed.     

Nonstationary model of an axisymmetric mirror trap with nonequilibrium plasma

The DOL nonstationary model intended to describe plasma processes in axisymmetric magnetic mirror traps is considered. The model uses averaging over the bounce period in order to take into account the dependence of plasma parameters on the coordinate along the facility axis. Examples of calculations of trap parameters by means of the DOL code based on this model are presented. Among the features of the DOL model, one can single out two points: first, the capability of calculating the terms of the collision integral with the use of a non-Maxwellian scattering function while evaluating the distribution function of fast ions and, second, concerning the background plasma, the capability of calculating the longitudinal particle and energy fluxes in confinement modes with the particle mean free path being on the order of the trap length. The influence of the scattering function approximation used to calculate the collision integral on the solution to the kinetic equation is analyzed. The dependences of plasma parameters on the power of heating injectors and the length of the fast-ion turning zone are presented as calculation examples. The longitudinal profile of the fusion reaction rate in the case of a trap with a long fast-ion turning zone is shown to depend strongly on the input parameters of the model.     

Molecular Dynamics Simulation of the Fast Ion Conductor δ-Bi2O3. II. Sub-lattice Structure

The results of molecular dynamics (MD) simulations of δ-B₂O₃ are analyzed with a view to obtaining an increased understanding of the structure of the Bi³⁺ and O^2- sub-lattices. The existence of cube-edge O^2- interstitials and of Willis-like disorder is confirmed by density maps. The onset of fast-ion conduction is associated with changes in the structure of both sub-lattices. Interpretation of the results suggests the existence of more than one fluorite form, differing in the structure of the O^2- sublattice.     

Study of fast-ion losses in experiments on neutral beam injection on the Globus-M spherical tokamak

The paper presents a review of the main results on the heating of plasma ions and behavior of fast ions in experiments on neutral beam injection (NBI) carried out in 2003–2010 on the Globus-M spherical tokamak. It is noticed that, along with significant success achieved in NBI plasma heating, there is experimental evidence indicating significant losses of the power injected into the plasma. Most probably, the power is lost due to so-called first-orbit losses, i.e., losses of fast ions that are produced in plasma after ionization of beam atoms and occur in unconfined trajectories. Until recently, the absence of appropriate diagnostic equipment did not allow one to verify this hypothesis. The use of the ACORD-M charge-exchange analyzer directed tangentially to the plasma column made it possible to measure the spectra of fast ions slowed down in plasma and confirm the assumption on the presence of substantial orbit losses of fast particles (～25–50% of the beam power). In addition to the review of the experimental results, the paper presents analysis of orbit losses on the basis of 3D simulations of fast-ion trajectories in plasma. The results of experiments on studying the influence of the magnitude of the tokamak magnetic field on the confinement of fast ions are also presented. Along with computer simulations, these experiments made it possible to formulate recommendations on the reduction of orbit losses in the Globus-M tokamak.     

Molecular Dynamics Simulation of the Fast Ion Conductor δ-Bi2O3. III. Ionic Motion

Dynamical aspects of molecular dynamics (MD) simulations are analysed with a view to determining the nature of fast-ion conduction in δ-Bi₂O₃. The ratio P _α of the moments of the self-correlation density distribution function, the velocity autocorrelation function (VAF), VAF integrals and VAF Fourier transforms, together with mean square displacement (MSD) data are interpreted in the light of experiment. It is shown that O^2- migration cannot adequately be described by either the hopping or liquid-like models of conduction but is best regarded as belonging to an intermediate category. Analysis of the fine structure of the P _α, MSD and VAF plots yields interesting correlations with vibrational modes.     

Liquid crystallinity in collagen solutions and magnetic orientation of collagen fibrils

Studies of the optical birefringence of solutions of acid-soluble collagen from rat-tail tendon at 22°C in the pH range 1.0–6.0 show that collagen exhibits an isotropic to mesophase transition only between pH 2.4 and 3.0 at 10% weight concentration. Such liquid crystalline order is probably essential for the orientation of collagen in a magnetic field. When solutions of neutral salt-soluble collagen were precipitated at pH 7.0 by warming to 37°C (“heat gelling”) in a magnetic field of ca. 20 kG, the resulting fibrils wee oriented perpendicular to the direction of the field. Heat gelling is shown to be a useful technique for maintaining the orientation induced in precursor solutions even after the sample is removed from the magnetic field.     

Localized states in an unbounded neural field equation with smooth firing rate function: a multi-parameter analysis

The existence of spatially localized solutions in neural networks is an important topic in neuroscience as these solutions are considered to characterize working (short-term) memory. We work with an unbounded neural network represented by the neural field equation with smooth firing rate function and a wizard hat spatial connectivity. Noting that stationary solutions of our neural field equation are equivalent to homoclinic orbits in a related fourth order ordinary differential equation, we apply normal form theory for a reversible Hopf bifurcation to prove the existence of localized solutions; further, we present results concerning their stability. Numerical continuation is used to compute branches of localized solution that exhibit snaking-type behaviour. We describe in terms of three parameters the exact regions for which localized solutions persist.     

Bifurcation analysis of a nonlinear field model of regeneration

The analysis of bifurcating solutions in the Totafurno and Trainor [23] model of supernumerary limb production in salamanders is re-examined using the symmetry analysis developed by Totafurno [22]. In particular, we show analytically that the appearance of field solutions possessing 2 and 4 singularities (the 2- and 4-centered solutions, respectively) also correspond to true bifurcations with reduced symmetries, just as had been previously found for a solution to the field equations not possessing such singularities (the twist solution). While the results have significance primarily for the biological problem, this work serves as an instructive example of the application of symmetry groups to the bifurcation analysis of nonlinear field equations arising from a variational principle. The relationship between the solutions of the nonlinear equations and the corresponding linear equations is discussed.Supported by the National Sciences and Engineering Research Council and the Medical Research Council of CanadaTo whom correspondence should be sent     

Ambipolarity condition and possibility of multivalued steady-state solutions to transport equations in stellarators

The possibility of steady-state multivalued solutions to transport equations in stellarators is considered. It is shown that the ambipolarity condition is necessary but not sufficient to find the ambipolar electric field, because the functions entering into it (the plasma density and temperature, as well as their spatial derivatives) depend on the ambipolar field. To do this correctly, it is necessary to solve the full set of time-independent transport equations (including diffusion and heat conduction equations). The possible existence of multivalued solutions to this set of equations is analyzed numerically. It is shown that, under certain conditions that depend on the form and magnitude of particle and heat sources, such solutions can exist. Their form is determined by the initial value of the ambipolar field, the source magnitudes, and the boundary conditions. Discontinuous solutions in which the radial profile of the ambipolar field undergoes jumps are found. In this case, however, the particle and energy fluxes remain continuous, because the discontinuities of the electric field are balanced by the discontinuities of the density and temperature gradients.     

A field theory of neural nets: II. Properties of the field equations

The field equation derived in Part I (Griffith,Bull. Math. Biophysics,25, 111–120, 1963a) is examined further. The stability of critical solutions is investigated and it is shown that, at least in certain cases, general solutions tend toward critical solutions. The relationship between the present field theory and a conventional matrix formulation is derived.     

Modulation of the intensity of fluorescence of aqueous solutions of proteins by magnetic field

Effect of the constant magnetic field with up to 3.2 X 10(-4) A/m intensity on the fluorescence of papain aqueous solutions was investigated. It has been shown that depending on the magnetic field direction a reversible decrease or increase of fluorescence intensity takes place. The variation of fluorescence intensity under the influence of magnetic field is maximal under excitation at long wave ultra-violet light. The effect increases with the increase of temperature, increases linearly with the increase of magnetic field intensity but doesn't depend on protein concentration in diluted solutions. The examination of the data leads to the conclusion on the existence of two possible mechanisms: the variation of properties of surface tryptophan residues environment and paramagnetic orientation of protein globule under the influence of a magnetic field.     

Enzyme-Substrate Reactions in Very High Magnetic Fields. II

We have examined the effect of conditioning the enzyme trypsin in solution at pH 8.2 in a large magnetic field before determining its reactivity towards a synthetic substrate N-benzoyl DL-arginine p-nitroanilide (BAPA). This "pretreatment" was allowed to proceed for as long as 3(2/3) hr in a magnetic field of 208 kgauss at temperatures 26 and 36 degrees C. No effect on reactivity was observed when such pretreated enzyme solutions were compared with identical but untreated enzyme solutions. A single such reaction, allowed to proceed directly in a magnetic field of 220 kgauss for 9 min, similarly showed no difference in rate from its control.     

Electric field effects on alanine tripeptide in sodium halide solutions

Abstract

The electric field effects on conformational properties of trialanine in different halide solutions were explored with long-scale molecular dynamics simulations. NaF, NaCl, NaBr and NaI solutions of low (0.2?M) and high (2?M) concentrations were exposed to a constant electric field of 1000?V/m. Generally, the electric field does not disturb trialanine's structure. Large structural changes appear only in the case of the supersaturated 2.0?M NaF solution containing NaF crystals. Although the electric field affects in a complex way, all the ions–water–peptide interactions, it predominantly affects the electroselectivity effect, which describes specific interactions such as the ion-pair formation.     

On-line concentration of neutral analytes for micellar electrokinetic chromatography: VI. Stacking using reverse migrating micelles and a water plug

Utility of a second enhanced field zone (water zone) is investigated for the on-line concentration of neutral analytes in micellar electrokinetic chromatography. Micellar solutions of sodium dodecyl sulfate prepared in acidic phosphate buffers are used as separation and sample solutions. Prior to long hydrodynamic injection of samples prepared in a low conductivity matrix, a long water plug is hydrodynamically injected to provide a second enhanced field zone. Practical and some fundamental considerations are presented. The technique is selective towards hydrophobic analytes. Notable detector response improvements (>100-fold) for several analytes are observed experimentally.     

根表面养分吸收通量和根围溶质浓度的近似解析解

该文用Nye-Tinker-Barber模型来研究植物根系表面的养分吸收通量和根围溶质浓度的近似解析解。将根围区域分为远场区域和近场区域, 在远场用相似变量, 在近场用尺度变换, 将远场解在根表面展开并与近场解进行待定函数的匹配, 从而获得对流扩散方程根表面通量和浓度的一阶近似解析解, 该解能够简化到扩散方程的解的形式。对氮、钾、硫、磷、镁、钙的养分吸收通量和氮、钾的浓度分别进行数值模拟, 比较模型的数值解、Roose的近似解析解和该文的近似解析解。结果表明: 在扩散方程中, 6种元素通量的解析解与Roose解析解相近, 但均高于数值解, 钾和磷的通量在短时间内迅速衰减; 钾和氮浓度的全局近似解析解与Roose解析解接近, 并与数值解的变化趋势一致。在对流扩散方程中, 除氮外的5种元素通量的近似解较Roose的解析解更接近于数值解, 且没有奇性。     

Correlation of chitosan's rheological properties and its ability to electrospin

Chitosan-based, defect-free nanofibers with average diameters ranging from 62 +/- 9 nm to 129 +/- 16 nm were fabricated via electrospinning blended solutions of chitosan and polyethylene oxide (PEO). Several solution parameters such as acetic acid concentration, polymer concentration, and polymer molecular weight were investigated to optimize fiber consistency and diameter. These parameters were evaluated using the rheological properties of the solutions as well as images produced by scanning electron microscopy (SEM) of the electrospun nanofibers. Generally, SEM imaging demonstrated that as total polymer concentration (chitosan + PEO) increased, the number of beads decreased, and as chitosan concentration increased, fiber diameter decreased. Chitosan-PEO solutions phase separate over time; as a result, blended solutions were able to be electrospun with the weakest electric field and the least amount of complications when solutions were electrospun within 24 h of initially being blended. The addition of NaCl stabilized these solutions and increased the time the blended solutions could be stored before electrospinning. Pure chitosan nanofibers with high degrees of deacetylation (about 80%) were unable to be produced. When attempting to electrospin highly deacetylated chitosan from aqueous acetic acid at concentrations above the entanglement concentration, the electric field was insufficient to overcome the combined effect of the surface tension and viscosity of the solution. Therefore, the degree of deacetylation is an extremely important parameter to consider when attempting to electrospin chitosan.     

Life in Zero Magnetic Field. V. E. coli Resistance to Antibiotics

Twenty‐six E. coli strains, isolated from human subjects, were tested for antibiotic drug resistance using the dilution of antibiotic solutions in agar culture medium. The bacterial strains were then exposed to zero magnetic field in a well‐controlled laboratory area, where a Helmholtz coil compensated the local geomagnetic field. The exposure time to the zero magnetic field was 6 days. The antibiotic drugs with antimicrobial large action spectra used to evaluate bacteria resistance were ampicillin, ceftazidime, tetracycline, ofloxacin, and kanamycin. The aqueous solutions of drug had dilutions of 0.25, 0.50, 4, 8, 16, 32, 64, and 128 µm/mL, respectively. Two types of microorganisms were detected: strains sensitive and strains nonsensitive to geomagnetic field compensation. We found that the magnetic‐sensitive strains represent about one‐third of the analyzed samples, statistical analysis emphasizing the general tendency of diminishing resistance against antibiotics.     

Emergence of oscillations in a model of weakly coupled two Bonhoeffer-van der Pol equations

Bifurcations of periodic solutions in a model of weakly coupled two Bonhoeffer-van der Pol equations are studied. The model realizes a half-center model with reciprocal inhibition, a typical model used in the field of neural motor control to account for the generation of alternating rhythmic bursts observed in motoneurons and spinal neural networks. Several oscillatory solutions such as in-phase, anti-phase as well as out-of-phase solutions emerge from the model's equilibrium as one of the parameters of the model changes. Among the variety of bifurcations exhibited by the model, we analyze Hopf bifurcations, by which several periodic solutions emerge, and illustrate generation mechanisms of alternating oscillations in the model.     

Approximate analytical solutions of root surface nutrient uptake flux and rhizosphere solute concentrations

该文用Nye-Tinker-Barber模型来研究植物根系表面的养分吸收通量和根围溶质浓度的近似解析解。将根围区域分为远场区域和近场区域, 在远场用相似变量, 在近场用尺度变换, 将远场解在根表面展开并与近场解进行待定函数的匹配, 从而获得对流扩散方程根表面通量和浓度的一阶近似解析解, 该解能够简化到扩散方程的解的形式。对氮、钾、硫、磷、镁、钙的养分吸收通量和氮、钾的浓度分别进行数值模拟, 比较模型的数值解、Roose的近似解析解和该文的近似解析解。结果表明: 在扩散方程中, 6种元素通量的解析解与Roose解析解相近, 但均高于数值解, 钾和磷的通量在短时间内迅速衰减; 钾和氮浓度的全局近似解析解与Roose解析解接近, 并与数值解的变化趋势一致。在对流扩散方程中, 除氮外的5种元素通量的近似解较Roose的解析解更接近于数值解, 且没有奇性。