Electrostatic instability in magnetically confined inhomogeneous plasma driven by nonlinear force

A theoretical investigation on amplification of electrostatic ion acoustic wave in magnetically confined plasma has been presented in this paper. This investigation considers nonlinear wave–particle interaction process, called plasma maser effect, in presence of drift wave turbulence supported by magnetically confined inhomogeneous plasma. The role of associated nonlinear dissipative force in this effect in a confined plasma has been analyzed. The nonlinear force, which arises as a result of resonant interaction between electrons and modulated fields, is shown to drive the instability. Using the ion fluid equation and the ion equation of continuity, the nonlinear dispersion relation of a test ion acoustic wave has been derived, and the growth rate of ion acoustic wave in presence of low frequency drift wave turbulence has been estimated using Helimak data.     

Consolidation of hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B magnets by spark plasma sintering

We have successfully consolidated hydrogenation–disproportionation–desorption–recombination (HDDR) processed Nd–Fe–Co–Zr–B–Ga powder by spark plasma sintering (SPS). The field compacted samples were sintered at different temperatures (T_S) from 550 to 600 °C with compressive pressure of 80 MPa for 20 min. Microstructural investigations by transmission electron microscopy indicated that the sintered specimen exhibits Nd₂Fe₁₄B grains of ~300 nm with Nd-rich grain boundary phase. The optimum magnetic properties of B_r: 1.22 T, H_c: 928 kA/m, _BH_c: 600 kA/m, (BH)_max: 210 kJ/m³ were obtained in the sample sintered at 550 °C. The strategy for further improving the coercivity and remanence is discussed based on the microstructure-property relationships.     

A nonextensive maximum entropy approach to a family of nonlinear reaction–diffusion equations

We consider a monoparametric family of reaction–diffusion equations endowed with both a nonlinear diffusion term and a nonlinear reaction one that possess exact time-dependent particular solutions of the Tsallis’ maximum entropy (MaxEnt) form. The evolution of these solutions is governed by a system of three coupled nonlinear ordinary differential equations that are integrated numerically. A simple population dynamics interpretation provides a qualitative understanding of the behaviour of the q-MaxEnt solutions. When the reaction term vanishes the time-dependent distributions studied here reduce to the previously known Tsallis’ MaxEnt solutions for the nonlinear diffusion equation.     

Deuteron energy of 15 MK in ultra-dense deuterium without plasma formation: Temperature of the interior of the Sun

Deuterons are released with kinetic energy up to 630 eV from ultra-dense deuterium as shown previously, by Coulomb explosions initiated by ns laser pulses at . With higher laser intensity at , the initial kinetic energy now observed by TOF-MS with variable acceleration energy is up to 1100 eV per deuteron. This indicates ejection of one deuteron by Coulomb repulsion from two stationary charges in the material. It proves a full kinetic energy release of 1260 eV or a deuteron temperature of 15 MK, similar to the temperature in the interior of the Sun. Plasma processes are excluded by the sharp TOF peaks observed and by the slow signal variation with laser intensity. Deuterons with even higher energy from multiple charge repulsion are probably detected. D + D fusion processes are expected to exist in the ultra-dense phase without plasma formation.     

Resonant enhancement of field-induced annihilation rate for (π–π) atom: a possibility to measure np–ns energy splitting

Some possibilities are discussed for measuring the np–ns energy splitting in (π⁺–π⁻) atoms in experiments with relativistic particle beams, using the electromagnetic field control of annihilation process. Significant resonant enhancement of annihilation probability may be observed in an oscillating field. The resonance provides much more spectacular changes in the decay rate than corresponding decay rate changes in a steady field. The position of resonance on the frequency axis gives an additional and more accurate information on the np–ns transition energy, than the data on the ratio between the field-free and dc-field-induced annihilation rates. Numerical results are presented for the states n=2 and n=3.     

Thermodynamics of binary liquid mixtures: application of the Prigogine–Flory–Patterson theory to excess molar volumes of acetonitrile+1-alkanol systems

Excess molar volumes of {(1−x_A)CH₃(CH₂)_n−1OH+x_ACH₃CN} for n=1, 2, 3 or 4 as a function of composition under atmospheric pressure at 288.15, 293.15, 298.15 and 303.15 K have been used to test the applicability of the Prigogine–Flory–Patterson theory. According to the model, interactional contribution is the most important one to explain the V_m^E behavior. Good agreement is only achieved for the mixtures containing methanol (C₁) or 1-butanol (C₄). For the mixtures containing ethanol (C₂) and 1-propanol (C₃), which show an S-shaped V_m^E behavior, the correlation fails.     

Mechanism for enhancing dispersion of Co3O4 nanoparticles in Co/SiO2 Fischer–Tropsch synthesis catalyst by adding glycol to impregnating solution: a quick‐XAFS study

In situ Co K‐edge quick‐EXAFS (QEXAFS) coupled with temperature‐programmed oxidation as well as ex situ XAFS was applied to investigating the mechanism for enhancing the dispersion of Co₃O₄ nanoparticles in a calcined Co/SiO₂ Fischer–Tropsch synthesis catalyst prepared by adding triethylene glycol (TEG) to a Co(NO₃)₂.6H₂O impregnating solution. Ex situ Co K‐edge XAFS indicated that, regardless of whether the catalysts were prepared with or without using TEG, the hexaaqua Co (II) complex was formed in impregnated samples which then underwent the dehydration process to some extent during the subsequent drying step at 393 K. In situ QEXAFS and ex situ EXAFS results also indicated that small oxide clusters were formed in the TEG‐modified catalyst calcined at ～400–470 K which interacted with polymer species derived from TEG. Since the Fischer–Tropsch synthesis activity of the TEG‐modified catalyst increased with an increase in the calcination temperature in a similar temperature range [Koizumi et al. (2011), Appl. Catal. A, 395 , 138–145], it was suggested that such an interaction enables the clusters to be distributed over the support surface uniformly, resulting in enhancing their dispersion. After combustion of polymer species, Co₃O₄‐like species were formed, and agglomeration of the Co₃O₄‐like species at high calcination temperatures was suppressed by the addition of TEG to the impregnating solution. It was speculated that the addition of TEG induced the formation of some surface silicate which worked as an anchoring site for Co₃O₄ and Co⁰ nanoparticles during calcination and H₂ reduction, respectively.     

Formation of tubular silicon carbide from a carbon–silica material by using a reactive replica technique: infra-red characterisation

Thermal treatment of carbon fibres covered with silica prepared by a sol–gel technique leads to the formation of a tubular silicon carbide material keeping the morphology of the carbon source. The conversion of silica into silicon carbide, its kinetics and the structure of the final material were mainly determined by infra-red (IR) spectroscopy. The analytical results were crossed examined with those obtained by gravimetric and microscopic methods. In particular, it is shown, here, that IR-spectroscopy is a suitable technique to quantitatively determine the amount of SiC formed during the heat treatment of a C/SiO₂ material.     

On the controversial formation of silver diboride: Processing of Ag + 2B powders by spark plasma sintering

Following recent theoretical studies based on electronic structure calculations conducted on Ag- and Au-borides which estimated their superconducting behaviour at elevated transition temperatures, the preparation of AgB₂ was attempted in this work by reactive Spark Plasma Sintering (SPS) from Ag and B elemental powders. It was found that, independently from the processing conditions adopted, the formation of a new phase, which corresponds to a small peak on the XRD pattern at 2θ equal to about 28°, cannot be attributed to AgB₂. In fact, it was shown that the new phase detected on sintered pellets is most likely boric acid which is formed only if the sample is left in contact with air. If SPSed samples were stored under inert (Ar) atmosphere, no additional phases other than unreacted elements were observed.     

The Influence of Ion – Neutral Collisions in the Plasma Sheath on the Ion Current to an Electrostatic Probe: Monte Carlo Simulation

We have carried out Monte Carlo simulation of the motion of Ar⁺ ions in the space charge sheath surrounding a cylindrical Langmuir probe. From these simulations the percentage of ions crossing the sheath boundary that are collected by the probe have been determined and thus the ion currents to the probe have been calculated. It is shown that the collisions of ions with neutral helium gas atoms in the sheath increase the percentage of ions collected by the probe above that predicted by collisionless orbital motion limited current (OMLC) theory and that the exponent, χ, of the power law dependence, i₊～U, of the ion current, i₊, on the probe voltage, U_p, increases above the value 0.5 predicted by OMLC theory. The results of the simulations are compared with recent Langmuir probe measurements made in flowing afterglow plasmas.     

Analysis of the rotational spectrum of C3v molecules by using factorization and diagonalization of the energy matrix: Application to CH3C15N

A method is given for the analysis of the rotational spectrum in the ground and excited states of C_3v molecules; it consists in a direct diagonalization of the energy matrix including all elements whose contribution can become significant for the analysis up to the sixth order of approximation.The method of factoring the energy matrix into four submatrices A₁, A₂, E, E, according to the symmetry species of the full point group C_3v, is given. The programm enables the calculation of the rotational frequencies and also carries out by a least-squares method the fitting of the molecular constants for vibrational states v = 0 (ground state) and v_E = 1, 2, 3, and 4, separately or simultaneously over several of these states.The analysis of the rotational spectrum of CH₃C¹⁵N in the v₈ = 0, 1, 2 states is given as an example.     

Comments to paper by Spitas “A continuous piecewise internal friction model of hysteresis for use in dynamical simulations (Journal of Sound and Vibration 324: 297-316)”

In this discussion paper, it is shown that the criticism given in the paper mentioned in the title and relating to the so-called modified hysteretic model is not justified.