[en] Bursting modes are observed on the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 40 (2000) 557], which are identified as bounce-precession-frequency fishbone modes. They are predicted to be important in high-current, low-shear discharges with a significant population of trapped particles with a large mean-bounce angle, such as produced by near-tangential beam injection into a large aspect-ratio device. Such a distribution is often stable to the usual precession-resonance fishbone mode. These modes could be important in ignited plasmas, driven by the trapped-alpha-particle population

[en] Nonlinear equations for the slow space-time evolution of the radial drift-wave envelope and zonal flow amplitude have been self-consistently derived for a model nonuniform tokamak equilibrium within the coherent four-wave drift wave-zonal flow modulation interaction model of Chen, Lin, and White [Phys. Plasmas 7, 3129 (2000)]. Solutions clearly demonstrate turbulence spreading due to nonlinearly dispersiveness and, consequently, the device-size dependence of the saturated wave intensities and transport coefficients

[en] A fluid-kinetic hybrid electron model for electromagnetic simulations of finite-beta plasmas is developed based on an expansion of the electron response using the electron-ion mass ratio as a small parameter (Here beta is the ratio of plasma pressure to magnetic pressure.) The model accurately recovers low-frequency plasma dielectric responses and faithfully preserves nonlinear kinetic effects (e.g., phase space trapping). Maximum numerical efficiency is achieved by overcoming the electron Courant condition and suppressing high-frequency modes. This method is most useful for nonlinear kinetic (particle-in-cell or Vlasov) simulations of electromagnetic microturbulence and Alfvenic instabilities in magnetized plasmas

[en] Using the doped polymeric system composed of host poly(N-vinylcarbazole) and dopant coumarin 6, the morphology, phase distribution, and polymer molecular conformation of polymer films were investigated with optical and atomic force microscopy, UV-visible absorption spectra, and Fourier transform infrared reflectance spectroscopy. Results show that the film morphology and dopant distribution in the polymer films cast with the conventional method are dependent on the positions of polymer films. To avoid this negative effect, a new spin method was put forward by locating the specimen at an appropriate distance from the center of the spin plate during spin casting. It is found that polymer films prepared with the new method are more uniform and their electroluminescence performances are independent of the positions

[en] Nonlinear equations for the slow space-time evolution of the radial drift wave envelope and zonal flow amplitude have been self-consistently derived for a model nonuniform tokamak equilibrium within the coherent 4-wave drift wave-zonal flow modulation interaction model of Chen, Lin, and White [Phys. Plasmas 7 (2000) 3129]. Solutions clearly demonstrate turbulence spreading due to nonlinearly enhanced dispersiveness and, consequently, the device-size dependence of the saturated wave intensities and transport coefficients

[en] Microbial transformation of polyfluoroalkyl phosphate esters (PAPs) into perfluorocarboxylic acids (PFCAs) has recently been confirmed to occur in activated sludge and soil. However, there lacks quantitative information about the half-lives of the PAPs and their significance as the precursors to PFCAs. In the present study, the biotransformation of 6:2 and 8:2 diPAP in aerobic soil was investigated in semi-dynamics reactors using improved sample preparation methods. To develop an efficient extraction method for PAPs, six different extraction solvents were compared, and the phenomenon of solvent-enhanced hydrolysis was investigated. It was found that adding acetic acid could enhance the recoveries of the diPAPs and inhibit undesirable hydrolysis during solvent extraction of soil. However 6:2 and 8:2 monoPAPs, which are the first breakdown products from diPAPs, were found to be unstable in the six solvents tested and quickly hydrolyzed to form fluorotelomer alcohols. Therefore reliable measurement of the monoPAPs from a live soil was not achievable. The apparent DT_5_0 values of 6:2 diPAP and 8:2 diPAP biotransformation were estimated to be 12 and > 1000 days, respectively, using a double first-order in parallel model. At the end of incubation of day 112, the major degradation products of 6:2 diPAP were 5:3 fluorotelomer carboxylic acid (5:3 acid, 9.3% by mole), perfluoropentanoic acid (PFPeA, 6.4%) and perfluorohexanoic acid (PFHxA, 6.0%). The primary product of 8:2 diPAP was perfluorooctanoic acid (PFOA, 2.1%). The approximately linear relationship between the half-lives of eleven polyfluoroalkyl and perfluoroalkyl substances (PFASs, including 6:2 and 8:2 diPAPs) that biotransform in aerobic soils and their molecular weights suggested that the molecular weight is a good indicator of the general stability of low-molecular-weight PFAS-based compounds in aerobic soils. - Highlights: • Biotransformation of 6:2 and 8:2 diPAPs in an aerobic soil was investigated. • The DT_5_0 values for 6:2 and 8:2 diPAPs were 12 and > 1000 d, respectively. • 5:3 Acid, PFPeA, and PFHxA were the major degradation products of 6:2 diPAP. • PFOA was the major degradation product of 8:2 diPAP. • The half-lives of 11 PFASs are linearly correlated with their molecular weights. - Aerobic biotransformation in soil of 6:2 diPAP differs significantly from that of 8:2 diPAP in terms of DT_5_0 values, and the yield and distributions of degradation products.

[en] Encouraged by curiosity-driven chemistry in the fabrication of hydride-centered octanuclear copper clusters surrounded by 1, 1-dichalcogenolate ligands, our research group has developed a new synthetic methodology, which can increase the cluster nuclearity from eight to thirty six simply by adding excess amount of borohydrides into solution containing copper salts and ligands. Herein two types of nanoscale polyhydrido copper clusters stabilized by sulfur-donor ligands are reported. The structure of [Cu₂₀(H)₁₁{S₂P(OⁱPr)₂}₉] can be expressed by a trigonalbipyramidal unit of [Cu₂H₅]^3- anchored within an elongated triangular orthobicupola polyhedron of eighteen copper atoms, which is further stabilized by eighteen sulfur atoms from nine dithiophosphate ligands and six capping hydrides. The core unit of copper hydride nanoparticle in [Cu₂₈(H)₁₅(S₂CNPr₂)₁₂]⁺ comprises one central interstitial and eight outer-triangular-facecapping hydrides. A further six truncating hydrides form an unprecedented bridge between the inner and outer copper atom arrays. The irregular inner Cu₄ tetrahedron is encapsulated within the Cu₂₄ rhombicuboctahedral cage, which is further enclosed by a 12 dithiocarbamate ligand array which subtends the truncated octahedron of 24 sulfur atoms concentric with the Cu₂₄ rhombicuboctahedral and Cu₄ tetrahedral arrays about the innermost hydride. All of the hydride positions in the nanospheric clusters were determined unequivocally by the single crystal neutron diffraction. These compounds display an intriguing, if limited, room temperature H₂ evolution upon exposure of solutions to sunlight, under mild thermolysis condition, and on reaction with weak (or strong) acids to provide excellent models useful in the hydrogen storage technology.

[en] The authors have analyzed field line resonances of Alfven waves in a rectangular box model with a straight uniform magnetic field but three-dimensionally varying density. Field line resonances are shown to exist even with this three-dimensional uniformity. For a given wave frequency they can construct the surface on which the resonance occurs and derive the local form of the singular solution. Magnetic perturbations are found to lie predominantly in the resonant surface. In the presence of azimuthal inhomogeneous the present theory could explain why some satellite measurements show geomagnetic pulsations of comparable magnitude in radial and azimuthal components

[en] The model ballooning mode equation of Connor, Hastie and Taylor for large-aspect-ratio circular tokamaks is analysed in the limit of large pressure gradient, and corresponding expressions for stability boundaries are derived. In particular, it is found that for fixed radial wavenumbers infinite sequences of unstable bands exist and that minimizing over the radial wavenumbers leads to asymptotic merging between the neighbouring bands, which significantly modifies the second stability boundary compared with that for zero radial wavenumbers. (author). Letter-to-the-editor. 10 refs, 2 figs

[en] Some pseudobinary and pseudoternary oxidenitrides (CeN-CeO₂; LaN-Ln₂O₃; CeN-Ln₂O₃, Ln = La, Y; and YN-Ln₂O₃, Ln = La, Lu, Y, Sc) were prepared in Ta, Nb, or Mo containers at temperatures between 1,500 and 1,800 degrees C and characterized by X-ray powder diffraction. Electrical and magnetic properties of two oxidenitrides, LaO_0.31N_0.69 (I) and LaO_0.45N_0.55 (II), were determined over the temperature range 2-300 K. Both are weakly paramagnetic and metallic. Room temperature (300 K) resistivities for I and II are 4.8 x 10^-3 and 5.9 x 10^-5 Ω cm, respectively. As the temperature is lowered, resistivities of LaO_xN_1-x initially decrease linearly. 23 refs., 5 figs., 2 tabs