A two-dimensional soliton in a positive ion-negative ion plasma

The authors describe a series of experiments performed in a positive ion-negative ion plasma that were designed to study the reflection and focusing properties of solitons. The nonlinear wave was compared with a theoretical model using linear waves. The two-dimensional soliton was created by reflecting an incident planar soliton from a concave hemispherical surface. The experimental results are interpreted in terms of the linear waves that can exist in a focused Fabry-Perot resonator     

Extensions of Vietoris''s Inequalities (Ⅱ)

It was shown by Vietoris[1] in 1958 that for n ≥ 1 and x ∈ (0, π), n∑k=0ckcos(kx)>0,(1)     

Positivity of Cotes numbers at more Jacobi abscissas

The positivity of certain finite sums of even ultraspherical polynomials has been identified by Askey as a specially interesting case of a more general problem concerning positivity of Cotes numbers at Jacobi abscissas. The authors establish several new inequalities of this type.This research was supported by a grant from the Australian Research Council.     

Characterization of the Fermi surface of the organic superconductor - by measurements of Shubnikov-de Haas and angle-dependent magnetoresistance oscillations and by electronic band-structure calculations

The electronic structure of the quasi two-dimensional (2D) organic superconductor -(ET)₂SF₅CH₂CF₂SO₃ was examined by measuring Shubnikov-de Haas (SdH) and angle-dependent magnetoresistance (AMRO) oscillations and by comparing with electronic band-structure calculations. The SdH oscillation frequencies follow the angular dependence expected for a 2D Fermi surface (FS), and the observed fundamental frequency shows that the 2D FS is 5% of the first Brillouin zone in size. The AMRO data indicate that the shape of the 2D FS is significantly non-circular. The calculated electronic structure has a 2D FS in general agreement with experiment. From the temperature and angular dependence of the SdH amplitude, the cyclotron and band effective masses were estimated to be and ,where g is the conduction electron g factor and the free electron mass. The band effective mass is estimated to be from the calculated electronic band structure. Received: 3 March 1997 / Revised: 5 May 1997 / Received in final form: 5 November 1997 / Accepted: 10 November 1997     

Goniometry for Interface Studies in Transmission Electron Microscopy

A method using a double-tilt goniometer stage for determining the orientation of crystalline specimens in transmission electron microscopy (TEM) is described. The procedure involves visual identification of two zone axes, and using the corresponding goniometer settings to plot these poles stereographically. Crystal orientations and misorientations can be established rapidly, and the method is intended for use as a practical complement to more precise but time-consuming techniques. The commutative operation of double-tilt stages and their goniometric capability are also discussed. Using Rodrigues-Frank space, it is shown that the set of attainable operations for such stages is represented by points on an hyperboloidal surface.     

A STUDY OF STRUCTURE AND PROPERTY CHANGES OF BIODEGRADABLE POLYGLYCOLIDE AND POLY(GLYCOLIDE-co-LACTIDE)FIBERS DURING PROCESSING AND IN VITRO DEGRADATION*

Structure and properties of bioabsorbable polyglycolide (PGA) and poly(glycolide-co-lactide) (PGA-co-PLA)fibers were investigated during several industrial processing stages and in vitro degradation by means of wide-angle X-raydiffraction (WAXD), dynamic mechanical analysis (DMA) and mechanical property tests. In the orientation stage, the PGAfibers were found to have higher degrees of crystallinity than corresponding PGA-co-PLA samples produced under similarconditions. In the hot-stretching and post-annealing stages, after fibers were braided, PGA samples were found to gain morecrystallinity and higher T_g than PGA-co-PLA samples. The higher crystallinity in PGA fibers resulted in a slower rate ofdegradation. DMA results showed that a great deal of internal stress that was built during orientation and hot-stretchingstages was released in the post-annealing stage for a1l PGA and PGA-co-PLA samples. During earlier stages of in vitrodegradation, both PGA and PGA-co-PLA samples exhibited the typical cleavage-induced crystallization mechanism. Theheat shrinkage in the glass transition area was found to disappear after 6-8 days of degradation for all PGA and PGA-co-PLAsamples, indicating the amorphous portions of the polymers lost orientation after a short period in the buffer solution, mostlikely due to relaxation of the cleaved chains.     

Electron paramagnetic resonance spectroscopic studies on the zero-valent rhodium complex [Rh(P(OPri)3)4] at X-and Q-band frequencies

The EPR spectroscopic properties of the zero-valent rhodium complex [Rh(P(OPrⁱ)₃)₄] have been examined at both X- and Q-band frequencies. The spectra show a large, essentially axial anisotropy and ligand hyperfine coupling to four equivalent ³¹P phosphorous nuclei. No resolved coupling to ¹⁰³Rh was detected. The data indicate a tetragonally compressed tetrahedral structure (D_2d) rather than the alternative C_3v geometry provisionally proposed for the related [Co(P(OMe)₃)₄] complex.     

Gas-phase reactions of protonated tryptophan

The gas phase reactions of protonated tryptophan have been examined in a quadrupole ion trap using a combination of collision induced dissociation, hydrogen-deuterium exchange, regiospecific deuterium labeling and molecular orbital calculations (at the B3LYP/6-31G* level of theory). The loss of ammonia from protonated tryptophan is observed as the primary fragmentation pathway, with concomitant formation of a [M + H - NH(3)](+) ion by nucleophilic attack from the C3 position of the indole side chain. Hydrogen-deuterium exchange and regiospecific deuterium labeling reveals that scrambling of protons in the C2 and C4 positions of the indole ring, via intramolecular proton transfer from the thermodynamically preferred site of protonation at the amino nitrogen, precedes ammonia loss. Molecular orbital calculations have been employed to demonstrate that the activation barriers to intramolecular proton transfer are lower than that for NH(3) loss.     

Phosphaalkynes as ligands in organometallic chemistry. Syntheses and 31p NMR spectra of platinum(II), palladium(II) and rhodium(I) complexes of dη5-cyclopentadienyltetracarbonyl-μ-(3,3-dimethyl-1-phosphabutyne)dimolybdenum, [Mo2(CO)4(η-c5H5)2tBuCP)]

Syntheses of the complexes trans-[PtCl₂(PR₃)Mo₂(CO)₄(η⁵-C₅H₅)₂(^tBuCP)], (PR₃=PEt₃, PPr₃, PBu₃, PPh₂Me, PPhMe₂) trans-[PdCl₂(PBu₃)Mo₂(CO)₄(η⁵-C₅H₅)₂(^tBuCP)], and trans[RhCl{(PF₂NMe)₂CO}Mo₂(CO)₄(η⁵-C₅H₅)₂(^tBuCP)] are described and their ³¹P NMR spectra presented and discussed.