Determination of the N=16 shell closure at the oxygen drip line

The neutron unbound ground state of (25)O (Z=8, N=17) was observed for the first time in a proton knockout reaction from a (26)F beam. A single resonance was found in the invariant mass spectrum corresponding to a neutron decay energy of 770_+20(-10) keV with a total width of 172(30) keV. The N=16 shell gap was established to be 4.86(13) MeV by the energy difference between the nu1s(1/2) and nu0d(3/2) orbitals. The neutron separation energies for (25)O agree with the calculations of the universal sd shell model interaction. This interaction incorrectly predicts an (26)O ground state that is bound to two-neutron decay by 1 MeV, leading to a discrepancy between the theoretical calculations and experiment as to the particle stability of (26)O. The observed decay width was found to be on the order of a factor of 2 larger than the calculated single-particle width using a Woods-Saxon potential.     

The heptakisoctahedral group and its relevance to carbon allotropes with negative curvature

We introduce the pollakispolyhedral groups and describe in detail the representational structure of PSL(2,7) or ⁷ O, the automorphism group of the Klein graph composed of 56 trivalent vertices arranged in 24 heptagonal faces. Leapfrog and quadruple transformations of the graph are described and their eigenvalue spectra derived. Considered as carbon frameworks on the “plumber's nightmare” surface these chiral structures exhibit significant steric strain which prevents the molecular realisation of the Klein symmetry. This revised version was published online in July 2006 with corrections to the Cover Date.     

Steady streaming flows near spheroids oscillated at multiple frequencies

The results of flow visualization and particle image velocimetry (PIV) studies of steady streaming flows near oscillating spheroids (aspect ratios of 0.75, 1, and 1.33) are reported for normalized amplitudes of 0.025–0.15 and Reynolds numbers of 27–89. The oscillations are described by either a single-frequency sine wave or the sum of two such sine waves with different frequencies. For normalized amplitudes of 5% or less, the PIV data suggest that steady streaming flow fields superpose. In other words, the time-independent portion of the velocity field created by forcing the spheroid simultaneously at two different frequencies is found to be the sum of the two steady streaming velocity fields created by forcing the body individually at each of the two frequencies.     

Post-buckling analysis for the precisely controlled buckling of thin film encapsulated by elastomeric substrates

The precisely controlled buckling of stiff thin films (e.g., Si or GaAs nano ribbons) on the patterned surface of elastomeric substrate (e.g., poly(dimethylsiloxane) (PDMS)) with periodic inactivated and activated regions was designed by Sun et al. [Sun, Y., Choi, W.M., Jiang, H., Huang, Y.Y., Rogers, J.A., 2006. Controlled buckling of semiconductor nanoribbons for stretchable electronics. Nature Nanotechnology 1, 201–207] for important applications of stretchable electronics. We have developed a post-buckling model based on the energy method for the precisely controlled buckling to study the system stretchability. The results agree with Sun et al.’s (2006) experiments without any parameter fitting, and the system can reach 120% stretchability.     

Oxyalkylene polymers with alkylsulfonylmethyl side chains: Gas barrier properties

Gas barrier properties of alkylsulfonylmethyl-substituted poly(oxyalkylene)s are discussed. Oxygen permeability coefficients of three methylsulfonylmethyl-substituted poly(oxyalkylene)s, poly[oxy(methylsulfonylmethyl)ethylene] (MSE), poly[oxy(methylsulfonylmethyl)ethylene-co-oxyethylene] (MSEE), and poly[oxy-2,2-bis (methylsulfonylmethyl)trimethylene oxide] (MST) were measured. MSEE, which has the most flexible backbone of the three polymers, had an oxygen permeability coefficient at 30°C of 0.0036 × 10⁻¹³ cm³(STP)·cm/cm²·s·Pa higher than that of MSE, 0.0014 × 10⁻¹³ cm³(STP)·cm/cm²·s·Pa, because the former polymer's T_g was near room temperature. MST with two polar groups per repeat unit and the highest T_g showed the highest oxygen permeability, 0.013 × 10⁻¹³ cm³(STP) · cm/cm²·s·Pa, among the three polymers, probably because steric hindrance between the side chains made the chain packing inefficient. As the side chain length of poly[oxy(alkylsulfonylmethyl)ethylene] increased, T_g and density decreased and the oxygen permeability coefficients increased. The oxygen permeability coefficient of MSE at high humidity (84% relative humidity) was seven times higher than when it was dry because absorbed water lowered its T_g. At 100% relative humidity MSE equilibrated to a T_g of 15°C after 2 weeks. A 50/50 blend of MSE/MST had oxygen barrier properties better than the individual polymers (O₂ permeability coefficient is 0.0007 × 10⁻¹³ cm³(STP)·cm/cm² ·s·Pa), lower than most commercial high barrier polymers. At 100% relative humidity, it equilibrated to a T_g of 42°C, well above room temperature. These are polymer systems with high gas barrier properties under both dry and wet conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 75–83, 1998     

Sodium trifluoroacetate as a tune/calibration compound for positive- and negative-ion electrospray ionization mass spectrometry in the mass range of 100–4000 Da

We have identified aqueous:acetonitrile solutions of alkali-metal trifluoroacetate compounds as tune/calibration standards for both positive- and negative-ion electrospray ionization mass spectrometry (ESI/MS). Each alkali-metal trifluoroacetate solution in water and acetonitrile (50:50, v/v) yields evenly spaced, singly charged peaks in the mass range of 100–3500 Da. Intense peaks are formed either by infusing the solution using a syringe pump, by infusing the solution into a stream of liquids [such as a high-performance liquid chromatography (HPLC) mobile phase] flowing to the electrospray needle, or by injecting the salt-containing solution into an HPLC mobile phase containing trifluoroacetic acid. The advantages of these compounds include: (i) generation of singly charged ions in both positive and negative ionization modes in the mass range of approximately 100–3500 Da, (ii) formation of evenly spaced peaks with similar intensity across the entire mass range, (iii) the most abundant isotope in each mass cluster is the lowest mass peak (monoisotopic mass), which is free from variation in natural isotope distribution, (iv) commercial availability, (v) they easily dissolve in common liquid chromatography solvents, and (vi) lack of any long-lasting memory effects or background problems.     

Propagation of Solitary Pulses in Optical Fibers with Both Self-Steepening and Quintic Nonlinear Effects

Pulse dynamics and stability in optical fibers in the presence of both self-steepening and quintic nonlinear effects are analyzed. Propagating profiles of the quintic derivative nonlinear Schrodinger model are isolated via two invariants of motion. The resulting canonical equation admits exact periodic propagating patterns in terms of the Jacobi elliptic functions, and solitary pulses are recovered in the long wave limit, i.e. degenerate cases of periodic profiles where each pulse is widely separated from the adjacent ones. Two families of such exact wave profiles are identified. The first one has a precise constraint concerning the magnitude of self-steepening and quintic nonlinear effects, while the second one permits more freedom. The reduction to the well established temporal soliton in an optical fiber waveguide in the absence of self-steepening and quintic nonlinearity is demonstrated explicitly. Numerical simulations are performed to identify regimes of parameter values where robust propagation patterns exist.