A new reagent for polypeptide synthesis: mu-oxo-bis-(tris-(dimethylamino)-phosphonium)-bis-tetrafluoroborate.

The products 1 and 2 (X = OTs) have been isolated from the reaction between hexamethylphosphortriamide and p-toluene sulfonic anhydride and the latter converted into μ-oxo-bis-[tris-(dimethylamino)-phosphonium]-bis-tetrafluoroborate 2 (X = BF₄). This is a practical reagent for the formation of the peptide link. Where racemisation is possible via oxazolone formation this can be decreased by the addition of 1-hydroxybenzotriazole or N-hydroxysuccinimide. These additives may also increase the efficiency of condensation at glycine and proline residues.     

Resonance raman scattering from metastable O2 molecules in γ-irradiated NaClO3

Resonance Raman scattering has been observed from metastable O₂ molecules produced in single crystals of NaClO₃ by γ-irradiation at 300 K. Evidence that the observed bands are due to O₂ is provided by the Raman spectrum of irradiated ¹⁸O enriched NaClO₃ in which bands due to ¹⁶O₂, ¹⁶O ¹⁸O, and ¹⁸O₂ were identified. The Raman band at 1544 cm^?1 ascribed to metastable O₂ disappears on bleaching with intense 4880 Å radiation enabling the identification of a weaker band at 1557 cm^?1 that is assigned to the stable form of O₂.     

Simulations of petawatt-class few-cycle optical-parametric chirped-pulse amplification, including nonlinear refractive index effects

We present three-dimensional simulations of optical-parametric chirped-pulse amplification stages for a few-cycle petawatt-class laser. The simulations take into account the effects of depletion, diffraction, walk-off, quantum noise, and the nonlinear refractive index (n(2)). In the absence of n(2) effects, we show these stages can generate 3.67J pulses supporting 4fs transform-limited pulse durations. Adding the nonlinear refractive index to the simulation, the energy output is reduced by ~11% and the bandwidth narrows by ~129nm, increasing the Fourier limit by ~17.5%.     

The spectral collocation method for efficiently solving PDEs with fractional Laplacian

We derive a spectral collocation approximation to the fractional Laplacian operator based on the Riemann-Liouville fractional derivative operators on a bounded domain Ω = [a, b]. Corresponding matrix representations of (?△) ^α/2 for α ∈ (0,1) and α ∈ (1,2) are obtained. A space-fractional advection-dispersion equation is then solved to investigate the numerical performance of this method under various choices of parameters. It turns out that the proposed method has high accuracy and is efficient for solving these space-fractional advection-dispersion equations when the forcing term is smooth.