Laser-induced break-up of water jet waveguide

In this article, an optical method to control the break-up of high-speed liquid jets is proposed. The method consists of focusing the light of a pulsed laser source into the jet behaving as a waveguide. Experiments were performed with the help of a Q-switched frequency doubled Nd:Yag laser (=532 nm). The jet diameter was 48 µm and jet velocities from 100 to 200 m/s. To study the laser-induced water jet break-up, observations of the jet coupled with the high power laser were performed for variable coupling and jet velocity conditions. Experimentally determined wavelength and growth rate of the laser-generated disturbance were also compared with the ones predicted by linear stability theory of free jets.     

Separation of ethoxylated bisphenol A dimethacrylates in dental composite after derivatisation to ionisable amines by capillary zone electrophoresis

Bisphenol A ethoxylate dimethacrylates (Bis-EMA) are transformed into ionisable amines by derivatisation in order to make the analytes applicable to capillary electrophoresis. For this goal, piperidine was added onto the C=C double bond of the alpha,beta-unsaturated ester group forming a tertiary amine with pKa values between 9 and 10. Formation of the derivatives was confirmed by electrospray ionisation MS. Commercial Bis-EMA is a mixture of homologues with different number of ethoxy groups; it is characterised by the average number of the ethoxy groups in the chains. These homologues were resolved by capillary zone electrophoresis at pH 4. It is shown for the product with an average of four ethoxy groups per Bis-EMA molecule that about seven homologues can be baseline separated when differing by only one ethoxy group. For Bis-EMA with 30 ethoxy groups in average, about 23 homologues could be differentiated. The high resolution power of capillary zone electrophoresis enables characterisation of commercial dental composite material concerning the Bis-EMA constituents.     

Correlation of Dative Bond Length and Donor Proton Affinity in Adducts of SO3: A Good Predictor for HCCCN-SO3

The rotational spectrum of HCCCN-SO₃ has been observed using Fourier transform microwave spectroscopy. The vibrationally averaged structure is that of a symmetric top, with the HCCCN axis along the C₃ axis of the SO₃, and the nitrogen end near the sulfur. The N-S bond length is 2.567(13) Å, which is slightly shorter than the sum of the van der Waals radii. The NSO angle is 91.7(4)°, indicating a small but distinct distortion of the SO₃ from planarity, and the N-S interaction can be described as a chemical bond in an early stage of its formation. The N-S bond lengths in a series of SO₃ adducts with amines, nitriles, and pyridine are shown to correlate well with the proton affinities of the bases. In addition, for the bases considered here, the proton affinities vary in a regular manner with the ionization energies corresponding to removal of a lone pair electron. Thus, the trend in proton affinities follows the variation in energy gap between donor and acceptor orbitals in these complexes, accounting for the utility of the proton affinity in correlating aspects of structure and bonding across the series.     

A study of the weinhold-wang bounds to overlap integrals

The Weinhold-Wang extension of the Braun-Rebane formula for bounds to overlap integrals has been investigated numerically for the first and second excited s states of the hydrogen atom. The effect of the choice of basis sets is demonstrated with particular emphasis on the difference between a complete set and an incomplete set of expansion functions