Temperature- and pressure-dependent absorption coefficients for CO2 and O2 at 193 nm

Absorption of laser radiation at 193 nm by CO₂ and O₂ was studied at a series of different temperatures up to 1273 K and pressures up to 1 bar. The spectrum for CO₂ was found to be broadband, so that absorption could be fitted to a Beer-Lambert law. On the other hand, the corresponding O₂ spectrum is strongly structured and parameterisation requires a more complex relation, depending on both temperature and the product (pressure 2 absorption path length). In this context, the influence of spectral structure on the resulting spectrally integrated absorption coefficients is discussed. Using the fitting parameters obtained, effective transmissions at 193 nm can be calculated for a wide range of experimental conditions. As an illustration of the practical application of these data, the calculation of effective transmission for a typical industrial flue gas is described.     

A problem on heat conduction in a wire enclosed by a cylindrical material solved by numerical inverse Laplace transform

The present paper describes the solution of a heat conduction problem by use of Laplace transformation and numerical inversion. Numerical results are given and compared with the asymptotic expressions and further the accuracy is discussed by comparing the values obtained from ten-point and eleven-point inversion formulas.     

Optically active low-temperature inversion stabilised 1,2-dithiane by photolysis with circularly polarised light

Optically active 1,2-dithiane has been produced in a hydrocarbon g ass at 77 K by photolysis with circularly polarised light. Its CD spectrum (above 270 nm) consists of a single symmetric component coinciding with the position of the low energy absorption band. The possibility of using the method to study any per se chiral but at room temperature statistically optically inactive molecule is stressed. A relation yielding Δ? is presented.     

Spatial distribution of competing ions around DNA in solution

The competition of monovalent and divalent cations for proximity to negatively charged DNA is of biological importance and can provide strong constraints for theoretical treatments of polyelectrolytes. Resonant x-ray scattering experiments have allowed us to monitor the number and distribution of each cation in a mixed ion cloud around DNA. These measurements provide experimental evidence to support a general theoretical prediction: the normalized distribution of each ion around polyelectrolytes remains constant when ions are mixed at different ratios. In addition, the amplitudes of the scattering signals throughout the competition provide a measurement of the surface concentration parameter that predicts the competition behavior of these cations. The data suggest that ion size needs to be taken into account in applying Poisson-Boltzmann treatments to polyelectrolytes such as DNA.     

Spectral compression of femtosecond pulses in photonic crystal fibers

We demonstrate efficient spectral compression of femtosecond pulses near the zero-dispersion wavelength in nonlinear photonic crystal fibers (PCFs). The highest measured compression factor is 21, in which case the spectral brightness increases by a factor of 5. We numerically model the pulse propagation and find good agreement with the experiment. We argue that the fibers studied allow for spectral narrowing of more than 2 orders of magnitude. With dispersion-shifted PCFs, efficient spectral compression can take place across the visible and near-infrared part of the spectrum.     

Time-multiplexed multifocal multiphoton microscope

We resolve the classical conflict between parallelization and axial resolution in three-dimensional fluorescence microscopy through time-multiplexed multifocal multiphoton excitation. A rotating array of microlenses on a disk splits ultrafast laser pulses in such a way that an array of high-aperture foci are created in the sample. Two rigidly mounted corotating glass disks with suitable arrays of holes ensure that adjacent foci illuminate the sample at different time points. Recordings of biological specimens demonstrate elimination of out-of-focus haze for densely packed foci and concomitant substantial improvement of contrast and resolution.     

Preparation of radioactive enantiomers of amino acids using labelled racemates only

It is shown from experiments on leucine, that is possible to obtain pure enantiomer tracers of amino acids by using radioactive racemates only. The resolution takes place in a single crystallization step after mixing the active racemate with the inactive enantiomer, due to an absolute stereoselection.     

Laser photodissociation of H2O at 157 nm: rotational energy distribution in product OH(X2II)

Water molecules are photolyzed into the electronic ground states of H and OH. A non-Boltzmann distribution of OH rotational levels is found, in disagreement with a previous measurement, and with analogous results for H₂S.