Femtosecond laser-induced Coulomb-explosion imaging of 3,5-dibromo-3 ,5-difluoro-4-cyanobiphenyl molecules prealigned in space is explored using a pixel-imaging mass-spectrometry (PImMS) camera. The fast-event-triggered camera allows the concurrent detection of the correlated two-dimensional momentum images, or covariance maps, of all the ionic fragments resulting from fragmentation of multiple molecules in each acquisition cycle. Detailed simulation of the covariance maps reveals that they provide rich information about the parent molecular structure and fragmentation dynamics. Future opportunities for imaging the real-time dynamics of intramolecular processes are considered.

In this paper we describe a semianalytical approach to computing the temperature and thermal stress inside a III-V compound grown with the Czochralski technique. An analysis of the growing conditions indicates that the crystal growth occurs on the conductive time scale. A perturbation method for the temperature field is developed for an arbitrary crystal profile using the Biot number as a (small) expansion parameter. The zeroth order solution is one-dimensional in the axial direction. Explicit solutions are obtained for a cylindrical and a conical crystal. Under typical growth conditions, a parabolic temperature profile in the radial direction is shown to arise naturally as the first order correction. As a result, the thermal stress is obtained explicitly and its magnitude is shown to depend on the zeroth order temperature and Biot number. Both the axial temperature gradient and crystal profile are shown to be important for controlling thermal stress and defect density. Some issues relevant to growth conditions are also discussed.

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Moisture measurement in bauxite ore as it is being offloaded from a ship is a challenge that was brought to a European Study Group with Industry at the University of Limerick in 2017. A refinery asked the Study Group to confirm if it is possible to calculate the moisture content once every second, by passing microwaves through the ore as it is being offloaded at about 2 m/s. The microwaves experience a phase shift and signal attenuation, depending on the amount of moisture present. We review the theory of microwave transmission through a polarising medium, and we present and study the data produced by the microwave analyser. We explore the consequences of the method for measuring phase change, and the effects of noise on the phase shifts observed. We provide an algorithm for lifting the measured phase shifts from their restricted range to an unlimited range for the true phase shift. Concurrent measurements of ore height are central to the lifting algorithm. We note the effect of interference on the attenuation seen in data.

Numerical predictions of underwater sound propagation are routinely carried out by applying marching algorithms to solve parabolic equations. These equations require initial field data to begin marching process. For many applications, a suitably normalized Gaussian or sinc function of depth (z) is used [E. R. Robinson and D. H. Wood, J. Acoust. Soc. Am. Suppl. 1 81, S10 (1987)]. These functions, however, do not model correctly the vertical-wavenumber (kz) spectrum associated with the farfield of a point source. In this paper, a new starting field is presented that matches the proper k, variation over the full spectral aperture needed by wide-angle parabolic equation models. The new field in the z domain is obtained numerically via a discrete Fourier transform of its bandlimited spectrum. Because of this efficient distribution of energy in the kz domain, a larger step-size (Δz) can be used than that required by the Gaussian initial field [H. M. Garon, J. S. Hanna, and P. V. Rost, J. Acoust. Soc. Am. Suppl. 1 61, S12 (1977)]. Numerical examples comparing the effects of different starting fields on wide-angle parabolic equation predictions are presented.