Water waves in the time domain

The initial-value problem for a structure floating on the surface of the sea is investigated under the assumptions of linear theory. Fourier transforms are used to connect the time- and frequency-domain representations of the coupled motion of the fluid and body. This allows the large-time asymptotics of the motion to be obtained from the singularity structure of the frequency-domain potential in the complex plane. Under certain initial conditions, the free motion of a body about a fixed, equilibrium position is shown not to exist for all time, and in this case the assumptions behind the linear theory are violated. For suitably moored structures, motion is found which is purely exponentially decaying in time and does not involve any oscillations.     

Frequency-tunable optically pumped carbon monoxide laser

Single-line frequency-tunable lasing was observed in an optically pumped, repetitively pulsed, room-temperature CO laser for the first time. The R(0) and R(7) ro-vibrational transitions in the (2,0) overtone of CO at 2.3 μm were optically pumped with a high-energy optical parametric oscillator. Single-line lasing was observed on (2,1) P(2)-P(17) transitions and R(0)-R(11) transitions (covering wavelengths within the range 4.6-4.9 μm) when using a diffraction grating as the spectrally selective reflector of the laser resonator. The observed CO laser pulse lengths were ~10^-7 s with peak power up to 10⁴ W. The influence of CO pressure, the addition of buffer gas (He, Ar), Q-factor of the laser resonator, and the pump pulse energy on CO laser pulse temporal characteristics and output energy spectral distribution was studied experimentally     

Nonlinear theory of a free-electron laser exploiting media with aperiodically modulated refractive index

The nonlinear theory of a free-electron laser (FEL) exploiting media with a periodically modulated refractive index is presented. The gain and the saturation parameters are found for different operating regimes of such a FEL. The system discussed could be used for the amplification of light in the optical and ultraviolet regions of the spectrum     

The application of the foam fractionation process to the removal of viruses process to the removal of viruses: Part II. The prediction of the residual surfuctant concentration

Variations in the initial concentration of the surfuctant. Arquad T50 (a blend of alkyl quaternary ammonium chlorides), and the gas to liquid flow ratio were assessed for their effect upon the residual surfactant level. This concentration was found to be dependent upon these variables as well as upon the bubble diameter in the liquid phase as determined by the gas rate. An equation was derived which represented the removal of surfactant as a power function of (i) its initial concentration, (ii) the gas to liquid flow rate ratio and (iii) the gas flow rate. The error of this equation established that this empirical approach accurately represented the removal of the surface-active agent.     

The application of the foam fractionation process to the removal of viruses process to the removal of viruses: Part III. An investigation of the toxicity of the surfuctant

The factors affecting the removal of viruses by a laboratory scale foam fractionation part were investigated. The virus chosen was Escherichia coli Bacteriophage MS-2 and the surfactant was Arquad T50 (a cationic agent composed of a blend alkyl quaternary ammonium chlorides). It was determined that virus removal was dependent upon two factors: (a) their adsorption to the surfactant and (b) their physical removal as free virus particles entrapped in the interstitial liquid. An equation was derived which represents these factors as a power function of the initial surfactant and a multiple of the ratio of the residual surfactant concentration to its initial level, respectively.     

Scattering of water waves by axisymmetric bodies in a channel

Methods are presented for the calculation of wave forces on a vertically axisymmetric body arbitrarily placed within a channel. Integral representations of singular solutions of the Helmholtz equation, called channel multipoles here, are derived and these allow straightforward solution of the scattering problem for a vertical cylinder extending throughout the depth. In contrast to previous methods there is no need to sum series of images. These multipoles are also used in deriving an approximate solution valid when the radius of the cylinder is small relative to the wavelength and channel width.To solve for arbitrary shaped axisymmetric bodies, a plane-wave approximation is developed based on the assumption that the wavelength is much less than the channel width. Comparisons with the accurate solution for a vertical cylinder suggest that this approximate method performs well even when this assumption is clearly violated. The results of calculations of wave forces on a truncated cylinder are also given.All of the methods described may be applied just as easily to the case of an off-centre body as to a centrally-placed body.     

Pulsed ion cyclotron resonance mass spectrometer for studying ion-molecule reactions

A pulsed ion cyclotron resonance mass spectrometer utilizes the cyclotron resonance principle for mass analysis of ions trapped at low pressures by electric and magnetic fields. Both mass analysis and ion trapping are accomplished in a one-region device called a trapped ion analyzer cell. A pulsing sequence is described which allows for generation of ions by electron impact, reaction with added gases, and mass analysis of the products of ion-molecule reactions. Methods are described for measuring rate constants and equilibrium constants for ion-molecule reactions. The high ion trapping efficiency and open geometry of the analyzer cell make it well suited for studying the interaction of laser radiation with gaseous ions and may also be useful for high-accuracy isotope ration mass spectrometry.