Table of contents

The most important part of a scanning acoustic microscope system is the wide-opening-angle lens which could have many shapes and sizes. Such lenses include several interfering surface modes which may obscure the measured acoustic properties. In this paper, we investigate the conventional spherical wide-angle lens whose central part has been covered by a circular aperture stop of varying diameter, D, to absorb the energy of acoustic modes. The influence of increasing D of such absorbers on the acoustic signatures, V(z), of plastic materials in which the speed of sound is slow (plexiglass) and materials in which the speed of sound is relatively fast (silica and stainless steel) is investigated theoretically and experimentally, leading to similar behaviours: a decrease in amplitude, a broadening of periodic spacings and the complete disappearance of the oscillatory form of V(z) for large D, namely for large excluded angles. A novel formula for periods, , is proposed for covered lenses, which explains the velocity shift associated with the period variation as the excluded angle increases.

We have investigated ordering at the (110) surface of using scanning tunnelling microscopy (STM) and reflectance anisotropy spectroscopy (RAS). The surface is found to adopt the L structure of , with double atomic height steps and the exclusive existence of a termination by rows of atoms believed to be Cu. These rows are revealed to be imperfectly ordered on a scale to which previous diffraction experiments would have been insensitive. RAS revealed the presence of a feature at about 2 eV similar to that observed on the surface of pure Cu(110), which we attribute to the rows of Cu atoms on the (110) surface. The intensity of the RAS feature was lower than that found for the Cu(110) surface, though it developed with annealing, implying that it may be used to monitor the disorder in the Cu rows observed by STM.

Low-energy cluster beam deposition (LECBD) has been used to synthesize cermets with controlled size nanoparticles. In the In - system, this technique allows the formation of In nanograins uniformly distributed in the insulating matrix. Optical spectra in the range 2 to 6 eV present plasmon resonance bands which have been interpreted by Mie and Maxwell-Garnett theories. XPS measurements have shown an oxidation of a fraction of the indium particles.

The control of a model system describing thin film growth processes from a multicomponent gas with chemical reactions occurring between components of source phase is studied. It is shown that condensation of thin films may be realized by different ways. In particular, for a low rate of particles arriving on a substrate the stable condensation mode occurs and any deviations from equilibrium are dumped. For a medium arrival rate, phase transitions take place in the oscillation mode (stable limit cycle). For a large arrival rate the stable limit cycle is destroyed and new phase condensation takes place in saw-tooth (accumulative) mode. A method of adaptive control of this oscillatory process - by varying the external parameters - is described based on recursive goal inequalities and an input - output linearized Poincaré map. The controlled system behaviour is analysed by means of computer simulations. It is found that the system being investigated has a peculiar memory because film condensation occurs in a different way for the same parameters but with differences in prehistory. It is noted that even small differences in the prehistory of the external parameters can lead to different modes of settling.

We report investigations of the repulsive forces between monodispersed ferrofluid droplets in the presence of a weak polyelectrolyte, poly(acrylic acid) (PAA), using a magnetic chaining technique. Two interesting observations were made during our investigations. At a PAA concentration of 0.01 wt%, a long-range repulsive force profile was observed due to the adsorption of polyelectrolyte onto the droplet, without any irreversible aggregates even at very small inter-droplet spacings. Above a concentration of 0.01 wt% of PAA, formation of irreversible chaining of droplets was observed at short inter-droplet separations due to polyelectrolyte binding or bridging. The onset of binding was also independently confirmed by microscopic observation.

An experimental study was conducted to clarify the control characteristics of a non-equilibrium plasma boundary layer flow over a biased and water-cooled flat plate in the tube induced by applying a magnetic field. Argon gas was partially ionized by a DC arc discharge at low pressure. The flat plate was set along the direction of flow in the tube, to which the positive and negative voltage could be alternatively biased. A mirror-type magnetic field was applied to the plasma boundary layer flow over the flat plate by two solenoids. The electron temperature was increased by applying the magnetic field, but the electron number density increased for the negative bias and decreased for the positive bias. Under these conditions, enhancement of the transport properties of electrons occurred. The heavy-particle temperature was increased and the thermal boundary layer thickness over the flat plate was decreased by applying the magnetic field, which resulted in an increase in the heat flux into the plate. The visualization study showed that the relative variation of the radiative temperature nearly corresponded to the electron temperature field in the applied magnetic field. This implies that the application of a combined electromagnetic field is an effective method by which to control the flow of a non-equilibrium plasma boundary layer over a flat plate.

The types of atomic short-range orders (SROs) in the amorphous alloy and its crystallization products under different thermal-treatment conditions were investigated by means of spin-echo nuclear magnetic resonance (NMR) and Mössbauer spectroscopy. It was found that there exist two kinds of SROs in the amorphous alloy: body-centred tetragonal (BCT) B- and orthorhombic (o) B-like SROs. The crystallization products differ at various annealing temperatures: the sample annealed at C for 10 min consists of BCT B containing Gd and -Fe, without the phase; the sample annealed at C for 60 min contains BCT B, and -Fe; and the sample crystallized at C for 10 min consists of B, -Fe, and . The experimental results indicate that the NMR peak shifts from 34.7 MHz for pure BCT B in the sample annealed at C for 60 min to 36.0 MHz for the sample annealed at C for 10 min and the relative intensity of the third Mössbauer sub-spectrum, corresponding to the (8g) site of BCT B, is about 6% less than those of the other two. These facts can be explained in terms of the entering of Gd atoms into the BCT B phase.

Piezomagnetism refers to a change in the intrinsic magnetization of a material subjected to mechanical actions such as tension or compression. In a ferromagnet such as a mild steel these effects are easily measured: typically a stress of or 140 MPa induces a magnetic moment of the order of emu or , resulting in flux densities in the range 10 mG or T in the vicinity of the specimen. Since piezomagnetic effects are due to interactions between the mechanical and magnetic mesostructure of materials microplastic processes that alter the arrangement of the ferromagnetic domain structure affect the intensity of the associated magnetic fields. The progressive degradation of such materials under cyclic loading can therefore be tracked by following the evolution of the piezomagnetic field. Specifically, if the measurements are displayed as loci in a three-dimensional stress - strain - field (B) space, the approach to fatigue failure is paralleled by a series of conspicuous geometric transformations of these curves. Complementary information also appears in continuous-time records of B(t): these magnetograms clearly show the abrupt incidence of `infarcts' (microcracks) and the cumulation of phase shifts as the material degrades.

A relationship between two well known, small-angle approximations of the radiative transfer theory was found. The first approximation was initially obtained using the Fourier transform technique to solve the small-angle radiative transfer equation. The expansion of the transmitted intensity by Legendre functions was used to obtain the second small-angle approximation. These approximations represent solutions of the small-angle radiative transfer equation in two coordinate systems (spherical and cylindrical) and should coincide at small scattering angles, where the difference between the two coordinate systems disappears. This was shown in this paper analytically using the asymptotical relation for Legendre functions at small angles and the Euler sum formula.

An analytical formula for the value of the coefficients of the expansion of the phase function of large particles by Legendre functions at was found.

The relationship between different optical sizing techniques under multiple-light-scattering conditions was discussed.

The power optimization of an endoreversible heat engine has been performed, and design characteristics have been described at maximum-power conditions. A technologically important example defined as heat exchange by combined radiation and convection has been considered. The analysis shows that the maximum power output of the heat engine is sensitive to the temperature, small values of the ratio of convective heat transfer coefficients of hot to cold ends and small values of the emittance ratio of heat source to heat sink. By considering the output power, and must be held around 0.2, 0.01 and 0.0125 for optimum design considerations, respectively.

The effects of thermal resistances and internal irreversibilities on the performance of combined heat-pump cycles (combined vapour compression - vapour compression heat pumping and combined vapour compression - absorption heat pumping) were investigated using a finite-time thermodynamic approach. Improved equations for the coefficient of performance of the systems under consideration were obtained. It was found that combined vapour compression heat pumping is more effective than combined vapour compression - absorption heat pumping for the same heating load regardless of its energy consumption being greater.

Although the ideal Carnot engine rejoices in the largest efficiency of any heat engine operating between given temperature extremes, alternative closed-loop four-step cycles in which a variable-temperature, straight-line transition replaces the Carnot high-temperature isothermal expansion appear ostensibly to offer a higher thermodynamic efficiency. This arises from the fact that higher maximal temperatures are attained; the efficiency of the equivalent Carnot engine operating between such temperature extremes reinstates Carnot supremacy by slightly transcending the unconventional engine's efficiency. Our investigations stress the importance of the second, as well as the first, law of thermodynamics, and consider operating characteristics quantitatively for specimen engines of various design.

In support of studies to determine cross sections in ionizing gases using swarm techniques, we have developed a set of statistically accurate transport parameters for a non-conservative model gas using Monte Carlo simulation. Study of this model highlights the effects of non-conservative collisions on electron transport in the absence of concerns over the validity of any particular `real' gas model and provides a benchmark model system that can be utilized in both Monte Carlo and Boltzmann studies of gaseous electronics. A method of analysis is presented which allows Monte Carlo simulation to separate the exact reactive and flux components of the measurable transport coefficient. The results of the simulation are compared with a multi-term Boltzmann analysis.

We have measured the density profiles of a pulsed gas jet expanding into vacuum in order to characterize its suitability as a target for laser - plasma interaction studies. A Mach - Zehnder interferometer has been used to measure the densities for gas-reservoir pressures in the range Torr with 1 and 1.75 mm diameter opening nozzles in and Ne gas. and Ne gas jets with the same nozzle opening were found to produce similar density profiles. The axial and radial density profiles of the gas jet are presented and shown to fit well to simple self-similar profiles with an exponentially decreasing density with the distance from the gas jet nozzle and Gaussian-shaped radial density profiles. It is shown that such profiles can be expected for the free expansion of a low-viscosity fluid into vacuum.

Spectrally resolved measurements of Thomson scattering were made in a freely burning arc in argon at a pressure of 1 atm. The radial and axial profiles in electron temperature and number density exhibited extensive regions of departure from local thermodynamic equilibrium, so confirming the findings of Snyder et al in E 48 4124 - 7, 1993. Electron temperatures at least 4000 K above those of the gas were found. Asymmetry in the Thomson electron feature was found and shown to depend on which segment of the laser-profile scattering data was sourced. This arises from an asymmetry in the arc - laser interaction. Also described is a simple technique for accurately defining the position of the cathode tip once an arc has been ignited.

Time-resolved laser-induced fluorescence detection of metastable and NO and time-resolved emission spectroscopy of the -band of NO have been applied to a - RF pulsed discharge in order to show that the process is responsible for NO(A) excitation in discharge systems of this kind. Highly resolved spectra obtained under such conditions have revealed that there is a non-Boltzmann rotational distribution in the ) state with a large excitation of levels J>20.

An explanation of the observed fact that the rate of evaporation of an electrode in the pulsed gas metal arc welding mode decreases when the frequency of pulsing is increased (thus producing less fumes) is presented. The major portion of the total evaporation in the pulsed mode occurs when the surface temperature of the electrode is close to its maximum value. Therefore, all the methods that decrease the maximum value of the surface temperature, such as increase in frequency and choice of the proper current waveform, reduce the fume generation rate. A mathematical model to describe the arc electrode evaporation in the pulsed mode is presented.

In predicting the overall thermal conductivity of composite porous structures such as building materials or soils, the thermal conductivities of their solid components must be known in order to apply some theoretical models. Horai proposed a method to determine the thermal conductivity of solid particles. The material under study is first ground to a fine powder. This powder is then carefully saturated with a fluid and the thermal conductivity of this mixture is measured using the `needle probe' method. Finally, the conductivity of the solid phase is evaluated using a mixing-law model, namely the mean of the so-called `Hashin and Shtrikman bounds'. We have introduced a slightly different version of this method that uses the `transient plane source' (TPS) technique recently developed by Gustafsson for simultaneously measuring both the thermal conductivity and the thermal diffusivity of solids or fluids. An adapted experimental device has been designed and our approach has been validated through measuring, at room temperature, the thermal conductivities of the well-known minerals quartz, calcite and kaolinite. Afterwards, while considering that our method had become fully operational, we studied the thermal conductivity of the solid aggregates of a light-weight, energy-saving concrete whose solid phase is a mixture of natural clay, hardened cement paste and wood aggregates in various proportions.

The predictions of a numerical model of the cathode-sheath region of high-pressure arcs using three different equations for the cathodic electron-emission current density are compared for two typical arc - cathode systems. These equations for cathodic electron emission include: (i) the field-enhanced thermionic emission (FEE) equation representative of the electron emission for high temperatures and moderate electric field strengths ; (ii) the Murphy and Good (MG) equation for thermo-field (T-F) emission valid for high temperatures and high surface electric field strengths in the range about - ; and (iii) the Murphy and Good equation for T-F emission enhanced by the presence of a high density of slowly moving ions in the cathode region (the MG+I equation). Results show that, in the case of a metal vapour arc (representative of vacuum arcs and high-pressure arcs on non-refractory cathodes) the use of the MG+I equation is always prescribed due to the formation of the high-local-pressure cathode-spot plasma. For high-pressure arcs on refractory cathodes the results show that, at atmospheric pressure, the generally used FEE equation introduces an underestimation by at least around 20% of the cathodic electron current density compared with the MG+I equation. The same comparison but for an ambient pressure of 50 atm shows that this underestimation becomes considerable.