Table of contents

In this communication we propose a calibration method for two-photon absorption laser induced fluorescence (TALIF). It can be carried out without any addition or modification to the O atom TALIF set-up. It is based on the measurement of the collision quenching of the laser-excited state (3p³ P₂ ) in a pure O₂system in which a high dissociation degree can be achieved. Since the collision rate constant by O is largely lower than that by O₂ , the quenching rate can be correlated to the O density. The incertitude in this procedure is comparable to other calibration techniques. We have applied this method to the spatially resolved measurement of O atom density in an O₂rf plasma jet.

We report a set of optical absorption measurements on x-irradiated high-purity sapphire. The results of the photothermal deflection absorption measurements at 1064 nm show an increase of the absorption at the x-irradiated areas. The x-ray damage recovery is achieved through annealing, where the absorption level at 1064 nm is brought from an average level of ~80 ppm cm^-1to ~24 ppm cm^-1 . UV-Vis spectroscopy results suggest that the residual absorption at 1064 nm is due to complex clusters of Ti and Fe ions and oxygen vacancies. We suggest that a further reduction of Ti and Fe in sapphire (<0.1 ppm) as well as oxygen vacancies (through post growth oxidizing annealing) would further reduce the absorption. Moreover, the absorption level of 20 ppm cm^-1remains within the requirements of the second generation laser interferometric gravitational-wave detectors.

Results are presented from studies of the relationship between the friction coefficient and environment, load and sliding velocity for a natural diamond stylus performing reciprocating sliding over a CVD diamond sample. The properties of CVD diamond are not necessarily similar to those of natural diamond. It is thus important to study the tribological properties of the former, both to attempt to understand the friction mechanism and because of its increasing potential applications as a coating material. Traditionally, friction for diamond sliding against diamond has been interpreted principally in terms of the adhesion and surface roughness theories. We put forward, here, a hypothesis based on a chemical transformation occurring during sliding, resulting in the production of graphitic material. The very low friction coefficients that have been measured under certain conditions of load and sliding velocity may thus be partly explained by the lubricating effect of graphite.

This contribution deals with test probes with flat cavities (height of gap h= 0.5 mm), which arise in reality from delamination processes caused by thermal expansion. These test probes are aged by means of partial discharges (pds). The different changes on the cavity's surface, for example the development of surface conductivity, increased surface roughness or crystal growth, have an obvious impact on the results of the phase-angle resolved pd measurement. This impact is physically substantiated and interpreted, so that it is thus possible to `look at' the cavity's surface and to assess the damaging relevance of a gap by means of phase-angle resolved pd measurement.

The effect of dipolar and exchange interactions on the magnetic behaviour of sputtered CoFe-Ag(Cu) granular alloys is examined through the study of remanence curves and Mplots as a function of the ferromagnetic volume content, x_v , and annealing temperature. As-deposited samples, with either a random distribution of weakly interacting fine magnetic particles (3 nm in size) at low x_vor with strong dipolar and exchange interactions (leading to a long range out-of-plane stripe-like domain structure) at x_v 0.25, display negative Mvalues. In the former, this is attributed to dipolar interactions being dominant in a random distribution of well separated particles. In the latter, M <0 is attributed to the flux closure between antiparallel neighbouring domains, which is strongly demagnetizing. Annealing causes phase segregation and particle growth, while particle clusterization occurs. These facts lead to an increase of the direct exchange through the surface of neighbouring grains in the same particle clusters, at the expense of dipolar interactions, which decrease as the clusters become more separated. Consequently, at high x_v , annealed samples display positive Mvalues.

In the flow regulation of a magnetically levitated pipeless flow system, solitary waves may occur, which will lead to pressure fluctuations and surface changes of the levitated diamagnetic liquid column. The present study analyses a soliton in a magnetic pipe both theoretically and experimentally. A two-fluid model is employed here. The theoretical analysis is carried out by a one-dimensional nonviscous and nonlinear method. The experimental study was also carried out by setting two magnetic like poles to produce the magnetic field, using water as the levitated diamagnetic liquid and a diluted kerosene-base magnetic fluid as the surrounding fluid, coupled with a cam system to produce the disturbance. It is found that the magnetic pressure acting on the interface can stabilize the interface. The effects of the magnetic bond number, density ratio of the two fluids and amplitude of the soliton on the soliton wave velocity are clarified.

The influence of film thickness on the microstructure and tunnelling magnetoresistance (TMR) in Fe-SiO₂granular films has been systematically studied using x-ray diffraction, transmission electron microscopy (TEM) and Mössbauer spectroscopy. The results indicate that the average Fe granule size and the size distribution, as well as the interface between the granules and SiO₂matrix, sensitively depend on the film thickness, which modifies the TMR effect. For the very thin films, the TEM image shows an indistinct interface between the Fe particles and SiO₂matrix, and the corresponding Mössbauer spectrum shows the existence of a strong non-magnetic Fe₂ SiO₄component, which is responsible for the small TMR of this film. While for the thickest film, the long sputtering time makes the Fe granules grow so large as to aggregate some of them, which also leads to the small TMR. The optimum thickness in our samples is 0.55 µm, which gives the largest TMR value of -3.3% at room temperature under a field of 1.6 T due to the uniform size of the small particles and the few in the Fe₂ SiO₄phase. Our results give evidence that small Fe particles with a narrow size distribution and without oxidation favours the TMR effect.

The effects of deterministic surface wavy roughness on the fluid flow inside annuli with microfabricated solid walls was investigated. The Navier-Stokes equations are solved using perturbation methods with incorporated microscopic slip conditions at the wavy wall. The volume flow rate thus obtained, considering fully-developed parallel flow cases, contains terms which are related to the Knudsen number (K_n ) of the fluid, roughness ratio ( ), phase shift ( ) and the wave number (k ) of the small wavy-roughness elements. The results show that if the phase shift is zero once K_nis ~0.1 then the increase of kwill reduce the second-order volume flow rate significantly. Meanwhile, there is a critical kfor the K_n= 0.1 case, in which increases and then this critical kincreases.

Particles suspended in fluid exhibit motion when subjected to ac electric fields. The applied field results in forces on both the particles and the fluid, the study of which is referred to as ac electrokinetics. The ac electrokinetic techniques can be used for the controlled manipulation and characterization of particles, and the separation of mixtures. For sub-micrometre particles, Brownian motion is important and strong electric fields are required to overcome these effects. Planar micro-electrode arrays, fabricated using semiconductor manufacturing processes, can generate electric fields of the required strength from low potentials over a wide range of frequencies. This paper reviews and discusses sub-micrometre particle dynamics under the influence of dielectrophoretic and electrohydrodynamic forces. New experimental observations of the movement of sub-micrometre particles are also presented.

A detailed self-consistent threshold simulation of the continuous wave (CW) operations at room temperature (RT) of possible GaN/AlGaN/AlN vertical-cavity surface-emitting lasers (VCSELs) is developed in a simple mathematical form in order to give an opportunity for it to be carried out using only PC-level computing power. In the analysis, the mismatch-related phenomena and temperature dependences of many model parameters are included with the aid of a self-consistent approach.

Multiple-quantum-well (MQW) structures are proved to be the best suited for RT CW nitride VCSEL devices. In contrast, currently available nitride technology practically excludes the possibility of an efficient RT CW operation of single-quantum-well (SQW) nitride VCSELs. Double-heterostructure (DH) nitride VCSELs are found to be less sensitive to increases in optical losses than other nitride VCSELs, therefore their RT CW operation, if possible, may occur for a wider current range than that in QW VCSELs. It is also revealed that substrate material has a critical influence on the possibility of reaching RT CW thresholds, which strongly favours the SiC substrate of very high thermal conductivity.

The linear stability properties of a sheet beam Cherenkov free-electron laser are analysed. The effects of the finite electron beam thickness and temperature on the radiation growth characteristics are studied.

Thermal conductivity, thermal diffusivity and heat capacity per unit volume of consolidated porous rocks have been studied as a function of temperature with air as a saturant, at atmospheric pressure. The transient plane source (TPS) technique is used for the simultaneous measurement of these parameters. An empirical formulation is shown to account for the computation of thermal conductivity of porous rocks in terms of porosity and thermal conductivities of mineral constituents. The measurements showed a linear increase in thermal conductivity with temperature.

A linear correlation between the depth and the length of the weld pool is found in laser beam welding experiments with varied laser beam power and constant welding speed. On the other hand, the weld pool length changes only slightly with increased welding speed and constant laser beam power. The existing analytical and numerical models fail to explain these dependences. The observed effects are essentially conditioned by the fluid flow in the weld pool caused by the thermocapillary effect, by the friction forces of the metal vapour passing through the capillary and by the convexity of weld pool and fusion zone caused by thermal expansion of the weld pool and the joined workpieces. In order to predict the weld pool length more accurately the model developed by Sudnik et alin 1996 is enlarged by the heat transport produced by the recirculating flow in radial sections of the weld pool. Verification of the model for 16MnCr5 steel with sheet thicknesses of 2 and 6 mm shows that it is suitable for predicting the weld pool geometry and for analysing the thermodynamics of the process. In order to gain a better understanding of the structure of heat transport in the weld pool, the different modes of transport are compared in respect of their contribution to the depth-to-length ratio of the weld pool. A calculation of the weld pool length for welding speeds of 1-8 m min^-1with a laser beam power of 2.5 kW shows that the relative contributions of the transport modes are as follows. Approximately 50-90% of the weld pool length (increasing with welding speed) results from conductive and translatory heat transport (with the fusion zone convexity contributing approximately 20-30%). The remaining 50-10% of the weld pool length (decreasing with welding speed) result from convective heat transport. The model predicts the shoulder in the weld pool trough. It also explains the change in the weld pool length by the effect of the gap width, by the transition from through welding to penetration welding and by improvements in beam quality.

We use the Jones matrix method to develop a numerical method which can be used to calculate the reflection of cholesteric liquid crystals. We derive the formula for the propagation of normally incident light in a cholesteric liquid crystal with multiple reflections taken into account. Using the derived formula, we numerically calculate the reflection spectra of the cholesteric liquid crystal under various conditions, and compare them with the results obtained using the Berreman 4 × 4 method.

This paper examines the effect of a Q-switched pulsed laser's temporal output on the induced temperature change profile of laser absorbing materials. The effect was also discussed in the light of the case of the temperature profiles that were induced by ideal Dirac- function, square and Gaussian laser pulses. The induced temperature profiles were found to be unique with respect to the laser pulse temporal shape and therefore none of them resembled each other, even among the temperature profiles that were induced by Q-switched laser outputs with different pumping level.

Theoretical models taking into account different feedback source terms (e.g., ion-impact electron emission, photo-electron emission, field emission, etc) have been proposed for the existence and explanation of the shape of negative corona current pulse, including the step on the leading edge. In the present work, a negative corona current pulse with the step on the leading edge is obtained in the presence of ion-impact electron emission feedback source only. The step on the leading edge is explained in terms of the plasma formation process and enhancement of the feedback source. Ionization wave-like movement toward the cathode is observed after the step. The conditions for the existence of current pulse, with and without the step on the leading edge, are also described. A qualitative comparison with earlier theoretical and experimental work is also included.

In spite of the fact that a great deal of research has been carried out on liquid metal ion sources, surprisingly few results exist on the temperature dependence of their electric characteristics. In this article we study two liquid metal alloy ion sources (LMAISs), namely Co₃₆ Nd₆₄and Au₇₇ Ge₁₄ Si₉ . While the results of the former alloy were as expected, the latter displayed an entirely different dependence of its electric characteristics on temperature. The unusual results of the Au₇₇ Ge₁₄ Si₉LMAIS are explained in terms of the abnormal behaviour of its surface tension coefficient with temperature.

The enhancement of yield stress of NaY/insulating oil electrorheological (ER) fluid is found by adding a liquid crystal additive with a higher dielectric constant than that of the carrier fluid. The yield stress increases with additive's concentration and saturates at high concentrations. A polarization model has been suggested to understand the role of the additives. The theoretical calculations agree with our experiments very well. We show that adding a small amount of additive with a high dielectric constant can drastically improve the yield stress even in a `dry' ER fluid if the conductivity or dielectric constant of the additive is still much smaller than that of the dispersed particles.

Differential scanning calorimetry (DSC) results of Bi₁₀ Se₉₀glass under non-isothermal conditions are reported. In the present work, the analyses have been focused on the endothermic peaks of the DSC curves. The models, used for calculation of the crystallization kinetics from the exothermic peaks, have been applied to obtain the pre-crystallization kinetics from the endothermic peaks. The activation energy of glass transition (E_g ), the Avrami index (n ) and the frequency factor (K₀ ) of the investigated glass are 186±0.2 kJ mol^-1 , 2.08 and 2.5 × 10²⁸s^-1 , respectively. The values obtained can be related to the kinetics of amorphous-crystalline transformations.

In an earlier paper, the spherical harmonics method for the solution of the time-dependent transport equation with the Marshak boundary conditions was presented in order to investigate the effect of a strongly anisotropic scattering law on the slab thickness. Here, the previous work is extended to the study of the time-dependent problems in a homogeneous sphere with the same scattering function as used in the previous work. The time-dependent neutron transport equation is solved in the manner used for a critical sphere and all radii for a given time-dependent system are determined by finding the critical radii for the corresponding critical system.

The P_Ncalculations of the critical radii were carried out for various combinations of the anisotropy parameters and the fundamental time eigenvalues. Some indications of the accuracy of the method were given for the problem of interest and the variation of the radius with anisotropic scattering was studied. We also obtained numerical values of the critical radii in the range of (1- ) , 1. Finally, some results were discussed and compared with those already obtained by various methods.

Using the analytic modified embedded atom method (MEAM), the embedding, potential and modifying functions for the Mg and rare earth (RE) metals (RE = Sc, Y, Pr, Nd, Gd, Tb, Dy, Ho and Er) are presented. The thermodynamic properties, such as the dilute-limit heats of solution, enthalpies of formation of disordered solid solutions and intermetallic compounds, for the binary Mg-RE alloys are calculated. The obtained results are in good agreement with the available experimental data and with the results calculated using Miedema theory. The calculations of the enthalpies of formation of Mg₃ RE, Mg₂ RE, MgRE, MgRE₂and MgRE₃with various ordered structures (DO₃ , DO₁₉ , L1₂ , C15, MoPt₂ , B2, W1 and L1₀ ) indicate that the trends in the structural stability can be interpreted directly in terms of the formation energy. Moreover, the lattice constants and volume contractions of alloys with various compositions are determined based on the relation between the formation energy and the interatomic distance. The correlation between the enthalpy of formation and volume contraction for intermetallic compounds is discussed.

The dielectric relaxation in hard, plasma-polymerized C:H films has been studied using the depolarization current method. These films were prepared by means of a dc unbalanced magnetron operated in a working gas mixture of Ar with n-hexane. The C:H films were sandwiched between two thin, aluminium-film electrodes. The measurements took place without breaking vacuum at temperatures ranging from 22 °C to 140 °C. The analysis of the respective depolarization currents was performed by means of the Kohlrausch-Williams-Watts depolarization function. Two dielectric relaxation processes were observed. The first is associated with high-dipole polar groups such as hydroxyl and carbonyl groups. The second relaxation process is observed only at the highest temperatures and cannot be explained in terms of permanent dipole reorientation. This finding shows that the C:H films are hard, highly crosslinked hydrocarbon plasma polymers.

The paper reviews the experimental and theoretical non-monotonic dependences of electromechanical properties on the volume concentration of one of the components in two-component piezoactive 2-2 composites. Specific attention is focused on the evolution of piezoelectric coefficients e_ij^*and d_ij^* , their anisotropy and electromechanical coupling factors k_ij^* , k_p^*and k_t^* . This evolution is analysed in terms of the ratios between some electromechanical constants of the components. Important results are concentrated in systems of analytical conditions for reaching max e₃₁^* >0 and max k_t^* . These systems are written in terms of introduced `basic' constants and other parameters depending on the electromechanical properties of the components, and the fulfillment of these conditions is analysed in connection with known experimental data of the components.

It is shown that the dependence of the piezoelectric coefficients of BaTiO₃ferroelectric ceramics on the remanent polarization is monotonic due to the influence of the domain structure of the grains. The effect of the 90° domain structure of the grains on the non-monotonic behaviour of the piezoelectric coefficients and their anisotropy in PbTiO₃ceramics is discussed. It is established that contradictions between results of some recent papers are removed by taking into account the role of the domain structure in forming the piezoelectric response of ferroelectric ceramics.

The sintered rhombohedral PbTi_0.1 Zr_0.9 O₃(PZT) ceramics with doped CeO₂were prepared and investigated by means of XRD, SEM, EDX, and dielectric property measurement. It is found that a 0.4% CeO₂doping has two major effects on the growth dynamics and electric properties of the PZT materials. First, the grain size, morphology flatness and growth rate are enhanced by four to eight times. Second, the Curie temperature of the PZT is lowered by about 40 °C as compared to the undoped PZT samples. It is also found that the cerium is richer at the grain boundaries and precipitates in a glass-like phase that fills the gap between grain boundary. A possible mechanism for the driving force is discussed.

In order to model fuse operation during circuit interruption, a detailed mass and energy transport analysis is needed. In this paper, using a novel method, the mass flow of the fuse element material, silver for this example, is presented. By neutron activation of part of the element, we are able, after interruption, to trace the distribution of the dispersed element material. We show that there is a silver mass coming from the arc ignition zone to the extremities, mainly in the direction of the anode.