Table of contents

The field of nanometre scale mechanical forming has seen rapid development with the arrival of high resolution, massive parallel techniques such as nanoimprint. Despite a growing number of devices and surface architectures demonstrated, a more fundamental understanding of the mechanics and physics underlying the forming operations is only beginning to emerge. In this review, recent developments in understanding the production of nanostructures through mechanical means at surfaces are surveyed. The main focus is on the replica moulding of viscoelastic liquids and the forging of amorphous solids, with fidelity to design specification judged in terms of shape. The effects of sub-continuum structure on the local specification of geometry will also be briefly considered.

A two-stage magnetization Brayton refrigeration cycle model using a paramagnetic material as the working substance is established, in which the regeneration and the irreversibility in the adiabatic processes are taken into account. On the basis of the thermodynamic properties of a paramagnetic material, the expressions of some important parameters such as the coefficient of performance, refrigeration load and work input are derived and used to analyse the performance characteristics of the refrigeration cycle. The influence of the inter-magnetization process, irreversibility in the adiabatic processes and regeneration on the performance of the cycle is discussed in detail. The advantage of adding the inter-magnetization process is expounded and the magnetic field ratio related to the inter-magnetization process is optimized. Moreover, the optimal values of the temperatures of the working substance at different state points and the optimally operating region of the cycle are determined. The results obtained here are compared with those derived from some relevant magnetic Brayton refrigeration cycles, and consequently, some significant conclusions are obtained.

The magnetoimpedance (MI) of as-spun amorphous Co_72−xFe_xZr₈B₂₀ (CFZB, x = 0, 2, 5, 7 at.%) alloys has been measured at a frequency ranging from 310 to 1110 kHz and a dc magnetic field between 0 to 70 Oe. The maximum MI ratio ΔZ/Z(%)_max of the CFZB alloys increases with increasing frequency for each sample and decreases with the increment of Fe content at any frequency. The most drastic MI effect, the maximum value of about 90% at 1110 kHz accompanied by the field sensitivity of 18% Oe⁻¹, is observed in CFZB without Fe. Magnetic measurements reveal that coercivity of CFZB decreases first and then increases with increasing Fe content, and the minimum value of about 1.6 Oe is obtained in the sample with x = 2 at.%. The permeability of CFZB was evaluated from quasi-static hysteresis loops, indicating that the Fe-free CFZB is of the largest permeability. Measurements on electrical resistivity suggest that the Fe-free sample possesses smaller resistivity while the sample with x = 7 at.% has a much larger resistivity compared with CFZB with 2 and 5 at.% Fe. The correlation between MI effect and magnetic properties together with electrical resistivity for the CFZB alloy is discussed in this paper.

Magnetic, electronic transport and magneto-transport behaviours of (Co_1−xMn_x)₂P (0.55 ⩽ x ⩽ 0.675) compounds have been systematically investigated. A typical metallic-conductivity behaviour is observed in the ferromagnetic compound (Co_0.45Mn_0.55)₂P. The increase in the Mn concentration gives rise to dramatic changes in magnetic, electronic transport and magneto-transport behaviours. With increasing temperature, a first-order phase transition from antiferromagnetism to ferromagnetism takes place at about 145 K, 185 K and 240 K for x = 0.60, 0.625 and 0.65, respectively. (Co_0.4Mn_0.6)₂P and (Co_0.375Mn_0.625)₂P compounds experience a metal-insulator transition (Anderson transition) with decreasing temperature. An external magnetic field of 5 T strongly influences the Anderson transition, lowering the transition temperature from 80 to 55 K for (Co_0.4Mn_0.6)₂P and from 115 to 70 K for (Co_0.375Mn_0.625)₂P. In contrast with this metal-insulator transition, an insulating behaviour appears in the temperature range from 10 to 300 K for (Co_0.35Mn_0.65)₂P and (Co_0.325Mn_0.675)₂P compounds. Below the antiferromagnetic–ferromagnetic transition temperature T_AF–F, a metamagnetic transition can be induced by an external magnetic field. The metamagnetic transition is accompanied by a maximum magnetoresistance ratio of −7%, −6.3% or −3.7% at 5 T in the (Co_0.4Mn_0.6)₂P, (Co_0.375Mn_0.625)₂P or (Co_0.35Mn_0.65)₂P compound at 10 K. The mechanisms of magnetoresistive behaviours are discussed in terms of the formation of a super-zone gap in the antiferromagnetic state.

The effects of a stress field and chemical diffusion on electronic behaviour in self-assembled InAs/GaAs quantum dots (QD) are investigated by using first-principle calculations. We find that a potential well appears in a QD without a lattice misfit and chemical diffusion, and both stress field and Ga chemical diffusion can induce the formation of a potential barrier, which strongly affects the electronic behaviour within the QD. The stress field can localize electrons to the base of the QD. And associated with Ga diffusion, the stress field will induce an inverted electronic alignment. The electronic behaviour in the QD without a stress field does not present the confined or localized characteristics caused by a lattice misfit, atomic size and Ga diffusion. This study provides useful information for modulating electronic behaviour by introducing a stress field and chemical diffusion.

A plane-wave-based approach for complex photonic band structure is developed and applied to analyse the behaviour of electromagnetic (EM) waves at the surface of semi-infinite and finite photonic crystals (PCs). The complex photonic band structures of two-dimensional and three-dimensional PCs have been calculated by the present approach and verified by conventional plane wave expansion method and plane-wave-based transfer matrix method. Based on the eigen modes of present approach, equations in matrix form are given to describe the boundary conditions of PCs, and consequently the behaviour of EM waves at the surface of semi-infinite and finite PCs is discussed. These results have also verified the validity and efficiency of the current approach.

Three-dimensional periodical microstructures can be fabricated by the interference of four noncoplanar beams. Generally the basis vector choice for a certain lattice is not unique and the same lattice structure can be formed with different recording geometries. It shows that, for certain special cases, the lattice constant can be tuned by proper single-exposure holographic design without distortion of the lattice element and then one can shift the photonic band gap to a different frequency range. In addition, a simple optical setup for fabricating body-centred cubic lattice with a large band gap is proposed.

In order to increase the transmission and speed of response of fibreoptic faceplates in imaging tubes a method is reported which used metallization only of the interfibre glass regions. This offers maximum transmission of the fibres whilst supporting high conductivity, as required for fast response times. An initial metal layer was laser ablated with light directed through the fibre array to provide a self-aligning process. Transmission has been increased threefold compared with earlier metal layer methods, which is of particular value for long wavelength sensitivity where the cathode efficiency is low. By allowing the use of more conductive pathways the more critical values of the response times have been reduced from the nanosecond to the picosecond range for these imaging tubes.

The optical properties of 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–0.35PT) single crystals were investigated by means of the optical transmittance spectrum. The refractive indices were measured in the visible region, and the dispersion behaviours of ordinary and extraordinary lights were well described in terms of the Wemple–Didomenico single oscillator dispersion model. The optical band gap values were obtained from the Tauc model. For (1 − x) Pb(Mg_1/3Nb_2/3)O₃ − xPbTiO₃ single crystals, as the PbTiO₃ content increases, the refractive index increases, while the optical band gap energy decreases.

Measurements of the temperature dependence of the dark current for standard commercial photomultipliers with multialkali photocathodes (type S20) have been contrasted with data from new prototype tubes with greatly enhanced long wavelength performance. The analyses suggest that for the larger structures part of the cathode is closer to a bialkali composition. This reduces the activation energy of the dark current from ∼1.1 eV for normal S20 cathodes down to ∼0.8 eV. Many tubes show a lower activation energy component near 0.6 eV which may represent a sensitization process from monolayers of molecular oxygen. Similarly, monolayers of water can play a significant role, but do so by reducing cathode sensitivity. Several tubes display a sharp transition in gain at the limiting temperature for water desorption (i.e. a sublimation transition). The commercial structured cathodes can show evidence for up to 70% improvements in quantum efficiency by operation at low temperature which can be immediately exploited. Prototype tubes with greatly improved performance were studied but for very small area illumination spots there can be problems of local variations in gain and wavelength response across the structural features of pyramidal modified cathode windows. Overall the data suggest that not only is improved performance already available with existing photomultiplier tubes but also with structured photocathode windows, and/or the introduction of surface 'defects' in the window, even further improvements are feasible.

The design, modelling and feasibility of a MEMS sensor based on a common gate metal-oxide-semiconductor field effect transistors (MOSFET) differential amplifier is presented. A pair of adjacent MOSFETs shares a common gate electrode that is suspended in a torsional configuration over the transistor gate regions. Rotation of the common gate alters the relative spacing between the gate tips and the substrate changing the gate capacitance of each transistor. Connection of the transistor pair in a differential readout configuration generates a differential current flow through the MOSFET pair. This sensor integrates transduction and amplification as movement of the MEMS gate modulates the relative gate capacitance and drain current of each transistor. The differential configuration provides a high common mode rejection ratio and the estimated sensitivity is 68 µA (fF⁻¹) and the responsivity of the sensor is 2.2 mV/degree.

In this work particle formation and growth from condensation of supersaturated carbon vapour was investigated. Atomic carbon vapour was generated under well-controlled conditions from UV-laser pulse photolysis of C₃O₂ at 193 nm. Particle formation and growth were studied in a wide range of conditions with varying carbon vapour concentration, bath gas composition and pressure. The formation of particulate matter was observed as a function of time by laser light extinction. Particle sizes were determined in situ by time-resolved laser-induced incandescence and ex situ by transmission electronic microscopy. The characteristic time of particle growth was 20–1000 µs. The final particle size was 5–12 nm, increased with pressure, and depends on bath gas composition. We propose a simple model for the description of carbon vapour condensation that assumes condensation of individual atoms on the cluster surface as the main growth mechanism. The comparison of experiments and simulations provides information about the initial concentration of carbon clusters for the different mixture conditions.

This paper describes the large eddy simulation modelling of unconfined large-scale explosions. The simulations are compared with the largest hydrogen–air deflagration experiment in a 20 m diameter hemispherical polyethylene shell in the open. Two combustion sub-models, one developed on the basis of the renormalization group (RNG) theory and another derived from the fractal theory, were applied. Both sub-models include a sub-grid scale model of the turbulence generated by flame front itself based on Karlovitz's theory and the observation by Gostintsev et al on a critical distance for transition from laminar to self-similar flame propagation regime. The RNG sub-model employs Yakhot's formula for turbulent premixed flame propagation velocity. The best fit flame propagation dynamics is obtained for the fractal sub-model with a fractal dimension D = 2.22. The fractal sub-model reproduces the experimentally observed flame acceleration during the whole duration of explosion, accurately simulating the negative phase of the pressure wave but overestimating by 50% the positive phase amplitude. The RNG sub-model is closer to the experiment in predicting the positive phase but under-predicts by 30% the negative phase amplitude. Both sub-models simulate experimental flame propagation up to 20 m and pressure dynamics up to 80 m with reasonable accuracy.

We report the first measurements of the optical emission spectra of mercury plasma produced by the fundamental, second and third harmonics of a Nd : YAG laser, which reveals numerous transitions due to the neutral and singly ionized mercury. The excitation temperature has been determined from the Boltzmann plots, whereas the electron number density is estimated from the Stark broaden profile of the spectral lines. The estimated range of the excitation temperature and the electron number density is (7000–14000) K and (3.6 × 10¹⁶ to 2.5 × 10¹⁷) cm⁻³, respectively. The behaviour of the excitation temperature and the electron number density with the laser irradiance has been studied. The spatial distribution of the temperature and the electron number density has also been investigated besides the studies of absorption in the plasma through inverse bremstrahlung and photoionization.

Electron and ion kinetics in a micro hollow cathode discharge are investigated by means of two-dimensional axisymmetric particle-in-cell Monte Carlo collision simulations. Argon discharges at 10 and 300 Torr are studied for various driving currents. Electron and ion energy probability functions (IEPF) are shown at various times and locations to study the spatio-temporal behaviour of the discharge. The electron energy probability function (EEPF) evolves from the Druyvesteyn type in the early stages of the discharge into a two (or three) temperature distribution when steady state is reached. In steady state, secondary electrons accelerated across the cathode fall populate the high energy tail of the EEPF while the low energy region is populated by trapped electrons. The IEPF evolves from a Maxwellian in the negative glow (bulk) to a two temperature distribution on the cathode surface. The overpopulation of low energy ions near the cathode surface is attributed to a larger collision cross section for low energy ions and ionization within the cathode fall.

Absolute total dissociation cross sections for electron impact, σ_t,diss, from 8 to 700 eV are reported for C₂F₆. A dense set of data was obtained in the technologically important 8–30 eV energy range relevant to modelling the type of plasmas used in both fundamental and applied scientific investigations. The threshold for dissociation was found to be 12.0 ± 0.2 eV and appears to be associated with a Rydberg state. Estimated values for the total neutral dissociation cross section, σ_neut,diss, were obtained by subtracting the ionization cross sections (all ionizing events cause dissociation) from the total dissociation cross section. It is shown that a calibration error in a paper by one of us (HFW) caused a distortion of several previous investigations. When the data from the present work are used to recalibrate data from swarm experiments, agreement becomes quite reasonable. There is now a consistent set of data obtained from several investigators which describe the dissociation of C₂F₆. Neutral dissociation cross sections are obtained from electron-impact excitation calculations and found to be in reasonable agreement with measurements over most of the energy range.

A surface dielectric barrier discharge (DBD) in atmospheric pressure air was excited either by low frequency (0.3–2 kHz) high-voltage ac or by short, high-voltage pulses at repetition rates from 50 to 600 pulses s⁻¹. The short-pulse excited discharge was more diffuse and did not have the pronounced bright multiple cathode spots observed in the ac excited discharge. The discharge voltage, current and average power deposited into the discharge were calculated for both types of excitation. As a measure of plasma-chemical efficiency, the ozone number density was measured by UV absorption as a function of average deposited power. The density of ozone produced by ac excitation did not increase so rapidly as that produced by short-pulse excitation as a function of average power, with a maximum measured density of ∼3 × 10¹⁵ cm⁻³ at 25 W. The maximum ozone production achieved by short-pulse excitation was ∼8.5 × 10¹⁵ cm⁻³ at 20 W, which was four times greater than that achieved by ac excitation at the same power level.

Convection and diffusion in the discharge region of a metal halide lamp is studied using a computer model built with the plasma modelling package Plasimo. A model lamp containing mercury and sodium iodide is studied. The effects of the total lamp pressure on the degree of segregation of the light emitting species are examined and compared to a simpler model with a fixed temperature profile. Significant differences are observed, justifying the use of the more complete approach.

The contributions of positive ions and neutral active particles, remaining from previous breakdown and discharge as well as contribution of gamma photons from and radiation sources and cosmic rays to the electrical breakdown initiation in commercial gas-filled surge arresters have been analysed. This analysis was performed on the basis of time delay mean value as a function of afterglow period τ ('memory curve') and the breakdown voltage mean value as a function of τ. The values of static breakdown voltage were estimated on the basis of the experimental breakdown voltage data as a function of voltage increase rate using a linear polynomial fit.

Ultrathin nanocrystalline silicon films have been fabricated by plasma enhanced chemical vapour deposition from hydrogen-diluted SiCl₄ at a low temperature of 250 °C. The Raman spectra measurements and high resolution transmission electron microscopy observations reveal that nanocrystalline silicon can be directly grown on an insulator glass substrate at the initial growth of the deposition process. The crystallinity and the grain size increase with the increase in the deposition period. Furthermore, the crystalline fraction as well as the grain size also increase with the decrease in the hydrogen dilution ratio. The I–V characteristic curves measured by a tuned Langmuir probe in the SiCl₄/H₂ plasma region at a substrate temperature of 100 °C show that silicon films with higher conductivity were deposited on the probe surface in the deposition process. This behaviour is completely different from that observed in the SiH₄/H₂ system. It is considered that the formation of nanometre size grains occurs in the gas phase reaction process at the initial stage of film growth, while the growth of grains is mainly governed by the surface reaction process where chlorine and hydrogen play an important role. The direct growth of nanocrystalline Si on the insulator surface at low temperatures using SiCl₄/H₂ opens up the possibility of directly fabricating nc-Si/SiO₂ or nc-Si/a-SiN_x systems at low temperatures.

Low energy ion implantation produces an accumulation of electric charge on the surface of insulators. This phenomenon can be used as a complementary tool to improve the efficacy of polymer surface treatments. Samples of polyethylene (PE) were implanted with 2.2 keV ions to a fluence of 3.9 × 10¹⁶D⁺ cm⁻² with and without the use of charge neutralization. The physical and physicochemical properties of the surface were characterized by elastic recoil detection −E × B, Rutherford backscattered spectroscopy (RBS), x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). AFM characterization showed that the roughness of the PE surface decreases after ion beam bombardment with neutralization, but increases during the implantation with charge accumulation. The surface wettability increases after implantation with both methods and this effect is enhanced with non-neutralized implantation. RBS analysis showed a physical trapping of oxygen following both treatments, the oxygen adsorption being more pronounced without neutralization of the sample surface. XPS characterization confirmed this result and revealed the formation of C–O, C=O and O–C=O molecular bonds, especially in samples implanted without neutralization. Our results show that the level of surface charging affects the topography and the kind of damage at the surface, providing a complementary tool to adjust the properties of polymer surfaces.

A surface plasma wave (SPW), propagating along a metal surface, embedded with regularly arranged nanoparticles, undergoes surface enhanced Raman scattering from molecules adsorbed over the particles. The enhancement in the scattered signal depends on the shape and dielectric constant of the metallic particles. The scattered signal can be detected above the metal surface as a space wave if the particles have a periodic arrangement with wave number q such that ω_R > (k_S − q)c, where ω_R is the frequency of the scattered signal and k_S is the wave number of SPW.

The transfer of the common slip system across grain boundaries was examined. Bicrystals of alloys Fe–Si with Si content 4 and 5.5 at% were used for both tension and compression straining. The progress of the deformation was followed by synchrotron radiation diffraction topography after straining and under increasing external stress. An x-ray sensitive camera was used for recording the topographs in addition to the classical technique using photographic plates. Three slightly different settings with different sensitivities to interplanar spacing (deformation) and orientation variations of the adjacent crystal regions were applied. The movement of the slip bands was followed. A distortion of the image appeared at the grain boundary when the slip bands stopped there and decreased or nearly disappeared when the slip bands crossed it after an increase in the applied stress. The distortion is explained by elastic deformation around the heads of the slip bands stopped at the boundary. True slip transfers are differentiated from the false ones by observing elastic deformation in early deformation stages and by optical observation of slip pattern after deformation. The transfer of the common slip system across a twin boundary, whereas expected to be direct, required stress accumulation. The twin boundary proved to be a real barrier. The results obtained for specimens with different Si content were compared.

A third generation synchrotron x-ray source and advanced imaging facilities were used to study dendritic solidification in metallic alloys in real time. A digital camera and a video camera with different time and spatial resolution were tested to capture growing dendrites during solidification of Sn–13 wt%Bi and Al–25 wt%Cu alloys. The captured digital images show that the morphology of the dendrites can be resolved with satisfactory resolution and contrast. The trade-off between spatial resolution and time resolution was discussed. The effect of beam characteristics such as intensity, parallelism and coherency on both spatial and time resolution was analysed, and potential improvements with higher image quality with reduced exposure time were also discussed.

The effects of the milling process on the characteristics of Ba₂Ti₉O₂₀ materials were investigated. The chemical analyses using transmission electron microscopy (EDAX in TEM) revealed that the SiO₂ species incorporated into the Ba₂Ti₉O₂₀ materials were expelled by the Ba₂Ti₉O₂₀ grains. It induced the dissociation of the Ba₂Ti₉O₂₀ materials near the grain boundaries and degraded the microwave dielectric properties of the materials. The same phenomenon was assumed to be the procedure by which the high-energy-milling (HEM) process using Si₃N₄ grinding media (Si₃N₄-HEM) deleteriously influenced the microwave dielectric properties for the Ba₂Ti₉O₂₀ materials. Utilizing the three-dimensional-milling (3DM) process in place of the Si₃N₄-HEM one markedly improved the characteristics of the Ba₂Ti₉O₂₀ materials. The 3DM-processed samples own the same crystallinity as the HEM-processed ones but possess a pronouncedly more uniform microstructure and, therefore, exhibit a superior quality factor [(Q × f)_3DM = 28 500 GHz and (Q × f)_HEM = 21,900 GHz] with the same large dielectric constant (K = 38–39), when sintered at the same conditions (1350 °C/4 h). Such a phenomenon is ascribed to the fact that the 3DM process can pulverize the powders efficiently but induce no SiO₂-contamination.

Ferroelectric and piezoelectric properties of Pb_1−xBa_x(Zr_0.532Ti_0.468)O₃ ceramic compositions for x = 0 to 40 mole% were investigated. As Ba concentration increased, the microstructural studies revealed that grain growth was inhibited and apparent density decreased in PZT ceramics. The room temperature dielectric response (ε_RT) increased up to 30 mole% with low values of dielectric loss (tan δ). The ferroelectric properties (P_r, P_s and E_c) have shown a decreasing trend as Ba concentration increased from 0 to 40 mole% in the PZT system. The optimum piezoelectric charge coefficient (d₃₃ = 473 pC N⁻¹), piezoelectric planar coupling coefficient (k_p = 0.584) and piezoelectric thickness coupling coefficient (k_t = 0.408) were found in 30 mole% Ba composition, respectively.

We investigate the impact of phonon grain boundary scattering in our thermal conduction measurements carried out on polycrystalline niobium samples in the superconducting state and of two different sizes. A simple model is developed which takes into account the average grain size d, the Kapitza resistance R_K at grain–grain boundaries and the number of grains n over which the measurements are performed. Our model predicts a strong spatial anisotropy in the thermal conductivity for which can account for the discrepancy in our experimental data. The analysis enables the determination of the Kapitza resistance R_K at Nb grain–grain boundaries. We show that with increasing temperature the grain boundary resistance remains dominant relative to the bulk thermal resistance.

The room temperature nanoindentation creep behaviour of a range of amorphous and semicrystalline polymers has been investigated. It was found that experimental data during the first 20 s at constant load were well fitted by a logarithmic equation relating the fractional increase in penetration depth during creep to [A/d(0)]ln(t/τ + 1) where A and τ are constants, d(0) is the initial penetration depth at the end of the loading period and t is the time at peak load. For samples of ultra-high molecular weight polyethylene and polypropylene, above their glass transition temperature at room temperature, it was found that the creep parameter A/d(0) increased at lower load and at higher loading rates when a Berkovich indenter was used. In contrast, samples of poly(methylmethacrylate) and poly(ethylene terephthalate), below their glass transition at the test temperature, showed no clear variation in A/d(0) with loading rate. The constant τ varied with loading rate (and hence loading time), following a power-law relationship. Fitting of creep data with the equation above enables prediction of the extent and rate of the creep occurring after any given combination of loading rate and maximum load with reasonable accuracy, particularly at higher load. Importance should be placed on the actual loading rate and time to reach peak load as this is shown to influence the initial creep kinetics dramatically.

In this paper we report a new model for predicting the thermal conductivity of nanofluids by taking into account the fractal distribution of nanoparticle sizes and heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids. The proposed model is expressed as a function of the average size of nanoparticles, fractal dimension, concentration of nanoparticles, temperature and properties of fluids. The model shows the reasonable dependences of the thermal conductivity on the temperature of nanofluids, nanoparticle size and concentration. The parameter c introduced in thermal boundary layer depends on fluids, but is independent of nanoparticles added in the fluids. The model predictions are in good agreement with the available experimental data. The model also reveals that there is a critical concentration of 12.6% of nanoparticles at which the contribution from heat convection due to the Brownian movement of nanoparticles reaches the maximum value, below which the contribution from heat convection decreases with the decrease in concentration and above which the contribution from heat convection decreases with the increase in concentration.

This paper presents electrocaloric measurements on 0.75(PbMg_1/3Nb_2/3O₃)–0.25(PbTiO₃) ceramics. Reversible heat exchanged up to 0.15 J g⁻¹ with an applied field of 1.35 kV mm⁻¹ was obtained. The interpretation of this observation is based on direct polarization measurements. Starting from the integration along the electric field of the derivative of the polarization versus temperature, it was possible to predict the heat upon a decrease in electric field for values up to 3 kV mm⁻¹. However the simulations differ from the experiments and the discrepancy is believed to be due to hysteresis in ferroelectric materials. Finally a practical limit of the use of ferroelectric 0.75(PbMg_1/3Nb_2/3O₃)–0.25(PbTiO₃) ceramics is evidenced through electric conductivity appearance when the electrothermal conversion is very high.

For a simple class of electrical systems, the principle of the maximum entropy production rate (MaxEP) is discussed. First, we compare the MaxEP principle and the principle of the minimum entropy production rate and illustrate the superiority of the MaxEP principle for the example of two parallel constant resistors. Secondly, we show that the Steenbeck principle for the electric arc as well as the ohmic contact behaviour of space-charge limited conductors follow from the MaxEP principle. In line with work by Dewar, the investigations seem to suggest that the MaxEP principle can also be applied to systems far from equilibrium, provided appropriate information is available that enters the constraints of the optimization problem. Finally, we apply the MaxEP principle to a mesoscopic system and show that the universal conductance quantum, e²/h, of a one-dimensional ballistic conductor can be estimated.

The conditions for the propagation of fast- and slow-modes of modulated waves on two coupled discrete nonlinear LC transmission lines are examined, each line of the network containing a finite number of cells. We show analytically that the use of an appropriate unit cell, a band-pass filter and a convenient associated choice of the intermediate coupling capacitor between the two lines permits the avoidance of the crucial problem of the mixing of waves of different modes in the network. It is observed that there is good qualitative and quantitative agreement between the analytical results and numerical experiments.

The estimation of exposures of humans to the various sources of radiation is important. Instrumental neutron activation analysis has been used for the determination of uranium and thorium in environmental samples such as Toshki soil, Aswan iron ore, gold vein deposits and phosphate samples from Upper Egypt. The specific activities due to ²³⁸U and ²³²Th have been measured and the radiation hazard to the workers, the Radium equivalent activities, representative level index and dose rates were also estimated. The lowest external γ-radiation dose received by the workers is 33.15 ± 6.06 µSv y⁻¹ which comes from gold samples and the highest one was 315.65 ± 7.98 µSv y⁻¹ which comes from phosphate samples which is far below the worldwide allowed dose of 20 mSv y⁻¹ for workers (ICRP-60 1990).