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Showing papers in "Journal of Physics D in 2007"


Journal ArticleDOI
TL;DR: A review of the literature on active flow control with non-thermal actuators can be found in this paper, where the main advantages of such systems are their robustness, simplicity, low power consumption and ability for real-time control at high frequency.
Abstract: Active flow control is a topic in full expansion due to associated industrial applications of huge importance, particularly for aeronautics. Among all flow control methods, such as the use of mechanical flaps, wall synthetic jets or MEMS, plasma-based devices are very promising. The main advantages of such systems are their robustness, simplicity, low power consumption and ability for real-time control at high frequency. This paper is a review of the worldwide works on this topic, from its origin to the present. It is divided into two main parts. The first one is dedicated to the recent knowledge concerning the electric wind induced by surface non-thermal plasma actuators, acting in air at atmospheric pressure. Typically, it can reach 8 m s−1 at a distance of 0.5 mm from the wall. In the second part, works concerning active airflow control by these plasma actuators are presented. Very efficient results have been obtained for low-velocity subsonic airflows (typically U∞ ≤ 30 m s−1 and Reynolds number of a few 105), and promising results at higher velocities indicate that plasma actuators could be used in aeronautics.

1,519 citations


Journal ArticleDOI
TL;DR: In this article, a review of microfluidic methods for synthesizing uniform streams of droplets and bubbles, focusing on those that utilize pressure-driven flows, is presented, and the results in the context of physical mechanisms for droplet breakup and simple theoretical models that have been proposed.
Abstract: Microfluidic technologies have emerged recently as a promising new route for the fabrication of uniform emulsions. In this paper, we review microfluidic methods for synthesizing uniform streams of droplets and bubbles, focusing on those that utilize pressure-driven flows. Three categories of microfluidic geometries are discussed, including co-flowing streams, cross-flowing streams, and flow focusing devices. In each category we summarize observations that have been reported to date in experiments and numerical simulations. We describe these results in the context of physical mechanisms for droplet breakup, and simple theoretical models that have been proposed. Applications of droplets in microfluidic devices are briefly reviewed.

789 citations


Journal ArticleDOI
TL;DR: The physical principles behind the phenomenon of slow light in photonic crystal waveguides, as well as their practical limitations, are discussed and put into context in this paper, including the nature of slow-light propagation, its bandwidth limitation, the scaling of linear and nonlinear interactions with the slowdown factor, issues such as losses, coupling into and the tuning of slow modes.
Abstract: The physical principles behind the phenomenon of slow light in photonic crystal waveguides, as well as their practical limitations, are discussed and put into context This includes the nature of slow light propagation, its bandwidth limitation, the scaling of linear and nonlinear interactions with the slowdown factor as well as issues such as losses, coupling into and the tuning of slow modes Applications in all-optical signal processing appear to be the most promising outcome of the phenomena discussed

627 citations


Journal ArticleDOI
TL;DR: In this paper, results of ab initio band structure calculations for A2BC Heusler compounds that have A and B sites occupied by transition metals and C by a main group element are presented.
Abstract: In this paper, results of ab initio band structure calculations for A2BC Heusler compounds that have A and B sites occupied by transition metals and C by a main group element are presented. This class of materials includes some interesting half-metallic and ferromagnetic properties. The calculations have been performed in order to understand the properties of the minority band gap, the peculiar transport properties and magnetic behaviour found in these materials. Among the interesting aspects of the electronic structure of the materials are the contributions from both A and B atoms to the total magnetic moment. The magnitude of the total magnetic moment shows a trend consistent with the Slater–Pauling type behaviour in several classes of these compounds. The total magnetic moment also depends on the kind of C atoms although they do not directly contribute to it. In Co2 compounds, a change of the C element changes the contribution of the t2g states to the moment at the Co sites. The localized moment in these magnetic compounds resides at the B site. Other than in the classical Cu2-based Heusler compounds, the A atoms in Co2, Fe2 and Mn2-based compounds may contribute significantly to the total magnetic moment. It is shown that the inclusion of electron–electron correlation in the form of LDA + U calculations helps to understand the magnetic properties of those compounds that already exhibit a minority gap in calculations where it is neglected. Besides the large group of Co2 compounds, half-metallic ferromagnetism was here found only in such compounds that contain Mn.

617 citations


Journal ArticleDOI
TL;DR: In this paper, a magnetic tunnel junction (MTJ) with an amorphous aluminium oxide (Al-O) tunnel barrier has been studied, which exhibits tunnel magnetoresistance (TMR) due to spin-dependent electron tunnelling.
Abstract: A magnetic tunnel junction (MTJ), which consists of a thin insulating layer (a tunnel barrier) sandwiched between two ferromagnetic electrode layers, exhibits tunnel magnetoresistance (TMR) due to spin-dependent electron tunnelling. Since the 1995 discovery of room-temperature TMR, MTJs with an amorphous aluminium oxide (Al–O) tunnel barrier have been studied extensively. Al–O-based MTJs exhibit magnetoresistance (MR) ratios up to about 70% at room temperature (RT) and are currently used in magnetoresistive random access memory (MRAM) and the read heads of hard disk drives. MTJs with MR ratios significantly higher than 70% at RT, however, are needed for next-generation spintronic devices. In 2001 first-principle theories predicted that the MR ratios of epitaxial Fe/MgO/Fe MTJs with a crystalline MgO(0 0 1) barrier would be over 1000% because of the coherent tunnelling of fully spin-polarized Δ1 electrons. In 2004 MR ratios of about 200% were obtained in MTJs with a single-crystal MgO(0 0 1) barrier or a textured MgO(0 0 1) barrier. CoFeB/MgO/CoFeB MTJs for practical applications were also developed and found to have MR ratios up to 500% at RT. MgO-based MTJs are of great importance not only for device applications but also for clarifying the physics of spin-dependent tunnelling. In this article we introduce recent studies on physics and applications of the giant TMR in MgO-based MTJs.

519 citations


Journal ArticleDOI
TL;DR: In this article, a review of single cell dielectric spectroscopy methods is presented, including ac electrokinetic methods of dielectrophoresis and electrorotation.
Abstract: Over the last century a number of techniques have been developed which allow the measurement of the dielectric properties of biological particles in fluid suspension. The majority of these techniques are limited by the fact that they only provide an average value for the dielectric properties of a collection of particles. More recently, with the advent of microfabrication techniques and the Lab-on-a-chip, it has been possible to perform dielectric spectroscopic experiments on single biological particles suspended in physiological media. In this paper we review current methods for single cell dielectric spectroscopy. We also discuss alternative single cell dielectric measurement techniques, specifically the ac electrokinetic methods of dielectrophoresis and electrorotation. Single cell electrical impedance spectroscopy is also discussed with relevance to a microfabricated flow cytometer. We compare impedance spectroscopy data obtained from measurements made using a microfabricated flow cytometer with simulation data obtained using an equivalent circuit model for the device.

408 citations


Journal ArticleDOI
TL;DR: In this article, the basic operation principle for MEMS with wide band gap semiconductors is described, and the first applications of SiC based MEMS are demonstrated, and innovative MEMS and NEMS devices are reviewed.
Abstract: With the increasing requirements for microelectromechanical systems (MEMS) regarding stability, miniaturization and integration, novel materials such as wide band gap semiconductors are attracting more attention. Polycrystalline SiC has first been implemented into Si micromachining techniques, mainly as etch stop and protective layers. However, the outstanding properties of wide band gap semiconductors offer many more possibilities for the implementation of new functionalities. Now, a variety of technologies for SiC and group III nitrides exist to fabricate fully wide band gap semiconductor based MEMS. In this paper we first review the basic technology (deposition and etching) for group III nitrides and SiC with a special focus on the fabrication of three-dimensional microstructures relevant for MEMS. The basic operation principle for MEMS with wide band gap semiconductors is described. Finally, the first applications of SiC based MEMS are demonstrated, and innovative MEMS and NEMS devices are reviewed.

352 citations


Journal ArticleDOI
TL;DR: In this paper, a keyhole model is developed and tested on tantalum, Ti-6Al-4V, 304L stainless steel and vanadium, and a turbulence model based on Prandtl's mixing length hypothesis is used to estimate the effective viscosity and thermal conductivity in the liquid region.
Abstract: Because of the complexity of several simultaneous physical processes, most heat transfer models of keyhole mode laser welding require some simplifications to make the calculations tractable. The simplifications often limit the applicability of each model to the specific materials systems for which the model is developed. In this work, a rigorous, yet computationally efficient, keyhole model is developed and tested on tantalum, Ti–6Al–4V, 304L stainless steel and vanadium. Unlike previous models, this one combines an existing model to calculate keyhole shape and size with numerical fluid flow and heat transfer calculations in the weld pool. The calculations of the keyhole profile involved a point-by-point heat balance at the keyhole walls considering multiple reflections of the laser beam in the vapour cavity. The equations of conservation of mass, momentum and energy are then solved in three dimensions assuming that the temperatures at the keyhole wall reach the boiling point of the different metals or alloys. A turbulence model based on Prandtl's mixing length hypothesis was used to estimate the effective viscosity and thermal conductivity in the liquid region. The calculated weld cross-sections agreed well with the experimental results for each metal and alloy system examined here. In each case, the weld pool geometry was affected by the thermal diffusivity, absorption coefficient, and the melting and boiling points, among the various physical properties of the alloy. The model was also used to better understand solidification phenomena and calculate the solidification parameters at the trailing edge of the weld pool. These calculations indicate that the solidification structure became less dendritic and coarser with decreasing weld velocities over the range of speeds investigated in this study. Overall, the keyhole weld model provides satisfactory simulations of the weld geometries and solidification sub-structures for diverse engineering metals and alloys.

350 citations


Journal ArticleDOI
Xuefeng Zhang1, Xin Dong1, Hui Huang1, B Lv1, J P Lei1, C J Choi 
TL;DR: In this article, carbon-coated Fe [Fe(C)] nanocapsules were synthesized by a modified arc-discharge method, and their microstructure and electromagnetic properties (2-18 GHz) were investigated by means of transmission electron microscopy, Raman spectroscopy and a network analyser.
Abstract: Carbon-coated Fe [Fe(C)] nanocapsules were synthesized by a modified arc-discharge method, and their microstructure and electromagnetic (EM) properties (2–18 GHz) were investigated by means of transmission electron microscopy, Raman spectroscopy and a network analyser. The reflection loss R of less than −20 dB was obtained in the frequency range 3.2–18 GHz. A minimum reflection loss of −43.5 dB was reached at 9.6 GHz with an absorber thickness of 3.1 mm. The in-depth study of relative complex permittivity and permeability reveals that the excellent microwave absorption properties are a consequence of a proper EM match in microstructure, a strong natural resonance, as well as multi-polarization mechanisms, etc.

325 citations


Journal ArticleDOI
TL;DR: In this paper, the basic mechanisms responsible for the electrohydrodynamic (EHD) force exerted by the discharge on the gas molecules were discussed and a parametric study of the EHD force as a function of voltage rise time and dielectric thickness was presented.
Abstract: Surface dielectric barrier discharges (DBDs) have been proposed as actuators for flow control. In this paper we discuss the basic mechanisms responsible for the electrohydrodynamic (EHD) force exerted by the discharge on the gas molecules. A two-dimensional fluid model of the DBD is used to describe the plasma dynamics, to understand the basic physics associated with the EHD force and to give some quantitative estimation of the force under simplified conditions. The results show that for ramp or sinusoidal voltage waveforms, the discharge consists of large amplitude short current pulses during which a filamentary plasma spreads along the surface, separated in time by long duration, low current discharge phases of a Townsend or corona type. The contribution of the low current phases to the total force exerted by the discharge on the gas is dominant because their duration is much longer than that of the current pulses and because the force takes place in a much larger volume. A description of the different discharge regimes and a parametric study of the EHD force as a function of voltage rise time and dielectric thickness is presented.

322 citations


Journal ArticleDOI
TL;DR: Polycrystalline n-ZnO/p-Cu2O heterojunctions have been fabricated by low-temperature eletrodepositions of ZnO and Cu2O layers in aqueous solutions as mentioned in this paper.
Abstract: Polycrystalline n-ZnO/p-Cu2O heterojunctions have been fabricated by low-temperature eletrodepositions of ZnO and Cu2O layers in aqueous solutions. The condition for forming the Cu2O layer significantly reflected the electrical rectification characteristic and the photovoltaic performance, and the heterojunction fabricated under optimized conditions showed an excellent electrical rectification characteristic and a photovoltaic performance of 1.28% in conversion efficiency under an AM 1.5 illumination.

Journal ArticleDOI
TL;DR: In this paper, the structural and optical properties of lattice-matching AlInN layers to GaN have been investigated and their specific use to realize nearly strain-free structures for photonic and electronic applications has been discussed.
Abstract: We report on the current properties of Al1-x InxN (x approximate to 0.18) layers lattice- matched ( LM) to GaN and their specific use to realize nearly strain- free structures for photonic and electronic applications. Following a literature survey of the general properties of AlInN layers, structural and optical properties of thin state- of- the- art AlInN layers LM to GaN are described showing that despite improved structural properties these layers are still characterized by a typical background donor concentration of ( 1 - 5) x 10(18) cm(-3) and a large Stokes shift (similar to 800 meV) between luminescence and absorption edge. The use of these AlInN layers LM to GaN is then exemplified through the properties of GaN/ AlInN multiple quantum wells ( QWs) suitable for near- infrared intersubband applications. A built- in electric field of 3.64MVcm(-1) solely due to spontaneous polarization is deduced from photoluminescence measurements carried out on strain- free single QW heterostructures, a value in good agreement with that deduced from theoretical calculation. Other potentialities regarding optoelectronics are demonstrated through the successful realization of crack- free highly reflective AlInN/ GaN distributed Bragg reflectors ( R > 99%) and high quality factor microcavities ( Q > 2800) likely to be of high interest for short wavelength vertical light emitting devices and fundamental studies on the strong coupling regime between excitons and cavity photons. In this respect, room temperature ( RT) lasing of a LM AlInN/ GaN vertical cavity surface emitting laser under optical pumping is reported. A description of the selective lateral oxidation of AlInN layers for current confinement in nitride- based light emitting devices and the selective chemical etching of oxidized AlInN layers is also given. Finally, the characterization of LM AlInN/ GaN heterojunctions will reveal the potential of such a system for the fabrication of high electron mobility transistors through the report of a high two- dimensional electron gas sheet carrier density ( n(s) similar to 2.6 x 10(13) cm(-2)) combined with a RT mobility mu(e) similar to 1170 cm(2) V-1 s(-1) and a low sheet resistance, R similar to 210 Omega square.

Journal ArticleDOI
TL;DR: In this article, the magnetic behavior of well-dispersed monodisperse Fe3O4 nanoparticles with sizes varying between 6.6 and 17.8?nm was investigated.
Abstract: The magnetic behaviour of well-dispersed monodisperse Fe3O4 nanoparticles with sizes varying between 6.6 and 17.8?nm prepared in a non-aqueous medium was investigated. The smaller nanocrystals exhibit superparamagnetism with the blocking temperatures increasing with the particle size, whereas the biggest particles are ferromagnetic at room temperature. The saturation magnetization values are slightly smaller than that of the bulk material, suggesting the existence of a disordered spin configuration on their surface. The thickness of the magnetically inert shell was estimated from the size variation of the magnetization at 1.9??. The dipole?dipole interactions between the particles were tuned by changing the interparticle distances, e.g. by diluting the nanopowders in a non-magnetic matrix at concentrations ranging from 0.25 to 100?wt%. As the strength of the interactions is decreased with dilution, the energy barrier is substantially lowered; this will induce a drastic decrease of both the blocking temperatures and the coercivity with decreasing concentration of the nanoparticles.

Journal ArticleDOI
TL;DR: Plasma-aided nanofabrication is a rapidly expanding area of research spanning disciplines ranging from physics and chemistry of plasmas and gas discharges to solid state physics, materials science, surface science, nanoscience and nanotechnology and related engineering subjects as discussed by the authors.
Abstract: Plasma-aided nanofabrication is a rapidly expanding area of research spanning disciplines ranging from physics and chemistry of plasmas and gas discharges to solid state physics, materials science, surface science, nanoscience and nanotechnology and related engineering subjects. The current status of the research field is discussed and examples of superior performance and competitive advantage of plasma processes and techniques are given. These examples are selected to represent a range of applications of two major types of plasmas suitable for nanoscale synthesis and processing, namely thermally non-equilibrium and thermal plasmas. Major concepts and terminology used in the field are introduced. The paper also pinpoints the major challenges facing plasma-aided nanofabrication and identifies some emerging topics for future research.

Journal ArticleDOI
TL;DR: A follow-up of a review written in 1999 addresses the basic physics of perpendicular recording with special emphasis on the read and the write process and the magnetic aspects of the recording media as discussed by the authors.
Abstract: After more than 30 years of research, hard disk drives using perpendicular recording are finally commercially available. This review is a follow-up of a review written in 1999 and addresses the basic physics of perpendicular recording with special emphasis on the read and the write process and the magnetic aspects of the recording media. The paper also surveys various technical difficulties which prevented an earlier implementation of perpendicular recording. The paper closes with a short overview of alternative technologies that allow even higher storage densities.

Journal ArticleDOI
TL;DR: In this paper, an overview of experimental and theoretical research in the field of physics and engineering of singlet delta oxygen (SDO) production in low-temperature plasma of various electric discharges is presented.
Abstract: An overview is presented of experimental and theoretical research in the field of physics and engineering of singlet delta oxygen (SDO) production in low-temperature plasma of various electric discharges. Attention is paid mainly to the SDO production with SDO yield adequate for the development of an electric discharge oxygen–iodine laser (DOIL). The review comprises a historical sketch describing the main experimental results on SDO physics in low-temperature plasma obtained since the first detection of SDO in electric discharge in the 1950s and the first attempt to launch a DOIL in the 1970s up to the mid-1980s when several research groups started their activity aimed at DOIL development, stimulated by success in the development of a chemical oxygen–iodine laser (COIL). A detailed analysis of theoretical and experimental research on SDO production in electric discharge from the mid-1980s to the present, when the first DOIL has been launched, is given. Different kinetic models of oxygen low-temperature plasma are compared with the model developed by the authors. The latter comprises electron kinetics based on the accompanying solution of the electron Boltzmann equation, plasma chemistry including reactions of excited molecules and numerous ion–molecular reactions, thermal energy balance and electric circuit equation. The experimental part of the overview is focused on the experimental methods of SDO detection including experiments on the measurements of the Einstein coefficient for SDO transition and experimental procedures of SDO production in self-sustained and non-self-sustained discharges and analysis of different plasma-chemical processes occurring in oxygen low-temperature plasma which brings limitation to the maximum SDO yield and to the lifetime of the SDO in an electric discharge and its afterglow. Quite recently obtained results on gain and output characteristics of DOIL and some projects aimed at the development of high-power DOIL are discussed.

Journal ArticleDOI
TL;DR: In this paper, the peculiarities of quasiperiodic order for the properties of photonic and phononic (sonic) heterostructures are discussed, and a review of the relationship between 1D and 2D structures based on one-dimensional substitutional sequences such as the Fibonacci, Thue-Morse, period-doubling, Rudin-Shapiro and Cantor sequence is presented.
Abstract: This review focuses on the peculiarities of quasiperiodic order for the properties of photonic and phononic (sonic) heterostructures. The most beneficial feature of quasiperiodicity is that it can combine perfectly ordered structures with purely point-diffractive spectra of arbitrarily high rotational symmetry. Both are prerequisites for the construction of isotropic band gap composites, in particular from materials with low index contrast, which are required for numerous applications. Another interesting property of quasiperiodic structures is their scaling symmetry, which may be exploited to create spectral gaps in the sub-wavelength regime. This review covers structure/property relationships of heterostructures based on one-dimensional (1D) substitutional sequences such as the Fibonacci, Thue–Morse, period-doubling, Rudin–Shapiro and Cantor sequence as well as on 1D modulated structures, further on 2D tilings with 8-, 10-, 12- and 14-fold symmetry as well as on the pinwheel tiling, the Sierpinski gasket and on curvilinear tilings and, finally, on the 3D icosahedral Penrose tiling.

Journal ArticleDOI
TL;DR: In this paper, a review of recent papers which have led to the capability of the prediction of weld depths for gas tungsten arc welding, for any given arc current, electrode shape or separation and welding gas, is given.
Abstract: This paper gives a review of recent papers which have led to the capability of the prediction of weld depths for gas tungsten arc welding, for any given arc current, electrode shape or separation and welding gas. The methodology is given for deriving plasma composition as a function of temperature and pressure from basic atomic and molecular properties. Transport coefficients of density, specific heat, enthalpy, electrical conductivity, thermal conductivity, viscosity and radiation emission coefficients can then be derived as a function of temperature. The conservation equations of fluid dynamics are then used to derive weld profiles for stainless steel for welding gases such as argon, helium, carbon dioxide and a 10% mixture of hydrogen in argon. The markedly different weld depths which are obtained are related to basic material functions such as specific heat, electrical and thermal conductivity. The temperature dependence of the surface tension coefficient has a marked effect on weld depth and profiles because it can influence the direction of circulatory flow in the weld pool. Electric arcs in helium and carbon dioxide are more constricted than arcs in argon and as a consequence the magnetic pinch pressure of the arc, transmitted to the weld pool, can force strong downward flows in the weld pool and thus lead to a deep weld. It is found that because of the interactions of the arc and the weld pool through effects such as viscous drag forces of the plasma on the weld pool, it is necessary to treat the arc, the electrode and the weld pool in a unified system.

Journal ArticleDOI
TL;DR: In this paper, the current status of SiC technology for a wide range of sensor applications is reviewed, and it is shown that SiC MEMs devices are well-established with operational devices demonstrated at high temperatures (up to 500 °C) for the sensing of motion, acceleration and gas flow.
Abstract: Silicon carbide has attracted considerable attention in recent years as a potential material for sensor devices. This paper reviews the current status of SiC technology for a wide range of sensor applications. It is shown that SiC MEMs devices are well-established with operational devices demonstrated at high temperatures (up to 500 °C) for the sensing of motion, acceleration and gas flow. SiC sensors devices using electrical properties as the sensing mechanism have also been demonstrated principally for gas composition and radiation detection and have wide potential use in scientific, medical and combustion monitoring applications.

Journal ArticleDOI
TL;DR: In this article, the formation of amine and phenyl-linker molecules on diamond was characterized using x-ray photoelectron spectroscopy, atomic force microscopy (AFM), cyclic voltammetry and field effect transistor characterization experiments.
Abstract: A summary of photo- and electrochemical surface modifications applied on single-crystalline chemical vapour deposition (CVD) diamond films is given. The covalently bonded formation of amine- and phenyl-linker molecule layers is characterized using x-ray photoelectron spectroscopy, atomic force microscopy (AFM), cyclic voltammetry and field-effect transistor characterization experiments. Amine- and phenyl-layers are very different with respect to formation, growth, thickness and molecule arrangement. We detect a single-molecular layer of amine-linker molecules on diamond with a density of about 1014?cm?2 (10% of carbon bonds). Amine molecules are bonded only on initially H-terminated surface areas to carbon. In the case of electrochemical deposition of phenyl-layers, multi-layer formation is detected due to three-dimensional (3D) growths. This gives rise to the formation of typically 25?? thick layers. The electrochemical grafting of boron-doped diamond works on H-terminated and oxidized surfaces.After reacting such films with hetero-bifunctional crosslinker molecules, thiol-modified ss-DNA markers are bonded to the organic system. Application of fluorescence and AFM on hybridized DNA films shows dense arrangements with densities of up to 1013?cm?2. The DNA is tilted by an angle of about 35? with respect to the diamond surface. Shortening the bonding time of thiol-modified ss-DNA to 10?min causes a decrease of DNA density to about 1012?cm?2. Application of AFM scratching experiments shows threshold removal forces of around 75?nN for DNA bonded on phenyl-linker molecules and of about 45?nN for DNA bonded to amine-linker molecules. DNA sensor applications using Fe(CN6)3?/4? mediator redox molecules, impedance spectroscopy and DNA-field effect transistor devices performances are introduced and discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss the development of localized arc filament plasma actuators and their use in controlling high-speed and high Reynolds number jet flows using a custom-built 8-channel high-voltage pulsed plasma generator.
Abstract: The paper discusses recent results on the development of localized arc filament plasma actuators and their use in controlling high-speed and high Reynolds number jet flows. Multiple plasma actuators (up to 8) are controlled using a custom-built 8-channel high-voltage pulsed plasma generator. The plasma generator independently controls pulse repetition rate (0–200 kHz), duty cycle and phase for each individual actuator. Current and voltage measurements demonstrated the power consumption of each actuator to be quite low (20 W at 20% duty cycle). Emission spectroscopy temperature measurements in the pulsed arc filament showed rapid temperature increase over the first 10–20 µs of arc operation, from below 1000 °C to up to about 2000 °C. At longer discharge pulse durations, 20–100 µs, the plasma temperature levels off at approximately 2000 °C.Modelling calculations using an unsteady, quasi-one-dimensional arc filament model showed that rapid localized heating in the arc filament on a microsecond time scale generates strong compression waves. The results of the calculations also suggest that flow forcing is most efficient at low actuator duty cycles, with short heating periods and sufficiently long delays between the pulses to allow for convective cooling of high-temperature filaments. The model predictions are consistent with laser sheet scattering flow visualization results and particle imaging velocimetry measurements. These measurements show large-scale coherent structure formation and considerable mixing enhancement in an ideally expanded Mach 1.3 jet forced by eight repetitively pulsed plasma actuators. The effects of forcing are most significant near the jet preferred mode frequency (ν = 5 kHz). The results also show a substantial reduction in the jet potential core length and a significant increase in the jet Mach number decay rate beyond the end of potential core, especially at low actuator duty cycles.

Journal ArticleDOI
TL;DR: A review of the available literature relating to the emerging research into the performance of coatings under combined wear and corrosion conditions is presented in this paper, which reveals the need for a more considered approach to tribo-corrosion testing and the way in which the results are analysed and presented.
Abstract: This paper reviews the available literature relating to the emerging research into the performance of coatings under combined wear and corrosion conditions. Understanding how coatings perform under these tribo-corrosion conditions is essential if the service life of equipment is to be predicted and to allow service life to be extended. Therefore, the tribo-corrosion performance of coatings deposited by a variety of techniques is discussed and the main mechanisms associated with their degradation under combined wear and corrosion highlighted. Coating composition, microstructure, defect level, adhesion, cohesion and substrate properties are seen as some of the critical elements in coating performance when subjected to tribo-corrosion contacts. The importance of post-coating deposition treatments such as laser resurfacing and sealing are also discussed. Interactions between wear and corrosion mechanisms are identified along with some models and mapping techniques that aim to inform coating selection and predict performance. Recent investigations into mono-layer as well as multilayered and functionally graded coatings are reviewed as candidates for wear–corrosion resistant surfaces. The review reveals the need for a more considered approach to tribo-corrosion testing and the way in which the results are analysed and presented. For example, the test conditions should be appropriate to the coating system under test; the level of in situ instrumentation deployed and the post-test analysis of in situ electrochemical data should be carefully selected as well as details given of the composition of any surface tribofilms formed and the identification of the degradation mechanisms.

Journal ArticleDOI
TL;DR: A comprehensive review of spin-polarized light-emitting diodes and surface emitting lasers is provided in this paper, concluding with a discussion of future prospects and operation principles and design of spinpolarised light sources.
Abstract: Spin-polarized light sources are a new class of devices in which the radiative recombination of spin-polarized carriers results in luminescence exhibiting a net circular polarization. The operation principles and design of spin-polarized light sources are discussed. A comprehensive review of experimental work on spin-polarized light-emitting diodes and surface-emitting lasers is provided, concluding with a discussion of future prospects.

Journal ArticleDOI
TL;DR: In this article, a review devoted to nanodiamonds as a member of new nanocarbon allotropes is presented, and the past results related to the main features of detonation technology for producing nanodes are highlighted.
Abstract: The review is devoted to nanodiamond as a member of new nanocarbon allotropes. The past results related to the main features of detonation technology for producing nanodiamond are highlighted. Effects of technology on the structure of nanodiamond particles as well as functionalization of nanodiamond surface to chemical properties are discussed. The real structure of single nanodiamond particles has been critically reviewed and its aggregation problem emphasized. Several applications of nanodiamonds mainly as precursors for CVD diamond film growth, for forming new magnetic nanomaterials and field electron emitters are reviewed. As a result, the availability of nanodiamonds as attractive building blocks for nanotechnology is concluded.

Journal ArticleDOI
TL;DR: In this article, the authors review the recent progress in the growth of ZnO epitaxial films, doping control, device fabrication processes including etching and ohmic contact formation, and finally the prospects for fabrication and characteristics of znO light-emitting diodes.
Abstract: ZnO is attracting considerable attention for its possible application to light-emitting sources due to its advantages over GaN. We review the recent progress in the growth of ZnO epitaxial films, doping control, device fabrication processes including etching and ohmic contact formation, and finally the prospects for fabrication and characteristics of ZnO light-emitting diodes.

Journal ArticleDOI
TL;DR: In this article, the structural information in the first nearest neighbor shell level, or first-shell atomic cluster, was used to derive the composition rules of two types of complex alloy phases, quasicrystals and bulk metallic glasses, both being composed of elements with negative enthalpies of mixing.
Abstract: Metallic elements having negative enthalpies of mixing tend to form characteristic local atomic clusters. In this review, we use the structural information in the first nearest neighbour shell level, or first-shell atomic cluster, to derive the composition rules of two types of complex alloy phases, quasicrystals and bulk metallic glasses, both being composed of elements with negative enthalpies of mixing. We first show the composition phenomena in quasicrystal-forming systems, where major composition rules such as cluster line, electron concentration and atomic size criteria are derived. Then we analyse the composition rules of bulk metallic glasses using the very same approaches. Finally, we summarize their common composition rules into more general rules and basic theories.

Journal ArticleDOI
TL;DR: In this article, the authors review progress in biomedical and biosensor related research on silicon carbide (SiC) and show that less biofouling and platelet aggregation when exposed to blood can be taken advantage of in a variety of medical implantable materials while the robust semiconducting properties can be explored in surface functionalized bioelectronic devices.
Abstract: The search for materials and systems, capable of operating long term under physiological conditions, has been a strategy for many research groups during the past years. Silicon carbide (SiC) is a material, which can meet the demands due to its high biocompatibility, high inertness to biological tissues and to aggressive environment, and the possibility to make all types of electronic devices.This paper reviews progress in biomedical and biosensor related research on SiC. For example, less biofouling and platelet aggregation when exposed to blood is taken advantage of in a variety of medical implantable materials while the robust semiconducting properties can be explored in surface functionalized bioelectronic devices.

Journal ArticleDOI
TL;DR: In this article, a new model for the effective thermal conductivities of nanofluids is proposed by taking into account the nanolayer and nanoparticles' aggregation, which is expressed as a function of the thickness of the nano-layer, the nanoparticle size and volume fraction.
Abstract: Nanofluids, which are produced by dispersing nanoparticles into conventional fluids, exhibit anomalously high thermal conductivity. Most experiments demonstrated that the nanolayer surrounding the solid particles and the clusters formed by nanoparticles' aggregation may play an important role in the enhancement of thermal conductivity of nanofluids. By taking into account the nanolayer and nanoparticles' aggregation, a new model for the effective thermal conductivities of nanofluids is proposed. This model is expressed as a function of the thickness of the nanolayer, the nanoparticle size, the nanoparticle volume fraction and the thermal conductivities of suspended nanoparticles and base fluid. The theoretical predictions on the effective thermal conductivities of nanofluids are shown to be in good agreement with the available experimental data.

Journal ArticleDOI
TL;DR: The early models of solid state ice sintering are based on power law models originally developed in metallurgy as discussed by the authors, and these models were used for hot isostatic pressing of metals and ceramics.
Abstract: Sintering of ice is driven by the thermodynamic requirement to decrease surface energy. The structural morphology of ice in nature has many forms—from snowflakes to glaciers. These forms and their evolution depend critically on the balance between the thermodynamic and kinetic factors involved. Ice is a crystalline material so scientific understanding and approaches from more conventional materials can be applied to ice. The early models of solid state ice sintering are based on power law models originally developed in metallurgy. For pressure sintering of ice, these are based on work on hot isostatic pressing of metals and ceramics. Recent advances in recognizing the grain boundary groove geometry between sintering ice particles require models that use new approaches in materials science. The newer models of sintering in materials science are beginning to incorporate more realistic processing conditions and microstructural complexity, and so there is much to be gained from applying these to ice in the future. The vapour pressure of ice is high, which causes it to sublime readily. The main mechanism for isothermal sintering of ice particles is by vapour diffusion; however other transport mechanisms certainly contribute. Plastic deformation with power law creep combined with recrystallization become important mechanisms in sintering with external pressure. Modern experimental techniques, low temperature scanning electron microscopy and x-ray tomography, are providing new insights into the evolution of microstructures in ice. Sintering in the presence of a small volume fraction of the liquid phase causes much higher bond growth rates. This may be important in natural snow which contains impurities that form a liquid phase. Knowledge of ice microstructure and sintering is beneficial in understanding mechanical behaviour in ice friction and the stability of snow slopes prone to avalanches. (Some figures in this article are in colour only in the electronic version)

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TL;DR: In this paper, the authors show that electrode polarization impedance can indeed influence the measurements and that also other phenomena such as negative sensitivity regions, separate current paths and common-mode signals may seriously spoil the measured data.
Abstract: Tetrapolar electrode systems are commonly used for impedance measurements on biomaterials and other ionic conductors. They are generally believed to be immune to the influence from electrode polarization impedance and little can be found in the literature about possible pitfalls or sources of error when using tetrapolar electrode systems. In this paper we show that electrode polarization impedance can indeed influence the measurements and that also other phenomena such as negative sensitivity regions, separate current paths and common-mode signals may seriously spoil the measured data.