Studies of structural,dielectric relaxor and electrical characteristics of lead-free double Perovskite:Gd2NiMnO6

In the current communication, structural, microstructural, dielectric, relaxor, impedance, AC conductivity, and electrical modulus characteristics of double perovskite Gd₂NiMnO₆ (synthesized by a solid state reaction route) as a function of temperature (25–125 °C) and frequency (1 kHz–1MHz) have mainly been reported. From preliminary X-ray structural analysis, it is found that the crystal structure of the material is monoclinic. In temperature dependence of dielectric constant analysis, relaxor behaviour of the material was observed. Such type of behaviour is described by modified Curie–Weiss law and a Vogel–Fulcher law. From Nyquist plots, the existence of grain and grain boundary effect in the material is observed. The non–Debye type of relaxation is confirmed from the complex impedance spectroscopy. From the impedance data, the determined grain resistance reduces with increment of temperature showing negative temperature co-efficient of resistance (NTCR)-type nature of the material which also confirmed from conductivity analysis. Again, non-Debye type of relaxation phenomena is observed from the analysis of modulus spectroscopy which is also proved by complex impedance plot. From these result it may be concluded that this material may be used for different high temperature applications.     

Dynamic behaviour at a nematic liquid crystal-rubbednylon interface using evanescent wave photon correlation spectroscopy

Photon correlation spectroscopy of light scattered by director fluctuations from an evanescent optical wave propagating in the nematic liquid crystal 5CB is used to study the interfacial dynamic behaviour of the liquid crystal. The intensity correlation function of light scattered by interfacial orientation fluctuations is measured by illuminating to give a short optical penetration depth within the nematic. These surface scattering correlation functions strongly differ from the bulk correlation function and are interpreted in terms of a nematic surface orientation mode arising from the coupling between the director field and the fluid velocity. It is shown that the analysis of the surface mode gives a method for measuring anchoring energies in liquid crystals. The anchoring energy obtained for rotation of the director away from the rubbing direction about an axis normal to the surface for 5CB at a rubbed nylon surface is 7.14±0.7 × 10-² ergcm-².     

Bulk electrical properties of single-walled carbon nanotubes immobilized by dielectrophoresis: evidence of metallic or semiconductor behavior

We report the electrical characterization of single-walled carbon nanotubes (SWCNTs) trapped between two electrodes by dielectrophoresis (DEP). At high frequency, SWCNTs collected by DEP are expected to be of metallic type. Indeed current-voltage (I-V) measurements for devices made at 10 MHz show high values of conductivity and exhibit metallic behavior with linear and symmetric electrical features attributed to ohmic conduction. At low frequency, SWCNTs attracted by DEP are expected to be of semiconducting nature. Devices made at 10 kHz behave as semiconductors and demonstrate nonlinear and rectifying electrical characteristics with conductivities many orders of magnitude below the sample resulting from high-frequency immobilization of SWCNTs. Conducting atomic force microscopy (C-AFM) and current density calculation results are presented to reinforce results obtained by I-V measurements which clearly show type separation of SWCNTs after DEP experiments.     

Geldart B 类颗粒气固流化床内的压力波动特性(英文)

采用多通道压力采集系统测量了Geldart B类颗粒（树脂）矩形流化床(2.000m×0.300m×0.025m)内的压力波动,探索了流化床内的压力波动特征;同时采用标准方差、自相关和互相关函数分析了表观气速和静床高度对压力波动、压力波速度和压力波主频的影响。结果表明,气泡行为（如：气泡的形成、发展、聚并和破碎）是影响流化床内压力波动的主要因素;密相和稀相界面处的压力波动幅值主要由气泡崩塌决定;压力波在流化床内进行传播,并且具有明显的周期性特征;此外,压力波动、压力波速度和压力波主频均与表观气速和静床高度密切相关。     

Theoretical consideration of the drop in threshold voltage at low frequencies in nematic liquid crystals

Research of numerical calculation and theoretical considerations have been applied in relation to the electrical double layer effect on the threshold voltage of liquid crystals in order to understand the drop in threshold voltage often observed at low frequencies. Decreased resistivity of an alignment film was found to contribute to this threshold voltage drop. Moreover, dielectric dispersion due to the electrical double layer at the interface between the liquid crystal and alignment film layers is thought to exist in the frequency range in which the drop in threshold voltage was obtained experimentally. Therefore Debye type dielectric dispersion of the electrical double layer in the system consisting of the nematic liquid crystal and the alignment film also influences the threshold behaviour at low frequencies.     

Electrical model of a liquid crystal pixel with dynamic, voltage history-dependent capacitance value

The voltage history-dependent nature of a liquid crystal pixel capacitance becomes an important issue in active matrix addressing as large storage capacitors are replaced with more intelligent circuitry such as in-pixel frame buffers. In this paper, a simple but flexible Spice macro model is introduced that allows accurate simulations of the electrical behaviour of a nematic liquid crystal pixel capacitance. The model correctly predicts voltage drops caused by the increasing dielectric constant when liquid crystal molecules align themselves to the electric field. An internal node of the macro model represents the average director orientation and can also be used to predict the optical response. In its basic embodiment, the model uses a first-order, low pass RMS filter to implement the dynamic behaviour of the pixel, which suffices to predict response delays and asymmetric rise and fall times. However, the model also supports more elaborated filters that offer more control over the simulated dynamic behaviour. A number of simulations are performed that illustrate the usefulness of the new model during the design of novel 'smart' pixel architectures.     

Study of aerodynamic and release properties of inhaled particles containing cyclodextrins

The aim of this study was to investigate the influence of different cyclodextrins (CyD) on physical characteristics of inhalation dry powders. The particle size was characterised by Aerosizer^® LD and aerodynamic behaviour of inhaled complexes assessed by twin-stage liquid impinger. The in vitro release profile of the powders was studied through Franz cell modified method. Produced particles showed a suitable size for pulmonary delivery, ranging between 1 and 5 μm. The nature of the CyD affected the powders performance on reaching the lower compartment (“Lungs”), mainly by the altering their aerodynamic properties, which is reflected on the different percentages of their emitted respirable fractions. HP-γ-CyD:fluticasone propionate complex showed a fast release of corticosteroid while γ-CyD had a constant release throughout time. The best characteristics for pulmonary delivery were obtained with acetyl-γ-CyD:fluticasone propionate complex.     

Traveling-wave electrokinetic micropumps: velocity, electrical current, and impedance measurements

An array of microelectrodes covered in an electrolyte and energized by a traveling-wave potential produces net movement of the fluid. Arrays of platinum microelectrodes of two different characteristic sizes have been studied. For both sizes of arrays, at low voltages (<2 V pp) the electrolyte flow is in qualitative agreement with the linear theory of ac electroosmosis. At voltages above a threshold, the direction of fluid flow is reversed. The electrical impedance of the electrode-electrolyte system was measured after the experiments, and changes in the electrical properties of the electrolyte were observed. Measurements of the electrical current during pumping of the electrolyte are also reported. Transient behaviors in both electrical current and fluid velocity were observed. The Faradaic currents probably generate conductivity gradients in the liquid bulk, which in turn give rise to electrical forces. These effects are discussed in relation to the fluid flow observations.     

Inertial Hydrodynamic Effects in Electrophoresis of Particles in an Alternating Electric Field

The influence of the effects associated with the inertia of particles and the surrounding fluid on the electrophoresis in an alternating electric field has been theoretically investigated. From solving the hydrodynamic equations the electrophoretic velocity of a spherical particle was found to depend on the frequency of the external electric field and on the particle-to-fluid-density ratio. It is shown that, due to inertial effects, the liquid flow around particles with a thin electrical double layer (EDL) is no longer potential. A mechanism of the formation of steady-state flow in the vicinity of oscillating particles with a thin EDL is proposed. Using numerical methods, a picture of the fluid streamlines in such a flow is obtained. The spatial distribution of the fluid velocity in the vicinity of a particle is also found. It was established that with an increasing frequency of the electric field the steady-state flow velocity passes through a maximum. The flow direction depends on the ratio between the densities of a particle and the surrounding fluid. The reversal of direction takes place when this ratio is about 0.7. The case of a thick EDL has also been considered, and a comparative analysis of the flow distributions around the particles with a thin and those with a thick EDL has been carried out.     

Theoretical analysis of electrokinetic flow and heat transfer in a microchannel under asymmetric boundary conditions

The main theme of the present work is to investigate the electrokinetic effects on liquid flow and heat transfer in a flat microchannel of two parallel plates under asymmetric boundary conditions including wall-sliding motion, unequal zeta potentials, and unequal heat fluxes on two walls. Based on the Debye-Huckel approximation, an electrical potential solution to the linearized Poisson-Boltzmann equation is obtained and employed in the analysis. The analytic solutions of the electrical potential, velocity distributions, streaming potential, friction coefficient, temperature distribution, and heat transfer rate are obtained, and thereby the effects of electrokinetic separation distance (K), zeta-potential level (zeta;(1)), ratio of two zeta potentials (r(zeta) identical with zeta;(2)/zeta;(1)), wall-sliding velocity (u(w)), and heat flux ratio (r(q) identical with q"(2)/q"(1)) are investigated. The present results reveal the effects of wall-sliding and zeta-potential ratio on the hydrodynamic nature of microchannel flow, and they are used to provide physical interpretations for the resultant electrokinetic effects and the underlying electro-hydrodynamic interaction mechanisms. In the final part the results of potential and velocity fields are applied in solving the energy equation. The temperature distributions and heat transfer characteristics under the asymmetrical kinematic, electric, and thermal boundary conditions considered presently are dealt with.     

Interactions Between Helium Plasma Jets and Electrolytes at Different Driving Voltages

This study reports the effects of the driving voltage on interactions between plasma jets and electrolytes. Plasma jets over electrolytes, which were generated using five kinds of driving voltages, were characterized by distinct optical emissions from the gas region and the gas–liquid interface with unique electrical characteristics. The generated plasma jets over electrolytes resemble the characteristics of dielectric barrier discharges; the plasma–liquid interactions are affected by external driving voltages that vary the surface charge at the gas–liquid interface because of the conductive and dielectric nature of the electrolyte. The findings suggest that selecting an adequate driving voltage waveform is critical for specific applications utilizing plasma–liquid interactions.     

Soil Type and Herbicides Adsorption

Abstract

Herbicides behaviour in soils greatly depends on adsorption through its influence on degradation and movement. The adsorption intensity depends on both the chemical structure of pesticides, the nature of soil constituents and soil physico-chemical factors such as the pH. In this paper, the role played by these factors is analysed and used to evaluate the possible use of soil surveys for assessing adsorption behaviour of pesticides in soils. The analysis is based on adsorption measurements of three herbicides (atrazine, terbutryn and 2,4-D) by several soils differing in their mineralogical composition, organic matter content and pH. Using statistical analysis, it is shown that some relations can be defined between soil types and adsorption behaviour. These relations are strongly dependent on the electrical state of the herbicide molecule (cationic, anionic and neutral).     

Voltammetry at a de Levie brush electrode as a model for electrochemical supercapacitor behaviour

Electrochemical supercapacitors provide electrical energy storage systems complementary to batteries. Based on the double layer capacitance of high area porous electrode materials, e.g. carbon powders, felts, foams, aerogels or on the redox pseudocapacitance of oxide or polymer films, specific capacitances of the order of 50100 F g⁻¹ are realizable. However, the porous nature of the electrode structures introduces a distribution of resistive and capacitative elements giving rise to electrical behaviour like that of a transmission line, as treated by de Levie, with a resulting complex power spectrum depending on charging or discharging rates. The present paper examines the cyclic voltammetry behaviour of de Levie type wire brush electrodes as models for porous electrodes, in comparison with that of single wire electrodes of the same metal. Comparisons are also made with constant current charging behaviour and with the electrochemical behaviour of specially made, 3 V, non aqueous solution, double layer capacitor modules, examined under similar conditions in relation to the current response profiles of a 5 RC element hardware model circuit. These approaches enable the effects of the distribution of R and C elements on charge acceptance and delivery at various rates to be quantitatively evaluated for various resistivities of the conducting electrolyte in pores.     

Comparison of Aluminium Nanostructures Created by Discharges in Various Dielectric Liquids

Synthesis of aluminium-containing nanoparticles (NPs) by electrical discharges was performed in three dielectric liquids (heptane, liquid nitrogen and water) with aluminium electrodes. The nature of the liquid plays an essential role in the synthesis yield and in the structural properties of NPs. Time-resolved optical emission spectroscopy of selected emission lines emitted during the discharge and its time afterglow was used to observe the chemical changes occurring in the gas phase. It turns out that in heptane and liquid nitrogen, crystalline metallic NPs (from 5 to 10 nm in diameter) are synthesized and oxidized next into amorphous alumina when they are in contact with air, once the liquid is evaporated. In heptane, the transformation of the liquid itself into hydrogenated amorphous carbon creates a kind a matrix in which the aluminium NPs are embedded. Sometimes, a protective graphite shell grows around the NPs and protects them from any further oxidation. In water, these crystalline metallic NPs are synthesized during the first 800 ns of the discharge process, when oxidation is limited by the outward flux of the metallic vapour. They are oxidized next in water. A second type of alumina NPs (several 10 s of nm in diameter) are produced from 800 ns on. They are likely formed from AlO molecules and no longer from aluminium atoms. In every liquid, sub-micrometric particles are also found due to droplet emission from the liquid well created during impacts of spark discharges on electrodes.     

Some considerations of the steady-state and transient behaviour of membrane-covered dissolved oxygen detectors

The behaviour of commercial, membrane-covered dissolved oxygen detectors is considerably more complicated than the orginal model of Mancy et al. would suggest. For example, the steady-state current is dependent both on the thickness and nature of the electrolyte behind the membrane. And transient currents obtained for switch-on of the detector are not completely described by the simple diffusional model. This paper examines these examples of more complicated behaviour. An analysis of the transient current for a step change in dissolved oxygen concentration is also given.     

Multichannel digital transmission in an optical network of communicating molecules

In present telecommunication networks, information transfer relies on the interplay of optical and electrical signals. Data are communicated optically but processed electronically. Methods to maintain the propagating signals solely at the optical level must be developed to overcome the transmission capacities and speed limits imposed by the electronic components. We have demonstrated that molecular switches can be used to gate optical signals in response to optical signals. We have realized a simple optical network consisting of three light sources, one cell containing a solution of three fluorescent molecules, one cell containing a solution of a three-state molecular switch and a detector. The light emitted by the three fluorophores is absorbed by the three states of the molecular switch. Using this simple operating principle, we have shown that multichannel digital transmission can be implemented on an ensemble of communicating molecules relying exclusively on the interplay of optical inputs and optical outputs.     

A pyrometric differential thermal analyser for high temperatures

An apparatus for differential thermal analysis to a temperature of 3400°C is described. The specimen is heated inductively with a frequency of 1 MHz either without crucible at its upper end only or in a crucible which is one of the components of the system investigated. The differential principle is applied by comparing the radiation emitted from the sample with the power fed to the sample, which is registered by a bulb coupled to the high frequency circuit. The emission of the sample and bulb are measured by two photodiodes. The different behaviour of sample and bulb is compensated electronically. Investigations in metal ceramic eutectics are given as an example.     

Lock-exchange experiments with an autocatalytic reaction front

A viscous lock-exchange gravity current corresponds to the reciprocal exchange of two fluids of different densities in a horizontal channel. The resulting front between the two fluids spreads as the square root of time, with a diffusion coefficient reflecting the buoyancy, viscosity, and geometrical configuration of the current. On the other hand, an autocatalytic reaction front between a reactant and a product may propagate as a solitary wave, namely, at a constant velocity and with a stationary concentration profile, resulting from the balance between molecular diffusion and chemical reaction. In most systems, the fluid left behind the front has a different density leading to a lock-exchange configuration. We revisit, with a chemical reaction, the classical situation of lock-exchange. We present an experimental analysis of buoyancy effects on the shape and the velocity of the iodate arsenous acid autocatalytic reaction fronts, propagating in horizontal rectangular channels and for a wide range of aspect ratios (1/3 to 20) and cylindrical tubes. We do observe stationary-shaped fronts, spanning the height of the cell and propagating along the cell axis. Our data support the contention that the front velocity and its extension are linked to each other and that their variations scale with a single variable involving the diffusion coefficient of the lock-exchange in the absence of chemical reaction. This analysis is supported by results obtained with lattice Bathnagar-Gross-Krook (BGK) simulations Jarrige et al. [Phys. Rev. E 81, 06631 (2010)], in other geometries (like in 2D simulations by Rongy et al. [J. Chem. Phys. 127, 114710 (2007)] and experiments in cylindrical tubes by Pojman et al. [J. Phys. Chem. 95, 1299 (1991)]), and for another chemical reaction Schuszter et al. [Phys. Rev. E 79, 016216 (2009)].     

First carbazole-based lamellar liquid crystal system

The synthesis and characterization of seven polysubstituted 9-arylcarbazole derivatives is described. The influence of the number of chains peripherally bonded to the core, as well as the length of the chains, on the mesophase behaviour of the synthesized systems has been studied. The nature of the linking group between the core and the peripheral chains has also been considered. One of these compounds displays liquid crystalline behaviour, as confirmed by optical polarizing microscopy, differential scanning calorimetry and X-ray diffraction, being the first carbazole-based lamellar liquid crystal system reported in the literature.     

含咪唑离子盐的环辛烯在离子液体中开环易位聚合微观研究

用核磁共振方法研究了带电荷的环辛烯单体在离子液体和CDCl3中开环易位聚合反应的微观特征,根据单体在化学位移δ=5.66~5.58处双键氢积分峰面积的减少和聚合物主链上不饱和双键氢移至高场δ=5.38~5.39处峰面积积分的增加来表征聚合反应的情况.检测和记录了单体在有离子液体参与的条件下均相聚合反应和在CDCl3中的异相聚合反应过程,根据在不同反应体系中Grubbs第二代崔化剂中与Ru相连的苯亚甲基上氢在核磁图谱上δ=19.2处的峰型变化,探讨在两种介质中的不同聚合行为.研究表明,该单体在离子液体介质中的均相聚合有可控聚合的微观特点,并通过ln[M]0/[M]与反应时间的关系曲线,证实了反应的活性特征.