Presence Of Conduction Research Articles

Non-Ohmic Electrical Transport in the Vicinity of the Superconducting Transition: Implications for the Study of the Phase Diagram of the Underdoped Cuprate Superconductors

In this paper, we present a theoretical discus- sion of the non-ohmic regime of the electrical conductivity of a type-II planar superconductor near its superconduct- ing transition, focusing mainly in the region between the phase-coherence and the pair-condensation critical temper- atures, Tphase <T < T cond. For that purpose, we extend down to those temperatures existing calculations for the so- called Aslamazov-Larkin conductivity in presence of finite electric fields, and the resulting exponent α of the fluctu- ation voltage-current characteristics E∼j α . These results are then discussed by considering two possible scenarios for the phase diagram of the superconducting fluctuations in the underdoped high-temperature superconductors. Our results suggest that the strong phase fluctuations scenario (i.e., large Tcond − Tphase) leads to a plateau in the T - dependence of the exponent α near Tphase, and that the T -region over which this plateau extends becomes wider when the applied electric field is increased. These features are much smaller in the conventional fluctuations scenario (i.e., small Tcond − Tphase).

MHD three-dimensional flow of Maxwell fluid with variable thermal conductivity and heat source/sink

Purpose – The purpose of this paper is to investigate the three-dimensional flow of Maxwell fluid with variable thermal conductivity in presence of heat source/sink. Design/methodology/approach – Similarity transformations are utilized to reduce the nonlinear partial differential equations into ordinary differential equations. The governing nonlinear problems are solved by homotopy analysis method. Findings – The paper found that the velocities decrease while temperature increases for higher Hartman number. It is also seen that the thermal boundary layer thickness and temperature are increased with an increase in variable thermal conductivity parameter and heat source/sink parameter. Practical implications – Heat transfer analysis with heat source/sink has pivotal role in many industrial applications like cooling of an infinite metallic plate in a cooling bath, drawing of plastic films, nuclear plants, gas turbines, various propulsion devices for missiles, space vehicles and processes occurring at high temperatures. Originality/value – This study discusses the magnetohydrodynamic three-dimensional flow of Maxwell fluid with variable thermal conductivity and heat source/sink. No such analysis exists in the literature yet.

Temperature Frequency Characteristics of Charge Transition in the Li0.5Fe2.4Ti0.1O4 Non-stoichiometric System

A study of conductivity temperature frequency dependence of Li0.5Fe2.4Ti0.1O4 non-stoichiometric spinel has exhibited frequency dispersion conductivity presence. The time of relaxation (τ) proved to make 2·10-6s within the limits of dispersion. The conductivity size was found to be dependant upon the amount of Fe2+ ions in the structure.

Hydrothermal synthesis of mixed crystal phases TiO2–reduced graphene oxide nanocomposites with small particle size for lithium ion batteries

A rutile and anatase mixed crystal phase of nano-rod TiO2 and TiO2–reduced graphene oxide (TiO2–RGO) nanocomposites with small particle size were prepared via a facile hydrothermal approach with titanium tetrabutoxide and graphene oxide as the precursor. Hydrolysis of titanium tetrabutoxide and mild reduction of graphene oxide were simultaneously carried out. Compared with traditional multistep methods, a novel green synthetic route to produce TiO2–RGO without toxic solvents or reducing agents was employed. TiO2–RGO as anode of lithium ion batteries was characterized by extensive measurements. The nanocomposites exhibited notable improvement in lithium ion insertion/extraction behavior compared with TiO2, indicating an initial irreversible capacity and a reversible capacity of 295.4 and 112.3 mA h g−1 for TiO2–RGO after 100 cycles at a high charge rate of 10 C. The enhanced electrochemical performance is attributed to increased conductivity in presence of reduced graphene oxide in TiO2–RGO, a rutile and anatase mixed crystal phase of nano-rod TiO2/GNS composites, small size of TiO2 particles in nanocomposites, and enlarged electrode–electrolyte contact area, leading to more electroactive sites in TiO2–RGO.

Studying the Effect of Paracetamol Drug on the Conductivity of 0.5M Hydrochloric Acid Solution at Different Temperatures

In this study paracetamol drug is used to reduce the conductivity of 0.5M hydrochloric acid at different concentrations for each one of them at different temperatures ranged (30-60)°C. Generally , increasing of the concentration of  the inhibitor leads to reducing in conductivity of the acid at constant temperature. On the other hand, at constant concentration of inhibitor, the conductivity is reduced as temperature increased i.e., paracetamol can adsorbed chemically on the metal or alloy. Furthermore the kinetic study of the molar conductance process reveal that in presence of paracetamol the activation energy and enthalpy of activation are negative compared with their values in absence of paracetamol where they are negative because the reducing the conductivity in presence of paracetamol where the non spontaneous property for the conductance of acid is increased as the paracetamol concentration increased in addition to increasing the negative value of entropy in presence of paracetamol that indicate to restrict for the mobility of hydrogen and chloride ions which correspond to 90.47% as efficiency of reducing the conductance of acid by paracetamol. On the other hand thermodynamic study is achieved which explained the adsorption of paracetamol obey to Freundlisch model.Â

MHD Free Convection Flow with Temperature Dependent Thermal Conductivity in Presence of Heat Absorption along a Vertical Wavy Surface

Abstract MHD (magnetohydrodynamic) free convection flow of viscous incompressible fluid with temperature dependent thermal conductivity in presence of heat absorption along a uniformly heated vertical wavy surface have been numerically solved and analyzed. Using suitable set of dimensionless variables the governing boundary layer equations are first transformed into a non-dimensional form. The resulting nonlinear system of partial differential equations are mapped into the domain of a vertical flat plate and then solved numerically employing the implicit finite difference method, known as the Keller-box scheme. The numerical results of the skin friction coefficient, the rate of heat transfer in terms of local Nusselt number, the streamlines as well as the isotherms are presented graphically for different values of thermal conductivity parameter and heat absorption parameter Q for a fluid having Prandtl number equal to 1.

Non-Gaussian resistance noise in the ferromagnetic insulating state of a hole-doped manganite

We report the observation of a large 1/f noise in the ferromagnetic insulating state (FMI) of a hole doped manganite single crystal of La0.80Ca0.20MnO3 which manifests hopping conductivity in presence of a Coulomb gap. The temperature dependent noise magnitude shows a deep within the FMI state, there is a sharp freeze out of the noise magnitude with temperature on cooling. As the material enters the FMI state, the noise becomes non-Gaussian as seen through probability density function and second spectra. It is proposed to arise from charge fluctuations in a correlated glassy phase of the polaronic carriers which develop in these systems as reported in recent simulation studies.

ELIMINATION OF GAS POLLUTANTS USING SnO2-CeO2 CATALYSTS

The surface behavior of a series of SnO2 (5, 10 and 20 wt.%) - CeO2 catalyst samples prepared by impregnation method and also pure SnO2, CeO2, was studied based on the response of the ac electrical conductivity. The electrical measurements were carried out in operando conditions in order to obtain information about the surface interaction with reactants during CO/hydrocarbon oxidation over these catalysts. The apparent activation energies of conduction in presence of CO:O2 and C3H6:air mixtures were presented. The catalyst samples were tested in catalytic oxidation of CO and C3H6 at temperature range of room temperature up to 400 C. The catalytic activity in both oxidation reactions and selectivity towards CO2 in propylene oxidation at 400 C exhibited by the SnO2-CeO2 systems were significantly higher to those exhibited by the pure ceria catalyst.

Holography of charged dilatonic black branes at finite temperature

We investigate bulk and holographic features of finite-temperature black brane solutions of 4D anti-de Sitter Einstein-Maxwell-dilaton-gravity (EMDG). We construct, numerically, black branes endowed with non trivial scalar hairs for broad classes of EMDG. We consider both exponential and power-law forms for the coupling functions, as well as several charge configurations: purely electric, purely magnetic and dyonic solutions. At finite temperature the field theory holographically dual to these black brane solutions has a rich and interesting phenomenology reminiscent of electron motion in metals: phase transitions triggered by nonvanishing VEV of scalar operators, non-monotonic behavior of the electric conductivities as function of the frequency and of the temperature, Hall effect and sharp synchrotron resonances of the conductivity in presence of a magnetic field. Conversely, in the zero temperature limit the conductivities for these models show a universal behavior. The optical conductivity has a power-law behavior as a function of the frequency, whereas the DC conductivity is suppressed at small temperatures.

A short review on AC electro-thermal micropumps based on smeared structural polarizations in the presence of a temperature gradient

An AC-field will influence smeared spatial charges in the bulk of a polarizable medium in the presence of conductivity and permittivity gradients. Such gradients can be generated by a temperature gradient induced by Joule heating by the AC-field itself or a separate heating element. Finally, the interaction of the AC-field with the spatial charges may drive an effective medium flow in asymmetric systems. The induced pumping force depends on the temperature and field gradients, as well as on the frequency of the driving AC-field. We present various designs for new AC electro-thermal micropumps (ETμPs) that exploit the spatially smeared bulk polarization principle. In some designs, an integrated heating element allows the temperature gradient to be adjusted. Advantages of the ETμP principle are the absence of any moving parts, force plateaus in broad frequency ranges, and a reversal of the pump direction in dependence on the driving frequency. The operating frequencies ranging from kHz to GHz avoid electrolytic electrode processes and electrode deterioration. Designs with evenly shaped cross-sections of the pump channel are possible. Maximum pumping velocities above 1 mm s −1 were observed in channels with a 120 × 60 μm 2 cross-section at an induced temperature increase below 10 °C. For pump volumes of approximately 100 nl the usable conductivity range for aqueous media spans from the extremely low to above physiological values. A further miniaturization of the pumps is viewed as quite feasible.

Influence of shear deformation on carbon nanotube networks in polycarbonate melts: Interplay between build-up and destruction of agglomerates

Shear-induced destruction and formation of conductive and mechanical filler networks formed by multi-wall carbon nanotubes in polycarbonate melts were investigated by simultaneous time-resolved measurements of electrical conductivity and rheological properties under steady shear and in the quiescent melt. The steady shear experiments were performed at shear rates between 0.02 and 1rad/s and for nanotube concentrations ranging from 0.5 to 1.5wt%. The influence of thermo-mechanical history on the state of nanotube dispersion and agglomeration was studied in detail.For melts with well-dispersed nanotubes a shear-induced insulator–conductor transition was observed, which is explained by the agglomeration of nanotubes under steady shear and the formation of an electrical conductive network of interconnected agglomerates. Simultaneously, a drastic decrease of the shear modulus (G∗=G′+iG″) during steady shear was observed, which can be related to a reduction of mechanical reinforcement due to agglomeration of dispersed nanotubes. These findings indicate a substantial difference in the nature of “electrical” and “mechanical” network and contradict earlier assumptions that steady (or transient) shear is always destructive for the conductive filler network in highly viscous polymer composites.It was also shown that after a certain time of steady shear the filler network asymptotically reaches its steady state characterized by the constant electrical conductivity and shear modulus of the composite melt. Such asymptotic behaviour of composite properties was experimentally shown to be related to the interplay of the destructive and build-up effects of steady shear. For modelling of the electrical conductivity in presence of steady shear a kinetic equation was proposed for filler agglomeration with shear-dependent destruction and build-up terms. This equation was coupled to the generalized effective medium (GEM) approximation for insulator–conductor transition.

MHD-conjugate heat transfer analysis for a vertical flat plate in presence of viscous dissipation and heat generation

In this paper, the effects of magnetic field, viscous dissipation and heat generation on natural convection flow of an incompressible, viscous and electrically conducting fluid along a vertical flat plate in the presence of conduction are investigated. Numerical solutions for the governing momentum and energy equations are given. A discussion is provided for the effects of magnetic parameter, viscous dissipation parameter and heat generation parameter on two-dimensional flow. Detailed analysis of the velocity profile, temperature distribution, skin friction, rate of heat transfer and the surface temperature distribution are shown graphically.

Experimental and numerical analyses on LiSO 4 and Li 2TiO 3 pebble beds used in a ITER test blanket module

One of the possible configurations of test blanket module (TBM) which will be tested during the ITER operation phase is made up of neutron multiplier and breeder as pebble beds. This paper describes an experimental device for the determination of the pebble bed conductivity in presence of interstitial air. The tests were performed with a simultaneous compression of the bed in order to obtain the effective bed conductivity versus the axial deformation for several values of the temperature. The effective conductivities of LiSiO 4 and Li 2TiO 3 pebble beds, both in air and in vacuum, were determined. The packing factors of the beds were measured by means an ad hoc built instrumentation, based on the gamma ray backscattering. The experimental results have been compared with those of a theoretical model developed by the authors, obtaining a good agreement in terms of bed conductivity and stiffness.

Surface State Model for Conductance Responses During Thermal-Modulation of SnO-Based Thick Film Sensors: Part IModel Derivation

Metal oxide gas sensors (MOXs) are widely used in olfactory electronic systems for their high sensitivity and low-cost. These sensors modify their conductivity in presence of oxidizing and reducing gases, and their performance is strictly dependent on the measurement technique adopted. In particular, it was already established by many works that a noticeable improvement in selectivity can be obtained by operating MOXs with a variable temperature. The temperature profile, however, must be tailored to the specific application, and the shape of the "optimum" profile for a given application depends both on the specific sensor and on the tested chemicals. In this context, there exists a strong interest in developing simplified models able to predict the sensor response, and aiming at a better comprehension of the mechanisms involved in sensing operations. In this paper, three simple gray-box models able to predict the behavior of some commercial thick film SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based sensors in presence of oxygen and a reducing gas (CO) are proposed and discussed, whereas in a second paper the experimental validation of the model is presented

Simultaneous immobilization of cobalt tetrasulfonated phthalocyanine during electropolymerization of pyrrole in presence of surfactants: a study of film morphology and its conductivity

An attempt was made to electrochemically immobilize tetrasulfonated phthalocyanine (CoTsPc) into polypyrrole in presence of three types of surfactants (cationic, anionic, and neutral) during the polymerization of pyrrole in an aqueous solution with different potential regions. The surface characteristics of anodically/cathodically prepared electrodes with cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Triton X-100 were investigated using the scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) measurements. The SEM and XPS measurements revealed the position and orientation of CoTsPc and surfactant, respectively, in the prepared films. The film conductivity was deduced from AC impedance and its conductivity values were found to be very low when compared to the literature results. The decrease of film conductivity in presence of the surfactant and CoTsPc could be associated with the fewer amounts of counter ions in the film and also the absence of conjugation for electron hopping within the film.

Electrical Measurement of Recombination Lifetime in Blue Light Emitting Diodes

ABSTRACTA recombination lifetime of approximately 25 ns was extracted from measured reverse recovery storage times in AlGaN/GaN/AlGaN double heterojunction blue light emitting diodes. This experimentally determined lifetime is expected to arise from a combination of radiative and non-radiative processes occurring in the diodes. The non-radiative processes are likely to be due the presence of a high concentration deep-states as identified from the current-voltage and capacitance-voltage measurements. Current-voltage characteristics of these diodes were highly non-ideal as indicated by high values of the ideality factor ranging from 3.0 – 7.0. Logarithmic plots of the forward characteristics indicated a space-charge-limited-current (SCLC) conduction in presence of a high density of “deep-level states” in the active region of the diodes. An analysis of these characteristics yielded an approximate density of these deep-level states as 2 × 1017/cm3. The density of deep-states extracted from capacitance-voltage measurements were in good agreement with that obtained from current-voltage measurements.

Identification and On-Line Estimation of the Unsaturated Hydraulic Conductivity in Presence of Forced Air Convection Based on a Distributed-Parameter Model

The goal of this study was to calibrate a numerical model aimed at describing simultaneous air and water flow in soil and, to build a model-based estimator of the unsaturated hydraulic conductivity. The experimental approach consisted of infiltration tests in a 1.5m high column of loamy sand. The numerical model correctly described water percolation without air convection, provided parameter adjustment of the predictive model of the unsaturated hydraulic conductivity was performed. An observer-based estimator was able to estimate on-line the hydraulic conductivity in steady-state but faced oscillation problems in unsteady-state. The difficulty in implementing the software-sensor can be explained by the strong nonlinearity of the dynamical model.

Photoconductivity in a-Se 90Ge 10− xIn x thin films

Temperature dependence of conductivity is studied in dark as well as in presence of light in amorphous thin films of Se 90Ge 10- x In x ( x=0, 2, 4, 6, 8 and 10) prepared by vacuum evaporation technique. The dark conductivity increases exponentially with temperature, between 293 and 373 K, indicating that the conductivity is a thermally activated process. Temperature dependence of conductivity in presence of light at different intensities indicate that photoconductivity is also thermally activated in the above temperature range in all the samples studied. The activation energy of photoconduction is found to decrease with the increase in the intensity which indicates the shift of the Fermi level on light shining due to splitting of Fermi level into quasi-Fermi levels. Transient photoconductivity measurements at different temperatures and intensities indicate that the decay of photoconductivity is quite slow. A persistent photocurrent is also observed which increases at higher temperatures. This is attributed to light-induced effects in these materials. Photoconductivity decay, even after subtraction of persistent photoconductivity, is found to be non-exponential in the present case indicating the presence of continuous distribution of defect states.

Magnetic quantum oscillations of the longitudinal conductivityσzzin quasi-two-dimensional metals

We derive an analytical expression for the longitudinal magnetoconductivity $\sigma_{zz}$ in layered conductors in presence of a quantizing magnetic field perpendicular to the layers and for short-range in-plane impurity scattering in frame of the quantum transport theory. Our derivation points out quite unusual temperature and magnetic field dependences for Shubnikov-de Haas oscillations in the two-dimensional limit, i.e. $\hbar \omega_{c} \gg 4 \pi t$, where $t$ is the interlayer hopping integral for electrons, and $\omega_{c}$ the cyclotron frequency. In particular, when $\hbar \omega_{c} \gg 4 \pi t$ and $\hbar \omega_{c} \geq 2 \pi \Gamma_{\mu}$ (here $\Gamma_{\mu}$ is the value of the imaginary part of the impurity self-energy at the chemical potential $\mu$), a pseudo-gap centered on integer values of $\mu/\hbar\omega_{c}$ appears in the zero-temperature magnetoconductivity function $\sigma_{zz}(\mu/\hbar\omega_{c})$. At low temperatures, this high-field regime is characterized by a thermally activated behavior of the conductivity minima (when chemical potential $\mu$ lies between Landau levels) in correspondence with the recent observation in the organic conductor $\beta''\text{-(BEDT-TTF)}_{2}\text{SF}_{5}\text{CH}_{2}\text{CF}_{2}\text{SO}_ {3}$.

Wolff-Parkinson-White Syndrome

The history of the Wolff-Parkinson-White (WPW) syndrome is a 50-year–long tale of speculation and discussion among physiologists, anatomists, and clinicians about how to explain the frequently occurring tachycardias in patients showing a strange ECG.1 That riddle was solved in 1967 in Amsterdam when Durrer and associates2 showed that the WPW syndrome was based on a second connection between the atrium and ventricle apart from the normal AV node–His pathway. The presence of conduction over such an accessory AV pathway was demonstrated by epicardial mapping during sinus rhythm. The crucial role of that structure in the tachycardia mechanism was proven by programmed electrical stimulation of the heart and mapping of cardiac activation by intracardiac catheters.3 It was shown that an impulse circulating in a circuit (consisting of atrium–AV node–His pathway–ventricle–accessory AV pathway) was responsible for the tachycardias usually found in these patients. Essential for initiation of the tachycardia is a difference in the electrophysiological properties of the 2 AV connections, which allows the occurrence of unidirectional block in 1 of the 2 structures. This difference can be exposed not only by critically timed atrial and ventricular premature beats but also by changes in the sinus rate (eg, during exercise). For perpetuation of the tachycardia, the circulation time of the impulse in the tachycardia circuit must be longer than the duration of the refractory period of the different parts of the tachycardia circuit.4 See p 3030 It also became clear that the anterograde refractory period of the accessory AV pathway determines the ventricular rate during atrial fibrillation.5 This helps to identify WPW patients at risk for dying suddenly when atrial fibrillation supervenes. The demonstration that an accessory AV pathway is an essential link both in the reentrant tachycardia mechanism and the ventricular rate during atrial fibrillation has …