Control of the aluminium-oxygen reaction in pure iron melts

Modified electrochemical oxygen sensors based on CaO-doped ZrO₂ and Y₂O₃-doped ThO₂ were developed and applied to study the aluminium-oxygen reaction in pure liquid iron with special regard to the provision of reliable experimental conditions and the attainment of true chemical equilibrium. The sensors represent valuable tools particularly for EMF long-term measurements over several hours. At 1600 °C, values of the constant and of the interaction parameters and were determined. When Fe-O-Al melts are covered with a slag phase at an activity a(Al₂O₃) < 1, e.g., CaO-saturated CaO-Al₂O₃ slag, the Al-O relationship in the iron may nevertheless be controlled by an equilibrium oxide phase at an activity a(Al₂O₃) = 1, presumably represented by inclusion particles consisting of pure Al₂O₃.     

将555定时器转换为脉宽调制器的模拟开关

本设计实例描述一种新方法,用一只基于555定时器的自激振荡器产生一个占空比可变波形.该电路有宽的调制范围,可在很宽的占空比值范围内作高度线性化控制,出色的线性使它最适合基于PWM(脉冲宽度调制)的控制应用.     

Copper bromide laser of 120-W average output power

A Ne-H₂-CuBr laser (λ510.6, 578.2 nm) is reported, which produced an average output power of 120 W at 2.5% efficiency (based on stored energy) and 100 W at 3% efficiency. These output power and efficiency figures are record values for copper bromide lasers. The sealed-off device produced maximum output power at a pulse recurrency frequency (PRF) of 17.5 kHz. Laser operating characteristics and electrical parameters are described     

Fundamentals of power spectra of extracellular potentials produced by a skeletal muscle fibre of finite length. Part I: Effect of fibre anatomy

To provide a thorough understanding of the changes in the power spectrum of electromyographic (EMG) signals, the formation of the power spectrum (PS) of extracellular potentials (EPs) produced by a skeletal muscle fibre of finite length was analysed. It was shown that, as in the case of an infinite fibre, the PS could be represented as the product of power spectra of the input signal (the first temporal derivative of the intracellular action potential, IAP) and of the impulse response (IR) of the fibre of finite length as a system of EP generation. The interrelations between the two multipliers determine the sensitivity of the EP power spectrum to alterations in parameters. The anatomical parameters of the fibre (length, depth, position of the end-plate in respect of the fibre ends) affect the EP power spectrum through IR power spectrum. Variations of the EP characteristic frequencies along the fibre length as well as oscillations in the PS are intrinsic properties of the fibre of finite length.     

Effect of activation/purification of multiwalled carbon nanotubes (MWCNTs) on the activity of non-platinum based hypo-hyper d-electrocatalysts for hydrogen evolution

Commercial multiwalled carbon nanotubes (MWCNTs) were used as a catalyst support for non-platinum hypo-hyper d-electrocatalysts. In order to improve the performance of these catalysts, activation/purification of MWCNTs in acid medium (HNO₃) was carried out. The physical and surface changes of MWCNTs were investigated by DTA/TGA analysis, Raman spectroscopy, and cyclic voltammetry. Structural changes of the electrocatalysts were observed by infrared spectroscopy and SEM. Their use as a support for electrocatalysts for hydrogen evolution was demonstrated, and shown to be more suitable compared to the traditional carbon support material − carbon black (Vulcan XC-72). The electrocatalysts consisted of 10% Co + 18% TiO₂ + MWCNTs. Activation/purification removes the amorphous carbon phase in the MWCNTs. As a result of both shortening and opening of carbon nanotubes, better dispersion of metallic particles (the active catalytic centers) was achieved. Thus, trans-particle and inter-particle porosity of the electrocatalytic material was improved, implying increase of catalytic activity for hydrogen evolution.     

A study of nanosize Fe3O4 deposited on carbon matrix

Nanosized crystalline Fe3O4 (with an average particle size of 16 nm) was successfully synthesized on a carbon matrix surface. The prepared sample was heat-treated in the temperature range 300 degrees C - 750 degrees C to remove residual impurities and to obtain a final product with a 77:23 ratio between magnetite and the carbon support. The sample was subjected to physicochemical and electrochemical tests. The purity of the phase and the particles size was determined by X-ray diffraction analysis and confirmed by field emission scanning electron micrographs. The specific surface area of the sample measured by the B.E.T method was 120 m2 g(-1). A series of electrochemical tests including EIS, CV and long-term constant current cycling have been performed. The obtained reversible capacity within 15 cycles was in the range 400-550 mA h x g(-1). The electrochemical behavior of the test sample and its possible practical use as an anode material in lithium secondary batteries are discussed.     

Directional synthetic aperture flow imaging

A method for flow estimation using synthetic aperture imaging and focusing along the flow direction is presented. The method can find the correct velocity magnitude for any flow angle, and full color flow images can be measured using only 32 to 128 pulse emissions. The approach uses spherical wave emissions with a number of defocused elements and a linear frequency-modulated pulse (chirp) to improve the signal-to-noise ratio. The received signals are dynamically focused along the flow direction and these signals are used in a cross-correlation estimator for finding the velocity magnitude. The flow angle is manually determined from the B-mode image. The approach can be used for both tissue and blood velocity determination. The approach was investigated using both simulations and a flow system with a laminar flow. The flow profile was measured with a commercial 7.5 MHz linear array transducer. A plastic tube with an internal diameter of 17 mm was used with an EcoWatt 1 pump generating a laminar, stationary flow. The velocity profile was measured for flow angles of 90 and 60 degrees. The RASMUS research scanner was used for acquiring radio frequency (RF) data from 128 elements of the array, using 8 emissions with 11 elements in each emission. A 20-micros chirp was used during emission. The RF data were subsequently beamformed off-line and stationary echo canceling was performed. The 60-degree flow with a peak velocity of 0.15 m/s was determined using 16 groups of 8 emissions, and the relative standard deviation was 0.36% (0.65 mm/s). Using the same setup for purely transverse flow gave a standard deviation of 1.2% (2.1 mm/s). Variation of the different parameters revealed the sensitivity to number of lines, angle deviations, length of correlation interval, and sampling interval. An in vivo image of the carotid artery and jugular vein of a healthy 29-year-old volunteer was acquired. A full color flow image using only 128 emissions could be made with a high-velocity precision.     

On singularities in the solution of three‐dimensional Stokes flow and incompressible elasticity problems with corners

In this paper, a numerical procedure is presented for the computation of corner singularities in the solution of three‐dimensional Stokes flow and incompressible elasticity problems near corners of various shape. For obtaining the order and mode of singularity, a neighbourhood of the singular point is considered with only local boundary conditions. The weak formulation of this problem is approximated using a mixed u , p Galerkin–Petrov finite element method. Additionally, a separation of variables is used to reduce the dimension of the original problem. As a result, the quadratic eigenvalue problem ( P +λ Q +λ² R ) d = 0 is obtained, where the saddle‐point‐type matrices P , Q , R are defined explicitly. For a numerical solution of the algebraic eigenvalue problem an iterative technique based on the Arnoldi method in combination with an Uzawa‐like scheme is used. This technique needs only one direct matrix factorization as well as few matrix–vector products for finding all eigenvalues in the interval ??(λ) ∈ (?0.5, 1.0), as well as the corresponding eigenvectors. Some benchmark tests show that this technique is robust and very accurate. Problems from practical importance are also analysed, for instance the surface‐breaking crack in an incompressible elastic material and the three‐dimensional viscous flow of a Newtonian fluid past a trihedral corner. Copyright © 2004 John Wiley & Sons, Ltd.     

Er,Yb:YVO4 waveguides deposited on amorphous SiO2 by PLD and UVPLD

In this work, erbium, and erbium and ytterbium co-doped YVO₄ waveguiding thin films were deposited on amorphous SiO₂ substrates by pulsed laser deposition (PLD) and ultraviolet-assisted pulsed laser deposition (UVPLD). The influence of the deposition technique on the structure, morphology, and optical properties of the films was investigated. At lower dopant concentrations the films prepared by UVPLD show better crystallinity and optical properties. All the samples show preferred orientation of the (001) zone axes parallel to the substrate surface. The polycrystalline samples show difference in the refractive indexes ?n (?n = n_TE − n_TM) for the TE and TM polarizations.     

A self-validating numerical method for the matrix exponential

An algorithm is presented, which produces highly accurate and automatically verified bounds for the matrix exponential function. Our computational approach involves iterative defect correction, interval analysis and advanced computer arithmetic. The algorithm presented is based on the “scaling and squaring” scheme, utilizing Padé approximations and safe error monitoring. A PASCAL-SC program is reported and numerical results are discussed.