A three-dimensional baroclinic current model with wave effects

Waves can have a significant impact on nearshore currents. A three-dimensional baroclinic current model including the influence of waves is presented for shallow water areas from Navier-Stokes equations. It has been found that the effects of waves on currents can be expressed in terms of the momentum flux by waves. The model uses non-orthogonal curvilinear coordinates in the horizontal directions and a Sigma coordinate in the vertical direction so that it can be more reasonably applied in estuarine and coastal regions.     

苯醌在银-汞(膜)微环电极上的循环扫描伏安波

首次报道采用化学镀法制作银－汞（膜）微环电极,并用于探讨苯醌的循环伏安曲线。还对伏安曲线的性质进行了详细的论述。结果表明：苯醌在Ｍｃｌｌｖａｉｎｅ缓冲液中的还原过程属地单电子可逆反应。根据不同扫描速度时还原波的峰电流值可以计算得到苯醌的扩散系数值。     

Epoxy resin based multilayered microwave absorbing coating system

A coating system based on different combinations of natural magnetite and carbon black filled epoxy resin has been developed. The influence of filler concentration and the ordering of the layers in the absorbing structure on the coefficients of attenuation and reflection of the electromagnetic waves in the frequency range 6.5‐12.0 GHz have been investigated. The results show that the coating system (total thickness of about 2.5‐3.0 mm) developed can be successfully used to reduce the overall signature and to prevent scattering from the sharp edges of complex shaped objects by attenuating surface currents.     

聚合物电解质(PEG/LiClO4)中L-抗坏血酸氧化的现场显微红外光谱电化学研究

L-抗坏血酸(H2A)由于在生物介质氧化还原过程中的重要作用,其分子及其衍生物已有广泛研究[1～5].聚合物电解质由于能溶解电活性物质和具有离子导电性而成为一种新的溶剂,可用于研究一些物质的电化学行为[6].H2A在聚合物电解质中的电化学及光谱电化学行为还未见报道.     

Effect of noise on chemical waves in three-dimensional reaction-diffusion systems with gradient

The effect of noise on chemical waves in a quasi-three-dimensional reaction-diffusion medium with a gradient in the third dimension is studied using the FitzHugh-Nagumo model [R. FitzHugh, Biophysics J. 1, 445 (1961)]. Numerical simulations reveal that noise of appropriate intensity can postpone the onset of turbulence and stabilize the three-dimensional (3D) waves which would otherwise undergo the gradient-induced collapse. It is also found that the 3D waves can be interrupted by incident irregularities when the noise is not too strong; it can be induced into complete turbulence when the noise is strong enough. A mathematical analysis is given based on the dependence of the oscillation frequency on the control parameter. It agrees qualitatively with our numerical findings.     

Voltammetric determination of papaverine and drotaverine

Isoquinoline derivatives (papaverine and drotaverine) are oxidized at a graphite electrode in a 0.1 M sulfuric acid solution to give voltammetric waves at 1.1 V for papaverine and at 1.05 and 1.28 V for drotaverine. Determination limits and linearity ranges of currents as functions of papaverine and drotaverine concentrations are estimated. Microgram amounts of papaverine and drotaverine are determined in model solutions (RSD = 1–4%). A procedure for the direct determination of papaverine and drotaverine in pharmaceuticals is proposed.     

Roughness-induced acoustic second-harmonic generation during electrochemical metal deposition on the quartz-crystal microbalance

This paper reports on the relation between the surface roughness and emission of compressional waves from the surface of an electrochemical quartz-crystal microbalance. The detection of the compressional waves took place with an ultrasonic microphone and the quartz crystal itself. As a model process, the electrochemical deposition of copper from an acidic copper sulfate solution has been chosen. For this system, the roughness of the layer can be tuned via the current density. Roughness may be a source of the longitudinal waves at twice the frequency of the exciting shear wave (acoustic second-harmonic generation, ASHG) if the flow profile above the quartz-crystal surface is not entirely laminar. Slight deviations from the laminar flow can be reached at high amplitudes of oscillation. Comparing the ASHG efficiency of a rough and smooth surface, we find that the rough surface is more efficient in generating second-harmonic waves. This suggests that ASHG can be used to obtain a roughness parameter independent from the resonance frequency or bandwidth (damping) of a quartz-crystal resonator. Such an independent determination of roughness should be very interesting in practical applications.     

Negative-tension instability of scroll waves and winfree turbulence in the oregonator model

Excitable media support self-organized scroll waves which can be unstable and give rise to three-dimensional wave chaos. Winfree turbulence of scroll waves results from the negative-tension instability of scroll waves; it plays an important role in the cardiac tissue where it may lead to ventricular fibrillation. By numerical simulations of the Oregonator model, we show that this instability and, thus, the Winfree turbulence may also be observed in the Belousov-Zhabotinsky reaction. The region in the parameter space, where the instability takes place, is determined, and a relationship between the negative-tension instability and the meandering behavior of spiral waves is found. The application of global periodic forcing to control such turbulence in the Oregonator model is discussed.     

Resolution of overlapping polarographic waves and derivative polarographic curves of multicomponent systems using matrix algebra

Matrix algebra has been applied to the resolution of overlapping polarographic waves and derivative curves of two- and three-component systems. Due to the complex exponential dependence of current on potential at the rising part of the waves, matrices were used to obtain the ratios of the concentrations of the components present, and the amount of each one of the components was calculated from the more reliable sum of the diffusion currents. The method proved successful for all cases of binary mixtures that were examined, but less so for the limiting case of a mixture of o-,m-, and p-nitrobenzoic acids in which all three half-wave potentials are found within 80 mV.     

极谱催化波的研究

本文综述北京大学化学系电化学分析小组二十多年来极谱催化波的研究工作。将已研究的二十五个元素的催化体系、灵敏度、催化波的性质和应用列于表1.催化波有足够的灵敏度和选择性,适用于半导体材料、高纯金属、合金、矿物、矿石、水、土壤等各方面的痕量分析。关于催化波的机理,用测量催化电流、悬汞电极、i～t曲线、循环伏安、电流积分、放射性示踪诸方法研究了反应历程、电极活性络合物的组成、稳定常数、化学反应的速率常数和吸附现象。介绍了现正着重研究稀土元素的极谱催化波的情况。     

Travelling waves in an open quadratic autocatalytic chemical system

The travelling waves that are initiated in an autocatalytic reaction–diffusion system with quadratic rate law are considered. The system is modelled on the basis of a continuous-flow, unstirred reactor. The model is used to determine whether any of the complex structures reported for cubic autocatalytic reaction–diffusion systems can also be observed in the quadratic model. This is found not to be the case. The range of behaviour of the quadratic model is much less complex, with only front waves being initiated under the necessary conditions, which are established. There are, however, some unusual transient features to be found after the initial passage of the wave front. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spatiotemporal chaos arising from standing waves in a reaction-diffusion system with cross-diffusion

We show that quasi-standing wave patterns appear in the two-variable Oregonator model of the Belousov-Zhabotinsky reaction when a cross-diffusion term is added, no wave instability is required in this case. These standing waves have a frequency that is half the frequency of bulk oscillations displayed in the absence of diffusive coupling. The standing wave patterns show a dependence on the systems size. Regular standing waves can be observed for small systems, when the system size is an integer multiple of half the wavelength. For intermediate sizes, irregular patterns are observed. For large sizes, the system shows an irregular state of spatiotemporal chaos, where standing waves drift, merge, and split, and also phase slips may occur.     

Reexamination of the theory of exaltation of the migration current by preceding electrode reactions

The effect of the preceding current of Hg(CN)₂, CdSO₄, ZnSO₄, and HCl on the K⁺ wave, of Hg(CN)₂ and CuSO₄ on the Cd²⁺ wave, of CdSO₄ on the Zn²⁺ wave, and of Hg(CN)₂ and CdSO₄ on the IO^?₃ wave was investigated. No exaltation of the Cd²⁺ wave was observed and only small variations of the Zn²⁺ and IO^?₃ waves. The increase of the K⁺ waves was roughly in accord with the prediction of the theory of the so-called exaltation of migration currents by preceding electrochemical reactions. However, the exaltation can be explained by concomitant reactions of K-amalgam with water and electrochemical reduction of hydrogen, which are accelerated by other ions (and also by the ions involved in the preceding reactions) and which, consequently, invalidate the equation of the exaltation of migration currents.     

Calculations of the contribution of ring currents to the chemical shielding anisotropy

Ring currents can exert a large effect upon the chemical shielding of NMR resonances. The analytical expression developed by Waugh and Fessenden (Waugh, J. S.; Fessenden, R. W. J. Am. Chem. Soc. 1957, 79, 846) and Johnson and Bovey (Johnson, C. E.; Bovey, F. A. J. Chem. Phys. 1957, 29, 1012) only quantifies the contribution of ring currents to the isotropic component of the shielding tensor. In the work described here an additional analytical expression is developed so that the contribution of ring currents to the full shielding tensor can be calculated, allowing an estimate of the influence of ring currents upon the chemical shielding anisotropy (CSA, Deltasigma). To test that this pair of analytical expressions can provide a reasonable estimate of the contribution of ring currents to the full shielding tensor a series of density functional calculations (DFT) were carried out. A shielding tensor in a model compound was calculated in two distinct ways. For the first series, DFT shielding calculations of the model compound were carried out in the presence of a benzene ring. For the second series a ring current contribution to the shielding tensor was calculated via the new expressions, and this was added to the result of a DFT shielding calculation which used in place of benzene the nonaromatic analogue 1,3 cyclohexadiene. The two series of results proved to be in excellent agreement. The pair of analytical expressions are used to calculate ring current contributions to the CSA (Deltasigma) of 1H(N) backbone amide resonances in a structure of the second type 2 module from the protein fibronectin. Significant CSA variations are predicted in particular for the 1H(N) of G42 which is most likely involved in a N-H...tpi aromatic hydrogen bond.     

Effects of HNO3 Concentration on the Electrochemical Behaviour of Lead

 The voltammogram of lead in nitric acid shows two well-defined anodic waves during the positive potential sweep. Upon reverse scanning, a wide current plateau followed by a cathodic peak associated with a shoulder at extreme negative potentials is observed. The overall behaviour was found to be quite complicated, and no simple relation between various variables like peak currents, peak potentials, and electrolyte concentrations could be found. The implications of these results with respect to the mechanisms of the electrode reactions are discussed.     

Redox reaction characteristics of ferritin-immobilized onto poly(l-lysine)-modified indium oxide electrodes

Ferritin-immobilized poly(l-lysine)-modified electrodes showed well-defined redox waves representing ferritin. Cathodic and anodic peak currents obtained from cyclic voltammograms were proportional to potential sweep rates. From charge flow values during oxidation or reduction reactions calculated by peak areas in cyclic voltammograms, and the surface coverage of ferritin, reacted iron atoms per ferritin molecule were calculated. Obtained numbers of reacted iron atoms were significantly smaller than expected values from iron atoms at ferrihydrite core surfaces of ferritin, which would be caused by the rate-determining ion flow through ion channels of ferritin to compensate for charges in the ferritin cavity. Anodic and cathodic peak potentials in cyclic voltammograms were significantly dependent on cationic species in the solution, though voltammetric shapes and peak currents were independent of cations. From the obtained results that structural changes in ferritin were not detected by fluorescent spectra, it is thought that the cationic dependence on ferritin redox peak potentials is caused by ferritin cores.     

6-取代嘌呤的电化学行为及与DNA的相互作用

应用循环伏安法和微分脉冲伏安法研究了6-糠氨基嘌呤(6-KT)和6-巯基嘌呤(6-MP)在汞电极上的电化学行为及与小牛胸腺DNA的相互作用.结果发现,6-KT和6-MP的循环伏安曲线均显示两对分别表征为扩散控制和吸附控制的氧化还原波.扩散控制波的氧化峰电流随6-取代嘌呤浓度在0.1~50.0μmol.L-1范围内呈现良好的线性关系.依据预吸附时间和溶液pH值对吸附控制波的还原峰电位和峰电流的影响,讨论了6-KT和6-MP在汞电极上的吸附机理.作者认为,6-KT乃通过部分插入作用与DNA结合,而6-MP与DNA间的相互作用为静电模式.     

Combustion waves in a model with chain branching reaction

In this paper the steady planar travelling waves in the adiabatic model with two-step chain branching reaction mechanism are investigated numerically. The properties of these solutions are demonstrated to have similarities with the properties of non-adiabatic combustion waves that is, there is a residual amount of fuel left behind the travelling waves and the solutions can exhibit extinction. It is also shown that the model possesses a new type multiple travelling wave solutions (which we call wave trains) with complex structure of the profiles and varying speeds     

Wave formation by heating in thin metal film on an elastomer

Wave formation by heating rather than the usual cooling in a thin metal film on an elastomer is presented. A simple model is used to relate the wavelength of the waves thus formed to the heating temperature. An indirect method of estimating Young's modulus at elevated temperatures emerges from the analysis. The waves formed by heating can be made to appear or not to appear by the selection of the temperature to which the sample is heated. A relationship is given for the critical temperature that determines the appearance or nonappearance of the waves. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1122–1128, 2001     

Electrochemical behaviour and analytical detection of ammonium ions in alkali nitrate melts

The voltammetric behaviour of ammonium ions was investigated in the (Na, K)NO₃ equimolar melt at 518 K. The voltammograms recorded at platinum, gold and vitreous carbon rotating-disc electrodes under one atmosphere of anhydrous nitrogen are characterized by three consecutive cathodic waves. The rapid disappearance of ammonium ions from the solution can be ascribed mainly to the evaporation of the salt, which is a more rapid process than thermal decomposition under the given experimental conditions. In order to be able to neglect the effect of evaporation and decomposition, the voltammograms were recorded within a few minutes from the addition of NH₄NO₃ to the melt. The experimental ratios between the limiting currents of the three waves recorded at a vitreous carbon rotating-disc electrode, the most suitable for analytical purposes, were found to have a constant value within the explored ammonium concentration range, i.e 8×10^?5 mol kg^?1<[NH₄⁺]<5.0×10^?3 mol kg^?1. A simple mechanistic model is proposed which permits a reasonable interpretation of the experimental results and, in particular, explains the origin of the three waves and their limiting current ratios. The diffusion coefficient of ammonium ions was found to be D=(4.0±0.4) 10^?6 cm² s^?1 at 518 K.