Direct synthesis of pseudo-random ternary perturbation signals with harmonic multiples of two and three suppressed

This paper proposes an analytical method to directly synthesise pseudo-random ternary perturbation signals for the identification of frequency response functions, through the multiplication of two components signals which satisfy a prescribed set of properties. The ternary signals generated have harmonic multiples of two and three suppressed; this specification is useful for reducing the effects of nonlinear distortion on the linear estimate. The signals have uniform magnitude in all, except two, of the nonzero harmonics. The method is significant in overcoming the existing problem of sparsity in the available periods when analytical methods are used, as well as the relatively long computational time required in approaches based on exhaustive search or computer optimisation. The proposed technique presents a breakthrough as it eliminates the sequence-to-signal conversion stage required in the existing conventional methods. A direct consequence is the increased signal power within amplitude constraints, which now equals the theoretical limit for the specification considered. If it is necessary to further increase the number of available periods, the mathematical derivation can be extended to a class of suboptimal direct synthesis signals; however, these possess reduced signal power compared with direct synthesis signals.     

SOLUBILITY AND TIE-LINE DATA FOR WATER + FORMIC ACID + METHYL ISOBUTYL KETONE TERNARY SYSTEM AT DIFFERENT TEMPERATURES

The solubility and tie-line data of the ternary system comprising water, formic acid, and methyl isobutyl ketone were experimentally determined at the temperatures 288.15, 298.15, and 308.15 K, and atmospheric pressure 101.3 kPa. The plait points were also determined using Treybal's method. The results indicate that formic acid distributes preferentially in MIBK compared to water. Experimental tie-line data were regressed with the NRTL model to obtain binary interaction parameters. It is found that the NRTL model correlates the present system satisfactorily with average root-mean-square deviation of 0.34%.     

金属硼化物的合成与应用

论述了几种重要的金属硼化物合成工艺在高新技术及在其他领域的应用,展示了金属硼化物在国民经济各领域及其相关行业中的应用前景.     

三元合金稳态平面前沿凝固的溶质再分配

本文对稳态平面前沿凝固的溶质再分配进行了理论分析。分析表明,合金元素间的相互作用将影响溶质再分配,但这种作用小到可以忽略时,三元台金的溶质再分配类似于二元合金。合金元素间的这种相互作用程度可由(Coi/ki)来评定。当(Com/km)>(Con/kn)时,m 组元强烈影响n组元的再分配,使其分布曲线变得平坦,即阻碍其扩散。而 n 组元对 m 组元几乎没什么影响。当(Com/km)≈(Con/kn)时,二者互相影响。作者认为(Coi/ki)判据可用于多元合金凝固过程。     

Electrodeposition behavior of zinc–nickel–iron alloys from sulfate bath

The present work is directed at collecting the properties of Zn–Ni and Zn–Fe alloys in one alloy via the electrodeposition of Zn–Ni–Fe ternary alloy. Electrodeposition of ternary Zn–Ni–Fe alloy was investigated and compared with the characteristics of Zn–Ni electrodeposits. The electrodeposition was performed from a sulfate bath onto a steel substrate. Structural analysis by X-ray diffraction (XRD) method revealed that the Zn–Ni–Fe alloys consisted of a mixture of zinc, and (γ-Ni₂Zn₁₁) and (Fe₃Ni₂) phases. The study was carried out using electrochemical methods such as cyclic voltammetry and galvanostatic for electrodeposition, while anodic linear polarization resistance and anodic linear sweeping voltammetry techniques were used for the corrosion study. Surface morphology and chemical composition of the deposits were also examined by using scanning electron microscopy and atomic absorption spectroscopy, respectively. It was found that the obtained Zn–Ni–Fe alloy exhibited more preferred surface appearance and better corrosion resistance without adding any organic brighteners to the plating bath in comparison to Zn–Ni alloy that electrodeposited at similar conditions. Results obtained revealed that the increase in corrosion resistance of ternary deposits is not only attributed to the formation of (γ-Ni₂Zn₁₁) phase, but also to iron codeposition and formation of (Fe₃Ni₂) phase.     

Electrical Switching in TlSbSe2 Chalcogenide Semiconductors

Electrical measurements were performed on TlSbSe₂ ternary crystals in the temperature range 293–413 K. The obtained I–V characteristics consist of two regions: an Ohmic region at low current densities, and nonlinear regions having negative differential resistance (NDR) at moderate and higher current densities. The nonlinear behavior of the I–V curves was studied at different ambient temperatures. The sample temperature and the threshold voltage of the NDR region were also examined as a function of the ambient temperature. We detected that the investigated samples exhibit threshold-type switching and propose that the switching mechanism has an electronic origin.     

Electrodeposition of Co-Ni and Co-Ni-Cu systems in sulphate-citrate medium

Electrodeposition of Co-Ni and Co-Ni-Cu alloys was performed in a sulphate-citrate medium. Experimental electrodeposition parameters (pH, cobalt(II), nickel(II) and citrate concentrations) were varied in order to analyse their influence on the deposition. Anomalous Co-Ni codeposition occured in the citrate medium. High [Ni(II)]/[Co(II)] ratios (above 5) were suitable for the preparation of homogeneous magnetic Co-rich Co-Ni deposits of hexagonal close-packed (hcp) structure or face centred cubic (fcc) structure as a function of the deposition potential.The presence of very low copper(II) concentrations (<10⁻² mol dm⁻³) in the nickel-cobalt bath makes it possible to incorporate copper in the deposits in amounts ranging from 5 to 60% Cu, although uniform deposits are obtained only for low copper percentages. These ternary deposits are solid solutions with fcc structure and magnetic behaviour both dependent on the deposition potential.     

Synthesis and compressive behavior of Cr2GeC up to 48 GPa

M_n+1AX_n compounds have gathered huge momentum because of its exciting properties. In this paper we report the synthesis of ternary layered ceramic Cr₂GeC, a 211 M_n+1AX_n compound by hot-pressing. Scanning electron microscopy and X-ray diffraction have been employed to characterize the new synthesized phase. High-pressure compressibility of Cr₂GeC were measured using diamond anvil cell and synchrotron radiation at room temperature up to 48 GPa. No phase transformation was observed in the experimental pressure range. The bulk modulus of Cr₂GeC calculated using the Birch–Murnaghan equation of state is 169 ± 3 GPa, with K′ = 3.05 ± 0.15.     

Theoretical phase diagram calculation and membrane morphology evaluation for water/solvent/polyethersulfone systems

Theoretical ternary phase diagrams with very good agreement with experimental cloud point data were constructed for water/N,N-dimethylacetamide (DMAc)/polyethersulfone (PES) and water/N-methyl-2-pyrrolidone (NMP)/polyethersulfone systems. Theoretical phase diagrams were determined based on the extended Flory-Huggins theory of polymer solutions. To construct the theoretical phase diagrams, all binary interaction parameters were determined accurately and thoroughly revisited. Also, the structures of membranes prepared of these systems by phase separation process were investigated. The morphological studies showed that in spite of better miscibility between water and DMAc compared to water and NMP, channel-like structures were observed in membranes prepared of water/NMP/PES systems but tear-like structures with more spongy areas were observed in membranes prepared of water/DMAc/PES system. According to the constructed theoretical ternary phase diagrams of these systems, these unexpected observations were attributed to the higher concentration of polymer in the polymer-rich phase of water/DMAc/PES system, which causes an early vitrification in this system which suppresses the growth of macrovoids.