Experimental and theoretical investigations on the compressibility of nanocrystalline nickel

We investigated nanocrystalline nickel experimentally (x-ray diffraction) and theoretically (cluster ab initio calculations). No phase transition was observed in nano-nickel. The volume, isothermal bulk modulus and its pressure derivative derived experimentally and theoretically are 43.56 (0.13) ų, 228(15) GPa, 4.02(0.51) and 44.00 ų, 217 GPa and 3.20, respectively. We found no appreciable change in the value of bulk modulus for nano-nickel as compared to the bulk-nickel.An erratum to this article can be found at     

Experimental and theoretical investigations of birefringent holey fibers with a triple defect

We have manufactured and characterized a birefringent holey fiber of a new construction. The birefringence in this fiber is induced by the highly elliptical shape of the core, which consists of a triple defect in a hexagonal structure. Using a hybrid edge-nodal finite-element method, we calculated the spectral dependence of phase and group modal birefringence for spatial modes E11 and E21 in idealized and in real fiber, whose geometry we determined by using a scanning-electron microscope. Results of our calculations show that technological imperfections significantly affect the fiber's birefringence. Normalized cutoff wavelengths for higher-order modes relative to the filling factor were also determined for the idealized structure. We observed a significant disagreement between theoretical and experimental values of cutoff wavelengths, which was attributed to high confinement losses near the cutoff condition. We also measured the spectral dependence of the phase and the group modal birefringence for spatial modes E11 and E21. The measured parameters showed good agreement with the results of modeling.     

Experimental and theoretical investigations of Mg2+-doped single-crystal fibres of lithium niobate

Pure and Mg-doped single-crystal LiNbO₃ fibres (molar concentrations up to 5 mol.% MgO) have been investigated via X-ray diffraction and micro-Raman scattering experiments in order to compare their structural (cell volume) and dynamical (modes) properties with those of bulk material. Novel first-principles calculations have been performed to ascertain definitely the frequency assignments of TO and LO zone-centre phonons involved in Raman spectra. Three main differences between fibres and bulk are (i) the fibre is not spatially homogeneous at low doping rates (macroscopic homogeneity is achieved when the doping rate reaches 5 mol.%); (ii) the doping dependence of Raman frequencies and linewidths is not the same for certain modes; (iii) the cell volume in the fibres decreases with increasing doping rate in the fibre in contrast with previously reported data on the bulk. Experimental results indicate the presence of two successive regimes when the Mg doping rate is increased up to 5%. This behaviour, already noticed though apparently to a lesser extent in the bulk, is discussed in the framework of a consistent double-vacancy model that encompasses previously proposed models as particular cases. This confirms that Mg²⁺ ions replace antisite Nb ions in a first stage (below 2% in the fibre) while, in a second stage (from 2% to 5% doping rates), Mg²⁺ ions are accommodated in remaining Li vacancies until these are completely filled. The reordering that ensues is undoubtedly linked with the recovered homogeneity of the fibre, the disappearance of photo-refractive effects and the considerable improvement of the resistance to optical damage observed for the 5 mol.% Mg doped crystal.     

Experimental and theoretical investigations on stiffened and unstiffened composite panels under uniform transverse loading

An experimental investigation on fibre-reinforced stiffened and unstiffened panels under transverse uniform pressure has been carried out. The deflections and strains measured inside the laminate are compared with a finite element analysis. The effect of one or two stiffeners within the panel is small since the stiffener fail at small loads. In contrary to this, the effect of a different lay-up is big, because the angle-ply panels [+45°/−45°]₂ carried higher loads than the cross-ply panels [0°/90°]₂. The failure of the panels near the centre of the long edge at the clamping is correctly predicted by the FEA. In addition, calculated and predicted stresses are close to each other.     

随机起伏界面声散射的实验与理论研究

进行了二维粗糙海面声波散射特性的水池实验,测量了不同入射角、散射角以及方位角条件下所对应的散射强度。实验通过不同位置风扇对水面的吹拂获得粗糙水面,分别对水平面上互相垂直的两个方向上的水面波高变化进行了测量,利用周期图法估计出这两个方向上的空间功率谱,验证了实验中的粗糙水面是各向同性的。利用改进的空间域处理技术去除了总声波信号中的直达波和其他固定位置散射体的散射信号,获得了粗糙水面的声波散射信号。利用小斜率近似方法计算了二维粗糙海面的声散射特性。实验与模拟计算结果比较,证实了计算二维粗糙海面声波散射特性的小斜率近似方法的有效性与准确性,相互印证了实验与理论。     

Experimental and theoretical investigations on the adsorption of 2'-deoxyguanosine oxidation products at oxidized boron-doped diamond electrodes

Electrochemical oxidation of 2'-deoxyguanosine has been performed on boron-doped diamond (BDD) electrodes, resulting in a strong adsorption of the formed oxidized products onto the BDD surface. The adsorption behavior has been investigated by studying the electrochemical behavior of a redox probe ([IrCl6]3-) using cyclic voltammetry. The most probable situations are the formation of (A) an insulating adsorbed film resulting in a partially blocked electrode behavior, (B) a porous film, or (C) an overall conductive film. Different parameters such as the standard rate constant, the charge-transfer coefficient, the electrode/adsorbed products/solution interface resistance, and the formal potential of the redox couple were determined. Through comparison of theoretical current-potential curves obtained by analytical calculations with experimental cyclic voltammograms, we found that the oxidized products of 2'-deoxyguanosine form a continuous conductive film on BDD.     

Effect of pH on surface energy of glass and Teflon and theoretical prediction of Staphylococcus aureus adhesion

The surface energy of glass and Teflon at various pH values was examined. Contact angle was used to determine physico-chemical substratum properties. The surface energy of both substratums including, hydrophobicity, and electron donor/electron acceptor (Lewis acid–base properties) were found to depend on pH of contact solution. The maximum of hydrophobicity (higher negative value of ΔG_iwi) was obtained at pH 11 and pH 6.5 for glass and Teflon respectively. The electron donor property was higher at pH 5 and pH 3 for glass and Teflon respectively. Moreover, prediction of Staphylococcus aureus adhesion on both substratums was estimated by calculating the total interaction free energy (ΔG^Tot). Based on the value of ΔG^Tot, S. aureus should adhere to glass at pH 2, pH 3 and pH 11 with the maximal adhesion obtained at pH 3 and pH 11. For Teflon, regardless of pH values, S. aureus should be able to attach on this substratum with the high adhesion level at pH 5. The relation between surface energy of substratum and the total interaction free energy was also examined. Based on this relation and the value of the components of total interaction free energy, we show that adhesion to glass could be governed by both short range forces (Lewis acid–bases forces) and by long range forces (van der Waals forces) and the adhesion to Teflon could be mediated only by the short range forces.     

Experimental and theoretical studies of the influence of surface conditions on radiative properties of opaque materials

Radiative properties of opaque materials strongly depend on their surface condition. The fabrication of superficial cavities of various forms and dimensions modifies the directional spectral emissivities or absorptivities. They are usually increased compared to those of optically smooth material; the gain depends on the material, the type of cavities, as well as the wavelength and the direction of the emitted or incident radiation. When grooves of dimensions larger than are fabricated in a sample, the models, taking into account the successive reflections on their inner sides, give a good agreement with experimental data. But a similar theory does not explain the substantial increase of the infrared emissivity of ballblasted samples.     

Experimental and theoretical investigation of Taylor-Görtler instability in the boundary layer on a concave surface

Results of experimental and theoretical investigations of centrifugal instability in the turbulent boundary layer on a concave surface are presented. Linear and nonlinear regularities in the development of this type of instability are revealed. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 2, pp. 279–283, March–April, 1997.     

Experimental and theoretical study of skylight polarization transmitted through Snell's window of a flat water surface

The celestial polarization pattern may be scrambled by refraction at the air-water interface. This polarization pattern was examined in shallow waters with a submersible polarimeter, and it was calculated by using land measurements ('semiempirical predictions') and models of the skylight polarization. Semiempirically predicted and measured e-vector orientations were significantly similar. Conversely, predicted percent polarization was correlated but lower than measurements. Percent polarization depended on wavelength, where at high sun altitudes maximal percent polarization generally appeared in the UV and red spectral regions. The wavelength dependency of polarization may lead to differential spectral sensitivity in polarization-sensitive animals according to time and type of activity.     

Experimental and theoretical investigations on the inhibition of mild steel corrosion in the ground water medium using newly synthesised bipodal and tripodal imidazole derivatives

Two new imidazole derivatives, namely 1,4-bis(N-imidazolylmethyl)-2-5-dimethoxybenzene (BIDM) and 1,3,5-tris(N-imidazolylmethyl)-2,4,6-trimethoxybenzene (TITM), were synthesised and their effects on the inhibition of mild steel corrosion in ground water medium are reported. The study was carried out using gravimetric and electrochemical techniques in order to determine the corrosion inhibition efficiencies of the bipodal and tripodal structured imidazoles. Further, the quantum chemical calculations using density functional theory (DFT) gave a profound insight into the inhibitory action mechanism of BIDM and TITM and their calculation parameters, such as E_HOMO, E_LUMO and ΔE were in good agreement with the results of the experimental studies. BIDM and TITM exhibited lowest corrosion current densities of circa 7.5 μA cm⁻² and 4.1 μAcm⁻² at the optimum concentrations of 0.67 and 0.49 mM, respectively. All measurements thus confirmed that both BIDM and TITM behaved as good inhibitors for mild steel corrosion in ground water medium.     

Laboratory and theoretical investigations on the deformation and strength behaviors of artificial frozen soil

In order to study the mechanical characteristic of artificial frozen soils, such as strength, and stress-strain relationship, a series of triaxial compression tests of frozen sand has been conducted under confining pressures varying from 0.0 to 14.0 MPa with different water contents at − 6 °C. Frozen sand presents strain softening during shearing process under low confining pressures; but with increasing confining pressure, the strain softening decreases, and even presents strain hardening under high confining pressures. The strength of frozen sand is affected by water content and confining pressure. The strength with low water content always increases with increasing confining pressure; however, for frozen sand with a high water content, the strength experiences an increase followed by a decrease with increasing confining pressure. To describe the strength characteristic of frozen sand, the non-linear Mohr-Coulomb criterion, in which the generalized internal friction angle and cohesion under various confining pressures are obtained from experimental results, has been presented. The result shows that the non-linear Mohr-Coulomb criterion can reflect the decrease of strength of frozen sand under high confining pressures. The stress-strain relationships of frozen sand are represented by hyperbolic functions, which can describe both the strain hardening behavior of frozen sand under high confining pressure and the strain softening behavior under a low confining pressure.     

The relevance of the surface structure and surface chemistry of carbon fibres in their adhesion to high-temperature thermoplastics

The surface structure and morphology of several high strength polyacrylonitrile (PAN) based carbon fibres was studied with the scanning electron microscope (SEM) on the micrometre scale and the scanning tunnelling microscope (STM) down to the atomic scale. In addition, active surface area measurements were made to determine the number of bonding sites/unit area. Prior to the observations, the surfaces of some of the samples were subjected to either the commercial surface treatment or to oxidation in air or ozone in our laboratory. The roughness and number of bonding sites on each fibre surface was determined. These values will be correlated with the mechanical properties of composites made with these fibres and thermoplastic polymers in Part III of this study.     

Experimental and theoretical study of the transient boiling mechanism

The heat-transfer mechanism in the transition boiling region is studied theoretically and experimentally.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 1, pp. 48–57, January, 1986.     

Experimental and theoretical studies of palygorskite clays

We have studied the structure and properties of palygorskite clays. A structure analysis was performed using two different models to reproduce the monoclinic and orthorhombic lattices, using the atomic positions and cell parameters of palygorskite structure suggested by several authors, we simulated structures using Molecular Dynamics and Quantum Mechanics. Modifications on the structure and elemental atom changes were made to obtain more stable configurations. X-ray diffraction patterns and high resolution electron microscopy images from simulated structures were compared with experimental results. It could be observed that orthorhombic model shows a better fitting than monoclinic models. These results might help to understand many of the properties of archaeological pigments, such as, Maya Blue, in which palygorskite clay was the main component.     

Correlation of surface morphology of polyethylene films to ink adhesion and removal

The basic phenomenon of ink adhesion and removal has been studied by looking at the surface of polyethylene films that have been subjected to a ceramic bead impact ink-removal process where printed polyethylene films, zirconium silicate beads, and water were agitated in a laboratory shaker. AFM images show that the polyethylene packaging film surfaces studied have a typical morphology of polyethylene films crystallized under mechanical stress which consists of rows, approximately 1 μm in width, of lamellar-like structures. Upon impact of the ceramic beads on the polyethylene films, the surface is roughened and the surface rows appear to be deformed. FTIR data show that the surface crystallinity of the PE film decreases with the impact ink removal process. A deinking mechanism is proposed where the beads tear the ink film, abrade the surface and deform the polyethylene substrate. Received: 18 September 2000 / Reviewed and accepted: 20 September 2000     

The relevance of the surface structure and surface chemistry of carbon fibres in their adhesion to high temperature thermoplastics

This paper has three principle thrusts: (i) the fabrication of unidirectionally reinforced composites made from carbon fibres subjected to different surface treatments in combination with various (polycarbonate, polyethersulphone and epoxy) matrices, (ii) a study of some of the mechanical properties (that is, the interlaminar-shear strength (ILSS) and the failure behaviour) of these composites; and (iii) determination of the correlations between the adhesion of the matrix polymers as measured by the ILSS and the surface structure as well as the surface chemistry of the various fibres. It will be shown that the surface structure of the fibres has a minor effect, while the surface chemistry appears to have an extraordinarily great influence on the adhesion of the fibres to high-temperature thermoplastics. The data clearly show that, depending on the processing temperature during the fabrication of the composites, chemical bonds can be formed at the fibre-polymer interface. This bond formation is initiated by the decomposition of carboxylic groups and, as a consequence, dangling carbon atoms are free to react with the functional groups of the polymer.     

The relevance of the surface structure and surface chemistry of carbon fibres in their adhesion to high temperature thermoplastics

The paper is concerned with the surface chemistry of several different carbon fibres subjected to various surface treatments. The microstructure and nanostructures of these fibres were investigated in the Part I of this series of papers. For analysis of the surface chemistry of the fibres, X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) were employed; the first method was used for identification and semi-quantitative determination of functional surface groups, while the second method was used for a quantitative determination of these groups. The possible interactions of the various carbon-fibre surfaces due to different surface treatments (and therefore to different functional groups) were analysed by wetting studies using the Wilhelmy technique and aqueous solutions of different pH values as test liquids. By variation of the pH value of the test liquids, the distinct acid-base complexes that formed with the functional groups were identified. The same test liquids were used for characterization of the surface chemistry of the high-temperature thermoplastics (polycarbonate and polyethersulphone) used as matrix materials in the fabrication of the composites in this study. Acid-base interactions at the carbon-fibre surfaces are mainly determined by carboxylic groups of different acidity. The concentration of these groups as determined by desorption of carbon dioxide up to 500 °C is shown to be directly proportional to the measured work of adhesion of each group.