Acoustic and thermodynamic properties of the binary liquid system <Emphasis Type="Italic">n</Emphasis>-dodecane+<Emphasis Type="Italic">n</Emphasis>-hexadecane

By the method of direct measurement of the pulse-passage time, the velocity of sound in a binary liquid mixture n-dodecane+n-hexadecane has been investigated in the temperature range 298–433 K and in the pressure range 0.1–100.1 MPa. The maximum measurement error is 0.1%. Experimental data on the velocity of sound for the investigated mixture have been obtained for the first time. On the basis of the data on the velocity of sound, we have determined the density, the isobaric expansion coefficient, the isobaric and isochoric heat capacities, and the isothermal compressibility coefficient of a mixture of three compositions in the 298–433 K temperature range and in the 0.1–100.1 MPa range of pressures. The coefficients of the Tate equations in the above range of parameters have been calculated. A table of thermodynamic properties of the mixture is presented.     

Liquid-liquid phase transition in aqueous solutions of <Emphasis Type="Italic">n</Emphasis>-hydrocarbons and amphiphiles

Phase transitions in ensembles of water clusters in aqueous solutions of C11–C28 n-hydrocarbons and C2–C12 amphiphiles have been studied as dependent on the concentration and size of dissolved molecules. A critical size (approximately corresponding to the volume of undecane molecule) for water clusters is determined, which triggers the phase transition that leads to the formation of bistable amphiphile micelles.     

Electrical impedance of ethylene-carbon monoxide/propylene-carbon monoxide (<Emphasis Type="Italic">EPEC</Emphasis>-<Emphasis Type="Italic">69</Emphasis>) thermoplastic polyketone

Electrical impedance technique was employed to investigate the electrical properties of ethylene-carbon monoxide/propylene-carbon monoxide terpolymer (EPEC-69). The measurements were performed in the frequency range 0.1–10⁵ Hz and in the temperature range 30–110 °C. The results reveal that the dielectric constant, loss factor, modulus, and ac conductivity are dependent of frequency and temperature. A Debye relaxation peak was detected in the plot of Z″ versus frequency where the activation energy was determined and found to be 1.26 eV. When the surface phenomenon effects were separated using the imaginary part of the complex admittance a second dielectric dispersion was observed in the low frequency region. Two models were proposed from the impedance measurements depending on temperature range.     

Structural and thermoelectric properties of Zr<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Er<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>NiSn solid solutions

We have studied the electronic and crystal structures and temperature-dependent resistivity and thermopower of Zr_{1 − x} Er _x NiSn (x = 0–0.20) substitutional semiconductor solid solutions (so-called half-Heusler alloys) in the temperature range 80–380 K. Heavily erbium doped semiconductors with the MgAgAs structure are described in terms of an amorphous semiconductor model. The erbium atoms in Zr_{1 − x} Er _x NiSn are shown to act as acceptors. Density of states calculation results for the Zr_{1 − x} Er _x NiSn alloys are consistent with experimental data.     

Optical band gap in the system ZnO<Subscript>1 – <Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>. An experimental and quantum chemical study

The synthesis of single crystalline and polycrystalline material is reported in the system ZnO_{1 – x} S _x . Substitution of oxygen by sulphur yields hexagonal wurtzite-type mixed crystals in the range 0 ≤ x ≤ 0.05. The cubic zincblende structure is observed for oxygen incorporation into ZnS for 0.96 ≤ x ≤ 1. At intermediate compositions, the system is two-phase. For both types of anion substitution, the band gap energies, as determined from optical transmission and remission experiments, are found to decrease from the pure end members. Quantum chemical calculations at density functional level identify local structural changes as the main factor responsible for the reduction of band gap energies.     

Preparation and Mechanical Properties of Carbon Fiber Reinforced (BC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>–SiC)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> Multilayered Matrix Composites

A boron doped carbon materials (BC _x ) was prepared by chemical vapor deposition and a 3D (BC _x –SiC) _n multilayered matrix composite reinforced by carbon fiber, C/(BC _x –SiC) _n , was prepared by chemical vapor infiltration (CVI). XPS and SEM results showed that the BC _x matrix had a boron content of 15 at.% and exhibited a very finely laminated structure. XRD analysis showed the BC _x matrix was mainly carbon with B₄C crystals in it. SEM and EDS results showed that the BC _x layers and the SiC layers were deposited within the interspaces of fiber bundles, alternately arranged and paralleled to each other as designed. The fracture energy of the composite was about 16.8 KJ m⁻². Flexural strength–displacement curve showed a remarkable metal-like yielding stage. Multiple fracture microstructures were induced by the multilayered matrix, such as delaminations of the multilayered matrix, deflections and propagations of cracks spread in the multilayered matrix layer by layer and long pullout of fiber bundles together with fiber clusters with multi-step pull-out structures. It was suggested that these special fracture behaviors absorbed a great deal of energy during the stress increasing and released the stress concentration, in this way, the toughness of the materials was improved.     

Optical,structural and electrical investigations on PbTe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys

The fabrication of devices with lead salts and their alloys with detecting and lasing capabilities has been an important technological development. The high quality polycrystalline thin films of PbTe_1−x S _x with variable composition (0 ≤ x ≤ 1) have been deposited onto ultra clean glass substrates by vacuum evaporation technique. Optical, structural and electrical properties of PbTe_1−x S _x thin films have been examined. Absorption coefficient and band gap of the films were determined by absorbance measurements in wavelength range 2,500–5,000 nm using FTIR spectrophotometer. Sample nature, crystal structure and lattice parameter of the films were determined from X-ray diffraction patterns. DC conductivity and activation energy of the films were measured in temperature range 300–380 K through I–V measurements.     

Electrical characterization of low temperature deposited oxide films on ZnO/<Emphasis Type="Italic">n</Emphasis>-Si substrate

Thin films of silicon dioxide are deposited on ZnO/n-Si substrate at a low temperature using tetra-ethylorthosilicate (TEOS). The ZnO/n-Si films have been characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The border trap density (Q_bt) and fixed oxide charge density (Q_f/q) of the SiO₂/ZnO/n-Si films are found to be 3.9 × 10¹⁰ cm⁻² and 1.048 × 10¹¹ cm⁻², respectively. The trapping characteristics and stress induced leakage current (SILC) have also been studied under Fowler-Nordheim (F-N) constant current stressing.     

Studies on a.c. properties of Ca<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> perovskites

A.c. measurements were preformed on bulk samples of Ca_1−x Sr _x TiO₃ (CST) perovskites with x = 0, 0.1 and 0.5 as a function of temperature range 300–450 K and frequency range 10³–10⁵ Hz . The experimental results indicate that the a.c. conductivity σ_a.c.(ω), dielectric constant ε′ and dielectric loss ε′′ depend on the temperature and frequency. The a.c. conductivity as a function of frequency is well described by a power law Aω ^S with s the frequency exponent. The obtained values of s > 1 decrease with increasing temperature. The present results are compared to the principal theories that describe the universal dielectric response (UDR) behavior.     

Growth and properties of nanostructured layers based on Pb<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> = 0−0.20) solid solutions

We have produced nanostructured layers based on supersaturated Pb_1−x Cd _x Se (x = 0−0.20) solid solutions with an efficient room-temperature photoluminescence in the range 3–5 μm and studied the effect of growth conditions on their chemical and phase compositions and properties. Their photoluminescence spectra have been measured, and the main radiative recombination mechanisms in activated solid-solution layers have been identified. The role of iodine in the formation of the emitting nanostructures has been discussed.     

Pre-exponential factor in<Emphasis Type="Italic">a</Emphasis>-Se<Subscript>75</Subscript>In<Subscript>25-<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

Temperature dependence of d.c. conductivity is studied ina- Se₇₅In_25-x Pb _x thin films wherex is varied from 0–10. From these measurements, the values of the pre-exponential factor (σ₀) and activation energy (ΔE) are calculated for each glassy alloy. An approximate linear dependence of ln σ₀ on AE is observed in this glassy system with good agreement between the expected and calculated σ₀ values using Meyer-Neldel rule. Linear dependence of ln σ₀ on ΔE in case of amorphous materials indicates that the conduction band tails a finite energy distance towards the valence band and Fermi level is controlled by fixed dominant hole levels deeper in the gap.     

The Viscosity and Density of <Emphasis Type="Italic">n</Emphasis>-Dodecane and <Emphasis Type="Italic">n</Emphasis>-Octadecane at Pressures up to 200 MPa and Temperatures up to 473 K

A vibrating-wire instrument for simultaneous measurement of the density and viscosity of liquids under conditions of high pressure is described. The instrument is capable of operation at temperatures between 298.15 and 473.15 K at pressures up to 200 MPa. Calibration was performed by means of measurements in vacuum, air, and toluene at 298.15 K. For n-dodecane measurements were made along eight isotherms between 298.15 and 473.15 K at pressures up to 200 MPa while for n-octadecane measurements were measured along seven isotherms between 323.15 and 473.15 K at pressures up to 90 MPa. The estimated uncertainty of the results is 2% in viscosity and 0.2% in density. Comparisons with literature data are presented.     

Asymmetric current transfer in isotype <Emphasis Type="Italic">n</Emphasis>-In<Subscript>2</Subscript>Se<Subscript>3</Subscript>/<Emphasis Type="Italic">n</Emphasis>-InSe heterocontacts

We have studied the mechanisms of current transfer and the capacitance-voltage characteristics of a radiation-resistant isotype n-In₂Se₃/n-InSe heterocontact in which the region depleted of major charge carriers is localized predominantly in a relatively low-ohmic semiconductor—the α-type In₂Se₃ with a large density of defects. The spectrum of the relative quantum efficiency of photoconversion in this structure depends on the thickness of the In₂Se₃ layer and on the geometry of illumination of the heterocontact.     

Photophysical characteristics of microlayer photodiode <Emphasis Type="Italic">p</Emphasis>AlGaInAs(Zn)-<Emphasis Type="Italic">n</Emphasis>GaAs-Au structures

The photoelectric characteristics of photodiode pAlGaInAs(Zn)-nGaAs-Au structures have been investigated. It has been established experimentally that an internal photoelectric amplification arises in these structures when the nGaAs-Au potential barrier is connected in opposition to the (p(Al_0.08Ga_0.82)_0.9In_0.1As-nGaAs) heterojunction. The p(Al_0.08Ga_0.82)_0.9In_0.1As-nGaAs-Au structure operates as an injection photodiode when the p-n junction operates in the forward-bias regime and as a photodiode when this junction operates in the reversebias regime. The influence of the depletion regions of the base zone containing deep impurity centers on the photosensitivity and the spectral range of the indicated structures has been investigated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 1, pp. 166–172, January–February, 2007.     

Thermoelectric power factor of Ti<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>NiSn alloys

Ti_{1 − x} V _x NiSn (x = 0–0.10) substitutional solid solutions have been prepared by doping the intermetallic semiconductor n-TiNiSn (half-Heusler phase) with vanadium, a donor impurity, and their resistivity and thermopower have been measured at temperatures from 80 to 380 K. The results demonstrate that, when doping of TiNiSn causes no type inversion, the thermoelectric power factor of the solid solution markedly exceeds that of the undoped ternary compound.     

Microstructure and magnetic properties of Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized by combustion reaction

An investigation was made of samples having a chemical formula of Ni_1−x Zn _x Fe₂O₄, where x = 0.3, 0.5 and 0.7. The samples were prepared by the reaction combustion synthesis method and sintered at 1,200 °C/2 h in a static air atmosphere. The influence of the Zn concentration on the relative density, microstructure and magnetic properties of the samples was studied. X-ray diffraction, scanning electron microscopy and magnetic hysteresis loop tracer were used to analyze the compositions. The samples were found to have a spinel cubic structure, sintered density of 92.9%–98.8% of the corresponding X-ray density, homogeneous microstructure with grain size ranging from 1.37 to 3.36 μm, maximum flux density of 0.16–0.35 T, field coercivity ranging from 17 to 168 A/m, and loss hysteresis of 1.5–105 W/kg. Increased grain growth, with fine pores inside the grains, was found to occur as the Zn concentration increased. The overall findings are discussed here in light of the existing understanding of these systems.     

Molecular dynamics simulation of the forces between colloidal nanoparticles in Lennard–Jones and <Emphasis Type="Italic">n</Emphasis>-decane solvent

Molecular-dynamics is utilized to simulate solvation forces between two nanoparticles immersed in two different solvents: Lennard–Jones spheres and and n-decane. Three different sizes and shapes of solvophilic nanoparticles are investigated. Nanoparticles in the Lennard–Jones liquid exhibit solvation forces that oscillate between attraction and repulsion as the nanoparticle separation increases. The magnitude of these solvation forces increases with particle size and depends on particle shape, consistent with the Derjaguin approximation. When n-decane is the solvent, the solvation forces are negligible for small nanoparticles, with sizes comparable to the end-to-end distance of all-trans decane. The solvation forces oscillate between attraction and repulsion for sufficiently large nanoparticles in decane—however the Derjaguin approximation does not appear to be effective at describing the dependence of nanoparticles forces on nanoparticle size and shape when decane is the solvent. For both the Lennard–Jones and n-decane solvents, it is apparent that the force profiles are influenced by the surface roughness of the nanoparticles. These factors should be taken into account in efforts to engineer colloidal suspensions.     

Magnetic ordering in Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Se crystals grown by solid-state recrystallization

Cr _x Hg_{1 − x} crystals grown by solid-state recrystallization have been characterized by electron paramagnetic resonance spectroscopy, transport measurements, and X-ray microanalysis. The results demonstrate that the crystals contain rectangular HgCr₂Se₄ inclusions elongated along one of their axes and irregularly shaped Cr _x Hg_{1 − x} and CrHg inclusions. In the range 77–400 K, the electrical properties of samples cut from different parts of the crystals are typical of semiconductors with a strongly degenerate electron gas.     

Detecting quasi-periodic {11<Emphasis Type="Italic">n</Emphasis>} (<Emphasis Type="Italic">n</Emphasis> = 7–11) faces in samples with Ge/Si quantum dots by grazing X-ray reflectometry

High-resolution grazing X-ray reflectometry is used to obtain experimental and theoretical data on the intensity of specular and diffuse reflection from self-organized structures grown by molecular beam epitaxy with single-layer (non-overgrown) and multilayer (overgrown) Ge/Si quantum dots (QDs). Using the positions of diffuse scattering peaks in the direct space, the slopes of quasi-periodic faces have been determined to within ±0.1° by a method employed previously for the investigation of In(Ga)As/GaAs quantum dots. Finding the quasi-periodic {11n} (n = 7−11) faces (typical of the growth of ordered QDs) in the samples with disordered Ge/Si quantum dots is evidence of the generality of mechanisms of QD formation in different systems.     

Application of a sensitivity equation method to the <Emphasis Type="Italic">k</Emphasis>–<Emphasis Type="Italic">ε</Emphasis> model of turbulence

In this paper, we present some examples of sensitivity analysis for flows modeled by the standard k–ε model of turbulence with wall functions. The flow and continuous sensitivity equations are solved using an adaptive finite element method. Our examples emphasize a number of applications of sensitivity analysis: identification of the most significant parameters, analysis of the flow model, assessing the influence of closure coefficients, calculation of nearby flows, and uncertainty analysis. The sensitivity parameters considered are closure coefficients of the turbulence model and constants appearing in the wall functions.