Effects Of Variations In Composition Research Articles

Magnetoresistance and magnetic properties measurements of Cu xZn 1− xFe 2O 4 system

A systematic study of longitudinal and transverse magnetoresistance in Cu x Zn 1− x Fe 2O 4 system with x=0.0, 0.25, 0.50, 0.75, 1.0 has been carried out to find out the optimal highest resistive state for practical applications. The variation in magnetoresistance is of the first-order effect as in semiconductors. The effect of compositional variation on saturation magnetization, remanence and coercivity at room temperature are also reported. It has been observed that the highest resistive state appears at the field value for which the saturation magnetization exists for each concentration.

Effect of compositional variations on characteristics of coarse intermetallic particles in overaged 7000 aluminium alloys

To provide an understanding of how compositional variations affect the characteristics of coarse intermetallic particles in 7000 aluminium alloys, three Al-Zn-Mg-Cu-Zr alloy plates with different zinc, magnesium, and copper contents have been studied by optical microscopy based image analysis, scanning electron microscopy SEM, energy dispersive X-ray spectroscopy EDS, and differential scanning calorimetry DSC. These coarse intermetallic particles are detrimental, especially to the toughness of the alloy. Experimental observations have been interpreted successfully on the basis of the phase diagram and the temperature dependent S phase solvus, derived in turn on the basis of the regular solution model. The temperature dependent S phase solvus indicates that some compositions in the composition windows of 7050 and 7x75 type alloys will give rise to the detrimental S phase, which cannot be dissolved during solution treatment. Also, the T phase has been analysed and conditions for its formation and dissolution are discussed. It is shown that the present results can produce useful information on alloy design and thermomechanical processing via microstructural control.

Syntheses and properties of thermotropic copolyesters of p-hydroxybenzoic acid

Two series of thermotropic copolyesters of p-hydroxybenzoic acid (HBA) were synthesized by direct thermal polycondensation. One comprised aromatic copolyesters from HBA, terephthalic acid, bis(4-hydroxyphenyl) ketone (BHP) and resorcinol. The other comprised semi-aromatic copolyesters from HBA, terephthalic acid, BHP and α,ω-diols with carbon atom number of 4, 6, 8, 10. The properties of the two series were characterized by polarized light microscopy, differential scanning calorimetry and wide angle X-ray diffraction. Most of the resulting copolyesters could form a nematic phase over a wide temperature range above their melting points. The effects of variation in composition and monomer structure on the properties of copolyesters were discussed.

Formation and Properties of Zr-(Ti, Nb)-Cu-Ni-Al Bulk Metallic Glasses

The effect of composition variations and of B or Si addition on the glass forming ability and thermal stability of Zr-M-Cu-Ni-Al (M = Ti, Nb) bulk metallic glass-forming alloys have been investigated. The structural, acoustic, thermal and elastic properties of the bulk metallic glasses (BMGs) are studied by X-ray diffractmetery (XRD), differential scanning calorimetry (DSC) and ultrasonic method. A small amount of boron and silicon addition can significantly affects the GFA and crystallization behaviors and microstructural nature of the glass-forming alloys. The small changes of the density and acoustic velocities in the BMGs relative to its corresponding crystallized state indicate a similar electronic state and similar atomic interactions between the glassy and crystalline states.

Cholesteric Polymer Liquid Crystals and their Optical Properties

Synthesis of a number of cholesteric polymer liquid crystals (PLCs) is reported. Phase behavior and structures of thermotropic cholesteric PLCs are discussed. Optical properties of such materials are reported also, including their textures, effects of composition variation on the helix twisting power and temperature dependence of the helix pitch. Effects of molecular mass variation on the optical properties of PLCs are determined. Prospects of applications of these materials are pointed out.

Effect of compositional variations on electrical properties in phase switching (Pb, La)(Zr, Ti, Sn)O3 thin and thick films

The composition-dependent electrical properties in (Pb,La)(Zr,Ti,Sn)O3 antiferroelectric-ferroelectric phase switching thin and thick films have been systematically studied and compared with bulk ceramics. The films were deposited on Pt-buffered silicon substrates by a sol-gel method. The results show that the dependence of low-field dielectric properties on compositions in the films is similar to that in bulk ceramics but the variation of high field properties (polarization or hysteresis loops) is quite different, which may be attributed to the special mechanical boundary condition of the films. While all the films with compositions in the antiferroelectric tetragonal region in the phase diagram demonstrate the existence of remanent polarization in the hysteresis loops, the films with zero remanent polarization can be obtained in the antiferroelectric orthorhombic region. This is because the films are under high tensile stress due to the thermal mismatch between the film and substrate, which tends to stabilize the ferroelectric phase and causes the retention of ferroelectric phase for the films in the antiferroelectric tetragonal region because of their relatively small free energy difference between the antiferroelectric phase and ferroelectric phase.

Effect of compositional variation and fineness on the densification of MgO–Al 2O 3 compacts

Single stage densification of magnesia—alumina compacts were studied with MgO to Al 2O 3 molar ratios 1:1 (stoichiometric spinel), 2:1 (magnesia rich spinel) and 1:2 (alumina rich spinel). Attritor milling has been adopted to produce variation in fineness. Milling greatly improved the densification. Densification was found to be easier for the magnesia rich composition and difficult for the alumina rich one. X-ray diffraction patterns showed the expected phases in stoichiometric and magnesia rich spinel. Alumina rich composition showed no free corundum phase on sintering at 1650°C and only spinel phase marks the complete solid solution of excess alumina in spinel at this composition. EDAX analysis also supports the event and also reflects that the impurities are mainly present at the grain boundaries.

The terrestrial ring current: Origin, formation, and decay

The terrestrial ring current is an electric current flowing toroidally around the Earth, centered at the equatorial plane and at altitudes of ∼10,000–60,000 km. Changes in this current are responsible for global decreases in the Earth's surface magnetic field, which are known as geomagnetic storms. Intense geomagnetic storms have severe effects on technological systems, such as disturbances or even permanent damage to telecommunication and navigation satellites, telecommunication cables, and power grids. The main carriers of the storm ring current are positive ions, with energies from ∼1 keV to a few hundred keV, which are trapped by the geomagnetic field and undergo an azimuthal drift. The ring current is formed by the injection of ions originating in the solar wind and the terrestrial ionosphere. The injection process involves electric fields, associated with enhanced magnetospheric convection and/or magnetospheric substorms. The quiescent ring current is carried mainly by protons of predominantly solar wind origin, while geospace activity tends to increase the abundance (both absolute and relative) of O+ ions, which are of ionospheric origin. During intense magnetic storms, the O+ abundance increases dramatically, resulting in a rapid intensification of the ring current and an O+ dominance around storm maximum. This compositional change affects, among other processes, the decay of the ring current through the species‐ and energy‐dependent charge exchange and wave‐particle scattering loss. Energetic neutral atoms, products of charge exchange, enable global imaging of the ring current and are the most promising diagnostic tool of ring current evolution. This review will cover the origin of ring current particles, their transport and acceleration, the effects of compositional variations in the ring current, the effects of substorms on ring current growth, and the dynamics of ring current decay with an emphasis on the process of charge exchange and the potential for wave scattering loss.

The effect of compositional disorder on electronic band structure in GaxIn1 − xAsySb1 − yalloys lattice matched to GaSb

A pseudopotential formalism coupled with the virtual crystal approximation are applied to study the effect of compositional disorder upon electronic band structure of cubic GaxIn1−xAsySb1−yquarternary alloys lattice matched to GaSb. The effects of compositional variations are properly included in the calculations. Our theoretical results show that the compositional disorder plays an important role in the determination of the energy band structure of GaxIn1−xAsySb1−y/GaSb and that the bowing parameter is dominated by the group V-anion-based sublattice. Moreover, the absorption at the fundamental optical gaps is found to be direct within a whole range of the x composition.

ELECTRON MOMENTUM DENSITIES IN GaxIn1-xAsySb1-y PROBED BY POSITRONS

Momentum densities of electron–positron pairs in cubic Ga x In 1-x As y Sb 1-y lattice matched to GaSb and InAs are studied for the first time to the best of our knowledge, with the aim of investigating the disorder and substrate effects on these quantities in the materials for interest. The electron wavefunction is calculated using the pseudopotential band model under the virtual crystal approximation with and without incorporating the effects of compositional variations. The calculations of the positron wavefunction is made in an identical manner, employing the point-core approximation for the ionic potential. It is found that while the electron–positron momentum densities in Ga x In 1-x As y Sb 1-y at x=0.50 are sensitive to the compositional disorder, they are not altered by the change of substrate.

Effect of composition variations on electrical and optical properties of La{sub 1{minus}x}(Ca,Sr){sub x}MnO{sub 3} thin films

Thin films of La0.67Ca0.33MnO3+δ(d ≈ 200 nm) grown at 750° C on MgO(100) substrates by pulsed laser deposition were annealed in various oxygen atmospheres. The LaF3, CaF2and Mn overlayers (d ≈ 5-10 nm) have been evaporated onto the films in order to saturate the compound by La, Ca or Mn during subsequent annealing at 900° C in air. Further, the pulsed injection CVD method has been utilized to prepare series of La1−xSrxMnO3films with x = 0÷0.5 on LaAlO3(100). The effect of composition variations on electrical resistivity and magnetoresistance of the films as well as on their optical transmission and reflection spectra in the energy range between 0.2 and 4.0 eV has been investigated.

Effects of composition variations and curing conditions on the gloss of water reducible clear coatings prepared from palm stearin alkyds

Water-based clear stoving coating materials could be prepared by mixing the water-reducible palm stearin alkyds with a commercial methylated melamine formaldehyde in ratios ranging from 1 to 9. TGA analysis could be used to estimate the solid content of each of the coatings, as well as the curing temperature that could be used to prevent thermal degradation. Gloss of the coating after cure is affected by the oil length, alkyd/melamine ratio and curing temperature, for the same curing duration. For each alkyd, monitoring the changes in gloss due to variation of alkyd/melamine ratio and curing temperature could be useful for designing the formulation to give the desired gloss.

Study of magnetic interactions in Co–Zn–Fe–O system

Cobalt–zinc ferrites with compositions Co 0.5Zn 0.34Fe 2O 4, Co 0.37Zn 0.51Fe 2O 4, Co 0.3Zn 0.6Fe 2O 4, Co 0.2Zn 0.74Fe 2O 4, were prepared by ceramic techniques. The effects of compositional variation on porosity, coercivity, remanence, saturation magnetisation, magnetic moments, and Y–K angles are reported. The coercivity exhibits almost similar behaviour to that of porosity, whereas, the remanence decreases with increasing Zn-content. The saturation magnetisation and magnetic moments exhibit decreasing behaviour with increasing Zn-content, which may be due to the increase of the B–B interaction followed by the decrease in A–B interaction. The Y–K angles increase with increasing Zn-concentration, which is attributed to the presence of triangular-type spin arrangement on B sites.

Determination of magnetic properties and Y–K angles in Cu–Zn–Fe–O system

The effects of compositional variation on magnetic susceptibility, saturation magnetization, Curie temperature and magnetic moments of Cu 1− x Zn x Fe 2O 4 ferrites, where x=0.0, 0.25, 0.50, 0.75, 1.00 are reported. The Curie temperatures have been evaluated by measuring AC magnetic susceptibility using a mutual inductance technique. On increasing Zn content from 0.0 to 0.75, the Curie temperature and the saturation magnetization increase. On further increase in Zn content, x>0.75, a decreasing trend is exhibited. This effect can partially be related to the low magnetic moments of Zn +2 ions. The Y–K angle increases gradually with increasing zinc content and extrapolates to 90° for ZnFe 2O 4. From the computation of Y–K angles for Zn substituted ferrites (0< x<0.75), it can be concluded that the mixed zinc ferrites exhibit a non-collinearity of the Y–K type while CuFe 2O 4 shows a Néel type of ordering.

Generalized Flory equations of state for copolymers modeled as square-well chain fluids

The Generalized Flory–Dimer (GFD) equation of state has been extended to fluids containing copolymers modeled as heteronuclear chains of freely-jointed tangent spheres that interact via a site–site square-well potential. Compressibility factors are obtained for block, alternating and random copolymer fluids. The GFD theory for square-well copolymers requires expressions for the insertion factors of SW monomers in SW monomer mixtures, SW dimers in SW dimer mixtures, and SW heteronuclear dumbbells in SW heteronuclear dumbbell fluids. These insertion factors are obtained using recently-derived perturbation-theory-based equations of state. The effects of variations in composition, segment size ratios, and well-depth ratios on the compressibility factor are studied. The predictions of the Generalized Flory–Dimer theory are compared to compressibility factors obtained from discontinuous canonical molecular dynamics simulation. The Generalized Flory–Dimer theory accurately predicts the compressibility factors of square-well copolymer fluids for a variety of cases including those in which the size ratio and well-depth ratio of the two components are different.

The study on the combustion model and combustion characteristics for stoker type incinerator

A combustion model for the incineration of municipal solid waste(MSW) in the stoker type incinerator was developed by considering the variation of physical composition of MSW. Theoretical analysis and numerical simulation for the combustion characteristics in incinerator were conducted by using the present model and the effects of compositional variation on the incineration characteristics of MSW was examined theoretically. It is found that large excess air enhances drying, but depresses volatilization. For the large value of moisture content, pyrolysis is fast but drying is slow. As the value of plastic content increases, devolatilization becomes slower. Larger amount of primary air supply to the rear side of stoker leads to increase the possibility of delaying the combustion.

The effect of compositional variations on the properties of rare-earth doped Ge-S-I chalcohalide glasses

The effect of compositional variations on the properties of rare-earth doped Ge-S-I chalcohalide glasses

Early Stages of Combustion in Internal Combustion Engines Using Linked CFD and Chemical Kinetics Computations and its Application to Natural Gas Burning Engines

The paper describes a numerical model for the early stages of combustion in Natural Gas engines using linked CFD and detailed chemical kinetics. The importance of such a combustion device stems from the characteristics of natural gas which make it an attractive near-term olution for the automotive emissions problem. The 3-D simulation, which incorporates a chemical model, turbulence model and ignition model is taken under engine-like conditions. This is achieved by coupling the numerical codes KIVA II, developed to solve the transient equations of conservation of turbulent chemically reacting mixture of ideal gases, CHEMKIN II, designed to facilitate simulations of elementary chemical reactions in flowing systems, TRANSPORT, used for the evaluation of gas-phase multicomponent transport properties, and LIOR - a linking code. The numerical tool has predictive capability for combustion behaviour under various conditions, an ability to interpret observed combustion phenomena and ability to guide the design of better natural gas engines. A justification of the validity of the approach is discussed in terms of the asymptotic structure of the methane-air flame. The early states of the combustion event are described in some detail and two specific studies are briefly reported, that of the effects of various ignition source types for natural gas burning domestic vehicle engines, and that of the effects of variation in composition of the natural gas.

The effect of compositional variations on the properties of rare-earth doped GeSI chalcohalide glasses

Undoped and Pr 3+-doped Ge x S y I z glasses, with atomic concentrations of germanium 0.33 ≤ x ≤ 0.43 and iodine 0 ≤ z ≤ 20, respectively, were synthesized and their optical and thermal properties measured. The properties followed the same compositional trends as the binary Ge x S 1 - x glasses, for which 0.33 ≤ x ≤ 0.43. The compositional dependences of the absorption edge and rare-earth solubility in Ge x S y I z glasses can be presented with a single parameter p = (y + z 2 ) x . Addition of iodine to the Ge-rich Ge x S 1 - x -base glass system resulted in increasing the optical bandgap energy and decreasing the glass transition temperature. Thermal stability of the Ge x S y I z glasses is a function of both S Ge ratio and iodine concentration. XPS and Raman spectroscopic measurements were conducted to obtain information about the structural changes accompanying the compositional variations. Properties-structure correlations are discussed. The results of the present study were used for selection of a compositional range within the Ge x S y I z glass system with optimal properties required for Pr 3+-doped fiber amplifier application.

Effect of composition variations in cloud droplet populations on aqueous‐phase chemistry

We prove that the use of a cloud or fog droplet population's volume weighted average pH results in the underestimation of the actual rate of sulfate production for most atmospheric conditions. To quantify the magnitude of this error, we have developed two aqueous‐phase chemistry models: a droplet size‐resolved model and a bulk chemistry model. The discrepancy between the results of these two models indicates the magnitude of the error introduced by using bulk aqueous‐phase properties. This error depends mainly on the availability of gas‐phase species (SO2, O3, H2O2, and NH3), the aerosol size/composition distribution, and the residence time of the air parcel in cloud containing air. The ratio of predicted sulfate production between the two models for the cases studied here varies from as low as unity to as high as 30. The largest ratios occur during the first few minutes of cloud formation. After this peak the difference in sulfate production rates between the two models decreases rapidly. For the scenarios simulated, the largest error introduced by the bulk modeling approach at the end of a cloud event was underprediction of the sulfate production by a factor of 2. The magnitude of the sulfate underprediction by the bulk model decreases with increasing initial levels of gas‐phase NH3 and H2O2 and is rather insensitive to the gas‐phase O3 and SO2 concentrations.