GEL FORMATION IN VACUUM GAS OIL. I. ROLE OF COMPOSITION

The compositional analysis of aromatics, saturates and urea non adductables obtained from vacuum gas oil (VGO) distillate (370-550°C) and its seven sub-fractions: (1) 370-400, (2) 400-425, (3) 425-450, (4) 450-475, (5) 475-500, (6) 500-525 and (7) 525-550°C, derived from both paraffinic and aromatic base crude oils have been done using thin layer chromatography/flame ionisation detection technique. The physico- chemical characteristics are measured using the ASTM/ standard test procedures and an attempt has been made to correlate the physico-chemical properties with the composition. The phenomenon of gel formation at low temperatures and the characteristics of the gel in these VGO sub-fractions have been studied by X-ray diffractometry and photomicrography. It is found that at low temperatures the gel formation takes place due to the development of a three dimensional network by the crystallizing n-paraffins, as well as by the agglomeration of molecules due to very high viscosity. Both processes proceed simultaneously and the concentration and composition of n-paraffins have been found to determine the dominance or otherwise of the crystallization process.     

Doppler-broadened positron annihilation studies in Y-Ba-Cu-O,Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O superconductors

Doppler-broadened annihilation radiation spectra have been measured as a function of temperature from 77 K to 300 K, for several high temperature oxide superconductors viz single-phase YBCO, single- and mixed-phase Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O compounds. The temperature-dependent parameters extracted respond to a change at the onset of superconducting transition. The observations point to involvement of oxygen valence electrons at the onset of superconducting transition. Also a possible structural change and/or increase in electron density at the oxygen vacancy/defect sites seem to accompany the transition. In addition, the parameters derived are seen to be sensitive to the presence of more than one superconducting phases in mixed phase samples.     

"Things that go bump in the light: On the optical specification of contact severity": Correction.

Reports an error in the original article by M. K. Kaiser and A. V. Phatak (Journal of Experimental Psychology: Human Perception and Performance, 1993[Feb], Vol 19[1], 194–202). Corrections are provided for Equation A3, the last entry in Table 1, and the 3rd to last line on page 194. (The following abstract of this article originally appeared in record 1993-20218-001.) Psychologists are intrigued with the idea that optical variables can specify not only the time until an object impacts an observer but also the severity of the impact. However, the mapping between the optical variables (τ and t) and the kinematic variables (velocity, acceleration) has been misstated, erroneously implying that there exist critical values of the optical variables used for locomotion and control. In this commentary, the mathematical relationship between the optical and kinematic variables is reexamined and the erroneous assumptions that have led to the proposal of critical values are shown. Also examined are the empirical data on deceleration to approach (particularly from active control paradigms) to assess whether the proposed optical variables are likely candidates for control strategies… (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of boundary lubrication characteristics by sem

The boundary lubrication characteristics of three lubricants used in the cold rolling of steel were evaluated on a disc machine using EN31 and mild steel as the disc pair materials. The surfaces, subject to superficial deformation, and the wear particles were examined by scanning electron microscopy (sem). The behaviour of the three lubricants could be clearly differentiated. This method, although not a precise representation of the process, could be used to evaluate the boundary lubrication characteristics of steel cold rolling oils     

Electrical properties of manganese doped Ga1−xInxAs grown by liquid phase epitaxy

Mn-doped Ga_1?xIn_xAs crystals (0 < x < 0.25) have been grown by the LPE technique, and the doping characteristics and electrical properties of the layers have been studied by Hall measurement. The distribution coefficient of Mn has been found to depend on the substrate orientation. The acceptor enerby level is about 77 meV and is comparable to that of Mn-doped GaAs. p-n junction diodes with high InAs compositions, grown using the step grading technique, showed a diode factor of 2. Electron diffusion lengths greater than 3μm have been measured in these Mn doped layers.     

A study of a water-reducing agent from cashew nutshell liquid

The water-reducing agent better known as superplasticizer is a recent development. A number of base materials have been used for the development of such water-reducing agents which can act better than ordinary plasticizers in concrete. The sulphonated salts of melamine, napthalene, lignin, hydroxycarboxylic acids and hydroxylated polymers are some typical compounds. Recently cashew nutshell liquid obtained from a natural product waste as a thick black phenolic compound has been converted into a water-reducing agent. This paper describes the results obtained on its effectiveness in influencing the rheological properties of flow, viscosity, particle size distribution, etc, of cement particles in hydrating cements and the water-reducing capabilities in cement mortars and concretes.     

Effect of ink organics on cambering of an Ag-metallized low temperature co-fired ceramics (LTCC)

Ceramic technology has had an important role in microelectronics since 1960s and ceramic seems to be a continuously developing, mature technology. Recently, development of low temperature co-fired ceramic technology (LTCC) has been geared up due to the huge demand of miniaturisation of electronic components. New materials are being developed for extending the demand of wide range of dielectric properties of LTCC, minimization of shrinkage, cambering of LTCC, high quality of conductors and patterning etc. This paper deals with formulation of silver conductor inks for LTCC and the effect of ink organics on the LTCC in particular to cambering/warpage, microstructure development were studied and presented.

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Vector field electron tomography of magnetic materials: theoretical development

The theory of vector field electron tomography, the reconstruction of the three-dimensional magnetic induction around a magnetized object, is derived within the framework of Lorentz transmission electron microscopy. The tomographic reconstruction method uses as input two orthogonal tilt series of magnetic phase maps and is based on the vector slice theorem. An analytical reconstruction of the magnetic induction of a single magnetic dipole is presented as a proof-of-concept. The method is compared to two previously reported approaches: a reconstruction starting from the gradient of the magnetic phase maps, and a direct reconstruction of the magnetic vector potential. Numerical examples as well as estimates of the reconstruction errors for a range of magnetic particle shapes are reported.     

Synthesis of Low Coercive BaFe12O19 Hexaferrite for Microwave Applications in Low-Temperature Cofired Ceramic

Polycrystalline M-type barium hexaferrite (BaFe₁₂O₁₉) samples have been synthesized by solution combustion route at different pH and calcination conditions in order to reduce the coercivity for microwave applications in low-temperature cofired ceramic (LTCC) substrates. Structural, morphological, and magnetic properties of BaFe₁₂O₁₉ were studied by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy, vibrating sample magnetometry (VSM), and Mössbauer spectroscopy. The formation of a single-phase hexagonal structure was confirmed by XRD. The Raman spectra reveal all characteristic peaks of BaFe₁₂O₁₉, illustrating the phase purity and crystal lattice symmetry of the synthesized material. Mössbauer spectra illustrate the existence of Fe³⁺ cations at all five crystallographic lattice sites. The microstructural features observed by FESEM disclose the growth of nanoregime particles into hexagonal platelet particles after calcination at temperatures from 800°C to 1200°C. The VSM results show a lower coercivity (1350 Oe to 3500 Oe) together with reasonably high saturation magnetization (55 emu/g to 60 emu/g) and a high bulk resistivity (>10⁹ Ω-cm) at room temperature. The dependence of magnetic and electrical properties on the preparation and processing conditions is also discussed.