Microwave heating in multiphase systems: evaluation of series solutions

The 1D electric field and heat-conduction equations are solved for a slab where the dielectric properties vary spatially in the sample. Series solutions to the electric field are obtained for systems where the spatial variation in the dielectric properties can be expressed as polynomials. The series solution is used to obtain electric-field distributions for a binary oil-water system where the dielectric properties are assumed to vary linearly within the sample. Using the finite-element method temperature distributions are computed in a three-phase oil, water and rock system where the dielectric properties vary due to the changing oil saturation in the rock. Temperature distributions predicted using a linear variation in the dielectric properties are compared with those obtained using the exact nonlinear variation.

Real-time kinetic analysis of hCG-monoclonal antibody interaction using radiolabeled hCG probe: presence of two forms of Ag-mAb complex as revealed by solid phase dissociation studies

Real-time kinetics of ligand-ligate interaction has predominantly been studied by either fluorescence or surface plasmon resonance based methods. Almost all such studies are based on association between the ligand and the ligate. This paper reports our analysis of dissociation data of monoclonal antibody-antigen (hCG) system using radio-iodinated hCG as a probe and nitrocellulose as a solid support to immobilize mAb. The data was analyzed quantitatively for a one-step and a two-step model. The data fits well into the two-step model. We also found that a fraction of what is bound is non-dissociable (tight-binding portion (TBP)). The TBP was neither an artifact of immobilization nor does it interfere with analysis. It was present when the reaction was carried out in homogeneous solution in liquid phase. The rate constants obtained from the two methods were comparable. The work reported here shows that real-time kinetics of other ligand-ligate interaction can be studied using nitrocellulose as a solid support. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of granularity on the insulator-superconductor transition in ultrathin Bi films

We have studied the insulator-superconductor transition (IST) by tuning the thickness in quench-condensed Bi films. The resistive transitions of the superconducting films are smooth and can be considered to represent ''homogeneous'' films. The observation of an IST very close to the quantum resistance for pairs R-square(N) similar to h/4e(2) on several substrates supports this idea. The relevant length scales here are the localization length, and the coherence length. However, at the transition, the localization length is much higher than the superconducting coherence length, contrary to expectation for a "homogeneous" transition. This suggests the invalidity of a purely fermionic model for the transition. Furthermore, the current-voltage characteristics of the superconducting films are hysteretic, and show the films to be granular. The relevant energy scales here are the Josephson coupling energy and the charging energy. However, Josephson coupling energies (E-J) and the charging energies (E-c) at the IST, they are found to obey the relation E-j < E-c. This is again contrary to expectation, for the IST in a granular or inhomogeneous system. Hence, a purely bosonic picture of the transition is also inconsistent with our observations. We conclude that the IST observed in our experiments may be either an intermediate case between the fermioinc and bosonic mechanisms, or in a regime of charge and vortex dynamics for which a quantitative analysis has not yet been done.

Electrical transport characteristics of Au/n-GaAs Schottky diodes on n-Ge at low temperatures

The current�voltage characteristics of Au/n-GaAs Schottky diodes grown by metal-organic vapor-phase epitaxy on Ge substrates were determined in the temperature range 80�300 K. The zero-bias barrier height for current transport decreases and the ideality factor increases at low temperatures. The ideality factor was found to show the T0 effect and a higher characteristic energy. The excellent matching between the homogeneous barrier height and the effective barrier height was observed and infer good quality of the GaAs film. No generation�recombination current due to deep levels arising during the GaAs/Ge heteroepitaxy was observed in this study. The value of the Richardson constant was found to be 7.04 A K?2 cm?2, which is close to the value used for the determination of the zero-bias barrier height.

Polymerization of pyrrole and processing of the resulting polypyrrole as blends with plasticised PVC

Polypyrrole was synthesized by chemical oxidation of pyrrole in water containing various sulphonic acids like toluene sulphonic acid (TSA), sulphosalicylic acid (SSA), and camphor sulphonic acid (CSA), as well as a combination of each sulphonic acid with sodium dodecyl benzene sulphonate (NaDBS) to investigate the effect of doping on conductivity, yield, and processability of the conducting polymer. Free-standing blend films of polypyrrole and plasticized polyvinyl chloride (PVC) were obtained by casting an homogeneous suspension of the two polymers in tetrahydrofuran. The maximum conductivity of the blend film is similar to 0.3 S/cm, corresponding to a weight fraction of 0.16 w/w polypyrrole. The blend film is semiconducting in the range 300-10 K. A TG-DTA scan indicates the blend film to be amorphous with a stepwise decomposition process similar to pristine PVC. The choice of a dual dopant system during synthesis and the plasticised polymer during subsequent processing were keys to obtaining homogeneous high-quality films. (C) 2001 John Wiley & Sons, Inc.

Wear of metals: a consequence of stable/unstable material response

Wear of metals in dry sliding is dictated by the material response to traction. This is demonstrated by considering the wear of aluminium and titanium alloys. In a regime of stable homogeneous deformation the material approaching the surface from the bulk passes through microprocessing zones of flow, fracture, comminution and compaction to generate a protective tribofilm that retains the interaction in the mild wear regime. If the response leads to microstructural instabilities such as adiabatic shear bands, the near-surface zone consists of stacks of 500 nm layers situated parallel to the sliding direction. Microcracks are generated below the surface to propagate normally away from the surface though microvoids situated in the layers, until it reaches a depth of 10-20 mum. A rectangular laminate debris consisting of a 20-40 layer stack is produced, The wear in this mode is severe.

A new beam finite element for the analysis of functionally graded materials

A new beam element is developed to study the thermoelastic behavior of functionally graded beam structures. The element is based on the first-order shear deformation theory and it accounts for varying elastic and thermal properties along its thickness. The exact solution of static part of the governing differential equations is used to construct interpolating polynomials for the element formulation. Consequently, the stiffness matrix has super-convergent property and the element is free of shear locking. Both exponential and power-law variations of material property distribution are used to examine different stress variations. Static, free vibration and wave propagation problems are considered to highlight the behavioral difference of functionally graded material beam with pure metal or pure ceramic beams. (C) 2003 Elsevier Science Ltd. All rights reserved.

Segregation in the MgO–MgAl2O4 system processed from nitrate precursors

The occurrence of segregation and its influence on microstructural and phase evolution have been studied in MgO–MgAl2O4 powders synthesized by thermal decomposition of aqueous nitrate precursors. When the nitrate solutions of Mg and Al were spray-pyrolyzed on a substrate held at 673 or 573 K, homogeneous mixed oxides were produced. Spraying and drying the nitrate solutions at 473 K resulted in the formation of compositionally inhomogeneous, segregated oxide mixtures. It is suggested that segregation in the dried powders was caused by the difference in solubility of the individual nitrate salts in water which caused Mg-rich and Al-rich salts to precipitate during dehydration of the solutions. The occurrence of segregation in the powders sprayed at 473 K and not 573 or 673 K is ascribed to the sluggish rate at which the early stages of decomposition occurred during which the cations segregated. The phase evolution in segregated and segregation-free MgO–MgAl2O4 powders has been compared. The distinguishing feature of the segregated powders was the appearance of stoichiometric periclase grain dimensions in excess of 0.3 μm at temperatures as low as 973 K. By comparison, the segregation-free powders displayed broad diffraction peaks corresponding to fine-grained and nonstoichiometric periclase. The grain size was in the range 5–30 nm at temperatures up to 1173 K. The key to obtaining fine-grained periclase was the ability to synthesize (Mg Al)O solid solutions with the rock salt structure. In the temperature range 973–1173 K, spinel grain size varied from 5 to 40 nm irrespective of its composition and did not appear to be influenced by segregation.

On an oscillatory point force in a rotating stratified fluid

The forced oscillations due to a point forcing effect in an infinite or contained, inviscid, incompressible, rotating, stratified fluid are investigated taking into account the density variation in the inertia terms in the linearized equations of motion. The solutions are obtained in closed form using generalized Fourier transforms. Solutions are presented for a medium bounded by a finite cylinder when the oscillatory forcing effect is acting at a point on the axis of the cylinder. In both the unbounded and bounded case, there exist characteristic cones emanating from the point of application of the force on which either the pressure or its derivatives are discontinuous. The perfect resonance existing at certain frequencies in an unbounded or bounded homogeneous fluid is avoided in the case of a confined stratified fluid.

Growth and Characterization of GaAs Epitaxial Layers by MOCVD

technique, on both semi-insulating and semi-conducting CraAs substrates with (100) orientation, offset by 2° towards (110) direction. Systematic variation of As/Ga was performed to gain an understanding of growth process, type of formation and other related physical properties. The films were characterized by using the variety of techniques, such as SEM, EDAX, HRTEM, XRD, and PL. Optical and electrical properties of undoped CyaAs epilayers are presented with reference to the growth conditions and AsH3/TMGa ratio. Photoluminescence measurements of GaAs epilayers were recorded at 4.2K and shows the emission of free exciton and confirmed their high purity. The dominant residual impurities in GaAs are presented by using PL. Finally, electrochemical depth profiling exhibited almost homogeneous background carrier distribution and excellent abruptness between the thin GaAs epilayer and substrate.

A two Roll Mill as a Rheomer for Pastes

Previous work involving the squeeze-film flow of a model paste substance, a mixture of clay particles and mineral oil commonly known as ‘Plasticine’, has suggested that it behaves as a simple Herschel-Bulkley fluid which exhibits little strain history. However, tensile measurements, which are naturally limited to small strains by the onset of necking, indicate that this material shows strain hardening. A two roll-mill is employed here to investigate the influence of larger extensional strains. The data are analysed using an available first order engineering plasticity solution. The results confirm that this material exhibits both extensional strain and strain rate hardening. This observed strain hardening effect, which is not observed in the squeeze-film experiments, is attributed, in part, to the more homogeneous deformation fields induced during rolling and tensile extension.

Synthesis of cnt-metal oxide nano-composite electrode materials for supercapacitator by low-pressure mocvd

Homogeneous composite thin films of Fe2O3-carbon nanotube were synthesized in a novel, single-step process by metalorganic chemical vapor deposition (MOCVD) using ferric acetyl acetonate as precursor. The deposition of composite takes place in a narrow range of CVD conditions, beyond which the deposition either multiwall carbon nanotubes (MWNTs) only or hematite (α-Fe2O3) only takes place. The composite film formed on stainless steel substrates were tested for their supercapacitive properties in various aqueous electrolytes.

Mapping of large scale 158 mu m [CII] line emission: Orion A

We present the first results of an observational programme undertaken to map the fine structure line emission of singly ionized carbon ([ CII] 157 : 7409 mum) over extended regions using a Fabry Perot spectrometer newly installed at the focal plane of a 100 cm balloon- borne far- infrared telescope. This new combination of instruments has a velocity resolution of similar to 200 km s(-1) and an angular resolution of 1.'5. During the first flight, an area of 30' x 15' in Orion A was mapped. These observations extend over a larger area than previous observations, the map is fully sampled and the spectral scanning method used enables reliable estimation of the continuum emission at frequencies adjacent to the [ CII] line. The total [ CII] line luminosity, calculated by considering up to 20% of the maximum line intensity is 0.04% of the luminosity of the far- infrared continuum. We have compared the [ CII] intensity distribution with the velocity- integrated intensity distributions of (CO)-C-13(1- 0), CI(1- 0) and CO( 3- 2) from the literature. Comparison of the [ CII], [ CI] and the radio continuum intensity distributions indicates that the largescale [ CII] emission originates mainly from the neutral gas, except at the position of M 43, where no [ CI] emission corresponding to the [ CII] emission is seen. Substantial part of the [ CII] emission from here originates from the ionized gas. The observed line intensities and ratios have been analyzed using the PDR models by Kaufman et al. ( 1999) to derive the incident UV flux and volume density at a few selected positions. The models reproduce the observations reasonably well at most positions excepting the [ CII] peak ( which coincides with the position of theta(1) Ori C). Possible reason for the failure could be the simplifying assumption of a homogeneous plane parallel slab in place of a more complicated geometry.

Vortex dynamics and upper critical fields in ultrathin Bi films

Current-voltage (I-V) characteristics of quench condensed, superconducting, ultrathin Bi films in a magnetic field are reported. These I-V's show hysteresis for all films, grown both with and without thin Ge underlayers. Films on Ge underlayers, close to superconductor-insulator transition, show a peak in the critical current, indicating a structural transformation of the vortex solid. These underlayers, used to make the films more homogeneous, are found to be more effective in pinning the vortices. The upper critical fields (B-c2) of these films are determined from the resistive transitions in perpendicular magnetic field. The temperature dependence of the upper critical field is found to differ significantly from Ginzburg-Landau theory, after modifications for disorder.

Regionalization of precipitation in data sparse areas using large scale atmospheric variables - A fuzzy clustering approach

Delineation of homogeneous precipitation regions (regionalization) is necessary for investigating frequency and spatial distribution of meteorological droughts. The conventional methods of regionalization use statistics of precipitation as attributes to establish homogeneous regions. Therefore they cannot be used to form regions in ungauged areas, and they may not be useful to form meaningful regions in areas having sparse rain gauge density. Further, validation of the regions for homogeneity in precipitation is not possible, since the use of the precipitation statistics to form regions and subsequently to test the regional homogeneity is not appropriate. To alleviate this problem, an approach based on fuzzy cluster analysis is presented. It allows delineation of homogeneous precipitation regions in data sparse areas using large scale atmospheric variables (LSAV), which influence precipitation in the study area, as attributes. The LSAV, location parameters (latitude, longitude and altitude) and seasonality of precipitation are suggested as features for regionalization. The approach allows independent validation of the identified regions for homogeneity using statistics computed from the observed precipitation. Further it has the ability to form regions even in ungauged areas, owing to the use of attributes that can be reliably estimated even when no at-site precipitation data are available. The approach was applied to delineate homogeneous annual rainfall regions in India, and its effectiveness is illustrated by comparing the results with those obtained using rainfall statistics, regionalization based on hard cluster analysis, and meteorological sub-divisions in India. (C) 2011 Elsevier B.V. All rights reserved.