Experimental analysis of particle deposition on single collectors

Experimental studies of particle deposition from liquid suspensions of monodispersed particles flowing past single spherical collectors were carried out and compared with theoretical results based on trajectory calculations. The experimental observations indicate the significant effect of particle flocculation and thus suggest the importance of sedimentation as a collection mechanism. The agreement between the theoretical results and the experimental data is good when the surface force interactions are favorable for collection. However, when the electrokinetic repulsion dominates in the neighborhood of the collector, the rate of collection drops rapidly, although not to zero as predicted by theory.     

Electrical and Optical Characterization of Melt-Grown Bulk InAs<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>P<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Crystals

Bulk ternary InAs_1−y P _y polycrystals with diameters up to 50 mm were grown from a pseudobinary InP-InAs melt using the vertical Bridgman technique. Electrical and optical properties were investigated as functions of alloy composition and sample temperature. As-grown undoped crystals have been found to exhibit n-type conductivity irrespective of alloy composition. Though the bulk InAs_1−y P _y substrates show high optical transmission out to long wavelengths as well as high carrier mobility, they exhibit random compositional fluctuations across the substrate area.     

Detection of Rotor Faults in Brushless DC Motors Operating Under Nonstationary Conditions

There are several applications where the motor is operating in continuous nonstationary operating conditions. Actuators and servo motors in the aerospace and transportation industries are examples of this kind of operation. Detection of faults in such applications is, however, challenging because of the need for complex signal processing techniques. Two novel methods using windowed Fourier ridges and Wigner-Ville-based distributions are proposed for the detection of rotor faults in brushless dc motors operating under continuous nonstationarity. Experimental results are presented to validate the concepts and illustrate the ability of the proposed algorithms to track and identify rotor faults. The proposed algorithms are also implemented on a digital signal processor to study their usefulness for commercial implementation     

Space-Variant Approaches to Recovery of Depth from Defocused Images

The recovery of depth from defocused images involves calculating the depth of various points in a scene by modeling the effect that the focal parameters of the camera have on images acquired with a small depth of field. In the approach to depth from defocus (DFD), previous methods assume the depth to be constant over fairly large local regions and estimate the depth through inverse filtering by considering the system to be shift-invariant over those local regions. But a subimage when analyzed in isolation introduces errors in the estimate of the depth. In this paper, we propose two new approaches for estimating the depth from defocused images. The first approach proposed here models the DFD system as a block shift-variant one and incorporates the interaction of blur among neighboring subimages in an attempt to improve the estimate of the depth. The second approach looks at the depth from defocus problem in the space-frequency representation framework. In particular, the complex spectrogram and the Wigner distribution are shown to be likely candidates for recovering the depth from defocused images. The performances of the proposed methods are tested on both synthetic and real images. The proposed methods yield good results and the quality of the estimates obtained using these methods is compared with the existing method.     

A Comparative Evaluation of Air-Jet Sieve for Particle Size Analysis of Pharmaceutical Powders

The performance of the air-jet sieve (AJS), for the particle size analysis of pharmaceutical powder, was evaluated and compared with the conventional sieve shaker (ESS). Two grades of acetaminophen (APAP) were used as test pharmaceutical powders. The particle size analysis by the AJS was simple, reproducible, efficient and accurate. The problematic powder, possessing excessive electrostatic charges and ranging in mean diameter from 17 nm to 800 nm (beyond the scope of ESS) could be evaluated accurately by AJS. The analysis time required by AJS was relatively less than that required by ESS. The accuracy of the determination by AJS was not affected by the sample size. Both the speed of rotation (vibrations and/or shaking) and the total time of sifting affected the results of the determination by ESS. The particle size value of APAP-special determined by ESS and AJS were 680.0 ± 0.14 nm and 40.0 ± 0.32 respectively, whereas the value assigned by the manufacturer was below 74 nm (-200 mesh). The precision of either method for particle size analysis of powder possessing excessive electrostatic charge was improved by the use of carbon black as an anti-static agent.     

Starch urea formaldehyde matrix encapsulation of solid agrochemicals. II. Release mechanism and release modeling

Based on experimental observation, a mechanism is proposed to describe the release of carbofuran from a starch-UF matrix. A simple mathematical model is developed to describe the diffusion-controlled release of a solid insecticide from a porous starch-UF matrix undergoing both volume and surface erosions. The model is tested with the release data collected for different matrices and with different pH values of the environmental liquid. The comparison between the model predictions and data is found to be reasonably good. The model describes the release process at different pH values by accounting for the influence of pH on the erosion rates.     

In search of novel water soluble forskolin analogues for positive inotropic activity

Using the novel lead from hydroxy acetyl substituted forskolin analogues, such as 7 beta-hydroxyacetyl-7 beta-deacetyl forskolin or 6 beta-hydroxyacetyl forskolin, a number of water soluble omega-amino acyl derivatives were synthesized. Two such compounds 6 and 18 showed better in vitro activity but failed to show in vivo activity.     

Mechanism of light fading of dyes on cellophane and poly(ethylene terephthalate)

Studies of relative rates of fading of dyes and Hammett σ-value of substituents in their molecules lead to further evidence that fading of azo dyes on Cellophane and poly-(ethylene terephthalate) is probably an oxidation type of reaction. Absorption spectra of the same dye on these two substrates tend to indicate a very high state of aggregation of dyes on Cellophane as compared to that on poly(ethylene terephthalate).     

SELF-DIFFUSION IN POTENTIALS OF MEAN FORCE IN WEAKLY- AND STRONGLY-INTERACTING DISPERSIONS

Studies of interactions in dispersions have traditionally focused on the stability and transport properties of such systems at extreme dilution, that is, at concentrations for which colloidal and hydrodynamic interactions are significant between at most two particles at a given time. In practice, however, dispersions of interest often do not satisfy this restriction, and, consequently, many-body colloidal interactions and hydrodynamic coupling have important roles in the observed macroscopic behavior. This paper presents an analysis of the effects of many-body interactions on the self-diffusion coefficient in interacting dispersions. Self-diffusion coefficients have been determined for dilute-gas dispersions and for Yukawa dispersions interacting through appropriate potentials of mean force. It is shown that the diffusion coefficients change negligibly with attraction for typical magnitudes of the Hamaker constant in an otherwise repulsion-dominated (i.e., stable) dispersion. The results show that, for thin electrical double layers, dilute dispersions can be approximated by hard-sphere dispersions, even for large values of surface potentials. However, for thick double layers (i.e., thickness comparable to particle radius), while the short-time diffusion coefficient is affected only negligibly, the long-time coefficient can decrease considerably because of the 'memory' effects—even for moderate or low values of the surface potentials. Corresponding results are presented for both dilute-gas dispersions and dispersions with significant local structures. The long-time diffusion coefficients in the latter are effectively linear in volume fraction (up to about 0.2)for thin double layers and are given with reasonable accuracy by the dilute-gas approximation.