Segregation in granular materials and the direct measurement of surface forces using atomic force microscopy

It is known that one of the dominant forces controlling the macroscopic motion of particles is the cohesive force due to the presence of liquid bridges between particles. In a mixing process, this force directly impacts the degree of homogeneity achievable by the system. The work presented here provides a quantitative analysis of this relationship through concurrent direct measurements of surface forces due to moisture and blending/segregation experiments. Atomic force microscopy (AFM) was employed to measure the force required to remove the AFM's cantilever from the surface of a glass bead with varying degrees of surface moisture. Corresponding blending/segregation experiments were performed using the same materials and conditions to develop a correlation between the interparticle forces due to the liquid layer and the final state of a mixing process. The extent to which greater moisture content increased the interparticle surface forces was quantified, and it was observed that segregation decreases proportionately to increases in surface forces.     

Analysis of multiple gas solid reactions

Multiple gas solid reactions involving one solid and N gaseous reactants are investigated in this study by using a matched asymptotic expansion technique. Two cases are particularly studied. In the first case all N chemical reaction rates are faster than the diffusion rate. While in the second case only M (M <N) chemical reaction rates are faster than the diffusion rate and the rates of the remaining (N-M) chemical reactions are comparable to that of diffusion. For these two cases the solid concentration profile behaves like a travelling wave. In the first case the wave front velocity is contributed linearly by all gaseous reactants (additive law) while in the second case this law does not hold.     

Useful representations of series solutions for transport problems

Simple techniques are presented for rearrangement of an infinite series in a systematic way such that the convergence of the resulting expression is accelerated. These procedures also allow calculation of required boundary derivatives. Several examples of conduction and diffusion-reaction problems illustrate the methods.     

Low-power 42 dB-linear single-stage digitally-controlled variable gain amplifier

A compact digitally-controlled single-stage variable gain amplifier (VGA) is introduced, which doubles the dB-linear range through the reconfiguration, saves power by 50% while maintaining the same linearity performance compared to those of the previous design. Implemented in 0.18 mum CMOS technology, the 5-bit digitally-controlled VGA achieves dB-linear gain range of 42 dB (-21 to 21 dB) with gain error less than plusmn0.55 dB, bandwidth of 84 MHz at maximum gain of 21 dB and maximum IIP3 of 14 dBm while consuming only 760 muA from a 1.8 V supply.     

Effects of starvation period on the locomotory response of Rhyzopertha dominica (F.)

In the context of developing a behavioural bioassay, the effects of 1-5 days starvation on the locomotory responses of Rhyzopertha dominica were investigated. Movements in an experimental arena with airflow were videoed and analysed using computerised tracking and motion analysis software. Beetle velocity and angular velocity (turning) were influenced adversely following 3 or 4 days of starvation, resulting in a lower number of beetles arriving at food. The highest number of beetles arriving at food was when they were starved for 1 day. Gender had a statistically significant effect on velocity; on average males walked 37% faster than females and there were significant decreases in the velocity of females from the fourth day and male velocity from the fifth day of starvation. Starvation significantly reduced angular velocity of beetles although the effect of gender was not statistically significant. There was a decline in angular velocity following the first day of starvation, although the negative effect of starvation on turning is not as clear-cut as on velocity, with a more gradual decline with increasing starvation. For undertaking behavioural bioassays with R. dominica, starvation beyond 1 day is unlikely to improve responsiveness.     

Endometrial expression of calbindin (CaBP)-d28k but not CaBP-d9k in primates implies evolutionary changes and functional redundancy of calbindins at implantation

The endometrium is hostile to embryo implantation except during the 'window of receptivity'. A change in endometrial gene expression is required for the development of receptivity. Calbindin-d9k (CaBP-d9k) and calbindin-d28k (CaBP-d28k) are proteins possessing EF-hand motifs which have high affinity for Ca2+ ions. Previously, it has been demonstrated that, in mouse endometrium, the expression of both calbindins is highly regulated during implantation and that both proteins play critical but functionally redundant roles at implantation. This study was the first to determine the expression of these two calbindins in the human and rhesus monkey endometrium. Initial RT-PCR analysis demonstrated that CaBP-d28k but not CaBP-d9k mRNA expression is detectable in the endometrium of both species. Western blot analysis confirmed the presence of immuno-reactive CaBP-d28k protein in the primate endometrium. Furthermore, the endometrial expression pattern of CaBP-d28k mRNA and protein was examined by Northern blot analysis and immunohistochemistry respectively in both species across the menstrual cycle and during early pregnancy. Semi-quantitative statistical analysis of the immunohistochemistry results revealed that, in the human, CaBP-d28k protein expression was maximal in luminal and glandular epithelium during the mid-secretory phase, coinciding with the time when the endometrium is receptive to embryo implantation. Expression in rhesus monkey showed a similar trend. These results suggest that, in the primate endometrium, only CaBP-d28k is expressed and that the specific regulation of this calbindin is potentially important for the establishment of uterine receptivity.