Experimental investigation of the band broadening originating from the top and bottom wall in micromachined non-porous pillar array columns

We report on the experimental investigation of the effect of the top and bottom wall plates in micromachined nonporous pillar array columns. It has been found that their presence yields an additional c-term type of band broadening that can make up a significant fraction of the total band broadening (at least if considering nonporous pillars and a nonretained tracer). Their presence also induces a clear (downward) shift of the optimal velocity. These observations are, however in excellent quantitative agreement with the theoretical expectations obtained from a computational fluid dynamics study. The presently obtained experimental results, hence, demonstrate that the employed high aspect ratio Bosch etching process can be used to fabricate micromachined pillar arrays that are sufficiently refined to achieve the theoretical performance limit

Age-dependent morphology and ultrastructure of the hypopharyngeal gland of Apis mellifera workers (Hymenoptera, Apidae)

The main secretory products of the hypopharyngeal gland are royal jelly compounds, as well as other substances such as $\alpha$-glucosidase. Our study of the morphology and ultrastructure of this gland in relation to worker’s age clearly shows a secretory cycle within the cells, although production of secretion is asynchroneous between different cells within an acinus. Secretory vesicles appear already in 3 day old bees, while peak production is around 6 days. Thereafter, the volume of the acini as well as the number of secretory vesicles decrease and no vesicles are visible after 3 weeks of age. Foragers display degenerative structures in their cells. The hypopharyngeal gland cells of winter bees contain large numbers of secretory vesicles, that are probably stored until spring

Trajectories of self-control in a forensic psychiatric sample stability and association with psychopathology, criminal history, and recidivism

The current study examined trajectories of two indicators of self-control—impulsivity and coping skills—in 317 forensic psychiatric patients, as well as associations with psychopathology, crime, and recidivism. Violent recidivism was positively associated with coping skills at admission to the clinic and with impulsivity at discharge. Only a small correlation was found between self-control and criminal history, and there was no association with psychopathology. We found multiple trajectories of self-control using Latent Class Growth Models: more than 89% improving over time. In addition, patients with Cluster C personality disorders showed greater improvement in coping skills. Patients showing less improvement in impulsivity had greater rates of crime and recidivism. We conclude that self-control can be influenced by interventions or treatment, and that both starting values and trajectories of self-control provide valuable information. Interestingly, the associations between self-control and psychopathology, crime and recidivism were not as strong as reported in other populations

Kinetic plot and particle size distribution analysis to discuss the performance limits of sub-2 mu m and supra-2 mu m particle columns

To contribute to the current debate about the "ideal" particle size range (sub-2 mu m vs. supra-2 mu m), the present study compares the kinetic performance of some commercially available sub-2 mu m and 3.5 mu m particles used under quasi-adiabatic conditions via the kinetic plot method. Under the adopted assumption that viscous heating effects can be neglected (which is uncertain in a pressure range above 400 bar), the obtained kinetic plots show that, provided each particle size is used in a column with properly optimized length, the gain in separation speed that sub-2 mu m particle columns might have over maximally performing 2.5 mu m particle columns is very small. Sub-2 mu m particle columns can only yield a gain in separation speed in the range of high-speed/low-resolution-separations (total time based on k = 10 below 5 or 10min). And even in this range, the actual gain that can be expected is only marginally small (only a few %). The present study hence suggests that the development and the use of particles in the 2-3 mu m range should deserve more attention than it did in the past few years. However, to be competitive, this 2-3 mu m material should be packed in relatively long columns, with a packing quality matching that of the current best performing 3.5 mu m particle columns. The supra-2 mu m particles should also be able to withstand the same pressures as the sub-2 mu m particle material one is comparing it to

Relation between the particle size distribution and the kinetic performance of packed columns. Application to a commercial sub-2 microm particle material

To study the influence of the particle size distribution (PSD), we measured the chromatographic performance of a series of sub-2 microm particle high performance liquid chromatography (HPLC) columns packed with four different particle mixtures having a purposely imposed different size distribution. Using the reduced kinetic plot representation by plotting the separation impedance (E(0)) versus the plate number ratio (N(opt)/N), the different columns could be classified according to their chromatographic performance without the need to specify a mean particle diameter or a molecular diffusion coefficient, as is needed in the classical reduced plate height and flow resistance analysis. The present analysis shows that it is not so much the width or span of the particle size distribution, but rather the presence of fines that greatly determines the chromatographic performance of particulate columns

Experimental investigation of the band broadening originating from the top and bottom walls in micromachined nonporous pillar array columns\ud

We report on the experimental investigation of the effect of the top and bottom wall plates in micromachined nonporous pillar array columns. It has been found that their presence yields an additional c-term type of band broadening that can make up a significant fraction of the total band broadening (at least if considering nonporous pillars and a nonretained tracer). Their presence also induces a clear (downward) shift of the optimal velocity. These observations are, however in excellent quantitative agreement with the theoretical expectations obtained from a computational fluid dynamics study. The presently obtained experimental results, hence, demonstrate that the employed high aspect ratio Bosch etching process can be used to fabricate micromachined pillar arrays that are sufficiently refined to achieve the theoretical performance limit.\ud \u