High-velocity transport of nanoparticles through 1-D nanochannels at very large particle to channel diameter ratios

We explore the possibility of generating high-velocity flows of nanoparticles through flat-rectangular nanochannels, which are only 50% deeper than the diameter of the particles. Using the shear-driven flow principle, 200-nm particles can, for example, be transported through a 300-nm-deep channel at velocities up to 35 mm/s (upper limit of our current setup). Working under high-pH conditions, the velocity of the carboxylated nanoparticles still respects the small-molecule velocity law, despite the high degree of confinement to which the particles are subjected. The high degree of confinement is also found to lead to a reduced band broadening. When injecting sharply delimited particle plugs, the plate heights observed for the flow of 0.2-microm particles through a 0.3-microm channel (with plate heights of the order of 1-2 microm) are, for example, approximately 1 order of magnitude smaller than for the flow of 1.0-microm particles through a 1.4-microm channel. It is also found that the band broadening is, within its statistical variation, independent of the fluid velocity over a large range of particle velocities (5-35 mm/s). The flow method distinguishes itself from pressure-driven field-flow fractionation and hydrodynamic chromatography in that the mean particle velocity is independent of the particle size over the entire range of possible particle to channel diameter ratios.     

Analysis of organoselenium compounds in human urine using active carbon and chemically modified silica sol-gel surface-assisted laser desorption/ionization high-resolution time-of-flight mass spectrometry

Laser desorption/ionization time-of-flight mass spectra of three thermally labile low molecular weight organoselenium compounds (selenomethionine, selenoethionine, trimethylselenonium iodide) in human urine matrix have been obtained by using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). Four active layers, active carbon, silica sol-gel, and silica sol-gel impregnated with crown ether and with active carbon, were deposited on three different support substrates: (i) microscope slide coverslips; (ii) Al foil; and (iii) Cu tapes. Primarily protonated molecular ions and alkali metal adducts were observed in the mass spectra. A mixed-silica sol-gel and active carbon substrate active layer gave the best signal response for all compounds. Sol-gel substrates offered very clean backgrounds compared to the pure active carbon layers; however, the mass spectral signal intensities acquired were substantially lower for the sol-gel surfaces than those of the pure active carbon under the same conditions. Cu tape and Al foil support materials gave strong mass spectra of molecular ions and alkali metal molecular ion adducts, with lower Na and K adducts found with the Cu tape than with Al foil. Glass coverslips gave no response under all experimental conditions examined. Aerosol deposition was used to prepare SALDI substrates to avoid the localized "sweet spot" phenomenon encountered in conventional SALDI substrate preparation. Various nebulizers were examined and found to be effective in producing SALDI films with controlled and reproducible thicknesses. We were able to obtain exact mass identification of all three selenium species by high-resolution TOF-MS. To the best of our knowledge, this is the first time low molecular weight organoselenium compounds have been identified by SALDI-high-resolution TOF-MS.     

Importance and reduction of the sidewall-induced band-broadening effect in pressure-driven microfabricated columns

The influence of the detailed design of the sidewall region upon the over-all band-broadening in microfabricated packed-bed or collocated monolithic support structure (COMOSS) columns has been investigated using computational fluid dynamics (CFD) simulation techniques. It is shown that, under unretained solute conditions, very small structural variations of the order of only 5% of the particle diameter can give rise to a 4-fold increase of the band-broadening. A comprehensive study has been made to quantify this effect as a function of the fluid velocity, the particle diameter, the channel widths, and of course, the sidewall region design. Because the sidewall effect can be fully attributed to a mismatch between the flow rates in the column center and in the sidewall region, it is fortunately also quite straightforward to avoid it. A very simple design, yielding band-broadening values identical to that of a hypothetical sidewall-less column for all possible values of the flow velocity, the particle diameter, or the channel width is proposed.     

‘Smart’ Raman/Rayleigh imaging of nanosized SiC materials using the spatial correlation model

Non-destructive Raman and Rayleigh microspectrometries were used to map nanostructural and topological variations across the diameter of the SCS-6 Textron SiC fibre. It is shown for the first time that Rayleigh imaging offers a competitive alternative to AFM measurements for materials containing carbon as a second phase. The Spatial Correlation Model has been used to decompose the SiC Raman spectra into amorphous and crystalline components. Smart Raman images, which contain the calculated structural parameters revealed the nanostructure distribution. A good agreement has been obtained at the nanoscale between these smart images and transmission electron microscopy (TEM) data. A major asset of Raman smart images is to give a non destructive and global view on the crystal quality, grain size and residual stress. The potential and the limitations of the procedure are discussed.     

Crystallisation Studies of Trimethylhexamethylene/Hexamethylene Terephthalate Copolymers and Polystyrene Blends

A study has been made of the influence of the non-crystallising component, trimethyl-hexamethylene terephthalate, on the crystallisation behaviour of crystallising component, hexamethylene terephthalate in a series of their copolymers. It was found, using Differential Scanning Calorimetry, that as the melting point decreased with composition, the level of crystallinity fell more rapidly than expected on a proportionality basis, the degree of supercooling increased, and there was the emergence of a double crystallisation process. A second study in which the polymers were blended with polystyrene revealed similar influences but with less supercooling.     

Effects of Transcendental Meditation versus resting on physiological and subjective arousal.

On 4 successive days, 10 highly trained and experienced meditators (aged 26–54 yrs) were asked to relax for 5 min, meditate for 20 min, and then relax for 5 min. In contrast, 10 other Ss (aged 22–32 yrs) who had no training or experience with meditation were asked to relax for 5 min, rest for 20 min, and then relax for 5 min. Physiological arousal (heart and respiration rates, skin resistance, and blood pressure) and subjective arousal (cognitive, somatic, and relaxation) were measured throughout the experiment. Prior to meditating or resting, meditators tended to have higher heart rates and diastolic blood pressure than did nonmeditators. Meditation was associated with generally reduced arousal; but while meditating, meditators did not evidence lower levels of arousal than nonmeditators did while resting. Results place qualifications on previous studies of the effects of meditation on arousal. Implications for the study of personality functioning, stress management, and psychotherapy are discussed. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)