Laminar,transitional and turbulent annular flow of drag-reducing polymer solutions

Mean and rms axial velocity-profile data obtained using laser Doppler anemometry are presented together with pressure-drop data for the flow through a concentric annulus (radius ratio κ = 0.506) of a Newtonian (a glycerine–water mixture) and non-Newtonian fluids—a semi-rigid shear-thinning polymer (a xanthan gum) and a polymer known to exhibit a yield stress (carbopol). A wider range of Reynolds numbers for the transitional flow regime is observed for the more shear-thinning fluids. In marked contrast to the Newtonian fluid, the higher shear stress on the inner wall compared to the outer wall does not lead to earlier transition for the non-Newtonian fluids where more turbulent activity is observed in the outer wall region. The mean axial velocity profiles show a slight shift (～5%) of the location of the maximum velocity towards the outer pipe wall within the transitional regime only for the Newtonian fluid.     

Evaluation of the separation characteristics of application-specific (volatile organic compounds) open-tubular columns for gas chromatography

The solvation parameter model is used to characterize the separation characteristics of two application-specific open-tubular columns (Rtx-Volatiles and Rtx-VGC) and a general purpose column for the separation of volatile organic compounds (DB-WAXetr) at five equally spaced temperatures over the range 60-140 degrees C. System constant differences and retention factor correlation plots are then used to determine selectivity differences between the above columns and their closest neighbors in a large database of system constants and retention factors for forty-four open-tubular columns. The Rtx-Volatiles column is shown to have separation characteristics predicted for a poly(dimethyldiphenylsiloxane) stationary phase containing about 16% diphenylsiloxane monomer. The Rtx-VGC column has separation properties similar to the poly(cyanopropylphenyldimethylsiloxane) stationary phase containing 14% cyanopropylphenylsiloxane monomer DB-1701 for non-polar and dipolar/polarizable compounds but significantly different characteristics for the separation of hydrogen-bond acids. For all practical purposes the DB-WAXetr column is shown to be selectivity equivalent to poly(ethylene glycol) columns prepared using different chemistries for bonding and immobilizing the stationary phase. Principal component analysis and cluster analysis are then used to classify the system constants for the above columns and a sub-database of eleven open-tubular columns (DB-1, HP-5, DB-VRX, Rtx-20, DB-35, Rtx-50, Rtx-65, DB-1301, DB-1701, DB-200, and DB-624) commonly used for the separation of volatile organic compounds. A rationale basis for column selection based on differences in intermolecular interactions is presented as an aid to method development for the separation of volatile organic compounds.     

A europium complex that selectively stains nucleoli of cells

A europium complex selectively staining the nucleolus of NIH 3T3, HeLa, and HDF cells is reported. This complex possesses not only the advantage of the long lifetime of europium emission (0.3 ms), but also a chromophore that allows excitation at a relatively long wavelength (lambda(max) = 384 nm) and gives rise to an acceptable quantum yield (9%). The complex can be used both in live cell and fixed cell imaging, giving an average intracellular concentration on the order of 0.5 microM. Strong binding to serum albumin has been demonstrated by examination of the analogous gadolinium complex, studying relaxivity changes with increasing protein concentration. The intracellular speciation of the complex has been examined by circularly polarized emission spectroscopy and is consistent with the presence of more than one europium species, possibly protein bound.     

Separation characteristics of phenyl-containing stationary phases for gas chromatography based on silarylene-siloxane copolymer chemistries

The solvation parameter model is used to characterize the retention properties of five open-tubular column stationary phases (ZB-5 ms, DB-5 ms, DB-XLB, DB-17 ms, and DB-35 ms) based on silarylene-siloxane copolymer chemistries at five equally spaced temperatures over the range 60-140 degrees C. System constant differences and regression models for varied compounds are used to establish the selectivity equivalence of the silarylene-siloxane copolymer stationary phases and to compare their separation characteristics with poly(dimethyldiphenylsiloxane) stationary phases containing a nominally similar concentration of phenyl groups. These studies demonstrate that ZB-5 ms and DB-5 ms are selectivity equivalent. DB-XLB is significantly more dipolar and polarizable than DB-5 ms. In general terms, the silarylenesiloxane copolymer stationary phases are slightly less cohesive and more dipolar and polarizable with similar hydrogen-bond basicity to the poly(dimethyldiphenylsiloxane) stationary phases they were designed to replace. None of the silarylenesiloxane copolymer or poly(dimethyldiphenylsiloxane) stationary phases are hydrogen-bond acidic. Selectivity differences between the two types of stationary phase are temperature dependent and tend to be smaller at higher temperatures within the temperature range studied. Consequently, selectivity differences cannot be globalized without reference to the temperature for the comparison.     

Enhanced quantum-well photoluminescence in InGaAs/InGaAsP heterostructures following excimer-laser-assisted surface processing

The influence of excimer-laser-assisted surface processing on quantum-well photoluminescence (QW PL) has been investigated in InGaAs/InGaAsP heterostructures capped with a thin layer of In_0.53Ga_0.47As. The PL mapping measurements carried out on samples before they were processed in a rapid thermal annealer indicated no significant differences in the QW PL signal intensity measured at the excimer-laser-processed sites and in their vicinity. However, a large difference in the QW PL signal, with its intensity significantly enhanced at the laser-processed sites, was observed after 10 s of rapid thermal annealing (RTA) at 750 °C. The largest contrast in the PL signal (an intensity difference up to about 100%) was obtained for a site processed with 50 pulses and a laser fluence of 123 mJ/cm². The changes in the QW PL signal intensity have been found to coincide with the changes in the surface chemical composition that were detected with Auger electron spectroscopy. The main difference concerns the development of a GaO_x layer on the laser-processed In_0.53Ga_0.47As surface.     

Formation of the chromophore of the pyoverdine siderophores by an oxidative cascade

The pyoverdine chromophore is formed in a reaction involving a two-electron oxidation, a conjugate addition, and a second two-electron oxidation. This oxidative cascade can be carried out with polyphenol oxidase (PPO), MnO(2), and cell-free extracts from Pseudomonas aeruginosa. [reaction: see text]     

A photoelectron study of the alkali bromides and iodides

Precise values have been determined for the binding energies of the outer electronic bands of the alkali bromides and iodides using 40.81 eV ultraviolet photoelectron spectroscopy. These values have been corrected for relaxation effects and then favourably compared with the Born model for ionic solids in terms of both the absolute values of binding energy and the energy separation between the outer valence bands.