Measurements of tortuosity in stereolithographical bone replicas using audiofrequency pulses

The tortuosity of five air-filled stereolithographical cancellous bone replicas has been obtained from measurements using audiofrequency pulses in a rectangular waveguide. The data obtained from the replicas yields information about anisotropy with respect to orthogonal axes of the passages that would be marrow filled in vivo. A strong relationship has been found between the acoustically measured tortuosity and the independently measured porosity. Use of stereolithographical bone replicas has the potential to simulate perforation and thinning of cancellous bone and hence evaluate the dependence of acoustic properties on cancellous bone microstructure. As an "extreme" illustration of such use, "inverses" of the original replicas have been manufactured and acoustic measurements have been made on them. The data reveal significantly greater tortuosity of the passages that are geometrically equivalent to the original solid bone structures.     

Suitability of real-time quantitative polymerase chain reaction and enzyme-linked immunosorbent assay for cry9C detection in Mexican corn tortillas: fate of DNA and protein after alkaline cooking

Alkaline-cooked corn, called nixtamal, is the basis for many traditional corn products such as tortillas, chips, and taco shells that are used widely in Mexico and Central America and in the preparation of snack foods that are consumed globally. To assess the effects of alkaline and thermal treatments on the detectability of DNA and protein for the presence of genetically modified sequences, various nixtamalized products were prepared from blends of conventional white corn containing 0.1, 1.0, and 10% transgenic corn (event CBH 351, StarLink). Real-time quantitative polymerase chain reactions (RTQ-PCR) and immunoassays were used to determine the cry9C gene and protein, respectively, in unprocessed corn kernels, freshly prepared alkaline-cooked and ground corn (masa), masa flour, tortillas prepared from masa by heat treatment, chips prepared from damp masa dough by deep frying, and from tortillas processed at high (200 degrees C) and low temperatures (70 degrees C). In spite of progressive degradation of genomic DNA during processing, RTQ-PCR genetic analysis allowed detection and quantification of the cry9C gene in all products prepared from 10, 1, and 0.1% StarLink corn, except deep-fried chips containing 0.1% StarLink. Enzyme-linked immunosorbent assays readily detected <1 ppm cry9C protein in all blends of unprocessed corn (10, 1, and 0.1% StarLink) as well as in nonfried tortilla and masa products. This technique was not suitable for thermally treated nixtamalized products containing <1% transgenic corn.     

Structural dependence of thermodynamics of alkene binding to yttrium alkyl complexes and of kinetics of alkyl migration to coordinated alkenes

Agostic interactions in yttrium alkyls are structure dependent. Primary alkyl yttrium complexes have beta-CH(2) agostic interactions at low temperature, but a shift toward alpha-agostic interactions occurs on warming. For the more crowded beta-disubstituted yttrium alkyls, an alpha-CH(2) agostic interaction is seen. The thermodynamics of alkene binding to the primary alkyl yttrium complex Cp(2)YCH(2)CH(2)CH(CH(3))(2) (2) depend strongly on the structure of the alkene. A single allylic substituent on the alkene has a small effect on alkene binding, but a second allylic substituent has a large destabilizing effect. Propene binding to yttrium alkyls is largely independent of the nature of the alkyl ligand. Equilibrium constants for propene binding to n-, gamma-substituted, beta-substituted, and secondary alkyl yttrium complexes are similar. The rate of migration of an alkyl group to a coordinated alkene depends strongly on the structure of the alkyl group: n-alkyl approximately gamma-substituted > beta-substituted > alpha-substituted. The approximately 200-fold slower insertion of propene into Cp(2)YCH(2)CH(CH(3))(2) (6) than that into Cp(2)YCH(2)CH(2)CH(CH(3))(2) (2) is therefore due to kinetically slow migration of the beta-disubstituted alkyl group of 6 and not to differences in the equilibrium binding of propene. Processes related to chain transfer and site epimerization at the metal center are also reported.     

Evidence of multiple electrohydrodynamic forces acting on a colloidal particle near an electrode due to an alternating current electric field

Total internal reflection microscopy was used to monitor the elevation of 4-7.5 mum diameter particles near an electrode in response to an oscillating electric field with amplitude up to 8.5 kV/m. The media were 0.15 mM electrolyte solutions of HNO(3), NaHCO(3), and KOH, and the frequency band was 40 Hz to 10 kHz. Polystyrene-sulfonate particles were used in bicarbonate and KOH solutions, while polystyrene-amine particles were used in nitric acid. At frequencies less than 500 Hz, large oscillations in elevation at the driving frequency with small superimposed Brownian excursions were observed. At frequencies above 1 kHz, deterministic oscillations in elevation were negligible compared to Brownian fluctuations, which allowed transformation of histograms of elevations into potential energy profiles. The ac field drew the particle closer on average to the electrode in KOH solutions (compared to the no-field average elevation) and the field pushed the particle farther from the electrode in NaHCO(3). In HNO(3) a reversal of average height was observed at a frequency of 300 Hz at 1.7 kV/m with the particle being drawn closer to the electrode at low frequencies and being pushed away at higher frequencies. The reversal reflects two different electrohydrodynamic mechanisms. Analysis of the data at a high frequency (10 kHz) revealed a net force that was attractive in KOH and repulsive in HNO(3). This net force scaled with E(2)omega(-)(1), where E is the amplitude and omega is the frequency.     

MOLECULAR EVOLUTION OF THE Ca2+-BINDING PHOTOPROTEINS OF THE HYDROZOA

Abstract— Alignment of the primary structures of the hydrozoan photoproteins, aequorin, mitrocomin, clytin and obelin showed very strong amino acid sequence identities. The Ca²⁺-binding sites of the proteins were found to be highly conserved. The Ca²⁺-binding sites were also homologous to the Ca²⁺-binding sites of other Ca²⁺-binding proteins. However, aequorin, mitrocomin, clytin and obelin differed from other Ca²⁺-binding proteins in that they contained a relatively large number of cysteine, tryptophan, histidine, proline and tyrosine residues, suggesting that these residues may have evolved as part of the light-emitting mechanism. Construction of a phylogenetic tree showed that aequorin, mitrocomin, clytin and obelin form a closely related group of proteins.     

Vertical motion of a charged colloidal particle near an AC polarized electrode with a nonuniform potential distribution: theory and experimental evidence

Electroosmotic flow in the vicinity of a colloidal particle suspended over an electrode accounts for observed changes in the average height of the particle when the electrode passes alternating current at 100 Hz. The main findings are (1) electroosmotic flow provides sufficient force to move the particle and (2) a phase shift between the purely electrical force on the particle and the particle's motion provides evidence of an E2 force acting on the particle. The electroosmotic force in this case arises from the boundary condition applied when faradaic reactions occur on the electrode. The presence of a potential-dependent electrode reaction moves the likely distribution of electrical current at the electrode surface toward uniform current density around the particle. In the presence of a particle the uniform current density is associated with a nonuniform potential; thus, the electric field around the particle has a nonzero radial component along the electrode surface, which interacts with unbalanced charge in the diffuse double layer on the electrode to create a flow pattern and impose an electroosmotic-flow-based force on the particle. Numerical solutions are presented for these additional height-dependent forces on the particle as a function of the current distribution on the electrode and for the time-dependent probability density of a charged colloidal particle near a planar electrode with a nonuniform electrical potential boundary condition. The electrical potential distribution on the electrode, combined with a phase difference between the electric field in solution and the electrode potential, can account for the experimentally observed motion of particles in ac electric fields in the frequency range from approximately 10 to 200 Hz.     

Dielectric response of aligned semiconducting single-wall nanotubes

We report measurements of the full intrinsic optical anisotropy of isolated single-wall carbon nanotubes (SWNTs). By combining absorption spectroscopy with transmission ellipsometry and polarization-dependent resonant Raman scattering, we obtain the real and imaginary parts of the SWNT permittivity from aligned semiconducting SWNTs dispersed in stretched polymer films. Our results are in agreement with theoretical predictions, highlighting the limited polarizability of excitons in a quasi-1D system.