The “One Source” cohort — evaluating the suitability of the human toenail as a manganese biomonitor

Numerous studies have demonstrated that the human toenail is a reliable biomonitor for the intake of Se and other elements. The objective of this study was to evaluate the use of the toenail as a biomonitor for Mn. Toenail specimens from One Source^™ multivitamin users and matched controls were selected. Se was measured using established NAA methods, then Mn was measured via a new procedure. The Se results confirmed the accurate classification of the cohort. However, the nail did not show significant, positive response to Mn supplementation. We hypothesize that the persistence of exogenous Mn confounded the results.     

Tunable DNA Origami Motors Translocate Ballistically Over μm Distances at nm/s Speeds

Inspired by biological motor proteins, that efficiently convert chemical fuel to unidirectional motion, there has been considerable interest in developing synthetic analogues. Among the synthetic motors created thus far, DNA motors that undertake discrete steps on RNA tracks have shown the greatest promise. Nonetheless, DNA nanomotors lack intrinsic directionality, are low speed and take a limited number of steps prior to stalling or dissociation. Herein, we report the first example of a highly tunable DNA origami motor that moves linearly over micron distances at an average speed of 40 nm/min. Importantly, nanomotors move unidirectionally without intervention through an external force field or a patterned track. Because DNA origami enables precise testing of nanoscale structure-function relationships, we were able to experimentally study the role of motor shape, chassis flexibility, leg distribution, and total number of legs in tuning performance. An anisotropic rigid chassis coupled with a high density of legs maximizes nanomotor speed and endurance.     

Using Monte Carlo transport to accurately predict isotope production and activation analysis rates at the University of Missouri research reactor

A detailed Monte Carlo N-Particle Transport Code (MCNP5) model of the University of Missouri research reactor (MURR) has been developed. The ability of the model to accurately predict isotope production rates was verified by comparing measured and calculated neutron-capture reaction rates for numerous isotopes. In addition to thermal (1/v) monitors, the benchmarking included a number of isotopes whose (n, γ) reaction rates are very sensitive to the epithermal portion of the neutron spectrum. Using the most recent neutron libraries (ENDF/B-VII.0), the model was able to accurately predict the measured reaction rates in all cases. The model was then combined with ORIGEN 2.2, via MONTEBURNS 2.0, to calculate production of ⁹⁹Mo from fission of low-enriched uranium foils. The model was used to investigate both annular and plate LEU foil targets in a variety of arrangements in a graphite irradiation wedge to optimize the production of ⁹⁹Mo.     

Dynamic characterization of compliant materials using an all-polymeric split Hopkinson bar

The split Hopkinson bar is a reliable experimental technique for measuring high strain rate properties of high-strength materials. Attempts to apply the split Hopkinson bar in measurement on more compliant materials, such as plastics, rubbers and foams, suffer from limitations on the maximum achievable strain and from high noise-to-signal ratios. The present work introduces and all-polymeric split Hopkinson bar (APSHB) experiment, which overcomes these limitations. The proposed method uses polymeric pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials, thus providing both a low noise-to-signal ratio data and a longer input pulse for higher maximum strain. The APSHB requires very careful data reduction procedures because of the viscoelastic behavior of the incident and transmitter pressure bars. High-quality stress-strain data for a variety of compliant materials, such as polycarbonate, polyurethane foam and styrofoam, are presented.     

A nonlinear dynamical systems analysis of child emotion displays in relation to family context and child adjustment: a cox hazard approach

This report examines how the relative attractor strengths of children's display of three emotion states, anger, sadness/fear, and neutral-engaged, are associated with exposure to maternal negative affect and care giving disruptions, and to child antisocial behavior and depression. Exposure to negative maternal affect was associated with a weaker attractor state for sadness or fear displays relative to those for anger and neutral-engaged displays. Exposure to care giving disruptions was associated with stronger attractor strength for anger and sadness/fear relative to that for neutral-engaged. Overt and covert antisocial behaviors were associated with weaker attractor states for sadness/fear displays relative that for the neutral-engaged displays. Overt antisocial behavior was associated with a stronger attractor state for anger displays relative to that for neutral-engaged displays, and covert antisocial behavior with a weaker attractor state for fear/sadness displays relative to that for neutral-engaged displays. Child depressive symptoms were marginally associated with a stronger attractor state for fear/sadness displays relative to neutral-engaged. The data suggest the attractor strengths for emotion display states are affected by social experience and that between-individual risk for various forms of psychopathology is related to the relative intra-individual attractor strength of various emotion displays in a multi-state emotion display system.     

Surface properties of dioleoyl-sn-glycerol-3-ethylphosphocholine, a cationic phosphatidylcholine transfection agent, alone and in combination with lipids or DNA

Long-chain cationic amphipaths are routinely used for transfecting DNA into cells, although the mechanism of DNA delivery by these agents is poorly understood. Since their interfacial properties are undoubtedly involved at some stage in the process, a comprehensive study of the surface behavior of at least one of these compounds is highly desirable. Hence, the behavior of the cationic transfection agent EDOPC (dioleoyl-sn-glycerol-3-ethylphosphocholine or O-ethyldioleoylphosphatidylcholine), has been characterized at the air-water interface, by itself and in mixtures with other phospholipids. Surface pressure-molecular area isotherms obtained at the argon-buffer interface revealed that EDOPC is considerably (5-10 A(2)) more expanded than the parent phosphatidylcholine (DOPC) and even more expanded than the corresponding phosphatidylglycerol (DOPG), which has a similar charge density (of opposite polarity) as EDOPC. A 1:1 mixture of EDOPC and DOPG is very slightly condensed relative to DOPG and considerably condensed relative to EDOPC. The surface/dipole potential of this mixture is the mean of those of EDOPC and DOPG and is almost the same as that of DOPC. When the composition of EDOPC mixtures was varied, several surface parameters, including surface dipole moment, collapse pressure, and compressibility, exhibited discontinuities at a 1:1 mole ratio. EDOPC is unusually surface-active; the equilibrium surface tension of its dispersion was lower and the rate of fall of the surface tension (dynamic surface activity) of a dispersion with an initially clean surface was more than an order of magnitude greater than that for dispersions of DOPG. A 1:1 mixture of the cationic lipoid and phosphatidylglycerol had lower surface activity than DOPC in water but similar surface activity in 0.1 NaCl. Analysis, in terms of surface concentration, of the formation of EDOPC monolayers at the air interface of vesicle dispersions revealed a simple exponential rise to a maximum, at least for higher concentrations. Addition of a small proportion of DNA to EDOPC increased its dynamic surface activity even though DNA alone has no detectable surface activity at the concentrations used. This enhancement by DNA is presumably due to the disruption of the continuity of the bilayer and creation of defects from which lipoid spreads readily. The surface properties of this cationic compound, both alone and in combination with anionic lipids, provide insight into the previously described nonbilayer phase preferences of cationic-anionic lipid mixtures. In addition, they provide critical data (area condensation of mixed cationic-anionic monolayers) supporting a previously proposed mechanism of fusion of cationic bilayers with anionic bilayers. Such a process, involving anionic cellular membranes, is believed to be required for release of DNA from lipoplexes and is therefore a key stage of transfection.