The 400 microsphere per piece "rule" does not apply to all blood flow studies. (1/51)

Microsphere experiments are useful in measuring regional organ perfusion as well as heterogeneity of blood flow within organs and correlation of perfusion between organ pieces at different time points. A 400 microspheres/piece "rule" is often used in planning experiments or to determine whether experiments are valid. This rule is based on the statement that 400 microspheres must lodge in a region for 95% confidence that the observed flow in the region is within 10% of the true flow. The 400 microspheres precision rule, however, only applies to measurements of perfusion to a single region or organ piece. Examples, simulations, and an animal experiment were carried out to show that good precision for measurements of heterogeneity and correlation can be obtained from many experiments with <400 microspheres/piece. Furthermore, methods were developed and tested for correcting the observed heterogeneity and correlation to remove the Poisson "noise" due to discrete microsphere measurements. The animal experiment shows adjusted values of heterogeneity and correlation that are in close agreement for measurements made with many or few microspheres/piece. Simulations demonstrate that the adjusted values are accurate for a variety of experiments with far fewer than 400 microspheres/piece. Thus the 400 microspheres rule does not apply to many experiments. A "rule of thumb" is that experiments with a total of at least 15,000 microspheres, for all pieces combined, are very likely to yield accurate estimates of heterogeneity. Experiments with a total of at least 25,000 microspheres are very likely to yield accurate estimates of correlation coefficients.  (+info)

Corrosion resistance of the Pt-Fe-Nb magnets for dental-casting. (2/51)

Magnetic attachments have been used in clinical dental practice, but there is some difficulties associated with removable bridges. One possible solution is to make whole bridges of Pt-Fe magnet alloys and its abutment out of magnetic stainless steel by casting. In terms of castability and magnetic properties, the promising composition of the Pt-Fe-Nb magnet alloy is Pt-30.0 mass% Fe-0.6 mass% Nb and Pt-30.0 mass% Fe-0.5 mass% Nb-0.03 mass% Si. In the present study, the corrosion resistance of these alloys was investigated based on the elusion test, electrochemical behavior and surface characterization by EPMA analysis. The released elements from the Pt-Fe-Nb magnets were mainly Fe ions in quantities similar to that of stainless steel for biomedical use, and the Pt-Fe-Nb magnet alloy, the Pt-Fe-Nb-Si magnet alloy and platinum resembled each other in electrochemical behavior. The present findings suggest, that the Pt-Fe-Nb magnet alloy provides excellent corrosion resistance and has important clinical dental applications.  (+info)

High refractive index substrates for fluorescence microscopy of biological interfaces with high z contrast. (3/51)

Total internal reflection fluorescence microscopy is widely used to confine the excitation of a complex fluorescent sample very close to the material on which it is supported. By working with high refractive index solid supports, it is possible to confine even further the evanescent field, and by varying the angle of incidence, to obtain quantitative information on the distance of the fluorescent object from the surface. We report the fabrication of hybrid surfaces consisting of nm layers of SiO(2) on lithium niobate (LiNbO(3), n = 2.3). Supported lipid bilayer membranes can be assembled and patterned on these hybrid surfaces as on conventional glass. By varying the angle of incidence of the excitation light, we are able to obtain fluorescent contrast between 40-nm fluorescent beads tethered to a supported bilayer and fluorescently labeled protein printed on the surface, which differ in vertical position by only tens of nm. Preliminary experiments that test theoretical models for the fluorescence-collection factor near a high refractive index surface are presented, and this factor is incorporated into a semiquantitative model used to predict the contrast of the 40-nm bead/protein system. These results demonstrate that it should be possible to profile the vertical location of fluorophores on the nm distance scale in real time, opening the possibility of many experiments at the interface between supported membranes and living cells. Improvements in materials and optical techniques are outlined.  (+info)

The effects of particulate metals on cell viability of osteoblast-like cells in vitro. (4/51)

Effects of fifteen particulate objects, fourteen metals and one non-metal on cell viability of osteoblast-like cells were studied in vitro, to determine whether an adverse effect on cells could be induced by the particulate form or soluble ions. The Al, Ti, Zr, Nb, Ta, Cr, Mo, and Fe particulates depressed cell viability at higher particulate concentrations, but their extracts yielded no effect on cells except for Mo. On the other hand, little difference in cell viability between particulates and extracts was observed for Cu, Si, V, W, and Co. However, Mn and Ni yielded more adverse effects on cells in the case of the particulates than the extracts. These findings suggested that the effects of particulates on cells depended upon the direct effects of contact between particulates and cells, the indirect effects of dissolved ions and the kinds of particulate elements.  (+info)

Calcium-ion incorporation into titanium surfaces accompanied by electrochemical apatite-deposition. (5/51)

The depths of calcium-ion incorporation into a commercially pure titanium and an experimental beta-type titanium alloy were determined using Auger electron spectroscopy. After the electrochemical deposition of apatite, new compositional gradients appeared in the profiles in which the Ca and P concentrations gradually decreased as a function of the depth up to 6-8 nm. The relative concentration of Ca in the outermost layer was higher than that of P. On the other hand, after the soaking in a simulated body fluid, the relative concentration of P was higher than that of Ca in the outermost layer. These results suggested that Ca ions were well incorporated into the outermost oxide layer of titanium accompanied by the electrochemical apatite-deposition on its surface.  (+info)

In vitro genotoxic effects of different combinations of cobalt and metallic carbide particles. (6/51)

Occupational exposure to hard metal dust, consisting of tungsten carbide (WC) and metallic cobalt particles (Co), is associated with an increased risk of lung cancer, while no increased risk was observed in workers exposed to Co alone. In vitro, in human peripheral blood mononucleated cells (PBMC), we previously demonstrated that WC-Co is more genotoxic than Co and WC alone. A possible mechanism underlying this higher genotoxicity is a specific physicochemical interaction between Co and WC particles leading to the enhanced short-term formation of active oxygen species. The aim of this study was to evaluate the in vitro genotoxicity of other combinations of Co with metal carbide particles in comparison with WC-Co. The ability of Cr(3)C(2), Mo(2)C and NbC and of their powder mixtures with Co to induce DNA strand breaks and alkali-labile sites was assessed by the alkaline Comet assay and their potential to induce chromosome(/genome) mutations by the cytokinesis-block micronucleus test on human PBMC from two donors. PBMC were treated in vitro for 15 min, 24 h after the onset of PHA stimulation. In the micronucleus test, while the metal carbides alone did not increase the micronucleus frequency, Co alone and the four tested carbide-Co mixtures induced a statistically significant concentration-dependent increase in micronucleated binucleates. In addition to WC, NbC and Cr(3)C(2) particles were able to interact with Co, producing a higher mutagenic effect than the individual metal particles. Mo(2)C particles did not display interactive mutagenicity with Co in the micronucleus test, possibly related to their small specific surface area, compactness and/or spherical shape. With the Comet assay, applied directly at the end of the treatment, less clear results, due to inter-experimental and inter-donor variation, were obtained. These data indicate that particular interaction of a metal carbide with Co leading to enhanced mutagenicity is not specific for WC.  (+info)

Evolution of planetary cores and the Earth-Moon system from Nb/Ta systematics. (7/51)

It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 +/- 0.3) and the Moon (17.0 +/- 0.8) are below the chondritic ratio of 19.9 +/- 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago.  (+info)

Mechanical properties and grindability of dental cast Ti-Nb alloys. (8/51)

Aiming at developing a dental titanium alloy with better mechanical properties and machinability than unalloyed titanium, a series of Ti-Nb alloys with Nb concentrations up to 30% was made. They were cast into magnesia-based molds using a dental casting machine and the mechanical properties and grindability of the castings were examined. The hardness of the alloys with Nb concentrations of 5% and above was significantly higher than that of titanium. The yield strength and tensile strength of the alloys with Nb concentrations of 10% and above were significantly higher than those of titanium, while the elongation was significantly lower. A small addition of niobium to titanium did not contribute to improving the grindability of titanium. The Ti-30% Nb alloy exhibited significantly better grindability at low grinding speed with higher hardness, strength, and Young's modulus than titanium, presumably due to precipitation of the omega phase in the beta matrix.  (+info)