Measuring Two Key Parameters of H3 Color Centers in Diamond

A method of measuring two key parameters of H3 color centers in diamond has been created as part of a continuing effort to develop tunable, continuous-wave, visible lasers that would utilize diamond as the lasing medium. (An H3 color center in a diamond crystal lattice comprises two nitrogen atoms substituted for two carbon atoms bonded to a third carbon atom. H3 color centers can be induced artificially; they also occur naturally. If present in sufficient density, they impart a yellow hue.) The method may also be applicable to the corresponding parameters of other candidate lasing media. One of the parameters is the number density of color centers, which is needed for designing an efficient laser. The other parameter is an optical-absorption cross section, which, as explained below, is needed for determining the number density. The present method represents an improvement over prior methods in which optical-absorption measurements have been used to determine absorption cross sections or number densities. Heretofore, in order to determine a number density from such measurements, it has been necessary to know the applicable absorption cross section; alternatively, to determine the absorption cross section from such measurements, it has been necessary to know the number density. If, as in this case, both the number density and the absorption cross section are initially unknown, then it is impossible to determine either parameter in the absence of additional information

Factorization of the Compressible Navier-Stokes Equations

The Navier-Stokes equations for a Newtonian ideal gas are examined to determine the factorizable form of the equations relevant to the construction of a factorizable relaxation scheme. The principal linearization of the equations is found by examining the relative magnitude of the terms for short-wavelength errors. The principal part of the operator is then found. Comparison of the factors of the Navier-Stokes and Euler equations differ qualitatively because of the coupling of entropy and pressure through thermal diffusion. Special cases of the factorization are considered

Determination of the Density of Fluid Bismuth by means of the Oncosimeter

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A Study of Multigrid Preconditioners Using Eigensystem Analysis

The convergence properties of numerical schemes for partial differential equations are studied by examining the eigensystem of the discrete operator. This method of analysis is very general, and allows the effects of boundary conditions and grid nonuniformities to be examined directly. Algorithms for the Laplace equation and a two equation model hyperbolic system are examined

Effect of Light-Cure Initiation Time on Polymerization Efficiency and Orthodontic Bond Strength with a Resin-Modified Glass-Ionomer

Objectives –  The polymerization and acid–base reactions in resin-modified glass-ionomers (RMGI) are thought to compete with and inhibit one another. To examine the effect of visible light-cure (VLC) delay on the polymerization efficiency and orthodontic bond strength of a dual-cured RMGI. Setting and Sample Population –  The Orthodontics Graduate Program at Marquette University. An in vitro study utilizing 72 freshly extracted human bicuspid teeth. Materials and Methods –  A RMGI light-cured immediately, 2.5, 5, or 10 min after mixing comprised the experimental groups. Isothermal and dynamic temperature scan differential scanning calorimetry (DSC) analysis of the RMGI was performed to determine extents of VLC polymerization and acid–base reaction exotherms. Human premolars (n = 18/group) were bonded with the RMGI. Shear bond strength and adhesive remnant index (ARI) scores were determined. Results –  Differential scanning calorimetry results showed the 10-min-delay RMGI group experienced significantly (p \u3c 0.05) lower VLC polymerization compared with the other groups. Acid–base reaction exotherms were undetected in all groups except the 10-min delay group. No significant differences (p \u3e 0.05) were noted among the groups for mean shear bond strength. A chi-square test showed no significant difference (p = 0.428) in ARI scores between groups. Conclusions –  Delay in light-curing may reduce polymerization efficiency and alter the structure of the RMGI, but orthodontic shear bond strength does not appear to be compromised

An Analysis of the Factors Affecting the Career Orientation of Federal Civilian Engineers

This study was conducted to analyze the factors that affect the career orientation of federal civilian engineers at the Naval Avionics Center in Indianapolis, Indiana. One hundred and sixty-seven scientists and engineers from several engineering divisions were surveyed regarding turnover intentions. Based on literature reviews in the area of turnover with this particular population, a model was developed containing several factors related to intent to remain in the organization. Results indicated that this model predicts the turnover intention with 87.5 percent accuracy. Findings are interpreted in light of ongoing efforts on an organization-wide basis to introduce change in the Center's culture through a quality management program. Keywords: Career orientation, Job satisfaction turnover. (sdw)Naval Avionics Center, Civilian Personnel Departmenthttp://archive.org/details/analysisoffactor00robeN0016389WR90118NAApproved for public release; distribution is unlimited

Evaluating multiple causes of persistent low microwave backscatter from Amazon forests after the 2005 drought

Amazonia has experienced large-scale regional droughts that affect forest productivity and biomass stocks. Space-borne remote sensing provides basin-wide data on impacts of meteorological anomalies, an important complement to relatively limited ground observations across the Amazon’s vast and remote humid tropical forests. Morning overpass QuikScat Ku-band microwave backscatter from the forest canopy was anomalously low during the 2005 drought, relative to the full instrument record of 1999–2009, and low morning backscatter persisted for 2006–2009, after which the instrument failed. The persistent low backscatter has been suggested to be indicative of increased forest vulnerability to future drought. To better ascribe the cause of the low post-drought backscatter, we analyzed multiyear, gridded remote sensing data sets of precipitation, land surface temperature, forest cover and forest cover loss, and microwave backscatter over the 2005 drought region in the southwestern Amazon Basin (4°-12°S, 66°-76°W) and in adjacent 8°x10° regions to the north and east. We found moderate to weak correlations with the spatial distribution of persistent low backscatter for variables related to three groups of forest impacts: the 2005 drought itself, loss of forest cover, and warmer and drier dry seasons in the post-drought vs. the pre-drought years. However, these variables explained only about one quarter of the variability in depressed backscatter across the southwestern drought region. Our findings indicate that drought impact is a complex phenomenon and that better understanding can only come from more extensive ground data and/or analysis of frequent, spatially-comprehensive, high-resolution data or imagery before and after droughts

Dependence of the Chiral Symmetry Restoration Transition on the Quark Self-Energy Kernel

The dependence of the dressed quark propagator on the quark chemical potential is investigated in various models based on the Dyson-Schwinger equations. We find that the critical chemical potential of the chiral symmetry restoration transition is strongly dependent on the nature of the interaction kernel in the infrared region.Comment: 10 pages, 3 figures, minor change to introduction, accepted for publication in Phys. Lett.