Neutron Reflectometry Characterization of Interface Width between Sol-Gel Titanium Dioxide and Silicon Dioxide Thin Films

Neutron reflectometry (NR) was used to directly measure the interface width between a titanium dioxide and a silicon dioxide film deposited by sol-gel processing. In a bilayer heated to 450°C, NR measurements showed that the interface width is 0.8 nm. This width is the same as the roughness of a sol-gel silicon dioxide surface after the same heat treatment, suggesting no interdiffusion or mixing at the bilayer interface.     

Microstructure and Dielectric Characteristics of (PbxBa0.5−xSr0.5)TiO3 Ceramics

Microstructural and dielectric properties of the Pb _x Ba _0.5__x —Sr_0.5TiO₃ system have been studied. It is found that this system forms a solid solution in the entire composition range (0.0≤ x ≤0.5) and is cubic for the x = 0, 0.1, and 0.2 compositions and tetragonal for other compositions. Measurements of the dielectric constant as a function of temperature reveal that this material is ferroelectric at room temperature for the x > 0.2 compositions and has a broad paraelectric-ferroelectric transition region. No shift in the dielectric maxima was noted; however, there is a slight spread in the dielectric constant with frequency for the x = 0.4 composition. A quantitative model to mathematically analyze the effect of composition fluctuations on the dielectric broadening for a ternary system is presented. Transmission electron microscopic studies reveal the presence of 90° ferroelectric domains oriented along the {01     } planes for the x = 0.3 and 0.4 compositions.     

Interrelations of social support measures: Theoretical and practical implications.

To obtain a clearer picture of what constitutes social support, we conducted three studies to compare measures of different conceptions of social support. Relations of these instruments to various personality measures were also investigated. Subdividing the construct into discrete functions did not add to the sensitivity of the indices. Measures of received support and support networks were not strongly related to most of the perceived available support measures. Interview and questionnaire approaches were similar in the information they evoked about close supportive relationships. The results suggest that measures of perceived available support, regardless of the way the instruments attempt to break down the construct, generally assess the extent to which an individual is accepted, loved, and involved in relationships in which communication is open. Psychometric characteristics of the measures were associated with differential sensitivity over the range of supportive relationships. The theoretical implications of the findings are discussed with emphasis on the common core underlying social support indices. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Familiarity and plausibility in conceptual combination: Reply to Gagné and Spalding (2006).

E. J. Wisniewski and G. L. Murphy (see record 2004-22496-015) suggested that the apparent effects of relation frequency in C. L. Gagné and E. J. Shoben's (1997; see record 1997-02349-004) conceptual combination experiments could be explained by differences between the familiarity and plausibility of their stimuli (noun-noun phrases). However, C. L. Gagné and T. L. Spalding (see record 2006-20573-017) argued that Wisniewski and Murphy's measures of plausibility and frequency are both sensitive to relation frequency. They also suggested that the stimuli were mostly novel, such that differences in familiarity could not explain Gagné and Shoben's findings. The current authors focus on the theoretical rationale for the plausibility and familiarity variables, arguing that the original interpretation of their findings is correct. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for Remote Effects of Dreissenid Mussels on the Amphipod Diporeia: Analysis of Lake Ontario Benthic Surveys, 1972–2003

The status of invasive dreissenid mussels (Dreissena polymorpha and D. bugensis) and native amphipods (Diporeia spp.) in Lake Ontario was assessed in 2003 and compared with historical data. D. polymorpha (zebra mussels) were rarely observed in 2003, having been displaced by D. bugensis (quagga mussels). D. bugensis expanded its depth range from 38 m depth in 1995 to 174 m in 2003 and this dreissenid reached densities averaging 8,000/m² at all sites < 90 m. During the same time period, Diporeia populations almost completely disappeared from 0–90 m depth, continuing a declining trend from 1994–1997 reported in previous studies. The average density of Diporeia in the 30–90 m depth interval decreased from 1,380/m² to 63/m² between 1997 and 2003. Prior to 2003, areas deeper than 90 m represented a refuge for Diporeia, but even these deep populations decreased, with densities declining from 2,181/m2 in 1999 to 545/m2 in 2003. Two common hypotheses for the decline of Diporeia in the Great Lakes are food limitation and a toxin/pathogen associated with dreissenid pseudofeces. The Diporeia decline in deep waters preceded the expansion of D. bugensis to these depths, and suggests that shallow dreissenid populations remotely influence profundal habitats. This pattern of decline is consistent with mechanisms that act from some distance including nearshore dreissenid grazing and downslope transport of pseudofeces.     

Carbon based electronic materials: applications in electron field emission

The influence of the different types of bonding present in a range of carbon based materials is discussed as a precursor to describing the field emission characteristics of carbon cold cathode materials. Some of the controlling factors which govern electron emission from carbon based cathodes are discussed. It is shown that from disordered carbon films the interplay between the clustered sp² phase and the insulating sp³ matrix is important. The transition from a ‘back contact’ to ‘front surface’ controlled emission mechanism is described in terms of the sp² content and field penetration. A possible reason for high field enhancement factors found in disordered films also is provided. It is further shown that changes to the sp² phase by current stressing can improve the field emission characteristics. Emission from carbon nanotubes is also discussed and the prospects for new types of nanotube – polymer composite based cathodes are also considered.     

Biophysical Model of Larval Yellow Perch Advection and Settlement in Lake Michigan

Potential for large-scale physical transport processes to affect recruitment of Lake Michigan yellow perch (Perca flavescens) was studied by examining the variation in larval distribution, growth rate, and settlement during June–August 1998–2003 using a 3D particle transport model linked with an individual-based bioenergetics growth model. In all years, virtual larvae were released nearshore in southwestern Lake Michigan, a known and important spawning region for yellow perch. For any given year, the same circulation pattern and water temperature either promoted or reduced yellow perch settlement depending on the consumption rates and settlement size chosen in the growth model. Increased consumption increased the number of settled larvae and expanded the total area where larvae settled, whereas increased settlement size reduced the number of settled larvae and reduced the overall settlement area. Interannual variability in circulation patterns and water temperature also resulted in contrasting larval settlement rates, settlement locations, and size of settlement areas between years. Model predictions were most consistent with field observations of age-0 yellow perch from Illinois and Michigan waters when settlement was assumed to occur at 50 mm. Moreover, our model suggests that larvae originating from southwestern Lake Michigan can recruit anywhere within the southern basin and even in the northern basin. Future model improvement will require information on the relative contribution of various sectors to the larval pool, their distribution with reference to the hydrodynamic landscape, the feeding and growth of yellow perch during their pelagic phase, and the size at transition to demersal stage.