Structural symmetry breaking of silicon‐containing poly(amide‐imide) oligomers and its relation to electrical conductivity and Raman‐active vibrations

Optically active poly(amide‐imide) oligomers were synthesized by direct polycondensation between an aromatic diamine and a dicarboxylic acid both containing a diphenylsilylene unit. The reaction was carried out using triphenyl phosphite/pyridine in the presence of CaCl₂ and N‐methyl‐2‐pyrrolidone as solvent. Oligomers were obtained in good yields and showed high solubility in common aprotic polar solvents. The precursors, monomers and poly(amide‐imide) oligomers were characterized using elemental analysis and Fourier transform infrared and NMR (¹H, ¹³C, ²⁹Si) spectroscopy. Additionally, the main vibrations of the functional groups (C?O, C?C or N? H) in the oligomers with respect to temperature were characterized using Raman spectroscopy. The glass transition temperature was determined by studying the Raman spectra and corroborated using differential scanning calorimetry. The thermal stability was studied using thermogravimetric analysis. The molecular mass of the compounds was obtained from matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry and their optical properties were analyzed using UV‐visible diode array spectrophotometry. The electronic properties of the oligomers as well as the delocalization of charge carriers within their structures were analyzed using conductance‐voltage curves, which showed that these materials are excellent candidates for integrated optoelectronic applications. Copyright © 2011 Society of Chemical Industry     

Finding Multiple Equivalence-Preserving Transformations in Combinational Circuits through Incremental-SAT

This paper introduces an approach to effectively exploit incremental SAT in order to search for multiple equivalence-preserving transformations of combinational circuits. Typical applications, such as redundancy removal with observability and external care conditions, adequate abstractions and other optimizations used in a state-of-the-art SAT-based model checker, can reap benefits from the proposed strategies. Our techniques exploit SAT incrementality, by iteratively refining the set of candidate transformations with a counter-example driven analysis, until an unsatisfiable point is reached. The key point of our technique is the ability to address satisfiable instances first, where SAT solvers are generally much faster than with unsatisfiable runs. We also discuss partitioning and problem reduction issues, that are fundamental in order to provide a scalable approach. Experimental results show the effectiveness of the proposed strategies.     

CONJUGATE HEAT AND MASS TRANSFER IN CONVECTIVE DRYING OF MULTIPARTICLE SYSTEMS. PART I: THEORETICAL CONSIDERATIONS

This is the first of two papers concerning conjugate transport in convective drying of multiparticle systems. In this study, a methodology for the solution of conjugate transport problems is proposed. The theoretical aspects and relevant assumptions are briefly discussed and the results for convective heat and mass transfer in assemblages of spheres are presented. It is shown that both heat and mass transfer rates for an assemblage of two spheres in tandem arragement are significantly different from those of a single sphere case, and that care should be taken when modeling multiparticle systems by means of single-particle analysis.     

Validating the Primary Care Posttraumatic Stress Disorder Screen and the Posttraumatic Stress Disorder Checklist with soldiers returning from combat.

The purpose of the research was to assess the diagnostic efficiency of the Primary Care Posttraumatic Stress Disorder Screen (PC-PTSD) and the Posttraumatic Stress Disorder Checklist (PCL) as clinical screening tools for active duty soldiers recently returned from a combat deployment. A secondary goal was to examine the item-level characteristics of both the PC-PTSD and the PCL. A validation study conducted with a sample of 352 service members showed that both the PC-PTSD and PCL had good diagnostic efficiency. The overall diagnostic efficiency assessed by the area under the curve (AUC) was virtually the same for both the PC-PTSD and PCL. The most efficient cutoff values for the PC-PTSD were either 2 or 3 "yes" responses with the latter favoring specificity. For the PCL, the most efficient cutoff values were between 30 and 34, mirroring recommended PCL cutoff values from some studies in primary care settings. The examination of item characteristics suggested a 4-item PCL with an AUC virtually identical to that of the full PCL. Item analyses also identified that the most discriminate item in both scales pertained to symptoms of avoidance. Implications and limitations are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chromium in basic foods of the Spanish diet: seafood, cereals, vegetables, olive oils and dairy products.

In the present study, graphite furnace atomic absorption spectrometry (GFAAS) was used to determine the content of total chromium in some basic foods of the Spanish diet. The seafood samples, vegetables and olive oils were mineralized previously with HNO3 and V2O5. A procedure of slurries with Triton X-100 was applied to dairy products. The temperature-time program was optimized for every type of sample. An assessment of the analytical characteristics of the method verifies their reliability. The content of Cr ranged between 0.004 and 0.079 microg/g in seafood (fresh wt.), from 0.007 to 0.456 microg/g in cereals and vegetables (fresh wt.), between not detectable and 0.625 microg/g in dairy products and between not detectable and 0.040 microg/g in olive oils. The high consumption of these products conditions the fact that they should be significant sources of Cr in the diet.     

Collaborative Learning vs. Lecture/Discussion: Students' Reported Learning Gains*

This study examined the extent to which undergraduate engineering courses taught using active and collaborative learning methods differ from traditional lecture and discussion courses in their ability to promote the development of students' engineering design, problem‐solving, communication, and group participation skills. Evidence for the study comes from 480 students enrolled in 17 active or collaborative learning courses/sections and six traditional courses/sections at six engineering schools. Results indicate that active or collaborative methods produce both statistically significant and substantially greater gains in student learning than those associated with more traditional instructional methods. These learning advantages remained even when differences in a variety of student pre‐course characteristics were controlled.     

Influence of nonionic emulsifiers on the properties of vinyl acetate/VeoVa10 and vinyl acetate/ethylene emulsions and paints

This paper presents results on the influence of the nonionic surfactant on the properties of vinyl acetate/VeoVa10^® and vinyl acetate/ethylene emulsions and paints made thereof. Emulsions were prepared in which the concentration of the nonionic surfactant and its degree of ethoxylation were varied. An increase of the nonionic emulsifier concentration and of the length of the ethylene oxide chain leads to dispersions with smaller particles and higher viscosities. Using these emulsions as binders in high pigmented paints, it was observed that the pigment binding capacity of the interior paints goes through a maximum which is located at a emulsifier concentration of about 2–3% and at a degree of ethoxylation of 17–28 mol ethylene oxide (EO). In (semi-) gloss paints, the gloss of the paint films improves with an increase of the emulsifier concentration and reaches a constant value at around 4% or a degree of ethoxylation of ca. 17 EO-moieties per molecule. The blocking of the films shows a drastic increase at a concentration above 4% and at a chain length of greater than 17 EO-moieties.