Quantum mechanical calculation of aqueuous uranium complexes: carbonate, phosphate, organic and biomolecular species

Background  

Quantum mechanical calculations were performed on a variety of uranium species representing U(VI), U(V), U(IV), U-carbonates, U-phosphates, U-oxalates, U-catecholates, U-phosphodiesters, U-phosphorylated N-acetyl-glucosamine (NAG), and U-2-Keto-3-doxyoctanoate (KDO) with explicit solvation by H₂O molecules. These models represent major U species in natural waters and complexes on bacterial surfaces. The model results are compared to observed EXAFS, IR, Raman and NMR spectra.     

The Cyclical Relationship Between Research and Standards: The Case of Principles and Standards for School Mathematics

The link between standards and research may not be clearcut. However, in this article the authors argue that there is a notable relationship between standards and research, one that is cyclical in nature. Using the standards for school mathematics developed by the National Council of Teachers of Mathematics (NCTM) as a case in point, the authors examine how NCTM's standards have influenced the agenda for mathematics education research and stimulated research on the impact of those standards. In turn, this and other research played a significant role in the development of NCTM's new Principles and Standards for School Mathematics. The authors conclude with a discussion of ways in which the Principles and Standards may continue this cyclical relationship in coming years, potentially promoting investigation of new research areas and systematic research on the impact of standards.     

Molecular modeling of cellulose in amorphous state. III. An innovative elastomeric crosslink system

The flexibility of molecular structures of rubber materials was evaluated using molecular modeling techniques to develop new crosslink agents which improve deformation recovery of cellulose without significant loss of the mechanical strength. Among the studied structures Poly(propylene oxide) (PPO) pentamer appears to be the most flexible and coiled one. Our calculation results showed that, cellulose crosslinked with PPO pentamers had similar deformation recovery to that crosslinked with DMDHEU. No conformation transitions were observed in these crosslinks when cellulose models were extended to 15% strain, which is consistent with the previous result that conformation transitions in crosslinks should be avoided upon extension to achieve a good recovery on crosslinked cellulose. In addition, PPO crosslinks did not significantly affect the breaking strain of cellulose based upon the cavity volume calculations, and they helped to remove the stress concentration among cellulose chains as suggested by the results of hydrogen bonding analysis. Thus, breaking strength of cellulose might not be significantly affected by PPO crosslinks as well. The preliminary experimental results confirmed above observations. Therefore, PPO pentamer appears to be a promising elastomeric backbone structure of crosslinking agents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1821–1833, 2007     

Phosphonium labeling for increasing metabolomic coverage of neutral lipids using electrospray ionization mass spectrometry

Mass spectrometry has become an indispensable tool for the global study of metabolites (metabolomics), primarily using electrospray ionization mass spectrometry (ESI‐MS). However, many important classes of molecules such as neutral lipids do not ionize well by ESI and go undetected. Chemical derivatization of metabolites can enhance ionization for increased sensitivity and metabolomic coverage. Here we describe the use of tris(2,4,6,‐trimethoxyphenyl)phosphonium acetic acid (TMPP‐AA) to improve liquid chromatography (LC)/ESI‐MS detection of hydroxylated metabolites (i.e. lipids) from serum extracts. Cholesterol which is not normally detected from serum using ESI is observed with attomole sensitivity. This approach was applied to identify four endogenous lipids (hexadecanoyl‐sn‐glycerol, dihydrotachysterol, octadecanol, and alpha‐tocopherol) from human serum. Overall, this approach extends the types of metabolites which can be detected using standard ESI‐MS instrumentation and demonstrates the potential for targeted metabolomics analysis. Published in 2009 by John Wiley & Sons, Ltd.     

Optical methods in experimental mechanics

Experimental Techniques -     

The emergence of local norms in networks

We develop an explanation of the emergence of local norms and the associated phenomenon of geographical variation in behavior. Individuals are assumed to interact locally with neighbors in an environment with a network externality. Although many patterns of behavior are possible, the dispersed interactive choices of agents are shown to select behavior that is locally uniform but globally diverse. The range of applications of the theory includes regional variation in the practice of medicine, technology choice, and corruption. The framework is also useful for further developing our understanding of important phenomena like lock‐in, critical thresholds, and contagion. © 2006 Wiley Periodicals, Inc. Complexity 11: 65–83, 2006     

Characterization of Astaxanthin Nanoemulsions Produced by Intense Fluid Shear through a Self-Throttling Nanometer Range Annular Orifice Valve-Based High-Pressure Homogenizer

Stable, oil-in-water nanoemulsions containing astaxanthin (AsX) were produced by intense fluid shear forces resulting from pumping a coarse reagent emulsion through a self-throttling annular gap valve at 300 MPa. Compared to crude emulsions prepared by conventional homogenization, a size reduction of over two orders of magnitude was observed for AsX-encapsulated oil droplets following just one pass through the annular valve. In krill oil formulations, the mean hydrodynamic diameter of lipid particles was reduced to 60 nm after only two passes through the valve and reached a minimal size of 24 nm after eight passes. Repeated processing of samples through the valve progressively decreased lipid particle size, with an inflection in the rate of particle size reduction generally observed after 2–4 passes. Krill- and argan oil-based nanoemulsions were produced using an Ultra Shear Technology™ (UST™) approach and characterized in terms of their small particle size, low polydispersity, and stability.     

Combining transmission geometry laser ablation and a non‐contact continuous flow surface sampling probe/electrospray emitter for mass spectrometry based chemical imaging

This paper describes the coupling of ambient pressure transmission geometry laser ablation with a liquid‐phase sample collection into a continuous flow surface sampling probe/electrospray emitter for mass spectrometry based chemical imaging. The flow probe/emitter device was placed in close proximity to the surface to collect the sample plume produced by laser ablation. The sample collected was immediately aspirated into the probe and onto the electrospray emitter, ionized and detected with the mass spectrometer. Freehand drawn ink lines and letters and an inked fingerprint on microscope slides were analyzed. The circular laser ablation area was about 210 µm in diameter and under the conditions used in these experiments the spatial resolution, as determined by the size of the surface features distinguished in the chemical images, was about 100 µm. Published in 2011 by John Wiley & Sons, Ltd.