In situ neutron powder diffraction investigation of the hydration of tricalcium aluminate in the presence of gypsum

The hydration of a 1:3 molar ratio of tricalcium aluminate, Ca₃Al₂O₆, to gypsum, CaSO₄·2D₂O, was investigated at temperatures of 25, 50, and 80 °C using time-of-flight powder neutron diffraction combined with multiphase Rietveld structural refinement. It was shown that ettringite, Ca₆[Al(OD)₆]₂(SO₄)₃·∼26D₂O, was the first and only hydration product of the system, in contrast to a prior investigation which suggested the occurrence of a precursor phase prior to the formation of ettringite. Kinetics data showed that the hydration reaction is very sensitive to temperature: hydration at 25 °C was characterized by a single kinetic regime while hydration at higher temperatures consisted of two distinct kinetic regimes. The presence of two kinetic regimes was attributed to a change in either the dimensionality of the growth process or a change in the rate controlling mechanism in the hydration reaction.     

Approximate importance sampling Monte Carlo for data assimilation

Importance sampling Monte Carlo offers powerful approaches to approximating Bayesian updating in sequential problems. Specific classes of such approaches are known as particle filters. These procedures rely on the simulation of samples or ensembles of the unknown quantities and the calculation of associated weights for the ensemble members. As time evolves and/or when applied in high-dimensional settings, such as those of interest in many data assimilation problems, these weights typically display undesirable features. The key difficulty involves a collapse toward approximate distributions concentrating virtually all of their probability on an implausibly few ensemble members.

After reviewing ensembling, Monte Carlo, importance sampling and particle filters, we present some approximations intended to moderate the problem of collapsing weights. The motivations for these suggestions are combinations of (i) the idea that key dynamical behavior in many systems actually takes place on a low dimensional manifold, and (ii) notions of statistical dimension reduction. We illustrate our suggestions in a problem of inference for ocean surface winds and atmospheric pressure. Real observational data are used.     

Sum List Coloring Graphs

Let G=(V,E) be a graph with n vertices and e edges. The sum choice number of G is the smallest integer p such that there exist list sizes (f(v):v ∈ V) whose sum is p for which G has a proper coloring no matter which color lists of size f(v) are assigned to the vertices v. The sum choice number is bounded above by n+e. If the sum choice number of G equals n+e, then G is sum choice greedy. Complete graphs K_n are sum choice greedy as are trees. Based on a simple, but powerful, lemma we show that a graph each of whose blocks is sum choice greedy is also sum choice greedy. We also determine the sum choice number of K_2,n, and we show that every tree on n vertices can be obtained from K_n by consecutively deleting single edges where all intermediate graphs are sc-greedy.     

Studies towards the total synthesis of an epoxy isoprostane phospholipid,a potent activator of endothelial cells

We report studies toward the total synthesis of an epoxy isoprostane, namely the preparation of compound 9 which is an analogue of the elimination product 7 of the naturally occurring epoxy isoprostane 4 by a straightforward route using a three-component coupling, and have shown by several spectroscopic criteria that it closely resembles the natural material.     

Über zwei neue projektive natürliche Geometrien

Ohne Zusammenfassung     

Assessment of Nitrones as In Vivo Redox Sensors

Spin traps such as 5,5-dimethyl-1-pyrroline N-oxide, α-phenyl-tert-butyl nitrone, α-(4-pyridyl-1-oxide)-N-tert-butyl nitrone and newer generation 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide analogs have been known for years. What are the desired properties of good probes for measuring in vivo redox reactions in biological systems? These are specificity, sensitivity, rapid, high yield kinetics, low toxicity, high stability and easy to administer and target. Unfortunately, the nitrones perform poorly in almost all of these categories. Typical in vivo concentrations of spin trap approach 100 mM (assuming solubility and toxicity are not an issue), frequently yield 1% nitroxide or less stoichiometry, are typically unstable with time and frequently lack specificity. In vivo electron paramagnetic resonance (EPR) experiments need to have strong signals that correlate with redox chemistry. The resultant signal should be stable and not rapidly interconvert to other diamagnetic species. Fortunately, some newer probes of in vivo redox reactions in biological systems have come upon the horizon. In fact some have been around for a long time, but their virtues are becoming increasingly appreciated. This paper summarizes the disadvantages of nitrones versus the clear advantages of other probes of free radicals, redox state and the like by EPR. It also expands on the properties of nitroxides and nitrones as therapeutics.