A Criterion for Stability of Two-Term Recurrence Sequences Modulo 2

The authors describe a technique for characterizing stable two-term recurrence sequences and apply the technique to identify stable sequences that were not previously known to be stable.     

Experimental demonstration of a pure third-order optical parametric downconversion process

We report what is, to the best of our knowledge, the first experiment on third-order optical difference frequency generation. The nonlinear medium is a phase-matched KTiOPO4 crystal pumped at 532 and 1665 nm in the picosecond regime. The proposed experimental configuration leads to an efficient and pure cubic process, with generation of 4.5 microJ/pulse at 1474 nm. This result opens the way to new quantum experiments on three-photon Greenberger-Horne-Zeilinger entanglement.     

Cloning, expression, and biochemical characterization of Streptomyces rubellomurinus genes required for biosynthesis of antimalarial compound FR900098

The antibiotics fosmidomycin and FR900098 are members of a unique class of phosphonic acid natural products that inhibit the nonmevalonate pathway for isoprenoid biosynthesis. Both are potent antibacterial and antimalarial compounds, but despite their efficacy, little is known regarding their biosynthesis. Here we report the identification of the Streptomyces rubellomurinus genes required for the biosynthesis of FR900098. Expression of these genes in Streptomyces lividans results in production of FR900098, demonstrating their role in synthesis of the antibiotic. Analysis of the putative gene products suggests that FR900098 is synthesized by metabolic reactions analogous to portions of the tricarboxylic acid cycle. These data greatly expand our knowledge of phosphonate biosynthesis and enable efforts to overproduce this highly useful therapeutic agent.     

On Deformations with the Same Principal Stretches

In the context of the finite strain theory, plane isochoric homogeneous deformations are considered. Inspired by two examples (plane elliptical and plane hyperbolic deformations), it is seen that for any such isochoric deformation the corresponding principal stretches are equal to those of simple shear provided there is a certain relation between the amount of shear of the simple shear and the parameters of the general plane deformation. Then, the link is established between any two homogeneous deformations which have identical principal stretches. It involves two rotations, one in the undeformed state and the other in the deformed state. These rotations are determined explicitly for an arbitrary isochoric homogeneous deformation and the simple shear with the same principal stretches.     

Evidence of C non-covalent isotope effects obtained by quantitative C nuclear magnetic resonance spectroscopy at natural abundance during normal phase liquid chromatography

Quantitative isotopic ¹³C NMR at natural abundance has been used to determine the site-by-site ¹³C/¹²C ratios in vanillin and a number of related compounds eluted from silica gel chromatography columns under similar conditions. Head-to-tail isotope fractionation is observed in all compounds at the majority of carbon positions. Furthermore, the site-specific isotope deviations show signatures characteristic of the position and functionality of the substituents present. The observed effects are more complex than would be obtained by simply summing the individual effects. Such detail is hidden when only the global ¹³C content is measured by mass spectrometry. In particular, carbon positions within the aromatic ring are found to show site-specific isotope fractionation between the solute and the stationary phase. These interactions, defined as non-covalent isotope effects, can be normal or inverse and vary with the substitution pattern present.     

Usefulness of capability indices in the framework of analytical methods validation

Analytical methods capability evaluation can be a useful methodology to assess the fitness of purpose of these methods for their future routine application. However, care on how to compute the capability indices have to be made. Indeed, the commonly used formulas to compute capability indices such as Cpk, will highly overestimate the true capability of the methods. Especially during methods validation or transfer, there are only few experiments performed and, using in these situations the commonly applied capability indices to declare a method as valid or as transferable to a receiving laboratory will conduct to inadequate decisions.