Charge density wave Madelung constant in a system of linear chains

The dependence of the Madelung constant upon the relative phase and distance between the charge density waves, occurring on the parallel chains of the chain system, is calculated. The position of the most unstable mode for the Peierls instability is discussed and an expression for the perpendicular correlation length in KCP suggested.     

Role of electronic correlations in the stability of diatomic and triatomic clusters of 5d adatoms on W(110)

The experimental interaction energy of 5d dimers on W(110) is weak and decreases when going from Ta₂ to Re₂ where it vanishes and raises again, although more slowly, from Re₂ to Pt₂. We show here that such a behaviour, which cannot be explained within a one electron theory, can be interpreted by taking into account electronic correlation effects.     

Phase distribution in vessels during depressurisation

Systematic vessel depressurisation experiments have been performed in the l laboratory and in a pilot plant using initially saturated refrigerant R12 as the model fluid. Transient (vertical) distribution of the void fraction across the vessel height and the two phase level swell are affected by the initial liquid level, relief cross-section initial pressure and initial degassing of the liquid pool. The measurements also show that at different times a variety of vertical phase distributions are obtained; only after 1.5 s at the earliest is a linearly increasing void fraction over the vessel height obtained     

Generation of a Genetically Encoded,Photoactivatable Intein for the Controlled Production of Cyclic Peptides

Cyclic peptides are important natural products and hold great promise for the identification of new bioactive molecules. The split‐intein‐mediated SICLOPPS technology provides a generic access to fully genetically encoded head‐to‐tail cyclized peptides and large libraries thereof (SICLOPPS=split‐intein circular ligation of peptides and proteins). However, owing to the spontaneous protein splicing reaction, product formation occurs inside cells, making peptide isolation inconvenient and precluding traditional in vitro assays for inhibitor discovery. The design of a genetically encoded, light‐dependent intein using the photocaged tyrosine derivative ortho‐nitrobenzyltyrosine incorporated at an internal, non‐catalytic position is now reported. Stable intein precursors were purified from the E. coli expression host and subsequently subjected to light activation in vitro for both the regular protein splicing format and cyclic peptide production, including the natural product segetalin H as an example. The activity of the intein could also be triggered in living cells.     

Synthesis of poly(p‐xylylene)s by base‐induced 1,6‐dehydrohalogenation – Control of the degree of polymerization

Phenylethyl‐substituted poly(p‐xylylene) (PEPPX) was prepared by base‐induced 1,6‐dehydrohalogenation of the corresponding 4‐chloromethyltoluene. Very high degrees of polymerization of about 3150 were obtained already at low conversions. Several standard retarders for radical polymerizations failed to limit the degree of polymerization significantly. However, best control was accomplished by the addition of dibenzoyl peroxide. The degree of polymerization of PEPPX was depressed to about 110 by addition of 10–15 mol‐% of dibenzoyl peroxide.     

Extrapolation of Laboratory Reaction Kinetic Data for Relief Vent Design in the Case of a Heterogeneous Runaway Reaction

The relief area sizing of safety devices in the case of a postulated thermal runaway condition requires reaction kinetic data, usually measured in dedicated adiabatic calorimeters. In the course of the design, it is then assumed that the same reaction kinetic data prevail on the laboratory and production scale. This assumption seems to be valid in the case of homogeneous reaction systems. In contrast to this the results of experiments with a heterogeneous system have shown that the stirring intensity and the reactor size have a considerable influence on the reaction progress.This revised version was published online in November 2005 with corrections to the Cover Date.     

A Perspective on Heterogeneous Catalysts for the Selective Oxidation of Alcohols

Selective oxidation of higher alcohols using heterogeneous catalysts is an important reaction in the synthesis of fine chemicals with added value. Though the process for primary alcohol oxidation is industrially established, there is still a lack of fundamental understanding considering the complexity of the catalysts and their dynamics under reaction conditions, especially when higher alcohols and liquid-phase reaction media are involved. Additionally, new materials should be developed offering higher activity, selectivity, and stability. This can be achieved by unraveling the structure–performance correlations of these catalysts under reaction conditions. In this regard, researchers are encouraged to develop more advanced characterization techniques to address the complex interplay between the solid surface, the dissolved reactants, and the solvent. In this mini-review, we report some of the most important approaches taken in the field and give a perspective on how to tackle the complex challenges for different approaches in alcohol oxidation while providing insight into the remaining challenges.     

Snake's perspective on heat: reconstruction of input using an imperfect detection system

Two groups of snakes possess an infrared detection system that is used to create a heat image of their environment. In this Letter we present an explicit reconstruction model, the "virtual lens," which explains how a snake can overcome the optical limitations of a wide aperture pinhole camera, and how ensuing properties of the receptive fields on the infrared-sensitive membrane may explain the behavioral performance of this sensory system. Our model explores the optical quality of the infrared system by detailing how a functional representation of the thermal properties of the environment can be created. The model is easy to implement neuronally and agrees well with available neuronal, physiological, and behavioral data on the snake infrared system.     

Genotyping fetal paternally inherited SNPs by MALDI-TOF MS using cell-free fetal DNA in maternal plasma: influence of size fractionation

The determination of fetal point mutations from fetal cell-free DNA (cf-DNA) in maternal plasma is technically challenging due to the preponderance of maternal sequences. It has recently been shown that fetal cf-DNA sequences are smaller than maternal ones and that the selection of small cf-DNA fragments by size fractionation by agarose gel electrophoresis leads to the enrichment of fetal cf-DNA sequences, thereby permitting the detection of otherwise masked fetal point mutations. In a separate development, the use of MALDI-TOF MS has also been shown to facilitate the detection of fetal point mutations from cf-DNA in maternal plasma. In this study, a combination of these approaches was examined. cf-DNA was extracted from 18 maternal plasma samples, 10 taken at term and 8 obtained early in the second trimester. A total of 41 SNP loci were examined in size-fractionated and total cf-DNA using either a conventional homogeneous MassEXTEND (hME) assay or a nucleotide-specific single allele base extension reaction (SABER) assay. The analysis of total cf-DNA indicated that size fractionation considerably enhanced the sensitivity of the standard hME assay, especially for samples taken early in pregnancy. Size fractionation also rendered the signals obtained by the SABER assay more precise.