Evidence for hard and soft substructures in thermoelectric SnSe

SnSe is a topical thermoelectric material with a low thermal conductivity which is linked to its unique crystal structure. We use low-temperature heat capacity measurements to demonstrate the presence of two characteristic vibrational energy scales in SnSe with Debye temperatures thetaD1 = 345(9) K and thetaD2 = 154(2) K. These hard and soft substructures are quantitatively linked to the strong and weak Sn-Se bonds in the crystal structure. The heat capacity model predicts the temperature evolution of the unit cell volume, confirming that this two-substructure model captures the basic thermal properties. Comparison with phonon calculations reveals that the soft substructure is associated with the low energy phonon modes that are responsible for the thermal transport. This suggests that searching for materials containing highly divergent bond distances should be a fruitful route for discovering low thermal conductivity materials.Comment: Accepted by Applied Physics Letter

The DNA/RNA-Dependent RNA Polymerase QDE-1 Generates Aberrant RNA and dsRNA for RNAi in a Process Requiring Replication Protein A and a DNA Helicase

The Neurospora RNA-dependent RNA polymerase QDE-1 is an RNA polymerase that can use both RNA and DNA as templates, suggesting a new mechanism for small RNA production

Transcription-replication conflicts: How they occur and how they are resolved

The frequent occurrence of transcription and DNA replication in cells results in many encounters, and thus conflicts, between the transcription and replication machineries. These conflicts constitute a major intrinsic source of genome instability, which is a hallmark of cancer cells. How the replication machinery progresses along a DNA molecule occupied by an RNA polymerase is an old question. Here we review recent data on the biological relevance of transcription-replication conflicts, and the factors and mechanisms that are involved in either preventing or resolving them, mainly in eukaryotes. On the basis of these data, we provide our current view of how transcription can generate obstacles to replication, including torsional stress and non-B DNA structures, and of the different cellular processes that have evolved to solve them

Biosorption of hexavalent chromium from aqueous solution by using prawn pond algae (Sphaeroplea)

284-289Biosorption of chromium (VI) on prawn pond biomass Sphaeroplea algae in natural and acid treated forms has been studied by using batch technique. The equilibrium biosorption level is a function of solution pH, agitation time, initial metal ion concentration and adsorbent dose at room temperature. Both Freundlich and Langmuir adsorption models are suitable for describing the biosorption of chromium (VI) on the two forms of algae while the adsorption process follows the Legergren kinetic model. The biomass has been characterized by FTIR spectra. Surface area values of the biomass are 0.9 and 2.1 m²/g for natural and acid treated forms respectively. At the optimum conditions, the maximum adsorption capacity is found to be 29.8 mg/g and 158.7 mg/g in natural and acid treated forms respectively