The application of neutron powder diffraction techniques for crystallographic studies at high pressures

Abstract

For phase transition studies, neutron powder diffraction offers a number of important advantages over x-ray based techniques, for example ab-initio structural determination. There are two distinct methods using either monochromatic angular dispersive geometry on a reactor cold source or time-of-flight energy-dispersive techniques requiring a pulsed neutron source. Both techniques offer comparable resolution but have differing advantages for high pressure studies. Recent studies illustrate the benefits of the two methods and the application of these to solve unknown crystal structures.     

Predictive model for ice formation on superhydrophobic surfaces

The prevention and control of ice accumulation has important applications in aviation, building construction, and energy conversion devices. One area of active research concerns the use of superhydrophobic surfaces for preventing ice formation. The present work develops a physics-based modeling framework to predict ice formation on cooled superhydrophobic surfaces resulting from the impact of supercooled water droplets. This modeling approach analyzes the multiple phenomena influencing ice formation on superhydrophobic surfaces through the development of submodels describing droplet impact dynamics, heat transfer, and heterogeneous ice nucleation. These models are then integrated together to achieve a comprehensive understanding of ice formation upon impact of liquid droplets at freezing conditions. The accuracy of this model is validated by its successful prediction of the experimental findings that demonstrate that superhydrophobic surfaces can fully prevent the freezing of impacting water droplets down to surface temperatures of as low as -20 to -25 °C. The model can be used to study the influence of surface morphology, surface chemistry, and fluid and thermal properties on dynamic ice formation and identify parameters critical to achieving icephobic surfaces. The framework of the present work is the first detailed modeling tool developed for the design and analysis of surfaces for various ice prevention/reduction strategies.     

Two-dimensional solvent-mediated phase transformation in lipid membranes induced by sphingomyelinase

The spatial pattern changes in model raft membranes during sphingomyelinase (SMase)-induced solvent-mediated phase transformation are characterized in terms of a model that combines three major kinetic processes suggested by experimental observations: the release of sphingomyelin (SM) by the dissolution of SM-enriched domains within the raft membrane, the diffusion of SM from the dissolution sites to the reaction site in a solvent-like fluid lipid phase, and the consumption of SM by the enzymatic reaction at this reaction site, termed an SMase feature. Such processes may be responsible for the control of morphological changes in cell membrane organization, which are suggested to influence the signal transduction through the cell membrane walls. The model predictions are shown to be consistent with our previously reported experimental results. We numerically evaluated the range of possible scenarios of spatial pattern change and provide analytical expressions for SM-domain-area change rates and total dissolution times for several limiting cases. The model results suggest that it may be possible to tune the pattern changes by adjusting the relative importance of each of the three kinetic processes, which can be discriminated through experimentally measurable time-dependent SM concentration distributions or SM-domain-area variations with time.     

Vibrational spectroscopy at very high pressures. Part 35.1 A Raman study of K2M(CN)4, (M = Zn,Cd, Hg)

Each of the complex cyanides K₂M(CN)₄, (M = Zn, Cd, Hg), shows two high pressure first-order phase transitions which have been characterized using Raman spectroscopy. The phase changes are at 1.5 and 8.5 kbar for M = Hg, 3 and 8 kbar for M = Cd, and 4 and 14 kbar for M = Zn. It is concluded that, for each material, phase II has the trigonally-distorted spinel structure of room temperature Rb₂Hg(CN)₄, whilst phase III is probably of the hausmanite type (a tetragonally-distorted spinel).     

Stage effects of negative emotion on spatial and verbal working memory

Background  

The effects of negative emotion on different processing periods in spatial and verbal working memory (WM) and the possible brain mechanism of the interaction between negative emotion and WM were explored using a high-time resolution event-related potential (ERP) technique and time-locked delayed matching-to-sample task (DMST).     

Mono‐ and Di‐Potassium Derivatives of Benzenepentacarboxylic Acid

The synthesis and structure of the hydrated mono‐ and di‐potassium salts of benzenepentacarboxylic acid are reported – [K(H₄BPC)(H₂O)₂]·(H₂O) 1 and [K₂(H₃BPC)(H₂O)₃]·(H₂O) 2 (BPC = benzenepentacarboxylate). In both instances the structures are complex coordination networks, predominantly containing η¹ binding modes of the carboxylate and carboxylic acid groups, although bridging (O,O) and (O,O′) carboxylates and μ₂‐H₂O ligands also feature. Extensive hydrogen bonding is present through the carboxylic acid groups and both coordinated and interstitial water molecules.