Oxygen deficient α-Fe2O3 photoelectrodes: a balance between enhanced electrical properties and trap-mediated losses

Intrinsic doping of hematite through the inclusion of oxygen vacancies (V_O) is being increasingly explored as a simple, low temperature route to preparing active water splitting α-Fe₂O_3–x photoelectrodes. Whilst it is widely accepted that the introduction of V_O leads to improved conductivities, little else is verified regarding the actual mechanism of enhancement. Here we employ transient absorption (TA) spectroscopy to build a comprehensive kinetic model for water oxidation on α-Fe₂O_3–x. In contrast to previous suggestions, the primary effect of introducing V_O is to block very slow (ms) surface hole – bulk electron recombination pathways. In light of our mechanistic research we are also able to identify and address a cause of the high photocurrent onset potential, a common issue with this class of electrodes. Atomic layer deposition (ALD) of Al₂O₃ is found to be particularly effective with α-Fe₂O_3–x, leading to the photocurrent onset potential shifting by ca. 200 mV. Significantly TA measurements on these ALD passivated electrodes also provide important insights into the role of passivating layers, that are relevant to the wider development of α-Fe₂O₃ photoelectrodes.     

Pyrolysis GC/MS analysis of a bacterial population in a saline activated sludge system—Identification of the origin of the pyrolysis product 2-methylpyrimidine

During the investigation of problems with the physical handling of sludge from a saline activated sludge wastewater system, pyrolysis/GC/MS was used in an attempt to determine whether changes in the bacterial population in the sludge were occurring. The pyrolysis GC/MS analysis revealed an unknown peak among other typical bacterial pyrolysis products. This unknown was identified as 2-methylpyrimidine. This pyrolysis product was only found in appreciable amounts in samples from other saline systems but not in freshwater systems analyzed as points of comparison for the system of concern. Further investigation confirmed the source of 2-methylpyrimidine to be ectoine, a compound produced by halophilic bacteria as a compatible solute for osmoadaptation. Pyrolysis GC/MS was shown to be a useful tool to indicate the presence of ectoine in halophilic bacteria.     

The Neutron Structure of the Formyl Peptide Receptor Antagonist Cyclosporin H (CsH) Unambiguously Determines the Solvent and Hydrogen-Bonding Structure for Crystal Form II

Abstract  

Single-crystal neutron diffraction data were collected at 20 K to a resolution of 1.05 ? on a crystal of the inverse formyl peptide receptor agonist cyclosporin H, CsH, (crystal form II, CsH-II) on the Laue diffractometer VIVALDI at the Institut Laue-Langevin (Grenoble). The solvent structure and hydrogen bonding network of CsH-II have been unambiguously determined by single-crystal neutron diffraction; the agreement factor R(F ²) is 13.5% for all 2726 reflections. All hydrogen atom positions, including methyl-group orientations, have been determined by crystallographic refinement. The neutron structure of cyclosporin provides unique and complementary insights into methyl orientation, hydrogen-bonding, and solvent interactions that are not available from X-ray analysis alone.     

Long-Range 31P-31P Spin Coupling Constants in the 31P NMR Spectra of Phosphite Triesters

Abstract

Data are presented on the magnitudes of ⁵ J _pp and ⁶ J _PP spin-spin coupling constants in the ³¹P NMR spectra of a variety of novel polyphosphite triesters.     

Back to the future: Polarised positron beams

Plans for the development of a polarised mono-energetic positron beam at the University of Bath are described. Pilot measurements with the existing beam, modified only by increasing the source-moderator separation, have demonstrated that the helicity of the present beam is sufficient to show sensitivity to ferromagnetism in bulk iron. However, an increase in flux and helicity is required if the beam is to be successfully used to probe magnetic structures of current technological interest, and strategies to achieve both are described. Potential applications in magnetic semiconductor structures and magnetic nanoparticles are discussed.     

Untersuchung von St?rke, Mehl, Teig und Backpulver

Ohne Zusammenfassung     

How Students “Unpack” the Structure of a Word Problem: Graphic Representations and Problem Solving

This research investigated how fourth and fifth grade students spontaneously ‘unpacked’ a word problem when generating a graphic representation to aid in problem solution. Relationships among the type of graphic representation produced, spatial visualization, drawing ability, gender, and problem solving also were examined and described. Instrumentation developed for the study included several math challenge tasks, a spatial visualization task, and a drawing task. For one of the math challenge tasks, students were instructed to draw a picture to assist them with problem solution. These graphic representations generated by students were rated as pictorial or as displaying some level of schematic representation. Schematic representations included germane information from the problem supportive of problem solution. Pictorial representations included expressive and extraneous elements not necessary for problem solution, with no schematic elements. Findings indicated that the majority of students rendered schematic representations, with girls more likely than boys to use schematic representations at a statistically significant level. Students who used schematic visual representations were more successful problem solvers than those pictorially representing problem elements. The more “schematic‐like” the visual representation, the more successful students were at problem solution. Drawing a pictorial representation in the math challenge task also was negatively correlated to drawing skill.     

Guaranteeing total balance in Metropolis algorithm Monte Carlo simulations

The condition of detailed balance has long been used as a proxy for the more difficult-to-prove condition of total balance, which along with ergodicity is required to guarantee convergence of a Markov Chain Monte Carlo (MCMC) simulation to the correct probability distribution. However, some simple-to-program update schemes such as the sequential and checkerboard Metropolis algorithms are known not to satisfy detailed balance for such common systems as the Ising model.     

Determination of barium,copper and yttrium in superconductor materials by inductively coupled plasma/atomic emission spectrometry

Barium, copper and yttrium (or a rare earth element) in superconductor and related materials were determined by inductively coupled plasma/atomic emission spectrometry. Relative standard deviations of repeated determinations were about 2%. The results obtained with this method agree within 2% (average relative deviation) of those obtained with chemical methods.