Optimization of magnetic field sweep and field modulation amplitude for continuous-wave EPR oximetry

For continuous-wave electron paramagnetic resonance spectroscopy, what settings of magnetic field sweep width and field modulation amplitude yield the best accuracy in estimated linewidth? Statistical bounds on estimation error presented in this work provide practical guidance: set the sweep width and modulation amplitude to 8 and 4 times the half-width half-maximum linewidth, Γ, respectively. For unknown linewidths in the range [Γ(min),Γ(max)] the worst-case estimation error is minimized by using settings designed for Γ(max). The analysis assumes a Lorentzian lineshape and a constant modulation amplitude across the extent of the irradiated paramagnetic probe. The analytical guidelines are validated using L-band spectroscopy with a particulate LiNc-BuO probe.     

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.     

TEM study of the origin of the surface microroughness in DSL photoetched Si-implanted GaAs wafers

TEM has been used to study the origin of the surface microroughness that formed in both ²⁹Si as-implanted and rapid thermal annealed LEC undoped GaAs wafers after DSL photoetching. The degree of microroughness increased as the implant dose increased from 3 × 10¹² to 3 × 10¹⁴ atoms/cm². It has been found that such a microroughness is due to the fine-scale damage induced by the implantation in the as-implanted wafers and to interstitial dislocation loops in the implanted and then annealed wafers. Microroughness appears during DSL etching because such defects are effective recombination centres for the holes involved in the dissolution of the GaAs surface so that the wafers etch slower at the point-defect clusters and dislocation loops.     

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.     

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.