Path integral evaluation of equilibrium isotope effects

A general and rigorous methodology to compute the quantum equilibrium isotope effect is described. Unlike standard approaches, ours does not assume separability of rotational and vibrational motions and does not make the harmonic approximation for vibrations or rigid rotor approximation for the rotations. In particular, zero point energy and anharmonicity effects are described correctly quantum mechanically. The approach is based on the thermodynamic integration with respect to the mass of isotopes and on the Feynman path integral representation of the partition function. An efficient estimator for the derivative of free energy is used whose statistical error is independent of the number of imaginary time slices in the path integral, speeding up calculations by a factor of 60 at 500 K. We describe the implementation of the methodology in the molecular dynamics package Amber 10. The method is tested on three [1,5] sigmatropic hydrogen shift reactions. Because of the computational expense, we use ab initio potentials to evaluate the equilibrium isotope effects within the harmonic approximation, and then the path integral method together with semiempirical potentials to evaluate the anharmonicity corrections. Our calculations show that the anharmonicity effects amount up to 30% of the symmetry reduced reaction free energy. The numerical results are compared with recent experiments of Doering and coworkers, confirming the accuracy of the most recent measurement on 2,4,6,7,9-pentamethyl-5-(5,5-$^2$H$_2$)methylene-11,11a-dihydro-12H-naphthacene as well as concerns about compromised accuracy, due to side reactions, of another measurement on 2-methyl-10-(10,10-$^2$H$_2$)methylenebicyclo[4.4.0]dec-1-ene.Comment: 14 pages, 8 figures, 6 table

Diffractive triangulation of radiative point sources

We describe a general method to determine the location of a point source of waves relative to a twodimensional single-crystalline active pixel detector. Based on the inherent structural sensitivity of crystalline sensor materials, characteristic detector diffraction patterns can be used to triangulate the location of a wave emitter. The principle described here can be applied to various types of waves, provided that the detector elements are suitably structured. As a prototypical practical application of the general detection principle, a digital hybrid pixel detector is used to localize a source of electrons for Kikuchi diffraction pattern measurements in the scanning electron microscope. This approach provides a promising alternative method to calibrate Kikuchi patterns for accurate measurements of microstructural crystal orientations, strains, and phase distributions

Multiplet ligand-field theory using Wannier orbitals

We demonstrate how ab initio cluster calculations including the full Coulomb vertex can be done in the basis of the localized, generalized Wannier orbitals which describe the low-energy density functional (LDA) band structure of the infinite crystal, e.g. the transition metal 3d and oxygen 2p orbitals. The spatial extend of our 3d Wannier orbitals (orthonormalized Nth order muffin-tin orbitals) is close to that found for atomic Hartree-Fock orbitals. We define Ligand orbitals as those linear combinations of the O 2p Wannier orbitals which couple to the 3d orbitals for the chosen cluster. The use of ligand orbitals allows for a minimal Hilbert space in multiplet ligand-field theory calculations, thus reducing the computational costs substantially. The result is a fast and simple ab initio theory, which can provide useful information about local properties of correlated insulators. We compare results for NiO, MnO and SrTiO3 with x-ray absorption, inelastic x-ray scattering, and photoemission experiments. The multiplet ligand field theory parameters found by our ab initio method agree within ~10% to known experimental values

The effect of the particulate phase on coal biosolubilisation mediated by Trichoderma atroviride in a slurry bioreactor

Low rank coal is currently under-utilised because of its low calorific value and high moisture and sulphur content. Its solubilisation by both bacterial and fungal cultures has been reported, the latter more commonly. Coal biosolubilisation processes have potential to convert low rank coal to either a clean, cost-effective energy source or complex aromatic compounds for biocatalytic conversion to value-added products. This can lead to an increased utilisation of low rank coal. In this study, the key variables of the slurry that affect biosolubilisation of low rank coal by Trichoderma atroviride in submerged culture were investigated. Results showed that the key operating variables that influence coal biosolubilisation in the slurry bioreactor are coal loading and particle size affecting available surface area. These factors affect the surface area available for coal biosolubilisation. The optimum coal loading occurred between 5 and 10% (w/v); an increase above this optimum led to inhibition of the fungal culture of T. atroviride (ES11) by fragmentation of the fungal mycelium. A decrease in particle size fraction led to an increase in the degree of coal solubilisation. Coal biosolubilisation was shown to increase 4-fold when particle size was decreased from 600–850 μm to 150–300 μm. A 28% biosolubilisation of coal of 150–300 μm, characterised by a surface specific area of 2.17 cm2 g−1 , was measured as coal weight loss over 14 days at solids loading at 5%. This can be compared with a 7.8% coal weight loss at 600–850 μm diameters (0.54 cm2 g−1 ). Soluble phenolic compounds are not a significant product of the coal biosolubilisation process. The change in pH observed in the presence of both coal and fungi was independent of coal loading and was not directly related to the extent of coal solubilisation. While soluble intermediates were observed as total organic, further metabolism resulted in complete oxidation of a significant fraction of the coal to CO2

The Probable Detection of SN 1923A: The Oldest Radio Supernova?

Based upon the results of VLA observations, we report the detection of two unresolved radio sources that are coincident with the reported optical position of SN 1923A in M83. For the source closest to the SN position, the flux density was determined to be 0.30 +/- 0.05 mJy at 20 cm and 0.093 +/- 0.028 mJy at 6 cm. The flux density of the second nearby source was determined to be 0.29 +/- 0.05 at 20 cm and 0.13 +/- 0.028 at 6 cm. Both sources are non-thermal with spectral indices of alpha = -1.0 +/- 0.30 and -0.69 +/- 0.24, respectively. SN 1923A has been designated as a Type II-P. No Type II-P (other than SN 1987A) has been detected previously in the radio. The radio emission from both sources appears to be fading with time. At an age of approximately 68 years when we observed it, this would be the oldest radio supernova (of known age) yet detected

Efficiency determination of resistive plate chambers for fast quasi-monoenergetic neutrons

Composite detectors made of stainless steel converters and multigap resistive plate chambers have been irradiated with quasi-monoenergetic neutrons with a peak energy of 175MeV. The neutron detection efficiency has been determined using two different methods. The data are in agreement with the output of Monte Carlo simulations. The simulations are then extended to study the response of a hypothetical array made of these detectors to energetic neutrons from a radioactive ion beam experiment.Comment: Submitted to Eur.Phys.J. A; upgraded version correcting some typos and updating ref.

Biomarker-based asthma phenotypes of corticosteroid response

BackgroundAsthma is a heterogeneous disease with different phenotypes. Inhaled corticosteroid (ICS) therapy is a mainstay of treatment for asthma, but the clinical response to ICSs is variable.ObjectiveWe hypothesized that a panel of inflammatory biomarkers (ie, fraction of exhaled nitric oxide [Feno], sputum eosinophil count, and urinary bromotyrosine [BrTyr] level) might predict steroid responsiveness.MethodsThe original study from which this analysis originates comprised 2 phases: a steroid-naive phase 1 and a 28-day trial of ICSs (phase 2) during which Feno values, sputum eosinophil counts, and urinary BrTyr levels were measured. The response to ICSs was based on clinical improvements, including a 12% or greater increase in FEV1, a 0.5-point or greater decrease in Asthma Control Questionnaire score, and 2 doubling dose or greater increase in provocative concentration of adenosine 5′-monophosphate causing a 20% decrease in FEV1 (PC20AMP). Healthy control subjects were also evaluated in this study for comparison of biomarkers with those seen in asthmatic patients.ResultsAsthmatic patients had higher than normal Feno values, sputum eosinophil counts, and urinary BrTyr levels during the steroid-naive phase and after ICS therapy. After 28-day trial of ICSs, Feno values decreased in 82% of asthmatic patients, sputum eosinophil counts decreased in 60%, and urinary BrTyr levels decreased in 58%. Each of the biomarkers at the steroid-naive phase had utility for predicting steroid responsiveness, but the combination of high Feno values and high urinary BrTyr levels had the best power (13.3-fold, P < .01) to predict a favorable response to ICS therapy. However, the magnitude of the decrease in biomarker levels was unrelated to the magnitude of clinical response to ICS therapy.ConclusionA noninvasive panel of biomarkers in steroid-naive asthmatic patients predicts clinical responsiveness to ICS therapy

Resonant soft X-ray Raman scattering of NiO

Resonant soft X-ray Raman scattering measurements on NiO have been made at photon energies across the Ni 2p absorption edges. The details of the spectral features are identified as Raman scattering due to d-d and charge-transfer excitations. The spectra are interpreted within the single impurity Anderson model, including multiplets, crystal-field and charge-transfer effects. At threshold excitation, the spectral features consists of triplet-triplet and triplet-singlet transitions of the 3d8 configuration. For excitation energies corresponding to the charge-transfer region in the Ni 2p X-ray absorption spectrum of NiO, the emission spectra are instead dominated by charge-transfer transitions to the 3d9L-1 final state. Comparisons of the final states with other spectroscopical techniques are also made.Comment: 9 pages, 2 figures, 2 tables, http://iopscience.iop.org/0953-8984/14/13/32

Being fluent and keeping looking

The complexities of the many concepts and models around information literacy are considered, and some personal views given as to how they may best be clarified, both theoretically and practically. A slightly adapted idea of the concept of information fluency can serve as a main general purpose for the promotion of information literacy, expressed as a more specific meta-model for the prevailing technological environment, and as still more specific components for a particular context. The focus of this relatively stable general formulation is on understanding, rather than skills or competences. It can incorporate the need for education, advice and counseling, as well as information provision, and with domain-specific literacies, as well as supporting personal information literacy