Uncertainty budget for determinations of mean isomer shift from Mössbauer spectra

The magnetite/maghemite content within iron oxide nanoparticles can be determined using the mean isomer shift (\(\overline {\delta }\)). However, accurate characterisation of the composition is limited by the uncertainty associated with \(\overline {\delta }\). We have identified four independent sources of uncertainty and developed a quantitative expression for the uncertainty budget. Sources of uncertainty are categorised as follows: that from the fitting of the Mössbauer spectrum (σ _fit), that of the calibration of the α-Fe reference spectrum (σ _cal), thermal corrections to the spectrum due to second order Doppler shift (SODS) (σ _Δδ ) and other experimental errors (σ _err). Each contribution is discussed in detail using ⁵⁷Fe Mössbauer spectra obtained from an iron oxide nanoparticle system at temperatures between 16 K and 295 K on different spectrometers in two different laboratories.     

Geometric Achromatic and Pseudoachromatic Indices

The pseudoachromatic index of a graph is the maximum number of colors that can be assigned to its edges, such that each pair of different colors is incident to a common vertex. If for each vertex its incident edges have different color, then this maximum is known as achromatic index. Both indices have been widely studied. A geometric graph is a graph drawn in the plane such that its vertices are points in general position, and its edges are straight-line segments. In this paper we extend the notion of pseudoachromatic and achromatic indices for geometric graphs, and present results for complete geometric graphs. In particular, we show that for n points in convex position the achromatic index and the pseudoachromatic index of the complete geometric graph are \(\lfloor \frac{n^2+n}{4} \rfloor \).     

Solvent effects on two-photon absorption of dialkylamino substituted distyrylbenzene chromophore

Solvent effects on the two-photon absorption of a symmetrical diamino substituted distyrylbenzene chromophore have been studied using the density functional response theory in combination with the polarizable continuum model. It is shown that the dielectric medium has a rather small effect both on the bond length alternation and on the one-photon absorption spectrum, but it affects significantly the two-photon absorption cross section. It is found that both one- and two-photon absorptions are extremely sensitive to the planarity of the molecule, and the absorption intensity can be dramatically reduced by the conformation distortion. It has led to the conclusion that the experimentally observed anomalous solvent effect on the two-photon absorption of dialkylamino substituted distyrylbenzene chromophores cannot be attributed to the intrinsic properties of a single molecule and its interaction with solvents.     

Neutrons produced by 1.22 GeV antiproton interactions with nuclei

Inclusive neutron energy spectra were measured by time of flight using 1.22 GeV antiprotons from LEAR, CERN, as projectiles and targets from natural Al, Cu, Ag, Ho, Ta, Au, Pb, Bi, U. The sum of two Maxwellian distributions was fitted to the spectra obtained at several forward and backward angles yielding neutron multiplicities M_i and slope or temperature parameters T _i for the low-energy (evaporative, i=1) and high-energy (pre-equilibrium,i=2) parts, respectively. M ₁ increases with A, proportional to the nuclear volume, and M ₂ is growing with A , proportional to the nuclear radius. The T parameters are nearly independent of A. The results are compared with previous multiplicity measurements with a neutron detector, intranuclear cascade calculations and neutron spectra from stopped antiproton annihilation on nuclei. With the measured proton spectra also the ratio of emitted neutrons to protons was determined for Au. Received: 25 February 2000 / Accepted: 19 May 2000     

X‐Ray Photoelectron Spectral Studies on Planar NiS4 and NiS2P2 Chromophores. Single Crystal X‐Ray Structural Study on [1, 4‐Bis(diphenylphosphino‐k,P, P')butane](piperidinecarbodithioato‐S,S')‐Nickel(II) Perchlorate

X‐ray photoelectron spectral study was made on the complexes Ni(nmedtc)₂( 1 ), [Ni(nmedtc)(PPh₃)₂]ClO₄( 2 ), [Ni‐(nmedtc)(dppe)]BPh₄( 3 ) (where nmedtc = N‐methyl, N‐ethanoldithiocarbamate, dppe = 1, 2‐bis(diphenylphosphino)ethane). The nickel 2p_3/2 binding energy values for chelated and free phosphine complexes are 854.0 and 854.1 eV which are significantly different from Ni2p_3/2 BE value of NiS₄ chromophore, indicating the relative dearth of electron density on Ni in NiS₂P₂ chromophores. The presence of two phosphine groups in NiS₂P₂ chromophore alleviates the electron density on the metal atom. More electron density is being pulled away from the metal atom in chelates than in the PPh₃ analogue. This observation is in line with solution studies by cyclic voltammetry. A one‐electron reduction potential was observed to be the minimum for NiS₂P₂ chromophores compared to the others. Also the crystal structure of the complex [Ni(pipdtc)(1, 4‐dppb)]ClO₄ (pipdtc^‐ = piperidinecarbodithioato anion, 1, 4‐dppb = bis(diphenylphosphino)butane) prepared by the reaction between Ni(pipdtc)₂, NiCl₂�6₂2O, and 1, 4‐dppb in CH₃CN‐CH₃OH is reported.     

Defect interaction and solid electrolyte transition in AgI-based materials

The first-order phase transition that leads to the superionic phase in AgI-based materials is studied by dc-conductivity measurements and a free energy model. By properly adjusting the model parameters, an abrupt change of disordering concentration, Δη?, is predicted at a transition temperature, T_t. The temperature dependence of the dc-conductivity, σ(T), is well fitted to the η?(T) equilibrium configuration obtained from the trial free energy function. The reported comparative study was done using an AgI–KI modified sample. The model also predicts a transition temperature, T_c for a continuous phase transition (Δη? = 0).     

Determination of sulfonamide residues in water samples by in-line solid-phase extraction-capillary electrophoresis

An in-line solid-phase extraction-capillary electrophoresis method with UV–vis detection was developed for the monitoring of residues of five sulfonamides (sulfadoxin, sulfadimethoxine, sulfamerazine, sulfachloropyridazine and sulfamethoxazole) in tap, bottled mineral and river waters. For this purpose an analyte concentrator was constructed, based on the introduction of a small portion of a solid-phase extraction sorbent into the electrophoretic capillary to carry out an in-line concentration step, improving sensitivity. A detailed study was carried out to optimize parameters affecting the in-line solid-phase extraction process, such as the design of the concentrator device, type of sorbent and conditions of elution and injection. The proposed method is simple for the environmental monitoring of these antibiotic residues in waters, allowing the direct injection of the samples without any off-line pretreatment and achieving limits of detection between 0.3 and 0.6 μg/L. Recoveries ranging 52.2–109.2% and relative standard deviations below 13.4% were obtained.     

Representation systems and undergraduate proof production: A comment on Weber

Weber (2009) suggested that counterexamples can be generated by a syntactic proof production, apparently contradicting our earlier assertion (Alcock & Inglis, 2008). Here we point out that this ostensible difference is the result of Weber working with theoretical definitions that differ slightly from ours. We defend our approach by arguing that Weber’s relies upon an as yet unspecific metric for gauging the amount of work conducted in each representation system, and that it does not recognize an important asymmetry between the status of representation systems in the context of undergraduate mathematics.     

Parallelization of the integral equation formulation of the polarizable continuum model for higher-order response functions

We present a parallel implementation of the integral equation formalism of the polarizable continuum model for Hartree-Fock and density functional theory calculations of energies and linear, quadratic, and cubic response functions. The contributions to the free energy of the solute due to the polarizable continuum have been implemented using a master-slave approach with load balancing to ensure good scalability also on parallel machines with a slow interconnect. We demonstrate the good scaling behavior of the code through calculations of Hartree-Fock energies and linear, quadratic, and cubic response function for a modest-sized sample molecule. We also explore the behavior of the parallelization of the integral equation formulation of the polarizable continuum model code when used in conjunction with a recent scheme for the storage of two-electron integrals in the memory of the different slaves in order to achieve superlinear scaling in the parallel calculations.