The role of OH ions in the stabilization of F colour centres in LiF

Thermally Stimulated Depolarisation Current (TSDC) and optical methods are applied to a range of alkali-fluoride crystals in order to establish a model for the stable F ₂ ⁺ - like colour centres in LiF:OH^-. The experimental results for LiF:OH^- suggest that the OH^- defects are partially destroyed under ionising irradiation or during crystal growth. The low-temperature dielectric relaxation signals in LiF:OH^- and LiF:Mg²⁺,OH^- are attributed to highly interacting hydroxide ions and products of their destruction located in extended lattice defects. In LiF:OH^-, in contrast to other alkali halides, the results advocate for a defect-structure model, which considers a neutral defect (ND, probably O₂ or H₂) sited at the anion vacancy of the O^2--V _a ⁺ dipole and which possibly is the “nucleus” for the F ₂ ⁺ centre. The proposed F ₂ ⁺ (ND, O^-) model seems to better explain the dielectric results, compared to the older F ₂ ⁺ (O^2-) and F ₂ ⁺ (O^-) models. The estimate for the electric dipole moment derived from the experimental TSDC bands, gives a value for the F ₂ ⁺ - like centre in LiF:OH^- between those of the F ₂ ⁺ (O^-) and F ₂ ⁺ (O^2-) defects, in good agreement with the proposed F ₂ ⁺ (ND,O^-) model. The reduction of the activation energy barrier of the (re)orientation process of the Mg²⁺V _c ^- (OH^-) complexes in LiF:Mg²⁺,OH^-, and the low-temperature shift of their TSDC band, compared to the single Mg ₂ ⁺ V _c ^- peak in LiF:Mg²⁺, are tentatively ascribed to an increase in the crystal-lattice parameters owing to the presence of OH^- and/or products of its destruction. Received 31 August 2001 / Received in final form 30 March 2002 Published online 9 July 2002     

Experimental study of the inclusiveη-spectrum fromp \bar p annihilations at rest in liquid hydrogen

The inclusive η-momentum spectrum from \(\bar p\) annihilations at rest in liquid hydrogen was measured at LEAR. Branching ratios were obtained for $$\begin{gathered} p\bar p \to \eta \omega \left( {1.04_{ - 0.10}^{ + 0.09} } \right)\% ,\eta \rho ^0 \left( {0.53_{ - 0.08}^{ + 0.20} } \right)\% , \hfill \\ \pi a_2 \left( {8.49_{ - 1.10}^{ + 1.05} } \right)\% ,\eta \pi ^0 \left( {1.33 \pm 0.27} \right) \times 10^{ - 4} , \hfill \\ \end{gathered} $$ , and ηη(8.1±3.1)×10^?5. An upper limit for \(p\bar p \to \eta \eta '\) of 1.8×10^?4 at 95% CL was found. The ratio of the branching ratios is BR(η?)/BR(ηω)=0.51 _?0.06 ^+0.20 . For the ratio of branching ratios into two pseudoscalar mesons, we have BR(ηπ⁰)/BR(π⁰π⁰)=0.65±0.14, BR(ηη)/BR(π⁰π⁰), BR(η η ^′ )/BR(π⁰π⁰) at 95% CL, and BR(ηη)/BR(ηπ⁰).     

A study on the utility of bismuth-film electrodes for the determination of In(III) in the presence of Pb(II) and Cd(II) by square wave anodic stripping voltammetry

This work is an investigation into the utility of bismuth-film electrodes (BiFEs) for the determination of indium in the presence of cadmium and lead by square wave anodic stripping voltammetry (SWASV). The purpose of this study was to demonstrate that, after judicious choice of the associated chemical and instrumental conditions, it is possible to achieve satisfactory separation of the relevant stripping peak and, thus, to determine simultaneously trace concentrations of cadmium, lead and indium. It was conclusively demonstrated that a BiFE performed better than the equivalent mercury-film electrode (MFE) in this particular application.     

Experimental determination of the branching ratiosp\bar p \to 2\pi ^0 ,\pi ^0 \gamma,and 2γ at rest

The branching ratios of \(p\bar p\) annihilations into the neutral final states 2π⁰, π⁰γ, and 2γ are measured by stopping antiprotons in liquid hydrogen. They are \(B_{2\pi ^0 } = \left( {2.06 \pm 0.14} \right) \times 10^{ - 4} \) , \(B_{\pi ^0 \gamma } = \left( {1.74 \pm 0.22} \right) \times 10^{ - 5} \) , andB _γγ<1.7×10^?6 (95% c.l.).     

The hydrogenation of olefins using a polymer supported ruthenium complex

RuCl₂(PPH₃)3 has been attached to a phosphinated polymer support (phosphinated polystyrene crosslinked with 2% divinylbenzene) and the reagent converted to the polymer supported analogue of RuClH(PPH₃)₃ in the presence of base. The polymer supported catalyst efficiently hydrogenates terminal olefins under ambient conditions. Hydrogenation of 1-hexene has revealed that the reaction rate is proportional to [Ru], [H₂] and [olefin]/(1 + [olefin]). The polymer support environment allows for selectivity in olefin hydrogenation and under suitable reaction conditions short chain terminal olefins are hydrogenated more rapidly than long chain terminal olefins. The extent of metal loading on the polymer and the reaction solvent composition also influence the reaction selectivity and these effects are discussed.     

Mass spectra of complexes of 8-quinolinol with trivalent metals (AL,Ga, In,Sc, Cr and Fe)

The main fragmentation of the compounds MX_3-nox_n (oxH=8-quinolinol. n = 3; M=AL, Ga, In, Sc, Cr or Fe. n = 2; M=In or Fe; X=Cl or Br. InIox₂. n = 1; M=AL, In or Fe; X= Cl or Br) involves loss of X and intact ox_. radicals. The comparative abundances of the fragments are primarily related to the common oxidation states of the metals. For example, all the Mox₃ compounds show the ions [Mox₃]⁺ and [Mox₂]⁺. The ions [Mox]⁺ and [M]⁺ are present when M=Ga, In, Cr or Fe but for the elements with only one oxidation state (Al or Sc) [M]⁺ is absent and [Mox]⁺ has only very low abundance. When M= Cr or Fe metal-containing ions arising from loss of species such as CO, H₂O, HX, C₂H₂, H and OH by fragmentation of the ox ligand are also present; this behaviour is rationalised in terms of the ability of these metals to undergo a unit change in oxidation state. When n=1 the ions [MXox₂]⁺ and [Mox₂]⁺ and when n= 2 the ions [MX₂ox]⁺ and [Mox₃]⁺ are present; these ions arise by ionization and fragmentation of species formed by redistribution reactions in the mass spectrometer.     

A deductive approach to the solution of the problem of optimal pairs trading from the viewpoint of stochastic control with time‐dependent parameters

In a fairly recent paper (2008 American Control Conference, June 11‐13, 1035‐1039), the problem of dealing with trading in optimal pairs was treated from the viewpoint of stochastic control. The analysis of the subsequent nonlinear evolution partial differential equation was based upon a succession of Ansätze, which can lead to a solution of the terminal‐value problem. Through an application of the Lie Theory of Continuous Groups to this equation, we show that the Ansätze are based upon the underlying symmetries of the equation (their (14)). We solve the problem in a more general context by allowing the parameters to be explicitly time dependent. The extension means thatmore realistic problems are amenable to the samemode of solution. Copyright © 2014 JohnWiley & Sons, Ltd.     

On conditions for optimality in least pth approximation withp → ∞

This paper presents a theoretical discussion of the necessary and sufficient conditions for optimality in generalized nonlinear leastpth approximation problems forp . In the limit, the conditions for a minimax approximation are derived, as is to be expected. Numerical examples involving the modeling of a linear time-invariant fourth-order system by a second-order model and the design of quarter-wave transmission-line transformers illustrate the results.This work was supported by the National Research Council of Canada under Grant No. A7239 and by a Frederick Gardner Cottrell Grant from the Research Corporation. This paper was presented at the 9th Annual Allerton Conference on Circuit and System Theory, Urbana, Illinois, October 6–8, 1971. The authors thank Mrs. J. R. Popovi for helping to correct Example 4.1.     

Hybrid artificial neural networks for efficient valuation of real options and financial derivatives

A hybrid valuation methodology is proposed and tested for improving the efficiency of contingent claims pricing by combining Artificial Neural Networks (ANN) and conventional parametric option pricing techniques. With one application on financial derivatives and one on real options the methods superiority is demonstrated. The resulting efficiency is instrumental for real time applications.MSC code: 90-08 Acknowledgements: Both authors are thankful for partial financial support to the HERMES European Center of Excellence on Computational Finance and Economics of the University of Cyprus and a University of Cyprus grant for research in ANNs and Derivatives, and to the anonymous referees for their helpful comments and discussions.     

Triangular to square flux lattice phase transition in YBa2Cu3O7

We have used the technique of small-angle neutron scattering to observe magnetic flux lines directly in a YBa2Cu3O7 single crystal at fields higher than previously reported. For field directions close to perpendicular to the CuO2 planes, we find that the flux lattice structure changes smoothly from a distorted triangular coordination to nearly perfectly square as the magnetic induction approaches 11 T. The orientation of the square flux lattice is as expected from recent d-wave theories but is 45 degrees from that recently observed in La(1.83)Sr(0.17)CuO(4+delta).