Holonomy groups andW-symmetries

Irreducible sigma models, i.e. those for which the partition function does not factorise, are defined on Riemannian spaces with irreducible holonomy groups. These special geometries are characterised by the existence of covariantly constant forms which in turn give rise to symmetries of the supersymmetric sigma model actions. The Poisson bracket algebra of the corresponding currents is aW-algebra. Extended supersymmetries arise as special cases.     

The relaxed hypermultiplet: An unconstrained N = 2 superfield theory

We present an off-shell version of the hypermultiplet, without a central charge or gauge antisymmetric tensors. We give the unconstrained superfield form of the action and its coupling to N = 2 super-Yang-Mills theory. This allows an N = 2 superspace formulation of the N = 4 super-Yang-Mills theory, whose ultraviolet finiteness is then ensured by N = 2 non-renormalization theorems.     

Higher order invariants in extended supergravity

On-shell linearized extended supergravity is presented in superspace for all N. The formalism is then used in the construction of higher order invariants which may serve as counterterm lagrangians. It is shown that three-loop counterterms exist for N ? 3 and (N ? 1)-loop counterterms for N ? 4. In the full non-linear theory, the presence of a global non-compact symmetry group for N ? 4 does not allow a simple extension of the (N ? 1)-loop term, but N-loop counterterms may be constructed.     

The supercurrent in five dimensions

The supercurrent multiplet is constructed for N=2 and 4 extended supersymmetries in five dimensions. The corresponding supergravity multiplets are also exhibited and have 40 + 40 and 128 + 128 components, respectively.     

Studies of layered uranium(VI) compounds. II. Thermal stability of hydrogen uranyl phosphate and arsenate tetrahydrates

By means of accurate TGA, we have shown that the proton-conducting solid electrolytes HUO₂PO₄·4H₂O (HUP) and HUO₂AsO₄·4H₂O (HUAs) are more correctly represented as $\text{HUO}{}_2\text{P}\text{AsO}{}_4\text{·(A?x)}\text{H}{}_2\text{O}$, where A is assumed to be the integral number 4. The water deficiency x was estimated to be less than 0.03 at 295°K, but increased respectively by less than 0.1 and 0.05 when HUP and HUAs were heated in air to approximately 315°K. At higher temperatures, dehydration of HUP under isothermal conditions produced, over a temperature interval of less than 2°K, a lower hydrate phase having approximately 1.5 waters of crystallization. Equilibrium dehydration temperatures were established for HUP over a range of humidities, and varied from 297°K at 0.4 mm Hg water vapor pressure, to 318°K at 16 mm Hg pressure. An explanation of the apparently high standard molar enthalpy for dehydration is suggested in terms of small losses of a phosphorus-containing compound accompanying the water loss. The overall phase relationships of HUP are discussed.     

The influence of grazing flow on the acoustic impedance of a cylindrical wall cavity

The acoustic impedance at low frequencies of a circular cylindrical cavity in the wall of a duct in the presence of a low Mach number mean flow is examined. A linearized theoretical model is proposed which involves the unsteady shedding of vorticity from the upstream edge of the cavity aperture. The shed vorticity causes a “potential difference” to be established across the aperture which modifies the reciprocating volume flux and results in the dissipation of acoustic energy. Comparison of theoretical predictions with preliminary experimental data obtained by Parrott (1978, private communication) at the NASA Langley Research Center provides tentative support for the present analysis. Certain difficulties associated with the linearized treatment of cavity oscillations are also discussed.     

Ultra-thin films and surface alloying of Pd on Cu(1 1 1) investigated by medium energy ion scattering

The structure of Pd films on Cu(1 1 1) and the alloying between the films and the substrate have been investigated by medium energy ion scattering (MEIS) using 100 keV H⁺ ions. Data are presented for the and alignments (nominal one- and three-layer alignments, respectively). It is found that beyond 1 ML the Pd grows in a twinned fcc structure, the incommensurate nature of which increases the visibility of the Cu(1 1 1) substrate to MEIS. Deposition of 0.2 ML of Pd produces a structure in which Pd mostly occupies the top two layers which have interlayer distances d₁₂ = 208 ± 4 pm and d₂₃ = 211 ± 4 pm. Some twinning is also present in this structure. Upon annealing 1.6 ML of Pd to 600 K for 1 min, the copper and palladium interdiffuse leaving around 0.4 ML of visible palladium. Energy plots show that there are several layers with an altered structure present over at least part of the surface. This may be due to large scale interdiffusion or alloy island formation. Incremental annealing to successively higher temperatures shows that the structural transformation begins around 500 K.     

Indirect determination of chemical shift by coupling evolution during adiabatic pulses

The use of adiabatic 180 degrees X-pulses within INEPT refocusing periods results in chemical shift-dependent evolution of J-couplings. This has been viewed as a disadvantage and several methods of overcoming it have been suggested. This article shows that there is the potential to use this chemical shift dependence to determine heteronuclear chemical shift without a heteronuclear evolution time. In this way, it possible to estimate heteronuclear chemical shift indirectly from a single one-dimensional proton-observe spectrum and determine it with high accuracy from a extensively-folded two-dimensional proton-observe spectrum.     

Interplay of Hole Transfer and Host–Guest Interaction in a Molecular Dyad and Triad: Ensemble and Single‐Molecule Spectroscopy and Sensing Applications

A new molecular dyad consisting of a Cy5 chromophore and ferrocene (Fc) and a triad consisting of Cy5, Fc, and β‐cyclodextrin (CD) are synthesized and their photophysical properties investigated at both the ensemble and single‐molecule levels. Hole transfer efficiency from Cy5 to Fc in the dyad is reduced upon addition of CD. This is due to an increase in the Cy5‐Fc separation (r) when the Fc is encapsulated in the macrocyclic host. On the other hand, the triad adopts either a Fc‐CD inclusion complex conformation in which hole transfer quenching of the Cy5 by Fc is minimal or a quasi‐static conformation with short r and rapid charge transfer. Single‐molecule fluorescence measurements reveal that r is lengthened when the triad molecules are deposited on a glass substrate. By combining intramolecular charge transfer and competitive supramolecular interaction, the triad acts as an efficient chemical sensor to detect different bioactive analytes such as amantadine hydrochloride and sodium lithocholate in aqueous solution and synthetic urine.