Correlated electromigration of H in the switchable mirror YH(3-delta)

Electromigration of hydrogen in YH(3-delta) is studied by exploiting the H concentration dependence of the optical transmission of YH(3-delta). We find the effective valence Z* of H in YH(3-delta) to be negative. Its value is dominated by a huge wind-force-like term, i.e., Z* approximately K/rho, with K approximately -60 mOmega cm. This value is 3 orders of magnitude larger than typical for H in metals. In an Arrhenius plot, the ratio of hydrogen and electron fluxes extrapolates to unity at infinite temperature, suggesting a one-to-one correlation of hydrogen and electron hopping. We discuss our results in the light of strong electron correlation theories which predict each proton to bind two electrons in a sort of Zhang-Rice singlet.     

Interpreting early land management through compound specific stable isotope analyses of archaeological soils

Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd.     

Amino acids with hydrogen-bonding side chains have an intrinsic tendency to sample various turn conformations in aqueous solution

Local structure in unfolded proteins, especially turn segments, has been suggested to initiate the hierarchical protein‐folding process. To determine the intrinsic propensity to form such turn structures, amide I′ band profiles of the Raman, IR, and vibrational circular dichroism (VCD) spectra, and several structure‐sensitive NMR J‐coupling constants, have been measured for a series of GxG (x=D, N, T, C) peptides, in which the central x residues are abundant in various turn motifs in folded proteins. In addition, we revisited earlier measured GSG experimental data. To check whether this relatively high propensity for these residues to sample turns reflects an intrinsic propensity, the experimental data were analyzed in terms of conformational distributions that can be described as a superposition of two‐dimensional Gaussian distributions associated with different so‐called mesostates. The analysis reveals that the investigated residues sample dihedral angles similar to those found in the corner residues of various turns, namely, type I/I′, II/II′, and IV β‐turns. Aspartic acid (D) was found to predominantly sample regions attributed to turns, including distributions at the upper border of the upper‐right quadrant of the Ramachandran plot, which bear some resemblance to asx‐turns observed in proteins. This conformation enables hydrogen bonding between the side‐chain carboxylate and the C‐terminal amide group. Altogether, the study shows that the high propensity for T, S, C, N, and D to be located in turn motifs reflects, to a substantial degree, an intrinsic property and supports the role of these residues as initiation sites for hierarchical folding processes that can lead to compact structures in the unfolded state of peptides and proteins.     

Vortex lattice transitions in YNi2B2C

We have performed extensive small-angle neutron scattering (SANS) diffraction studies of the vortex lattice in single crystal YNi₂B₂C for B‖c. High-resolution SANS, combined with a field-oscillation vortex lattice preparation technique, allows us to separate Bragg scattered intensities from two orthogonal domains and accurately determine the unit cell angle, β. The data suggest that upon increasing field there is a finite transition width where both low- and high-field distorted hexagonal vortex lattice phases, mutually rotated by 45°, coexist. The smooth variation of diffracted intensity from each phase through the transition corresponds to a redistribution of populations between the two types of domains.     

Centred TVD schemes for hyperbolic conservation laws

New first- and high-order centred methods for conservation lawsare presented. Convenient TVD conditions for constructing centredTVD schemes are then formulated and some useful results areproved. Two families of centred TVD schemes are constructedand extended to nonlinear systems. Some numerical results arealso presented.     

An interferometric linear in-plane position transducer

When mutally coherent light beams overlap on an optically rough surface, the scattered light fields or speckle patterns interfere. The intensity at any point depends on the phase difference between the light fields. By matching the sensitive area of a photodetector to speckle size, an electronic signal is obtained which can be used to monitor in-plane rigid body translations of the surface with interferometric precision. Two reliable methods of obtaining directional sensitivity based on polarization properties are described and it is shown that depolarization effects due to rough surfaces, do not cause any difficulty. Intensitivity to motion orthogonal to the plane of the apparatus is demonstrated.     

Simple phase-shifting lateral shearing interferometer

A phase-shifting electronic speckle pattern shearing interferometer with a very simple shearing device is proposed. Two partially reflective glass plates are used to introduce the shear in this new interferometer. The reflection coefficients of the coatings on the two plates are 0.3 and 0.7. The distance between the two glass plates controls the size of the shear. The proposed new interferometric system is simple, flexible, and low cost.     

Luminescent oligo(tetraphenyl)silole nanoparticles as chemical sensors for aqueous TNT

Colloidal oligo(tetraphenyl)silole nanoparticles in THF/H2O suspensions show increased luminescence and offer a method to detect TNT in an aqueous environment.     

Simple versatile shearing interferometer suitable for measurements on a microscopic scale

Micro-electromechanical systems (MEMS) behave differently from massive samples. Conventional testing and inspection techniques usually fail at the microscale. Recently there has been an increasing interest in the application of optical techniques for microstructure testing, because they are high-resolution, non-contact, full-field, fast and relatively inexpensive. New interferometric systems, which are suitable for microscopic optical metrology, are of interest for engineering and industrial applications.A modified electronic speckle pattern shearing interferometer (ESPSI) with a very simple shearing device has been designed for metrology applications on the microscale. The shearing device consists of two partially reflective glass plates. The reflection coefficients of the coatings are 0.3 and 0.7, respectively. The distance and the tilt between the two glass plates control the size of the shear. A long working distance microscope objective is attached to the CCD camera to form a field of view variable over several millimetres in width. The suitability of the system for microscopic measurements is demonstrated. The capability of the system for phase shifting is also demonstrated. The results obtained are promising for future applications of the ESPSI system for testing and characterisation of MEMS.