Variational symmetries and Lagrangian multiforms

Letters in Mathematical Physics - By considering the closure property of a Lagrangian multiform as a conservation law, we use Noether’s theorem to show that every variational symmetry of a...     

The synthesis and evaluation of unsymmetrical dimeric X-ray contrast agents

Novel dimeric iodinated contrast agents with low osmolality have been prepared and evaluated with the aim of improving the already good safety profile of such agents. The aim of low osmolality was achieved, and the viscosity of these dimeric agents was also found to be beneficially lower than current dimeric agents in clinical use.     

High-Resolution Laser Spectroscopy of YbCl: The A(2)Pi-X(2)Sigma(+) Transition

The A(2)Pi-X(2)Sigma(+) transition of (174)Yb(35)Cl and (172)Yb(35)Cl has been rotationally analyzed for the first time. Doppler-limited laser excitation spectroscopy with selective detection of fluorescence was used to obtain spectra of the 0-0 and 1-0 bands with a measurement accuracy of approximately 0.0035 cm(-1). Resolved fluorescence was used to record the 0-1, 0-2, and 0-3 bands and to unequivocally assign the rotational numbering, N, to the laser excitation spectra. In total, over 1300 line positions have been measured and assigned for each of the two isotopomers and employed in least-squares fits of molecular parameters. The principal results for the A(2)Pi state are A(e) = 1491.494(2) cm(-1) and R(e) = 2.4433(1) ?, and for the X(2)Sigma(+) state, R(e) = 2.4883(2) ? and gamma(e) = 4.59(2) x 10(-3) cm(-1). The interaction between the X(2)Sigma(+) and A(2)Pi states has been investigated and is shown to be the main contributor to the spin-rotation splitting in the ground state. Copyright 2000 Academic Press.     

Diborane: High resolution infrared rovibration studies of 11B2H6 and 11B2D6

Ground state rotation and quartic distortion constants were obtained for ¹¹B₂D₆ from the analysis of high resolution (～0.05 cm^?1) Fourier transform infrared spectra. The bands studied comprised the ν₁₇, ν₁₈ type A, and ν₁₄, ν₉ + ν₁₅ type C bands of ¹¹B₂H₆ and the ν₁₆, ν₁₇, ν₁₈ type A, ν₈ type B, and ν₁₄ type C bands of ¹¹B₂D₆. In the case of ¹¹B₂H₆, the authors' ground state data were combined with those of Lafferty et al. obtained from a previous study (J. Mol. Spectrosc.33, 345–367 (1970)) at comparable resolution of the ν₁₆ type A and ν₈ type B fundamentals. Information on the ground state rotational energy manifold of ¹¹B₂H₆ was accumulated up to J = 23, K_a = 18, and of ¹¹B₂D₆ up to J = 32, K_a = 22. This permitted rather precise determination of the distortion constants Δ_J⁰, Δ_JK⁰, Δ_K⁰, although δ_J⁰ and δ_K⁰ proved to be too small (< 10^?7 cm^?1) and were constrained to values calculated from the force field. Sets of upper state parameters were determined for all vibrational levels studied. Although these appear to be essentially unperturbed globally, several localized perturbations were observed and identified.     

Possibilities for refining an object program compiled with an ALGOL translator

The paper discusses possible improvements in connection with compilation of computer programs. Four different areas are mentioned where contributions should be possible: The language, the computer, the compiler, and the programmer. Although many of the points are quite general, ALGOL 60 is specifically taken into account.This paper was presented at the NordSAM conference in Stockholm, Aug. 1964.     

Advanced Polymer Designs for Direct-Ink-Write 3D Printing

The rapid development of additive manufacturing techniques, also known as three-dimensional (3D) printing, is driving innovations in polymer chemistry, materials science, and engineering. Among current 3D printing techniques, direct ink writing (DIW) employs viscoelastic materials as inks, which are capable of constructing sophisticated 3D architectures at ambient conditions. In this perspective, polymer designs that meet the rheological requirements for direct ink writing are outlined and successful examples are summarized, which include the development of polymer micelles, co-assembled hydrogels, supramolecularly cross-linked systems, polymer liquids with microcrystalline domains, and hydrogels with dynamic covalent cross-links. Furthermore, advanced polymer designs that reinforce the mechanical properties of these 3D printing materials, as well as the integration of functional moieties to these materials are discussed to inspire new polymer designs for direct ink writing and broadly 3D printing.     

Explicit Construction and Uniqueness for Universal Operator Algebras of Directed Graphs

Given a directed graph, there exist a universal operator algebraand universal C*-algebra associated to the directed graph. Inthis paper we give intrinsic constructions for these objects.We also provide an explicit construction for the maximal C*-algebraof an operator algebra. We discuss uniqueness of the universalalgebras for finite graphs, showing that for finite graphs thegraph is an isomorphism invariant for the universal operatoralgebra of a directed graph. We show that the underlying undirectedgraph is a Banach algebra isomorphism invariant for the universalC*-algebra of a directed graph.     

A.C. loss and related effects in type II superconductors

This review gathers together information important to the understanding of superconducting materials under a.c. conditions, and points out some features which are at present not too well understood. The idea is to try to build a consistent picture of the performance of superconductors rather than to present a historical account of the subject.

The basic behaviour of fluxons in the bulk of type II superconductors can be explained by the critical state model, but some of the details of flux pinning and the method of flux motion are in doubt. Flux instabilities under d.c. conditions have received a lot of attention and so have the methods of stabilization, but instabilities under a.c. conditions have not been studied in so much detail, and the problem of stabilization is more difficult than for f.c.

Generally surface effects are less well understood than bulk effects, partly because there are a number of possible phenomena to contend with. A.C. loss in the Meissner state can be explained by field enhancement and flux penetration at peaks in the surface. For fields between H _c3 and H _c2 present solutions of the Ginzburg-Landau equations for the currents in the surface sheath do not give sufficient agreement with experiment and some alternative explanation, such as flux pinning, may be necessary. There are a number of effects between H _c2 and H _c1, but the most important are Meissner currents and flux pinning.     

Direct Form I Realization of Active Photonic Filters

Abstract

An integrated photonic architecture is introduced and used to realize an optical filter with direct form I realization. The architecture offers gain from semiconductor optical amplifiers, and this gain results in an active optical filter whose filter response depends on the individual gains. The presence of gain provides advantages in filter performance, and tunable and adaptive functionality. The optical filter is modeled as a discrete time system and the z-transform is used in its analysis and design. A low-pass filter design example is presented and the filter coefficients are derived in terms of gains and coupler splitting ratios. The region of stable operations is derived by applying the Schur-Cohn stability test.