Influence of long-range dipolar interactions on the phase stability and hysteresis shapes of ferroelectric and antiferroelectric multilayers

Phase transition and field driven hysteresis evolution of a two-dimensional Ising grid consisting of ferroelectric–antiferroelectric multilayers that take into account the long range dipolar interactions were simulated by a Monte–Carlo method. Simulations were carried out for a 1 + 1 bilayer and a 5 + 5 superlattice. Phase stabilities of components comprising the structures with an electrostatic-like coupling term were also studied. An electrostatic-like coupling, in the absence of an applied field, can drive the ferroelectric layers toward 180° domains with very flat domain interfaces mainly due to the competition between this term and the dipole–dipole interaction. The antiferroelectric layers do not undergo an antiferroelectric-to-ferroelectric transition under the influence of an electrostatic-like coupling between layers as the ferroelectric layer splits into periodic domains at the expense of the domain wall energy. The long-range interactions become significant near the interfaces. For high periodicity structures with several interfaces, the interlayer long-range interactions substantially impact the configuration of the ferroelectric layers while the antiferroelectric layers remain quite stable unless these layers are near the Neel temperature. In systems investigated with several interfaces, the hysteresis loops do not exhibit a clear presence of antiferroelectricity that could be expected in the presence of anti-parallel dipoles, i.e., the switching takes place abruptly. Some recent experimental observations in ferroelectric–antiferroelectric multilayers are discussed where we conclude that the different electrical properties of bilayers and superlattices are not only due to strain effects alone but also due to long-range interactions. The latter manifests itself particularly in superlattices where layers are periodically exposed to each other at the interfaces.     

Book review: Food Biotechnology

Modern Food Microbiology, Third Edition. J.M. Jay. Van Nostrand Reinhold, 115 Fifth Ave., New York, NY 10003. 642 pp. 1986. $29.95 (US).

Title: Fermentation and Biochemical Engineering Handbook; Principles, Process Design, and Equipment Author(s): Henry C. Vogel (Editor) Publisher: Noyes Publications, Park Ridge, NJ. 1986

Principles of Fermentation Technology P.F. Stanbury and A. Whitaker Pergamon Press Inc., Elm3ford, NY, USA 225 pp., 1984, $19.25 (soft cover), $48.00 (hard cover)

Biotechnology in Agricultural Chemistry H.M. Le Baron, R.O. Mumma, R.C. Honeycutt and J.H. Duesing (eds) ACS Symposium Series 33t, American Chemical Society, Washington, DC 367 pp., 1987, $64.95 (US)

Supercritical Fluids ‐ Chemical and Engineering Principles and Applications T.G. Squires and M.E. Paulaitis (Editors) ACS Symposium Series #329, 294pp., $59.95 (US & Canada), $71.95 (Export)

Title: Biogeneration of aromas. Authors: Parliment, T. H. and R. Croteau (Editors) Publishers: ACS Symposium Series, Washington, DC, 1986

Title: Ecology and Metabolism of Plant Lipids Author(s): Glenn Fuller and W. David Nes (Editors) Publisher: American Chemical Society. Symposium Series, Washington DC, 1986

Title: Chemistry and Function of Pectins Author(s): Fishman, M.L. and Jen, J.J. Publisher: ACS Symposium Series, Washington, DC 1986

“Plant Proteins: Applications, Biological Effects and Chemistry”; R.L. Ory (ed), ACS Symposium Series, American Chemical Society 1155 Sixteenth Street NW, Washington, DC 20036, USA 285 PP, 1986, $59.95 (U.S. and Canada)     

Photoclickable Surfaces for Profluorescent Covalent Polymer Coatings

The nitrile imine‐mediated tetrazole‐ene cycloaddition reaction (NITEC) is introduced as a powerful and versatile conjugation tool to covalently ligate macromolecules onto variable (bio)surfaces. The NITEC approach is initiated by UV irradiation and proceeds rapidly at ambient temperature yielding a highly fluorescent linkage. Initially, the formation of block copolymers by the NITEC methodology is studied to evidence its efficacy as a macromolecular conjugation tool. The grafting of polymers onto inorganic (silicon) and bioorganic (cellulose) surfaces is subsequently carried out employing the optimized reaction conditions obtained from the macromolecular ligation experiments and evidenced by surface characterization techniques, including X‐ray photoelectron spectroscopy and FT‐IR microscopy. In addition, the patterned immobilization of variable polymer chains onto profluorescent cellulose is achieved through a simple masking process during the irradiation.     

Investigations concerning multi-component current contact tips for automatic MIG/MAG welding

Abstract

A report is given in this document on investigations concerning the development of multi-component current contact tips for MIG/MAG robot welding torches. Bi-metal pressure units were fitted in the guide channels to improve the current transmission.     

An a posteriori error estimate and a comparison theorem for the nonconforming <Emphasis Type="Italic">P</Emphasis><Subscript>1</Subscript> element

A posteriori error estimates for the nonconforming P ₁ element are easily determined by the hypercircle method via Marini’s observation on the relation to the mixed method of Raviart–Thomas. Another tool is Ainsworth’s application of the hypercircle method to mixed methods. The relation on the finite element solutions is also extended to an a priori relation of the errors, and the errors of four different finite element methods can be compared.      

A scanning visualizer of the magnetic field distribution

A facility consisting of a three-coordinate positioning system, a personal computer, and a Hall probe is capable of measuring and visualizing the configuration of magnetic fields above objects with a spatial resolution of 0.1 mm or better. The potential of the facility is demonstrated by measuring the configuration of the magnetic field above the system of two Sm-Co magnets with oppositely connected poles. The visualizer can be used in nondestructive testing and quality control of parts made of ferromagnetic materials and, in particular, welded joints.     

NAFLA – Ein Simulationswerkzeug zur analytischen Abschätzung von Schadstofffahnenlängen

Groundwater pollution with organic contaminants remains a world-wide problem. Before selection of any remediation technique, it is important to pre-assess contaminated sites with respect to their hazard. For this, several analytical and numerical approaches have been used and an initial assessment of contaminated sites the MS-Excel^© tool “NAFLA” was developed. “NAFLA” allows a quick and straightforward calculation and comparison of some analytical approaches for the estimation of maximum plume length under steady-state conditions. These approaches differ from each other in source geometry, model domain orientation, and in the consideration of (bio)chemical reaction within the domain. In this communication, we provide details about the development of “NAFLA”, its possible usage and information for users. The tool is especially designed for application in student education, by authorities and consultants.     

Decidable First-Order Theories of One-Step Rewriting in Trace Monoids

We prove that the first-order theory of the one-step rewriting relation associated with a trace rewriting system is decidable but in general not elementary. This extends known results on semi-Thue systems but our proofs use new methods; these new methods yield the decidability of local properties expressed in first-order logic augmented by modulo-counting quantifiers. Using the main decidability result, we define several subclasses of trace rewriting systems for which the confluence problem is decidable.