Simulations of energy and switching in AFLCDs with different boundary conditions

Using standard expressions for the various terms in the Gibbs free energy, the switching in antiferroelectric liquid crystal (AFLC) displays is simulated and the time evolution of various energy terms and of the liquid crystal director distributions are calculated. It is shown that when returning from a strong positive voltage to zero, one can reach two types of antiferroelectric state: the normal alternating state with the two bulk polarizations perpendicular to the electrodes and opposite to each other, and the alternative splayed symmetric state with two bulk polarizations parallel to the electrodes and again opposite to each other. The former case gives rise to tri-state switching characteristics, the latter to V-shaped switching. In general strong polar interaction with the alignment layer favours V-shaped switching while weak or no polar interaction give rise to tri-state switching characteristics. Since the V-shaped characteristic has so far only been demonstrated experimentally in ferroelectric liquid crystals (or antiferroelectric liquid crystals being in the ferroelectric state), the difference in AFLCs is discussed and the conditions for continuous switching are modelled. The simulations show that the switching characteristics of the antiferroelectric display can be controlled by the surface parameters.     

Metal- and proton-binding properties of a core-shell latex: interpretation in terms of colloid surface models

The cadmium binding properties of a core-shell latex were investigated using differential pulse polarography. The latex particles have a polystyrene core which is surrounded by a hydrophilic shell containing a low density of sulphonic and carboxylic groups. For this core-shell latex dispersion, the binding of protons and metal ions can be analyzed reasonably well using Donnan's potential model [J.T. Davies and E.K. Rideal, Interfacial Phenomenon, Academic Press, New York, 1961]. However, the correction of Ohshima and Kondo [H.O. Ohshima and T. Konda, Biophys. Chem., 39 (1991) 181] of the Donnan model for the distribution of ions in the double layer near and in the shell is a real improvement. In this way, the binding constants of cadmium(II)with the surface groups of latex were separated into their intrinsic and electrostatic parts. The intrinsic constant for binding of cadmium(II) to carboxylic groups, obtained in this way, was similar to literature values.     

Elliptic Genera of Symmetric Products and Second Quantized Strings

In this note we prove an identity that equates the elliptic genus partition function of a supersymmetric sigma model on the N-fold symmetric product of a manifold M to the partition function of a second quantized string theory on the space . The generating function of these elliptic genera is shown to be (almost) an automorphic form for . In the context of D-brane dynamics, this result gives a precise computation of the free energy of a gas of D-strings inside a higher-dimensional brane. Received: Received: 16 August 1996 / Accepted: 3 October 1996     

Sparse geometric graphs with small dilation

Given a set S of n points in , and an integer k such that 0k<n, we show that a geometric graph with vertex set S, at most n−1+k edges, maximum degree five, and dilation O(n/(k+1)) can be computed in time O(nlogn). For any k, we also construct planar n-point sets for which any geometric graph with n−1+k edges has dilation Ω(n/(k+1)); a slightly weaker statement holds if the points of S are required to be in convex position.     

Partial least-squares path modelling with latent variables

A partial least-squares treatment of multivariate data related through a complex model allows simultaneous evaluation of the interactions between large numbers of features. Results are given for a model in which water sources flow together; each source is represented by water quality data to allow the influence of the various sources to be evaluated with respect to their importance on the resulting flow downstream.     

Enzymatically generated polyphenols as array-based metal-ion sensors

Phenolic polymers containing fluorescent reporter molecules were prepared via soybean hull peroxidase (SBP) catalysis, and used as metal-based sensor components. Specifically, we generated a variety of phenolic homopolymers containing p-cresol, p-phenylphenol, or p-methoxyphenol containing one of the two fluorophores: fluorescein and calcein. The fluorescence of the resulting polyphenols was dependent on the presence of metal ions, including Cu²⁺, Fe²⁺, Zn²⁺, Mn²⁺, and Fe³⁺. The fluorescence response was dependent on both, the metal ion and the phenolic monomer used in polyphenol synthesis, indicating that significant control over the selectivity and sensitivity of metal sensing can be achieved by varying the components that comprise the phenolic polymer. In some cases, metal-ion concentrations as low as 10 μM can be analyzed. The broad reactivity of SBP toward phenolic monomers enables the use of a wide array of structures and chemistries that can assist in metal-ion detection.     

New FIR lasers from CO2 laser-excited 1,1-difluoroethene

Forty two new far-infrared laser lines have been obtained from CH₂CF₂ by pumping with a 60 W CO₂ laser. Several of these emissions have been assigned to rotation transitions within the v4 and v9 vibration manifolds; hot and combination band transitions are suspected for the others.this work was funded by the Ministry of Defence