Simple Gallager codes for BSC

We investigate the performance of Gallager type error- correcting codes for Binary Symmetric Channels, where the code word comprises products of K bits selected from the original message and decoding is carried out utilizing a connectivity tensor with C connections per index. Shannon's bound for the channel capacity is recovered for large K and zero temperature when the code rate K/C is finite. Close to optimal error-correcting capability, with improved decoding properties is obtained for finite K and C.

Zwitterionic and charge-balanced polyampholyte copolymer hydrogels

Zwitterionic copolymers were synthesised from N,N-dimethyl-N-(2- acryloylethyl)-N-(3-sulfopropyl) ammonium betaine (SPDA) and 2-hydroxyethyl methacrylate (HEMA) produce a series of polyzwitterion hydrogels. For the synthesis of the charge-balanced copolymer hydrogels, two cationic monomers were selected: 2-(diethylamino) ethyl methacrylate (DMAEMA) and 3-(dimethylamino) propyl methacrylamide (DMAPMA), and an anionic monomer; 2-acrylamido-2- methylpropane sulphonic acid (AMPS). Two series of charge-balanced copolymers were synthesized from stoichiometrically equivalent ratios of DMAEMA or DMAPMA and AMPS with HEMA as a termonomer. All synthesized copolymers produced clear and cohesive hydrogels. The zwitterionic and charge-balanced copolymers displayed similar equilibrium water contents together with similar mechanical and surface energy properties. The swelling of the zwitterionic and the charge-balanced copolymers shows some features of antipolyelectrolyte behavior.

Casemix accounting systems and medical coding:organisational actors balanced on "leaky black boxes"

The adoption of DRG coding may be seen as a central feature of the mechanisms of the health reforms in New Zealand. This paper presents a story of the use of DRG coding by describing the experience of one major health provider. The conventional literature portrays casemix accounting and medical coding systems as rational techniques for the collection and provision of information for management and contracting decisions/negotiations. Presents a different perspective on the implications and effects of the adoption of DRG technology, in particular the part played by DRG coding technology as a part of a casemix system is explicated from an actor network theory perspective. Medical coding and the DRG methodology will be argued to represent ``black boxes''. Such technological ``knowledge objects'' provide strong points in the networks which are so important to the processes of change in contemporary organisations.

Carrier lifetime and exciton saturation in a strain-balanced InGaAs/InAsP multiple-quantum-well

The bleaching of the n = 1 heavy-hole and light-hole exciton absorption has been studied at room temperature and zero bias in a strain-balanced InGaAs/InAsP multiple quantum well. Pump-probe spectroscopy was used to measure the decay of the light-hole absorption saturation, giving a hole lifetime of only 280 ps. As only 16 meV separates the light- and heavy-hole bands, the short escape time can be explained by thermalization between these bands followed by thermionic emission over the heavy-hole barrier. The saturation density was estimated to be 1 × 1016 cm-3; this is much lower than expected for tensile-strained wells where both heavy and light holes have large in-plane masses. © 1998 American Institute of Physics.

Zwitterionic and charge-balanced (polyampholyte) copolymer hydrogels

Zwitterionic compounds, or zwitterions, are electrically neutral compounds having an equal number of formal unit charges of opposite sign. In common polyzwitterions the zwitterionic groups are usually located in pendent groups rather than the backbone of the macromolecule. Polyzwitterions contain both the anion and cation in the same monomeric unit, unlike polyampholytes which can contain the anion and cation in different monomeric units. The use of cationic and anionic monomers (or monomers capable of becoming charged) in stoichiometric equivalent proportions produces charge-balanced polyampholyte copolymers. Hydrogel materials produced from zwitterionic monomers have been proposed for use and are used in many biomaterial applications but synthetic charge-balanced polyampholyte are less common. Certain properties of hydrogels which are important for their successful use as biomaterials, these include the equilibrium water content, mechanical, surface energy, oxygen permeability, swelling and the coefficient of friction. The zwitterionic monomer N,N-dimethyl-N-(2-acryloylethyl)-N-(3-sulfopropyl) ammonium betaine (SPDA) was synthesized with 2-hydroxyethly acrylate (HEMA) as the comonomer to produce a series of polyzwitterion hydrogels. To produce charged-balanced copolymer hydrogels two “cationic” monomers were selected; 2-(diethylamino) ethyl methacrylate (DMAEMA) and 3-(dimethylamino) propyl methacrylamide (DMAPMA) and an anionic monomer; 2-acrylamido 2,2 methylpropane sulphonic acid (AMPS). Two series’ of charge-balanced copolymers were synthesized from stoichiometric equivalent ratios of DMAEMA or DMAPMA and AMPS with HEMA as a terpolymer. The zwitterionic copolymer and both charge-balanced copolymers produced clear, cohesive hydrogels. The zwitterionic and charge-balanced copolymers displayed similar EWC’s along with similar mechanical and surface energy properties. The swelling of the zwitterionic copolymer displayed antipolyelectrolyte behavior whereas the charge-balanced copolymers displayed behaviour somewhere between this and a typical polyelectrolyte. This work describes some aspects of the polymerisation and properties of SPDA copolymers and charge-balanced (polyampholyte) copolymers relevant to their potential as biomedical / bioresponsive materials. The biomimetic nature of SPDA together with its compatibility with other monomers makes it a useful and complimentary addition to the building blocks of biomaterials.

Charge-balanced copolymer hydrogels:potential as biomedical materials

Polyzwitterionic-containing hydrogel materials been proposed for use in biomaterial applications. Polyzwitterions contain anions and cations in the same monomeric unit, unlike polyampholytes which contain them in different monomeric units. The use of cationic and anionic monomers in stoichiometrically equivalent proportions produces charge-balanced polyampholytes (PA) copolymers. Membranes prepared using either betaine-containing (BT) polyzwitterionic copolymers or PA copolymers can share similar properties, but the range of EWCs offered by membranes incorporating BT and PA monomers is greater than that for conventional neutral hydrogels and methacrylic acid-based systems. Here we compare properties of BT-containing and PA-containing copolymer membranes, relevant to their potential as biomedical materials. Membranes of the copolymers were prepared as previously described. Surface energy was determined using a GBX Digidrop (GBX Scientific Instruments), with diidomethane and water as probes. The absorption of proteins was determined by soaking the membranes in 1mg/ml protein solutions for a predetermined time, and measuring UV absorption of the membranes at certain wavelengths. The BT and PA copolymer membranes displayed similar values for the polar components and dispersive components of total surface free energy. This was perhaps not surprising when the structures of the monomers were considered. The BT and PA copolymer membranes displayed differences in their protein absorption over time, with the PA demonstrating higher uptake of protein than the BT. In addition to the aforementioned greater EWC range, the use of BT and PA copolymer membranes also avoids some of the problems associated with net anionicity. Comparison of the BT copolymer with the “pseudo” zwitterionic PA copolymers shows that controlled molecular architecture is required to gain the benefits of balancing the charges present in the copolymers in a way that will make them beneficial to hydrogel design.

Nonlinear multicore waveguiding structures with balanced gain and loss

We study existence, stability, and dynamics of linear and nonlinear stationary modes propagating in radially symmetric multicore waveguides with balanced gain and loss. We demonstrate that, in general, the system can be reduced to an effective PT-symmetric dimer with asymmetric coupling. In the linear case, we find that there exist two modes with real propagation constants before an onset of the PT-symmetry breaking while other modes have always the propagation constants with nonzero imaginary parts. This leads to a stable (unstable) propagation of the modes when gain is localized in the core (ring) of the waveguiding structure. In the case of nonlinear response, we show that an interplay between nonlinearity, gain, and loss induces a high degree of instability, with only small windows in the parameter space where quasistable propagation is observed. We propose a novel stabilization mechanism based on a periodic modulation of both gain and loss along the propagation direction that allows bounded light propagation in the multicore waveguiding structures.

Differential Balanced Trees and (0,1) Matrices

* The research was supported by INTAS 00-397 and 00-626 Projects.

Recursive Methods for Construction of Balanced N-ary Block Designs

2000 Mathematics Subject Classification: Primary 05B05; secondary 62K10.

Methodology for Creating of Objective and Balanced Linear Tests Based on the Item Response Theory

Report published in the Proceedings of the National Conference on "Education and Research in the Information Society", Plovdiv, May, 2014

A diagnostic framework for demand amplification problems in supply chains

This dissertation delivers a framework to diagnose the Bull-Whip Effect (BWE) in supply chains and then identify methods to minimize it. Such a framework is needed because in spite of the significant amount of literature discussing the bull-whip effect, many companies continue to experience the wide variations in demand that are indicative of the bull-whip effect. While the theory and knowledge of the bull-whip effect is well established, there still is the lack of an engineering framework and method to systematically identify the problem, diagnose its causes, and identify remedies. ^ The present work seeks to fill this gap by providing a holistic, systems perspective to bull-whip identification and diagnosis. The framework employs the SCOR reference model to examine the supply chain processes with a baseline measure of demand amplification. Then, research of the supply chain structural and behavioral features is conducted by means of the system dynamics modeling method. ^ The contribution of the diagnostic framework, is called Demand Amplification Protocol (DAMP), relies not only on the improvement of existent methods but also contributes with original developments introduced to accomplish successful diagnosis. DAMP contributes a comprehensive methodology that captures the dynamic complexities of supply chain processes. The method also contributes a BWE measurement method that is suitable for actual supply chains because of its low data requirements, and introduces a BWE scorecard for relating established causes to a central BWE metric. In addition, the dissertation makes a methodological contribution to the analysis of system dynamic models with a technique for statistical screening called SS-Opt, which determines the inputs with the greatest impact on the bull-whip effect by means of perturbation analysis and subsequent multivariate optimization. The dissertation describes the implementation of the DAMP framework in an actual case study that exposes the approach, analysis, results and conclusions. The case study suggests a balanced solution between costs and demand amplification can better serve both firms and supply chain interests. Insights pinpoint to supplier network redesign, postponement in manufacturing operations and collaborative forecasting agreements with main distributors.^