Multi‐functional initiator and poly(carboxybetaine methacrylamides) for building biocompatible surfaces using “nitroxide mediated free radical polymerization” strategies

Biomaterials generally suffer from rapid nonspecific protein adsorption, which initiates many deleterious host responses, and complex chemistries that are employed to facilitate cellular interactions. A chemical approach that, based upon current literature, combines a nonfouling architecture with a biomemtic cell‐adhesive end‐group, is presented. Namely, surface‐initiated polymerization of zwitterionic [poly (carboxybetaine methacrylamide)] brushes, with controlled charge densities and phosphonate head groups. Nitroxide mediated free radical polymerization (NMFRP) was employed for various reasons: reduces presence of potentially cytotoxic organometallic catalysts common in atom transfer radical polymerization (ATRP); and it allows a phosphonate end‐group instead of the common brominated end‐group. Thermally oxidized silicon wafers were covalently functionalized with diethyl‐(1‐(N‐(1‐(3‐(trimethoxysilyl)propylcarbamoyl)ethoxy)‐N‐tert‐butylamino)ethyl)phosphonate. NMFRP was used to graft zwitterionic carboxybetaine methacrylamide monomers of varying inter‐charge separation. The resulting thin films were characterized using Attenuated Total Reflectance‐Fourier Transform Infrared (ATR‐FTIR) and X‐ray photoelectron (XPS) spectroscopy, ellipsometry, water contact angle analysis, and thermo gravimetric analysis (TGA). The effect of spacer group on the surface charge density was determined using zeta potential techniques. It is thought that this stratagem will facilitate the ability to tailor systematically both the interior and terminal polymer properties, providing a platform for further understanding how these conditions affect protein adsorption as well as cell‐surface interactions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Relation of structure to performance characteristics of monolithic and perfusive stationary phases

Commercially available polymer-based monolithic and perfusive stationary phases were evaluated for their applicability in chromatography of biologics. Information on bed geometry, including that from electron microscopy (EM), was used to interpret and predict accessible volumes, binding capacities, and pressure drops. For preparative purification of biologics up to at least 7 nm in diameter, monoliths and perfusive resins are inferior to conventional stationary phases due to their low binding capacities (20–30 g/L for BSA). For larger biologics, up to several hundred nanometers in diameter, calculations from EM images predict a potential increase in binding capacity to nearly 100 g/L. The accessible volume for adenovirus calculated from the EM images matched the experimental value. While the pores of perfusive resins are essentially inaccessible to adenovirus under binding conditions, under non-adsorbing conditions the accessible intrabead porosity is almost as large as the interbead porosity. Modeling of breakthrough curves showed that the experimentally observed slow approach to full saturation can be explained by the distribution of pore sizes.     

Randomly chosen chaotic maps can give rise to nearly ordered behavior

Parrondo’s paradox [J.M.R. Parrondo, G.P. Harmer, D. Abbott, New paradoxical games based on Brownian ratchets, Phys. Rev. Lett. 85 (2000), 5226–5229] (see also [O.E. Percus, J.K. Percus, Can two wrongs make a right? Coin-tossing games and Parrondo’s paradox, Math. Intelligencer 24 (3) (2002) 68–72]) states that two losing gambling games when combined one after the other (either deterministically or randomly) can result in a winning game: that is, a losing game followed by a losing game = a winning game. Inspired by this paradox, a recent study [J. Almeida, D. Peralta-Salas, M. Romera, Can two chaotic systems give rise to order? Physica D 200 (2005) 124–132] asked an analogous question in discrete time dynamical system: can two chaotic systems give rise to order, namely can they be combined into another dynamical system which does not behave chaotically? Numerical evidence is provided in [J. Almeida, D. Peralta-Salas, M. Romera, Can two chaotic systems give rise to order? Physica D 200 (2005) 124–132] that two chaotic quadratic maps, when composed with each other, create a new dynamical system which has a stable period orbit. The question of what happens in the case of random composition of maps is posed in [J. Almeida, D. Peralta-Salas, M. Romera, Can two chaotic systems give rise to order? Physica D 200 (2005) 124–132] but left unanswered. In this note we present an example of a dynamical system where, at each iteration, a map is chosen in a probabilistic manner from a collection of chaotic maps. The resulting random map is proved to have an infinite absolutely continuous invariant measure (acim) with spikes at two points. From this we show that the dynamics behaves in a nearly ordered manner. When the foregoing maps are applied one after the other, deterministically as in [O.E. Percus, J.K. Percus, Can two wrongs make a right? Coin-tossing games and Parrondo’s paradox, Math. Intelligencer 24 (3) (2002) 68–72], the resulting composed map has a periodic orbit which is stable.     

Yang-Lee zeros of a planar Ising model with a boundary magnetic field

A planar Ising ferromagnet is investigated with a magnetic field acting on one surface. The Yang-Lee zeros associated with this field are located exactly on the imaginary axis and their limiting distribution is given. Above the critical temperature, this distribution has a gap, near which the pair correlation for spins in the surface exhibits cirtical behaviour. The zeros of certain antiferromagnets are located, in particular those for an antiferromagnetic ring coupled ferromagnetically to a planar Ising ferromagnet.On leave from: University of Oxford. Current Address: Department of Mathematics, The University of Texas at Austin, Austin, Texas 78712, USA     

Microfluidics structures for probing the dynamic behaviour of filamentous fungi

Although filamentous fungi live in physically and chemically complex natural environments that require optimal survival strategies, both at colony and individual cell level, their growth dynamics are usually studied on homogenous media. This study proposes a new research methodology based on the purposeful design, fabrication and operation of microfluidics structures to examine the temporal and spatial responses of filamentous fungi. Two model fungal strains, the wild type of Neurospora crassa – a commonly used model organisms – and the ro-1 mutant strain of this species impaired in hyphal growth and morphology, have been chosen to demonstrate the potential of this new methodology. Time-lapse observations of both species show that filamentous fungi respond rapidly to the physically microstructured environment without any detectable temporal or spatial adjustment period. Despite their genetic differences, and consequently different growth behaviour, both strains present efficient space-search strategies enabling them to solve the microsized networks successfully and in similar periods, thus demonstrating that the space-searching algorithms are robust and mutation-independent. Additionally, the use of the proposed methodology could put in evidence new biological mechanisms responsible for the apical extension of filamentous fungi, beyond the classical theory based on the central role of Spitzenkörper.     

Embracing the giant component

Consider a game in which edges of a graph are provided a pair at a time, and the player selects one edge from each pair, attempting to construct a graph with a component as large as possible. This game is in the spirit of recent papers on avoiding a giant component, but here we embrace it. We analyze this game in the offline and online setting, for arbitrary and random instances, which provides for interesting comparisons. For arbitrary instances, we find that the competitive ratio (the best possible solution value divided by best possible online solution value) is large. For “sparse” random instances the competitive ratio is also large, with high probability (whp); If the instance has ¼(1 + ε)n random edge pairs, with 0 < ε ≤ 0.003, then any online algorithm generates a component of size O((log n)^3/2) whp , while the optimal offline solution contains a component of size Ω(n) whp . For “dense” random instances, the average‐case competitive ratio is much smaller. If the instance has ½(1 ? ε)n random edge pairs, with 0 < ε ≤ 0.015, we give an online algorithm which finds a component of size Ω(n) whp . © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2005     

Superlattice barrier 1528-nm vertical-cavity laser with 85/spl deg/C continuous-wave operation

We report 85/spl deg/C continuous-wave electrically pumped operation of a 1528-nm vertical-cavity laser. An InP-InGaAsP active region was wafer bonded to the GaAs-AlGaAs mirrors, with a superlattice barrier to reduce the defect density in the active region.     

A Web-Based Molecular-Level Inquiry Laboratory Activity

This paper presents a new computer-based atomic level simulation of an ideal gas. The simulation is written in Java and is accessed by students through a Web browser. This software is used in conjunction with a written laboratory experiment developed within the framework of an inquiry instructional strategy. This molecular-level laboratory experiment is used in combination with a parallel macroscopic laboratory experiment. We hypothesize that students exposed to these kinds of parallel activities will be better able to link the macroscopic, microscopic, and symbolic understanding of chemical concepts.Presented at the ACS Division of Chemical Education sponsored symposium on web-assisted learning in chemistry at its 221st national meeting in San Diego, CA April 1–5, 2001.