Formation of alkane‐phosphonic acid self‐assembled monolayers on alumina: an in situ SPR study

The formation process of n‐alkane phosphonic acid CH₃ (CH₂)_n?1 PO(OH)₂ (n = 10,12,14,18) self‐assembled monolayers (SAMs), deposited from ethanol solutions on aluminum oxide, has been monitored in situ using surface plasmon resonance (SPR) spectroscopy. In addition, the two‐solvent approach is used to obtain both film thickness and refractive index of the fully formed adsorbed layers. A densely packed adsorbed layer is formed only for the longest molecules with n = 18. The chain length and solution concentration dependence of formation kinetics are studied, and the existence of two distinct kinetic steps is revealed. Fittings of the experimental results with various kinetic models are performed. Our analysis suggests that during the first kinetic step, a transition from a lying‐down to a standing‐up phase takes place, and the growth of this standing‐up phase is governed by second‐order kinetics. The second slow kinetic step is described by a modified first‐order Langmuir law. Copyright © 2009 John Wiley & Sons, Ltd.     

Higher-order accurate polyspectral estimation with flat-top lag-windows

Improved performance in higher-order spectral density estimation is achieved using a general class of infinite-order kernels. These estimates are asymptotically less biased but with the same order of variance as compared to the classical estimators with second-order kernels. A simple, data-dependent algorithm for selecting the bandwidth is introduced and is shown to be consistent with estimating the optimal bandwidth. The combination of the specialized family of kernels with the new bandwidth selection algorithm yields a considerably improved polyspectral estimator surpassing the performances of existing estimators using second-order kernels. Bispectral simulations with several standard models are used to demonstrate the enhanced performance with the proposed methodology.     

Development of recombinant protein-based influenza vaccine. Expression and affinity purification of H1N1 influenza virus neuraminidase

The influenza virus surface glycoprotein antigen neuraminidase (NA) is a crucial viral enzyme with many potential medical applications; therefore, the development of efficient upstream and downstream processing strategy for the expression and purification of NA is of high importance. In the present work the NA gene from the H1N1 influenza virus strain A/Beijing/262/95 was cloned from viral RNA and expressed in expresSF+ insect cells using the baculovirus expression vector system (BVES). A limited affinity-ligand library was synthesized and evaluated for its ability to bind and purify the recombinant H1N1 neuraminidase. Affinity-ligand design was based on mimicking the interactions of the lock-and-key (LAK) motif (Phe-Gly-Gln), a common structural moiety found in the subunit interface of glutathione S-transferase I (GST I), and plays an important structural role in subunit-subunit recognition. Solid-phase combinatorial chemistry was used to synthesize 13 variants of the lock-and-key lead ligand (Phe-Trz-X, where X was selected alpha-amino acid) using the 1,3,5-triazine moiety (Trz) as the scaffold for assembly. One immobilized ligand, bearing phenylalanine and isoleucine linked on the chlorotriazine ring (Phe-Trz-Ile), displayed high affinity for NA. Absorption equilibrium and molecular modeling studies were carried out to provide a detailed picture of Phe-Trz-Ile interaction with NA. This LAK-mimetic affinity adsorbent was exploited in the development of a facile purification protocol for NA, which led to 335-fold purification in a single-step. The present purification procedure is the most efficient reported so far for recombinant NA.     

Diffusion damping during adiabatic z-rotation pulses for NMR spectroscopy in inhomogeneous magnetic fields

High-resolution nuclear magnetic resonance spectra from samples located in inhomogeneous static and radio frequency magnetic fields can be obtained by applying a train of z-rotation radio frequency pulses to repeatedly refocus the inhomogeneous broadening during signal detection. z-rotation pulses based on an adiabatic double passage are effective over wide bandwidths using a limited amount of radio frequency power at the expense of being time consuming and, consequently, sensitive to motion of the spin bearing molecules. The signal damping resulting from molecular self-diffusion during the pulse was studied experimentally and using Brownian dynamics simulations. The results show that the analytical expression for diffusion damping during a double spin echo is a reasonable approximation for the signal decay during an adiabatic z-rotation pulse. Methods to alleviate the effects of diffusion are discussed.     

Enhancing the acquisition efficiency of fast magnetic resonance imaging via broadband encoding of signal content

Current efficient magnetic resonance imaging (MRI) methods such as parallel-imaging and k-t methods encode MR signals using a set of effective encoding functions other than the Fourier basis. This work revisits the proposition of directly manipulating the set of effective encoding functions at the radiofrequency excitation step in order to increase MRI efficiency. This approach, often termed "broadband encoding," enables the application of algebraic matrix factorization technologies to extract efficiency by representing and encoding MR signal content in a compacted form. Broadband imaging equivalents of fast multiecho, parallel and k-t MRI are developed and analyzed. The potential of these techniques to increase the time efficiency of data acquisition is experimentally verified on a commercial MRI scanner using simple spin-echo imaging. A three-dimensional gradient-echo dynamic imaging application that demonstrates the potential benefits of this approach compared to the present state of the art for certain applications is also presented.     

Enzymatic reductions for the regio- and stereoselective synthesis of hydroxy-keto esters and dihydroxy esters

Ketoreductases were utilized for the stereoselective synthesis of δ-hydroxy-β-keto esters, β-hydroxy-δ-keto esters, and β,δ-dihydroxy esters. Seven out of eight possible stereoisomers were obtained from the enzymatic reduction of the corresponding β,δ-diketo ester in high enantio- and diastereomeric excess.     

Instabilities in quantum-dot spin-VCSELs

A modified spin-flip model is used to investigate the stability of optically-pumped quantum-dot spin-vertical cavity surface-emitting lasers. in terms of pump intensity and polarization. The stability maps exhibit pronounced polarization switching in the stable regions. Periodic oscillations in unstable regions are attributed to competition between spin relaxation and birefringence.     

A new multi-objective self-organizing optimization algorithm (MOSOA) for spatial optimization problems

Spatial planning is an important and complex activity. It includes land use planning and resource allocation as basic components. An abundance of papers can be found in the literature related to each one of these two aspects separately. On the contrary, a much smaller number of research reports deal with both aspects simultaneously. This paper presents an innovative evolutionary algorithm for treating combined land use planning and resource allocation problems. The new algorithm performs optimization on a cellular automaton domain, applying suitable transition rules on the individual neighbourhoods. The optimization process is multi-objective, based on non-domination criteria and self-organizing. It produces a Pareto front thus offering an advantage to the decision maker, in comparison to methods based on weighted-sum objective functions. Moreover, the present multi-objective self-organizing algorithm (MOSOA) can handle both local and global spatial constraints. A combined land use and water allocation problem is treated, in order to illustrate the cellular automaton optimization approach. Water is allocated after pumping from an aquifer, thus contributing a nonlinearity to the objective function. The problem is bi-objective aiming at (a) the minimization of soil and groundwater pollution and (b) the maximization of economic profit. An ecological and a socioeconomic constraint are imposed: (a) Groundwater levels at selected places are kept above prescribed thresholds. (b) Land use quota is predefined. MOSOA is compared to a standard multi-objective genetic algorithm and is shown to yield better results both with respect to the Pareto front and to the degree of compactness. The latter is a highly desirable feature of a land use pattern. In the land use literature, compactness is part of the objective function or of the constraints. In contrast, the present approach renders compactness as an emergent result.     

A constitutive theory for shape memory polymers. Part II: A linearized model for small deformations

A constitutive theory is developed for shape memory polymers. It is to describe the thermomechanical properties of such materials under large deformations. The theory is based on the idea, which is developed in the work of Liu et al. [2006. Thermomechanics of shape memory polymers: uniaxial experiments and constitutive modelling. Int. J. Plasticity 22, 279-313], that the coexisting active and frozen phases of the polymer and the transitions between them provide the underlying mechanisms for strain storage and recovery during a shape memory cycle. General constitutive functions for nonlinear thermoelastic materials are used for the active and frozen phases. Also used is an internal state variable which describes the volume fraction of the frozen phase. The material behavior of history dependence in the frozen phase is captured by using the concept of frozen reference configuration. The relation between the overall deformation and the stress is derived by integration of the constitutive equations of the coexisting phases. As a special case of the nonlinear constitutive model, a neo-Hookean type constitutive function for each phase is considered. The material behaviors in a shape memory cycle under uniaxial loading are examined. A linear constitutive model is derived from the nonlinear theory by considering small deformations. The predictions of this model are compared with experimental measurements.