Evaluation of automated synthesis for chain and step‐growth polymerizations: Can robots replace the chemists?

This article explores current challenges in the use of automated parallel synthesizers in polymeric materials research. Four types of polymerizations were investigated: carbodiimide‐mediated polyesterification, diphenol phosgenation, free radical, and reversible addition‐fragmentation chain‐transfer (RAFT). Synthetic challenges of condensation polymerization, such as liquid and solid dispensing accuracy, dropwise addition, and toxic chemical handling, were successfully met using the automated synthesizer. Both solid and liquid dosing of the diphenol and diacid were successful for polyarylate synthesis. The high precision of liquid dispensing made it possible to achieve stoichiometric balance using reagent stock solutions. For all reactions, molecular weights and their reproducibility were comparable to those obtained with manual synthesis. For RAFT polymerizations, solvent and mol ratio of chain transfer reagent to initiator were successfully optimized on the automated synthesizer and a library of over 60 polymethacrylate copolymer compositions was generated. Considerable savings in time relative to manual methods were achieved when generating polymer libraries (e.g., 4.5× faster for 96 polymethacrylates and 20× faster for 45 for polycarbonates). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 49–58, 2009     

Determination of phosphorus in steel by the combined technique of laser induced breakdown spectrometry with laser induced fluorescence spectrometry

Laser induced breakdown spectrometry (LIBS) combined with laser induced fluorescence spectrometry (LIFS) has been applied for detection of trace-level phosphorus in steel. The plasma induced by irradiation of Nd:YAG laser pulse for ablation was illuminated by the 3rd harmonic of Ti:Sapphire laser tuned to one of the resonant lines for phosphorus in the wavelength region of 253–256 nm. An excitation line for phosphorus was selected to give the highest signal-to-noise ratio. Fluorescence signals, P213.62 and P214.91 nm, were observed with high selectivity at the contents as low as several tens µg g^− 1. Fluorescence intensities were in a good linear correlation with the contents. Fluorescence intensity ratio of a collisionally assisted line (213.62 nm) to a direct transition line (214.91 nm) was discussed in terms of the analytical conditions and experimental results were compared with a calculation based on rate equations. Since the fluorescence signal light in the wavelength range longer than 200 nm can be transmitted relatively easily, even through fiber optics of moderate length, LIBS/LIFS would be a versatile technique in on-site applications for the monitoring of phosphorus contents in steel.     

Microdeformation behavior in nanotemplated epoxy thermosets: A study with in situ tensile deformation technique in transmission electron microscopy

Microdeformation behavior in nanostructured block copolymer‐toughened epoxy resins, or templated epoxy thermosets, was studied using an in situ tensile deformation technique performed directly in a transmission electron microscope. The observed microdeformation modes were found to correlate well with the macroscopic mechanical properties of the materials. In the order of decreasing macroscopic fracture toughness, the microdeformation modes were observed to change from large uniform plastic deformation over an extensive area, to localized plastic deformation bands, to little plastic deformation observed in the most brittle material. A similar trend was also observed when samples of the same material were tested at different temperatures, reflecting changes in the deformation mechanism as a function of temperature. Structural defects were observed in nanotoughening phases when plastic deformation was observed. The implication of the observed microdeformation modes to the macroscopic toughening mechanisms is discussed in the context of the micromorphology of the nanometer sized toughening phases and parameters of the epoxy matrix chemistry such as bromination, molecular weight, and interfacial miscibility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 393–406, 2009     

Numerical investigation of the effect of inlet condition on self‐excited oscillation of wet steam flow in a supersonic turbine cascade

Self‐excited oscillation can be induced due to the interaction between condensation process and local transonic condition in condensing flow, which is an important problem in wet steam turbine. With an Eulerian/Eulerian numerical model, the self‐excited oscillation of wet steam flow is investigated in a supersonic turbine cascade. Owing to supercritical heat addition to the subsonic flow in the convergent part of the cascade, the oscillation frequency decreases with increased inlet supercooling. Mass flow rate increases in the oscillating flow due to the greater supersaturation in condensation process, while the increase will be suppressed with the flow oscillation. Higher inlet supercooling leads to the fact that the condensation process moves upstream and the loss increases. Moreover, some predictions of oscillation effects on outflow angle and aerodynamic force are also presented. Finally, heterogeneous condensations with inlet wetness and periodic inlet conditions, as a result of the interference between stator and rotor, are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Numerical study of magnetohydrodynamic laminar flow separation in a channel with smooth expansion

The flow of an electrically conducting incompressible viscous fluid in a plane channel with smooth expansion in the presence of a uniform transverse magnetic field has been analysed. A solution technique for the governing magnetohydrodynamic equations in primitive variable formulation has been developed. A co‐ordinate transformation has been employed to map the infinite irregular domain into a finite regular computational domain. The governing equations are discretized using finite‐difference approximations in staggered grid. Pressure Poisson equation and pressure correction formulae are derived and solved numerically. It is found that with increase in the magnetic field, the size of the flow separation zone diminishes and for sufficiently large magnetic field, the separation zone disappears completely. The peak u‐velocity decreases with increase in the magnetic field. It is also found that the asymmetric flow in a symmetric geometry, which occurs at moderate Reynolds numbers, becomes symmetric with sufficient increase in the transverse magnetic field. Thus, a transverse magnetic field of suitable strength has a stabilizing effect in controlling flow separation, as also in delaying the transition to turbulence. Copyright © 2008 John Wiley & Sons, Ltd.     

Laser Microbeams and Optical Tweezers in Ageing Research

We show how a technique developed within the framework of physics and physical chemistry—in a true interdisciplinary approach—can answer questions in life sciences that are not solvable by using other techniques. Herein, we focus on blood‐pressure regulation and DNA repair in ageing studies. Laser microbeams and optical tweezers are now established tools in many fields of science, particularly in the life sciences. A short glimpse is given on the wide field of non‐age‐research applications in life sciences. Then, optical tweezers are used to show that exerting a vertical pressure on cells representing the inner lining of blood vessels results in bursts of NO liberation concomitant with large changes in cell morphology. Repeated treatment of such human umbilical vein endothelial cells (HUVEC) results in stiffening, a hallmark of manifest high blood pressure, a disease primarily of the elderly. As a second application in ageing research, a laser microbeam is used to induce, with high spatial and temporal resolution, DNA damages in the nuclei of U2OS human osteosarcoma cells. A pairwise study of the recruitment kinetics of different DNA repair proteins reveals that DNA repair starts with non‐homologous end joining (NHEJ), a repair pathway, and may only after several minutes switch to the error‐free homologous recombination repair (HRR) pathway. Since DNA damages—when incorrectly repaired—accumulate with time, laser microbeams are becoming well‐used tools in ageing research.     

Probing particle-particle interactions in flocculated oil-in-water emulsions using ultrasonic attenuation spectrometry

The flocculation of silicone oil-in-water emulsions ( φ = 0.1) containing quasi-monodisperse droplets was studied by ultrasound. The ultrasonic attenuation spectra of emulsions with different particle sizes (200-1600 nm) were measured between 0.5 and 10 MHz using an interferometer. Flocculation was induced by adding excess sodium dodecyl sulphate micelles to the emulsions to increase the attractive forces between the droplets. Droplet flocculation decreased the ultrasonic attenuation at low frequencies because of overlap of the thermal waves caused by the close proximity of the droplets within the flocs. A mean-field model which takes into account this effect was used to determine the droplet volume fraction within the flocs and thus to estimate the distance between the droplets. Received 17 July 2000     

Magnetic Thomas-Fermi-Weizsäcker model for quantum dots: A comparison with Kohn-Sham ground states

The magnetic extension of the Thomas-Fermi-Weizs?cker kinetic energy is used within density-functional-theory to numerically obtain the ground state densities and energies of two-dimensional quantum dots. The results are thoroughly compared with the microscopic Kohn-Sham ones in order to assess the validity of the semiclassical method. Circular as well as deformed systems are considered. Received 26 October 2000 and Received in final form 14 December 2000     

Coalescence process of monodispersed Co cluster assemblies

Cluster-cluster coalescence process of monodispersed Co clusters with mean diameter d = 8.5 and 13 nm deposited a plasma-gas-condensation-type cluster beam deposition system was investigated by in situ electrical conductivity measurements and ex situ scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and analyzed by percolation concept. The electrical conductivity measurement and TEM observation indicated that, below temperature T≈ 100^°C, the Co clusters in the assemblies maintain their original structure as deposited at room temperature, while that the inter-cluster coalescence takes place at T > 100^°C, although the size distribution and the interface morphology of the clusters showed no marked change at substrate temperatures T _s≤200^°C. Received 29 November 2000     

Characterization of complex networks by higher order neighborhood properties

A concept of higher order neighborhood in complex networks, introduced previously [Phys. Rev. E 73, 046101 (2006)], is systematically explored to investigate larger scale structures in complex networks. The basic idea is to consider each higher order neighborhood as a network in itself, represented by a corresponding adjacency matrix, and to settle a plenty of new parameters in order to obtain a best characterization of the whole network. Usual network indices are then used to evaluate the properties of each neighborhood. The identification of high order neighborhoods is also regarded as intermediary step towards the evaluation of global network properties, like the diameter, average shortest path between node, and network fractal dimension. Results for a large number of typical networks are presented and discussed.