Phase behavior and photocrosslinking kinetics of semi-interpenetrating polymer networks prepared from miscible polymer blends

Mixtures of polystyrene derivatives (PSCS) and poly(vinyl methyl ether) (PVME) were made photocrosslinkable by chemically labeling PSCS chains with photoreactive anthracene. Miscibility of these anthracene-labeled PSCS/PVME blends was examined by light scattering under several crosslinking conditions in the one-phase region via photodimerization of anthracenes. As the reaction proceeds, the coexistence curve of PSCS/PVME blends shifts toward the low temperature side. By following the changes in concentration of anthracenes with irradiation time, it was found that the crosslinking reaction of PSCS chains in the blends does not follow the mean-field kinetics. However, it can be well expressed by the Kohlrausch–Williams–Watts (KWW) relaxation mechanism, indicating that the crosslinking reaction proceeds inhomogeneously in the blends. By scaling the reaction time with the average reaction rate obtained from the KWW equation modified for the reaction kinetics, all the crosslinking data obtained in the miscible region of the reacted blends fall on a single master curve. These experimental results suggest the universal behavior of the photocrosslinking kinetics obtained under the “shallow quench” conditions in the region far away from the coexistence curve of the reacting blends. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 455–462, 1998     

A Narrative Review of Sulfur Compounds in Whisk(e)y

The production process of whisky consists of malting, mashing, fermentation, distillation and maturation. Sulfur volatile compounds generated during this process have long attracted interest because they influence quality in general. More than forty compounds have been reported: they are formed during malting, fermentation, and distillation, but some may decrease in concentration during distillation and maturation. In sensory analysis, sulfur characteristics are described as sulfury, meaty, cereal, feinty, and vegetable, among others. Their contribution to overall quality depends on their concentration, with a positive contribution at low levels, but a negative contribution at high levels. Chemical analyses of sulfur volatiles have been developed by using sulfur-selective detectors and multi-dimensional gas chromatography to overcome the numerous interferences from the matrix. Formation pathways, thresholds, and contribution have not been elucidated completely; therefore, methods for integrating diverse data and knowledge, as well as novel technical innovations, will be needed to control sulfur volatiles in the future.     

Standard realizations of crystal lattices via harmonic maps

An Eells-Sampson type theorem for harmonic maps from a finite weighted graph is employed to characterize the equilibrium configurations of crystals. It is thus observed that the mimimum principle frames symmetry of crystals.

     

A directional acoustic array using silicon micromachined piezoresistive microphones

The need for noise source localization and characterization has driven the development of advanced sound field measurement techniques using microphone arrays. Unfortunately, the cost and complexity of these systems currently limit their widespread use. Directional acoustic arrays are commonly used in wind tunnel studies of aeroacoustic sources and may consist of hundreds of condenser microphones. A microelectromechanical system (MEMS)-based directional acoustic array system is presented to demonstrate key technologies to reduce the cost, increase the mobility, and improve the data processing efficiency versus conventional systems. The system uses 16 hybrid-packaged MEMS silicon piezoresistive microphones that are mounted to a printed circuit board. In addition, a high-speed signal processing system was employed to generate the array response in near real time. Dynamic calibrations of the microphone sensor modules indicate an average sensitivity of 831 microV/Pa with matched magnitude (+/-0.6 dB) and phase (+/-1 degree) responses between devices. The array system was characterized in an anechoic chamber using a monopole source as a function of frequency, sound pressure level, and source location. The performance of the MEMS-based array is comparable to conventional array systems and also benefits from significant cost savings.     

1-N-acylation of aminocyclitol antibiotics via zinc chelation and regiospecific N-trifluoroacetylation

Amikacin and 1-N-[(S)-4-amino-2-hydroxybutyryl]-3′,4′-dideoxykanamycin B have been prepared from kanamycin A and dibekacin by a novel, efficient sequence of reactions involving complex formation with Zn²⁺ and regiospecific N-trifluoroacetylation using ethyl trifluoroacetate.     

A novel carbon-carbon bond formation by the Lewis acid catalyzed reaction of β-styrylsilane with acetal

Treatment of (E)- and (Z)-β-styryltrimethylsilanes with benzaldehyde diethyl acetal in the presence of Lewis acid affords selectively 1,3,5-tri-phenyl-(E,E)- and (E,Z)-1,4-pentadienes, respectively.