Low‐temperature sol–gel transformation of methyl silicon precursors to silica‐based hybrid materials

Six new methyl silicon (IV) precursors of the type [MeSi{ON?C(R)Ar}₃] [when R = Me, Ar = 2‐C₅H₄N ( 1 ), 2‐C₄H₃O ( 2 ) or 2‐C₄H₃S ( 3 ); and when R = H, Ar = 2‐C₅H₄N ( 4 ), 2‐C₄H₃O ( 5 ) or 2‐C₄H₃S ( 6 )] were prepared and structurally characterized by various spectroscopic techniques. Molecular weight measurements and FAB (Fast Atomic Bombardment) mass spectral studies indicated their monomeric nature. ¹H and ¹³C{¹H} NMR spectral studies suggested the oximate ligands to be monodentate in solution, which was confirmed by ²⁹Si{¹H} NMR signals in the region expected for tetra‐coordinated methylsilicon (IV) derivatives. Thermogravimetric analysis of 1 revealed the complex to be thermally labile, decomposing to a hybrid material of definite composition. Two representative compounds ( 2 and 4 ) were studied as single source molecular precursor for low‐temperature transformation to silica‐based hybrid materials using sol–gel technique. Formation of homogenous methyl‐bonded silica materials (MeSiO_3/2) at low sintering temperature was observed. The thermogravimetric analysis of the methylsilica material indicated that silicon‐methyl bond is thermally stable up to a temperature of 400 °C. Reaction of 2 and Al(OPrⁱ)₃ in equimolar ratio in anhydrous toluene yielded a brown‐colored viscous liquid of the composition [MeSi{ON?C(CH₃)C₄H₃O}₃.Al(OPrⁱ)₃]. Spectroscopic techniques ¹H, ¹³C{¹H}, ²⁷Al{¹H} and ²⁹Si{¹H} NMR spectra of the viscous product indicated the presence of tetracoordination around both silicon and aluminum atoms. On hydrolysis it yielded methylated aluminosilicate material with high specific surface area (464 m²/g). Scanning electron micrography confirmed a regular porous structure with porosity in the nanometric range. Copyright © 2008 John Wiley & Sons, Ltd.     

Non-linear response of a string to random excitation

The mean square deflection of a non-linear string subjected to nonplanar Gaussian white noise excitation is determined by the perturbation method. It is shown that increase in tension due to stretching, and transverse transverse mode coupling tend to reduce the mean square deflection; while longitudinal-transverse mode coupling tends to counter this effect to some extent. These results are in conformity with the trend observed in the case of periodic excitation.     

Advantages of endoscopic laser arytenoidectomy using yag laser scalpel

The surgical management of bilateral vocal cord paralysis has been performed through an endoscope in the past. The etiology of bilateral vocal cord paralysis is usually secondary to trauma; to secure an adequate airway, a tracheostomy is performed. Endoscopic laser arytenoidectomy offers a safe method of decannulating patients with maintenance of good voice quality and a rima glottidis of 4–6 mm posteriorly. Several wavelengths are available to carry out this procedure, and this article will focus on Nd:Yag laser scalpel applications. The advantage of this method is the preservation of good voice quality with an option of an external procedure, if the need arises. The laser application offers excellent hemostasis, and decreased edema and scar tissue formation. The results of our study on 10 patients appear encouraging and superior with respect to other available wavelengths.     

Determination of compressive residual stress in a doubly-clamped microbeam according to its buckled shape

In this work, an analytical relationship is derived for a doubly-clamped microbeam when it buckles after release from the substrate. In terms of the relationship, compressive residual stress in the doubly-clamped microbeam can be determined according to its buckled shape, allowing one to find the compressive residual stress directly without much experimental effort. This relationship has been used to determine compressive residual stresses in four types of doubly-clamped SiO₂ microbeams. In addition, four methods have been applied to find the elongations of these SiO₂ microbeams, and the corresponding results are compared. Finally, the residual stresses in doubly-clamped SiO₂ microbeams predicted according to the derived relationship are compared with those found in SiO₂ microcantilevers, and the results have a good match.     

A tandem mass spectrometric approach to the identification of O‐glycosylated glargine glycoforms in active pharmaceutical ingredient expressed in Pichia pastoris

Glycoforms of glargine expressed in Pichia pastoris were isolated by high‐performance liquid chromatography and analyzed by a series of chemical and mass spectrometric methods for the identification of various glycoforms, glycosylation position, nature and structure of glycans. Reduction and alkylation, peptide mapping techniques were used to decipher the amino acid site at which glycosylation had taken place. Chemical methods were coupled with mass spectrometry techniques such as electrospray ionization and matrix‐assisted laser desorption/ionization for identification of the glycosylation site. Copyright © 2009 John Wiley & Sons, Ltd.     

GaAs monolithic Schottky junction pairs for W-band crossbar mixers

A GaAs monolithic planar chip consisting of two antiparallel Schottky junctions has been designed, processed and tested as a millimetre-wave crossbar mixer. The planar chip exhibited a broadband RF performance with a low conversion loss of 5.2013;70dB and noise temperature of 750 K at 94 GHz. The structure also exhibits a high burnout capability at W-band frequencies.     

Initiation of localized shear bands in plane strain

This study is concerned with the initiation of localized shear bands in plane-strain tension and compression. A theoretical framework which views the initiation of such shear bands as a bifurcation phenomenon from a homogeneous equilibrium field in an elastic-plastic body is first briefly reviewed, and then the predictions of the theory are compared with some experimental observations on an aged maraging steel. The experiments support the physical relevance of the theory within the framework of continuum mechanics.Specifically, the comparison between theory and experiment is concerned with the critical strains to localization and the orientation of the shear bands relative to the load axis. The theoretical predictions are only in qualitative agreement with the experimental observations. A better agreement is obtained with use of the constitutive equations corresponding to the classical deformation theory (a simple vertex model) than with use of the constitutive equations of the classical flow theory. It is concluded that better constitutive equations for elastic-plastic materials are needed before theoretical predictions can be obtained which might be expected to be in closer quantitative accord with experiment.