The effect of flexibility on the photodegradation of aromatic diisocyanate-based polyurethanes

The photolytic degradation of 2,4-TDI/aliphatic diol polyurethanes is directly dependent on the flexibility of the polymer backbone. The extent of photodegradation is accelerated above the glass transition temperature, indicating the role of chain flexibility and/or oxygen diffusion in the decomposition process. Photolysis of the model compound ethyl N-phenylcarbamate (EPC) in neutral host polymer matrices indicates that the para photo-Fries to ortho photo-Fries product ratio experiences an accelerated increase with temperature above the glass transition of the polymer matrix.     

Ultrasmall Zeolite L Crystals Prepared from Highly Interdispersed Alkali‐Silicate Precursors

The preparation of nanosized zeolites is critical for applications where mass‐transport limitations within microporous networks hinder their performance. Often the ability to generate ultrasmall zeolite crystals is dependent upon the use of expensive organics with limited commercial relevance. Herein, we report the generation of zeolite L crystals with uniform sizes less than 30 nm using a facile, organic‐free method. Time‐resolved analysis of precursor assembly and evolution during nonclassical crystallization highlights key differences among silicon sources. Our findings reveal that a homogenous dispersion of potassium ions throughout silicate precursors leads to the formation of a metastable nonporous phase, which undergoes an intercrystalline transformation to zeolite L. The generation of highly interdispersed alkali‐silicate precursors is seemingly critical to enhancing the rate of nucleation and facilitating the formation of ultrasmall crystal.     

Transition Metal Ion-binding Properties of a 14-Membered N2O2S2- Macrobicyclic Ligand

The selective liquid–liquid extraction of various transition metal cations from the aqueous phase to the organic phase was carried out using a 14-membered N₂O₂S₂-macrobicycle. Metal picrates such as Pb²⁺, Co²⁺, Zn²⁺, Ni²⁺,Cu²⁺ and Cd²⁺ were used in this extraction studies. It was found that the ligand showed moderate selectivity towards Pb²⁺ only among the other metals. The extraction constant (log K _ex) was determined to be 13.8 for Pb²⁺ complex.     

Evaluation of sulphuric acid treatment as the clean-up step for the estimation of BHC and DDT in fatty and non-fatty foods

The potential of sulphuric acid treatment for clean-up of 10 food composites comprising 36 food items of north Indian total diet has been evaluated for the estimation of BHC and DDT residues by gas chromatography with electron-capture detection. In all cases the clean-up was satisfactory without resort to column chromatography. The chromatograms obtained were free from interference by the co-extractives. The method is simple, rapid and economical.     

Phase-lag analysis of explicit Nyström methods fory″=f(x,y)

We examine phase-lag (frequency distortion) of the two-parameter familyM ₄(₁, ₃) of fourth order explicit Nyström methods of [1] by applying these to the test equation:y+ ² y=0, >0. While the methodM ₄(1/6, 5/6) possessing the largest interval of periodicity of size 3.46 has a phase-lag of (1/4320)H (H ⁴=h, h is the step-size), we show that there exist two fourth order methods ofM ₄(₁, ₃) for which the phase-lag is minimal and of size (1/40320)H ⁶; interestingly, both methods also possess a sizable interval of periodicity of length 2.75 each.     

Heterocyclic compounds. X. A new synthesis of thiadiazasteroids

The reaction of ν-ketoacids or ν-aldehydo acids with o-amino amides results in the formation of 4-quinazolones. Using this reaction a number of polyheterosteroid analogs were synthesized. Thus, when 2-amino-3-carboxamido-4,5,6,7-tetrahydrobenzothiophene (9) was refluxed with levulinic acid (10) in a high boiling solvent, thiadiazasteroid analog (11) was obtained in 78% yield. It was found that this facile one-step reaction could be used to synthesize a variety of tetra and pentacyclic compounds. Nmr spectroscopy was used to assign stereochemistry to the 17-methyl “steroids” (31) and (32).     

In-plane magnetization with high coercivity in terbium iron garnet thin films deposited on Pt/Si substrate by PLD

We report on the growth of terbium iron garnet (TbIG, Tb₃Fe₅O₁₂) thin films having anomalously large coercivity and in-plane easy axis of magnetization. The TbIG thin films were prepared at room temperature (RT) on Pt/Si(1 0 0) substrates by pulsed laser deposition technique. The films deposited at RT were X-ray amorphous and do not show any magnetic order. Annealing of the RT deposited film at 900 °C resulted into fully textured (532) TbIG film. Atomic force microscopy and cross-sectional scanning electron microscopy studies of the TbIG films showed good surface quality with an average surface roughness of 5.0 nm and thickness of about 300 nm, respectively. The M-H loops measured at 20 K for TbIG films, exhibit about an order of magnitude enhancement in the coercivity value (H_c) than the single crystal. In-plane and out-of-plane M-H loops revealed that the easy axis of the magnetization lies within the film’s plane. In-plane magnetization combining with large H_c value of the TbIG thin film may be of scientific interest for the possible applications.     

Finite difference methods for two-point boundary value problems involving high order differential equations

We discuss the construction of finite difference schemes for the two-point nonlinear boundary value problem:y ⁽²ⁿ⁾+f(x,y)=0,y ^(2j)(a)=A _2j ,y ^(2j)(b)=B _2j ,j=0(1)n–1,n2. In the case of linear differential equations, these finite difference schemes lead to (2n+1)-diagonal linear systems. We consider in detail methods of orders two, four and six for two-point boundary value problems involving a fourth order differential equation; convergence of these methods is established and illustrated by numerical examples.