Studies on the curing kinetics of epoxy resins using mixture of nadic/or maleic anhydride and 4,4′-diaminodiphenyl sulfone

Curing kinetics of diglycidyl ether of bisphenol-A (DGEBA) in the presence of maleic anhydride (MA)/or nadic anhydride (NA) or mixture of MA/NA: 4,4′-diaminodiphenyl sulfone (DDS) in varying molar ratios were investigated using differential scanning calorimetry. Curing behaviour of DGEBA in the presence of varying amounts of DDS:MA/NA was evaluated by recording DSC scans at heating rates of 5, 10, 15 and 20°C min⁻¹. The peak exotherm temperature depends on the heating rate, structure of the anhydride as well as on the ratio of anhydride: DDS. Thermal stability of the isothermally cured resins was evaluated by thermogravimetry. The char yield was highest in case of resins cured using mixture of DDS:MA (0.75:0.25; sample EM-1) and DDS:NA (0.75:0.25, sample EN-1).     

Hadron production near threshold

Final state interaction effects inpp→ pΛK ⁺ andpd →³Heη reactions are explored near threshold to study the sensitivity of the cross-sections to thepΛ potential and theηN scattering matrix. The final state scattering wave functions between Λ andp andη and³He are described rigorously. The Λ production is described by the exchange of one pion and aK-meson between two protons in the incident channel. Theη production is described by a two-step model, where in the first step a pion is produced. This pion then produces anη by interacting with another nucleon     

Photodecomposition of several compounds commonly used as sunscreen agents

The photolysis reactions of three compounds commonly used as a sunscreen agents, Parsol 1789 (1-[4-(1,1-dimethylethyl)phenyl]-3-(4-methoxyphenyl)-1,3- propanedione), Oxybenzone ((2-hydroxy-4-methoxyphenyl)phenyl-methanone) and Padimate O (2-ethylhexyl-4-(dimethylamino)benzoate), were investigated to provide a chemical background to aid in the understanding of the photosensitization of the sunscreen agents. Photolysis was carried out in cyclohexane for 70–140 h using a mercury vapor lamp (450W) without excluding oxygen.

Irradation of Parsol 1789 in cyclohexane yielded tert-butylbenzene, p-tert-butylbenzoic acid and p-methoxybenzoic acid; products obtained from the combination of the sunscreen with the solvent included the cyclohexyl esters of p-methoxybenzoic acid, p-tert-butylbenzoic acid and methanoic acid; products obtained from the solvent included cyclohexanol, cyclohexanone and dicyclohexyl ether.

Irradiation of Oxybenzone in the cyclohexane for 100 h produced no detectable products by either gas or liquid chromatographic analysis. Oxybenzone was recovered unchanged and no products were observed from the photoinitiated reaction of oxygen with the solvent.

Irradiation of Padimate O in cyclohexane yielded the ethylhexyl esters of p-aminobenzoic acid, p-monomethylaminobenzoic acid and p-dimethylamino (o/m)-methylbenzoic acid, as well as products from the photoinitiated reaction of oxygen with the solvent.     

Low-density close-closed loop burst error detecting codes

In this paper, we study cyclic codes detecting a subclass of close-closed loop bursts viz. low-density close-closed loop bursts. A sub-class of CT close-closed loop bursts called CT low-density close-closed loop bursts is also studied.     

Glasses for lithography

The highest resolution in a lithographic process is often determined by the properties of the resist material. With the currently used polymeric resists, a resolution of better than 100 nm has been achieved under manufacturing conditions, but the future nanoscale devices will require a 10 times superior resolution. In this paper we present an overview of the resist materials, especially with regard to limiting resolution. In principle, inorganic resists should have higher limiting resolution than polymer resists due to smaller fundamental structural units and stronger bonds in the former. However, compositional and/or structural inhomogeneities may limit their ultimate resolution. New results are presented that indicate chalcogenide glasses as promising photo and electron beam resists, which also have the advantages of greater hardness, resistance to acids, easy fabrication in thin film form, and the unique phenomena like radiation enhanced diffusion.     

Model based online diagnosis of unbalance and transverse fatigue crack in rotor systems

A model based technique for online identification of malfunctions in rotor systems is discussed. Presence of fault changes the dynamic behavior of the system. This change is taken into account by equivalent loads acting on the undamaged system model. Equivalent loads are fictitious forces and moments acting on the undamaged system model, which generate a dynamic behavior identical to that of the real damaged system. The mathematical representation of equivalent loads is referred to as Fault Model. The work focuses on developing a fault model for a transverse fatigue crack in shaft and testing it through simulated studies. The basic principle of the technique is validated for unbalance identification, through numerical simulations as well as by experiments on a real rotor system.