Effect of organoclay addition on the two-body abrasive wear characteristics of polyamide 6 nanocomposites

Polymer clay nanocomposites (PCN) exhibit improved mechanical properties due to nanolevel dispersion of clay in the polymer matrix. They also exhibit good tribological performance under dry sliding conditions. Abrasive wear behaviour of these materials would be different from dry sliding behaviour as the mechanisms of the both are entirely different. Hence the abrasive wear behaviour of these materials needs to be investigated. The abrasive wear characteristics of polyamide 6 nanocomposites, with 1, 3 and 5% (wt.) clay prepared by melt intercalation technique, under two-body abrasive wear conditions have been reported. Abrasive wear tests were conducted using a pin-on-disc tribometer containing an abrasive counterface. All the polyamide nanocomposites investigated exhibited a low abrasive wear resistance compared with pristine Nylon. The wear performance of the nanocomposites was correlated with the mechanical properties. Dominant ploughing and cutting wear were observed in polymer clay nanocomposites. The amount of clay present alters the wear mechanism.     

Epoxidation of natural rubber studied by nmr spectroscopy

Epoxidation of natural rubber with peroxyacids in homogeneous solution (CHCl₃, benzene) and in latex occurs without main chain fission or isomerization of the cis configuration. There are two possible modes of addition of oxygen to the double bond, which gives rise to diastereoisomers in dyad structures, as shown by the occurrence of splitting of ¹³C NMR resonances in 100% epoxidized rubber. In partially epoxidized rubber the ¹³C NMR resonances of the methylene carbon atoms have been fully assigned using pulse sequences and lanthanide shift reagents, in terms of triad sequences. Resonances in the olefinic region of the spectrum require assignment in terms of pentad sequences whereas those from the oxirane region are much more closely spaced and are assigned using triads. Intensity measurements on the methylene carbon NMR resonances show that the epoxidation reaction is a random process in both homogeneous solution and in latex particles.     

A fuzzy logic system for channel equalization

We present a new method for channel equalization using fuzzy logic. The membership functions are derived from the training data set, and a method to estimate the delay of the communication channel is proposed. The performance of the fuzzy equalizer is compared with that of a transversal filter equalizer. It is shown using simulations that the transversal filter requires a much larger training set to achieve the same error rate. It is also shown, using simulations, that the fuzzy equalizer performs better in the presence of channel nonlinearities     

The Effect of Moisture Content on the Conversion of Ergosterol to Vitamin D in Shiitake Mushrooms

The distribution of ergosterol in different parts of shiitake mushrooms was studied in order to optimize the conversion of ergosterol to vitamin D₂ during drying. The effect of moisture on the conversion of ergosterol to vitamin D₂ was also investigated by adjusting the moisture content of fresh mushrooms to different levels in a large vacuum desiccator and subjecting them to UV irradiation at 290-320 nm wavelength, for 2 h. The moisture, ergosterol and vitamin D₂ contents were determined using standard procedures. It was found that the ergosterol content on a dry matter basis of fresh shiitake mushroom was highest in the gills (10.6 ± 0.99 mg/g DM), followed by the cap or pileus (5.34 ± 0.64 mg/g DM) and was least in the stalk or stipe (2.97 ± 0.56). The moisture content had a marked influence on the conversion of ergosterol to vitamin D₂, the best conversion taking place at a moisture content of about 70% on a wet basis.     

Rates of reinfection with Echinococcus granulosus, Taenia hydatigena, taenia ovis and other cestodes in a rural dog population in Uruguay

Forced thinking is an incompletely understood and rarely described epileptic aura. We studied three patients with forced thinking from left frontal lesions, two neoplastic and one vascular. All three experienced repetitive, intrusive thoughts at the onset of seizures. Their forced thinking was associated with the desire to vocalize, orobuccal movements, and speech arrest. The episodes occurred with other ictal manifestations and responded to antiseizure therapy. These patients suggest that epileptic forced thinking is a heterogeneous phenomenon; forced thinking from left frontal lesions is a manifestation of expressive language and is distinct from experiential thoughts arising from temporal limbic foci.     

Surface modification of natural rubber laces

Epoxidation has been applied to modify the surface of natural rubber laces. When very thin laces of fractionated bleached rubber are used, about 6% of the double bonds could be modified. Using ¹H nuclear magnetic resonance (NMR) and infrared (IR) analysis the best condition for the reaction was worked out. Both ¹³C NMR and differential scanning calorimetry (DSC) results indicate that the 6% epoxide groups are placed in a predominantly block manner. Modification in yellow fraction rubber however gives lower epoxy contents. Increase in glass transition tempreature by epoxidation results in more damping and better abrasion resistance. The resultant polymer acts very similar to a 90/10 natural rubber/50% epoxidized natural rubber (NR/ENR-50) blend.     

Maximum quasi-likelihood estimation for the near(2) model

Abstract.  Maximum quasi-likelihood estimation is investigated for the NEAR(2) model, an autoregressive time series model with marginal exponential distributions. In certain regions of the parameter space, simulations indicate that maximum quasi-likelihood estimators perform better than two-stage conditional least squares estimators in terms of the per cent of estimates falling in the parameter space. The problem of out-of-range estimates is shown to be caused by the lack of information in the data rather than the characteristics of the method of estimation.     

Nitrogen-containing aluminium titanate

In the Ti-Al-O-N system a phase isostructural to aluminium titanate but with expanded unit cell dimensions was observed. It was stable between 1400 and 1700 °C and has unit cell dimensions of a=0.3719 nm, b=0.9703 nm and c=0.9869 nm with a composition of Ti _1.00 ⁴⁺ Al _0.54 ³⁺ Ti _1.46 ³⁺ N _0.28 ^3– O _4.58 ^2– _0.14 Several samples were prepared by reaction sintering mixtures of TiN, Al₂O₃ and AlN powders at 1400 to 1470 °C for 4 h in a nitrogen atmosphere to maximize this phase. One specific advantage of the nitrogen-containing aluminium titanate over aluminium titanate is that the former is unchanged at 1150 °C in a nitrogen atmosphere whereas the latter decomposes. In the Al₂O₃-TiO₂ oxide system Al₂TiO₅ solid solution extends to approximately Al_0.75Ti_2.25O₅ at 1470 °C under the mildly reducing conditions of a graphite furnace. The unit cell volume increases linearly with the increasing replacement of Al³⁺ by Ti³⁺.