Microkinetics of Lamellar Crystallization in a Long Chain Polymer

The growth kinetics of single crystal lamellae grown from poly(isoprene) melts have been determined by thin film electron microscopy which also reveals the relevant microstructure. The growth rate of a continuous lamellar crystal is independent of the length of the crystal and (in the absence of crosslinks) depends only upon temperature and the chemical composition of the polymer. The temperature dependence is closely similar to that observed for bulk crystallization and spherulite growth, with a maximum crystallization rate around —24° C. The growth rate at a given temperature is extremely sensitive to the chemical composition of the poly(isoprene), being for a polymer containing 10 per cent trans-poly(isoprene) one thousandth of that for pure cis-poly(isoprene). Between these extremes the logarithm of the growth rate decreases linearly with increasing trans content. A similar effect is produced by the introduction of chemical crosslinks instead of trans units. These effects are attributed to a reduction in the probability of formation of the ‘secondary nucleus’, whose size can be calculated from the experimental data. The secondary nucleus is found to correspond to three molecular folds and this agrees well with an independent estimate obtained, by using thermodynamical theory, from the dependence of lamellar thickness on temperature.

INSTABILITY OF S MALE-STERILE CYTOPLASM IN MAIZE

A number of S male-sterile plants from several shrunken-2 inbred lines were crossed initially with an R138-TR inbred line pollinator carrying the nonrestoring genotype for S sterile cytoplasm. One such cross, involving a male-sterile female parent from inbred line M825, produced, unexpectedly, a number of male-fertile F1 progeny, along with the expected male-sterile off-spring. Pollen records of plants in F2, F3 and F4 progenies in the exceptional pedigree, and of a variety of testcross and backcross progenies from these male-fertile exceptions, indicate that the exceptional male fertility is not attributable to the action of either dominant or recessive nuclear restorer genes. They are, however, consistent with the hypothesis that the event responsible for the appearance of exceptional male-fertile offspring among progeny of the original cross involved a change from male-sterile to male-fertile condition in the cytoplasm of the male-sterile M825 plant involved as the female parent in this cross. It appears that this plant bore an ear in which there was a relatively early mutational event at the cytoplasmic level resulting in a chimera involving some kernels which carried S male-sterile cytoplasm, and others which carried the mutated fertile cytoplasmic condition. The finding of a number of additional ear chimeras supports this contention.—The evidence suggests that the change from sterile to fertile cytoplasm has occurred in a number of other instances. The male-sterile line M825 is especially prone to this change. These findings are of particular interest because it has heretofore been considered that both S and T types of male-sterile cytoplasm are highly stable.—The data presented here are not sufficient to support the notion that the exceptional event involves a qualitative change, analogous to gene mutation, in a cytoplasmic entity governing the expression of male fertility. It is equally plausible that the exceptional male fertility is the result of occasional transfer of normal cytoplasm through the male germ cells of maintainer parents.

Preservation of lipid reesterifying enzymes in the microsomal fraction of the rat jejunum

Studies were performed on methods of storage of rat jejunal tissue that would preserve activities of the lipid reesterifying enzymes, acyl CoA:monoglyceride acyltransferase and fatty acid CoA ligase. Storage at -80 degrees C of microsomes prepared from jejunal mucosa or storage of lyophilized microsomes at -20 degrees C was shown to preserve acyl CoA:monoglyceride acyltransferase very well for a matter of weeks. Preservation of fatty acid CoA ligase activity was adequate with either method, but results were not as good as for the transacylase enzyme.

Subtotal colonic replacement of the oesophagus in infancy

Twelve subtotal replacements of the oesophagus by the colon in infants with oesophageal atresia were performed. The right colon was used and it was led through a retrosternal tunnel. This procedure was carried out when the child was at least 8 kg. in weight and was thriving and in good health. The literature on the subject is reviewed and the technique and results in this small series are presented. Although this is an extensive operation and complications are not uncommon, colonic substitution of the oesophagus can confidently be recommended in infancy.

Plant Growth Promotional Effect of Azotobacter chroococcum, Piriformospora indica and Vermicompost on Rice Plant

The activities of rhizospheric organisms have been well recognized in non-leguminous plants such as tropical grasses, rice and maize. Such activities include nitrogen fixation, phosphate solubilization and mineralization that are beneficial for the overall growth and development of the plant. An experiment was carried out to study the growth promotion of rice (Oryza sativa L.) due to dual inoculation of Azotobacter chroococcum and Piriformospora indica along with vermicompost. The effects on shoot length, root length, fresh shoot and root weight, dry shoot and root weight, and panicle number on 45th day and 90th day were investigated. In both the stages these parameters of all the treated plants were significantly (P<0.05) greater than the uninoculated control. Dual inoculated plants in presence of vermicompost gave better positive effects on both 45th day and 90th day, in comparison to single inoculation of A. chroococcum, P. indica and vermicompost. However, A. chroococcum treated plants showed significant decrease in dry root weight as compared to control plants on 90th day observation. This suggested that dual inoculation of A. chroococcum and P. indica had beneficiary response on growth of rice plant. Key words: rice; Azotobacter chroococcum; Piriformospora indica; vermicompost; mycorrhizae nitrogen fixation DOI: 10.3126/njst.v9i0.3170 Nepal Journal of Science and Technology 9 (2008) 85-90

Role of exfoliative cytology in oral lesions: with special reference to rule out malignancy

Oral malignancy is quite common in country like India because of tobacco chewing and smoking. Cytology is cheaper and easy procedure that can be carried out at outdoor patient department to diagnose malignancy at early stage. The present study carried out to detect cancer pre-invasive stage by use of exfoliative cytology and to explore the possibility of using this technique in diagnosis of other oral lesions considered as premalignant ones. A total 102 patients referred from OPD and surgery department of J.A. Group of Hospital, Madhav Dispensary and Cancer Hospital, Gwalior, between July 2004 to October 2005, were included in this study. Two smears by scrap method, from each patient were prepared and after air dried stained with RAPID PAP stain. The smear were evaluated along with clinical, epidemiological data and classified in group I to IV according to the Papanicolaou classification. In our result 25 cases were normal. 47 were Leukoplakia with mean age 47.5 years, 85% male. Smear show anucleated squames predominantly 53%. Six cases were submucous fibrosis 66.7% female with mean age 38.3 years and, smear revealed rarification of nuclei in 66% cases. Two cases of mucosal hyperemia (Erythema), one-one case of traumatic ulcer and granular buccal mucosa included. Out of Twenty cases of malignancy, male were 75% with mean age of 46 year. Cheek and tongue were the common site with incidence of 60%. The smear revealed inflammatory cells in 100%, malignant cells in 75% cases either in groups or in singles. The third type of cells 60%, the undifferentiated cells 37%, and Tadpole cells in 5% cases. In study 75% cases were positive for cancer, 10% were suspicious for cancer and remaining 15% were given as negative for cancer. Cytology is reliable diagnostic tool in diagnosis of presence or absence of malignancy in a lesion with high accuracy rate. The oral cytologic technique is easy to do and can provide the help of surgeon/physician, where he/she might hesitate to perform an invasive procedure, like a biopsy, or desire more information regarding a lesion before referring the patient. Key words: Cancer; exfoliative cytology; leukoplakia; oral malignancy. DOI: 10.3126/jcmsn.v6i2.3614 Journal of college of Medical Sciences-Nepal, 2010, Vol.6, No-2, 29-37

Thermal Stability of Polyester vs. Polyether-Based Urethans

It has been shown, by means of continuous and intermittent stress relaxation measurements and oven aging studies, that polyester-based urethans are more resistant to thermal degradation than the corresponding polyether-based urethans at temperatures in the range of 50° to 150° C. It has also been shown that this difference in thermal stability is due to irreversible, oxidative cleavage of polyether chain segments. Addition of representative antioxidants of the hindered phenolic and amine types to the polyether-based prepolymers prior to curing was found to be ineffective in improving the thermal stability of the resultant polyurethan elastomer. And, finally, the practical significance of these thermal stability studies has been demonstrated through heat buildup measurements.