Impact of terminal polar substitution on elastic, electro-optic and dielectric properties of four-ring bent-core nematic liquid crystals.

Here we report the influence of terminal -F, -Cl and -NO2 substitution on the elastic, dielectric and polar switching behavior of four-ring bent-core liquid crystals (LCs). Elastic constants of nematic liquid crystals are the key parameters in determining the threshold voltage and sensitivity to electro-optical response in a device. The elastic properties of bent-core liquid crystal systems show atypical temperature dependence and there is no hard-core theory to explain the behavior. However based on molecular simulation and atomistic calculations it is found in earlier studies that the bend angle dominates the behavior of elastic constants and the terminal or lateral substitutions have very little effect. Here we have studied three bent-core compounds which are differentiated only by their terminal polar substitution. The bend angle is identical (∼146°) for all the three compounds yet they show dramatically different elastic properties. In the fluoro-substituted compound K 11 > K 33, while for the other two compounds K 33 > K 11. Thus it is evident that the terminal polar substitution plays vital role in determining the elastic properties of bent-core systems. Correlating the mesophase ranges with the respective dipole moments of the samples it is observed that the fluoro-substituted compound (11-2M-F) with lowest dipole moment favours only nematic phase with smallest mesophase range (46.1 °C), compound 11-2M-Cl with moderate dipole moment favours short range nematic, broad range smectic with moderate mesophase range (53.1 °C), whereas the compound 11-2M-NO2 possesses the widest mesophase range (99.8 °C) with a very narrow nematic and a broad smectic phase amongst the three studied compounds.

Human aspects of shift work in the developing countries--I: A case study in Bangladesh.

There currently is little information available that allows objective prediction of psychosocial risks and benefits associated with the shift work in the developing countries. To provide such information, this study assessed possible differential effects of fatigue associated with the shift workers' attitude, job satisfaction, psychosocial problems, and other difficulties. Data were collected from the subjective responses on various scales using questionnaire among sixty adult male subjects working on a weekly rotating three-shift system in a shoe factory in Bangladesh. The results indicated that shift work is associated with negative aspects of disturbing their family, conjugal and social lives, curtailed leisure activities, created difficulties in meeting their friends, caused irregularity of their mealtime, affected sleep and caused health problems. However, the effect is significant only for such feelings of social and family aspects, as well as sleepy and lively hood but no significant main effects of shift schedule are observed for any of the behavioural and organizational context.

Isolation and characterization of a cellulase-free pectinolytic and hemicellulolytic thermophilic fungus.

A thermophilic fungus belonging to the Deuteromyces, having pectinase and xylanase activities, was grown at its optimum temperature of 55°C. It grew over a wide pH range of 4 to 10, being optimal at 6. The fungus grew well on modified Mandels' medium in which cellulose was substituted either with hemicellulose or pectin. With citrus pectin as carbon source, 121 units/ml of pectinase activity were obtained and with larch wood xylan as carbon source, 83 units/ml of xylanase activity were obtained.

Work-related problems in metal handling tasks in Bangladesh: obstacles to the development of safety and health measures.

Many manual labourers in Bangladesh are involved with metal-handling tasks that are both physically demanding and stressful. The metal workers have been significantly exposed to prolonged hammering and cutting activities in excessive noise and with awkward body postures. Moreover, stressors from heat and humidity, welding fumes and metal dusts often cause excess strain, and are reflected in a deterioration of their physical work performance. Indeed, physical work is the economic source in many developing countries for the support of worker's family and relatives. Unfortunately, there are many obstacles and a lack of efficient steps to restore ergonomics principles as well as occupational safety and health measures. Thus, in this paper, tasks, and jobs are classified and analysed from the results of an ergonomics survey from 343 subjects (293 adults men, age 20-40 years; 17 women, 19-32 years) and 33 child workers (14-17 years). Four types of metal working sites from two districts in Bangladesh were surveyed using questionnaires and interviews. The results showed that a significant number of workers experienced a high prevalence of work-related problems. The main aim was to identify stressful task that are related to musculoskeletal and psychosocial symptoms. Moreover, the findings reveal the possibility of why ergonomics measures are unsuccessful; and if they could have an immediate effect on the safety and health of metal workers in Bangladesh.