Free volume and the physico‐mechanical behaviour of polyurethane/polyacrylonitrile interpenetrating polymer networks: positron annihilation results

A series of semi‐interpenetrating polymer networks (SIPNs) of polyurethane (PU) and polyacrylonitrile (PAN) in the weight ratios 90/10, 70/30, 60/40 and 50/50 PU/PAN were prepared using polyethylene glycol, 4,4′‐diphenylmethane diisocyanate and acrylonitrile by sequential polymerization. Differential scanning calorimetry and scanning electron microscopy techniques were used to find the glass transition temperature and surface morphology of SIPNs. The tough and transparent SIPN films were characterized for physico‐mechanical properties such as density, surface hardness and tensile properties. Positron annihilation lifetime spectroscopy (PALS) was used to measure the free volume behaviour of the IPNs. The sorption behaviour of IPNs with benzene penetrant was also measured. An attempt was made to correlate the PALS results with the mechanical and sorption properties of the SIPNs. Copyright © 2005 Society of Chemical Industry     

Doses to patients in routine X-ray examinations in Malaysia

A collaborative national survey initiated by the University of Malaya and the Ministry of Health was conducted from 1993 to 1995 to establish baseline patient dose data for seven common types (12 projections) of X-ray examinations in Malaysia. A total of 12 randomly selected public hospitals and 867 patients were included in this survey. The entrance surface doses (ESD) received by the patients were measured using thermoluminescent dosemeters (TLDs) attached to the patient's skin. Histograms are presented showing wide, positively skewed distributions of measured entrance surface doses for each examination. Mean, median, first and third quartile values of ESD and median effective dose are reported. Survey results are generally comparable with those reported in the UK, USA and by the International Atomic Energy Agency (IAEA). The results also provide information on dose level for a lower weight population (mean weight 60 kg) compared with the international reference dose values based on a 70 kg standard. The findings support the importance of the on-going national quality assurance programme to ensure doses are kept to a level consistent with optimum image quality. The data will also be useful for the formulation of national guidance levels as recommended by the IAEA. Furthermore, this study provides patient dosimetry information on healthcare level II countries.     

Riboflavin-binding protein induces early death of chicken embryos

Maternal riboflavin-binding protein (RfBP) mediates the deposition of riboflavin in avian eggs. A strain of Single-Comb White Leghorn chicken, genetically unable to synthesize RfBP, produces eggs deficient in riboflavin. Embryos in these eggs die on or about 13 of incubation, with severe hypoglycemia and impaired fatty acid oxidation. Injection of free riboflavin prior to incubation allows these embryos to survive and hatch normally. The egg whites of eggs from the RfBP-deficient strain were injected with different relative amounts of riboflavin and RfBP to determine their effects on the developing embryo. Injection of protein-bound riboflavin resulted in a substantial number of the embryos (27%) surviving until the end of the experiment (d 19) with an average weight of 13.7 g, demonstrating that some embryos were able to use the bound riboflavin. In control groups injected with riboflavin alone, 10 of 17 embryos survived until d 19 with an average weight 18.5 g, whereas those injected with saline died between d 10 and 13 with an average weight of 3.8 g. A fourth group, injected with apo-RfBP, produced embryos with an average weight of 0.24 g. This early death suggests that the protein scavenges the small amount of riboflavin normally available to the early embryo. Further studies showed that titration of RfBP-binding sites with exogenous riboflavin lessens this effect. These studies show that although riboflavin-binding protein is essential for the deposition of riboflavin in eggs, its presence in excess can diminish the availability of riboflavin to the chicken embryo.     

Are you treating youngsters who are or should be receiving mental health services?

Psychiatrists now recognize that the disorders of children are serious, treatable conditions and as precursors of adult psychopathology. These conditions can seriously influence the patient's behavior when undergoing dental treatment. The dentist will probably assume that the behavior problems are directly related to the nature of the dental service, rather than particular underlying personality characteristics of preschool and school-age children. It is important that practitioners recognize and understand these conditions as they attempt to provide adequate treatment. No national epidemiological studies have been conducted in this country that would provide valid indicators of either the prevalence or incidence of mental disorders among children. Local studies, however, have been done that diagnosable disorders in children range from 17.6 percent to 22 percent, including 3 percent to 5 percent who have severe emotional or behavioral problems. The prevalence of many mental disorders is greater in males than in females, ranging from a ratio of 2:1 to 9:1. Lifetime prevalence of mental disorders, first diagnosed in infancy, childhood, and adolescence range as high as 15,000 cases per 100,000 persons. It is important for the dentist to recognize that (1) even the youngest of children seen in a dental practice may be in need of mental health services, (2) management problems may stem from mental health problems, and (3) families are unaware or unwilling to admit that a child may need help.