Supersonic Jet Noise Reduction by Coaxial Jets with Coplanar and Staggered Exits

Far-field noise radiated from coaxial cold underexpanded jet flows issuing from convergent two-nozzle configurations with coplanar and staggered-exits is investigated experimentally. The coaxial jets are operated in the "inverted" mode, i.e., the outer (annular) jet flow Mach number is higher than that of the inner (round) jet. Keeping all other geometrical and operating conditions the same, the exit-stagger of the inner (round) and the outer (annular) nozzles was varied. It is shown that the extent of the exit-stagger affects both the flows and the radiated noise from such coaxial underexpanded jet flows and that comparatively, the lowest noise levels are achieved when the coaxial nozzle-exits are coplanar. Moreover, the effectiveness of the co-flowing inner jet flow in reducing the noise radiated from either the annular or the coaxial underexpanded jet flows decreases noticeably as the exit-stagger is increased

Barriers for dental treatment of primary teeth in East and West Germany

Background. In many countries, restorative treatment in primary teeth is suboptimal. Aim. Thus, this study tried to detect barriers for dentists to restore primary teeth in kindergarten children (3–6 years). Design. For a representative survey, 320 dentists (184 West, 136 East Germany) were randomly selected from the dental associations’ registers and asked to answer a questionnaire on their profile, their view of the National Health System, and possible barriers for restoring primary teeth. Results. The analysis (response rate 57.7%) showed that the parents were no barrier and the dentists felt the need of restoring primary teeth. In addition to the children’s anxiety, the inadequate reimbursement for fillings were perceived as clear barrier. The comparison of West and East German dentists detected statistically significantly higher barriers in West Germany, where – in contrast to the German Democratic Republic – no structured training in paediatric dentistry was compulsory before unification. Only 35% of the East German dentists rated restorative treatment in 3- to 6-year-olds as stressful in contrast to 65% in West Germany, where especially male dentists found no time to treat children. Conclusion. This study reveals that dentists can also be a considerable barrier to restorative treatment in small children, especially without adequate training in dental schools