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Acoustic waves that transmit phase information spatially have recently been applied to navigation and communications systems. This paper will describe a helical wave, a type of wave that transmits phase information across a section of the plane linearly about the azimuth. The wave will be described from the ground up. First, a circular baffled transducer pressure field will be derived. Next, the field generated using two crossed circular transducers will be derived and approximations given for the far field. The general expression for the acoustic field from this arrangement is derived in the far field utilizing a paraxial ray approximation for ideal sources but applied to the more complex conceptualization of the monopole source being given by the circular piston source. In addition, the work presented was investigated numerically in comparison to a different approximation made in the field dependence on monopole separation of the two sources making up the dipole. Next, numerical examination of two crossed dipoles is examined with visualizations of the pressure and discussion of transients created when the direction of spiral changes. Finally, there is a discussion for the detection and estimation of helical waves and potential uses. [ABSTRACT FROM AUTHOR]

The combined records of two 20th-century observers (Martin Bourgoin and Julian Ford) of Night Parrots Pezoporus occidentalis at permanent springs on the Ethel River amount to more published records of this elusive bird over a longer timespan (1912–1964) than anywhere else in Western Australia. Likely Night Parrot habitats persisting in the Ethel River area in 2019–2020 include extensive areas of mature Limestone Spinifex Triodia wiseana with other native perennial grasses, hard spinifex on sandplains, patchy perennial tussock grasses on minor floodplains and chenopod shrublands including perennial saltbush. We evaluate these habitats for their past uses and likely continuing changes that might have affected Night Parrots. With a mine under construction upstream in the sub-catchment headwaters and indications that the species is not extinct in the district, there is an urgent need to raise awareness of a uniquely important area and to survey the area for the species. Monitoring and coordinating protective measures across intersecting land uses is likely to improve the future of rare permanent springs and sensitive habitats. [ABSTRACT FROM AUTHOR]

Comments on the article concerning medicine-related issues published in the 'British Medical Journal'. Mortality rate due to asthma; Comparison between the safety of salmeterol and salbutamol in treating asthma; Difficulty to diagnose streptococcal pharyngitis.