Search

Many jurisdictions compare model predicted odour concentration statistics against regulatory exposure limits or criteria in order to assess the risk of proposed developments resulting in nuisance odour impacts. However dose response studies designed to calibrate such criteria have returned widely divergent findings, particularly regarding the degree of influence that the frequency and intensity of odour impact events have on adverse community response (annoyance). In the absence of clear guidance from empirical data, jurisdictions have adopted a wide range of odour impact criteria and harmonisation has proven difficult to progress. This lack of harmonisation constitutes a significant gap in best-practice standards for odour impact assessment methodology and creates a substantial risk of poor assessment outcomes. In this paper a conceptual framework is developed which facilitates close investigation of the relationship between annoyance levels, the frequency and intensity dimensions of nuisance odour and exposure criteria. Within this framework the efficacy of single-percentile odour criteria to limit nuisance odour impacts is examined for several models of annoyance. Significant short-comings in single-percentile criteria are identified in those models in which both the frequency and intensity of impact events are assumed to influence annoyance on time-scales such as a year. The merits and limitations of an alternative multi-percentile criterion framework approach are examined. Models of annoyance developed within the framework suggest an improved concept of odour criteria that may lead to better assessment outcomes, assist with the reconciliation of some seemingly disparate dose response study findings and aid harmonisation of jurisdictional exposure limits.

In transvaginal scanning the tissues intervening between the fetus and transducer are relatively thin. The average thickness in the first trimester is 25 mm and reduces to 15 mm by the third trimester; the minimum thicknesses are 14 and 8 mm, respectively. Two models are proposed for calculating exposure in transvaginal scanning. The models are considered in terms of the overlying tissues and the target tissues. A fixed path, constant attenuation of 0.3 dB/MHz describes the properties of the overlying tissues throughout pregnancy. In the model used in first-trimester scanning, the target tissues of the embryo/fetus are considered to have properties similar to those of soft tissues, and they attenuate the energy at the same rate as the overlying tissues. In the model used in second- and third-trimester scanning, the bony structures of the fetus are the target tissues. These reflect 30% of the incident energy and attenuate all of the transmitted energy at their surface.

The reaction of selenium tetrachloride with the dichlorothiophene diselenolate 3,4-C4Cl2S(SeLi)2 gives triselenole (I) in 38% yield. Purification of I is difficult due to the occurrence of a facile decomposition on attempted dissolution in a variety of solvents.