title: 3D-printed Acoustic Directional Couplers

authors: MacDonell, Marcus Scott Glengarry

subjects: Acoustical engineering

abstract: Acoustic Directional Couplers permit separation of forward and reverse sound pressure waves. This separation opens the way to traceable precision acoustic reflection measurements. In order to span the audio frequency range, multiple couplers will be required, as each operates over a frequency range of slightly more than one octave. To reach 20kHz or above requires vary small, mechanically precise construction. We achieve this by 3D printing techniques. We manufactured two otherwise-identical couplers, one made with a powder-type 3D printer with photopolymer support structure, the other made with an ABS-filament thermoplastic-type 3D printer. We compare the measured acoustic performance of these two couplers. The wavelength of sound at 20 kHz is comparable to that encountered at a microwave frequency of 18 GHz. We expect to be able to fabricate couplers that reach 55 kHz where the wavelength is 6 mm, corresponding to a frequency of 50 GHz in the electromagnetic spectrum.

text: 3D-printed Acoustic Directional Couplers Acoustic Directional Couplers permit separation of forward and reverse sound pressure waves. This separation opens the way to traceable precision acoustic reflection measurements. In order to span the audio frequency range, multiple couplers will be required, as each operates over a frequency range of slightly more than one octave. To reach 20kHz or above requires vary small, mechanically precise construction. We achieve this by 3D printing techniques. We manufactured two otherwise-identical couplers, one made with a powder-type 3D printer with photopolymer support structure, the other made with an ABS-filament thermoplastic-type 3D printer. We compare the measured acoustic performance of these two couplers. The wavelength of sound at 20 kHz is comparable to that encountered at a microwave frequency of 18 GHz. We expect to be able to fabricate couplers that reach 55 kHz where the wavelength is 6 mm, corresponding to a frequency of 50 GHz in the electromagnetic spectrum.

year: 2014

title: Fitness consequences of population bottlenecks in an invasive blowfly

authors: Croft, Lillian

subjects: biological invasion

abstract: Invasive species often undergo demographic bottlenecks that cause a decrease in genetic diversity and associated reductions in population fitness. Despite this, they manage to thrive in novel environments. Investigating the effects of inbreeding and genetic bottlenecks on population fitness for invasive species is, therefore, key to understanding how they may survive in new environments. We used the blowfly Calliphora vicina (Sciences, Mathématiques et Physique, 1830, 2, 1), which is native to Europe and was introduced to Australia and New Zealand, to examine the effects of genetic diversity on population fitness. We first collected 59 samples from 15 populations across New Zealand and one in Australia, and used 20,501 biallelic SNPs to investigate population genomic diversity, structure and admixture. We then explored the impacts of repeated experimental bottlenecks on population fitness by creating inbred and outbred lines of C. vicina and measuring a variety of fitness traits. In wild-caught samples, we found low overall genetic diversity, signals of genetic admixture and limited (<3%) genetic differentiation between North and South Island populations, with genetic links between the South Island and Australia. Following experimental bottlenecks, we found significant reductions in fitness for inbred lines. However, fitness effects were not felt equally across all phenotypic traits. Moreover, they were not enough to cause population collapse in any experimental line, suggesting that C. vicina (when under relaxed selection, as in laboratory settings) may be able to compensate for population bottlenecks even when highly inbred. Our results demonstrate the value of a tractable experimental system for investigating processes that may facilitate or hamper biological invasion.

text: Fitness consequences of population bottlenecks in an invasive blowfly Invasive species often undergo demographic bottlenecks that cause a decrease in genetic diversity and associated reductions in population fitness. Despite this, they manage to thrive in novel environments. Investigating the effects of inbreeding and genetic bottlenecks on population fitness for invasive species is, therefore, key to understanding how they may survive in new environments. We used the blowfly Calliphora vicina (Sciences, Mathématiques et Physique, 1830, 2, 1), which is native to Europe and was introduced to Australia and New Zealand, to examine the effects of genetic diversity on population fitness. We first collected 59 samples from 15 populations across New Zealand and one in Australia, and used 20,501 biallelic SNPs to investigate population genomic diversity, structure and admixture. We then explored the impacts of repeated experimental bottlenecks on population fitness by creating inbred and outbred lines of C. vicina and measuring a variety of fitness traits. In wild-caught samples, we found low overall genetic diversity, signals of genetic admixture and limited (<3%) genetic differentiation between North and South Island populations, with genetic links between the South Island and Australia. Following experimental bottlenecks, we found significant reductions in fitness for inbred lines. However, fitness effects were not felt equally across all phenotypic traits. Moreover, they were not enough to cause population collapse in any experimental line, suggesting that C. vicina (when under relaxed selection, as in laboratory settings) may be able to compensate for population bottlenecks even when highly inbred. Our results demonstrate the value of a tractable experimental system for investigating processes that may facilitate or hamper biological invasion.

year: 2024

title: Young people, technology and the future of te Reo Māori

authors: Keegan, Te Taka Adrian Gregory

abstract: After decades of neglect and, in some instances, suppression, te reo Māori has achieved a degree of recognition and support from the Government and people. Language strategies have been written, schooling is available in both languages, and since 1987 the language has had official status. However, despite demonstrable progress in some areas, it remains a small-minority language. Within New Zealand there are 157,000 speakers of te reo Māori, about 4.1 percent of the population (Statistics New Zealand: Te Tari Tatau, 2007), and the language is classified as 'vulnerable' by UNESCO (Mosley, 2010). The language continues to face considerable pressure from English, not just because English is a majority national language but because it is an increasingly global language, with a significant presence in culture, science, media and technology. This chapter considers the relationships between young people, technology and te reo Māori. It argues that technology is an important domain of use for te reo Māori, particularly the continued use of the language by young people.

text: Young people, technology and the future of te Reo Māori After decades of neglect and, in some instances, suppression, te reo Māori has achieved a degree of recognition and support from the Government and people. Language strategies have been written, schooling is available in both languages, and since 1987 the language has had official status. However, despite demonstrable progress in some areas, it remains a small-minority language. Within New Zealand there are 157,000 speakers of te reo Māori, about 4.1 percent of the population (Statistics New Zealand: Te Tari Tatau, 2007), and the language is classified as 'vulnerable' by UNESCO (Mosley, 2010). The language continues to face considerable pressure from English, not just because English is a majority national language but because it is an increasingly global language, with a significant presence in culture, science, media and technology. This chapter considers the relationships between young people, technology and te reo Māori. It argues that technology is an important domain of use for te reo Māori, particularly the continued use of the language by young people.

year: 2014