title: Scaling acoustic directional couplers using 3D printing

authors: MacDonell, Marcus Scott Glengarry

subjects: Directional coupler

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 spectrum, multiple couplers will be required as each coupler only operates slightly over one octave. To reach 20 kHz or above requires very small, mechanically-precise construction. We achieve this precision using 3D printing techniques.
The Lagasse design method was used by Pennington to create a coupler that operated over a designed range of 1-2 kHz. This design was scaled to create an acoustic directional coupler with a designed range of 10-20 kHz. Because frequency scales inversely with the size of the coupler, the coupler needs to be built with a very high degree of precision. The coupler was therefore designed and modeled in SolidWorks and 3D printed to high precision. 
Characterization of the couplers was achieved using two distinct methods. The first, a preliminary measurement method to test the hypothesis and the second, a high precision automated measurement. The automation was scripted in python on a Ubuntu Linux distribution.
Future work may include an Acoustic coupler to be used in ultrasound, to do this the coupler would need to be scaled a further 2.5 times. This would likely prove difficult as the wavelengths at 50 kHz are in the order of mm, comparable with those of electromagnetic waves at 44 GHz.

text: Scaling acoustic directional couplers using 3D printing 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 spectrum, multiple couplers will be required as each coupler only operates slightly over one octave. To reach 20 kHz or above requires very small, mechanically-precise construction. We achieve this precision using 3D printing techniques.
The Lagasse design method was used by Pennington to create a coupler that operated over a designed range of 1-2 kHz. This design was scaled to create an acoustic directional coupler with a designed range of 10-20 kHz. Because frequency scales inversely with the size of the coupler, the coupler needs to be built with a very high degree of precision. The coupler was therefore designed and modeled in SolidWorks and 3D printed to high precision. 
Characterization of the couplers was achieved using two distinct methods. The first, a preliminary measurement method to test the hypothesis and the second, a high precision automated measurement. The automation was scripted in python on a Ubuntu Linux distribution.
Future work may include an Acoustic coupler to be used in ultrasound, to do this the coupler would need to be scaled a further 2.5 times. This would likely prove difficult as the wavelengths at 50 kHz are in the order of mm, comparable with those of electromagnetic waves at 44 GHz.

year: 2015

title: Possible Jurassic age for part of Rakaia Terrane: implications for tectonic development of the Torlesse accretionary prism

authors: Kamp, Peter J.J.

subjects: Torlesse Complex

abstract: Greywacke sandstone and argillite beds comprising Rakaia Terrane (Torlesse Complex) in mid Canterbury, South Island, New Zealand, are widely regarded as Late Triassic (Norian) in age based on the occurrence of Torlessia trace fossils, Monotis, and other taxa. This paleontological age assignment is tested using published 40Ar/39Ar mica and U-Pb zircon ages for these rocks and published and new zircon fission track (FT) ages. The youngest U-Pb zircon ages in the Rakaia Terrane rocks in mid Canterbury are Norian, whereas 10-20% of the 40Ar/39Ar muscovite ages are younger than Norian. Numerical modelling of these mica ages shows that they cannot have originated from partial thermal overprinting in the Torlesse prism if the thermal maximum was short-lived and early in the prism history (210-190 Ma), as commonly inferred for these rocks. The young component of mica ages could, however, be explained by extended residence (200-100 Ma) at 265-290deg.C in the prism. Early Jurassic (c. 189 Ma) zircon FT ages for sandstone beds from Arthur's Pass, the Rakaia valley, and the Hermitage (Mt Cook) are interpreted not to have experienced maximum temperatures above 210deg.C, and therefore cannot have been reduced as a result of partial annealing in the Torlesse prism. This is based on identification of a fossil Cretaceous, zircon FT, partial annealing zone in low-grade schists to the west, and the characteristics of the age data. The Early Jurassic zircon FT ages and the young component of 40Ar/39Ar mica ages are regarded therefore as detrital ages reflecting cooling in the source area, and constrain the maximum depositional age of parts of the Rakaia Terrane in mid Canterbury. The zircon FT data also show the initiation (c. 100 Ma) of marked and widespread Late Cretaceous cooling of Rakaia Terrane throughout Canterbury, which is attributed to uplift and erosion of inboard parts of the Torlesse prism due to continuing subduction accretion at its toe. 
The critical wedge concept is proposed as a new framework for investigating the development of the Torlesse Complex. The Rakaia Terrane may have formed the core of an accretionary wedge imbricated against the New Zealand margin during the Middle or Late Jurassic. Late Jurassic nonmarine sediments (e.g., Clent Hills Formation) accumulated upon the inner parts of the prism as it enlarged, emerged, and continued to be imbricated. Exhumation of Otago Schist from c. 135 Ma may mark the development of a balance (steady state) between sediments entering the prism at the toe and material exiting at the inboard margin. The enlargement of the area of exhumation to all of Canterbury from c. 100 Ma may reflect a dynamic response to widening of the prism through the accretion of Cretaceous sediments. The model of a dynamic critical wedge may help to explain the various expressions of the Rangitata Orogeny.

text: Possible Jurassic age for part of Rakaia Terrane: implications for tectonic development of the Torlesse accretionary prism Greywacke sandstone and argillite beds comprising Rakaia Terrane (Torlesse Complex) in mid Canterbury, South Island, New Zealand, are widely regarded as Late Triassic (Norian) in age based on the occurrence of Torlessia trace fossils, Monotis, and other taxa. This paleontological age assignment is tested using published 40Ar/39Ar mica and U-Pb zircon ages for these rocks and published and new zircon fission track (FT) ages. The youngest U-Pb zircon ages in the Rakaia Terrane rocks in mid Canterbury are Norian, whereas 10-20% of the 40Ar/39Ar muscovite ages are younger than Norian. Numerical modelling of these mica ages shows that they cannot have originated from partial thermal overprinting in the Torlesse prism if the thermal maximum was short-lived and early in the prism history (210-190 Ma), as commonly inferred for these rocks. The young component of mica ages could, however, be explained by extended residence (200-100 Ma) at 265-290deg.C in the prism. Early Jurassic (c. 189 Ma) zircon FT ages for sandstone beds from Arthur's Pass, the Rakaia valley, and the Hermitage (Mt Cook) are interpreted not to have experienced maximum temperatures above 210deg.C, and therefore cannot have been reduced as a result of partial annealing in the Torlesse prism. This is based on identification of a fossil Cretaceous, zircon FT, partial annealing zone in low-grade schists to the west, and the characteristics of the age data. The Early Jurassic zircon FT ages and the young component of 40Ar/39Ar mica ages are regarded therefore as detrital ages reflecting cooling in the source area, and constrain the maximum depositional age of parts of the Rakaia Terrane in mid Canterbury. The zircon FT data also show the initiation (c. 100 Ma) of marked and widespread Late Cretaceous cooling of Rakaia Terrane throughout Canterbury, which is attributed to uplift and erosion of inboard parts of the Torlesse prism due to continuing subduction accretion at its toe. 
The critical wedge concept is proposed as a new framework for investigating the development of the Torlesse Complex. The Rakaia Terrane may have formed the core of an accretionary wedge imbricated against the New Zealand margin during the Middle or Late Jurassic. Late Jurassic nonmarine sediments (e.g., Clent Hills Formation) accumulated upon the inner parts of the prism as it enlarged, emerged, and continued to be imbricated. Exhumation of Otago Schist from c. 135 Ma may mark the development of a balance (steady state) between sediments entering the prism at the toe and material exiting at the inboard margin. The enlargement of the area of exhumation to all of Canterbury from c. 100 Ma may reflect a dynamic response to widening of the prism through the accretion of Cretaceous sediments. The model of a dynamic critical wedge may help to explain the various expressions of the Rangitata Orogeny.

year: 2001

title: Te whakahuatanga i te reo Māori: Kua ahatia e tātou i roto i ngā tau 100 kua hipa nei? (The pronunciation of Māori: What have we done to it in the last 100 Years?)

authors: Harlow, Ray

subjects: Te reo Māori

abstract: In the words of the proverb: 'The land remains, but humankind vanishes.' One should perhaps extend this to read: 'The land remains, humankind vanishes, and language changes.' For languages are old, handed down from one generation to another, but no matter what, they change. Present-day English is not Shakespeare's or Chaucer's language. The pronunciation has changed, new words have entered the language, some words have been lost, the grammar is now different. Māori is like that as well. Over the last two centuries, many aspects of the language have become different. Many words have been borrowed from English, and become part of the language. Many new words have been created in recent years to accommodate the new topics now being spoken about in Māori. Many words have changed their meaning, e.g., 'pūtea' originally a type of basket, but now a 'fund', source of money. In the grammar, there are now constructions being used which were not correct in earlier centuries.So far as the pronunciation is concerned, how is one to observe its development? That is the substance of a research project which has only just now begun, and it is the purpose of this paper to explain the nature of that research and show some of the preliminary findings. Hence the title: The pronunciation of Māori: What have we done to it in the last 100 years? The project is supported by the Marsden Research Fund.

text: Te whakahuatanga i te reo Māori: Kua ahatia e tātou i roto i ngā tau 100 kua hipa nei? (The pronunciation of Māori: What have we done to it in the last 100 Years?) In the words of the proverb: 'The land remains, but humankind vanishes.' One should perhaps extend this to read: 'The land remains, humankind vanishes, and language changes.' For languages are old, handed down from one generation to another, but no matter what, they change. Present-day English is not Shakespeare's or Chaucer's language. The pronunciation has changed, new words have entered the language, some words have been lost, the grammar is now different. Māori is like that as well. Over the last two centuries, many aspects of the language have become different. Many words have been borrowed from English, and become part of the language. Many new words have been created in recent years to accommodate the new topics now being spoken about in Māori. Many words have changed their meaning, e.g., 'pūtea' originally a type of basket, but now a 'fund', source of money. In the grammar, there are now constructions being used which were not correct in earlier centuries.So far as the pronunciation is concerned, how is one to observe its development? That is the substance of a research project which has only just now begun, and it is the purpose of this paper to explain the nature of that research and show some of the preliminary findings. Hence the title: The pronunciation of Māori: What have we done to it in the last 100 years? The project is supported by the Marsden Research Fund.

year: 2005-05