New Zealand Journal of Geology and Geophysics, 1997
... carried out under the same analytical conditions and on the same instrument (Froggatt 1982, 1... more ... carried out under the same analytical conditions and on the same instrument (Froggatt 1982, 1983; Froggatt & Solloway 1986; Lowe 1988; Alloway 1989; Froggatt & Rogers 1990; Donoghue 1991; Pillans & Wright 1992: Stokes et al. 1992; Pillans et al. 1993; Shane & Froggatt ...
New Zealand Journal of Geology and Geophysics, 1996
A large eruption of dacite tephra (Sandy Bay Tephra) caused collapse of the flanks of the submari... more A large eruption of dacite tephra (Sandy Bay Tephra) caused collapse of the flanks of the submarine volcano, to form a caldera immediately northwest of the present island. Renewed basaltic volcanism produced scoria cones, flows, and tephra (Haszard Formation), and the final stage of this ...
New Zealand Journal of Geology and Geophysics, 2001
... D = Cockeye. in the south. Later, Mew et al. (1988) provided grain-size data to substantiate ... more ... D = Cockeye. in the south. Later, Mew et al. (1988) provided grain-size data to substantiate loess accumulation at The Lamplough, 6 km west of the sites selected for this study. The 22 590 yr old (Wilson et al. 1988) Aokautere ...
New Zealand Journal of Geology and Geophysics, 1999
... Zealand is dominantly (>90%) rhyolitic, with considerably lesser andesitic activit... more ... Zealand is dominantly (>90%) rhyolitic, with considerably lesser andesitic activity and sparse (>1%) basaltic volcanism (Cole 1986; Gamble et al. ... Mount Ruapehu is a composite andesitic stratovolcano which forms part of the Tongariro Volcanic Centre (Graham & Hackett 1987 ...
Laser surgical procedures involving photocoagulation of soft tissue have relied on subjective vis... more Laser surgical procedures involving photocoagulation of soft tissue have relied on subjective visual endpoints. The thermal damage to the denatured tissue in these procedures is highly dependent on the tissue temperatures achieved during laser irradiation. Therefore, a system capable of real time temperature monitoring and closed loop feedback was used to provide temperature controlled photocoagulation (TCPC). The TCPC system consisted of a 1.32 microns Nd:YAG laser, an infrared thermometer, and a microprocessor for data acquisition and feedback control. A porcine skin model was used. Tissue welds were completed to evaluate the photocoagulation effects at different predetermined temperatures. A quantitative measurement of tissue photocoagulation was obtained by tensile strength measurements of the laser repairs. Histology of the irradiated tissue was used to determine the extent of thermal injury associated with different photocoagulation temperatures. The TCPC system was capable of maintaining a relatively constant temperatures (+/- 4 degrees C) during laser irradiation. The tensile strengths of acute repairs increased with temperature over the range studied (65-95 degrees C). Tensile measurements made after several days of healing showed that higher temperature (95 degrees C) welds had lower strengths than repairs completed at lower (65 degrees C or 75 degrees C) temperatures and were significantly lower at 3 days. Acute histology showed that the amount thermal damage was strongly dependent on the tissue temperature and increased both in tissue depth and lateral to the repair with temperature. The histologic results suggest that the increase in the acute repair tensile strength as the weld temperature increased was due to an increase in the depth of tissue photocoagulation. The increase in the lateral tissue injury measured histologically for higher temperature welds likely resulted in the decreased chronic tensile strengths, as a healing response to excessive thermal damage. Tissue temperatures can be controlled during laser photocoagulation of skin. The degree of acute and chronic tissue damage is highly dependent on the temperature during welding. By controlling the tissue temperature during laser procedures, the surgical outcome can be more reliably predicted and reproduced, as compared to the conventional open loop methods. In addition, the use of a TCPC system should significantly reduce the learning curve for photothermal surgical procedures.
Mineral assemblages in volcanic rocks record both pre-eruptive conditions and changes experienced... more Mineral assemblages in volcanic rocks record both pre-eruptive conditions and changes experienced by magma as it rises. Titanomagnetite in andesitic magmas is especially sensitive to changes in temperature and oxygen fugacity immediately prior to and during eruptions. Two end-...
New Zealand Journal of Geology and Geophysics, 1997
... carried out under the same analytical conditions and on the same instrument (Froggatt 1982, 1... more ... carried out under the same analytical conditions and on the same instrument (Froggatt 1982, 1983; Froggatt & Solloway 1986; Lowe 1988; Alloway 1989; Froggatt & Rogers 1990; Donoghue 1991; Pillans & Wright 1992: Stokes et al. 1992; Pillans et al. 1993; Shane & Froggatt ...
New Zealand Journal of Geology and Geophysics, 1996
A large eruption of dacite tephra (Sandy Bay Tephra) caused collapse of the flanks of the submari... more A large eruption of dacite tephra (Sandy Bay Tephra) caused collapse of the flanks of the submarine volcano, to form a caldera immediately northwest of the present island. Renewed basaltic volcanism produced scoria cones, flows, and tephra (Haszard Formation), and the final stage of this ...
New Zealand Journal of Geology and Geophysics, 2001
... D = Cockeye. in the south. Later, Mew et al. (1988) provided grain-size data to substantiate ... more ... D = Cockeye. in the south. Later, Mew et al. (1988) provided grain-size data to substantiate loess accumulation at The Lamplough, 6 km west of the sites selected for this study. The 22 590 yr old (Wilson et al. 1988) Aokautere ...
New Zealand Journal of Geology and Geophysics, 1999
... Zealand is dominantly (>90%) rhyolitic, with considerably lesser andesitic activit... more ... Zealand is dominantly (>90%) rhyolitic, with considerably lesser andesitic activity and sparse (>1%) basaltic volcanism (Cole 1986; Gamble et al. ... Mount Ruapehu is a composite andesitic stratovolcano which forms part of the Tongariro Volcanic Centre (Graham & Hackett 1987 ...
Laser surgical procedures involving photocoagulation of soft tissue have relied on subjective vis... more Laser surgical procedures involving photocoagulation of soft tissue have relied on subjective visual endpoints. The thermal damage to the denatured tissue in these procedures is highly dependent on the tissue temperatures achieved during laser irradiation. Therefore, a system capable of real time temperature monitoring and closed loop feedback was used to provide temperature controlled photocoagulation (TCPC). The TCPC system consisted of a 1.32 microns Nd:YAG laser, an infrared thermometer, and a microprocessor for data acquisition and feedback control. A porcine skin model was used. Tissue welds were completed to evaluate the photocoagulation effects at different predetermined temperatures. A quantitative measurement of tissue photocoagulation was obtained by tensile strength measurements of the laser repairs. Histology of the irradiated tissue was used to determine the extent of thermal injury associated with different photocoagulation temperatures. The TCPC system was capable of maintaining a relatively constant temperatures (+/- 4 degrees C) during laser irradiation. The tensile strengths of acute repairs increased with temperature over the range studied (65-95 degrees C). Tensile measurements made after several days of healing showed that higher temperature (95 degrees C) welds had lower strengths than repairs completed at lower (65 degrees C or 75 degrees C) temperatures and were significantly lower at 3 days. Acute histology showed that the amount thermal damage was strongly dependent on the tissue temperature and increased both in tissue depth and lateral to the repair with temperature. The histologic results suggest that the increase in the acute repair tensile strength as the weld temperature increased was due to an increase in the depth of tissue photocoagulation. The increase in the lateral tissue injury measured histologically for higher temperature welds likely resulted in the decreased chronic tensile strengths, as a healing response to excessive thermal damage. Tissue temperatures can be controlled during laser photocoagulation of skin. The degree of acute and chronic tissue damage is highly dependent on the temperature during welding. By controlling the tissue temperature during laser procedures, the surgical outcome can be more reliably predicted and reproduced, as compared to the conventional open loop methods. In addition, the use of a TCPC system should significantly reduce the learning curve for photothermal surgical procedures.
Mineral assemblages in volcanic rocks record both pre-eruptive conditions and changes experienced... more Mineral assemblages in volcanic rocks record both pre-eruptive conditions and changes experienced by magma as it rises. Titanomagnetite in andesitic magmas is especially sensitive to changes in temperature and oxygen fugacity immediately prior to and during eruptions. Two end-...
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Papers by Robert Stewart