title: Hydraulic resistance of developing Actinidia fruit

authors: Mazzeo, Mariarosaria

subjects: Calcium concentration

abstract: Background and Aims Xylem flows into most fruits decline as the fruit develop, with important effects on mineral and carbohydrate accumulation. It has been hypothesized that an increase in xylem hydraulic resistance (RT) contributes to this process. This study examined changes in RT that occur during development of the berry of kiwifruit (Actinidia deliciosa), identified the region within the fruit where changes were occurring, and tested whether a decrease in irradiance during fruit development caused an increase in RT, potentially contributing to decreased mineral accumulation in shaded fruit.

Methods RT was measured using pressure chamber and flow meter methods, the two methods were compared, and the flow meter was also used to partition RT between the pedicel, receptacle and proximal and distal portions of the berry. Dye was used as a tracer for xylem function. Artificial shading was used to test the effect of light on RT, dye entry and mineral accumulation.

Key Results RT decreased during the early phase of rapid fruit growth, but increased again as the fruit transitioned to a final period of slower growth. The most significant changes in resistance occurred in the receptacle, which initially contributed 20 % to RT, increasing to 90 % later in development. Dye also ceased moving beyond the receptacle from 70 d after anthesis. The two methods for measuring RT agreed in terms of the direction and timing of developmental changes in RT, but pressure chamber measurements were consistently higher than flow meter estimates of RT, prompting questions regarding which method is most appropriate for measuring fruit RT. Shading had no effect on berry growth but increased RT and decreased dye movement and calcium concentration.

Conclusions Increased RT in the receptacle zone coincides with slowing fresh weight growth, reduced transpiration and rapid starch accumulation by the fruit. Developmental changes in RT may be connected to changes in phloem functioning and the maintenance of water potential gradients between the stem and the fruit. The effect of shade on RT extends earlier reports that shading can affect fruit vascular differentiation, xylem flows and mineral accumulation independently of effects on transpiration.

text: Hydraulic resistance of developing Actinidia fruit Background and Aims Xylem flows into most fruits decline as the fruit develop, with important effects on mineral and carbohydrate accumulation. It has been hypothesized that an increase in xylem hydraulic resistance (RT) contributes to this process. This study examined changes in RT that occur during development of the berry of kiwifruit (Actinidia deliciosa), identified the region within the fruit where changes were occurring, and tested whether a decrease in irradiance during fruit development caused an increase in RT, potentially contributing to decreased mineral accumulation in shaded fruit.

Methods RT was measured using pressure chamber and flow meter methods, the two methods were compared, and the flow meter was also used to partition RT between the pedicel, receptacle and proximal and distal portions of the berry. Dye was used as a tracer for xylem function. Artificial shading was used to test the effect of light on RT, dye entry and mineral accumulation.

Key Results RT decreased during the early phase of rapid fruit growth, but increased again as the fruit transitioned to a final period of slower growth. The most significant changes in resistance occurred in the receptacle, which initially contributed 20 % to RT, increasing to 90 % later in development. Dye also ceased moving beyond the receptacle from 70 d after anthesis. The two methods for measuring RT agreed in terms of the direction and timing of developmental changes in RT, but pressure chamber measurements were consistently higher than flow meter estimates of RT, prompting questions regarding which method is most appropriate for measuring fruit RT. Shading had no effect on berry growth but increased RT and decreased dye movement and calcium concentration.

Conclusions Increased RT in the receptacle zone coincides with slowing fresh weight growth, reduced transpiration and rapid starch accumulation by the fruit. Developmental changes in RT may be connected to changes in phloem functioning and the maintenance of water potential gradients between the stem and the fruit. The effect of shade on RT extends earlier reports that shading can affect fruit vascular differentiation, xylem flows and mineral accumulation independently of effects on transpiration.

year: 2013

title: Speed control with low armature loss for very small sensorless brushed DC motors

authors: Scott, Jonathan B.

subjects: DC motor drives

abstract: A method for speed control of brushed dc motors is presented. It is particularly applicable to motors with armatures of less than 1 cm3. Motors with very small armatures are difficult to control using the usual pulsewidth-modulation (PWM) approach and are apt to overheat if so driven. The technique regulates speed via the back electromotive force but does not require current-discontinuous drives. Armature heating in small motors under PWM drive is explained and quantified. The method is verified through simulation and measurement. Control is improved, and armature losses are minimized. The method can expect to find application in miniature mechatronic equipment.

text: Speed control with low armature loss for very small sensorless brushed DC motors A method for speed control of brushed dc motors is presented. It is particularly applicable to motors with armatures of less than 1 cm3. Motors with very small armatures are difficult to control using the usual pulsewidth-modulation (PWM) approach and are apt to overheat if so driven. The technique regulates speed via the back electromotive force but does not require current-discontinuous drives. Armature heating in small motors under PWM drive is explained and quantified. The method is verified through simulation and measurement. Control is improved, and armature losses are minimized. The method can expect to find application in miniature mechatronic equipment.

year: 2009

title: The chronology of Waikato pā: A spatio-temporal investigation of pā in the middle Waikato basin

authors: McBride, Rowan

subjects: pā

abstract: This study considers the chronology of pā construction, proliferation, and development within the 
Middle Waikato Basin through a spatio-temporal investigation of palisade construction activity as 
identified at six pā (fortified places). The chronological approach applied in this thesis uses 14C 
wiggle-match dating to provide an accurate and precise calendar date for the felling of a tree 
(Felling Date) used to construct a palisade defence at a pā. These Felling Dates are interpreted using 
the theory of time perspectivism, focusing on three distinct scales of analysis: Event, Local, and 
Regional. The event scale of analysis successfully produced twenty high-precision felling dates on 
posts recovered from Lake Mangakaware 1 (MA1), Lake Mangakaware 2 (MA2), Lake Mangahia 
(MGA), Taraheke Pā (TAR), Te Uapata Pā (TEU) and Lake Rotokauri (ROT). The local scale 
analysis utilised these felling dates to track the development of the identified palisade defences 
over time, identifying multiple palisade construction phases, representing construction, repair and 
redevelopment episodes at MA1, MA2, MGA, TAR and TEU. Finally, the regional scale analysis 
integrated this evidence into a broader chronological framework, identifying shared episodes of 
palisade construction activity within the Middle Waikato Basin. This analysis highlights three 
critical periods of proposed socio-political stress and stability between the late fifteenth and early 
nineteenth centuries, related to hypothesised influential variables from the broader cultural and 
archaeological landscape that are proposed to be responsible for the emergence, proliferation and 
development of pā over time.

text: The chronology of Waikato pā: A spatio-temporal investigation of pā in the middle Waikato basin This study considers the chronology of pā construction, proliferation, and development within the 
Middle Waikato Basin through a spatio-temporal investigation of palisade construction activity as 
identified at six pā (fortified places). The chronological approach applied in this thesis uses 14C 
wiggle-match dating to provide an accurate and precise calendar date for the felling of a tree 
(Felling Date) used to construct a palisade defence at a pā. These Felling Dates are interpreted using 
the theory of time perspectivism, focusing on three distinct scales of analysis: Event, Local, and 
Regional. The event scale of analysis successfully produced twenty high-precision felling dates on 
posts recovered from Lake Mangakaware 1 (MA1), Lake Mangakaware 2 (MA2), Lake Mangahia 
(MGA), Taraheke Pā (TAR), Te Uapata Pā (TEU) and Lake Rotokauri (ROT). The local scale 
analysis utilised these felling dates to track the development of the identified palisade defences 
over time, identifying multiple palisade construction phases, representing construction, repair and 
redevelopment episodes at MA1, MA2, MGA, TAR and TEU. Finally, the regional scale analysis 
integrated this evidence into a broader chronological framework, identifying shared episodes of 
palisade construction activity within the Middle Waikato Basin. This analysis highlights three 
critical periods of proposed socio-political stress and stability between the late fifteenth and early 
nineteenth centuries, related to hypothesised influential variables from the broader cultural and 
archaeological landscape that are proposed to be responsible for the emergence, proliferation and 
development of pā over time.

year: 2024