title: Laser light scattering as a probe of bovine sperm motility

authors: Woolford, Murray W.

abstract: Laser light scattering measurements of sperm motility have traditionally assumed spermatozoa to behave as point scatterers at small forward scattering angles, and motile cells to exhibit an isotropic distribution of translation vectors. Such assumptions have lead to interpretations of fluctuations in the detected optical field as arising from Doppler-beats.
Experimental and theoretical results presented in this thesis show that for bull spermatozoa, the large dimensions (>> λ) and slab-like conformation of the rotating head result in large intensity fluctuations at the photodetector which call into question the role of coherence and render the Doppler-beat interpretation untenable.
A sharply peaked scattering lobe (width ~ 20°) lying in the equatorial plane of the head is shown to give an intensity peak when the normal to the head plane becomes aligned with the scattering vector. Consequently only those motile cells swimming with appropriately aligned translation vectors contribute to the detected signal. Immotile cells, which are shown to exhibit geotaxis, become visible only to a detector aligned in the horizontal plane. A marked concentration dependence in the ratio of motile and immotile autocorrelation components is modelled on the basis of hydrodynamic interactions between motile and immotile fractions, which result in immotile cells being reoriented outside the range of visible alignments.
A complex opto-dynamic system is defined by a series of experiments which demonstrate that the traditional laser light scattering geometry gives only an empirical measure of the percent motile spermatozoa but may be used to obtain an absolute measurement of the head rotation rate. 
Discussion is given to variations in the scattering geometry and sample chamber design which are more appropriate to the phenomenology within the system.

text: Laser light scattering as a probe of bovine sperm motility Laser light scattering measurements of sperm motility have traditionally assumed spermatozoa to behave as point scatterers at small forward scattering angles, and motile cells to exhibit an isotropic distribution of translation vectors. Such assumptions have lead to interpretations of fluctuations in the detected optical field as arising from Doppler-beats.
Experimental and theoretical results presented in this thesis show that for bull spermatozoa, the large dimensions (>> λ) and slab-like conformation of the rotating head result in large intensity fluctuations at the photodetector which call into question the role of coherence and render the Doppler-beat interpretation untenable.
A sharply peaked scattering lobe (width ~ 20°) lying in the equatorial plane of the head is shown to give an intensity peak when the normal to the head plane becomes aligned with the scattering vector. Consequently only those motile cells swimming with appropriately aligned translation vectors contribute to the detected signal. Immotile cells, which are shown to exhibit geotaxis, become visible only to a detector aligned in the horizontal plane. A marked concentration dependence in the ratio of motile and immotile autocorrelation components is modelled on the basis of hydrodynamic interactions between motile and immotile fractions, which result in immotile cells being reoriented outside the range of visible alignments.
A complex opto-dynamic system is defined by a series of experiments which demonstrate that the traditional laser light scattering geometry gives only an empirical measure of the percent motile spermatozoa but may be used to obtain an absolute measurement of the head rotation rate. 
Discussion is given to variations in the scattering geometry and sample chamber design which are more appropriate to the phenomenology within the system.

year: 1980

title: The effect of age and experience on hazard perception and speed  choice in male drivers

authors: Crosswell, Rebekah Jane

subjects: hazard perception

abstract: There are many deaths on New Zealand roads each year, due to speeding related incidents. Teenage drivers (aged 15 to 24 years) are excessively represented in crash statistics. Young drivers seem to have poor hazard perception abilities compared to that of Older Experienced drivers, and may have problems choosing the appropriate speed for the road conditions.
While speeding is difficult to measure in real world situations, the use of a laboratory speed choice task in the current study allowed for speed choice to be studied in a controlled laboratory setting, in an objective way. The current experiment investigated hazard perception and speed choice in males (with higher crash statistics compared to females) using four groups, Young Novice, Advanced Novice, Young Experienced and Older Experienced drivers. Independent variables included age (ranging from 15 to 60 years), experience (Young Novice, Advanced Novice, Young Experienced and Older Experienced) and differing weather conditions (dry and wet) on rural roads and day and night conditions on urban roads. Participants were given a hazard perception dual task as per where they had a primary task of detecting immediate hazards, as well as performing a secondary task of keeping a small dot within a small square, stimulating the steering in real driving. For the Video Speed Choice Task (VST), participants were shown the video clips and asked “how fast do you think you were travelling?” And “what would be the ideal speed appropriate for the road conditions?” The results showed that younger drivers were more likely to select slower speeds, closer to the speed limit, whereas Older Experienced drivers chose greater speeds. Slower speeds were chosen during night-time conditions, and wet conditions. These unexpected results may be for a number of reasons, to be discussed in the following thesis. They will be examined in terms of the current literature on hazard perception, speed choice and driver safety in New Zealand and overseas. Implications of the current study and future research will also be discussed.

text: The effect of age and experience on hazard perception and speed  choice in male drivers There are many deaths on New Zealand roads each year, due to speeding related incidents. Teenage drivers (aged 15 to 24 years) are excessively represented in crash statistics. Young drivers seem to have poor hazard perception abilities compared to that of Older Experienced drivers, and may have problems choosing the appropriate speed for the road conditions.
While speeding is difficult to measure in real world situations, the use of a laboratory speed choice task in the current study allowed for speed choice to be studied in a controlled laboratory setting, in an objective way. The current experiment investigated hazard perception and speed choice in males (with higher crash statistics compared to females) using four groups, Young Novice, Advanced Novice, Young Experienced and Older Experienced drivers. Independent variables included age (ranging from 15 to 60 years), experience (Young Novice, Advanced Novice, Young Experienced and Older Experienced) and differing weather conditions (dry and wet) on rural roads and day and night conditions on urban roads. Participants were given a hazard perception dual task as per where they had a primary task of detecting immediate hazards, as well as performing a secondary task of keeping a small dot within a small square, stimulating the steering in real driving. For the Video Speed Choice Task (VST), participants were shown the video clips and asked “how fast do you think you were travelling?” And “what would be the ideal speed appropriate for the road conditions?” The results showed that younger drivers were more likely to select slower speeds, closer to the speed limit, whereas Older Experienced drivers chose greater speeds. Slower speeds were chosen during night-time conditions, and wet conditions. These unexpected results may be for a number of reasons, to be discussed in the following thesis. They will be examined in terms of the current literature on hazard perception, speed choice and driver safety in New Zealand and overseas. Implications of the current study and future research will also be discussed.

year: 2012

title: New Zealand’s indigenous forests – their status and drivers of change

authors: Allen, Robert

abstract: New Zealand’s remaining indigenous forests and shrublands are of immense cultural, environmental, and economic significance. A representative plot-based sample of these forests and shrublands has recently allowed an unbiased depiction of their composition
and structure. This is necessary for international reporting, performance assessment and management prioritisation. Their composition, structure, and function are driven by a diverse array of factors, many of which are complexly interrelated. The imprint of disturbances is pervasive and it is necessary to understand disturbances to interpret human-related impacts. For example, understanding impacts of exotic browsing mammals is only possible within a context of forest ecosystem development and tree demographic processes. There are now extensive areas of shrublands successional to forest, often composed of mixtures of indigenous and exotic species. These shrublands expand the pportunities for ecosystem services from, for example, carbon sequestration to water quality. An increasing area of indigenous forests and shrublands are managed for distinctive Māori aspirations that include sustainable use.

text: New Zealand’s indigenous forests – their status and drivers of change New Zealand’s remaining indigenous forests and shrublands are of immense cultural, environmental, and economic significance. A representative plot-based sample of these forests and shrublands has recently allowed an unbiased depiction of their composition
and structure. This is necessary for international reporting, performance assessment and management prioritisation. Their composition, structure, and function are driven by a diverse array of factors, many of which are complexly interrelated. The imprint of disturbances is pervasive and it is necessary to understand disturbances to interpret human-related impacts. For example, understanding impacts of exotic browsing mammals is only possible within a context of forest ecosystem development and tree demographic processes. There are now extensive areas of shrublands successional to forest, often composed of mixtures of indigenous and exotic species. These shrublands expand the pportunities for ecosystem services from, for example, carbon sequestration to water quality. An increasing area of indigenous forests and shrublands are managed for distinctive Māori aspirations that include sustainable use.

year: 2015