Commercialisation of precision agriculture technologies in the macadamia industry

A prototype vision-based yield monitor has been developed for the macadamia industry. The system estimates yield for individual trees by detecting nuts and their harvested location. The technology was developed by the National Centre for Engineering in Agriculture, University of Southern Queensland for the purpose of reducing labour and costs in varietal assessment trials where yield for individual trees are required to be measured to indicate tree performance. The project was commissioned by Horticulture Australia Limited

Precision weed detection via colour and depth data fusion in real-time for automatic spot spraying

Broadacre and row crop farming in Australia uses no-till and minimum-till farming systems which have led to the overuse of specific herbicides for weed control, causing resistance to those specific herbicides to build-up in weeds. Automatic weed spot spraying can help reduce resistance build-up by specifically detecting weeds for targeted control with alternative herbicides, hence breaking the resistance cycle. Existing commercial weed spot sprayers are only capable of distinguishing green from brown, i.e. plant material in a fallow situation, and image analysis research for weed discrimination typically was not developed for commercial on-farm conditions. The research in this thesis has developed a real-time, real-world machine vision spot spray system that can operate at groundspeeds up to 20 km/h and discriminate green from green (i.e. weed from crop) under commercial conditions for two very different crop types and size scales, specifically sugarcane (grass-like) and pyrethrum (broadleaf). Occlusion of a weed leaf by another leaf or plant is a major impediment for real-world operation of a machine vision weed spot sprayer. A Depth Colour Segmentation Algorithm (DCSA) has been developed which combines depth data and colour image data to segment individual leaves from each other, based on pixel connectedness in height and colour, providing an accuracy when occluded of greater than 99%. The DCSA has a �filtering capability that can reduce the amount of data requiring further analysis by an observed 83% for sugarcane and 53% for pyrethrum. Existing feature extraction techniques have been evaluated in the thesis and have been shown to be unsatisfactory in discriminating weed from crop especially when the weed and crop are similar species, e.g. grass-like weed (guinea grass) from grass-like crop (sugarcane). Depth features were added to the extracted features of a local binary pattern function, improving the accuracy from 63% to 90% for pyrethrum identification, and showing that depth data combined with 2D data can improve the discrimination result. Additional real-world custom algorithms have been developed to achieve an identification accuracy of 87% (where 86% of the weed was occluded) with a 3.5% false positive rate for sugarcane. The Depth, Colour, Size and Spatial (DCSS) algorithm developed for pyrethrum achieved 98% accuracy for pyrethrum identification with a 1.2% false positive rate. Real-time functionality has been obtained by the development of a Synchronised Parallel Processing (SPP) technique. The SPP technique maintains a high frame rate (which determines the maximum groundspeed) by assigning the workload in a permanently allocated pipeline synchronised by the incoming video image. Calculations for sugarcane and pyrethrum show that speeds up to 18.5 and 17.2 km/h respectively are achievable based on the algorithms developed and a higher core count CPU (six cores were used in the calculation) would achieve higher groundspeeds. The gains from the additional processing availability provided by SPP can be used to achieve a higher groundspeed, or undertake additional image analysis, if required. It is concluded that the machine vision components developed in this thesis comprise a real-time, real-world machine vision spot sprayer that can operate at commercial groundspeeds up to 20 km/h and discriminate weed from crop

A global picture of quantum de Sitter space

Perturbative gravity about a de Sitter background motivates a global picture of quantum dynamics in `eternal de Sitter space,' the theory of states which are asymptotically de Sitter to both future and past. Eternal de Sitter physics is described by a finite dimensional Hilbert space in which each state is precisely invariant under the full de Sitter group. This resolves a previously-noted tension between de Sitter symmetry and finite entropy. Observables, implications for Boltzmann brains, and Poincare recurrences are briefly discussed.Comment: 17 pages, 1 figure. v2: minor changes, references added. v3: minor changes to correspond to PRD versio

Anthropic reasoning in multiverse cosmology and string theory

Anthropic arguments in multiverse cosmology and string theory rely on the weak anthropic principle (WAP). We show that the principle, though ultimately a tautology, is nevertheless ambiguous. It can be reformulated in one of two unambiguous ways, which we refer to as WAP_1 and WAP_2. We show that WAP_2, the version most commonly used in anthropic reasoning, makes no physical predictions unless supplemented by a further assumption of "typicality", and we argue that this assumption is both misguided and unjustified. WAP_1, however, requires no such supplementation; it directly implies that any theory that assigns a non-zero probability to our universe predicts that we will observe our universe with probability one. We argue, therefore, that WAP_1 is preferable, and note that it has the benefit of avoiding the inductive overreach characteristic of much anthropic reasoning.Comment: 7 pages. Expanded discussion of selection effects and some minor clarifications, as publishe

A novel shading analysis method for PV systems using sun path plots and high resolution performance data

This paper presents a technique for identifying and quantifying shading losses in PV systems. Five minute interval monitored data from domestic UK PV systems is used to assess the effects of trees and other shading objects on annual energy generation. Poor performance is identified from the relationship between in-plane irradiance and performance ratio. Shading events are identified by plotting the occurrences of poor performance on a ‘sun path plot’ of solar azimuth and elevation axes. Poor performance which concentrates about particular sun positions is identified as shading. Once identified, the energy loss due to shading is quantified

Is Double Reionization Physically Plausible?

Recent observations of z~6 quasars and the cosmic microwave background imply a complex history to cosmic reionization. Such a history requires some form of feedback to extend reionization over a long time interval, but the nature of the feedback and how rapidly it operates remain highly uncertain. Here we focus on one aspect of this complexity: which physical processes can cause the global ionized fraction to evolve non-monotonically with cosmic time? We consider a range of mechanisms and conclude that double reionization is much less likely than a long, but still monotonic, ionization history. We first examine how galactic winds affect the transition from metal-free to normal star formation. Because the transition is actually spatially inhomogeneous and temporally extended, this mechanism cannot be responsible for double reionization given plausible parameters for the winds. We next consider photoheating, which causes the cosmological Jeans mass to increase in ionized regions and hence suppresses galaxy formation there. In this case, double reionization requires that small halos form stars efficiently, that the suppression from photoheating is strong relative to current expectations, and that ionizing photons are preferentially produced outside of previously ionized regions. Finally, we consider H_2 photodissociation, in which the buildup of a soft ultraviolet background suppresses star formation in small halos. This can in principle cause the ionized fraction to temporarily decrease, but only during the earliest stages of reionization. Finally, we briefly consider the effects of some of these feedback mechanisms on the topology of reionization.Comment: 13 pages, 5 figures, in press at ApJ (reorganized significantly but major conclusions unchanged

Oxidative phosphorylation and the realkalinization of intracellular pH during recovery from anoxia in Artemia franciscana embryos

The contribution of mitochondrial oxidative phosphorylation to the realkalinization of intracellular pH (pHi) and resynthesis of purine nucleotides during recovery from anoxia was investigated in embryos of Artemia franciscana by assessing the sensitivity of mitochondrial respiration to pH, calculating proton consumption by oxidative phosphorylation, and measuring changes in pHi using 31P nuclear magnetic resonance. Following short-term anoxia, pHi increased from 6.7 to 7.7 during 20 min of aerobic recovery and was temporally correlated with a large increase in ATP. State 3 respiration rates of isolated mitochondria were not substantially compromised at the acidic pH corresponding to the pHi during anoxia (pH 6.3-6.8) compared to values obtained at pH 7.7. Both state 3 respiration rates and respiratory control ratios exhibited broad, substrate-specific pH optima, whereas state 4 respiration rates increased gradually with increasing pH. P:O flux ratios were near their mechanistic limits and did not vary appreciably with pH below 7.5. Estimates of intracellular buffering capacity indicate that between 18 and 37 mmol H+ (1 cytosol)-1 must be consumed to elevate pHi from 6.7 to 7.7. Phosphorylation of mono- and diphosphate purine-nucleotides during the first 20 min of recovery may account for the consumption of up to 4.79 mmol H+ (1 cytosol)-1. An additional 4.77 to 8.18 mmol H+ (1 cytosol)-1 may be consumed through the oxidation of mono- or dicarboxylic acids, respectively, in the Krebs cycle. Taken together, these data are consistent with a role for oxidative phosphorylation in the realkalinization of pHi and resynthesis of purine nucleotides in A. franciscana embryos during recovery from anoxia. © 1995