Towards Quantifying The Economic Effects Of Poor And Fluctuating Water Quality On Irrigation Agriculture: A Case Study Of The Lower Vaal And Riet Rivers

Irrigation farmers in the lower reaches of the Vaal and Riet Rivers are experiencing substantial yield reductions in certain crops and more profitable crops have been withdrawn from production, hypothesised, as a result of generally poor but especially fluctuating water quality. In this paper secondary data is used in a linear programming model to test this hypothesis by calculating the potential loss in farm level optimal returns. The model is static with a time frame of two production seasons. Linear crop-water quality production functions (Ayers & Westcot, 1983; adapted from Maas & Hoffmann, 1977) are used to calculate net returns for the eight most common crops grown. Results show optimal enterprise composition under various water quality situations. Leaching is justified financially and there is a strong motivation for a change in the current water pricing system. SALMOD (Salinity and Leaching Model for Optimal irrigation Development) is the Excel Solver model used to derive the preliminary results, but is currently being developed further in GAMS (General Algebraic Modelling System). Useful results have already been obtained on which this paper is based. The ultimate aim for SALMOD is a mathematical model using dynamic optimisation, simulation and risk modelling techniques to aid in whole farm and system level management decisions to ensure sustainable irrigation agriculture under stochastic river water quality conditions.Crop Production/Industries, Resource /Energy Economics and Policy,

SALMOD, a Salinity Management Tool for Irrigated Agriculture

This paper presents an irrigation farm management tool, SALMOD (Salinity And Leaching Model for Optimal irrigation Development), that calculates the profit maximizing crop enterprise composition and irrigation management options for farm specific soil type, drainage status and irrigation system composition subject to various regional control measures and expected irrigation water salinities. After stating the water quality problem, and particularly salinisation in Southern Africa, the input data requirements and the results of SALMOD and their usefulness at farm level, are discussed. The impact of various possible regional or policy regulations are then discussed. SALMOD was developed for irrigators in the lower Vaal and Riet Rivers in South Africa. These farmers have been experiencing rapidly fluctuating salinity levels in their irrigation water, resulting in soil salinisation, yield loss and subsequent financial instability. SALMOD calculates the profit maximizing crop choice and distribution over the farm, matching the crop choice with soil type, drainage status and irrigation system, indicating the optimal leaching vs. yield reduction seasonal management options as well as calculate long term management options such as underground drainage installation, a change in irrigation system or the construction of on farm storage dams. Leaching is necessary to maintain an acceptable salt balance in the root-zone of irrigated crops. This however contributes to point and non-point source water pollution externalities if not managed correctly. Results show valuable policy information regarding the interactions between artificial drainage subsidisation, return flow restrictions and on-farm storage.Irrigation, water quality, return flows, salinisation, leaching, non-point source pollution, on-farm storage, SALMOD, linear programming, GAMS, Farm Management, Land Economics/Use,

Achieving Contextual Ambidexterity Through the Implementation of High Performance Work Systems (HPWS)

Small information technology and management consulting businesses face increasingly contradictory strategic choices as they develop products and services for the marketplace. Building contextual ambidexterity is essential to the survival of small businesses as they seek to attain a desired balance of alignment and adaptability. Human Resource Management practices facilitate the development of ambidexterity within individuals thereby facilitating ambidexterity of the organization as a whole. Studies suggest that in order for an organization to be ambidextrous, its human resource management function also needs to ambidextrous. High-performance work systems are human resource practices designed to enhance the ability, motivation, and opportunity of employees with the overarching goal of attracting, retaining, and motivating human resources toward the completion of organizational goals. Based on Gibson and Birkinshaw’s concept of organizational ambidexterity, a qualitative case study of a small technology solution provider was conducted to explore the process by which CloudCo attempted to build contextual ambidexterity by implementing a high-performance work system. Findings show that executive management of small technology solution providers can build contextual ambidexterity and sustain a competitive advantage through the implementation of high-performance work systems but must overcome a series of important tensions to do so

Charge noise at Cooper-pair resonances

We analyze the charge dynamics of a superconducting single-electron transistor (SSET) in the regime where charge transport occurs via Cooper-pair resonances. Using an approximate description of the system Hamiltonian, in terms of a series of resonant doublets, we derive a Born-Markov master equation describing the dynamics of the SSET. The average current displays sharp peaks at the Cooper-pair resonances and we find that the charge noise spectrum has a characteristic structure which consists of a series of asymmetric triplets of peaks. The strongest feature in the charge noise spectrum is the triplet of peaks centered at zero frequency which has a peak spacing equal to the level separation within the doublets and is similar to the triplet in the spectrum of a driven, damped, two-level system. We also explore the back-action that the SSET charge noise would have on an oscillator coupled to the island charge, measurement of which provides a way of probing the charge noise spectrum.Comment: 14 pages, 7 figure

Discrete time translation symmetry breaking in a Josephson junction laser

A Josephson junction laser is realised when a microwave cavity is driven by a voltage-biased Josephson junction. Through the ac Josephson effect, a dc voltage generates a periodic drive that acts on the cavity and generates interactions between its modes. A sufficiently strong drive enables processes that down-convert a drive resonant with a high harmonic into photons at the cavity fundamental frequency, breaking the discrete time translation symmetry set by the Josephson frequency. Using a classical model, we determine when and how this transition occurs as a function of the bias voltage and the number of cavity modes. We find that certain combinations of mode number and voltage tend to facilitate the transition which emerges via an instability within a subset of the modes. Despite the complexity of the system, there are cases in which the critical drive strength can be obtained analytically.Comment: 6 pages, 4 figures (supplement: 4 pages, 1 figure

Effect of positron-atom interactions on the annihilation gamma spectra of molecules

Calculations of gamma spectra for positron annihilation on a selection of molecules, including methane and its fluoro-substitutes, ethane, propane, butane and benzene are presented. The annihilation gamma spectra characterise the momentum distribution of the electron-positron pair at the instant of annihilation. The contribution to the gamma spectra from individual molecular orbitals is obtained from electron momentum densities calculated using modern computational quantum chemistry density functional theory tools. The calculation, in its simplest form, effectively treats the low-energy (thermalised, room-temperature) positron as a plane wave and gives annihilation gamma spectra that are about 40% broader than experiment, although the main chemical trends are reproduced. We show that this effective "narrowing" of the experimental spectra is due to the action of the molecular potential on the positron, chiefly, due to the positron repulsion from the nuclei. It leads to a suppression of the contribution of small positron-nuclear separations where the electron momentum is large. To investigate the effect of the nuclear repulsion, as well as that of short-range electron-positron and positron-molecule correlations, a linear combination of atomic orbital description of the molecular orbitals is employed. It facilitates the incorporation of correction factors which can be calculated from atomic many-body theory and account for the repulsion and correlations. Their inclusion in the calculation gives gamma spectrum linewidths that are in much better agreement with experiment. Furthermore, it is shown that the effective distortion of the electron momentum density, when it is observed through positron annihilation gamma spectra, can be approximated by a relatively simple scaling factor.Comment: 26 pages, 12 figure

Entanglement and decoherence of a micromechanical resonator via coupling to a Cooper box

We analyse the quantum dynamics of a micromechanical resonator capacitively coupled to a Cooper box. With appropriate quantum state control of the Cooper box, the resonator can be driven into a superposition of spatially separated states. The Cooper box can also be used to probe the environmentally-induced decoherence of the resonator superposition state.Comment: 4 pages, 3 figure

Inferring mechanisms of copy number change from haplotype structures at the human DEFA1A3 locus

Background: The determination of structural haplotypes at copy number variable regions can indicate the mechanisms responsible for changes in copy number, as well as explain the relationship between gene copy number and expression. However, obtaining spatial information at regions displaying extensive copy number variation, such as the DEFA1A3 locus, is complex, because of the difficulty in the phasing and assembly of these regions. The DEFA1A3 locus is intriguing in that it falls within a region of high linkage disequilibrium, despite its high variability in copy number (n = 3–16); hence, the mechanisms responsible for changes in copy number at this locus are unclear. Results: In this study, a region flanking the DEFA1A3 locus was sequenced across 120 independent haplotypes with European ancestry, identifying five common classes of DEFA1A3 haplotype. Assigning DEFA1A3 class to haplotypes within the 1000 Genomes project highlights a significant difference in DEFA1A3 class frequencies between populations with different ancestry. The features of each DEFA1A3 class, for example, the associated DEFA1A3 copy numbers, were initially assessed in a European cohort (n = 599) and replicated in the 1000 Genomes samples, showing within-class similarity, but between-class and between-population differences in the features of the DEFA1A3 locus. Emulsion haplotype fusion-PCR was used to generate 61 structural haplotypes at the DEFA1A3 locus, showing a high within-class similarity in structure. Conclusions: Structural haplotypes across the DEFA1A3 locus indicate that intra-allelic rearrangement is the predominant mechanism responsible for changes in DEFA1A3 copy number, explaining the conservation of linkage disequilibrium across the locus. The identification of common structural haplotypes at the DEFA1A3 locus could aid studies into how DEFA1A3 copy number influences expression, which is currently unclear

Peculiar Features of the Interaction Potential between Hydrogen and Antihydrogen at Intermediate Separations

We evaluate the interaction potential between a hydrogen and an antihydrogen using the second-order perturbation theory within the framework of the four-body system in a separable two-body basis. We find that the H-Hbar interaction potential possesses the peculiar features of a shallow local minimum located around interatomic separations of r ~ 6 a.u. and a barrier rising at r~5 a.u. Additional theoretical and experimental investigations on the nature of these peculiar features will be of great interest.Comment: 13 pages, 6 figure

Dynamical instabilities of a resonator driven by a superconducting single-electron transistor

We investigate the dynamical instabilities of a resonator coupled to a superconducting single-electron transistor (SSET) tuned to the Josephson quasiparticle (JQP) resonance. Starting from the quantum master equation of the system, we use a standard semiclassical approximation to derive a closed set of mean field equations which describe the average dynamics of the resonator and SSET charge. Using amplitude and phase coordinates for the resonator and assuming that the amplitude changes much more slowly than the phase, we explore the instabilities which arise in the resonator dynamics as a function of coupling to the SSET, detuning from the JQP resonance and the resonator frequency. We find that the locations (in parameter space) and sizes of the limit cycle states predicted by the mean field equations agree well with numerical solutions of the full master equation for sufficiently weak SSET-resonator coupling. The mean field equations also give a good qualitative description of the set of dynamical transitions in the resonator state that occur as the coupling is progressively increased.Comment: 23 pages, 6 Figures, Accepted for NJ