604,955 research outputs found

    Development of an in vitro assay to screen Agathis australis (kauri) for resistance to Phytophthora agathidicida : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science at Massey University, Manawatū, New Zealand

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    The iconic Agathis australis (kauri) of New Zealand, is under serious threat from kauri dieback disease caused by the soil-borne pathogen Phytophthora agathidicida. Infected kauri express symptoms of root and collar rot, bleeding resins at the base of the trunk, yellowing of foliage, canopy thinning, and tree mortality. Phytophthora agathidicida was first associated with kauri decline in 1972, where it was initially identified as P. heveae however, there was some uncertainty about its significance and taxonomy. The pathogen was officially identified as a new organism in 2008 and was called Phytophthora taxon Agathis until its formal description as Phytophthora agathidicida in 2015. This pathogen is easily vectored through root to root contact and mobile zoospores. Management and research has focused on mapping pathogen distribution, reducing spread, improving detection, ex situ conservation and clonal production using tissue culture techniques. In order to gain better understanding of the disease epidemiology and to develop better breeding programmes, a reliable in vitro resistance screening assay is required. This research focused on the development of a screening assay using detached leaves from tissue culture material as a means of accelerating screening assays compared to the more labour-intensive root inoculation assays. Foliar inoculations and assessment techniques were initially optimised on kauri leaves from tissue culture lines. The most successful inoculation method involved placing P. agathidicida-colonised agar plugs on wounded detached leaves. The assay was further tested on 2 year old kauri seedlings. Variation in susceptibility across kauri genotypes and leaf age, and variation in virulence among P. agathidicida isolates was observed. To further investigate the impact of leaf age on lesion extension, an assay was conducted on detached leaves from six rooted kauri saplings over 5 years of age, across three leaf age groups with P. agathidicida, P. multivora, and P. cinnamomi. Variation in virulence among these Phytophthora species was observed. Leaf necrosis was most severe with young tissue and susceptibility tended to decrease with increasing leaf age. Preliminary studies with 50 kauri clones identified different levels of susceptibility and tolerance across the different genotypes to P. agathidicida. The methods developed within this study have increased our understanding of the overall response of kauri to P. agathidicida foliar inoculations. This study demonstrated variation in the susceptability of kauri foliage to Phytophthora inoculation, although no complete resistance was observed. Further work is required to determine if there is a relationship between root and leaf responses which will help establish if in vitro genotypic variation can accurately predict natural genotypic variation seen within kauri forests

    ECONOMIC CONDITION OF POST TIN MINING (CASE STUDY ON BANGKA BELITUNG ISLAND AS ONE OF THE LARGEST TIN PRODUCERS IN THE WORLD)

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    This study aims to determine the effect of economic conditions of the Bangka Belitung island on the level of public purchasing power and the active role of local government policy when the natural resources of tin that can be produced by the public is very minimal. Along with the passage of time, the economic growth of Bangka Belitung has decreased even though there is still non-tin potential in the form of plantation and fishery. The research instrument in the form of questionnaires was used to 40 respondents. The data analysis used is the analysis of frequency descriptive and factor analysis to process the data that have been collected. The result of data analysis shows that the variable of public purchasing power and active role of dominant government have medium category (57,5% and 52,5%) whereas factor of public purchasing power and active role of society have value 67,593% in explaining economic condition of post tin mining

    Non-linear echo cancellation - a Bayesian approach

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    Echo cancellation literature is reviewed, then a Bayesian model is introduced and it is shown how how it can be used to model and fit nonlinear channels. An algorithm for cancellation of echo over a nonlinear channel is developed and tested. It is shown that this nonlinear algorithm converges for both linear and nonlinear channels and is superior to linear echo cancellation for canceling an echo through a nonlinear echo-path channel

    Estimation of ejection fraction with ventriculography versus echocardiography in patients referred for cardiac surgery

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    Abstract: Aim: The aim of this study was to compare the estimation of ejection fraction (EF) by ventricuography (VG) and echocardiography (ECHO) in patients referred for surgery and to validate the results by comparison with other published data. Methods: One hundred patients who underwent VG prior to surgery were subjected to a trans-thoracic ECHO. Radiographers calculated the EF by tracing the outer border of the ventriculogram during systole and diastole. A single cardiologist, who was blinded to the angiogram result, measured EF during trans-thoracic ECHO using the biplane Simpson’s method. Results: EF was significantly higher by VG versus ECHO for the whole group (67.9±13.2 vs 55.7±8.5, p=0.000). In 81 patients the EF estimated at VG was higher than that calculated at ECHO (71.7±10.2 vs 55.9±7.2, p=0.000). In 19 patients the EF estimated at VG was lower than that calculated at ECHO, but the difference was not significant (51.8±12.9 by VG vs 55.4±12.8, p=0.387). In 13 patients, with an EF less than 50% on VG, the correlation with ECHO was very good (42.0±9.0 vs 42.0±8.3, p=0.995). Two patients with an EF fraction under 30% had similar measurements by VG and ECHO. The EF range as measured by ECHO was consistent with published data. Conclusion: Ventriculography overestimates EF when compared with ECHO. When EF is less than 50% on VG, ECHO findings were similar. The value of ventriculography in patients referred for cardiac surgery is now being brought into question when ECHO, a better and less invasive test that measures EF, is available.peer-reviewe

    Hahn echo and criticality in spin-chain systems

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    We establish a relation between Hahn spin-echo of a spin-12\frac 1 2 particle and quantum phase transition in a spin-chain, which couples to the particle. The Hahn echo is calculated and discussed at zero as well as at finite temperatures. On the example of XY model, we show that the critical points of the chain are marked by the extremal values in the Hahn echo, and influence the Hahn echo in surprising high temperature. An explanation for the relation between the echo and criticality is also presented.Comment: 5 pages, 6 figure

    Dephasing of a superconducting flux qubit

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    In order to gain a better understanding of the origin of decoherence in superconducting flux qubits, we have measured the magnetic field dependence of the characteristic energy relaxation time (T1T_1) and echo phase relaxation time (T2echoT_2^{\rm echo}) near the optimal operating point of a flux qubit. We have measured T2echoT_2^{\rm echo} by means of the phase cycling method. At the optimal point, we found the relation T2echo≈2T1T_2^{\rm echo}\approx 2T_1. This means that the echo decay time is {\it limited by the energy relaxation} (T1T_1 process). Moving away from the optimal point, we observe a {\it linear} increase of the phase relaxation rate (1/T2echo1/T_{2}^{\rm echo}) with the applied external magnetic flux. This behavior can be well explained by the influence of magnetic flux noise with a 1/f1/f spectrum on the qubit
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