Magic wavelengths for the 5s−18s5s-18s transition in rubidium

Magic wavelengths, for which there is no differential ac Stark shift for the ground and excited state of the atom, allow trapping of excited Rydberg atoms without broadening the optical transition. This is an important tool for implementing quantum gates and other quantum information protocols with Rydberg atoms, and reliable theoretical methods to find such magic wavelengths are thus extremely useful. We use a high-precision all-order method to calculate magic wavelengths for the $5s-18s$ transition of rubidium, and compare the calculation to experiment by measuring the light shift for atoms held in an optical dipole trap at a range of wavelengths near a calculated magic value

Modelling the temporal variation of the ionosphere in a network-RTK environment

The Global Positioning System (GPS) has been widely used for precise positioning applications throughout the world. However, there are still some limiting factors that affect the performance of satellite-based positioning techniques, including the ionosphere. The GPS Network-RTK (NRTK) concept has been developed in an attempt to remove the ionospheric bias from user observations within the network. This technique involves the establishment of a series of GNSS reference stations, spread over a wide geographical region. Real time data from each reference station is collected and transferred to a computing facility where the various spatial and temporal errors affecting the GNSS satellite observations are estimated. These corrections are then transmitted to users observations in the field. As part of a Victorian state government initiative to implement a cm-level real time position ing service state-wide, GPSnet is undergoing extensive infrastructure upgrades to meet high user demand. Due to the sparse (+100km) configuration of GPSnet's reference stations, the precise modelling of Victoria's ionosphere will play a key role in providing this service. This thesis aims is to develop a temporal model for the ionospheric bias within a Victorian NRTK scenario. This research has analysed the temporal variability of the ionosphere over Victoria. It is important to quantify the variability of the ionosphere as it is essential that NRTK corrections are delivered sufficiently often with a small enough latency so that they adequately model variations in the ionospheric bias. This will promote the efficient transmission of correctional data to the rover whilst still achieving cm-level accuracy. Temporal analysis of the ionosphere revealed that, during stable ionospheric conditions, Victoria's double differenced ionospheric (DDI) bias remains correlated to within +5cm out to approximately two minutes over baselines of approximately 100km. However, the data revealed that during more disturbed ionospheric conditions this may decrease to one minute. As a preliminary investigation, four global empirical ionospheric models were tested to assess their ability to estimate the DDI bias. Further, three temporal predictive modelling schemes were tested to assess their suitability for providing ionospheric corrections in a NRTK environment. The analysis took place over four seasonal periods during the previous solar maximum in 2001 and 2002. It was found that due to the global nature of their coefficients, the four global empirical models were unable to provide ionospheric corrections to a level sufficient for precise ambiguity resolution within a NRTK environment. Three temporal ionospheric predictive schemes were developed and tested. These included a moving average model, a linear model and an ARIMA (Auto-Regressive Integrated Moving Average) time series analysis. The moving average and ARIMA approaches gave similar performance and out-performed the linear modelling scheme. Both of these approaches were able to predict the DDI to +5cm within a 99% confidence interval, out to an average of approximately two minutes, on average 90% of the time when compared to the actual decorrelation rates of the ionosphere. These results suggest that the moving average scheme, could enhance the implementation of next generation NRTK systems by predicting the DDI bias to latencies that would enable cm-level positioning

The early siliceous component of planetary crusts: experimental petrology of the tonalite-trondhjemite rock series

There are two approaches to understanding the processes that lead to the formation of planetary crusts. The first is to determine the geology and geochemistry of rocks in the field and try to develop a consistent petrogenetic scheme to account for their occurrence. This approach has been extensively pursued on Moon and Earth, and remotely so on Mars. Another method is to establish the phase relationships of these rocks and their possible sources under various conditions of pressure, temperature, volatile content, etc., and apply the results to a petrogenetic model that is also consistent with isotope and trace-element geochemistry. This technique has been applied to the relationship between planetary mantles and basalts, and the formation of andesites and more siliceous rocks in subduction zones. Observations of rocks from Archean terranes on Earth reveal that the most prominent types are komatiites, tholeiites, tonalites and trondhjemites (grey gneisses), potassic granites (pink gneisses), and rare syenites. Early magmatic activity was dominated by the production of basalts which were subsequently followed, and intruded by, large volumes of the tonalite-trondhjemite series magmas. Approximately 80% of nine Archean cratons are composed of rocks that are chemically of tonalite-trondhjemite affinity (1)

SynGAP isoforms exert opposing effects on synaptic strength

Peer reviewedPublisher PD

An efficient record linkage scheme using graphical analysis for identifier error detection

Integration of information on individuals (record linkage) is a key problem in healthcare delivery, epidemiology, and "business intelligence" applications. It is now common to be required to link very large numbers of records, often containing various combinations of theoretically unique identifiers, such as NHS numbers, which are both incomplete and error-prone

Magnetocardiography with a modular spin-exchange relaxation free atomic magnetometer array

We present a portable four-channel atomic magnetometer array operating in the spin exchange relaxation-free regime. The magnetometer array has several design features intended to maximize its suitability for biomagnetic measurement, specifically foetal magnetocardiography, such as a compact modular design, and fibre coupled lasers. The modular design allows the independent positioning and orientation of each magnetometer, in principle allowing for non-planar array geometries. Using this array in a magnetically shielded room, we acquire adult magnetocadiograms. These measurements were taken with a 6-11 fT Hz^(-1/2) single-channel baseline sensitivity that is consistent with the independently measured noise level of the magnetically shielded room.Comment: 15 pages, 5 figure

Structure and expression of nuclear oncogenes in multi-stage thyroid tumorigenesis.

We have investigated the possibility that structural alterations of the 'nuclear' oncogene family (c-myc, N-myc, L-myc, fos, myb and p53) leading to aberrant expression might, as in several other tumour types, play a role in the multi-stage development of tumorigenesis in the human thyroid follicular cell. Direct analysis of expression by slot and Northern blot RNA hybridisation showed that normal thyroid expresses surprisingly high levels of fos, and to a lesser extent c-myc, c-myc expression was markedly increased in all tumours, both benign and malignant, but no increase was seen in any other nuclear oncogene. fos expression was reduced specifically in one type of malignant tumour-follicular carcinoma-in inverse correlation with differentiation. Southern blot analysis showed no evidence of rearrangement or amplification of c-myc, or of any other 'nuclear' oncogene in any thyroid tumour. We conclude that there is no evidence that a primary abnormality of these genes plays a role in thyroid follicular cell tumorigenesis and suggest that the observed changes in expression can be adequately explained as secondary consequences of the tumour phenotype