DEPARTMENT OF PHYSICS & ASTRONOMY College of Science

27TH

DEPARTMENTAL CONFERENCE

Tuesday 24th August and Wednesday 25th August 2010

ERSKINE 031

PROGRAMME

Tuesday 24th

August 10.30 – 10:55 MORNING REFRESHMENTS – ERSKINE 031 Session 1 Chairperson: Juergen Meyer Welcome David Wiltshire 11:00 – 11:15 Juergen Meyer Medical Physics research at UC 11:15 – 11:30 Jack Coggins Spatial statistics: the key to Antarctic temperature reconstructions? 11:30 – 11:45 Dimitri Schritt Scalar-Tensor Theory of Gravity 11:45 – 12:00 Masaed Almotari Using XPS technique to detect trace amounts of Rare earth ions in ZnO thin film 12:00 – 12:15 Phil Butler MARS Imaging: Biomedical 3D spectroscopic X-ray imaging. 12:15 – 12:30 Stuart Lansley Stem contribution to the performance of synthetic diamond x-ray detectors for radiotherapy 12:30 – 1:30 LUNCH Session 2 Chairperson Ahsan Nazer 1:30 – 1:45 Karen Pollard Astronomy research in the Department 1:45 – 2:00 Anas Sedayo Using MARS-2 Spectroscopic CT Scanner to Distinguish Fat from Liver 2:00 – 2:15 Andolsa Arevalo-Torres Unexpected large chlorine activation over Antarctica. 2:15 – 2:30 Mike Reid Probing excited states of lanthanide phosphor materials. 2:30 – 2:45 Adrian Reynolds Study of optical line widths in cerium doped phosphors 2.45 – 3.00 Pubudu Senanyake Spectrally and temporally resolved emission of The CaF2:Yb

2+ exciton

3:00 – 3:30 AFTERNOON REFRESHMENTS – ERSKINE 101 Session 3 Chairperson: Dimitri Schritt 3.30 – 3.45 Rafidah Zainon Calibration of X-ray source with Medipix2 MXR detector/CdTe assembly 3.45 – 4.00 Cheng-Yang Lee The symmetry of flavour fields 4:00 – 4.15 Ahsan Nazer Inhomogeneous cosmology and averaging 4.15 – 4.30 Robert Ward Elliptical diagnostics of Antarctic sea ice extent

END OF DAY ONE

Wednesday 25th

August Session 1 Chairperson: Robert Doesburg 9:00 – 9:15 Sebastian Horvath Matter rods and clocks as the origin of event-space Symmetries 9:15 – 9:30 Alicia Cavan Pseudo-calorimetric dosimetry for microbeam Radiotherapy using holographic interferometry 9:30 – 9:45 Bob Hurst Ring Laser Gyros – Mundane and Esoteric 9:45 – 10:00 Anthony Brown Neutrino Astronomy – ANTARES & Acoustics…. 10:00 – 10:15 Emily Brunsden “The Music of Stars” 10:15 – 10:30 John Holdaway Investigating Methods for Improving Performance In Large Ring Lasers 10.30 – 11:00 MORNING REFRESHMENTS – ERSKINE 031 Session 2 Chairperson: Florian Maisonnueve 11:00 – 11:15 Daniel Robertson Constructive Alignment in Physics Education 11:15 – 11:30 Ojas Mahapatra Salt as never seen before 11:30 – 11:45 Raja Amir Pixel sensitivity variations in CdTe-Medipix-2 detector 11:45 – 12:00 Peter Smale Precision cosmology with Type IA supernovae 12:00 – 12:15 Sarah Bouckoms IceCube Standard Candle and Flasher analysis

12:15 –12:30 Simon Parsons Classification of Synotopic Climatology in New Zealand 12:30 – 1:30 LUNCH Session 3 Chairperson: Stuart Lansley 1:30 – 1:45 Nishanthan Rabeendran Development of Rare Earth Lasers 1:45 – 2:00 James Duley The timescape model with radiation 2:00 – 2:15 Jeffrey Simpson Range of barium abundances of stars in Omega Centauri 2:15 – 2:30 Stephanie Hickford Cascade Analysis for IceCube 2.30 – 2:45 Syen Nik Optimal material discrimination using spectral CT 2:45 – 3:00 Young-Wook Song Photoluminescence study of Mg doped InN 3:00 – 3:15 Ishwaree Neupane Embedding of our universe in a five-dimensional de Sitter spacetime 3:15 – 3:30 Florian Maisonneuve Frequency determination and pulsational Identification of variable stars

CONFERENCE CLOSES 4:30 onwards Retire to Staff Club for end-of-conference function and presentation of prizes.

BBQ from about 5:15.

ABSTRACTS

Tuesday 24

th August

Juergen Meyer

Medical Physics research at UC

The postgraduate programme in medical physics was established in the department in 2004. Besides running postgraduate courses to produce graduates for the health workforce there is a strong emphasis on medical physics research within the group. The research activities range from nuclear medicine to diagnostic imaging to radiation therapy. In this talk I will give an overview of the past and present medical physics research activities within the department and will introduce current projects and opportunities for future students.

Jack Coggins

Spatial statistics: the key to Antarctic temperature reconstructions?

Jack Coggins1, Adrian McDonald

1 and Wolfgang Rack

2

1Dept of Physics and Astronomy, University of Canterbury,Christchurch, New Zealand.

jack.coggins@pg.canterbury.ac.nz, adrian.mcdonald@canterbury.ac.nz 2Gateway Antarctica, University of Canterbury,Christchurch, New Zealand.

wolfgang.rack@canterbury.ac.nz

Antarctic surface temperature records are historically sparse, particularly in the continental interior

before the satellite era. Recent research into surface temperature trends on the continent display

complex spatial patterns, which vary with position and observation period. The ability of such

studies to determine significant trends is limited by the lack of records. Thus, scientists have

developed methods to extrapolate the historical records to the entire continent by utilising spatial

statistics derived from contemporary measurements. Understanding of the spatial statistics of the

surface temperature is crucial to such schemes and the development of new methods.

We analyse temperature data supplied by automatic weather station records from 1984 onwards

using the second-order structure function, a fractal analysis technique developed specifically for

use with geophysical datasets. This method allows us to characterize the relationship between

the temperature of two weather stations and their spatial separation using a simple power law

model. Using this information, we have investigated the tendency of the spatial temperature

pattern to vary in time and the climatological drivers which potentially force these variations.

We find that the surface temperature varies more quickly with distance in the winter. However,

there also exists a high degree of variability on inter-annual time scales, such that seasonal

variation does not capture all the variability in the temperature pattern. Thus, applying spatial

relationships on a seasonal basis may not adequately correct for these changes in

reconstructions. We find no correlation between the index of the derived power law and the two

dominant modes of climate variability in the Southern Hemisphere, namely SAM and ENSO.

However, we find that the index is significantly anti-correlated with the mean temperature. We

conclude that reconstructions which do not explicitly allow for inter-annual variation potentially

under-represent the ability of the Antarctic temperature field to change. However, we can also

conclude that reconstruction schemes which account for seasonal variations are preferable to

those which do not.

Dimitri Schritt

Scalar-Tensor Theory of Gravity

As some of you will be aware I recently spent two months at Harish Chandra Research Institute (HRI) in Allahabad, India. I will give a brief overview my research with Sudhakar Panda, HRI. The majority of the talk will be devoted to the historical background to and the theoretical motivation for a scalar-tensor theory of gravity.

Masaed Almotari

Using XPS technique to detect trace amounts of rare earth ions in ZnO thin films.

X-ray Photoelectron Spectroscopy (XPS) is considered as a powerful spectroscopic tool. It is widely used to quantitatively investigate the surface of solids. Its basic concept is based on the photoelectric effect that was discovered in 1887 by Hertz. However, when it is used important information such as the sample composition, its stoichiometry across the surface and the dopants concentrations can be obtained. Furthermore, importantly it is known to be of a non-destructive nature. In this talk, I will explain how the XPS works, its advantages, drawbacks and a typical XPS spectrum from my own research data will be discussed.

Phil Butler

MARS Imaging: Biomedical 3D spectroscopic X-ray imaging

Our current MARS-CT small animal scanner obtained its first image in 2008. It has given good spectroscopic (multienergy) CT images using Medipix2 detectors. However there is room for improvement. Version 3 of the MARS-CT scanner has features that will soon give us the ability to do a full spectroscopic CT scan of a live sedated biological specimen, such as a mouse. I review some of the technical issues and give an overview of some of the many possible uses in biomedical research - and future human imaging.

Stuart Lansley

Stem contribution to the performance of synthetic diamond x-ray detectors for radiotherapy Synthetic diamond x-ray detectors show promise for dosimetry applications in radiotherapy, for reasons including their small size and near-tissue equivalence. These detectors have been used to look at a range of clinical measurements such as: the measurement of dose with depth in a phantom (percentage depth dose, PDD); the measurement of the dose profile across the x-ray beam (off-axis ratio, OAR); and the change in dose when the size of the x-ray field is varied (output factor, OF). Good results have been obtained, but it appears that a non-negligible proportion of the detector signal is coming from ionisation in the detector stem. The diamond crystal is attached to the end of a long strip of printed circuit board (PCB) for mechanical rigidity and electrical connections, and is housed in a cavity which may be (partially) filled with a wax. It appears that this PCB and its surrounding environment are responsible for the additional signal which is measured. I will present a model of the whole detector, show the relative signal contributions from the difference conduction paths (diamond, PCB surrounded by wax and PCB surrounded by air) and demonstrate the effect that the stem has had on the detector response.

Karen Pollard

Astronomy research in the Dept I will talk about various astronomy research projects that are underway in the Department and that are being undertaken at the Mt John University Observatory. Specific examples discussed will be the MUSICIAN project to detect and characterise the surface vibrations of non-radially pulsating stars.

Anas Sedayo

Using MARS-2 Spectroscopic CT Scanner to Distinguish Fat from Liver

Introduction: Fatty liver is one of the most common diseases of the digestive system. The condition is being detected more frequently with the increased use of CT. The condition can be improved with treatment and by diet; otherwise liver cirrhosis may be the final result. It is very important to know the extent of fatty liver (the content of fat in liver tissues). Although CT is very useful for diagnosis of focal fatty infiltration of the liver with diffuse fatty liver showing low attenuation, biopsy of liver tissue is the most effective modality. However, biopsy is invasive. Images produced by the Medipix-2 spectroscopic detector in the MARS-CT scanner have been analysed by using different techniques. Hounsfield Units have been obtained. These show the variation between fat and liver. However PCA (Principal Component Analysis) can distinguish often between components but fat and liver are not clearly distinguished due to cupping artefact. Methods: Fat, liver and plastic tube filled with water was placed in the Perspex tube; the sample scanned using the Medipix2 scanner with a CdTe sensor layers. Energy setting of 560, 580, 600, 620, 640, 660, 680 and 700 THL units were used with two detector steps, 303 projection images were taken to cover the sample. The image was processed using Matlab code. Octopus (a commercial tomography reconstruction package for cone beam) was used to construct the 3D image and to create CT slices. PCA applied to the reconstructed slices were used to distinguish between the different components. Hounsfield Units were compared with theoretical data. Conclusions: The results showed the ability of the Medipix2 detector to obtain spectral x-ray images. Hounsfield Units were obtained and compared with the theoretical ones, the comparison is not perfect, but clearly can distinguish fat and liver. The analysis still going on with expectation of getting better data.

Andolsa Arevalo-Torres

Unexpected large chlorine activation over Antartica.

An enhanced number of type I and type II Polar Stratospheric Cloud (PSC) particles are observed in a highly activated Antarctic Polar vortex (APV) in the Southern hemisphere winter, where a set of heterogeneous chemical reactions occur on the surface of these particles and ultimate destroy stratospheric ozone by Spring. We present in this study an examination of the spatial and temporal evolution of type I-II PSC inferred from temperature variations in the lower-middle atmosphere over the APV, derived from MLS satellite observations and NCEP/NCAR reanalysis. We then utilize MLS chemical concentration observations to correlate the role of temperature variations on PSC formation with stratospheric chlorine partitioning. In particular, we present our latest results by tracking the chemistry of hydrochloric acid (HCl), an important chlorine reservoir in the stratosphere and daytime ClO change signal calculations as a way to unambiguously determine PSC formation and evaporation temperatures together with an assessment of the likely periods of the year where PSC and chlorine activation events occur. Lastly, we will present a set of preliminary results to show how dynamics affects PSC formation and thereby stratospheric chlorine-chemistry over the Antarctic region. corresspondence to: andolsa.arevalotorres@pg.canterbury.ac.nz Mike Reid

Probing excited states of lanthanide phosphor materials

This presentation will give an overview of the research project that I am working on with Jon-Paul Wells, Roger Reeves, and several students. Our aim is to use various laser setups to probe the energy level structure, excited state geometry, and excited state dynamics of lanathanide ions in various host crystals. By using one laser to put

the system in an excited state and another to probe the structure and dynamics of that state we are able to access details that conventional spectroscopy is unable to reveal. Current work is focussed on using the Dutch Free Electron Laser (FELIX) to study excitons in CaF2:Yb2+, and visible and IR lasers at Canterbury to study excited states of various materials containing Tm2+.

Adrian Reynolds

Study of optical line widths in cerium doped phosphors In this experiment we are studying the positions of and temperature dependence of the zero phonon line of the 4f to 5d transitions of trivalent cerium in CaF2, BaF2, SrF2 and LiYF4. We are doing this by studying the excitation-emission spectra of the 4f to 5d Ce3+ transitions at a range of temperatures. The energy levels of the Cerium in its hosts are determined by theoretical models. The models are created using the crystal field fitting program created by Mike Reid. The models are then compared with experimental values. This helps to refine the crystal field parameters.

So far, we have just been looking at the CaF2:Ce3+

zero phonon line, trying to resolve it by emission when it is excited by a xenon lamp. From there, it should be relatively simple to apply the same methods to the other hosts.

Pubudu Senanyake

Spectrally and temporally resolved emission of the CaF2:Yb2+

exciton

As the demand for energy increases globally, one of the primary uses of energy is lighting. As such the importance of having efficient lighting devices is self evident. Rare earth doped materials are a possible candidate for use in such devices as they have very high quantum efficiency. To this end research is being undertaken here at the University of Canterbury to understand such systems. This talk will focus on the anomalous emission observed in CaF2:Yb2+, a result of a bound exciton with energy levels between the 4f - 5d levels of Yb. For the first time, such a structure has been directly probed, using a Free Electron Laser (FEL) - with a tunable wavelength range from 5 to 250 μm - after initial excitation into the exciton state using a pulsed UV laser. We have observed emission peaking in the excitation wavelength range of 12 to 26 μm and 30 to 50 μm, in agreement with theoretical calculations. Temporally we have observed the lifetimes of the exciton states to be around 250μs and on the order of 10 ms. A rate equation model has so far been able to reproduce these results with some success. Rafidah Zainon

Calibration of X-ray source with Medipix2 MXR detector/CdTe assembly

R Zainon1, R Aamir

1, Stuart Lansley

1, AP Butler

2-4, PH Butler

1,4

1 Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand.

2 Centre for Bioengineering, University of Otago, Christchurch, New Zealand. 3 Department of Academic Radiology, University of Otago, Christchurch,

New Zealand. 4 European Organisation for Nuclear Research (CERN), Geneva, Switzerland. Purpose: The aim of this work is to develop calibration methods for X-ray sources as functions of energy and angle, using Medipix2 and Medipix3 detectors. Accurate calibration is needed for high quality spectral CT images. Materials and Methods: The MXR version of the Medipix2 ASIC bump bonded to a CdTe sensor layer was used to image the open beam of a Thermo Scientific Kevex PXS11-150-75 X-ray source in the MARS-CT scanner. The trial calibration was performed by irradiating the Medipix2 detector with the X-ray source set to 75 kVp and 0.15 mA, and 0.5mm aluminium filtration. The source spot size is 40 μm. A scan was performed with six detector positions, 36

energy thresholds and the exposure time for each energy thresholds was varied, so as to collect about 3000 photon counts per pixel. Results: The images were analysed at different rows, columns and energy thresholds to evaluate the X-ray source characteristics convolved with the detector characteristics. A quadratic curve fitted using least square techniques describes angular variation of the measured data. The energy profile of the source is not symmetric and further work is needed to understand this. Future work will study other x-ray sources and other sensors (silicon and GaAs) and the Medipix3 ASIC. Conclusion: We have successfully implemented a technique to measure the changes in X-ray intensity as detected by the Medipix-2 detector, as functions of beam angle and measured energy. Cheng-Yang Lee

The symmetry of flavour fields

The phenomenology of particle oscillation is now a well-known phenomenon in particle physics and has been extensively studied in various theories and experiments. In recent years, the focus has been on neutrino oscillation.

It is well-known that the standard Pontecorvo theory of neutrino based on linear superposition of mass eigenstates is only an approximation based on relativistic quantum mechanics. A consistent theory of neutrino oscillation in quantum field theory still remains to be formulated. In this presentation, we review the Blasone Vitiello (BV) formalism on particle oscillation in quantum field theory. In addition, we will present some recent results and insights we have obtained on the symmetries underlying the quantum field theoretic treatment of particle oscillation.

Ahsan Nazer

Inhomogeneous cosmology and averaging

Studies of the expansion history of the universe, through observations such as Type Ia supernova suggest an apparent acceleration in the rate of expansion of the universe. This in turn necessitates the inclusion of a cosmological constant, or some other “dark energy” in the Einstein field equations. However, the issue is far from settled and one can argue that apparent acceleration is a model dependent interpretation, owing to the assumptions of spatial homogeneity and isotropy. The real universe is highly inhomogeneous on scales below 200Mpc. Inhomogeneous cosmology explores the possibility of explaining this apparent acceleration without resorting to a genesis of something as mysterious as dark energy. In this talk, I review some of the work on averaging that has been carried out in inhomogeneous cosmology over the past decade.

Robert Ward

Elliptical diagnostics of Antarctic sea ice extent

There are a large number of factors, including ice formation and melt processes, ocean currents and wind patterns, which determine the location of the Antarctic sea ice edge and make this parameter difficult to simulate. Recent studies have suggested that significant positive and negative trends in sea ice extent have occurred in the Ross and Amundsen-Bellingshausen Seas respectively, but the realistic simulation of these observations is a significant challenge. Thus far, the quality of climate model analyses has been judged by the examination of the total sea ice area. However, the different sign of changes in different regions means that observations of changes in the sea ice area are perhaps unrepresentative. Given that the sea ice extent around Antarctica forms a roughly elliptical shape for a large portion of the year, we examine the potential for using elliptical diagnostics to summarise changes in area and spatial variability. Our analysis fits an ellipse to the edge of this sea ice using Taubin’s non-iterative algorithm. By applying this algorithm to multiyear datasets such as the Hadley Centre Global Sea Ice Coverage and Sea Surface Temperature data (HadISST), trends in the sea ice extent can be analysed in

terms of the ellipse parameters. Using various error metrics and comparisons between the behaviour of the model and that of the sea ice, we can validate this model.

So far, our results suggest that elliptical diagnostics are a useful tool in understanding the factors controlling the Antarctic sea ice extent. For example, the seasonal variations in the area of the ellipse match those derived directly from the data sets analysed. In addition, the ellipse parameters provide additional information on the Antarctic sea ice, such as the orientation of the major axis of the ellipse which provides some measure of relative regional changes.

ABSTRACTS

Wednesday 25th

August

Sebastian Horvath

Title: Matter rods and clocks as the origin of event-space symmetries

In a recent departmental seminar the case was made that the natural arena for the Cohen and Glashow very special relativity (VSR) theory is not the Planck scale, but in the dark matter sector at the Standard Model scale. As part of the motivation for this it was pointed out that the well known Lorentz transformation does not need to be an intrinsic property of space- time, but can be dependent on the type of matter being transformed. A recent result shows that this contention is no longer mere speculation. In this talk we give justification why this ``dynamical'' view of space-time should be taken seriously. Furthermore, we show that the new VSR Elko dark matter rods and clocks directly imply the transformation properties of VSR space-time events, just as the standard model rods and clocks imply the transformation properties of special relativity space-time events.

Alicia Cavan

Pseudo-calorimetric dosimetry for microbeam radiotherapy using holographic interferometry Microbeam radiotherapy using synchrotron generated microbeams is a promising technique for cancer treatment. One of the current obstacles to clinical implementation is the lack of modalities capable of accurate characterisation of the dose profiles, in particular the peak-to-valley dose ratios. This research is based on the use of optical interferometry to perform pseudo-calorimetry to determine experimentally the dose profiles produces by the microbeam array. The fundamental idea is to infer the absorbed dose from the change in refractive index of the absorbed media as a result of a small increase in temperature. A Michelson interferometer with a HeNe laser and a CCD camera is used to measure striated heating patterns in water. The dose temperature profile was simulated at a macroscopic level using both a 200 mW laser, and a phantom consisting of a variable temperature copper heat sink with parallel pins protruding into a cell. The resulting interferograms of the high temperature gradient and subsequent thermal diffusion are recorded,and will be shown as initial results. The development of an algorithm to create differential holographic interferometry images for analysis is ongoing.

Nishanthan Rabeendran Development of Rare Earth Lasers The ring laser group has been building large ring laser gyroscopes for over a decade. All of the gyroscopes built by the group relied on He-Ne gas. Recently, the focus has shifted to new type of ring laser which uses rare earth doped crystals. The talk will focus on the construction of a linear solid state laser with slope effieciecy of 23 % and the extension to a solid state ring cavity.

Anthony Brown

Neutrino Astronomy – ANTARES & Acoustics....

Neutrino Astronomy offers us a unique view of the Universe. Due to their small interaction cross-section and neutral charge, neutrinos are able to escape from some of the most dense and violent regions of the Universe. To utilise neutrinos as cosmic information carriers, IceCube is building a cubic kilometer sized neutrino detector in the glacial ice of Antarctica. While only partially completed, IceCube currently allows us to view the neutrino flux from the Northern sky with unprecedented sensitivity and accuracy.

Completed in May 2008, the ANTARES neutrino telescope is located in the Mediterranean Sea, 40 km off the coast of Toulon, at a depth of 2500 m. Consisting of 12 detector lines housing nearly 900 optical modules, the ANTARES telescope is currently the largest neutrino detector in the northern hemisphere and nicely complements its southern rival, IceCube. In this talk we will review the current status of the ANTARES neutrino detector as well as discuss how ANTARES and IceCube are hoping to extend their scientific capabilities by listening for neutrinos as well as looking for them.

Emily Brunsden

"The Music of the Stars"

Astroseismology is the study of vibrational physics in stars. These vibrations are analogous to the vibrations in musical instruments and thus we title our study "The Music of the Stars". The study of the pulsations resulting from vibrations allows us to probe the deep internal workings of a star and is the best known way to determine interior properties and dynamics. I will present the techniques used to analyse spectroscopic data in order to find the pulsation frequencies and modes of variable stars. I will present as an example non-radial pulsations in a g-mode pulsator (HD 135825), from the observations to the results.

John Holdaway

Investigating Methods for Improving Performance in Large Ring Lasers

Large ring lasers are essentially gyroscopes which are used to measure fluctuations in the rotation rate of the Earth to a high degree of accuracy. The cavity of a ring laser supports two independent, oppositely directed travelling waves in closed paths: one beam traverses the cavity clockwise, while the other simultaneously travels in the anticlockwise direction. The oscillation frequencies of these two waves are dependent on the speed with which the cavity rotates in inertial space. In the absence of any rotation, the clockwise and anticlockwise waves would oscillate at the same frequency, and no frequency difference would be recorded between them. However, for a ring laser cavity on the rotating Earth, there will be a difference in the oscillation frequency of the two waves due to a slight path length difference on each circuit of the cavity; measuring this frequency difference (the Sagnac frequency) allows precise measurements of the rotation rate of the Earth.

In this talk I will discuss some of the methods being investigated for improving performance in large ring lasers, focussing on previously unpresented results from a recent four month course of experiments with the G ring laser in Wettzell, Germany. After relatively problematic performance in previous years, the G ring laser underwent an upgrade to a set of four very low transmission Silica mirrors, which has resulted in markedly better performance than ever before. The precision of data is now such that daily polar motion can be readily extracted from the Sagnac signal, which has previously proved difficult or impossible. Data precision increased even further via the means of measuring and monitoring an optical beat frequency between the G ring laser and an iodine-stabilized reference laser, as well as by installing and implementing a pressure stabilization vessel, which has drastically reduced problematic frequency shifts primarily caused by atmospheric pressure variations and room temperature fluctuations. This has had the effect of almost completely removing Sagnac frequency drift, improving the precision of measured rotation data remarkably.

Daniel Robertson

Constructive Alignment in Physics Education

What is constructive alignment, and how can we apply it to physics education here at the University of Canterbury? Constructive alignment is a way for educators to align their teaching and learning activities, as well as their assessment tasks, with the intended learning outcomes for the course, major and programme. In the interests of time, I will focus on what this means for the teaching of PHYS101, but the general principles apply to all tertiary courses. The intent is essentially to work backwards, to find what the intended learning outcomes are (or should be) for PHYS101, and then arrange the teaching and assessment so that those goals are met. Suggestions will be provided not only on how to improve the teaching of PHYS101 by looking at tutorials, labs, exams etc., but also how students can be better prepared for further study, either towards a physics degree or an engineering degree. Suggestions include changing the assessment structure so that student motivation increases and a greater depth of learning is encouraged, changing course content so that the topics covered are more relevant to students, and changing teaching practice to emphasise deep learning (time permitting). Ojas Mahapatra Salt as never seen before

Co-Supervisor- Dr Pawel Kowalczyk Supervisor- Assoc Prof Simon Brown Department of Physics and Astronomy, University of Canterbury

Salt is a very familiar molecule which is encountered on a day to day basis by everyone. This project studies the morphology of NaCl molecules grown on a graphite substrate. Graphite is an inert substrate which has flat terraces in the size range of few hundred micrometers. These flat regions are playgrounds for the adatoms of NaCl to roam around, collide and grow into defined structures.

Experiment: Clean graphite was cleaved in air and baked in situ in UHV-SPM. The baking time and temperature were 17 hrs and 600

0C respectively. After the substrate cooled, sodium chloride was

evaporated from an effusion cell which is integrated with the SPM. Predefined monolayers(ML) of the salt were grown i.e. 2, 4, 6 MLs in different experiments. The morphology of the structures was studied by Non Contact Atomic Force Microscopy. Discussion: Salt is an interesting material. In this course of experiment we came across cross shaped islands of sodium chloride. The cross shape is interplay between growth kinetics and thermodynamic stability of the material. Nanoparticle Sodium Chloride Substrate Sodium Chloride is an insulator. The long term goal of this project is to obtain thin layers of salt on top of a substrate. This salt layer would then support metallic or semi-metallic nanoparticles on top of it. The configuration looks like Substrate-Insulator-Metallic or semimetal nanoparticle( as shown in figure above). These nanoparticles will be studied by Scanning Tunneling Spectroscopy (STS). The presence of an insulating barrier partially decouples the electronic states of the nanoparticles or the nanostructures from the underlying substrate and provides a clear picture of the electronic properties of the material.

Raja Aamir

Pixel sensitivity variations in CdTe-Medipix-2 detector R Aamir1, R Zainon1, S P Lansley1,2, P H Butler1,3, A P H Butler3,4,5

1) Dept of Physics & Astronomy, University of Canterbury, Christchurch, New Zealand 2) The MacDiarmid Institute for Advanced Materials & Nanotechnology, University of Canterbury, Christchurch, New Zealand 3) European Centre for Nuclear Research (CERN), Geneva, Switzerland 4) Dept of Electrical & Computer Engineering, University of Canterbury, Christchurch, New Zealand 5) University of Otago Christchurch, New Zealand

The construction and operation of small animal computed tomography (CT) scanner system (MARS-CT) using a Medipix-2 detector chip [1] and colour x-ray CT spectroscopic imaging of a mouse using this system [2] have previously been reported. In these reports silicon sensor layers were used with Medipix-2 detectors. Cadmium telluride (CdTe) is expected to be a useful sensor layer for clinical CT imaging detectors because of its good stopping power for x-rays in the energy range up to 100 keV. We have bump-bonded CdTe sensor layers to Medipix-2 detector chips and have imaged a flat field (i.e. without an attenuating specimen between the x-ray source and the detector) using the MARS-CT scanner system. In the figure, (a) shows one quadrant of a homogeneity scan taken with an applied bias voltage of 300 V, and (b) shows the profile of column 114 (as indicated in (a)) for a hundred 35 ms exposures. A region of increased sensitivity is observed around the outside of the detector; top and left edges in (a), left side in (b). A reasonably periodic, repeatable variation in pixel sensitivity is observed with some regions having very low sensitivity; regions yielding zero signal are also observed (shown in (a) but not (b)). The repeatability is ~1% of the mean signal. This is better than expected Gaussian noise of ~2%. Stability of the x-ray tube is quoted as ~0.1% and the stability of the timer on the Medipix chip is better than 1%. In this presentation we will present our understanding of the origin of these features as well as a flat field of the detector to compensate these sensitive variations.

Figure (a) Homogeneity scan of CdTe-Medipix assembly, (b) 100 responses of column 114 (as indicated in (a)). References [1] R. Zainon, A. Butler, N. Cook et al., 2009, Proceedings of International Conference on

Instrumentation, Control and Automation (ICA 2009), Bandung, Indonesia, pp. 79-84 [2] N. Anderson, A. Butler, N. Scott et al., 2009, European Radiology, vol. 19, p. S228

Peter Smale

Precision cosmology with Type IA supernovae

For distance estimation on the largest scales, we use Type Ia supernovae (SNe 1a) as standard candles. Computing fits to the SNe Ia data is a well-established way of testing cosmological models. However, there are many subtleties associated with turning observations of SNe Ia fluxes into magnitudes for comparison with model predictions. We now have sufficient numbers of

supernova observations for statistical uncertainties to be outweighed by systematic uncertainties, which are deep and many. Despite the pervasive systematics, one often sees cosmological parameters quoted with a precision of three decimal places. How realistic is such “precision cosmology” given the systematics? How does “precision” relate to “accuracy”? This talk explores some of the vagaries of supernova cosmology in the context of the standard model and the inhomogeneous Timescape model.

Sarah Bouckoms

IceCube Standard Candle and Flasher analysis I'll try and not bore you to tears with another IceCube talk, so ill try to make this as entertaining as possible. I'm sure you are all familiar with the giant grid of detectors at the South Pole that isn't so much of a cube as an octogonal shape. The plus side of using the ice as a natural medium is that it is cheap. The downside is that it takes a lot of time and effort to figure out how the properties of the ice, ie absorption and scattering of light. This is important as the light from the Cherenkov radiation tells all about these elusive neutrinos. I've been using two 337nm nitrogen lasers and flashers to work out some of these properties as described by different ice models. It involves lots of computer simulations so get ready to feast your eyes on some very pretty plots...

Simon Parsons

Classification of Synoptic Climatology in New Zealand Understanding climate change and variability at a regional level is a significant challenge for the current generations of climate models. This research intends to explore regional climate variability by classifying present day weather patterns (synoptic scale features) and comparing the current frequency of these patterns to the frequency in the future using climate model output. Climate regimes or classifications originated from meteorologists looking for improved weather forecasting techniques and a multitude of classification methodologies exist. However they all attempt to achieve the same purpose, to group similar synoptic situations in an effort to simplify and interpret climatic variability. In New Zealand, the work of John Kidson forms the basis of the current synoptic classification. This scheme uses Principal component analysis (PCA) on 1000 hPa geo potential height data from the NCEP/NCAR reanalysis project.

The initial goal of this research is to create an objective analysis tool which completes the Kidson analysis. A series of testing will be required to ensure the tool produces robust results which can be used for predictive research. Subsequently an expansion on Kidson’s work to incorporate future climate model data under different (IPCC AR4) emission scenarios will begin. This predictive work will be the mainstay of the project. It is envisioned that further regional climate modelling will be undertaken at later stages in the project, to further reinforce the project findings.

Dr Bob Hurst

Ring Laser Gyros - Mundane and Esoteric

Ring Laser Group

In the last 10 years the Ring Laser research group has built the World's largest ring laser gyro about four times in succession, each bigger than the last. However our latest (UG-3) is actually a step downward in size, although upward in performance. These lasers can measure subtleties in Earth rotation - tidal deformations, polar motions, possibly Chandler wobble. ('Mundane' in the title has the original meaning: pertaining to the World.) Recently we have been developing a version of ring laser based on solid-state laser materials rather than the earlier He-Ne gas lasers.

Our ambition is to take the Earth rotation measurements several steps further, and with a new triangular ring laser make measurements of absolute rather than relative rotation rate of the Earth. This would allow us to detect the small daily variations in Length of Day attributable to sharing of angular momentum between the solid Earth and the oceans and atmosphere. Ultimately we may be able to detect relativistic effects: Lense-Thirring effect ('frame dragging') due to the rotating gravitating Earth, and de Sitter precession due to orbital motion around the Sun.

James Duley

The timescape model with radiation

The timescape cosmology proposed by Wiltshire is a viable alternative to homogeneous cosmology with smooth dark energy. I extend the current timescape model with the inclusion of radiation, having previously been ignored due to its negligible contribution at late times. Results are presented showing how the model continues into the early universe when radiation dominated.

Jeffrey Simpson

Range of barium abundances of stars in Omega Centauri

Using a large atlas of low resolution spectra of post-main sequence stars of the globular cluster Omega Centauri, stellar parameters (temperature, surface gravity and metallicity) are being determined.

This is then being used to find the amount of barium in the stars using the ionized barium spectral line at 499.6 nm. It has been found that there was a large spread of barium abundances throughout the cluster, with some having ten times more than others. Using this large data set, it should be possible to overcome some of the small number statistics that affect previous work.

Stephanie Hickford

Cascade Analysis for IceCube

IceCube is a neutrino telescope currently under construction at the South Pole. When completed this summer it will be a cubic kilometre in volume capable of detecting extraterrestrial neutrinos of all flavours. IceCube will consist of 5160 digital optical modules (DOMs) deployed under the ice on 86 strings. The DOMs house photomultiplier tubes that detect Cherenkov light from charged particles produced when neutrinos interact with nucleons in the surrounding ice and bedrock. One type of event that can be detected when a neutrino interacts with a nucleon is a cascade of particles. This signal is a spherical pattern of light inside the telescope. Monte Carlo simulation of background and signal is produced and used together with a 10% experimental data sample to develop algorithms and cut variables. These cut variables reduce the background while retaining high signal efficiency in order to discover neutrino induced cascade events within the remaining experimental data. Preliminary results from this analysis will be presented, showing the current work in identifying cascade events from the 2008 experimental data.

Syen Nik

Optimal material discrimination using spectral CT

S. J. Nik, J. Meyer, R. Watts Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand Spectral computed tomography (CT) using novel X-ray photon counting detectors (PCDs) with energy resolving capabilities is capable of providing energy- selective images. This extra energy information may allow materials such as iodine and calcium, or water and fat to be distinguished. PCDs have energy thresholds, enabling the classification of photons into multiple energy bins. The information content of spectral CT images depends on how the photons are grouped together. In this work, a method is presented to optimise energy windows for maximum material discrimination. Given a combination of thicknesses, the reference number of expected photons in each energy bin is computed using the Beer-Lambert equation. A similar calculation is performed for an exhaustive range of thicknesses and the number of photons in each case is compared to the reference, allowing a statistical map of the uncertainty in thickness parameters to be constructed. The 63%-con_dence region in the two- dimensional thickness space is a representation of how optimal the bins are for material separation. The model is demonstrated with 0.1mm of iodine and 2.2mm of calcium using two adjacent bins encompassing the entire energy range. Bins bordering at the iodine k-edge of 33.2keV are found to be

optimal. When compared to two abutted energy bins with equal incident counts as used in the literature (bordering at 54keV), the thickness uncertainties are reduced from approximately 4% to less than 1% (see _gure). This approach has been developed for two materials and is expandable to an arbitrary number of materials and bins.

Young-Wook Song

Photoluminescence study of Mg doped InN InN is a narrow-gap (~0.65 eV) semiconductor which has received considerable research interest for its potential in applications ranging from photovoltaics to terahertz detectors to high-speed transistors. The realization of p-type InN through in-situ Mg doping has recently been reported by number of research groups. In fact, many basic problems of the material are now well understood. However, its distinctive physical properties due to surface accumulation layer and unexplained recombination dynamics of p-type InN remain a formidable challenge to overcome. A new series of Mg doped InN epilayer films were grown by plasma-assisted molecular beam epitaxy. Detailed photoluminescence study has drawn further interpretation on optical properties of p-type InN. Eight different Mg cell temperatures were varied from 197 to 320˚C. In flux was operated at significantly high temperature at 760˚C to produce In-rich InN. Metal-organic chemical vapor deposition GaN templates were placed between InN layer and sapphire substrate to minimize compressive or tensile strain effect.

In PL, a typical n-type characteristic was determined by lightly doped films, with typically showing a single feature near the bandedge. Many moderately doped films however, exhibit multi radiative pathway between wide ranges of spectrum. This phenomenon, coupled with a dramatic drop of quantum efficiency in such Mg cell temperature region suggests the existence of potential p-type layer embedded inside InN layer.

A systematic study of temperature and excitation power dependent PL provides insight into the processes governing the luminescence. The near band edge power dependent PL analysis of sample with significant Mg content shows the manifestation of band to band transition with a strong theoretical support. Among others, a combination of extracted power law coefficient and non-radiative Arrenhius decay behavior in temperature dependent PL, assigning observed transitions are in fact, Mg related.

Ishwaree Nuepane

Embedding of our universe in a five-dimensional de Sitter spacetime

Abstract: Brane worlds are promising theories with extra spatial dimension(s) in which ordinary matter is localized on a (3+1) dimensional submanifold. Such theories are known to have interesting consequences for gravitational and astroparticle physics. In this talk I would indicate a

possible explanation of the smallness of the cosmological constant within a framework where the physical universe is embedded in a five-dimensional de Sitter spacetime.

Florian Maisonneuve

Frequency determination and pulsational mode identification of variable stars

I will review the basics of variable stars, in particular non radial pulsations. I will then present and compare the results of our analysis of three variable stars: one beta-Cephei, HD 61068 and two gamma-Doradus, HD 189631 and HD 40745. Each offer a different challenge, from a simple case to a very puzzling one.

NOTES FOR SPEAKERS

1. Please keep your presentation to the allocated time of 10 minutes.

5 minutes is allowed for discussion after your talk.

2. A computer and data projector will be available. Please load your presentations onto it before the start of your session from a memory stick or CD.

3. Talks will be recorded for educational and historical purposes. If you do not want your talk recorded please let the chairman of your session or Juergen Meyer know as soon as possible.

RESEARCH STUDENT TALKS

The B.G. Wybourne prize will be awarded for the best research student talk while the Department will be awarding prizes for 2

nd, 3

rd and 4

th placed research student talk.

Last year the B G Wybourne Prize went to Jeffrey Simpson and the Department prize was shared by

Domagoj Belic, Nikolai Kreutzmann and Richard Graham.

$200 (B.G. Wybourne prize) - Jeffrey Simpson

$150 (2nd) - Domagoj Belic

$100 (3rd) - Nikolai Kreutzmann

$50 (4th) - Richard Graham

AFTER-CONFERENCE GATHERING

Members of the Department are all welcome to attend the end-of-conference BBQ and prize-giving to be held at the Staff Club following the last talk.