2005 Seminars
Tuesday 6 December, 2005
Dr Steve Marsh
Department of Physics and Astronomy
University of Canterbury
Aerosol Retrievals from ATSR-2 and an Overview of the University of Canterbury Ring Lasers
Remote or indirect measurements are used for a wide variety of purposes, from examining the structure of the nucleus to the structure of the stars. However, when such measurements are made, due to difficulty or expense in acquiring the measurement, they often leave in their wake the complex problem of interpretation generally known as the inverse problem. Optimal Estimation is a technique, based on Bayesian statistics, which has been developed to retrieve the solution to such problems.
This presentation will begin with a discussion of the retrieval scheme I developed while at the University of Oxford for obtaining aerosol properties using measurements from the ATSR-2 satellite instrument. I will then go on to discuss the University of Canterbury ring lasers and their possible application to areas as diverse as geodesy, GPS and general relativity.
Friday 2 December, 2005
Geoff Stedman
Department of Physics and Astronomy
University of Canterbury
Is the moon still there when no one is looking? (Einstein to Pais)
I will re-run a lecture ‘demonstration' which I had built in the 1900s. It shows the essentials of the photon correlation experiments that first made the EPR paradox (Einstein Podolsky Rosen) clear and illustrates the inevitability of the Bell theorem which says that ‘hidden variable' reinterpretations of quantum mechanics are impossible. I would like to tell you the history of the demonstration since then, and to suggest two possible extensions arising from more recent developments.
Tuesday 29 November, 2005
Dr Jon-Paul Wells
Department of Physics and Astronomy
University of Sheffield , United Kingdom
Ultrafast Spectroscopy of Insulators and Semiconductors
The advent of widely tunable free electron lasers (FELs) has revolutionised spectroscopy in the infrared. I will discuss highlights from seven years of operation with the Dutch FEL (dubbed ‘FELIX') in Nieuwegein, near Utrecht. In particular, I will cover infrared free induction decay measurements made on hydrogen localised vibrational modes in hydrogenated alkaline earth fluoride crystals in collaboration with co-workers from the Physics and Astronomy department at Canterbury. In these measurements, which are essentially four-wave-mixing experiments on a homogeneously broadened spectral line, a unique form of quantum beat behaviour is observed due to vibrational ladder climbing.
Spectrally, the other extreme is represented by amorphous solids such as amorphous silicon or germanium (a-Si or a-Ge) where the infrared absorption spectra of vibrational modes show linewidths as great as 100 cm-1 (compared to 0.25 cm-1 for the substitutional H- local mode in CaF2). Amorphous thin films such as a-Si:H (hydrogenated amorphous silicon) have attracted considerable interest as cheap alternatives for use in transistors and as solar cells (the solar cells in most common calculators are constructed from a-Si:H). A perennial problem with this material is the degradation of the solar cell efficiency upon exposure to light, an effect termed the Staebler-Wronski effect. Hydrogen is used in the growth of a-Si based devices to passivate defect states and recently it has been observed that if deuterium is used as an alternative, the Staebler-Wronski effect is greatly reduced (by a factor of 50 in some cases). Evidently, the explanation lies in the additional neutron mass and therefore most likely in the vibrational properties. I will discuss our measurements of vibrational population relaxation and dephasing for the hydrogen/deuterium stretching modes in a range amorphous silicon and germanium based samples with some attempt to relate the information gathered to the observed light induced degradation.
If any time remains, a brief review of semiconductor physics based at Sheffield will be given, highlighting some semiconductor ‘spintronics' activities.
FRIDAY 28 OCtober 2005
11am - Room 701
George Mullenger
Department of Civil Engineering
Decomposition of Random Motion
Between the uncoordinated random motion of molecules within a rarefied gas and the locally coordinated but random motion that can exist within some liquid flows it seems possible to contemplate an intermediate category which combines aspects of both.
In certain physical situations behaviour which appears to fall into this category is observed.
An approach to modelling the behaviour might be possible through theories of materials with microstructure.
Attempts to construct new theories of material behaviour require first balance equations and then constitutive equations needed to close them.
There has been substantial effort to model gas-like random behaviour beginning with the kinetic theory of gases; in which the random motion is order of magnitude faster than any average physically measurable motion. Interestingly, in plasma flows, where the physically averaged motion of a very rarefied gas begins to reach speeds commensurate with random motion speeds, issues relevant to the present study arise, such as material frame indifference and the loss/gain of sub-particles from neighbourhoods. Initial work on liquid random motion appears to have been influenced by the kinetic theory of gases.
In the present work is proposed an approach which overlays uncoordinated random motion on top of affine deformation within the material point. Further progress has required that constitutive equations be suggested, and in the absence so far of a contribution from thermodynamics these have been surmised from sources in the literature and in acknowledgement of issues of equipresence and invariance.
A first requirement for a thermodynamics concerns an appropriate concept for temperature, for which we have made some suggestions.
Observations in solid state physics show that the behaviour we suggest is a phase transition phenomenon, which may depend upon temperature in some cases or volume fraction in others.
FRIDAY 21 OCtober 2005
11am - Room 701
Franck Natali
Postdoctoral Fellow, Department of Physics and Astronomy
Molecular Beam Epitaxy of Group-III Nitrides on Silicon Substrates: Growth, Properties and Device Applications
Since the successful development of high performance AlGaInN light emitting diodes (LEDs) and laser diodes, there is a considerable interest in the other III-nitrides optical devices including vertical cavity surface emitting lasers (VCSELs), resonant cavity light emitting diodes (RCLEDs), but also in electronics particularly for the realisation of high-power and high-frequency transistors. For all these applications, the III–V nitrides layers are usually grown on sapphire or silicon carbide substrates. However the development of some of these applications on silicon (111) substrates has obvious technological advantages (cost, integration….). This is the reason why significant research efforts have been made during the last decade in this direction as shown by the wide variety of techniques which have been assessed. Indeed, techniques including conventional growth by molecular beam epitaxy (MBE) or metal organic chemical vapour deposition (MOCVD) using various buffer layers, combinations have all been already used in order to find a successful process for the growth and/or the realization of GaN-based devices on silicon substrates. Even if significant progress has been made, it is clear that nitride layers grown on Si(111) have a strong tendency for cracking due to the tensile strain which appears during cooling of the samples after growth. It is obviously a critical issue in order to fabricate nitride-based devices.
This seminar will discuss about the growth, properties and device applications of group III-nitrides grown by MBE on Si(111) substrates. Most of the results presented, will come from my Ph.D work at the National Research Centre for Semiconductor Epitaxial Growth, CRHEA-CNRS, Valbonne, France.
We will describe an efficient growth procedure that has been devised in order to overcome the difficulties encountered during the growth of nitrides on silicon substrates (No nitridation, no Si diffusion and autodoping coming from the substrate, strain balance engineering….). This growth procedure allows us to grow thick GaN epilayers (up to 3 m) without formation of cracks. The structural, optical and electrical properties of these films will be presented. In order to evaluate the potential of III-nitrides grown on silicon substrate, we have grown heterostructures to fabricate LEDs, photodetectors and high electron mobility transistors. These results will be compared with the performances of devices fabricated on sapphire and silicon carbide substrates.
FRIDAY 14 OCtober 2005
11am - Room 701
Thomas H Myers
Department of Physics, West Virginia University
Polarization Electronics - A Path to Multifunctional Materials
The Group III-Nitrides lack inversion symmetry that leads to a large crystal polarization. Thus, polarization plays an important role in device structures, and both spontaneous and piezoelectric polarization must be considered. One new approach has been to utilize polarization discontinuities to produce regions of localized charge, allowing electronic devices to be fabricated without doping. Indeed, this approach has been used to fabricate high electron mobility transistor structures without external doping. The concept of polarization electronics provides a new vista in semiconductor research. In particular, combination with other materials such as ferroelectrics provides promise for improved performance and functionality.
I will review the basic ideas behind polarization electronics, and then present some of the experimental work at WVU concerning the difficult task of growing heteroepitaxial ferroelectrics on polar semiconductors.
FRIDAY 7 OCtober 2005
11am - Room 701
Sergei Gulyaev
Centre for Radiophysics and Space Research Auckland University of Technology
Astrophysics with the Square Kilometer Array
FRIDAY 30 September 2005
11ama - Room 701
Professor Malcolm Longair FRS
Jacksonian Professor of natural Philosophy at the Institute of Astronomy
and Head of the Cavendish Laboratory in the University of Cambridge
The most luminous radio galaxies
This will be a review of our recent work trying to disentangle the physics of the most luminous radio galaxies and the origins of their evolution with cosmic epoch. We have some nice new results.
FRIDAY 23 September 2005
11am - Room 701
Dr Barry Welsh
Space Sciences Laboratory, University of California, Berkeley
The local interstellar gas: some like it hot?
The Local Bubble is a giant cavity, some 300 light years across, that has been carved out of the interstellar gas that surrounds the Sun's neighbourhood in the Milky Way galaxy. The size, shape and physical characteristics of this "almost empty" cavity in interstellar space will be discussed and the question as to whether the rarefied gas atoms contained within the local bubble are really at a temperature of a million degrees as most X-ray astronomers maintain.
You can decide whether some like it hot...or not!
FRIDAY 16 September 2005
11am - Room 701
Dr Richard Gray
Department of Physics, University of Auckland
Silicon Pixel Gamma Imaging
Conventional gamma cameras suffer from an inverse relationship between spatial resolution and acceptance. I will discuss the concept of a Compton effect gamma camera and describe some initial research into x-ray imagers using silicon pixel detectors which could provide a stepping stone to Compton camera development.
FRIDAY 9 September 2005
11am - Room 701
Dr John Campbell
Department of Physics & Astronomy
Rutherford and Einstein
1905 was a good year for Albert Einstein and for Ernest Rutherford. Both had done the key work for which they were to receive a Nobel Prize, and Rutherford had dated the age of the Earth. As the years rolled on they had some interesting interactions, and there are some interesting contrasts, between these two pioneers. Rutherford is to the atom what Newton is to mechanics, Darwin to evolution, Faraday to electricity and Einstein to relativity.
Thursdays and Fridays at 2 pm, Physics Room 701:
August 18,19 and 25,26
Dr Peter Jarvis,
Department of Physics and Astronomy
(Visiting Erskine Fellow, School of Mathematics and Physics, University of Tasmania)
Introduction to Quantum Information and Quantum Computation
These informal lectures will attempt to discuss some of the basic ideas of quantum information and quantum computation starting with a lightning review of the notation and language of state vectors in quantum mechanics. The material should be accessible to interested honours and postgrad students, and researchers with some awareness of quantum physics and a willingness to use vector spaces.
The text is Nielsen and Chuang, Quantum Computation and Quantum Information (CUP, 2000).
The main aim is to introduce quantum circuits in enough detail to discuss some of the new algorithms for quantum computers.
FRIDAY 12 August 2005
11am - Room 701
Dr Peter Jarvis
School of Mathematics and Physics, University of Tasmania
Impossible party games, unbreakable codes, and spooky action-at-a-distance: what is UP with entanglement?
The talk will give a basic introduction to the surprising behaviour of physical systems (and the consequences for observers) possible if entangled quantum states can be regularly produced and distributed. Some of the implications for quantum computing will be discussed and illustrated.
This colloquium also serves as the introductory lecture in a short course on quantum computing and quantum information to be given in the department over the next couple of weeks.
FRIDAY 29 July 2005
11 am - Room 701
David Wiltshire
Department of Physics & Astronomy
Fractal Bubble Universe – Cosmology Without Dark Energy
I will present a viable alternative to "dark energy": a model universe with only clumped matter at the present epoch, consistent with general relativity and inflation. It is based on a new solution to the problem of averaging lumpy geometries in cosmology.
The observed universe has an inhomogeneous structure of galaxy clusters on bubble walls surrounding voids. Despite being inhomogeneous, the growth of initial perturbations from primordial inflation provides a particular self-similar fractal structure to this inhomogeneity. An observer at an average spatial position finds herself in a void, and I argue that the clocks of such a comoving void "observer" differ from those of the average galaxies in the gravitational wells of bubble walls. Nonetheless the scale-invariant nature of the perturbations generated by inflation means that there is a homogeneous cosmic time in average galaxies, defined by the epoch at which they broke from the Hubble flow.
This understanding means a recalibration of cosmic clocks and rulers, which I quantify, with far-reaching consequences. The age of the Universe is 15 +/- 1 billion years. The universe is much older at high redshifts than is conventionally assumed, explaining the existence of complex galaxies at such redshifts, which are otherwise a mystery. The fraction of baryonic matter predicted by primordial nucleosynthesis bounds is three times larger than is conventionally assumed, significantly changing the issues associated with dark matter.
A statistical analysis of type Ia supernova data shows that the model fits comfortably. Although the standard "dark energy" model with a cosmological constant wins on a Bayesian analysis, the present Fractal Bubble model is the first approximation in averaging, and further corrections are expected. This makes the Fractal Bubble model is a serious candidate to describe the Universe in which we live.
FRIDAY 15 July 2005
11 am - Room 701
Adrian McDonald
Dept Physics & Astronomy, University of Canterbury
Radar observations of the atmosphere at Scott Base
The Medium Frequency (MF) radar at Scott Base (78°S), Antarctica, has been measuring winds in the Mesosphere/Lower Thermosphere region since December 1982. These o bservations have highlighted the wave-driven nature of the circulation in this region. This circulation is generally dominated by features associated with atmospheric tides, these waves having 24 and 12 hour periods. However, the atmospheric tides represent a small proportion of the wave field present in the atmosphere and studies have suggested that other waves have a stronger effect on the structure of the winds at these altitudes. This presentation will discuss the importance of planetary waves and internal gravity waves on the winds observed in the mesosphere. Planetary wave breaking is known to cause Stratospheric Sudden Warming (SSW) which are perhaps the most dramatic meteorological phenomena to occur in the stratosphere. SSWs occur primarily in the stratosphere of the Northern hemisphere during winter and are associated with temperatures rises by up to 80 oC in just a few days. However, a major SSW was observed in the southern hemisphere in 2002 for the first time and the response of the mesospheric winds to this phenomenon are detailed using radar aand reanalysis data. A recent upgrade to the MF radar system also allows the possibility of examining short period internal gravity waves and initial findings are also discussed.
FRIDAY 10 June 2005
11 am - Room 701
Dr Kent Cullers
Department of Physics and Astronomy
- This seminar has been cancelled but Dr Cullers will give a seminar next semester.
FRIDAY 3 June 2005
11 am - Room 701
Assoc Prof Mike Reid
Department of Physics and Astronomy
Science, Education, and Rare Earths in Asia
November/December I embarked on an Erskine-funded trip to Japan, Hong Kong, and China. In the 13 years since I left Hong Kong for New Zealand, many things have changed, and many things have stayed the same. In this seminar I will share my impressions of education, science, and other issues in these countries.
FRIDAY 6 May 2005
11 am - Room 701
Milo Kral
Department of Mechanical Engineering
Using Electron Diffraction for Identifying Phases, Determining Crystal Structure and Orientation
Materials scientists can answer all sorts of questions about crystalline phases using electron diffraction. For example, we can use electron backscatter diffraction pattern analysis (EBSD) in combination with energy dispersive X-ray spectroscopy (EDS) to quickly identify phases by their composition and crystal structure if their minimum dimension in cross-section is greater than about 200 nm. Not only can we identify the phase, but we can also determine the crystallographic orientation with respect to other phases or the specimen dimensions. If the crystal is smaller than 200 nm, we can use convergent beam electron diffraction in the transmission electron microscope although the technique is much more demanding of the operator. At Canterbury, we have the necessary instruments available in the JEOL JSM 6100 scanning electron microscope and the Hitachi H600 transmission electron microscope. In this presentation, the basics of the experimental techniques listed above will be explained with examples of recent results in on-going research.
FRIDAY 29 April 2005
11 am - Room 701
Suruj Seunarine
Dept of Physics & Astronomy
Einstein and Brownian Motion
Einstein's description of Brownian motion and the statistical methods he used have found applications in diverse fields of physics. His accurate determination of molecular sizes finally resolved to debate between the atomists and sceptics regarding the existence of atoms. The mathematical description of Brownian motion lends itself to applications in medicine, finance, traffic flow and couples on a crowded dance floor. This talk is a repeat of a public lecture given at the Great Hall earlier this year to mark the world year of physics and to celebrate 100 years since Einstein's great papers. We will discuss the history, mystery and resolution of the Brownian motion phenomenon and we will discuss modern applications, from quantum fluctuations in the early universe to medical imaging.
NOTE: The material is presented at a level suitable for the non physicist.
FRIDAY 22 April 2005
11 am - Room 701
Michele Bannister Aurora Scholar 2004,
Dept of Physics & Astronomy
Around the world in 80 days
My work as Aurora Scholar at Keck, Hawaii, and visits to JPL, Pasadena, the VLA, New Mexico, the AAS Conference, San Diego, and the big telescopes in Chile. (With lots of pretty pictures of observatories).
William Tobin
Dept of Physics & Astronomy
The gyroscope from Foucault to Gravity Probe B
I will show how both Foucault's gyroscope from 1852 and the gyroscopes launched last year in the Gravity Probe B satellite were inspired by the same goal of measuring the properties of space in the vicinity of the Earth. (With demonstrations and pretty pictures of gyroscopes.)
Please Note: These talks will be attended by the twenty Year 12 & 13 students participating in the Aurora School in Astronomy. They will therefore also be suitable for undergraduates so please advertise them in your classes.
FRIDAY 4 March 2005
11 am - Room 701
Prof. Hans Zinnecker
Deputy Director and Head of the Star and Planet Formation group
Astrophysikalisches Institut in Potsdam, Germany
Star formation in star clusters