The May 2008 research newsletter
Welcome to the May edition of the Research Newsletter of the Department of Physics, SUPA at Strathclyde. As announced previously, the newsletter will be run by the new Director of Marketing & Communication (DMC) who will be happy to consider your stories for this newsletter, the SUPA newsletter, Research Matters, the Physics website, and elsewhere. The offer previously made is still valid: the DMC is willing to take photographs of you and your labs under the condition that they may be used to promote the department. Steady progress is being made with the academic staff pages. Check it out for yourself and send your bio and research description to the DMC. Your publications and grants are pulled from the Big Brother database so make sure that your record is up to date (not the DMC’s responsibility – go here to update your publications – go to Kirsten to make sure your grants are entered correctly).
In related matters, the Strathclyde Press Office has a new press officer – Paul Gallagher (see below) – whose responsibility is the Science and Business faculties. You may have noticed quite a few more press releases from the Science faculty appearing recently. As DMC, I would like to urge all of you to consider your stories for a press release. It will not just appear on the University homepage but might get you an interview with the press. Essentially any science story mentioning the physics department is good for us. Come and talk to me if you need to know more or contact Paul Gallagher at, t: 0141- 548-2370, e: paul.gallagher strath.ac.uk [K]
Resonances appear in virtually all branches of physics and we all assume that the response of a given system to external modulations is mainly determined by the difference between its natural and forcing frequencies. This simple picture turns out to be true only when the modes of the original system are ‘orthogonal’ as are, for instance, the modes of a harmonic oscillator. The coupling between non-orthogonal modes can lead to a response to a periodic forcing orders of magnitude larger than what the separation between forcing and natural frequencies would suggest. This leads also to a quantum effect, the ‘excess noise’, whereby the level of spontaneous emission noise in a device is more than the one photon per mode expected from basic quantum considerations. When resonances are observed in nonlinear systems, two main questions arise: (1) what are the modes that we should consider? (2) Are these modes orthogonal? In a recent letter (Phys. Rev. Lett, 100, 123905 (2008)), we have shown that – in the case of lasers – the response to modulation is not determined by the modes of the optical cavity but by the modes of the linear stability operator. These modes can be orthogonal or not depending on the way in which the laser operates. As a consequence, in nonlinear systems strong response to non-resonant modulations and excess noise can affect some output states but be completely absent from others. We then proceeded to extend the phenomenon of ‘state-dependent resonance’ to general nonlinear models with relevance not only to optics but to all spatially extended systems near an oscillatory instability. In particular, we found cases (see the figure) where the response to modulations can be enhanced by an order of magnitude with obvious relevance to the field of control of complex systems.
Figure: Comparison of two systems with identical resonance frequencies and losses: the solid blue line (||R||22) is the maximum response of the system with non orthogonal modes; the dashed red line (dist2(Λ)) is the maximum response of the system with orthogonal modes. (click on figure for bigger version)
[F. Papoff1, G. D’Alessandro2, and G.-L. Oppo1]
1 SUPA, Department of Physics, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG, UK
2 School of Mathematics, University of Southampton, Southampton SO17 1BJ, England, UK
An international group of scientists from the UK, Germany, and Australia has discovered the reason why syrup is so sticky by comparing it with traffic jams. When salts or sugars are added to water, the resulting mixture is very ‘sticky’ and flows with great difficulty or – to use the scientific term – it has a high viscosity. This effect is probably most familiar in mixtures of sugars and water such as in syrup and honey.
A debate has been raging for decades as to the scientific reason why things like honey are so sticky. The consensus had been that sugar and salt molecules in water would bind to the water molecules and thereby alter the structure of water. So-called structure inducers (with the beautiful scientific name ‘kosmotropes’) would make liquid water more ice-like and thus stickier... Unfortunately, work by a Dutch group threw a spanner in the works by suggesting that no such structure-inducing effect exists (DOI: 10.1126/science.1084801) leaving chemists and physicists at a loss how to explain stickiness.
A new study published in the Journal of Chemical Physics puts an end to all the confusion (DOI: 10.1063/1.2906132). The team consists of researchers from the University of Regensburg, Murdoch University, and the University of Strathclyde. Leader of the team, Professor Klaas Wynne explains that ‘the German, Australian, and British teams use complimentary techniques making it possible for the first time to understand the motions of water molecules in solution on time scales of about one-trillionth of a second’ (that is: 1/1,000,000,000,000 seconds).
The team studied solutions of metal salts rather than those of sugars because the salt ions are simpler appearing like smooth spheres rather than knobbly molecules. He continues ‘The metal ions we have studied hold on tightly to a few neighbouring water molecules forming tacky spheres that randomly jam together at high enough concentration like cars in a traffic jam.’ His colleague Dr David Turton explains: ‘You can think of a crystal as oranges in a box at the supermarket, neatly arranged in rows and layers. If you instead throw the oranges into the box, they jam into a random jumble – what physicists call – a glass. We find that ions and sugar molecules in water jam like oranges while the water is free to spin in the pockets between the “oranges”.’
This type of jamming has now been seen in the most unlikely collection of situations such as the movement of dunes in the desert, the flow of grains in silos, and – yes – traffic jams. So, next time you are stuck in traffic, think about how you are simply following the laws of physics like sugar in the cup of coffee you had for breakfast that morning.
[David Turton, Klaas Wynne]
Part-time PhD student Neil Thompson and supervisor Brian McNeil have invented a method of generating attosecond pulse trains from Free Electron Laser amplifiers. Their work, to be published in Phys. Rev. Lett. at the end of May, borrows techniques from conventional mode-locked lasers. These conventional lasers use phase-locking of the longitudinal cavity modes to great effect, generating few femtosecond pulses, e.g. the ubiquitous Ti:Sapphire laser. Thompson & McNeil have predicted that a cavity-like longitudinal mode structure can be synthesised in a FEL amplifier. These modes may be locked and in the x-ray, at wavelength 1.5 Å, to generate attosecond pulse trains of duration 23as separated by 150as with peak powers of a few GW – see figure. Such pulses could, for the first time, enable the spatiotemporal imaging of atoms and their interactions.
(See: http://arxiv.org/abs/0802.4159 for pre-print)
SPRITES (Structure changes in Protein Reactions via Infrared Time Evolution Spectroscopy) a € 1M ERC Starting Grant Scheme proposal submitted by Neil Hunt has been approved for funding. The project, one of only ~300 funded projects from more than 9000 Europe-wide applications, will apply a derivative of the new ultrafast laser technique of transient 2D-IR spectroscopy1 to study enzymatic and protein reactions in real time.
2D-IR spectroscopy uses a train of mid-infrared pulses to observe interactions between vibrational modes of a molecule.2 In a similar way to multidimensional NMR spectroscopy, 2D-IR spreads the infrared spectrum of a molecule over two frequency axes; peaks corresponding to the normal linear spectrum appear on the diagonal, while off-diagonal peaks show interactions between the modes. These interactions can take the form of direct coupling or population transfer from one mode to another – effectively observing energy flow through the molecule. Of particular relevance to the SPRITES project, 2D-IR spectroscopy can also detect changes in molecular structure with ultrafast time resolution and by adding a visible-light pulse to initiate a biological process such as a change in protein structure or enzymatic reaction, SPRITES will effectively create real-time molecular movies of biological processes.
Anyone wishing to learn more about 2D-IR spectroscopy is subtly directed to Neil’s recent article in Spectroscopy Europe for more information – it’s worth a look for the impressive web-browser alone!!!
(1) Kolano, C.; Helbing, J.; Kozinski, M.; Sander, W.; Hamm, P. Nature 2006, 444, 469.
(2) Khalil, M.; Demirdoven, N.; Tokmakoff, A. J. Phys. Chem. A 2003, 107, 5258.
- Resonances, but not as you know them
- Strathclyde Research in Laser Nuclear Physics at the University of Jena, Germany
- The science of syrup and traffic jams
- European Research Council Funds SPRITES!
- Attosecond pulses
New grants as registered by Kirsten since the start of the year:
- Professor Ken Ledingham - AWE - Laser Driven Nuclear Physics - Start Date: 1st September 2007 - £333,628.00
- Dr Nick Lockerbie - QinetiQ Consultancy - Date: April 2008 - £30,000
- Dr Nick Lockerbie - STFC - Investigation in Gravitational Radiation - Start Date: 1 October 2007 - £578,066.26
- Dr Brian McNeil - STFC - Free Electron Lasers and Advanced Light Sources - Start Date: 1 April 2008 - £186,255.00
- Professor Hugh Summers - UKAEA - Atomic Physic Research and Development at UKAEA - Mr O'Mullane - Start Date: 1 January 2008 - £76,538.00
Keep Big Brother happy!
The Big Brother database keeps track of your grants and publications as they appear in various places on the Physics website. If you have new publications in high impact factor journals, go to Adding papers to the "Selected Publications" page to feed them to Big Brother. [K]
In March 2008, Stephen M. Barnett and Gian-Luca Oppo were elected “outstanding referees” by the American Physical Society. See American Physical Society initiates recognition program for "Outstanding Referees" (March 10, 2008) [K]
Claire Neil has been awarded the Neil McDougall Bursary in Practical Oceanography by the Scottish Association for Marine Science. This is a competitively awarded scholarship which will allow her to spend 9 weeks at Dustaffnage Marine Laboratory and participate in a month-long cruise on the Royal Research Ship James Cook in the Celtic Sea. The cruise is highly relevant to her PhD work on interactions between physical mixing and optical properties in UK shelf seas. [AC]
Prof David Birch was invited to give a seminar at the University of Uppsala in Sweden on 16 April where he was hailed as a "hero scientist".
Fred Stern Prize
Nominations are sought for the 2007 Fred Stern Prize, our most prestigious prize for a postgraduate student. We are looking for candidates of exceptionally high quality who had their PhD viva in the calendar year 2007. Nominations should be submitted to the Postgraduate Tutor (John Jeffers) by 23 May 2008. The nominator will normally be the supervisor and/or external examiner, but any member of staff can submit a nomination. Nominations will be assessed by the Head of Department and the Postgraduate Tutor, taking advice as appropriate, and any proposed award(s) will be reported to the Departmental Committee/Exam Board for endorsement. It is expected that any Prize(s) will be awarded at the Summer Graduation. [JJ]
Strathclyde will host the "International Workshop on Ultrafast Chemical Physics 2008 (UCP ‘08)" on 30/31 October 2008 to be held in the Senate/Court suite. Plenary speaker is Prof Robin Hochstrasser FRSE (University of Pennsylvania). Confirmed invited speakers are Casey Hynes (CNRS, Paris and University of Colorado, Boulder), Charles Schmuttenmaer (Yale), Majed Chergui (Ecole polytechnique fédérale de Lausanne), Mischa Bonn (AMOLF, Amsterdam), Peter Hamm (University of Zurich), and Thomas Elsaesser (Max Born Institute, Berlin). The workshop is organised by Angus J. Bain (UCL), David Klug (Imperial), Steve Meech (UEA), Neil Hunt (Strathclyde), and Klaas Wynne (Strathclyde). [K]
Two publications appearing in the March/April editions of the New Journal of Physics describe in detail Strathclyde research carried out recently at the Friedrich Schiller University, Jena. The first article entitled “Study of Photo-Proton Reactions Driven by Bremsstrahlung Radiation of High-Intensity Laser Generated Electrons” was carried out by the SUPA collaboration between Strathclyde and Paisley. In 2000, a team at Livermore pointed out that once lasers were more reliable then much work on photo-nuclear cross sections could be carried out using high intensity lasers. Now, some eight years later in direct response to this aspiration, the above paper has been published. The Jena high intensity laser was directed at high Z targets and produced a bremsstrahlung spectrum very similar to a low energy electron linac. Our investigation is the most comprehensive study of photo-proton reactions driven by bremsstrahlung radiation of laser accelerated electrons to date and a number of (γ, n)/(γ, p) cross sections were measured for the first time in Mg, Ti, Zn, and Mo isotopes. The experiments were supported by extensive statistical model calculations, one of the strengths of our SUPA collaboration. This single laser-driven research programme has provided almost 20% of the total σint(γ, n)/σint(γ, p) ratio measurements in the Giant Dipole Regime to date. This is shown in the diagram below (New Journal of Physics 10, 2008, 043037). This paper has been selected by the IoP as one of the novel, significant and potentially high impacting of all physics papers published in IoP this week!
Fig 1 The six new measurements are shown with a square cap.(click on figure for bigger version)
Our future programme will concentrate on measuring photo cross sections of astrophysical significance. This research will be carried out from 2008 onward at the new SUPA beam line at the Forschungszentrum Dresden-Rossendorf, where for the first time a direct comparison between laser-driven and traditional accelerator based nuclear measurements will be made.
The second publication (New Journal of Physics 10, 2008, 033034) entitled “Spectral Shaping of Laser Generated Proton Beams” describes the rapid advancement made in the laser generation of mono-energetic proton beams which has been made over the last two years since our first paper on mono-energetic protons was published in Nature in 2006 (Nature 439, 2006, 445). We show that the surface cleaning effect through laser ablation of structured targets resulted in a significant improvement of the reproducibility of monoenergetic beam profiles. Using a robust statistical analysis, we have derived a scaling law between proton peak energy and laser pulse energy (laser intensity). This has been supported by new numerical simulations. An example of the improved data and simulation is shown in Fig 2.
Fig 2 (a) The black spectrum in the above picture shows the conventional exponential spectrum and the red peaked spectrum shows a monoenergetic peak from a dotted target which had been cleaned by an ablation laser prior to laser-driven proton production. (b) A 2D-PIC simulation, which demonstrates the important point that inert heavier ions are essential for obtaining a monoenergetic response from a lightly doped proton layer.(click on figure for bigger version)
It is expected that this work can be extended using the new laser Gemini at RAL which will be commissioned late in 2008 or early 2009, where according to recent simulations, proton energies could reach above 150 MeV, which is of significance to laser applications in proton oncology.
Finally the University of Strathclyde is heavily involved in organising the first International Workshop in “UltraHigh Intensity Laser Nuclear and Particle Physics” at the European Centre for Theoretical Studies in Nuclear and Related Areas, TRENTO, Italy, 23-27 June 2008 (Thomas Heinzl, University of Plymouth, Burkhard Kämpfer, Forschungzentrum Dresden-Rossendorf and Ken Ledingham University of Strathclyde).
[Wilf Galster, Klaus Spohr, Ken Ledingham ]
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