Issue 1, 2014

See photos from Nordita


Many greetings from us at Nordita (and some of our friends at the Astronomy Department)! <br>Here we are celebrating Nowruz, the Iranian new year.

Katherine Freese New Nordita Director from September 2014

Professor Katherine Freese of the University of Michigan has begun a three year term as Director of Nordita starting September 1, 2014. Professor Freese is an internationally recognized researcher working on a wide range of topics in theoretical astro-particle physics and cosmology. She received her PhD in Physics 1984 from the University of Chicago and held postdoctoral appointments at Harvard University, the Institute for Theoretical Physics at UC Santa Barbara, and UC Berkeley. From 1987 to 1991 she was an Assistant Professor at MIT and then moved to the University of Michigan, where she is currently the George Eugene Uhlenbeck Professor of Physics. In 2012 she was awarded an honorary doctorate at Stockholm University and it was recently announced that she will receive a Grant for the International Recruitment of a Leading Researcher from Vetenskapsrådet (Swedish Research Council) for a total of 101 500 000 SEK over a period of 10 years. We congratulate her on this well-deserved recognition and wish her every success during her time at Nordita.

Meet the Norditians.

Outgoing Nordita Director Larus Thorlacius has now returned to his position as Professor of Physics at the University of Iceland, but will continue to spend part of his time in Stockholm as a Guest Professor of Theoretical Physics at Stockholm University.

Lárus Thorlacius (left) receiving a gift that will kickstart his new career from Nordita board chairman Kalle-Antti Suominen.
(Photo: Per Osland)

John Wettlaufer to return to Nordita on 10 year VR Grant

John Wettlaufer of Yale University (USA) is a familiar figure at Nordita. During the fall of 2008, he spent his sabbatical at Nordita; see Nordita Newsletter 2008/3, funded in part by the Wenner Gren Foundation, the Stochholm Astrobiology Graduate School, and Nordita. He came back to Nordita in 2011, again supported by the Wenner Gren Foundation; see Nordita Newsletter 2011/2. He was then awared the distinguished Tage Erlander Guest Professorship of 2012; see Nordita Newsletter 2011/3.

The Swedish Research Council (VR) has now awared him a 106 MSEK grant for a 10 year stay under the scheme "Grants for international recruitment of leading researchers". We wish John a prosperous time at Nordita!

John Wettlaufer (left) at the inaugural lecture of the Tage Erlander Guest Professorship for 2012, together with Prof. Sven Stafström, head of the Swedish Research Council. (Photo: Fabio Del Sordo)

Axel Brandenburg Elected to the Royal Swedish Academy of Sciences

At its general meeting on April 9, 2014, the Royal Swedish Academy of Sciences elected Nordita Professor Axel Brandenburg as Foreign Member of the Academy's class for astronomy and space science. This honor recognizes the numerous significant contributions and leadership of Axel Brandenburg within the fields of magnetohydrodynamics and turbulence in astrophysical plasmas. For more information see the news release of the Academy.

Norwegian Research Council Grant Awarded Jointly to Groups at Nordita and NTNU in Trondheim

For the first time in its history, the Norwegian Research Council has accepted applications from scientists working at research institutes funded by the Nordic Council of Ministers, including Nordita, and in Fall 2013 Nordita won its first Norwegian grant when it was decided to fund a concentrated 4-year effort at Nordita in Stockholm and NTNU in Trondheim to improve our understanding of particle transport and clustering in stratified turbulent flows. This work couples large-scale numerical simulations with numerically guided analytical approaches. An ultimate goal is to have a physically consistent model of particle transport in raindrop formation.

Particle motion and particle accumulation in turbulent flows with temperature gradients are also of great importance for many critical applications in the modern world. Examples include the Diesel engine, industrial boilers, and prediction of rain initiation in the atmosphere. There are also astrophysical applications, in particular the conglomeration of dust in the context of protoplanetary accretion discs.

For further details, see the home page on the project Particle transport and clustering in stratified turbulent flows.

KAW Grant Awarded for Dark Matter Studies using XENON 1T

The Knut and Alice Wallenberg Foundation has granted 28.5 MSEK for the "Discovering Dark Matter Particles in the Laboratory", an experimental project with Jan Conrad of Stockholm University leading the Swedish effort and with Nordita's Katherine Freese as Co-PI.

The nature of the dark matter in the Universe that comprises 95% of the mass in galaxies including our own Milky Way is as yet unknown. The XENON 1T experiment consists of a tonne of Xenon liquid that produces two pulses of scintillation light when struck by a dark matter particle coming in from the Galaxy. The discovery of dark matter would solve one of the longest outstanding problems in all of modern physics.

KAW Grant to Study Bottlenecks for Particle Growth in Turbulent Aerosols

The Knut and Alice Wallenberg Foundation has granted 33 MSEK to Bernhard Mehlig of Gothenburg University, Sweden, to understand "Bottlenecks for Particle Growth in Turbulent Aerosols". Axel Brandenburg and Dhrubaditya Mitra of Nordita are involved in this work as Co-PIs. A kickoff meeting will be held at Nordita on 7 November.

Bernhard Mehlig protecting himself from intermittent showers of turbulent aerosols in Gothenburg.
(Photo: Johan Wingborg)

Two New VR International PostDocs Administrated by Nordita

Nordita is happy to be the administrative host for two VR (Swedish Research Council) International PostDocs for the next three years. One of them is former Nordita fellow Mikhail Modestov, who chose Princeton University as his host university and the other one is Fabio Del Sordo, former PhD student at Nordita, who chose Yale University as his host university. Both are expected to spend a fraction of their time at Nordita.

Completion of the ERC AstroDyn Project 2008-2014

Six years have passed since the ERC AstroDyn Project at Nordita was born. On 24 July 2008, a sunny day, an email said that "the panel has recommended your proposal for funding at a sufficiently high position on the priority list, which is expected to allow actual funding." In the original proposal of 2008, fourteen milestones were set. All of them have been addressed and have led to publications; see this project progress report for details. Particularly productive outcomes include Task 2 on the test-field method (10 publications), Task 7 on dynamos in spherical shell segments (13 publications), Task 8 on magnetic flux concentrations near the surface (18 publications), Task 9 on coronal mass ejections from a dynamo (6 publications), and Task 10 on convective dynamos in spherical shell (7 publications). The outcomes of these five tasks make up more than half of the 105 publications that acknowledge the ERC Advanced Grant. Some of these achievements have been reported in earlier issues of this Newsletter (two articles in issue 2/2013 and one in issue 2/2011). The Pencil-Code is an open source community effort and used heavily in this project. Over the period of the grant, the code has grown significantly: from revision 10328 of 1 February 2009 to 21669 on 9 April 2014. And that's not all: the solar activity has recovered from its deepest low since 1908 to peak sunspot numbers of around 100, as pointed out by the PI in the picture.

Center: What should a solar physics group do if not take a whiteboard under the arm and move the group meeting out onto the sun-basked lawn in front of the Nordita building.
Right: At the cake and coffee reception in January 2014 marking the conclusion of the AstroDyn project, project leader Axel Brandenburg used the most recent ISES Solar Cycle Sunspot Number Progression chart to illustrate the close correlation between the growth of the project and the number of sunspots; from the time the project ends the sunspot number is predicted to decrease again.

Nordita Winter School on Theoretical Condensed Matter Physics

The fifth annual Nordita Winter School on Theoretical Physics took place at Nordita in Stockholm January 6-17, 2014. This year the focus was on theoretical condensed matter physics, and the school was organized by David Abergel (Nordita), Eddy Ardonne (Stockholm University), Alexander Balatsky (Nordita) and Stephen Powell (University of Nottingham).

The winter school attracted students from all five Nordic countries, along with Latvia and Poland. They were given an overview of the most important ideas underlying modern condensed matter theory and an introduction to current trends of particular interest with the aim of providing them with useful tools for entering into rapidly developing areas of research. Topics included strongly correlated electrons, topological states of matter, unconventional superconductivity, and the physics of low-dimensional structures.

Lecturers included David Abergel (Nordita), Alexander Balatsky (Nordita), Annica Black-Schaffer (Uppsala University), Piers Coleman (Rutgers University), Vladimir Fal'ko (Lancaster University), Hans Hansson (Stockholm University), Dirk van der Marel, University of Geneva), Felix von Oppen (Freie Universität Berlin), Nicola Spaldin (ETH Zurich) and Mikael Fogelström (Chalmers University).

The Nordita Winterschool 2015 will be held at Nordita 7—16 January 2015. The focus will be on high-energy physics. Deadline for applications is 30 November, 2014.

Thesis Defences at Nordita

Sarah Jabbari, PhD student at Nordita and Stockholm University, successfully defended her licentiate thesis "Origin of Solar Surface Activity and Sunspots" on 19 May 2014, with Vasilis Archontis of the University of St Andrews as opponent. Her thesis is based on three papers in which she combines for the first time the so-called negative effective magnetic pressure instability with the dynamo instability. Her model may provide an alternative to the current paradigm of sunspot formation. Sarah is supported through the VR project grant 621-2011-5076,  Turbulent dynamo simulation in a spherical shell segment , awared to Axel Brandenburg in January 2012.

Left to right: Axel Brandenburg (supervisor, Nordita), Vasilis Archontis (opponent, U. of St. Andrews), and Sarah Jabbari (licentiate); absent are committee members Jesper Sollerman and Jorrit Leenaarts (Dept. of Astronomy, Stockholm U.)

On 21 May 2014, Apostolos Vasileiadis, master student at Stockholm University, successfully defended his masters thesis "Particle Diffusion in Periodic Obstacle Arrays".

Left to right: Ralf Eichhorn (supervisor, Nordita) and Apsotolos Vasileiadis (master); absent are Astrid de Wijn (co-supervisor) and Hannes Hübel and Cristophe Clément (committee members; all three from Stockholm U.).

Future Researchers Trained at Nordita

Rays - Research Academy for Young Scientists, is a non-profit organization that organizes summer research schools for second-year high-school students that want to pursue a career in science. The 2014 school, where the young scientists spent four weeks of their summer vacations, was held in beautiful Strängnäs, south-west of Stockholm.

The programme consisted of training sessions in scientific methodology, inspirational talks by invited researchers, visits to research insititutes and corporate R&D departments, and work on the student's own research project under the supervision of researchers from Stockholm University, KTH Royal Institute of Technology and Karolinska Institute. One of this year's supervisors was Nordita assistant professor Dhrubaditya Mitra, with support from postdoc Bidya Binay Karak. Students spent the final week writing their reports, which then were presented at a public seminar at the Stockholm Technical Museum on 12 July 2014.

The three Rays at Nordita, left to right: Ottilia Andersson (Södra Latins gymnasium, Stockholm), Toomas Liiv (Danderyds gymnasium, Stockholm), and Jakob Broman (ProCivitas, Malmö).

New Norditans Arriving in Fall 2014

New Nordita Fellows

Four new Nordita Fellowships have been awarded to

  • Lavinia Heisenberg - University of Geneva - gravitation and cosmology (joint appointment with the Oskar Klein Centre at Stockholm University)
  • Matin Mojaza - CP3 Origins, University of Southern Denmark - high energy physics
  • Yen Chin Ong - National Taiwan University - gravitation and cosmology
  • Alexandra Veledina - University of Oulu - astrophysics

In addition, Marcelo Dias, formerly of Brown University, has taken up a joint postdoctoral position in soft condensed matter physics at the Aalto Science Institute (AScI) and Nordita, with residence at AScI for two years followed by a third year as a Nordita Fellow.

There were 399 fellowship applications this year. They were evaluated and ranked by the three Nordic Research Committees and by the Nordita faculty. We would like to take this opportunity to thank committee members for their time and commitment to Nordita.

New Postdocs at Nordita

The "Nordita Fellowships" are postdoctoral positions supported by Nordita. In addition, we have several PhD and postdoctoral positions financed by various grants won by Nordita senior staff. These are new postdocs arriving in fall 2014:

  • Pawel Caputa - Wits University - high-energy physics
  • Amit Dekel - University of Uppsala - high-energy physics
  • Sergey Pershoguba - University of Maryland - condensed matter physics
  • Christopher Savage - University of Utah - high-energy physics

New Nordita PhD Students

  • Saikat Banerjee - Harish Chandra Research Institute - condensed matter physics
  • Xiang-Yu Li - Chinese University of Hong Kong - astrophysics
  • Daniel Medina Rincon - Utrecht University - high-energy physics

New Senior Lecturers

For the first time ever, Nordita and Uppsala University have advertised jointly a tenured position as assistant professor in high energy physics. Due to fortunate circumstances, two people have now been hired:

  • Monica Guic? - University of Pennsylvania - high-energy physics
  • Henrik Johansson - CEA-Saclay - high-energy physics

They are expected to share their time between both places to conduct research in high-energy physics and to teach.

Welcome lunch for some of the new Norditians in September.

Recent Departures of Nordita Staff

Nordita postdoctoral fellow Juha Jäykkä left Nordita in December 2013 to take up a position at Cambridge University.

Juha receives his farewell present, a souvenir from Sweden, from condensed matter physics group leader Sasha Balatsky.

In January 2014, visiting professor Matthias Rheinhardt ended his second longer visit at Nordita, to return to the University of Helsinki.

Astrophysics group leader Axel Brandenburg thanks Matthias at the occasion of the completion of the ERC AsdroDyn project, an event attended by both Norditians and Stockholm University astronomers.

Then in July and August, four more Nordita postdoctoral fellows left Nordita: Sreejith Ganesh Jaya (to the Max Planck Institute for the Physics of Complex Systems in Dresden), Blaise Goutéraux (to Stanford University), Mikhail Modestov (to Princeton University), Anthony van Eysden (to Montana State University).

Around the same time, James Gordon ended his one-year stay at Nordita as a visiting PhD student. He now continues his studies at the University of British Columbia.

We would like to take this opportunity to thank Juha, Matthias, Sreejith, Blaise, Mikhail, Anthony and Jamie for their time at Nordita and for their contribution to the vitality of the institute. They have our best wishes for their future career.

Travel Grants to Nordita PhD Students

Various travel grants were awared to Nordita's PhD students. Among them are two Dahlmark Grants from the Astronomy Department at Stockholm University. One went to Sarah Jabbari and one to Illa R. Losada for conferences in Germany, the US, and India. Sarah Jabbari also won a travel grant from the Jubilee donation of the Knut and Alice Wallenberg Foundation for a conference in the US.

Detecting Helical Magnetic Fields with Modern Radio Telescopes

For many decades, polarized radio emission from external galaxies has been used to infer the strength and structure of their magnetic field. This emission is caused by relativistic electrons gyrating around magnetic field lines and producing the polarized synchrotron emission. The plane of polarization gives an indication about the electric (and thus magnetic) field vectors at the source of emission. The line-of-sight component of the field can be inferred through the Faraday effect that leads to a wavelength-dependent rotation of the plane of polarization.

Set of cells each with a singly helical magnetic field of positive helicity. (From arXiv:1401.4102)

In practice, an observer will always see a superposition of different polarization planes from different depths, which can lead to a reduction in the degree of polarization. Firstly, the orientation of the magnetic field changes, causing different polarization planes at different positions. Secondly, Faraday rotation causes the plane of polarization to rotate. The decrease in polarized emission resulting from this superposition is referred to as Faraday depolarization. This was regarded as a problem that can be alleviated partially by restricting oneself to observations at shorter wavelengths. This situation has changed with the advent of new generations of radio telescopes that can measure polarized emission over a broad and continuous range of wavelengths. This allows one to apply the method of Burn (1966, Mon. Not. Roy. Astron. Soc. 133, 67) that utilizes the wavelength-dependent depolarization to determine the distribution of radio sources with respect to Faraday depth.

This was also the topic of a one-week workshop organized by form Nordita fellow Oliver Gressel in September 2013. As a direct outcome of this workshop, two papers have now appeared that examine the possibility of detecting helical magnetic fields in the radio sky; one is by the Nordita astrophysics research committee member Cathy Horellou (Onsala) together with Andrew Fletcher (Newcastle) and the other one is by Axel Brandenburg (Nordita) and Rodion Stepanov (Perm). Both papers appeared on 16 January on the arXiv (arXiv:1401.4152 and arXiv:1401.4102) and have now been published.

New Videos Presenting Research at Nordita

The Nordita Youtube Channel has been extended with two new five-minute videos highlighting research and researchers at Nordita.

Research Presentation: Statistical Physics - Ralf Eichhorn

Research Presentation: Black Hole Physics - Sabine Hossenfelder and Lárus Thorlacius

For other video presentations of research at Nordita, see

Also check out our comments on what's on in the world of physics on the Nordita Facebook Page, and for deeper analysis read Sabine Hossenfelder's Blog 'Backreaction'.

Just an Ordinary Day at Nordita

One of the best things with working at Nordita is the international atmosphere at the institute. Our students and researchers come to us from all over the world, and thanks to our scientific programs we have hundreds of international visitors, enriching the institute both scientifically and culturally.

The theme of this year's Nordita Winter School was condensed matter physics. One of the lecturers at the school, Nicola Spaldin from ETH Zurich, is an inspiring virtuoso not only in questions concerning the Berry phase, ferroelectrics, and topological insulators, but also on the clarinet. Whenever she travels to Stockholm she takes the opportunity to play together with the Fjord Quintet. And we at Nordita are treated with an exclusive concert.

The Fjord Quintet at the Winter School concert, 14 January 2014: Sigrid Neumann (violin 1), Lars-Arne Axelsson (violin 2), Krister Persson (violoncello), Erik Hagersten (viola), and Nicola Spaldin (clarinet). On the program: Brahms' Clarinet Quintet and Debyssy's "Petit Pièce".

As mentioned on the top of this page, we celebrated Nowruz earlier this year. This is what Nordita PhD student Sara Jabbari taught us about the Persian new year: Nowruz marks the first day of spring and the beginning of the year in the Persian calendar. It is celebrated on the day of the astronomical Northward equinox, which usually occurs on March 21 or the previous/following day depending on where it is observed. The moment the sun crosses the celestial equator and equalizes night and day is calculated exactly every year and families gather together to observe the rituals. Last time it happened was on 20 March 2014 at 6 pm, and Norditians were ready, standing around our version of Haft S?n (or the seven "S"s), a traditional table setting at Nowruz, with seven items that start with the letter "S" or S?n in the Persian alphabet, each item symbolizing qualities like love, patience, health and affluence. Can you spot our Haft S?n items? s?b (apples), sabzeh (wheat, barley or lentil sprouts), samanu (a sweet pudding made from germinated wheat), senjed (the dried fruit of the Oleaster tree), s?r (garlic), somaq (sumac berries) and serkeh (vinegar).

If the Persian spring celebration Nowruz made us all healthy and affluent for the remainder of the year, it unfortunately didn't bring out the Swedish spring. This was our second attempt to use culture to quash the Nordic winter, after our 1 March Maslenitsa party, the Russian version of the celebration of the end of the winter or the start of the lent, like Swedidh Fettisdagen, French Mardi Gras, or British Shrove Tuesday.

Nordita postdoc Alexander Krikun (leftmost in the first photo) promised to make the pancakes traditionally eaten at Maslenitsa (in frying pans on the Nordita BBQ, no less), and the rest of us brought caviar and other salty and sweet fillings. The sunny-golden pancakes inspired Sarah to a major break-through in her work on determining the origin of sunspots (rightmost photo).

After that we gave up on spring magic, even neglecting the Swedish arrival-of-spring bonfire rituals at Valborg, 30 April. Braving the cold, we had our first BBQ, this most Norditian of rituals, on 7 March, continuing grilling outdoors on and off to Midsummer Eve, 20 June, when the weather still was about the same. Can you guess which photos were taken on which of these dates?

Next Nordita Board Meeting

The next Nordita Board Meeting will be in Stockholm on 6 February 2015.

Participants of the Nordita Board meeting in September 2014. Back row, left to right: Jes Madsen (Aarhus U.), Ivan Shelykh (U. of Iceland), Leif Kari (KTH), David Abergel (Nordita), Helle Kiilerich (Nordita/NBI), Asle Sudbø (NTNU). Middle row, left to right: Jonathan Edge (Nordita), Ulf Wahlgren (Nordita), Katri Huitu (U. of Helsinki), Susanne Viefers (U. of Oslo), Måns Henningsson (Chalmers). Bottom row, left to right: Marianne Persson-Söderlind (Nordita), Kalle-Antti Suominen (U. of Turku), Katherine Freese (Nordita), Mikko Alava (Aalto U.), Axel Brandenburg (Nordita), Gunnlaugur Björnsson (U. of Iceland).

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