Issue 1, 2014

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Towards an understanding of the Sun's Butterfly Diagram

It's hot, round, and you're not supposed to stare at it: The Sun has attracted curiosity since we crawled out of the primordial pond. And even though we now have a pretty good idea of how the Sun does its job, some puzzles stubbornly remain. One of them is where sunspots form and how their location changes with the solar cycle. A recent computer simulation has now managed to reproduce a pattern that brings us a big step closer to......  [Read more]

Uncertainty About Future Funding of Nordita

The Nordic funding of Nordita and several other Nordic research institutes has come under renewed pressure at the Nordic...

The Origin of Galactic Magnetic Fields:...

This issue's feature article reported on recent progress on understanding the solar cycle with help of computer simulations of...

Nordita's Workshop for Science Writers,...

From May 27-29, George Musser from Scientific American and Sabine Hossenfelder from Nordita ran a workshop with lectures for...

New Finnish Centers of Excellence

In June, the Academy of Finland decided on designating 14 new Centres of Excellence in Research for the period 2014-2019, a...

Graphene Appointed EU FET Flagship

The European Commission has chosen Graphene as one of Europe's first 10-year, 1,000 million euro FET (Future Emerging...


Towards an understanding of the Sun's Butterfly Diagram

It's hot, round, and you're not supposed to stare at it: The Sun has attracted curiosity since we crawled out of the primordial pond. And even though we now have a pretty good idea of how the Sun does its job, some puzzles stubbornly remain.

One of them is where sunspots form and how their location changes with the solar cycle. A recent computer simulation has now managed to reproduce a pattern that brings us a big step closer to understanding this.

Solar Interior

The layered structure of the sun. Image credits: NASA

The Sun spins about a fixed axis, but since it's not solid its rotation frequency is not uniform: At the visible surface, the equator rotates in about 27 days whereas close by the poles it takes 35 days. The plasma that forms the Sun is held together by its own gravitational pull with a density that is highest in the center. In this high density core, the sun creates energy by nuclear fusion. Around that core, there's a layer, the radiative zone, where the density is already too small for fusion, and the heat created in the core is just passed on outwards by radiative transfer. Further outside, when the density is even lower, the plasma then passes on the heat by convection, basically cycles of hot plasma moving upwards and cooler plasma moving downwards. Even further outside, there's the photosphere and the corona.

The physics of the convection zone is difficult because the motion of the plasma is turbulent, so it's hard to understand analytically and numerical simulations require enormous computing power. Some generic features are well understood. For example the granularity of the sun's surface comes about by a mechanism similar to Rayleigh–Bénard convection: In the middle of the convection cell there's the hot plasma rising and towards the outside of the cell there's the cooler plasma moving down again.

It also has been known since more than a century that sunspots are not only colder than the normal surface of the sun, but are also regions with strong magnetic fields. They arise in pairs with opposite magnetic polarity. Sunspot activity follows a cycle of roughly 11 years, after which polarity switches. So the magnetic cycle is actually 22 years, on the average.

A big puzzle that has remained is why sunspots are created predominatly in low latitudes (below 30°N/above 30 S) and, over the course of the solar cycle, their production region moves towards the equator. When one plots the latitude of the sunpots over time, this creates what is known as the "Butterfly diagram", shown below:

Butterfly Diagram

You can find a monthly update of the butterfly diagram on the NASA website. The diagram for the magnetic field strength follows the same pattern, except for the mentioned switch in polarity, see for example page 54 of this presentation. On the slide, note that in the higher latitudes the magnetic fields move towards the poles rather than towards the equator.

Numerical simulation of the convection zone have been made beginning already in the early 80s, but so far something always left the scientists wanting. Either the sunspots didn't move how they should or the rotation wasn't faster towards the equator, or the necessary strong and large-scale magnetic fields were not present, or something else just didn't come out right.

At Nordita in Stockholm, there's a very active research group around Axel Brandenburg, which has developed a computer code to simulate the physics of the convection zone. It's called the 'pencil code' and is now hosted by Google code, for more information see here. Basically, it's an integration of the (non-linear) hydrodynamics equations that govern the plama with magnetic fields added. In the video below you see the result of a very recent simulation done with his collaborators in Helsinki:

The colors show the strength of the magnetic field (toroidal component), with white and blue being the strongest fields, blue for one polarity and white for the other. Two things you should be able to see in the video: First, the rotation is faster at the equator than at the poles, second, the spots of strong magnetic fields in low latitudes migrate towards the equator. One can't see it very well in the video, but in the higher latitudes the magnetic fields do move towards the poles, as they should. In the time-units shown in the top-left corner, about 600 time steps correspond to one solar cycle. A computation like this, Axel tells me, takes several weeks, run on 512 to 2048 cores.

Details on how the movie was made can be found in this paper:

Cyclic magnetic activity due to turbulent convection in spherical wedge geometry
Petri J. Käpylä, Maarit J. Mantere, Axel Brandenburg
arxiv: 1205.4719

The model has six parameters that quantify the behavior of the plasma. For some of these parameters, values that would be realistic in the sun are too large to be possible to simulate. So instead, one uses different values and hopes to still capture the essential behavior. The equations and boundary conditions can be found in the paper, see eqs (1)-(4) and (6)-(11).

The calculation doesn't actually simulate the whole convection zone, but only a wedge of it with periodic boundary conditions. In the video this wedge is just repeated. The poles are missing because there the coordinate system becomes pathological. In the part that they simulate, they use 128 x 256 x 128 points. A big assumption that goes on here is that the small scales, scales too small to be captured at this resolution, don't matter for the essential dynamics.

If you found the video was too messy, you can see the trend of the magnetic fields nicely in the figure below, which shows the average strength of the magnetic fields by latitude as a function of time.

Butterfly Diagram Simulation

Fig 3 from arxiv:1205.4719

Not all is sunny of course. For example, if you gauge the timescale with the turnover time in the convection zone which can be inferred from other observatons, the length of the magnetic solar cycle is about 33 years instead of 22. And while the reason for the faster rotation towards the equator can be understood from the anisotropy of the turbulence (with longitudinal velocity fluctuations dominating over latitudinal ones), the butterfly trend is not (yet) analytically well understood. Be that as it may, I for certain am impressed how much we have been able to learn about the solar cycle despite the complicated turbulent behavior in the convection zone.

The original movie (in somewhat better resolution) and additional material can be found on Petri's website.

New Finnish Centers of Excellence

Academy of Finland In June, the Academy of Finland decided on designating 14 new Centres of Excellence in Research for the period 2014-2019, a total of EUR 45 million for the first three years of the six-year programme term.

In the list of funded Centers of Excellence we find the following in the fields of physics, mathematical physics, space physics and biophysics:

  • Centre of Excellence in Molecular Engineering of Biosynthetic Hybrid Materials Research, Aalto University
    Other parties: VTT Technical Research Centre of Finland
  • Centre of Excellence in Atmospheric Science - From Molecular and Biological Processes to the Global Climate, University of Helsinki
    Other parties: University of Eastern Finland, Finnish Meteorological Institute
  • Centre of Excellence in Analysis and Dynamics Research, University of Helsinki
    Other parties: University of Oulu, University of Jyväskylä
  • Centre of Excellence in Research on Solar Long-Term Variability and Effects, University of Oulu
    Other parties: University of Helsinki, Finnish Meteorological Institute
  • Centre of Excellence in Biomembrane Research: From Lipid-Protein Interactions to Functions, University of Helsinki
    Other parties: Tampere University of Technology

Kalevi Mursola, director of ReSOLVE As reported elsewhere, the astrophysics group at Nordita is one of the key collaborating teams involved in the activities at the CoE in Research on Solar Long-Term Variability and Effects (ReSOLVE), led by Kalevi Mursola, at the University of Oulo.

Graphene Appointed EU FET Flagship

The European Commission has chosen Graphene as one of Europe's first 10-year, 1,000 million euro FET (Future Emerging Technology) flagships (the other being Human Brain Project). The mission of Graphene is to take graphene and related layered materials from academic laboratories to society, revolutionize multiple industries and create economic growth and new jobs in Europe. The flagship is coordinated by professor Jari Kinaret at Chalmers University of Technology in Gothenburg, a former Nordita fellow 1992-1994.

Several research groups from the Nordic countries participate in the project: from Denmark groups at the Universities of Copenhagen and Aarhus, and DTU, from Finland groups at the Universities of Jyväskylä, Helsinki, Eastern Finland, Aalto, and Åbo Akademi, from Norway groups at NTNU, and from Sweden groups at the Universities of Chalmers, Linköping, Umeå, and Karolinska Institute, in addition to several companies and independent research facilities.

Read more on the official website of the FET Graphene Flagship.

Nature Paper on Polariton Lasers

Ivan Shelykh and Ivan Savenko Ivan Shelykh, professor at the University of Iceland and member of the Nordita board, and his PhD student Ivan Savenko, are co-authors of an article published in Nature, with the title "An electrically pumped polariton laser", based on an international collaboration involving also experimentalists from Würtzburg, Stanford, Moscow, and Tokyo.

The basic mechanism behind the "polariton laser" is that strongly coupled exciton-polaritons (excitations mixing light and matter), as those in quantum well micro-cavity, can dynamically condensate by stimulated polariton scatterings, and consequently decay by the leakage of photons from the micro-cavity, emitting coherent and monocromatic light.

Coherent polariton emissions have been previously realized in optically pumped semiconductor micro-cavities. However, here for the first time, the authors realize an electrically pumped polariton laser, which is more relevant for technical applications, as well as more energy-efficient compared to conventional semiconductor lasers.

NBIA Summerschool on Computational Astrophysics

The Niels Bohr Academy in Copenhagen is organizing a summerschool on computational astrophysics 19-23 August 2013. Nordita's Axel Brandenburg is one of the lecturers. The topics covered in the school include

  • astrophysical fluid dynamics
  • MHD turbulence and dynamics
  • kinematic plasma processes
  • multi-scale plasma modelling
  • accretion disks, jets, and winds
  • planet-disk interactions

Astrobiologists Meet at Höör

A couple of dozen astrobiologists met at Åkersberg Herrgård in Höör, Sweden, from June 6th-9th, at the first International Workshop on Education in Astrobiology.

Co-organizers of the astrobiology meeting at Höör The workshop was organized by Dr. Wolf Geppert of Stockholm University, Director of the Stockholm University Astrobiology Centre, in co-ordination with the Nordic Network of Astrobiology, Société Française d'Exobiologie and Centro de Astrobiología., with attendees from across Europe, the Americas and Middle East.

The workshop consisted of a series of expert presentations on current research in astrobiology, mixed with energetic discussion and presentations on pedagogical issues. A lively group of doctoral students provided critique of the presentations and feedback on the science issues. During the meeting there were extensive and productive discussions of the challenges and opportunities in presenting a heterogenous science, like astrobiology, to different audiences, ranging from the general public and school students, through undergraduate, masters and doctoral university students. The different approaches in different educational systems were compared, and the lecture notes were archived to nucleate a resource on astrobiology for teachers worldwide.

There are plans to for future sessions on astrobiology education during major international science conferences in 2014 and 2015.

Can Nordic Companies Profit from the Higgs Search?

It is of course heartworming to know that the CERN membership fee of EUR 13 million that Norway pays each year supports important basic research in physics, Civil Engineering at CERN but are there also other more immediate benefits to be gained from this investment? Norwegian online science journal forskning.no in a recent article (English translation) notes that unless passive Norwegian companies get their act together, they will miss the opportunities of securing contracts and exchanging knowledge that can come out of tighter collaborations with CERN.

Susanne Åberg The Swedish experience of science-business cooperation is the subject of the doctoral thesis of Susanne Åberg at Uppsala University. From her inteviews with 15 Swedish companies that have collaborated with CERN a clear picture emerges: the real benefits, often quite unexpected ones, come from establishing long-term relationships.

And, as always, nothing happens if you just sit around and wait.

IN BRIEF

Swedish Focus on Mathematics Research

In a joint effort to strengthen Swedish mathematics, grants totalling EUR 15 million per year during 5-6 years will be awarded for fundamental research in mathematics. The initiative was announced in April 2013 by four Swedish funding agencies, the Swedish Research Council, the Swedish Foundation for Strategic Research, the Royal Swedish Academy of Sciences, and the Knut och Alice Wallenberg Foundation. Increased funding for the Institut Mittag-Leffler in Stockholm is part of this initiative.

Gender Biases in Academic Career Advancement

It is equally hard for a woman to become a professor today as it was 20 years ago. The often non-transperant hiring processes are in particular blamed for the non-vanishing gender gap, according to a recent study by sociologists Rickard Danell and Mikael Hjerm at Umeå University, presented in an article in the online science journal Curie, "Women are discriminated against at Swedish universities" (in Swedish).

A recent Nature news feature "Inequality quantified: Mind the gender gap" concludes that despite improvements, female scientists continue to face discrimination, unequal pay and funding disparities.

Nothing Finally Defined

Nordita corresponding scientist Bengt Gustafsson was one of the panelists in a discussion on the definition of nothing following the public lecture by Lawrence Krauss, cosmologist at Arizona State University and best selleing author, entitled "A Universe out of nothing". The event was arranged in March 2013 by the Royal Swedish Academy of Sciences and Fri Tanke (Free Thought) Publishers, and broadcast by UR Samtiden, a section of the Swedish Educational Broadcasting Company (UR).



On 21 June, Norditians and astronomers from Stockholm University celebrate Swedish Midsummer with a BBQ. The Nordita buildings are barely visible just behind the yellow buildings in the back of the left-most photo.

Gerry Brown, Former Nordita Professor, Has Died

We are sad to report the death of Gerald E. (Gerry) Brown, who was Professor at Nordita for two periods, 1960-1964 and 1968-1985.

With his enthusiasm, gregariousness, deep insights and broad interests, Gerry left his mark on Nordita and educated a generation of students, many of whom went on to be leaders in the field. He was an internationally recognized leader in nuclear physics, and in the latter part of his career worked extensively on problems in astrophysics, including stellar collapse, and the formation of neutron stars and black holes. He was recognized by memberships of national academies in Denmark, Finland, Norway, and the USA, and by honorary degrees from the Universities of Helsinki and Copenhagen. His other awards include both the Tom W. Bonner and Hans A. Bethe prizes of the American Physical Society and the Max Planck medal of the German Physical Society.

Obituary at Stony Brook University.

Uncertainty About Future Funding of Nordita

The Nordic funding of Nordita and several other Nordic research institutes has come under renewed pressure at the Nordic Council of Ministers (NMR). At a meeting earlier this year the Committee of Senior Officials for Education and Research (EK-U) opted for a 20% cut in the NMR financing of each of the institutes in 2014 and is considering further cuts in 2015-16. A total phasing out of all NMR funding for the institutes by the end of 2016 has even been discussed. The proposed 20% cut in the funding of the Nordic research institutes goes far beyond the proposed 3.8% reduction in the overall budget of the Education and Research sector at NMR in 2014 and appears to be motivated by administrative expedience without an objective evaluation of the scientific quality of the work carried out at the institutes in question. At the same time, unchanged funding is proposed for NordPlus and NordForsk in 2014.

Sharply reducing or eliminating the NMR financing of Nordita puts at risk the Nordic character that has been key to the long-standing success of Nordita and may cause the institute to fail altogether. Members of the Nordita Board and the Director have met with ministry officials in all the Nordic countries and with NMR staff members to protest these deep funding cuts. Informing decision makers about Nordita and its relevance to the Nordic countries may help turn the ongoing debate about the future of Nordic research cooperation in a more positive direction.

The NMR budget proposal for 2014 is being presented in the home countries over the summer and may get amended by the Ministers for Cooperation before it is submitted to the Nordic Council for debate and final decision at the Nordic Council session in late October. Unless changes are made to the proposal from EK-U during this process, Nordita will have to contend with a reduced budget next year. While, Nordita cannot expect to be exempt from budget pressures faced by NMR, Nordita representatives have emphasized to ministry officials that funding priorities for research should be based on a thorough assessment of scientific quality and long-term impact.

The Origin of Galactic Magnetic Fields: Oliver Gressel

This issue's feature article reported on recent progress on understanding the solar cycle with help of computer simulations of hot plasma and magnetic fields. Computer simulations like this are good not only to understand the physics of stars like our sun, but also for other systems. Oliver Gressel from Nordita's astrophysics group uses them to study the interstellar plasma and galactic magnetic fields. In this video, Oliver describes how we observe the magnetic fields of galaxies and how to explain these observations. A key role for the origin of galactic magnetic fields is played by supernovae explosions that create turbulence in the interstellar plasma.

For other video presentations of research at Nordita, see   www.nordita.org/video

Nordita in Collaboration with Finnish Center of Excellence

The Academy of Finland has selected the Centres of Excellence in Research (CoE) for the 2014-2019 CoE programme. As reported elsewhere, the new CoE programme will consist of 14 units, involving research teams from twelve universities or research institutes. The Academy has reserved a total of EUR 45 million for the first three years of the six-year programme term.

The first CoE ever to be funded in the field of space physics and astronomy, Research on Solar Long-Term Variability and Effects (ReSoLVE), lead by Prof. Kalevi Mursula from Oulu University with partners from Aalto University, Finnish Meteorological Institute and Sodankylä Geophysical Observatory, concentrates on Research on Solar Long-Term Variability and Effects. The astrophysics group at Nordita is one of the key collaborating teams involved in the CoE activities.

Recent observations have disclosed how dramatically variable the Sun is, and how exceptional current solar activity is. From 1930s until about 2000, the Sun was more active than during the last few thousand years. This time interval is now called the Grand Modern Maximum (GMM). However, GMM is now approaching its end, and recent minimum activity equaled low levels of a hundred years ago. ReSoLVE will study the causes and consequences of this exceptional recent past of the Sun, improve modelling of the solar dynamo, and study the effects in near-Earth environment, including the ionization in the Earth's upper atmosphere. ReSoLVE connects to a large international collaboration, comprising of a large European network, COST Action ES1005 "Towards a more complete assessment of the impact of solar variability on the Earth’s climate", a European Infrastructure project ESPAS (Near-Earth Space Data Infrastructure for e-Science), and a Space project called eHEROES. The picture shows a recent global simulation result from members of the Center, where a dynamo-generated magnetic is found to propagate gradually equatorward.

Nordita's Workshop for Science Writers, Astrophysics and Cosmology


Organizers George Musser (left) and Sabine Hossenfelder (right), together with workshop speaker and public lecturer Robert Nemiroff.

From May 27-29, George Musser from Scientific American and Sabine Hossenfelder from Nordita ran a workshop with lectures for science writers. The workshop website is here and slides of the lectures can be found here. This workshop was funded by Nordita with an additional grant from the Swedish Research Council, Vetenskapsrådet.

Here Sabine summarizes her motivation for this workshop:

George and I came up with the idea for this workshop exactly one year ago at a reception of an earlier Nordita workshop, says Sabine Hossenfelder. Yes, alcohol was involved. We talked about how science writers often feel like they're running on a treadmill, having to keep up with the frenetic pace of publishing, only seldom getting a chance to take a few days off to gain some broader perspective. And we talked about how researchers too are running on a treadmill, having to keep up with the pace of their colleagues' publications, and often feel that science writers miss the broader perspective.

And so we set ourselves the goal to get everybody off the treadmill for a few days.

Our "workshop for science writes" was devised for both, the writers and the physicists: For the writers to hear what topics in astrophysics and cosmology will soon be on the agenda and what science journalists really need to know about them. And for the physicists to share both their knowledge and their motivation, and to caution against common misunderstandings.

We modeled the workshop on "boot camps" organized by the Space Telescope Science Institute, Woods Hole Oceanographic Institute, Knight Foundation, U.C. Santa Cruz, and other institutions. It was a very intense and tightly packed meeting, with lectures by experts on selected topics in astrophysics and cosmology, followed by question and answer sessions.

On Tuesday afternoon, we visited the phonetics lab at Stockholm University, which was a fun excursion into a totally different area of science. At the lab, participants could analyze their voice spectra and airflow during speech, and learn the physics behind speech production. On Tuesday evening, one of the participants of the workshop, Robert Nemiroff, gave a public lecture at CosmoNova. The fully booked lecture took the audience on a tour through the solar system and beyond, explaining the science behind the amazing photos and videos.

While it was quite an organizational challenge to find the right level of technical details for an audience that physicists rarely deal with, the question and answer sessions as well as a large number of breaks were useful for participants to talk to lectures individually. We also had many interesting discussions about the tension between scientific accuracy and popular science writing.

Only a week after the workshop, I knew of at least four participants who are planning on using what they learned at the workshop for an article or radio program. We also got very useful feedback on the organization of the event that will be valuable if we plan on repeating a meeting of this type.

Recently, I hear a lot of talk about the relevance of science communication. It seems to me though the most relevant thing is to actually do it.


Top row from left: Patrick Sutton dispelled myths about gravitational waves, while Illa Losada detected brain waves at the phonetics lab. After what seemed like an eternity, George Musser, Alberto Aparici and Patrick were happy to escape from the silence room. Bottom row: Ray Jayawardhana generously shared his hottest tricks for finding your own new expolanet. Alberto, Daniel Fischer, Ernesto Lozano, and Claudia Di Giorgio got invaluable tips from Francisco Lacerda, head of the phonetics lab, on how to interpret the spectra of their recently recorded voices.

Turbulent Self-Assembly of a Magnetic Spot

In the Nordita Newsletter of October 2011, we reported on the numerical detection of what is now referred to as negative effective magnetic pressure instability (NEMPI). This work has led to a number of new papers since then and, in particular, the award of a VR "breakthrough grant" to Nordita. One of the goals of this project is to underpin the recent suggestion that solar magnetic activity may be a shallow phenomenon and is not deeply rooted as is commonly believed.

In a recent preprint, members of the AstroDyn group at Nordita presented results of simulations that showed for the first time the self-assembly of a magnetic spot from just two ingredients: fully developed turbulence and strong density stratification. The picture above shows horizontal and vertical cross-sections through the magnetic spot. Future will show whether this also explains the spontaneous formation of sunspots.

Ebru Devlen Receives Turkish Astronomy Award

We are proud to report that Ebru Devlen, who is currently spending a 1-year sabbatical at Nordita (see our last newsletter), received the Nüzhet Gökdoğan Astronomy Science Prize of Istanbul University for her paper "The Anisotropic Transport Effects on Dilute Plasmas" published by Astrophysical Journal in 2011.

This prize is given every five years and is in honor of Prof. Dr. Nüzhet Gökdoğan, who was the first Turkish woman astronomer and the founder of Astronomy Department of Istanbul University. The photo shows Istanbul University's Rector Prof. Dr. Yunus Söylet presenting this prize to Dr. Ebru Devlen on 30 April 2013 in the Senate Hall of Istanbul University.

Chris Pethick Elected Honorary Member of the AAAS

Chris Pethick

Nordita/NBIA Professor Chris Pethick is one of two Foreign Honorary Members elected to the Physics section of the American Academy of Arts and Sciences this year, citing his leadership and numerous important contributions across a broad range of theoretical physics.

News item on Niels Bohr International Academy homepage.

Sabbatical Visit of Shashikumar M. Chitre

Nordita had the pleasure of hosting Professor Shashikumar M. Chitre, University of Mumbai, India, for the full month of June. During his stay, he worked on aspects of helioseismology, trying to infer the structure and strength of subsurface solar magnetic fields.

The Nordita Astrophysics group in June 2013

In a astrophysics group picture taken in June of this year, Shashikumar is pictured in the second row (third one from the left). We look forward to welcoming him again at Nordita in the future.

Long-Term Visitors at Nordita

Visiting postdoc Daniele Marmiroli

Subatomic Physics

Daniele received his Ph.D. in 2012 from University of Parma, Italy. His thesis work mainly focused on Wilson loops in the context of the AdS/CFT correspondence for three-dimensional superconformal Chern-Simons theory. As a main result, he collaborated in computing at weak coupling the generalized cusp anomalous dimensions for ABJ theories, which unveiled a double-exponentiation structure in quiver theories. Over the past year Daniele has been working on the resummation of perturbative series in (non-)covariant gauges and on "less supersymmetric" Wilson loops in ABJM. At present he is interested in investigating the string/gauge theory correspondence for non-maximally supersymmetric Yang-Mills theories in four dimensions. He is also interested in localization and matrix models.

Visiting PhD student Martha Lasia

Condensed Matter Physics

Martha is a visiting PhD student from the Instituto de Ciencia de Materiales de Madrid (ICMM) at Universidad Autonóma de Madrid in Spain, where she is studying electronic properties of topological insulator slabs under the supervision of Professor Luis Brey. Her visit to Nordita is supported by a grant from the Spanish Ministry of Education.

Recent Departures of Nordita Staff


Master chefs Oksana and Juha prepare the Midsummer BBQ.

In June, two postdoctoral fellows who have been with us since 2011 left Nordita, both working in condensed matter physics.

Oksana Manyuhina takes up a position in Syracuse University in September, continuing her work on soft condensed matter which we highlighted in Nordita Newsletter 2013, issue 1.

Juha Suorsa leaves for London, where he joins a newly started company in the financial sector.

We would like to take this opportunity to thank both scientists for their time at Nordita and for their contribution to the vitality of the institute. They have our best wishes for their future careers.


Nordita Dissertations

PhD Dissertation of Jörn Warnecke

On 31 May 2013, Jörn Warnecke, the last of four PhD students supported by the ERC AstroDyn project, successfully defended his dissertation on "Combining Models of Coronal Mass Ejections and Solar Dynamos".

In his thesis consisting of 6 refereed papers, Jörn produced the first dynamo models coupled self-consistently to an outer corona-like layer. His first models consisted of a Cartesian domain in which plasmoid ejections were produced above the surface as a consequence of the time variability of the dynamo beneath the surface. He then extended his work to spherical wedge-like domains which produced ejections that strongly resemble coronal mass ejections in the Sun. His models were based on convection-driven dynamo action. Unlike earlier models without outer coronal layer, he found more realistic differential rotation contours with more nearly spoke-like contours of constant angular velocity, as opposed to cylindrical contours.

Professor Juri Toomre from JILA acted as opponent. The examination committee consisted of Drs. Henrik Lundstedt from the IRF in Lund, Anita Kullen from the Alfvén Lab at KTH, and Dan Kiselman from the astronomy department in Stockholm.

Atefeh Barekat Presented Her Master's Thesis

On 29 May, Atefeh Barekat presented her Master's thesis on "Hydrodynamic simulations with a radiative surface".


Atefeh and Jörn on the formal and informal receptions after their thesis defences.

In her work, she began bridging the gap between more idealized simulations of solar convection using fixed radiative conductivity profiles in the optically thick approximation on the one hand and realistic simulations with table lookups for opacity and the equation of state on the other. Using a power law dependence of opacity on density and temperature, and allowing for the transition to the optically thin regime, she showed that one recovers a family of polytropic solutions in the optically thick lower part of the domain, together with an isothermal part in the upper optically thin part. The polytropic index depends in a simple manner on the power law exponents of the opacity. She also showed that the Peclet number (a measure of the degree of nonlinearity) can be controlled by changing the prefactor of the opacity. For numerical reasons, it cannot be too large. In fact, simulations without ad-hoc numerical diffusivities, must use prefactors that are lower than in the Sun by approximately five orders of magnitude.

New Nordita Board

The presidents of Stockholm University and KTH Royal Institute of Technology have appointed a new Nordita Board for a three-year period starting July 1, 2013. The board members are:

Chairman

Kalle-Antti Suominen - University of Turku

Denmark

Jes Madsen - Aarhus University
Karsten Flensberg - University of Copenhagen (reserve)

Finland

Katri Huitu - University of Helsinki
Mikko Alavaa - Aalto University (reserve)

Iceland

Gunnlaugur Björnsson - University of Iceland
Ivan Shelykh - University of Iceland (reserve)

Norway

Asle Sudbø - NTNU Trondheim
Susanne Viefers - University of Oslo (reserve)

Sweden

Olle Eriksson - Uppsala University
Måns Henningsson - Chalmers University (reserve)

Nordita à la Carte

Each year, Nordita recruits new post-docs and assistant professors from all over the world; see our staff list for names and their fields of interest.

They are keen to become more familiar with the work done in the Nordic countries and would appreciate being invited for a seminar or a colloquium. Nordita has allocated funds to reimburse their expenses.

Many of our staff have placed links to their talks on their individual home pages; see, e.g., Alexander Balatsky, Axel Brandenburg, Oliver Gressel, Sabine Hossenfelder, Dhrubaditya Mitra, Christopher Pethick, Stephen Powell, Dmytro Volin, Jörn Warnecke.

UPCOMING SCIENTIFIC EVENTS

→ See List of all Nordita Events: www.nordita.org/events

Beyond the LHC

Program

1—27 July 2013

The 14 TeV LHC will look further above the electroweak scale, but where do we go beyond that to improve our understanding of the fundamental constituents of the Universe? Should we look to the results of a high-luminosity SLHC or a higher energy VLHC, do we need a precision linear collider at ILC or CLIC energies, are neutrino or flavour experiments essential to move forward, what can we learn from astrophysics?

Coordinators:  Paolo Di Vecchia, Per Osland, Are Raklev

Beyond the LHC Workshop

Workshop

25—27 July 2013

The workshop is part of the program Beyond th LHC

Coordinators:  Paolo Di Vecchia, Per Osland, Are Raklev

Superconductivity: the Second Century

Program

5—30 August 2013

Superconductivity has been of central scientific interest for more than a century, and yet the progress to date has been largely empirical: despite the tremendous progress in many-body theory there is as yet no general set of rules to predict and “design” new kinds of superconductors. With the rapidly growing list of new superconductors we feel it is time to have a high level workshop, bringing together theorists and experimentalists and focusing on the established facts and challenges in understanding the fundamental properties and basic mechanisms of superconductivity.

Coordinators:  Asle Sudbø, Alexander Balatsky, Andrew Millis, Yunkyu Bang

Lyman Alpha as an Astrophysical Tool

Program

2—27 September 2013

This program is about the Ly α transition in Hydrogen and its astrophysical applications. Young stellar populations are dominated by massive, hot and short-lived stars that ionize their surroundings, which is hence a powerful, but complicated, probe of star forming and high redshift galaxies. This programs aims to bring together experts in modeling Ly α radiative transfer and galaxy formation, and observations of Ly α in local galaxies and the distant universe.

Coordinators:  Göran Östlin, Matthew Hayes, Garrelt Mellema

Lyman Alpha as an Astrophysical Tool Workshop

Workshop

9—13 September 2013

The workshop is part of the program Lyman Alpha as an Astrophysical Tool

Coordinators:  Matthew Hayes, Göran Östlin, Garrelt Mellema

Galactic Magnetism in the Era of LOFAR and SKA: Developing Tools for Synthetic Polarization Maps

Workshop

23—27 September 2013

Cosmic magnetic fields reveal themselves in the form of polarized synchrotron emission. This non-thermal emission originates from relativistic electrons gyrating around the field lines and is routinely observed in the radio wavelength. The upcoming generation of radio telescopes will give polarization maps of nearby galaxies with unprecedented detail. Existing data are limited in resolution and suffer from various shortcomings related to projection effects and the finite bandwidth of radio frequencies used.

Coordinators:  Sui Ann Mao, Oliver Gressel, Cathy Horellou, Bryan Gaensler, Axel Brandenburg, Andrew Fletcher, Rainer Beck

OPEN POSITIONS AT NORDITA

→ See Current Open Postitions: www.nordita.org/positions

Nordita Visiting PhD Student Fellowships

Application deadline: 10 May 2025

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