Sunday, June 21, 2015

Perl 5.22 testers needed!

Gentoo users rejoice, for a few days already we have Perl 5.22.0 packaged in the main tree. Since we don't know yet how much stuff will break because of the update, it is masked for now. Which means, we need daring testers (preferably running ~arch systems, stable is also fine but may need more work on your part to get things running) who unmask the new Perl, upgrade, and file bugs if needed!!!
Here's what you need in /etc/portage/package.unmask (and possibly package.accept_keywords) to get started (download); please always use the full block, since partial unmasking will lead to chaos. We're looking forward to your feedback!
# Perl 5.22.0 mask / unmask block

# end of the Perl 5.22.0 mask / unmask block
After the update, first run
emerge --depclean --ask
and afterwards
perl-cleaner --all
perl-cleaner should not need to do anything, ideally. If you have depcleaned first and it still wants to rebuild something, that's a bug. Please file a bug report for the package that is getting rebuilt (but check our wiki page on known Perl 5.22 issues first to avoid duplicates).

Sunday, May 10, 2015

Reviving Gentoo VMware support

Sadly over the last months the support for VMware Workstation and friends in Gentoo dropped a lot. Why? Well, I was the only developer left who cared, and it's definitely not at the top of my Gentoo priorities list. To be honest that has not really changed. However... let's try to harness the power of the community now.

I've pushed a mirror of the Gentoo vmware overlay to Github, see

If you have improvements, version bumps, ... - feel free to generate pull requests. Everything related to VMware products is acceptable. I hope some more people will over time sign up and help merging. Just be careful when using the overlay, it likely won't get the same level of review as ebuilds in the main tree.

Monday, May 4, 2015

PRB accepted: Transport across a carbon nanotube quantum dot contacted with ferromagnetic leads: experiment and non-perturbative modeling

It's time to announce yet another nice result. Our manuscript "Transport across a carbon nanotube quantum dot contacted with ferromagnetic leads: experiment and non-perturbative modeling" has been accepted as a regular article by Physical Review B.
When ferromagnetic materials are used as contacts for a carbon nanotube at low temperature, the current is strongly influenced by the direction of the contact magnetization via the so-called tunneling magnetoresistance (TMR). Since the nanotube contains a quantum dot, in addition its electronic energy levels play an important role; the TMR depends on the gate voltage value and can reach large negative and positive values. Here, in another fruitful joint experimental and theoretical effort, we present both measurements of the gate-dependent TMR across a "shell" of four Coulomb oscillations, and model them in the so-called "dressed second order" framework. The calculations nicely reproduce the characteristic oscillatory patterns of the TMR gate dependence.

"Transport across a carbon nanotube quantum dot contacted with ferromagnetic leads: experiment and non-perturbative modeling"
A. Dirnaichner, M. Grifoni, A. Prüfling, D. Steininger, A. K. Hüttel, and Ch. Strunk
Phys. Rev. B 91, 195402 (2015); arXiv:1502.02005 (PDF)

Wednesday, March 11, 2015

PRB accepted: Broken SU(4) symmetry in a Kondo-correlated carbon nanotube

We're happy to be able to announce that our manuscript "Broken SU(4) symmetry in a Kondo-correlated carbon nanotube" has been accepted for publication in Physical Review B.
This manuscript is the result of a joint experimental and theoretical effort. We demonstrate that there is a fundamental difference between cotunneling and the Kondo effect - a distinction that has been debated repeatedly in the past. In carbon nanotubes, the two graphene-derived Dirac points can lead to a two-fold valley degeneracy in addition to spin degeneracy; each orbital "shell" of a confined electronic system can be filled with four electrons. In most nanotubes, these degeneracies are broken by the spin-orbit interaction (due to the wall curvature) and by valley mixing (due to, as recently demonstrated, scattering at the nanotube boundaries). Using an externally applied magnetic field, the quantum states involved in equilibrium (i.e., elastic, zero-bias) and nonequilibrium (i.e., inelastic, finite bias) transitions can be identified. We show theoretically and experimentally that in the case of Kondo correlations, not all quantum state pairs contribute to Kondo-enhanced transport; some of these are forbidden by symmetries stemming from the carbon nanotube single particle Hamiltonian. This is distinctly different from the case of inelastic cotunneling (at higher temperatures and/or weaker quantum dot-lead coupling), where all transitions have been observed in the past.

"Broken SU(4) symmetry in a Kondo-correlated carbon nanotube"
D. R. Schmid, S. Smirnov, M. Marganska, A. Dirnaichner, P. L. Stiller, M. Grifoni, A. K. Hüttel, and Ch. Strunk
Phys. Rev. B 91, 155435 (2015) (PDF)

Saturday, January 31, 2015

Choice included

Some time ago, Matteo Pescarin created the great "Gentoo Abducted" design. Here are, after some minor doodling for the fun of it, several A0 posters based on that design, pointing out the excellent features of Gentoo. Released under CC BY-SA 2.5 as the original. Enjoy!






Wednesday, January 14, 2015

Cool Gentoo-derived projects (I): SystemRescueCD

Gentoo Linux is the foundation for quite some very cool and useful projects. So, I'm starting (hopefully) a series of blog posts here... and the first candidate is a personal favourite of mine, the famous SystemRescueCD.
Ever needed a powerful Linux boot CD with all possible tools available to fix your system? You switched hardware and now your kernel hangs on boot? You want to shrink your Microsoft Windows installation to the absolute minimum to have more space for your penguin picture collection? Your Microsoft Windows stopped booting but you still need to get your half-finished PhD thesis off the hard drive? Or maybe you just want to install the latest and greatest Gentoo Linux on your new machine?

For all these cases, SystemRescueCD is the Swiss army knife of your choice. With lots of hardware support, filesystem support, software, and boot options ranging from CD and DVD to installation on USB stick and booting from a floppy disc (!), just about everything is covered. In addition, SystemRescueCD comes with a lot of documentation in several languages.

The page on how to create customized versions of SystemRescueCD gives a few glimpses on how Gentoo is used here. (I'm also playing with a running version in a virtual machine while I type this. :) Basically the internal filesystem is a normal Gentoo x86 (i.e. 32bit userland) installation, with distfiles, portage tree, and some development files (headers etc.) removed to decrease disk space usage. (Skimming over the files in /etc/portage, the only really unusual thing which I can see is that >=gcc-4.5 is masked; the installed GCC version is 4.4.7- but who cares in this particular case.) After uncompressing the filesystem and re-adding the Gentoo portage tree, it can be used as a chroot, and (with some re-emerging of dependencies because of the deleted header files) packages can be added, deleted, or modified.

Downsides? Well, not much. Even if you select a 64bit Kernel on boot, the userland will always be 32bit. Which is fine for maximum flexibility and running on ancient hardware, but of course imposes the usual limits. And rsync then runs out of memory after copying a few TByte of data (hi Patrick)... :D

Want to try? Just emerge app-admin/systemrescuecd-x86 and you'll comfortably find the ISO image installed on your harddrive in /usr/share/systemrescuecd/.

From the /root/AUTHORS file in the rescue system:
SystemRescueCd (x86 edition)

* Main Author:  Francois Dupoux
* Other contributors:
  - Jean-Francois Tissoires (Oscar and many help for testing beta versions)
  - Franck Ladurelle (many suggestions, and help for scripts)
  - Pierre Dorgueil (reported many bugs and improvements)
  - Matmas did the port of linuxrc for loadlin
  - Gregory Nowak (tested the speakup)
  - Fred alias Sleeper (Eagle driver)
  - Thanks to Melkor for the help to port to unicode

Monday, January 12, 2015

DFG magazine "forschung" publishes article about our research group (in German)
The 4/2014 edition of the "forschung" magazine of the DFG, published just a few days ago, includes an article about the work of our research group (in German)! Enjoy!

"Zugfest, leitend, defektfrei"
Kohlenstoff-Nanoröhren sind ein faszinierendes Material. In Experimenten bei ultratiefen Temperaturen versuchen Physiker, ihre verschiedenen Eigenschaften miteinander in Wechselwirkung zu bringen – und so Antworten auf grundlegende Fragen zu finden.
Andreas K. Hüttel
forschung 4/2014, 10-13 (2014) (PDF)