Complex non-equilibrium dynamics in plasmas

Two new forms of strongly coupled plasmas will be discussed. They have become possible to create and observe in the laboratory only recently and exhibit a wealth of intriguing complex behavior which can be studied, in many cases for the first time, experimentally. Plasmas, gases of charged particles, are universal in the sense that certain properties of complex behavior do only depend on ratios of characteristic parameters of the plasma, not on the parameters themselves. Therefore, it is of fundamental and far reaching consequence, to be able to create and observe a strongly coupled plasma since its behavior is paradigmatic for an entire class of plasmas.Comment: 14 pages, to be published in European Revie

Signal analysis of impulse response functions in MR- and CT-measurements of cerebral blood flow

The impulse response function (IRF) of a localized bolus in cerebral blood flow codes important information on the tissue type. It is indirectly accessible both from MR- and CT-imaging methods, at least in principle. In practice, however, noise and limited signal resolution render standard deconvolution techniques almost useless. Parametric signal descriptions look more promising, and it is the aim of this contribution to develop some improvements along this line.Comment: 15 pages, 6 figure

Attosecond light pulse induced photo-association

We explore stimulated photo-association in the context of attosecond pump-probe schemes of atomic matter. An attosecond pulse -- the probe -- is used to induce photo-association of an electronic wave packet which had been created before, typically with an attosecond pump pulse at an atomic center different from the one of photo-association. We will show that the electron absorption is maximal for a certain delay between the pulses. Two ways of enhancing and controlling stimulated photo-association are proposed, namely using an additional infrared pulse to steer the electronic wave packet and using a train of attosecond pulses instead of a single pair. A direct application of ultrafast stimulated photo-association is the measurement of atomic distances.Comment: 7 pages, 8 figure

Floquet approach for dynamics in short and intense laser pulses

We present a two-timescale Floquet method that allows one to apply the Kramers-Henneberger approach to short pulses and arbitrary laser frequencies. An efficient numerical procedure to propagate the Floquet Hamiltonian is provided that relies on the Toeplitz matrix formalism and Fast Fourier Transformations. It enables efficient time propagation with large Floquet expansions, while still taking advantage of the cycle-averaged Kramers-Henneberger basis. Three illustrative cases of ionization with different photon energies are analyzed, where the envelope of a short and intense pulse is crucial to the underlying dynamics.Comment: 39 pages, 11 figure

Polyatomic trilobite Rydberg molecules in a dense random gas

Trilobites are exotic giant dimers with enormous dipole moments. They consist of a Rydberg atom and a distant ground-state atom bound together by short-range electron-neutral attraction. We show that highly polar, polyatomic trilobite states unexpectedly persist and thrive in a dense ultracold gas of randomly positioned atoms. This is caused by perturbation-induced quantum scarring and the localization of electron density on randomly occurring atom clusters. At certain densities these states also mix with a s-state, overcoming selection rules that hinder the photoassociation of ordinary trilobites

Polyatomic trilobite Rydberg molecules in a dense random gas

Trilobites are exotic giant dimers with enormous dipole moments. They consist of a Rydberg atom and a distant ground-state atom bound together by short-range electron-neutral attraction. We show that highly polar, polyatomic trilobite states unexpectedly persist and thrive in a dense ultracold gas of randomly positioned atoms. This is caused by perturbation-induced quantum scarring and the localization of electron density on randomly occurring atom clusters. At certain densities these states also mix with a s-state, overcoming selection rules that hinder the photoassociation of ordinary trilobites

Commentary: I'm only trying to help: A role for interventions in teaching listening

In my work as an author and teacher trainer, I have the opportunity to travel around the world and talk to teachers in a variety of settings. Though I meet teachers with a range of backgrounds and a wide disparity of resources, I find that a few common themes come up whenever I talk with teachers about language teaching and technology. One of the familiar refrains is that most of us claim to lack the technological resources we feel we need to teach effectively. There’s always something new on the horizon that we feel we just have to have. Another recurring theme is the lament that most of our students just don’t seem to take advantage of the extra learning opportunities we present them anyway! Teachers want to help, but often feel under appreciated for their efforts. Personally, I have relished the ongoing advances in technology over the course of my teaching career. I started out as a secondary school teacher in Togo, West Africa with chalk – sometimes yellow or pink! – and a blackboard as my only teaching technology. When teachers express a sense of being overwhelmed by new technology, I sometimes talk about my own beginnings and also remind them of a few of Donald Norman’s principles of human-centered design. According to Norman (2004), for any new technology to be effective, it must be intuitively helpful and elegantly efficient. In the case of language teaching, this means the technology must – immediately and transparently – help us teach better than we do already. If it doesn’t, we simply shouldn’t use it. In addition, Norman says, for any new technology to be widely adopted, it must appeal to the emotions as well as to reason. If people don’t enjoy using a particular technology, no matter how logically useful it may be, they will tend to shun it. Perhaps because as language teachers we tend to favor eclecticism, we will often throw any emerging technology into the mix as a "helpful resource." As Doughty and Long (2003) point out, teachers often do not distinguish between new technological tools that are innovative but not actually helpful and those which are innovative and genuinely helpful. In my own instructional design, I have identified three "intervention phases" in the listening process: decoding, comprehension, and interpretation. Before we assume any new technology or intervention is actually going to be supportive, I believe we need to understand the learners' goals during these listening processes. What actually motivates the learners towards achieving these goals is what ultimately will be useful