Plasma emission spectroscopy of solids irradiated by intense XUV pulses from a free electron laser

The FLASH XUV-free electron laser has been used to irradiate solid samples at intensities of the order 10¹⁶ W cm^?2 at a wavelength of 13.5 nm. The subsequent time integrated XUV emission was observed with a grating spectrometer. The electron temperature inferred from plasma line ratios was in the range 5–8 eV with electron density in the range 10²¹–10²² cm^?3. These results are consistent with the saturation of absorption through bleaching of the L-edge by intense photo-absorption reported in an earlier publication.     

Three-dimensional magnetic correlations in multiferroic LuFe2O4

We present single crystal neutron diffraction measurements on multiferroic LuFe(2)O(4). Magnetic reflections are observed below transitions at 240 and 175 K indicating that the magnetic interactions in LuFe(2)O(4) are three-dimensional in character. The magnetic structure is refined as a ferrimagnetic spin configuration below the 240 K transition. Below 175 K a significant broadening of the magnetic peaks is observed along with the buildup of a diffuse component to the magnetic scattering.     

Novel longitudinal mode in the coupled quantum chain compound KCuF3

Inelastic neutron scattering measurements are reported that show a new longitudinal mode in the antiferromagnetically ordered phase of the spin- 1/2 quasi-one-dimensional antiferromagnet KCuF3. This mode signals the crossover from one-dimensional to three-dimensional behavior and indicates a reduction in the ordered spin moment of a spin- 1/2 antiferromagnet. The measurements are compared with recent quantum field theory calculations and are found to be in excellent agreement. A feature of the data not predicted by theory is a damping of the mode by decay processes to the transverse spin-wave branches.     

Self-organized criticality in a nutshell

In order to gain insight into the nature of self-organized criticality (SOC), we present a minimal model exhibiting this phenomenon. In this analytically solvable model, the state of the system is fully described by a single-integer variable. The system organizes in its critical state without external tuning. We derive analytically the probability distribution of durations of disturbances propagating through the system. As required by SOC, this distribution is scale invariant and follows a power law over several orders of magnitude. Our solution also reproduces the exponential tail of the distribution due to finite size effects. Moreover, we show that large avalanches are suppressed when stabilizing the system in its critical state. Interestingly, avalanches are affected in a similar way when driving the system away from the critical state. With this model, we have reduced SOC dynamics to a leveling process as described by Ehrenfest's famous flea model.     

FLUORESCENCE ENERGY TRANSFER BETWEEN DIMETHYLDIAZAPEROPYRENIUM DICATION AND ETHIDIUM INTERCALATED IN POLY d(A-T)

Dimethyldiazaperopyrenium is one of the largest known DNA intercalators. Fluorescence energy transfer occurred between dimethyldiazaperopyrenium (donor) and ethidium (acceptor) when these dyes were bound to a double-stranded polynucleotide such as poly d(A-T). The addition of increasing amounts of ethidium bromide led to a marked shortening of the fluorescence lifetime of the donor, whereas the excited state of the acceptor was progressively populated via energy transfer from the donor. Critical Förster distance between these two chromophores was calculated to be 3.8 nm. The observed transfer efficiency was lower than that calculated on the basis of this critical distance and a statistical distribution of bound drugs. These results are discussed taking into account the conformational change induced by intercalation of dimethyldiazaperopyrenium in the double-stranded polynucleotide.