Ultrafast magneto-optics in nickel: magnetism or optics?

Several magnetic and optical processes contribute to the magneto-optical response of nickel thin films after excitation by a femtosecond laser pulse. We achieved a first complete identification by explicitly measuring the time-resolved Kerr ellipticity and rotation, as well as its temperature and magnetic field dependence in epitaxially grown (111) and (001) oriented Cu/Ni/Cu wedges. The first hundreds of femtoseconds the response is dominated by state filling effects. The true demagnetization takes approximately 0.5-1 ps. At the longer (sub-ns) time scales the spins are found to precess in their anisotropy field. Simple and transparent models are introduced to substantiate our interpretation.     

Observation of negative group delays within a coaxial photonic crystal using an impulse response method

An impulse response experiment is described which independently verifies the recently observed result of negative group delayed propagation within a coaxial photonic crystal. This result was unexpected when it was reported and has been the subject of enduring controversy because theoretical models predict that negative group delays should not be possible in passive linear media. The impulse response method allows for the determination of both the transmission amplitude and the group delay for narrow-band wave packets over a wide frequency range in one simple experiment. The impulse response results presented here confirm our earlier finding of negative group delays within the band gap region and are in excellent agreement with the more traditional approach of measuring transit times for wave packets. However, negative group delays are observed only over very narrow frequency ranges within the wider band gap suggesting that another interference mechanism is involved.     

The role of precursor gases on the surface restructuring of catalyst films during carbon nanotube growth

Catalyst films undergo considerable surface morphology restructuring prior to carbon nanotube nucleation, deeply influencing the nanostructures obtained. Here we study the influence of different gaseous atmospheres on the structure of thin Fe films. The morphology is influenced by process temperature and substrate interactions and varying the gas type and pressure can control the average catalyst island height.     

Untersuchung von Handschriften und Nachweis von Schriftfälschungen

Analytical and Bioanalytical Chemistry -     

Bounds on some van der Waerden numbers

For positive integers s and k₁,k₂,…,ks, the van der Waerden number w(k₁,k₂,…,ks;s) is the minimum integer n such that for every s-coloring of set {1,2,…,n}, with colors 1,2,…,s, there is a ki-term arithmetic progression of color i for some i. We give an asymptotic lower bound for w(k,m;2) for fixed m. We include a table of values of w(k,3;2) that are very close to this lower bound for m=3. We also give a lower bound for w(k,k,…,k;s) that slightly improves previously-known bounds. Upper bounds for w(k,4;2) and w(4,4,…,4;s) are also provided.     

Journal Review: Cybernetics & Human Knowing: A journal of second-order cybernetics,autopoiesis and cyber-semiotics. Quarterly,Thorverton, UK: Keith Sutherland,Imprint Academic. $55.00. Editor: Søren Brier

Nonlinear Dynamics, Psychology, and Life Sciences -