Hot carrier motion in crystalline anthracene

During interaction of an intense pulse of a frequency-doubled Nd laser with an anthracene crystal a fast photo-current transient is observed which is attributed to the motion of electrons in a high mobility state.     

Comparative Raman studies of molecular interactions at a dye/polymer and a dye/glass interface

Integrated optical techniques and resonance Raman spectroscopy have been combined to investigate the intermolecular interactions at dye/polymer and dye/glass interfaces. Frequency shifts and intensity changes of bands assigned to the stretching vibrations of the bridged quinoline rings of the cyanine dye chromophore have been utilized to gain insight into the relative strength of adhesive forces at the surface. Polarized Raman measurements were made to determine the orientation of the chromophores on a poly(vinyl alcohol) surface. This was done to assess the possibility of hydrogen bond formation between the ring nitrogen atoms and the polar hydroxyl groups at the surface.     

Popular branchings and their dual certificates

Mathematical Programming - Let G be a digraph where every node has preferences over its incoming edges. The preferences of a node extend naturally to preferences over branchings, i.e., directed...     

Femtosecond dynamics of the collinear-to-spiral antiferromagnetic phase transition in CuO

We report on the ultrafast dynamics of magnetic order in a single crystal of CuO at a temperature of 207 K in response to strong optical excitation using femtosecond resonant x-ray diffraction. In the experiment, a femtosecond laser pulse induces a sudden, nonequilibrium increase in magnetic disorder. After a short delay ranging from 400 fs to 2 ps, we observe changes in the relative intensity of the magnetic ordering diffraction peaks that indicate a shift from a collinear commensurate phase to a spiral incommensurate phase. These results indicate that the ultimate speed for this antiferromagnetic reorientation transition in CuO is limited by the long-wavelength magnetic excitation connecting the two phases.     

A novel method for resonant inelastic soft X‐ray scattering via photoelectron spectroscopy detection

A method for measuring resonant inelastic X‐ray scattering based on the conversion of X‐ray photons into photoelectrons is presented. The setup is compact, relies on commercially available detectors, and offers significant flexibility. This method is demonstrated at the Linac Coherent Light Source with ～0.5 eV resolution at the cobalt L₃‐edge, with signal rates comparable with traditional grating spectrometers.     

Parameterized graph cleaning problems

We investigate the Induced Subgraph Isomorphism problem with non-standard parameterization, where the parameter is the difference |V(G)|−|V(H)| with H and G being the smaller and the larger input graph, respectively. Intuitively, we can interpret this problem as “cleaning” the graph G, regarded as a pattern containing extra vertices indicating errors, in order to obtain the graph H representing the original pattern. We show fixed-parameter tractability of the cases where both H and G are planar and H is 3-connected, or H is a tree and G is arbitrary. We also prove that the problem when H and G are both 3-connected planar graphs is NP-complete without parameterization.     

Molecular orientation in thin monolayer films by infrared spectroscopy

Fourier transform infrared spectroscopic measurements have been made on monolayer samples of cadmium arachidate in order to determine orientation and molecular packing on the surface. This was accomplished by using both grazing angle reflection methods, where the polarization of the infrared radiation is very close to being perpendicular to the surface, and transmission methods, where the incident optical electric field is polarized parallel to the surface. Hence these two methods are sensitive to molecular vibrations whose change in dipole moment lies along different directions. Our results showed that independent of the substrate, silver for the reflection experiments and silver bromide for the transmission experiments, the chains of the fatty acid salt (no evidence for any free acid was found) are oriented within a few degrees of the normal to the surface of the substrate. From a detailed analysis of the observed vibrational bands in the two orientations, combined with the known literature values and assignments, we were able to make a “complete assignment” of the observed bands. Our experimental results and conclusions will be presented.     

Stable assignment with couples: Parameterized complexity and local search

We study the Hospitals/Residents with Couples problem, a variant of the classical Stable Marriage problem. This is the extension of the Hospitals/Residents problem where residents are allowed to form pairs and submit joint rankings over hospitals. We use the framework of parameterized complexity, considering the number of couples as a parameter. We also apply a local search approach, and examine the possibilities for giving FPT algorithms applicable in this context. Furthermore, we also investigate the matching problem containing couples that is the simplified version of the Hospitals/Residents with Couples problem modeling the case when no preferences are given.     

Luminescence conversion of blue light emitting diodes

3 Al₅O₁₂:Ce³⁺(), has also been realized. Received: 6 February 1997/Accepted: 27 February 1997