Average distance in growing trees

Two kinds of evolving trees are considered here: the exponential trees, where subsequent nodes are linked to old nodes without any preference, and the Barab\'asi--Albert scale-free networks, where the probability of linking to a node is proportional to the number of its pre-existing links. In both cases, new nodes are linked to $m=1$ nodes. Average node-node distance $d$ is calculated numerically in evolving trees as dependent on the number of nodes $N$. The results for $N$ not less than a thousand are averaged over a thousand of growing trees. The results on the mean node-node distance $d$ for large $N$ can be approximated by $d=2\ln(N)+c_1$ for the exponential trees, and $d=\ln(N)+c_2$ for the scale-free trees, where the $c_i$ are constant. We derive also iterative equations for $d$ and its dispersion for the exponential trees. The simulation and the analytical approach give the same results.Comment: 6 pages, 3 figures, Int. J. Mod. Phys. C14 (2003) - in prin

Some selected and functionalised organometallic molecules for NLO applications

Organometallics nano complexes are important targets for the construction of advanced materials, the investigation of electron-transfer processes and of novel devices for non-linear optical (NLO) applications. In this work the diagnostic and characterisation of novel molecular organics nano complexes thin films functionalized for NLO applications will be discussed. On other hand a rich study of the formation of surface-relief gratings (SRGs), using a picosecond pulsed laser at 532 nm, resulted in instantaneous inscription will be presented

Study of surface relief gratings on azo organometallic films in picosecond regime

Materials for optical data storage and optical information processing must exhibit good holographic properties. Many materials for these applications have been already proposed. Here we describe a grating inscription process characterized by short inscription time and long-time stability. A series of ruthenium-acetylide organometallic complexes containing an azobenzene fragment were synthesized. Photo-induced gratings were produced by short pulse (16 ps, 532 nm) laser irradiation. The surface relief gratings formed at the same time were observed by atomic force microscope. In this work, we highlight the short inscription times brought into play as well as the good temporal stability of these gratings stored at room temperature. We study the influence of the polarization states and the light intensity of writing beams on the dynamics of the surface relief gratings formation and we compare these results with those of a known representative of azobenzene derivative (Disperse Red 1). Lastly, we show that it is possible to write two-dimensional surface relief gratings

IMPROVING WHEAT TRITICUM AESTIVUM L. BY INTERSPECIFIC AND INTERGENERIC HYBRIDIZATION WITH POACEAE FAMILY SPECIES

The related species of the family Poaceae (Triticeae) are the source of unprecedented new genes that allow the extension of genetic variation of common wheat Triticum aestivum L. These species have similar homoeologous chromosomes and rDNA sequences very similar to T. aestivum L. [1-3]. This allows the introgression of alien genes and their incorporation into the genomes A, B and D of wheat, where they can function permanently in the wheat genetic systems. Many of them have already been transferred to the varieties of T. aestivum L. [4].The experimental material consisted of 28 lines of winter wheat obtained using the interspecific and intergeneric hybridization of T. aestivum L. with alien species T. durum Desf., T. timopheevii Zhuk., Lolium perenne L. and Aegilops speltoides Taush. Among them, 15 lines were developed from the cross-combination with tetraploid species (AABB) T. durum Desf., 4 lines from the combination with other tetraploid species of different genome composition (AAGG) T. timopheevii Zhuk., 4 lines from cross with L. perenne L. and 5 lines were the double hybrids (three-generic) derived with two related species, T. durum Desf. (AABB) and Ae. speltoides Taush (BB).The anther culture method was used for obtaining DH lines from these interspecific and intergeneric hybrids. In in vitro culture 124 green plants were regenerated. The method of cluster analysis grouped hybrids in terms of comprehensive general similarity of the studied traits

Photoinduced Gratings in Functionalized Azo-Carbazole Compounds in Picosecond Regime

We report results of diffraction grating inscription on thin films prepared from epoxy resin doped with azo-carbazole based dyes. Diffraction gratings were recorded at the wavelength 532 nm and monitored through intensity of first order of diffraction (632 nm). Atomic force microscope scans of the gratings show that a surface relief grating also appeared

Comparison of bevel and tulip triggered pultruded tubes for energy absorption

The crushing behavior of E-glass/polyester and E-glass/vinyl ester pultruded tubes has been found to be significantly different for tulip triggered specimens as compared with bevel triggered specimens. Up to 100% more energy per unit weight was absorbed by tulip triggered tubes. In addition, the crushing was more controlled and predictable with the tulip trigger. The morphology of the material in the crushing zone differed in the amount and the pattern of fracture. The fracture pattern and crushing behavior initiated by both triggers were found not to change during crushing. The difference in crushing appeared to arise from the different abilities of the tubes to support load because of the different geometry of individual load-carrying structures that resulted from triggering.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29526/1/0000613.pd

Backward phase-matched second-harmonic generation from stacked metasurfaces

We demonstrate phase-matched second-harmonic generation (SHG) from three-dimensional metamaterials consisting of stacked metasurfaces. To achieve phase matching, we utilize a novel mechanism based on phase engineering of the metasurfaces at the interacting wavelengths, facilitating phase-matched SHG in the unconventional backward direction. By stacking up to five metasurfaces, we obtain the expected factor of 25 enhancement in SHG efficiency. Our results motivate further investigations to achieve higher conversion efficiencies also with more complex wavefronts.Comment: 5 pages, 3 figures, supplementary materia