Multiphonon emission model of spin-dependent exciton formation in organic semiconductors

The maximum efficiency in organic light-emitting diodes (OLEDs) depends on the ratio, $r=k_S/k_T$, where $k_S$ ($k_T$) is the singlet (triplet) exciton formation rate. Several recent experiments found that r increases with increasing oligomer length from a value $r \approx 1$ in monomers and short oligomers. Here, we model exciton formation as a multi-phonon emission process. Our model is based on two assertions: (i) More phonons are emitted in triplet formation than in singlet formation. (ii) The Huang-Rhys parameter for this phonon emission is smaller in long oligomers than in short ones. We justify these assertions based on recent experimental and theoretical data.Comment: 8 pages, 7 figure

Large magnetoresistance at room-temperature in semiconducting polymer sandwich devices

We report on the discovery of a large, room temperature magnetoresistance (MR) effect in polyfluorene sandwich devices in weak magnetic fields. We characterize this effect and discuss its dependence on voltage, temperature, film thickness, electrode materials, and (unintentional) impurity concentration. We usually observed negative MR, but positive MR can also be achieved under high applied electric fields. The MR effect reaches up to 10% at fields of 10mT at room temperature. The effect shows only a weak temperature dependence and is independent of the sign and direction of the magnetic field. We find that the effect is related to the hole current in the devices.Comment: 3 pages, 4 figure

Overseeding Methods for Communal Grassland

Two establishment methods, cultivator+roller and grassland drill, in combination with four plant mixtures were evaluated for the improvement of degraded communal grassland in two provinces of Eastern Anatolia. The establishment had been satisfactory with both methods and no significant differences were observed between two overseeding methods. Sainfoin, alfalfa, smooth brome and crested wheatgrass were used in this work and plant mixtures consisted of one legume and one grass species. Compatibility of introduced seedlings with existing vegetation was very weak. Although, the contribution of introduced plant mixtures to DM yield was significantly higher under protected condition, the survival and regeneration rates of these forages under traditional grazing conditions was low and their disappearance from the vegetation was very fast. Hence, it was concluded that renovation of deteriorated communal grassland with available erect type legumes is not feasible and improvement of creeping type, grazing and drought resistant legume species is urgently needed

Monitoring Productivity and Quality of Grass-Legume Pastures Under Irrigated Condition

The performance of six grass-white clover mixtures were evaluated in winter cold zone of Eastern Anatolia. In combination with white clover, ryegrass (Lolium perenne L) cocksfoot, (Dactylis glomerata L) and smooth brome (Bromus inermis Leyss) were used in double and triple plant mixtures. Average DM production ranged from 7.5 to 10 t/ha , with no significant differences observed among the mixed swards. DM production of all mixed swards significantly varied between cutting periods and years. A gradual decrease in DM production was observed both from the first to forth cut and from the first to third year. Clover and consequently CP content increased from the first to second year and decreased in the third year. The increasing proportion of clover after first cut was also reflected in a higher content of CP. On the other hand, the persistence of grass species to frequent cutting varied but ryegrass became dominant to cocksfoot and smooth brome in triple mixtures

Strategy revision opportunities and collusion

This paper studies whether and how strategy revision opportunities affect levels of collusion in indefinitely repeated two-player games. Consistent with standard theory, we find that such opportunities do not affect strategy choices, or collusion levels, if the game is of strategic substitutes. In games of strategic complements, by contrast, revision opportunities lead to more collusion. We discuss alternative explanations for this result

Investigation on the blood cell counts of Chalcides ocellatus (Sauria: Scincidae) population in Anatolia [Anadolu'daki Chalcides ocellatus (Sauria: Scincidae) populasyonlarinin kan hücrelerinin sayisi bakimindan incelenmesi]

In this investigation, the blood cell counts (erythrocyts and leucocyts) of 136 Chalcides ocellatus specimens (75 ++ + 61 > >), collected from different locations in Anatolia have been investigated from the view point of the effects of geographical distance and altitude factors. The blood cell counts are found to be highest in the population from Gaziantep-Urfa and the cause of this difference is evaluated as due to geographic variation