Extracting Light from Polymer Light‐Emitting Diodes Using Stamped Bragg Gratings

In this paper, we describe a method for increasing the external efficiency of polymer light‐emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings. We numerically model the waveguide modes in a typical LED structure and demonstrate how optimizing layer thicknesses and reducing waveguide absorption can enhance the grating outcoupling. The gratings were created by a soft‐lithography technique that minimizes changes to the conventional LED structure. Using one‐dimensional and two‐dimensional gratings, we were able to increase the forward‐directed emission by 47 % and 70 %, respectively, and the external quantum efficiency by 15 % and 25 %.     

Effects of age, system experience, and navigation technique on driving with an advanced traveler information system

This paper explores the effects of age, system experience, and navigation technique on driving, navigation performance, and safety for drivers who used TravTek, an Advanced Traveler Information System. The first two studies investigated various route guidance configurations on the road in a specially equipped instrumented vehicle with an experimenter present. The third was a naturalistic quasi-experimental field study that collected data unobtrusively from more than 1200 TravTek rental car drivers with no in-vehicle experimenter. The results suggest that with increased experience, drivers become familiar with the system and develop strategies for substantially more efficient and safer use. The results also showed that drivers over age 65 had difficulty driving and navigating concurrently. They compensated by driving slowly and more cautiously. Despite this increased caution, older drivers made more safety-related errors than did younger drivers. The results also showed that older drivers benefited substantially from a well-designed ATIS driver interface.     

Approaching and contacting the object another manipulates: A social skill of the 1-year-old.

Assigned 48 11–23 mo old infants at random to 1 of 4 groups distinguished by how an unfamiliar female adult acted on toys. The infant, in a room containing his or her mother and several toys, observed an adult who did nothing with the toys, periodically approached and sat down beside a predesignated toy either in a repetitive way for 1 group or in a varied manner for another. Contrasting which toys the infants of the different groups contacted indicated that the infants systematically went to and contacted the toy that the adult manipulated. Smiling, vocalizing, and gesturing to the adult, being near her, and contacting her were all reliably linked in time to the infants' contacting her toy. Further, the infants duplicated the adult's actions on the toy reliably more often than expected by a chance matching of activity. The findings suggest that approaching and contacting the object another manipulates is a basic social skill of the 1-yr-old; such behavior functions to facilitate the generation of social interaction. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

APA finances: Introduction.

Discusses the profits and investments of the American Psychological Association (APA). Other topics include the financial control system, which provides for 5-yr advance planning, annual budgeting, and current reporting built around programs. These programs are divided into such categories as publications and services and activities. APA revenues, expenses, and net earnings for 1951–70 are listed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The factor V Leiden mutation increases the risk of venous thrombosis in patients with inflammatory bowel disease

BACKGROUND & AIMS: Thromboembolic disease is a significant cause of morbidity and mortality in patients with inflammatory bowel disease (IBD). The aim of this study was to determine the incidence and possible association of the factor V Leiden mutation with the development of thrombosis in patients with IBD. METHODS: This retrospective study included 11 patients with IBD and arterial or venous thrombosis and 51 patients with IBD and no history of thrombosis who were matched for age, sex, ethnic/racial origin, and type of IBD (controls). The presence of the factor V Leiden mutation was determined by coagulation assay and confirmed by a polymerase chain reaction method. RESULTS: Four of 11 IBD patients (36%) with thrombosis and 2 of 51 IBD controls (4%) were heterozygotes for the factor V Leiden mutation (relative risk, 14.00; 95% confidence interval, 1.55-169.25; P = 0.009, Fisher exact test). All thrombotic events in the patients with activated protein C resistance were venous with a calculated prevalence of 50% (4 of 8 patients) and a relative risk of venous thrombosis in IBD patients with factor V Leiden of 23 (95% confidence interval, 2-294; P = 0.005). CONCLUSIONS: In patients with IBD, inheritance of the factor V Leiden mutation results in a significant increased risk of venous thrombosis.     

Bimolecular Crystals of Fullerenes in Conjugated Polymers and the Implications of Molecular Mixing for Solar Cells

The performance of polymer:fullerene bulk heterojunction solar cells is heavily influenced by the interpenetrating nanostructure formed by the two semiconductors because the size of the phases, the nature of the interface, and molecular packing affect exciton dissociation, recombination, and charge transport. Here, X‐ray diffraction is used to demonstrate the formation of stable, well‐ordered bimolecular crystals of fullerene intercalated between the side‐chains of the semiconducting polymer poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene. It is shown that fullerene intercalation is general and is likely to occur in blends with both amorphous and semicrystalline polymers when there is enough free volume between the side‐chains to accommodate the fullerene molecule. These findings offer explanations for why luminescence is completely quenched in crystals much larger than exciton diffusion lengths, how the hole mobility of poly(2‐methoxy‐5‐(3′,7′‐dimethyloxy)‐p‐phylene vinylene) increases by over 2 orders of magnitude when blended with fullerene derivatives, and why large‐scale phase separation occurs in some polymer:fullerene blend ratios while thermodynamically stable mixing on the molecular scale occurs for others. Furthermore, it is shown that intercalation of fullerenes between side chains mostly determines the optimum polymer:fullerene blending ratios. These discoveries suggest a method of intentionally designing bimolecular crystals and tuning their properties to create novel materials for photovoltaic and other applications.     

Semiconducting (Conjugated) Polymers as Materials for Solid‐State Lasers

Light‐emissive polymers are outstanding laser materials because they are intrinsically “4‐level” systems, they have luminescence efficiencies higher than 60 % even in undiluted films, they emit at colors that span the visible spectrum, and they can be processed into optical quality films by spin casting. The important materials issues are reviewed and the prospects for making polymer diode lasers are discussed.