Determination of the trap-assisted recombination strength in polymer light emitting diodes

The recombination processes in poly(p-phenylene vinylene) based polymer light-emitting diodes (PLEDs) are investigated. Photogenerated current measurements on PLED device structures reveal that next to the known Langevin recombination also trap-assisted recombination is an important recombination channel in PLEDs, which has not been considered until now. The dependence of the open-circuit voltage on light intensity enables us to determine the strength of this process. Numerical modeling of the current-voltage characteristics incorporating both Langevin and trap-assisted recombination yields a correct and consistent description of the PLED, without the traditional correction of the Langevin prefactor. At low bias voltage the trap-assisted recombination rate is found to be dominant over the free carrier recombination rate.

Aeroservoelastic design definition of a 20 MW common research wind turbine model

Wind turbine upscaling is motivated by the fact that larger machines can achieve lower levelized cost of energy. However, there are several fundamental issues with the design of such turbines, and there is little public data available for large wind turbine studies. To address this need, we develop a 20 MW common research wind turbine design that is available to the public. Multidisciplinary design optimization is used to define the aeroservoelastic design of the rotor and tower subject to the following constraints: blade‐tower clearance, structural stresses, modal frequencies, tip‐speed and fatigue damage at several sections of the tower and blade. For the blade, the design variables include blade length, twist and chord distribution, structural thicknesses distribution and rotor speed at the rated. The tower design variables are the height, and the diameter distribution in the vertical direction. For the other components, mass models are employed to capture their dynamic interactions. The associated cost of these components is obtained by using cost models. The design objective is to minimize the levelized cost of energy. The results of this research show the feasibility of a 20 MW wind turbine and provide a model with the corresponding data for wind energy researchers to use in the investigation of different aspects of wind turbine design and upscaling. Copyright © 2016 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134256/1/we1970.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134256/2/we1970_am.pd

Time to full enteral feeding after necrotizing enterocolitis in preterm-born children is related to neurodevelopment at 2-3 years of age

BACKGROUND: Necrotizing enterocolitis (NEC) is associated with poorer neurodevelopment. It is, however, unclear which factors besides surgery affect neurodevelopment in preterm-born children surviving NEC. AIMS: We determined whether time to full enteral feeding (FEFt) and post-NEC complications after NEC were associated with neurodevelopment. STUDY DESIGN: Prospective observational cohort study. SUBJECTS: Two to three year old preterm-born children who survived NEC (Bells stage ≥ 2). We categorized children in two groups, one group shorter and equal and one group longer than the group's median FEFt. Post-NEC complications included recurrent NEC and/or post-NEC stricture. OUTCOME MEASURES: Bayley Scales of Infants and Toddler Development III (Bayley-III) and Child Behavior Checklist (CBCL). Associations between Bayley-III and CBCL scores with FEFt and Post-NEC complications were determined using linear regression analyses, adjusted for severity of illness and potential confounders. RESULTS: We included 44 children, median gestational age of 27.9 [IQR: 26.7-29.3] weeks, birth weight 1148 [IQR: 810-1461] grams. Median FEFt after NEC was 20 [IQR: 16-30] days. Median follow-up age was 25.7 [IQR: 24.8-33.5] months. FEFt > 20 days was associated with lower cognitive and lower motor composite scores of the Bayley-III (B: -8.6, 95% CI -16.7 to -0.4, and B: -9.0, 95% CI, -16.7 to -1.4). FEFt was not associated with CBCL scores. Post-NEC complications (n = 11) were not associated with Bayley-III scores nor with CBCL scores. CONCLUSIONS: Prolonged FEFt after NEC in preterm-born children surviving NEC is associated with lower cognitive and lower motor composite scores at the age of 2-3 years. These results show the importance of limiting the duration of the nil per mouth regimen if and when possible

Unification of trap-limited electron transport in semiconducting polymers

Electron transport in semiconducting polymers is usually inferior to hole transport, which is ascribed to charge trapping on isolated defect sites situated within the energy bandgap. However, a general understanding of the origin of these omnipresent charge traps, as well as their energetic position, distribution and concentration, is lacking. Here we investigate electron transport in a wide range of semiconducting polymers by current-voltage measurements of single-carrier devices. We observe for this materials class that electron transport is limited by traps that exhibit a Gaussian energy distribution in the bandgap. Remarkably, the electron-trap distribution is identical for all polymers considered: the number of traps amounts to 3 × 1023 traps per m3 centred at an energy of ∼3.6 eV below the vacuum level, with a typical distribution width of ∼0.1 eV. This indicates that the electron traps have a common origin that, we suggest, is most likely related to hydrated oxygen complexes. A consequence of this finding is that the trap-limited electron current can be predicted for any polymer. © 2012 Macmillan Publishers Limited. All rights reserved

Plasma citrulline during the first 48 h after onset of necrotizing enterocolitis in preterm infants

Background: Levels of plasma citrulline (citrulline-P), a biomarker for enterocyte function, might be useful for the monitoring the course of necrotizing enterocolitis (NEC). Our aim was to evaluate whether citrulline-P levels during the first 48 h (h) after NEC onset were associated with need for surgery, survival, and intestinal recovery. Methods: In preterm infants with NEC (Bell's stage ≥2) we measured citrulline-P levels during the first 48 h after NEC onset. Categorizing the measurements into 0–8 h, 8–16 h, 16–24 h, 24–36 h, and 36–48 h, we determined the course of citrulline-P using linear regression analyses. Next, we analyzed whether citrulline-P levels measured at 0–24 h and 24–48 h differed between conservative and surgical treatment, survivors and nonsurvivors, and equal/below and above total group's median time to full enteral feeding (FEFt). Results: We included 48 infants, median gestational age 28.3 [IQR:26.0–31.4] weeks, birth weight 1200 [IQR:905–1524] grams. Citrulline-P levels decreased the first 48 h (B per time interval: -1.40 μmol, 95% CI, −2.73 to −0.07, p = 0.04). Citrulline-P was not associated with treatment, nor with survival. Citrulline-P at 0–24 h, but not 24–48 h, was higher in infants with FEFt ≤20 days than in infants with FEFt >20 days (20.7 [IQR:19.9–25.3] µmol/L (n = 13) vs. 11.1 [IQR:8.4–24.0] µmol/L (n = 11), p = 0.049), with a citrulline-P cut-off value of 12.3 μmol/L. Conclusion: Citrulline-P levels decreased the first 48 h after NEC onset, suggesting on-going intestinal injury. In survivors, measuring citrulline-P in the first 24 h after NEC onset may provide an indication for intestinal recovery rate

Predicting intestinal recovery after necrotizing enterocolitis in preterm infants

Background: Intestinal recovery after NEC is difficult to predict in individuals. We evaluated whether several biomarkers predict intestinal recovery after NEC in preterm infants. Methods: We measured intestinal tissue oxygen saturation (rintSO2) and collected urinary intestinal-fatty acid binding protein (I-FABPu) levels 0–24 h and 24–48 h after NEC onset, and before and after the first re-feed. We assessed intestinal recovery in two ways: time to full enteral feeding (FEFt; below or equal/above group’s median) and development of post-NEC complications (recurrent NEC/post-NEC stricture). We determined whether the rintSO2, its range, and I-FABPu differed between groups. Results: We included 27 preterm infants who survived NEC (Bell’s stage ≥ 2). Median FEFt was 14 [IQR: 12–23] days. Biomarkers only predicted intestinal recovery after the first re-feed. Mean rintSO2 ≥ 53% combined with mean rintSO2range ≥ 50% predicted FEFt < 14 days with OR 16.7 (CI: 2.3–122.2). The rintSO2range was smaller (33% vs. 51%, p < 0.01) and I-FABPu was higher (92.4 vs. 25.5 ng/mL, p = 0.03) in case of post-NEC stricture, but not different in case of recurrent NEC, compared with infants without complications. Conclusion: The rintSO2, its range, and I-FABPu after the first re-feed after NEC predicted intestinal recovery. These biomarkers have potential value in individualizing feeding regimens after NEC

Intestinal Oxygenation and Survival After Surgery for Necrotizing Enterocolitis:An Observational Cohort Study

OBJECTIVE: To assess whether regional intestinal oxygen saturation (rintSO2) and regional cerebral oxygen saturation (rcSO2) measurements aid in estimating survival of preterm infants after surgery for NEC. SUMMARY OF BACKGROUND DATA: Predicting survival after surgery for NEC is difficult yet of the utmost importance for counseling parents. METHODS: We retrospectively studied prospectively collected data of preterm infants with surgical NEC who had available rintSO2 and rcSO2 values measured via near-infrared spectroscopy 0-24 hours preoperatively. We calculated mean rintSO2 and rcSO2 for 60-120 minutes for each infant. We analyzed whether preoperative rintSO2 and rcSO2 differed between survivors and non-survivors, determined cut-off points, and assessed the added value to clinical variables. RESULTS: We included 22 infants, median gestational age 26.9 weeks [interquartile range (IQR): 26.3-28.4], median birth weight 1088 g [IQR: 730-1178]. Eleven infants died postoperatively. Preoperative rintSO2, but not rcSO2, was higher in survivors than in non-survivors [median: 63% (IQR: 42-68) vs 29% (IQR: 21-43), P 53% survived, whereas all infants with rintSO2 <35% died. Median C-reactive protein [138 mg/L (IQR: 83-179) vs 73 mg/L (IQR: 12-98), P < 0.01), lactate [1.1 mmol/L (IQR: 1.0-1.6) vs 4.6 mmol/L (IQR: 2.8-8.0), P < 0.01], and fraction of inspired oxygen [25% (IQR: 21-31) vs 42% (IQR: 30-80), P < 0.01] differed between survivors and non-survivors. Only rintSO2 remained significant in the multiple regression model. CONCLUSIONS: Measuring rintSO2, but not rcSO2, seems of added value to clinical variables in estimating survival of preterm infants after surgery for NEC. This may help clinicians in deciding whether surgery is feasible and to better counsel parents about their infants' chances of survival