242 research outputs found
Perioperative Course and Socioeconomic Status Predict Long-Term Neurodevelopment Better Than Perioperative Conventional Neuroimaging in Children with Congenital Heart Disease.
The objective of the study was to compare the use of neonatal conventional brain magnetic resonance imaging (MRI) with that of clinical factors and socioeconomic status (SES) to predict long-term neurodevelopment in children with severe congenital heart disease (CHD).
In this prospective cohort study, perioperative MRIs were acquired in 57 term-born infants with CHD undergoing cardiopulmonary bypass surgery during their first year of life. Total brain volume (TBV) was measured using an automated method. Brain injury severity (BIS) was assessed by an established scoring system. The neurodevelopmental outcome was assessed at 6 years using standardized test batteries. A multiple linear regression model was used for cognitive and motor outcomes with postoperative TBV, perioperative BIS, CHD complexity, length of hospital stay, and SES as covariates.
CHD diagnoses included univentricular heart defect (n = 15), transposition of the great arteries (n = 33), and acyanotic CHD (n = 9). Perioperative moderate-to-severe brain injury was detected in 15 (26%) patients. The total IQ was similar to test norms (P = .11), whereas the total motor score (P < .001) was lower. Neither postoperative TBV nor perioperative BIS predicted the total IQ, but SES (P < .001) and longer hospital stay (P = .004) did. No factor predicted the motor outcome.
Although the predictive value of neonatal conventional MRIs for long-term neurodevelopment is low, duration of hospital stay and SES better predict the outcome in this CHD sample. These findings should be considered in initiating early therapeutic support
Impact of exciton delocalization on exciton-vibration interactions in organic semiconductors
Organic semiconductors exhibit properties of individual molecules and
extended crystals simultaneously. The strongly bound excitons they host are
typically described in the molecular limit, but excitons can delocalize over
many molecules, raising the question of how important the extended crystalline
nature is. Using accurate Green's function based methods for the electronic
structure and non-perturbative finite difference methods for exciton-vibration
coupling, we describe exciton interactions with molecular and crystal degrees
of freedom concurrently. We find that the degree of exciton delocalization
controls these interactions, with thermally activated crystal phonons
predominantly coupling to delocalized states, and molecular quantum
fluctuations predominantly coupling to localized states. Based on this picture,
we quantitatively predict and interpret the temperature and pressure dependence
of excitonic peaks in the acene series of organic semiconductors, which we
confirm experimentally, and we develop a simple experimental protocol for
probing exciton delocalization. Overall, we provide a unified picture of
exciton delocalization and vibrational effects in organic semiconductors,
reconciling the complementary views of finite molecular clusters and periodic
molecular solids
Directional quantum dot emission by soft-stamping on silicon Mie resonators
We present a soft-stamping method to selectively print a homogenous layer of CdSeTe/ZnS core–shell quantum dots (QDs) on top of an array of Si nanocylinders with Mie-type resonant modes. Using this new method, we gain accurate control of the quantum dot's angular emission through engineered coupling of the QDs to these resonant modes. Using numerical simulations we show that the emission into or away from the Si substrate can be precisely controlled by the QD position on the nanocylinder. QDs centered on a 400 nm diameter nanocylinder surface show 98% emission directionality into the Si substrate. Alternatively, for homogenous ensembles placed over the nanocylinder top-surface, the upward emission is enhanced 10-fold for 150 nm diameter cylinders. Experimental PL intensity measurements corroborate the simulated trends with cylinder diameter. PL lifetime measurements reflect well the variations of the local density of states at the QD position due to coupling to the resonant cylinders. These results demonstrate that the soft imprint technique provides a unique manner to directly integrate optical emitters with a wide range of nanophotonic geometries, with potential applications in LEDs, luminescent solar concentrators, and up- and down-conversion schemes for improved photovoltaics
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