Anomalous independence of multiple exciton generation on different group IV-VI quantum dot architectures

Multiple exciton generation (MEG) in PbSe quantum dots (QDs), PbSe(x)S(1-x) alloy QDs, PbSe/PbS core/shell QDs, and PbSe/PbSe(y)S(1-y) core/alloy-shell QDs was studied with time-resolved optical pump and probe spectroscopy. The optical absorption exhibits a red-shift upon the introduction of a shell around a PbSe core, which increases with the thickness of the shell. According to electronic structure calculations this can be attributed to charge delocalization into the shell. Remarkably, the measured quantum yield of MEG, the hot exciton cooling rate, and the Auger recombination rate of biexcitons are similar for pure PbSe QDs and core/shell QDs with the same core size and varying shell thickness. The higher density of states in the alloy and core/shell QDs provide a faster exciton cooling channel that likely competes with the fast MEG process due to a higher biexciton density of states. Calculations reveal only a minor asymmetric delocalization of holes and electrons over the entire core/shell volume, which may partially explain why the Auger recombination rate does not depend on the presence of a shell.     

Magneto-optical studies of perylene tetracarboxylic acid diimide thin films

N,N′-Dimethyl perylene tetracarboxylic acid diimide (Me-PTCDI) thin films were prepared by vapor deposition technique. The photogeneration and recombination of singlet and triplet excitons were characterized, utilizing absorption, PL and optically detected magnetic resonance (ODMR) spectroscopy. The results suggest the creation of molecular dimers, which gives rise to the creation of split singlet exciton states and enhancement of population in the triplet exciton state.     

Containment system for the preparation of vitrified-hydrated virus specimens

A guillotine-type quick freezing device and a bio-hazard containment box have been designed, constructed, and used to prepare vitrifiedhydrated specimens of viruses in their native environment. Special design considerations include the preservation of the specimen in its natural state in vitrified ice, prevention of virus aerosols escape, and control of the potentially explosive air-coolant vapor mixtures.     

Improved high-intensity microwave discharge lamp for atomic resonance absorption and fluorescence spectrometry

An unusually good combination of high intensity and narrow line has been achieved in a microwave discharge lamp by placing the optical window in the center of the microwave cavity. Construction details and performance characteristics are described.     

Relationship between maternal obesity and infant feeding-interactions

Background  

There are no data regarding the relationship between maternal adiposity and interaction and feeding of infants and possible contribution to childhood obesity. In this study we determined the relationship between maternal body weight and composition and infant feeding patterns and maternal-infant interaction during 24-hour metabolic rate measurements in the Enhanced Metabolic Testing Activity Chamber (EMTAC).