Diameter and Chirality Dependence of Exciton Properties in Carbon Nanotubes

We calculate the diameter and chirality dependences of the binding energies, sizes, and bright-dark splittings of excitons in semiconducting single-wall carbon nanotubes (SWNTs). Using results and insights from {\it ab initio} calculations, we employ a symmetry-based, variational method based on the effective-mass and envelope-function approximations using tight-binding wavefunctions. Binding energies and spatial extents show a leading dependence with diameter as $1/d$ and $d$, respectively, with chirality corrections providing a spread of roughly 20% with a strong family behavior. Bright-dark exciton splittings show a $1/d^2$ leading dependence. We provide analytical expressions for the binding energies, sizes, and splittings that should be useful to guide future experiments

Early catastrophic acetabular failure in Furlong total hip replacements

The use of uncemented hip arthroplasty prostheses with ceramic articulations are popular, especially in the young, because of a perceived reduction in wear. We highlight a complication of ceramic on polyethylene articulating couples not previously described in the Furlong replacement. Despite widespread metalosis and particulate debris, osteolysis was not initially seen. The contamination compromised subsequent revision

Surface Charge Control of Quantum Dot Blinking

A characteristic property of colloidal semiconductor nanocrystal quantum dots (QDs) is their emission intermittency. Although a unifying theory of QD photoprocesses remains elusive, the importance of charged states is clear. We now report a new approach to directly study the role of surface charge on QD emission by adding metal ions to individual, core-only QDs immobilized in aqueous solution in an agarose gel. The CdTe QDs show very stable emission in the absence of metal ions but a dramatic and reversible increase in blinking due to the presence of trivalent metal ions. Our results support a charge-separation model, in which the major blinking pathway is the surface trapping of electrons; transiently bound metal ions close to the QD surface enhance this process

Breaking the Smallsat Barriers to Sub-50cm Imaging

New cutting-edge imaging sensors can now reduce instrument size and mass, leading to mission cost savings, and bring sub-50cm imaging capability into the realm of small satellites. Whilst aperture is essential to achieving resolution, half-pixel shifted sensor architectures decouple achievable Ground Sampling Distance (GSD) from the native ground projected pixel. This facilitates the deployment of Very High Resolution (VHR) small satellite constellations featuring improved Signal-to-Noise performance and increased area collection rates compared to push-frame systems. A fundamental limitation to the theoretical performance of an optical system is imposed by its aperture diameter; hence, for a given aperture, the aim is to maximize the information content resolved up to this limit. This is achieved by minimizing losses caused by aberrations in the optical system and enhancing platform stability on-orbit. Further information is lost due to aliasing at higher spatial frequencies; however, the recovery of such information is unlocked through the novel sensor technology and processing techniques proposed. Funded under the European Space Agency (ESA) “Investing in Industrial Innovation” (InCubed) program, this paper reports on the build and verification campaign of a sub-50cm capable instrument Proto-Flight Model (PFM), the beneficial properties of half-pixel offset sensors, and the platform supporting such a payload

Selection Rules for One- and Two-Photon Absorption by Excitons in Carbon Nanotubes

Recent optical absorption/emission experiments showed that the lower energy optical transitions in carbon nanotubes are excitonic in nature, as predicted by theory. These experiments were based on the symmetry aspects of free electron-hole states and bound excitonic states. The present work shows, however, that group theory does not predict the selection rules needed to explain the two photon experiments. We obtain the symmetries and selection rules for the optical transitions of excitons in single-wall carbon nanotubes within the approach of the group of the wavevector, thus providing important information for the interpretation of theoretical and experimental optical spectra of these materials.Comment: 4 pages, 1 figure, 1 tabl

Frequency-Modulated Orocutaneous Stimulation Promotes Non-nutritive Suck Development in Preterm Infants with Respiratory Distress Syndrome or Chronic Lung Disease

Background—For the premature infant, extrauterine life is a pathological condition which greatly amplifies the challenges to the brain in establishing functional oromotor behaviors. The extent to which suck can be entrained using a synthetically patterned orocutaneous input to promote its development in preterm infants who manifest chronic lung disease is unknown. Objective—To evaluate the effects of a frequency-modulated orocutaneous pulse train delivered through a pneumatically-charged pacifier capable of enhancing non-nutritive suck (NNS) activity in tube-fed premature infants. Methods—A randomized trial to evaluate the efficacy of pneumatic orocutaneous stimulation 3x/day on NNS development and length of stay (LOS) in the NICU among 160 newborn infants distributed among 3 subpopulations, including healthy preterm infants (HI), respiratory distress syndrome (RDS), and chronic lung disease (CLD). Study infants received a regimen of orocutaneous pulse trains through a PULSED pressurized silicone pacifier or a SHAM control (blind pacifier) during gavage feeds for up to 10 days. Results—Mixed modeling, adjusted for the infant’s gender, gestational age, postmenstrual age, and birth weight, was used to handle interdependency among repeated measures within subjects. A significant main effect for stimulation mode (SHAM pacifier vs PULSED orosensory) was found among preterm infants for NNS Bursts/minute (p=.003), NNS events/minute (p=.033), and for Total Oral Compressions/minute [NNS+nonNNS] (p=.016). Pairwise comparison of adjusted means using Bonferroni adjustment indicated RDS and CLD infants showed the most significant gains on these NNS performance indices. CLD infants in the treatment group showed significantly shorter LOS by an average of 2.5 days

Frequency-Modulated Orocutaneous Stimulation Promotes Non-nutritive Suck Development in Preterm Infants with Respiratory Distress Syndrome or Chronic Lung Disease

Background—For the premature infant, extrauterine life is a pathological condition which greatly amplifies the challenges to the brain in establishing functional oromotor behaviors. The extent to which suck can be entrained using a synthetically patterned orocutaneous input to promote its development in preterm infants who manifest chronic lung disease is unknown. Objective—To evaluate the effects of a frequency-modulated orocutaneous pulse train delivered through a pneumatically-charged pacifier capable of enhancing non-nutritive suck (NNS) activity in tube-fed premature infants. Methods—A randomized trial to evaluate the efficacy of pneumatic orocutaneous stimulation 3x/day on NNS development and length of stay (LOS) in the NICU among 160 newborn infants distributed among 3 subpopulations, including healthy preterm infants (HI), respiratory distress syndrome (RDS), and chronic lung disease (CLD). Study infants received a regimen of orocutaneous pulse trains through a PULSED pressurized silicone pacifier or a SHAM control (blind pacifier) during gavage feeds for up to 10 days. Results—Mixed modeling, adjusted for the infant’s gender, gestational age, postmenstrual age, and birth weight, was used to handle interdependency among repeated measures within subjects. A significant main effect for stimulation mode (SHAM pacifier vs PULSED orosensory) was found among preterm infants for NNS Bursts/minute (p=.003), NNS events/minute (p=.033), and for Total Oral Compressions/minute [NNS+nonNNS] (p=.016). Pairwise comparison of adjusted means using Bonferroni adjustment indicated RDS and CLD infants showed the most significant gains on these NNS performance indices. CLD infants in the treatment group showed significantly shorter LOS by an average of 2.5 days