Generalized Theory of Forster-Type Nonradiative Energy Transfer in Nanostructures with Mixed Dimensionality

Cataloged from PDF version of article.Forster-type nonradiative energy transfer (NRET) is widely used, especially utilizing nanostructures in different combinations and configurations. However, the existing well-accepted Forster theory is only for the case of a single particle serving as a donor together with another particle serving as an acceptor. There are also other special cases previously studied; however, there is no complete picture and unified understanding. Therefore, there is a strong need for a complete theory that models Forster-type NRET for the cases of mixed dimensionality including all combinations and configurations. We report a generalized theory for the Forster-type, NRET, which includes the derivation of the effective dielectric function due to the donor in different confinement geometries and the derivation of transfer rates distance dependencies due to the acceptor in different confinement geometries, resulting in a complete picture and understanding of the mixed dimensionality

Forage Quality of Cereal–Common Vetch at Different Age and Proportions

Cereal plant age at harvesting and the proportion of vetch in the harvested forage from cereal-common vetch mixtures might influence total forage quality. The objectives were to determine forage of a forage mixture cereal-vetch, from cereal harvested at two development stages and vetch at different proportion. Cereals were oats and triticale, cultivars: Chihuahua, Bicentenario and Siglo XXI, the last two were triticale; cereal development stages at harvest were: 50% flowering and hard grain. Vetch was harvested at two development stages: 100% flowering and pod formation, while vetch proportions in the forage mix were: 0, 0.25, 0.5, 0.75 and 1.0. Forage quality measures were: crude protein (CP), neutral detergent fiber (NDF), organic matter (OM), ether extract (EE) and dry matter digestibility (DMD). Statistical analysis was by linear regression; cereal cultivar was a categorical variable. Models developed showed a R2≥0.7871. As vetch proportion increased in the mix so did CP while NDF decreased, CP increased from 9.2 to 17.5% and 9.2 to 14.4% and NDF decreased from 71.4 to 57.6% and 79.1 to 58.9%, as vetch proportion increased, when cereal was harvested at 50% flowering and grain hard, respectively. OM and EE showed small changes over vetch proportion and cereal development stage. DMD showed major (p\u3c 0.05) changes with cereal development stage at harvesting. It was concluded that forage quality of cereal-vetch mix depends on vetch proportion and stage of development of the cereal at the time of harvest

Changes in Crude Protein and Fiber Contents of Small Grain Cereals for Forage over Time

Oat, triticale, wheat and barley are small grain cereals used as forage in many temperate Mexican regions. The objective was to determine crude protein and van Soest fiber contents of these forages cut at 80, 96, 108, 121, 138 and 153 days after seeding. Cultivars used were: Chihuahua (OC) for oat; Arne (TA), Bicentenario (TB) and Siglo XXI (TS) for triticale; Saturno (WS) for wheat; and San Marcos (BSM) for barley. Experiment was under greenhouse conditions from November 2015 to May 2016. Crude protein (CP), neutral (NDF) and acid (ADF) detergents fibers were determined on the forage harvested at each time. Statistical analysis was by linear regression with cultivar as a dummy variable (R2= 0.5843 to 0.6861), response variables were CP, NDF and ADF contents over days after seeding (R2≥ 0.7693), the model included first grade interaction. Models developed were compared based on the slopes calculated. First grade interaction was significant (p\u3c 0.05) in CP due to the pattern change in TS, and in NDF due to the pattern change in OC and in ADF due to the pattern change in TA. So that, individual models and coefficient confident intervals were developed for each species and cultivar to compare them and to declare similarities or differences at p\u3c 0.05. Overall, CP decreased (p\u3e 0.05) from 0.11 to 0.39; while NDF and ADF increased (p\u3e 0.05) from 0.60 to 1.10, and from 0.20 to 0.83 percentage units day-1 respectively. It was concluded that crude protein, neutral and acid detergent fiber contents in small grain cereals are not dependent on harvesting time when measured at development stages close to physiological maturity

Excitonic enhancement of nonradiative energy transfer to bulk silicon with the hybridization of cascaded quantum dots

Cataloged from PDF version of article.We report enhanced sensitization of silicon through nonradiative energy transfer (NRET) of the excitons in an energy-gradient structure composed of a cascaded bilayer of green-and red-emitting CdTe quantum dots (QDs) on bulk silicon. Here NRET dynamics were systematically investigated comparatively for the cascaded energy-gradient and mono-dispersed QD structures at room temperature. We show experimentally that NRET from the QD layer into silicon is enhanced by 40% in the case of an energy-gradient cascaded structure as compared to the mono-dispersed structures, which is in agreement with the theoretical analysis based on the excited state population-depopulation dynamics of the QDs. (C) 2013 AIP Publishing LLC

Active contour following to explore object shape with robot touch

In this work, we present an active tactile perception approach for contour following based on a probabilistic framework. Tactile data were collected using a biomimetic fingertip sensor. We propose a control architecture that implements a perception-action cycle for the exploratory procedure, which allows the fingertip to react to tactile contact whilst regulating the applied contact force. In addition' the fingertip is actively repositioned to an optimal position to ensure accurate perception. The method is trained off-line and then the testing performed on-line based on contour following around several different test shapes. We then implement object recognition based on the extracted shapes. Our active approach is compared with a passive approach, demonstrating that active perception is necessary for successful contour following and hence shape recognition

Effect of Build Parameters and Build Geometries on Residual Microstructures and Mechanical Properties of Ti-6Al-4V Components Built by Electron Beam Melting (EBM)

In this study, involving additive manufacturing (AM) using electron beam melting (EBM), we have examined build defects which result from beam tripping, porosities (including unmelted or unsintered zones) due to excursions from optimal build parameters (especially variations in melt scan beam current and scan speed), and gas bubbles trapped in atomized Ti-6Al-4V starting powder as well as recycled powder, and retained in the build. At optimized build conditions we have also examined microstructure-mechanical property (hardness, tensile strength, and elongation) variations for multiple rake building and multiple melt scans using optical metallography and scanning and transmission electron microscopy (SEM and TEM). These build variances cause cooling rate variances which promote α-phase growth and variations in dislocation density, as well as α-to-α' (martensite) phase changes, all of which produce some degree of mechanical property variations. These features (especially α-to-α' phase changes) are notable on comparing solid builds in comparison with a variety of mesh arrays where strut dimension and build-element complexities alter the cooling rates in a significant way. We illustrate these microstructure variations with corresponding variations in microindentation hardness measurements made directly on fine mesh (strut) structures. Finally, we have examined Ti-6Al-4V powder chemistries and solid build chemistries which for single-pass melt scans at optimized build conditions are shown to be relatively constant up to 40 cycles of powder reuse with the exception of Al content which was reduced by 10 to 15% in solid builds at optimized conditions. However, Al loss in solid builds approached 25% for multiple (2 and 3) melt scans, while no changes in Ar gas-bubble density were observed with changes in α-phase (grain) width which increased from 3 µm for a single melt scan to 4.5 and 6 µm for 2 and 3 melt scans, respectively. Corresponding Rockwell C-scale (HRC) hardness varied from 37, 36, and 35, respectively; with ultimate tensile strengths exceeding 1.2 GPa at elongations of 12% or higher for this melt scan sequence.Mechanical Engineerin

Phonon-Assisted Exciton Transfer into Silicon Using Nanoemitters: The Role of Phonons and Temperature Effects in Forster Resonance Energy Transfer

Cataloged from PDF version of article.We study phonon-assisted Forster resonance energy transfer (FRET) into an indirect band-gap semiconductor using nanoemitters. The unusual temperature dependence of this energy transfer, which is measured using the donor nanoemitters of quantum dot (QD) layers integrated on the acceptor monocrystalline bulk silicon as a model system, is predicted by a phonon-assisted exciton transfer model proposed here. The model includes the phonon-mediated optical properties of silicon, while considering the contribution from the multimonolayer-equivalent QD film to the nonradiative energy transfer, which is derived with a d(-3) distance dependence. The FRET efficiencies are experimentally observed to decrease at cryogenic temperatures, which are well explained by the model considering the phonon depopulation in the indirect band-gap acceptor together with the changes in the quantum yield of the donor. These understandings will be crucial for designing FRET-enabled sensitization of silicon based high-efficiency excitonic systems using nanoemitters

Excitonic enhancement of nonradiative energy transfer from a quantum well in the optical near field of energy gradient quantum dots

Cataloged from PDF version of article.We report strong exciton migration with an efficiency of 83.3% from a violet-emitting epitaxial quantum well (QW) to an energy gradient colloidal construct of layered green-and red-emitting nanocrystal quantum dots (NQDs) at room temperature, enabled by the interplay between the exciton population and the depopulation of states in the optical near field. Based on the density matrix formalization of near-field interactions, we theoretically model and demonstrate that the energy gradient significantly boosts the QW-NQDs exciton transfer rate compared to using mono-dispersed NQDs, which is in agreement with the observed experimental results. (C) 2012 American Institute of Physics