Optical Spin Initialization and Non-Destructive Measurement in a Quantum Dot Molecule

The spin of an electron in a self-assembled InAs/GaAs quantum dot molecule is optically prepared and measured through the trion triplet states. A longitudinal magnetic field is used to tune two of the trion states into resonance, forming a superposition state through asymmetric spin exchange. As a result, spin-flip Raman transitions can be used for optical spin initialization, while separate trion states enable cycling transitions for non-destructive measurement. With two-laser transmission spectroscopy we demonstrate both operations simultaneously, something not previously accomplished in a single quantum dot.Comment: Accepted for publication in Phys. Rev. Let

Spatial and Temporal Genetic Analyses Show High Gene Flow Among European Corn Borer (Lepidoptera: Crambidae) Populations Across the Central U.S. Corn Belt

European corn borer, Ostrinia nubilalis (Hübner), adults were sampled at 13 sites along two perpendicular 720-km transects intersecting in central Iowa and for the following two generations at four of the same sites separated by 240 km in the cardinal directions. More than 50 moths from each sample location and time were genotyped at eight microsatellite loci. Spatial analyses indicated that there is no spatial genetic structuring between European corn borer populations sampled 720 km apart at the extremes of the transects and no pattern of genetic isolation by distance at that geographic scale. Although these results suggest high gene flow over the spatial scale tested, it is possible that populations have not had time to diverge since the central Corn Belt was invaded by this insect ≈60 yr ago. However, temporal analyses of genetic changes in single locations over time suggest that the rate of migration is indeed very high. The results of this study suggest that the geographic dimensions of European corn borer populations are quite large, indicating that monitoring for resistance to transgenic Bt corn at widely separated distances is justified, at least in the central Corn Belt. High gene flow further implies that resistance to Bt corn may be slow to evolve, but once it does develop, it may spread geographically with such speed that mitigation strategies will have to be implemented quickly to be effective

Genetic structure and gene flow among European corn borer populations from the Great Plains to the Appalachians of North America

1 Earlier population genetic spatial analysis of European corn borer Ostrinia nubilalis (Hubner) indicated no genetic differentiation even between locations separated by 720 km. This result suggests either high dispersal resulting in high gene flow or that populations are not in migration–drift equilibrium subsequent to their invasion of the central U.S.A. in the 1940s. 2 To discriminate among these two possibilities, samples were collected at 12 locations in eight states from New York to Colorado, a geographic scale that is three-fold greater than previously tested. Eight microsatellite markers were employed to estimate genetic differentiation and gene flow among these populations, and to test for isolation-by-distance. 3 Although pairwise FST estimates were very low, there was a significant isolation-by-distance relationship. 4 Wright’s neighbourhood area (i.e. the surface area covered by a panmictic group of individuals within a larger continuous distribution) was calculated as 433 km 2,and the radius indicates that approximately 13% of O. nubilalis adults disperse a net distance \u3e12 km per generation from their natal source. 5 Analyses indicated significant differentiation between the north-eastern region (New York and Pennsylvania) and the region combining sample locations from Ohio to Colorado, suggesting the potential for isolation of populations by topographic barriers in the Northeast. 6 Taken together, the results suggest that O. nubilalis exhibits substantial gene flow over long distances and that the lack of genetic differentiation between populations across hundreds of kilometres is not simply a result of migration–drift disequilibrium arising from the recent range expansion

Citrus black spot detection using hyperspectral image analysis

A recently discovered fungal disease called citrus black spot, is threatening the Florida citrus industry.  The fungal disease, which causes cosmetic lesions on the rind of the fruit and can cause a tree to drop its fruit prematurely, could possibly lead to a ban on sales of fresh Florida citrus in other citrus-producing states.  The objective of this research is to develop a multispectral imaging algorithm to detect citrus black spots based on hyperspectral image data.  Hyperspectral images of citrus fruits (Valencias) were collected in the wavelength range of 480 nm to 950 nm.  Five surface conditions were examined, citrus black spot, greasy spot, melanose, wind scar, and normal one.  The first part of the image analysis determined the optimal wavelengths using correlation analysis based on the wavelength ratio (l1/l2) and wavelength difference (l1 - l2).  Four wavelengths were identified, 493 nm, 629 nm, 713 nm, and 781 nm.  In the second part, pattern recognition approaches namely linear discriminant classifier and artificial neural networks were developed using the four selected wavelengths as the input.  Both pattern recognition approaches had an overall accuracy of 92%.  The detection accuracy was improved to 96% by using the NDVI band ratio method of 713 nm and 781 nm.  The multispectral image algorithm developed in this study haspotential to be adopted by a real-time multispectral imaging system for citrus black spot detection.     Keywords: activation energy, effective diffusivity, foam-mat drying, foam characteristics, modeling, Shrim

Structural Dynamic Analysis of a Spacecraft Multi-DOF Shaker Table

Finite element enforced response analysis was performed on a three axis expander head shaker table to aid in the design of the table structure and vibration control system. The payload for this shaker system is a generic spacecraft with a multitude of flexible modes across a broad frequency band. A Craig-Bampton representation of the spacecraft was used to expedite analysis of multiple shaker table designs. The analysis examines the required forces in the actuators for a constant amplitude base acceleration sine sweep test, the resulting forces in the spacecraft and table attachment restraints, and the resulting accelerations on the spacecraft structure. The results show the spacecraft response is very high at the spacecraft center of gravity (CG) due to the high CG offset and cantilever effect of the low frequency spacecraft bending modes. The high response can be addressed by "notching" the input vibration levels to avoid over-testing the spacecraft. At frequencies above 25 Hz, the spacecraft modal effective masses are very small, and the response of the shaker table dominates the response. Anti-resonances of the shaker table in the frequency range of interest reduce the acceleration output and require much higher actuator forces to achieve the acceleration specification. These effects may require stiffening the shaker structure to move the modes out of the test frequency range or increasing the shaker table damping