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We report on the operation of a novel single-photon detector, where a layer of self-assembled quantum dots (QDs) is used as an optically addressable floating gate in a GaAs/Al0.2Ga0.8As delta-doped field-effect transistor. Photogenerated holes charge the QDs, and subsequently, change the amount of current flowing through the channel by screening the internal gate field. The photoconductive gain associated with this process makes the structure extremely sensitive to light of the appropriate wavelength. We investigate the charge storage and resulting persistent photoconductivity by performing time-resolved measurements of the channel current and of the photoluminescence emitted from the QDs under laser illumination. In addition, we characterize the response of the detector, and investigate sources of photogenerated signals by using the Poisson statistics of laser light. The device exhibits time-gated, single-shot, single-photon sensitivity at a temperature of 4 K. It also exhibits a linear response, and detects photons absorbed in its dedicated absorption layer with an internal quantum efficiency (IQE) of up to (68 plusmn18)%. Given the noise of the detection system, the device is shown to operate with an IQE of (53 plusmn 11)% and dark counts of 0.003 counts per shot for a particular discriminator level. [ABSTRACT FROM PUBLISHER]

The article discusses research being done on the role of breast stromal enhancement on magnetic resonance imaging (MRI) in response to neoadjuvant chemotherapy. It references a study by J. Hattangadi et al in a 2008 issue of the "American Journal of Roentgenology." It was hypothesized that signal enhancement ratios from dynamic contrast-enhanced breast MRI could be used to analyze the contrast kinetics of microvasculature in breast stroma beyond the tumor margin.

Reports on the generation of first-order terahertz optical devices in asymmetric coupled quantum wells. Peak assignments in the photoluminescence excitation and reflectivity spectra; Measured resonance behavior of the sideband intensity as a function of near-infrared probe beams.

• Effects of the initial microstructure of the railway wheel steel on adiabatic shearing behavior is examined. • The localized deformation of proeutectoid ferrite is preferent to that of pearlite. • The localized deformation is more serious in the wide lamellar structure than in the narrow lamellar structure. • The rim is more prone to adiabatic shearing compared with the web. Adiabatic shearing behavior in the web and the rim of high-speed train railway wheel steel was investigated using a split Hopkinson pressure bar (SHPB) with hat-shaped punch shear technique. Different initial microstructure characteristics were observed in the web and the rim specimens experiencing different heat treatment. For the first time we show that the pre-eutectoid ferrite deforms at first and pearlite interlamellar spacing has a significant influence on structural softening sequence during shear band evolution in the railway wheel steel, and shear bands are more prone to emerge in the rim. [ABSTRACT FROM AUTHOR]