Showing papers by "Christopher B. Murray published in 2008"

Temperature-Tuning of Near-Infrared Monodisperse Quantum Dot Solids at 1.5 µm for Controllable Förster Energy Transfer

Abstract: We present the first time-resolved cryogenic observations of Forster energy transfer in large, monodisperse lead sulfide quantum dots with ground-state transitions near 1.5 µm (0.8 eV), in environments from 160 K to room temperature. The observed temperature-dependent dipole−dipole transfer rate occurs in the range of (30−50 ns)−1, measured with our confocal single-photon counting setup at 1.5 µm wavelengths. By temperature-tuning the dots, 94% efficiency of resonant energy transfer can be achieved for donor dots. The resonant transfer rates match well with proposed theoretical models.

Temperature-tuning of near-infrared monodisperse quantum dot solids at 1.5 um for controllable Forster energy transfer

Abstract: We present the first time-resolved cryogenic observations of Forster energy transfer in large, monodisperse lead sulphide quantum dots with ground state transitions near 1.5 um (0.83 eV), in environments from 160 K to room temperature. The observed temperature-dependent dipole-dipole transfer rate occurs in the range of (30-50 ns)^(-1), measured with our confocal single-photon counting setup at 1.5 um wavelengths. By temperature-tuning the dots, 94% efficiency of resonant energy transfer can be achieved for donor dots. The resonant transfer rates match well with proposed theoretical models.

‘‘TITAM’’ thermionic integrated transient analysis model: Load‐following of a single‐cell TFE

Abstract: TITAM, a dynamic model that simulates transient and steady‐state operation of a fully integrated single‐cell thermionic fuel element (TFE), has been developed. Operation modes investigated include transient response to a step input in reactivity, effects of changing the Cs pressure and/or the width of the interelectrode gap on the load electric power, overall conversion efficiency, and the load‐following characteristics of a TFE. Results show that although the nuclear reactor is always load following, a TFE is only partially load‐following. Results also show that in a thermionic (TI) nuclear power system, which employs single‐cell TFEs having a large interelectrode gap, it is desirable to conserve Cs by lowering its vapor pressure at the beginning‐of‐life, since increasing the Cs pressure insignificantly affects the load electric power. However, should fuel swelling, after operating for an extended period of time, reduce the width of the interelectrode gap, both the conversion efficiency and the load electric power will decrease. In this case a partial compensation in the load electric power may be achieved by increasing the fission power and/or the Cs vapor pressure in the interelectrode gap of the TFEs.

Steady‐State Model of a Low CS Pressure Discharge in a Triode

Abstract: The plasma discharge conditions in a low Cs pressure triode is of interest to the understanding of the processes in the Cs‐Ba tacitron. A good understanding of the processes occurring in the three discharge regions of the device is absent; especially the processes responsible for extinguishing the discharge after applying a negative voltage pulse to the grid. This work outlines the preliminary development of a steady‐state triode model that describes the conditions in the three regions of the low pressure Cs discharge. This model is used to analyze the stationary discharge in a triode and understand the relationship between each region. Model results are compared with experimental data for various Cs and Ba vapor pressures.

Observation of efficient Förster energy transfer at 1.5 μm through temperature-tuning of monodisperse quantum dot solids

Abstract: We present time-resolved cryogenic observations of Forster energy transfer in large, monodisperse lead sulphide quantum dots with ground state transitions near 1.5 mum (0.8 eV), in environments from 160 K to room temperature.