Electrically switchable electro-optic filters for spectral line emission detection.

Remote detection of spectral line emission is an important capability in a number of areas, including defense and environmental science. In this paper, we report on a mechanism for spectral line emission detection that is not based on narrow bandpass filters or hyperspectral imagers, but is instead based on the use of switchable spectral filters. The use of a switchable filter enables a single sensor to perform remote sensing tasking in a broad passband, while also detecting emission in a particular spectral line. In this case, the switchable spectral filter studied is a holographic polymer dispersed liquid crystal (HPDLC) reflection grating. The concept is demonstrated through modeling a sensor with an integrated HPDLC filter and building a detection algorithm capable of detecting spectral line emission. The modeling framework is built upon four components: the background scene, the spectral line source, the HPDLC filter, and the sensor. Results from the model show probability of detection and probability of false alarm for spectral line sources of varying strength for a particular background scene.

Ion Pairing and Diffusion in Magnesium Electrolytes Based on Magnesium Borohydride.

One obstacle to realizing a practical, rechargeable magnesium-ion battery is the development of efficient Mg electrolytes. Electrolytes based on simple Mg(BH4)2 salts suffer from poor salt solubility and/or low conductivity, presumably due to strong ion pairing. Understanding the molecular-scale processes occurring in these electrolytes would aid in overcoming these performance limitations. Toward this goal, the present study examines the solvation, agglomeration, and transport properties of a family of Mg electrolytes based on the Mg(BH4)2 salt using classical molecular dynamics. These properties were examined across five different solvents (tetrahydrofuran and the glymes G1-G4) and at four salt concentrations ranging from the dilute limit up to 0.4 M. Significant and irreversible salt agglomeration was observed in all solvents at all nondilute Mg(BH4)2 concentrations. The degree of clustering observed in these divalent Mg systems is much larger than that reported for electrolytes containing monovalent cations, such as Li. The salt agglomeration rate and diffusivity of Mg2+ were both observed to correlate with solvent self-diffusivity: electrolytes using longer- (shorter-) chain solvents had the lowest (highest) Mg2+ diffusivity and agglomeration rates. Incorporation of Mg2+ into Mg2+-BH4- clusters significantly reduces the diffusivity of Mg2+ by restricting displacements to localized motion within largely immobile agglomerates. Consequently, diffusion is increasingly impeded with increasing Mg(BH4)2 concentration. These data are consistent with the solubility limitations observed experimentally for Mg(BH4)2-based electrolytes and highlight the need for strategies that minimize salt agglomeration in electrolytes containing divalent cations.